STATE OF ARIZONASILVER CREEKSUBDMSION

TUCSON, PIMA COUNTY, ARIZONA

JUNE 3, 2005

u.s. DEPARTMENT OF HEALTH AND HUMAN SERVICESPublic Health Service

Agency for Toxic Substances and Disease RegistryDivision of Health Assessment and Consultation

Atlanta, Georgia 30333

Health Consultation: A Note of Explanation

An ATSDR health consultation is a verbal or written response from ATSDR to a specificrequest for information about health risks related to a specific site, a chemical release, orthe presence of hazardous material. In order to prevent or mitigate exposures, aconsultation may lead to specific actions, such as restricting use of or replacing watersupplies; intensifying environmental sampling; restricting site access; or removing thecontaminated material.

hI addition, consultations may recommend additional public health actions, such asconducting health surveillance activities to evaluate exposure or trends in adverse healthoutcomes; conducting biological indicators of exposure studies to assess exposure; andproviding health education for health care providers and community members. Thisconcludes the health consultation process for this site, unless additional information isobtained by ATSDRwhich, in the Agency's opinion, indicates a need to revise or appendthe conclusions previously issued.

You May Contact A TSDR TOLL FREE at1-888-42ATSDR

orVisit our Home Page at: http://www.atsdr.cdc.gov

HEALTH CONSULTATION

ST ATE OF ARIZONASILVER CREEK SUBDIVISION

TUCSON, PllvIA COUNTY, ARIZONA

Prepared by:

u.s. Department of Health and Human ServicesAgency for Toxic Substances and Disease RegistryDivision of Health Assessment and Consultation

Purpose

The Arizona Department of Health Services (ADHS) completed this health consultationat the request of the Arizona Department of Environmental Quality (ADEQ). Thisconsult evaluates whether soil vapors from volatile organic compounds in the subsurfacenear the Silver Creek Subdivision in Tucson, Arizona are present at levels that may causeadverse health effects.

Background

The Silver Creek subdivision is located approximately 4 miles northwest of downtownTucson. Approximately 700 residents live in the 288 home subdivision. A gasolinerelease from a ruptured high-pressure pipeline occurred in the Silvercroft Wash near theSilver Creek subdivision on July 20, 2003. Over 50,000 gallons of gasoline have beenrecovered from the subsurface. Five homes under construction in the area weredemolished following the pipeline rupture because of gasoline contamination. Thehomes in this portion of the subdivision have not been rebuilt.

Levine Fricke (LFR) on behalf of pipeline owner Kinder Morgan Energy Partners(KMEP) perfomled a soil vapor survey as part of the Silvercroft Wash Fuel Release siteassessment and remediation project. In addition to total petroleum hydrocarbons (TPH)and their related compounds (benzene, toluene, ethylbenzene, and xylenes [BTEX],methyl-t-butyl ether [MTBED, LFR sampling detected non-fuel related chlorinatedsolvents, such as tetrachloroethene (PCE) and tricWoroethene (TCE) in soil vapor andgroundwater samples beneath the study area. As the study focused only on fuel-relatedvolatile organic compounds, it did not fully evaluate the extent of the non-fuel relatedvolatile organic compounds. The Arizona Department of Environmental Qualityconducted additional soil vapor sampling to obtain analytical soil vapor data toindependently verify and expand upon soil vapor data collected by Levine Fricke.

Exposure Pathways

Five elements are considered in the evaluation of exposure pathways:

.....

A source of contaminationTransport through an environmental mediumA point of exposureExposure routeA receptor population.

The Arizona Department of Health Services categorizes an exposure pathway either as"completed" or as a "potential" exposure pathway if the pathway cannot be eliminated.

In completed exposure pathways, all five elements exist, and exposure to a contaminanthas occurred in the past, is presently occurring, or will occur in-the future.

In potential exposure pathways, at least one of the five elements is missing but couldexist. Potential pathways indicate that exposure to a contaminant could have occurred in

1

the past, or may occur in the future. A potential exposure pathway may be eliminated ifone of the five elements is missing and is unlikely ever to be present.

