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RECORD OF DECISION DECLARATION
SITE NAME AND LOCATION
DuPont Impoundment of the Todtz Farm SiteCamanche, Iowa
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial actionfor the DuPont Impoundment of the Todtz Farm Site in Camanche,Iowa. This final plan has been developed in accordance withCERCLA as amended by SARA, and, to the extent practicable, theNational Contingency Plan. The decision is based on theadministrative record for this site. The attached indexidentifies the items which comprise the administrative recordupon which the selection of the remedial action is based.
DESCRIPTION OF THE SELECTED REMEDY
This remedial action represents the final action for theDuPont Impoundment of the Todtz Farm Site. The selected remedyincludes the following major components:
- A 2-foot soil cover over the DuPont Impoundment;- Access restrictions which include deed limitations andsite fencing;
- Site maintenance which includes mowing the grass andrepairing the fence;
- A ground water monitoring system which includesimplementation of further remedial actions if certainchemical specific action levels are exceeded;
- Replacement of the Bark residence drinking water well inthe deeper bedrock aquifer.
DECLARATION
The selected remedy is protective of human health and theenvironment, attains Federal and State requirements that areapplicable or relevant and appropriate to this remedial action,and is cost-effective. This remedy utilizes permanent solutionsand alternative treatment technologies to the maximum extent-practicable for this site. However, because implementation oftreatment at this time was determined not to be cost-effective
S00013339SUPERFUND RECORDS
based on the relative overall risk to public health and theenvironment, this remedy does not satisfy the statutorypreference for treatment as a principal element of the remedy.However, if the exceedance of certain chemical specific actionlevels (as detected in the ground water monitoring system) areexceeded in the future, there will be provisions to implementtreatment if it is feasible at that time.
This remedy will result in hazardous substances remainingonsite above health based levels, that will be covered by a2-foot soil cover. Since these hazardous substances will remainonsite, a review will be conducted within five years aftercommencement of remedial action to ensure that the remedycontinues to provide adequate protection of human health and theenvironment .
Date Morris KayRegional AdministratorRegion VII
RECORD OF DECISION
FOR
THE DUPONT IMPOUNDMENT
OF
THE TODTZ FARM SITE
CAMANCHE, IOWA
Prepared by:
U.S. ENVIRONMENTAL PROTECTION AGENCY
October, 1988
TABLE OF CONTENTS
1.0 INTRODUCTION1.1 BACKGROUND1.2 HYDROGEOLOGIC SETTING1.3 PREVIOUS STUDIES1.4 COMMUNITY RELATIONS HISTORY1.5 ROLE AND SCOPE OF REMEDIAL ACTION1.6 ENFORCEMENT ACTIVITIES1.71 SITE CHARACTERISTICS1.72 SUMMARY OF SITE RISKS1.8 DOCUMENTATION OF SIGNIFICANT CHANGES
2.0 ALTERNATIVES EVALUATED2.1 NO ACTION2.2 SOIL COVER2.2A ALTERNATIVE 2 WITH TREATABILITY STUDY2.3 GEOMEMBRANE MULTILAYER CAP2.3A ALTERNATIVE 3 WITH TREATABILITY STUDY2.4 GEOMEMBRANE - CLAY MULTILAYER CAP WITH BENTONITE
SLURRY WALL
3.0 SUMMARY OF THE COMPARATIVE ANALYSIS OF THE ALTERNATIVES3.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT3.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS3.3 REDUCTION OF TOXICITY, MOBILITY OR VOLUME3.4 SHORT-TERM EFFECTIVENESS3.5 LONG-TERM EFFECTIVENESS AND PERMANENCE3.6 IMPLEMENTABILITY3.7 COST3.8 COMMUNITY ACCEPTANCE3.9 STATE ACCEPTANCE
4.0 THE SELECTED ALTERNATIVE4.1 SOIL COVER4.2 ACCESS RESTRICTIONS4.3 MAINTENANCE4.4 GROUND WATER MONITORING4.5 HEALTH AND SAFETY4.6 TIME SCHEDULE
5.0 STATUTORY DETERMINATIONS
FIGURE NO. -PAGE NO.
1-3 TOPOGRAPHIC SURVEY AREAS la1-4 SITE SAMPLING LOCATION MAP 2a7-la DISTRIBUTION OF ORGANIC CONSTITUENTS IN TEST
PIT SOILS . 4a7-lb DISTRIBUTION OF INORGANIC CONSTITUENTS IN TEST
PIT SOILS 4b7-lC DISTRIBUTION OF ORGANIC CONSTITUENTS IN TEST
PIT WATER 4c7-Id DISTRIBUTION OF INORGANIC CONSTITUENTS IN TEST
PIT WATER 4d7-le DISTRIBUTION OF ORGANIC CONSTITUENTS IN GROUND
WATER, SURFACE WATER 4e7-lf DISTRIBUTION OF INORGANIC CONSTITUENTS IN GROUND
WATER 4 f2-1 MONITORING WELL LOCATIONS 8a4-1 SOIL COVER 17a
TABLE NO. PAGE NO.
7-2a POSSIBLE HUMAN EXPOSURE SETTINGS 4g7-2b POSSIBLE ENVIRONMENTAL EXPOSURE SETTINGS 4h7-2C SUMMARY OF CONTAMINANT CONCENTRATIONS 5a2-la IMPLEMENT ALT 4 OR TREATMENT REMEDY . lOa2-lb IMPLEMENT GROUND WATER REMEDIATION lOb3-2 ARARS IDENTIFIED 12a
1.0 INTRODUCTION
1.1 BACKGROUND
The 2.7 acre DuPont Impoundment is located within the12-acre parcel of land known as the Todtz Farm Landfilllocated on the 120 acre Todtz family farm, 1-1/4 miles west ofCamanche, Iowa. Camanche is located on the Mississippi riverabout 2 miles south of Clinton, Iowa.
Between 1959 and 1969, sand and gravel were mined fromthe 12-acre parcel of land. The mined area was used as alandfill for disposal of municipal refuse from 1969 to 1975. TheDuPont Impoundment was constructed in the northwest corner of theTodtz Farm Landfill sometime in 1971. An estimated 4300 tons ofwet end cellophane process wastes from DuPont's Clinton, Iowaplant were disposed of in the impoundment between 1971 and itsclosure in 1975.
1.2 HYDROGEOLOGIC SETTING
A sand and gravel terrace associated with glacial outwashactivity forms the natural uppermost aquifer around the site.Ground water in the uppermost water bearing unit flows generallyin a southeasterly direction toward the Mississippi River.Domestic wells are located downgradient of the site and arepotential receptors for contaminated ground water. It ispossible that the municipal water supply wells of Camanche mayalso may be impacted.
In the vicinity of the landfill, the sand and gravelunit is underlain by a thick sequence of low permeability claysand silts with occasional lenses of silty to clayey fine sands.These low permeability soils directly overlie dolomite bedrockthat also serves as a source of drinking water to localresidents. The low permeability soils appear to behave as anaquitard preventing hydraulic connection between the two waterbearing units.
Surface water bodies in the vicinity of the site whichare potential receptors for contaminated run-off and/or rechargeare the north and south ponds, Murphy's Lake and Bandixen Lake.Secondary potential receptors include other downgradient lakesand the federally owned and managed Upper Mississippi River Fishand Wildlife refuge located less than one mile from the site.(Refer to Figure 1.3)
L,'. J*' '<
^6^LV-4_.0• \-~ I f\ .. .1 ' .' .^. f
TOPOOHAFMIC lUMVf V ARf1 INCH-200 FEir
"j- -frs. I.'.LJ^
-^^^cc3f>
*f ^/-CX^ sAjS-s^
^- ri:> ..-/ c^^crSv^l'1 I xIOU«CI U5r.SrilNION4HOCAU.WMf VV 4^"^ J • I / l<3^ ^H
.(.'•'
TOTCKJRAPMIC IUMVIY AHiAI INCH-JO Mil
SI Al I I N f f f l
Fiaunt i-jTOPOGRAPHIC SURVEY AREASt>w"'^1 'M^OtlNOWf *4l ni'l$
1.3 PREVIOUS STUDIES
The Todtz Farm Landfill was identified as a potentialuncontrolled hazardous waste site in 1979. A preliminary siteinspection was conducted by EPA's Field Investigation Team (FIT)Contractor in 1980. The site was given a Hazard Ranking. System(HRS) score of 52.11 in March 1985, and added to the NationalPriorities List (NPL) in June 1986.
FIT returned to the site in August 1985 to takeadditional surface water, sediment, and residential drinkingwater samples.
In September 1986, EPA's REM II contractor installed sixground water monitoring wells around the landfill and near theDuPont Impoundment and collected additional surface water,sediment, soil and residential well samples. The monitoringwells were sampled five times through August 1987 by REM II.Ground water samples taken from the monitoring wells installed inthe downgradient impoundment berm (monitoring wells MW-3, MW-4,and MW-5 as shown on Figure 1.4) have shown the presence oflevels as high as 3600 ug/1 for carbon disulfide, 400 ug/1 forlead, 8,800 ug/1 for toluene, 97,000 ug/1 for tetrahydrofuran,1,000 ug/1 for 4-methyl phenol, 1.10 ug/1 for mercury, 160 ug/1for arsenic, and 209 ug/1 for benzene. Except for arsenic andbenzene, these compounds are among those reported by DuPont asbeing used at the Clinton cellophane plant and were disposed inthe DuPont Impoundment.
1.4 COMMUNITY RELATIONS HISTORY
The local community has not recently expressed concernregarding remediations of the Lawrence Todtz Farm site.
A 21-day public comment period was held from August 20through September 10, 1988. In that time period, no publiccomments from the local community were received and there were norequests for a public meeting. A comment letter was receivedfrom DuPont's consultant. A phone call was also received fromthe Bark residence. These comments are addressed in theResponsiveness Summary.
All community relations activities have been in conformancewith the requirements of Sections 113 and 117, CERCLA, and theNational Contingency Plan (NCP) in 40 CFR 300.
1.5 ROLE AND SCOPE OF REMEDIAL ACTION
Based on investigations conducted onsite prior to 1988, 'itwas evident that there was a release or a threat of release ofhazardous substances from the DuPont Impoundment. EPA had also
-2a-
W I L L O W L A K E
MURPHYR E S I D E N C E
DUPONTINDUSTRIAL
CELLA R E A
NSOUTHPOND
SANITARY LANDFILL
COUNTY R O A D
JIM BARKRESIDENCE
RW-4
BANDIXEN L A K E
OEOTECHNICAL BORINGO MONITORING WELLS
RW RESIDENTIAL WELL0 LANDFILL BORING LOCATION
• NEAR SURFACE SOIL SAMPLEA SURFACE WATER AND SEDIMENT
SAMPLE LOCATION
® TEMPORARY BENCH MARK SETBY FIELD PERSONNEL ON UTILITYPOLE PIER. ASSUMED ELEVATION100.0 FT
SOURCE: FIT REPORT. AUGUST. 1 BBS. RE VISIONS BASED ONSITE VISIT MAY. 1966.
