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NAS Patuxent River Health Consultation - March 1998


The USEPA Region 3 Remedial Project Manager for NAS Patuxent River requested that ATSDRperform an independent review of recently available data (data sheets dated 2/18/98) from analysisof soil, sediment, and groundwater samples at IRP Site 23, the Defense Property Disposal Office(DPDO) Salvage Yard. This site is located in the northwest corner of the Naval Air Station,adjacent to the Patuxent River and 1000 feet east of the West Patuxent Basin. Arsenicconcentrations were elevated in some of the samples, and ATSDR was asked to assess whetherthese concentrations pose a public health hazard. Sample designations and corresponding arsenicconcentrations are listed in Appendix 1. Appendix 2 contains the analytical data in their entiretyand includes maps of sampling locations.


Arsenic in Soil

Soil samples were taken at Site 23 during 1996 and 1997 in a variety of locations, including areasfrom which previously stored materials had been moved. Of about 40 such samples, 17 containedarsenic at concentrations above the method detection limit. Two of these 17 contained over 100ppm (g/g) arsenic. Sample PX-S23-SS-03-996 contained 102 g/g, and PX-S23-SS-15-597contained 161 g/g. The average concentration for samples positive for arsenic is 20.6 g/g.

Noncancer Risk Assessment

    Assumptions for adults evaluated for incidental ingestion of soil:
      Body weight = 70 kg
      Soil ingestion rate = 100 mg/person-day = 0.100 g/person-day

    Average Daily Dose = (20.6 g/g) (0.100 g/person-day) = 2.06 g of arsenic/person-day

    For comparison, the ATSDR chronic oral MRL (minimum risk level) is 21 g/person-dayfor a 70-kg adult. The chronic oral MRL and EPA chronic oral RfD are identical. Theaverage concentration of arsenic found in soil at Site 23 is one-tenth of these conservativecomparison values. No noncarcinogenic public health hazard is posed by arsenic at theseconcentrations. Use of average values is justified by the nature of expected exposure, thatof workers who would divide their time among the various areas of the DPDO Yard in theperformance of their duties. The analysis is conservative in that all arsenic is assumed tobe in the more toxic inorganic form.

Cancer Risk Assessment

    To evaluate the cancer risk (CR) from incidental soil ingestion:
      CR = Intake x CSF; where CSF denotes Cancer Slope Factor

      Intake =CS x IR x FI x CF x EF x ED
      BW x AT x 365 days/year

      Intake =20.6 x 100 x 1 x 0.000001 x 250 x 30
      70 x 70 x 365

      Intake =8.6 x 10-6 mg/kg-day

      For the arsenic oral CSF of 1.75 (mg/kg-day)-1, CR = 8.6 x 10-6 x 1.75 = 1.5 x 10-5

      CR = 1.5 X 10-5

      This is well within the USEPA range of acceptable risk (10-4 to 10-6) . The levels ofarsenic found in soil pose no public health hazard.

Exposure Parameters and Values Used to Calculate Cancer Risk from Incidental Soil Ingestion

Concentration in sedimentCSAveragemg/kg
Ingestion RateIR100mg/day
Fraction IngestedFI1
Conversion FactorCF.000001kg/mg
Body WeightBW70kg
Exposure FrequencyEF250days/year
Exposure DurationED30years
Averaging Time (Cancer)AT70years

Arsenic in Sediment

Three of seven sediment samples were positive for arsenic and contained the contaminant in arange of 0.61 ppm to 19.2 ppm; the average concentration was 7.0 ppm. This corresponds to one-third the noncarcinogenic risk and one-third the carcinogenic risk calculated for arsenic insoil. Arsenic concentrations in sediment do not pose a public health hazard.

Arsenic in Groundwater

Of 14 groundwater samples three contained measurable arsenic. The range was 12.2 to 66.5ppm. The average was 44.0 ppm. Potable water for NAS Patuxent River is supplied by deepwells tapping confined aquifers. There is no pathway by which persons can be exposed to arsenicin DPDO (Site 23) groundwater. Arsenic found in samples of Site 23 groundwater represents no public health hazard.


Arsenic concentrations detected in soil, sediment, and groundwater of the NAS Patuxent RiverDPDO SalvageYard (IR Site 23) do not pose a public health hazard to on-site workers.

No recommendation

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