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March 28, 2007 l NOA Project Number: E06122A 3.4 Future On-Site Sources of Nitrate 3.4.1 Quantity and Quality ofDomestic Wastewater From Proposed Project The following discussion is for determining the long-term waste water flow generated from the proposed residences or commercial usage 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. F! The three warehouse buildings are proposed to have approximately 130 parking spaces and win serve a variety of employees serving construction,manufacturing, professional administrative and retail businesses. Some of the businesses will also serve customers. Based on these ratios, the average ¢ daily flow is estimated to be approximately 1,186 gallons per day. Please see Table 1 for details regarding this average daily flow. P 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 1Vastewater Disposal Standards (2003),Crites and Tchobanoglous (1998), and EPA (1980). The references indicate that 13 gallons ry for each employee is typical for an office worker. For the retail businesses an average of 2 gallons is estimated for customer use. (Crites and Tchobanoglous, 1998). F! The following es presents resents the septic waste water uses associated with the Site. The rates presented from the references provide general guidance but do not always reflect a match in usage. Careful examination,professional judgement, and experience are necessary to select a reasonable flow rate estimate. The flow rates selected for the uses associated with this project are presented next. } Table 1.1 Typical Quantity of Effluent Category Total People per Average Quantity per Average Daily Flow Day Person Per Parcel 2.0 gal/day/customer (50 customers x 2.0 gpd) + Commercial 170 13al da / /em to ee 120 employees x 13 d = 1,660 gpd Note —gpd is gallons per day. F1 For the subject property, the total daily wa a water quantity is 1,660 gallons per day. A five-sevenths conversion was used to account for a five day work week. Five-sevenths of 1.660 gallons per day is approximately 1.186 gaIlons per day average. The average total nitrogen concentration of domestic waste water is normally considered to be 20-85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is estimated that commercial use will have higher concentrations of total nitrogen when compared to 5 �_i