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i Fo� RODUCTION Consulting has been retained by Mr. Don Lawley to complete the requirements of the San ounty Environmental Health Department(EHD) for property he owns, or has an interest in,near the southeast area of Stockton. The Environmental Health Department has been at the forefront of nitrate impact investigations and the prevention or mitigation of environmental contamination from various sources of nitrate, particularly septic systems. EHD requires these investigations and corresponding septic system operational criteria under Community Development Title 9-1105.2 (d) for projects in unsewered areas, in areas currently impacted with nitrate, or for projects that may potentially impact the underlying groundwater with nitrate. The EHD's main concerns regarding this project are 1.) The current environmental condition of the soil and groundwater under the property, 2.)Nitrate impact that has occurred throughout the study area, 3.)Discussion of mitigation measures through possible future septic system operation to alleviate nitrate impact to the underlying groundwater, 3.) Assurance that sufficient wastewater disposal area exists to accommodate the average daily flow from a proposed septic system, 4.) Assurance that there is sufficient 100%replacement area that will remain designated as such, in the event of system failure, or a need to "rest"the primary disposal area, and 5.)Assurance that the primary disposal field and 100% replacement area comply with the 100-foot rule, as stated in the S.J.C. Sewage Standards Section 8.1,Page 15, in which a sewage disposal area must be 100 feet from a non-publicly operated domestic well. In addition, the EHD has specified that if commercial development of Parcels APN 179-160-18 and 19 should ever occur, it will be a requirement that public water and sewer serve these two Parcels. A. SUMMARY OF FINDINGS The findings of our study reveal there are highly favorable soil characteristics in the upper surface soil strata where septic effluent may be distributed. These characteristics include a high clay content surface soil that may: 1.) Create anaerobic microsites to prevent nitrification,2.) Nitrification that does occur maybe denitrified during soil saturation, and 3.)Promotion of evapotranspiration because of the microscopic soil porosity. The percolation test results reveal differing penmeabilities apparently attributable to soil compaction from the parking of Mr. Lawley's heavy equipment used in his contracting business. The eastern area --- ----- perc test where heavy equipment was oarked revealed slow erc rates,while the north perc test area w ere no equipment was parked had favorable perc rates. The on-site domestic well that serves Mr. Lawley's house has a comparatively high nitrate concentration at 34 ppm as nitrate. The Maximum Contaminant Level is 45 ppm. This concentration may be attributable to a relatively high density of septic systems in the surrounding area. Page-2- Chesney Consulting