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F73V�aluessumptions: =357,700 gals=total W W/vr=47 821 cu ft =4.24in/yr Ac x 43,560 sq ft/Ac x (1 ft/12 in) Nw=62 mg N/L d = Assume 30%due to very high percentage of fine-grained clay soil. R = 9 in/yr. Nb= Assumed to be 0.1 ppm NO3 N 4.24 in/yr(62 mg N/L) CL-0.30)+(9 in/yr x 0 1 mg/L) Nr = (4.24 in/yr+9 in/yr) Nr = 14 ppm as nitrate-nitrogen(NO3-N) or 62 ppm as nitrate (NO3) The primary and 100%replacement areas must be denoted on the Site Plan and/or septic system installation permit to be drawn for submittal to EHD and other possible County Departments. The proposed septic system operation is as follows: Effluent will gravity flow from the septic tank,travel to a D-box to be equally distributed between perforated piping within a conventional leachfield. A 100% replacement area can easily be accommodated since a walnut orchard surrounds the proposed second unit dwelling. CONCLUSIONS AND RECOMMENDATIONS NLS§4.2. The shallow subsurface soils underlying the subject property where the new leachfield is to be installed, reveals a high clay content soil material with a high degree of denitrification potential. The existing on-site domestic well has a nitrate concentration of 65 mg/L, which is 20 mg/L over the Maximum Contaminant Level(MCL)of 45 mg/L. NLS§4.1. The nitrate loading calculations show the resultant effluent from the entire subject property will theoretically possess a concentration of approximately 14 ppm as nitrate-nitrogen,which is 1.4x over the MCL. Given that the ADF of 980 gpd has two extreme components promulgated by EHD of two people per bedroom, and that this flow volume will occur every single day of any given year, has created a very large nitrate loading safety factor. This factor is conservatively estimated at greater than 2.5. Due to this exceedance of the nitrate loading Maximum Contaminant Level, the EHD requires that the on- site domestic well that will serve the existing house and future pre-manufactured home must be monitored by sampling and testing for nitrate concentration on a yearly basis. Because of the upgradient agricultural production, it will be extremely difficult, if not impossible,to distinguish between human waste nitrogen and fertilizer/organic matter nitrogen influences. However, from the soil test results, it appears the surrounding walnut orchard is carefully fertilized with nitrogen. In addition, Mr. Vink must comply with the Regional Water Board's requirements of completing a Nitrogen Management Plan for his farms every year. Having completed hundreds of these Plans, I can attest to the fact that this method of nitrogen monitoring from agricultural inputs is currently a highly beneficial procedure. Page 6 of 12 Chesney Consulting