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21300 MANN ROAD Project No.2019-00095 Page 15 <br /> 5.0 SOURCES AND IMPACT OF NITRATE TO GROUNDWATER <br /> 5.1 Current Off-Site Sources of Nitrate <br /> Septic systems and agriculture in the area may be the most significant sources of nitrate. In an <br /> attempt to determine the septic system density for the vicinity of the site,our office reviewed a recent <br /> aerial photograph available from GoogleEarthTM.We counted the clusters within approximately one <br /> square mile of the site, with the assumption each building cluster has one septic system. Using this <br /> method, we determined there are approximately 140 septic systems per square mile in the <br /> immediate vicinity of the site. This is a low amount of septic systems, with the majority of these <br /> systems located on large tracts of agricultural land. <br /> There is one domestic well on site which was inoperable due to a lack of power to the parcel, <br /> therefore,no groundwater was sampled. <br /> 5.2 Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The <br /> estimate of deep percolation of rain is based on the average monthly precipitation of rain fall for Lodi, <br /> California, based on the nearest weather station to the site available. The estimate first determines <br /> whether the average monthly precipitation exceeds average monthly potential evapotranspiration. <br /> If so, then the difference is potential deep percolation. This method does not consider runoff. See <br /> Plate 8 for the data and calculation. <br /> Average potential evapotranspiration was obtained from the Western Regional Climate Center <br /> (Station 045032).The site is located within evapotranspiration zone number 12 was obtained from <br /> California Irrigation Management Information Systems (www.cimis.water.ca.gov). The average <br /> rainfall for the Lodi area was found to be 17.27 inches per year for years 1893 to 2015. <br /> Based on this method,the average deep percolation of rain for the Lodi area is estimated to be 5.29 <br /> inches. The nitrate concentration of rain fall was estimated to be 1 mg/L-N (Hantzsche and <br /> Finnemore, 1992). <br /> 5.3 Current On-Site Sources of Nitrate <br /> The site no longer has any residential housing, and the septic systems associated with <br /> demolished structures will be demolished.Therefore,only rainfall is recognized as potential <br /> current on-site sources of nitrate. <br /> 5.4 Future On-Site Sources of Nitrate <br /> 5.4.1 Quantity and Quality of Domestic Wastewater from Proposed Project <br /> The following discussion is for determining the long-term wastewater flow anticipated from <br /> the planned residential house for the site,to be incorporated into the nitrate loading analysis. <br /> The anticipated wastewater flow determined is not intended to be used for septic system <br /> design because septic system sizing includes a peak use factor, whereas the numbers <br /> discussed herein are based on a long-term conservative measure of estimated effluent <br /> volume. <br /> Petralogix Engineering,Inc <br /> 26675 Bruella Road,Galt,Ca 95632 <br /> (209)-400-5729 <br /> www.petralogix.com <br />