NOTE:
N
LOCATION OF ROADS AND SURFACE WATER F E A T U R E SAPPROXIMATED BY FIELD PERSONNEL
NOTE: LOCATION OF ROADS ANDSURFACE WATER FEATURESAPPROXIMATED BY FIELDPERSONNEL. SCALE
200
EET
OUPONT LANDFILLGROUNDWATER CONTAMINATION SITE
CAMANCHE. IOWA
£^ Woodward-Clyde Consultant:^fc^T i"«iHll«i. •lOlOQKIt *BO I «»IIO«»I -1 •>. iCJl. ' . l-t
SITE
DON BY M£
c»*-a *v fr-Z^S
SAMPLING LOCATION MAP
o*i£ 4/rr/&7D * T E y/>F^7
pAOJtc : NO ' - •.(3 2 0 E S 1 d"7/
-3-
sent CERCLA 104/RCRA 3007 information request letters tocompanies who reportedly had sent wastes to the municipal -landfill. Responses to these letters did not indicate thathazardous substances had been disposed in the municipal landfill.It seemed likely that the source of contamination for theLawrence Todtz Farm Site was the DuPont Impoundment and that theremedial alternative selected for the impoundment would be asufficient final remedy for the entire site.
1.6 ENFORCEMENT ACTIVITIES
During the REM II site investigation, EPA begannegotiations with E.I. DuPont de Nemours and Co. for DuPont toconduct a Remedial Investigation/Feasibility Study (RI/FS) forthe site. DuPont agreed to conduct a RI/FS focused on theirimpoundment. On April 5, 1988, a CERCLA 104/122 Consent Order wassigned by both EPA and DuPont, finalizing the agreement forDuPont to conduct the RI/FS.
Dupont conducted the RI/FS pursuant to the "DuPontImpoundment Operable Unit RI/FS Work Plan" dated February 12,1988. This workplan, prepared by DuPont's consultant CH2M Hill,was approved by EPA and included as an attachment to the CERCLA104/122 Consent Order. The purpose of the RI/FS was to fullycharacterize the DuPont Impoundment, determine the extent ofcontamination, evaluate the risk to downgradient receptors, andevaluate appropriate remedial alternatives for the DuPontImpoundment.
1.71 SITE CHARACTERISTICS
The RI was conducted during the spring of 1988 and consistedof the following tasks: a source area characterization study toevaluate physical and chemical characteristics of theimpoundment; a hydrogeologic investigation to define sitestratigraphy, ground water flow paths and contaminant migrationpathways; and an environmental sampling task to define the natureand extent of contaminants of concern in ground water and surfacewater.
The upper ground water aquifer at the site generally flowsin a southeast direction with the majority of the ground waterrecharge occurring upgradient of the site. The impoundmentwastes are periodically in direct contact with the ground water.The bedrock aquifer is separated from the upper aquifer by athick sequence of low permeable clays and silts that appear tobehave as an aquitard. Although the Todtz and Bandixen residencewells are completed in bedrock, ground water quality in thebedrock aquifer has not been fully investigated at this time.
-4-
As part of the source area characterization, soil andwater samples were taken from test pits excavated within theimpoundment. Figures 7-la and 7-lb indicate levels of organicand inorganic substances detected in the test pit soils.Comparing the test pit samples (TP-01, TP-02, and TP-03) with thebackground location (FB-04), the levels of organics andinorganics in the impoundment soils exceed backgroundconcentrations. Figures 7-lc and 7-ld indicate levels of organicand inorganic substances detected in the test pit water.Comparing test pit water samples (TW-01, TW-02, and TW-03) to thebackground ground water sample (DP-01), it was concluded thatground water in the impoundment exceeds background concentrationsof organic and inorganic constituents.
As indicated on Figures 7-le and 7-lf, analysis of groundwater samples confirms the presence of elevated levels of organicand inorganic constituents significantly above background in themonitoring wells (MW-03, MW-04, and MW-05) located downgradientof the DuPont Impoundment in the impoundment berra, as wasconcluded by the REM II Investigation. Above backgroundconcentrations of several inorganic constituents were detected inother downgradient wells (DP-05, DP-02, PZ-02 and the Barkresidence well). Arsenic was also detected in the ground watersample from PZ-03 in concentrations above background. Also, EPAsplit samples for DP-05, DP-02 and PZ-02 detected results oftetrahydrofuran of 7 ug/1, 2 ug/1 M and 1 ug/1 M respectively.(The "M" code designates that the compound was detected, but thelevels are below the EPA contract detection limits. Therefore,the quantification is an estimate). The tetrahydrofuran found inthe split sample analysis was not confirmed during a subsequentsampling event.
1.72 SUMMARY OF SITE RISKS
The Endangerment Assessment (EA) is included in the RIreport and presents an evaluation of the existing and potentialfuture impacts of contamination at the DuPont Impoundment onhuman health and the environment. One of the major objectives ofthe assessment was to assist in identification of the principalroutes of human and environmental exposure to site contaminantsin order to focus the FS on remedial alternatives that would mosteffectively prevent or preclude adverse impacts.
Several potential human and environmental exposuresettings that could be impacted by the contaminants of concernwere evaluated on a qualitative basis by the EA (Refer to Tables7-2a and 7-2b). Those exposure settings that had a lowprobability of occurrence were not evaluated on a quantitativebasis.
One of the more likely scenarios would be a setting in whichchildren trespassing on the site to play might be exposed bydirect contact with or inadvertent ingestion of contaminated
APPROXIMATEIMPOUNDMENTBOUNDARY
HCTH 4DTOL RDTHF 702J
ff -\[ ' MARSHI v\
DP-5 .')
C
LEGENDMONITORING WELL INSTALLED BY EPAWELLS/PIEZOMETERS INSTALLED BY CH2M HILLEXPLORATORY BORING
l TEST PIT LOCATION tB«•ETHTOLACETETmeTHFPhi4MCS,
tethylTollMO*
Tto
T*trachloro«th7lB*thyl«thyl btoo*(2-batanotM)TetrahydrofuranPtanol4-MethylplMDOl
• Bthylbenx« 2-fl«xanone• Total Xylencs• Vain* MtiBatcd« Not detectwl at
limitdetection FIGURE 7- la
DISTRIBUTION OF ORGANICCONSTITUENTS IN TESTPIT SOILS (ug/ka)DUPONT IMPOUNDMENT RI/FSTODTZ FARM LANDFILL SITE
i'i^vl^^^^A^'^'Xx" £Af^^$^X>Q^~£xj.?.f.^3^'y£;. ",:V^^v^=;fe, • ; &- .:V£4:-v.^v/?t/;_ •:•«- •-.•••£":•*
r^f&-£F.•f-««F
-1\ "•".* £^*?^V/^.'U" )•''k *-^"'*'"•"•• '.--^fv '-**«• -. -V* •- "*. ••>•* ""'"^^-Ir^" "* - •' "-" • ,.i"T-'-,"•--Cf.-''"*
/^ • r-^v^1.- '*4^,. "r*-v*».^-'
«"; fWr ' / f Ml**f ^> 1 « •**
APPROXIMATEIMPOUNDMENTBOUNDARY
MARSH8800 15500ID 2.3
Ba\ 59.9 93.4Be\ O.V 0.3JCr -BBO. 28Co 7.1J\.».8JCu 5\ 27Fe 3200 2ISOOR> 5.7 JL2Ha 130J $MJV 27 Ot4Za 35 U16MnMl
LEGENDMONITORING WELL INSTALLED BY EPA
„ • WELLS/PIEZOMETERS INSTALLED BY CH2M HILLO EXPLORATORY BORING»• TEST PIT LOCATIONBBG - AT OR BELOW BACKGROUND LEVELS
Al-AluminumAc-AfMnieBa-Bwlum
Ft- Iron
Cr- ChromiumCo-CooartCu«Coppw
/«-:^..vNfl • Sodium
V • VMMdiumZn-Zhw
FIGURE 7-Jb"DISTRIBUTION OF INORGANICCONSTITUENTS (tng/kg) INTEST PIT SOILSOUPONT IMPOUNDMENT RI/FS < fTODTZ FARM LANDFILL SITE . . - * ; .
m
APPROXIMATEIMPOUNDMENTBOUNDARY
*»_1610J
, METH 107000/ (OX 5740/ /TOL 79700/ CSJ 401000/ HOC 6000
MARSH\
. i I -iLEGEND
A MONITORING WELL INSTALLED BY EPA• WELLS/PIEZOMETERS INSTALLED BY CH2M HILL
'O EXPLORATORY BORING - • r -mm TEST PIT LOCATION i „, % - -T .^7 •'
Bs » Benzene ' " '., _, -*XT * M-Xyleae
KEZB * •ethyleoe chloride V. THF • TetrabydroCuranT»t - lyBtrachloroetbyleae * -Ph ' * PhenolTol • Toloeoe 4B - 4-Metlr
CS2• y^Btone- Carbon dlsulfide* Hetbyletliyl ketone
t2-trataaone)• }—BezanoiM
4-MethylpbenolEstljuted value.None detected atdetection limits used
o ^—" 100SCALE IN FEET
FIGURE 7~fcDISTRIBUTION OF ORGANICCONSTITUENTS (ug/l) INTEST PIT WATERDUPONT IMPOUNDMENT RI/FSTODTZ FARM LANDFILL SITE
.
.c^y; '*^ . ^^^
, .
BackgroundCoocutratlOBS
Hg NDMl 0.003JNa 23.4V HDZn O.OS
APPROXIMATEIMPOUNDMENTBOUNDARY
\ J
fi
-'Iii
AMW-4PZ-06S
-OLB-01
AMW-5
tf
iOP-5
LEGENDINSTALLED BY ERA
WELLS/»>IE20»«eTER5 INSTALLED BY CH2M HILLEXPLORATORY BORIMO
— TEST PIT LOCATION
MD - Hot O*t«ctad at OetacUoo Llalt DMdAl -Sb - Antimony
Ba - Bvlum
Pb " LMdUn-K%ngHg • Mveury
Cd-Cadmium ""*** Na - SodiumCr- ChromiumCo-Coba*Cu-Coppar
Th-ThalliumV • VanadiumZn-Zbw
•' -•4J,.0 ^—' 100
SCALE IN FEET
FIGURE 7^ IdDISTRIBUTION OF INORGANIC(*ng/l) CONSTITUENTS INTEST PIT WATEROUPONT IMPOUNDMENT RI/FS -~f* - -' t
LANDFILL SITE " ""*: = • . . - - - - . . - :*- . . ' • • . •*--"••• - v.Jji' -•"••'-V.. ••>•*•.-•"-i '-;i"*-•?•;-•- -"--'#- • "" ••H^^s^^^^r-"-: ^-j*- ——.,-- * -," •* • -- • '^-r -^ •>*?." •-.*"=• •*'**• »:"?-jV-^ -.-*. •'?&»' • *^* '.^• ' - ' - • • - • • • • - - ' ' ' * * "
• ••M^ ^ ^ ""- ' "•"
(M;jt|^>> • , ' • • • ?iK»:-Trt. . t i . ; -.*.'' . >. .- .
