RECORD OF DECISION FOR PEOPLES NATURAL GAS … · peoples natural gas coal gasification site dubuque, ... 6.0 summary of comparative analysis of alternatives ... organic compounds,

RECEIVED

OCT *

VII

RECORD OF DECISION

PEOPLES NATURAL GAS COAL GASIFICATION SITE

DUBUQUE, IOWA

Prepared by:

U. S. ENVIRONMENTAL PROTECTION AGENCY

REGION VII

KANSAS CITY, KANSAS

SEPTEMBER 1991

DECLARATION

Declaration for the Record of Decision

Peoples Natural Gas Coal Gasification SiteDubuque, Iowa

Statement of Basis and PurposeThis decision document presents the selected remedial action

for the Peoples Natural Gas Coal Gasification site, in Dubuque,Iowa. The selected remedy was chosen in accordance with therequirements of the Comprehensive Environmental Response, Compen-sation, and Liability Act of 1980 (CERCLA), as amended by theSuperfund Amendments and Reauthorization Act of 1986 (SARA) andthe National Oil and Hazardous Substances Pollution ContingencyPlan (NCP). This decision document explains the factual andlegal basis for selecting the remedy for this site. The informa-tion supporting this remedial action decision is contained in therrl^inistrative record for this site.

The State of Iowa concurs with the selected remedy.

Assessment of the Site

Actual or threatened releases of hazardous substances fromthis site, if not addressed by implementing the response actionselected in this Record of Decision (ROD), may present acurrent or potential threat to public health, welfare, or theenvironment.

Description of the Selected Remedy

The principal threat at this site is buried coal tar wasteand cyanide bearing woodchips that present a direct contactthreat to on-site workers and has contaminated the ground water.Volatile organics and polynuclear aromatic hydrocarbons haveleached from the tars into the ground water.

The major components of the selected remedy include thefollowing:

• Excavation and off-site incineration of coal tar contami-nated soil;

• Extraction of contaminated ground water to reduce concen-trations to acceptable levels and treatment and discharge ofextracted ground water to the City of Dubuque sewer system;

• The in-situ treatment of certain coal tar contaminatedareas by the injection of nutrients into the aquifer to stimulatebiological degradation, and

• Ground water monitoring to assure successful implementa-tion of treatment systems.

Declaration of Statutory Determinations

The selected remedy is protective of human health and theenvironment, complies with federal and state requirements thatare legally applicable or relevant and appropriate to theremodial action, and is cost-effective. This remedy utilizespermanent solutions and alternative treatment technologies to themaximum extent practicable, and it satisfies the statutorypreference for remedies that employ treatment that reducetoxicity, mobility, or volume as their principal element.Institutional controls will be installed at the site to insurethat the remedy provides protection of human health and theenvironment. This protection is based on health-based levelsthat have been determined to be protective in conjunction withinstitutional controls. Because these controls will not allowfor unlimited use and unrestricted exposure at the site, a reviewwill be performed no less often than every five years afterinitiation of the selected remedial action.

Kay DateRegional AdministratorUnited States Environmental Protection AgencyRegion VII

TABLE OF CONTENTS

DECISION SUMMARY

1.0 SITE BACKGROUND1.1 SITE LOCATION AND DESCRIPTION1.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES1.3 REMOVAL ACTIONS1.4 COMMUNITY RELATIONS ACTIVITIES

2.0 SCOPE OF RESPONSE ACTIVITIES

3.0 SUMMARY OF SITE CHARACTERISTICS3.1 CONTAMINANT CHARACTERIZATION3.2 CHARACTERIZATION OF THE NATURE AND EXTENT OF

CONTAMINATION3.3 NATURE AND EXTENT OF CONTAMINATION

3.3.1 SURFACE AND SHALLOW SUBSURFACE RESULTS3.3.2 DEEP SUBSURFACE RESULTS3.3.3 GROUND WATER RESULTS

4.0 SUMMARY OF SITE RISKS4.1 OVERVIEW OF BASELINE RISK ASSESSMENT4.2 INDICATOR COMPOUNDS4.3 EXPOSURE ASSESSMENT4.4 TOXICITY ASSESSMENT4.5 RISK CHARACTERIZATION

4.5.1 RISKS FROM NON-CARCINOGENIC COMPOUNDS4.5.2 RISKS FROM CARCINOGENIC COMPOUNDS4.5.3 RISKS FROM EXPOSURE TO SOILS4.5.4 RISKS FROM EXPOSURE TO GROUND WATER4.5.5 UNCERTAINTIES4.5.6 CONCLUSION

4.6 REMEDIATION GOALS

5.0 SUMMARY OF ALTERNATIVES5.1 NO ACTION5.2 REMOVAL ACTION WITH GROUND WATER QUALITY MONITORING5.3 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER

EXTRACTION AND TREATMENT5.4 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER

EXTRACTION AND TREATMENT, CAPPING OF SOURCE SOILS, ANDIN-SITU BIOREMEDIATION

5.5 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATEREXTRACTION AND TREATMENT AND REMOVAL OF SOURCE SOILS

6.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES6.1 OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT6.2 COMPLIANCE WITH ARARS6.3 LONG-TERM EFFECTIVENESS AND PERMANENCE6.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME6.5 SHORT-TERM EFFECTIVENESS6.6 IMPLEMENTABILITY6.7 COST6.8 STATE ACCEPTANCE6.9 COMMUNITY ACCEPTANCE

7.0 SELECTED REMEDY

8.0 STATUTORY DETERMINATIONS8.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT8.2 COMPLIANCE WITH APPLICABLE RELEVANT AND APPROPRIATE

REQUIREMENTS8.3 COST-EFFECTIVENESS8.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE

TREATMENT TECHNOLOGIES TO THE MAXIMUM EXTENTPRACTICABLE

8.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT

9.0 DOCUMENTATION OF SIGNIFICANT CHANGES

APPENDIX A RESPONSE TO PUBLIC COMMENTS ON THE PROPOSED PLAN

LIST OF FIGURES

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Location Map - Peoples Natural Gas Site

Vicinity Map - Peoples Natural Gas Site

Site Plan - Existing Conditions, 1990

Proposed U.S. Highway 61 Alignment

Geologic Cross Section Locations

Geologic Cross Section 4 - 4'

Completed Removal Action Site Plan, 1990

Location of Tar/Ammonia Tanks and Gas Plant WasteDisposal Area

Estimated Limits of PAH Soil Contamination

PAH Cross Section 4 - 4'

Estimated Limits of BETX Soil Contamination

Distribution of PAHs in Ground Water, February 1990

Distribution of BETX in Ground Water, November 1989

Distribution of BETX in Ground Water, January 1990

LIST OF TABLES

Table 1 Summary of Maximum Contaminant Concentrations forDisposal Area

Table 2 Summary of Maximum Contaminant Levels in Ground Water

Table 3 Summary Statistics for Analytical Data, DetectedCompounds in Soil

Table 4 Summary Statistics for Analytical Data, DetectedCompounds in Ground Water

Table 5 Remediation Levels in Ground Water

Table 6 Indicator Compounds for Risk Assessment Compounds

Table 7 Calculated Incremental Lifetime Cancer Risks and GlobalHazard Indices

Table 8 Carcinogenic Risks - Residential Exposure Ingestion ofChemicals in Soil by Children

Table 9 Carcinogenic Risks - Residential Exposure Ingestion ofChemicals in Soil by Adults

Table 10 Carcinogenic Risks - Residential Exposure Ingestion ofChemicals in Soil by Municipal Garage Workers

Table 11 Carcinogenic Risks - Residential Exposure Ingestion ofChemicals in Soil by Construction Workers

Table 12 Ground Water Results for Risk Assessment

Table 13 Carcinogenic Exposure Calculations for Ingestion ofChemicals in Drinking Water - Alluvial Aquifer

Table 14 Carcinogenic Exposure Calculations for Ingestion ofChemicals in Drinking Water - Water Table Wells

Table 15 Noncarcinogenic Exposure Calculations for Ingestion ofChemicals in Drinking Water - Alluvial Aquifer

Table 16 Noncarcinogenic Exposure Calculations for Ingestion ofChemicals in Drinking Water - Water Table Wells

Table 17 Cost Estimate Summary for Selected Remedy

RECORD OF DECISION

DECISION SUMMARY

1.0 SITE BACKGROUND

1.1 SITE LOCATION AND DESCRIPTION

The Peoples Natural Gas site is located in Dubuque, Iowa, acity of approximately 100,000 people, in eastern Dubuque County.The address of the site is 925 Kerper Boulevard. Maps of thevicinity and site location are shown in Figures 1-3.

The site occupies approximately 5 acres. It is bounded byllth Street to the north, Kerper Boulevard to the south and east,and the Soo Line railroad track that parallels Pine Street to thewest. The southeast boundary of the site extends to within 300feet of Dove Harbor on the Mississippi River.

The eastern portion of the site is owned and occupied by theCity of Dubuque. The City of Dubuque Street Division operatesout of the public works garage built on the site. The garage andthe surrounding land are used to store street maintenance vehi-cles and cars for city officials. Also, the Street Divisionst-ores snow removal chemicals (rock salt and liquid calciumchloride) as well as sand on the City's portion of the site. Thewestern portion of the site is owned by the Iowa Department ofTransportation (IDOT). A highway is scheduled for constructionon this portion of the site with a projected completion date ofJuly 1992. The highway corridor is diagramed in relation to thesite in Figure 4.

The site is located 300 feet west of the Mississippi Riveron a broad Mississippi River flood plain. Sediments underlyingthe fill material at the site generally consist of unconsolidatedsilts, sands, and clays. The hydrogeologic setting of the siteconsists of surficial material and an underlying clay unit (upperconfining unit), and an underlying thin silty sand (silty sandunit) which is separated from an alluvial sand (alluvial aquifer)by a thin clay unit (lower confining unit). Ground water in thesilty sand unit and the alluvial aquifer flow to the northeasttoward a high capacity well field located 1,800 feet north of thesite. Ground water in the alluvial aquifer in the vicinity ofthe site is classified as Class IIB, a potential source of drink-ing water. The geologic features are shown in Figure 6 as avertical cross section through the site shown as section 4 - 4'in Figure 5.

A well search was conducted for the area within a one-mileradius of the Peoples site to identify wells in the vicinity thatcould be affected by the site and to identify local wells thatpump large enough volumes of water to influence ground water inthe vicinity of the site. The results of the well search indi-cate that there are no wells on or near the site that are used asa source of drinking water.

1.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES

The Peoples site is the location of a former coalgasification plant formerly owned and operated by the Key CityGas Company. The manufacture of gas at the site occurred fromapproximately the 1930's to 1954 and ceased with the availabilityof natural gas to the community.

During operations, the plant produced as by-products coaltar and cyanide-bearing woodchips and stored them on the site.The coal tar was stored in one 14,000 gallon underground concretetank and one 7,000 gallon above ground tank. A large portion ofthe coal tar was transferred to railroad cars and sold for use aswood preservative and road treatment. The woodchips were buriedon the eastern portion of the site. The hazardous constituentsof concern associated with the coal gas process include: polycy-clic aromatic hydrocarbons (PAHs); phenols; aromatic volatileorganic compounds, including benzene, ethylbenzene, toluene, andxylene (BETX); and cyanide.

North Central Public Service Company acquired ownership ofKey City Gas in approximately 1954. Northern Natural GasCompany, which later became Peoples Natural Gas (PNG), acquiredownership of the site in approximately 1957. PNG used the siteas a natural gas distribution, storage, and maintenance facility.The City acquired the site property in 1964. IDOT acquired thewestern one-third of the site in 1985.

In November 1986 the Environmental Protection Agency (EPA)conducted an Expanded Site Investigation (ESI) at the site. TheESI documented extensive soil contamination and ground waterreleases of phenol, cyanide, and PAHs.

EPA proposed that the site be listed on the National Priori-ties List in June 1988. On August 30, 1990, the Peoples site waslisted as a National Priorities List site.

On April 19, 1989, EPA issued an Administrative Order onConsent to Midwest Gas, a division of Iowa Public ServiceCompany, the successor to North Central Public Service Company;the Iowa Department of Transportation; and the City of Dubuque.All three entities are parties to the Administrative Order onConsent. The order required these parties to conduct a removalaction and a Remedial Investigation and Feasibility Study(RI/FS). The purpose of the Remedial Investigation was to deter-mine the source as well as the nature and extent of contaminationat the site and to collect the data necessary to determine theproper alternatives to be evaluated in the Feasibility Study.Midwest Gas contracted with Barr Engineering of Minneapolis,Minnesota to conduct sampling at the site, which included surfacesoil, ground water, sediment, and surface water samples. MidwestGas prepared an RI/FS Report which was reviewed by EPA. The

final RI/FS Report was completed in May 1991. Based on thefindings of the FS, EPA prepared a Proposed Plan which describedthe selected remedy for this site.

The Administrative Order also required that the partiesconduct a Site Characterization and Removal Alternative Study(SC/RAS) to determine the extent of contamination of soils in theHighway 61 corridor. Midwest Gas conducted the study and pre-pared a SC/RAS Report which was reviewed by EPA and used todetermine the scope of removal activities in the highway corri-dor. The final SC/RAS Report was completed in January 1990.Based on information presented in the SC/RAS report EPA developeda Removal Action Decision Document (RADD) dated June 6, 1990which presented the selected removal action for the highwayportion of the site. The RADD also presented the factual andlegal basis for the selected removal action.

1.3 REMOVAL ACTIONS

Midwest Gas is nearing completion of a removal action on thewestern portion of the Peoples site within the constructioncorridor for U.S. Highway 61. Figure 7 shows the extent ofexcavation conducted during the removal action. The excavationportions of the removal action were completed in July 1991 andincluded excavation of contaminated soils, removal of undergroundtanks used to store coal tar, installation of a leachate collec-tion system to prevent contamination from leaching into thealluvial aquifer, and institutional controls to prevent publicexposure to soils exceeding 100 mg/kg (milligrams per kilogram orPPM) carcinogenic PAHs. All soils exceeding the cleanup stand-ards, which were excavated as part of removal action, will beincinerated off-site. Approximately 5,500 cubic yards of soilsand stabilized coal tar sludges were excavated. Cyanide bearingwoodchips were not encountered during removal activities.

As part of the removal action, soils to a depth of 6 feetwere excavated which contained concentrations in excess of 100mg/kg carcinogenic PAHs and 500 mg/kg total PAHs. This depth ofexcavation and these cleanup levels were selected to remove thethreat of direct contact with site soils by persons working onthe site or potential onsite residents. In addition, soils wereexcavated below 6 feet that contained concentrations in excess of200 mg/kg carcinogenic PAHs and 2,900 mg/kg total PAHs. Thisdepth of excavation and these cleanup levels were selected toprotect the ground water from future leaching of volatile organiccompounds and PAHs into the aquifers. The Agency for ToxicSubstances and Disease Registry (ATSDR) was consulted regardingthe cleanup level for soils excavated below 6 feet. As stated inATSDR's response to EPA " ATSDR considers a concentration of200 mg/kg total PAHs and 2,900 mg/kg carcinogenic PAHs remainingin the subsurface soils to be protective of human health."

Midwest Gas prepared a Removal Action Report (RAR) in July1991. The RAR summarizes the removal action that was completedat the Peoples site within the Highway 61 corridor. Detaileddescriptions of construction and excavation activities are in-cluded in the RAR.

1.4 COMMUNITY RELATIONS ACTIVITIES

The RI/FS Report and the Proposed Plan for the Peoples sitewere released to the public for comment. The public commentperiod was from June 17, 1991 to August 17, 1991. These twodocuments were made available to the public with the administra-tive record, which is located at the information repositoriesmaintained at the Dubuque Public Library and at the EPA RegionVII office. The notice of availability for these documents waspublished in the Dubuque Telegraph Herald on June 17, 1991. Apublic meeting was held on July 9, 1991 in Dubuque, Iowa. Atthis meeting, representatives from EPA, the State of Iowa, andthe Agency for Toxic Substances and Disease Registry (ATSDR)answered questions about problems at the site and the remedialalternatives under consideration. A summary of comments receivedat this meeting and during the comment period and EPA's responseto those comments, the Responsiveness Summary, is attached heretoas Appendix A. Community involvement activities were conductedas a requirement of Sections 113 and 117 of CERCLA.

2.0 SCOPE OF RESPONSE ACTIVITIES

The response activities described in this Decision Summaryaddress all contaminants known at the site. When implemented,these actions will eliminate the need for future response actionsat the site. This ROD is intended to be the final ROD for thesite. The principal threat at this site is buried coal tar wasteand cyanide bearing woodchips that present a direct contactthreat to on-site workers and have contaminated the ground water.Volatile organics and polynuclear aromatic hydrocarbons haveleached from the tars into the ground water.

3.0 SUMMARY OF SITE CHARACTERISTICS

3.1 CONTAMINANT CHARACTERIZATION

Coal tar waste contains polynuclear aromatic hydrocarbons(PAHs) such as naphthalene and benzo(a)pyrene. Also producedfrom coal tar wastes are volatile organic contaminants, such asbenzene, ethylbenzene, toluene, and xylene (BETX), and semi-vola-tile contaminants, such as methylphenol, dibenzofuran, andphenol. Cyanide can also be associated with coal tar wastesincluding woodchips used for gas purification.

3.2 NATURE AND EXTENT OF CONTAMINATION

The Remedial Investigation identified the source of contami-nation and characterized the nature and extent of contaminationat the site. The discussion of these findings is divided intofour main groups: surface and shallow subsurface results, deepsubsurface results, and ground water results. A site diagramdisplaying areas of soil contamination is shown in Figure 8. Theremoval action involved excavation of soil contamination in thetar tank area. The area excavated as part of the removal actionis shown in Figure 7. Areas of contamination discussed in thissection pertain to the soils not addressed during the removalaction which are currently located on the eastern portion of thePeoples site.

Maximum contaminant concentrations for soil and source areasremaining at the site are summarized in Table 1. Maximum contam-inant concentrations for ground water are summarized in Table 2.Standards for these contaminants are summarized in Table 5.

3.2.1 SURFACE AND SHALLOW SUBSURFACE RESULTS

The highest concentrations of PAHs in surface and shallowsubsurface borings are at a location 4.5-6.5 feet deep northeastof the City of Dubuque public works garage at boring #21 (SB-21)with 4,300 ing/kg (milligrams per kilogram or parts per million)total PAHs and 1,800 mg/kg carcinogenic PAHs. Other areas withsignificant PAH concentrations in soil are borings SB-16 and SB-17 which are located along the northern edge of the site with150-900 mg/kg total PAHs and 7.5-89 mg/kg carcinogenic PAHs at4.5-6.5 feet below surface. Soil boring SB-12 contained 8,000mg/kg total PAHs at 4.5-6.5 feet below surface and is locatedappi oximately 50 feet northeast of SB-21. Figure 10 displays PAHcontamination in the subsurface as a vertical cross sectionthrough the site shown as section 4-4' in Figure 4.

