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V ,� In KLEINFELDER NITRATE LOADING CALCULATIONS We have been requested by San Joaquin County PHS/EHD to calculate the nitrate loading for the proposed leach fields in the subdivision. As you are aware, the drinking water standard for nitrate is 45 mg/1 as (NOD and 10 mg/1 as Nitrogen (N). In our evaluation of nitrate loading, we have used the Hantzsche mass balance equation, which is presented below with an explanation for each factor and the value used in our study. Since there is a deed restriction limiting the number of homes on each lot to one, we have used that value (i.e. A=1) in our calculation. The selection of other peramaters was based on previous studies by our firm, as well as the report dated March 19, 1997 by Questa Engineering Corporation and authored by Mr. Norm Hantzsche. Mr. Hantzsche prepared his report for an adjacent subdivision which had similar fine-grained silts and clay soils. For these reasons, we have chosen to use the same values considered appropriate for Mr. Hantzsche for this project, with the exceptions of an increased value for"D," which has been modified based on recent local testing. The equation is as follows: N AW x Nw(1-D)+(Nn)r AW+r Where: Nc = calculated nitrate concentration in groundwater resulting from domestic sources and precipitation —mg/l, as N A = number of dwelling units per acres on septic tanks (unit/acre)= 1 W = annual wastewater loading per dwelling unit per acre (inches) = 2 inches (from Questa Report) Nw = nitrate concentration of nitrified leachfield effluent (mg/1) = 45 mg/l as N (per discussion on September 20, 2001 with EHD, still within the limit recommended by Questa but in the low range to reflect dilution impact of residential flow) D = percent dentrification of leachfield effluent = 0.35 (per discussion on September 20, 2001 with the Environmental Health Division(EHD) r = annual deep percolation of precipitation (inches) = 3.0 inches (based on 13.5 inches precipitation, 2 inches runoff and 8.5 inches ET) Nb = background nitrate concentration of the deep percolating precipitation—mg/l = 2.2 mg/l as N Our calculation is as follows: Ne = 1 (2) x 45 0 -.35) + 2.2 (3) 1(2) +3 58.5 + 6.6= 13mg/l asN 5 As noted, our calculations indicate that the Nitrate concentration in groundwater resulting from the proposed new leach fields and precipitation slightly exceeds the maximum value of 10 mg/1 (as N). In the past, we have used procedures by the Regional Water Quality Control Board (RWQCB) regarding the attenuation of nitrate in soil profiles consisting of predominantly silts and clay soils. As discussed with you, for the past several years our firm has been sampling groundwater in the Morada area in the process of completing Nitrate Loading tests, and have yet to obtain values close to the theoretical value using the Hantzsche formula. Admittedly, our water samples have been taken mostly from existing wells and may not reflect the quality of the 20-2921-02/201 IRI 169 Page 3 of Copyright 2001 Kleinfelder,Inc. September 25,2001