Lead Abatement a ConcernEnvironmental Control Speeds Water Tank Project

Concerns about expenses, deadlines and the environment all came into play when the Helix Water District near San Diego, Calif., had to recoat a four-million-gallon water storage tank.

The key to addressing those concerns, according to Roland Reesby, West Coast regional manager of Munters Moisture Control Services, was an environmental control system that used newly developed gas regenerated dehumidifiers in conjunction with lead abatement equipment. Eliminating condensation inside the tank during blasting and coating at the Helix project benefited both the coating process and the lead abatement effort.

?Helix saved more than $4,000 per week using an advanced system developed by Munters,? Reesby said. ?At the same time, the project moved forward on schedule, without any fear of weather changes slowing progress down.?

Tight Deadline

The four-million-gallon tank had been scheduled to have lead-based paint removed from its roof and support structure during the winter months. Helix required that it be returned to service by summer ? a predictably dry time when Southern California communities can experience severe water shortages or be jeopardized by fires. The advent of summer heat also threatened to raise temperatures to unsafe levels inside the tank, creating a dangerous situation for the workers.

?In tank coating there?s no substitute for desiccant dehumidification,? said Reesby. ?With dew points kept low in the tank, condensation can not occur. As a result, no new corrosion will form on the skin after blasting.?

Because dehumidification allowed a continuous work process, the tank was entirely blasted, and then required only a single cleanup. After that, the coating was applied in a monolithic process. Working this way ensured the shortest work period and precluded later coating failures caused by corrosion.

While this was the ideal way to proceed, running diesel generators around-the-clock to power electrical dehumidifiers would have driven up project energy costs and at the same time created objectionable noise pollution in nearby residential neighborhoods.

As a result, the solution Munters proposed was rental dehumidifiers regenerated by propane gas. The cost of renting this equipment for the entire job plus the propane fuel was less than the cost of the painting contractor operating its own electrical dehumidifiers. The gas-fired equipment created no noise or air pollution.

Controlling the Lead

To ensure that during the blasting process lead did not escape from the work area, Munters was asked to design a dehumidification system that would work in conjunction with the contractor?s dust collectors.

?We created negative pressure in the tank by expelling air from the work area and passing it through the contractor?s HEPA filters before exhausting it to the outside. At the same time, dry air from the dehumidifiers was pumped into the tank controlling humidity levels,? said Reesby.

Lowering humidity inside the tank facilitated the coating contractor?s use of steel shot abrasive, which was designed to be reclaimed. This had two major advantages.

?Without moisture in the tank, the steel shot abrasive could not corrode and clump together. This allowed the reclaim unit to function efficiently,? Reesby said. ?Using a reclaimable steel shot also meant that the lead could not contaminate the abrasive ? as would have happened with sand. This reduced the amount of hazardous waste which had to be managed.?