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KLEINFELDER File No. 20-2983-03' october 26, 1990 .1 . prepared b Jahn in' their letter, dated October 24 , 1990, prep y Quinn, 1 laboratory director for FGL, the tests were rerun with the same results. Finally, the samples were spiked with a known amount of nitrate. Tests on these samples confirmed the elevated levels of y II nitrate. The samples were then allowed to stand 3 days at which k time considerably lower nitrate levels were measured. The tests IF ' destroyed and incorporated into verified that nitrate is being septic biomass, according to FGL. To be conservative and somewhat . , in line with the lower limits of published information, we have used in our study a Nw value of 30 mg/l. s � Percent Denitrification of Leach Field Affluent According to Reference No. 4 denitrifying bacteria require a source + of carbon for energy. Therefore, denitrification usually occurs where organic matter is abundant, such as directly beneath the trench beds. In the study by the CRWQCB, deep sandy and well drained soils with low organic matter content were described as having negligible denitrification potential. Sandy loam soils are described as having a medium denitrification potential (10 to 20 I percent N loss) while finer textured soil such as silts and clays have high potential for denitrification in the range of 20 to 40 percent. Reference is made to the test borings included with this report for our previous studies in the area. These test borings i generally indicate fine grained materials to the depth explored. For this reason, we have used for D a value of 35 percent. k Annual Deep Percolation of Precipitation i According to the National Weather Service, the 15 year rainfall average for this area is on the order of 10 inches. We note that i in the "Hantzche" equation the greater r the lower Nc. For this reason we have conservatively neglected any landscape watering or Copyright 1990 Kleinfelder, Inc. 5