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FORMER AMERICAN FOREST_ PRODUCTS 3.0 Groundwater Closure Summary Report July 2009 URS Project 17322736 Page 3-1 3.0 GROUNDWATER 3.1 HYDROGEOLOGY The former AFP site is within the geomorphic province known as the Great Central Valley.This province is characterized by downwarping and subsequent filling with a sedimentary sequence of alluvial sands, silts, clays and gravels eroded from surrounding mountains. The near-surface sediments beneath the site are composed of unconsolidated Quaternary sediments of the Victor Formation and underlying Laguna I Formation. These sediments consist of interfan or flood basin deposits and are heterogenous both laterally and vertically. The lithology of these deposits consists of clays, silts, and fine sands. Boring logs -� (Appendix A) show a preponderance of fine-grained materials containing a minor amount of coarse- grained materials as discontinuous lenses. The fine-grained sediments consist of clays, silty clays, clayey silts,and silts, and the coarse-grained materials consist of silty fine sands and silty fine to medium sands.' As shown in the lithologic cross section(Figure 3),these materials occur predominantly as lenses without strong lateral continuity. Historical groundwater elevation data for the Site are presented in Table 2, and a groundwater elevation contour map for the second quarter 2009 monitoring round is provided as Figure 4. A plot of groundwater elevations versus time for monitoring well DMW-1 is provided on Figure 5. The groundwater,gradient on June 6, 2009, was toward the north-northeast at a gradient magnitude of 0.002 feet per foot. An examination of quarterly groundwater monitoring data collected since the beginning of 2004 shows that the gradient direction has been consistently to the north-northeast for the past three years, at magnitudes ranging from 0.001 to 0.011 feet per foot. The plot of water level elevation versus time for.DMW-1 (Figure 4) shows a response to cycles of wet and dry years,tWatef-leveis`rose-approximately;30-feet_l etween the early,1990s;and,1999,,to mft r surface(bgs)in June 1999.After 1999,the trend reversed and water approximately 35 feet below ground levels declined approximately 15 feet through September of 2004 to about 53 feet bgs. Water levels then rose through March of 2007 to approximately 39 feet bgs,and then began again to drop. In June 20V9 groundwater levels were approximately 46-feet`bgs;�-or an elevation of about-29 feet with respect to mean f- sea level. r Comparing water levels measured in the two deeper wells,DMW-8 and DMW-9,which are screened to r depths of 80 to 90 feet bgs and 60 to 70 feet bgs respectively with water levels measured in the shallower ! 1 wells shows no notable difference. This suggests that there is no vertical gradient between the two depth intervals, and indicates that all of the wells are screened within the same shallow hydrogeologic zone. An examination of lithology in the aquifer's shallow portion where the monitoring wells were completed supports this conclusion, as no continuous aquitard has been identified within the depth range of the ' monitoring wells. 3.2 - GROUNDWATER USE In its 2001 closure request report(URS, 2001),URS presented well survey results, which demonstrated that there were n�o�ezissting-water supply wells.threatenedby.contammants-in groiuidwater7That survey was prepared using sources including the California Division of Water Resources,the State of California Department of Health Services—Public Water Supply Branch,.and the San Joaquin County Flood Control and Water Conservation District.A�total U 7 water-wells excluding monitoring'wells,were identified } KAWprocess%2273&Amencan ForestlClosure-Summary-Report-RmOl.doe f