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August 11,2000 -5 - 003-7170 Review of the 7.5 Minute Series USGS Topographic Map, indicates that the Delta Mendota Canal is the nearest surface water body approximately 1,500 feet west and south the facility(Figure 1). Several waters 1 wells are located in the vicinity of the site r supply ty (Figure 3). Existing industrial and agricultural water wells in the area draw water from lower aquifers in the 250 feet to 530 feet depth range below the clay layer. There are no known municipal,industrial, and agricultural wells producing water in the uppermost aquifer because of its limited thickness and yield(Nolte, 1994). 2.2 Site Hydrogeologic Setting As described above the site is underlain by fine grained sediments derived from the adjacent hills and colluvium. The previous investigations completed by Nolte identified the presence of clayey gravel and silty sand overlying a 100 foot thick layer of stiff, silty clay from a depth of 70 feet to 170 feet. The uppermost ground water zone at the Owens-Brockway site was reported to occur above the clay layer with a depth to the top of the clay layer of approximately 70 feet. Previous water level data for ` the site indicates that depth to ground water ranges from 46 to 70 feet and ground water flow is towards the northeast(Figure 2). Depth to ground water reported during previous monitoring events indicates water levels are in general declining. Ground water levels reported for the most recent monitoring event conducted in June 2000 ranged from approximately 49 feet below ground surface (ft bgs) to 59 ft bgs. Historical water level measurements are presented in Table 2. Analyses that have been performed to date include tests of standard mineral, inorganic and organic parameters. Samples were collected from the onsite water supply well in July 1994 and July 2000 and the results are presented in Table 3. Samples were collected from the process ponds in July 1994 and June 2000 are presented in Tables 4 and 5. The results of the analyses performed on ground water samples collected from onsite monitoring wells in June 1995, August 1996, June 1998, September 1999,and June 2000 are presented in Tables 6 and 7. Representative samples from the onsite monitoring and water supply wells were collected in June and ` July 2000, for an evaluation of existing ground water quality. 2.3 General Mineral Quality Ground water at the site is, in general, poor in quality. Based on the results collected to date, no primary drinking water standards have been exceeded but a number of secondary drinking water standards have been surpassed including the onsite water supply well and upgradient well MW-2. TDS concentrations exceed the recommended upper limit secondary MCL of 1,000 mg/l at virtually every location sampled. In addition, secondary MCLS for chloride, iron, manganese, and sulfate are exceeded in both upgradient wells (MW-2) and downgradient wells MW-3 and MW4. The hardness .. of ground waters ranges from hard to very hard and the pH from nearly neutral to slightly alkaline (MW-2). ` The composition of the waters have been represented by a trilinear plotting technique (Piper, 1944) and stiff diagrams. Graphical representation of the analytical results for samples collected in June and July 2000 is presented in Figures 4 and 5. These procedures consider only the major dissolved ionic constituents in milliequivalents per liter. Potassium and sodium are lumped together as are nitrate with chloride. The values are expressed as percentages of the total milliequivalents per liter of cations and anions. The composition of the waters can then be closely approximated in terms of three anionic and three cationic species. Simple inspection of the resulting ion percentages, in conjunction with the TDS `- Roo-37 d« Golder Associates