ARCHIVED REPORTS XR0000363 - Laserfiche WebLink

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GERAGHTY & MILLER, INC 2 SITE HYDROGEOLOGY The site is underlain by interbedded clays, silts, and sands to a depth of about 30 feet below ground surface (bgs), the total depth explored. Depth-to-water measurements show significant seasonal variation, from approximately 10 to 17 feet bgs The direction of groundwater flow is to the northeast, towards the Swenson Park Golf Course ' BACKGROUND ON-SITE FACILITIES The service station was constructed in 1973. At that time, four single-walled,fiberglass underground storage tanks (USTs) were installed one 6,000-gallon (for gasoline), two 10,000-gallon (for gasoline), and one 550-gallon waste-oil tank The former locations of the ' USTs are shown in Figure 2 In January 1989, the four single-walled USTs were removed. The removal of the ' USTs is documented in the Blaine Tech report dated January 17, 1989. No holes were found in any of the tanks during tank-removal activities. A new tank pit was constructed in the location shown in Figure 2 A total of five double-walled, fiberglass tanks have been installed in the new tank pit(four for gasoline, one for methanol) ' The station was renovated to include additional pump islands and product lines in the ' winter of late 1996/early 1997 These pump islands and product lines are shown in Figure 2 OFF-SITE FACILITIES The ARCO station across West Benjamin Holt Drive,crossgradient from the Chevron station, reported a spill of approximately 2,000 gallons in May 1989. An additional, ' unquantified release was reported in 1995 ARCO has installed several monitoring wells, including one off-site well bordering the Chevron boundary in the West Benjamin Holt Drive sidewalk (BHD-1), and other off-site wells downgradient (northeast) of the ARCO property. It is likely that the Chevron and ARCO plumes are commingling This is particularly evident ' due to the elevated concentrations of MTBE recently observed in Well MW-9 on the Chevron property Concentrations of MTBE in groundwater in ARCO monitoring wells near West Benjamin Holt Drive have been an order of magnitude greater than the highest concentrations observed at the Chevron facility ARCO is currently operating a combination SVE and Project No RC0309 010