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x_ 7IV. CONCLUSIONS AND RECOMMENDATIONS The percolation rates obtained indicate an acceptable soil permeability for the shallow(42 inches) and deep (23 ft) percolation test borings. Effluent management, and therefore design criteria should be based on the permeability of the soil eventually reaching a long term application rate (LTAR) of approximately 0.5 gals/ft2/day due to biomat formation. Several scientific studies have shown that the infiltration capacity of a soil absorption system is dependant primarily by the formation of the biomat and not by the permeability of the soil. The biomat is a biological, slimy substance which forms on the soil-effluent interface over time. Considering four square feet of infiltration surface (2 sq ft on each sidewall, excluding the floor of the leachline) for each leachline: 4 sq ft/ft x 100 ft=400 sq ft x 4 leachlines — 1,600 sq ft leachline infiltrative surface+651 sq ft seepage pit infiltrative surface=2,251 total sq ft 2,251 sq ft x 0.5 gals/ft2/day = 1,126 gals/day. The highest wastewater flow from the chart on Page 7 will be May through June at 1,020 gallons/day. Therefore, adequate infiltration surface area exists for the heaviest projected flows. In addition, the new septic system can "rest and rehabilitate" during October through January of each year when there will be minimal wastewater flow. From the chemical analytical test results, it appears that there is denitrification occurring from the 25-ft depth to the 45-ft depth. At 25 ft below grade, the soil nitrate-nitrogen concentration was S ppm and at 45 ft, the nitrate-nitrogen concentration was 3 ppm. Leachline and seepage pit installation must include scarification of the floors and sidewalls of the F leachline trenches and sidewalls of the seepage pits, at the proper moisture content of soil. The soil cannot be too wet or too dry. The subject property and surrounding land has been farmed for more than 50 years. From the well water test results and hydraulic conductivity determination, impact to the underlying groundwater has apparently occurred. Although three seepage pits have been determined through the calculations, a fourth pit may be f installed at the end of the fourth leachline, to be considered as a safety factor. The application of nitrogen fertilizer to the walnuts by Mr. Foppiano is the correct amount, and by split applications, reduces the potential for nitrate leaching. This was evident by the analytical test results illustrating the surface soils (0-6")possess a nitrate-nitrogen concentration of 10 ppm. At 5 ft below the surface,the nitrate-nitrogen concentration was 4 ppm. It is our understanding that during the asparagus season, wash wastewater from the washing process will be pumped from the detention f pond and used as.irrigation water. This water will be analyzed for nitrogen(TKN and nitrate- nitrogen) concentrations so that potential adjustments can be made to the fertilization program. The number of people at the subject site is anticipated to exceed 23 2eoplei da s ear dear. Therefore, the on-site water supply will be considered a public water supply and must meet the regulations of the San Joaquin County Environmental Health Department. f 11 Valfey Ag Research