AN ALTERNATIVE TO SUBMITTING CAA RISK MANAGEMENT PLANS: GAS TO LIQUID CHEMICAL FEED SYSTEM CONVERSION AT SEVEN WASTEWATER TREATMENT PLANTS

摘要

Under the USEPA抯 Clean Air Act (CAA), the Accidental Release PreventionProvisions require submittal of Risk Management Plans (RMPs) for facilities storingspecific quantities of toxic or flammable materials. At wastewater treatment facilitiesthe most common chemicals used that are subject to the CAA RMP requirements arechlorine and sulfur dioxide gases. Facilities storing more than 2,500 pounds of chlorineor 5,000 pounds of sulfur dioxide are covered by the CAA RMP requirements. Thedeadline established for submittal of the RMPs was June 21, 1999. An alternative tosubmitting the RMPs is to remove the hazardous gases from the plant sites.The Hampton Roads Sanitation District (HRSD) owns and operates nine wastewatertreatment facilities in southeastern Virginia. Issues involved in converting fromgaseous to liquid chemical feed systems include: potential health impacts to HRSDstaff and to the public; treatment plant process impacts; and costs to the rate payers.After careful consideration, HRSD decided to remove all chlorine and sulfur dioxide gasfrom seven of the nine treatment plants prior to the June 21, 1999 deadline. Thisdecision was made in part as an alternative to submitting the RMPs for these facilities.The remaining two plants were previously made complaint by retrofitting the facilitieswith hazardous gas leak containment and scrubbing facilities.Operational issues considered during facility design include sodium hypochloriteleakage, sodium hypochlorite degradation and off-gassing, dilution water usage,disinfectant mixing, temporary chemical feed and storage, chemical crystallization,and disinfection and dechlorination control loops.This paper will discuss the design, construction, and startup issues encounteredduring the conversion from gaseous to liquid disinfection and dechlorinationchemicals at the seven regional treatment plants.