Laserfiche WebLink
Soil Suitability/ Nitrate Loading Study Irerracon <br /> Manteca Farm Improvement Manteca, California <br /> October 29, 2019 Terracon Project No. NA197073 <br /> • Septic System No. 1 - Existing Classroom Building = 577 gpd <br /> • Septic System No. 2 — Existing Office Building = 85 gpd <br /> • Septic System No. 3— Proposed 15,000 SF Agricultural Building = 352 gpd <br /> The average total nitrogen concentration of domestic wastewater is normally considered to be 20 <br /> to 85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is estimated <br /> that commercial use will have higher concentrations of total nitrogen when compared to residential <br /> use. For the purpose of the nitrate loading study, the average concentration for total nitrogen in <br /> commercial wastewater will be calculated at approximately 85 mg/L-N over the long term. <br /> 2.3.4.2 Denitdfication Estimate <br /> Denitrification is an important process which occurs within the leach field whereby certain bacteria <br /> utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the atmosphere. <br /> Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 <br /> percent. Soils with higher clay content, moist soil conditions, high pH, and organic material <br /> denitrify by about 35 percent, and soils with high sand content and fast percolation rates are <br /> estimated to denitrify at a lower rate, about 10 percent to 15 percent. Based on the soils <br /> encountered during our borings, a denitrification estimate of 10 percent was selected. <br /> 2.3.5 Nitrate Loading Scenario <br /> A nitrate loading scenario was performed to determine the impact from the proposed project. The <br /> scenario utilizes the variables discussed previously which represent the estimated conditions and <br /> uses associated with this project. The following table presents a summary of the nitrate loading <br /> calculation for the site using the long term average daily flow rates. A copy of the nitrate loading <br /> calculation is included in Appendix F. <br /> Table 11. <br /> Summary of Nitrate Mass Balance Equation. <br /> Result Average Effluent Leachfield Deep <br /> (Nc)* Concentration Percolation <br /> Septic System No. (mg/L_ Acres(A) Daily Flow (Nw) Denitrification of Rainfall <br /> N) (Q)(gpd) (mg/L-N) td) (R)(in) <br /> 1. Existing 13.9 14.0 577 85 10% 2.70 <br /> Classroom Building <br /> 2. Existing Office 3.2 14.0 85 85 10% 2.70 <br /> Nitrate as N Total 17.1 <br /> Septic Systems <br /> No. 1 &2 <br /> Responsive■ Resourceful ■ Reliable 17 <br />