ARCHIVED REPORTS XR0003442 - Laserfiche WebLink

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Ms Marla D Guenslcr Exxon Company, U S A August 20, 1997 Page 2 MW-2, MW-7, and MW-8 have generally been below laboratory detection limits Ground water samples collected from monitoring well MW-3 (Iocated furthest downgradient on-site) have shown concentrations of benzene ranging from 8 1 to 580 gg/L within the last four quarters Within this same time period, ground water samples collected from downgradient off-site monitoring wells (MW-4, MW-5, and MW-6) have reported nondetectable concentrations of benzene and total purgeable petroleum hydrocarbons (TPPH) as gasoline (Table 2) with the exception of the February 1997 sample collected from MW-4 This sample reported benzene at a concentration of 14 pg/L In March 1994, four steel, single wall underground storage tanks (USTs) were removed from the site one 1,000-gallon used oil tank, one 6,000-gallon premium gasoline tank, one 8,000-gallon plus unleaded gasoline tank, and one 10,000-gallon unleaded gasoline tank Analytical results of soil samples collected from beneath the former USTs are summarized in Table 3 and analytical results of soil samples collected from beneath the former product Ines are summanzed in Table 4 Soil sample locations are shown in (Figure 4) In January 1995, five soil bonngs were advanced at the site to depths of approximately 10 to 13 feet bsg Two of the borings were completed as SVE wells VEW-1 and VEW-2 The locations of the wells and borings are presented in Figure 2 Analytical results for collected samples are summarized in • Table 1 In December 1995, a new tank basin area was excavated and approximately 550 cubic yards of soil were generated during the excavation VEW-2 was destroyed during excavation activities Analytical results of soil samples collected during excavation activities are summarized in Table 5 Soil sample locations are shown in Figure 5 A ground water sample collected from the tank pit was also collected during excavation activities and the results are summarized in Table 6 Based on cumulative soil sample analytical results, petroleum impacted soil remains m the area along the western, northern, and eastern sidewalls of the new tank excavation located on the eastern side of the property Soil Boring Results On May 8, 1997, a Delta geologist observed Soils Exploration Services, of Rancho Cordova, California, drill one soil boring to a depth of approximately 10 feet bsg Following drilling, the boring was completed as SVE well VEW-3 Soil samples were collected from the soil boring at 5 and 10 feet bsg The soil samples from the boring were logged using visual and manual methods according to the Unified Soil Classification System (USCS) Materials encountered ranged from sand with silt to sand with gravel The methods used to drill and sample the soil boring are described in Enclosure B Copies of the soil boring log containing USCS descriptions of the soils encountered and other drilling information are included in Enclosure C Soil samples collected in the field were screened for the presence of petroleum hydrocarbon vapors . using a photononization detector (PID) Soil samples chosen for chemical analyses were selected based on depth, soil type, and field screening results