Vapor intrusion and inhalation of those vapors is a potentially complete exposurepathway. Soil vapor intrusion refers to the migration of volatile chemicals from thesubsurface into overlying buildings. Volatile chemicals in contaminated soils, buriedwastes and/or contaminated groundwater can emit vapors that may migrate throughsubsurface soils and into indoor air spaces of overlying buildings similar to the seepageof radon gas into homes. Residents are likely to be exposed to the soil vapors that migrateinto homes in the Silver Creek neighborhood resulting in a completed exposure pathway.

ADEQ Flux Chamber Sampling -Silver Creek Subdivision

The Arizona Department of Environmental Quality conducted additional soil vaporsampling to evaluate the potential public health impact to the residents of the SilverCreek subdivision from vapors detected previously during investigation of SilvercroftWash Fuel Release.

The Arizona Department of Environmental Quality collected soil vapor samples byplacing a flux chamber over open soil and on concrete. The data set available for thishealth consultation is limited to the results of environmental. samples collected at 60 fluxchambers samples collected at a fixed point in time. One of the flux chambers was set updirectly adjacent to the pipeline where no homes are present and was excluded from thedatabase. In addition, there were 2 background samples that were collected but excludedfrom the database because they are not specific to the neighborhood. Data from a total of57 flux chambers were used in this health consultation.

An extensive list of target contaminants, including volatile organic compounds notassociated with gasoline was evaluated. The results of the evaluation found elevatedconcentrations of compounds that are consistent with materials that have been previouslydetected at and near known sources in the area as well as compounds that may beassociated with the gasoline pipeline release.

The results from the flux chambers samples were used to estimate indoor airconcentrations using standard box models (SECOR 2005). The models provide aconservative estimate of predicted indoor air concentrations. This formula takes intoaccount the mobility of the contaminants and use factors designed to result in the highest(and thus most protective) concentration estimates of contaminants in the air. Thefollowing expressions display the model equations and assumptions used to calculatepredicted indoor air concentration at both the open soil and concrete slab samplinglocations:

2

Open Soil Flux Chamber Expression:

Cair = Fj x SA x CL x CF

AERxVWhere:

Cair

FiSACLCFAERV

- hldoor air concentration in micrograms per cubic meter (~g/m3)Site specific hlfiltration flux, in micrograms per feet a minute (~g/ft-min)Surface Area Perimeter, 144 square meters (m2)Crack level, estimated to be 0.01 (unitless) (ASTM 1997)Conversion factor 60 minutes per hour;Air exchange rate, assumed at 0.25 hour-1 (USEPA 2003)Average volume of residential structure, assumed 351 cubic meters (m3)estimated for a home measuring 12 meters (m) by 12 meters (m) and a ceilingheight of2.44 meters (m)

Concrete Slab Flux Chamber Expression:

Cair= Fi x P x CFl~CF2.AERxV

Where:

Cair

FjPCF1CF2AERV

- Indoor air concentration in micrograms per cubic meter (J.1g/m3)Site specific Infiltration flux, in micrograms per feet a minute (J.1g/ft-min)Perimeter, 48 meters (m)Conversion factor 1, 0.3 feet per minute (ft/m)Conversion factor 2, 60 minutes per "hourAir exchange rate, assumed at 0.25 hour-1 (USEP A 2003)Average volume of residential structure, assumed 351 cubic meters (m3) for a

home measuring 12 meters (m) by 12 meters (m) and a ceiling height of 2.44meters (m).

Modeling results for each flux chamber are available in the document entitled Soil VaporSampling Report, Silver Creek Subdivision. (SECOR 2005)

Risk Analysis

Contaminants of Concern (CaCs) were evaluated for systemic toxicity andcarcinogenicity. Systemic toxicity refers to the potential for a compound to cause eithersymptomatic or asymptomatic health problems in humans. Carcinogenicity refers to thepotential for compounds to cause cancer in humans.

Systemic ToxicityThe Arizona Department of Health Services selected contaminants of concern bycomparing the average predicted indoor air concentrations to the Agency for ToxicSubstances and Disease Registry (ATSDR) Comparison Values (CVs) and the UnitedStates Environmental Protection Agency (USEP A) Reference Concentrations (RfC).

