Laserfiche WebLink
EXAMPLE <br /> 3.3 Requirements for Pressure Distribution Trenches <br /> A. DESCRIPTION <br /> Pressure distribution (PD) trench systems are a variation of a conventional gravity <br /> drainfield system that use a pump and small-diameter pressure piping to achieve broad, <br /> uniform distribution of wastewater throughout the dispersal field for improved soil <br /> absorption and better treatment of percolating effluent. Pressure distribution can be <br /> used in conjunction with standard trench designs and for chamber systems; and can be <br /> used in conjunction with either septic tank effluent or with supplemental treatment. <br /> B. APPLICATIONS <br /> Pressure distribution trench systems are permitted and/or required for the following <br /> situations: <br /> • To allow reduction of vertical separation to groundwater or soil depth below <br /> trench bottom from 5 feet to: (a) 3 feet for septic tank effluent; or (b) 2 feet for <br /> effluent receiving supplemental treatment; <br /> • For large flow systems, e.g., with dispersal field lengths (primary) exceeding 500 <br /> lineal feet; and <br /> • Others as may be determined necessary due to site-specific soil, geology or <br /> other conditions. <br /> C. SITING CRITERIA <br /> 1. Setbacks. Horizontal setback requirements for PD trench systems shall be those <br /> applicable to conventional dispersal fields as specified in this Manual. <br /> 2. Vertical Separation Requirements. <br /> a. Depth to Groundwater. Minimum depth to seasonal high groundwater for PD <br /> trench systems receiving septic tank effluent, as measured from trench bottom, <br /> shall be three (3) feet. <br /> b. Soil Depth. Minimum depth of soil, as measured from trench bottom to <br /> impermeable soil or rock, for PD trench systems shall be three (3) feet. <br /> 1 <br />