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Additio%*Lundwater Investigation Work Plan M0 419 S.Main Street,Manteca,CA June 25,2003 Page 2 MW-3, and MW-4. MTBE was detected in groundwater samples collected from MW-1, MW-3, and MW- 4, tert-butanol (TBA) was detected in the sample collected from MW-1, and tert-amyl methyl ether (TAME) was detected in the samples collected from MW-1 and MW-3. Quarterly groundwater monitoring at the site began in the fourth quarter of 1999. On December 20-22, 2000, WHF completed four soil borings which varied in total depth between 20 and 25 feet bgs. The borings were subsequently converted into monitor wells MW-5 through MW-8. According to a representative of the SJCEHD, aquarium sand purchased at a pet store was used in the construction of MW-5. Laboratory analytical results of twelve soil samples collected from the borings indicated petroleum hydrocarbons were not detected at or above the laboratory reported detection limits in any of the samples. r On February 2, 2001, WHF advanced two 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. On April 25, 2001, WHF installed a deep monitor well, MW-9, to a depth of 50.5 feet bgs. The screen interval for the well was placed at 40.5-50.5 feet bgs. Two soil samples were collected from the borehole at depths of 43.5 feet and 50 feet for laboratory analyses. BTEX, TPH-G, and MTBE were not detected at or above the laboratory reported detection limits in the soil samples collected from the borehole. Laboratory analytical results of a groundwater sample collected from MW-9 indicated that none of the analytes of �• concern (BTEX, TPH-G, and selected gasoline oxygenates/additives) were detected, with the exception of MTBE, which was detected at a concentration of 14 micrograms per liter(pg/L). �. On September 26, 2002, a representative of Condor was onsite to measure water levels in, and collect groundwater samples from, monitor wells MW-1 through MW-9 for the third quarter 2002 groundwater monitoring event. Monitor wells MW-4, MW-5, and MW-6 were heavily silted, and MW-4 and MW-5 were dry. Mr. Jeffrey Wong of the SJCEHD was onsite to observe a portion of the field activities. At the request of the SJCEHD, a Condor representative was onsite to redevelop monitor wells MW-4, MW-5, and MW-6 on September 27, 2002. The redevelopment activities failed to significantly reduce the amount of sediment inside the well casings of MW-4 and MW-5. MW-6 was successfully redeveloped by removing a significant amount of the sediment from inside the well casing. A groundwater sample was 6w collected for laboratory analyses from MW-6 on September 30, 2002. Condor has conducted quarterly groundwater monitoring activities at the site since the third quarter of 2003. On November 20, 2002, Condor conducted a sensitive receptor survey (SRS) within a 2,000-foot radius of the site to identify potential areas of groundwater recharge or discharge, schools, and potential water well users that could be impacted by migration of groundwater from the site. The findings of the SRS included the identification of a municipal well located approximately 1,500 feet west of the site. A detailed description of the SRS was presented in Condor's Groundwater Monitoring Report, Third Quarter 2002, dated January 16, 2003. L On May 15, 2003, a Condor representative met with SJCEHD representatives to discuss Condor's recommendations presented in the quarterly monitoring reports for the third and fourth quarters of 2002 and the first quarter of 2003, and to address concerns the SJCEHD had regarding the site. In a letter dated `r May 29, 2003, the SJCEHD directed the submittal of a work plan to install, test, and operate an interim remediation system and a work plan to adequately define the lateral and vertical extent of the contamination V is CONDOR .r