ARCHIVED REPORTS XR0010859 - Laserfiche WebLink

Home Browse Search

`... Groundwater occurred at depths of about 8-to 10-feet and rose slightly in the uncased boreholes, suggesting the aquifer strata are unconfined to weakly confined. A northwesterly groundwater flow direction was plotted from the monitoring well data under a gradient of 0.008 (see Figures 1 and 2). Regional lithologic lateral and vertical variation are present in the shallow aquifer strata and underlying confining (aquitard) strata, which are typical for river and floodplain deposits in this portion of the San Joaquin Valley (see Geologic Cross Section, Figure 2). While lateral and vertical variations are present in the aquifer strata, these strata as a whole form the uppermost water bearing aquifer (or hydro-) stratigraphy between about 12- to 24-feet in the area explored. These underlying confining strata below 26-feet display some lateral lithologic variation, and were not observed to yield water, although they could be leaky. Nearby Department of Water Resources Drillers (DWR) Log Nos. 145680 (and 219475 for the Water Well) indicate deeper clayey strata underlying the on- site uppermost aquifer (that is, strata between about 15-and 25-feet deep). The clay strata identified in the Water Well log and sampled in B-10 did not yield water, and on the basis of thickness is assumed to have lateral extent beyond the site property. Chemical Analysis Thirteen soil samples, and eight groundwater samples were analyzed at a Chromalab, Inc., a State certified analytical laboratory from the exploratory borings. These samples were tested for the following; Total Petroleum Hydrocarbons as Gasoline (TPHG) and Diesel (TPHD), Benzene (B), Toluene (T), Ethylbenzene (E) and Xylene (X), Methyl- tert-butyl-ether (MTBE) and fuel oxygenates, 1,2 Dichloroethane and Ethylene Dibromide using EPA Methods 3510/8015, 8020, 8240 and 8260. The analyses were run on a "normal" turnaround (five- to ten working days). The results are tabulated and presented in Tables 1 and 2 below. Previous chemical data reported in the May 10 report are presented in Tables 4 and 5 for reference. Discussion March, 2000 Soil and Groundwater Data-Review The initial data revealed that highly degraded contaminants were present in the capillary fringe soil, with the highest groundwater concentrations presumably dissolved in the former tank pits (see Figures 1, 2 and 3). Soil samples from Boring B-1 in and near the former tank pit showed low TPHD and TPHG concentrations with 0.0057 parts per million (ppm) Xylene detected. Boring B-2 showed 83 ppm TPHD with all other contaminants not detected. Only 0.4 ppm TPHD (just over the detection limit) was detected in the deeper underlying confining strata soil sample at B-1. The B-2 underlying �.✓ confining strata sample (also advanced through the former tank pit) showed that contaminants were not detected (see Figure 3). Page 5