Pueblo West Water Treatment Plant - Executive Summary |
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INTRODUCTION AND OVERVIEW OF THE PUEBLO WEST WTP AND REGULATED SUBSTANCES HANDLED United Sates Environmental Protection Agency (EPA) Risk Management Program (RMP) regulations, promulgated on June 20, 1996 under the Clean Air Act, require facilities that have a regulated substance above the listed threshold quantities to develop a formal Risk Management Program (RMProgram) and to register and submit a Risk Management Plan (RMPlan). The RMP rule regulates 140 chemical for their toxic or flammable characteristics. Of the chemicals regulated, one or more of the following typically triggers RMP requirements at water treatment plants (threshold quantities noted in parentheses): Chlorine (2,500 pounds); anhydrous ammonia (10,000 pounds); aqueous ammonia (20,000 pounds); and chlorine dioxide, (1,000 pounds). If any of these chemicals are handled, stored, or used above the threshold quantity, the water treatment plant (WTP) is subject to the RMP rule. Pueblo West WTP uses chlorine above the 2,500 lb. threshold quantity and therefore must prepare a RMProgram. The chlorine room is equipped to store three, one-ton containers. Two chlorine cylinders are on scales and hooked up to feed and the third is on the floor on permanent trunnions. There are make-shift trunnions as well to store an additional cylinder. Most of the time, there are three cylinders in the room, but occasionally there are four. Thus, the maximum chlorine inventory is 8,000 lbs. The two cylinders on the scales are each equipped with regulators, rotometers and heated drip legs. They are connected to an automatic switch-over valve, which is connected to the manifold system for the four eductors (two eductors are for pre-chlorination, and two are for post-chlorination of the potable water). Below is a brief summary of the Pueblo West WTP Risk Management Program. ACCIDENTAL RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES The purpose of the RMP rule is to lesson the number of serious chemical ac cidents that could affect public health and the environment, and also to improve the response to those accidents that do occur and thereby reduce the severity of the chemical accident. Operators and management at the Pueblo West WTP have several measures already in place, and have initiated other meaures as well, to minimize the likelyhood of an accidental chlorine release. In fact, to date there has not been any accidental chlorine releases at the facility since the building was constructed in 1994. All operators at the WTP are trained in operating the chlorine process, and follow all appropriate safety procedures. Both management and staff are committed to ensuring safety at the WTP. Training and safety meetings are held on a regular basis. GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAM AND CHEMICAL-SPECIFIC PREVENTION STEPS The Pueblo West facility follows all recommended safety, design, and operational and maintenance guidelines developed by the Chlorine Institute. In additi on, refresher training is routinely conducted. The chlorine containers are stored in an enclosed building that meets 1994 Uniform Fire Code requirements, including the installation of a 1-ton chlorine scrubber. The scrubber is connected to the chlorine room by a vent through the wall which has an intake approximately 8-inches off the floor. The scrubber is activated upon alarm from the chlorine monitor. The chlorine room also has a sprinkler system. A control panel, located in the adjacent filter room, contains the chlorine monitor, exhaust fan control, lighting control and scrubber control. WORST-CASE AND ALTERNATIVE RELEASE SCENARIOS For Pueblo West WTP's chlorine process, the worse-case release quantity is 2,000 lbs., i.e. the capacity of a 1-ton container. As defined by the RMP rule, the worst-case release scenario for toxic gases (such as chlorine) to be modeled is "For regulated toxic substances that are normally gases at ambient temperature and handled as a gas or as a liquid under pressure, the owner or operator shall assume that the quantity in the vessel or pipe, is released as a gas over 10 minutes. The release rate shall be assumed to be the total quantity divided by 10 unless passive mitigation systems are in place." Therefore, the worst-case release rate for chlorine at Pueblo West is 200 lbs. per minute. Although, the chlorine vessels are kept indoors, based on recommendations made in RMP guidance manuals, passive mitigation from the building was not included in the worst-case release scenario because the cylinders are unloaded outside the building upon delivery to the site and therefore the cylinders are some times outdoors. As required, the worst-case scenario release was assumed to take place at ground level. The toxic endpoint for chlorine for modeling the worst-case release is 0.0087 mg/L (3 ppm). Note, that a guidance manual (versus a site-specific model) was used to estimate the chlorine release distance to toxic endpoint and th erefore the estimated release distance of 3.07 miles is considered to be a very conservative number. Alternative release scenarios are intended to reflect more likely releases than the worst-case release scenario. Program 2 facilities, such as Pueblo West WTP, are required to evaluate and present at least one alternative release scenario. For alternative release scenarios, both active and passive mitigation systems can be taken into consideration. In this analysis, the chlorine scrubber at the Pueblo West WTP was included. For the alternative-release scenario, failure of the 1/2-inch piping connected to two 1-ton containers was considered. From the "Compliance Guidance and Model Risk Management Program for Water Treatment Plants" manual, the chlorine release rate from this scenario would be limited by the flow through the 5/16-inch valve openings at the chlorine containers rather than the flow through a 1/2-inch pipe. The rate of release would be 23.4 lbs/minute. The maximum du ration of release was assumed to be 60 minutes. This duration was selected because of the close proximity that the fire department is to the WTP. The total chlorine release from this scenario is 1,404 lbs. Because the plant has a scrubber, with a 2,000 lb capacity, the release to the environment is anticipated to be minimal and is not anticipated to migrate beyond the boundary of the site. Thus, for our alternative release scenario, there is no estimated off-site distance to toxic endpoint. FIVE-YEAR ACCIDENT HISTORY Pueblo West WTP has had no accidental releases of chlorine in the past five years. EMERGENCY RESPONSE PLAN Pueblo West WTP has chosen to rely on local community emergency responders. In the event of a chlorine accident, a staff person will call 911, and the fire department will respond to the accident. The fire department is located in close proximity to the WTP and will be able to be on site within minutes of a call. PLANNED CHANGES TO IMPROVE SAFETY The prima ry changes that have been made as a result of implementing an RMProgram are greater staff and management awareness and commitment to safety. |