SU0002223 SSNL - Laserfiche WebLink

Home Browse Search

�KL KL € INFELDER Where: N, = Average calculated nitrate-nitrogen (N) in groundwater resulting from domestic sources and precipitation—mg/l, as N A = Number of dwelling units per acre on septic tanks (unit/acre)=0.03 W = Annual wastewater loading per dwelling unit per acre (inches) = 2.02 inches (based on 150 gallons/day per dwelling unit) N, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 to 45 mg/l typical (Hantzsche and Finnemore(1992)) D = Percent dentrification of leachfield effluent= 0.1 to 0.25 percent typical per Hantzschc and Finnemore (1992). - r = Annual deep percolation of precipitation (inches) = 3 inches (used by Mr. Hantzsche in the Stockton area to reflect the silt and clay soil conditions anticipated at the percolation depths for the leach trenches) Nb = Background nitrate-nitrogen concentration (N) of rainfall recharge at the water,table — r mgll = 1.0 mg/1 (per Hantzsche and Finnemore (1992) the nitrate nitrogen loading, Nb, typically falls in the range of 0.5 to 1.0 mg/1) Since little information is available regarding the amount of waste-water that will ;need to be disposed by the new septic system, in order to develop the above `A' factor (number of dwelling units per acre on septic tanks), we have very conservatively assumed the new system will need to dispose of 2,000 gallons/day (or an amount equal to the anticipated maximum size of the new septic tank). Based on the. common assumption that a single dwelling unit produces 150 gallons/day of wastewater, the disposal of 2,000 gallons/day would equate to an equivalent 13.3 dwelling units. The BNSF property encompasses approximately 470 acres, therefore the `A' factor would equal 13.3 dwelling units divided by 470 acres or 0.03. The `Nb' factor (Annual ' deep percolation of precipitation) was selected based on a March 19, 1997 report,by Questa Engineering Corporation and authored by Mr. Hantzsche. The report was prepared for a subdivision in Stockton that had fine-grained silt and clay soils, similar to those encountered at the BNSF site, and referenced an `Nb' factor of 3 inches. Our calculation is as follows: C ' . Low Estimate N, = 0.03(2.02)(35)(1 —0.25)+1.0 3 — 1.59+3.0 = 1.5 mg/l,as N 0.03(2.02)+3 0.06+3 High Estimate N, = 0.03 (2.02)(45)(1 0.1)+1.0 3 = 2.45+3.0 = 1.8 mgll as N 0.03(2,02)+3 0.06+3 Average N, = 1.65 mg/1 as N One of the factors that may be required by the SJCPHS is to determine the existing value of nitrate in the groundwater below the site. Based on our previous discussions with Mr. Huggins, we have been advised to use a background nitrate (NO3) concentration of 10 ',mg/1 in the . - groundwater. While Mr-Hixggiris-has,-0riois . I ::d' a background level of nitrate''as N in the LZ 3 �R t;:;o 20-1 l0&-31.G02/2000R1099 N 0 V 2-7 2060 November 21,2000 D 2000 Kieinfelder,Inc. ON CO. Page 3 of 4 GN�i i;l�e.slli�d i'i'�`iv d r S 9OCKTON