SR0081524 SSNL - Laserfiche WebLink

Home Browse Search

Soil Suitability / Nitrate Loading Study Irerracon Jeremy Winery Lodi, CA May 7, 2019 Terracon Project No. NA197008 2.3.4.2 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. Based on the results of the shallow soil borings, the proposed new leach field is expected to be located within sandy silt soils that are stiff and cemented with depth. Based on the soils encountered during our borings and anticipated slow percolation rate, a denitrification estimate of 15 percent was selected. 2.3.5 Nitrate Loading Scenario A nitrate loading scenario was performed to determine the impact from the proposed project. The scenario utilizes the variables discussed previously which represent the estimated conditions and uses associated with this project. The following table presents a summary of the nitrate loading calculation for the site. A copy of the nitrate loading calculation is included in Appendix F. Table 11. Summary of Nitrate Mass Balance Equation. Result Average Effluent Leachfield Deep Acres Concentration Percolation Land Use (Nc)* (A) Daily Flow (Nw) Denitrification of Rainfall (mg/L-N) (a) 19Pd1 (mg/L-N) (d) (R) (in) Proposed Winery 6.0 16.41 416.10 85 15% 4.49 Maximum contaminant level(MCL)for nitrate in drinking water is 10 mg/L-N. Based on the nitrate loading balance calculation, nitrate levels for the proposed development is anticipated at 4.9 mg/L N below the MCL of 10.0 mg/L-N. 2.3.6 Impact of Nitrate Loading to Nearby Water Sources The Mokelumne river is located to the south of the site, approximately 120+ feet south of the proposed leach field area which will meet OWTS setback requirements of 100 feet. Based on the topographic maps, the site is situated approximately 20 to 25 feet higher than the river with a westerly topographic gradient. The addition of 25 foot deep seepage pits (if applicable) would place the pits at an elevation equal to the river. Groundwater was reported at depths greater than or equal to 90 feet bgs; therefore, if seepage pits were to be utilized, there would be a significant buffer of soil mass between the bottom of the seepage pit and groundwater. Based on depth to Responsive ■ Resourceful ■ Reliable 17