SU-2601156_SSNL - Laserfiche WebLink

Home Browse Search

The EHD utilizes the depth to groundwater water information from the 1983 and 1999 groundwater maps when"groundwater levels were recorded to be at the anticipated highest levels." From these two maps,the water table was measured at 82 ft below grade and 85 ft below grade, respectively. For the most recent groundwater depth,the 2025 Lines of Equal Depth Map shows the underlying groundwater to be more than 100 ft. NITRATE LOADING STUDY ADDENDUM Three parameters used in the AGI Nitrate Loading Study calculations have been changed: First, the background nitrate-nitrogen concentration of rainfall recharge has been changed from 1.0 ppm to 0.1 ppm. Rainfall in California has virtually no nitrate, while in regions such as Florida, where there is significant lightning, nitrate-nitrogen concentration in rainfall can be comparatively high. Secondly, from the soil nitrate-nitrogen analysis, a denitrification factor indicates a 35% decrease in nitrate- nitrogen concentrations between the 12 ft and the 25 ft depths. Thirdly,rainfall data is typically obtained from the California Irrigation Management Information System(CIMIS). Deep percolation is estimated by quantifying the average monthly rainfall in comparison to the average monthly evapotranspiration. Theoretically, if the rainfall exceeds the evapotranspiration,the potential for deep percolation may occur. The Net Rainfall Recharge (NRR) is referenced as 8.82 inches/yr in the Stockton area, based on a Water Balance Analysis by N. Hantzsche. This document is found in Appendix D. By installing a 2,000 gallon septic tank in lieu of a required 1,200 gallon, should reduce the septic tank nitrogen concentration based on the following premise: From the September 2004 Symposium "University Curriculum Development for Decentralized Wastewater Management- Onsite Nitrogen Removal," Dr. Stuart Oakley of California State University Chico states that"approximately 20% of the total nitrogen generated is removed in the septic tank"(Ref. 4). Consequently, if an approximate 20% nitrogen removal occurs in septic tanks, and if the tank volume is increased a specified percentage from a baseline volume,then it is reasonable to assume that the percentage increase in tank volume will remove that percentage of nitrogen above the 20%baseline. This nitrogen removal occurs from increased area contributing to increased anaerobic digestion of organic material and scheduled tank pumping. Therefore, increasing the tank volume for the proposed SFR from the required 1,200 gallons to 2,000 gallons, is a 67%increase in capacity,thus substantiating a 67% increase in nitrogen reduction, above the initial 20%N reduction: 20%+(20%x 0.67) = 33%decrease in nitrogen concentration by installing a 2,000 gallon tank to serve the SFR. This percentage decrease in nitrogen concentrations will be used in the nitrate loading calculations below. WASTEWATER FLOW VOLUME PROJECTIONS To determine nitrate-nitrogen loading from any project, wastewater flow volumes must be determined as accurately as possible. Domestic flows are typically approximated from the USEPA Onsite Wastewater Treatment Systems Manual, Pg. 3-4. However, for nitrate loading calculations, the EHD currently requires wastewater flow volume projections from SFR structures to be calculated as follows: Page-3- Chesney Engineering, Inc.