By Cat Holmes
University of Georgia
A University of Georgia scientist has rediscovered a quick,
simple method to identify sources of fecal contamination in
water, and it has the potential to save state and federal
agencies a lot of money.
The method, called targeted sampling, is simple. Instead of
using statistical models and fixed locations, targeted sampling
uses shoe leather and common sense.
Targeted sampling is based on what used to be called a sanitary
survey. For a sanitary survey, a person walked along sewer
pipes and sampled for leaks. Targeted sampling is the same,
except a person samples for sources of fecal contamination in
creeks and waterways.
“It’s akin to the children’s game of hot and cold,” said Peter
Hartel, the UGA crop and soil scientist who devised the
method. “You sample the water until you find areas where high
numbers [of fecal bacteria} are present. Then you look around.
It’s commonsensical: Are there cows in the water? A broken
sewer pipe?”
The current methods used to track down sources of fecal
contamination in water are time consuming and expensive. That’s
because scientists often use set sampling locations and
databases instead of their eyes and legs to determine where a
problem has likely occurred.
Unfortunately, set sampling locations are often chosen because
they are easy to get to, like bridges, but they may not be
anywhere near the source of the problem.
“If you actually go out and walk the waterways and sample
everything that looks suspicious – every pipe, every tributary –
you generally uncover [the problem] quickly and easily,”
Hartel said.
Targeted sampling greatly enhances the accuracy of bacterial
source tracking. Chemical and DNA-based tests for bacterial
source tracking are typically 65-85 percent accurate; when the
same tests are combined with targeted sampling, they are 95-99
percent accurate.
“It’s like looking for a needle in a haystack, except you’re
looking for a needle with a great big magnet,” Hartel
said. “For example, if targeted sampling identifies a hotspot
of fecal
contamination and I know that there’s a nearby dog park and
septic field, then I only have to sample the dog park, septic
field and water source to determine how much the dogs or septic
tank are contributing to the overall fecal contamination.”
So far, Hartel has been able to find fecal contamination
quickly and easily with targeted sampling. When he tried it on
the Sapelo River, he found that half the fecal contamination in
the river was due to a malfunctioning private wastewater
treatment facility. It took one day to find the source of the
problem.
“I have yet to come across a case where targeted sampling and
common sense didn’t work,” Hartel said. He is preparing to use
the method along the beach of a coastal island.
“Because the coast has a high water table, failing septic tanks
are a common problem,” Hartel said. With targeted sampling, a
hotspot can be quickly identified and the site can be double-
checked for optical brighteners common in laundry
detergent. “If we find optical brighteners, we know what the
problem is. It sure isn’t the deer doing their laundry.”
The method does have a couple of drawbacks, Hartel said. One is
that it requires a lot of manpower. He has used volunteers and
there could be liability issues if a volunteer were to get
injured or hurt. Another potential problem is trespassing.
However, Hartel is confident that these issues could be
addressed.
“I wanted to find a method to identify sources of fecal
contamination that’s fast and cheap,” he said. “This method
works fine. And the beautiful part is it’s common sense.”
Cat Holmes is a news editor for the University of Georgia
College of Agricultural and Environmental Sciences.
