July 2009, Vol. 21, No.7
Leaky Gasket Leads to Facility Flood
Quick action prevents further problems
During Valentine’s Day weekend this year, a simple rubber ring almost spoiled everyone’s plans in Redwood Shores, Calif. One leaky rubber gasket on an ordinary junction box flooded the South Bayside System Authority (SBSA) supervisory control and data acquisition (SCADA) system with hundreds of alarms. And if it weren’t for the quick action of operators on duty, this one faulty gasket would have sent wastewater flowing through the streets.
No joke — the “spill that was not” would have made national news. “It could’ve been pretty catastrophic,” said Dan Child, general manager of SBSA’s wastewater treatment plant.
That afternoon, the 5-ac (2-ha) treatment facility was handling 45 mgd (170,325 m3/d — about 16 mgd (60,560 m3/d) more than its average daily flow — when it began flooding. The inlet valve to the chlorine contact tank’s tertiary filter had closed suddenly, and electrical signals were unresponsive. A team was quickly mobilized to open the valve manually.
Operators later learned later that a leaky gasket, located on a junction box attached to the facility exterior, had allowed about 0.5 gal (1.9 L) of rainwater to slip inside. This box houses an instrumentation-control conduit that connects various SCADA equipment.
This water was enough to short-out a portion of the SCADA system in direct communication with the chlorine contact tank, closing its valve.
“It found the path of least resistance,” Child said.
Sifting Through Alarms
According to Child, the operator on duty analyzed the most serious alarm — indicating that the chlorine contact valve was causing intense flooding and threatened the electrical room and total collection system shutdown — in about 30 to 45 minutes.
When a SCADA alarm sounds, procedures exist to determine the source. When hundreds of alarms go off, there are numerous procedures to follow.
“Don’t always depend on the SCADA Alarm Summary Screen,” advised Mike Serrano, the SBSA operator who quickly found the main problem causing all of the alarms during SBSA’s near catastrophe.
“It’s better to scroll down and check out each graphic,” Serrano said. “Get familiar with the current plant [operations] status readings and know what you’re looking for. If the SCADA graphic does not look right, send an operator to investigate right away.”
Fording the Floodwaters
Once the source of flooding was detected, the chlorine contact valve rescue team had trouble getting through water-filled stairwells.
The operators entered from another area of the plant and trudged through an equipment tunnel filling with about 3 ft (1 m) of water to get to the tank.
“Getting through the flooded galleries is very scary and dangerous, but if you work safely, [are] cautious of the surroundings, and don’t panic, it can be done,” Serrano said.
If another hour had gone by, the water would have reached the main electrical room, and wastewater would have backed up in four municipalities. Within SBSA’s service area, 100% of the flow is pumped — and there is no bypass around the plant.
Prompt detection, Child said, avoided a reportable spill of partially treated wastewater to San Francisco Bay, a violation of the Clean Water Act.
Because of swift operator reaction, service was not interrupted, and SBSA did not have to initiate a crisis communication protocol, Child said. Even so, the plant sustained more than $500,000 of damage from this one-in-a-million fluke.
Learning From the Experience
Child reported that the operation and post-analysis were successful; he added that SBSA learned a lot from the experience. For example, SBSA did not have a standard operating procedure in place for facility flooding, since this hadn’t happened since the plant was built in 1980. “Now we will,” he said.
“Like almost any good treatment plant, we have hundreds of plans,” said Child, who has been plant manager for the last 3 years. “We hadn’t anticipated this problem,” he said.
Gaskets on junction boxes are “pretty much an out-of-sight, out-of-mind kind of thing,” Child said. If there’s one piece of advice he would give other plant managers, it would be, “Look at your junction boxes.”
— Andrea Fox, OF
|Tips for Protecting Your Junction Boxes|
After its close call, the South Bayside System Authority (SBSA; Redwood Shores, Calif.) is keeping a closer eye on the gaskets on its electrical boxes. Nathan Murphy and Brian Kettler, SBSA electricians, have developed the following checklist for routine junction-box maintenance and protection.
- Ensure that all conduits coming into junction boxes are sealed with a gasket or a meyers hub.
- With any conduit bodies, verify that gasket seals are intact and the cover is not deformed.
- If steel boxes are used, ensure that rust is contained. If it’s not, consider a possible swap with a stainless steel enclosure that is sealed.
- Try to use duct seal to ensure waterproof seals on conduits that are above programmable logic controllers or any critical process-related controls.
- Ensure that all junction boxes are kept clean.
©2009 Water Environment Federation. All rights reserved.