ARCHIVED REPORTS XR0013118 - Laserfiche WebLink

Home Browse Search

Site Closure Request Pombo Property June 14,2005 �.� portions of the property has been delineated, but recommended further investigation of the affected soils and groundwater north of GMX-32;the revised health risk assessment was approved by the DTSC in July 2002. The updated risk assessment and a January 2,2002 Geomatrix response to regulatory comments are included as Appendix C. August 2001. Petroleum-impacted soil was removed from the western portion of the property to 15 feet during construction of a 50,000 square foot storm water retention basin. The material was reused on the adjacent parcel as fill material beneath an asphalt parking lot. January 2005. SAIC conducted soil and groundwater investigations November 5,2003 and February 25, 2004 to further assess off-site soil and groundwater impacts along the WSID easement and to delineate the extent of petroleum-affected soil and groundwater in the residential housing development north(down gradient)of the Pombo Property. Eleven soil borings were advanced to depths ranging from 12 to 16 feet. TPHc was only detected in one soil sample located on the WSID easement(5.6 mg/kg, SB-4 at 5 feet bgs). Toluene and total xylenes were reported as trace concentrations in one sample located in the WSID easement(SB-3 at 8 feet bgs). Grab groundwater samples were collected from all 11 borings;dissolved TPHd was detected in all samples except SB-4 and SB-9,in concentrations ranging from 88 to 370 pg/L (SB-1). Grab groundwater samples re-analyzed for TPHd following silica-gel cleanup reported concentrations in SB-1 through SB-3, SB-5,and SB-6 at concentrations ranging from 140 to 210µg/L (SB-6). BTEX compounds and PAHs were non-detected in all groundwater samples with the exception of a single phenanthrene concentration of 0.4 µg/l,(SB-1). The SAIC investigation concluded that petroleum-affected groundwater north(down gradient)of the Pombo Property has been delineated by borings SB-8 and SB-9,completing the analytical data set for the Pombo Property. The January 2005 report is included in Appendix D. January 2005. In April 2004 SAIC conducted a 2,000 foot-radius well survey of Department of Water Resources(DWR)files,which was included in the 2005 Soil and Groundwater Investigation Report. The `.. well survey identified nine water supply wells within the search area. The single well located down gradient of the site was identified as an industrial supply well in the vicinity of boring SB-9, approximately 1,000 feet northeast of the site. No specific location or well construction information was available;boring SB-9 reported no detectable concentrations for all constituents, including TPHd. All other identified wells were located cross gradient or up gradient to the Pombo Property. Results of the well survey are included in the report presented as Appendix D. March 2005. In a March 8,2005 letter(Appendix A)reviewing the 2005 SAIC investigation report,the RWQCB concurred that lateral and vertical extent of soil impacted by petroleum hydrocarbons has been adequately characterized and that the groundwater plume has been adequately delineated off site. The RWQCB concluded that the plume appears to be limited in extent,stable,and meets the criteria for closure in accordance with the draft RWQCB"Low Risk Criteria,"Appendix B-No Further Action Requests(1996,updated September 2001). 3. HUMAN HEALTH AND ECOLOGICAL RISK SCREENING EVALUATION Geomatrix performed a revised human health screening risk evaluation(HHSE)for the Pombo Property based on the supplemental analytical data generated by the Geomatrix investigations conducted in January and December 2000. The HHSE assessed the potential exposure to residual petroleum constituents on the Pombo Property. The Geomatrix evaluation was based on the methodology presented in the HHSE section of the Preliminary Endangerment Assessment Guidance Manual (PEA; Cal-EPA, 1994). The PEA evaluation consists of a compilation of methods,models, and assumptions commonly used by California and United States Environmental Protection Agencies(Cal-EPA and US EPA)to 9 quantify human health risks and hazards at a site. The PEA evaluation is intended to provide conservative ! estimates of the theoretical lifetime excess cancer risk and non-cancer hazard index based on reasonable maximum exposure in a residential setting,even when the present land use is commercial. 3 e