,00 Sr UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION VIII 999 18th STREET - SUITE 500 DENVER, COLORADO 80202-2466
April 27, 2004 Ref: 8EPR-PS
MEMO.RANDUM Subject: Rocky Mountain Arsenal, Off-Post Area Vapor Intrusion Assessment.
From: Helen Dawson, Ph.D., Hydrogeologist, Superfund Program Support Dawson.Helen(a-)el2a.gov; (303) 312-7841 Bob Benson, Ph.D., Toxicologist

...... (303) 312 Denson.Bob@e a. ov -7070
To: Laura Williams, Team Leader Rocky Mountain Arsenal Federal Facility Site

SUMMARY OFFINDINGS Concentrations ofvolatile organic compounds (VOCs) present in groundwater north ofRocky Mountain Arsenal (RMA)were evaluated using the Johnson and Ettinger Model (GW-SCREEN) as implemented by EPA (US EPA, March 14, 2003). Estimated indoor air concentrations and potential cancer and non-cancer risks were calculated for theoretical inhalation exposure to groundwater vapors in aresidential setting. An initial evaluation yielded estimated cancer risk values slightly above the 1. 0 x 10'5 screening level for four chemicals (carbon tetrachloride, chloroform, tetrachloroethene, and trichloroethene). Non-cancer risks were below the acceptable screening level of 1.0 for all chemicals. When site-specific information about the subsurface is incorporated into the model, estimated potential cancer risks are reduced to 3.5 x 10 6or less for all chemicals in the off-post area. As the refined site-specific estimated cancer and non-cancer risks are below their respective screening levels, no further evaluation ofthe vapor intrusion pathway is warranted at this time. Consequently, there is no need to require vapor intrusion controls in buildings overlying the contaminant plumes in the off-site area. Potential vapor intrusion-related risks were calculated for each chemical detected above its reporting limit in each off-post well. The site-specific information input to the model included groundwater concentrations, soil type, and depth to groundwater. The most recent groundwater concentrations for analytes detected in each ofthe off-post wells were used to predict potential future indoor air concentrations and the associated human health risks due to vapor intrusion. These predictions assume constant groundwater concentrations over 30 years. This approach is conservative as concentrations are expected to continue to decrease due to the ongoing

_00033830 11452-2

### groundwater treatment required forthe RMA site. Three different soil types were used inthis evaluation-loaMY sand, sandy loam and silt loarn-to evaluate the range ofsoil types observed inthe vadose zone in the off-post area. The coarsest grained soil provides the most conservative predicted indoor air concentrations and associated inhalation risks. The average depth to groundwater in each well was used as input to the model. The future residential scenarios assumed either basement or slab-on-grade foundation structures, depending onthe depth to groundwater. The toxicological factorsused inthe analysis arethose listed in Appendix D of EPA's Draft Vapor Intrusion Guidance WS EPA, November 2002), except as noted in the text below. Because Inhalation UnitRisk Factors are not yetpublished in IRIS for tetrachloroethene and trichloroethenc, arange ofvalues was evaluated. The remainder ofthe'madel input parameters used were the default values described inAppendix GofEPA's Draft Vapor Intrusion Guidance (US EPA, November 2003). The assumptions usedinthis assessment are conservative and therefore provide conservative estimates ofthe potential indoor air concentrations and the associated cancer and non-cancer risks due to vapor intrusion.

DATA EVALUATIED 

### The following datawere reviewed for this assessment: 1. A map showing the location ofoff-post monitoring wells andthe interpreted extent of contaminant plumes (US Army, December 1,2003. Estimated Areas Exceeding Containment System Remediation Goals for Water Year 2002). 2. Groundwater concentrations fromthe 2002 and 2003 rounds ofsampling in the off-post area.Table I presents the most recent analytical data for thewells in which VOCs and other compounds ofconcern for vapor intrusion were detected above reporting limits. 3. Historical concentrations ofVOCs inthe off-post wells in Sections 11, 12, 13, and 14. 4. Bore logs ofoff-post wells in which VOCs and other compounds ofconcern for vapor intrusion were detected above reporting limits. 5. Current and historical waterlevel data for off-post wells in Sections 11, 12, 13, and 14.

