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1 <br /> Mr. John Trinkle - 2 - 3 October 2008 <br /> chlorobenzene, 1 ,4-dichlorobenzene, and diuron at concentrations that exceed water quality <br /> objectives, as shown in Table 2. The constituents 1,3-dichlorobenzene, 2,4-D, and dicamba <br /> were also detected, but at concentrations significantly below the applicable water quality <br /> objectives. <br /> Table 2. Detected Grab Groundwater Sample Results and Water Quality Objectives <br /> Number of Detected Water Quality Basis for Water <br /> Constituent Detections Concentration Range Objective Quality Objective <br /> California Dept. Of <br /> 1,3-dichlorobenzene 1 11 ug/L 600 ug/L Pesticide Regulation <br /> Notification Level for <br /> drinking water <br /> 1,2-dichlorobenzene 2 32—40 ug/L 24 ug/L Odor Threshold <br /> California Primary <br /> 1,4-dichlorobenzene 2 6.6—22 ug/L 5 ug/L Maximum Contaminant <br /> Level <br /> USEPA, Office of <br /> Diuron 1 30 ug/L 2 ug/L Pesticide ProgramsCancer Potency Factor <br /> as a drinking water level <br /> 2,4-D 3 2.7—23 ug/L 70 ug/L California Public Health <br /> Goal for Drinking Water <br /> USEPA, Office of <br /> Dicamba 1 0.7 ug/L 4,000 ug/L Pesticide Programs <br /> Drinking Water Health <br /> Advisory- non-cancer <br /> In our 1 May 2008 letter concurring with the Site Investigation Work Plan, Regional Water <br /> Board staff requested analyses for carbamate/urea compounds, including diuron. The <br /> analytical laboratory only analyzed for diuron, not other carbamate/urea compounds. When <br /> Trinkle & Boys obtains groundwater samples from monitoring wells, these samples should be <br /> analyzed for the carbamate/urea suite of compounds. <br /> One of the scenarios we discussed in our 7 February 2008 meeting included the scenario that <br /> we find today- the eastern portion is suitable for development, but the operations area is not. <br /> As we discussed in that meeting, the Remedial Action Plan for this site could include a remedy <br /> for groundwater in the operations area and no action necessary on the eastern portion of the <br /> site. <br /> Next Steps <br /> Trinkle and Boys should install three monitoring wells in the operations areas to confirm the <br /> findings of the grab groundwater investigation. On occasion, water samples obtained from <br /> groundwater monitoring wells show lower concentrations than those obtained from grab <br /> groundwater samples. <br /> As Regional Water Board staff requested in its 1 July 2008 letter, Trinkle & Boys needs to <br /> either locate the monitoring wells that were identified in 1991, or demonstrate that there are no <br />