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«Project_Nameo Page 9 Our Project Number: LGS080005 February 28, 2008 2.3 Sources and Impact of Nitrate to Groundwater 2.3.1 Current Off-Site Sources of Nitrate Septic systems, agriculture, and dairies in the area may be the most significant sources of nitrate in ground water. Septic tank use in the vicinity is discussed in Section I.3.4. 2.3.2 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 and evapotranspiration for South Stockton, 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. See Plate 9 for the data and calculation. Average potential evapotranspiration was obtained from the California Irrigation Management Information System (CIMIS). Stockton is located within evapotranspiration zone number 12. Average rainfall was obtained from the Western Regional Climate Center (Station 048558). Based on this method, the average deep percolation of rain for the South Stockton area is estimated to be 3.3 inches. The nitrate concentration of rainfall was estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 2.3.3 Current On-Site Sources of Nitrate There are no current on-site sources of nitrate except for natural processes. 2.3.4 Future On-Site Sources of Nitrate 2.3.4.1 Quantity and Quality of Domestic Wastewater From Proposed Project The following discussion is for determining the long-term waste water flow generated from the proposed construction 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 equipment sales and rental office is proposed to have one (1) employee per day and no customers. We understand that the office is planned to be open approximately eight (8) hours per day, five (5) days per week. 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). The references indicate that 13 gallons for each employee is typical for an office worker. (Crites and Tchobanoglous, 1998). .*44v 902 Industrial Way•Lodi,CA 95240.209.367.3701 -Fax 209.369.4228 02008 Neil o.Anderson&Associates,Inc