A rapid drop in pH was the primary cause in an Oct. 15 fish kill on Brier Creek, according to a report released Wednesday that concludes 12,522 fish were killed.
The 11-page summary, compiled by fisheries biologists from Georgia’s Wildlife Resources Division, categorizes the event as “severe” and determined that water quality was compromised along 18.5 miles of waterway in Burke and Jefferson counties.
Although the report does not assign blame, biologists who arrived one or two days after the event found a dangerously low pH level of 4.8 in untreated groundwater that was being pumped into a Brier Creek tributary – Reedy Creek – from a kaolin mining facility.
According to the report, a safe pH of 6 was observed at the U.S Highway 221 bridge, but it had dropped to just 4 at U.S. Highway, the next bridge downstream. The kaolin facility where the untreated groundwater was tested was between those two highways.
The Wildlife Resources Division’s report has been turned over to the state Environmental Protection Division, which regulates industries that discharge water or waste into lakes and rivers and administers permitting programs designed to maintain acceptable water quality. That investigation remains incomplete.
Fish killed in the event were sunfish, shiners, spotted sucker, largemouth bass, creek chubsucker, madtoms, darter, chain pickerel, channel and bullhead catfish, and crappie.
Including an additional $3,441 in investigative costs, the total cost of the fish kill was estimated at $20,860, the report said.
According to the U.S. Geological Survey, changes in pH – or levels of acidity – can be fatal to fish and other organisms. Its measurements are in logarithmic units, like the Richter earthquake scale, in that each number represents a 10-fold change in acidity. For example, a pH of 5 is 10 times more acidic than a pH of 6 and 100 times more acidic than a pH of 7.
In general, a pH of 7 is considered healthy and neutral. When water has a pH of 4 to 5, fish reproduction is affected, and adult fish die at levels of 3 to 4.
By comparison, vinegar has a pH of about 3, while pure battery acid has a pH of 1, the USGS said.