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LW No Further Action Request 640 N.Sart Joaquin Street,Stockton,CA October 9,2002 Page 4 +r Condor conducted a Tier 2 risk evaluation using the spreadsheet-based computer program RBCA Tool Kit for Chemical Releases, Version 1.4, developed by Groundwater Services, Inc. The software was developed to meet the requirements of the ASTM PS-104 Standard Provisional Guide for Risk-Based t.+ Corrective Action. The soil and groundwater sample analytical results for the June I0, 2002 and July 26, 2002 fieldwork were used for site-specific values in the analysis. The exposure pathways considered in the analysis were volatilization to outdoor air inhalation and indoor air inhalation from impacted soil and groundwater. The receptor was considered to be a residential building because the residential risk factors are more conservative than the commercial site risk factors. The assumptions used in the evaluation are the following: • The majority of petroleum hydrocarbons remaining in the subsurface are composed of long carbon chain components and the short carbon chain components have naturally degraded and are no longer present. The predominance of motor oil range petroleum hydrocarbons relative to kerosene range petroleum hydrocarbons supports this assumption. x • The petroleum hydrocarbons remaining in the subsurface are located under an asphalt covered L area and not under a building, as shown in Figure 4 and Figure 6, Appendix A. The risk evaluation software assumes the contamination is beneath the building when performin4 the risk evaluation. This will result in a conservative risk evaluation because the building is not located directly over the source in the subsurface. It is also assumed the asphalt paving serves as a seal to inhibit volatilization of petroleum hydrocarbons in the subsurface to outdoor air. Iw. Neither ASTM E 1739-95 Standard Guide for Risk-Based Corrective Action Applied`at Petroleum Release Sites nor RBCA Tool Kit for Chemical Releases identifies diesel or motor oil as constituents of concern. The risk evaluation was conducted using TPH-Aliphatic >Cl2-C16, TPH-Aliphatic>C16--C21, b TPH-Aromatic >C12-C16, and TPH-Aromatic >C]6-C21 as constituents of concern as surrogates for diesel. TPH-Aliphatic >C21-C34 and TPH-Aromatic >C21-C35 were used as constituents of concern as surrogates for motor oil in the evaluation. PNA's were not used as constituents of concern in the risk evaluation because laboratory analytical results indicated that PNAs were not detected at or above the laboratory reported detection limits in the soil sample analyzed for these compounds. The evaluation results indicate that there is no Baseline Carcinogenic Risk due to contamination of soil and groundwater at the site. The evaluation results also indicate that the Baseline Toxic Effects limit of 1.0 is not exceeded by either the Hazard Quotient or the Hazard Index. A copy of the results of the risk evaluation using RSCA Tool Kit for Chemical Releases is located in Appendix D. L. 4.0 CONTAMINATION REMAINING IN SOIL AND GROUNDWATER The estimated lateral extent of petroleum hydrocarbons remaining in the soil is shown in Figure 4, Appendix A. The estimated vertical extent of hydrocarbons remaining in the soil is shown in the cross- sections in Figures 5 and 6. The mass of hydrocarbons remaining in the soil was calculated based on the estimated lateral and vertical extent of hydrocarbons remaining in the site subsurface as shown in Figures V 4 through 6. L.. L A 1 CONDOR 1�.