Summit pump test data provides clues about impacts

Sunday , February 15, 2015 - 12:00 AM

EDEN — State scientists have weighed in on Summit’s controversial pump test, and appear to have some positive implications for the ski resort owners.

A Utah Geological Survey team evaluating Powder Mountain’s well and water situation said Summit’s pump test data was adequate, and showed that while drawdown would take water from both Weber and Cache counties, there was no statistically significant impact on the springs and streams during Summit’s test.

That doesn’t mean Summit is off the hook, however.

“Depending on recharge conditions and the amount of pumping and number (and) placement of wells, we could see impact on streams and springs on both sides of the mountain,” said Paul Inkenbrandt, project geologist with the UGS. 

The geologists cautioned that summer fieldwork is needed to provide more insight. UGS is investigating the issue for the Utah State Engineer and Utah Division of Water Rights, and the geologists stressed that their work is still in its early phases.

“It has had no peer review, and we made that clear to the state engineer,” Inkenbrandt said. “It will take some time before we get to the publishing stage, probably by the end of this fall, even though some people might be expecting it sooner than that.”

Last spring, Summit Mountain Holding Group filed an exchange application with the Division of Water Rights seeking approval to draw water locally from its Hidden Lake Well instead of piping water from Pineview Reservoir.

The request caused a stir among water users in the Ogden and Cache valleys. Residents and landowners worried a new well on Powder Mountain would interfere with existing water rights downhill.

State Engineer Kent Jones required a pump test from Summit’s proposed well to collect data showing any possible interference with nearby springs and creeks.

After reviewing data from the pump test and their own studies on local hydrology, the UGS geologists presented findings to the Division of Water Rights and regional engineers last month. They made their presentation available to the public on Feb. 3.

The UGS must present the State Engineer with a draft report and firmer findings on the proposed well’s impacts by October 2015.

“Our job is to provide objective scientific information, and it’s just that,” said Mike Lowe, geological program manager with UGS. “It’s not our job to make any decisions.”

Test adequacy

Summit delayed its pump test until December, which raised more concerns with the public. Well tests are typically conducted in the late fall, when conditions are stable and more representative of seasonal base flows. There’s no spring runoff or summer thunderstorms to cloud the data.

Concerned parties worried that a wintertime test would provide inconclusive results.

“You want the driest time of year after the runoff,” said Stefan Kriby, a geologist with UGS conducting much of the fieldwork for the Powder Mountain study.

Last year saw little precipitation in October and November, however, creating good conditions for Summit’s test, Kirby said.

“This happened to be an incredibly dry fall, so it was actually a pretty good setup for this late pump test, in reality,” he said.

“If I were conducting an aquifer test, I’d be happy with this one,” Inkenbrandt said. “It’s hard to do a two-week-long test without any precipitation.”

While the Division of Water Rights allowed Summit to proceed with its pump test in December, it did so with the caveat that additional testing might be necessary. UGS scientists, however, said Summit’s pumping data is adequate.

“We doubt we’ll get any significantly more relevant information by doing another (pump test),” Lowe said. “It depends on what the State Engineer requests, of course, but I think it’s safe to say we think this aquifer test was not that bad.”

How the water goes down

UGS scientists used Summit’s data along with some of their own research to compose a hydrogeological picture of the Powder Mountain area. They measured springs, stream flows and collected water chemistry samples. They also studied existing reports on the area’s geology.

Powder Mountain straddles a ridge dividing Weber and Cache counties. Below the ridge sits a system of carbonate rocks, mostly limestone and dolomite, which are porous enough to hold water and create an aquifer system. That aquifer gets deeper and slopes gently as it extends from Weber County into Cache Valley.

“So it kind of forms a bathtub that dips to the north,” Kirby said.

Within that bathtub is another, smaller carbonate bathtub, called the Nounan formation. Around 20 percent of the Nounan’s rock sits in Weber County, but the vast majority dips broadly north into Cache County. At the top of the Nounan sits Summit’s proposed well.

“That’s also where Lefty’s Spring issues from, and also some springs on the Cache side issue from it,” Kirby said.

Those springs run downhill and feed major creeks, like Wolf Creek and Wellsville Creek – important sources of water for residents downstream.

“So it’s an important carbonate unit within that larger carbonate package,” Kirby said.