- -BIO
if- t «i^!t-"L-*; '.v.
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URN »/«lM1OI ND/JIJACI W/191• Df-fl
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3MJ/514J0 ,„. M)/74,OOOJ go lei, iiao/7ioj v
MIT 1*0/174Ml ItJ/JI
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V-
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P»-?s« .V" , >-P'» '«,> •
]>,,''(t. *CALI IN FIIT' v.4. OOMTOim INTINVAL>r
0 OT-M ItAIMLIM (Till MONITONINO WILL' tt^t ^vc piuoMirm4 MW«I WILL MtTALUID IT If A•^ HWfll MIIOINTIAL WILL lAMCLINO LOCATION
O M-01 tUltrACI WATIN IAMPLINO LOCATION
IthrltMUMMthrlM* eklorite
CutwM Initial}-HtUMM
tnr Tttrthrftnfaroi
Notii ;
fMplt ditu (or BfOJ tanlu «r»i1/l/M (»CtM)3/2»/§l (ACtDI)»/H/ll (VOA-ljJ/JO/81 (VOA'l)Groundnvtcr Mticti d IPM/Mvntt K, tVH•urfM Wmr On> MM Only:
Mireh », tIM
;; L
*«-«*iANN*| n>/m
*"' .J lPill.:".;•;• W». -ki W . •^^^^^^VCift'-f1^ liii irfi
CONtTITUEimil^lW^^. ,_OHOUNOWATCR «UHfA<ii«»At1lH^J 'DUMNT IMfOUNDMINT NI/TI '1TODTZ f AHM LAHD'ILL Iff I
o.iM) M> 0.001
U MD Ml l.SM 0.1 Hg M>I* W) HI 0.001C4 ID ta ]|.4Cr IB Ib 0.001C» H>CM 0.01W IB O.OS Iritis m
,U:• .*«sn smiffitsftML&.z ****** 3
'"? ^V-i ' BS- ^- ^u-r- - !
•l-lvkim . H|*Mmiry
M-CMmhim NCr • Chromium Th • TTwIHvm0>-0»Mt • V-VimflvniCv-Copptr . Xn«Zlnt
llli<SS£=r.•"Sife ——too•o«li IN nrr
OOMTOUN INTIHVAL-r
-4g-
Table 7-2aPOSSIBLE HUMAN EXPOSURE SETTINGS
Medium Settina
Air
Surface soils andimpoundment wastes
Surface water
I
Groundwater fromsurficial orbedrock aquifers
Agriculturalproducts
Inhalation of vapors orcontaminated dusts re-leased from contaminatedareas of the site
Ingestion of contaminatedsoils or wastes duringrecreational, residentialor occupationalactivities onsite
Ingestion of contaminatedfish from the Murphy andBandixen Lakes
Dermal absorption ofcontaminants whileswimming in the Murphy andBandixen Lakes
Ingestion of contaminatedgroundwater from surfi-ciai aquifers
Inhalation of volatileorganic contaminantsreleased during showersor other household usesof groundwater
Dermal contact with con-taminants during showers,baths, or other householduse of groundwater
Ingestion of dairy pro-ducts or beef from cattlegrazing onsite or drink-ing from north and southponds
Population-at-P.isk
Nearby residents
Children playing/riding bikes;adults working/gardening;constructionworkers
Recreationalfishermen and theirfamilies
Local families
Families withprivate wellsdowngradient ofsite, or onsiteassuming futuredevelopment
Same as above
Same as above
Consumers of meat anddairy products
GLT766/59
1-4h-
Table 7-POSSIHLF ENVIFCNMENTAL, EXPOSURE. SETTINGS
.Vedium Settir.c
Surface soils Direct contact with/ingestior: of contain: njtcdsoils or wastes duringforaging, burrowing
Ingestior. of contaminatedoraar.isms
• Pcpulatior.-at-P: s'<
Eurrowir.'.; nama l s ,insects
Burrowing martrals ,birds
.rocs cr
Surface water
Ingestior. of contaminatedcrops grown cr.site
Ir.gestior. of contaminateddrinking water fromcr.site ponds or nearbylakes
Grazing wildlifeor domestic ar.ir.ils
Wildlife or dor.esti:animals
Ingestior. of contaminatedfish or aquatic organismsin cnsite ponds andnearby lakes
Faccoons, d'jcks,other aquaticfeeders
, 60
-5-
surface and impoundment soils. This scenario was, therefore,evaluated on a quantitative basis. Possible future exposureswere also evaluated on a quantitative basis for a scenario inwhich the site was assumed to be developed for residential use.In this scenario, both soil ingestion and ground water use wereevaluated for adults and young infants. All of the exposuresettings assumed long-term exposures to existing levels of con-taminants, which provides conservative assessments, since somedegradation of contaminants may occur over time.
To evaluate the potential adverse effects of exposure tosurface and impoundment soils at the concentrations ofcontaminants present, the hazard index (HI) was calculated. TheHI, which is calculated by the summation of the DI/RfD (dailyintake/reference dose) ratio for each chemical present, isintended to provide a measure of possible effects of exposure toseveral toxic chemicals. The daily intake (DI) or estimated doseis calculated based on soil ingestion. The reference dose (RfD)is defined as an estimate of a daily exposure to the humanpopulation that is unlikely ,to result in appreciable risk ofdeleterious effects during a lifetime. An HI of one or greaterindicates the possibility of adverse health effects. For all ofthe contaminants detected in the surface and impoundment soils,the His were calculated to be below one.
To evaluate the health risks associated with consumptionof contaminated drinking water, it was assumed that ground waterfrom monitoring wells MW-3, MW-4, and MW-5 would be ingested.These wells were chosen because they contain elevatedconcentrations of contaminants associated with the DuPontImpoundment. The concentrations of contaminants in the wellswere evaluated on the basis of hazard index, increased lifetimecancer risk, and comparison with EPA National Primary DrinkingWater Standards established for the protection of human health.The ground water assessment concluded that the Hazard Indexexceeded one for both mean and maximum concentrations ofcontaminants detected in the three monitoring wells. Thecontaminant concentrations also exceeded a number of MCLs andMCLGs (refer to Table 7-2c). Lifetime cancer risk, based onexposure to concentrations of benzene and arsenic in the threewells, was also greatly increased.
The following conclusions have been reached based on theexposure scenarios evaluated in the EA.
1. Risks to human health or the environment associated withdirect contact and ingestion of surface soils or surfacedowngradient to the impoundment appear to bebelow those used by EPA in determining whether humanhealth or the environment are protected.
2. There would be an unacceptable risk to human health orthe environment through ingestion of ground water withinimpoundment and at the impoundment berm.
-5a-
SLMMA8Y OF CONTAMINANT CONCENTRAT I ONS IN MM-03. MN-04.
COMPARISON TO DRINKING WATER STANDARDS OR GUIDELINESMW-05.
MINIMUM
VAIUE
MAXIMUMVALUE
MEAN
VALUEMEDIAN
VALUE
NATIONAL PRIMARYOK II* INC WATER STANDARDS
MCI MCLC
ORGANIC CO-POLIOS Conceni:ation (ug/l)
ACETONEBENZENECARBON DISU1.F1DErTWL BENZENEatfTMYLENE CHLORIDEMETHYL ETHYL KETONE4 -ME TMYl PHENOLPHENOL
TETHACHLOROETHVLENETETRAHYDROFURANTOLUENEXYLENES (TOTAL)
2O •
2]12
14 714 1
2222
2000209
42 K33 3
2SOO7S
1000185
295500
6400S 3
2511i
10562
226S
109- 40
224630
6202
6.66145320602
22
360222
2914.7
22600
22
*a
aaa
aa
aa
S
660
0
440
INORGANIC COMPOUNDS
AH SEN 1CBARIUM6ERYLL IUMCADMIUM
Q-flOMIUM (Total )LEAD
5285
0 2S12 1S50 40S
2 S
16001900
1460360400
349 0620 0
2 67 9
121 563 »
89585
o 2:12 155
1507 1
501000
10SOSO
SO
512020
NO! aetected value D'esenled is one ha'f the detection l i m i t and is used Tor the purposes of calculationand because aDsense of a quantifiable value does not necessarily mean o ug/l
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3. Risks to human health or the environment throughingestion or direct contact with ground water from theshallow aquifer at or near the southern or southeasternboundaries of the Todtz Landfill Site perimeter,which is several hundred feet downgradient from theDuPont Impoundment, appear to be below those used by EPAin determining whether human health or the environmentare protected. Concentrations of 60 ug/1 and 80 ug/1of arsenic have been detected at PZ-03 on the easternboundary of the landfill. These concentrations exceedthe Maximum Contaminant Level of 50 ug/1. However, risksto human health or the environment in this portion of thelandfill would appear to be acceptable because theaquifer would not be considered a viable drinking watersupply at this location.
The findings of the RI and the EA indicate that the DuPontImpoundment is the source of contamination for the Lawrence TodtzFarm Site. The focus of the FS was on the development of cost-effective remedial actions for controlling potential release ofwaste constituents from the impoundment.
1.8 DOCUMENTATION OF SIGNIFICANT CHANGES
There are no significant changes between the Record ofDecision and the Proposed Plan. A few non-significant changeshave been made throughout the Record of Decision to clarifyvarious aspects of site conditions and the selected remedy.
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2.0 ALTERNATIVES EVALUATED
Remedial alternatives were screened based on effectiveness,implementability, and relative capital, operations, andmaintenance costs. Excavation of the impoundment wastes.anddisposal at a RCRA landfill or treatment onsite usingincineration, stabilization or in-situ treatment technologieswere eliminated since they were not cost-effective based on therelatively low risk to the public health and the environment andthe large capital cost.
The EPA has evaluated four basic alternatives and twovariations for remediation of the DuPont Impoundment of the TodtzFarm Landfill Site. These alternatives are 1) no action, 2)soil cover, 3) geomembrane multilayer cap, and 4) geomembrane-clay multilayer cap with bentonite slurry wall. Alternatives 2TSand 3TS have also been developed as variations of Alternatives 2and 3 which would allow for permanent treatment remedies to beconsidered as further remedial actions. Alternatives 2, 3, and 4would also include ground water monitoring (with contingencytriggers for further remedial actions if certain action levelsare exceeded), institutional controls, fencing, and deedrestrictions. Installation of a new well in the deeper aquiferfor the Bark residence would be included as part of Alternatives2, 3, 4, 2TS and 3TS. A description of the alternatives isprovided below.
2.1 ALTERNATIVE 1 - NO ACTION
The no action alternative would allow site conditionsto remain as they currently exist. Evaluation of the no actionalternative is required by the National Contingency Plan (NCP)and also provides a baseline of comparison for the otheralternatives.
