In the depths of the wastewater treatment plant

This wastewater treatment plant houses a facility that is as discreet as it is essential: a basin dedicated to storing rainwater and treating wastewater carried by two collectors, including one coming from Versailles and passing through the castle grounds. Beneath the grounds, far from the gilding and mirrored galleries, the wastewater continues its journey. It leaves the royal estate and travels 25 meters underground to the wastewater treatment plant basin.

Although invisible to the public, this structure requires complex maintenance that is vital to the proper functioning of the plant.

Imagine a vast underground basin covering more than 2,000 m², at the bottom of which wastewater has gradually deposited 700 m³ of sludge. To extract it, the Séché Assainissement teams prepared for a particularly technical operation lasting nearly fourteen days.

Rigorous and cool-headed: vital qualities for working in confined spaces

Crane operator, roll-off truck driver, and sanitation technicians: a team of five specialized operators is mobilized to oversee pumping and cleaning operations. All are specifically trained for this type of intervention and aware of the risks inherent in working in confined spaces. Working 25 meters underground is no trivial matter. In these conditions, strict adherence to safety rules is essential. Everyone must know how to perform their role calmly, without leaving any room for improvisation. In this type of tank, gas accumulations can form and pose a risk of poisoning for our operators. To prevent this risk, a strict protocol is applied: before any descent, the atmosphere is checked using detectors that verify the possible presence of gas. At the same time, a ventilation system is activated to continuously renew the air. Once the safety protocol has been validated, the operators meticulously equip themselves for the descent. Inside, personal protective equipment is essential: helmet, waterproof goggles, gloves, 4-gas detector, coveralls, and self-rescue mask for respiratory protection.

Mechanical cleaning: a tailor-made technical solution

Access to the basin is an additional challenge. The technical hatch, which is particularly narrow, allows only minimal room for maneuver. Each time equipment is lowered or raised, extreme caution and perfect coordination with the crane operator and technicians positioned 25 meters below is required. To meet this need, Séché Assainissement mobilized specific equipment:

• a 100-ton mobile crane for lifting machinery and skips,
• a hydrocleaning truck for the initial pumping of liquid sludge,
• a mini-excavator and a bobcat for mechanical cleaning,
• two rotating metal skips for the removal of residues,
• and an ampliroll truck for transfer to the WWTP's discharge lines.

Rigorous, fast-paced, and efficient

Exceeding even the most optimistic forecasts, the team manages to remove an average of nearly 50 m³ of waste per day, which is equivalent to up to eight truckloads per day. The pumped sludge is treated directly on site, at the WWTP discharge lines, thus limiting transfers and environmental impact.

After fourteen days of intense but meticulously planned work, the mission was accomplished! The tank is operational again, and all the sludge was removed on schedule and without incident. Safety is the top priority on this site, as on all others.