Wet Well Blockage With a Deteriorating Atmosphere

No entry - the space fails on two parameters.

Parameter	Reading	Program limit	Pass?
Oxygen	19.2%	19.5-23.5%	Fail
LEL	0%	0%	Pass
H2S	48 ppm	<10 ppm	Fail
CO	12 ppm	typically <25-35 ppm	Pass

Two failures means an automatic no-entry, regardless of how urgent the backup is. Also note: 48 ppm H2S at the hatch is a warning, not a reassurance - hydrogen sulfide is heavier than air, so the concentration at the inlet 12 ft down will be higher, and the atmosphere can be stratified. The meter is also only as good as its last bump test; confirm it was bump-tested that day and check the battery and the sample pump before relying on any reading.

Clearing without entry

• Use the vacuum/jetter truck from the upstream manhole or the inlet structure above the wet well, working from outside with hand tools on a pole. A grease-and-wipes mat usually can be broken up and pulled back from the upstream side.
• Set the tripod and harness at the hatch so the vac hose and jetter nozzle can be worked from a standing position beyond the edge - this is not entry, but the area still needs to be barricaded and the attendant still needs to be present.
• If the structure allows, throttle or divert flow upstream to drop the sewage level so the blockage can be reached from the top.
• If the blockage truly cannot be cleared from outside, ventilate with a high-volume blower (3,000+ cfm) for a defined period, re-test, and re-evaluate. If the readings do not come down, the answer remains no entry - get a contractor with supplied-air respiratory protection and a written entry plan.

Do not head-in on a ladder with a hose just because the backup is getting worse. That is exactly the scenario that produces fatalities.

Before any entry, the permit requires

• A completed, signed entry permit with the space identified, hazards listed, and the entry supervisor signing on. The supervisor is 40 minutes away, so either a trained entry supervisor is on site or the entry does not happen. Urgency is not an exception.
• Pre-entry testing with a calibrated, bump-tested meter, in the order oxygen, combustibles, then toxics, taken at multiple depths (top, middle, bottom) after ventilation has stopped for a few minutes.
• Forced-air ventilation running for the duration of the entry, not just before it.
• An attendant stationed outside at the opening, in continuous communication with the entrant, with the retrieval system rigged and ready and the attendant not leaving for any reason.
• Rescue provisions: either a trained on-site rescue team or a written arrangement with the local fire department that has been briefed on the site and can respond. For a 12-ft wet well the non-entry retrieval system is the primary method.
• Communication - radios or a rope signal - and a means to summon help immediately.

If a worker collapses inside

1. Call 911 immediately. State "confined space rescue" and give the address and the readings.
2. Attempt non-entry retrieval with the tripod and harness. This is the only rescue an attendant may perform.
3. The attendant does not enter. Most confined-space multiple fatalities are would-be rescuers. H2S above about 500-700 ppm causes immediate knockdown, and at 100 ppm it rapidly deadens the sense of smell, so a worker may not notice the exposure building. Without supplied-air breathing apparatus, entry means a second victim.
4. Ventilate into the space while waiting, from outside, and keep everyone back from the opening.
5. When the fire department arrives, brief them on the readings, the product, and the layout. Do not let untrained responders enter either, without SCBA.

Sanitary sewer overflow reporting

• Notify the state regulatory agency within 24 hours (many states require immediate oral notice, then a written report within five days) of the overflow: location, estimated volume, start and end time, receiving water or basement affected, and corrective action taken.
• Quantify the volume as best you can: the backed-up interceptor length times the cross-sectional area, plus the reported basement. Even a rough number with the method shown is better than "unknown."
• Notify the local health department and the affected property owner, and follow your public-notice procedure if the spill reached surface water or a drinking water source.
• Check the NPDES permit's bypass and upset provisions: an overflow that reaches waters of the state is a discharge and needs the same 24-hour notice as an effluent violation.
• Compile the written report with the pump station run-time data and the maintenance history - if the station was cycling abnormally, the report needs to say so honestly.

Confined-space program follow-up

• Investigate the near-miss: why was a crew sent to a space that failed atmospheric testing, and did anyone start to enter before the meter was read? Review the permit, the meter calibration log, and the blower availability.
• Retrain the crew on the no-entry decision. Praise the person who read the meter and stopped work - that is the behavior you want repeated.
• Verify that the station is posted as a permit-required confined space and that the blower is actually at the station.
• If any worker was injured or became ill (even briefly), record it on the OSHA 300 log within 7 days if it meets the recordability criteria.
• Consider a permanent fix at this station: a grinder or chopper pump upstream, a bar screen at the wet well inlet, or a larger inlet to stop wipes from matting.

Documentation to keep Meter readings at each depth and time, meter bump-test and calibration records, ventilation duration, who was on site, who authorized/denied entry, the 911 call time, and the spill volume calculations. Write it the same night, while the times are accurate.