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Dog Kennel Building-Soil Suitability Study Page 7 of 13 Our Project Number: NA157000G June 2,2015 discharge to the septic system. Septic system design should be based on the San Joaquin County On-Site Wastewater Disposal Standards or other engineering recommendations. 4.0 GROUNDWATER INFORMATION 4.1 Groundwater Depth and Gradient In October 2014, Neil O. Anderson & Associates, Inc. performed a geotechnical investigation (NOA Project Number: NA145054) for the site. As part of the geotechnical investigation two exploratory test holes were drilled to depths between 111/2 feet and 16'/2 feet with a truck mounted CME 75 drill rig, utilizing 6-inch continuous (hollow stem) flight auger. Groundwater was not encountered in any of the borings drilled for the investigation therefore, groundwater for the site is determined to be at a greater depth than 161/2 feet bgs. The California Department of Water Resources Groundwater Information Center groundwater depth maps (2013 and 2014) were reviewed to determine the groundwater levels near the site. According to these maps (Plates 3 and 4) groundwater depth was approximately 100 feet below grade surface (bgs) in areas located approximately 2.5 miles east of the site. According to the Department of Water Resources (DWR) Water Data Library', a well located approximately 0.55 miles west of the site had historic depth to groundwater levels ranging from 205.3 feet bgs to 249.6 feet bgs, another well located approximately 0.90 miles east of the site had historic depth to groundwater levels ranging from 156.6 feet bgs to 282.8 feet bgs, and a third well located approximately 2.15 miles northwest of the site had historic groundwater levels ranging from 87.5 feet bgs to 165 feet bgs. Based on the above-mentioned historic groundwater well _ measurements, the groundwater flow gradient has been estimated to have been approximately 0.009 feet per foot to the east-southeast. 4.2 Potential Groundwater Contamination Issues The presence of nitrates is not uncommon in shallow groundwater aquifers in San Joaquin County and other parts of the Central Valley. Nitrate in groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates in the shallow groundwater zones. In the early 1900s, natural levels of nitrate in groundwater were measured in forty-three (43) wells throughout the Sacramento Valley by Kirk Bryan (1923). It was thought that groundwater at that time was close to "natural" conditions. Based on the work by Bryan, it is estimated that under "natural" conditions, groundwater concentration containing nitrate is no more than about ' htto://www.water.ca.gov/waterdatatibrary/ Groundwater level station local well I.D.37711ON1215122WO01 Groundwater level station local well I.D.377293N1215322W001 Groundwater level station local well I.D.377074N1214869W001 1 ©2015 Neil O.Anderson&Associates,Inc.A Terracon Company