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Groundwater lnvestigat�and Groundwater Extraction Work Plan Boyett Petroleum,419 S.Main Street,Manteca May 16,2006 Page 2 V On February 2, 2001, WHF advanced two cone penetration test (CPT) borings at the site. CPT-1 and CPT-2 were completed to depths of 76 and 76.4 feet bgs, respectively. Both borings were terminated due to refusal. Beds of clay were encountered in CPT-1 at depths of 20 to 24.1 feet and 50.2 to 57.6 feet bgs. In CPT-2, beds of clay were encountered at depths of 23.8 to 26.4 feet, 49.7 to 56.4 feet, and 62.7 to 66.9 feet bgs. Y�r On April 25, 2001, WHF completed a deep monitoring well, MW-9, to a depth of 50.5 feet bgs. The screened interval for the well was installed at approximately 40.5 to 50.5 feet bgs. The depth to �+ groundwater was reported to be approximately 17 feet bgs. On October 20 through 23, 2003, Condor conducted a groundwater investigation using direct push boring methods. Condor supervised the completion of four deep CPT boring pairs (CPT-3 through CPT-6) and five shallow hydropunch borings (HP-1 through HP-5). Borings CPT-3, CPT-4, and CPT-6 were advanced to depths of approximately 125 feet bgs; boring CPT-5 encountered refusal and was terminated " at a depth of approximately 66 feet bgs. At each deep boring pair location, the first boring was advanced to provide a near-continuous log of the subsurface soil profile. The second boring at each pair location was advanced near the first boring to collect discrete depth groundwater samples from saturated horizons identified in geologic logs from the first borings. One soil sample was collected from each of borings y CPT-3 through CPT-5 from immediately above a clay horizon defined in each boring's lithologic profile. Five hydropunch borings were advanced to collect groundwater grab samples to investigate the lateral extent of contamination in shallow groundwater cross-and down-gradient of the plume. r On October 29, 2003, Condor supervised the destruction of monitoring wells MW-1, MW-4, and MW-5. On October 30, 2003, three four-inch diameter groundwater monitoring wells (MW-4R, MW-10, and r MW-11)and one four-inch diameter extraction well(EW-1)were installed. From November 18 through 21, 2003, Condor conducted a 72-hour constant rate pump test at well MW- 11. Pump test activities were described in Condor's Additional Groundwater Investigation, Monitor Well Destruction and Installation, and Interim Remediation Pump Test Report, dated January 30, 2004. Condor prepared the No Further Action Request (NFAR) dated October 7, 2005. The NFAR was w submitted to the SJCEHD and the CRWQCB for consideration. In a letter dated April 14, 2006, Jeffrey Wong of the SJCEHD described the results of a discussion with the CRWQCB regarding the NFAR. Mr. Wong stated the SJCEHD and the CRWQCB agreed that the site is not quite ready for closure. Mr.Wong bw requested a work plan to complete the lateral definition of the dissolved MTBE plume toward the northwest, to provide a fate-and-transport model showing the path of travel of the plume before it reaches background levels, and to discuss and evaluate the risk of soil vapor intrusion into all nearby structures. He also recommended conducting limited batch groundwater extraction at monitoring wells MW-11 and EW-1 since the MTBE concentrations at these wells are still above the MCL. Mr. Wong requested the work plan be submitted to the SJCEHD by June 1, 2006. Detailed site background information is in r., Appendix B. 3.0 GROUNDWATER INVESTIGATION PROCEDURES This section includes a description of the site preparation and groundwater sampling procedures. br V CONDOR V