Field screening indicated that BETX concentrations in thesurface and shallow subsurface were below 50 mg/kg with theexception of SB-34 which gave a field screening result of 250mg/kg at 2-4 feet below surface. Figure 11 displays BETX contam-ination in the subsurface. Table 3 summarizes contaminantsdetected in soils and source areas for each of the parametergroups addressed during the RI/FS; i.e., volatile organics, semi-volatile organics, and cyanide.

3.2.2 DEEP SUBSURFACE RESULTS

The highest concentrations of contaminants in the deepsubsurface testing were in three borings northeast of the publicworks garage. SB-21 resulted in concentrations of 5,400 mg/kgtotal PAHs, 120 mg/kg carcinogenic PAHs at a depth of 27-29 feet.SB-22 contained 2,700 mg/kg total PAHs, 240 mg/kg carcinogenic

PAHs at a depth of 7-9 feet. SB-12 contained 4,100 mg/kg totalPAHs at a depth of 9.5-11.5 feet. Figure 9 shows the areas ofPAH contamination in the silty sand unit.

The results obtained for BETX compounds confirm the PAHresults. The highest concentrations were located at SB-22 with560 mg/kg BETX compounds at 12-14 feet. SB-21 contained 98 mg/kgBETX compounds at 27-29 feet.

3.2.3 GROUND WATER RESULTS

Ground water samples were collected from 20 monitoring wellson and offsite in four rounds of sampling. Water samples werecollected from both the silty sand and the alluvial aquifers.The analytical results of these samples show that both aquiferscontain detectable levels of PAH and BETX compounds both on andoff site. Table 4 summarizes contaminants detected in groundwater for each of the parameter groups addressed during theRI/FS; i.e., volatile organics, semi-volatile organics, andcyanide.

The highest PAH concentrations were found in water tablemonitoring well W-2, adjacent to the west edge of the publicworks garage with 580 ug/1 (micrograms per liter or part perbillion) total PAHs and 52 ug/1 carcinogenic PAHs. Alluvialaquifer monitoring well W-17 contained 43 ug/1 total PAHs andsilty sand aquifer P-110 monitoring well contained 18 ug/1 totalPAHs. Figure 12 displays locations of PAHs detected in theground water.

The wells were analyzed for BETX compounds and similarresults were found. Well W-2 had a total BETX concentration of250 ug/1, W-17 500 ug/1 total BETX, and P-110 had 5.0 ug/1 totalBETX. Many of the samples exceeded EPA primary drinking waterstandards for the BETX compound benzene. Alluvial aquifer moni-toring well W-16, which is approximately 200 feet north of thesite, contained 360 ug/1 BETX. Figures 13 and 14 display loca-tions of BETXs in the ground water.

Results of the RI indicate that the primary ground waterflow is to the northeast while the exact ground water flow pat-terns will be investigated further during the Remedial Design,sufficient information is available from the RI to select aproper remedy for the ground water.

4.0 SUMMARY OF SITE RISKS

4.1 OVERVIEW OF BASELINE RISK ASSESSMENT

A baseline risk assessment is an evaluation of the potentialthreat to human health and the environment in the absence of anyremedial action. A base line risk assessment is done in part to

help EPA determine whether remedial action is necessary at asite. A baseline risk assessment was conducted for this site todetermine the potential effects of the contamination on humanhealth and the environment. In this evaluation, both current andfuture land-use scenarios were evaluated.

4.2 INDICATOR COMPOUNDS

Fifteen chemicals were identified in the Risk Assessment tobe of potential concern, 13 of which were PAHs. Toxicity infor-mation was evaluated for all chemicals of concern, includingcancer potency factors and noncarcinogenic effects. Contaminantsof concern (COCs) are contaminants that have been detected at thesite, have inherent toxic or carcinogenic effects, and are likelyto pose the greatest concern with respect to the protection ofhuman health and the environment. The compounds selected includethe more mobile and persistent chemicals at the site, as well asthose present at the highest concentrations. These indicatorcompounds are listed in Table 6. Toxicity information was evalu-ated for all indicator chemicals, including cancer potency fac-tors and noncarcinogenic effects.

4.3 EXPOSURE ASSESSMENT

The exposure assessment identified potential pathways androutes for contaminants of concern to reach the receptors and theestimated contaminant concentration at the points of exposure.Pathways by which humans could be exposed to the chemicals ofconcern at the site were evaluated based on reasonable assump-tions about current and future land uses. Calculations for siterisks are based on upper bound values for contaminants of con-cern. The following pathways were evaluated:

• Exposure of public works garage workers on-site tocontaminated soil through dermal contact and ingestion;

• Exposure of future construction workers on-site tocontaminated soil through dermal contact and ingestion;

• Exposure of adults and children as potential on-siteresidents to contaminated soil through dermal contact andingestion;

• Exposure of future adult and children residents tocontaminated ground water used as a primary potable water source.

4.4 TOXICITY ASSESSMENT

Reference doses (RfDs) have been developed by EPA forindicating the potential for adverse effects from exposure tochemicals exhibiting noncarcinogenic effects. RfDs, which areexpressed in units of mg/kg/day (parts per million/day), are

estimates of daily exposure levels for humans that are likely tohave an appreciable risk of adverse health effects. Estimatedintakes of chemicals from environmental media (e.g., the amountof a chemical ingested from contaminated drinking water) can becompared to the RfD. The RfDs applicable at the Peoples site arelisted in Tables 15 and 16.

Cancer potency factors (CPFs) or slope factors have beendeveloped for estimating excess lifetime cancer risks associatedwith exposure to potentially carcinogenic chemicals. CPFs, whichare also expressed in units of parts per million/day, are multi-plied by the estimated intake of a potential carcinogen to pro-vide an upper-bound estimate of the excess lifetime cancer riskassociated with exposure at that intake level. The CPFs applica-ble to the Peoples site are listed in Tables 8-14.

4.5 RISK CHARACTERIZATION

The risk characterization quantifies present and/or poten-tial future risk to human health that may result from exposure tothe contaminants of concern found at the site. The site-specificrisk values are estimated by incorporating information from thetoxicity and exposure assessments.

Two quantitative evaluations are made: the incremental riskto the individual resulting from exposure to a carcinogen; or,for noncarcinogens, a numerical index or ratio of the exposuredose level to an acceptable reference dose.

4.5.1 RISKS FROM NON-CARCINOGENIC COMPOUNDS

A Hazard Index (HI) was calculated for each pathway evaluat-ed. An HI of less than 1.0 (unity) indicates that the risksassociated with that pathway are low. An HI above 1.0 indicatesthat some risk of noncarcinogenic effects exist and these risksincrease proportional to the HI value. The HI value for poten-tial offsite residents using the water table aquifer as a drink-ing water source is 3.8 (Table 16), which indicates that they arepotentially at risk. However, the water table aquifer does notproduce a continuous and reliable source of water for potentialusers of the aquifer, and therefore does not present a risk topotential residents. The HI for future workers on and offsitewas determined to be less than one, indicating no significantnoncarcinogenic risks.

4.5.2 RISKS FROM CARCINOGENIC COMPOUNDS

EPA has determined that remedial actions should mitigaterisk to fall within a range of 10~4 to 10 , which the Agencybelieves to be a generally acceptable level of risk. A risk of1 X 10 would mean that one person in a million is in potentialdanger of developing cancer from the site contaminants. The

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carcinogenic risks were calculated for the evaluated pathways atthe site. The carcinogenic risk to future onsite residents is3.7 X 10~4. The risk to future offsite residents is 1.7 X 10~4.Onsite risk to future construction workers at the site was calcu-lated to be 3.4 X 10~5 and the risk to future onsite workers atthe public works garage is 1.1 X 10~. Table 7 summarizes siterisks for the various pathways.

4.5.3 RISKS FROM EXPOSURE TO SOILS

Based on the pathway analysis it was also determined thatexposure to site soils results in an unacceptable risk to personshaving direct contact with these site soils. Site soils contami-nated with carcinogenic PAHs are the principal threat at thePeoples site due to the threat of direct exposure by public worksgarage workers to these soils. The risk for residential exposureby ingestion of chemicals in the soil by children is 1.2 x 10(Table 8). The risk for residential exposure by ingestion ofchemicals in the soil by adults is 2.0 x 10~4 (Table 9)_. Therisk to workers at the public works garage is 1.1 x 10 based onexposure by ingestion of chemicals in the soil (Table 10). Therisk for residential exposure by ingestion of chemicals in soilby construction workers is 3.4 x 10~5 (Table 11).

4.5.4 RISKS FROM EXPOSURE TO GROUND WATER

It was determined that exposure could result from groundwater in zones contaminated by chemical compounds from the site,based on the potential ground water yield and consumption fromboth the silty sand and alluvial aquifers. A listing of welllocations, compounds, and contaminant concentrations used in therisk calculations is provided in Table 12. The alluvial aquiferpresents a carcinogenic risk of 1.70 x 10~4 for residentialconsumption of ground water by adults (Table 13).

4.5.4 CONCLUSION

In conclusion, based on the results of the risk assessment,EPA has determined that actual or threatened releases of hazard-ous substances from this site, if not remediated by the selectedremedy may present a current or potential threat to publichealth, welfare, or the environment.


No federal and state cleanup standards for the contaminantsof concern in soil have been established at this time. There-fore, it is appropriate to determine soil cleanup levels on asite-specific basis using the carcinogenic risk factors developedin the risk assessment. At this site, the 10~6 risk level wouldbe protective if no institutional controls were in place. Usingthe proper institutional controls at the site, EPA believes that

the cleanup of soil at this site would be adequately protectiveof human health and the environment when using the 10~4 risklevel. Based on this risk level, EPA considers a cleanup levelfor soil, from surface level to six feet below surface, of 500mg/kg for total PAH contaminants and 100 mg/kg carcinogenic PAHcontaminants to be protective of human health. This cleanuplevel calculated to a risk of 5.8 x 10 ~4 for incidental soilingestion by public works garage workers, the population with thehighest potential for incidental exposure. PAH contaminantsbelow 6 feet are not considered by EPA to constitute a directcontact threat to persons at the site. The purpose of clean upof soils below 6 feet would be to protect ground water from con-tamination from coal tar materials. The developed cleanup levelsspecify a concentration in the soil that is sufficiently protec-tive of human health and the environment when considering insti-tutional controls required at the site.

The 40 C.F.R. 300.430 states that preliminary remediationgoals are to be set at a 10~6 excess upper bound lifetime cancerrisk level as a point of departure, but may be revised to a risklevel in the acceptable range (10~4 to 10 ) based on considera-tion of appropriate factors, including uncertainty, technical,and exposure factors.

Federal and state cleanup standards have been establishedfor ground water. EPA has established the Safe Drinking WaterAct National Primary Drinking Water Standards' MaximumContaminant Levels (MCLs) as cleanup criteria for drinking wateraquifers. The Iowa Administrative Code Chapter 133, effectiveAugust 16, 1989, established action levels for contaminatedground water in Iowa. The level to first be considered is theEPA lifetime health advisory level (HAL), then the EPA negligiblerisk level (NRL), and finally MCLs. The most stringent level isconsidered to be the appropriate cleanup criteria for contaminat-ed ground water. These levels correspond to a protective risklevel of 10~6.

For the Peoples site, EPA believes that a cleanup level of1 ug/1 (parts per billion) benzene, the most abundant volatileorganic present in the contaminated ground water, would be pro-tective of human health, based on the NRL. The level that EPAbelieves would be protective for carcinogenic PAHs such asbenzo(a)pyrene is 0.2 ug/1 (parts per billion), based on theanalytical detection limit.

For carcinogenic PAHs for which there are no state or feder-al standards, the proposed cleanup levels will be establishedusing the detection limits for each specific compound, based onthe best available technology at the time of the signing of thisROD. The goal for these cleanup levels is to achieve a levelprotective of human health and the environment. EPA believesthat a level established using the current best available detec-

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tion limits will fulfill this goal. The minimum laboratorydetection limits that can be achieved under ideal conditions forcarcinogenic PAHs corresponds to a protective risk level of 10~ .The best level that can be measured practically during routinelaboratory operating conditions correspond to a protective risklevel of 10~ . The 10~4 risk level is considered appropriate forthis site based on the uncertainty factor and the technicalfactors associated with the detection/quantification limits forcontaminants.

The levels discussed in this section have been reviewed andapproved by ATSDR. Table 5 lists the remediation levels thatwill be used for ground water remediation at this site, includingthe practical detection limits for the carcinogenic PAHs.

4.7 ENVIRONMENTAL RISKS

The U.S. Fish and Wildlife Service (USFWS) manages 194,000acres of the upper Mississippi River from Wabasha, Minnesota toRock Island, Illinois as the Upper Mississippi Wildlife and FishFefuge. Although the industrial corridor of Dubuque is notmanaged as part of the refuge, areas in Wisconsin and Illinoisdirectly across form Dubuque are included in the refuge. TheUSFWS has identified two endangered species that may be locatedin the general vicinity of Dubuque. These species are the Hig-gins eye pearly mussel and the bald eagle. The USFWS indicatedthat the selected remedy will not impact these species or otheraquatic organisms associated with the Mississippi River if dis-charged site-related waters are treated to meet ARARs.

The principal threat to ground water is coal tar contaminat-ed source materials which will be treated in the selected remedy.Remediation of the source materials will also diminish environ-mental exposures by removing the direct contact threat to contam-inated soils.

5.0 SUMMARY OF ALTERNATIVES

The National Contingency Plan (NCP), 40 CFR Part 300,requires that certain alternatives be developed for evaluation inthe Proposed Plan:

• An alternative that removes or destroys the hazardousconstituents to the maximum extent feasible and eliminates theneed for long-term monitoring and management;

• One or more additional alternatives that reduce thetoxicity, mobility, or volume of the hazardous constituents;

• One or more alternatives that involve little or notreatment, but provide protection of human health and the

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environment by containing the hazardous constituents to controlexposure to the wastes;

• One or more innovative treatment technology alternativesif those technologies offer the potential for comparable orsuperior performance or implementability, fewer adverse effects,or lower costs than demonstrated technologies;

• A limited number of remedial alternatives for ground waterthat attain site-specific remediation levels witiin differentrestoration time periods utilizing one or more differenttechnologies; and

• The no-action alternative.

The alternatives that were evaluated in detail in theFeasibility Study are described in this section. Fivealternatives were determined to be appropriate for considerationat this site. These alternatives provided a range of variousremedial options to satisfy the requirements in the NCP. Thefollowing descriptions summarize the alternatives, includingtheir treatment components, implementation requirements and theestimated time for completion and costs.

5.1 NO ACTION

The NCP requires that the no-action alternative be evaluatedfor every site. This alternative (Alternative 1) provides abaseline for comparing the effectiveness of other remedialoptions. This alternative involves no further action at the siteto prevent the migration of contaminants from the site. Therewould be no costs associated with this alternative.

5.2 REMOVAL ACTION WITH GROUND WATER MONITORING

Alternative 2 does not include any remedial action beyondthe removal action currently being completed in the highwaycorridor. This alternative would also include ground watermonitoring involving periodic collection of ground water samplesfrom upgradient and downgradient wells in both the silty sand andalluvial aquifer. The objective of ground water quality monitor-ing for Alternative 2 would be to provide a quantitative assess-ment of the effectiveness of the technologies implemented in theremoval action toward minimizing the migration of coal tar con-taminants to the aquifers.

The technologies previously incorporated as part of theremoval action include: removal and treatment of contaminatedsoils in the highway corridor; incineration of excavated soils; aleachate collection system for residual contamination andgradient control in the silty sand aquifer; and institutionalcontrols for the site that include deed restrictions.

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It is estimated that the ground water monitoring plan wouldinclude semi-annual collection of samples for analysis of vola-tile organic chemicals (VOCs) and annual collection of samplesfor analysis of PAHs and other contaminants for a total of thirtyyears. It is assumed that samples would be collected from oneupgradient and five downgradient wells in the alluvial aquiferand one upgradient and three downgradient wells in the silty sandaquifer. The present worth total cost for the ground watermonitoring program is estimated to be $370,000 (excluding cost ofthe removal action).

5.3 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATEREXTRACTION AND TREATMENT.

Alternative 3 includes remedial actions to address the twomajor potential routes of exposure; direct contact with coal tarderived contamination in the soils and ingestion of contaminatedground water.

Surface soils would be excavated and removed from the sitefor treatment or disposal. It is estimated that 5,500 cubicyards of soil would be removed and treated or disposed offsiteusing one of three options. These options for treatment ordisposal of excavated soils are incineration, land disposal, andbiological treatment. Biological treatment of excavated soilswould consist of either land treatment or aerobic biologicalreactor treatment. During excavation air monitoring would beconducted to determine potential contaminant exposure to arearesidents and workers. Berms would be constructed to collectsurface runoff from excavation and soil storage areas.

Alternative 3 includes land disposal and biological treat-ment as options for disposal and/or treatment of excavated soils.This is a flexible alternative with regard to treatment of soils.If soil is treated biologically and replaced in the excavatedareas, some residual contamination may be present in the soilafter treatment thus reducing but not eliminating PAH contamina-tion. Current technologies for biological treatment of PAHs insoil have not been demonstrated to effectively reduce concentra-tions of all PAHs to environmentally acceptable concentrationsfor the quantities of excavated soils which would be generated byAlternative 3. Biological treatment technologies are in develop-ment which may effectively reduce PAH concentrations to environ-mentally acceptable concentrations in large quantities of soil.

A ground water extraction system would be installed toremove contaminated ground water from the alluvial and silty sandaquifers. Ground water would be treated to achieve the remedia-tion goals listed in Table 5. Extracted water from the alluvialaquifer would be treated with an air-stripper to remove VOCs anddischarged to the storm sewer. Extracted water from the siltysand aquifer would be discharged to the sanitary sewer. This

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ground water extraction system would minimize the migration ofcontaminants to the alluvial aquifer from either the silty sandor the contaminated soils above the silty sand.

The ground water monitoring system described in Alternative2 would be operated to determine the effectiveness of the soilremoval and ground water extraction system in preventing migra-tion of contaminants to the alluvial aquifer. The alluvialaquifer would be monitored for 10 years and the silty sand aquif-er would be monitored for 30 years.

