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Soil Suitability and Nitrate Loading Evaluation Page 6 25071 South Lammers Road Tracy, California June 16, 2023 NATS Job No. 22-355G 7.1 Percolation Testing Procedure Upon completion of the percolation test hole drilling, loose material was removed and a 4-inch diameter open-ended slotted drain pipe and 2-inches of fine gravel were installed to control potential sidewall caving of the hole. Pre-saturation of the soils to be tested was accomplished by adding water to 12-inches above the base of the test hole approximately 24 hours preceding the test. After the 24-hour pre-saturation period the 12-inch column of water had dissipated and no water remained in the test hole. After the 24-hour pre-saturation period, percolation testing was performed immediately by adding water to a level of 6± inches above the top of the 2-inch gravel layer placed at the base of the test hole. Recordings were made of the change (drop) in water level at 30 minute time intervals and water level was refilled to 6-inches after each interval. Specific details are included on the attached percolation test data sheets located in Appendix-A. The certified test results are shown on Figure-3. 7.2 Percolation and Infiltration Rates The soil percolation rate is defined by the average time in minutes for a 1-inch column of water to "seep" into the soil. Percolation rate was calculated in minutes per inch (MPI) by dividing the time (in minutes) by the change (drop) in water level (in inches). No correction factor was used in the calculation for the 6-inch boring diameter. Percolation test "P-1" achieved a steady percolation rate of 30 MPI at 36± to 42± inches depth. In general, the percolation rates are considered representative of the gravelly clay encountered within the test hole. 4713 ENTERPRISE WAY * SUITE 4*MODESTO *CALIFORNIA * 95356 * 209-545-1108