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L M KLEINFELDER L NW = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/1. (Considered L conservative. In August 2003, Chesney Consulting obtained a sample of sewage from the existing septic tank for laboratory testing. The results of the testing indicated a total nitrogen concentration of 9.2 mg/l, with approximately 70 percent of the nitrogen present in the existing septic tank effluent as ammonium-nitrogen 6- with organic nitrogen making up the remainder. A copy of the test results is attached (Plate 19). The Hantzsche and Finnemore (1992) technical paper indicates that the average total nitrogen concentration in septic tank effluent ranges form 35 to 6. 45 mg/l. This range was also reported in the 1996 Dames and Moore technical memorandum.) D = Percent dentrification of leachfield effluent = 30 percent (10 to 35 percent typical per Hantzsche and Finnemore (1992). The 30 percent value was selected given groundwater in the project area is fairly deep and that the soils are interbedded with ` clay strata that would inhibit or slow infiltration to groundwater.) �. R = Annual deep percolation of precipitation (inches) = 10.5 inches (representing 70 percent of average annual rainfall of approximately 15 inches in project area. Remaining 30 percent of rainfall is assumed to drain off-site into natural or ` manmade drainages.) Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table - 0.5 mg/L(per Dames and More technical memorandum, page 6 (1996) Our calculation for Phase 1 is as follows: N, = 2.01(2)(35)(1 -0.3) + 0.5(10.5) = 98.49 + 5.25 = 7.15 mg/L as N 2.01(2) + 10.5 4.02 + 10.5 Our calculation for Phase 2 is as follows: Ne = 3.07(2)(35)(1 -0.3)+0.5(10.5) = 150.43 + 5.25 = 9.36 mg/L as N 3.07(2) + 10.5 6.14+ 10.5 S. CONCLUSIONS r,. The results of our soil classification boring and soil suitability tests indicate that a stratum of silty sand underlies the new leach field area from a depth of about 18.5 to 24 feet that exhibits suitable soil percolation characteristics for disposal of waste/septic flow. The overlying shallow clay did not exhibit suitable soil percolation characteristics. Based on our previous experience, intermediate silt and clay encountered will most likely not exhibit suitable soil percolation characteristics. For reference; a suitable soil stratum is defined by S7CEHD as a soil stratum capable of percolating water at a rate of 60 minutes per inch (min/inch) within the ` 40141.GOI/ST04R206 February 24,2004 ©2004 Kleinfelder,Inc. Page 6 of 7