It is estimated that the soil could be excavated and removedfrom the site in 6 to 12 months at a cost of $720,000 forexcavation and $700,000 for soil treatment or disposal. Groundwater extraction and treatment systems could be placed inoperation in approximately two years. It is estimated that thealluvial aquifer extraction system would be operated for 10 yearsand the silty sand system for 100 years. The present worth costfor the extraction system is estimated at $790,000 (cost assumes30 years operation and maintenance for silty sand system). Thepresent worth cost for Alternative 3 with incineration is esti-mated at $2,800,000 (excluding cost of the removal action). Thepresent worth cost estimate for Alternative 3 with land disposalis $2,600,000 and with biological treatment of excavated soils is$2,700,000.

5.4 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATEREXTRACTION AND TREATMENT, CAPPING OF SOURCE SOILS, AND IN SITUBIOREMEDIATION

Alternative 4 includes all the elements of Alternative 3plus in-situ bioremediation and capping of source soils. Thiswould provide further reduction of contaminated source areas anddecrease infiltration of water into the source areas. The opera-tional lifetime of the ground water extractions systems presentedin Alternative 3 would be reduced with biological treatment ofsource soils at depth.

In-situ bioremediation of contaminated soil and ground waterwould be conducted in the silty sand layer. An injection andextraction system would be developed to reduce the concentrationof coal tar derived contaminants through biological degradation.Bioremediation should treat coal tar derived contamination in theground water and contamination sorbed to the soil particles.Although capping and ground water extraction and treatment mightachieve the remedial action objectives for the ground water,bioremediation should significantly reduce the time required tomeet these objectives.

Capping is included in Alternative 4 to reduce leachateproduction by limiting infiltration. This would reduce the rateof release to the underlying silty sand and alluvial aquifers.

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The cap would include a low permeability zone of compacted clayand a high density polyethylene (HOPE) membrane which is estimat-ed to reduce infiltration by a minimum of 99 percent.

It is estimated that construction of the cap would require 4to 8 months after completion of the soil excavation described inAlternative 3 and would cost $64,000. The time required forin-situ bioremediation would depend on completion of treatabilitystudies to determine site-specific requirements. It is estimatedthat treatability testing and initial implementation of anin-situ bioremediation could be completed in two years at apresent worth cost of $765,000 including 10 years of operation.The present worth cost for Alternative 4 with incineration ofexcavated soils is estimated at $3,500,000 (excluding cost of theremoval action). The present worth cost estimate for Alternative4 with land disposal is $3,300,000 and with biological treatmentof excavated soils is $3,400,000.

5.5 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATEREXTRACTION AND REMOVAL OF SOURCE SOILS

Alternative 5 would include all the elements of Alternative3 with additional removal of coal tar contaminated source soilsat depth (greater than 6 feet below surface). Compared toAlternative 3, the operational lifetime of the ground waterextraction systems would be reduced with removal of the sourcesoils at depth.

This alternative includes the additional removal of coal tarcontaminated soils at depth that may contribute contaminants tothe silty sand or the alluvial aquifer. This removal wouldreduce the total mass of contaminants on the site and wouldresult in a shorter operation of the silty sand ground waterextraction system. The soil volume calculation includesexcavation of all visibly contaminated soils as described in theboring logs. This soil volume estimate exceeds that provided inthe RI/FS because it includes excavation to the lower confiningunit.

It is estimated that 24,200 cubic yards of source soilswould be removed and disposed or treated for this alternative.The overall present worth cost for Alternative 5 with incinera-tion is estimated at $8,000,000 (excluding cost of the removalaction). The present worth cost estimate for Alternative 5 withland disposal is $7,200,000 and with biological treatment ofexcavated soils is $7,500,000.

6.0 SUMMARY AND COMPARATIVE ANALYSIS OF ALTERNATIVES

The NCP has established nine criteria that are used toevaluate remedial alternatives. These criteria serve as thebasis for conducting detailed analyses during the Feasibility

15

Study and subsequently are used to determine the appropriateremedy for the site.

A detailed analysis of the remedial alternatives was con-ducted, consisting of an assessment of the individual alterna-tives against each of the nine criteria and a comparative analy-sis that focused on the relative performance of each alternativeagainst those criteria. As a result of this detailed analysis,EPA has determined that a combination of Alternatives 4 and 5provides the best balance among the alternatives with respect tothe criteria.

When conducting the analysis, the nine criteria areorganized into three categories. The first such category isthreshold criteria. An alternative must meet the following tworequirements to be considered as a final remedy for the site:

6.1 OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

The selected remedy would involve the excavation andincineration of the source soil areas and contaminated soilareas. The highly contaminated soil areas remaining in the siltysand unit would also be addressed by in-situ bioremediation.Ground water from the alluvial aquifer would be treated with anair stripper and discharged to the storm sewer and the groundwater from the silty sand aquifer would be discharged to thesanitary sewer. This would reduce exposure to contaminated soilsand ground water to protective levels and also minimize thepotential for contaminant migration. Air monitoring would beconducted to determine if concentrations of airborne contaminantsexceed air quality criteria. If these criteria are exceededcontrol measures will be implemented. Access restrictions wouldprevent direct exposure to site soils by the general population.

The no-action alternative does not provide overallprotection to human health and the environment and therefore willnot be evaluated further because this threshold criteria is notattained. The alternatives involving incineration, 3 - 5 , pro-vide the permanent elimination of long-term residual risk. Thelong-term residual risk would also be eliminated by in-situbiological treatment in the silty sand unit to health-basedlevels of the contaminated soil in alternatives 4 and the select-ed remedy. Alternative 2 would not permanently eliminate residu-al risk and therefore does not provide for protection of humanhealth and the environment. The alternatives which includeground water treatment and the selected remedy, provide foroverall protection of human health and the environment.

6.2 COMPLIANCE WITH ARARS

The selected remedy would comply with all federal and stateapplicable or relevant and appropriate requirements (ARARs).

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Applicable requirements are those state or federal requirementslegally applicable to the release or remedial action contemplatedthat specifically address a hazardous substance, pollutant,contaminant, remedial action, location, or other circumstancefound at the site. If it is determined that a requirement is notapplicable, it may still be relevant and appropriate to thecircumstances of the release. Requirements are relevant andappropriate if they address problems or situations sufficientlysimilar to the circumstances of the release or remedial actioncontemplated', and are well-suited to the site.

Applicable chemical-specific requirements associated withthis alternative include the National Ambient Air QualityStandards, promulgated under the Clean Air Act. Source controlon emissions from the air-stripper would be implemented if airmonitoring indicate exceedances of applicable air quality crite-ria. The MCLs for this site would be applicable and would haveto be achieved. Also identified as applicable for this site arethe Iowa Administrative Code Chapter 133 standards discussed inSection 4.6.

No location-specific ARARs were identified for the site.The federal action-specific ARARs that the selected remedy wouldhave to comply with are: all pertinent Occupational Safety andHealth Act requirements and all Hazardous MaterialsTransportation Act regulations; the Resource Conservation andRecovery Act (RCRA) regulations applicable to solid wastes, 40C.F.R. 257; the Clean Water Act regulations applicable to dis-charge to POTWs and surface waters; and the Clean Air Act re-quirements applicable to incinerators. The action-specific stateARARs include the Iowa Environmental Quality Act regulations; theIowa Air Pollution Control Regulations, Sections 22.4, 22.5,23.1, 23.3, and 23.4; and the Iowa Water Pollution Control regu-lations, Sections 61.3, 62.1, 62.6, 62.8, 62.9 63, 64.2 and 64.3.

The hazardous waste treatment storage and disposal regula-tions under RCRA are applicable to wastes at this site where coaltars, when tested by the toxicity characteristic leachate proce-dure (TCLP), are found to contain concentrations of hazardousconstituents in excess of regulatory values. Otherwise, RCRAregulations are considered relevant and appropriate, due to thehazardous nature of coal tars. Therefore the substantive re-quirements of RCRA, specifically 40 C.F.R. Parts 264 and 270,must be met for non-TCLP wastes, including the requirement thatan incinerator destroy the contaminants at an efficiency of99.99%. A trial burn was conducted and demonstrated this removalefficiency. Both the administrative and substantive requirementsof Subtitle C of RCRA must be met for those hazardous constitu-ents that exceed regulatory levels.

All waste generated as a result of remedial actions at thePeoples site are subject to requirements of the EPA off-site

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policy. The off site policy, as stated in CERCLA §121(d)(3),requires that hazardous substances, pollutants, or contaminantstransferred off site for treatment, storage, or disposal during aCERCLA response action be transferred to a facility operating incompliance with §3004 and §3005 of RCRA and other applicable lawsand regulations.

Alternative 2, which calls only for ground water monitoringrather than treatment, does not reduce the spread of contaminantsin ground water and therefore does not provide adequate protec-tion of human health and the environment. Also this alternativedoes not meet the chemical-specific ARARs associated with thissite. Therefore, this alternative will not be further consideredbased on the threshold criteria.

Alternatives 3-5 would meet the ground water cleanupstandards previously identified. Other chemical-specific ARARs,such as the Clean Air Act, would be met for all other alterna-tives. Air monitoring would be conducted to assure compliancewith applicable air standards.

The action-specific ARARs would be met for all otheralternatives considered. These ARARs include all OSHArequirements, all Hazardous Materials Transportation Actregulations, and the RCRA requirements previously discussed.

The second category of criteria is primary balancingcriteria. The following five criteria are used to evaluate thealternatives to determine the option that provides the mostbalance for the final remedy for the site:

6.3 LONG-TERM EFFECTIVENESS AND PERMANENCE

The incineration of the contaminated soils and the treatmentof ground water in alternatives 3-5 and the selected remedieswould eliminate the long-term risks associated with directcontact and potential migration of these areas, providing apermanent solution. Highly contaminated source soil areas wouldcontinue to leach contaminants into the environment if nottreated or removed. The source soil removal of Alternative 5 andthe enhanced in-situ biodegradation process of Alternative 4would reduce contamination in these areas, adding to the long-term effectiveness of these alternatives. The selected remedyinvolves a combination of these technologies which would reducecontamination and provide for long-term effectiveness.

The alternatives involving incineration as a soil disposaloption, 3-5 and the selected remedy would eliminate the risksassociated with source areas and provide a permanent remedy forcontaminated soils. The residual risk associated withcontaminants in ground water above health-based levels would beeliminated by alternatives 3-5 and the selected remedy. Long-

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term ground water monitoring would be required for allalternatives. Alternative 3 does not involve excavation ofcontaminated soils at depth and would not permanently eliminateresidual risk, requiring long-term control measures throughoutthe life of the alternative, estimated at 100 years.

Alternative 4 would reduce contamination in the silty sandunit through the in-situ biodegradation process. However, thisalternative does not remove highly contaminated source soil areasfrom 6 feet below surface to the top of the upper confininglayer. This would leave a large volume of contaminated soils asa source of chemicals of concern that could potentially leachinto the ground water over time. Alternative 5 relies on groundwater extraction to remove contaminants form the silty sand unitwhich would require a much longer period to reduce contaminantconcentrations to acceptable levels.

6.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME

The selected remedy treats contaminated surface soils(surface to 6 feet below surface), highly contaminated soilareas, and ground water to achieve reduction of toxicity,mobility and volume of contaminants at the site. Theincineration of these soils provides permanent treatment. Theexcavated nonhazardous waste materials would be incineratedoffsite in accordance with the substantive requirements of RCRA,with a 99.99% destruction and removal efficiency (ORE) of contam-inants. Those materials that exceed TCLP levels would be managedin accordance with all RCRA requirements. The enhanced in-situbioremediation process would reduce the toxicity, mobility, orvolume of the highly contaminated soils in the silty sand unit.This would also reduce the volume of contaminated ground waterthat will eventually need to be treated at the site, since thesehighly contaminated areas will continue to leach contaminantsinto the environment. The biodegradation process would treatthese areas.

The other alternatives involving incineration (3 - 5), wouldprovide a permanent treatment for the excavated contaminatedsoils. The ground water treatment alternatives would also pro-vide a permanent treatment. Alternative 3 would not treat highlycontaminated source soils and therefore not provide for thepermanent reduction of the toxicity, mobility or, volume of thecontaminants in the source soil areas. Alternative 4 does notremove a large volume of contaminated soil above the silty sandunit and relies on a cap to reduce mobility which will requirelong-term maintenance.

Alternatives 3-5 include land disposal and biologicaltreatment as options for disposal and/or treatment of excavatedsoils. If soil is treated biologically and replaced in theexcavated areas, some residual contamination may be present in

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the soil after treatment thus reducing but not eliminating PAHcontamination. Current technologies for biological treatment ofPAHs in soil have not been demonstrated to effectively reduceconcentrations of all PAHs to environmentally acceptable concen-trations for the quantities of excavated soils which would begenerated by Alternatives 3 - 5, or the selected remedy.Biological treatment technologies are in development which mayeffectively reduce PAH concentrations to environmentally accept-able concentrations in large quantities of soil. Land disposalof contaminated soils would not provide a reduction of toxicityor volume, but would reduce mobility. Land disposal would notprovide treatment of excavated soils.

6.5 SHORT-TERM EFFECTIVENESS

The short-term risks associated with the selected remedywould involve the normal construction hazards associated with theexcavation of source and soil areas and with the construction andinstallation of wells. Volatile emissions might also be releasedduring excavation and materials handling, and during the drillingand sampling of wells. This alternative would involve thetransportation of wastes and would have short-term risksassociated with offsite transport.

Any potential for exposure can be effectively minimized orcontrolled by compliance with the action-specific ARARs and byimplementing engineering controls at the site, such asrestricting access to the site, monitoring for volatileemissions, and adhering to a site-specific safety plan. Inconformance to OSHA standards, all site workers would be health-and-safety trained, wear the appropriate protective clothing, andparticipate in a medical monitoring program.

Workers at the City of Dubuque public works garage may beworking on the Peoples site during excavation of contaminatedsoils. Air monitoring would be conducted during soil excavationactivities to determine airborne concentrations of PAHs andBETXs. If levels of these contaminants exceed OSHA standards theCity of Dubuque would be notified.

.The selected remedy would require 24 to 36 months tocomplete the removal and treatment of source areas and contami-nant soil. Incineration of excavated soils is estimated torequire 24 months. The time estimated for installation of theground water extraction system and the establishment of the plumecontainment is 24 months. The time necessary to achieve a reduc-tion in contaminant levels to the health-based standards isestimated at 10 to 20 years. Installation of the biologicalremediation system is estimated at 24 months.

Alternative 5 will require excavation of larger soil volumesthan the selected remedy or Alternatives 3 and 4. Incineration

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would require storage onsite while soil is transported offsitefor incineration. It is estimated that soils may be stored onsite for a period of 8 months longer than the selected remedy.As previously noted, compliance with the action-specific ARARswould effectively minimize and control the potential exposureduring implementation of the alternative.

Incineration for alternatives 3 and 4 would require 6 to 12months to complete the removal and treatment of contaminatedsoil. Construction of the cap in alternative 3 would require 4to 8 months. All the remaining alternatives would require 24months for installation of the ground water system and the estab-lishment of the plume containment. The biological treatment ofthe soil areas in Alternative 4 is estimated to take 24 months.

6.6 IMPLEMENTABILITY

Implementation of the selected remedy would involveconventional construction technologies. Excavation, pumping,decontamination, and gradient control are frequently usedtechnologies that have been proven to be effective. Incinerationis a proven technology for coal tar wastes and a trial burnconducted at a power plant boiler has demonstrated it can achievethe RCRA destruction efficiency for site derived coal tar wastes.The enhanced in-situ bioreroediation process has not been exten-sively used at coal gas sites and therefore would be implementedafter conducting an extensive treatability study.

The other alternatives involving incineration and the groundwater treatment system would have the same ease in implementabil-ity. Capping is also a frequently used technology. Excavationbelow the upper confining unit would not be practical near thepublic works garage and Kerper Boulevard as it would requireexcavation to approximately 30 feet. Insufficient space isavailable on the site for the setback requirements to excavate tothis depth. Sheet pilings may not provide sufficient stability.

Biological treatment of excavated soils would require suffi-cient space onsite to construct a biological reactor system. Itwould be difficult to locate this system on the site due to spacelimitations. Biological treatment by land farming technologieswould require offsite facilities in order to have the necessaryspace to implement this technology.

6.7 COST

The cost of the selected remedy would be the cost foralternative 4 plus the additional cost for source soils removalless construction costs for capping. The present worth cost forthe selected remedy is estimated at $8,000,000 (excluding costfor the removal). This includes operation and maintenance costsfor 10 years of operation.

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The selected remedy would remove highly contaminated sourcesoil areas below 6 feet to the top of the upper confining layer.This would remove a source of chemicals of concern that couldpotentially leach into the ground water. Alternative 4 would notremove these source soil areas below 6 feet potentially causingan increase in the time requirements for ground waterremediation.

The range of total present worth costs for the alternativesis from $370,000 for alternative 2 to $8,000,000 for alternative5 (excluding costs for the removal action).

The present worth cost estimates stated above include incin-eration as the disposal method for excavated soils. Costs forbiological treatment or land disposal of soils do not differsignificantly from those for incineration.

The third category of criteria is modifying criteria. Thefollowing two criteria are considered when evaluating thealternatives and are used to help determine the final remedy forthe site:

6.8 STATE ACCEPTANCE

The State of Iowa supports the remedy selected for thecleanup of contaminated soils and ground water at the Peoplessite.

6.9 COMMUNITY ACCEPTANCE

Community acceptance of the selected remedy was evaluatedduring the public comment period. The comments received arecontained in the Responsiveness Summary, Appendix A.

7.0 SUMMARY OF SELECTED REMEDY

Based on the evaluations prepared for each of the proposedalternatives, EPA has made a determination that the appropriateremedy for the Peoples site is a combination of Alternatives 4and 5 described as follows: excavation and incineration ofcontaminated soil from surface to 6 feet below grade that exceed100 ing/kg carcinogenic PAHs and 500 mg/kg total PAHs; excavationand incineration of contaminated source soils that have visiblecoal tar contamination from 6 feet below grade to the surface ofthe upper confining unit; enhanced in-situ bioremediation totreat the contaminated ground water and contaminated source soilsin the silty sand unit; ground water extraction of both the siltysand and alluvial aquifers to reduce concentrations to levelsrequired by the State of Iowa Administrative Code Chapter 133;and ground water monitoring of both the silty sand and alluvialaquifers to assure successful implementation of ground water

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treatment systems. This alternative provides the best balance ofthe factors identified by the nine criteria.

The selected remedy would require 24 to 36 months to com-plete the removal and treatment of source areas and contaminatedsoil. Incineration of excavated soils is estimated to require 24months. The time estimated for installation of the ground waterextraction system and the establishment of the plume containmentis 24 months. The time necessary to achieve a reduction incontaminant levels to the health-based standards is estimated at10 to 20 years. Installation of the biological remediationsystem is estimated at 24 months.

