SR0085800_SSNL - Laserfiche WebLink

Home Browse Search

12958/12970 E Jahant Road Project No. 2022-00037 Page 15 5.0 SOURCES AND IMPACT OF NITRATE TO GROUNDWATER 5.1 Current Off -Site Sources of Nitrate Septic systems and agriculture in the area may be the most significant sources of nitrate. In an attempt to determine the septic system density for the vicinity of the site, our office reviewed a recent aerial photograph available from GoogleEarth"I'M. We counted the clusters within approximately one square mile of the site, with the assumption each building cluster has one septic system. Using this method, we determined there are approximately 110 septic systems per square mile in the immediate vicinity of the site. This is a low amount of septic systems, with the majority of these systems located on large tracts of rural residential land. As discussed above, the domestic well was sampled for Nitrate as N; the analysis reports the groundwater is 2.3 mg/L, which is well below the EPA maximum contaminant level of 10 mg/L. 5.2 Contribution of Rainfall An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall for Lodi, California, based on the nearest weather station to the site available. 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. See Plate 8 for the data and calculation. Average potential evapotranspiration was obtained from the Western Regional Climate Center (Station 045032). The site is located within evapotranspiration zone number 12 was obtained from California Irrigation Management Information Systems (www.cimis.water.ca.gov). The average rainfall for the Lodi area was found to be 17.27 inches per year for years 1893 to 2015. Based on this method, the average deep percolation of rain for the Lodi area is estimated to be 5.29 inches. The nitrate concentration of rain fall was estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 5.3 Current On -Site Sources of Nitrate Current on-site sources of nitrate are the three (3) currently in operation septic systems associated with the three (3) single-family homes on site. 5.4 Future On -Site Sources of Nitrate 5.4.1 Quantity and Quality of Domestic Wastewater from Proposed Project The following discussion is for determining the long-term wastewater flow anticipated from the planned residential house for the site, to be incorporated into the nitrate loading analysis. The anticipated wastewater flow determined is not intended to be used for septic system design because septic system sizing includes a peak use factor, whereas the numbers discussed herein are based on a long-term conservative measure of estimated effluent volume. Petralogix Engineering, Inc. 26675 Bruella Road, Galt, Ca 95632 (209)400-5729 www.petralogix.com