Kirby and Inkenbrandt were able to roughly confirm the carbonate system’s extent, as well as the reaches of its waters, by measuring water chemistry. The limestones and dolomites partly dissolve in water, giving it a chemical fingerprint. The quartzite rock surrounding the Nounan, the same quartzite rock seen in Geertsen Canyon, doesn’t dissolve as well as carbonate rock, and leaves behind its own mark.

The distribution of hydrogen and oxygen atoms also indicates whether water came from snowmelt or a different source in the valley. Scientists can use these measurements to tell where waters meet and how they mix.

Knowing waters’ sources and which creeks and streams they feed, the UGS geologists measured flows as Summit drew down its well for two weeks during the pump test.

Although water discharge to the north, at Hidden Lake and at Lower Lefty’s, declined during the pump test, Inkenbrandt said it doesn’t necessarily mean drawing down Summit’s well resulted in decreased water reaching the springs.

“Even though you might be able to look at it and say that, it’s hard to prove there’s a statistically significant impact,” he said. “So we can’t say whether or not there is impact. We’re not saying there isn’t, but we can’t prove that there is.”

The drop in discharge velocity to nearby creeks also correlated with a trend in the aquifer over time as water levels dipped, the USGS scientists said.

“There was a downward trend before pumping, and that just continued. It’s not necessarily the pumping that’s making it go down,” Lowe said.

Inkenbrandt used different computer models to plot different aquifer fluctuation scenarios, and some showed nearly identical declines from climate and temperature influences.

“I could reproduce them without having that pumping influence,” he said. “So it’s totally possible they happened like that without the pumping.”

Predicting prolonged pumping

Beyond the well’s influence over a two-week period, the UGS scientists modeled aquifer conditions if Summit operated its well at 100 gallons per minute continuously over the next 10 years to see how water levels might change.

The model shows 26 feet of drawdown near Lefty’s Spring in Weber County and about four feet of drawdown near the Hidden Lake seeps and springs to the north – bringing the aquifer low enough for these springs to run dry.

According to the model, deeper drawdown occurs on the Weber County side of the divide because of the aquifer’s limit in the county.

“There’s a lot more water volume to the north to take from,” Inkenbrandt said. “All of your rock volume is up there, (around) 80 percent.”

The extent of the aquifer’s dip is alarming at first read, but the model leaves out an important factor – snowmelt and recharge.

“This is just assuming nothing is really coming in, they’re just taking out of a pool, and that’s really important,” Inkenbrandt said.

In other words, the model includes a worse-case scenario that’s not likely in the real world.

“The reality is, there’s going to be less (drawdown) than this because there’s going to be recharge,” Kirby said.

Information gaps

This summer, once the snow melts and the ground dries, the next step for UGS will be to visit the area and conduct fieldwork.

Plenty of unknowns still exist regarding the aquifer, unknowns that could alter their findings a little or a lot. The porosity of the carbonate rock, for example, could vary throughout the Nounan formation and impact how much water it holds. Fractures in the formation could have significant influence as well.

The UGS scientists noted Summit’s test well was low-yielding, and doesn’t produce much water. Changing the location of the well could produce more water, particularly if it reached a large fracture in the Nounan formation, but that could have different impacts downstream. More than likely, the well runs through smaller fractures already, meaning the water is drawn more in an oval shape than a uniform circle around the well. Drawdowns could then have a different field of influence than currently modeled.

“One of the reasons we emphasize that this is preliminary, that things can change, that we’re early in the study, is because we haven’t gone up and done the fieldwork to measure the direction of the fractures,” Lowe said. “After we do fieldwork, when we measure the trend of the fractures, the shapes and the curves, it’ll likely change.”

Models also assume there’s a rock boundary at the base of the Nounan foundation, so the well won’t be impacting any water below it in the larger carbonate bathtub formation.

“It could be connected; we don’t know that,” Kirby said.

One takeaway from the geologists’ findings so far, however, is the definite connection between north and south. Summit’s well sits at the top of a geological and geograhical divide, and any real water impacts will trickle down to both counties.

“You can say that there will likely be impacts on both sides,” Inkenbrant said. “How much, the relative amounts, those are harder to be firm with.”

To view a copy of UGS’s presentation and data from its preliminary study, visit http://geology.utah.gov/geologic-resources/data-databases/#tab-id-3.

Contact reporter Leia Larsen at 801-625-4289 or llarsen@standard.net. Follow her on Twitter @leialarsen or on Facebook.com/leiaoutside

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