It is estimated that 18,500 cubic yards of contaminatedsoils would be removed and treated by incineration. It is esti-mated that operation of the alluvial extraction system wouldcontinue for 10 years, 5 years for the silty sand aquifer extrac-tion system, and 5 years for the bioremediation system. However,the operation of these systems would continue as long as neces-sary if results of the ground water monitoring indicate contarai-rint concentrations have not attained the remedial criteria.Injection of ground water into any aquifer would not be used as amethod of disposal for ground water. Ground water removed fromthe silty sand extraction system will be discharged to the Cityof Dubuque sanitary sewer system. Ground water removed from thealluvial extraction system will be treated and discharged to theCity of Dubuque storm sewer system.

The selected remedy is in addition to the removal actioncompleted in July 1991 which eliminated contamination sources inthe Highway 61 corridor on the western portion of the site. Theprovisions of the removal order require institutional controlsincluding restriction of site access and deed restrictions allow-ing only commercial use of the property. The site will remainsecured to prevent access by the general population. The tech-nologies previously incorporated as part of the removal actioninclude: removal and treatment of contaminated soils in thehighway corridor; incineration of excavated soils; a leachatecollection system for residual contamination and gradient controlin the silty sand aquifer.

The horizontal extent of excavation will be determined usingthe 100 mg/kg carcinogenic PAH/500 mg/kg total PAH level. Thevertical extent of excavation may also be adjusted in the field,with a maximum vertical excavation of 6 feet based on this level.Excavation from 6 feet below grade to the top of the upper con-fining unit will be based on visible coal tar contamination. Aprocedure will be developed to determine the existence of visiblecoal tar contamination. Excavation will cease at the top of theupper confining unit. The base of each excavation area will bedivided into sections and sampled to determine the concentrationof contaminants that remain. The base of the excavation areas

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will be determined by either the 100 mg/kg carcinogenic PAH/500 rog/kg total PAH level or the visible coal tar standarddepending on which is applicable as previously described.

This cleanup level of 500 mg/kg total PAH/100 rog/kgcarcinogenic PAH calculates to a risk of 5.8 x 10 forincidental soil ingestion by public works garage workers, thepopulation with the highest potential for incidental exposure.PAH contaminants below 6 feet are not considered by EPA toconstitute a direct contact threat to persons at the site. Thepurpose of clean up of soils below 6 feet would be to protectground water from contamination from coal tar materials.

Excavated material will be separated to remove materials notcompatible with the incineration process. All material greaterthan 2 inches in diameter will be separated. Materials less than2 inches in diameter will be placed in the contaminated soilstorage area, along with source tars, before being transported tothe incinerator. This pad will meet the substantive requirementsof RCRA. All material that cannot be reduced to a manageablesize will be steam-cleaned and sent for disposal in accordancewith RCRA. The proper transportation requirements will be metand the trucks will be decontaminated.

Chemical dust-suppressants and/or water will be used fordust control during activities at the site. Volatile emissionswill be monitored during all operations. Berms will be con-structed and grading performed to control water run-on and run-off, and sumps will collect water for treatment. Clean fill willbe added to excavated areas. Storage piles of contaminatedexcavated soils will be covered with 60-mil high density polyeth-ylene (HOPE) until removed for incineration.

Monitoring wells will be installed at various locations atthe site to confirm the efficacy of the ground water extractionsystem. Extraction wells will be installed in both the siltysand and alluvial aquifers for the removal of ground water andsubsequent treatment. The goal of the treatment process will be1 ug/1 (ppb) benzene, which corresponds to the 10~6 risk level.The process will also meet the ground water remediation levelslisted in Table 5, which includes the current practical detectionlimits for carcinogenic PAHs. If, in EPA's judgment, implementa-tion of the selected ground water remedy clearly demonstratesthat it will be technically impracticable to achieve and maintainthe ground water remediation levels established in this ROD, EPAwill re-evaluate those levels. For example, the cleanup levelsfor ground water may be re-evaluated if it has been demonstratedthat contaminant levels have ceased to decline over time and areremaining constant at some statistically significant level aboveremediation goals. In such a case, an alternate concentrationlevel may be established and/or a chemical-specific ARAR waivermay be invoked. Any newly established remediation levels must be

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protective of human health and the environment. The ROD will beamended or an explanation of Significant Differences will beissued to inform the public of the details if such actions occur.

The water pumped from the alluvial aquifer will be treatedusing air stripper technology and discharged to the City ofDubuque storm sewer system. Water pumped from the alluvialaquifer will be analyzed as required by the Clean Water Act (CWA)prior to discharge to a surface water body. Water discharged tothe storm sewer must meet all applicable CWA requirements andmust be treated as necessary to remove contaminants as requiredby the CWA. Air modeling and/or analysis will be conducted todetermine potential requirements for emission controls on the airstripper. Emission controls will be installed as required by EPAand State of Iowa regulations.

The water pumped from the silty sand aquifer will be dis-charged to the City of Dubuque sanitary sewer system for treat-ment at the publicly-owned treatment works (POTW). Water dis-charged to the sanitary sewer must meet all CWA pretreatment: ccrjirerncnts for discharge to the POTW through the sanitary sewersystem.

Air monitoring will be conducted in connection with both theexcavation activities and the air stripping of water pumped fromthe alluvial aquifer. All applicable National Ambient Air Quali-ty Standards, promulgated State of Iowa air standards, or otherpromulgated federal air standards must not be exceeded at thesite boundaries. Appropriate control measures will be implement-ed as necessary to achieve all applicable air quality standards.Air monitoring and/or modeling will be conducted to determine airquality control measure requirements.

The in-situ bioremediation process will begin with a pilotstudy to determine the proper types and amounts of nutrients andpossible engineered organisms to inject into the aquifer forstimulating natural biological degradation. The nutrients,dissolved oxygen, and organisms will be added to treated groundwater and reinjected into the aquifer using injection wells.Injection well placement will be determined through ground watermodeling. The system will use injection and extraction wells asdetermined through ground water modeling and treatability stud-ies. Procedures for determining the efficacy of the bioremedia-tion system will be determined and implemented. The system willbe modified as necessary to reduce concentrations of contaminantsin the silty sand unit.

The goal of this remedial action is to restore the groundwater to its beneficial use as required by IDNR regulations.Based on information obtained during the remedial investigation,and the analysis of the remedial alternatives EPA and the Stateof Iowa believe that the selected remedy may be able to achieve

25

this goal. Ground water contamination may be especially persist-ent in the immediate vicinity of the contaminants' source. Theability to achieve cleanup levels throughout the area of attain-ment, or plume, cannot be determined until the extraction systemhas been implemented, modified as necessary, and plume responsemonitored over time. If the selected remedy cannot meet thespecified remediation at any or all of the monitoring pointsduring implementation, the contingency measures described in thissection may replace the selected remedy and the remediationlevels for these portions of the plume. These measures areconsidered to protect human health and the environment, and aretechnically practicable under the corresponding circumstances.

The selected remedy will include ground water extraction foran estimated period of 10 years for the alluvial aquifer and anestimated 5 years for the silty sand aquifer, during which timethe system's performance will be monitored on a regular basis andadjusted as warranted by the performance data collected duringoperation. Modifications may include any or all of thefollowing:

• Discontinuing pumping at individual wells where cleanupgoals have been attained

• Alternating pumping at wells to eliminate stagnationpoints

• Pulse pumping to allow aquifer equilibrium and encourageadsorbed contaminants to partition to the ground water

Installing additional extraction wells to facilitate oraccelerate cleanup of the contaminant plume

To ensure that cleanup levels are maintained, the aquiferwill be monitored at those wells where pumping has ceased follow-ing discontinuation of ground water extraction.

If it is determined, on the basis of the preceding criteriaand the system performance data, that certain portions of theaquifer cannot be restored to their beneficial uses, all of thefollowing measures involving long-term management may occur, foran indefinite period of time, as a modification of the existingsystem:

Engineering controls such as physical barriers or long-term gradient control provided by low level pumping, willbe implemented as containment measures

Chemical Specific ARARs will be waived for cleanup offor those portions of the aquifer based on the technicalimpracticability or achieving further contaminantreduction

26

Institutional control will be provided and maintained torestrict access to those portions of the aquifer thatremain above remediation levels

• Monitoring of specified wells will continue

• Remedial technologies for ground water restoration willbe reevaluated periodically

The decision to invoke any or all of these measures may bemade during a periodic review of the remedial action, which willoccur at a minimum of 5 year intervals in accordance with Section121(C) Of CERCLA.

The site will be fenced and ground water and land-use re-strictions will be implemented to minimize activities which wouldprovide direct contact with contaminants. Initially, well-moni-toring will be performed bimonthly after the remedy is implement-ed. After the first year, monitoring will be performed quarterlyfor 5 years, then biannually for the next thirty years, to r-nsurethat the remedy was successful.

A review of the effectiveness of the selected remedy will beconducted each five years following completion of constructionactivities as required for implementation of the selected remedy.Five year reviews are conducted pursuant to Section 121(c) ofCERCLA which requires the review of remedial actions no lessoften that each five years for sites where the remedial actionresults in any hazardous substances, pollutants, or contaminantsremaining at the site. The purpose of the five review is toassure that human health and the environment are being protectedby the implementation of the selected remedy.

Table 17 lists the capital costs for each major component ofthe selected remedy. The total construction costs are estimatedto be $7,000,000 and the total operations and maintenance costsare estimated to be $1,000,000 giving a total present worth of$8,000,000.

Changes may be made to the selected remedy during remedialdesign work and the processes of construction.

8.0 STATUTORY DETERMINATIONS

The selected remedy satisfies the statutory requirements ofSection 121 of CERCLA, 42 U.S.C. § 9721, as follows:

8.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

The selected remedy will be protective of human health andthe environment by providing for the permanent destruction ofcontaminated soil areas. These areas will be excavated to a

27

level protective of human health and the environment that corre-sponds to the 10~4 risk level. Proper institutional controlswill be taken at the site, including site fencing, ground wateruse restrictions and land use restrictions.

The ground water will be treated until the off-sitecontaminants are below health-based standards, providingprotection to the 10~6 risk level for benzene and the 10~4 risklevel for carcinogenic PAHs. Ground water from the alluvialaquifer will be treated with an air stripper and discharged tothe storm sewer. Air monitoring will be conducted to determineif concentrations of airborne contaminants exceed air qualitycriteria and if these criteria are exceeded control measures willbe implemented. The enhanced in-situ bioremediation process willaddress contaminated soil areas that will not be excavated.

The selected remedy will provide maximized long-termeffectiveness and will reduce the toxicity, mobility and volumeof wastes to the greatest extent practicable. The selectedalternative will also have minimal short-term risks and theproper controls will be taken to minimize these risks.

8.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATEREQUIREMENTS

The selected remedy complies with all ARARs associated withthis site. All chemical-specific ARARs will be met, includingCAA, RCRA and the Iowa Administrative Code Chapter 133, whichrequires one of three standards, MCLs, HALs, or NRLs. Allaction-specific ARARs, including all OSHA, RCRA, and DOTrequirements, will also be met. No location-specific ARARs wereidentified at this site.

8.3 COST-EFFECTIVENESS

The overall effectiveness of the selected remedy isproportional to its estimated cost of $8,000,000. The soilexcavation and incineration and the ground water treatment proc-ess are necessary to provide protection of human health and theenvironment. The added cost of the bioremediation system isreasonable when considering the added protection that will beprovided for human health and the environment in addressing thecontaminants. There would be a reduction in the time needed fortreatment of the aquifer, resulting in a decreased cost.

8.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVETREATMENT TECHNOLOGIES TO THE MAXIMUM EXTENT PRACTICABLE

The EPA has determined that the selected remedy representsthe maximum extent to which permanent solutions and treatmenttechnologies can be utilized in a cost-effective manner for thePeoples Natural Gas Site. Of those alternatives that are protec-

28

tive of human health and the environment and comply with ARARs,EPA has determined that this selected remedy provides the bestbalance in terms of long-term effectiveness and permanence,reduction in toxicity, mobility, or volume achieved throughtreatment, short-term effectiveness, implementability, and cost.Also EPA considered the statutory preference for treatment as aprincipal element, and considered input from the community. TheState of Iowa agrees with these determinations.

The selected remedy utilizes proven technologies inincineration and the ground water treatment system that can beeffectively implemented. These processes provide the best solu-tions in addressing the contaminants at the site. The enhancedin-situ bioremediation process will provide treatment for thecontaminated silty sand unit which would otherwise have to beleft unattended and therefore significantly add to the timerequired for treating the ground water. Therefore this remedyprovides treatment technologies to the maximum extent practicableat this site.

The selected remedy permanently destroys the contaminatedsoil areas and treats the off-site ground water to below health-based standards, providing for long-term effectiveness and perma-nence. Alternatives 2 does not permanently eliminate risks atthe site. All other alternatives provide permanent protection.

The selected remedy provides maximum reduction of toxicity,mobility, and volume. The other alternatives involvingincineration, 3, 4, and 5, also provide for the reduction oftoxicity, mobility, or volume, however alternative 2 would nottreat the contaminated ground water. The other alternativesinvolving incineration (3 - 5), would provide a permanent treat-ment for the excavated contaminated soils. The ground watertreatment alternatives would also provide a permanent treatment.Alternatives 3 would not treat highly contaminated source soilsand therefore not provide for the permanent reduction of thetoxicity, mobility, or volume of the contaminants in the sourcesoil areas. Alternative 4 does not remove a large volume ofcontaminated soil above the silty sand unit and relies on a capto reduce mobility which will require long-term maintenance.

The short-term risks associated with the selected remedy areminimal and will be attended to with the proper controls at thesite. The same general short-term risks apply to allalternatives utilizing excavation and transport of waste whichinvolve more short-term risks. These risks will be minimizedthrough compliance with ARARs.

The selected remedy utilizes proven and implementabletechnologies in excavation, incineration, and ground water treat-ment. The in-situ biological alternative portions provide addedreduction in the toxicity, mobility, and volume at a reasonable

29

cost. Alternative technologies for biological treatment of PAHsin excavated soils will require further development before beingconsidered for implementation at the site.

In order to satisfy the preference for a permanent solution,alternatives 2 was eliminated. The incineration of the contami-nated soils and the treatment of ground water in alternatives 3 -5 and the selected remedy would eliminate the long-term risksassociated with direct contact and potential migration of theseareas, providing a permanent solution. Highly contaminatedsource soil areas would continue to leach contaminants into theenvironment if not treated or removed. The source soil removalof Alternative 5 and the enhanced in-situ biodegradation processof Alternative 4 would reduce contamination in these areas,adding to the long-term effectiveness of these alternatives. Theselected remedy involves a combination of these technologieswhich would reduce contamination and provide for long-term effec-tiveness.

The alternatives involving incineration as a soil disposaloption, 3-5 and the selected remedy, would eliminate the risksassociated with source areas and provide a permanent remedy forcontaminated soils. The residual risk associated withcontaminants in ground water above health-based levels would beeliminated by alternatives 3-5 and the selected remedy. Long-term ground water monitoring would be required for allalternatives. Alternative 3 does not involve excavation ofcontaminated soils at depth and would not permanently eliminateresidual risk, requiring long-term control measures throughoutthe life of the alternative, estimated at 100 years.

Alternative 4 would reduce contamination in the silty sandunit through the in-situ biodegradation process. However, thisalternative does not remove highly contaminated source soil areasfrom 6 feet below surface to the top of the upper confininglayer. This would leave a large volume of contaminated soils asa source of chemicals of concern that could potentially leachinto the ground water over time. Alternative 5 relies on groundwater extraction to remove contaminants form the silty sand unitwhich would require a much longer period to reduce contaminantconcentrations to acceptable levels. Alternative 5 would involvethe excavation of 24,200 cubic yards of soil as opposed to 18,500cubic yards for the selected remedy.

For these reasons, the selected alternative provides thebest balance of trade-offs with respect to these criteria.

8.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT

The selected remedy involves treatment of the contaminatedsoil and source areas by incineration. The ground water istreated by the City of Dubuque POTW or by other technologies yet

30

to be determined. The unexcavated source areas will be treatedby the in-situ enhance bioremediation process. Therefore, thestatutory preference for remedies that employ treatment as aprincipal element is satisfied.

9.0 DOCUMENTATION OF SIGNIFICANT CHANGES

No significant changes were made in selecting the preferredalternative as described in the Proposed Plan.

31

FIGURES

SKANSAS C I T Y

MISSOURI

Figure 1LOCATION MAP

PEOPLES NATURAL GAS SITE

&?$ \'"Vno# \ '

PEOPLES NATURALGAS SITE LOCATIO

2000 4000

Scale in Feet

Figure 2

VICINITY MAPPEOPLES NATURAL GAS SITE

Mgure 3SITE PLAN: EXISTING CONDITIONS. 1*90

Peoples Natural Gas Site

Figure *PROPOSED U.S. HIGHWAY (1 ALIGNMENT

People* Natural Ga* Site

Figure SGEOLOGIC CROSS SECTION LOCATIONS

Peoples Natural Gas Site

4WEST

4'EAST

(10

600

590

x•*V

e- 580o

570

560

550

HYDROCEOLOCICUNIT

100 200 300 *00Dl l t ince , feet

500 600 700 800

Fill

Upper ConfiningUnit

Sllty Sand Unit

Lower ConfiningUnit

Alluvial Aquifer

Figure 6GEOLOGIC CROSS SECTION «-•'

People* Natural Ga* Site

««TT3» TMUUOMrOUMO Mil

Umlt. of Sodi In th« FIB Unit wtth Concentration*of Total PAH« >500 mg/kg (Loboralory).Corcinoo^nle PAH* >100 mg/kg (Laboratory), or>1.0OO mg/kg Total PAH* M«o»ur»d wtth

Serening IMhod.