The flux chamber samples were used to predict indoor air concentrations by applyingconservative assumptions that provide an upper-bound estimate of actual indoor airconcentrations. These modeled results represent conditions observed on the days samples

3

were collected and do not predict potential variations in contaminant concentrations thatmay occur over time.

The Arizona Department of Health Services selected the contaminants of concern byaveraging the predicted indoor air concentrations and comparing the resultingconcentrations to screening levels. Compounds were selected as a contaminant ofconcern if the predicted average concentration exceeded a screening level.

The average indoor air concentrations, rather than the maximum indoor airconcentrations, were chosen for comparison with the screening levels to optimize thelimited dataset available from this single sampling event, to provide a broader statisticalbase to make comparisons, and to provide a better benchmark for drawing conclusionsfor the entire neighborhood.

The primary screening levels that were used to select contaIninants of concern are calledAir Comparison Values (CVs). These screening levels are concentrations in air that areunlikely to pose a health threat. Where the air comparison values were not available for aspecific compound, the modeled results were compared to the United StatesEnvironmental Protection Agency's Reference Concentration (RfC) or preliminaryremediation goals (pRGs). The air reference concentrations and the preliminaryremediation goals are applicable to both indoor and outdoor air and are based on aresidential exposure scenario using standard exposure factors. These screening levelsmay also be used as a health protective indoor air target for determining soil gasscreening levels for the evaluation of the subsurface vapor intrusion pathway (ATSDR2005).

Arizona Ambient Air Quality Guidelines were us,ed as screening levels when nocomparison values, reference concentrations or preliminary remediation goals wereavailable. These guidelines are developed by the Arizona Department of Health Services,and are protective of human health, including children, over a lifetime. Chemicalconcentrations in air that exceed any of these guidelines may not necessarily represent ahealth risk (AAAQG 1999).

Predicted indoor air concentrations that exceed a screening criteria do not necessarilypose a health threat, but require further evaluation.

Table 1. Predicted Indoor Air Concentrations Compared to Screening Values

AveragedOc'"":""Rre I..~~~d" "fn~oQi~jr~

"Concentration

meter(l.J;9!m~)"c"

Healthc'Eff~ct

,Screening, ", ,Value"(fi§Jfu3) ,

FrequencyDetect~d

..(n=57')

AirConcentration

~v~rageAboveScr~~ning

VariJe?

Chemica] ofC ?oncern.Compound

0.510.060.060.470.11

0

I

13000~

i 22I

1;j~O2 37.r

na5 -

No

No

NoNo

No

No

Acetone

AcrylonitrileAllyl chlorideBenzeneBenzyl chloride

No

No

NoNo

No

No

17

632

80Bromodichloromethane

4

AveragePredicted: Indoor Air

Concentration.(micrograms

per cubicmeter (!-1g/m3)

I Health Effect!

ScreeningI ValueI

(~g/m3)

AirConcentration

Average AboveScreeningValue?

FreguencyDetected

(n=57)

Chemical ofConcern?

Compound

35024181905627

40

0.160.03

00.060.240.02

00.080.030.040.12

0

No

No

No

NoNo

No

No

No

No

No

No

No

NoNo

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

NoNo

NoNo

1./~

na50002

~-1951

na1000Q21~

~~

No

No

No

NoNo

No

No

No

No

No

No

No

NoNo

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

NoNo

No

No

No

No

No

No

No

No

No

No

NoNo

5056474705

00

221100

1105

5

14

120

471785710203

0.210

0.250.180.140.150.080.030.020.060.062.700.080.08

00

0.030

0.030.160.110.04

0.070.120.830.060.1392

0.120.189.060.14

na21

nana

-92-~

6001

~na

6001

-~-.:?:Q~

4.13-~

nanana-21

na202

10002

3001

310003

na35002

0.863

403

15003:~~r~nana

300021104

5

I AverageI PredictedI Indoor Air

Concentration

(microgramsper cubic

meter (~g'm3)

HealthEffect

ScreeningValue

3(/-lg/m )

Frequency.' .'Detected

(n=57)

AirConcentration...

