SU0004490 SSNL - Laserfiche WebLink

Home Browse Search

The second physical tests to be conducted were percolation and infiltration tests in the location of the future filter bed. Percolation testing was done at 24 inches, 42 inches and 7.5 feet below existing grade and in accordance with EHD Regulations. Only the 24 and 42 inch perc tests were witnessed by EHD staff. After the three test borings were drilled on September 24,two inches of pea gravel was placed in each boring, along with a three-inch O.D. PVC perforated pipe. Each four-inch diameter boring was completely filled with water four times to ensure complete soil saturation. Perc testing commenced on September 25 and was conducted under Procedure#2. The tests could have been run under Procedure #3 for a one-hour period, but the four-hour test period was run instead to induce and ensure maximum soil saturation. The final percolation rate obtained was 4.9 minutes per inch(mpi)for the 24-inch deep boring and 6.1 mpi for the 42 inch boring. These perc rates do not exceed (are not faster)than the minimum value of< 1 mpi as determined in USEPA Onsite Wastewater and Treatment and Disposal Systems. Coincidentally, these two perc test rates are the inverse of the water drop in inches for the two respective test borings. The unofficial 7.5 foot test boring had a final percolation rate of 5.5 mpi. The second test conducted was the Double Ring hzfiltrometer test(ASTM D-3385)which measures the rate of one-dimensional water infiltration and flow through the soil/water interface. This test is more representative of the hydraulic conductivity properties of the soil than the standard percolation test,particularly with respect to measuring infiltration at the soil/effluent interface. Since a filter bed design is proposed, and the soil/effluent interface will be approximately 18 inches below grade,the Infiltrometer test was conducted at this depth. Test results as calculated on the field test form indicate a rate of 17.9 centimeters/hour(cm/hr),or 8.5 mpi under saturated soil conditions. This translates to an application rate of 0.857 gallons/ftZ/day, according to published sewage application rates correlated with percolation rates. B. Soil Chemical Test Results As referenced above, two soil samples were submitted to the laboratory for analytical testing. The attached Soil Analysis Report denotes the samples as 2 FT and 10 FT. Analyzed constituents relating to nitrate loading include the organic matter content of the soil, pH, Cation Exchange Capacity (CEC), the nitrate-nitrogen (NO3-N) content. Of significance are the nitrate-nitrogen concentrations, revealing low concentrations of 7 ppm NO3-N at both the 2 foot and 10 foot depth. This nitrate-nitrogen concentration is typical of non-agricultural land. The CEC potential to trap and hold ammonium exists in the upper soils, but is non-existent in the deeper soils. The denitrification capacity of the soil is predominately dependant upon the abundance of an organic carbon substrate, high soil moisture content leading to anaerobic environment, and high soil pH. The organic content of the soil is understandably very low since it has not been farmed for probably 15 to 25 years. The pH is alkaline near the surface at 7.8 and even more alkaline at 10 feet with a pH of 8.5. Although saturated soil conditions may develop near the soil/effluent interface, sufficient organic carbon substrate from the wastewater and an alkaline soil pH may induce denitrification. As discussed below, by using peat at the soil/effluent interface, this may theoretically advance the denitrification potential. Page -3- C&snq Comufting