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<br />' SITE HISTORY
<br /> A Phase 1 Preliminary Hazardous Materials Site Assessment(PSA)was prepared by Kleinfelder of
<br />' Sacramento, California, and dated November 16 1988 The PSA was prepared for Nomellini Construction
<br /> Company, a construction and tool rental operator
<br /> Three underground storage tanks (USTs) located at the subject site were removed in August, 1988 The tank
<br />' numbers, sizes, contents and histones were as follows two 1,000 gallon fuel tanks (containing regular
<br /> and unleaded gasoline)were excavated from southeast of the warehouse building One 550 gallon waste oil
<br /> tank was excavated from a separate site The subsurface investigations that followed relate to the two
<br /> 1,000 gallon fuel tanks The tanks reported to store unleaded gasoline may also have held kerosene at one
<br />' time Analytical results of soil samples collected beneath the tanks indicated that petroleum hydrocarbons
<br /> and gasoline related constituents were present in the soil beneath the two 1,000 gallon tanks
<br /> Constituents were detected below levels of concern in the sample collected beneath the waste oil tank
<br /> Results of this investigation were presented in a Kleinfelder report dated September 22 1988
<br />' According to the Kleinfelder Report dated June 14, 1989, additional soil was removed from the fuel tanks
<br /> excavation on November 9, 1988 to further assess the extent of petroleum hydrocarbon contamination
<br /> One section of the former tank pit was excavated to a depth of 19 feet from about I1 feet below ground
<br />' surface Soil samples were screened for organic vapors using a photoionization detector (PID) Organic
<br /> vapor readings were detected at 408 parts per million (ppm) from a sample collected at a depth of 19 feet
<br /> within the former tank pit and 740 ppm from a sample collected 10 feet away from the excavation at a depth
<br /> of 16 feet Based on the positive organic vapor screening results, Nomellim Construction decided to
<br />' backfill the excavation with clean fill and further assess the extent of the contamination with a soil boring
<br /> program
<br /> In May, 1989, Kleinfelder supervised the drilling of nine soil borings (B-1 through B-9) in the vicinity of
<br /> the former tank pit Samples were analyzed from depths of 10 5 to 26 feet. Ten of 15 soil samples
<br /> contained total petroleum hydrocarbons as gasoline at levels ranging from non-detect to 450 ppm
<br /> High concentrations of TPH as gasoline (TPH-g) benzene, toluene, ethylbenzene, and xylenes (BTEX)
<br /> I were detected lust above and below the groundwater surface in boring B-1, located adjacent to the south edge
<br /> of the excavation Similarly, high TPH-g concentrations were detected just above the groundwater surface
<br /> in B-2, approximately 20 feet north of the former tank excavation The remaining samples had relatively
<br /> low concentrations detected but TPH,s were consistently detected just above the groundwater surface
<br /> Groundwater was encountered at a depth of about 25 feet below ground surface
<br /> In February, 1991, Kleinfelder drilled three borings B-10 through B-12 These borings were subsequently
<br /> converted into monitor wells MW-1 through MW-3 TPH-g was detected in the groundwater on February,
<br /> 1991 in MW-1 through MW-3 at concentrations of 1 700 ppm, 10,000 ppm and 1,500 ppm respectively
<br /> In June, 1991, 15 feet of free product was measured in MWA
<br /> Artesian Environmental Consultants measured hydrocarbon thickness in MW-1 on March 16, 1992 to be
<br /> 1 82 feet Groundwater flow direction on March 16, 1992 was to the southeast Water depth was measured
<br /> on March 16, 1992 for MW-1 through MW-3 at 32 5, 32 7 and 32 4 feet below ground surface,
<br /> respectively
<br /> Artesian Environmental Consultants (Artesian) drilled three soil borings, B-1 through B-3 on the property
<br /> an May 1, 1992 The soil borings B-1 through B-3 were drilled to depths of 45, 45 and 43 feet
<br /> respectively, below ground surface All three borings were drilled into native material All three borings,
<br /> B-1 through B-3 were subsequently converted into monitor wells MW-4 through MW-6, respectively
<br /> Shallow groundwater was encountered in all the wells at approximately 32 feet below ground surface
<br /> The soils were logged by a project geologist under the supervision of a California-registered geologist
<br /> Soil samples were collected at least every 5 feet for lithologic, and hydrologic characterization, as well as
<br /> possible chemical analyses The soils were screened with a PID Using a PID, organic vapor was not
<br /> detected in the soil borings
<br /> Soils Analysis
<br /> Soil samples were below detection limits (ND) for total petroleum hydrocarbons as gasoline (TPH-g) with
<br /> the exception of B-1 Borehole B-1 contained 17 ppm and 5 1 ppm TPH-g at depths of 25 5' and 30 5',
<br /> respectively Benzene was detected at levels of 47, 82, 150, 190, and 67 ppm at depths of 15 5, 20 S,
<br /> 25 5, 30 5, and 35 5 feet, respectively Toluene was present at 25 5', 30 5' and 35 5' at levels of 15 ppm,
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