Environment
Underground stormwater system raises concern about impact on Pawleys Creek
Capturing stormwater from a proposed residential development on Pawleys Creek in an underground system has the potential to increase pollution, neighbors told county officials at a hearing last week. The creek has been closed to shellfishing for generations because of high bacteria levels.
“Their water quality appears to be in compliance,” said Robert Turner, manager of Georgetown County’s Stormwater Division.
Magic Oaks LLC is seeking approval of a stormwater system that will collect runoff in a series of chambers contained in gravel-lined trenches under the street in the 27-lot subdivision between Highway 17 and Pawleys Creek. The county’s approval of the development as a “flexible design district” is being challenged in court by neighbors who say the 8.3 acres should have been zoned “conservation preservation” to conform with the county’s future land use maps.
The system, called Stormtech chambers, will hold the water until it can soak into the ground or run into Pawleys Creek, depending on the volume of rain. The county granted Magic Oaks a waiver to its requirement that runoff after development be no higher than the runoff before development because of its location on the creek. But because of the shellfish beds, the system must be able to hold 267,167 gallons of water, the amount equal to 1.5 inches of rain on the developed site.
Micky Stikas, owner of the Village Shops on the south side of the development, said he was required to store all of his stormwater on site.
“That knocks the socks off the stormwater ordinance,” he said of the waiver. “We’ve got water quality issues, ongoing water quality issues.”
“It happens all the time on the coast,” Turner told him, adding that the waiver was based on the fact that there are no properties downstream that will be flooded.
But Gary Weinreich, a retired environmental engineer who looked at over 500 pages of permit documents obtained by neighbors through open records requests, pointed out that Turner initially denied the waiver.
“I think you were right in your first decision,” Weinreich said.
In a 25-year storm, a theoretical event used to design drainage systems, more than 8 inches of water would fall on the property in 24 hours.
“You’re going to bypass that water directly into the marsh,” Weinreich said.
The underground system doesn’t have the same ability as a retention pond to reduce the bacteria in stormwater by exposing it to sunlight, he said.
“Obviously this system is designed to maximize the number of lots,” Weinreich said.
He also questioned how the county would ensure that the system is designed properly without better information about the water table. A study of the site estimated the water table at 4 feet. But it noted “groundwater will fluctuate due to climatic and tidal conditions. During and following extended or heavy rainfall events, the groundwater table can occur at shallow elevations.”
The stormwater plan for the development calls for the Stormtech chambers to be installed above the water table. To ensure that happens the area closest to the creek will be filled 3 to 5 feet, according to the plan prepared by Earthworks.
“It is anticipated that a retaining wall may be required along the marsh front due to the fill height,” according to the plan.
In arguing successfully for the county to reconsider its initial denial of a waiver, Steve Strickland, owner of Earthworks, said that the Magic Oaks system would create “a slight improvement” in the watershed by capturing and treating water that now flows over the land.
But neighbors said raising the level of the Magic Oaks property will increase their current drainage problems.
“I’m not a engineer. I just live next door and see water,” said Kathy Reid, who showed photos of standing water on the site. “This does not drain quickly.”
The fill means that when water overflows a ditch between her house and Magic Oaks it will only have one place to go, Beth Martin said.
“The ditch has not been maintained at all,” she said.
Turner said that existing drainage problems can be addressed in their review of the Magic Oaks project.
“It could all have been solved with retention ponds,” Martin said.
A retention pond isn’t required by state regulations unless the site is over 10 acres, Turner said.
But he agreed that the concern about the water table was “legitimate” and said he would check the numbers. He also said he would contact the manufacturer of Stormtech to ask about its requirements, which the Magic Oaks plan says will be followed.
He agreed that the underground systems are not common in Georgetown County, but said that didn’t make them new technology.
“Just because we don’t have them here doesn’t mean they aren’t all over the coast,” he said. “They are plentiful in many places.”
Weinreich said afterward that the issue of permitting near the shellfish beds “is complicated and unclear.” He contacted the state Department of Environmental Services seeking clarification.
Turner said the 1.5 inches of retention is the state standard.
