SSO at Station 14+00
At 2:14 a.m. on a Sunday the high-level alarm sounds at the Route 9 lift station. Both pumps are running but the wet well keeps rising. A crew finds sewage surfacing from the manhole at Station 14+00 on an 8-inch vitrified clay gravity main, running about 250 feet down a grass swale into a tributary of Mill Creek, a designated fishing stream. They estimate 4,000 gallons escaped over 45 minutes before the pumps caught up. Grease and roots are visible in the manhole, and flow from an upstream commercial district is heavy. The station cycles every 40 minutes in dry weather but ran 8-minute cycles the previous week during a storm. The crew chief wants to send two men into the 300-foot downstream manhole to jet the line immediately and wants to wash the sewage off the grass with a fire hydrant.
1. Walk through the first two hours and the reporting obligations.
Read the worked answer
Site control, containment, then notification - in that order, but all within hours.
First two hours:
- Stop the discharge. Get the blockage cleared, but do it from above grade - vacuum truck at the manhole, or jet from the upstream manhole with the nozzle run down the pipe. Confirm the wet well is falling and the pumps are keeping up.
- Contain what already escaped. Block the swale with soil, sandbags or a berm before the tributary, and use a vac truck to recover sewage. Do not let the recovery effort push more into the stream.
- Take photographs and notes - time, duration, estimated volume, the receiving water, the weather, and visible sheen - before anything is disturbed or washed away.
- Sample the tributary upstream and downstream for bacteria and report what you find.
- Notify the state and the local health department as soon as the site is stable. A spill reaching waters of the state is a reportable event; your NPDES permit and the state's SSO reporting guidance set the deadline, and 24 hours is the common outer limit, with immediate notification expected for larger or ongoing discharges. Do not wait for the volume estimate to be finalized - report the number you have and update it.
- Notify downstream users and whoever owns the stream access. Post the site.
- Notify the plant manager and the utility's designated spokesperson so only one voice is talking to the press.
Reporting resumes after the fact: a written follow-up report with root cause and corrective action is almost always required after the verbal notice.
2. Evaluate the crew chief's two proposals.
Read the worked answer
Both proposals are wrong, for different reasons.
Sending two men into the downstream manhole: That manhole is a permit-required confined space - sewage, hydrogen sulfide, methane, oxygen deficiency, and the possibility of a surge. Entering it requires a written permit, atmospheric testing before and during entry, forced ventilation, an attendant outside, retrieval equipment, a rescue plan and trained rescuers, and continuous communication. Two men going in with a jet hose is the exact configuration that kills collection system workers. And it is unnecessary: the clog can be jetted from the upstream manhole, which lowers the water level in the downstream manhole anyway, or pulled with a vac truck. If entry truly is needed, it happens after the line is drained and under a full permit, with a rescue-capable crew.
Washing the sewage off the grass with a hydrant: That converts a spill on grass into a second, larger discharge into the tributary and destroys the evidence of the spill volume - which is what the state and any enforcement action will turn on. The right move is to recover with a vacuum truck, till or remove contaminated soil, and apply lime if the health department requires it. Hydrant water is only appropriate for a final rinse into a containment area, with the wash water captured. Take the photographs first regardless.
3. What does this incident tell you about the collection system, and what would you do over the next 12 months?
Read the worked answer
Two separate problems wearing one manhole.
- Grease: the commercial district upstream is sending grease that the line cannot carry. Grease control is a program, not a cleaning schedule.
- I&I: a station cycling every 40 minutes dry and every 8 minutes in a storm is a five-fold peaking factor. The pumps and wet well are being asked to pass stormwater that the sanitary sewer should not accept, and the surcharge at Station 14+00 appears when the peak arrives.
Twelve-month response:
- Grease program: inspect and permit every food service establishment on the upstream reach, require and verify grease interceptor pumping, and put the worst offenders on a compliance schedule with surcharges.
- Flow monitoring: temporary metering at three or four points to locate where the storm water is getting in, then CCTV and smoke testing of that reach. Root intrusion at joints is already visible in this manhole and is a likely I&I source as well as a blockage source.
- Cleaning frequency based on measured grease and root buildup, not on a fixed calendar.
- Capacity: compare the measured peak flow with the pump station and the 8-inch main's capacity. If the peak exceeds capacity, the fix is pipe replacement or storage, not more cleaning.
- Emergency response: keep a written SSO procedure at the station, stock the vac truck and containment materials, and drill the confined space entry with a rescue team so nobody improvises at 2 a.m. again.