The complicated, jargon-laden way to describe bioswales, one of the latest trends in low-impact urban design, is this: They use simulated hydrogeology and restorative vegetation to filter out stormwater pollution. More simply put, the system operates by keeping water in a sloped bit of ground as long as possible while the plants do their work. When done right, a bioswale looks like an ordinary ditch.

One San Luis Obispo County bioswale running parallel to Florence Street in Templeton even fooled a county road maintenance crew, who paved over a portion of the expensive installation just three years into its 50-year lifespan.

“We became aware of it a few months ago,” said Frank Honeycutt, Development Services Manager of SLO County Public Works. “We’re waiting for the rains to stop before we fix it.”

The local office of the state water board—which gave the county money to build the bioswale—became aware of the damage sometime later when neighborhood residents complained. At least one nearby homeowner wrongly suspected that Public Works paved over the bioswale on purpose to avoid long-term maintenance costs.

Staff e-mails instead show that a crew foreman simply wanted to shore up some erosion on the side of the bioswale before the start of the winter and spring rains.

“Our road crew, who meant well, was trying to arrest an erosion issue within that swale,” Honeycutt wrote in a May 23 e-mail to the water board. “They are new to that part of the county since the project was built and did not know about the bioswale and infiltration trench that were put there.” 

The water board’s particular interest in the bioswale stems from a 2006 grant agreement with the county. Three-quarters of the cash to build the $600,000 Florence Street bioswale came from a state grant administered by the regional water board office. The contract requires Public Works to maintain the installation in working condition for half a century.

“Definitely part of the project has been damaged,” water board Grants Program Manager Katie McNeill said. “They are in breach.” 

McNeill wrote a letter to the county on March 28 demanding a report on the damage and a promise to get the bioswale working again by the fall. The water board also asked the county to come up with a plan to prevent a similar accident from happening in the future.

Public Works responded in April that it considered some of the information requested by the water board duplicative and burdensome in light of budget conditions. SLO County later missed the water board’s May 17 reporting deadline. The two agencies have been in contact since then. 

The 2006 grant agreement requires the county to “maintain a self-insurance program against fire, vandalism and other loss, damage or destruction of the facilities.”

“These projects need to stay in for 50-plus years, not just three years,” McNeill said. 

Honeycutt characterized the situation as a compliance request by the water board rather than a breach of contract matter. He estimated the extent of the damage at no more than 50 to 100 feet.

“Most of the water is benefiting from the bioswale, but not the last 50 to 100 feet,” he said. “There’s no vegetation for it to flow down into.” 

Florence Street serves as a popular arterial for Templeton because it connects Las Tablas Road and the freeway onramp to Templeton Park and the downtown commercial area. The bioswale was designed to prevent some automotive pollution from reaching Toad Creek—a waterway targeted for restoration efforts.

Public Works offered various solutions on May 23 to retrofit the damaged bioswale with permeable concrete or slotted drains, but a state consultant from UC Davis recommended against the county’s proposed fixes in mid June. 

Public Works maintains one other bioswale in SLO County—a larger installation near Murphy and F streets in Santa Margarita, built with another 2006 water board grant. Since they function a lot like small marshes, bioswales operate best in low-flow situations where simple grading can slow runoff for processing. Also, the more arid landscapes of northern and eastern SLO County see less rainfall that can dilute pollution.

Bioswales have become a standard feature in recent development plans in Paso Robles, but remained relatively unheard of when the county applied for the state water board grants in 2006. Honeycutt pointed out that, despite the recent problems, the county’s pilot project to install bioswales in unincorporated Templeton and Santa Margarita beat the local cities to the punch. 

“Public Works is not only interested in low-impact design, but we consider ourselves a leader in it,” he said.

Staff Writer Patrick M. Klemz can be reached at [email protected].