ARCHIVED REPORTS_REVISED DRYWELL CLOSURE AND INVESTIGATION WORK PLAN

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NOA Drywell Closure and Investigation Work Plan Page 3 of 16 March 18, 2014 Revised March 20, 2014 2.3 Facility History and Current Operations The two (2) on-site drywells were installed in January, 2004 to dispose of water from a Fog Curing Concrete system. This curing method involves a sprinkler system that frequently applies a fine fog mist to keep concrete samples moist inside of a closed, high humidity Concrete Cure Room. The water in the Concrete Cure Room is drained into the two (2) exterior drywells, located two and one-half (2.5) east of the eastern Concrete Cure Room wall. The Concrete Cure Room floor drain is located in the northeast corner of the room. This circular 5-inch diameter drain extends 17 inches below ground surface (bgs) beneath the building foundation and runs due east approximately six (6) feet, emptying into the two (2) drywells. The drywell 1 casing is five (5) inches in diameter, surrounded by eight (8) inch gravel packs. The depth of casing of the drywells is forty (40) feet bgs, the total drilled depths are approximately fifty (50) feet bgs. 2.4 Physical Setting ' Based on a review of the United States Geological Survey (USGS) 7.5-Minute Topographic Series, Lodi North, California Quadrangle Map (2012), the Site lies at an approximate elevation of 50 feet above mean sea level (MSL) in a relatively flat region, see Plate 4. 2.5 Geologic Conditions The Site geologic conditions were obtained from the Department of Conservation, the United States Geological Survey (USGS), the California Geological Survey (CGS), and the UC Davis Online Soil Survey. 2.5.1 Reoional Geology The subject property is located in the Great Valley Geomorphic Province. The Great Valley is an alluvial plain in the central region of California, approximately 50 miles wide and 400 miles long. Sediments have been deposited almost continuously into the Great Valley trough since the Jurassic. To the west the Great Valley sedimentary rocks overlie the Franciscan Assemblage of the Coast Range Geomorphic Province and to the east onlap onto the granitic rocks of the Sierra Nevada Geomorphic Province.'. The surficial geology of the Site is composed of Pleistocene age arkosic alluvium forming the Mokelumne River alluvial fang. The sediments are chiefly sand. Atwater (1982)3 describes the surficial geology of the subject property as consisting of ' Pleistocene age loose sand eolian deposits, loose sand and silt fluvial deposits, and compact silt and very fine sand (Qm) of the Modesto Formation. California Geologic Survey, 2002,California Geomorphic Provinces, Note 36 z Marchand, D.E.and Atwater, B.F., 1979, Preliminary Geologic Map Showing Quaternary Deposits of the Lodi Quadrangle,California; USGS Open-File Report 79-933, scale 1:62,500 ' 3 Atwater, B.F., 1982, Geologic Maps of the Sacrament-San Joaquin Delta,California, Lodi South. USGS Miscellaneous Field Studies Map MF-1401,Scale 1:24,000 902 Industrial Way•Lodi,CA 95240-209.367.3701 •Fax 209.369.4228 ®2014 Neil O.Anderson&Associates,Inc