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River, as well as lacustrine and marsh deposits. The underlying Cretaceous and possibly Upper Jurassic sediments were deposited in marine environments. Fresh groundwater occurs principally in continental deposits of Late Tertiary to Recent age that extends to depths ranging from a few hundred feet to more than 3,000 feet (Calif. Groundwater Bull. 118, 2006). The base of the main fresh-water body beneath the area of the site is at an approximate depth of 1,400 feet below mean sea level. Water supply wells in the City of Tracy are completed to 44 and 665 feet (average at 188 feet), suggesting the water supply aquifers are Tertiary to Recent age. Recharge of the aquifers is by infiltration from rainfall, streams, lakes, canals, ditches, and irrigation water. 1.3 Site Geology and Hydrogeology Historical field investigation data revealed that subsurface soils at the subject property consist mainly of sandy gravels and gravelly sands. The groundwater table depth is more than 100 feet bgs. Historical geological cross-sections are - o,/o 0C) attached in Appendix A. During the 2004 and 2005 groundwater monitoring events, groundwater was observed to flow north-northeast at an approximate gradient of 0.0033 ft/ft, except during Q2 2005, when standing water in each well fell approximately 8 feet and the gradient changed to approximately 0.0058 ft/ft. During the 2009 and 2010 groundwater monitoring events, groundwater appeared to flow northeast. 1.4 Existing Site Wells The following table summarizes screening intervals for existing site wells: Total Well Screen Depth to Depth to Installed Depth (feet Interval (feet Sand pack Groundwater Wells toc) bgs) (feet bgs) Sept 23, 2010 (feet toc) MW-4 140 120- 140 118 126.97 MW-5 140 120- 140 118 127.57 ._ MW-6 140 120- 140 118 NS MW-7 140 120- 140 118 126.73 MW-8 1 140 1 120- 140 118 127.41 These wells were more recently monitored by SOMA in September 2013 based on the request from CEMEX environmental staff. Workplan for Decommissioning Monitoring Well MW-4 2 SOMA Environmental Engineering, Inc.