ASSUMPTIONS AND METHODOLOGY 

### The model applied in this assessment ofthe vapor intrusion pathway is the Johnson and Ettinger Model (GWSCREEN) as implemented byEPA (US EPA, March 14, 2003), which incorporates default parameters as described in Appendix G ofEPA's Draft Guidance for Evaluating the Vapor Intrusionto Indoor Air Pathway from Groundwater and Soil (November, 2002). The site-specific information used as input tothe model included groundwater concentrations, soil type, and depthto groundwater (Tables I and 2).

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### The most recent groundwater concentrations for analytes detected in each ofthe off-postwells (Table 1)were used to predict indoor air concentrations and the associated human health risks due to vaporintrUsion. Historical trends indicate that VOC concentrations in the off-post wells are decreasing. Therefore, the mostrecent groundwater concentrations canbe used as a conservative estimate ofpotential future concentrations. The predicted indoor airconcentrations and associated risks assume constant groundwater concentrations over 30 years. In fact, concentrations are expected to continueto decrease dueto theongoing groundwater treatment required for the RMA site. Forcompounds that werebelow detection inthe off-postwells, onehalfthe detection limit was used asthe groundwater concentration (Table 2). The vadose zone lithology observed in the off-post wells includes sands, silty sands, sandy silt, sandy clay, and siltyclay. To evaluate thisrange oflithologies and because the model is very sensitive to soil type,three different soil types were evaluated with the model: loamy sand, sandy loam and silt loani.The model's default values forthe soil specific properties - bulk density, moisture content, and porosity - were used foreach soiltype. The values used for Qr,ýjj inthis evaluation were those calculated by the model foreach soil type. The resulting values are lower than the default value of5L/min recommended byEPA's vapor intrusion guidance. This was done in order to compensate forthe conservative assumption that groundwater concentrations remain at the sarne level for 30years. The impact ofsoil type can be seenin the range of predicted indoor air concentrations and associated inhalationrisks shown in Table 1.The coarsest grained soil-loarny sand-provides the most conservative predicted indoor air concentrations and associated inhalation risks. Historical water levels suggest the depths to groundwater for mostwells fluctuate aboutamean level with no significant increasing or decreasing trendover the 10+ years onrecord. Consequently, average depth to groundwater in each well was used as inputto the model. Vapor intrusion-related risks were calculated using the available data for each well, because depthto groundwater as well as groundwater concentrations varied from well to well. Depending on the depth to groundwater, either abasement or slab-on-grade foundation was assumed, as EPA's vapor intrusion guidance recommends a minimumvadose zone thickness of5feetbetween the groundwater andthe base ofthe foundation formodel applications. Thus, foroff-post wells with depths to groundwater greater than 11 feet, the future residential scenario assumed the residences would be constructed withbasements. For wells with depths to groundwater less than 11 feet, slab ongrade foundations were assumed. The remainder ofthemodel input parameters used inthis evaluation were the defaultvalues described in Appendix G ofEPA's Draft Vapor Intrusion Guidance (US EPA, November 2002). These default parameters incorporate conservative assumptions forbuilding- and soil-related parameters. Thetoxicological factors used in this analysis are listed inTable 3. Except as noted below the toxicological factors used in the analysis were those in Table D-I ofEPA's Draft Vapor Intrusion Guidance (US EPA, November 2002). An RfC for benzene of3E-02 Mg/M3 

### was addedto the IRIS file inApril 2002 and isused in this analysis. A new IRIS file dated February 2003

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### established the RX forall xylene isomers at IE-0Img/141'. The Inhalation Unit Risk on IRIS for chloroform is currently under review and likely willbe replaced by an RfC that will protect for both cancer and non-cancer endpoints. The final value that likelywill be established for the RfC for chloroform and that will be used to calculate theHazard Index will result inmuchhigher screening level concentrations than those calculated using the value shown in Table 3.However, since the review has notbeen completed, this evaluation calculated the risks using the existing Inhalation Unit Risk on IRIS. Fortetrachloroethene there is no Inhalation UnitRisk on IRIS. The "old ORD" Inhalation Unit Risk fortetrachloroethene was 5.8 E-07 (gg/M3),l 

