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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the proposed septic disposal area for the new house on the Site were found to be suitable for a septic system. A satisfactory soil percolation rate of 3.79 min/in was observed in the shallow soil zone at the test location. The soil in the test location was found to be clay and sandy clay. Based on maps of recent aquifer levels, the depth of ground water is approximately 50 to 63 feet below ground surface. Ground water flows generally to the east or southeast in the area at a rate of approximately 2 to 4 feet per mile. A water sample was collected from the domestic well on the Site. Nitrate was detected at a concentration of 9.2 m/L-N in the sample, under the MCL of 10 mg/L. The nitrate level near the MCL is likely due to the close proximity of the well to the existing septic system; it is also likely that this well is older and relatively shallow. DBCP was not detected in the sample. Based on the methods and assumptions described, the nitrate loading calculation indicates that existing and future on-site septic drain field systems on the Site have the potential to cause a buildup of nitrate in the aquifer up to 16.2 mg/L-N, above the MCL of 10 mg/L-N. It should be remembered that the Hantzsche and Finnemore equation is a conservative method for determining potential impacts, and actual nitrate loading experienced on the Site over time may be less than predicted. The clay soil and relatively deep ground water in the area may serve to limit the transportation of nitrate to the aquifer. Existing wells in the area do not show nitrate exceedances, and the actual nitrate loading experienced on the Site over time may be significantly less than predicted. Recent San Joaquin County Environmental Health Department policy has been to evaluate each project on a case-by-case basis to determine the level of nitrate mitigation warranted. Although Live Oak cannot make engineering recommendations, we are aware that the San Joaquin County Environmental Health Department often allows the use of an oversized septic tank to mitigate nitrate impacts; this option may be worth exploring for the Site. Use of a shallow system (sumps rather than seepage pits) could provide additional nitrate mitigation due to adsorption of nitrate ions to the clay soil over the increased vadose zone. Alternatively, an engineered nitrate-mitigating septic system could be utilized to address nitrate loading. Another point to consider is that the Site is located in a small neighborhood of Stockton that utilizes septic systems (approximately 30 systems by our estimation), while the surrounding neighborhoods utilize municipal sewer services. As a result, septic impacts in this area should be quite low considering the density of development in the area. It is possible that sewer connections could be offered to these remaining properties in the LOGE 2325 Page 15