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Soil Suitability/ Nitrate Loading Study Addendum Irerracon <br /> Arriaga Property Stockton, California <br /> August 31, 2020 Terracon Project No. NA207046 <br /> Number of people per Average effluent Maximum Septic <br /> Residence Number of bedrooms bedroom quantity per person Tank Usage <br /> (gpd`) (gpd*) <br /> Total 560 <br /> Gallons per day(gpd) <br /> The maximum daily flow rate for the existing residence is 280 gpd. The proposed residence is <br /> anticipated to add 280 gpd for a combined total of 560 gpd. <br /> 1.4 Groundwater Information <br /> 1.4.1 Groundwater Depth and Gradient <br /> Groundwater was not encountered within our borings which were drilled between 3.33 and 6.0 <br /> feet below ground surface (bgs). <br /> According to the California Department of Water Resources Sustainable Groundwater <br /> Management Act (SMGA) Data Viewer, in 2018, depth to groundwater was reported between <br /> approximately 90 to 100 bgs. The groundwater flow direction and the depth to shallow, <br /> unconfined groundwater, if present, would likely vary depending upon seasonal variations in <br /> rainfall and other hydrogeological features. Without the benefit of on-site groundwater monitoring <br /> wells surveyed to a datum, groundwater depth and flow direction beneath the site cannot be <br /> directly ascertained. <br /> Terracon's 2019 NLS reported, depth to groundwater is anticipated to be greater than 97 feet bgs. <br /> Refer to Terracon's prior NLS report dated April 26, 2019 (Terracon Project No. NA187059) for <br /> further discussion. <br /> 1.4.2 Potential Groundwater Contamination Issues <br /> Potential groundwater contamination can occur from a number of sources including historical <br /> petroleum hydrocarbon use, agricultural activities, dairies, septic systems, and storm water <br /> infiltration. As per EHD requirements nitrate as N and 1,2-dibromo-3-chloropropane (DBCP) have <br /> been included as part of the SSS discussion. Identifying potential groundwater contamination <br /> other than nitrates and DBCP is beyond the scope of work for this report. <br /> The presence of nitrates is not uncommon in shallow groundwater aquifers in San Joaquin County <br /> and other parts of the Central Valley. Nitrate in groundwater occurs as a result of the application <br /> of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often <br /> accumulates in the shallow groundwater zones. <br /> In the early 1900s, natural levels of nitrate in groundwater were measured in forty-three (43)wells <br /> throughout the Sacramento Valley by Kirk Bryan (1923). It was thought that groundwater at that <br /> time was close to "natural" conditions. Based on the work by Bryan, it is estimated that under <br /> Responsive ■ Resourceful ■ Reliable 7 <br />