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Soil Suitability/ Nitrate Loading Study Irerracon <br /> Pickens Property■ Tracy, California <br /> May 12, 2020 n Terracon Project No. NA207032 <br /> Table 4. <br /> Expected On-Site Maximum Septic Tank Usage <br /> Number of people per Average effluent Maximum Septic <br /> Residence Number of bedrooms bedroom quantity per person Tank Usage <br /> (gpd") (gpd') <br /> Existing 3 2 70 420 <br /> Proposed Modular 3 2 70 420 <br /> Total 840 <br /> Gallons per day(gpd) <br /> The maximum daily flow rate for the existing residence is 420 gpd. The proposed residence is <br /> anticipated to add 420 gpd for a combined total of 840 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 and 10.0 feet <br /> 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 160 to 170 bgs. A groundwater well completion report located within approximately <br /> 0.14 miles southwest of the site reported depth to groundwater at 180 feet bgs. Based on a review <br /> of the sources, depth to groundwater is anticipated to be greater than 160 feet bgs. <br /> The groundwater flow direction and the depth to shallow, unconfined groundwater, if present, <br /> would likely vary depending upon seasonal variations in rainfall and other hydrogeological <br /> features. Without the benefit of on-site groundwater monitoring wells surveyed to a datum, <br /> groundwater depth and flow direction beneath the site cannot be directly ascertained. <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 /> Responsive ■ Resourceful ■ Reliable 7 <br />