0

Aquifer

Dallas has plan for water

DALLAS -- City officials are considering a bold new way to meet the growing demand for water: taking the water they already have and pouring it into a hole in the ground.

More precisely, pumping it in. And then pumping it out.

Called aquifer storage and recovery, it involves diverting water during high-flow winter months and storing it in an underground well.

Used across the country, aquifer storage and recovery, or ASR, is still in its trial phase at several sites in Oregon. Relatively inexpensive, ASR gives cities a quick way to hold more water without building an expensive new reservoir.

For Dallas officials, it's like buying time. If the city continues to grow at the current rate, Dallas would experience a water shortage by around 2012.

Mercer Reservoir, built on Rickreall Creek, can't hold any more water. In fact, it holds less and less as sediments build up.

Drilling an ASR well would provide enough water, combined with the reservoir, to meet growth until 2020. "It gives us a lot of breathing room," said City Manager Roger Jordan.

City officials continue to explore other options for water, including a county-wide study on using Willamette River water from Adair Village. Officials also have identified five sites for additional reservoirs, two of them along Rickreall Creek.

Dallas could store 100 million gallons in an ASR site -- a 20- to 25-percent increase in capacity, said Public Works Director Fred Braun. The well would provide 1 million gallons per day; average summer use is 4 million gallons per day.

Jordan said the project's cost excited him. An ASR system would cost around $1 million to $1.5 million.

A new reservoir would cost $15 million to $20 million.

The Dallas City Council will discuss drilling a test ASR well in late December or early January, Jordan said, at a cost of $500,000. Drilling would begin as early as February 2004 in order to get the project on-line by early 2006.

-----

Rivers and creeks in the Willamette Valley flow heaviest in melt. In the summer and early fall, water levels drop.

Cities like Dallas that use dammed waterways for their water source have more than enough water during the winter. In the summer, they rely on water stored in reservoirs.

Sometimes, that's not enough.

An ASR system would take some of the water during winter months -- when water typically flows over the dam -- and inject it deep into the ground. In the summer, that water would still be there to be withdrawn and used.

Aquifers, or underground stores of water, exist naturally. Many cities have tapped into aquifers for their water.

Some view aquifers as vast underground lakes or flowing rivers, said Phil Brown, hydrogeologist for engineering firm CH2M Hill. Brown doesn't like that analogy.

He compares aquifers to a bathtub full of sand or a sponge. Both hold water.

Dallas sits on basalt deposits from ancient volcanoes. Basalt makes an ideal rock for ASR, Brown said. CH2M Hill has developed ASR sites in Beaverton and the Tualatin Valley in basalt formations.

Water travels very slowly through the rock, Brown said. As a result, most water pumped into one site will stay where it was injected.

The new water forms a bubble that pushes away the native aquifer water, Brown said. That native water could be salty, Brown said, and it wouldn't mix with the fresh water quickly enough to cause problems.

Water stored underground generally remains safe for drinking, said Donn Miller, a groundwater geologist for the Oregon Water Resources Department, the agency responsible for overseeing ASR projects. Since state law requires the water be treated before it is pumped into the ground, the water coming out generally needs only chlorine before heading to water users' pipes.

The City of Salem started Oregon's first ASR site in 1996, Miller said. Water from that site, still in its test stage, has taken on tastes and smells from the rock, Miller said.

Neither affects its potability, Miller's said; his own home gets water from that site. That aquifer, however, had been depleted and likely won't store as much water as Salem officials had hoped, Miller said.

Unlike Salem, Dallas has not tapped into the aquifer slated for ASR, Brown said. "Dallas is a little different," Brown said.

"Typically you store in an aquifer that someone has already been using. The wells around Dallas stop at the top of the Siletz River Volcanics," Brown said, the layer the ASR well would penetrate. The Dallas well would reach 2,000 feet below ground.

Even if Dallas had no water shortage on the horizon, Miller said he would still recommend something like ASR. "In general, cities really need multiple sources of water," he said.

If an earthquake or flood damaged one water source, Miller said, the other could keep water flowing. "There's a vulnerability to each one of them," he said.

With two very different water sources, if one gets damaged, "it's more than likely the other one would not be degraded in large measure," Miller said.

In terms of water shortages, however, the best solution could be the oldest -- conservation. Dallas has steps in place, Jordan said, including smarter irrigation, to reduce water use.

City officials encourage residents to limit water use in the summer. Heavy users get charged at a higher rate for water over a certain allowance.

Adding a monetary penalty makes conservation attractive even for those who don't care about saving water, Jordan said. "If you're a water waster, do it because it's good for your wallet."

Comments

Use the comment form below to begin a discussion about this content.

Sign in to comment

CLOSE X

Information from the Itemizer-Observer and our advertisers (Want to add your business to this to this feed?)