ARCHIVED REPORTS_XR0001988 - Laserfiche WebLink

Home Browse Search

AFAM Working To Restore Nature March 19, 1993 ARCO Station No. 548, Stockton, California analytically identified in groundwater samples collected from monitoring well MW-1- Dissolved gasoline hydrocarbons were not detected in ground-water samples collected from the remaining wells (RESNA, June 26, 1992, Report No. 30004-6). • GROUND WATER MONITORING A technician from Emcon visited the site on December 4, 1992, to take water-level measurements and collect groundwater samples from monitoring wells MW-1 through MW- 4 for subjective and laboratory analyses. The field methods and procedures used are presented in an attachment to this report. The technician did not observe floating product or product sheen on samples collected from the wells (Table 1). The surveyed elevations of the top of casing and the depth-to-groundwater measurements (summarized in Table 1) were used to evaluate the potentiometric surface beneath the site. On December 4, 1992, the direction of ground-water flow was southeast with a gradient of approximately 0.004 (Plate 3). The direction of ground-water flow has generally been southeast since our investigation began. The ground-water surface has risen an average of 1.00 foot since the last monitoring event. • Ground-water samples from each well were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using Environmental Protection Agency Method 5030/8020/DHS/LUFT Method. The samples were analyzed at Columbia Analytical Services, Inc. in San Jose, California (Hazardous Waste Testing Laboratory Certificate No. 1426). The results of these analyses are summarized in Table 1. Copies of the laboratory analysis reports are attached. Results of analyses indicated TPHg and BTEX concentrations were below laboratory detection limits in ground-water samples collected from wells MW-2, MW-3, and MW-4. TPHg and benzene were detected at concentrations of 150 and 7.0 parts per billion (ppb), respectively, in the ground-water sample collected from well MW-1. Concentrations-of benzene and TPHg are shown on Plate 2. WORK IN PROGRESS RESNA is currently conducting an additional onsite investigation to evaluate the extent of hydrocarbons in soil and to assess the ground-water quality directly downgradient of the underground fuel storage tanks. i 011&car 30004-6 2