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Groundwater Investigation Report Country Club Drain System Project • City of Stockton Municipal Utilities Department October pg2003 e 2 ' Avenue along the east side of 1-5 its elevation drops into and below the groundwater table The storm drain line also passes between three known sites of groundwater contamination The three sites are ' The Shell gas station at 2575 Country Club Blvd The Exxon/USA gas station at 2705 Country Club Blvd The 7-11 gas station at 2725 Country Club Blvd ' Following the discovery of groundwater contamination along the storm drain, the storm drain replacement contractor (Kenko Contractor, Inc) retained Kleinfelder, Inc , (Meinfelder) to conduct soil ' and groundwater investigations near the intersection of Country Club Blvd and Plymouth Road, along Country Club Blvd between Franklin and Carlton Avenues, near the intersection of Country Club Blvd and Mission Road, and near the intersection of Country Club Blvd and Pershing Avenue Klcinfelder advanced CPT and Geoprobe borings at these locations and collected soil and groundwater samples ' There were no volatile organic compounds (VOCs) detected in the soil or samples collected in the area southeast of the Shell Oil Station (2575 Country Club Blvd) The samples collected by Kleinfelder were not collected from locations adjacent to the storm drain, and therefore provide a southeast boundary for MTBE, TBA, and tertiary-amyl methyl ether (TAME) impacted groundwater The storm drain along Country Club Blvd is located southwest of the Shell Oil site MTBE and TBA were also detected in samples collected from the other locations sampled during the Kleinfelder investigation 21 SMELL OIL SITE The Shell Oil site is located at 2575 Country Club Blvd , the northeast comer of Country Club Blvd and Plymouth Road (Figure 2, Appendix A) On December 7, 1994, San Joaquin County Environmental ' Health Department (SJCEHD) was notified that gasoline was released from USTs on the property An estimated 8,500 gallons of gasoline was discharged to the environment On May 1, 1995, four USTs were ' removed from the southeast corner of the site and approximately 1,400 cubic yards of contaminated soil were excavated from the tank pit Shell installed soil vapor extraction (SVE) and recovery wells at the site in order to conduct soil remediation and gasoline recovery The lateral and vertical extent of the gasoline contamination was characterized through soil sampling, CPT borings, and shallow and deep well installations A corrective action plan (CAP) was submitted to SJCEHD on February 13, 2003 The CAP presented a detailed summary of the site background and investigation history, as well as recommendations for remedial actions Currently, Shell utilizes 14 wells (seven offsite and seven onsite) (11 shallow, two deep, and one groundwater extraction well)for site monitoring and remediation The shallow subsurface geology encountered during soil boring installation activities consisted of clay, silt, and silty sand to approximately 25 feet bgs Groundwater was first encountered between 10 and 16 feet bgs The groundwater flow direction ranges from southwest to northeast, with the primary flow direction to the southwest A cone of depression exists around RW-1A due to groundwater extraction from this well, influencing the groundwater flow gradient and direction at the site The groundwater elevation at this site can fluctuate within a two-foot range, with the highest elevations in the spring and lowest elevations in the fall The groundwater elevation in MW-8 (Shell Oil monitoring well closest to the storm drain) during the Kleinfelder groundwater investigation (April 2003) was -7 64 feet mean sea level (ms], 8 71 feet bgs) In October 2002, the groundwater elevation in MW-8 was -8 85 feet msl (9 92 feet bgs) 1 Groundwater monitoring is currently being conducted quarterly at this site in some, but not all of the wells Quarterly groundwater samples are analyzed for total petroleum hydrocarbons quantified as • gasoline (TPH-G), benzene, toluene, ethyl benzene, total xylenes (BTEX), and MTBE Shell is required �� CONDOR