SITE INFORMATION AND CORRESPONDENCE

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Mr. Arnold Hof -2 - 30 April 2003 needed for these constituents. The applicable water quality limits are discussed below and for your convenience are summarized in attached Table 1. The results of the monitoring events of 2002 confirm the following: • Ammonium is detected in three monitoring wells at concentrations of 0.1 to 0.2 mg/1 which are below the water quality limit of 1.5 mg/l (taste and odor threshold). • Triazine pesticides were last detected in 1997, but were not detected in any subsequent monitoring events (1998, 1999, and 2002). • Prior to 2000, chlorinated herbicides were only routinely detected in MW-3, but were not detected in 2002. In 1999, MW-3 contained the chlorinated herbicide 2,4,5-TP at 0.5 ug/1, which is below the water quality limit of 50 ug/l (California Primary Maximum Contaminant Level), and contained dinoseb at about 4 ug/l,which is below the water quality limit of 7 ug/l (California Primary Maximum Contaminant Level). Chlorinated herbicides were not detected in 2002. • In 2002,monitoring well MW-3 contained beta-benzene hexachloride (b-BHC) at 0.1 ug/l, which is above the water quality limit of 0.025 ug/1 and above the detection limit of 0.05 ug/1. MW-3 has not contained any other organochlorine compounds in any monitoring events since 1990 (1994, 1995, 1997, 1998, 1999, 2002). • In 2002,MW-1 contained petroleum constituents and the fuel oxygenate MTBE at concentrations greater than the water quality limits, and MW-5 contained MTBE. Petroleum hydrocarbons and fuel oxygenates were not detected in any other wells. We concur with your request to remove ammonium, triazine pesticides, and chlorinated herbicides from the MRP, although we may request that you resample for these constituents before we evaluate a request for a No Further Action designation. We also concur that monitoring for petroleum compounds should continue in MW-1, and monitoring for MTBE should continue in MW-1 and MW-5,but may be discontinued in MW-8. When petroleum hydrocarbons are no longer above the water quality objectives in MW-1,you should request No Further Action for the underground fuel tank portion of the investigation. The organochlorine compound b-BHC should continue to be included in the analytical schedule for MW-3. The results of the 2002 sampling events show that it is appropriate to reduce the monitoring frequency for all constituents to annually, as we had discussed in our 31 October 2001 meeting. The data confirm that annual sampling should occur in the third quarter,July through September, since constituents are typically at greatest concentrations during that quarter. The above changes are incorporated into the draft MRP, which is enclosed for your review and comment. Redundant Monitoring Wells Two of the monitoring wells are upgradient of the former Cal Farm Supply facility. Monitoring well MW-9 is about 75 feet upgradient, and MW-4 is on your upgradient property boundary. Monitoring well MW-9 is redundant, may be removed from the analytical monitoring schedule, and should be destroyed according to San Joaquin County Public Health Services regulations. In