Average AboveScreening

Value?

Chemical ofConcern?

Compound

6

6182177267106501303

362214

05

5

11.310.100.460.100.070.080.100.150.080.861.480.040.030.030.060.110.190.110.21

00.620.19

-~

424

3.51

.:!J.§~2401

2581

~-~

401

~3204

Na7001

na562002~~

6.236.23~-

na4351

~

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

NoNo

No

No

No

No

No

No

No

No

No

Methyl ten butyl ether

Methylstyrene

NapthaleneOctane

Propionitrile

Styrene1,1,1,2 Tetrachloroethane

1,1 ,2,2 Tetrachloroethane

T etrachloroetheneToluene

1,2,4 Trichlorobenzene

1,1,2 Trichloroethane1,1,1 Trichloroethane

TrichloroetheneTrichlorofluoromethane

1,2,3 I rlCnloropropane

_J!2,4 Trimethylbenzene

~

Trimethylbenzene.vinyl acetate

Vinyl chloride

XyleneXylene

~0-

I ATSDR EMEG2 EP A Reference Concentration3 EP A Region 9 Preliminary Remediation Goal4 Arizona Ambient Air Quality Value

5No screening value available (na)6 Simple asphyxiant value is the Lower Explosive Limit

As shown in Table 1, no chemicals of concern were selected for further analysis,indicating that for all of the compounds, predicted indoor air concentrations in theneighborhood do not pose a systemic health hazard.

CarcinogenicityCarcinogepic risk is calculated as the incremental probability of an individual developingcancer over a lifetime (70 years), due to exposure to a carcinogenic compound. This isalso referred to as incremental or excess lifetime cancer risk (ELCR) and represents theincreased risk of developing cancer abQve the background rate, which is estimated to beabout 33%.

While the criteria for selecting the contaminants of concern for cancer are the same aswith the systemic health effects, predicted indoor air concentrations are compared to adifferent set of air comparison values. The guidelines used for this selection are also fromthe Agency for Toxic Substances and Disease Regeistry's air comparison values, but are

6

values used to screen contaminants that are suspected of causing cancer. These guidelinesare known as cancer risk evaluation guides (CREGs).

If there are no cancer risk evaluation guides for contaminants, then the U.S.Environmental Protection Agency's Cancer Preliminary Remediation Goal is used todetennine if more evaluation is warranted. The contaminants of concern were selected bycomparing the average predicted indoor air concentrations to the air comparison values.Contaminants of concern were selected for further analysis if the average predictedindoor air concentration exceeded its screening level. Table 2 displays a list of allsuspected carcinogens observed in the sampling and their screening value.

Table 2. Predicted Indoor Air Concentrations Compared to Cancer Screening Values

AyeragePredictedIndoor Air,Concentration!

I I 3),Hgm 1

!c'" I

AirConcentration

AverageAbove

ScreeningValue?

CancerScreenina

Value

(""91m3)

rrequ~~cyDetected'

(11=511

Chemicalof IConcern?Compound

7

6

32

0

3

0

1-9

5:

6

0

4

7

5

22

1

11

5

7

18

2

6

7

5

1

0

0.060.060.47

00.16

00.020.080.03

00.120.150.022.700.080.030.030.830.460.100.150.030.040.03

0

0.01'31

0.110.112M1Q'Q31-ow2]20]41b:oar

0.0034~Q]'4;l-31

--ow~

0.31~

-~~ow-~~o:o1r~

Yes

NoYes

No

No

No

No

No

No

No

Yes

No

No

No

No

No

No

Yes

Yes

No

Yes

No

No

Yes

No

Yes

NoYes

No

No

No

No

No

No

No

Yes

No

No

No

No

No

No

Yes

Yes

No

Yes

No

No

Yes

NoA TSDR Cancer Risk Evaluation Guideline

2 USEr A Region 9 Preliminary Remediation Goal

There were 7 contaminants with an average predicted indoor air concentration thatexceeded the screening levels. Table 3 summarizes these 7 contaminants.

