WORK PLANS - Laserfiche WebLink

Home Browse Search

Work Platt For Additional Subsurface Investigation - Chevron Service Station #9-3232 March 26, 1999 In December 1993 , dispensers and product lines were removed. The dispensers were replaced and the product lines were upgraded from single-walled fiberglass to double-walled fiberglass. The USTs were not removed or upgraded. Soil samples were collected from beneath the product lines and the waste oil UST remote fill pipe. Total Petroleum Hydrocarbons as gasoline (TPHg) were detected in one soil sample from beneath the product lines at a concentration of 7 parts per million (ppm). Benzene was detected in one sample at a concentration of 0. 81 ppm . Lead was detected in three of the five soil samples at concentrations of 5 and 6 ppm. The soil sample collected beneath the waste oil UST remote fill pipe contained TPHg (3 ppm) . Total Petroleum Hydrocarbons as diesel (TPHd) were also detected in this sample at a concentration of 350 ppm, along with Oil and Grease (O&G) at a concentration of 1 ,700 ppm and trichloroethene (TCE) at a concentration of 0 .037 ppm . In October 1998, GR installed three groundwater monitoring wells (MW- 1 through MW-3). The soil samples analyzed from borings MW- 1 and MW-3 did not contain detectable concentrations of TPHg, BTEX or MIRE with the exception of the sample from boring MW-3 at 49 .5 feet bgs. This sample contained TPHg and benzene at concentrations of 52.6 and 0.901 ppm, respectively. Samples from 10 or 25 .5 feet bgs in boring MW-2 did not contain TPHg, BTEX or MtBE. However, TPHg and benzene were detected in the samples from 30.5, 40 . 5 and 50 .5 feet bgs. TPHg concentrations ranged from 2.94 to 593 ppm, and benzene concentrations ranged from 0. 184 to 6.4 ppm. On November 4, 1998, groundwater was recorded at depths between 31 .93 and 36.07 feet below top of well casing. The flow direction was to the southwest at a gradient of 0.05 . Samples from each of the wells contained concentrations of TPHg and BTEX. Well MW-2, located downgradient of the dispenser islands had the highest concentrations of TPHg ( 120,000 parts per billion, or ppb) and benzene (23,000 ppb). Fuel oxygenate compounds were not detected in any of the groundwater samples. The gasoline and waste oil USTs were removed on March 11 , 1999. Petroleum Hydrocarbons were not detected in the samples collected beneath the dispenser island or the product piping. TPHg were detected in the soil samples collected beneath the middle gasoline UST. The highest concentration was detected in the sample from beneath the southern end of the middle tank at 19 feet bgs (680 ppm). ' A sample from 21 feet bgs in this area contained only 51 ppm of TPHg. MtBE was detected in eight of the nine soil samples collected beneath the gasoline USTs at concentrations between 0. 11 and 0.96 ppm. Benzene was not detected in any of the sample from beneath the gasoline USTs. One soil sample from 10 feet bgs beneath the waste oil UST contained TPHg (2.0 ppm), TPHd (810 ppm), tetrachloroethene (0.5 ppm), and O&G (2,700 ppm). After additional excavation of the waste oil UST pit, a sample from 17 feet bgs in this area did not contain TPHg, TPHd, or tetrachloroethene, but did contain O&G (79 ppm). A soil sample from the opposite end of the waste oil UST pit at 10 feet bgs contained O&G (I 10 ppm). A groundwater sample from the gasoline UST pit did not contain TPHg or benzene, but did contain MtBE (6 .0 ppb). The UST removal and soil sampling report is currently in preparation. SCOPE OF WORK To further evaluate the distribution of residual petroleum hydrocarbons in soil beneath the site, GRproposes to advance 4 soil borings to depths up to 60 feet bgs. The borings will be advanced hydraulically using a GeoProbe or similar technology. This proposed scope of work is intended to provide both vertical and horizontal delineation of impacted soil beneath the site. It is not the intent of this scope of work to further 346463.04-1 2 -