A wet well is the chamber that collects sewage before pumping. A wet-well/dry-well station keeps pumps in a separate dry pump room; a submersible station puts sealed pumps in the wet well. The layouts change access, space and maintenance. Approved plans and local requirements determine the design.
What does the dry well do?
It provides a space for equipment beside the sewage chamber. EPA's 2000 lift-station fact sheet says that in dry-well stations, pumps and valves are housed in a pump room that is accessible for inspection and maintenance. The chambers are separate; piping carries sewage from the wet well through the pumps and into the discharge line.
That access is an advantage when technicians need to inspect running equipment or repair it. The room itself also needs suitable drainage, ventilation, access and other systems specified by the approved design. Being dry during normal operation does not make entry automatically safe.
How is a submersible station different?
The pumps are sealed units designed to work submerged in sewage. EPA's fact sheet describes submersible stations as typically less expensive than dry-well stations and able to operate without frequent pump maintenance. That is a design comparison in a dated technical publication, not a claim that any particular pump needs no service.
Guide rails and lifting equipment commonly allow the pump to be removed for hands-on repair without a person entering the wet well. Operating checks can also use the controls, alarms, level readings and electrical measurements; checking a station does not always require lifting every pump.
| Feature | Wet-well/dry-well layout | Submersible layout |
|---|---|---|
| Sewage collection | Wet well | Wet well |
| Pump location | Separate dry room | In the wet well |
| Hands-on equipment access | In the pump room under the site's access procedure | Remove the pump using the designed lifting arrangement |
| Other equipment | Pump-room drainage, ventilation and controls as designed | Controls, alarms and often a separate valve vault |
| Maintenance plan | Covers pumps and pump-room equipment | Covers pumps, seals, controls and wet-well equipment |
EPA's 2000 fact sheet reported replacement of some small and medium dry-well stations with submersible designs because of cost, footprint and maintenance considerations. Use that as background, rather than evidence of what every new Valley station uses today.
### Can pumps sit above the wet well?
Yes. Some layouts use self-priming pumps outside or above the sewage chamber. Gorman-Rupp describes pumps mounted above the liquid with the suction line submerged. The layout has limits: Arizona's ADEQ 4.01 rule prohibits suction pumps when the sewage lift exceeds 15 feet. The approved design and pump operating limits determine whether this arrangement fits the site.
What does Arizona require?
A sewage collection system covered by ADEQ's 4.01 General Permit must meet rule R18-9-E301. Its lift-station provisions include wet-well sizing and sewage retention limits, at least two pumps with design-flow capacity while one is out of service, level alarms, and backup power/redundant level controls for stations above the rule's stated flow threshold.
Those requirements concern the permitted system, not every small residential ejector pump. Check whether this permit applies, the approved engineering plans and the local authority's additional requirements. Cities can prescribe their own details. Our Valley lift-station and ejector rules and private lift-station ADEQ permits explain that distinction.
Is this the same as an Arizona stormwater drywell?
No. A dry pump room at a sewage station is different from a stormwater drywell, which disposes of runoff into the subsurface. The University of Arizona's WRRC describes those stormwater structures and the state restrictions on their use. Do not direct sewage, grease or wash water into a stormwater drywell. Confirm which structure a site drawing or inspection report refers to.
What should an owner check?
Start with the station's plans and operation-and-maintenance manual. Identify pump type, lifting arrangements, alarms, backup systems, maintenance responsibilities and the entry procedure. ADEQ's rule requires applicable confined-space rules to be followed; use qualified personnel and the site's procedure for inspection or entry.
Both layouts need an appropriate maintenance plan. See how often to service a commercial lift station and who maintains a private station. If the system is alarming, start with what to do when a lift-station alarm sounds. For related systems, see sump pump, ejector pump and lift station differences and what a sewage lift station is.
HQ Plumbing & Air handles the building drain and sewer lines carrying waste to the station. For those lines, our commercial drain-cleaning team provides clog clearing and camera inspection, with licensed and insured service and upfront pricing.