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r i ' a II. SOIL SUITABILITY STUDY FINDINGS The percolation test results for infiltrative and percolative capacity of the subsurface soils indicate a rapid perc rate for the 20 ft deep test and a medium rate for the shallow 42 inch test. Considering the indigenous clay throughout the soil profile, much slower percolation rates were exp tc ed. 1 Explanations as to why the percolation rates were faster than anticipated are due to the unusually high rainfall that has occurred this year,the individual clay particles are surrounded with water molecules throughout the soil horizons. Since water possesses a great affinity for itself, percolative capacity is enhanced. However, this phenomenon does not occur in all clay type soils, r but is one explanation for the medium perc rate for the shallow perc test. r Secondly, it is our understanding there was an ancient creek bed which ran through the subject property. A gravel stratum was encountered at nine feet below grade during our drilling procedures and was approximately two feet thick. This may have been the ancient creek bed. Below this strata was a fissured silty clay extending down to boring termination of 30 feet, where a sand stratum was encountered. This fissuring may explain the accelerated percolation rates which were observed at the deep pert test depth. In addition to percolation testing, applications for permits at the Environmental Health Department +, for repairs/additions to existing septic systems were reviewed. Permits give an indication of the r. viability of septic systems in the study area. Records reveal there have been at least eleven permits issued within the one-half mile study area. This is considered a high number and indicates significant problems with the subsurface soils accepting and disposing of septic effluent. Design considerations of the project's septic system will be implemented to mitigate potential problems which include increasing seepage pit capacity. y t , III. SURFACE AND SUBSURFACE SOIL INFORMATION To assess the soils under the subject property for nitrate formation and the potential for denitrification, a soil analysis was performed on a composite sample from the surface to a depth of 42 inches. The Soil Analysis Report in the Appendix illustrates several parameters of the on-site soils. For this study, the more important factors include the organic matter fraction and the nitrogen (NO3 I) content,which are both low. Consequently, only a very small percentage of future nitrate formation can be assigned to the on-site soils. The pH is slightly alkaline at 7.3 and the cation exchange capacity(CEC)is high, indicating a clay-type soil. Cation exchange capacity can measure the ability of a clay soil to trap and hold ammonium molecules and prevent the conversion from ammonium to nitrate. Usually, the higher the CEC number, the lower the possibility of nitrate 2 Vaffey Ag Ppearch