WORK PLANS - Laserfiche WebLink

Home Browse Search

underlain by sand and silty sand. A stratum of varying silt and clay content occurs frorn depths of about 25 to 30 .feet that in turn is underlain by sandy strata. Sand, silt and clay strata may occur contained within any of the aforementioned strata(see Figures 1, 2, 3 and 4). Stained soil and petroleum vapor was observed in B-8,B-10,B-11,B-127 MW-1, MW-2, andMW-3. Groundwater occurs at depths of about 14 to 15 feet and appeased to be'Kunconfined. Contaminant stain and vapor was observed in B-8, B-10, B=1.1 and B-1.2, and sheen and separate phase product was present in the water at B-1 I and :B-12 and MW-1. Groundwater monitoring wells were installed to depths of 25 feet at the approved locations. A groundwater contour elevation flow plot is presented in.Figure 5. Groundwater was plotted flowing to the north and northeast at a calculated gradient of 0.001 Table I. Monitoring Well Groundwater Data,February 12,x001 Monitoring Depth to Groundwater Top of Casing Groundwater Comments Well Number from Top of.Casi.n 13 Elevation(ft Elevation ft i Mw-1 14.23 57.77 I 43.54 Sheen on water MW72 14.50 57.98 43.48 Sheen on water M.W-3 t4.3'1 57.31 43.00 None MWA 14,56 58.48 43.92 None Monitoring Wetl Casing elevations surveyed to NGVD by City of Tracy. 10.0 results and Discussion Previous subsurface data from the 2003 study showed petroleum contaminants in the arca of the former-tank pit and north of the.Boyd office building (Borings B-1 through. B-6). What was analyzed as "bunker oil" was present in. those borings. The dissolved groundwater data Iron) 2003 and 2008 is plotted on Figure I; on the basis of that data contaminant plume appeared to 1 have moved north from the tank pit. MTBE was observed at B-3 at the UST pit and at B-5 north of the office building, ":Bunker oil" was observed at B-1, 13-2, B-3, B-5 and B-6. The occurrence of the "buriker oil" appeared anomalous since "bunker oil" had not been stored in USTs, and initially attributed to historic railroad use of the property. 10.1 GeoProbe Soil and Groundwater Data GeoProbe data showed TPED was detected in soil with the highest concentrations Between 440 to 7,400 .milligrams per kilogram (Mg/kg) in Borings B-8; B-1.0, :13-11 and B-1.2. ` PHG was detected in soil with the highest. concentrations between 4.8 to 330 indligratns per kilogram (Mg/kg) in Borings B-8, B-10, B-1.1 and B-12. The highest eoncentrations of TPHG and TPHD appeared to occur near the capillary fringe/ first occurrence of groundwater BTEX, MTBE and related fuel oxygenates were not detected in the soil samples (see Figures 2 through 7 and Tables 2, 3 and 4). Page 7 of 14