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rrIV. LOCAL GROUNDWATER AND SURFACE WATER INFORMATION The 1999 Lines of Equal Depth Map published by the San Joaquin County Flood Control does not illustrate the groundwater depth on their maps in this or the Tracy, California. The 1999 Lines of Equal Elevation Map also do not illustrate the groundwater elevation and therefore the directional flow under the subject property. It is generally accepted that groundwater flows with the topography of the land surface. Consequently, groundwater flow can be assumed to be in a northeasterly direction. Two Well Driller's Logs were found for nearby wells, as noted in Appendix F. Underground lithology surrounding the subject property consists of several different soil types. The property is not subject to 100-year flooding. Therefore, it is highly unlikely there would be surfacing of effluent from inundated conditions. Surface water will be managed by on-site retention basins. As referenced in the Introduction,no water samples were obtained for this study since there are no wells on the property. It will be at the discretion of EHD to require testing for nitrate and DBCP of each domestic well drilled on each Parcel. It is known that a groundwater nitrate concentration of 28 ppm exists upgradient to the project. To determine the depth to groundwater, a domestic well approximately one mile to the east of the project was sounded with an electronic water level meter. The standing water level depth was found to be 78 feet deep. The ground elevation of this domestic well is approximately seven to ten feet lower than the northeast corner of the subject property. Consequently, it can be assumed that the groundwater under the project site may range from 85 feet to 100 feet below ground surface. V. CALCULATED IMPACT FROM NITRATE-NITROGEN LOADING The calculated or estimated nitrate impact to the soil and ultimately to the groundwater from this project is difficult to determine due to the number of variables involved. There are various formulas and methods to estimate nitrate loading. The following calculations are based upon using a conventional or traditional type of septic system consisting of a septic tank, leachlines and seepage pits, or sumps. The nitrate loading method presented is the Hantzsche/Finnemore Equation. It is generally regarded that this equation is the most representative and accurate regarding nitrate-nitrogen loading. The primary variables involved in quantifying nitrate impact to the underlying groundwater are Total Nitrogen concentrations, volume of yearly wastewater flows, extent of denitrification, and evapotranspiration potential. Denitrification capabilities of the indigenous clayey surface and shallow subsurface soils are expected to contribute to the denitrification potential. Ammonium retention in the clay soils that are present should also be a factor, as has been observed in other projects with similar soils. Evapotranspiration was not factored in the nitrate loading calculations; however, it may be a significant part of wastewater management and consequently nitrate-nitrogen loading. Page -6- Chesney Consulting