75th Street Wastewater Treatment Plant - Executive Summary

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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.  The City of Boulder's 75th Street  
WWTP uses chlorine above the 2,500 lb. threshold quantity and sulfur dioxide above the 5,000 lb. threshold quantity and therefore must prepare a RMProgram. 
The chlorine room is equipped to store fifteen, one-ton containers.  Six chlorine cylinders are on scales (three per manifold) and hooked up to feed and the remainder are on the floor on permanent trunnions.  The maximum chlorine inventory is 30,000 lbs.  Each manifold is equipped with a regulator and connected to an automatic switch-over valve.  The storage room is equipped with an evaporator, however, it is not in use. 
The sulfur dioxide room is equipped to feed, two one-ton containers.  Furthermore, up to 7 additional sulfur dioxide containers are stored outdoors.  Both of the sulfur dioxide cylinders in the feed room are on scales and hooked up to feed.  The maximum sulfur dioxide inventory is 18,000 lbs.  The two cylinders on the scales are each equipped with regulators and heat-traced trap legs and are connected to an automa 
tic switch-over valve.  The storage room is equipped with an evaporator, however, it is off-line. 
Below is a brief summary of the 75th Street WWTP Risk Management Program. 
The purpose of the RMP rule is to lessen the number of serious chemical accidents 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 75th Street WWTP have several measures already in place, and have initiated other meaures as well, to minimize the likelyhood of an accidental chlorine  or sulfur dioxide releases.  
All operators at the WWTP are trained in operating the chlorine and sulfur dioxide processes, and follow all appropriate safety procedures.  Both management and staff are committed to ensuring safety at the WWTP.  Training and safety meetings are held on a regular basis. 
The 75th Street WWTP facility follows all recommended safety, design, and operational and maintenance guidelines developed by the Chlorine Institute.  In addition, refresher training is routinely conducted. 
The chlorine containers are stored in an enclosed building.  Sulfur dioxide containers that are in-use or on stand-by (i.e., two containers) are housed in an enclosed building.  Spare sulfur dioxide containers are stored in a protected area outdoors.  Both the chlorine and sulfur dioxide rooms contain control panels for their respective chlorine or sulfur dioxide monitors, exhaust fan control, and  lighting control. 
For either the chlorine or sulfur dioxide 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 and sulfur dioxide) t 
o 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 and sulfur dioxide at the 75th Street WWTP is 200 lbs. per minute.  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 and sulfur dioxide for modeling the worst-case release is 0.0087 mg/L (3 ppm) and 0.0078 mg/L, respectively.   Note, that a site-specific model, the 
Computer Assisted Protective Action Recommendation System (prepared by the Regional Atmospheric Response Center for the Denver Metro Area) is being developed to estimate the chlorine and sulfur dioxide release distances to toxic endpoint.  The model is not finalized yet,  therefore, in the meantime, the worst-case release distance to toxic endpoint was estimated using EPA's "Risk Management Program Guidance for Wastewater Treatment Plants."  The estimated worst-case release distance is 3.0 miles and 3.1 miles for chlorine and sulfur dioxide, respectively. 
Alternative release scenarios are intended to reflect more likely releases than the worst-case release scenario.  Program 2 facilities, such as the 75th Street WWTP, are required to evaluate and present at least one alternative release scenario.  For the alternative-release scenario, failure of 5/16-inch pigtail tubing connected to a single chlorine or sulfur dioxide 1-ton container was considered.  From the "Risk Management Program 
Guidance for Wastewater Treatment Plants" manual Exhibit 4-15, the chlorine and sulfur dioxide vapor release rate from this scenario would be 15 and 7 lbs/minute, respectively.  Based on the guidance manual, the estimated alternative release distance to toxic endpoint for chlorine and sulfur dioxide is 0.2 and 0.1 miles, respectively. 
The 75th Street WWTP has had no reportable accidental releases of chlorine or sulfur dioxide in the past five years. 
The 75th Street Plant has a written Emergency Response Plan that is routinely reviewed and ammended.   The plant's Emergency Response Team, currently with 7 active members, meets three times per month.  In addition the plant's Safety Committee, also consisting of 7 members, meets one time per month.  Both the meetings are "open" for anyone else to attend, if they so choose.  Plant-wide safety training is held once per month.  In addition, national or local safety conferences are attend 
ed by various personnel each year. 
Below is a brief summary of emergency response operations for the Emergency Response Team (ER Team).  When an alarm sounds (or the person is called in, or hears a P.A. announcement), each ER Team member is to report to the safety room, or alternate location if announced.  The senior member will become the Incident Commander (I.C.).  Two individuals will then verify the alarm condition. These individuals will put on self-contained breathing apparatus (SCBAs) and will enter the chlorine or sulfur dioxide are to check the leak status and close all tank valves and start evacuating ejectors located in the feed rooms.  Subsequently, these individuals will return to the safety room and report the leak status to the I.C.  The I.C. will announce the status over the P.A. system, and depending on the situation will do one or more of the following: (1) call for a plant-wide evacuation if need be;  (2) call 911; and/or (3) send ER Team members, or another operato 
r, out to the plant entrance at 75th Street with a cell phone.  The individual at the plant entrance will be responsible for a head count, communications with the safety room I.C., and directing police, fire, and the HAZMAT Team to the safety room (or alternate location).  The I.C. will be in charge of direction of repairs and decontamination of personnel, equippment, and clothing that have been exposed.  After the Emergency Response, the I.C., or another designated individual, will record incident events.  The I.C. will also direct a debriefing.  The ER Team will convene to review response activities and discuss any deficiencies and if need be, revise the Emergency Response Plan.  
The primary changes that have been made as a result of implementing an RMProgram are greater staff and management awareness and commitment to safety.
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