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September 20,2001 Job Number: LGO1-098 Page I 1 An engineered septic system which performs onsite reduction of nitrates would decrease the impact to a level below the maximum contaminate level for drinking water. A buildup of nitrates above the maximum contaminate level would probably not occur if such a system could ffi achieve an average nitrate concentration no greater than 17 mg/L-N. This type of performance is reported to be available utilizing pre-designed systems such as Orenco or MicroSeptic. VIII. CONCLUSIONS AND RECOMMENDATIONS -,Ick" ,,_0 In conclusion, a satisfactory percolation rate was achieved on the property. We encountered silty-sand type soils at the surface followed by fine sandy soils to a depth of exploration of 8 feet. The septic permit review has shown that conventional septic systems are used in the area. The depth to ground water at the site was found to be about 34 feet in the east well. The nitrate level measured in a functioning well located at the fire station across the street is 0.71 mg/L as nitrate N or 710 ug/L as nitrate N. The Environmental Protection Agency maximum contaminate level for drinking water for nitrate is 10 mg/L as nitrate N and 1,000 ug/L as nitrate N (or 45 mg/L as NO3). The source of the high nitrate found in the onsite well is probably nonrepresentative of the aquifer and may be due to an unsuitable water sample collected from the idle well. The nitrate loading analysis has shown that the use of a"typical"or standard type of septic system could potentially cause a build up of nitrogen in the shallow aquifer above the maximum contaminate level of 10 mg/L-N. Utilizing an engineered septic system, designed to reduce nitrates in effluent, will not cause a build up of nitrates above the maximum contaminate level of 10 mg/L-N. Based on the results of this study, the proposed project is suitable for use with an engineered septic sstem specially desi ed to reduce nitrates. If this system is utilized,we do not believe it will cause a but -up of nitrates above the maximum contaminant level of 10 mg/L- N. The recommendations for the project are as follows: 1) An engineered septic system, designed to reduce nitrate levels below 17 mg/L-N prior to leachfield disposal, is required to prevent a build up of nitrates above maximum contaminant level for drinking water of 10 mg/L-N. Some leach field improvements will be needed to reduce percolation and obtain a denitrification factor of 35 percent. 2) A qualified civil engineer or professional should be consulted regarding the r. design and performance of the engineered septic system.As part of a separate scope of work, we would be pleased to provide these services. �pERSO � S Y w C A .�Ssoc. r