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y File No. 20-3775-01.602 _ k, KLEINFELDER June 30, 1994 actual storm water. Variations in the materials exposed within the basin may also affect percolation characteristics. Therefore, we suggest that a representative from our office be given an opportunity to observe the materials exposed in the basin excavations to confirm they are consistent with those encountered in our test drilling and percolation testing. We also suggest that a review copy of the drainage plans be submitted to our office prior to final design. Based on the percolation test results, the factors noted above, and our experience with other drainage basins in the area, we recommend that a factor of safety on the order of approximately 11/z to 2 be applied to the above values for use in design. Assuming the basin will be between approximately 5 and 10 feet deep, it appears that using the higher value (with the factor of safety applied) will be appropriate. Even with highly permeable material exposed on the bottom of the basin, it has been our experience that silt build-up on the bottom of the basin can significantly reduce the actual percolation rate over time. The amount of silt build-up can be reduced by periodically disking the bottom of the basin. If silt build-up becomes a problem and percolation is restricted, a trench drain system can be installed in the bottom of the basin with elevated inlet structures. We can provide assistance with the design of such a system if requested. W. SEPTIC SYSTEM 1. Percolation Tests Two approximate 3-foot deep percolation tests were performed at the approximate location of the proposed septic system. The percolation test holes were filled to the surface with relatively- clean water on June 27, 1994 and left to soak overnight. On June 28, 1994 our representative returned to the site and performed the tests following San Joaquin County guidelines. The tests were performed for a period of 4 hours, and the last 30 minutes of each test were observed by a County sanitarian. The last 30 minutes of each tests were used to calculate the following percolation rates in minutes per inch (min/in). SEPTIC SYSTEM PERCOLATION TESTS Depth Percolation Rate Test Number (feet) (min/in) P-1 3 51/2 P-2 3 4 We note that San Joaquin County considers 60 minutes per inch the maximum rate acceptable for standard leach field use. Therefore, based on the test results both percolation tests produced passing tests. A copy of the County approved field test sheet is included with this report. Copyright 1994 Kleinfelder,lie. page 3 of 4 I