Katie Herrera, manager of Beaufort County’s Stormwater Management Department, points out features of the system in the Evergreen Regional Water Quality Retention Basin, one of several basins in the county designed to manage roadway runoff. GWYNETH J. SAUNDERS

There’s nothing like going to your mechanic for an oil change and fluid top-up just to have him give you the bad news that – unobserved by you – your tires are balding. 

While you stand there deciding which brand and how many you need, have you ever given serious thought to what happened to all that tread?

Beaufort County’s Stormwater Management Department knows what happens to ground rubber – as well as the oils, dirt, vegetation, trash and everything else that collects on our roadways. Without any barriers, the stormwater runoff quickly washes that debris into the marshlands and bodies of water that run through our communities.

“Beaufort County has had water quality standards since the ’90s, which is because we’re a very progressive area,” said Katie Herrera, the department’s manager. “The Evergreen Regional Water Quality Retention Basin is designed to improve water quality within the Okatie River watershed. We want [the river] to be fishable and swimmable. Our little Okatie River is never going to be drinkable, but we want to make sure that the harvesting resource is there to make sure the shellfish is safe for everyone’s consumption.”

The basin is the in the 24-acre Evergreen Tract on SC 170 next to Seagrass Station. It is one of the solutions the county has developed to collect the runoff. A series of those are being constructed along SC 170 from SC 46 to US 278. They are part of an agreement with the South Carolina Department of Transportation after more than four miles of the highway was widened in 2014.  

The Evergreen basin is barely visible to passing traffic, and the camber of the highway slanting toward the road edge is hardly noticeable. A curbside conduit leads untreated stormwater runoff into a concrete box, where a 24-inch intake pipe channels it out into a 7.5-acre pond. About a third of the distance away from the intake pipe is a line of stones that crosses the width of the pond.

“In front of the pipe, there’s a big riprap channel called a ‘forebay.’ That’s where all of the sediment collects. When you go to maintain it, you just are digging up small areas, you’re not having to do the whole thing,” said Herrera. “All pollutants are basically attached to the sediment, and what the riprap does is allow that to settle in the forebay.”

It will take a while for sediment to fill up the forebay, but the county will be monitoring and maintaining the ponds, redredging as necessary to remove the collected sediment and pollutant particles. 

Should there be a 100-year storm that brings a deluge into the area, causing the pond to overflow the riprap, there are follow-on steps in place to catch whatever escapes the forebay. 

At the end distant from the road is a second concrete box to catch trash and slow the flow of water out of the pond. Any water rolling through the box will then filter through a rock creek dam that ultimately leads to nearby wetlands and into the start of the Okatie tributary. 

While concrete boxes and stones insure much of the water that reaches the Okatie is clean, one method of treatment requires no human intervention: UV exposure.

“In 2018, the county built Okatie West, another project for water quality improvements. This is a pond that’s on the same property, just slightly south,” said Herrera. “What we saw with that is we’re getting extremely good treatment numbers. When the water’s coming into the system, you’ve got relatively high levels of bacteria. The UV treatment that the sun provides for the bacteria is really effective for reducing the amount of bacteria going into the system before it outfalls.”

The Evergreen project was paid for in part with $299,000 from a 319 Grant administered by the Environmental Protection Agency through South Carolina Department of Health and Environmental Control. The remainder of the $700,000 project came from the Stormwater Management Utility fund. Planning began in 2018, and construction from start to finish took just under 10 months. 

As a requirement of the funding, the department has been doing public outreach and education on the project and has hosted two tours so far to the site. More outreach on this and future projects is planned and those meetings will be open to the public.

The pond is set back far enough from the road that it is nearly invisible and is not designed for recreational activities. Herons, egrets and – judging from the tracks – numerous deer have found it appealing, but one of the engineers accompanying a recent tour suggested wandering around is not advisable.

“I feel like we may already have an alligator,” he said.

Gwyneth J. Saunders is a veteran journalist and freelance writer living in Bluffton.