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During the February 2001 CPT investigation, relatively high concentrations of GRO (150,000
<br /> pg/L), BTEX (benzene at 23,000 µg/L), and 1,2-DCA (560 µg/L) were reported' in a depth
<br /> discrete groundwater sample collected from sandy strata identified within boring CPT-10 at 88
<br /> feet bgs. Impacted groundwater is also reported at mid-depth wells MW-16 and MW-18 at this
<br /> depth interval. GRO and benzene have been detected in the well MW-16 (490 µg/L and 0.73
<br /> µg/L maximum concentration, respectively) and MW-18 (2,600 µg/L and 430 µg/L maximum
<br /> concentration, respectively) samples.
<br /> Relatively high concentrations of GRO and BTEX have historically been reported at deeply
<br /> screened well MW-8, situated east of the former UST area and southeast of the former Sunland
<br /> Gasoline/Stockton City Cab Company site. Dissolved hydrocarbon concentrations at the other
<br /> deeply screened downgradient monitoring wells (MW-10 and MW-17) are generally low.
<br /> The highest concentrations of 1,2-DCA have historically been reported at deeply screened well
<br /> MW-9 (maximum 1,400 µg/L). 1,2-DCA also impacts deeply screened wells MW-10 (13 µg/L
<br /> to 53 [,g/L), MW-11 (1.0 µg/L to 3.2 µg/L), and MW-17 (1.2 µg/L to 8.4 µg/L). 1,2-DCA
<br /> impact to shallow groundwater extends to the areas surrounding wells MW-2 (3.1 µg/L to
<br /> 390 Vg/L), MW-5 (1.4 µg/L to 40 µg/L), MW-6 (1.5 µg/l, to 37 µg/L), and MW-15 (3.0 µg/L to
<br /> 7.7 µg/L).
<br /> MTBE concentrations in the monitoring well samples are consistently below laboratory detection
<br /> limits. TBA impact has been documented across much of the site in the shallow and deeper
<br /> • water bearing strata. TBA concentrations are generally low, with 170 pg/L representing
<br /> maximum historical well sample concentration. TBA concentrations in the well samples are
<br /> predominately less than 50 µg/L.
<br /> Volatile organic compounds (VOCs) that are normally not analyzed for under the standard
<br /> monitoring protocol for service station properties in San Joaquin County are also present in j
<br /> groundwater beneath the property. At the request of SJCEHD personnel, VOCs identified during
<br /> the USEPA Method 8260 analysis of groundwater samples have been reported as tentatively
<br /> identified compounds in the quarterly monitoring reports submitted on behalf of the site since the
<br /> fourth quarter 2002. Butane, ethyl methyl benzene, isobutene, ethyl cyclopropane, cyclopentane,
<br /> methyl cyclopentane, indane, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, naphthalene,
<br /> thiophene, methyl cyclohexane, tetrahydrothiophene, isopropylbenzene, n-propylbenzene,
<br /> n-butylbenzene, 1-ethyl-2-methyl-benzene, tert-butylbenzene, bis(2-chloroethyl)disulfide,
<br /> methyl mercaptan, 2-methyl 1-propene, 1-methyl-indan, 1,2,3,4 tetramethylbenzene, acetone,
<br /> and lighter-end aliphatic and aromatic hydrocarbons (C-3 through C-12) have been tentatively
<br /> identified during the Method 8260 analysis of groundwater samples collected beneath the site.
<br /> Approximate concentrations of these compounds, and the dates detected, are presented on a table
<br /> included in Appendix G.
<br /> Farmer Sunland Gasoline/Stockton City Cab Compgny Facili
<br /> A quarterly groundwater monitoring program was initiated at this property in October 2003.
<br /> During this monitoring period, the highest concentrations of GRO and BTEX have consistently
<br /> been reported for samples collected from shallow screened well MW-1. GRO concentrations
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