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Soil Suitability/Nitrate Loading Study Ripon Winery Proposed Warehouse ■ Ripon, CA 1 ferracon January 20, 2017 ■ Terracon Project No. NA167059 1.6.7 Discussion of Percolation Test Results The sandy soils within the 0 to 3.0 foot range of the proposed septic disposal area at the site demonstrate a satisfactory percolation rate for a standard septic system per EHD requirements. Even though not required, pits may be installed at the end of the leach lines given the deeper clay layer and hardpan encountered. 1.6.8 Discussion of Septic System Sizing In general, septic system construction should follow the San Joaquin County On-Site Wastewater Disposal Standards where applicable. The foregoing investigation and percolation test results indicate the site consists of surface silty sand where leach lines may be utilized, however as , indicated, the area is known for subsurface clay statum and hardpan. For this reason, even though not required, seepage pits may be installed at the end of the leach lines as secondary absorption measure. 2.0 NITRATE LOADING STUDY Because of concern regarding nitrate leaching into groundwater from septic systems, a nitrate loading analysis is required by the EHD for the proposed development to determine the potential concentration of percolating effluent and rain fall over the long term. Where percolating effluent / leaches into the ground, groundwater quality may be impacted to some degree should the effluent reach groundwater. 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 groundwater nitrate impacts on an area- wide basis. Hantzsche and Finnemore found that over a long period of time, water quality in the upper saturated groundwater 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 groundwater flow from up-gradient areas. These processes would generally contribute to additional reduction of nitrate-nitrogen concentrations in groundwater to the extent that the nitrate-nitrogen concentration of groundwater flow from up-gradient areas is lower." The Hantzsche and Finnemore approach is"...a conservative (worst case)first approximation of groundwater 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- Responsive■ Resourceful ■ Reliable 11