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r RECEIVED JAN 13 W ENVIRUNW-N IAL HEALTH DEPARTMENT 5.4 Discussion of all proposed future on-site sources of nitrate to soil and groundwater and the contribution of nitrate load from these sources to the project site: The future use of the site, if the rezone is approved, could be residential with the existing lot being subdivided to add six new lots,with each lot containing a minimum of 2 acres. The projected 14.6 acres will be used for rural residential purposes. For residential use,the approximate flow rate that is expected to be used is between 50 to 70 gallons per person per day. (Crites and Tchobanoglous). The San Joaquin County Environmental Health Department requires that a safety factor of 2 be used. Therefore,the approximate values used should be doubled. As this method of determining nitrate loads is conservative on its own,the value of 70 gallons per person per day was used. This method is conservative as it does not include lateral dispersion or mixing of groundwater. These factors of safety are additional to the County's factor of safety. The residential homes are expected to be between 3 and 4 bedrooms, so 4 was used. Taking into consideration a safety factor of 2, 70 gallons per person per day of effluent, and the number of people contributing to the effluent levels being 4, the number of 560 gal/day of effluent was used. The average total nitrogen concentration of domestic wastewater is about 20-85 mg/L-N, although 35-45 mg/L-N is a better approximation (Crites and Tchnobanoglous). The value selected for this site was 35 mg/L-N. The site will experience a process of denitrification as the soil naturally treats surface material through natural forms. Denitrification is a process that occurs when bacteria uses oxygen in the nitrate(NO3) and release nitrogen(N2) into the atmosphere. Denitrification can be variable to the type of soils,chemical properties,moisture content and other variables. Based on the sandy loams on site and the high percolation rates,this site's soil has low levels of denitrification. It is expected that a site with soil of these characteristics shall have about 10-15%of denitrification. The value used for this site was 15%. 5.5 Calculate mass balance of nitrogen loading considering all potential sources identified using Hantzche/Finnemore equation: Using the data mentioned within this report and the attached Soil Suitability Report, the mass balance of nitrogen loading for this site was calculated. This was done using Hantzche/Finnemore formula. Based on the Hantzche/Finnemore equation this 14.6-acre site would contain a Nitrate Load (Nc) of 9.20 mg/L-N for every 2-acre lot. The site can generate approximately 560 gal/day of effluent per the proposed 2 acre lots. It is unlikely that a flow would surpass an amount that could cause an impact to the site's nitrate load and surpass the maximum contaminant level(MCL) of 10.0 mg/L-N for Nitrate in drinking water. 6.0 Discussion of nitrate loading results relative to proposed method of wastewater disposal 6.1 Discussion of total nitrate impact from proposed project: There are possibilities that the percolating effluent could affect water conditions. The Hantztche/Finnemore equation added to the County's factor of safety of two diminish those risks, but no major additions should be made beyond the proposed improvements mentioned previously without an update to this report. 3