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disposal trench and surrounding soils will increase the uptake of nitrogen and other wastewater constituents by soil microbes. Groundwater Groundwater in the vicinity of the parcel is variable depending on the year and season. Groundwater has been documented at an approximate elevation of-50' (msl), or approximately 85' below the ground surface in the Spring of 2015, with the groundwater gradient trending eastward toward an apparent cone of depression near Waterloo.' Conversely,groundwater depth in the area was observed in the Spring of 2016 to be nearly-90(msl)with a steeper eastward gradient with a focal point near the Calaveras County line. Groundwater in the area of the subject parcel is used for agricultural and domestic purposes;future use will likely be similar. No documentation of degraded local groundwater was found during the course of our research. B. Sources of Nitrogen The land use in the immediate vicinity of the subject parcel is rural/suburban, with the immediate neighborhood consisting of half to one-acre lots and subdivisions with smaller lots located to the west, or up-gradient location. Lots within the existing subdivision are served by OWTS and appear to be of a recent vintage. It is noted that existing subdivisions west of Freesia Avenue are served by public sewer. Factors effecting nitrate loading will be primarily the OWTS and commercial nitrogen based lawn fertilizer. Nitrate loading from OWTS is relatively straightforward. While concentrations of nitrate-nitrogen in individual systems vary widely, it has been demonstrated that the total amount of nitrogen exiting a septic tank is relatively consistent across diverse populations. For the purposes of this analysis,the industry standard of nitrate contributed by the OWTS of 34 pounds of nitrogen per year per home is used.' Nitrogen leaching from domestic lawns is based primarily on the homeowner's application rates of fertilizer and water and not possible to accurately calculate from a theoretical stance. That being said,the industry standard for nitrogen application rates to ryegrass,fescue,and/or Bermuda grass is 3 pounds per 1000 sf per year.' An analysis of surrounding parcels reveals that the typical lawn size is between 0.3 and 0.6 acres in size. Using a nominal value of 0.5 acres of lawn, we can calculate a total nitrogen loading rate of 6 pound per year. Nitrogen removal from the soil column, through the process of microbial nitrification/denitrification is a function of detention time, BOD:N ratio and anoxic conditions. Denitrification rates up to 60 Ib/acre*d can be achieved in some situations,' with an average reduction due to denitrification is 25%.$ Vegetative uptake will also remove nitrogen from the soil column. Lawn grasses can consume 200+/- pounds of nitrogen/year/acre. However, for the purposes of this assessment, we will assume that no vegetative nitrogen uptake occurs other than the consumption of commercial fertilizer. C. Mass Balance This analysis looks specifically at the nitrogen loading of the local soil and groundwater due to development activities on the parcel. Sources of nitrogen loading, as discussed above, are the OWTS and commercial fertilizers. For the sake of simplicity, we have expressed our findings in terms of pounds of nitrogen. However,the movement of nitrogen through the soil column will be aided by water. Sources of water on the parcel are confined to wastewater exiting the OWTS, precipitation, and irrigation water. Our mass balance model takes into consideration the overall size of the property and ^San Joaquin County Flood Control District,2016 6 Zone 7 Nutrient Management Plan 6 www.dummies.com/home-garden/lawn-care/how-much-fertilizer-to-apply-to-your-lawn/ 'Land Treatment systems for Municipal and Industrial Wastes,Crites et al,2000 8 Small and Decentralized Wastewater Management Systems,Crites,1998 Applied Wastewater Solution, Inc. Page 3 of 4