GAINESVILLE -- The conventional wisdom is that septic tanks are bad for the environment.
But in a drought, a properly maintained septic system actually can ease a water shortage by recharging local streams, ultimately returning water to reservoirs such as Lake Lanier.
Todd Rasmussen, a professor of hydrology at the University of Georgia, says septic tanks have gotten a bad rap.
"The level of ignorance about this is amazing," he said. "The science is at odds with the public perception."
Rasmussen confesses that he himself was uninformed about the issue until he began studying it.
"I came into this as ‘anti-septic,' but the data has convinced me otherwise," he said. "During a drought, the only streams we see flowing are those that are near septic systems."
Rasmussen feels so strongly about this issue that he and other hydrologists have voiced their concerns at recent public hearings about Georgia's proposed statewide water management plan.
Specifically, he objects to statements in Section 9 of the draft plan.
The section says, in part: "Some portion of the water treated in septic systems is not returned to the water source in a time frame that allows ... reasonable use of that returned water. For practical purposes, this temporarily absent water contributes to the cumulative consumptive use in a sub-basin or watershed."
"Consumptive use" refers to water that does not go back into the watershed. Irrigating a lawn, for example, is consumptive because the water is either lost to evaporation or is taken up through plants and does not reach the groundwater.
But Rasmussen said septic tanks are deep enough underground that their effluent bypasses plant roots. Instead, the wastewater gradually trickles down through layers of soil, which filters out pollution. It then joins the groundwater table and flows toward streams.
Maj. Daren Payne, deputy commander of the U.S. Army Corps of Engineers' Mobile district, which manages Lake Lanier, said the corps does not consider septic effluent to be "lost" water.
"From the corps' perspective, it makes no difference," he said. "There is no net loss of water using septic versus using a public utility system. Either way, most of the water does make it back to a river or lake. And a functioning septic system next to a lake can be a good thing, because the water does return fairly quickly."
Rasmussen said Georgia's draft water plan is misleading when it uses the phrase "temporarily absent water."
"Most septic systems are in a relatively steady state," he said. "People in a household use about the same amount of water every day, so it's a constant discharge over time."
Depending on where the house is, the wastewater could take anywhere from a few weeks to a year to reach Lake Lanier. But Rasmussen said there is no gap in availability, because groundwater flows seamlessly, like an undammed river.
"The state plan is saying that septic systems cause a hydrologic lag, and that's not really the case," he said.
If septic systems did somehow worsen the effects of drought, Hall might be in a dire predicament because so many of the county's households are on septic.
Pat Braswell, environmental health manager for Hall, said nobody knows exactly how many septic tanks there are in the county, because many were installed before permits were required.
"But the (Metropolitan North Georgia Water Planning District) asked us to make an educated guess, and we estimated that more than 75 percent of the single-family homes in Hall are on septic," she said.
That's by far the highest percentage in any of the district's 16 metro Atlanta counties.
"Hall has been rural for longer than most of those other counties," Braswell said. "Sewer lines are now being extended farther out into the county, and eventually most new homes will be hooked up to sewers. But Hall will always have a lot of septic tanks, because most houses that are already on septic will probably stay that way."
According to U.S. Census data, about 38,000 of Hall's 61,000 housing units are owner-occupied. If more than 75 percent of single-family homes are on septic, there could be as many as 30,000 tanks in the county.
And it's not just residential areas that use septic systems.
"We can permit anything that has a flow of up to 10,000 gallons a day," Braswell said. "That's the equivalent of an apartment complex with 50 to 70 bedrooms. We also have many retail and office buildings that are on septic, though high water users such as restaurants, grocery stores, animal clinics and beauty shops generally need to be on sewer."
Many of those septic systems, assuming their tanks are pumped out regularly and are not leaking raw sewage, may be benefiting Lake Lanier. But not all of them.
"A lot of homes get their drinking water from the municipal source but they don't have sewer service," said Rasmussen. "That's OK if they're in the same area that their water comes from, because their septic system sends the water back into the basin.
"The issue is when drinking water is used by communities in another watershed. Those homes that are on septic are not returning water back to the lake."
That may be the case for some homes in East Hall, part of which is in the Oconee River watershed rather than the Lanier basin.
But Rasmussen said even water that does not return to Lanier can still help the regional drought situation.
The Athens area depends entirely on the Bear Creek reservoir, which draws its water from the Middle Oconee River. With the reservoir almost dry, Athens is in danger of running out of water by the end of the year.
"That East Hall water goes into the Oconee watershed, and Athens definitely needs it," Rasmussen said.