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16475 TIDE ROAD Project No.2019-00072 Page 15 method,we determined there are approximately 50 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 agricultural land. There is currently no domestic well onsite,therefore no onsite well water was tested for nitrate. 4.2 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 Ripon, 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 7 for the data and calculation. Average potential evapotranspiration was obtained from the California Irrigation Management Information System (CIMIS).The site is located within evapotranspiration zone number 12, as well as the Manteca station (Station 70) used in the analysis. The average rainfall for the area,as well as the average evapotranspiration data,was obtained from CIMIS (https://cimis.water.ca.gov/) where the average rain fall for the Manteca area was found to be 12.32 inches per year for years 1988 to 2018. Based on this method, the average deep percolation of rain for the Manteca area is estimated to be 2.74 inches. The nitrate concentration of rain fall was estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 4.3 Current On-Site Sources of Nitrate There is currently no home on-site where the septic system is planned. Rainfall and a vineyard are recognized as potential current on-site sources of nitrate. 4.4 Future On-Site Sources of Nitrate 4.4.1 Quantity and Quality of Domestic Wastewater from Proposed Project The following discussion is for determining the long-term wastewater flow anticipated from the current and planned residential houses 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. The site is vacant land. There is currently a 4-bedroom, 3 bath residence with associated septic system planned for the site. Per San Joaquin County Environmental Health requested guidelines based on previous nitrate loading studies,an average daily flow of 140 gallons per bedroom per day is estimated for the site. The following table presents the nitrate contributing septic wastewater flowrates anticipated for the site. Petralogix Engineering,Inc 26675&cella Road,Galt,Ca 95632 (209)-400-5729 www.petralogix.com