City of Midland Paul Davis Well Field - Executive Summary
Facility Description |
The City of Midland Paul Davis Well Field provides treated water to rural customers and supplements treated water for the City and surrounding areas. Raw water is processed and disinfected with chlorine in the treatment process. The Well Field maintains a maximum inventory of 6,000 pounds of chlorine in one-ton containers, which above the threshold level and is therefore subject to the requirements of the Risk Management Program.
Chlorine, a chemical required by regulation to be used in the disinfection process, has been in use at the Well Field since operation began. No accidental releases of chlorine meeting the requirements of the five year accident history have occurred at the facility.
Offsite Consequence Analysis
The off-site consequences of potential accidental releases of chlorine at the Plant were assessed in accordance with requirements established in 40 Code of Federal Regulations, Part 68 SLAB Atmospheric Dispersion Model, an EPA-recognized comp
uter modeling program, was used to model a worst case release scenario and an alternative release scenario for chlorine.
The worst case scenario is a model of a release under specific conditions established by EPA, including release volume, duration, and weather conditions. Active safety systems in place at the Plant that are designed to minimize the effects of a chlorine release cannot be considered in the worst case scenario.
The worst case release scenario is required to assume the release in a ten minute period of the entire contents of the largest vessel of the regulated chemical onsite, which for the Well Field is a one-ton chlorine container. Meteorological conditions required by EPA rules are assumed for the release. The toxic endpoint for the worst case release scenario is estimated to reach a point offsite of the facility. Since this facility is located in a populated area, the chlorine vapor would reach offsite endpoints and nearby public receptors. No sensitive envi
ronmental receptors designated by EPA are located within the release area.
The alternative release scenario represents the results more likely to occur in the event of a chlorine release at the Well Field. Active safety systems at the Well Field are considered for the alternative release scenario. Average weather conditions at the facility are used for this release scenario, as recommended by EPA regulations.
For the chlorine alternative release scenario, failure of a gas valve on a chlorine container is assumed. While the toxic endpoint for the chlorine alternative release scenario is estimated to reach a point beyond the facility boundary, no sensitive environmental receptors designated by EPA are affected by this release scenario. Two residences associated with the Well Field are the only public receptors within the release area.
The Well Field is subject to Prevention Program 2 of the Risk Management Program. In accordance with the requirements of Progra
m 2, the Well Field maintains specifications for the equipment associated with the chlorine feed system and has documented the codes and standards adhered to in designing, constructing, and operating the system. The safe operating ranges for the chlorine system are documented, and it is operated within these safe ranges.
A hazard review has been conducted for the chlorine system and identified action items are expected to be completed by December 31, 2002. When a major process change is made to the system, there are procedures in place to conduct a hazard review. Otherwise, a hazard review is conducted every five years.
Written procedures for the operation and maintenance of the chlorine system are also in place at the Well Field. Procedures are reviewed and updated periodically by facility personnel and whenever a major process change occurs.
Well Field operators receive training in the operation of the chlorine system through classes and on-the-job instruction. Competency is
determined through supervisor observation and operator demonstration of activities. Operators receive refresher training at least every three years, or more often as necessary. Only qualified operators operate the chlorine system.
In accordance with the regulations, a team of facility personnel will conduct a compliance audit of the facility operations and procedures once every three years and whenever a major process modification is made. A compliance audit checklist has been developed based on American Water Works Association recommendations. A system to correct any deficiency discovered during the compliance audit is in place.
In the event of an accidental release, or a situation that could lead to an accidental release, there are procedures in place to investigate such incidents, develop findings and recommendations for corrective action, and implement the recommendations.
Facility personnel are trained to notify emergency personnel in the event of a significant chlorine lea
k. In the unlikely event a chlorine release requiring the assistance of offsite emergency response personnel occurs, the City of Midland Fire Department is responsible for responding to the accident, coordinating the emergency response effort, and notifying potentially affected areas in the surrounding community.