2.2 ALTERNATIVE 2 - SOIL COVER
The major component of Alternative 2 is a 2-foot soilcover which consists of an 18-inch thick soil layer overlain by a6-inch layer of topsoil and vegetation over the DuPontImpoundment. Site fencing, ground water monitoring, covermaintenance, and deed restrictions would also be incorporated.Installation of a drinking water well for the Bark residence inthe deeper aquifer is also included in this alternative.
The cover would prevent erosion and subsequent directcontact with the contaminated materials or contaminant transportby wind or surface water run-off and would also reduce the volumeof surface water currently infiltrating into the impoundment byas much as 10% per year.
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The installation of a new well in the deeper aquifer for theBark residence is necessary because the residence well is locatedin the shallow aquifer and would be the immediate receptor of anyground water contamination from the DuPont Impoundment that wouldmigrate beyond the landfill. The Bark well has already detectedconcentrations above background for sodium and arsenic which mayindicate that ground water quality is being impacted by the site.
The ground water monitoring system is depicted in Figure2-1. If the ground water monitoring system at any timedetects the exceedance of any specified chemical specific actionlevels, the exceedance would first be verified throughstatistical analysis and additional sampling. If the exceedanceis verified, a cap and slurry wall containment system would thenbe installed.
If these action levels are exceeded and the slurry wallcontainment system is constructed, another set of action levelswould immediately be in effect in the event of failure of thecontainment system. In this case, if any of these action levelswould be exceeded (which will be verified by statistical analysisand additional sampling), ground water remediation wouldimmediately be incorporated.
2.2A ALTERNATIVE 2TS - ALTERNATIVE 2 WITH TREATABILITY STUDY
In order to incorporate the preference for permanenttreatment remedies, EPA has developed a version of Alternative 2that will allow for treatment as a further remedial action if anyof the chemical specific action levels are exceeded and iftreatment would be determined to be feasible at that time.
Chemical specific action levels as specified in Table2-la and b have been established to trigger further remedialactions prior to any adverse effects on human health and theenvironment. The first set of specified chemical action levelsare as listed on Table 2-la. If any of these action levels areexceeded (which will be verified by statistical analysis andadditional sampling), a treatability study of the impoundmentwaste will immediately be conducted. If the cost of thetreatment remedy is comparable to the cost of the slurry wall,either Alternative 4 (cap and slurry wall) or a permanenttreatment remedy of the impoundment material will be selected byEPA.
If a second set of action levels, as listed in Table 2-Ib, are exceeded (which will be verified by statistical analysisand additional sampling), ground water remediation wouldimmediately be incorporated.
- 8a -
tf . '• s"
ii
X
CDCJ
/
• IWhSHSiQW WFLL»>*»"'- -. r;/ .-> V-y*^ /If •>-J=<-:^V; ~ - ,-
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--./^•OPTl^Yi^O l ^Sl U^
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SCALE IN PICT
FIGURE 2-1MONITORING WELL LOCCATIONSFOR ALTERNATIVE 2T3OUPONT IMPOUNDMENT RI/F5TOOTZ FARM LANDFILL SITE
-9-
2.3 ALTERNATIVE 3 - GEOMEMBRANE MULTILAYER CAP
This multilayer cap would consist of a geomembrane,gravel drainage layer, geotextile and a soil cover. The othercomponents, including fence, deed restrictions, cap maintenanceand the contingent slurry wall would be the same for Alternative3 as Alternative 2. Like Alternative 2, this alternative wouldprevent erosion and direct contact with contaminated soils, andwind or surface run-off. This alternative would also virtuallyeliminate surface water infiltration into the impoundment.
2.3A ALTERNATIVE 3TS - ALTERNATIVE 3 WITH TREATABILITY STUDY
Alternative 3TS has the same components as Alternative 3.However, Alternative 3TS, like Alternative 2TS, has beendeveloped to allow the consideration of treatment as a furtherremedial action if the chemical specific action levels, as listedin Table 2-la, are exceeded.
2.4 ALTERNATIVE 4 - GEOMEMBRANE-CLAY MULTILAYER CAP WITHBENTONITE SLURRY WALL
Alternative 4 would include construction of a soil-bentonite slurry wall in the native soil surrounding theimpoundment in addition to the other components as described inAlternative 3. A collection system (trench) would also beinstalled within the perimeter of the slurry wall to collectenough ground water to maintain gradient control. This groundwater would be hauled to a publicly owned treatment works (POTW)for treatment. This alternative would prevent surface waterinfiltration through the impoundment and prevent migration ofcontaminated ground water from the impoundment.
-lOa-
TABLE 2-la
IMPLEMENT ALTERNATIVE 4 OR TREATMENT REMEDY
COMPOUND HEALTH BASED STANDARD ACTION LEVEL1(UG/L) (UG/L)
ORGANICS:
Carbon disulfide 3500 500/25Q2Tetrahydrofuran 700 100/5O2
INORGANICS:
Arsenic 50 125/503Chromium (VI) 50 100/502
Notes:
1. Action level = Concentration to go to treatability studyprior to implementing Alternative 4 or atreatment based alternative at comparablecost.
2. The binary values apply to monitoring wells DP05/andperimeter monitoring wells respectively.
3. The binary values apply to monitoring wells FS-03, FS-02/andMW-2, FS-01.
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TABLE 2-lb
IMPLEMENT GROUND WATER REMEDIATION
COMPOUND HEALTH BASED STANDARD ACTION LEVEL1(UG/L) (UG/L)
ORGANICS:
Carbon disulfide 3500 3500/17502Tetrahydrofuran 700 700/3502
INORGANICS:
Arsenic 50 250/753Chromium (VI) 50 504
Notes:
1. Action level requiring ground water extraction and treatmentto Maximum Contaminant Level.
2. The binary values apply to monitoring wells DP05/andperimeter monitoring wells respectively.
3. The binary values apply to monitoring wells FS-03, FS-02/andMW-2, FS-01.
4. Landfill perimeter wells only.
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3.0 SUMMARY OF THE COMPARATIVE ANALYSIS OF THE ALTERNATIVES
The alternatives described in Section 2.0 wereevaluated using evaluation criteria presented in EPA Directive9355.3-02, "Draft Guidance on Preparing Superfund DecisionDocuments: The Proposed Plan and Record of Decision." Thesecriteria relate directly to factors mandated by Section 121 ofCERCLA and as amended by the Superfund Amendments andReauthorization Act (SARA) of 1986 and considerations whichmeasure the overall feasibility and acceptability of the remedy.These evaluations are summarized below.
3.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
Protection of human health and the environment is thecentral mandate of CERCLA, as amended by SARA. Protection isachieved by minimizing risks and taking action to ensure thatthere will be no future unacceptable risks to human health andthe environment through any pathway. Each remedial alternativewill have different long-term and short-term effects on theprotection of human health and the environment.
Alternative 1, which would allow site conditions to remainunchanged, would not be protective of human health and theenvironment. Under this alternative, there would be continuedcontaminant migration from onsite wastes to ground water and anunacceptable threat to human health through potential ingestionof ground water contained within the impoundment or at theimpoundment perimeter.
Alternatives 2, 2TS, 3, 3TS, and 4 would all be protectiveof human health and the environment. Alternative 4 would be moreprotective than Alternatives 2, 2TS, 3, and 3TS since it wouldessentially eliminate contaminant migration to ground water.However, at this time, there is no confirmed evidence of groundwater contamination by hazardous substances downgradient of thesite, with the possible exception of arsenic at PZ-03. SinceAlternative 4 would be less dependent on ground water monitoring,it is considered more reliable in the protection of human healthand the environment. A substantial difference in protection ofhuman health and the environment between Alternatives 2 and 3 andAlternatives 2TS and 3TS is not anticipated because the onsitesurface water recharge component to the ground water underneaththe impoundment is thought to be minimal.
3.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATEREQUIREMENTS
Section 121 (d) of CERCLA, as amended by SARA, requires'that remedial actions comply with applicable or relevant andappropriate requirements (ARARs) under Federal and State
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environmental laws. All of the alternatives considered, with theexception of the no action alternative, meet or exceed ARARsidentified for the site at the landfill boundary. Refer to Table3.2 which provides a list of the appropriate ARARs for the site.
The trigger levels for monitoring wells installed in thecauseway between the Todtz Landfill Site and Murphy's Lake havebeen established at values above Maximum Contaminant Levels(MCL). The ground water between this zone is not considered aviable water supply, since it is in a mined-out gravel pit areabetween two hydraulically connected surface water bodies on theboundary of the municipal landfill. Therefore, the MCLs wouldnot be considered applicable, relevant or appropriate.
3.3 REDUCTION OF TOXICITY, MOBILITY OR VOLUME
This evaluation criteria relates to the performance of atechnology or remedial alternative in terms of eliminating orcontrolling risks posed by the toxicity, mobility, or volume ofhazardous substances.
None of the six alternatives include treatment of thecontaminated source material of the impoundment as a component toreduce toxicity, mobility, or volume of hazardous substances.Treatment of the source material was considered during theinitial phase of the feasibility study, was determined not to becost-effective based on the relative low overall risk to publichealth and environment, and, therefore, was eliminated during thescreening process. Treatment of a certain amount of groundwater, collected to maintain gradient control would take place inAlternative 4. This is, therefore, the only alternative whichwould use treatment to reduce toxicity and volume of contaminantsat this time. However, Alternatives 2TS and 3TS would allowtreatment of the source material if any of the specified chemicalaction levels are exceeded, if the treatment alternative wascost-effective.
Since the contaminated source material would not initiallybe treated or removed for Alternatives 2, 2TS, 3, 3TS, and 4, thetoxicity and volume of the source would not be reduced. However,Alternatives 2, 2TS, 3, 3TS, and 4 would all be effective inreducing mobility of contaminated soils because capping wouldprevent erosion and reduce mobility by wind and surface watertransport. Alternatives 3, 3TS, and 4 would, in addition,eliminate surface water migration into the ground water.However, since the waste will remain in contact with the groundwater for Alternatives 2, 2TS, 3, and 3TS and onsite surfacewater recharge is relatively small, Alternatives 2 and 2TS wouldbe virtually as effective as Alternatives 3 and 3TS in reducingthe mobility of the contaminants via surface water recharge toground water.
