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and/or Destruction Workplan (Master Well Workplan) shall be submitted to the
<br /> Regional Water Quality Control Board (RWQCB). The purpose of the Master
<br /> Well Workplan is to direct monitoring well installation and destruction activities
<br /> required for future RWERs submitted by the City of Lathrop.
<br /> As required by the WDRs, this Master Well Workplan is consistent with:
<br /> Attachment F to the WDRs "Requirements for Monitoring Well Installation
<br /> ' Workplans and Monitoring Well Installation Reports", California Well Standards
<br /> Bulletin 74-90, and the San Joaquin County Well Standards. Additionally, the
<br /> workplan includes the Sampling and Analysis Plan (SAP) and recommended
<br /> ' quality assurance protocols for continued groundwater monitoring to ensure that
<br /> background water quality is adequately characterized and that potential future
<br /> water quality impacts from the discharge are detected.
<br /> Local Hydrogeologic Conditions
<br /> ' The Lathrop area is located in the basin-trough geologic zone of the San Joaquin
<br /> Valley, which consists of continental Pleistocene and Holocene stream-laid and
<br /> still-water deposits. These deposits are derived from a mixture of Sierra Nevada
<br /> ' and Coast Range rockS2. The near surface deposits are mapped primarily as
<br /> Quaternary alluvial flood plain deposits3. The local depositional environment is a
<br /> sedimentary river basin, and the shallow sediments are primarily flood plain and
<br /> ' over bank deposits of sand, silt and clay. The near surface deposits are
<br /> characterized by discontinuous inter-bedded silty sand, sandy silt, silty clay, clay,
<br /> and sand deposits4. Soils are derived from mixed Sierran and Coast Range
<br /> ' source materials, and are characterized by poor drainages.
<br /> The Lathrop area groundwater basin is comprised of an approximately 150-feet
<br /> ' thick upper water-bearing zone overlying a 75 to 1,000 feet thick lower water-
<br /> bearing zone. The lower water-bearing zone provides a source of drinking water
<br /> to the City of Lathrop. The hydraulic connection between the upper and lower
<br /> ' zones appears limited because they are separated by extensive low permeable
<br /> sediment beds6.
<br /> ' Depth to groundwater varies depending on location, season, and local
<br /> influences. The shallowest groundwater is generally observed adjacent to the
<br /> San Joaquin River, and groundwater depths tend to increase in depth away from
<br /> Jennings, C.W. and Strand, R.G., 1958, "Geologic map of California, Santa Cruz Sheet",
<br /> California Division of Mines and Geology, Sacramento, California.
<br /> ' s Miller, R.E., Green, J.H., Davis, G.H..,1971, U.S. Geological Survey Professional Paper497-E.
<br /> 'Atwater, B. F., 1982, Geologic maps of the Sacramento-San Joaquin Delta, California, US
<br /> Geological Survey Miscellaneous Field Studies Maps, MF-1401.
<br /> 4 Kleinfelder, "Hydrogeology of the Mossdale and Reiter Property, Lathrop, California', November
<br /> 24, 2004.
<br /> e Soil Conservation Service, 1992, Soil Survey of San Joaquin County
<br /> e Page, R.W., 1985, Geology of the fresh groundwater basin of the Central Valley, California, with
<br /> texture maps and sections. U.S. Geological Survey Professional Paper 1401-C.
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