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March 13,2000 Job Number: LGOO-067 Page 9 Table: Results and Variables Used in the Mass Balance Analysis (see worksheets in Appendix for calculations) Result of Denitrifi- Deep Rain Waste level` Rain Acres Analysis cation 7 Percolation' Concentration` .. 2.2 m -N 20% 7.86 inches 1 45.9 m N 1 0.17 m N 1 32.4 The results of the analysis indicates that viewing the combined septic loads of 1137 gallons per day(average)effluent at a concentration of 45.9 mg/l N and 7.86 inches of rain at a concentration of 0.17 mg/1 N for the 32.4 acre site for an average year, the total combined concentration of nitrates from these two sources before mixing with ground water is estimated to be 2.2 mg/1-N using a denitrificaiton factor of 20%. This concentration is about 22% of the maximum contaminate level for the drinking water standard of 10 mg/1-N. VIII. CONCLUSIONS AND RECOMMENDATIONS In conclusion, analysis of the percolation test result indicates the onsite soils percolate 8.0 minutes per inch at a depth of 3.5 feet. The septic permit review has shown that generally the standard leach-field design and sumps have been used near on site and in the area. The 10-ft exploratory boring did not encounter ground water. Recent County ground-water depth maps have shown the depth to ground water ranges between 15 feet to 22 feet through the year. The estimated total average yearly nitrate loading concentration for the property is estimated to be 2.2 mg/1-N, about 22% of the maximum contaminate level for the drinking water. The analysis has shown that the addition of the new septic system for FTG Construction Materials project should not impact water quality. It is important that any new septic system built in sandy areas are designed and constructed properly. Based on the results of this project, our recommendations are as follows: 1) Due to the sandy near-surface soils,the leach line trenches should be supplemented with an organic carbon source such as a organic silt, organic clay, or an ordinary gardening peat supplement. An appropriate amount of peat soil supplement could be purchased from a gardening store for example, and lined in the trenches to form lr 7 Hantzshe N.N.,FinnemoM E.J. 1991,Predicating Ground-Water Nitrate-Nitrogen Impacts. Ground Water Vol. 30,No. 4. =OEf JO i