GDIVI Federal Programs Corporation A Subsidiary of Camp Dresser & McKee Inc. 125 Maiden Lane, 5th Floor New York, New York 10038 Tel: 212 785-9123 Fax:212785-6114 February 15, 1996 Ms. Caroline Kwan U.S. Environmental Protection Agency 290 Broadway New York, NY 10278 PROJECT: DOC. NO. SUBJECT: EPA ARCS Contract 68-W9-0024 Work Assignment 073-2P1D Tutu Well Field Site St. Thomas, U.S. Virgin Islands 7720-073-EP-CJWW Addendum to Final Human Health Risk Assessment Dear Ms. Kwan: Per your request of January 31, 1996, CDM Federal Programs Corporation (COM Federal) has recalculated the risks for exposure to soils at the Tillett Gardens and Art Center Area of the Tutu Wells Site to reflect the current concentrations of volatile organic compounds detected in soil samples collected by EPA in August 1995. A brief addendum and revised risk tables are attached. EPA collected additional samples following development of the Feasibility Study to confirm soil concentrations of polychlorinated biphenyls (PCBs) reported in 1988 samples and to better delineate the area potentially requiring remediation. The new sampling results showed that PCBs are no longer present in soils from this area. Therefore, as the attached risk tables show, the carcinogenic risks from exposure to soils at the Tillett Gardens and Art Center Area now fall within or below EPA's target risk range. The non-carcinogenic hazard index of 6.1 for children, however, still exceeds the target level of 1. This risk was generally unchanged from the original baseline risk assessment since it is attributed to inorganics (manganese), which were not re-analyzed in the August 1995 samples. DM Federal believes the manganese levels in soil in the Tillett Gardens and Art Center Area do not represent a remediation concern for the following reasons: 1) The maximum manganese concentrations fall within the range of concentrations detected in background samples; 2) Current soil concentrations may be lower than the concentrations used in the baseline risk assessment; and *65055* 65055 Federal Programs Corporation C - |Ci ^^~ w -, ° r x\ i /V»^~J , • v/y A 3) The principal adverse health effect of manganese is increased hypertension. Soils are therefore not usually remediated based on a manganese risk alone. It should also be noted that EPA is currently re-evaluating the reference dose (RfD) for manganese. If the proposed new RfD for manganese was used in the calculations, the non- carcinogenic hazard index for children would drop to 3.6. If you have any questions concerning this addendum, please call me at (212) 785-9123. Sincerely, CDM FEDERAL PROGRAMS CORPORATION Sally Odland, P.G. Work Assignment Manager cc: A. Devine, EPA M. Hauptman, EPA R. Goltz, CDM Federal, D. Listemick, CDM Federal J. Naugle, CDM Federal Document Control ADDENDUM /—v TO THE BASELINE HUMAN HEALTH RISK ASSESSMENT TUTU WELLS SITE February 1996 The baseline human health risk assessment for the Tutu Wells Site was completed in 1994. The conclusions of the assessment indicated that residential exposure to surface soils in the Tillett Gardens and Art Center Area showed carcinogenic risks in exceedance of the upper- bound of the target risk range (i.e., greater than l.OE-04) (Table 5-1). These risks were due largely to Aroclor 1242 which had been reported in surface soil samples collected in 1988. The total hazard index for child ingestion and inhalation of surface soil exceeded the target level of 1.0 (HI = 6.1) (Table 5-2). The exceedance was due largely to manganese. Additional surface soil samples were collected from the Tillett Gardens and Art Center Area ^^-•^ in August 1995 to confirm the contaminant concentrations and to better define the area of soil that would be remediated. Grab samples were collected from five locations. In addition, a blind duplicate was collected from one location. Each sample was analyzed for volatile organic compounds (VOCs) and PCBs (Aroclors). No PCBs were detected in any of the samples (Table 1). Three VOCs, including acetone, 2-hexanone, and 