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Nw = 35 mg N/L. From the value used in the LiveOak Study. d = 45%. From the soil texture test results of 46.3% clay soil at 12 ft below grade referenced above. R = 6.39 in/yr as derived above. Nb = Assumed to be 0.1 ppm NO3-N 5.6 in/yr (35 mg N/L) (1 - 0.45)+6.39 in x 0.1 m Nr = (5.6 in/yr + 6.39 ac -ft) Nr = 9.1 ppm as nitrate -nitrogen (NO3-N); 40.3 ppm as nitrate. ONSITE WASTEWATER TREATMENT SYSTEM: OPERATIONAL COMPONENTS AND PARAMETERS The Site Plans found in Appendix B, illustrate the effluent disposal structure to serve the ADU to be a 20 ft x 40 ft = 800 sf filter bed. Per EHD requirements, a filter bed for a two-bedroom structure in this locale should be 880 sf. Therefore, an additional 6 ft x 13.5 ft = 81 sf of filter bed area should be extended at the NEC of the primary filter bed, and the NWC of the 100% replacement area, as illustrated on the Site Plans. CONCLUSIONS AND RECOMMENDATIONS The exploratory test boring reveals a clay stratum at the 12 ft depth under the proposed filter bed. This clay content is significant enough to promote denitrification to 45%, as has been observed in many projects throughout San Joaquin County. Percolation testing of this stratum reveals a very slow perc rate of 125 min/in, thus promoting anaerobic conditions and therefore, denitrification. The Net Rainfall Recharge was changed from the value used in the LiveOak Study of 2.67 in/yr to 6.39 in/yr and based upon the scientific parameters presented above and accepted by the EHD for project SR0082464/65. Regarding the nitrate mitigation benefits of installing a larger tank, wastewater researchers place the nitrogen reduction occurring in septic tanks at 10% to 20%. From the September 2004 Symposium "University Curriculum Development for Decentralized Wastewater Management - Onsite Nitrogen Removal," Dr. Stuart Oakley of California State University Chico states that "approximately 20% of the total nitrogen generated is removed in the septic tank" (Ref. 4). If Dr. Oakley's premise of an approximate 20% nitrogen removal occurs in septic tanks, then if the tank size is increased a specific percentage from a baseline size, then it is reasonable to assume that the percentage increase in tank size will remove that percentage of nitrogen above the 20% baseline. This nitrogen removal occurs from anaerobic digestion of organic material and scheduled tank pumping. Therefore, increasing the tank size for this project from the required 1,200 gallon to 1,600 gallon is a 33% increase in capacity, thus substantiating a 33% increase above this 20% N reduction: 20% + (20 x 0.33) = 27% decrease in nitrogen concentrations by installing a 1,600 gallon tank in lieu of a 1,200 gallon tank. Therefore, it is recommended to install a 1,600 gallon septic tank, which should theoretically lower the nitrate loading from 9.1 ppm NO3-N to 6.6 ppm NO3-N. Page -4- Chesney Consulting