U S IP* IfGUAllONS fO* iDlNlimWG IftZAIDOUS tASlI
40 crt 161 Identities those Miles subject to regulation as harardoui w a s t e s
PRtllllAl«INt
ll wastes arc discharged or delivered lor treatment al a pirMlcly owned irt-Atmeni workslarl l l ly trot»l the treatment process muit not a l low wane lo pats ihruuuh tiniieMcil orresu l t In conlimlnaled sewage sludge
Appl
Appl If altlelo A I if in-ai i vr 4
the c r l l e r l . 1 and l im i ta t ions user! lo I d e n t i t y » J t t P < at brini]lu/^i(i»ut In <o OR Hi are appl icable in all pimtofd « le.»t»
it.i^.itdi'tn 01 ruin-i ,M i him a I lUe
etl.thliili ftltrlhei nidi Hnii*l ipgnU I KHif *t^ -M'Mif I'm | AS' i i 'M** ilixi HIP iviPnni m4>rtunitM>>Ml rt«>M irii-1 nirif iindt'f HIM Ipyulnloii
llllut'il IrnM (he drairuor ireuth Hindi: tin- linn* »»M *i\ t-r dt tdutqr<|or <ti livi-ipil In a PQl» the r l lrd iiri linm.tm e M.ui'ltiil mil itiln-t iu i ' '< mutrt
4n (it 401 «HMI Id b*1 appt it ,it)le lo (Dili an A c t i o n Din* HII* ru le a l t o mikrtIdf.ir I'OIW i Mint mm ii U JDpI I fJtale
IQWA INVIR
4«t 304
Q4MU IV *CI
IOWA
Chapter
I continuous monitoring ol groundwater tor a perlnd nl )0 yean a r i r » r cloiure ol asani tary w a s t e disposal f a c i l i t y the monitoring period m,iy he reduced nr eilended basedon sllC'Speclllc circumstances.
Sanitary masle disposal s i tes In the state ol ln«a shall he Included on a registry ihlir e g i s t r y shall, lor each regulated s i t e , s p e c i f y l i m i t a t i o n s On fu ture land uiei and onother transactions
this chattel, legislated In t4tr. Is a bfoatf antideotHatlon iitle loi pintftilnn offioundMlef icsnurces In IOM. the IOM Drpa»l*wol ol r«tutal acsouicei ihall advlnl i traieHie letiulallofii ol *5!1 on a s i t e * ipecll Ic basi l to ptevent unfuiilltrtf gioundMaieiquality tfegrldallon
IOWA $0110 WASH DISPOSAI tuts
to) mil
ID)
10) 1III*
101 im a
10) iim
ihe llnlihed surlicc tl Ihe silt shall be fttaltetf as tewtlred. covered w i th toll, andseeded •Hh nallvt f iasses tt other lullable vegetal Ion
ftonltoflnt vrttU ihall be poll Honed tan led and anilyred iccottflng to lethnlcalc r i t e r i a and a schedule (Decided by the IOM Department ol miural «c sources
fhe IOM Department ol Nituial tcsouices shall B» nollllrd II a leachatc r e l e a s e Isdetected ine s i t e operator shall Iben sub*l I I plan lor contro l l ing and Heatingthe leichale ihls »lan ilia 1 1 be l*«le«enied iMvdlately upon anpioval
ten In ihall be nade lo the Una I cover as necessary lor a period ol live y e a r sfollowing closure lo ensure the Integri ty ol the llnal covn
•eoultcs at least a two teel ol <n«»>aclrd soil rover nvrr a solltf wat ie ta rd i ly thai• HI nol be used lor iw»ie than two wuntht. the cover shall hr giadrd to ,itUi*» itulace•alei ruiotl .
ihr Una) cover tat least two leel thlchl shall be designed to beproposed s i te land use
wlHi the
a p p r p r l a t e Ariffiitii t l ' a 11 VP (ndet tpec l l y adnlnl II r a I ( ve imtinr»"MM loi |hr miH.igrmrnl ollot all l»l til »nir In lo*a the leouirrmrnit cilrd lini-m *ie (•uuiilro-fl lelpvjnl anda I Irrna 11 ve S appi «l» r.i IP I'M (he (mronl I wiititdMenr t Me IIPI AM ve Ilir-t t|n-i 11 y i r<iui i rmrnl \ lor
pi» i t - ( In tur e i Me m,t i n |uritanr eAt atMive
Applicable nulei nl this chaple* lie considered applicable in artioui thai rould cautelo all grnim<l»a ler qual i ty degrldatlon S i t e ipecl l lc guld-mie nit 4)51 regulat ionsa l t e r n a t i v e s would be re<}i i l red I rom the Department under any ol ihe ixnpoiPd rrmedlal
a I Irr na11 ve s
IM
Relevant $ substant ive (design- r e l a t e d ) s t a l e regulation! regarding c losure ol a san i ta ry |^rappropriate lanrfllll (Including those died herein) have been deemrd re levant and appropilate ^lor all lor the Dupnnt impmindBent s i t e bated on a pr r l lm lna iy dr t r rmtnat Ion Dial Ia l t e r n a t i v e s ln»>itndmcnl w a n e t are non ha/ardout Al l piopoird remrdlal a l t p rna l l ve i are
coni ldered (unpllani w i t h thete AIAIS
Ai above
Ai above wtr thai A l t e r n a t i v e 4 Includes a le.irtii|e co l l ec t ion s v t i p m drilgnpd to controla iraihMe re lea ie as de ic r lbed nndn thl t i eguia I *<">
At above
AS altove All pioiHUPtl a l ierna l lve i wiuld meet »n putrni | tu« Mctiin ir>|tiit ^mrnt
Hn . t r i tv r me of |hr il|p Is ant 1C Ilia ted In th* tm <i-*-.ih IP 1uHir«-
nirt rlii-ni K.-v(r*(n* l l t lime 70.
-13-
Alternative 4 is the only alternative which would not onlyreduce the toxicity and volume of the contaminated ground water,but would also eliminate the mobility of contaminated groundwater outside of the site. However, Alternatives 2, 2TS, 3, and3TS would contain the necessary contingency triggers to implementfurther remedial actions if any of the predetermined chemicalaction levels are exceeded in the future.
3.4 SHORT-TERM EFFECTIVENESS
Short-term effectiveness addresses how well an alternativeis expected to perform, the time to achieve performance and thepotential adverse impacts of its implementation.
Adverse impacts to nearby residents and construction workersinvolved in impoundment remedial actions will not be significantfor any of the alternatives if the mitigative actions and healthand safety precautions outlined in the feasibility study aretaken. The relatively minor impacts from noise, dust, andvehicular traffic that do occur during construction are greatestdue to the truck traffic to and from the site. The truck trafficwould be about:
- 1,000 truckloads for Alternatives 2 and 2TS- 1,400 truckloads for Alternatives 3 and 3TS- 1,800 truckloads for Alternative 4
The time required between signature of the Record ofDecision (ROD) and completion of remedial actions is notsignificantly different between alternatives. The estimatedtimes range from 10 to 12 months for Alternatives 2 and 2TS, 12to 14 months for Alternatives 3 and 3TS, and 13 to 15 months forAlternative 4.
3.5 LONG-TERM EFFECTIVENESS AND PERMANENCE
Long-term effectiveness and permanence address the long-term protection and reliability an alternative affords.
All of the alternatives, except Alternative 1, are nearlyequal in their effectiveness in preventing erosion of thecontaminated source material given proper construction andmaintenance. They also rely equally on deed restriction and theIDNR state registry to prevent future development of the site.
Alternatives 2, 2TS, 3, 3TS, and 4 would all provideprotection to human health and the environment by minimizingcontact with contaminated ground water within the impoundment
-14-
and, through monitoring, possible future contact withcontaminants potentially released from the impoundment. Thedifferences in effectiveness of the alternatives result from thevarying levels of reliance on ground water monitoring andimplementation of contingency plans to achieve protection.
Alternatives 2 and 2TS would reduce contaminant loadings toground water by a maximum of 10 percent and would notsubstantially alter contaminant migration when compared to the noaction alternative. The RI results detected elevated levels ofsome inorganic constituents, indicating that the ground water mayhave already been impacted by the site. Therefore, ground watermonitoring of Alternatives 2 and 2TS is necessary to detect thepredetermined chemical specific action levels in order to providethe time necessary to implement further remedial actions.
Alternatives 3 and 3TS further reduces contaminant loadingto the ground water by essentially eliminating infiltration ofwater through the impoundment waste. Because 25 to 50 percent ofthe waste would remain in periodic contact with the water table,it is anticipated that the contaminant loading to ground watercould remain substantial. However, since the onsite surfacewater component of ground water recharge is believed to be aminimal amount of the ground water volume, the reduction ofcontaminant loading by Alternatives 3 and 3TS would probably notbe much different than Alternatives 2 and 2TS. Therefore,Alternatives 3 and 3TS are similar to Alternatives 2 and 2TS inthe reliance on monitoring and the contingency for implementationof further remedial actions.
Alternative 4 relies least on ground water monitoring sincethe potential for future contaminant levels to exceed health risklevels in offsite residential wells would be less. The slurrywall and cap containment would be effective in minimizing futurecontaminant contributions to the ground water given propermaintenance. The contaminants that would remain outside thecontainment structure would diminish over time as a result ofdispersion, adsorption, biodegradation, or volatilization.Ground water monitoring would still be implemented to monitor themigration of residual contamination.
3.6 IMPLEMENTABILITY
Implementability addresses how easy or difficult, feasibleor infeasible, an alternative would be to carry out from designthrough construction, operation and maintenance.
The various components of Alternatives 2, 2TS, 3, 3TS, and 4are proven technologies and materials necessary to implement themshould be readily available. Implementation of thesealternatives will require detailed design and competentsupervision.
-15-
Implementation time ranges from 10 to 12 months forAlternatives 2 and 2TS, 12 to 14 months for Alternatives 3 and3TS, and 13 to 15 months for Alternative 4.
3.7 COST
CERCLA requires that EPA select the most cost-effective (notmerely the lowest cost) alternative that protects human healthand the environment and meets other requirements of the law.Treatment alternatives were eliminated during the screeningprocess since they were not cost-effective. The no actionalternative, which would involve no cost, was considered in orderto meet requirements of the law.
Total capital costs are estimated at $520,000, 880,000 and2,300,000 respectively for Alternatives 2, 3, and 4. Presentworth operation and maintenance costs (at 5%) are estimated at$510,000, 560,000, and 520,000 for Alternatives 2, 3, and 4respectively. The total present worth costs are, therefore,estimated at $1,030,000 for Alternative 2, $1,440,000 forAlternative 3, and $2,820,000 for Alternative 4. These costswere taken directly from the FS Report and are presented forcomparative purpose. Costs for Alternatives 2TS and 3TS areassumed to be the same as Alternatives 2 and 3, respectively.Final costs will be developed during design.
Alternative 2TS is the most cost-effective alternative sinceit is the least costly alternative that is protective of humanhealth and the environment and meets other requirements of thelaw.
3.8 COMMUNITY ACCEPTANCE
This evaluation criteria addresses the degree to whichmembers of the local community support the remedial alternativesbeing evaluated.
The local community has not recently expressed concern overremediation of the Todtz Farm Site. There were no writtencomments received from the community during the 21-day publiccomment period which began on August 20 and ended onSeptember 10, 1988.
3.9 STATE ACCEPTANCE
The state acceptance criteria addresses the concern anddegree of support that the state government has expressedregarding the remedial alternatives being evaluated.
-16-
This is an EPA enforcement-lead site. The State hasparticipated in the review of all of the RI/FS documents and innegotiations with DuPont.
