By John Schaffner
The watershed protection specialist for the Upper Chattahoochee Riverkeeper organization discovered alarming levels of E.coli contamination in Tanyard Creek on April 8—much higher than any previous readings.
The samplings were taken upstream of Tanyard Creek Park.
The April 8 reading, taken upstream from where the concrete channel ends near apartments and I-75, registered 81,640 mpn/100 millileters. The previous high reading from the creek water taken March 11 within Tanyard Creek Park was 52,310 mpn/100 millileters.
Following obtaining the March 11 high reading, Riverkeeper watershed protection specialist Jason Ulseth met with officials of Atlanta’s Department of Watershed Management on March 22 to try and determine the cause of the high reading, which was taken during a dry period.
Ulseth said he walked Tanyard Creek on April 8 “and took a few additional samples of the creek.”
“I found a very high level upstream of the park, right where the concrete channel ends,” he said. “As I went downstream, the levels dropped, and I assume this is because of downstream dilution.”
After recording a level of 81,640 mpn/100 mi at the end of the concrete channel. Ulseth said the levels recorded on April 8 dropped to 1,580 mpn/100 mi at the railroad trestle over the creek at the southern end of the park. He got a reading of 1,350 mpn/100 mi at the pedestrian bridge within Tanyard Creek Park, where readings are taken every Thursday at 1 p.m. by Collier Hills neighborhood volunteers.
The lowest of those readings was significantly higher than the level the U.S. Environmental Protection Agency (EPA) considers safe for water used for recreation. The EPA says such waters should not contain more than 235 cfu/100 mi.
The Riverkeeper uses mpn (most probable number) measurements, which is virtually the same as the cfu (colony forming units) used by the EPA, according to Ulseth.
Ulseth said the dramatic drop in mpn/100 mi moving from the I-75 area to the park “shows that the contamination is not coming from the park. So we are now focusing on areas upstream of the concrete channel. I will be taking additional samples of storm drains and tributary streams to try and narrow down the source,” he added.
Ulseth said a reading taken April 15 from the pedestrian bridge within the park “was surprisingly low, less than 100 mpn/100 mi.” One factor may be that there had been virtually no rainfall for days prior to that reading.
Ulseth said the Riverkeeper organization has been communicating with the city “and they will be initiating a new source tracking effort on Tanyard. However, all of their inspectors are busy right now on a deadline for another major project, so they are hoping to be able to start in May.”