ST. PAUL — An expert witness for the Department of Natural Resources (DNR) believes climate change and not groundwater pumping is the primary cause of low lake levels.
The plaintiff’s expert said his opinion has not changed since his original 2013 report: that groundwater withdrawals permitted by the DNR directly impact the lake surface water level, impairing White Bear Lake and the aquifer beneath it.
Whose testimony carries the most weight will be up to Ramsey County Judge Margaret Marrinan to decide.
There is much to sort out among the scientific reports and anecdotal evidence provided the judge since the trial began March 6.
Witnesses for the plaintiff, the White Bear Lake Restoration Association (WBLRA) and intervenor Lake Homeowners Association, included hydrogeologists and lake homeowners who are members of the WBLRA. The defending DNR called its own scientists and regulatory people to the stand. Intervenors for the defense, White Bear Township and the city of White Bear Lake, called staff to testify, including retired City Manager Mark Sather. Closing arguments were expected March 29.
The expert witness for the DNR was Matthew Tonkin, PhD, a hydrogeologist and president of S.S. Papadopulos & Associates, an environmental and water-resources consulting firm based in Bethesda, Maryland.
While Tonkin agreed that groundwater extraction from aquifers “hydraulically connected” to White Bear Lake has the potential to change the level of surface water, he testified that based on data received and calculations made, climate fluctuation is the dominant factor in both reduction in lake levels and subsequent increases in recent years.
During his testimony, Tonkin said mitigation measures proposed by the plaintiff’s experts are “likely to be hydraulically inefficient and possibly punitive.”
“Mitigating declines in White Bear Lake water levels through manipulation of groundwater extraction rates and/or lake augmentation can only provide a fraction of the relief sought by the plaintiff,” Tonkin said, “since changes recorded at White Bear Lake are dominantly symptomatic of regional climate fluctuations. Manipulation of minor contributing factors will not provide substantial relief.”
Plaintiff expert Stu Grubb, a hydrogeologist with Emmons & Olivier Resources in Oakdale, said he stands by his original conclusions after site visits, field tests and analysis of the new USGS report.
That 2016 report analyzed groundwater/surface water interactions in lakes of the northeast Twin Cities area from 2002 through 2015, including White Bear Lake.
Based on his recent review, Grubb has changed his mind about one thing.
Where his previous report recommended a 25 percent reduction in annual water use, Grubb now recommends a total ban on irrigation in municipalities near White Bear Lake.
According to Grubb’s calculations, a ban on watering lawns could reduce overall annual water use by at least 15 percent and raise the level of White Bear Lake by 0.75 feet. He suggests implementing a ban when the lake water level falls below a target elevation of 923.5 feet. The DNR established a protective elevation of 922 feet.
“Additional data and reports confirm my expert opinion that groundwater is flowing into and out of White Bear Lake, that pumping from the Prairie du Chien aquifer is lowering the water level and that if no changes are made, the water level will be even further suppressed in the future,” he wrote in his report to Judge Marrinan.
Grubb said wells near the lake, particularly on the southwest side, are pumping water that originated in the lake and are decreasing the hydraulic pressure in the aquifer, which causes more water to move from the lake to the aquifer below and to the wells.
“This opinion,” Grubbs explained, “is supported by Chapters A and B of the new USGS studies.”
Chapter B of the yet-to-be-released USGS study, “Simulation of Groundwater Flow and Surface Water Exchanges in Lakes of the Northeast Metro,” is technically still in peer review but was provided to partners in the research, one being the DNR. The report documents the Northeast Metro Lakes Groundwater-flow model created to calculate and predict the effect that changes to the environment — for example, groundwater pumping or changing rainfall — will have on water levels in area lakes, including White Bear.
According to Grubb, USGS used the model to calculate the influence groundwater pumping is having on the lake: When pumping rates of all the wells in the model were increased 30 percent, the water level fell by about 1.5 feet. When pumping rates were decreased by 30 percent, the water level rose by about 1.5 feet.
USGS also used the model to calculate the influence of precipitation changes.
When precipitation is reduced from 32.3 to 30.7 inches, a 5 percent decrease, water level fell by about 3 feet. When it increased to 33.9 inches, water level rose by about 2.5 feet.
“This means that during a dry period, the effect of increased pumping will be added to the effects of decreased precipitation to cause an even greater decrease in lake level,” Grubb noted. “If pumping increases by 30 percent and there is a 5 percent decrease in precipitation, the model predicts the level of White Bear Lake will decrease by about 5 feet.”
Tonkin criticized the USGS model during his testimony, calling it a limited tool to explain a complex physical phenomena.
“I would hesitate to give this to someone and say, ‘make a decision,’” he said. “Steady-state modeling (used by USGS) will overpredict the effects of pumping.”
Principal researcher on the USGS study, Perry Jones, was not in the courtroom to defend his work. He was subpoenaed, but was not allowed to testify by the overseer of USGS, the Department of the Interior. His boss, USGS Director Jim Stark, was present for Tonkin’s testimony.
“It was hard to sit here and not say anything,” Stark told the Press, when Tonkin was picking apart the modeling work.
The model that USGS designed is complicated and the review process long and involved, Stark said. Behind schedule for its release, there are 1,300 technical comments to resolve before the report goes to layout. A draft was sent to USGS partners prior to trial, including the DNR, the Metropolitan Council and the Minnesota Department of Health.
DNR attorney Oliver Larson asked hydrogeologist Tonkin his conclusions after a review of the USGS Part A report, to which the expert witness said the researchers did not identify a correlation between groundwater pumping and the level of White Bear Lake.
“It is difficult to discern an effect of pumping; it has a small magnitude on White Bear Lake,” Tonkin said.
The DNR witness was likely referring to page 48 of the 2016 USGS report that states “closed basin lake level changes were not correlated with mean groundwater withdrawals within their watershed or within a 2-mile buffer around the lake.”
When asked what kind of conditions would recreate levels of 919 feet, Tonkin replied, “a change in the balance between precipitation and evaporation.”
During her cross examination, plaintiff attorney Katie Crosby Lehmann asked Tonkin if he did any field tests? “No.”
Was he aware that the drinking water contains 11 to 58 percent surface water? “Yes,” Tonkin replied. “It confirms the lake loses to groundwater in the down gradient.”
She also asked the expert for the DNR if groundwater extraction has the potential to change the level of White Bear Lake? Tonkin answered, “Yes,” again adding it is “subsidiary to climate.”