ARCHIVED REPORTS_DRYWELL CLOSURE AND INVESTIGATION

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NOA Drywell Closure and Investigation Page 2 of 26 ' May 30, 2014 to allow for evaluation of the case for closure by EHD or determine the need for remedial 1 action. 1.2 Guidance Documents This well closure and investigation has been prepared in accordance with the EHD approved Drywell Closure and Investigation Work Plan prepared by NOA, dated March 18, 2014, and revised on March 20, 2014, the Environmental Protection Agency Region 9 Guidelines for Closure of Shallow Disposal Wells (1992) and San Joaquin County Environmental Health Department Well & Boring Permit Application Requirements (2012). 2.0 BACKGROUND 2.1 Site Location The subject property is NOA's Lodi Office located at 902 Industrial Way, Lodi, San Joaquin County, California; Assessor's Parcel Number 049-150-120. The site is located in Section 7, Township 3 North, Range 7 East, Mount Diablo Base & Meridian. 2.2 Site Description ' The site consists of a warehouse style building with offices, a large shop that consists of a laboratory, a Fog Curing Concrete Room, a drill supply storage and fabrication shop, and miscellaneous equipment. The eastern section of the Site is a paved parking area and the ' southern portion is equipment, trailer and vehicle storage. The location of the subject property is depicted graphically on the Vicinity and Site Map, see Plate 1, Appendix A. ' There are two (2) drywells located just east of the center of the warehouse/office building. An illustration of the Site that includes the locations of the drywells is presented on Plate 2, Appendix A. ' 2.3 Facility History and Current Operations I 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) feet 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 1 and runs due east approximately six (6) feet, emptying into the two (2) drywells. The drywell casing is four (4) inches in diameter (i.d.), 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. "04 ' 902 Industrial Way• Lodi, CA 95240• 209.367.3701 • Fax 209.333.8303 02014 Neil 0.Anderson&Associates, Inc.