The Virginia Department of Environmental Quality said Tuesday that it has completed its analysis of raw water samples collected from the Dan River and tributaries, but the results remain inconclusive in determining the source of the odd taste and odor in the city’s drinking water.
In addition, Danville Utilities has received test results from a private lab that show no presence of pesticides detected in raw water samples.
“We have not had reason to suspect pesticides as the cause of the taste and odor issues we have experienced, but we are trying to rule out all possibilities,” Barry Dunkley, division director for water and wastewater treatment, said Tuesday.
At the recommendation of the Virginia Department of Health’s Office of Drinking Water, operators at the city’s water treatment plant are feeding a higher dosage of carbon to remove the earthy and musty taste and odor in the treated water.
The city also has flushed out water storage tanks across the city as recommended by the Office of Drinking Water to remove in them any water with a bad taste and smell.
Customers may continue to notice an odd taste and odor in their tap water until it purges out of the city’s distribution system. The water in the system has been through all of the treatment processes, and although the earthy taste and odor of the drinking water are unacceptable to both Danville Utilities and its customers, the Office of Drinking Water confirms all tests show Danville’s water is safe to drink.
While test results from samples collected two weeks ago by the state Department of Environmental Quality (DEQ) are inconclusive, city and state officials continue to suspect biological activity is the culprit of the taste and odor event.
Biological activity can produce non-toxic, non-regulated taste- and odor-causing compounds that can be detected by humans in low levels, according to Jeffrey Wells, engineering field director for the Danville office of the state Office of Drinking Water.
When the taste and odor issues first emerged in early February, raw water samples analyzed at Old Dominion University confirmed the presence of algae species. The species identified were Synura, Asterionella and Synedra.
Following the re-emergence of an earthy, musty taste and odor in the raw water, the city requested DEQ’s assistance.
Two weeks ago, field teams from both DEQ and the North Carolina Department of Environment and Natural Resources surveyed the Dan River and its major tributaries, including the Smith River, to observe the water and riverbanks and to collect water samples. The teams did not find the presence of algal blooms or unusual sources of nutrients that would stimulate blooms.
The water samples were tested for the presence of nutrients that would feed the growth of algae. Bill Hayden, DEQ public affairs director, said Tuesday that all test analyses failed to find nutrient levels to be out of the ordinary.
“DEQ will continue to work with the city and the Virginia Department of Health on any questions that come up, and will be available if any additional testing is needed,” Hayden said.
Last week, Hayden said the North Carolina Department of Environment and Natural Resources reported that its initial test results showed nutrient levels within normal ranges.
Danville Utilities collected raw water samples on March 25 to be tested for the presence of pesticides. A private lab in Ohio tested for 33 pesticides and herbicides, including Atrazine and Lindane. The test results did not detect their presence.
In addition, the city has twice sent water samples to a private lab in North Carolina to be tested for the presence of volatile organic chemicals such as benzene. These contaminants are both manufactured and naturally occurring. Test results on both occasions have not detected the presence of these chemicals.