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San Joaquin County Environmental Health Department DIRECTOR — � Donna Heran, REHS z 600 East Main Street Q: a �I Stockton, California 95202-3029 PROGRAM COORDINATORS Margaret Lagorio, REHS Robert McClellon, REHS Jeff Carruesco, REHS, RDI CqF O R// Website: www.sjgov.org/ehd Kasey Foley, RENS Phone: (209) 468-3420 Fax: (209) 464-0138 November 17, 2009 Mr. Dung Thanh and Ms. Nhuan Le 2224 Manthey Road Stockton, California 95206 Subject: California Stop 2224 Manthey Road Stockton, California 95206 The San Joaquin County Environmental Health Department (EHD) has reviewed Quarterly Monitoring Report —Third Quarter 2009, dated October 27, 2009, prepared and submitted by Advanced GeoEnvironmental, Inc. (AGE) on your behalf for the above-referenced site. Analytical results from the September semi-annual sampling event appear to indicate that the methyl tertiary-butyl ether (MTBE) plume has once again shifted toward the south. This is inferred from the significant decrease of MTBE concentrations in groundwater samples collected from monitoring wells MW-7 and MW-8, and the increase of MTBE concentrations in groundwater samples collected from MW-1 and MW-2. Based on the analytical results from the September sampling event, AGE has recommended that groundwater be collected semi-annually, instead of annually, from MW-1. The EHD concurs with this recommendation. In addition, also collect groundwater samples semi- annually from MW-2. To clarify the sampling schedule, MW-1 through MW-3, MW-7, and MW-8 will be sampled semi-annually, and MW-4 through MW-6 will be sampling annually. By letter dated June 5, 2009, the EHD approved a reduction in groundwater monitoring analyses to include total petroleum hydrocarbons quantified as gasoline (TPHg); benzene, toluene, ethyl benzene, and total xylenes (BTEX); MTBE, tertiary-amyl methyl ether (TAME), tertiary- butyl alcohol (TBA), and 1,2-dichloroethane (1,2-DCA). It is not necessary to include the analyses for di-isopropyl ether (DIPE), ethyl tertiary-butyl ether (ETBE), and 1,2- dibromoethane (EDB). In the third quarter 2009 report, AGE recommended postponing the installation of the EHD- approved groundwater extraction well (EW-1) since the proposed location may not be appropriate based on the on-going shift in the migration of the MTBE plume. Instead, AGE recommends that groundwater be pumped during the fourth quarter 2009 from existing groundwater monitoring wells MW-1 through MW-3, and MW-6 using above-ground piping secured by traffic control instead of below-ground piping. The EHD approves postponing the installation of the extraction well and proceeding with the pump test using MW-1 through MW-3 and MW-6 during the fourth quarter 2009. The above- ground piping system should have all appropriate safety features to minimize the tripping hazard and to protect the system from being damaged by pedestrians, or vehicular traffic.