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-2- Depth to the watertable may be determined eit:ter by direct meas- urement 24 hours after the boring is made or by measuring the depth to soil mottling. The first method will determine if at the time the borings are conducted the soil is saturated. Often during wet seasons there are perched watertables present. These watertables do not re- flect regional aquifers but rather areas of saturated soil. These seasonal watertables interfer with the functioning of the standard subsurface trench systems. When the trenches are in- stalled in the saturated soil zone, effluent entering the system during wet periods cannot move away resulting in the effluent surfacing or backing into the house. D- to soil mottling indicates the location and presence of seasonal watertable. Mottled soil consists of spots of contrasting color, mostly gray and red. Unmottled well -drained soil is often brcwn. The diff- erence between thr two is due to the periodic saturation. Where the mottled soil occurs it can be assumed that during certain wet periods the soil is saturated. The depth to mottling there- fore tells what depth the soil treatment trenches should be placed to maintain the ,ninimum 3 to 4 foot separatiLun between trench bottoms and watertables recommended in the PCA Standards. rom this information the proper to ion, sire and design of your home sewage tre ment system ca., be determined. POTENTIAL 01: SOILS rOR ON -SITE WASTE TREATMENT Hayden soils which predominate may be suitable for the installation of a conventional subsurface trench system. However, a shallow subsurface trench system installed with the trenches no deeper than 12 inches will provide a greater probability for the system to function properly. The shallow trench system utilizes the more permeable portions of the soil profile. Size of the system -hould probably be based on having 2.2 square feet of soil treat - it area at the bottom of the trenches per gallon of waste per uay as determined above. The system must be located in an area of soils suitable for the proposed soil treatment system as det rmined by an on -site eval- uation consisting of soil borings and percolation tests. The area which is designated as the waste treatment site must be left undisturbed during all other construction activities. Soil treatment systems are designed assuming that the system will be installed in the natural undisturbed soil. The area should not be graded and heavy construction equipment prevented from ari%ing over the area. This will reduce the )otential for compaction• of the soil which will reduce its potential for the treatment of septic tank effluent.