ARCHIVED REPORTS XR0001736 - Laserfiche WebLink

Home Browse Search

• Quarterly Ground-Water Monitoring March 8, 1989 Beacon Station No. 1-502, Lodi, California AGS 86091-6 Hazardous Waste Testing Laboratory Certificate No. 153) , and analyzed for total petroleum hydrocarbons (TPH) as gasoline by modified Environmental Protection Avency (EPA) Method 8015 and the purgable hydrocarbon constituents benzene, toluene, C„% ethylbenzene, and total xylene isomers (BTEX) by EPA Method 8020. The results of these and previous laboratory analyses are presented in Table 2 and copies of the laboratory analysis reports are attached to this letter report. The results of the laboratory analyses indicate that the concentrations of benzene, toluene and ethylbenzene in the samples collected from monitoring wells MW-1 and MW-2 have increased since the September 1988 sampling event. The benzene and ethylbenzene concentrations also increased in the sample from well MW-4. An increase in most of these constituents was also evident in the September 1988 sampling event (reported in AGS Report No. 86091-6, dated December 1, 1988) . The benzene concentration in the samples collected from wells MW-1, MW-2 and MW,-4 exceeded the action level recommended for drinking water by the California Department of Health Services. The concentration of total xylene isomers and TPH as gasoline decreased in the samples from wells MW-1 and MW-2 ; however, the concentration of TPH increased in samples from wells MW-3 and MW-4 . BTEX concentrations in samples collected from monitoring wells MW-3 and MW-5 remained below the detection limits of the analytical ~J` methods used. The ground-water gradient across the site was evaluated by combining measurements of the static water level with the relative elevation of the top of the casing in each monitoring well. The relative elevation of the top of the casing in each well was previously evaluated with a Lietz/Sokkisha C3E Automatic Level. The static water levels were adjusted using the top of the casing in well MW-3 as a common datum. These data are summarized in Table 3 , and were used to evaluate the gradient of the static ground-water surface at the time of this quarterly monitoring event (Plate P-3) . The evaluated ground-water gradient was 0.003, and the flow direction was toward the southwest. The orientation of the ground-water gradient is similar to that in previous sampling events; the most recent data, however, show a variation in the magnitude of the gradient across the site. Because hydrocarbon contaminant concentrations in ground-water samples collected from wells MW-1, MW-2, and MW-4 have increased during the last two monitoring events, and benzene concentrations remain above recommended action levels in samples from those T wells, it is the opinion of Applied GeoSystems that active 3