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Soil Suitability/Nitrate Loading Study Irerracon <br /> Pickens Property■ Tracy, California <br /> May 12, 2020 ■ Terracon Project No. NA207032 <br /> 2.1.2 Mass Transport Soil Properties <br /> The longer the effluent remains near the surface, the more treatment is enhanced due to natural <br /> processes within the soil. The percolation test has revealed that the onsite soils have a <br /> moderately rapid percolation at shallow depths (<3.5 feet bgs). <br /> 2.2 Groundwater Analysis <br /> 2.2.1 Regional Groundwater <br /> A discussion of regional groundwater, including depth to groundwater is included in Section 1.4.1. <br /> No significant seasonal trends were evident from the sources consulted. <br /> 2.2.2 Potential Ground Water Contamination Issues <br /> A discussion of issues related to potential groundwater contamination is included in Section 1.4.2. <br /> 2.2.3 Current and Future On-Site Ground Water Uses <br /> The proposed modular home wil be connected to the existing onsite domestic well. <br /> 2.3 Sources and Impact of Nitrate to Groundwater <br /> 2.3.1 Current Off-Site Sources of Nitrate <br /> Agriculture land use and septic systems in the area may be the most significant sources of nitrate <br /> in groundwater. Septic tank use in the vicinity is discussed in Section 1.3.5. <br /> 2.3.2 Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. <br /> Average precipitation and potential evapotranspiration (ETo) data was obtained from the <br /> California Irrigation Management Information System (CIMIS) from the Tracy (167) station. The <br /> estimate first determines whether the average monthly precipitation exceeds average monthly <br /> evapotranspiration (ET). If so, then the difference is potential rainfall recharge. This method does <br /> not consider runoff, although due to the relatively flat nature of the site, runoff should be minimal. <br /> In February 2020, the EHD approved an adjustment to the evapotranspiration (ET) rate based on <br /> net rainfall recharge calculation utilizing University of California (UC) plant factors (PF) for <br /> established landscape plants. Terracon calculated the ET adjustment factor(actual ET) based on <br /> the anticipated residential landscape. Refer to Appendix F Water Balance Recharge Analysis for <br /> monthly precipitation and ET averages. <br /> Responsive■ Resourceful ■ Reliable 13 <br />