FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

' • Kennedy/Jenks Consultants ' Section 3: Groundwater Quality This section describes hydrogeology and groundwater quality in the reclamation area near Jepsen Webb Ranch and Valley View Thoroughbred Farm. Groundwater quality data from the surrounding area and sample data from wells near the two reclamation properties was used to ' construct isoconcentration contours, which allowed analysis of regional total dissolved solids (TDS) concentrations. ' 3.1 Regional Hydrogeology The Jepsen Webb Ranch and Valley View Thoroughbred Farm properties are approximately 2.5 miles to the north-northeast of the Lawrence Livermore National Laboratory Site 300 (LLNL Site 300) and approximately 4 miles southwest of the City of Tracy. ' 3.1.1 Site 300 Site 300 is generally underlain by gently dipping sedimentary bedrock dissected by steep ' ravines. The bedrock is made up primarily of interbedded sandstone, siltstone, and claystone. Most groundwater occurs in the Neroly Formation upper and lower blue sandstone aquifers. Significant groundwater is also locally present in permeable Quaternary alluvium valley fill. ' Much less groundwater is present within perched aquifers in the unnamed Pliocene nonmarine unit. Perched aquifers contain unconfined water separated from an underlying main body of water by impermeable layers; normally they are discontinuous and highly localized. According to ' information from LLNL, these perched water-bearing zones do not meet the RWQCB criteria for aquifers that are potential water supplies because water quality generally is poor and yields are low. t Fine-grained siltstone and claystone interbeds may confine the groundwater and act as aquitards, confining layers, or perching horizons. Groundwater is present under confined conditions in parts of the deeper bedrock aquifers but is generally unconfined elsewhere. Groundwater flow in most aquifers follows the attitude of the bedrock. In the northwest part of Site 300, groundwater in bedrock generally flows northeast except where it is locally influenced by the geometry of alluvium-filled ravines. In the southern half of Site 300, groundwater in bedrock flows roughly south-southeast, approximately coincident with the attitude of bedrock strata. The groundwater gradient data is based primarily on water levels measured in the Neroly lower blue sandstone aquifer. (LLNL, 2001) ' The thick Neroly lower blue sandstone, which is stratigraphically near the base of the formation, generally contains confined water. Wells located in the southeast edge of Site 300 are completed in this aquifer and are used to supply drinking and process water. (LLNL, 2001) In the area of Site 300, recharge occurs predominantly in locations where saturated alluvial fill is in contact with underlying permeable bedrock in the uplands, or where permeable bedrock strata crop out because of structure or topography. Local recharge mostly occurs on hilltops, creating some perched water-bearing zones. Low rainfall, high evapotranspiration, steep topography, and intervening aquitards generally preclude direct vertical recharge of the bedrock aquifers (LLNL, 2001). Reclamation Report, Page 5 Musco Family Olive Company g 4s,roupMnlb!DUTlm ldmaWw lq� AIB.12.M.dM