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Environment: Scientists still study impact of ‘1,000-year flood’
By Nikki Best
It is impossible to predict how harshly a weather event will affect the coast, but it’s better to be prepared.
“Our study was merely a first hint of how extreme weather events, such as hurricanes and flooding, can impact drinking water quality, but it is too early to translate our laboratory results into politics or governmental declarations,” said Alexander Ruecker, a scientist at Clemson University’s Baruch Institute of Coastal Ecology and Forest Science at Hobcaw Barony.
In October 2015, the passage of Hurricane Joaquin offshore and a low pressure system to the west combined to drench South Carolina with rainfall that was better measured in feet than inches. It was called a “1,000-year flood,” by then Gov. Nikki Haley.
The stormwater soaked the ground to the water table and flooded the rivers. Days later it receded, but was the water safe?
Ruecker studied the speed of the Waccamaw River’s discharge when at flood stage and possible contaminants. He presented some of his research at a lecture earlier this month.
“Here on the Winyah Bay area we saw 21 inches of rain in four days,” Ruecker said. Educating the public about potential negative consequences of water quality following hurricanes or flooding is an important goal, he said. He and his fellow researchers collected water samples from Oct. 4 though Nov. 30, 2015 at Wachesaw Landing and in Socastee.
Drinking water is federally regulated. The Safe Water Drinking Act was passed in 1974, but water treatment is done at the local level.
In his experiment, Ruecker assessed the water quality based on laboratory tests that simulated conditions in water treatment plants.
According to the Centers for Disease Control and Prevention, there are five steps to community water treatment: coagulation, flocculation, sedimentation, filtration and disinfection. The first two are similar, positively charged chemicals are added to the water to attract the negatively charged “dirt” particles. The negative and positive come together and are weighed down. These new larger particles, called floc, settle to the bottom of a container and that is the sedimentation step.
Then comes filtration. The newly cleared water at the top of a container is sent through a filter made of porous materials like gravel, charcoal or sand to remove dissolved particles like dust, parasites, bacteria, viruses, and unwanted chemicals.
“The most important step is disinfection,” Ruecker said. The community would be most familiar with this step in reference to swimming pools and the addition of chlorine to kill pathogens in the water. “As a negative side effect we form these disinfection byproducts in the treated waters when dissolved organic carbon reacts with disinfectants.”
Disinfection byproducts (DBPs) can negatively affect human health. The high levels of dissolved organic carbon in flood waters can lead to even higher levels of DBPs in treated water and might have impacted coastal drinking water. “In our laboratory study we could show that the formation of DBPs increased during the flooding, which was most likely a direct consequence of elevated dissolved organic carbon levels in Waccamaw River waters,” Ruecker said.
He postulated a higher dose of coagulants could reduce DBP precursors before chlorination.
It’s not just the university scientists on Hobcaw Barony monitoring water quality. The Waccamaw Riverkeeper records this information as well. Samples are regularly taken from Wachesaw and Hagley landings. “After Joaquin in 2015, we saw a significant decrease in conductivity due to the large freshwater influx. Sites on the southern end of the Waccamaw took several months to return to normal conductivity levels,” Cara Schildtknecht, the riverkeeper, said. “However, there were not significant increases in nutrients or E. coli. E. coli measurements remained below the daily maximum established by Department of Health and Environmental Control.”
Conductivity is a measure of water’s ability to carry electrical current, an indication of salinity. Saltwater conducts electricity better than freshwater. “When you see lower conductivity levels during storm events, you can assume there has been a large freshwater influx thus diluting the river water,” Schildtknecht said.
Water quality tests performed around the time of Hurricane Matthew in October 2016 presented similar conclusions. “Conductivity decreased but rebounded more quickly,” Schildtknecht said. “This is probably due to the fact that Joaquin had an average rainfall around 20 inches during the storm while Matthew only had 10 inches of rainfall.”
Following both storms there were several weeks of high water levels due to water flowing from the rest of the watershed into the Waccamaw River. The higher flow acted as a deterrent to the contamination of the river by fecal coliform bacteria in the water system, but Ruecker said, “the main concern was that even after the river returned to base flow, we still found elevated levels of dissolved organic carbon.”
In 2015, it was only a few days before the DBPs returned to normal, but in 2016 following Hurricane Matthew it was more than 50 days.
Conflicting or comparative information can appear when the slightest piece of controlled science is altered. From where water was sampled during the storms to how it was analyzed can create different information and purposes. Ongoing research means conclusions are evolving all the time because more data comes to light.
“I would recommend to wait for information from the authorities concerning drinking water quality and safety. This decision is made by experienced experts at DHEC,” Ruecker said.
Clemson’s Baruch Institute is plans to offer more lectures on the impact of hurricanes and climate changes later this year.