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r,— %owl Site Background Information -Ripon Farm Service Page 3 of 10 Domestic Wells: Drinking water at the site is currently supplied by a domestic well, located approximately 250 feet southeast of well MW-5. A second well, located 75 feet north of the site, supplies water for the Jimco Track Stop. A third well serves the residence southeast of the site. Municipal Wells: The City of Ripon has established twelve wells.Five of the twelve wells have been either abandoned or are off-line due to high inorganic contamination. Seven wells are operational and are tested or have been tested for California Title 22 contaminants. One well is located approximately 750 feet west of the site. This well was recently established and has not been activated. This well is the only municipal well within 2,000 feet of the site, with the other wells located more than 2,000 feet southeast of site. The distance of this well from the subject site limits its potential to be adversely impacted by the release of petroleum hydrocarbons on the site. Threatened Well:As described below,the domestic well for the Jimco Truck Stop is located within the northen margin of the soil and ground water petroleum plumes,in a down-gradient direction from the site,and is therefore the well most likely to be effected by the release of petroleum hydrocarbons on the subject site. UST REMOVAL Four underground storage tanks (USTs) were removed from the site010,000- a O 10,000-gallon diesel tank(Tank#1) and one 7,500-gallon diesel tank(Taar the tuning shop. One 10,000-gallon unleaded gasoline tank(Tank#3) and ieseltank(Tank#4)were located approximately 120 feet east of the shop.After was collected below each UST at depths between 18 feet and 21 feet bsg. Petroleum hydrocarbons were detected in soil samples collected below Tanks #1, #2, and#3. ASSESSMENT OF HYDROCARBON-IMPACTED SOIL AND GROUND WATER In April 1994,eight soil borings(B1 through B8)were advanced at the site;three of the borings were completed as ground water monitoring wells (MW-1,MW-2, and MW-3).During drilling, ground water was encountered at a depth of approximately 20 feet bsg. • Total petroleum hydrocarbons quantified as gasoline (TPH-g) were detected in ten soil samples at concentrations as high as 3,800 milligrams perkilogram(mg/kg).Total petroleum hydrocarbons quantified as diesel(TPH-d)were detected in twelve samples at concentrations as high as 9,000 mg/kg. The maximum concentration of TPH-g was detected in sample B4-20; the maximum TPH-d was detected in sample B8-20. • TPH-g was detected in ground water samples from MW-1, MW-2, and MW-3 at concentrations of 1,700 micrograms per liter(µg/l), 14,000µg/l,and 2,600 gg/l,respectively. Advanced GeoEnvironmental,Inc.