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I 6.0 INSTITUTIONAL CONTROLS The Site is zoned industrial/agriculture and is bound on the east and south by the City Sewer Plant. The Bunker and UST B are located more than 400 feet upgradient of the property boundary. UST A is located more than 900 feet upgradient of the property boundary. County is well construction standards require a 100-foot seal on all water supply wells with the exception ii of agricultural wells which have a 50-foot seal requirement. �� i A deed restriction has been executed that restricts the construction or use of a well for the pmP ose of extractingwater for any use. The deed restriction encompasses an area of it approximately 12.68 acres located downgradient of the UST B, Motor/Hydraulic Oil UST, and b Bunker locations (RWQCB, 2010) ii 7.0 LOW-RISK CLOSURE SUMMARY f i The unauthorized releases were petroleum hydrocarbon in nature. • Three UST's and the Bunker have been removed and are no longer a potential. source of contamination. • The unauthorized releases occurred in unconsolidated material. The upper12 to 14 feet ' consist of clay or clay-silt-sand mixtures. The Corcoran Clay underlies the Site between .; 250 and 300 feet bgs. , 1 Free product has been removed to the extent possible. Soil excavation was chosen as the best available technology for the Site. All locations (UST A, UST B, Motor/Hydraulic Oil UST, and Bunker) have been over excavated to the extent possible. Further excavation of j UST B and the Motor/Hydraulic Oil UST areas were limited by an 8-inch gas,line along the northern face of the excavation. Approximately 168 pounds of TPHg and 0.2 poun s ofi benzene remain bound to the soil. Further excavation of the Bunker area was limited by I�I' f railroad and fire hydrant infrastructure. Approximately 91 pounds of TPHd and 375 pounds J of oil and grease remain bound to the soil. ' T h • MTBE was detected in groundwater near UST A below the taste and odor threshold and no II I other analyzed constituents were reported above laboratory detection limits. i I • Groundwater contaminants are decreasing and there is no drinking water well within 250 feet of any UST or Bunker location. MTBE is below the taste and odor threshold, benzene is currently below the MCL, and TPH will attenuate in less than 30 years. • The shallow groundwater is unusable and untreatable for domestic and/or agricultural purposes due to elevated TDS chloride nitrate and sulfate levels. i �i ,