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Soil Suitability I Nitrate Loading Study Irerracon Thornton Road Trailer Parking Facility ■ Lodi, California December 15, 2021 ■ Terracon Project No. NA217079 11-22-2021 Note: A satisfactory percolation rate is 60 minutes per inch or less for shallow leach lines and 30 minutes per inch or less for septic pits per San Joaquin County Onsite Wastewater Treatment Systems Standards (EHD 42-014), January 2017. 1.6.7 Discussion of Percolation Test Results Based on the percolation tests results, all percolation test borings at 3, 3.5, and 6.3 feet bgs demonstrated satisfactory percolation rates for standard shallow leach lines and/or deep seepage pits. 1.6.8 Discussion of Septic System Sizing In general, septic system construction should follow the San Joaquin County On -Site Wastewater Disposal Standards (OWTS) where applicable. 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- term effect (i.e., over years) on groundwater quality, and is not intended for prediction of seasonal changes" (Hantzsche and Finnemore, 1992). Responsive ■ Resourceful ■ Reliable 11