ARCHIVED REPORTS_XR0003923 - Laserfiche WebLink

Home Browse Search

THIRD QUARTER, 1998 GROUNDWATER MONITORING REPORT USA STATION#65-LODI AUGUST, 1998 2.3 Local Hydrogeology Groundwater elevations in S-1 and S-2 were approximately 1-foot below MSL when the wells were drilled in 1987. By September, 1991, the water level elevations had dropped to approximately 13-feet below MSL. Groundwater elevations have since recovered to 1987 levels or higher. The direction of groundwater flow and magnitude of the hydraulic gradient across the site have remained relatively consistent, flowing southerly at a gradient between 0.002 and 0.004- feet/feet(ft/ft). Water level records are summarized in Table 1. 2.4 Summary of Previous Investigations A limited site investigation completed in March, 1987 detected petroleum hydrocarbon compounds in the soil and groundwater beneath the site. The investigation included the drilling and sampling of four soil borings, two of which were completed as groundwater monitoring wells (S-1 and S-2). In August, 1987, Applied Geosystems installed three additional groundwater monitoring wells (MW-1, MW-2 and MW-3). USA requested that Applied Geosystems complete four additional monitoring wells(MW-4, MW-5, MW-6, and MW-7) in the downgradient direction to further define the lateral extent of the impacted groundwater. Applied Geosystems then prepared a Problem Assessment Report (PAR) after completing monitoring wells MW-6 and MW-7. The PAR concluded that petroleum hydrocarbon impacted water had migrated beyond the-property boundaries, and that the groundwater in the upper aquifer, above 42-feet below ground surface (bgs), was not in hydraulic continuity with the deeper aquifers. It was their opinion that further delineation of the impacted soil and water was not required. - - On February 8, 1993, Western Geo-Engineers (WEGE) completed monitoring well MW-8 to a depth of approximately 60-feet bgs. The well is approximately 8-feet downgradient and southeast of the tank field. On March 14, 1995, WEGE completed a one day vapor extraction treatability test, using monitoring wells MW4, MW8, S-1 and S-2. Test results are summarized in the WEGE report ----"Results of Pilot'Test for Vapor Extraction , dated April 17, 1995. USA retained The Park Corporation(Park)to prepare a Remedial Action Plan (RAP). The rationale and design of the necessary environmental remediation and sampling activities at the site were-presented in-Park's November-, 1995-RAP-and in a-February28, 1996 letter'to the-County. In July- 1997, GHH was retained to provide environmental monitoring and remediation at the subject site. On October 6, and 7, I997, USA removed and replaced the three existing UST's and product distribution plumbing. USA also removed approximately 500 cubic yards of hydrocarbon impacted soil during the excavation and retrofit activities. 2 Y