Approilmal* Location of Sorfoc*OwooMl ATM of Go* Ptant Wart*

5.000 mg/kg—• TOW. fun

Approximot* LocationHeavily Contaminated

Figure 8LOCATION OF TAR/AMMONIA TANKS

AND GAS PLANT WASTE DISPOSAL AREAPeoples Natural Gas Site

2.900 mg/kg— BiMnns IMR or m. WTNrow. MH >2joo mtA< onCWKMOOCMC MH >I

/ N. I «tt HOUXf \

on or guwoucnm. run

Flgurt 9ESTIMATED LIMITS OF PAH SOIL

CONTAMINATION (SILTY SAND UNIT)Peoples Natural Cat Site

tWEST

*'

EAST

610

600

590

e- 580o

570

560

550

HYDROCEOLOCICUNIT

Fill

Upper ConfiningUnit

Sllty Sand Unit

Lower ConfiningUnit

Alluvial Aquifer

Llnlti of Soil With Concentrationsof Total PAHs > 500 mg/kg or CarcinogenicPAHs » 100 mg/kg

Units of Soil With Concmtratlontof Total PAHt>2.»00 wg/kg, orCarclnogwlc PAHt >20« »g/kg

100 200 300 liOOPittance, feet

500 600 700 800

Figure 10PAH CROSS SECTION 4 - 4 'People* Natural Cat Site

^S _l_ GREATER THAN 10 rnfl/kgJM TOTAL BETX * THE

ESTIMATED IMITS

GREATER THASUM TOTAL BETX

SILTY SANO UNIT

Flgur. 11ESTIMATED LIMITS OF

BETX SOIL CONTAMINATIONPeoples Natural Ca« Sit*

1/ttO «US«CT(0 CANCMOOCMCFAHl/TOTAI. PAW

MD HOT OCTICTTO

SCALE IN FEET

DISTRIBUTION OF PAH* INTHE CROUNOWATER

FEBRUARY 22 AND 23. l»»0(Concent ritloof In og/L)Peoples Natural G»* Sit*

Figure

DISTRIBUTIONTHE CROUNDWATER

NOVEMBER 1M»(Concentrations

SCALE IN FEIT

Figure UDISTRIBUTION OF BETX IN

THE CROUNOWATERJANUARY U»0

(Concentration In ug/L)Peoples Natural Cat Sit*

TABLES

TABLES

TABLE 1

SUMMARY OF MAXIMUM CONTAMINANT CONCENTRATIONS FOR WASTE DISPOSAL AREA

PEOPLES NATURAL GAS SITEDUBUQUE, IOWA

Compound of Concern

Total Carcinogenic PAHs (in mg/kg)

Total PAHs On mg/kg)

Sum of VOCs (in ppb)

Total Cyanides (in mg/kg)

WASTE DISPOSAL AREABoring 12*

Soil

920

8.000

140,000

870

Boring 21Soil

1800

5,400

98,000

41

Boring 22Soil

240

2,700

560,000

1,100

Boring 34Soil

44

350

14,000

38

Data Source: Barr Engineering Company, May 1991 (Table 2.1-2)* Barr Engineering Company, January 1991 (Table 8)

PAHs - Polynudear Aromatic HydrocarbonsVOCs - Volatile Organic Compounds

TABLE 2

SUMMARY OF MAXIMUM CONTAMINANT CONCENTRATIONS IN GROUNDWATER


(Concentration in ug/1)

COMPOUND OF CONCERN

Total Carcinogenic PAHs

Total PAHs

Sum of Volatile Organlcs (BETX)

Total Cyanides

WATER TABLE/UPPERCONFINING UNfT

Well W2

52

580

250

620

ALLUVIAL AQUIFERWell W8

350

9300

7500

4700J

Well W9

ND

48

-

18J

WellW12

ND

0.56

21

100

WellW16

ND

8

360

-

We(IW17

ND

43

500

160

SILTY SAND AQUIFERPiezometer 112

ND

4

8100

30

Data Source: Barr Engineering Company, May 1991 (Table 2.5-4, 2.5-6, 2.5-7)

BETX - Benzene, Ethyl Benzene, Toluene, XyleneND • Not detected

- Not analyzedj - Estimated Value

rodtbl-2.wk1

TABLE 3

SUMMARY STATISTICS FOR ANALYTICAL DATADETECTED COMPOUNDS - SOILPEOPLES NATURAL GAS SHE

DUBUQUE. IOWA

PARAMETER

SOIL DATA 0-6 FEET

BASE/NEUTRAL COMPOUNDS

AcenaphtheneAcenaphthyleneAnthraceneBenzo(a)anthraceneBenzo(a)pyrene&en20(b)fluorantheneBenzo(ghi)peryleneBenzo(k)fluorantheneChryseneDibenzo(ah)anthracenelndeno(1 ,2.3,cd)pyreneFluorantheneFluorenePhenanthrenePyreneNaphthalene2-MethylnaphthaleneDibenzofuranBenzo(e)pyreneCarbozoleIndenePeryleneTriphenyleneBis(2-ethylhexyl)phthalateDi-n-butyl phthalate

PHENOLS

Benzole acid

Positive/Total

6 / 1B14 / 1815 / 1816 / 1814 / 1813 / 1812 / 1813 / 1816 / 189 / 18

12 / 1817 / 1813 / 1817 / 1817 / 18

16 / 1810 / 1811 / 18

1 / 11 / 11 / 11 / 11 / 12 / 91 / 9

1 / 9

Range ofPositives(ug/Kg)

470 - 850.000200 - 380.000190 - 360.00070 - 240.000

150 - 420,000990 - 310,000590 - 230.000910 - 330,00071 - 240.000

190 - 64.000520 - 250.000100 - 770.000100 - 410.000110 - 820.00066 - 480.000

79 - 2.800.000210 - 720,000200 - 230.000

5.000 - 5.000370 - 370770 - 770

1.700 - 1.7004.700 - 4.700

140 - 16041 - 41

140 - 140

ArithmeticMean

(ug/Kg)

16.00042.47436,15234,52139,64135.56726.71237.95233,51912,97627.18091,19840.85497.71667.318

283.88489,59923.235

5.000370770

1.7004.700

19.75319.802

94,321

Data Source: Barr Engineering Company, May 1991 (Table 4.1-1)

Arithmetic means were calculated assuming a concentration of half the detection limit forcompounds below the detection limit.

TABLE 3(continued)

SUMMARY STATISTICS FOR ANALYTICAL DATADETECTED COMPOUNDS - SOILPEOPLES NATURAL GAS SITE

DUBUQUE. IOWA

PARAMETER

VOLATILE ORGANIC COMPOUNDS

BenzeneEthyl BenzeneTolueneXylene

CYANIDE

Cyanide

SOIL DATA BELOW 6 FEET


AcenaphtheneAcenaphthyleneAnthraceneBenzo(a)anthraceneBenzo(a)pyreneBenzo(b)fluorantheneBenzo(ghi)peryleneBenzo(k)fluorantheneChryseneDibenzo(ah)anthraceneldeno(l ,2,3,cd)pyreneFluorantheneFluorenePhenanthrenePyreneNaphthalene2-MethylnaphthaleneDibenzofuran

Positive/Total

1 / 11 / 11 / 11 / 1

7 / 8

37 / 10135 / 10134 / 10132 / 10125 / 10120 / 10111 / 10119 / 10136 / 1013 / 101

14 / 10140 / 10135 / 10145 / 10142 / 101

56 / 10147 / 10133 / 101


29 - 291,100 - 1.100

140 - 1402,600 - 2,600

1.200 - 1.100.000

64 - 360.00053 - 2.500.00051 - 1,300.00046 - 610.00052 - 360.00060 - 290,000

260 - 170.00034 - 260.00049 - 520,000

800 - 3.20042 - 160.00063 - 1.700.000

120 - 2.200.00067 - 3.600.00064 - 1.100.000

74 - 7.700.00058 - 3.400.00047 - 1.000.000

ArithmeticMean

(uQ/Kg)

291.100

1402.600

222,000

10.95040.86621 .67710.2246.5736.6444,5195,9799,1227.4744,381

28.35137.25863.10020.007

134,03967.88815.341


Arithmetic means were calculated assuming a concentration of half the detection limit forcompounds below the detection limit.

TABLE 3(continued)

SUMMARY STATISTICS FOR ANALYTICAL DATADETECTED COMPOUNDS - SOILPEOPLES NATURAL GAS STTE

DUBUOUE. IOWA

PARAMETER

Methylnaphthalene2,3-DihydroindeneBenzo(b)thiopheneBiphenylDibenzothiopheneIndeneIsoquinolineTriphenyleneBis(2-ethylhexyl)phthalateButyl benzyl phthalateDiethyl phthalateDi-n-butyl phthalate

PHENOLS

2,4-Dimethylphenol4-Chloro-m-cresolo-Cresolp-CresolPhenol



CYANIDE

Cyanide

Positive/Total

4 / 41 / 12 / 21 / 61 / 64 / 62 / 61 / 6

11 / 405 / 407 / 401 / 40

23 / 1011 / 478 / 478 / 472 / 101

24 / 4321 / 4315 / 4322 / 43

8 / 27


80 - 49.000180 - 180210 - 700

1,200 - 1.2001.500 - 1.500

100 - 35.00061 - 62

1.200 - 1.20046 - 61066 - 410

130 - 89.00038 - 38

170 - 270,0002.100 - 2.100

250 - 55.000770 - 160.000200 - 13.000

1 - 55.0002 - 110.0002 - 29.0005 - 390.000

1.000 - 48.000

ArithmeticMean

(ug/Kg)

9.9263.9443.7583.8433,8936.5783.9013,843

14,83414,83116,36514.851

10.24813.16713.52116.1947.705

1,8393.1492.255

11.138

4,600

Data Source: Barr Engineering Company. May 1991 (Table 4.1-1)

Arithmetic means were calculated assuming a concentration of half the detection limit lorcompounds below the detection limit.

TABLE 4SUMMARY STATISTICS FOR ANALYTICAL DATA

DETECTED COMPOUNDS - GROUNDWATERPEOPLES NATURAL GAS SHE

DUBUOUE. IOWA

PARAMETER


2,3-Benzofuran2,3-DihydroindeneIn deneNaphthaleneBenzo(b)ThiopheneQuinolineIsoquinoline2-Methylnaphthalene1 -MethylnaphthaleneBiphenylAcenaphthyleneAcenaphtheneDibenzofuranFluoreneDibenzothiophenePhenanthreneAnthraceneCarbozoleFluoranthenePyreneTriphenyleneBenzo(e)pyrenePeryleneBenzo(ghi)peryleneBis(2-ethylhexyl)phthalate

Benzo(a)anthraceneChryseneBenzo(b)fluorantheneBenzo(k)fluorantheneBenzo(a)pyreneldeno(! ,2,3,cd)pyrene

Positive /TotaJ

8 / 2214 / 2217 / 2226 / 6813 / 222 / 223 / 22

12 / 6816 / 2210 / 2211 / 6826 / 681 1 / 6 813 / 675 / 22

18 / 681 1 / 6 89 / 22

16 / 6816 / 687 / 223 / 222 / 222 / 688 / 27

8 / 688 / 686 / 685 / 684 / 683 / 68


0.0054 - 80.0021 - 180.0064 - 330.0052 - 5.8000.0064 - 22

3 - 42 - 18

0.0023 - 8300.0012 - 220.0012 - 39

0.043 - 6300.0028 - 3800.033 - 200

0.0045 - 3000.0069 - 130.0037 - 5200.0016 - 1800.0024 - 650.0036 - 2200.0028 - 1700.0011 - 9

0.02 - 50.0049 - 2

0.028 - 51 - 1.100

0.017 - 1000.0011 - 780.0024 - 920.0024 - 150.026 750.019 6

ArithmeticMean

(ug/xg)

1.082.2

4.42207.14

3.040.741.64

17.133.232.52

15.7319.2113.5212.96

1.1419.579.094.49

11.5610.080.930.790.657.61

56.67

7.667.337.657.777.267.61

Data Source: Barr Engineering Company. May 1991 (Table 4.1-1)

Arithmetic means were calculated assuming a concentration of hall the detection limit (or compoundsbelow the detection limit.

TABLE 4(continued)

SUMMARY STATISTICS FOR ANALYTICAL DATADETECTED COMPOUNDS - GROUNDWATER

PEOPLES NATURAL GAS SITEDUBUQUE. IOWA

PARAMETER

PHENOLS

Phenol2,4-Dimethylphenol



CYANIDE

Cyanide

Positive /Total

4 / 468 / 41

19 / 591 1 / 5 91 1 / 5 915 / 59

33 / 41


5 9,8004 - 25,000

1 - 4,4003 - 1.5001 - 2,0001 - 5.000

10 - 4.700

ArithmeticMean

(ug/Kg)

231634

1753463

117

373


Arithmetic means were calculated assuming a concentration of half the detection limit for compoundsbelow the detection limit.

TABLE 5

REMEDIATION LEVELS IN GROUNDWATERPEOPLES NATURAL GAS SITE

DUBUQUE, IOWA

Contaminant

BenzeneEthylbenzeneTolueneXyleneNaphthaleneBenzo(a)pyreneBenzo(a)anthraceneBenzo(b)fluorantheneBenzo(k)fluorantheneChryseneDibenz(a,h)anthraceneIndenopyrene

RemediationLevel (ppb)

1700

2.00010,000

200.20.10.20.20.20.20.4

Standard/Detection Limit

Negligible Cancer Risk LevelLifetime Health Advisory LevelLifetime Health Advisory LevelLifetime Health Advisory LevelLifetime Health Advisory Level

Practical Detection LimitPractical Detection LimitPractical Detection LimitPractical Detection LimitPractical Detection LimitPractical Detection LimitPractical Detection Limit

TABLE 6

INDICATOR COMPOUNDS USED FOR RISK ASSESSMENT CALCULATIONSPEOPLES NATURAL GAS SITE

DUBUQUE, IOWA

CARCINOGENIC INDICATOR COMPOUNDS

- Benzene- Benzo(a)anthracene- Benzo(a)pyrene- Benzo(b)fluoranthene- Benzo(k)fluoranthene- Chrysene- Dibenzo(a.h)anthracenelndeno(l ,2,3-c,d)Pyrene

NONCARCINOGENIC INDICATOR COMPOUNDS

- Fluorene- Fluoranthene- Pyrene- Acenaphthene- Anthracene- Naphthalene- Cyanide

Reference: Barr Engineering Company. May 1991

TABLE 7

CALCULATED INCREMENTAL LIFETIME CANCER RISKS AND GLOBAL HAZARD INDICES

BASELINE ENDANGERMENT ASSESSMENTPEOPLES' NATURAL GAS SITE

DUBUQUE, IOWA

RISKS/HAZARD INDICES

RECEPTORExposure Scenario M

CARCINOGENIC RISKSVOC Inhalation During Excavation ActivitiesVOC Inhalation During Routine ActivitiesIngestion of On-Site (Alluvial Zone) GroundwaterIngest ion of Site SoilsDermal Contact with Site Soils

Incremental Lifetime Cancer Risks

NONCARCINOGENIC HAZARDSVOC Inhalation During Excavation ActivitiesVOC Inhalation During Routine ActivitiesIngestion of On-Site (Alluvial Zone) GroundwaterIngestion of Site SoilsDermal Contact with Site Soils

Global Hazard Index

lunicipal Local ResidentWorker (Adult)

1.17E-07 5.64E-101.70E-04

1 .09E-02 8.83E-042.92E-06 5.47E-08

1.09E-02 1.05E-03

ND ND2.27E-01

1.40E-01 3.51 E-039.68E-01 2.42E-02

1.11E+00 2.55E-01

ConstructionWorker

9.69E-10

3.40E-054.10E-08

3.40E-05

ND

6.12E-029.17E-01

9.78E-01

Local Resident(Child)

2.85E-095.83E-051.20E-032.50E-04

1.51 E-03

ND2.34E-016.26E-026.26E-02

3.59E-01


LIST OF ACRONYMS


TABLES 8, 9, 10, AND 11

AT - Averaging Time (ED years x 365 days/year; days)BW - Body Weight (kg)CF - Conversion Factor

CPF - Cancer Potency Factor (mg'kg/day)-1CS - Chemical Concentration in Soil (mg/kg)ED - Exposure Duration (years)EF - Exposure Frequency (days/yr; events/yr)Fl - Fraction Ingested (unitless)IR - Ingestion Rate (L/day)

RfD - Reference Dose (mg/kg/day)

TABLE 8

CARCINOGENIC RISKS

RESIDENTIAL EXPOSURE INGESTION OF CHEMICALS IN SOIL BY CHILDRENPEOPLES NATURAL GAS SITE

DUBUQUE, IOWA

CS* IR CF Ft EF ED BW AT INTAKE CPF"CONTAMINANT (MG/KG) (MG/DAY) (10-6 KG/MG) (UNITLESS) (EVENTS/YR) (YRS) (KG) (DAYS) (MG/KG-DAY) (MG/KG-DAY>1 RISK

AVERAGE CASEBENZENE 7.1BENZO(a)ANTHRACENE 58BENZO(a)PYRENE 82BENZO(b)FLUORANTHENE 64BENZO0QFLUORANTHENE 63CHRYSENE 57DIBENZO(A,H)ANTHRACENE 15INDENO(1,2,3-C,d)PYRENE 43

UPPER BOUNDBENZENE 55BENZO(a)ANTHRACENE 240BENZO(a)PYRENE 420BENZO(b)FLUORANTHENE 310BENZO(K)FLUORANTHENE 330CHRYSENE 240DfBENZO(A,H)ANTHRAC£NE 64INDENO(1,2,3-c.d)PYR£NE 250

200 1.0E-06 1 26 10 34 25550 4.25E-07200 1.0E-06 0.95 26 10 34 25550 3.30E-06200 1.0E-06 0.95 26 10 34 25550 4.66E-06200 1.0E-06 0.95 26 10 34 25550 3.64E-06200 1.0E-06 0.95 26 10 34 25550 3.58E-06200 1.0E-06 0.95 26 10 34 25550 3.24E-06200 1.0E-06 0.95 26 10 34 25550 8.53E-07200 1.0E-06 0.95 26 10 34 25550 2.45E-06

TOTAL CARO

200 1.0E-06 1 26 10 34 25550 3.29E-06200 1.0E-06 0.95 26 10 34 25550 1.36E-05200 1.0E-06 0.95 26 10 34 25550 2.39E-05200 1.0E-06 0.95 26 10 34 25550 1.76E-05200 1.0E-06 0.95 26 10 34 25550 1.88E-05200 1.0E-06 0.95 26 10 34 25550 1.36E-05200 1.0E-06 0.95 26 10 34 25550 3.64E-06200 1.0E-06 0.95 26 10 34 25550 1.42E-05

TOTAL CARCI

0.029211.511.511.511.511.511.511.5

NOGENICRISK

0.029211.511.511.511.511.511.511.5

NOGENICRISK

1.24E-083.79E-055.36E-054.19E-054.12E-053.73E-059.81 E-062.81 E-05

2.50E-04

9.61 E-061.57E-042.75E-042.03E-042.16E-041.57E-044.19E-051.63E-04

1.21E-03

Data Source: Barr Engineering Company, May 1991

• BASED ON ARITHMETIC MEAN OR MAXIMUM CONCENTRATION FROM BARR ENGINEERING COMPANY (TABLE 4.4-3)• *CPF FOR CARCINOGENIC PAHs BASED ON THE CPF FOR B(a)P. ND-NOT DETERMINED

