ARCHIVED REPORTS XR0012580 - Laserfiche WebLink

Home Browse Search

NEW ab DU P0111, I3i0SV tCl11S Page 7 August 10, 1989 .lob No.211-71-6 3. On May 28, 1985 monitoring wells MW-8 and MW-9 were installed at the site by IT Corporation to total depths of 53 feet and 55 feet, respectively. Ground water was reportedly encountered at 48 feet during drilling. In addition,monitoring well MW-1 was redrilled and completed with a 38-foot surface seal (the prior surface seal was 4 feet). 4. Early water sample results (April 1985)show that gasoline constituents were detected in the deep monitoring wells(i.e.,MW-1, MW-8,and MW-9). Approximately 4 feet of free product was observed in monitoring well MW-8 (IT Corporation, July 12, 1985). In addition,gasoline constituents were reported in water samples collected from MW-5,MW- 6, and MW-7 (perched water?). Some of the data, however, contains sampling dates which are inconsistent with the well completion dates, thus we consider the April 1985 water sample results questionable. 5. Five additional monitoring wells (MW-10 through MW-14) were. installed at the site between July 9th and August 21st, 1985. These wells were drilled,logged,and completed by The Twining Laboratories, Inc. under the direction of Fox Environmental Services, Inc. Water samples collected from the wells showed that gasoline constituents were detected in all five monitoring wells. 6. On February 17. 1987 gamma-neutron logging was conducted on alb of the monitoring wells by Colorado Well Logging, Inc. under the direction of GMS and Associates. As a result of the well logs,GMS and Associates recommended in a letter dated June 5, 1987, the redrilling and reconstruction of monitoring wells MW-1 and MW-8 wilh the screen interval set at lower depths. In addition, GMS and Associates recommended the destruction of monitoring wells MW-11, MW-12 and MW-13 with the boreholes grouted to the surface. These tasks were conducted in 1987. GMS and Associates later, recommended the destruction and grouting of monitoring well MW-14 (letter dated j` October 13, 1987). r� F REGIONAL GEOLOGIC AND HYDROGEOLOGIC SETTING The Douglas Gas Station site is located in the San Joaquin Valley within the Central Valley physiographic province. A regional geologic map of the Lodi 15-minute quadrangle by Marchand and Atwater (USGS, 1979) shows that the life is underlain by Late-PleistrWeae-age alluvium----- belonging to the Modesto Formation (see the Regional Geologic Map, Figure 3). Marchand and Atwater describe these sediments as consisting primarily of sand with minor gravel and silt. The alluvial deposits are interpreted as alluvial fan and river terrace deposits associated with the nearby Mokelumne River (located approximately 13/4 miles to the north).