Report has good news on C-U water supply
CHAMPAIGN — It turns out that the Mahomet Aquifer, the enormous underground water source for Champaign-Urbana and other area communities, is even more enormous than previously believed.
A study of the aquifer, undertaken by the Illinois State Water Survey, finds that at current use rates, there would be more than enough water to meet demand even 40 years from now.
"The model budget indicates that the available 2050 water supply for the aquifer as a whole is 2.3 times greater than the projected (annual) baseline demand," said the recently released report, which is available as a 179-page 15-MB pdf file here.
It's good news for Champaign-Urbana, which gets its water from wells that dot the landscape north and west of the cities.
"On the groundwater side, there are no new concerns; there is actually more groundwater in the Mahomet Aquifer than we previously stated," said George Roadcap, a hydrologist with the water survey, who said he's been studying the aquifer "off and on for 10 years."
"It's a good, solid scientific report," said Tom Berns, an Urbana engineer who is vice chairman of the board of the Mahomet Aquifer Consortium. "It's not Pollyanna. It's not gloom and doom. Even those areas that have some bad news, whether it's Decatur or Springfield or Bloomington, the message is they need to keep their head up. It's not a disaster, but if you don't do something, it will be a problem."
In fact, while the report is positive for Champaign-Urbana, it's less so for the communities to the west, all of which get their water from aging, man-made reservoirs.
Springfield's water supply is already classified as inadequate, meaning "there is greater than a 50 percent probability that most of the city's electricity generating units (located on Lake Springfield, which was created in the early 1930s) would need to be shut down during a drought of record condition," according to the report. Bloomington's and Decatur's supplies are considered at-risk, meaning that there is a greater than 10 percent possibility of a water shortage. Both could come to be inadequate by 2020 unless supplemental water sources are developed by then, said the report.
Danville's water source is considered adequate, "but with both projected growth in demand and sedimentation losses in Lake Vermilion, the supply is projected to become at-risk by 2040," the report said.
How the aquifer would be affected if any or all of those communities opted to tap into it hasn't been studied yet, Roadcap said.
"This report doesn't address that," he said. "That's the next phase of the project, some what-if scenarios. In this report, we looked at who are the current users and what are we projecting their growth to be.
"Now we're going to go ahead and say, what if Bloomington develops big water supply in the Mahomet Aquifer?"
Springfield, Bloomington and Decatur all are considering adding groundwater sources to supplement their reservoirs. Decatur already has an emergency well field that can take water from the aquifer and discharge it into Friends Creek, which flows into the Sangamon River and eventually into Lake Decatur.
The study of the aquifer, which in Champaign County exists between 200 and 350 feet below the surface, uncovered a few surprises, Roadcamp said.
It recharges "much faster than we thought it was," he said. And much of that recharging occurs in two areas: along the Sangamon River near Allerton Park and in Rantoul and east of the village.
"These are areas where there is sand at the surface," he said. "Most of Piatt County, for example, is covered in clay. But where there is that surface sand and it's connected to the aquifer, you get much higher recharge rates."
And the area around Rantoul "has a large sand area at the surface where there is this major source of water that is actually replenishing the Champaign-Urbana supply."
Further, he said, "we were surprised to find that we're having far less impact on the surface streams than we thought we were having. When you pump 30 million gallons a day from underground (the approximate public water use from Champaign-Urbana), that water has to come from somewhere, and one of the main areas it comes from are streams. Out at the Sangamon River there is a connection in that the Sangamon River is losing water to the aquifer to support Champaign-Urbana.
"But it's largely occurring during high flows. The surface water can come up and push a lot of water into the groundwater. What we don't see is the stream going dry during low flow. We're not drying the stream out. So the actual impact of our water use is less than we might have expected."
The overall takeaway from the report about the aquifer, Roadcap said, "is sort of an anti-alarmist message. It's hard to keep a hole in the ground dry. Water wants to get back in and fill it up. That's the easiest way I can explain it."