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The second physical test was the Double Ring Infiltrometer test(ASTM D-3385), which measures the rate of one-dimensional water infiltration and flow through the approximate soil/water interface. This test is representative of the infiltration that will initially take place at this interface. This test is more representative of the hydraulic conductivity properties of the soil than the standard percolation test, since the disposal of effluent will be through a filter bed arrangement. The first four test cycles indicated very slow infiltration. This may be attributed to to compacted clay soils directly underneath the compacted aggregate base. It would have been preferable to run the test at 30 to 36 inches below existing grade; however, this was not possible due to height limitation of the rings. Test results indicate a final rate of 0.896 centimeters/hour(cnvbr), or 170 mpi after complete saturated soil conditions. This translates to an application rate of 0.22 gallons/ft'/day, according to published sewage application rates correlated with rates (inverse of rate) in minutes per inch. PERCOLATION AND INFILTRATION TEST RESULTS 36 INCH DEEP TEST BORING INFILTRATION RATE IN PERCOLATION RATE/APPLICATION RATE MINIIN AND APPLICATION RATE 31.3 min/inch / 0.553 gallons/ft'/day 170 min/in / 0.15 gallons/ft'/day D. GROUNDWATER INFORMATION- Groundwater depths and elevations are illustrated on maps published by the San Joaquin County Flood Control and Water Conservation District. However, due to the variability in groundwater elevations in the Tracy area, groundwater lines are not drawn for this area. The last map denoting lines of equal elevation for the Tracy area was published in 1992 and indicate the general groundwater flow to be in a northeasterly direction, toward the San Joaquin River. The directional flow of the groundwater should be assumed to be approximate since there are many influences on flow direction,primarily by domestic and irrigation wells. As with all groundwater tables, there will be fluctuations in elevation. Well logs indicate an 8 ft water table depth in 1987, which is nearly equal to the current static water table measurement of 9.0 ft. It is highly probable that there has not been dramatic fluctuations in groundwater elevation under the subject property for many years. The critical issue regarding the groundwater elevation is that there must be sufficient distance between the bottom of soil/effluent interface and the highest anticipated depth to groundwater for sufficient treatment of effluent to occur. This is generally accepted to be five feet. A well log from an adjacent domestic well illustrates varied geological strata of clay, sand and sandy gravel down to depths of 160 ft. From this well log, it can be observed that the upper zone of saturation consists of a clay-fype, fine soil fraction. There is ongoing research which suggests that there may be a significant denitrification potential within aquifers composed of a fine (vs. a coarse) soil fraction. Chesney Consulting