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December 8, 1997 •
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<br />northeast of the site. South of the site is a City of Stockton maintenance yard, which we
<br />understand had a UST removed from the site approximately 2 years ago. To the
<br />southeast is a former bakery which reportedly had underground storage tanks (USTs)
<br />for delivery trucks. Northwest of the site is a transmission shop which also reportedly
<br />had USTs at one time.
<br />In March 1995, Groundwater Technology installed three monitoring wells onsite to
<br />depths of 50 feet below ground surface each. Initial soil testing reported nondetectable
<br />levels of total petroleum hydrocarbons calculated as gasoline (TPH-g) in Wells MW -I
<br />and MW -2 and concentrations of 3.8 and 250 milligrams per kilogram (mg/kg) in
<br />MW -3 at 25 and 35 feet bgs, respectively. Benzene, toluene, ethylbenzene, and total
<br />xylenes (BTEX compounds) were reported in MW -3 at 1.0, 4.6, 1. 1, and 8.3 mg/kg,
<br />respectively at 35 feet bgs. Benzene was also reported in MW -3 at 30 feet bgs at a
<br />concentration of 0.012. Benzene was reported in MW -1 at 25 feet bgs at a
<br />concentration of 0.034 mg/kg. All other soil samples were found nondetect for BTEX
<br />compounds, total petroleum hydrocarbons calculated as diesel (TPH-d) and total oil and
<br />grease. Soil samples from MW -1 were analyzed for metals and reported concentrations
<br />of chromium, lead, nickel and zinc at 23, 7.8, 21, and 50 mg/kg (10 feet bgs) and 31,
<br />6.5, 42, and 59 mg/kg (35 feet bgs), respectively.
<br />Wells MW -1 through MW -3 have been sampled quarterly by Blaine Tech Services
<br />since May 1995. Concentrations of TPH-g have increased in MW -1 from 340 to 5,900
<br />parts per billion (ppb). Benzene concentrations have also increased from 67 ppb in May
<br />1995 to 1,100 ppb in August 1997. Well MW -I has also showed increasing levels of
<br />1,2 -DCA. Well MW -2 has remained consistently nondetect For TPH-g, BTEX, and
<br />methyl tertiary butyl ether. Well MW -3 has reported decreasing levels of TPH-g and
<br />BTEX compounds between May 1995 and August 1997, with levels decreasing from
<br />44,000 to 7,100 (TPH-g) and 2,900 to 800 ppb (benzene), respectively.
<br />On September 9, 1996, Touchstone Developments oversaw the excavation and removal
<br />of the USTs , hydraulic hoists, product dispensers and associated product lines. Soil
<br />samples were collected from beneath the USTs, hydraulic hoists, product piping, and
<br />dispensers. The highest concentrations of hydrocarbons were reported underneath the
<br />southern product island with (P6) with 3,000 parts per million (ppm) TPH-g and BTEX
<br />concentrations of 2.6, 20, 47, and 240 ppm, respectively (3.5 feet bgs). On September
<br />11, 1996, over -excavation was performed in the areas below the USTs, product
<br />dispensers and associated product lines. The highest levels of hydrocarbons were
<br />reported beneath the southern product island (sample PXB2) at concentrations of 1,700
<br />ppm TPH-g and 3.2 ppm benzene, (6 feet bgs) and west of the southern product island
<br />(sample PXB7) at concentrations of 1,300 ppm TPH-g and 14 ppm benzene (7 feet bgs).
<br />PROPOSED SCOPE OF WORK
<br />The scope of work will include 1) a County records review on nearby sites, 2) record
<br />research and review of Chevron's historical files for the subject site; 3) the drilling of 2
<br />soil borings to an approximate depth of 90 feet; 4) preparation of geologic cross
<br />920-124 LVWKPI..AN
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