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1 February 10,2005 NOA Project Number: E05001A 3.4 Future On-Site Sources of Nitrate 3.4.1 Quantity and Quality ofDomestic Wastewater Fram Proposed Project The following discussion is for estimating.the long-term waste water flow generated from the proposed group care facility for the nitrate loading analysis. This estimate should not be used for septic system design purposes. Typically,use estimates for the sizing o£septic systems include a peak use factor,whereas the numbers discussed here are based on long-term averages. The estimated effluent is for a group care facility with 14 clients and a care staff of 9 which works over three shifts. Ms. Helen Kutil of a Phoenix Program Inc., facility in Stockton provided our office with water use records from January 2000 to January 2005-for their facility located at 8 E. Flora Street, Stockton, CA 95202. The record of meter use is attached to this letter. This facility has 14'clients and a staff of 9 over three shifts which is identical to the subject site. No significant landscape irrigation occurs at the facility in Stockton, CA. The meter readings were first converted into average daily flows per month over the five year period then run through a statistical interpretation. The result indicated the median number for the data set is 1,190 gallons per day,average daily flow. The standard deviation of the dataset is 482 gallons. Therefore,we will assume the.effluent generated from the site roughly 1 190 +- 482 alio a er da average daily flow_. The wide spread in standard deviation error probably represents several months adhere plumbing leaks were present and where the facility may not have been at full capacity. 1190 gallons per day average daily flow, derived from the water records, agrees well with published use numbers for a care facility (90 gpd adf. The average total nitrogen concentration of domestic waste water is normally considered to be 20-85 mg/L-N'(Crites and Tchobanoglous; 1998).- For the purposes of the nitrate loading estimate, the long-term average concentration for total nitrogen in waste water is estimated to be 45 m L-N which reflects residential uses. 3.4.2 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N� to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content;moist soil conditions;'high pH,and organic material. denitrify by about 35 percent,and soils with high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. A denitrification factor of 10 percent was selected for the Site. 5