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T WORK PLAN • FOR GROUND WATER WELL INSTALLATION AND MONITORING PORT OF STOCKTON-ROUGH AND READY ISLAND,CALIFORNIA island's eastern boundary, and Burn's Cutoff forms the island's western and southern boundaries. 2.2 REGIONAL SETTING 2.2.1 Development of the Delta Levee System MO-1 is located on Rough and Ready Island, which is part of the Sacramento-San Joaquin Delta (Delta) system. Between the Sacramento and San Joaquin Rivers flowing to the Pacific Ocean, this area forms the West Coast's largest estuary (DWR, 2014). Beginning with the discovery of gold at Sutter's Mill in 1848, the Delta began to be developed, first to accommodate miners, but later to accommodate a growing number of farmers (DWR). In the 1850's Congress passed legislation that allowed reclamation to occur in the marshy Delta (CALFED, 2007). The State Board of Swamp and Overflowed Land was created in 1861 to manage projects funded by the sale of swamp and marsh lands. The management authority was transferred to the local county level in 1866, and by 1871, most of the swamp land was privately owned. In 1873, President Ulysses S. Grant commissioned a study into California's water resources by the U.S. Army Corps of Engineers (DWR, 2014). A State Water Plan was introduced in a 1931 report, which suggested that the Bay-Delta water systems be used to divert northern California's water to southern California (DWR, 2014). Today there are over 1,300 miles of levees that are protected and maintained by the State of California (CALFED, 2007). 2.2.2 Regional Geologic and Hydrogeologic Setting Unconsolidated Deltaic Deposits underlie the island to a depth of approximately 1,500 feet below ground surface (bgs). These Pliocene, Pleistocene, and recently deposited deltaic sediments are comprised of interbedded clay, silt, sand, gravel, and organic soils. The Deltaic Deposits are laterally contiguous with the relatively coarser grained Valley Fill Deposits to the east. The Mehrten Formation underlies the Deltaic Deposits from approximately 1,500 feet to 2,300 feet bgs. The Mehrten Formation was formed in the late Miocene, about 7 to 9 million years ago, and consists of andesitic conglomerate and agglomerate, and interbedded silt, clay, and black sands (CDWR 1956; Piper and Others, 1939). Ground water in the Mehrten Formation underlying the Stockton area is saline and contains natural gas (CDWR, 1955). The Valley Springs Formation underlies the Mehrten Formation from approximately 2,300 feet to 2,800 feet bgs. The Valley Springs Formation was formed in the middle September 2014 2 Environmental Risk Services Corporation