Borough of Carlisle Water Treatment Plant - Executive Summary |
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a. The Borough of Carlisle Municipal Authority owns a potable water treatment system and distribution system for the Borough of Carlisle, county seat for Cumberland County, Pennsylvania, and for some surrounding communities. This system is operated by the Borough of Carlisle. The water treatment plant located at 165 Long's Gap Road processes up to 7.0 million gallons per day of water drawn from the Conodoguinet Creek to yield potable water. Treatment processes include pretreatment, coagulation, flocculation, sedimentation, filtration, fluoridation, and chlorine disinfection. Chemicals are also added to control taste, odor, and corrosion. The plant is operated 24 hours per day, every day of the year. b. The water treatment plant includes a chlorination room, which contains two (2) one-ton cylinders of chlorine liquified under pressure, a chlorinator, various safety equipment, and instrumentation consisting of flow recorders, electrical panels, and a gas detector/a larm unit. The chlorinator system uses remote-vacuum-actuated feed lines and has high pressure regulators attached directly to the chlorine vessel gas valves, mitigating against high-pressure gas releases through the chlorinator system. Water treatment operators regularly check the room and its equipment, inventorying the rate of chlorine use and adjusting the rate as necessary. The maximum intended inventory is 4,000 pounds. The average operating inventory is 2,750 pounds. c. The off-site consequence analysis includes consideration of two chlorine release scenarios, one "worst-case" and one "alternative-case." The first scenario is defined by the regulations as the "maximum quantity in the largest vessel" being released "as a gas over ten minutes," due to an unspecified failure. The alternative-case scenario is defined as "more likely to occur than the worst-case scenario." Atmospheric dispersion modeling was performed using the RMP*Comp program distributed by the Chemical Emergency Preparedness and Prevention Office of the EPA. This model determined the distance traveled by the chlorine released until its concentration decreases to the"toxic endpoint" selected by EPA of 3 ppm, (0.0087 mg/L,) which is the Emergency Response Planning Guideline Level 2, defined by the American Industrial Hygiene Association 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 Carlisle Water Treatment Plant involves a failure of one of the two chlorine containers, or a 2,000 pound release. The off-site consequence analysis was performed under the prescribed EPA conditions of all volume released as gas within a ten minute period, to an ERPG-2 endpoint radius of 1.3 miles according to the RMP*Comp model. Within the 5.4 square-mile area bounded by this circle reside 8,054 people who may potentially be affected by the release. The alternative-case scenario chosen involves a leak from a rust-hole in one of the vessels, as defined in the RMP Program Guidance for Wastewater Treatment Plants. The RMP*Comp model was run assuming a 23 minute duration release at 87 pounds per minute from a rust hole in the liquid portion of the cylinder, mitigated by enclosure, which yielded a distance to endpoint of 0.1 miles and an area of twenty acres surrounding the facility. The meteorological conditions used were taken from the Guidance to be stability class D and wind speed of 3.0 m/sec. Approximately 30 people would be affected by this release. Actuation of a chlorine gas detector and al arm system is an active mitigation considered. d. The Borough of Carlisle Municipal Authority's water treatment plant accidental release prevention program is based upon the following elements: 1) High level of training for the operators. 2) Preventative maintenance program for equipment. 3) Use of state-of-the-art process and safety equipment. 4) Use of accurate and effective operating procedures, written with the participation of the operators. 5) Performance of a hazard review of the equipment and procedures. 6) Implementation of an auditing and inspection program. Chemical-specific prevention steps include availability of self-contained breathing apparatus (SCBA,) awareness of the hazards and toxic properties of chlorine, and the presence of a chlorine gas detector. e. No accidental releases of chlorine have occurred at this facility in the past five years. f. The facility has an emergency response program which has been reviewed and coordinated by the Cumberland County Local Emergency Planning Committee (LEPC) in Carlisle and by the Empire-Friendship Fire Companies of Carlisle and the Cumberland County HAZMAT Response Team. This program includes an emergency response decision tree and a notification plan. Emergency response drills have been conducted with the fire companies, and the operation and response procedures are reviewed and updated on a regular basis. g. Changes to improve safety (recommended actions) were made following a February 4, 1999, inspection of the disinfection systems by the Borough's consulting engineer. These recommendations included third-party training of all water plant employees in chlorine usage and safety, done on June 2, 1999, improvement to written emergency operating procedures, and the installation of a security system to prevent unauthorized entry. |