In a letter to EPA dated September 10, 1988, the Stateindicated a preference for Alternative 4 rather than Alternative2TS. Subsequently, the EPA and the State discussed the data,information, technical considerations and legal constraintsinvolved. The State issued their concurrence on the selectedremedy in a letter dated October 20, 1988.
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4.0 THE SELECTED ALTERNATIVE
Based on the information available to evaluate the remedialoptions against the required nine criteria, EPA has concludedthat Alternative 2TS is the preferred remedy (Figure 4-1).
The major components of Alternative 2TS are a 2-foot soilcover, ground water monitoring, site fencing and deedrestrictions. The soil cover will provide protection of humanhealth and the environment against direct contact with the waste.If the monitoring system detects exceedance of the predeterminedchemical action levels, either a cap and slurry wall containmentsystem or treatment remedy will be implemented. The monitoringsystem and contingency plans would protect human health and theenvironment by providing adequate protection against contact withcontaminants in the ground water. Installation of a new well inthe deeper aquifer for the Bark residence will provide additionalprotection of human health because the present Bark well wouldprobably be the immediate receptor of releases of contaminantsfrom the site.
The preferred remedy satisfies the remedy selectionrequirements under CERCLA, as amended, and the NationalContingency Plan (NCP). The preferred remedy at the site isprotective of human health and the environment, satisfies allidentified applicable or relevant and appropriate environmentalrequirements, and is the most cost-effective. The advantages ofthis alternative outweigh those offered by the otheralternatives.
In order to initiate construction of the preferredalternative, detailed design plans and specifications will needto be prepared. Implementation of the plans and specificationswill need to be conducted by qualified field personnel.Following is a summary of the components that will beimplemented.
4.1 SOIL COVER
Clearing, grubbing and preliminary grading would be thefirst phases of construction. A geotextile layer would then beplaced to provide a distinct boundary between the potentiallycontaminated soil and the cover materials and to lessen thepossibility of their mixing in the future.
An 18-inch thick soil layer would then be placed over thegeotextile layer, followed by a 6-inch layer of topsoil (Figure4-1) . The cover will prevent erosion and subsequent directcontact with the contaminated materials or contaminant transportby wind or surface run-off. The vegetation and slope of the-cover will reduce the volume of surface water currentlyinfiltrating into the impoundment by as much as 10 percent.
=UI=I1I=1J
GRASS
TOPSOIL
SOILCOVER
QEOTEXTILE
FILL TO GRADE
WASTE
0)i
FIGURE 4-1ALTERNATIVE 2SOIL COVERUIIPONT IMPOUNDMENT Ml/FS1OOTZ FARM IANOI II L SI I f
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4.2 ACCESS RESTRICTIONS
A restrictive covenant will be placed on the deed for theproperty on which the DuPont Impoundment is located. Deedlimitations would prevent future development of the area withoutfurther remedial action or consideration of impacts to publichealth and the environment. The site is being placed on the IowaState registry of hazardous waste sites. This action willinclude a notice on the deed preventing sale of the property orchange in land use without approval by the State.
A site fence will also be installed a minimum of 10-feetoutside of the perimeter of the impoundment to limit access byhuman or animal traffic to the contaminated source. The fencewill include a locking gate to allow entry for regularmaintenance, such as mowing or cover repair.
4.3 MAINTENANCE
Site maintenance will consist of mowing the grass andrepairing the fence. The soil cover will require routineinspection semiannually for the first 5 years and annuallythereafter. Maintenance would consist of repairing damage causedby erosion, freeze-thaw, and settlement. It is estimated that500 cu yards of soil (10 percent of cover, 1-foot thick) willneed to be replaced every 5 years to fill depressions and replacesoil lost by erosion. The actual amount of settlement anderosion occurring will depend on the properties of the materialsdisposed in the impoundment and the finished surface slopes.
4.4 GROUND WATER MONITORING
Ground water monitoring will consist of monitoring wellsupgradient and downgradient of the site to be sampled and testedroutinely. The ground water monitoring wells included in theplan are as indicated on Figure 2-1. Bedrock monitoring wellshave been included to document the water quality in the bedrockaquifer. Monitoring is considered an integral part of thisalternative because detection of contaminants at concentrationsabove target levels at or within the landfill will call forimmediate implementation of further remedial actions as discussedfurther in Section 4.5. The target levels are as stated inTables 2-la and 2-lb.
All of the shallow wells would be sampled semiannually forthe first 5 years, and on an annual basis thereafter. The deepwells would be sampled semiannually until four consecutivesamples show no traces of contamination, and once every 5 yearsthereafter.
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Ground water well samples will be tested for volatileorganic compounds (including tetrahydrofuran), sulfates,sulfides, chloride, iron, manganese, phenols, pH, conductivity,total organic carbon, total organic halogen, sodium, arsenic,lead, chromium. EPA plans to periodically conduct an independentanalysis of all semi-volatile organic and inorganic compounds.
The ground water monitoring program will include thefollowing components to detect changes in ground water qualityover time and to verify the exceedance of target contaminantaction levels through statistical analysis.
a. If contamination is found within 50% of action levels atany of the perimeter wells or DP-05, quarterly samplingat the well will be done for 1 year with 4 replicates ofeach sample.
b. A treatability study will be conducted and either atreatment remedy (if feasible) or Alternative 4 will beimplemented if in 2 successive sampling episodes, themean of any of the concentrations of compounds listed inTable 2-la (using the 4 replicates) is significantlygreater than the indicated action level at the 0.05significance level using the Student's t-test.
c. Construction of a ground water collection system andtreatment of ground water to MCLs if, in 2 successivesampling episodes, the mean of any of the concentrationof compounds listed in Table 2-lb (using the 4replicates) is significantly greater than the indicatedaction level of 0.05 significance level using theStudent's t-test.
4.5 FURTHER REMEDIAL ACTIONS
EPA has determined that further remedial actions will beimmediately implemented in the event that certain trigger levelsas shown in Tables 2-la and 2-lb are met or exceeded (which willbe verified by statistical analysis).
If any of the first set of trigger levels as shown in Table 2-laare met or exceeded (which will be verified by statisticalanalysis), a treatability study will immediately be conducted.The treatability study will include an evaluation of the mostappropriate technologies that will be available at that time andtheir comparative costs. Suitable pilot tests and/or bench scalestudies will be conducted as needed. At the conclusion of thetreatability study, EPA will decide whether the remedial actionwill consist of treatment of the impoundment waste orencapsulation by a slurry wall. If the second set of triggerlevels shown in Table 2-lb are met or exceeded (which will bestatistically verified), remedial action including pumping andtreatment of ground water will immediately be implemented.
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The trigger levels, as indicated on Tables 2-la and 2-lbhave been established to protect human health and theenvironment. It should be noted that for carbon disulfide andtetrahydrofuran, the two contaminants that are the mainfingerprint constituents of DuPont's cellophane waste, actionlevels that will trigger treatment or encapsulation of the DuPontImpoundment have been established at less than 10 percent of thedrinking water equivalent level (DWEL) at the landfill boundary(i.e., 50 ug/1 for tetrahydrofuran which has a DWEL of 700 ug/1).For the implementation of ground water extraction and treatment,the action levels of these two compounds have been set at half ofthe DWEL at the landfill boundary (i.e., 350 ug/1 fortetrahydrofuran which has a DWEL of 700 ug/1).
For Chromium VI the action levels have been set at the MCLat the landfill boundary for both sets of trigger levels.
Arsenic, unlike tetrahydrofuran and carbon disulfide, isfound at elevated concentrations in both the DuPont Impoundmentand the municipal landfill as well as some lesser concentrationsupgradient and offsite. Arsenic is not a known constituent ofthe DuPont cellophane process. However, a high concentration ofarsenic was found in the DuPont Impoundment.
In the area of PZ-03, where monitoring wells FS-02 and FS-03will be installed, trigger levels of arsenic higher than the MCLof 50 ug/1 can be allowed because the ground water at thislocation cannot potentially be used as a drinking water source.
The major component of ground water flow in the area ofPZ-03 would be towards Murphy's Lake. The surface waterconcentration of arsenic detected in Murphy's Lake is 1 ug/1.That is substantially less than the U. S. EPA Ambient WaterQuality Criteria of 48 ug/1 for the more toxic form of arsenicwhich has been developed for the protection of aquatic life.
If the concentration of arsenic of 125 ug/1 in monitoringwells FS-02 and FS-03 is met or exceeded (which will bestatistically verified), a treatability study will immediately beconducted. The treatability study will include an evaluation ofthe most appropriate technologies that will be available at thattime and their comparative costs. Suitable pilot tests and/orbench scale studies as needed will be conducted. At theconclusion of the treatability study, EPA will decide whetherthe remedial action will consist of treatment of the impoundmentwaste or encapsulation of the impoundment by a slurry wall.
If the second trigger level of 250 ug/1 of arsenic at FS-02and FS-03 is met or exceeded (which will be statisticallyverified), a ground water extraction and treatment system will beimplemented. The resulting cleanup level will be the MCL of 50ug/1.
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In regard to the trigger levels set for arsenic in FS-01 andMW-02, it should be noted that ground water flow from the PuPontImpoundment would be expected to flow primarily in thesoutheasterly direction toward FS-01. However, the onsitemonitoring wells located downgradient of the impoundment andbetween the impoundment and FS-01 have detected relatively lowlevels of arsenic as compared to the levels found in theimpoundment, PZ-03 and Bark's well, the immediate downgradientreceptor. EPA has established that monitoring will be conductedand treatment or encapsulation of the impoundment will beimplemented if the MCL of 50 ug/1 of arsenic is met or exceededin FS-01 and MW-2. An additional trigger of 75 ug/1 of arsenicat FS-01 and MW-02 has been established for implementation ofground water extraction and treatment. If triggered, groundwater extraction and treatment will continue until the MCL of 50ug/1 for arsenic is achieved and maintained at the site boundary.
The only known receptor located directly downgradient of thesite is the Bark's drinking well, which is presently screened inthe upper sand and gravel aquifer. For an extra measure ofsafety, this well will be decommissioned and a new drinking waterwell will be installed in the deeper bedrock aquifer, below theclay aquitard. EPA anticipates that an onsite trigger level of75 ug/1 would not result in contamination of usable ground waterat levels exceeding the MCL of arsenic of 50 ug/1 due to thenatural ground water attenuation and the influence of theremedial pumping and treatment which would be triggered by alevel of 75 ug/1.
4.6 HEALTH AND SAFETY
A health and safety plan, similar to the one successfullyutilized during the RI/FS activities will be prepared andfollowed during the remedial action.
It is anticipated that Level D protection will be necessaryfor clearing, grubbing, preliminary site grading, and placementof the geotextile and that minimal protection will be necessaryfor placement of the soil cover.
4.7 TIME SCHEDULE
It is estimated that the entire action will takeapproximately 10 to 12 months from the beginning of the onsitemobilization.
