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06/16/01 THU, 16:a4 FAX 2004 <br /> k4 klcl :NFELt3FK <br /> NITiA-A,TE LOADING CALCULA'f IONS <br /> For new developments,the San Joaquin! County Public Health Services Department(SJCPHS)of <br /> the Environmental Health Division requires a study to evaluate if discharge from an on-site <br /> sewage disposal system at the property could load or increase the nitrate levels in groundwater <br /> above the state drinking water R4CL standard. As you may be aware, the drinking water MCL <br /> standard for nitrate as NO3 is 45 mg/1 and for nitrate.-nitrogen as N is 10 nig/1. For the purpose of <br /> our evaluation,we have relied upon the application of an equation intended to predict the level of <br /> nitrate in groundwater often referred to as the Hantzsche mass balance equation` that is presented <br /> below with an explanation for each factor and the values used in our study. <br /> 11 + <br /> .AW+r <br /> Where: <br /> N, = Average calculated nitrate-nitrogen (N) in groundwater resulting from domestic sources and <br /> precipitation—mg/l,as N <br /> A — Number of dwelling units per acre on septic tanks(unit/acre)=0.30 <br /> W = Annual wastewater loading per dwelling unit per acre (inches) = 1.75 inches (based on 80 <br /> gallons/day) <br /> Na, = Nitrate concentration of nitrified leachfield effluent(mg/1)= 35 to 45 mg/1 typical (Hantzsche <br /> and Finnemore(1992)) <br /> D = Percent dentrification of leachfield effluent = 0.1 to 025 percent typical per Hantzsche and <br /> Finnemore(1992). 0.1 selected given t'tie sand soil conditions. <br /> T = Annual deep percolation of precipitation (inches) = 3 inches (used by Mr. Hantzsche in idle <br /> Stockton area to reflect the sandy sail conditions anticipated at percolation depths for the <br /> !each t;enches) <br /> Ni ,,, = Background nitrate-nitrogen concentration(N)of rainfall recharge at the water table—mg/1= <br /> 1.0 mg/1(per Hantzsche and Finnemore(1992)the nitrate-nitrogen loading,Nb,typically falls <br /> in the range of 0.5 to 1.0 mg/1) <br /> For the purpose of our analysis, we have assumed that each of the four employees will generate <br /> approximately 20 gallons per person per day of wastewater (SO gallons total or approximately <br /> equal to one-half a residence). The property encompasses approximately 1.68 acres; therefore <br /> the `A' factor would equal 1).5 dwelling units divided by 1.68 acres or 0.30. <br /> Our calculation is as follows: <br /> Low Estimate <br /> Nc _ 0.3(1.75)(35)(! —0.1)+1.0(3) = 16.5 +3.0 = 5.52 mg/1 as <br /> 0.3(1.75) +3 0.53+3 N <br /> Hantzsche N., Finnemore J (1992), Predicting Grolinrl-Wnwr Nitrata Ivitrogrn Nparts, <br /> Ground TYwer, l-'al_ 30, AT6.4 <br /> 20-4630-0].GO 1/2011 R986 page 3 of 5 <br /> Copyright 2001 Kleinfelder,Inc. August 16,2001 <br />