SR0080264 SSNL - Laserfiche WebLink

Home Browse Search

Soil Suitability / Nitrate Loading Study Ernst Property Tracy, CA Irerracon February 21, 2019 Terracon Project No. NA197000 2.3.2 Contribution of Rainfall An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. Average precipitation and potential evapotranspiration data was obtained from the California Irrigation Management Information System (CIMIS)from seven active and inactive CIMIS station in San Joaquin County including Manteca (070), Staten Island (242), Holt(248), Ripon (249), Lodi (042), Lodi West (166), and Tracy (167) over an approximately 34 year period. The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall an evapotranspiration for San Joaquin County, California. The estimate first determines whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is potential deep percolation. This method does not consider runoff, although due relatively flat nature of the site runoff should be minimal. Table 4. Estimate of Deep Percolation of Rain 72 Location Average Deep Percolation of Rain San Joaquin County I 12.78 inches per year Based on this method, the average deep percolation of rain for San Joaquin County is estimated to be 12.78 inches/year. The nitrate concentration of rainfall is estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 2.3.3 Current On-Site Sources of Nitrate The current on-site sources of nitrate include the existing septic system and natural processes. 2.3.4 Future On-Site Sources of Nitrate Future on-site sources of nitrate are discussed in section 1.3.7. 2.3.4.1 Quantity and Quality of Wastewater from Project The following discussion is for determining the long-term wastewater flow generated from the proposed development for the nitrate loading analysis and should not be used for septic system design purposes. Typically, use estimates for the sizing of septic systems include a peak use factor, whereas the numbers discussed here are based on long-term averages. The estimated sewage flow rates for use categories are available from a number of references. The uses presented below were guided by the San Joaquin County On-Site Wastewater Disposal Standards (2003), Crites and Tchobanoglous (1998), and EPA (1980). Table 4-2 of the text from Crites and Tchobanoglous indicates that the typical residential use rate is 70-gallons per day per bedroom. The EPA Design Manual (Table 4-6) indicates the typical use rate is 45-gallons per day per resident. Based on a review of the USGS California Water Science Center California Responsive ■ Resourceful ■ Reliable. 13