SU0006024 SSNL - Laserfiche WebLink

Home Browse Search

B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS The United States Department of Agriculture-Soil Conservation Service(USDA-SCS)indicates the on-site soils to consist of a Capay Clay-UrbanLand Complex (#122). This correlates with the average clay soil texture test results o£38% from the samples analyzed from the future filter bed soil. SS 5.2 a surface and subsurface soil investigation and testing began with three, 15464t deep borings 7 drill$d wi atruck-mounted drill rig: One boring near the center of the Future Filter Bed area, one boring in the Ex' mg LeachBeldarea,and one boring near the center of the Reserve.Le�chfield area. The Existing Leachfield area is presumably directly west of the office building, where there appeared to be a"green stripe"in the lawn area signifying a potential leachline. The soil boring was drilled next to this green stripe. Soil samples were taken every five feet for chemical and physical a lysis. In addition; soil samples were also taken from two shallow percolation test borings at the 24",and 366 depths from the future filter bed. These three deep borings provided: 1.)A profile of the underlying sl characteristics, 2.)Depth to groundwater, which was found to be approximately 11 feet below grade, 3.) Saturated formation(first aquifer)material type, analyzed to be predominately a clay soil type,and 4.)A water table sample for analysis, which is discussed on Page 7. No rust mottling was observed in any of the borings that would be indicative of seasonal soil saturation caused by a dramatic rise in the water table elevation. As discussed below,the water table has apparently risen t 8 feet below gr nd surface(bgs)from on-site monitoring well data. NLS§ 1.1, 1.�2�As the noted on the SOIL ANALYSIS REPORTS,chemical analyses of the soil samples quantify several constituents that will influence_nitrate.loading from this project. The important parameters for nitrate loading assessment are the organic matter,pH cation exchange capac-4(CEC ,clay dontent percentage,along with nitrate-nitrogen content and Total Kjeldahl Nitrogen(TKN)content.TION measures the organic and ammonia fractions of nitrogen. It was tested for two reasons: 1.)To determine any increase in TKN concentrations under the existing leachfield for comparison with the other two sample sites, and 2.) To establish a baseline in the event soil under the future filter bed is ever tested for a monitoring program. There was no significant difference among the three soil samples for TKN. As noted,the organic matter in the soil is expectedly low. This suggests a very low potential for future nitrate-nitrogen loading from indigenous nitrogen soil content. Since septic effluent is composed predominately of ammonium(NH4), the pH, along with the CEC, are significant influences on ammonium molecules. The pH of the soil is moderately alkaline which may slightly inhibit ammonium formation and j stability,and may create a small propensity for ammonia(NH,) formation. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. Cation Exchange Capacities of the soil samples are in the high teens and twenties, which suggests there is some potential for the retention of LLdniveway onium molecules for microbial uptake, and suppression of nitrification. Standard Penetration Test(SPT)results illustrated i Table l are the number of blows required to drive ndard two-inch O.D. split spoon sampler one foot into-undisturbed soil with a 140-pound weight falling ches. Relative condition of clay soils from this procedure can be classified as soft,medium, stiff,very and hard. As observed,only two of the SPT tests show a very stiff clay soil, while the remaining soil is ified as stiff. These two tests classifying the soil as stiff were found in the future filter bed area. equently, it was decided to drill two additional 15 ft deep borings south of the existing entrance to test for not only for this very stiff clay stratum,but also for more permeable strata(borings d not be drilled to the north because of railroad tracks). The very stiff stratum was not encountered to outh of the proposed filter bed location, signifying this stratum is intermittent. Strata with greater eability(e.g., sand, silty sand)were also not encountered. 3 Chesney Consulting