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Attachment D Map and Cross Sections of USDWs Application Requirements Submit maps and cross sections indicating the vertical limits of all underground sources of drinking water within the AOR (both vertical and lateral limits for Class I);their position relative to the injection formation; and the direction of water movement,where known,in every underground source of drinking water that may be affected by the proposed injection. Approach This section focuses on potable groundwater conditions near the STIG-LEC facility. The geologic information contained in Attachment D of the original 1993 permit application has been moved to Attachment F. Geologic and Hydrogeologic Setting Northern San Joaquin County is located in the Central Valley,and is considered the northernmost portion of the San Joaquin Valley. The STIG-LEC facility is located in the portion of the Central Valley referred to as the Sacramento-San Joaquin River Delta (Delta) (Figure D-1). In the Delta,the confluence of the Sacramento and San Joaquin rivers is influenced by tidal action to produce a biologically-rich estuarine environment. Additionally, the Delta has been highly modified by channelization and water diversions for municipal,industrial, and agricultural uses,resulting in a patchwork of islands and tracts surrounded by natural and man-made channels and sloughs. An extensive levee system protects most Delta islands because they are now below sea level as a result of subsidence. Geologic History The Central Valley is underlain by thousands of feet of sediment deposited in shallow marine and continental environments. Beginning during the late Jurassic Period (150 to 175 million years before present),the Central Valley was a large inland sea receiving sediment input both from the rising Sierra Nevada to the east and the Coast Ranges to the west. Influx of sediments occurred from erosion of the surrounding uplands,regional volcanic activity,and marine influences possibly from multiple openings to the ocean. During the Pliocene Epoch (1.8 to 5 million years before present),the inland sea drained through the Carquinez Straits, and the local environment was dominated by brackish and freshwater lakes (Norris and Webb, 1990). The Central Valley is now dominated by a series of rivers that primarily drain the Sierra Nevada, and to a lesser extent,the Coast Ranges.These rivers empty into either the SAC/371322/082550019(ATTACHMENT-D.DOC) D-1