### . The Superfund Technical Support Center as ofJune 2003 isrecommending fortetrachloroethene anInhalation Unit Risk of5.9 E-06 (gg/M3),l 

### .Both values are used to compute tetrachloroethene risks inthis analysis. Likewise, there is no Inhalation UnitRisk on IRIS for trichloroethene and, consequently, this analysis usesboth the "old ORD" Inhalation UnitRisk of 1.7E-06 (gg/rn3)-l 

### and the newprovisional value of 1.1 E-04 (gg/M3)-' 

### recommended inEPA's draft 2001 reassessment. The calculated tetrachloroethene andtrichloroethene risks shown in Tables I and 2 are based on the most conservative cancer risk factors; the impact ofusing the lower cancer risk factors is described inthe table notes and below in the Results section. The cancer risk andhazard index were calculated usingthe residential'scenario described in Appendix D ofEPA's draftvapor intrusion guidance (US EPA 2002). The residential scenario assumes that an individual willbe in aresidence 24 hours/day, 350 days/year, for30 years. The averaging time forcarcinogens is24 hours/day, 365 days/year, for 70 years; the averaging time for non-carcinogens is 24 hours/day, 365 days/year, for30 years.

RiEsuLTs 

### The calculated indoor air concentrations and potential cancer andnon-cancer risks are summarized in Table I forthe off-post wells inwhich compounds ofconcern for vapor intrusion were detected above reporting limits. This table shows that, when site-specific information is incorporated into the model, the maximum estimated potential cancer risk for any individual detected chemical in any individual off-post well is 3.5 x 10-6 

### for trichloroethene in well 37391 assuming loamy sand forthe vadose zone, 1.3 x 10-6 

### assuming sandy loam, and 6.7 x 10-7 

### assuming silt loam. Ifcumulative risks are calculated for each well, the total estimated maximum potential inhalation risk for any individual well is 6.7 x 10-6 

### assuming loamy sand, 2.5 x 10-6 assuming sandy loam, and 1.3 x 10-6 

### assuming silt loam. Thus, for any individual well the estimated site-specific cancer risksfall below the 1.0 X jo-5 

### screening level. Non-cancer risks are below ahazard index of 1.0 for all chemicals and all wells. As stated above, the estimated risks fortetracholorethene and trichloroethene risks were calculated using the most conservative Inhalation Unit Riskvalues. Ifinstead the less conservative Inhalation Unit Risk values are used, the estimated risks forthese compounds decrease by approximately an order ofmagnitude. In that case, the maximum risk corresponding to any individual chemical in a well is 3.1 x 10-6 

### (for chloroform inwell 37095 assuming loamy sand forthe vadose zone). Excluding chloroform, the maximum risk corresponding to any

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### individual cheynical in awell is2.3 x 10'6 (for carbon tetrachloride inwell 37094 assuming loamy sand for the vadose zone). Table 2 shows the indoor air concentrations and potential inhalation risks associated withnondetected compounds, assuming their actual concentrations are represented by alevel one-half theirrespective reporting limits. The maximum contribution to cancer risk ineach well from analytes with concentrations belowtheir reporting limits is 5.5 x 10,7 

### or less assuming loamy sand, 1.9 X 10-7 

### or less assuming sandy loam, and 9.8 x 10-8 

### or less assuming silt loam.

CONCLUSIONS 

### These results ofthis assessment indicate that no further evaluation ofthe vapor intrusion pathway is warranted at this time and there is no need to implement vapor intrusion controls inbuildings overlying the contaminant plumes inthe off-site area.

REFERENCES 

### US EPA, "Draft Guidance for Evaluating the Vapor Intrusion toIndoor Air Pathwayfrom Groundwater and Soils," November, 2002. US EPA, "User's Guide for Evaluating Subsurface Vapor Intrusion Into Buildings," March 14, 2003.

