Avenue Water Treatment Plant - Executive Summary

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The City of San Buenaventuras (City) Avenue Water Treatment Plant (Avenue WTP) is a 13.5 million gallon per  
day conventional water treatment plant.  When the plant was originally built in 1938, it was a lime-soda softening  
plant which was then converted to a zeolite softening plant in 1956, and then to a conventional water treatment  
process in 1973.  A gaseous chlorine system is used for oxidation and disinfection of raw water.  The facility is  
equipped with chlorine gas detectors. 
The Avenue WTP uses chlorine in quantities large enough to trigger the Environmental Protection Agencys  
Accidental Release Prevention Program (EPAs ARPP) and Californias Accidental Release Prevention Program  
(Cal ARPP).  One-ton cylinders of liquid chlorine are delivered to the plant by truck.  Typically, the City stor 
es a  
maximum of 10 one-ton chlorine cylinders onsite under a covered storage area and 4 one-ton chlorine cylinders  
within the chlorine dispensing room.  The covered storage area also has enough trunions to store an additional 5  
one-ton cylinders. 
The facility has not had any releases during the past 5 years that resulted in any injuries, off-site evacuations, or  
property damage. 
The facility is subject to OSHAs Process Safety Management (PSM) rule.  The City has developed a stringent PSM  
safety program that includes the following elements: 
? Review of the design of all equipment and controls for the chlorine system to ensure they are properly designed  
and installed. 
? Updating of standard operating procedures to include specific information on safety procedures.  All procedures  
must be reviewed and certified annually. 
? Initial safety training and 3-year refresher training  
for all operators and maintenance staff. 
? Procedures to ensure that all contractors receive the same safety training that the City provides for its own  
? Regular inspection of all equipment, monitoring systems and controls, with stringent documentation of all  
? Prompt corrective action for any non-conforming items identified by the regular inspections. 
? Rigorous safety reviews conducted prior to system startup, if any equipment or operations are modified. 
? Stringent investigation of any incidents that have the potential to have caused chlorine releases. 
? Periodic evaluation of the safety records of all outside contractors who work on the RMP-regulated systems. 
? Development of an effective emergency response plan. 
? Implementation of an employee participation program to ensure that all plant-wide staff are aware of the PSM  
program, and are actively consulted regarding safety issues. 
? Independent audits of the entire PSM program and RMP  
program every three years. 
City staff uses its Emergency Action Plan to provide step-by-step procedures for emergency response in the unlikely  
event of an accidental release.  The key elements of the emergency preparedness program are as follows: 
? All plant staff (including administrative and clerical staff) are trained in the specific elements of the program. 
? The chlorine building is equipped with an electronic chlorine detector.  The chlorine detector has an audible  
alarm and alerts the Citys central operations control room in the event of a chlorine leak. 
? In the event of a large release, the facility would immediately contact the City of San Buenaventura Fire  
? A team of City supervisors and operators are fully trained, certified and equipped for hazardous materials  
(HazMat) emergency operations to repair accidental releases.  The Fire Department and the City HazMat team  
would jointly repair any major leaks. 
Based on recent safety reviews that were conducted as part of the evaluations for EPAs Accidental Release  
Prevention Program, the City has implemented the following actions to either reduce the likelihood or severity of  
potential chemical releases: 
New Chlorine Facility and Chlorine Scrubber - The City plans to proceed with the construction of a new chlorine  
facility with a chlorine gas scrubber system. 
Rubber Mat  Provide rubber mat for unloading cylinders. 
Wheel Chocks  Provide wheel chocks for the delivery trucks to assist with the unloading/loading of cylinders. 
Operating Procedures  Update written operating procedures to include all PSM-required information. 
Labeling  Improve labeling on process piping. 
Smoke Detectors - The City plans to install smoke detectors at the loading dock and the existing chlorine room. 
Update Emergency Repair Kit  The City will purchase rubber sheets that can be strapped around a damaged 1-ton  
er to reduce leakage.  This repair method will be useful in reducing the impacts of an accident similar to the  
Alternate Release Scenario described below. 
The Risk Management Plan must assess the downwind impacts of hypothetical accidental releases.  EPA requires  
facilities to model the distance that a plume of released gas would travel before it dispersed to an ambient  
concentration equal to the Toxic Endpoint Concentration.  Toxic Endpoint Concentrations for various compounds  
were specified by EPA, and are generally concentrations that would cause no physical harm but could interfere with  
peoples ability to leave the area.  The Toxic Endpoint Concentration for chlorine is 3 parts per million (ppm).  In  
accordance with EPAs rule, the following hypothetical accidental release scenarios were developed: 
Worst-Case Release Scenario for Chlorine   
Liquid chlorine (chlorine gas that is stored as a liquid under pressure at ambient temp 
erature) is imported to the site  
by truck and stored in one-ton containers for use in the oxidation/disinfection process.  The Administrative Worst- 
Case Release Scenario assumes that the entire contents of one of the chlorine cylinders (2000 pounds of chlorine) is  
emitted as a gas cloud in 10 minutes, during a period of exceptionally calm winds and stagnant atmospheric  
conditions (1.5 meter/second wind speed and F stability) which would result in minimal dispersion of the gas  
cloud as it blew downwind.  The thermodynamic properties of  chlorine indicate that such a large instantaneous gas  
release is probably impossible.  If the entire 2000 lbs of liquid chlorine were somehow discharged from the cylinder,  
it would spill on to the ground and immediately cool itself until it formed a puddle of chlorine ice, which would  
take much longer than 10 minutes to evaporate into a gas cloud.   Nevertheless, the RMP rule dictates that the  
Worst-Case Scenario assumes the release of 2000  
lbs of gaseous chlorine.  
Graphs from EPAs RMP Guidance for Wastewater Treatment Plants were used to calculate the downwind  
impacts.  EPAs graphs indicate that the chlorine gas cloud would travel 1.3 miles before it dispersed to the 3 ppm  
Toxic Endpoint Concentration.  Figure 1 shows a circle defined by the worst-case 1.3 mile downwind distance.  
Alternate Release Scenario for Chlorine   
The Alternate Release Scenario for chlorine assumes that one of the 1-ton cylinders is dropped from the delivery  
truck on to the ground outside the chemical building.  To be conservative it was assumed that the dropped cylinder  
lands on its weakest point, splitting a seam to cause an 8 x < crack.  It was also assumed that the dropped cylinder  
comes to rest with the crack below the liquid level in the cylinder, allowing half of the liquid contents to  
immediately drain on to the ground.  The thermodynamic properties of chlorine dictate that 12% of the spilled  
chlorine would immediately f 
lash to a vapor that would form a dense cloud that could blow downwind.  The  
thermodynamic properties also dictate that the spilled liquid would immediately chill to chlorines boiling point    (- 
29 degrees F), forming a puddle of chlorine ice.  To be conservative it was assumed that 60% of the spilled  
chlorine ice would evaporate in the first 30 minutes.  The rate of evaporation would decrease as the chlorine ice  
puddle shrank.  Of the 1,000 pounds of liquid spilled from the dropped cylinder, 649 pounds would be emitted as a  
gas during the first 30 minutes. 
Graphs from EPAs RMP Guidance for Wastewater Treatment Plants were used to calculate the downwind  
impacts.  EPAs graphs indicate that the chlorine gas cloud would travel only 0.1 mile before it dispersed to the 3  
ppm Toxic Endpoint Concentration.  Figure 1 shows a circle defined by the worst-case 0.1 mile downwind distance.   
The dispersing chlorine gas cloud would barely reach the facility boundary. 
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