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KLE/NFELOER Bright People.Right Solutions. The selection of parameters used in the equation was based on previous studies and investigations performed by our firm and others, San Joaquin County Sewage Standards, and information provided in a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by Mr. Hantzsche for a development in the Stockton area. Average calculated nitrate-nitrogen in groundwater resulting from leach field source Nc and precipitation —mg/l, as N. Volume rate of wastewater entering the soil averaged over the gross developed area I = = 0.26 Inches per year (calculated as follows: ((525 gal/week x 52 weeks/year x 0.1337 cubic ft/gal)/(3.94 acres x 43,560 sq ft/acre)) x 12 inches/ft) Nitrate concentration of nitrified leach-field effluent (mg/1) = 45 mg/I (The Hantzsche and Finnemore (1992) technical paper indicates that the average total nitrogen Nw concentration in septic tank effluent ranges from 35 to 45 mg/l. This range was also reported in the 1996 Dames and Moore technical memorandum.) Fraction of nitrate-nitrogen loss due to dentrification of leach field effluent = 0.10 D = percent (Per Hantzsche and Finnemore (1992), 0.10 to 0.35 is typical). The 0.10 value was selected as a conservative estimate. Average recharge rate of rainfall = 12.2 inches per year (representing 90 percent of the average annual rainfall of approximately 13.6 inches. The average annual rainfall R _ is based on data presented on the National Oceanic and Atmospheric Administration website for the last 70 years in the Stockton Area. The remaining 10 percent of rainfall is assumed to drain off-site into natural or manmade drainages or be lost to evapotranspiration.) Background nitrate nitrogen concentration of rainfall recharge at the water table= 0.5 Nb = mg/I (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico Urban Area, page 6, Dames and Moore, April 1996) Our calculation is as follows: Nc __ 0.26(45)(1-0.10) + 12.2(0.5) = 1.3 mg/I as N (0.26 + 12.2) Given the above factors, we estimate that the proposed septic system would require an average waste/sewage flow of over 7,800 gal./week or more than 74 daily occupants per week in order to exceed the state drinking water standard for nitrogen (N) of 10 mg/I in groundwater. 20210068.001A/ST020R110989 Page 10 of 14 April 30, 2020 ©2020 Kleinfelder www.kleinfelder.com /9 ^b I,