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Watts Winery % ,.� Page 8 of 14 Our Project Number: LGS090507 May 11, 2009 1.6.8 Discussion of Septic System Sizing Septic system construction utilizing leach lines and pits should follow the San Joaquin County On-Site Wastewater Disposal Standards where applicable. If cobbles prevent excavation of seepage pits, sumps should be used in their place. Due to the depth of groundwater, (90 to100 feet) and the likely existence of fine-grained soils deeper, the impact to groundwater from percolating effluent is estimated to be low. 2.0 NITRATE LOADING STUDY Because of concern regarding nitrate leaching into ground water from septic systems, a nitrate loading analysis was required by the EHD for the proposed development to measure the potential concentration of percolating effluent and rain fall over the long term. Where percolating effluent leaches into the ground, ground water quality may be impacted to some degree should the effluent reach ground water. The method utilized for the nitrate loading analysis is based on a simple mass balance formula, discussed in a published article by Hantzsche and Finnemore (1992), which provides a convenient and simplified method to estimate long-term ground-water nitrate impacts on an area-wide basis. Hantzsche and Finnemore found that over a long period of time, water quality in the upper saturated ground-water zone closely approximates the quality of percolating recharge waters. They believe that their method is a good planning tool and provides useful information to planners and local officials but with some real limitations. In their article published in Ground Water, Hantzsche and Finnemore mention that "...the equation ignores dispersion, lateral flow, and mixing with ground water flow from up-gradient areas. These processes would generally contribute to additional reduction of nitrate-nitrogen concentrations in ground water to the extent that the nitrate-nitrogen concentration of ground-water flow from up-gradient areas is lower." The Hantzsche and Fennemore approach is "...a conservative (worst case) first approximation of ground-water nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and precipitation. This (the equation and approach) is for estimation of long-term effect (i.e., over years) on ground-water quality, and is not intended for prediction of seasonal changes" (Hantzsche and Finnemore, 1992). The method takes into account the development area, soil denitrification factor, rainfall volume, rainfall nitrate concentration, waste effluent quantity, and waste effluent nitrate concentration. The formula, assumptions and calculations used for the analysis are shown on Plates 7 and 8. The units of nitrate used in the mass balance equation are nitrate-N, whose maximum drinking water contaminant level is 10 mg/L. 902 Industrial Way•Lodi,CA 95240.209.367.3701 •Fax 209.369.4228 02009 Neil O.Anderson&Associates,Inc