SITE INFORMATION AND CORRESPONDENCE

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page 2, 6100 N. Hwy 99 The monitoring wells were developed and sampled on June 16, 2000. Results of the analyses of the collected samples indicate that groundwater beneath this site has been impacted by petroleum hydrocarbons and fuel oxygenating compounds. All four monitoring wells had total petroleum hydrocarbons as gas, benzene and MtBE at maximum quantities of 8,910 micrograms per liter(µgh), 2,310 µg/I and 3,200 pg/l, respectively. In addition, MW4 had tertiary butyl alcohol at 807 µg/I, tertiary amyl methyl ether at 4.48 pg/I and 1,2-dichloroethane at 84.4 µg/I. MW-2 and MW-3 had 1,2-dichloroethane at 38.8 µg/1 and 70.2 µg/I respectively. Routine quarterly groundwater monitoring must be initiated at this site, and must continue until directed otherwise from PHS/EHD. PHS/EHD has not approved the use of a no-purge method of groundwater sampling at this site. Both the California State Water Resources Control Board, as referenced in the Leaking Underground Fuel Tank (LUFT) Field Manual, and the United States Environmental Protection Agency(EPA) recommend that monitoring wells are purged until a minimum of three well volumes are removed, or until measured parameters of pH, temperature and conductivity of the discharged water stabilize to +/- 10% over two successive well volumes. There is a domestic well on the property that is used to provide water to the business on site. This well is located approximately 15 feet from MW-3. This domestic well must be sampled and analyzed for petroleum hydrocarbons and fuel oxygenates as soon as possible, and should be placed on the routine quarterly monitoring schedule. Analysis for all oxygenates, 1,2- dichloroethane and ethylene dibromide must be completed by EPA Method 8260. SECOR included in this"Site Assessment Report"a well survey covering a half mile radius area surrounding the subject site. The submitted survey documented only five wells within the search area, and noted that none of these wells are municipal wells. This well survey is very incomplete. There is no public water distribution to areas along the Highway 99 East Frontage Road. All occupied parcels along this corridor and to the east of this area, the subject site included, are supplied by private domestic or agricultural wells. Some of these wells may be very old, and records or permits are not available for them. A physical search of the target area must be conducted to locate all domestic, municipal, agricultural, industrial or other wells that may be influencing, or influenced by, the subject site's contaminant plume. Reports of findings are due to PHS/EHD within 60 days following the completion of each phase of work at a site. The above referenced report was overdue. Please have your reports submitted to PHS/EHD in a timely manner in the future. Prepare a work plan to continue the investigation of the vertical and lateral extent of the documented contamination at this site and submit it to PHS/EHD by December 1, 2000. Depth discrete samples will be required to define the vertical extent of the contaminant plume at depths below the screen intervals of the current onsite monitoring wells. Deep, discretely screen monitoring wells will be required. The lateral extent of the contaminant plume should be determined as soon as possible, and, if MtBE is found to be migrating off site, measures should be taken to contain the plume. If you have any questions call Lori Duncan at(209)468-0337. Donna Heran, REHS, Director Environmental Health Division cc-tA a Lori Duncan, Senior REHS Dot Lofstrom, RG LOP/Site Mitigation Unit IV Engineering Geologist cc: Marty Hartzell, CVRWOCB Rusty Benkosky, SECOR