SR0082520_SSNL - Laserfiche WebLink

Home Browse Search

Soil Suitability and Nitrate Loading Evaluation CTE Job # 25-0726G Custom Home 5388 Fig Road Manteca, California May 18, 2020 Page 6 of 9 time (in minutes) by the change (drop) in water level (in inches). No correction factor was used in the calculation for the 4 -inch boring diameter. Percolation test "P-1" achieved a steady percolation rate of 6.67 minutes/inch at 36 -inches begs. The percolation rate obtained from testing is fast and considered consistent with "Dune Sand" deposits with Hydrologic Class "A" characteristics as described above. Based on our experience these soils and corresponding percolation rates are not inconsistent with those typical of the soil types encountered in the vicinity. Owing to variations in material type and depth, percolation rates would typically be expected to fluctuate somewhat across a site and are also dependent upon actual construction, depth, size, location, and workmanship of the drainage element. Based on percolation test results, the soil in the upper 42 -inches of the site are moderately permeable (percolation rate>5min/inch<30 min/inch) and are considered suitable for a conventional septic tank/leach trench disposal systems. The percolation test measures the length of time required for a quantity of water to infiltrate into the soil and is commonly referred to as the "percolation rate". It should be noted that the percolation rate is related to, but not equal to, the infiltration rate. While an infiltration rate is a measure of the speed at which water progresses downward into the soil, the percolation rate measures not only the downward progression but the lateral progression through the soil as well. This reflects the fact that the surface area for infiltration testing would include only the horizontal surface while the percolation test includes both the bottom surface area and the sidewalls of the test hole. The calculated conversion from percolation rate to infiltration rate is located within Appendix A. Based on the test results and conversions, the resulting percolation rate in min/inch and infiltration rate in gal/sf/day is listed in Table 8.3 below. The observed infiltration rate listed below does not include a safety factor. It is commonly accepted practice that a minimum factor of safety of 2 be utilized in infiltration design. Therefore, based on the infiltration rate observed in P-1 and utilizing a factor of safety of 2, a design infiltration rate of 10.7 gal/sf/day is recommended as indicated in Table 8.3 below.