ARCHIVED REPORTS XR0001115 - Laserfiche WebLink

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' SITE HISTORY ' A Phase I Preliminary Hazardous Materials Site Assessment (PSA) was prepared by Kleinfelder of Sacramento, Califoinra, and dated November 16, 1988 The PSA was piepared for Nomellinr Construction Company, a construction and tool rental ' operator Three underground storage tanks (USTs) formerly located at the subject site were removed in August, 1988 The tank numbers, sizes, contents and histories were as ' follows two 1,000 gallon fuel tanks (containing regular and unleaded gasoline) were excavated from southeast of the warehouse building One 550 gallon waste oil tank was excavated from a separate site The subsurface investigations that followed relate ' to the two 1,000 gallon fuel tanks The tanks were reported to store unleaded gasoline may also have held kerosene atone time Analytical results of soil samples collected beneath the tanks indicated that pets oleum hydi ocarbons and gasoline related constituents were present in the soil beneath the two 1,000 gallon tanks Constituents ' were detected below levels of concern in the sample collected beneath the waste oil tank Results of this investigation were presented in a Kleinfelder report dated September 22, 1988 According to the Kleinfelder Report dated June 14, 1989, additional soil was temoved from the fuel tanks excavation on November 9, 1988 to further assess the extent of petroleum hydrocarbon contamination One section of the former tank pit was excavated to a depth of 19 feet from about 11 feet below ground surface Soil samples were screened for organic vapors using a photoronization detector(PID) Organic vapor readings were detected at 408 parts per million (ppm) from a sample ' collected at a depth of 19 feet within the former tank pit and 740 ppm from a sample collected 10 feet away from the excavation at a depth of 16 feet Based on the positive organic vapor screening results, Nomellini Construction decided to backfill ' the excavation with clean fill and further assess the extent of the contamination with a soil boring program ' In May, 1989, Kleinfelder supervised the drilling of nine soil borings (B-1 through B-9) in the vicinity of the former tank pit Samples were analyzed from depths of 10 5 to 26 feet Ten of 15 soil samples contained total petroleum hydrocarbons as gasoline at levels ranging from nondetect to 450 ppm ' High concentrations of TPH as gasoline (TPH-g), benzene, toluene, ethylbenzene, and xylenes (BTEX) were detected just above and below the groundwater surface in ' boring B-1 which was located adjacent to the south edge of the. excavation Similarly, high TPH-g concentrations were detected just above the groundwater surface in B-2, approximately 20 feet north of the former tank excavation The ' remaining samples had relatively low concentrations detected, but TPHs were consistently detected just above the groundwater surface Groundwater was encountered at a depth of about 25 feet below ground surface In February, 1991, Kleinfelder drilled three boi Ings B-10 through B-12 These borings were subsequently converted into monitor wells MW-1 thiough MW-3 TPH-g was detected in the groundwater in February, 1991 in MW-I through MW-3 at concentrations of 1,700 ppm, 10,000 ppm and 1,500 ppm, respectively In June, 1991, 15 feet of free product was measured to MW-1 The groundwater gradient has generally varied between the northeast to southeast