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### Table 1 Vapor Pathway Analysis Off-Post Wells with Analytes Detected Above Reporting Limits

Well and Chemical Name Model I put Mod Output Mode Output Mode Output Most Recent Avg. Cale. Cale. Cale. Ground Depth Indoor Indoor Indoor Water to Air Air Air Sample Conc. Water Foundation Soil Cone. Cale. Cale. Soil Cone. Cale. Cale. Soil Cone. Cale. Cale. Well ID Symbol Chemical Name Date (uv/L) (ft b2s) Type IType fttm.3) Risk In Type (u&Lm3 Risk III Type .(upJm3) Risk HI 1 37039 JCCLA carbon tetrachloride 8/12/2003 0.42 20.8 Basement I LS 5.88E-02 3.62E-071 NA SL 2.11"2 1,3011-07 NA SIL 1. 11E-02 6.82E-08 NA 37039 CHCU chloroform 8/12/2003 0.624 20.8 Basement I-S 1.26E-02 1.19E-071 N SL 4.64E-03 4.39FA8 NA SIL 2,27E-03 2.14E-08 - NA 37040 DLDRN dieldrin 7/11/2002 0.122 23.8 Basement IS 1.39E-06 2.63E-0917.64E-06 SL 7.57E-07 1.4311-09 4.1 SE-06 SIL 4.4213-07 8.3611-10 2,4211-06 37065 12DCLE 1,2-dichloroethane 8/13/2003 3.86 6.8 Slab IS 3.0513-02 3.26E-07 NA SL 1.2513-02 1.34E,07 NA SIL 6.1411-03 6.5611-08 NA 37065 ITCLEE tetrachloroethylene 8/13/2003 5.541 6.8 Slab LS 15.21E-01 1.2613-06 NA SL 1.8311-01 4AM-07 NA SIL 1.0913-01 2.65E-07 NA 37065 TRCLE trichloroethylene 8/13/2003" 0.958 6.8 Slab LS 5.92E-02 2,68E-06 1.4213,031 SL 2.11E-02 9.53"7 5.0513-04 SIL 1.23E-02 5.56E-07 2.9511-04 37081 DI-DRN dieldrin 7111/2002 0.267 -4.2 (5)_ Slab LS 8.66E-06.1.64E-08 4.75E-05 SL 4-32E-06 8.16E-09 2.36E-05 SIT, 2.3413-06 4.43E-09 1.28E-05
37083 12DCLE I2-dichloroethane 7/15/2002 1.73 4.7(5) Slab IS 1.4013-02 1.50E-07 NA SL- 5.71E-03 6. 1013,08 NA SIL 2.79E-03 2.98E-08 NA 37083 TCLEE tetrachloroeLhylene 7/15/2002 4.54 .7 5 Slab IS 4.38E-01 1.0613,06 NA SL 1.52E-01 3.68E-07 NA . SIL 9.09E-02 2.20E-07 NA 37083 TRCLE trichlorocthylene 7/15/2002 0.764 _L_U_ - - - 7.69E-07 4.08E SIL 9.9412,03 4.49E-07 2-38E-04 7J5 IS 4,84E-02 2.1913-06 1.1611-03 SL 37094 CCLA carbon tetrachloride 7/22/2003 2.64 19.3 Basement LS 3.74E-01 2-31E-06 NA SL 1.33"l 8.22E-07 -NA SIL 6."E-02 4.3113-07 NA 37094 CHCU chloroform 7/2212003 1.83 19.3 Basement LS 3.7313-02 3.53E-07 NA SL 1.37E-02 1.2913-07 NA - SIL 6.68E-03 6.31E-08 NA
37095 12DCLE 1.2-dichloroethane 7/22/2003 0.22 19.3 Basement LS 1. 1613-03 1.24&08 NA SL 4.5211-04 4.83E-09 NA SIL 2.07E-04 2.21E-09 NA -37095 CHCL3 chloro 712212003 16.0 19.3 Basement LS 3.2611-01 3.08E-06 NA SL 1.20E-01 1.13E-06 NA SIL 5.84E-02 5.5213-07 NA 37095 DBCP d Lhý ý 7/22/2003 0.257 19.3 Basement IS 3-14E-04 8.8511-11 1.50E-03 SL 1.5213-04 4.29E.11 .7.30" SIL 6.86E-05 1.93&11 3.2911-04 IS 8.12E-01 1.97E-06 NA SL 2.92"1 7. E-07 NA SIL 1,53E-01 3. 37095 TCLEE tetrachloroeLbyLene 7/2212003 11.4 19.3 Basement -- - 72F-07 ___ý!A 37095 TRCLE trichloroethviene 7/22/2003 0.449 19.3 Basement LS -.2,06 9,30E-07 4.93]3-041ýSl, 7.45E",03 3-3711-07 1.79"4 SIL 3.8413-03 1,7311-07 9.20E-05
LS T 1.

