WASTEWATER
Upgrading sewage pumping stations can be challenging By Syed Q. Raza
A
sewage pumping station contains pumps and appurtenant piping, valves, supporting mechanical and electrical equipment, and can be designed and installed in several different configurations. Key components include wet/dry wells and electrical/control rooms. The wet well in a pumping station receives and temporarily stores wastewater for the purpose of pumping it to the treatment plant. The dry well houses raw sewage pumps and some controls and electrical power distribution equipment. This area is designed to be completely and permanently isolated from wastewater or wastewater-derived atmospheres. The electrical/control room is usu-
facility. To make matters more complicated, dry wells are found directly connected with the control/electrical areas which become classified as Class I Div. 2, as per the current codes. Generally, this issue arises during the design of the pumping station upgrade and means that the existing building has to be brought up to code. As the circumally above grade and contains the electri- stance of each location can be unique, cal power distribution equipment, pump designers use different methods to address motor starters and any control equipment. them. The dry well of a sewage pumping station that pumps wastewater from a DECLASSIFICATION sanitary or combined sewer system, is THROUGH VENTILATION This approach uses declassification of classified as Class I Division 2 location as per National Fire Protection Asso- the Class I Div. 2 rated area by increased ciation (NFPA) 820 Table 4.2.2 Row 17 ventilation as per NFPA Table 4.2.2 Row Line b, or, Class I Zone 2 as per Ontario 17 line a. This requires six continuous air Electrical Safety Code (OESC), when the changes per hour and there are several continuous ventilation is less than six air important requirements: • The six air changes per hour should changes per hour. Many existing dry well installations provide 100% fresh air. do not conform to the requirements of • Electrical power distribution system Class I Div. 2 locations, and unclassified should have provision to accept power equipment can be found throughout the from an alternate power source, in case
Yea, it’s kind of like that.
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38 | August 2018
Environmental Science & Engineering Magazine