SR0081797_SSNL - Laserfiche WebLink

Home Browse Search

February 24, 2020 BGG Job No. G123.02 NITRATE LOADING STUDY Due to concerns of nitrate leaching into groundwater from septic systems,a nitrate loading analysis was required by the San Joaquin County Environmental Health Department(SJC EHD)for approval of the proposed Zinc House Winery septic system. The intent of the study is to estimate the potential concentration of percolating effluent produced by the proposed septic system for an extended period. Where percolating effluent leaches into the ground, groundwater quality may be impacted to a degree, should the effluent reach the groundwater table. The method utilized for the nitrate loading analysis is based on a simple and convenient mass balance formula, discussed in a published article by Hantzsche and Finnemore (1992). Hantzsche and Finnemore (H&F) have concluded from investigations conducted in the Chico, California area that the water quality in the upper,saturated groundwater zone closely approximates the quality of percolating effluent from septic systems. A simple method was developed that is appropriate for estimating the impact of percolating effluent from septic systems. The intent of the method is to simulate the worst-case effluent impact that the upper aquifer would potentially experience from the use of on-site septic systems. The concentrations of percolating effluent are typically substantially reduced by mixing and dilution in the aquifer as well as absorption and adhesion in the soil. The H&F equation is a conservative approximation of groundwater nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and rainfall precipitation. The H&F equation and method are appropriate for estimating longterm effects on groundwater quality;it is not intended for use in predicting seasonal fluctuations (H&F, 1992). The method takes into account the development area,soil denitrification factor,rainfall,rainfall nitrate concentration,waste effluent quantity, and waste effluent nitrate concentration from onsite septic systems. Mass Transport Soil Properties Field percolation test results indicate that the surface soils are moderatelyppeuxwable.The site soils will permit some infiltration of water through the surface soils.The longer the effluent remains near the surface, the more biologic treatment may occur. If permeable soils exist to the depth of the ground water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. Nitrate Sources Septic systems and dairies have been identified to be the most significant sources of nitrate impact to groundwater. Orchard fertilization in sandy soils is also a significant source of nitrate contamination in shallow or sandy aquifers in San Joaquin County. Rainfall Contribution An estimate for rainfall quantity and quality was required for this nitrate loading analysis. The H&F method utilizes the"average recharge rate of rainfall"for calculating potential nitrate impacts to the aquifer. Some portion of total rainfall will dissipate by evapotranspiration,the sum of evaporation and plant transpiration, hence reducing the amount of rainfall percolation into the aquifer and percolating effluent, especially in summer months. BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-Zinc House Winery Page 6