TABLE 9

CARCINOGENIC RISKS

RESIDENTIAL EXPOSURE INGESTION OF CHEMICALS IN SOIL BY ADULTSPEOPLES NATURAL GAS SITE

DUBUQUE, IOWA

CS* IR CF Fl EF ED BW AT INTAKE CPF"CONTAMINANT (MG/KG) (MG/DAY) (10-6KG/MG) (UNfTLESS) (EVENTS/YR) (YRS) (KG) PAYS) (MG/KG-DAY) (MG/KG-DAY)-1 RISK

AVERAGE CASEBENZENE 7.1BENZO(a)ANTHRACENE 58BENZO(a)PYRENE 82BENZO(b)FLUOflANTHENE 64BEN20(K)FLUORANTHENE 63CHRYS6NE 57CHBENZO(A,H)ANTHRACENe 15INDENO(U,3-C.d)PYRENE 43

UPPER BOUNDBENZENE 55BENZO(a)ANTHRACENE 240BENZO(a)PYRENE 420BENZO(b)FLUORANTHENE 310B6NZO(K)FLUORANTHENE 330CHRYSENE 240DIBENZO<A,H)ANTHRACENE 64INDENO(1,2,3-c.d)f»YRENE 250

100 1.0E-06 1 6 30 70 25550 7.15E-08100 1.0E-06 0.95 6 30 70 25550 5.55E-07100 1.0E-06 0.95 6 30 70 25550 7.84E-07100 1.06-06 0.95 6 30 70 25550 6.12E-07100 1.0E-06 0.95 6 30 70 25550 6.02E-07100 1.0E-06 0.95 6 30 70 25550 5.45E-07100 1.0E-06 0.95 6 30 70 25550 1.43E-07100 1.0E-06 0.95 6 30 70 25550 4.11E-07

TOTAL CARd

100 1.06-06 1 6 30 70 25550 5.54E-07100 1.0E-06 0.95 6 30 70 25550 2.29E-06100 1.06-06 0.95 6 30 70 25550 4.02E-06100 1.0E-06 0.95 6 30 70 25550 2.96E-06100 1.06-06 0.95 6 30 70 25550 3.16E-06100 1.0E-06 0.95 6 30 70 25550 2.29E-06100 1.0E-06 0.95 6 30 70 25550 6.12E-07100 1.06-06 0.95 6 30 70 25550 2.396-06

TOTAL CARd

0.029211.511.511.511.511.511.511.5

NOGENICRISK

0.029211.511.511.511.511.511.511.5

NOGENICRISK

2.096-096.38E-069.02E-067.04E-066.93E-066.Z7E-061.65E-064.73E-06

4.206-05

1.62E-062.64E-054.62E-053.41 E-053.63E-052.64E-057.04E-062.75E-05

2.04E-04


• BASED ON ARITHMETIC MEAN OR MAXIMUM CONCENTRATION FROM BARR ENGINEERING COMPANY. MAY 1991 (TABLE 4.4-3)• 'CPF FOR CARCINOGENIC PAHs BASED ON THE CPF FOR B(a)P. ND-NOT DETERMIN6D

TABLE 10

CARCINOGENIC RISKS

INGESTION OF CHEMICALS IN SOIL FOR MUNICIPAL GARAGE WORKERSPEOPLES NATURAL GAS SITE

DUBUQUE, IOWA

cs*CONTAMINANT (MG/MQ)

AVERAGE CASEBENZENE 7.1BENZO(a)ANTHRACENE 58BENZO(a)PYRENE 82BENZO(b)FLUORANTHENE 64BENZO(K)FLUORANTHENE 63CHRYSENE 57DIBENZO(A,H)ANTHRACENE 15INOENO(1,2.3-C,d)PYRENE 43

UPPER BOUNDBENZENE 55BENZO(a)ANTHRAC£NE 240BENZO(a)PYRENE 420BENZO(b)FLUORANTHENE 310BENZO(K)FLUORANTHENE 330CHRYSENE 240DtBENZO(A.H)ANTHRACENE 64INDENO(U,3-CXJ)PYRENE 250

IR CF Fl EF ED BW AT INTAKE(MG/DAY) (10-6KG/MG) (UNPTLESS) (EVENTS/YR) (YRS) (KG) (DAYS) (MG/KG-DAY)

100 1.0E-06 1 240 40 70 25550 3.81 E-06100 1.0E-06 0.95 240 40 70 25550 2.96E-05100 1.0E-06 0.95 240 40 70 25550 4.18E-05100 1.0E-06 0.95 240 40 70 25550 3.26E-05100 1.0E-06 0.95 240 40 70 25550 3.21 E-05100 1.0E-06 0.95 240 40 70 25550 2.91 E-05100 1.0E-06 0.95 240 40 70 25550 7.65E-06100 1.0E-06 0.95 240 40 70 25550 2.19E-05

TOTAL CARd

100 1.0E-06 1 240 40 70 25550 2.95E-05100 1.0E-06 0.95 240 40 70 25550 1.22E-04100 1.0E-06 0.95 240 40 70 2S550 2.14E-04100 1.0E-06 0.95 240 40 70 25550 1.58E-04100 1.0E-06 0.95 240 40 70 25550 1.68E-04100 1.0E-06 0.95 240 40 70 25550 1.22E-04100 1.0E-06 0.95 240 40 70 25550 3.26E-05100 1.0E-06 0.95 240 40 70 25550 1.27E-04

TOTAL CARCI

CPF**(MG/KG-DAYM

0.029211 JS11.511.511.511.511.511.5

NOGENICRtSK

0.029211.511.511.511.511.511.511.5

NOGENtCRISK

RISK

1.11E-073.40E-044.81 E-043.75E-043.69E-043.34E-048.80E-052.52E-04

2.24E-03

8.62E-071.41E-032.46E-031.62E-031.94E-031.41E-033.75E-041.47E-03

1.09E-02

Data Source: Barr Engineering Company. May 1991

• BASED ON ARITHMETIC MEAN OR MAXIMUM CONCENTRATION FROM BARR ENGINEERING COMPANY. MAY 1991 (TABLE 4.4-3)* 'CPF FOR CARCINOGENIC PAHs BASED ON THE CPF FOR B(a)P. ND-NOT DETERMINED

TABLE 11

CARCINOGENIC RISKS

INGEST1ON OF CHEMICALS IN SOIL FOR CONSTRUCTION WORKERSPEOPLES NATURAL GAS SITE

DUBUQUE, IOWA

cs*CONTAMINANT (MQ/NQ)

AVERAGE CASEBENZ6NE 7.1BENZO(a)ANTHRACENE 58BENZO(a)PYRENE 82BENZO(b)FLUORANTHENE 64BENZO0QFLUORANTHENE 63CHRYSENE 57DIBENZO(A>H)ANTHRACENE 15INDENO(1.2,3-C,d)PYRENE 43

UPPER BOUNDB6NZ6NE 55BENZO<a)ANTHRACENE 240B6NZO(a)PYRENE 420BENZO(b)FLUORANTHENE 310BENZO(K)FLUORANTHENE 330CHRYSENE 240DIBENZO<A.H)ANTHRACEN6 64INDENO(1,2,3-C,d)PYRENE 250

IR CF Fl EF ED BW AT INTAKE(MG/DAY) (10-6KG/MG) (UNITLESS) (EVENTS/YR) (YRS) (KG) (DAYS) (MG/KG-DAY)

100 1.0E-06 1 30 1 70 25550 1.19E-08100 .06-06 0.95 30 1 70 25550 9.24E-08100 .OE-06 0.95 30 1 70 25550 1.31E-07100 .OE-06 0.95 30 1 70 25550 1.02E-07100 .OE-06 0.95 30 1 70 25550 1.006-07100 .OE-06 0.95 30 1 70 25550 9.08E-08100 .OE-06 0.95 30 1 70 25550 2.396-08100 .OE-06 0.95 30 1 70 25550 6.85E-08

TOTAL CARCI

100 1. OE-06 1 30 1 70 25550 9.23E-08100 1. OE-06 0.95 30 1 70 25550 3.82E-07100 1. OE-06 0.95 30 1 70 25550 6.69E-07100 1. OE-06 0.95 30 1 70 25550 4.94E-07100 1. OE-06 0.95 30 1 70 25550 5.26E-07100 1. OE-06 0.95 30 1 70 25550 3.82E-07100 1.0E-06 0.95 30 1 70 25550 1.02E-07100 1. OE-06 0.95 30 1 70 25550 3.98E-07

TOTAL CARCI

CPF**(MG/KG-DAYH

0.029211.511.511.511.511.511.5115

NOGENrcWSK

0.029211.511.511.511511511.511.5

NOGcNKs rVoK

RISK

3.48E-101.06E-061.506-061.17E-061.15E-061.04E-082.756-077.88E-07

7.00E-06

2.69E-094.40E-067.70E-065.686-066.056-064.406-061.17E-064.586-06

3.40E-05


• BASED ON ARfTHMETIC MEAN OR MAXIMUM CONCENTRATION FROM BARR ENGINEERING COMPANY. MAY 1991 (TABLE 4.4-3)• 'CPF FOR CARCINOGENIC PAHs BASED ON THE CPF FOR B(a)P. ND-NOT DETERMINED

TABLE 12

GROUND WATER RESULTS FOR RISK ASSESSMENT PURPOSESPEOPLES NATURAL GAS SITE

DUBUQUE, IOWA

CHEMICAL

BENZENEBENZO(A)ANTHRACENEBENZO(A)PYRENEBENZO(B)FLUORANTHENEBENZO(K)FLUORANTHENECHRYSENEDIBENZO(A.H)ANTHRACENEINDENO(1 ,2,3-C,D)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

HIGHEST CONCENTRATION FOR ALL SAMPLING ROUNDS/ALL WELLS (UG/L)*

WATER TABLE WELLS(W1 THRU W7)

2300.045

NONDNONDNDND13011086

38023

51001.3

WELL NO.

W2W6

W2W2W2W2W2W2W4

ALLUVIAL AQUIFER WELLS(W1 0 THRU W1 5, W1 7, W1 8)

4100.12

0.026NDNDNDND

0.0190.0510.610.47

90.035

310.16

WELL NO.

W17W10W10

W10W10W10W10W17W10W17W17

DATA SOURCE: BARR ENGINEERING COMPANY, MAY 1991SEMIVOLATILE ORGANIC COMPOUNDS TABLE 2.5-4VOLATILE ORGANIC COMPOUNDS TABLE 2.5-6INORGANIC COMPOUNDS TABLE 2.5-7

ND - NOT DETECTED ABOVE QUANTTTAT1ON LIMIT OR WITHOUT A DATA QUALIFIER

LIST OF ACRONYMS


TABLES 13. 14, 15. AND 16

AT - Averaging Time (ED years x 365 days/year; days)BW - Body Weight (kg)

CPF - Cancer Potency Factor (mg/kg/day)-1CW - Chemical Concentration in Water (mg/L)ED - Exposure Duration (years)EF - Exposure Frequency (days/yr; events/yr)IR - Ingestion Rate (L/day)

RfD - Reference Dose (mg/kg/day)

TABLE 13CARCINOGENIC EXPOSURE CALCULATION FOR INGEST1ON OF CHEMICALS IN DRINKING WATER

ALLUVIAL AQUIFERINCLUSION OF ALL CHEMICALS/ON -SITE CONCENTRATIONS

PEOPLES NATURAL GAS STTE. DUBUOUE. IOWA

CW* IR EF ED BW AT INTAKE CPFCONTAMINANT (MG/L) (L/DAY) (DAYS/YR) (YRS) (KG) (DAYS) (MG/KG-DAY) (MG/KG-DAY)-1 RISK

RESIDENTIAL ADULTS - UPPER BOUND ESTIMATEBENZENEBENZO(>)ANTHRACENEBENZO(B)PYRENEBENZO(b)FLUORANTHENEBENZO(k)FLUORANTHENECHRY8ENEDIBENZO<«.h)ANTHRACENEINDENOO 7.3-c.d)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

4.10E-OI1.20E-04200E-06

NONONONO

1.00E-OS6.10E-060.10E-044.70E-O4900E-OJ3.SOE-053.10E-021.WE-04

2 305 30 70 25550

2 MS 30 70 25550

2 305 30 70 255502 305 30 70 25550

2 305 30 70 25550

2 305 30 70 25550

2 305 30 70 255502 305 30 70 256602 306 30 70 25650

2 305 30 70 266602 305 30 70 256602 306 30 70 266602 305 30 70 266502 306 30 70 266602 366 30 70 26660

502E-031.47E-00M8E-07

NDNDNDNO2-33E-070.246-077.47E-068.76E-001.10E-044.2WE-073.80E-041.06E-00

0.020211.511.5113113113113113

—— (b)__— .————————

TOTAL CARCINOGENIC RISK

147E-O41BOE-06»OOE-00

NONONDND

2.«*E-00NDNDNONONONONO

1. TOE-04

RESIDENTIAL CHILDREN - UPPER BOUND ESTIMATEBENZENEBENZOWANTHRACENEBENZOMPYRENEBENZO(b)FLUORANTHENEBENZO(k)FLUORANTHENECHRYSENEDIBENZO(t.h)ANTHRACENEINDENO(1 £.»-c.d)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

4.10E-011 JOE-042.00E-06

NDNONDND

1.90E-OS6.10E-058.10E-044.70E-04900E-03asoE-osJ.10E-021.00E-04

1 306 10 34 26660

1 306 10 34 25650

1 306 10 34 25650

1 306 10 34 256501 306 10 34 265601 306 10 34 266601 306 10 34 265601 305 10 34 256601 306 10 34 266601 305 10 34 26550

1 305 10 34 256601 305 10 34 25550

1 306 10 34 266601 305 10 34 256601 306 10 34 25660

1.72E-036.04E-071 .006-07

NONDNDND7.ME-482.14E-07230E-001.07E-093.78E-451.47E-071.30E-046.72E-07

0.020211311.8113113113113113

— <b)————__—

————


6.03E-05830E-OS1JOE-00

NDNONDNO

0.1IE-07NONDNDNONONDND

6.UE-06

M O*TA KXMCC. MMM CNOMCtMM CO . MAY IWI (TAMO It-4, t »-• AMD t »-1 ctr VAUUU H*vt NOT inn otvrvorto iv u t CM fo* TMCW CHOBCM*.

TABLE 14CARCINOGENIC EXPOSURE CALCULATION FOR INGEST1ON Of CHEMICALS IN DRINKING WATER

WATER TABLE WELLSINCLUSION OF ALL CHEMICALS/ON-STTE CONCENTRATIONS

PEOPLES NATURAL GAS STTE. DUBUQUE. IOWA

CW* IR EF ED BW AT INTAKE CPFCONTAMINANT (MG/L) (L/DAY) (DAYS/YR) (YRS) (KG) (DAYS) (MG/KG-DAY) (MG/KG-DAY)-1 RISK

RESIDENTIAL ADULTS - UPPER BOUND ESTIMATEBENZENEBENZO<a)ANTHRACENEBENZO(a)PYRENEBENZO(b)FLUORANTHENEBENZO{k)FLUORANTHENECHRYSENEDIBENZO(a.h)ANTHRACENEINDENO(1 .2.3-C,d)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

£30E-014.50E-05

NONDNDNDNDND

1.30E-011.10E-018.60E-023.80E-012.30E-025.10E*001.30E-03

2 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 255502 365 30 70 25550

2.82E-035.51 E-07NDNDNDNDNDND1.59E-031.35E-031.05E-034.65E-032.82E-046.24E-021.59E-05

0.029211.511.511.511.511.511.511.5

~- <b). ——............


8.22E-056.34E-06NDNDNDNDNONONDNDNDNDNDNDNO&86E-05

RESIDENTIAL CHILDREN - UPPER BOUND ESTIMATEBENZENEBENZO(a)ANTHRACENEBENZO(a)PYRENEBENZO(b)FLUORANTHENEBENZO(k)FLUORANTHENECHRYSENEDIBENZO(a,h)ANTHRACENEINDENO(1 ,2.3-C,d)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

2.30E-014.506-05

NDNDNDNONOND

1.30E-011.10E-01a60E-023.80E-012.30E-025.10E»001.30E-03

1 365 10 34 255501 365 10 34 255501 365 10 34 255501 365 10 34 255501 365 10 34 255501 365 10 34 255501 365 10 34 255501 365 10 34 255501 365 10 34 25550

365 10 34 25550365 10 34 25550365 10 34 25550365 10 34 25550365 10 34 25550365 10 34 25550

9.66E-041.896-07NDNDNDNDNDND5.46E-044.62E-043.61 E-041 .606-039.66E-052.14E-025.46E-06

0.029211.511.511.511.511.511.511.5

— <b)......—

• ......—


2.82E-052.17E-06NDNDNDNDNDNDNONONDNDNDNDND3.04E-OS

OAT* K>U«CC: MMH UH ••UHf* CO . HAY ltd (TAMO t *-«. 11-» AND l.t-l)

TABLE 15CHRONIC NONCARONOGENIC EXPOSURE CALCULATION FOR INGESDON OF CHEMICALS IN ORINKINQ WATER

ALLUVIAL AQUIFER WELLSINCLUSION OF ALL CHEMICALS/ON-SITE CONCENTRATIONS

PEOPLES NATURAL GAS STTE. DUBUQUE. IOWA

CW(a) IR EF ED BW AT INTAKE RIO HAZARDCONTAMINANT (MG/L) (L/DAY) (DAYS/YR) (YRS) (KG) (DAYS) (MG/KG-DAY) (MG/KG-DAY) INDEX

RESIDENTIAL ADULTS - UPPER BOUND ESTMATEBENZENEBENZO(a)ANTHRACENEBENZO(a)PYRENEBENZO(b)FLUORANTHENEBENZO00FLUORANTHENECHRYSENEDIBENZO(a.h)ANTHRACENEINDENO(1 .2.3-c.d)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

4.10E-011.20E-042.606-05

NDNDNDNO

1. 906-055.10E-056.10E-044.70E-049.00E-033.506-053.10E-021.60E-04

2 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 10950

1.17E-023.43E-067.43E-07NONDNDND5.436-071.46E-061.74E-OS1.34E-OSi57E-041.006-068.86E-044.57E-06

... (b)

—.———...

