Problem: Runoff during storms overwhelms wastewater treatment facilities and causes overflows.
Solution: Automatic stormwater diversion system redirects runoff to infiltrate the ground, or to be held in a stormwater retention tank.
Stormwater posed a problem at two California locations. The concerns of residents and local officials led local authorities to install several systems that would protect local waterways from runoff and help wastewater treatment plants avoid overflows.
Santa Monica Beach solves shower drainage problem
New bathroom and shower facilities were being installed at Santa Monica Beach. The original plan was to connect shower drains to the same sanitary sewers used by nearby toilets, but rainwater posed a problem.
Because the area’s wastewater treatment plant was operating at or near capacity, handling additional rainwater draining from the open-air showers could lead to treatment plant overflows. Installing a roof above the showers was considered, but this solution would block views of the ocean from the surrounding area, said Jamie Aderhold, vice president of C.I.Agent StormWater Solutions (Louisville, Ky.).
Rather than install roofs, which also would be a costly proposition, the City of Santa Monica decided to install the Attitude Technology Automatic Stormwater Diversion System (ASWDS). The automated system, manufactured by C.I.Agent StormWater Solutions, operates without supervision. In dry weather, the drain line carries shower water to the sanitary sewer; when it rains, the system’s switch signals a controller to close the valve to the sewer. Then, through a system of pumps and valves, the system’s diverter causes precipitation to overflow the shower pad and drain into the surrounding sand.
“The system is all about slowing the water in big rainstorms from going to the wastewater plant,” Aderhold said. The system protects the nearby Santa Monica Bay by carrying shower wastewater to the treatment plant and reducing load on the treatment plant during storms, he added.
The system is designed to be preconfigured to user requirements, easily installed, and low-maintenance. The controller functions can be reconfigured based on customer needs. Diversion events are recorded, so users can supply reliable compliance data.
San Diego Zoo redirects runoff
The San Diego Zoo also encountered a problem with runoff from 61 ha (150 ac) that was feeding directly into the wastewater treatment plant. During heavy rains, the runoff overflowed the system and carried animal waste to the storm drains, Aderhold said. The zoo decided to install a system similar to that used at the beach to capture stormwater onsite.
The zoo’s system includes a 114-million-L (30-million-gal) holding tank next to an existing retention pond. At the top of the pond, two box channels were installed, one leading to the pond, one leading to the tank. The channels were outfitted with slide gates to direct water flow into either channel. When pond overflow is detected by a float measuring device, the controller signals the diverter gates to redirect excess rainwater to the holding tank. An indicator light shows zoo personnel which channel is open.
The tank acts like a retention pond during storms, slowly releasing water to the treatment plant instead of the storm drain. This setup ensures treatment of all water, Aderhold explained. An automatic exerciser cycles the valves weekly to ensure that the system is operational.
Low-maintenance system provides cost savings
Within these systems, the switches, valves, and pumps should be checked annually to ensure proper operation. The inspection should include a check for debris or water preventing proper movement and activation of automatic controls, Aderhold said.
“The Attitude Technology ASWDS is very cost-effective,” Aderhold said. The system is less costly than others because the components are sourced independently and pre-engineered, he added.
Systems with the standard switch and control panel cost about $6000, with the remaining cost dependent on the size and number of pumps and valves needed, Aderhold said. Installing roofing above an open-air drain is a common alternative to installing this type of system. But often, roofs are more expensive and have other repercussions, such as insurance costs and fire-regulation requirements, he added.
© 2012 Water Environment Federation. All rights reserved.