A tank is defined in Title 124 - On-site Wastewater Treatment Systems as a watertight structure or container used to hold wastewater for such purposes as aeration, dilution, disinfection, equalization, mixing, sedimentation, storage, collection for transport, treatment, or addition of chemicals. The following are the most common types/uses of tanks associated with onsite wastewater treatment systems:
- Septic Tank - A watertight, covered receptacle designed and constructed to receive wastewater from a building sewer, attenuate flows, store digested solids through a period of detention to allow settleable and floating solids to separate from liquids, allow digestion of organic matter by anaerobic bacteria and allow the clarified liquid to discharge for additional treatment and final dispersal to a soil absorption system
- Dosing Chamber or Dosing Tank – A watertight receptacle for retaining wastewater containing a pump or siphon device and that retains effluent until it is intermittently pumped or siphoned to the distribution system or soil absorption system.
- Holding Tank - A tank for the storage of wastewater until it can be transported to a point for proper disposal.
- Pump Tank - A watertight container which houses a pump or pump unit and associated appurtenances used to convey effluent or sewage.
- Pump Chamber or Pump Basin - A watertight container which houses a float or liquid level activated pump and associated appurtenances used to convey sewage or effluent.
- Grease Trap or Grease Trap Tank or Grease Interceptor - A watertight tank designed for the collection and retention of fats, oils, and grease and which is accessible for periodic removal of the contents.
A septic, dosing, holding, pumping, grease trap or other tank used in an onsite wastewater treatment system must be watertight and constructed of materials not subject to excessive corrosion or decay. Acceptable tank construction materials are concrete, fiber reinforced plastic, high density plastic and fiberglass. To minimize corrosion and degradation of the concrete, all concrete interior surfaces of a tank that are exposed to air must be coated with a bitumastic or similar protective compound beginning 3 inches below the normal effluent operating level.
Concrete block and metal are not acceptable materials for new tank construction. When an existing system is being replaced, reconstructed, altered, or modified, and there is an existing concrete block or metal tank that is part of the system, the tank must be inspected. The existing tank must be replaced with a tank meeting current requirements unless the existing tank is determined to be structurally sound and watertight.