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LOGE 1847: Jhamat SS/NLS Addendum Page 2 March 6, 2019 The Hantzsche and Finnemore equation is a conservative approximation of ground- water nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and percolating recharge waters. The equation and method is for estimation of long-term effect ground-water quality, and is not intended for prediction of seasonal changes (Hantzsche and Finnemore, 1992). The method takes into account the development area, soil denitrification factor, rate of recharge from percolating waters, waste effluent quantity, and waste effluent nitrate concentration from on-site septic systems, and predicts the nitrate concentration of percolating effluent. Mass Transport Soil Properties The percolation tests have revealed that the surface soils are moderately permeable. The soil will allow infiltration of water through the surface soils. The longer the effluent remains near the surface, the more biologic treatment may occur. If permeable soils exist to the depth of the ground water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. Sources of Nitrate Dairies, orchards that require fertilization in sandy soils, and septic systems have been found to be the most significant sources of nitrate in ground water in San Joaquin County. Percolating Recharge Waters Background One of the most determinant factors in the Hantzsche and Finnemore equation is the rate of recharge from percolating waters, which mix with the downward-percolating effluent generated by on-site septic systems. In the original Hantzsche and Finnemore paper, only "average recharge rate of rainfall" was considered. For the Chico area, Hantzsche and Finnemore present an average rainfall of 22.5 inches per year and an estimated recharge of 16.8 inches per year; the recharge value is 75 percent of the average rainfall. The source of the recharge value is not cited in the paper. Since the 1992 publication of the Hantzsche and Finnemore paper, numerous consultants have attempted to apply the method to calculate nitrate loading rates of projects and developments. Most notably, the City of Chico has continued to use the method to calculate desired urban density (County of Butte, 2000). In a 1996 technical memorandum published to support Chico's urban density requirements, the consulting firm Dames and Moore has discussed that "recharge ... is comprised of two major components: applied water ... and precipitation and streams."