On Oct. 18, the Selbyville Water Department released a public notice informing residents that the town’s drinking water recently violated a drinking-water standard, by having a maximum contaminant level (MCL) violation of trihalomethanes (TTHM) 7.3 parts per billion (ppb) over the permitted maximum, at 87.3 ppb.
“What [TTHM] is – it’s a disinfectant byproduct,” explained Town Administrator Robert Dickerson. “We have high organic carbons in our water, and carbon is a naturally occurring thing in water, but when it’s treated with chlorine, when it sits for a while, the chlorine starts breaking down and creating these byproducts.
“We have to have disinfectant in the water to disinfect any bacteria,” he noted. “But the chlorine reacts to the carbon and breaks down when it sits in contact with it for a long time. It’s pretty common in this area to encounter this kind of disinfectant byproduct.”
Dickerson said the violation is different from the methyl tert-butyl ether violation, which the town recently passed a referendum for new drinking wells to address. He added that the Delaware Division of Health and Social Services’ Office of Drinking Water monitors the town’s water and tests it quarterly.
“Compliance is determined every quarter,” explained Public Water System Supervision Program Manager Anita Beckel. “So right now we’re in the October-November-December quarter and we’ll sample in December. Compliance is determined on a running annual average.”
Dickerson emphasized that users of the town’s water system should not panic because of the violation. If there was a water emergency, residents would be notified within 24 hours.
“It’s not an emergency. If it had been an emergency, we would’ve notified them immediately,” he said. “People drink water containing trihalomethanes in excess of the maximum contaminant level over many years may experience problems,” he acknowledged.
The public notice stated that residents do not need to boil their water or take other corrective actions before consuming it. It did however, state that residents with a “severely compromised immune system” or those who “have an infant, are pregnant, or elderly could be at an increased health risk” and should consult a doctor about consuming the water.
Officials at the Office of Drinking Water said that the Environmental Protection Agency recently lowered the MCL for TTHMS from 100 parts per billion to 80 parts per billion because some disinfectants and disinfection byproducts “have been shown to cause cancer and reproductive effects in lab animals and suggested bladder cancer and reproductive effects in humans.”
“That’s why we notified them, so they can make an informed decision,” said Beckel.
“To understand the possible health effects,” explained Dickerson, “a person would have to drink 2 liters of water every day at the maximum contaminant level for a lifetime to have a 1 in a million chance of having any health effects.”
Dickerson noted that the town’s TTHM levels have been decreasing over the last two quarters.
“I think we’ll be off notice the next quarter because our average has been coming down since December of 2010, when we had our highest level.”
He added that the December 2010 reading was 188.9 ppb, followed by a reading of 66 ppb and 14 ppb.
Beckel said that such a fluctuation is normal, but not entirely what she would expect.
“There is a high fluctuation. It’s a little bit opposite of what I would expect. Normally, we see TTHMS higher in the summertime, during the warm-weather months. With some of these ground water systems, what I’m seeing is higher levels in the winter. I’m attributing that to lower turnovers, that they’re not using as much water so there’s longer residence time in this distribution system, which allows more TTHMS to form over time.”
Dickerson said the Town is taking an active role in trying to find a solution to improve the quality of its drinking water.
“It’s something we’ve been working on. Our new wells that we’ve tested have a lower percentage of total organic carbon, so the chlorine will have less to react with.”
He added that the Town is also looking into pretreatments to lower total organic carbon for its processing system.
For more information, call Selbyville Town Hall at (302) 436-8313 or Sharon Scheers with the Office of Drinking Water at (302) 741-8627.