Logan Outfall Disinfection Facility - Executive Summary

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RMP EXECUTIVE SUMMARY 
 
Facility and Substances  
 
Logan City's lagoon outfall disinfection facility (LODF) currently treats about 16 million gallons per day (MGD) of lagoon effluent.  The treated wastewater is either used for irrigation during the growing season or is released to the Logan River.  Lagoon effluent disinfection is the primary activity of the LODF.  The City uses chlorine gas, mixed and injected into the discharging effluent,  to reduce pathogens in the water to levels that will not threaten public health.  The chlorine concentration in the treated effluent dissipates to discharge permit limits at the outfall of the contact basin.   
 
There are (2) processes involved. The first process includes all the equipment and handling procedures to meter and inject the gas.  The second includes the actual injection, mixing, and contact time of the gas to disinfect the water.  The rate of chlorine use is about 150 lbs. per day based on 16 MGD discharge flow.  The information that foll 
ows applies to both processes. 
 
The LODF maintains onsite (8) one ton cylinders of chlorine gas comprising two manifolded sets of four tanks.  One set is in service while the other group is in standby storage.  When the operational group becomes depleted, the standby set is put into service and the LODF orders new tanks to replace the empty ones. 
 
Worst Case Release Scenarios  
 
The "worst case scenario" for Logan's LODF is defined as a "one ton release of chlorine gas".  The scenario is based on discussions with EPA and upon EPA'S GUIDANCE FOR WASTEWATER TREATMENT PLANTS-REFERENCE TABLES & EQUATIONS.  In addition, the scenario has these elements: 
 
q Passive mitigation effects of the LODF building reduce the amount of the gas leaving the building by 45%.  Total release outside the building is 1,100 lbs. 
q Duration of release to the environment outside the building is 10 minutes, with a release rate of 110 lbs./min. 
q Assuming a wind speed of 1.5 m/s(4.92 mph) and class F atmospheric con 
ditions, the chlorine plume forms an influence radius of about 2 miles with the LODF as locus. 
 
The projected "worst case" chlorine plume will have offsite impacts to humans.  The demographics within this influence radius include: 
 
q 50 persons estimated total population 
q No schools 
q 4  commercial establishments 
q One parks 
q One highway 
 
Logan City's management of the LODF is geared to prevent any leakage of chlorine gas from the facility.  The emphasis on any leakage being unacceptable creates a safety mentality that drives inspection, handling, and maintenance procedures.  The combination of attention to safety along with the realization of the seriousness of a major gas release minimizes the potential for the "worst case scenario".  Logan City has formalized these procedures for the LODF in a manual and reinforces them with continuing training.  These procedures include: 
 
q Yearly training or whenever a new LODF employee is hired 
q Equipment  maintenance schedules  
q Daily and mo 
nthly observation/inspection schedules 
q All operators are State Certified 
q Formal transfer procedures removing and installing new tanks 
q The buddy system - operators are always paired when work is performed. 
q Monthly inspection of unused emergency air packs.  Packs are refilled immediately after use. 
 
Alternate Case Release Scenarios 
 
The "alternate case scenario" for Logan's LODF assumes a minor leak from a tank pigtail.  Orifice flow through a 3/16" hole in the pigtail creates a total release of about 760 lbs. of gas.  The scenario is based on discussions with EPA and upon EPA'S GUIDANCE FOR WASTEWATER TREATMENT PLANTS-REFERENCE TABLES & EQUATIONS.  In addition, the scenario has these elements: 
 
q Passive mitigation effects of the LODF building reduces the spread of the gas by 45%.  Total release outside the building is 420 lbs. 
q Duration of release to the environment outside the building is (1) hour, with a release rate of 7 lbs./min. 
q Assuming a wind speed of 3 m/s(9.84 mph)  
and class D atmospheric conditions, the chlorine plume forms an influence radius of about 0.2 miles with the LODF as locus. 
 
The projected "alternate case" chlorine plume will have offsite impacts to humans.  The demographics within this influence radius include: 
 
q No total population 
q No schools 
q 2  commercial establishments 
q One parks 
q One highway 
 
General Accidental Release Prevention Program 
 
LODF staff has no recollection of any regulatory inspections by state or federal agencies since the facility was constructed in 1986.  The rules and regulations they comply with are based on periodic formal chlorine management training by Utah State and Logan City's Safety Department.  Important prevention practices derive from these training sessions and from the routine maintenance of the LODF equipment and alarms. 
 
5 Year Accident History 
 
The LODF has had no accidental chlorine release within the last 5 years. 
 
Emergency Response Program 
 
Logan City has a specific emergency response p 
lan (ERP) in place.  Features of the ERP are as follows: 
 
q Alarms and Exclusion Barriers.  The LODF and perimeter buildings are equipped with gas detectors along with audible alarms and visual flashing lamps.  The LODF alarms are telemetered to Logan City Operation Control Center.  The Control Center notifies Logan City Fire Department and key emergency Logan City personnel.  The LODF is fenced and posted with warning placards. 
q Coordination with Local Emergency Responders.  It is Logan City policy to let the hazardous material specialists in the Fire Department respond first to the leak.  City crew is instructed to call 911 first.  Trained Logan City personnel respond to fix the leak only if the Fire Department is unable to do so. 
q Training.  Only those Logan City personnel who are trained in repair of the chlorination equipment, and in the proper suiting and use breathing gear and other equipment are allowed to respond to the leak. 
q Repair kits.  The LODF stocks onsite A&B repair 
kits for tank and plumbing repairs. 
q Evacuation and Notification.  The ERP lists steps to be taken in event of a leak.  Evacuation procedures are for onsite personnel only.  The 911 call initiates response from Cache County LEPC. 
 
Some items not included in the plan include: 
 
q Drills.  Drills are initiated and coordinated by Cache County LEPC. 
q Public Notification and Alert Systems.  The first response to a leak is delegated to Logan City Fire Department.  The 911 call initiates Cache County's LEPC procedures for evacuation and notification. 
 
Planned Changes to Improve Safety 
 
Planned changes in the operation of the LODF to improve safety deal mainly with coordination refinements between Logan City and Cache County emergency response agencies.
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