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Request For Closure,Former Unocal Station#0123,Tracy,CA April 19,2001 At the request of GR,Mr Alan Kemp of Sequoia Analytical(ELAP#1271)reviewed the analytical report and concluded that the discrete peaks were not caused by diesel, nor did any other type of petroleum hydrocarbons cause them He could not determine from available information what caused the peaks Depth to water during this monitoring event ranged from 9 34 to 10 64 feet bgs and groundwater flow was to the north at a gradient of 0 003, which is consistent with available historical data RATIONALE FOR NO FURTHER ACTION , The former Unocal service station operated until 1962 All site structures and USTs have been removed from the site, except for one UST located near the northwest comer of the site, which was properly abandoned in place in 1996 Soil impacted by petroleum hydrocarbons has been delineated and is restricted to the vicinity of the former UST cluster located in the northwest corner of the site Groundwater impacted by petroleum hydrocarbons is also delineated, and is restricted to the same area, with consistent detections only in well U-4,which is located in the area of the former UST cluster Based on these data, additional investigation or remediation of soil or groundwater is not warranted, and the site should be closed In support of the closure request, we summarize the information requested in Table 1 of Appendix B of the CRWQCB No Further Action Requests guidelines This information is presented point by point as outlined in Table 1 1) Distance to production wells for municipal, domestic, agriculture, industry and other uses within 2000 feet of the site. Based on well search data presented in Pacific Environmental Group, Inc report #910-017 IA, Soil and Groundwater Investigation, dated December 2, 1998, 17 wells are located within 2,000 feet of the site Table 2 lists these wells and their distances from the site Figure 1 shows the locations of these wells Based on the prominent north-northwest groundwater gradient at the site, only one well, a City of Tracy municipal well located 0 26 mile north of the site is in the downgradient direction The other wells are located cross-or upgradient of the site 4 2) Site maps,to scale,of area impacted showing locations of former and existing tank systems, excavation contours and sample locations, boring and monitoring well elevation contours, gradients,'and nearby surface waters,buildings,streets,and subsurface utilities. Available maps are in Appendix A Groundwater contour maps for historic monitoring events are in Appendix B 3) Figures depicting lithology(cross section),treatment system diagrams. Cross sections are shown on Figures 5 and 6 Htstoncal cross sections are included in Appendix C No treatment system was ever installed at this site 240073 06 3