4-methyl-2- pentanone, were detected in sample Tutu 6. VOCs were not detected in any other samples collected in 1995. Because the new sampling results represent current site conditions, CDM Federal substituted the VOC and PCB results from the additional samples were substituted for VOC and PCB concentrations used in the original baseline risk calculations. Since inorganics analysis was not conducted on the additional samples, it was assumed that inorganics concentrations were unchanged from the original data. Risks for adult and children residents for the ingestion, dermal contact, and inhalation routes 1 'f'UT 008 O614 of exposure were recalculated (Tables 2 through 4). The maximum concentrations of VOCs were conservatively used in the risk calculations, rather than the 95% upper confidence limit (UCL) concentrations. It should be noted that VOCs were not selected as chemicals of concern (COCs) for the Tillett Gardens and Art Center Area in the original baseline risk assessment. The revised risk calculations indicate that carcinogenic risks at the Tillett Gardens and Art Center area are within the EPA target risk range of 10"4 to 10"6 and approximately two orders of magnitude lower than the original calculated baseline risks of 10"3 . The individual pathway and receptor risks are 8.2E-06 (adult ingestion), 5.5E-07 (adult inhalation), 1.9E-05 (child ingestion), and 6.4E-07 (child inhalation) (Table 5). The 30-year combined risk for adult + child is 2.9E-05. These risks were solely attributed to arsenic. Risks for dermal contact were not calculated as no dermal absorption factors were available for COCs. The hazard index of 6.1 for the child, calculated using additional VOC and PCB data and baseline inorganics data, was generally unchanged, since the baseline hazard index was. attributed to inorganics (Table 6). The additional VOC data had no significant impact on the hazard index. TA1T TUTU WELLS SITE SUMMARY OF CHEMICALS IN SURFACE SOIL TILLETT GARDENS AND ART CENTER CONCENTRATION (ug/kg) CHEMICALS VOCs Acetone 2- Hexanone 4-Methyl-2-Pentanone Pesticides/PCBs Aroclors Frequency of Detection 1/5 1/5 1/5 0/5 Range of Concentrations Minimum Maximum 19 19 7 J 7 J 21 21 Location of Maximum Tutu 6 Tutu 6 Tutu 6 Ranae of Non-detect Concentrations Minimum - Maximum 11 U - 27 U 11 U - 11 U 11 U - 11 U 33 U - 87 U Sample Group: Tutu 1, Tutu 2, Tutu 3 (duplicate of Tutu 2), Tutu 4, Tutu 5, and Tutu 6. 2/6/96 SS-IN-REF "^LS TABLE 2 SURFACE SOIL INGESTI \THWAY ) TUTU WELLS SITE - PRESENT/PUT u ,£ - USE SCENARIO • .* REVISED RISKS TO RESIDENTS IN THE TILLETT GARDENS AND ART CENTER AREA CARCINOGENS - REASONABLE MAXIMUM CASE SURFACE SOIL INGESTION EXPOSURE: Adults Chronic Daily lntake= (mg/kg-day) Chemicals Arsenic Soil X Concentration mg/kg X Soil Concentration 1.00E+01 CARCINOGENS - REASONABLE MAXIMUM Chronic Daily lntake= (mg/kg-day) Chemicals Arsenic Soil X Concentration mg/kg X Soil Concentration 1.00E+01 Ingestion Rate 100 mg/day Ingestion Rate 100 X Conversion X Factor X 1kg X 1 000000 mg Conversion Factor 1.0E-06 Fraction Ingested 1 (unitless) Fraction Ingested 1 X Exposure X Frequency X 350 days/year X Exposure Frequency 350 Exposure X Duration 24 years X Exposure Duration 24 1 Body Weight 1 70kg Body Weight 70 X 1 Averaging Time X 1 25550 days Averaging Chronic Daily Slope Time Intake (GDI) Factor (SF) 25550 4.7E-06 1.75E+00 TOTAL RISK = RISK = (CDrSF) 8.2E-06 8.2E-06 CASE SURFACE SOIL INGESTION EXPOSURE: Children (0 - 6 years) Ingestion Rate 200 mg/day Ingestion Rate 200 X Conversion X Factor X 1 kg X 1 000000 mg Conversion Factor 1 .OE-06 Fraction Ingested 1 (unitless) Fraction Ingested 1 X Exposure X Frequency X 350 days/year X Exposure Frequency 350 Exposure X Duration 6 years X Exposure Duration 6 1 Body Weight 1 15kg Body Weight 15 X 1 Averaging Time X 1 25550 days Averaging Chronic Daily Slope Time Intake (GDI) Factor (SF) 25550 1.1E-05 1.75E+00 TOTAL RISK = 30-YEAR COMBINED RISK (ADULT + CHILD) = RISK = (CDI'SF) 1.9E-05 1.9E-05 2.7E-05 CO Page 1 2/6/96 SSrlN-RF \