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In sizing the disposal fields, various factors were considered including wastewater flow rate, application rate, topography and bed width. A value of 113 gal/bedroom/day was used for the wastewater flow rate. The application rate was calculated from the percolation rate using the standard formula q=5/\t where q=application rate and t=percolation rate. Using the percolation rate from Parcel 1, an application rate of 0.52 gal/sf/day is calculated. For design purposes for both parcels a more conservative application rate of 0.45 gal/sf/day was used. The application area, the area required to properly dispose of the entire volume of wastewater generated by the dwelling, is calculated by dividing the wastewater flow rate by the application rate [(113 gal/bedroom/day x 5 bedrooms) / 0.45 gal/sf/day = 1248 square feet]. Due to hydraulic flow considerations, it is important to design at grade beds as long and narrow as possible. Therefore, a bed width of 7 feet (downslope of the distribution lateral) was used for the design. 1248 sf / 7 sf/lineal foot = 172 lineal feet of at grade bed required. A total length of 180 lineal feet of at grade bed was specified in the design. The hydraulic component of the design is typical of other pressure dosed systems. A flow rate of 30 gpm through the system is achieved by placing 1/8" orifices on 34" centers with a residual head of six feet. The residual head will provide adequate scour velocity to ensure that the distribution laterals and orifices remain relatively free of sediment. Construction of an at grade bed is comprised of four basic steps : native ground preparation, gravel bed construction, distribution lateral installation and final cover. The single most important step in the installation process is the native ground preparation. This process is started by gently removing the grass from the entire disposal field area with a bulldozer blade. Medium grade sand (ideally from Ohe) is then placed on the ground surface in the area of the gravel disposal bed and ripped to a depth of 12" with riper teeth. The purpose of this action is to loosen the surface crust and break up the root mat—facilitating infiltration of the wastewater into the soil. The sand falls into the ripped furrows, keeping them open. Initially, only the disposal bed area is ripped, the area of the capping fill will be ripped after construction of the gravel bed. Care should be taken not to rip the soil excessively or to rip the soil when the ground is too wet. Both of these actions will result in reduced soil permeability. The gravel bed is constructed on contour using pea gravel or drainrock. Rock should be loaded from the uphill side of the bed and raked by hand to the required depth. Only clean rock should be used. The distribution lateral is next placed into the gravel bed. Orifices are drilled into the lateral as specified on the plans. Orifice sizing is 1/8" and all due care should be used during the drilling process to produce an orifice that is clean and free of burrs. Reaming out the hole to remove burrs is to be avoided as it will cause variability in the flow rate per orifice and may lead to uneven loading of the bed. Prior to placing the cover over the bed, the area immediately downslope of the at grade bed should be ripped to a depth of 12 inches. The entire disposal field area is then capped with 12 inches of soil to the dimensions specified in the design. The v-ditch is constructed at this time upslope of the capping fill to intercept surface water and divert it around the bed. Our design delineates installation inspections by the designer during specific points in the construction process. The first inspection is a "tailgate" meeting with the installer, designer and V v —