City of Milton Wastewater Treatment Plant - Executive Summary |
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EXECUTIVE SUMMARY a. The City of Milton Waste Water Treatment Plant chlorination system has been installed to disinfect the wastewater treatment plant effluent prior to discharge into the Blackwater River. The plant serves the City of Milton and surrounding sewer service area. The chlorination system is located on the south side of the wastewater treatment plant, at East Walker Street, between Elmira and Henry Streets. The chlorination system is located within the chemical treatment building, an all-metal building constructed on a raised foundation with vented enclosing walls on three sides, which contains two interconnected one-ton liquid chlorine containers, a chlorinator, and various safety equipment, as well as a similar sulfur-dioxide treatment system. The maximum amount of chlorine on hand at any time does not exceed 4,000 pounds. While the plant is manned sixteen hours each day, the chemical treatment building is normally unmanned. Wastewater treatment operators visit the b uilding several times daily, and respond to any trouble alarms that may occur. b. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case scenario" and "alternative case scenario." The first scenario is defined by EPA, which states that "the owner or operator shall assume that the maximum quantity in the largest vessel is released as a gas over 10 minutes," due to unspecified failure. The alternative scenario is defined as "more likely to occur than the worst-case release scenario." The RMP*Comp program was utilized to determine the distance traveled by the chlorine in each scenario before its concentration decreases to the "toxic endpoint," selected by EPA of 3 PPM, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the American Industrial Hygiene Association (AIHA) as the "maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action." The residential population within a circle with a radius corresponding to the toxic endpoint distance has to be defined, "to estimate the population potentially affected." The worst-case release scenario at the City of Milton Waste Water Treatment Plant involves a failure of one of the two one-ton chlorine containers within the chemical treatment building, causing a release of the entire amount of chlorine as a gas in a 10-minute period. The offsite consequence analysis for this scenario was performed utilizing the RMP*Comp program, using EPA guidelines. The distance to toxic endpoint was determined to be 0.9 miles from the point of release, and included an estimated potentially affected residential population of 2,069. Within the distance to the endpoint are located two schools, one nursing home, commer cial/office areas, many residences, and nearly two miles of the Blackwater River. The alternative release scenario, which "must be one that is more likely to occur than the worst-case scenario and that reaches an endpoint offsite," involves a leak in the body of the container. As the chemical treatment building is located well away from any other buildings or structures which could expose it to fire, on a raised foundation protected from vehicular damage, and away from any combustible, flammable, or explosive materials, it is highly unlikely that the process would be acted upon by any external event. As the chlorine and sulfur dioxide containers are not filled on-site, but delivered to the plant, there is no potential for overfilling. The most likely potential cause for a release is damage to the container, either through mishandling and breakage or puncturing, or through rust and/or corrosion to the container resulting in a release of chlorine. The alternative release scenario considered involves a 0.02 square inch hole in the container, located 24 inches below the liquid level of the container. This scenario was also calculated using the RMP*Comp program, and would result in a release rate of 63.3 pounds per minute, emptying the container in approximately 32 minutes, and results in an endpoint of 0.1 mile from the point of release. An estimated residential population of 5 persons is located within this distance, as well as a small area of the Blackwater River. c. The City of Milton Waste Water Treatment Plant's accidental release prevention program is based on the following key elements: - Training of all operators - Preventive maintenance program - Use of state-of-the-art process and safety equipment - Use of accurate and effective operating procedures, written with the participation of the operators - Performance of a hazard review of equipment and procedures - Implementation of an auditing and inspection program. Chemical-specific prevention st eps include availability of self-contained breathing apparatus (SCBA), worn by the operators during connection/disconnection of chlorine supply, awareness of the hazardous and toxic properties of chlorine, and presence of chlorine detectors. d. No accidental releases of chlorine have occurred at this facility in the past five years. e. The facility has an emergency response program, which has been coordinated with the City of Milton Fire Department, which is a member of the Local Emergency Planning Committee (LEPC). This program includes an emergency response decision tree and a notification plan. |