37110 CffC--13 chloroform Slab 9.46E-03 8.94E-08 NA S. 1 35522IR-03 3-3313-087 NA

Notes: The mostrecent value foreach analyte foreach wellislisted unless ahigherreporting limitwasused in2003. Ifaverage depth togroundwater isless than 5feet,5feetwas usedas inputtothe model. Basements am assumed toextend 200cmbelowground surface; slabfoundations areassumed toextend 15 cmbelowground surface. The TRCLE riskvalues shownabove am calculated using aURFof 1. 1 E-04 (mg/m3)-l. For aURF of1.713-6 (mgtm3)-I, thecalculated risks area factor of 1.55E-02 lower. 'Me TCLEEriskvalues shown above atecalculated using aURFof5.913-6 (mg1m3)-l. Fora URFof5.8E-7 (m&/m3)-l, the calculated risksare a factor of9.83E-02 lower.

### Table I (Cont'd) Vapor Pathway Analysis Off-Post Wells with Analytes Detected Above Reporting Limits

Well and Chemical Name Model I put I Mode 0utput Mod Output Mod Output Most Recent Avg. Cale. Cale. Cale. Ground Depth Indoor Indoor Indoor Water to Air Air Air Sample Cone. Water Foundation Soil Cone. Cale. Cale. Soil Cone. Cale. Cale. Soil Cone. Cale. Cale. Well ID symbol Chemical Name Date (uPJL) I (ft has) Type Type (uglm3) Risk HI Type (uZtm3) Risk III Type I(ug/m3) Risk HI

37339 CHCU chloroform 8/26/2003 1.28 15,9 Basement LS 2.68E-02 2.53E.07 NA SL 9.70E-03 9.17E-08 NA SIL 4,73E-03 4.47E-08 NA I . Iý 37368 12DCLE 1,2-dichloroetharie 7/15/2002 0.301 25.4 Basement LS 11.5113-03 1.6211-08 NA SL 6.03E-04 6.44E-09 NA SIL 2.77E-04 2.96E-09 NA 37369 CHCL3 chloroform 7/15/2002 15.4 25.4 Basement LS 3.OOE-0I 2.84E-06 NA SL 1.13E-01 1.06E-06 NA SIL 5.5 1 E-02 5.2 1 E-07 NA 37368 DBCP dibromochloropropane 7/15/N02 0.364 25.4 Basement LS 3.9 1 E-04 I.IOE-10 1.88E-03 SL 1.9813-04 5.58E-11 9.48E-04 STI, 9.07E-05 2.56E-11 4.35E-04 37368 TCLEE tetrachloroeklene 7/15/2002 15.5 25.4 Basement LS 1.05E+00 2.54E-06 NA SL 3,86E-01 9.36E-07 NA I SIL 10413-01, 4.94E-07 NA ,1]7 37368 ITRCLE trichloroelftlene 7/15/2002 0.661 25.4 Basement LS 2.87E-0211.30E-06 6.88E-04 SL 1.07E-02 4.82E-07 2.56E-04 SIL 5,5113-03 2.4913-07 1.3213-04
37374 CHCU chloroform 6/24/1999 1.47 11.3 Basement LS 3.1913-02 3.02E-07 NA SL 11.1313-02 1.07E-07 NA_ SIL 15.51E-03 5.21E-08 NA I --- 37389 CHCU chloroform 7/15/2002 0.283 6.6 Slab LS 8.32E-03 7.86E-08 NA SL 13.05E-03_ 188E-08 NA SIL 1.66E-03 1.57E-08 _NA 37389 TCLEE tetrachloroethylene 7/1512002 5.64 6.6 Slab- LS 5.31 E-01 1.2913-06 NA SL 1.8611-01 4.52E-07 NA SIL 1.12E-01 2.70E-07 NA
37391 ICHCL3 _ýh_lorofbrm 7/10/2002 0.6 27.5 Basement LS 1.15E-02 Iý09&07. NA ST.- 4 35E-03 IIE-08 NA SIL 2.1313-03 2.02E-08 _NA 37391 ITCLEE teftachlomethylene 7/10/2002 3.83 27.5 Basement LS 2.54"1 6.15E-07 NA' SL 9.46E-02 2,2913-07 NA SIL 4.9913-02 1.21E-07 NA 37391 TRCLE triqN2ýý 7/10/2002 1.79 27.5 Basement LS 7.65E-02 3.46E-06 1,8313-03 SL 2.87E-02 1.30E-06 6.88E-04 SIL 1.48E-02 6.70E 7 3.55E-04

