10.3 Sanitary Sumps, Ejectors & Discharge Points (SPS 382.30 (10), 382.38)
Key Takeaways
All sanitary building subdrains discharge into an approved, vented sump with an airtight cover, at least 25 feet from any water well.
A one-pump sump is at least 24 inches in diameter and a two-pump sump at least 30 inches; the pump must run at least 20 seconds, and the low water level is at least 4 inches above the bottom.
Duplex pumps with alternation and an alarm are required in public buildings where 3 or more water closets or more than 20 dfu enter a sump, and where 2 or more dwellings share a sump.
Grinder pumps need at least 1-1/4 inch discharge; nongrinder pumps serving water closets must pass a 2-inch solid with 2-inch discharge; all ejectors give at least 2 ft/s.
Discharge connects to the gravity drain with a wye, with a full-flow check valve (plus a shutoff valve downstream of each check on duplex systems) and no fixtures on the discharge line.
Sanitary sumps (SPS 382.30 (10) (a))
All sanitary building subdrains discharge into an approved, vented sump with an airtight cover, placed to receive waste by gravity and at least 25 feet from any water well (or as DNR approves). Removable covers may be penetrated only for the electrical supply, the vent and the pump discharge.
Sump capacity (based on one pump):
- Determine peak input in gpm by the water supply fixture unit method for the fixtures draining to the sump. A note allows using the flush-tank conversion.
- The sump must let the pump, when started by the lowest "pump on" switch, run at least 20 seconds.
- Between the highest "pump on" switch and the inlet, the sump holds the input exceeding pump discharge over a 5-minute peak period, and never less than 3 inches of vertical distance.
- Low water level per the manufacturer, but at least 4 inches above the bottom.
- One-pump sumps are at least 24 inches in inside diameter; two-pump sumps at least 30 inches.
Ejectors and pumps (SPS 382.30 (10) (b))
| Requirement | Detail |
|---|---|
| Lifting | Automatic ejectors, pumps or another approved method |
| Duplex required | Public building with 3 or more water closets or more than 20 dfu into the sump; or sanitary waste of 2 or more one- or 2-family dwellings into one sump |
| Duplex controls | Automatic alternation, both units running when one can't keep up, and an audible or visual alarm with manual reset for pump failure |
| Velocity | At least 2 ft/s in the forced discharge |
| Grinder pumps | At least 1-1/4 inch discharge opening and piping |
| Nongrinder pumps serving water closets | Pass a 2-inch solid; at least 2-inch discharge |
| Other sanitary pumps | Rated as effluent pumps; pass a 1/2-inch solid; at least 1-1/4 inch discharge |
| Discharge connection | Wye fitting; on a horizontal drain, the bottom of the wye branch above the horizontal centerline |
| Check valve | Full-flow check valve in each discharge (except exterior sumps) |
| Duplex shutoffs | A gate or ball valve downstream of each check valve |
| Air relief | Air relief valves at high points that trap air |
| Prohibited | No fixtures connected to the discharge pipe before it enters the gravity drain |
Pressurized building sewers from ejectors or pumps are at least 2 inches (1-1/4 inch for grinders) and keep 2 ft/s (section 2.4).
Prefabricated sumps and macerating toilets meet ASME A112.3.4/CSA B45.9. If the manufacturer doesn't size them, they must handle peak input by the wsfu method. Exterior sumps meet SPS 384.25. Instead of duplex pumps, a simplex exterior system may provide one day of holding capacity above a high-level alarm.
Sump vents (SPS 382.31 (8) and (14) (i))
- Interior sanitary sumps are vented to the sump above the inlet, or to the inlet drain within 12 inches of the sump.
- Exterior sumps vent per SPS 382.31 (16) (h): 12 inches above grade with a cap or return bend.
- Vent size comes from Table 382.31-4 by pump capacity. For example, a 40 gpm pump allows a 1-1/4 inch vent up to 72 ft, 1-1/2 inch up to 160 ft, and 2 inches with no limit. Exterior sump vents are at least 2 inches.
- A pneumatic ejector's air relief pipe may not connect to the sanitary, storm or chemical vent system. It is at least 1-1/4 inches (2 inches outdoors) and terminates like a vent.
- Air admittance valves may not vent a sump.
Worked example. A basement in a public building has 2 water closets (12 dfu), 2 lavatories (2 dfu) and a floor drain (2 dfu), for 16 dfu. With fewer than 3 water closets and no more than 20 dfu, a simplex system is allowed. Add a third water closet and duplex pumps with alternation and an alarm become mandatory. The sump would then need a 30-inch minimum diameter.
Discharge points (SPS 382.38 and Table 382.38-1)
Wastewater must discharge only to the points Table 382.38-1 allows. Uses not listed are decided by the department case by case. Selected lines:
| Use | POWTS | Municipal sanitary | Municipal storm | Ground surface | Combined sewer | Subsurface dispersal |
|---|---|---|---|---|---|---|
| Domestic wastewater | Yes | Yes | No | No | Yes | No |
| High-efficiency furnace or water heater condensate | Yes | Yes | No | No | Yes | No |
| Stormwater, groundwater, fire sprinkler test and clearwater | Yes | Yes, 50 gpd max | Yes (DNR permit may be needed) | Yes (unless locally prohibited, no nuisance) | Yes | Yes |
| Water heater T&P valve discharge | Yes | Yes | Yes | Yes (no nuisance) | Yes | Yes |
| Water treatment device wastewater | Yes | Yes | Yes (permit may be needed) | Yes (permit may be needed) | Yes | Yes |
| One- and 2-family garage floor area | Yes | Yes | No | Yes (no nuisance) | Yes | No |
| Garage catch basin or oil interceptor, public building | Holding tank only | Yes | No | No | No | No |
| Elevator pit drain | No | No | Yes | Yes | Yes | Yes |
| Secondary roof drains | No | No | No | Yes, separate and observable | No | No |
"Yes" for POWTS means the POWTS was designed for that wastewater. Subsurface dispersal must meet SPS 382.365. Diatomaceous earth pool filter backwash goes only to a POWTS, sanitary sewer or combined sewer.
When is duplex ejector or pumping equipment required in a public building under SPS 382.30 (10) (b) 2.?
When any water closet in the building discharges to the sump
When 3 or more water closets or more than 20 dfu discharge into the sump
Only when the sump is located outside the building foundation wall
Whenever the sump basin is larger than 24 inches in inside diameter
What is the minimum inside diameter of a sanitary sump containing one pump?
18 inches
30 inches
20 inches
24 inches
Under Table 382.38-1, how much clearwater may discharge to a municipal sanitary sewer?
Up to 50 gallons per day
Unlimited, if trapped
None
Up to 500 gallons per day
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