Trench configuration with 2 ft Separation

A RaceTrac gas station-convenience store in Central Florida was plagued with rising maintenance costs due to a problematic aerobic wastewater system and an associated failed drain field. The company’s engineers found the solution was to retrofit this store’s existing wastewater tanks with pumps, then convert to a pressure-dosed system. Selection of the low profile “rockless” drain field system available from Advanced Drainage Systems, Inc. (ADS) (NYSE: WMS) met all the required project criteria. Made up of perforated four-inch diameter high-density polyethylene (HDPE) corrugated pipe with both holes and slots, it can take the place of a conventional gravel system while providing more capacity and can be installed with shallow cover. With a project life expectancy of more than 30 years, the new system is rated at 10.9 gallons a foot, whereas a traditional four-inch pipe in gravel system of the same size could handle 7.9 gallons per foot by contrast.
“The use of HDPE pipe for sanitary installations has many benefits,” stated Tony Radoszewski, CAE, president of the Plastics Pipe Institute, Inc. (PPI), the major North American trade association representing all segments of the plastic pipe industry. “The first applications were in Scandinavian countries and in Germany during the mid-sixties. An independent testing agency examined the systems and reported that no significant changes in the pipes’ chemical or physical properties after more than 25 years in service existed. Sanitary sewage is itself not highly corrosive, but, under anaerobic conditions, bacteria may decompose sanitary sewage and form hydrogen sulfide gas. The gas combines with moist air above the fluid stream and creates sulfuric acid, which then attacks metallic or concrete pipe, but has no effect on polyethylene pipe. HDPE pipe is highly resistant to the wet, hydrogen sulfide gas and the low concentrations of sulfuric acid found in a sanitary sewer. For example, this type of pipe is resistant to 90 percent sulfuric acid solution at service temperatures up to 120°F so, it’s a perfect product to use in this installation.”
At the store, the 1,200-square foot system involved eight 50-foot long runs of four-inch diameter HDPE distribution pipe nestled between two bundles of VOID pipe. The VOID pipes are specially manufactured by ADS, a member company of PPI, with both holes and slots to allow for the passage of the effluent, allowing for evaporation and transpiration. Over time, grease would bridge slots and holes would clog — HDPE pipe alleviates both of these issues.
The distribution pipe, marked with a white line, is the only one to be connected to the outflow of the tank. A one-inch diameter PVC pressure-dosed pipe was fed through HDPE end caps on the distribution pipe. Cover was six inches of native, sandy soil. Flanking the HDPE corrugated distribution pipe with bundles of the VOID pipe eliminated the need for gravel.
Additional information can be found at www.ads-pipe.com.

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