Des Moines Water Works Maffitt Treatment Plant - Executive Summary |
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The Des Moines Water Works accidental release prevention policy involves a unified approach that integrates technologies, procedures and management practices. All applicable procedures of the Iowa Department of Natural Resources and the U.S. Environmental Protection Agency (EPA) are adhered to. The Des Moines Water Works emergency response policy involves the preparation of a response plan tailored for our facility and to the emergency response services available from the community, and is in compliance with the EPA Emergency Response Plan. The Des Moines Water Works Treatment Plant at Maffitt is a brand new facility which is going online on May 15, 2000. The hazardous substances stored and used on this site allow us to disinfect and purify the water we provide to our customers. The covered process involves a chlorine room, chlorinators, monitoring and detection equipment, instrument panels and additional safety equipment. The amount of chlorine handled inside the room is normall y eight one-ton containers. The facility is normally unmanned, and is operated via computer controls from our Fleur Drive treatment plant which has operators present 24 hours per day. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case scenario" and "alternate scenario". The first scenario is defined by the EPA, which states that the "owner or operator shall assume that the ... maximum quantity in the largest vessel... is released over 10 minutes," due to an unspecified failure. The alternate scenario is defined as "more likely to occur than the worst case release scenario". Atmospheric dispersion modeling has to be performed to determine the the distance traveled by the chlorine released before its concentration decreases to the "toxic endpoint" selected by the 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 radius corresponding to the toxic endpoint distance has to be defined,"to estimate the population potentially affected". The worst case scenario at the Des Moines Water Works Treatment Plant at Maffitt facility involves a failure of one one-ton container for a total of 2000 pounds of chlorine. The offsite consequence analysis for this scenario was performed using a model program developed jointly by the American Metropolitan Sewerage Association and the EPA. Using the EPA's criteria for a worst case scenario the toxic endpoint is 1.3 miles. The alternative release scenario involves the failure of the flexible connections (pigtails) or a valve con nected to one container. The amount of chlorine released is 317 pounds over a 60 minute duration with a maximum average release rate of 10.5 pounds per minutes. The distance to the toxic endpoint is 0.01 miles. The chlorinators are of the vacuum type which reduces the amount of chlorine should a pigtail rupture. This release would occur inside the facility which would activate a scrubber, removing the chlorine gas from the air. The Des Moines Water Works accidental release prevention program is based on the following: 1. High level of training of the operators. 2. Preventative maintenance program. 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 equipment and procedures. 6. Implementation of an auditing and inspection program. Chemical specific prevention steps include availability of an in-house hazmat team, ope rators trained in release response, awareness of the hazardous and toxic properties of chlorine and the presence of chlorine detectors. This is a new facility, therefore, no accidental releases of chlorine having offsite consequences have occurred. The facility has an emergency response program with a response team capable of responding and controlling most releases. The facility has plans to bring the Bloomfield Volunteer Fire Department to the site for an information session. The Des Moines Water Works has also coordinated with the Des Moines Fire Department(DMFD) HazMat team in the past. The Des Moines Water Works is a member of the Polk County Local Emergency Planning Committee, which has a public notification program. |