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SECOR
<br /> i 76 Station No. 11193
<br /> August 13, 2004
<br /> Page 3
<br /> In February 1995, Alisto conducted baildown testing to determine aquifer properties
<br /> beneath the site. Pumping occurred from well MW-1, generating approximately 1.5 feet of
<br /> drawdown at an extraction rate of 6 gallons per minute (gpm). Alisto concluded that the
<br /> rapid recovery may be due to the sand unit encountered in the lower portion of well MW-1,
<br /> and may not be representative of the material in the saturated zone (Alisto, 1995). Revised
<br /> calculations of hydrogeologic parameters were submitted in October 1995. Resulting
<br /> hydraulic conductivity (K) values for wells MW-1, MW-2, and MW-5 ranging from 2.25x10
<br /> to 8.68x105 centimeters per second (cm/s) were within the lower range of expected K
<br /> values associated with the soil types encountered beneath the site (1 to 1x10$ cm/s,
<br /> Freeze and Cherry, 1979), which consist of silt and silty sand underlain by fine to medium
<br /> sand (Alisto, 1995).
<br /> Between December 10 and 22, 1998, Gettler-Ryan Incorporated (GR) supervised the
<br /> removal of two 10,000-gallon USTs and one 8,000-gallon single-walled UST, dispensers,
<br /> and associated product dispenser piping. Laboratory analysis of soil samples collected
<br /> from the UST excavation reported maximum concentrations of TPHg at 31 ppm (3W),
<br /> benzene at 0.27 ppm (3W), and MtBE at 80 ppm (3E). Laboratory analysis of soil samples
<br /> collected from the beneath the dispensers and product piping detected maximum
<br /> concentrations of TPHg at 1,600 ppm (131) and MtBE at 1.8 ppm (D3). Additionally,
<br /> approximately 15,000 gallons of water was removed from the excavation during the
<br /> installation of the new USTs. Laboratory analysis of a grab groundwater sample reported
<br /> maximum concentrations of TPHg, benzene, and MtBE at 17,000 micrograms per liter
<br /> (µg/L), 1,500 µg/L, and 120,000 gg/L, respectively. Groundwater Monitoring Well MW-1
<br /> ' was destroyed to allow the enlargement of the existing UST excavation to allow for the
<br /> installation of the new USTs (GR, 1999).
<br /> On October 7 and 8, 1999, Cambria Environmental Technology, Incorporated (Cambria)
<br /> conducted Cone Penetration Testing (CPT) by advancing six borings (CB-1 through CB-6)
<br /> for soil and groundwater sampling and two borings (CB-2E and CB-4E) for electric soil
<br /> logging. Soil samples were collected every five feet to approximately 20 feet bgs. Water
<br /> samples were collected using a hydropunch at depths of 16 and 29 feet bgs in borings CB-
<br /> 1, CB-2, and CB-4 through CB-6. Water samples were collected at depths of 16 and 29
<br /> feet bgs in boring CB-3. Laboratory analysis of soil samples collected from the soil borings
<br /> detected E'maxi mum concentrations of gasoline range organics (GRO) at 27 milligrams per
<br /> kilogram (mg/kg) (CB-3-13.5), MtBE at 27 mg/kg (CB-3-13.5), and tert amyl methyl ether
<br /> (TAME) at 0.058 mg/kg (CB-3-13.5). Benzene, toluene, ethylbenzene and total xylenes
<br /> (BTEX) were not detected above laboratory detection limits. Laboratory analysis of
<br /> groundwater samples collected from the soil borings detected maximum concentrations of
<br /> GRO at 87,000 lug/L (CB-4-16HP), benzene at 1,300 µg/L (CB-4-16HP), MtBE at 38,000
<br /> µg/L (CB-1-16HP), and TAME at 160 Rg/L (CB-1-16HP) (Cambria, 1999).
<br /> Also in late 1999, Cambria conducted a sensitive receptor survey. Based on a review of
<br /> United States Geological Survey (USGS) topographic maps and recent area maps, an
<br /> unnamed levy-restricted slough was identified 2,000 feet south of the site, and a man-
<br /> made lake was located in a residential area approximately 1,500 feet southwest of the site.
<br /> Well logs obtained through the State of California, Department of Water Resources (DWR)
<br /> indicated the presence of an irrigation well owned by the California Department of
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