7

Table 3. Suspected carcinogenic contaminants detected above the screening levels

lA veragePredictedI

i rh~OorA!r'I Cpncentration

(pglm3) .,

CancerScreening

Value(~g/m3)

FrequencyDetected

(n=57)

Compound

AcrylonitrileBenzeneDibromoethaneHexachlorobutadieneNapthaleneTetrachloroethane

T richloroethene

7

32

4718

6

0.060.470.120.830.460.150.03

0:01'Qm10.0034

~~"'0m2-Q"i)2T

0:0172

YesYes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

1..2

~

'ATSDR Cancer Risk Evaluation Guideline2 USEP A Region 9 Prelirnmary Remediation Goal

Using the list of contaminants of concern, estimates of estimated lifetime cancer riskwere developed by evaluating potential exposure pathways, estimating exposureconcentrations and intake, and combining exposure estimates with toxicologyinformation (USEPA 1991).

;::U!

The dose-response relationship is considered to be linear under the low dose conditionsusually encountered in environmental exposures. Under this assumption, the USEnvironmental Protection Agency slope factor (SF) for a compound is a constant, andrisk is directly related to intake. Therefore, the linear low-dose cancer risk is:

Risk = Cancer Inhalation Unit Risk (l/J.lglm3) x Concentration (J.lglm3)

where:

-RiskUnit RiskConcentration

a unitless probability of an individual developing cancer;Dose averaged over 70 years (1/J.l.glm3) (USEPA 2005); andPredicted indoor air concentration (J.l.glm3).

Table 4 summarizes estimated lifetime cancer risk using average predicted indoor airconcentrations. Cancer inhalation unit risk is the upper-bound excess lifetime cancer riskestimated to result from continuous exposure to a compound at a concentration 1 ~g/m3in air. The unit risk values are developed by the US Environmental Protection Agencyafter careful and detailed analyses of data regarding the potential cancer potency of a

compound.

8

Table 4. Estimated Excess Cancer Risk

otal Excess Lifetime Cancer Risk 0.00007Micrograms per cubic meter of air

2 Source: (USEPA 2005)3 Average Air Concentration X Unit Risk

The estimated upper-bound excess cancer risk estimate of 0.00007 or seven-in-one-hundred-thousand represents the increased risk of developing cancer. This estimate wascalculated by multiplying average predicted contaminant concentrations by the Unit Risk.

There is general (although not unanimous) consensus anlong the scientific and regulatorycommunities on what level of estimated excess cancer risk is acceptable. An increasedlifetime cancer risk of one in one million or less is generally considered negligible.According to the United States Environmental Protection Agency National ContingencyPlan and subsequent guidance, an estimate of excess cancer risk between one in a millionto less and one in ten thousand is within a range of acceptable risk (USEP A 1990, 1991).Risks greater than one in ten thousand do not necessarily pose a significant cancer risk,but require additional in-depth analysis in order to draw conclusions about potentialcancer risk.

The upper-bound estimated risk from indoor infiltration of contaminants is within therange of acceptable risk and poses no apparent public health hazard to neighborhoodresidents.

LimitationsThere are many sources of uncertainty in every risk analysis. The objective of this healthconsultation is to determine whether soil vapors from compounds in the subsurface nearthe Silver Creek Subdivision in Tucson, Arizona are present at levels that may causeadverse health effects. This health consultation is a screening level analysis of healthrisks, meaning that the report uses a conservative (or upper-bound) analysis.