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5.0 STATUTORY DETERMINATION
Based upon available information, the selected remedysatisfies the remedy selection requirements under CERCLA, asamended, and the National Contingency Plan. The selected remedyat the site is protective of public health and the environment,satisfied all applicable or relevant and appropriateenvironmental requirements and is cost-effective.
The 2-foot soil cover would provide adequate protection ofhuman health and the environment against direct contact with thewaste. If the ground water monitoring system indicatesexceedance of predetermined chemical specific action levels,either a cap and slurry wall or treatment remedy will beinstalled. The monitoring system and contingency plans wouldalso provide adequate protection of human health and theenvironment against contact with contaminants in ground water.
It should be noted that the concentrations of arsenic fromthe ground water samples taken at PZ-03 were 80 ug/1 and 60 ug/1during the two remedial investigation sampling events, whichexceed the Maximum Contaminant Level (MCL) of 50 ug/1. The MCLwas established for the protection of human health. However, theMCL is applicable only if the ground water is a public drinkingwater supply and would be considered relevant and appropriateonly if the ground water could be used for human consumption. Inthis case, the ground water at PZ-03 would not be considered aviable water supply and, therefore, the MCL is not applicable orrelevant and appropriate. The trigger levels for the monitoringwells to be installed adjacent to PZ-03 have been establishedabove the MCL because of the same rationale. However, MCL is thecleanup level established in the event ground water remediationis triggered.
The estimated total present worth cost of the selectedremedy is $1,030,000 which includes the cost of soil coverconstruction and maintenance and ground water monitoring. Theremedy is the most cost-effective of those that were evaluated.
In evaluation of treatment alternatives, it was determinedthat these alternatives are not cost-effective based on therelatively low overall risk of the site to public health and theenvironment. The selected alternative also provides fortreatment in the future if the predetermined chemical actionlevels are exceeded and treatment would be comparable in cost tothe cap and slurry wall.
Based on the cost-effectiveness, the consideration oftreatment to the maximum extent practicable, and satisfaction ofthe remaining nine criteria, the selected remedy provides thebest combination of attributes of all of the remedies availablefor the site.
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The Agency has determined that a five-year review will needto be conducted onsite since contamination will remain abovehealth based criteria.
RESPONSIVENESS SUMMARY
Record of Decision forThe DuPont Impoundment ofThe Todtz Farm Site in
Camanche, Iowa
This Responsiveness Summary presents the responses of theEnvironmental Protection Agency (EPA) to public comments receivedregarding the Proposed Plan and the Remedial Investigation/Feasibility Study (RI/FS) report for the DuPont Impoundment ofthe Todtz Farm Site in Camanche, Iowa. This document addressesthe comments received by EPA during the public comment periodconducted as part of the remedy selection process. The publiccomment period ended on September 10, 1988.
The only comment received from the local community was inregard to replacement of a local resident's drinking water well.A comment letter was also received from the Iowa Department ofNatural Resources (IDNR). All of the remaining comments, whichwere in regard to the Proposed Plan, were submitted on behalf ofDuPont by their consultant, CH2M Hill.
Comment: The commentor wanted clarification as to whether thelocal resident's drinking water well would automically bereplaced as part of the remedial alternative or whetherreplacement of the well would be contingent on exceedance ofchemical specific action levels. The preference is to have thewell replaced as soon as possible.
Response: Although analyses of samples from the resident's wellhas not detected the presence of any compounds which exceed EPAPrimary National Drinking Water Standards (established forprotection of human health), analyses has detected exceedance ofsome of the Secondary Drinking Water Standards (sodium andmanganese) which indicate taste and odor characteristics. Also,the well would be the immediate receptor of any contaminationmigrating from the site.
In response to the comment, the resident's drinking waterwell is to be replaced as part of the remedial action and is nota contingency. Since the remedial action will probably not takeplace until next year, EPA will discuss the possibilty ofreplacing the local resident's well as soon as possible with'DuPont.
Comment from the Iowa Department of Natural Resources (IDNR):
In a letter to EPA dated September 10, 1988, IDNR indicatedthat Alternative 4 was preferable (among the alternativesconsidered in the FS) because it would not allow furthercontaminant migration from the DuPont Impoundment. IDNR furthersaid that it did not support Alternative 2TS, because it wouldallow contaminant concentrations to increase to a level in excessof the MCL at or beyond the site boundary.
At a meeting between EPA and IDNR on October 18, 1988, EPAexplained how the offsite ground water would be protected by themonitoring program, trigger levels and further contingentremedial actions. Since tetrahydrofuran and carbon disulfidetriggers would be set at a fraction of the DWEL, the discussionfocused primarily on the arsenic contamination at PZ-03 whichexceeds the MCL of 50 ug/1. The ground water at PZ-03 would notbe a potential drinking water source and the MCL would not beconsidered applicable, relevant or appropriate. EPA furtherexplained that the trigger levels would provide adequateprotection of human health and the environment and that anappropriate remedial response would be implemented if and whenthe staged trigger levels were met or exceeded. Further, it waspointed out that any agreement with a private party to performthe remedy as contemplated in the ROD would be incorporated in ajudicial Consent Decree as required by SARA.
In a letter to EPA dated October 20, 1988, IDNR concurredthat the selected alternative would be an appropriate remedialresponse for the site.
The remaining comments are in regard to the Proposed Plan.The section, page, and paragraphs referred to below are inreference to those in the Proposed Plan.
Comment: p. 2, Section 1.3, 1st paragraph, last sentence
The City of Camanche water supply wells are not locateddowngradient of the Todtz Farm Landfill Site and are not likelyto be affected by any contaminants leaving the site. Further, itis our understanding that the two water supply wells completed inthe alluvial aquifer are no longer in use due to nitratecontamination from other sources.
Response: According to the Iowa Department of Natural Resources(IDNR), the City of Camanche has three municipal water wellscompleted in the alluvial aquifer and one deep well completed inthe Jordon aquifer. At this time, the City is using the deepwell exclusively because of nitrate problems in the alluvialwells. However, the alluvial wells are maintained for use should
the need arise. Since these wells lie in the generaldowngradient direction of ground water flow, they may possibly beimpacted sometime in the future.
Comment: p. 2, Section 1.3, 3rd paragraph
The North and South Ponds are located onsite, are in directcontact with municipal refuse, and do not support a thrivingaquatic community.
The Mississippi Wildlife Refuge is so far removed from thesite and so unlikely to be affected by the Todtz Farm LandfillSite that its mention as a potential receptor of sitecontaminants is, in our opinion, inappropriate and should bedeleted.
Response: The Proposed Plan does not state that the onsite pondssupport a thriving aquatic community.
The Upper Mississippi Fish and Wildlife Refuge is apotential secondary receptor. Since the HRS scoring systemassigns values to critical habitat within one mile of a Superfundsite, this area meets that criterion. Also, the CERCLA Consent104/122 Order, signed by both EPA and DuPont acknowledges theRefuge as a potential secondary receptor. However, EPA agreesthat the Refuge is far removed from the site and not likely to beaffected.
Comment: p.3, Section 1.4, 1st full sentence
It should be mentioned that the site was listed based ontrace levels of phthalate detected in nearby residential wells,and that the results of the analyses were questionable becausethey were also found in blanks.
Phthalate compounds are ubiquitous in the environment andare a common constituent of municipal landfill leachate.
It should also be mentioned that the FIT investigationconcluded that there was no evidence of any release havingoccurred from the DuPont Impoundment. However, EPA continuedwith additional phases of remedial investigation.
Response: The HRS site scoring for the NPL did include a releaseof phthalates at a nearby resident's drinking water well and inone of the onsite ponds. These samples were collected andanalyzed in August of 1980 according to quality control andquality assurance procedures that were in effect at that time".Apparently, no blanks were analyzed.
During the October 1985 FIT Site Investigation, phthalateswere detected in several surface water locations. However, theresidential well used in the HRS scoring was not resampled due toaccess problems. In June of 1986, a qualification checkconducted of the October 1985 samples indicated that sincephthalates were also detected at certain concentrations in theblanks, the data were suspect.
EPA acknowledges that phthalate compounds are consideredubiquitous in the environment and may be a constituent ofmunicipal landfill leachate. However, they were also reported byDuPont as being part of the feed stock and waste productsassociated with the manufacturing of cellophane and, therefore,are likely to have originated from the DuPont Impoundment.
Since the phthalate data from the FIT Site Investigation wasinconclusive and it had not been resolved whether there was arelease or threat of release, EPA concluded that furtherinvestigation was required. During the REM II investigation,tetrahydrofuran and carbon disulfide were detected in elevatedconcentrations in MW-3, MW-4, and MW-5. These compounds wereknown to be used in DuPont's cellophane manufacturing process.They became the main contaminants of concern.
Comment: p. 3, 2nd full paragraph, last sentence
DuPont did not use lead, arsenic, benzene, or mercury in itsmanufacturing process nor did it report the use of thesecompounds to EPA.
Response: In a response to a CERCLA 104 letter dated August 25,1986, DuPont acknowledged the use of lead acetate and mercury intheir laboratory and maintenance but not necessarily in thecellophane manufacturing process. These constituents were foundin the DuPont Impoundment which was reportedly used only byDuPont.
It is true that in the same letter, DuPont did not reportthe use of arsenic or benzene in the cellophane process to EPA,however, these constituents also were found in the DuPontImpoundment during the RI.
Comment: p.3, Section 1.5
The first two sentences of this paragraph are false. First,the REM II data do not show a release of hazardous substancesfrom the DuPont Impoundment. Samples collected from wells placedin the impoundment berm showed the presence of hazardoussubstances. The berm is part of the impoundment and hence partof the containment structure. The REM II data do not show a
release of hazardous substances beyond the berm of the DuPontImpoundment. The REM II data do not indicate the presence of anyhazardous substances in the municipal landfill either. Secondly,the scope of the REM II investigation was insufficient to makethe blanket statement that "a significant release of hazardoussubstances from the municipal landfill was not observed." TheREM II contractor placed only one monitoring well at theperiphery of the municipal landfill. Examination of the REM IIground water data clearly show that this well (MW-2) isdowngradient of only a small portion of the municipal landfill.Therefore, EPA has no basis in fact for making this statement.
Response: EPA acknowledges that it would be more correct to say,"Based on investigations conducted prior to 1988, it was evidentthat there was a release or threat of release of hazardoussubstances from the DuPont Impoundment." The presence ofhazardous constituents in the berm wells indicates that theconstituents have migrated at least as far as the outsideperiphery of the berm.
EPA considers the second sentence of page 5, Section 1.5 ofthe Proposed Plan to be a correct statement, but acknowledgesadditional work was needed that was conducted in the RI/FS.
Comment: p.3, Section 1.5, last sentence
What contamination is EPA referring to? The REM II data,collected prior to 1988, do not show hazardous substances havingbeen released from the DuPont Impoundment, therefore, it is notclear what contamination EPA is referring to. The REM II datashowed some elevated concentrations of sodium in a residentialwell downgradient of the Todtz Farm Landfill. Is this thecontamination EPA is referring to? If so, there is no conclusiveevidence that the DuPont Impoundment is the source of thiselevated sodium. In fact, the municipal landfill is as likely asource of the elevated sodium as the DuPont Impoundment.