0.040.040.030.060.3

0.0040.02

TOTAL NONCARQNOGENtC HAZARD

NDNDNONDNDNDNDND3.646-054.36E-044.486-044.296-03a 336-082.21E-012.296-042JZ7E-01

RESIDENTIAL CHILDREN - UPPER BOUND ESTMATEBENZENEBENZO(a)ANTHRACENEBENZO(a)PYRENEBENZOQ>)FLUORANTHENEBENZO03FLUORANTHENECHRYSENEDIBENZO(a.h)ANTHRACENEINDENO(1 .2.3-c.d)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

4.10E-011.20E-042.60E-05

NDNDNDND

1.90E-055.10E-066.10E-044.70E-049.00E-033.50E-053.10E-021.606-04

365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650365 10 34 3650

1.216-023.536-067.656-07NDNDNDND5.59E-071.506-081.79E-051.38E-OS2.656-041.03E-069.12E-044.71 E-06

~fl»...«..

. —— -— >—

0.040.040.030.060.3

0.0040.02

TOTAL NONCARCtNOGENIC HAZARD

NDNDNDNDNDNONDND3.7SE-054.49E-044.61 E-044.41E-031436-062.286-012.356-042.34E-01

M OAT* (OUNCC I CO.. MAT 1WI (T*KC* t *-«. tK «MO MO«NOT OCTtMflMD

TABLE 16CHRONIC NONCARCINOGENIC EXPOSURE CALCULATION FOR INGESHON OF CHEMICALS IN DRINKING WATER

WATER TABLE WELLSINCLUSION OF ALL CHEMICALS/ON-STTE CONCENTRATIONS

PEOPLES NATURAL GAS SITE. DUBUQUE. IOWA

CW(a) IR EF ED BW AT INTAKE RfD HAZARDCONTAMINANT (MG/L) (L/DAY) (DAYS/YR) (YRS) (KG) (DAYS) (MG/KG-DAY) (MG/KG-DAY) INDEX

RESIDENTIAL ADULTS - UPPER BOUND ESTIMATEBENZENEBENZO(a)ANTHRACENEBENZO(a)PYRENEBENZO(b)FLUORANTHENEBENZO(k)FLUORANTHENECHRYSENEDIBENZO(a.h)ANTHRACENEINDENO(1 ,2.3-c.<OPYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

2.30E-014.50E-05

NDNDNDNDNONO

1.30E-011.10E-018.60E-023.80E-012.30E-025. 106+001.30E-03

2 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 109502 365 30 70 10950

6.57E-031.29E-06NDNDNDNDNDND3.71 E-033.14E-032.46E-031.09E-026.57E-041.46E-013.71 E-05

— (b)

—..-.__——...

0.040.040.030.060.3

0.0040.02

TOTAL NONCARCINOGENIC HAZARD

NDNONONDNDNDNDND9.29E-027.86E-028.19E-021.81E-01&19E-033.64E*011.86E-033.69E*01

RESIDENTIAL CHILDREN - UPPER BOUND ESTIMATEBENZENEBENZO(a)ANTHRACENEBENZO(a)PYRENEBENZO(b)FLUORANTHENEBENZO(k)FLUORANTHENECHRYSENEDIBENZO(a.h)ANTHRACENEINDENO(1 ,2.3-C.d)PYRENEFLUORENEFLUORANTHENEPYRENEACENAPHTHENEANTHRACENENAPHTHALENECYANIDE

2.30E-014.50E-05

NDNDNDNDNDND

1.30E-011.10E-018.60E-023.80E-012.30E-025.10E+001.30E-03

1 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 36501 365 10 34 3650

6.76E-031.32E-06NDNDNDNDNDND3.82E-033.24E-032.53E-031.12E-026.76E-041.50E-013.82E-05

— <b)

————...—

0.040.040.030.060.3

0.0040.02

TOTAL NONCARCINOGENIC HAZARD

NDNDNDNDNONONDND9.56E-026.09E-028.43E-021.86E-012.25E-03a75E*011.91 E-033.806+01

M O*T» KKMCt MM* BMMRMN* CO . MAT 1W1 (TMf* 1 *-4. t »-«. «MO I (-7)

TABLE 17

COST ESTIMATE SUMMARY FOR SELECTED REMEDY

Item Cost

I. Site Work ' 2,200,000

II. Soil Transportation and Treatment 3,700,000

III. Ground Water Extraction and Treatment

1. Alluvial Aquifer

Capital 240,000O & M: Present Worth (10 Yrs. @ 9%) 313,000

2. Silty Sand Aquifer

Capital 13,000O & M: Present Worth (5 Yrs. § 9%) 130,000

3. Bioremediation System

Capital 195,000O & M: Present Worth (10 Yrs. § 9%) 345,000

IV. Ground Water Quality Monitoring

1. Alluvial Aquifer: Present Worth (10 Yrs. § 9%) 106,000

2. Silty Sand: Present Worth (10 Yrs. e 9%) 129,000

V. Subtotal Cost of Selected Remedy 7,341,000

VI. Contingency for Commercial Soil Disposal 629,000

Total Estimated Cost for Selected Remedy 8,000,000

APPENDIX A

RESPONSE TO PUBLIC COMMENTSON THE

PROPOSED PLANFOR THE


Response to Public Commentson the

Proposed Planfor the

Peoples Natural Gas Superfund SiteDubugue, Iowa

1.0 INTRODUCTION

The United States Environmental Protection Agency (EPA) helda public comment period form June 17 through August 17, 1991 onthe EPA Proposed Plan for the Peoples Natural Gas Superfund Sitein Dubugue, Iowa. The purpose of the public comment period wasto provide interested parties with an opportunity to comment onthe Proposed Plan. The Proposed Plan was made available on June27, 1991 at the Carnegie-Stout Public Library in Dubugue, Iowa.Notification of the public comment period was published in theDubuque Telegraph Herald.

A public meeting was held on July 9, 1991 at the Carnegie-Stout Public Library in Dubugue, Iowa. At this meeting EPArepresentatives described the alternatives evaluated, presentedthe EPA preferred alternative, and answered questions about thePeoples site and the remedial alternatives under consideration.

Section 113(k)(2)(B)(iv) of the Comprehensive EnvironmentalResponse, Compensation, and Liability Act (CERCLA) requires thatEPA respond to significant comments on the EPA Proposed Plan.This Response Summary provides a review and summary of signifi-cant comments on the Proposed Plan. In addition to summarizingsignificant concerns and questions, the Response Summary presentsEPA's responses to those concerns.

2.0 PUBLIC COMMENTS AND EPA RESPONSES

2.1 COMMENTS FROM INTERESTED CITIZENS

Comment fl

A member of the general public expressed concern that allu-vial aquifer pumping program nay cause "pressure problems" on theaquifer and inquired what effect taking water out would have onthe pressure.

EPA Response

The volume of water that the alluvial aquifer pumping pro-gram will remove from the aquifer should be minimal in relation

to aquifer capacity and have no adverse effects on the ability ofthe aquifer to produce usable volumes of water. The MississippiRiver alluvial aquifer in Dubuque contains large volumes of waterand production well fields in the aquifer in the Dubuque area arepumping high volumes of water from the aquifer.

2.2 COMMENTS FROM MIDWEST GAS

MIDWEST GAS GENERAL COMMENTS

GENERAL COMMENT fl

Midwest Gas believes that alternatives 3, 4, and 5 presentedin the Remedial Investigation/Feasibility Study (RI/FS) areprotective of human health and the environment to the extentrequired by the Environmental Protection Agency (EPA) guidancedocuments. It is Midwest Gas1 opinion that the Proposed Plansubmitted by the EPA is more protective than is necessary for thesite. This plan will increase site excavation activities, pro-long the cleanup process, and increase remediation costs. Theremediation goals for ground water for the site are set at ornear the detection limits for those chemical compounds, essen-tially eliminating the ability to prove compliance with thosegoals.

EPA Response

Alternatives 3, 4, and 5 and the rationale for their exclu-sion during the selection process are explained in the ProposedPlan for the Peoples site. Alternative 3 would not treat highlycontaminated source soils and therefore not provide for thepermanent reduction of the toxicity, mobility, or volume of thecontaminants in the source soil areas. Alternative 4 does notremove a large volume of contaminated soil above the silty sandunit and relies on a cap to reduce mobility which will requirelong-term maintenance. Alternative 4 would reduce contaminationin the silty sand unit through the in-situ biodegradation proc-ess. However, this alternative does not remove highly contami-nated source soil areas from 6 feet below surface to the top ofthe upper confining layer. This would leave a large volume ofcontaminated soils as a source of chemicals of concern that couldpotentially leach into the ground water over time. Alternative 5relies on ground water extraction to remove contaminants from thesilty sand unit which would require a much longer period toreduce contaminant concentrations to acceptable levels.Alternative 3 does not involve excavation of contaminated soilsat depth and would not permanently eliminate residual risk,requiring long-term control measures throughout the life of thealternative, estimated at 100 years. EPA estimates the alterna-tive 5 as described in the RI/FS would require the excavation anddisposal of approximately 6,000 additional cubic yards of soil as

compared to the selected alternative as described in the ProposedPlan.

Analytical methods are available that can detect contamina-tion at or below the remediation goals for the compounds ofinterest (see specific comments).

GENERAL COMMENT I2

The EPA and Iowa Department of Natural Resources (Iowa DNR)should give consideration to factual exposure scenarios andcancer potency factors. Risk assessments must contain a factorof safety. However, the calculation of risk factors based onevery theoretical contingency may be unrealistic and only in-flates the time and cost of the remedial action without corre-sponding public benefit.

EPA Response

Current EPA policy relative to development of a baselinerisk assessment (assessment of risks posed by a site if notcleaned up) requires that a reasonable maximum exposure to humansand the environment posed by site contaminants be estimated.This maximum exposure estimate may be based either on actualcurrent identified uses of the site or on some reasonable futureuse of the site. Since it is EPA's goal to restore sites to alevel allowing unrestricted use, the policy does not place par-ticular emphasis on either use of the site in estimating a rea-sonable maximum exposure.

GENERAL COMMENT #3

The chemical compounds found at this former manufactured gasplant (MGP) site are present in our everyday environment. Thesame polynuclear aromatic hydrocarbon (PAH) compounds that are ofconcern at this site are present in creosote used for wood treat-ing, in asphalt used for roads, in roofing tars, and road tars toname a few. A popular over the counter dandruff shampoo, Deno-rex, contains 9% coal tar solution. PAH compounds are formed asproducts of incomplete combustion of fossil fuels. The list cango on.

The point is that this and other MGP sites should beevaluated from a realistic scientific perspective so thatexcessive costs and delays are not incurred that produce littleor no benefit.

EPA Response

EPA regulation and policy require the remediation of envi-ronmental hazards when determined necessary by the endangerment

assessment process. The risk calculated for the Peoples site isof a magnitude requiring the implementation of cleanup actions toreduce the risk. The remedial action for the risk reduction isdescribed in the selected remedy.

GENERAL COMMENT I4

Midwest Gas, a division of Iowa Public Service Company, hasa very strong commitment to protecting the environment forcurrent and future generations. For this reason, Midwest Gas iscommitted to implementing the Record of Decision as determined bythe Environmental Protection Agency.

EPA Response

EPA recognizes the commitment of Midwest Gas to implementthe selected remedy as described in the Record of Decision.

MIDWEST GAS SPECIFIC COMMENTS - All page references and quota-tions refer to the EPA Proposed Plan for the Peoples site datedJune 1991. The section numbers that follow are used to identifythe sections of the Proposed Plan for which Midwest Gas providedcomments.

2.3 NATURE AND EXTENT OF CONTAMINATION

Statement Page £: "The results of the well search indicate thatthere are no wells on or near the site that are used as a sourceof drinking water."

Conment: See following comment.


Statement Page £: "Pathways by which humans could be exposed tothe chemicals of concern at the site were evaluated based onreasonable assumptions about current and future land uses. Thefollowing pathways were evaluated: ... Exposure of future adultand children residents to contaminated ground water used as aprimary potable water source. ..."

Comment; The preceding statement indicates that the well searchdid not identify wells on or near the site used as a source ofdrinking water. The statement above indicates that reasonableassumptions were used to determine exposure pathways. One of thepathways evaluated includes using the ground water from the siteas a primary potable water source. The second statement seems tocontradict the first statement, and does not appear to be areasonable assumption.

This issue is certainly a very important issue since theexposure scenarios drive first the need for remedial action andsecond the resulting cleanup standards.

EPA Response

The fact that there are no wells on or near the site used asa source of drinking water and the evaluation of potential resi-dents exposure to ground water in the risk assessment are notcontradictory. It is EPA policy to assume future residentialland use which is independent of current uses of ground water.The contaminated alluvial aquifer could be used as drinking watersource by potential future residents. EPA guidance states thatif ground water is not currently used in the area of a site as asource of drinking water but is of potable quality, future usesof ground water must be considered (Risk Assessment Guidance forSuperfund. December 1989).


Statement Page £: "Pathways by which humans could be exposed tothe chemicals of concern at the site were evaluated based onreasonable assumptions about current and future land uses. Thefollowing pathways were evaluated: ... Exposure of adults andchildren as potential on-site residents to contaminated soilthrough dermal contact and ingestion; ..."

Comment; The site location is zoned "heavy industrial". Thisprohibits the development of this area for residential use.Other institutional controls including a ground water hazardstatement have been attached to the property deeds restrictingfuture land use were in place prior to the final RemedialInvestigation/Feasibility Study (RI/FS) submittal to the EPA onMay 15, 1991. The site is listed on the Iowa Uncontrolled orAbandoned Waste Site list.

One third of the site will be occupied by the relocated U.S.Highway 61. The highway itself will be elevated approximately 20feet on top of the western portion of the site with theembankment and access roads adjacent to the embankment. The Cityof Dubuque owns the eastern two thirds of the site and uses thisproperty as a maintenance garage. The surrounding area includesan electrical generating facility, grain storage and shipmentfacilities, and other heavy industrial facilities.

This heavy industrial area is not suitable for developmentas a residential area. Evaluation of the residential exposurescenario does not represent a "reasonable assumption about thecurrent and future land use".

This is an extremely important issue as it effects thebaseline endangennent assessment which determines the scope ofthe remediation and the resulting appropriate cleanup standards.

EPA Response

Current EPA policy relative to development of a baselinerisk assessment (assessment of risks posed by a site if notcleaned up) requires that a reasonable maximum exposure to humansand the environment posed by site contaminants be estimated.This maximum exposure estimate may be based either on actualcurrent identified uses of the site or on some reasonable futureuse of the site. Since it is EPA's goal to restore sites to alevel allowing unrestricted use, the policy does not place par-ticular emphasis on either use of the site in estimating a rea-sonable maximum exposure. While EPA recognizes that the site islocated in an industrial area, it is also EPA's position that nooverriding physical or demographic factors have been identifiedto preclude development of the site for a residential use. Thereare a number of residences in the vicinity of the site (within0.2 miles). As such, use of a potential residential scenario isappropriate in development of a reasonable maximum exposureestimation. The workers at the public works garage are thepopulation with the greatest risk as calculated by theendangennent assessment. This represents current use of the siteand calculation of the risk factors were conducted according toEPA policy and guidance.

The cleanup standards developed for the selected remedyaccount for the institutional controls attached to the propertydeeds. Unrestricted property usage would require lower cleanupstandards than those required in the selected remedy. The riskcalculated in the baseline endangennent is a point of departurefor determining the requirements for site remediation.


Statement Page 2.: "The carcinogenic risks were also calculatedfor pathways at the site. The carcinogenic risk to future resi-dents is 1.1 x 10~3."

Comment: The risk calculation is overly conservative because ofthe lack of a factual basis for the residential assumption.

EPA Response

EPA guidance requires the assumption of future residentialland use. If the site is industrial and located near residentialareas in an urban area, future residential land use is a reasona-ble possibility. The workers at the public works garage are thepopulation with the greatest risk as calculated by the endanger-

ment assessment. This represents current use of the site andcalculation of the risk factors were conducted according to EPApolicy and guidance.


Statement Page 2: "Federal and state cleanup standards for thecontaminants of concern in soil have not been established at thistime. Therefore, it is appropriate to determine soil cleanuplevels on a site-specific basis using the carcinogenic riskfactors developed in the risk assessment. The developed cleanuplevels specify a concentration in the soil that would be protec-tive of human health if no actions were taken at the site. Atthis site, the 10~6 risk level would be protective if no institu-tional control were in place. Using the proper institutionalcontrols at the site, EPA Region VII believes that the cleanup ofsoil at this site would be adequately protective of human healthand the environment when using the 10~* risk level. Based onthis risk level, EPA considers a cleanup level for soil, fromsurface level to six feet below surface, of 500 mg/kg for totalPAH contaminants and 100 mg/kg carcinogenic PAH contaminants tobe protective of human health. PAH contaminants below 6 feetare not considered by EPA to constitute a direct contact threatto persons at the site. The purpose of clean up of soils below 6feet would be to protect ground water from contamination fromcoal tar materials."

Comment: The remediation goals as proposed in the RI/FS(200 mg/kg carcinogenic PAH contaminants) are equally protectiveof human health. The inappropriate use of the residentialexposure scenario lowered the cleanup standards to levels thatare lower than necessary to protect human health.

Another difference between the RI/FS endangerment assessmentand the EPA's assessment was the application of cancer potencyfactors to the carcinogenic or suspect carcinogenic PAH compoundsof interest. The RI/FS uses the values reported in the ICFClement report. This study, conducted for the EPA, indicatesthat not all PAH compounds have equal carcinogenic effects. TheEPA did not use the values in this report. More conservativevalues were used resulting in a more conservative cleanupstandard.

The result of these two factors is higher costs and longertime to conduct the work with little or no additional benefit tothe protection of human health.

EPA Response

The future residential risk calculated in the endangermentassessment did not drive the determination of the soils cleanup

level for surface level to six feet below the surface. Thegreatest risk is to workers at the public works garage with anestimated carcinogenic risk of 1.1 x 10~. The 100 mg/kg totalcarcinogenic PAH cleanup level calculated to a risk of5.8 x 10 ~4 for incidental soil ingestion by public works garageworkers. A cleanup level of 200 mg/kg total carcinogenic PAHs asproposed in the RI/FS would be half as protective as the 100mg/kg cleanup level in the selected remedy with a calculated riskof 1.2 x 10~3.

The ICF - Clement (1988) report has not been accepted as anofficial method for determining the cancer potency factors (CPF)for polynuclear aromatic hydrocarbons (PAHs) based on their car-cinogenic potential relative to benzo(a)pyrene (BaP). CurrentEPA guidance states that all carcinogenic PAHs must be summed andthe CPF factor for BaP applied to determine the total carcinogen-ic risk for PAHs.


Statement Page 8_: For the Peoples site, EPA believes that acleanup level of 1 ug/1 benzene, the most abundant volatileorganic present in the contaminated ground water, would be pro-tective of human health, based on NRL."

