FOURTH CREEK WASTEWATER TREATMENT PLANT - Executive Summary
The City of Statesville management and Fourth Creek plant management are committed to the safe and environmentally sound operation of the Fourth Creek Wastewater Treatment Plant (WWTP). In providing wastewater treatment services for the City, the Fourth Creek plant must use chlorine as a disinfectant to ensure proper treatment of wastewater to maintain public health and receiving stream water quality. Fourth Creek WWTP has safely operated a disinfection process for over 15 years through an aggressive chlorine safety program including standard operating procedures and training. |
The Fourth Creek WWTP is a 6.0 million gallons per day (MGD) facility that treats 3.0 MGD of wastewater on the average. Incoming wastewater is biologically treated and disinfected with the use of chlorine and then returned to the receiving stream, Fourth Creek. In the disinfection process, treated wastewater is chlorinated using equipment (a chlorinator) designed to mix chlorine gas with water to make a chlor
ine solution. The treated wastewater is allowed to mix with the chlorine solution in a contact chamber for not less than thirty minutes. The chlorine kills pathogens that are dangerous to humans, animals and aquatic life that remain in the treated wastewater after biological treatment. Disinfection of wastewater ensures that public health and receiving stream water quality are preserved.
Per EPA requirements 40 CFR Part 68, chlorine is a regulated toxic chemical and therefore processes utilizing over 2,500 pounds of chlorine must implement Risk Management Plan (RMP) requirements. The Fourth Creek plant stores a maximum of six one-ton chlorine cylinders (approximately 12,000 pounds of chlorine) and is therefore subject to RMP requirements. The Fourth Creek plant is also subject to OSHA Process Safety Management (OSHA PSM) requirements (29 CFR 1910.119).
The worst case, toxic release scenario that was evaluated for the Fourth Creek facility assumes chlorine is released as a gas in
to the Chlorine Building. The release is assumed to empty a one-ton (2,000 pounds) cylinder in ten minutes. The area impacted is down wind at a distance of 2.6 miles.
The alternative toxic release scenario evaluated was identified through the OSHA PSM process hazard analysis review of the disinfection process. Through this process hazard analysis, it was identified that the most likely release that could occur would be due to tubing failure or bad connection on the chlorine vacuum supply line or valve failure at the chlorine cylinder. In this scenario, the release was assumed to come from a horizontal one-ton chlorine cylinder that was feeding gaseous chlorine. Approximately 317 pounds of chlorine would be released in approximately 60 minutes. The area impacted by this release is down wind at a distance of 0.56 miles.
In order to prevent toxic releases of chlorine from the disinfection process, Fourth Creek WWTP complies with the OSHA PSM standard. PSM requires that Fourth Cr
eek's prevention program include process safety information, process hazard analysis, operating procedures, training, mechanical integrity, management of change, pre-startup review, compliance audits, incident investigation, employee participation, hot work permitting and contractor guidelines. Operating standards are in place such that all aspects of equipment operation and maintenance for the disinfection process are covered. The facility is required to conduct inspections of equipment, test emergency procedures and train employees in all aspects of process safety. The chlorination system used is equipped with automatic shutoff in the event of loss of vacuum pressure. Further, the process is monitored by a chlorine gas detection monitor and alarm and operators are trained to thoroughly inspect process equipment daily.
The Fourth Creek WWTP has not had a chlorine release in the past five years. Emergency response to accidents and releases is coordinated with the Statesville Fire
Department's Hazardous Materials Response Team (HAZMAT Team). In the event of a chlorine accident or release, Fourth Creek personnel are trained to notify the HAZMAT team and evacuate personnel upwind and to high ground. Through coordination with the Iredell County ECOM, all of the effected surrounding area would be evacuated.