Why is EPA discussing "the remedial alternative selected forthe impoundment" at this point in reference to the REM II workwhen the REM II contractor did not perform a feasibility study.Any discussion of remedial action should be in reference to thefeasibility study performed by DuPont's contractor.
Response: EPA believes that the DuPont Impoundment is apotential source of contamination for the Todtz Farm Landfill.This fact is evidenced based on the levels of contaminantsobserved in MW-3, MW-4 and MW-5. These wells are located on theoutside periphery of the berm and indicate that hazardousconstituents are migrating into and at least as far as the backedge of the berm.
The contamination referred to is tetrahydrofuran and carbondisulfide which are fingerprint constituents of the cellophanemanufacturing process.
EPA acknowledges that discussion of remedial alternativesfor the impoundment is more appropriate in reference to the RI/FSas opposed to the REM II investigation alone. On the basis ofthe RI/FS, EPA believes that the selected remedy will suffice forthe entire Todtz Landfill Site.
Comment: p.4, Section 1.6 1st paragraph
The objective of the RI/FS was to determine the physical andchemical characteristics of the DuPont Impoundment, determinewhether a release of DuPont related constituents had occurredbeyond the confines of the DuPont Impoundment and, if a releasehad occurred, evaluate the extent of the released constituentsand determine if released constituents presented a risk to humanhealth or the environment.
Response: EPA believes that the objective of the RI/FS statedabove is consistent with that stated in the Proposed Plan.
Comment: p. 4, Section 1.7.1, 1st paragraph
The first sentence should be changed to read . . . . ; andenvironmental sampling task to determine whether DuPont relatedconstituents had migrated from the impoundment to surroundingsurface water bodies and ground water.
The impoundment wastes are periodically in contact withground water.
Samples from the Todtz and Bandixen residential wells,completed in bedrock, provide some indication of local bedrockaquifer ground water quality.
Response: EPA acknowledges that the statement as provided aboveis that presented in the DuPont RI/FS report. However, theDuPont-related constituents contain the contaminants of concernso there is no need for revision of the sentence.
EPA stands by the statement as given. Figure 3-12, 3-13,3-14, and 3-15 in the DuPont RI report do not illustrate aninstance when at least a portion of the waste material is not indirect contact with the ground water.
EPA acknowledges that samples from the Todtz and Bandixenresidential wells do provide some indication of local bedrockaquifer ground water quality. However, ground water quality inthe bedrock has not been specifically investigated at this time.
Comment: p.4, Section 1.71, 2nd paragraph
EPA should mention that only one background soil sample wascollected and that this one sample may not reflect truebackground conditions.
Response: EPA acknowledges that only one background soil samplewas collected. However, the information obtained from thissingle sample is more useful than a strict comparison toliterature values in estimating background concentrations.
Comment: p. 4, Section 1.71, 3rd paragraph
The use of the word "significantly" is inappropriate.
PZ-01 should be changed to PZ-02.
The above background concentrations of inorganicconstituents in DP-02, DP-05, and PZ-02 and the Bark well couldvery well be from the municipal landfill.
Response: EPA believes that order of magnitude differences aresignificant.
EPA acknowledges that PZ-01 is incorrectly identified andthat the well referred to should be PZ-02.
The statement does not assert that the inorganicconstituents originated from the DuPont Impoundment. It simplystates that they were also observed in these wells.
Comment: p. 4-5, Section 1.71, last paragraph
DuPont feels that this paragraph is biased against DuPont bynot presenting the complete facts relative to this matter.
EPA fails to mention that tetrahydrofuran was not detectedin the three rounds of sampling the same wells by DuPont'scontractor including the first round, for which EPA splitsamples. EPA also fails to mention that independent review ofEPA's data package showed that the EPA contract laboratory didnot meet the criteria for identification of tetrahydrofuran.Therefore, the EPA data are suspect.
In our opinion there is no conclusive evidence of DuPontrelated constituents being present in monitoring wells DP-02,DP-05, PZ-02 and the Bark residential well.
Again, based on the findings of the DuPont RI, it is notclear exactly what contamination EPA is referring to.
Response: EPA acknowledges that the tetrahydrofuran (THF) foundin the split sample analysis was not confirmed during asubsequent sampling event and that two of the values were belowthe contract detection limit (M-coded) and are, therefore,estimates. EPA also acknowledges that DuPont's laboratoryreviewed the data and questions whether the contract laboratorymet identification criteria. However, EPA Region VII laboratoryre-reviewed the data and believes that the THF was present in thesamples. The commenter also did not mention that the detectionlimit utilized by DuPont's laboratory was higher than that usedby EPA (10 ug/1 versus 5 ug/1) during the sampling event in whichEPA identified the presence of THF in DP-02, DP-05, and PZ-02.
EPA does not refer to contamination of any kind in thisparagraph.
Comment: p. 6, last paragraph, 1st sentence
Dupont cannot agree with this statement. First,, it is notclear to what contamination EPA is referring. Secondly, thefindings of the RI conclude the following:
While there is evidence that ground water degradation hasoccurred downgradient of the DuPont Impoundment, degradationcannot be conclusively tied to the DuPont Impoundmentbecause of the intervening presence of municipal refusebetween the DuPont Impoundment and downgradient samplingpoints. There is also no conclusive evidence that the uppersand and gravel aquifer has been contaminated by DuPont-related constituents beyond the perimeter of the DuPontImpoundment with the exception of arsenic which is presentin low concentrations in piezometer PZ-03.
Potential human environmental exposures resulting fromdirect contact or ingestion of surface water downgradient ofthe impoundment do not exceed criteria used by EPA inevaluating whether human health or the environment areprotected with the exception of arsenic. Concentrations ofarsenic in onsite surface water bodies exceed the AmbientWater Quality Criteria for the Protection of Human Health ata 1 x 10 protection level but do not exceed the MCL.
Exposures to human health or the environment throughingestion or direct contact with ground water from theshallow aquifer at or near the Todtz Farm Landfill perimeterare also below the criteria used by EPA in evaluating whetherhuman health or the environment are protected with theexception of arsenic which exceed the MCL at PZ-03.
None of these statements imply or conclude that the DuPontImpoundment is the source of any "contamination" at the TodtzFarm Site with the possible exception of arsenic in PZ-03.
Response: EPA believes that the DuPont Impoundment is the sourceof the tetrahydrofuran (THF) observed in the EPA split samplesand at least one of the sources of the elevated arsenic level inPZ-03. EPA also believes that the DuPont Impoundment iscontributing to the elevated sodium levels observed in wellsdowngradient of the landfill. The RI/FS does not appear toidentify any contaminants of concern migrating from the TodtzLandfill Site that are not present in significant concentrationsin the DuPont Impoundment. Tetrahydrofuran and carbon disulfidefound at high concentrations in the DuPont Impoundment appear tobe in the process of migrating and remain sources ofcontamination at the Todtz Farm Landfill Site as a whole.
Comment: p.7, Section 2.0, 1st paragraph
The second sentence should be changed to read: "Excavationof the impoundment wastes and disposal at a RCRA landfill ortreatment onsite using incineration."
Response: EPA acknowledges that this statement, as presentedabove, is consistent with statements made in the DuPont RI/FSreport. However, the statement does not acknowledge that othertechnologies were also screened out. The sentence in theProposed Plan should be restated as follows: "Excavation of theimpoundment wastes and disposal at a RCRA landfill or treatmentonsite using inceration, stabilization, or in-situ treatmenttechnologies were eliminated since they were not cost-effectivebased on the relatively low risk to public health and theenvironment and the large capital cost."
Comment: p. 8, 1st paragraph
All references to the DuPont Impoundment in this paragraphshould be changed to the Todtz Farm Landfill.
Response: EPA believes that this comment is correct and wouldconsent to changing references to the Todtz Farm Landfill.However, EPA notes that sodium and arsenic detected in the Bark'swell are in much higher concentrations in the DuPont Impoundment.
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Comment: p.8, 2nd paragraph
This statement is not quite true. If an exceedance of atrigger compound is detected, steps will be taken to verify thisexceedance through statistical analysis and additional sampling.If the exceedance is verified, then DuPont will undertaketreatability studies to determine whether a treatment basedremedial action is appropriate. If the treatment based option isdetermined to be appropriate and is comparable in cost toAlternative 4, the treatment based remedial action will beimplemented.
Response: EPA acknowledges that a statistically based analysiswill be performed to verify if the action levels have beenexceeded. It should also be noted that there is a differencebetween Alternative 2, which is described in the RI/FS report andSection 2.2 of the Proposed Plan, and Alternative 2TS, which isdescribed in Sectiion 2.2A. Alternative 2TS is similar toAlternative 2 except that Alternative 2TS calls for a treatmentstudy and implementation of a treatment remedy if action levelsare exceeded and if treatment is determined to be cost-effectiveat that time.
Comment: p. 10, Table 2-lb
Chromium (Total) should be changed to Chromium (VI).
Response: EPA acknowledges the change.
Comment: p. 13, Section 3.2, 2nd paragraph
Change the word berm to causeway. Confusion may resultbecause the word berm is used consistently in reference to theberm encapsulating the DuPont Impoundment.
Response: EPA acknowledges that the use of the word berm may beconfusing and agrees that causeway is an appropriate description.However, EPA further wants to point out that the berm does notencapsulate the impoundment but surrounds.
Comment: p.14, Section 3.4, 1st paragraph
Short-term effectiveness addresses the effect of analternative during construction and implementation.
Response: EPA agrees that short-term effectiveness does addressthe effect of an alternative during construction andimplementation. However, it also defines the period of timeneeded to achieve protection of human health and the environment
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during implementation of a remedy and until cleanup goals arereached. This definition is consistent with that provided in theProposed Plan.
Comment: p. 15, 2nd paragraph, 2nd sentence
The sentence should be modified to reflect that themunicipal landfill may also be affecting ground water quality.
Response: EPA acknowledges that the municipal landfill may alsobe affecting ground water quality.
Comment: p. 18, Section 4.0, 2nd paragraph
The paragraph should be clarified that deed restrictionswill be placed on the Todtz property and that the DuPontImpoundment will be fenced as part of the remedial action, notthe entire Todtz Farm Landfill.
Response: EPA agrees with the comment. This clarificatiion ismade in Section 4.2.
Comment: p.20, 3rd paragraph
Ground water samples will be analyzed for all of thecompounds listed EXCEPT lead, barium, beryllium, and mercury. Tothe best of our knowledge, DuPont agreed to add arsenic, sodiumand chromium to the list of analytes, but at no time agreed to addlead, barium, beryllium, or mercury. EPA should delete thesecompounds from the list.
Response: EPA acknowledges that DuPont did not agree to analyzefor lead, barium, beryllium or mercury. However, EPA intends toinclude these metals in the list of analytes.
