PERFORMANCE EVALUATION OF ALTERNATIVE ON-SITE PA SMALL FLOW TREATMENT FACILITIES IN TWO STATE PARKS

The soil suitability requirement, where seasonal high water table is the limiting zone (LZ), is 20 inches for an elevated sand mound in Pennsylvania. A state permitted chlorinated-intermittent sand filter system with a stream discharge is commonly used where the LZ is <20 inches. Pressure dosed intermittent and recirculating sand filters using final soil treatment/disposal units consisting of A/B soil horizon infiltrative beds and trenches were installed in two state parks. Performance of the sand filters as well as the shallow placed and at-grade infiltrative/treatment soil units were monitored. The residential prototype system at Bendigo State Park demonstrated median removal efficiencies for CBOD5, TSS and NH3-N of greater than 98%. Actual pollutant concentrations reaching groundwater, as measured by vacuum lysimeters below the treatment trenches, averaged 0.6 mg/L CBOD5, 9.0 mg/L TSS, less than 0.1 mg/L NH3-N, 9.87 NO3-N and less than 12.0 mg/L Total N. Transport of fecal coliform (FC) bacteria into the shallow perched water table, as measured in samples from shallow monitoring wells, indicated 0 FC/100ml in 106 of 154 samples. Virus transport was not monitored. Based on these results, Pennsylvania has added an alternate on-site sewage treatment system to its 25 Pa. Code Section 73 Alternate Systems Guidance (DEP, 2002) document referred to as the A/B Soil System. The design requirements consist of a two-compartment septic tank, a recirculating subsurface sand filter, UV disinfection, with final treatment and disposal using an at-grade absorption area. The final treatment and dispersal configuration is based on linear loading rates derived from soil morphological analysis and a hydraulic linear loading chart developed at the University of Wisconsin-Madison (Tyler, 2001).