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I December 22, 1998 Harding Lawson Associates 16 4034405 Margaret Lagorio, Supervising REHS San Joaquin County Public Health Services Environmental Health Division ' Page 7 Analytical Results- Hydropunch Groundwater Sample Analytical results from the Hydropunch groundwater sample are listed in Table 1 TPHd and TPHmo were detected at concentrations of 1,800 and 2,700 micrograms per liter (ug/L), respectively As discussed further below, these data are suspect, and appear to be the result of downhole contamination within the I borehole Benzene, ethylbenzene, and total xylenes were not detected above the normal respective method reporting limits Toluene was detected at 57 ug/L, just above the method reporting limit of 50 ug/L ' Results of Insitu Bioremediation Feasibility Studies The results of the plate counts are summaiized in Table 2 The results indicate that the existing microbial population in the site soils includes a subpopulation of microorganism capable of degrading petroleum hydrocarbons and this population is within the range acceptable for biological degradation of TPH Results of Assessment of Risk to Human Health and Safety A RBCA process was employed to evaluate iisk to human health and safety in accordance with ASTM E 1739-95 (ASTM, 1995) The first step includes identification of the COCs and the RPESs at the Site Because of the paucity the light aromatic hydrocarbons (BTEX), the COCs associated with heavy fuel oils (# 6 fuel) are generally restricted to the PAHs (Table X1 3 in ASTM, 1995) Here both BTEX and PAHs are considered as COCs for the Site A qualitative risk analysis of the Site, in accordance with ASTM E 1739-95, reveals that the RPESs identified at the Site include the following ' 1 Ingestion/dermal contact/inhalation. of CDCs from surface soils in the courtyard by staff of Newark Sierra ' 2 Inhalation of COCs from subsurface soils in courtyard by staff of Newark Sierra Development of a site conceptual model in accoidance with the ASTM, h 1739-95 Exposure Scenario Evaluation Flowchart (Figure 2 0) indicates that no primary sources (product storage USTs or drums) ' remain on the site Secondary sources include impacted surface and subsurface soils In RPES #1 no transport mechanism but direct contact occurs for ingestion/dermal contact, and for inhalation the transport mechanism is wind erosion and atmospheric dispersion In RPES #2 the transport mechanism is volatilization and atmospheric dispersion The exposure pathways are ingestion, dermal contact, and inhalation of vapors As an industrial facility, characterization of the receptor would be commercial/industrial Calculation of RBSLs for the COCl and RPES identified foi the Site is performed using the chemical, physical, and toxicological properties of the hydrocarbons, the relevant fate and transport models, the media physical properties, and default assumptions utilized in ASTM-E 1739-95 (ASTM, 1995) The assumptions and the parameters utilized in these equations have been reviewed for appropriateness to the RPESs identified for the Site and the toxicological properties have been checked for currency The RBSLs calculated for the Site and the maximum concentrations of the CDCs detected on Site are shown in the table below 1 