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' Nitrate Loading Study Irerracon Arriaga Property Stockton, California April 26, 2019 e� Terracon Project No. NA187059 Hollenbeck silty clay soils are located on the southern portion of the site and consist of moderately well drained soils with 0 to 2 percent slopes. The soils between 36 and 42 inches are fine to medium grained. The rate of water in-take in irrigated areas is anticipated at 0.1 inches per hour. For homesite development with septic tank absorption fields, the main limitations are slow permeability, low strength, and shrink swell potential. Due to the presence of cemented soils "hardpan"and slow permeability, water may briefly perch above the hardpan. For sites with septic systems, permeability can be improved by increasing the size of the absorption field, backfilling leach field trenches with sandy material, and installing long absorption lines. Jacktone clay soils are located on the northern portion of the site and consist of somewhat poorly drained soils with 0 to 2 percent slopes. The soils between 36 and 42 inches are fine to medium grained with slow permeability and slow runoff. The rate of water in-take in irrigated areas is anticipated at 0.1 inches per hour. For homesite development with septic tank absorption fields, the main limitations are slow permeability, low strength, high shrink swell potential and depth to hardpan. Due to the presence of hardpan, water may briefly perch above the hardpan. For sites with septic systems, permeability can be improved ripping the hardpan and increasing the size of the absorption field. Based on a review of the USDA soil map, the existing and proposed leachfields are anticipated to be located within the Jacktone clay soil type. Terracon searched the Department of Water Resources online Well Completion Records for additional information regarding soil lithology up to one mile of the site. The following two water supply wells were identified nearest the site. Well Number Latitude Longitude Depth Approximate Distance/Direction from Site WCR2013-001185 37.905833 -121.151667 260.00 3,400 feet/East-southeast WCR2016-010767 37.905000 -121.146389 500.00 5,000 feet/East-southeast Based on a review of the Well Completion records, the soils within the vadose zone (80 to 120 feet bgs) are comprised of alternating sand and/or clay strata which extend to depths of 500 feet bgs. Copies of the Well Completion records are included in Appendix D. Boring logs were not identified for the onsite groundwater well. Refer to Section 2.1 for further discussion regarding regional groundwater information. The longer effluent remains near the surface, the more treatment is enhanced due to natural processes within the soil. Layered soils and sediments such as some fine to medium grained soils anticipated on the site typically provide a degree of protection between percolating effluent at the surface and groundwater aquifers. Based on the clay and/or cemented soils anticipated on the site, the leaching potential to groundwaterfrom sewage effluent or other surface contaminants appears low. 2.0 GROUNDWATER ANALYSIS 2.1 Regional Groundwater Responsive a Resourceful im Reliable 4