Several conservative assumptions were made in this analysis. Infiltration intoneighborhood homes was assumed to be a complete exposure pathway even though thispathway may not actually be complete. Compounds that were detected in flux chambersat levels less than the reporting limits (called J Flagged Data -meaning that they werequalitatively but not quantitatively accurately identified) were still included in thedatabase to ensure that no compounds were left out of the analysis. The screening levelsthat were used to select contaminants of concern have a large margin of safety. The

9

exposure assumptions used to develop the screening levels assume continuous 30-yearexposure averaged over a 70-year lifetime. Finally, the US Environmental ProtectionAgency unit risk values used to calculate cancer risk are upper-bound estimates thatalmost certainly overestimate risk. \

The average air concentrations used in this health consultation are estimates based onflux chamber air sampling data collected at the site. The results were used to estimateindoor air concentrations. The air concentrations used in this health consultation'represent environmental conditions at one point in time. Ideally, for where vaporintrusion is a concern, pennanent sub-surface monitoring points for sample collectionwould be used to evaluate the long-tenn behavior of soil vapors. In addition, it may benecessary to collect soil gas samples at different time intervals to compensate for theeffects of weather events, such as recent rainfall or barometric fluctuations (DTSC 2004).

Child Health Issues

The Agency for Toxic Substances and Disease Registry recognizes that the uniquevulnerabilities of infants and children demand special emphasis in communities facedwith contaminants in air. Children's developing body systems can sustain permanentdamage if toxic exposures occur during critical growth stages. Children breathe a greatervolume of air relative to body weight, resulting in higher burden of pollutants.Furthermore, children, even those without pre-existing illness or chronic conditions, aresusceptible to air pollution because their lungs are still developing, and they often engagein vigorous outdoor activities, making them more sensitive to pollution than healthyadults. All calculations and health analyses in this report take into consideration theunique vulnerability of children. -'

Conclusion

.

The predicted indoor air concentrations in Silver Creek neighborhood suggest thatthe subsurface contaminants pose no apparent public health hazard.

Recommendations

The Arizona Department of Health Services has no recommendations at this time.

10

References

AAAQG 1999. Arizona Annual Air Quality Guidelines. Arizona Department of HealthServices. May, 1999.

ASTM 1997. American Society for Testing and Materials. Standard Guide for Risk-basedCorrective Action Applied at Petroleum Release Sites. E 1739-95. 1997

ATSDR 1995. Agency for Toxic Substances and Disease Registry, ToxFAQs forHexachlorobutadiene. September 1995.

ATSDR 2005. Agency for Toxic Substances and Disease Registry, Air Comparison ValuesJanuary 2005

DTSC. 2004. Vapor Intrusion Guidance Document. State of California. DTSC/CALEPA. December 15, 20-4.

NIST/SEMATECH e-Handbook of Statistical Methods,ht!Q:/ /www.itl.nist.gov/div898/handbook/. March 3, 2005.

USEP A 1990. USEP A National Oil and Hazardous Substances Pollution ContingencyPlan (NCP), 40 CFR Part 300, July 16, 1982 (47 FR 31180) and comprehensive revisionMarch 8, 1990 (55 FR 8666) http://www.epa.gov/superfund/sites/nDl/f900830.htm

USEPA 1991. Risk Assessment Guidance for Superfund (RAGS), SupplementalGuidance Standard Default Exposure Factors (OSWER Directive, 9285.6-03) datedMarch 25, 1991.

USEP A 1992. Technology Transfer Network Air Toxics Web site. Hexachlorobutadeine.httQ://www.eDa.gov/ttnatw01/hlthef/hexa-but.html. March 3, 2005.

USEP A 2003. User Guide for Johnson and Ettinger Model.

USEPA 2005. Integrated Risk Infoffilation System. Online service at:htiD:/ /www .epa.gov/iris/

SECOR 2005. Soil Vapor Sampling Report. Silver Creek Subdivision, Silverbell LandfillWater Quality Assurance. February 2005.

Preparers of Report

Arizona Department of Health Services, Office of Environmental Health

Kristina Schaller, Environmental Health Scientist

Don Herrington, Principle Investigator

Will Humble, Bureau Chief

11

Certification

This Silver Creek Subdivision Public Health Consultation was prepared by the ArizonaDepartment of Health Services under a cooperative agreement with the federal Agencyfor Toxic Substances and Disease Registry (ATSDR). It was completed in accordancewith approved methodologies and procedures existing at the time the health consultationwas initiated. Editorial review was completed by the Cooperative Agreement partner.

;:JJ /J/l~ ~ ~ss1f~ {tPTechnical Project Officer, CAT, SPAB, DHAC