37396 12DCLE 1,2-dichloroethane .235 6.2 slab LS 7F-03 TO-OF,08 _NA SL 7.68E-04 8,20E-09 NA SIL 3,75E-04 4.0113-09 NA 37396 TCLEE tetrachloroethvlene 8/12/2003 0.394 6.2 Slab LS 3.73E-02 9.0513,08 NA SL 1-3013-02 3.1613-08 NA SIL 7.82E-03 1.90"ll NA

37408 CHCU chloroform 7/22/2003 1.04 _Y22_,6 Ba ment LS 2.07E-02 1.95E-07 NA SL 7.68E-03 7.26E-08 NA SIL 3.7613-03 3.55E-08 NA 7/2 1,44E-07 NA SL 2.16E-02 5.2413-08 NA SIL 1.1413-02 2.7613-08 NA 37408 TCLEE tetrachloroethylene 2/2003 0.857 22.6 -Basement Is 5.92E-02 - 37409 CHCU .13E-06 ýSL 4.41E 4,1713-07 NA SIL 2 1513-02 ýL0413.07 NA chloroform 7/22/2003 5.93 20.8 Basomont LS 1.20ýEljl I NA

-tam 3 some SL NA Y iE - L __17 37409 TCLEE chloroeth lone 17/22/2003 12 20.8 Basement LS :8.:43E-01 2.04E-06 NA SL 3.05E-01 7,40E.07 A L89E 8 2E semot LS S -07 9.3313-05 .u a a 37409 TRUE trichloroethylene 7/271200, ,E0.1458 20.8 I Basement LS 2.07F-07 9.36F-07 4.9713-04 SL 7.55E-03 3.41 E-07 I.SIE-041 1.76E

Notes: Themost recent value for each analyte foreach well is listedunless a higher reporting limitwas used in 2003. Ifaverage depth to groundwater is less than5 feet, 5 feetwas used as input tothe model. Basements are assumed to extend 200cm below ground surface; slab %undations areassumed to extend 15 cm below ground surfkce. TheTRCLE risk values shown above are calculated using aURF of1.IE-04 (mg/m3)-l. For aURF of1.7E-6 (mgtm3)-1,the calculated risks are a factor of 1 .5513-02 lower. The TCLEE risk values shown above arecalculated using a URF of5.9E-6 (mgtrn3)-l. Fora URF of5.8E-7 (mg/m3)-I, thecalculated risks are afactor of9.83E-02 lower.

