Jefferson County eliminates chlorine hazard
As Jefferson County, Colo., approached the 21st century, its Water Sanitation District (WSD) had a problem: Chlorine gas used by the North Table Mountain surface water treatment plant was producing concerns about safety.
The North Table Mountain plant is situated approximately 30 miles northwest of Denver. It serves 10,000 residents in the unincorporated portion of Jefferson County and in parts of Golden and Arvada. The area’s population has grown steadily since the plant went online in 1961, and, as new homes advanced on the facility, concern about chlorine gas exposure grew.
That changed earlier this year, however, when the district installed a mixed-oxidant generator at the 11-mgd facility, allowing the WSD to reduce its dependency on chlorine and lime. “Safety concerns were the primary reasons for upgrading to on-site generation,” says Rick Jeschke, WSD district engineer and manager. “New residential neighborhoods are being developed close to the water plant, and the poisonous chlorine gas used for water disinfection posed a significant liability issue for the plant.”
Prior to installation of the new generator, the WSD was using 100 pounds of chlorine gas per day to treat up to 5 mgd of water. As residential growth continued, the district would face the prospect of using even more chemicals to treat the increasing water load.
Additionally, because of the chlorine gas risk, the district would have to comply with EPA requirements for developing a Risk Management Plan (RMP). As part of that process, the WSD would have to prepare an analysis of off-site consequences, a five-year accident history, a prevention program and an emergency response plan. Every three years, it would be audited for compliance.
In June 1999, the WSD identified a means to reduce its chlorine usage, improve safety and eliminate its need to develop the RMP. The answer was a generator that employs only salt, water and electricity to create a mixed-oxidant solution for water disinfection. Supplied by Albuquerque, N.M.-based MIOX, the unit consists of three electrolytic cells, each with the ability to produce 50 pounds of chlorine per day.
Installation of the Model 503 unit, which went online in January, took one week. The mixed-oxidant solution is produced on-site as needed, eliminating the need to store chlorine gas at the plant. By ridding itself of that liability, the district was no longer obligated to produce an RMP.
Today, during peak loads, the WSD is treating 5 mgd, for which the generator produces 75 pounds of chlorine. The excess capacity in the generator will accommodate future demand increases, and it serves as a backup should one of the cells need to be taken off-line.
In addition to eliminating chlorine gas from its treatment process, the WSD noted a 33 percent reduction in chlorine dosage and a 50 percent decrease in its use of lime for pH adjustment. According to Jeschke, the new generator has made the North Table Mountain plant safer for residents and employees alike.
