Wicks Water Treatment Plant - Executive Summary |
|
The Wicks Water Treatment Plant (Wicks WTP) is owned and operated by City of The Dalles, Oregon, a municipal corporation. This plant, which treats surface water from South Fork Mill Creek, is located in a rural setting and provides 90% of the water used within the city for residential, commercial, and industrial purposes. Disinfection is a critical aspect of water treatment, essential to providing a safe drinking water supply. The Wicks WTP utilizes chlorine as its primary and residual disinfectant. The chlorine is received and stored as a liquified gas under pressure in one-ton containers; up to five containers may be on-site at any one time for a total maximum inventory of 10,000 pounds of chlorine. Due to the quantity of chlorine stored at the Wicks WTP, US-EPA regulation 40 CFR Part 68, Section 112 (r)(7) has mandated the development of the following Risk Management Plan (RMP). A Process Safety Management (PSM) program for chlorine had already been developed for the Wicks WTP as required by OSHA regulation 29 CFR 1910.119. This PSM program was developed with input from all operational levels of staff and includes, in part, a summary of process safety information, the methodology and results of a site-specific Process Hazard Analysis, written operating procedures for all aspects of the chlorine processes, and required training schedules for all affected personnel. The purpose and goal of the PSM program is to prevent any uncontrolled or catastrophic releases of chlorine and to protect on-site personnel in event of such a release. Compliance with all aspects of the PSM program is mandatory for all affected employees by City policy. There have been no accidents at the Wicks WTP relative to the chlorine processes within the last five years. A Chlorine Emergency Response Plan has been also developed for the Wicks WTP. In this plan, plant personnel and other City resources coordinate with support services of local emergency response agencies to protect emp loyees and the public in event of a chlorine release. The Chlorine ERP also provides for mitigation of the release. During development of the Risk Management Plan for Chlorine, an Offsite Consequences Analysis (OCA) was conducted which evaluated one worst-case and one alternate release scenarios. The assumed conditions of the worst case scenario were established in the rule and are outlined in the Offsite Consequences Analysis section of this RMP. No passive mitigation was considered in this scenario although the entire chlorine system is contained in a building. The distance to toxic end point determined in the worst-case scenario using EPA's RMP*Comp Version 1.06 program was 3.04 miles. The LANDVIEW III mapping program with 1990 census information was utilized to estimate the residential population within the area of concern (AOC); 170 people are estimated to reside within the worst-case AOC. There are no other public, institutional, or sensitive environmental receptors within the worst-case AOC. Since the results of the worst-case OCA scenario indicated a potential for offsite impacts and since the chlorine process at the facility is regulated under PSM regulations, the chlorine process at the Wicks Water Treatment Plant has been determined to be a Program 3 process. The alternate release scenario assumed the same quantity and duration of chlorine release from a single container as did the worst-cases scenario, but modified the assumed atmospheric conditions and applied a correction factor for the passive mitigation which would be provided by the containment effects of the building. Again using RMP*Comp and LANDVIEW III, the resulting distance to toxic end point for this scenario was determined to be 0.51 miles with 5 residents within the alternate scenario AOC. A map was developed using USGS 7.5-minute quadrangle maps identifying the AOC's for each release scenario. |