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Nitrate Loading Study Arriaga Property a Stockton, California Irerracon April 26, 2019 w Terracon Project No. NA187059 NITRATE LOADING STUDY ARRIAGA PROPERTY (APN 181-060-09) 10966 E. MARIPOSA ROAD STOCKTON, SAN JOAQUIN COUNTY, CALIFORNIA OUR PROJECT NUMBER: NA187059 Our office was contacted by Mr. Ismael Solario, architect, to conduct a Nitrate Loading Study (NLS)for the property at 10966 E. Mariposa Road, Stockton, San Joaquin County, California. The formatting of this report has been designed to follow, to the greatest degree possible, San Joaquin County Environmental Health Department(EHD) Nitrate Loading Study Requirements Checklist, dated July 14, 2003. Based on information received from Mr. Solorio and recent Google Earth aerial photos, we understand the site consists of an approximately 1.25-acre tract of land (APN 181-060-09) currently improved with a 1,246 square foot (SF) two bedroom residence with septic system, utilities, and a groundwater well. The site is proposed to be developed with an additional two bedroom modular residence and additional septic system. Because of concern regarding nitrate leaching into groundwater from septic systems, a nitrate loading analysis is required by the EHD for the proposed development to determine the potential concentration of percolating effluent and rain fall over the long term. Where percolating effluent leaches into the ground, groundwater quality may be impacted to some degree should the effluent reach groundwater. The method utilized for the nitrate loading analysis is based on a simple mass balance formula, discussed in a published article by Hantzsche and Finnemore (1992), which provides a convenient and simplified method to estimate long-term groundwater nitrate impacts on an area- wide basis. Hantzsche and Finnemore found that over a long period of time, water quality in the upper saturated groundwater zone closely approximates the quality of percolating recharge waters. They believe that their method is a good planning tool and provides useful information to planners and local officials but with some real limitations. In their article published in Ground Water, Hantzsche and Finnemore mention that "...the equation ignores dispersion, lateral flow, and mixing with groundwater flow from up-gradient areas. These processes would generally contribute to additional reduction of nitrate-nitrogen concentrations in groundwater to the extent that the nitrate-nitrogen concentration of groundwater flow from up-gradient areas is lower." The Hantzsche and Finnemore approach is "...a conservative (worst case)first approximation of groundwater nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and precipitation. This (the equation and approach) is for estimation of long- Responsive ong-Res onsive iv Resourceful a Reliable 2