In preparation for a painting maintenance project at one of its water reservoirs, Arroyo Grande drained a water tank last week, generating some concern from residents who saw some water running into the city’s storm drain system during a drought.
The Central Coast Regional Water Quality Control Board is also looking into the discharge to see whether it violated any permit or laws in the Clean Water Act.
However, the water didn’t reach Arroyo Grande Creek, so water board staff does not believe there was a threat to water quality or any aquatic species, particularly steelhead.
The tank, located on Stagecoach Road outside city limits, holds about 250,000 gallons of water, Arroyo Grande Public Works Director Geoff English said. About 215,000 gallons of water were put into the city’s water distribution system on Sept. 3 through an outlet pipe located about 2 feet from the ground on one side of the tank.
The rest — approximately 35,000 gallons of water — was emptied into the storm drain through a floor drain in the tank, English said.
“That water is generally ladened with sediment and is typically drained into the storm drain system,” if ever the tank is drained for maintenance or repairs, he said. The water held there comes from Lopez Lake’s water treatment plant.
English said a discharge for maintenance activities is an allowable activity under its municipal stormwater permit.
Harvey Packard, a supervising engineer with the Central Coast regional water board, said staff there would have liked to know about the planned discharge first so they could have considered issuing a general permit for low-threat discharges.
“There are some provisions covered in the permit to allow this kind of discharge,” he said of Arroyo Grande’s permit. “It’s a gray area subject to interpretation.”
But Packard said the storm water drains into a small tributary leading to Arroyo Grande Creek, which is likely dry at this time. He said the water was de-chlorinated before it was discharged.
“There’s little chance the water would reach the creek,” he said. “Our concern with these types of discharges is the chlorine and its effect on aquatic organisms.”
The painting task is part of a larger capital improvement project to recoat and seismically evaluate and repair two of the city’s reservoirs. The painting project, which will cost about $59,000, is expected to start at the beginning of October.
English said the city did not notify residents of its plan but “given heightened sensitivity for the need for water conservation, it would have been in our best interest to provide some advance notice of our activities.”
The exterior of the tank hasn’t been painted since it was constructed in 1978. When asked if the project could wait until the Central Coast receives some rain, English said it’s better to get the work done before the rainy season starts.