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Table 3-1 <br /> Pro erties of Model Layers <br /> Vertical Resistance to <br /> Thickness Transmissivity Flow from Overlying <br /> Layer (feet) (ft2lda ) Layer (days) <br /> Layer 1 - Shallow A Zone 40 25 . , infinite <br /> to ed by monitoring wells <br /> Layer 2 -Deeper B Zone tapped 40 . 11 691 <br /> by monitoring wells <br /> Layer 3 - Interbedded alluvial 55 2,250 1,000 <br /> sediments between Layer 2 and <br /> deeper zones that are the source <br /> of water for large wells in the <br /> area <br /> Layer 4-Upper portion of 200 4,000 2.5 <br /> principal aquifer <br /> Layer 5 - Lower.portion of 200 4;000 2.5 <br /> principal uifer <br /> The model was calibrated by direct simulation of the monitoring well drawdown that <br /> occurred during _pump testing. Qualitative calibration was assured by comparison of the <br /> calculated groundwater velocity with the actual distance the plume has moved in 25 years or <br /> f so.since the Disco Station closed. <br /> } The model was also used to evaluate the effect of pumping the production wells that tap the <br /> deep aquifers at the Del Monte property. The model forecasts that the Del Monte wells would <br /> have little if any impact on groundwater flow directions in the shallow contaminated zones. <br /> Hydrogeological Observations <br /> Local Geology <br /> Subsurface materials encountered during this phase of the investigation confirmed that the <br /> site is underlain by alluvial sediments. The soil types include clay, silt, sand, and gravel. <br /> Typically, these units are thickly interbedded with one another. The predominant lithologies <br /> are sandy clay and silty sand. Boring logs from this investigation are included in Appendix B. <br /> Geologic logs of the new boreholes reveal that the hydraulically downgradient and <br /> upgradient areas of the study area consist of geologic materials similar to those described <br /> from previous investigations. The upper 50 to 60 feet consist primarily of interbedded sandy <br /> clay and silt. Typically, below 60 feet bgs, there is an increase in the amount of interbedded <br /> 1 sand. Frpm 75 to 81.5 feet bgs, the subsurface stratigraphy is dominated by clayey sand and <br /> sand considerably more permeable than the overlying clayey soil. Drill cuttings from the <br /> sF010030982.poc 3•-14 <br />