Lift Station Losing the Race Against Storm Inflow

The deficit Inflow 900 gpm − both pumps 700 gpm = 200 gpm net accumulation

So the wet well rises because you cannot pump what you are receiving. The pumps are not broken - they are undersized for this inflow.

Time to alarm

• 5 ft of freeboard at 1 ft per 12 minutes is roughly 60 minutes to the high-level alarm, assuming the rise rate holds and nothing else changes.
• Beyond the alarm you have whatever distance is left to the inlet invert - that is the real definition of when the SSO starts.

What shortens the clock

1. Rain continuing or intensifying - the 900 gpm estimate is a snapshot; paving a commercial lot turns rainfall into runoff almost instantly, with very little lag. More rain means a bigger deficit, not the same one.
2. Pump wear or a clog. A rebuilt lag pump is not a proven pump; check amps, discharge pressure, and flow. One pump down takes you to a 550 gpm deficit.
3. Power interruption. If the generator can only carry one pump, a power failure at peak inflow turns a 200 gpm deficit into 550 gpm. That is the biggest single risk on the site.
4. Downstream surcharge. The collection system below is already full, so extra pumping may just move the problem - or cause backups at the manhole 900 ft away. Check head conditions; your pump curve is not the same at elevated static head.
5. Debris and check valve failure - a failed check valve lets pumped flow run back into the well and quietly erases capacity.

First 30 minutes

1. Verify both pumps are actually moving 350 gpm each. Read discharge pressure, amps, and check flow if there is a meter. Confirm by drawdown test if you can. Do not assume a rebuilt pump performs.
2. Notify. Supervisor, utility management, and the state construction programs/regulator per your SSO policy - early notification beats a late excuse. Alert downstream customers and any sensitive sites.
3. Call in resources now, not at the alarm: vactor truck, portable bypass pump, additional generator, and a pumper truck for wet-well drawdown as a last resort.
4. Pre-position a crew at the downstream surcharged manhole to watch for backups and protect public contact.

Generator decision

• Do not rely on the 100 kW unit as your primary defense. One pump means a 550 gpm deficit - the wet well fills twice as fast.
• Request a second generator sized to carry both pumps before the storm's peak, while roads are passable.
• Test the transfer before you need it. Verify the generator actually starts the submersible under load - starting current on submersibles is not the same as running current.

Next several hours

• Keep both pumps running continuously; continuous running is better than trying to cycle.
• Use the vactor to keep the wet well drawn down if a pump is lost.
• Track the level every 15 minutes and record it. Your record is your defense and your maintenance data.
• If an SSO is unavoidable, contain it, disinfect, and document volume and location.

Rank the fixes by cost per gallon of risk removed.

1. Source control first - this is an inflow problem, not a pump problem. The new paved lot is delivering stormwater to the sanitary sewer. Confirm with smoke testing, dye testing, and a rainfall/inflow correlation. Disconnecting or permitting the storm drainage (or requiring on-site detention) is typically far cheaper than upsizing a station, and it attacks the root cause. The lot owner's drainage permit is where the argument should start.
2. I/I rehabilitation in the basin: manhole inspection, sealed covers, cured-in-place lining of the worst segments, and lateral inspections. Do the smoke/dye work and let the data prioritize the spending.
3. Pump station capacity and redundancy. If inflow truly peaks near 900 gpm, a 700 gpm station is undersized. Options: larger pumps, a third pump, larger wet well, or a flow equalization/detention basin upstream - often the cheapest capacity.
4. A permanent standby generator sized for the whole station, with automatic transfer. Given that an SSO during a power failure is the highest-consequence scenario, this belongs high on the list even though it does not add pumping capacity.
5. Telemetry and alarms that call out at multiple levels, so nobody learns about a rising well by driving past it.

Budget argument: present the cost of the next SSO - cleanup, enforcement, public notice, and fines - against the cost of the fix. Also point out the pumps are being asked to do something they were never sized for, so they will fail early and cost even more. Source control plus standby power is the strongest first package.