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California Regional Water Quality Control Board Central Valley Region Alan C.Lloyd,Ph.D.h.D. Robert Schneider,Chair Arnoldrn Agency Secretary Sacramento Main Office Schwaraenegger 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 Governor Phone(916)464-3291 •FAX(916)464-4645 �� http://www.waterboards.ca.gov/centralvalley G(u1^LLLIIIl CE§V 29 August 2005 r �� S' - 7 2005 ENVIROW ENT Mr. Michael Desso PEQ1T1SERVHEASTH Nestl6 USA, Inc. 800 North Brand Boulevard Glendale, California 91203 FINAL INDOOR AIR VAPOR INTRUSIONRISK EVALUATION, FORMER NESTLE USA, INC. FACILITY, RIPON, SAN JOA QUIN CO UNTY Central Valley Regional Water Quality Control Board staff(Regional Board staff) has reviewed the Final Indoor Air Vapor Intrusion Risk Evaluation (Final Risk Evaluation) received on 23 July 2005. Regional Board staff comments on the Final Risk Evaluation are provided below. 1. Regional Board staff concurs with the recommendation to collect vapor samples from buildings near the Industrial Avenue source area. The specific buildings that Nestle is proposing to sample are not specifically identified, but the Final Risk Evaluation states that they will be within 100 feet of one of six sample locations (OB-3-13', OB-5-8', OB-5-23', VE-11, VE-12, or M-6B). These six sample locations show a potential risk of greater than 1 x 10-6 when evaluated using the EPA's guidance on assessing potential for vapor intrusion into indoor air. Regional Board staff agrees with sampling these buildings, but additional buildings beyond 100 feet from one of these sample locations should be included in the initial phase of sampling. The final confirmation soil vapor data that was collected in 2001 is very limited and the extent of the soil vapor contamination was not defined because it was attributed to off-gassing from the groundwater plume. Based on a cursory review of the known hotspots in the Industrial Avenue area, the buildings immediately south and more than 100 feet from M-6B hotspot could be at risk because there are no monitoring wells between M-6B and these buildings and it is difficult to accurately predict how plume concentrations decline with distance from this groundwater hotspot. Regional Board staff request that Nestle add these buildings to the proposed sampling program and carefully review the available groundwater/soil vapor data to determine if other buildings beyond 100 feet from one of the six sample locations warrants inclusion in the initial phase of sampling. 2. Regional Board staff does not concur with the conclusion that the pathway is incomplete for the Stockton Avenue property. The available soil vapor data is not sufficient to draw any conclusions on residual TCE contamination that may still be present. When the soil vapor extraction (SVE) system was permanently shut down in 1994, only vapor extraction well VE-8 was sampled to assess the effectiveness of SVE. While the sample results for VE-8 suggest this well removed VOCs in the California Environmental Protection Agency C i Recrcied Paper