Comment: The RI/FS remediation goal for water is 5 ug/1. Thislevel is equally protective of human health when consideration isgiven to the institutional controls in place at the site.

Other sources of benzene contamination may be present on ornear the site contributing to the benzene concentration. Theaction level for UST contaminated ground water is 5 ug/1. Pleaseexplain why benzene from MGP sites is considered more hazardousthan benzene from other sources.

The practical quantitation limit for benzene listed in EPAMethod 8000 is 5 ug/1. Please clarify how compliance can beverified when the practical quantitation limit is in excess ofthe remediation goal.

Midwest Gas does not consider this remediation goal astechnically feasible or practical.

EPA Response

The EPA document Methods for the Determination of OrganicCompounds in Drinking Water. EPA/500/4-88/039, December 1988lists 3 methods for analysis of benzene in water with methoddetection limits below 1 ug/1. These are EPA methods 502.2,503.1, 524.1, and 524.2. Method detection limits for benzenepublished in these methods range from 0.01 to 0.1 ug/1.

8

The cleanup level of 1 ug/1 is required by the State of IowaAdministrative Code Chapter 133 regulations to restore the groundwater to beneficial uses. Section 121(d)(2) of CERCLA, as amend-ed by the 1986 Superfund Amendments and Reauthorization Act(SARA), requires that remedial actions initiated at Superfundsites must attain more stringent State applicable or relevant andappropriate requirements (ARARs), such as Iowa's anitdegradationrequirements, upon completion of the remedial actions.


Statement Page fi: "The level that EPA believes would be protec-tion for carcinogenic PAHs such as benzo(a)pyrene is 0.2 ug/1,based on the analytical detection limit."

Comment: EPA Method 8270 identifies the practical quantitationlimit for benzo(a)pyrene as 10 ug/1. The statement aboveidentifies the remediation goal as the analytical detectionlimit. Use of the detection limit for a compound as a compliancepoint will result in frequent false results in excess of thecompliance limitation making routine compliance under anyconditions essentially impossible.

Midwest Gas does not consider this remediation goal astechnically feasible or practical.

EPA Response

Methods for analysis of organic compounds in water werepublished in 40 CFR Part 136, October 26, 1984; "Guidelines forEstablishing Test Procedures for the Analysis of Pollutants Underthe Clean Water Act." EPA method 610 lists method detectionlimits for the analysis of polynuclear aromatic hydrocarbons(PAHs) below the 0.2 ug/1 cleanup level listed in the selectedalternative. For example method 610 lists a method detectionlimit for benzo(a)pyrene of 0.02 ug/1. Method 610 has beendeveloped by EPA for analysis of environmental water samples.

4.0 SUMMARY OF ALTERNATIVES

Statement Page £: "The National Contingency Plan (NCP), 40 CFRPart 300, requires that certain alternatives be developed forevaluation in the Proposed Plan. ... One or more innovativetreatment technology alternatives if those technologies offer thepotential for comparable or superior performance orimplementability, fewer adverse effects, or lower costs thandemonstrated technologies: ..."

Comment; Midwest Gas supports innovative treatment technologyalternatives and is actively pursuing biological treatment ofPAHs in soils.

EPA Respons*EPA also supports innovative technologies for treatment of

wastes from Superfund sites and will consider implementation ofthese technologies when they can be demonstrated to be suffi-ciently protective of human health and the environment.

4.3 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATEREXTRACTION AND TREATMENT

Statement Page Ifl: "Current technologies for biologicaltreatment of PAHs in soil have not been demonstrated toeffectively reduce concentrations of all PAHs to environmentallyacceptable concentrations for the quantities of excavated soilswhich would be generated by Alternative 3. Biological treatmenttechnologies are in development which may effectively reduce PAHconcentrations to environmentally acceptable concentrations inlarge quantities of soil."

Comment: Midwest Gas is currently conducting a cooperative MGPsoil biological degradation research project with the Instituteof Gas Technology (IGT) and the Gas Research Institute (GSI).IGT has recently completed the laboratory treatability study.The results observed in that study appear to be capable ofachieving levels within the cleanup standards in the ProposedPlan. A new process developed by IGT, consisting of bothchemical and biological treatment, is responsible for thesuccess. The continuation of this project will result in a fieldexperiment consisting of controlled land treatment yet thissummer. The final report for the project is expected to beavailable in approximately one year.

This developing technology was not available for evaluationduring the preparation of the RI/FS. If the field experiment issuccessful as the laboratory study suggests, Midwest Gas willrequest that the EPA seriously consider the use of this technolo-gy for contaminated soils removed from the eastern portion of thesite.

It would be appropriate for the EPA to include a statementin the ROD regarding the possible use of bioremediation as wasmentioned by the EPA Remedial Project Manager at the publichearing on July 9, 1991, in Dubuque.

10

EPA Response

EPA has reviewed the workplans for the biological degrada-tion research project and supports the development of alternativetechnologies for treatment of wastes from Superfund sites. EPAmay consider significant information submitted after completionof the Record of Decision including information about bioremedia-tion consistent with 40 CFR 300.825(c).

4.5 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATEREXTRACTION AND REMOVAL OF SOURCE SOILS

Statement Page 12; "The soil volume calculation includesexcavation of all visibly contaminated soils as described in theboring logs. This soil volume estimate exceeds that provided inthe RI/FS because it includes excavation to the lower confiningunit.H

Comment; Use of all visibly contaminated soils as identified inthe boring logs will likely overestimate the quantity of contami-nated soil requiring excavation. Relatively low concentrationsof PAH compounds have been visibly observed during previous siteactivities under certain conditions.

EPA Response

With regard to the selected remedy at the Peoples site, EPAwill not require excavation of contaminated soils and sourcematerial that are less that 200 mg/kg carcinogenic PAHs/2900mg/kg total PAHs below 6 feet from surface level. These cleanuplevels below 6 feet are consistent with the requirements of theremoval action in the Highway 61 corridor. As part of the Reme-dial Design phase a method for determining what constitutes"visible coal tar" will need to be developed.

5.2 COMPLIANCE WITH ARARS

Statement Page 14; "The hazardous waste treatment storage anddisposal regulations under RCRA are applicable to wastes at thissite where coal tars, when tested by the toxicity characteristicleachate procedure (TCLP), are found to contain concentrations ofhazardous constituents in excess of regulatory values. Other-wise, RCRA regulations are considered relevant and appropriate,due to the hazardous nature of coal tars. Therefore the substan-tive requirements of RCRA, specifically 40 C.F.R. Parts 264 and270, must be met for non-TCLP wastes, including the requirementthat an incinerator destroy the contaminants at an efficiency of99.99%. A trial burn was conducted and demonstrated this removalefficiency."

11

Conunent; Midwest Gas proposes to burn the non-TCLP wastes atNeal Unit 1, in accordance with its approved work plan. Theinitial shipments of non-TCLP coal tar contaminated soils to NealUnit 1 commenced on July 29, 1991. However, a lesser volume ofcoal tar contaminated soils may remain at the site, and afterremoval of concrete, bricks, timbers, pipe, and other debris, maycontain toxicity characteristics in excess of those allowed underthe TCLP rules. Midwest Gas and the Edison Electric Institute(EEI) are continuing their efforts with the AssistantAdministrator, Solid Waste and Emergency Response, U.S. EPA, toaddress the cleanup of historic manufactured gas plant sites,including this site, to ascertain if Subtitle C regulation ofcoal tar wastes can be avoided under sound regulatory policy.

On July 3, 1991, U.S. EPA Region VII issued a letter toMidwest Gas advising that the informal dispute resolution periodpermitted under the Administrative Order on Consent would beterminated, because of a failure of such parties to reachresolution on the issue of the disposal of coal tar wastes thatexceed TC levels. Midwest Gas has requested that Region VIIreconsider its position in light of the continuing discussions onthe rule with the Agency.

If the Subtitle C regulation of coal tar wastes can beavoided under sound regulatory policy as determined by the SolidWaste and Emergency Response Administrator, Midwest Gas willrequest that the revised regulatory interpretation be madeapplicable to any of the coal tar wastes that are to be removedfrom the site. Midwest Gas does not oppose or object to thesubstantive requirements of RCRA, but objects to the applicationof RCRA Subtitle C regulations as they pertain to coal tar wastesmanaged at historical waste sites such as this site.

EPA RESPONSE

The hazardous waste treatment storage and disposal regula-tions under RCRA are applicable to wastes at this site where coaltars, when tested by the toxicity characteristic leachate proce-dure (TCLP), are found to contain concentrations of hazardousconstituents in excess of regulatory values. Otherwise, RCRAregulations are considered relevant and appropriate, due to thehazardous nature of coal tars. If the regulatory status of thesewastes changes in the future, the Agency will address the effectof the change on the selected remedy at that time in accordancewith the N.C.P.

5.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME

Statement Page 16; "If soil is treated biologically and replacedin the excavated areas, some residual contamination may bepresent in the soil after treatment thus reducing but not

12

eliminating PAH contamination. ... Biological treatmenttechnologies are in development which may effectively reduce PAH

concentrations to environmentally acceptable concentrations inlarge quantities of soil."

Comment; Soils that have been treated biologically and arereduced in PAH contamination to appropriate levels do not pose athreat to the environment if replaced in excavated areas.

The limiting step in bioremediation of MGP soils is the masstransfer of the contaminants from the soil matrix to the aqueousphase. Once in the aqueous phase, the PAH contaminants can bereadily biodegraded by indigenous bacteria. When the soilreaches the point as which the PAH compounds are held in the soilmatrix so tightly that they will not transfer to the aqueousphase under ideal transfer conditions they will not pose anythreat to the environment under less than ideal transferconditions. This could be referred to as a "biological treatmentend point" which will likely be accepted in the future since itresults in the same effect as solidification and encapsulationmethods that are currently used to immobilize metal wastes. Thedifference is that the "environmentally available" contaminantsare biologically degraded.

EPA Response

EPA agrees that soils that have been biologically treated tolevels of PAH contamination below the required cleanup standardsmay be placed in the excavated areas. However, the selectedremedy requires the incineration of excavated soils contaminatedabove the cleanup standards, because biological treatment as analternative to incineration has not yet been demonstrated to besufficiently protective of human health and the environment.

Acceptance of the "biological treatment end point" withrespect to equivalency compared to the solidification process isspeculative and would have to be demonstrated in scientificstudies. The selected remedy requires that soils remaining atthe site have PAH contaminants reduced to concentrations belowthe required cleanup standards as determined by acceptable ana-lytical methodology.


Statement Page 16; "The short-term risks associated with thepreferred alternative would involve the normal constructionhazards associated with the excavation of source and soil areasand with the construction and installation of wells."

13

Comment; As reported in the RI/FS there are significant risksassociated with construction activities. (See Section 8.2.5.2page 8-35, Alternative 5) These risks are an offset to the riskscreated by the site if left without remedial removal action.According to the national average for heavy construction work,the expected number of serious injuries during the remedialactivities is 1.6. The expected number of fatalities during theconstruction work is 5 x 10~ . The expected number of seriousinjuries to railroad workers during the transportation is 1.2with 6 x 10"2 fatalities. These factors should be compared tothe risks calculated for the baseline endangerment so that thenet risk reduction for remedial action can be fully assessed.

EPA Response

EPA does not include or compare risk associated with physi-cal hazards in determining site related risks due to exposure tohazardous materials. The Endangerment Assessment risks associat-ed with the Peoples site were calculated according to current EPApolicy and guidance.


Statement Page 17; "The preferred alternative would require 24to 36 months to complete the removal and treatment of sourceareas and contaminant soil. Incineration of excavated soils isestimated to require 24 months. The time estimated for installa-tion of the ground water extraction system and the establishmentof the plume containment is 24 months. The time necessary toachieve a reduction in contaminant levels to the health-basedstandards is estimated at 10 to 20 years. Installation of thebiological remediation system is estimated at 24 months."

Comment; The listed requirements for the individual phases ofthe project are the shortest completion schedule estimatescurrently available. It should be noted that not all of thesesteps can occur concurrently. Some of these steps are dependentupon completion of others first. The attached time line(Figure 1) identifies the major field activities and an estimatedschedule based upon current knowledge of the site.

It is critically important to conduct the Removal Action inphases so that the City of Dubuque maintenance garage is notcompletely isolated and no longer usable. If this were the caseand the City was forced to temporarily relocate their facilities,this would create an unnecessary work load and financial burdenon the City. Careful coordination between Midwest Gas and theCity for the phased excavation activities should not render thefacility inaccessible.

14

The attached tine line for 1992 through 1996 identifies thecompletion of the incineration of the materials from the westernportion of the site (highway corridor) by the end of October1992. At this point the storage facility can be removed and theRemedial Design completed, estimated at 5 months. The stagedexcavation activities and incineration of soils will continue forapproximately 36 months. An additional 6 months of constructionseason will be required to complete the incineration and installthe ground water extraction <.nd treatment system and the in situbioremediation system. Based on current knowledge of the site,Midwest Gas1 estimate of completion date for all these activitieswould be September 1, 1996.

The total time required for the removal and treatment ofsource areas and contaminated soils and ground water treatmentsystem installation is estimated to be 46 to 48 months aftercompletion of the highway corridor incineration and storagefacility removal.

EFA Response

EPA agrees that the implementation of the selected remedyshould be phased to minimize the impact on the operations of thepublic works garage. EPA recognizes the difficulty in estimatingthe time line for implementing and completing the constructionactivities required in the selected remedy. These constructionactivities should be expedited for protection of human health andthe environment.


Statement Page 18; "The other alternatives involving incinera-tion and the ground water treatment system would have the sameease in implementability. Capping is also a frequently usedtechnology. Excavation below the upper confining unit would notbe practical near the Public Works Garage and Kerper Boulevard asit would require excavation to approximately 30 feet. Insuffi-cient space is available on the site for the setback requirementsto excavate to this depth. Sheet pilings may not provide suffi-cient stability."

Comment; Midwest Gas concurs with this statement.


Statement Page 18; "Biological treatment of excavated soilswould require sufficient space onsite to construct a biologicalreactor system. It would be difficult to locate this system onthe site due to space limitations. Biological treatment by landfarming technologies would require offsite facilities in order tohave the necessary space to implement this technology."

15

Comment; Off site biological treatment in a land treatmentfacility could be completed in a safe and effective manner shouldit become a viable alternative as discussed above. This methodof treatment is under field testing by Midwest Gas, GRI, and IGTas previously stated.

EPA Response

EPA recognizes that Midwest Gas, GRI, and IGT are developingbiological land treatment as an alternative for treatment of PAHcontaminated soils. EPA also supports innovative technologiesfor treatment of wastes from Superfund sites. EPA may considersignificant information submitted after completion of the Recordof Decision including information about bioremediation consistentwith 40 CFR 300.825(C).


Statement Page 18; "The preferred alternative would removehighly contaminated source soil areas below 6 feet to the top ofthe upper confining layer."

Comment; See comment below.

6.0 SUMMARY OF PREFERRED ALTERNATIVE

Statement Page 19; "...excavation and incineration ofcontaminated source soils that have visible coal tarcontamination from 6 feet below grade to the surface of the upperconfining unit: ..."

Comment; As stated in a previous comment, relatively lowconcentrations of coal tar can be observed in soil under certainconditions. Midwest Gas will submit for EPA review guidelines onthe visual criteria that will be used for field implementation inthe Remedial Action. In the case of disagreements between theEPA or it's agents and Midwest Gas regarding the definition of"highly contaminated source soil areas" or "visible coal tarcontamination" it would be appropriate to use risk based clean upstandards that are no more restrictive than those established forthe highway corridor portion of the site below 6 feet in depth.This standard was established at 2,900 mg/kg total PAHs and200 mg/kg carcinogenic PAHs.

EPA Response

With regard to the selected remedy at the Peoples site, EPAwill not require excavation of contaminated soils and sourcematerial that are less that 200 mg/kg carcinogenic PAHs/2900mg/kg total PAHs below 6 feet from surface level. These cleanup

16

levels below 6 feet are consistent with the requirements of theremoval action in the Highway 61 corridor.

2.3 COMMENTS FORM THE CITY OF DUBUQUE

COMMENT |1

The City of Dubuque fully supports the comments submitted byMidwest Gas Company of Section 5.5 of the EPA Proposed Plan,that it is critically important that the remedial action beperformed in phases in order to ensure that the City of DubuquePublics Works Garage can continue to be used by the City for theentire duration of the remedial action. The Publics Works Garagerepresents a major financial investment to the City of Dubuque.We are grateful for and support the comments in the Proposed Planand the comments made at the public hearing that the garagefacility will not have to be relocated and that there will be noexcavation necessary under the garage.

We agree with the Midwest Gas statement found on the bottomof Page 7 of its comments that "It is critically important toconduct the removal action in phases so that the City of Dubuquemaintenance garage is not completely isolated and no longerusable. If this were the case, and the City were forced totemporarily relocate their facilities, this would create anunnecessary workload and financial burden on the City. Carefulcoordination between Midwest Gas and the City for the phasedexcavation activities should not render the facility inaccessi-ble." We need, support, and request a cleanup phasing whichprovides for the continued operation of the garage facility. Weunderstand that the cleanup activities adjacent to the garagewill be inconvenient to its effective operation, and we can livewith that. What we cannot live with is the loss of the garagefacility either temporarily or permanently.

The City remains fully committed to working with Midwest GasCompany and federal and state agencies to ensure that the remedi-al action can be done in a manner that is protective of humanhealth and the environment and yet allows Dubuque to continue useof its garage.

EPA Response

EPA agrees that the implementation of the selected remedyshould be phased to minimize the impact on the operations of thepublic works garage. It will be necessary for Midwest Gas andthe City of Dubuque to coordinate efforts to allow continuedoperation of the garage facility during the remedial activities.

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COMMENT |2

The City of Dubugue disagrees with the comments of MidwestGas Company, however, as they are expressed with regard to Sec-tion 3.2 of the Proposed Plan. The City of Dubugue does notbelieve that any investigations have determined that leaking hasoccurred from historical or current underground storage tanksthat is impacting ground water at the site. The City of Dubuque,however, does not disagree with Midwest Gas1 request for a modi-fied remediation goal for benzene.

EPA Response

The cleanup level of 1 ug/1 is required by the State of IowaAdministrative Code Chapter 133 regulations to restore the groundwater to beneficial uses. Section 121(d)(2) of CERCLA, as amend-ed by the 1986 Superfund Amendments and Reauthorization Act(SARA), requires that remedial actions initiated at Superfundsites must attain more stringent State applicable or relevant andappropriate requirements (ARARs) upon completion of remedialactions. State standards that are more stringent than EPA stand-ards may be imposed by State antidegradation requirements.

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