7 Pff"tedonRwycled PaperTable 2 Vapor Pathway Analysis Analyte Reporting Limits

ModelOutput Model Output Modd Output Well and Chemical Name (based on 1/2RP (based on 112RPU (based o 112RPL) Most Recent Cale. Cale. Cale. Ground Indoor Indoor Indoor Water 1/2 Air Air Air Cale. Calc. Sample RPL RPL Soil Cone. Cale. Calc. Soil Cone. Cale. Cale. SoH Conc. Symbol lChemicalName Date (uZ/L) I (ug/L) Type (ugJm3) I Risk- III Type (uR/m3) I Risk HI Type (ux/T& Risk HI 12DCLE 1,2-dichlomethane 2003-08-12 0.30 0.15 LS 9.47E-04 9.05E-09 NA SL 3.20E-04 3.41 E-09 NA SIL 1.45E-04 1.5513-09 NA CCU carbontetrachloride 2003-09-13 0.38 0.19 LS 19013-02 1.7913,07 NA SL 9.9511-03 &OF-08 NA SIL 5.20E.03 3.21E-08_ NA CHCL3 chloroform 2ý0_3-08-13 _03 -I 30.25 LS 5.44E-03 5.14E-08 SL 1-9313-03 1.83E-08 NA siL -04 9.8713-09 NA 0.18 LS 3.78E-03 NA 1.04 _SL -1.38E-03 _NA -3.77 SIL NA 1.97E-05 C12DCE cis-1,2-dichloroeklene 2003ý08-13 6-37- 0.19 E-04 "5 SIL 6.82E-04 00 LS 1.20E-04 3.3913-11 5.75F-04 SL 5.4113-05 1.5313-11 2.5913-04 SIL 2.3613-05 0.1 L dibromochloropropnL 2003ý07-22 0.15 0.08 DBCP - SIL 6.66F-12 1.13E-04 DLDRN rin - 02 0.01 LS 2,19E-07 4.14E-10 1.2013-06 9.09E-09 1.72E-10 419RE-07 SIL 4.26E-( -07 TCLEE itetrachloroothylene 2003-08-12 0.20 LS 7.7012-03 1 ý87&081 NA SL 2.6613-03 6.45E-09 NA T12DCE Itrans-1,2-dichloroeftlene 2003-08-13 0.31 0.16 LS 1.07E-04 2.76E-03 513.05

n 01 ILIILSIL TRCLE itrichlaroethylene 20-1 0.13 LS 6.42E-03 12,9013-0-71 1eAIP-nA I Note. All calculations assumed basement foundations that extend 200 cm below ground surface anddepth towaterequal to IIfeet. TheTRCLE risk value shown above iscalculated using aURF of 1. 1 E-04 (mg1m3)-l. For aURFof 1.713-6 (mg1m3)-l, the calculatedrisk isafactor of 1.5513-02 lower. TheTCLEE risk value shownabove iscalculated using a URFof5.913-6 (mgtm3)-l. Fora URF of5.8E-7 (mg/m3)-I, the calculatedrisk isa factor of9.83E-02 lower.

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### Table 3 Toxicological Factors
Unit Risk

Factor Reference URF) Conc. Chen-deal Symbol (Ag/m)-' (mg/M) 1,2-DichloToethane 12DCLE 2.6E-05 0-013+00 1,3-Dicblorobcnzene 13DCLB O.OE+00 LIE-01 Aldrin ALDRN 4.913-03 LIE-04 Benzene C6116 7.813-06 3.OE-02 Carbon tetrachloride CCL4 1.513-05 0.013+00 Chlordane CLDAN LOE-04 7.OE-04 Chlorobenzene CLC6HS 0.013+00 6.oE-02 Chloroform CHCL3 2.313-05 0.013+00 cis-1,2-Dicliloroethylene 12DCE O.OE+00 3.5E-02 Dicldrin DLDRN 4.6E-03 I.gE-04 Ethylbenzene ETC6H5 LIE-06 IOE+00 Hexachlorocyclopentadiene CL6CP O.OE+00 2.OE-04 Methylenc chloride CH2CL2 4.713-07 3.013+00 o-Xylene XYLEN 0.013+00 1.013-01 p-Xylene XYLEN 0.013+00 1.013-01 Tetrachloroethene TCLEE 5.913-06 O.OE+00 Tetrachloroethene TCLEE 5.8E-07 0.013+00 Toluene MEC6115 O.OE+00 4.OE-01 trans- 1,2-Dichloroethylene 12DCE 0.013+00 7.OE-02 Trichloroethene TRCLE 1.713-06 4.OE-02 Trichloroethene MCLE 1.113,04 4.0-02