MANKATO — It was clear and a mild 72 degrees on the morning of Aug. 8 in Mankato's Germania Park neighborhood.
Tim Slipy thought it was a great day to get some home improvement work done. He was painting a garage at the corner of Seventh Avenue and Harper Street.
On such a beautiful summer morning, Dave and Julie Kreiselmeier's two pre-teen daughters would normally have been playing in the yard of their home abutting the Jefferson Quarry. Instead, the yard at 601 Harper Street was quiet. The girls were visiting their grandmother.
And in the quarry less than 300 feet away, workers were pouring 4,124 pounds of ammonium nitrate and fuel oil into 47 holes that had been drilled deep into a shelf of limestone. Known as ANFO, the legal explosive was the same type used by terrorist Timothy McVeigh in 1995's Oklahoma City bombing, and the amount was only about 18 percent less than the 4,800 pounds McVeigh detonated outside the Alfred P. Murrah Federal Building, killing 168 people.
This time the ANFO was being used by certified explosives experts with hundreds of blasts on their resumes.
Blasting at the Jefferson Quarry was a bit different for the workers from Olson Explosives, Inc., a Decorah, Iowa, company working in the Mankato quarry for the first time in 2017. None of their previous quarry jobs put them so close to a residential neighborhood. Houses were only a stone's throw away from where they had just placed two tons of explosives.
In regard to loading and detonating the explosives, though, everything was pretty routine other than one or two holes that seemed to be leaking explosives, the workers later told Mankato fire and police officials.
But when the detonator was triggered at 10:28 a.m., the blast was anything but ordinary.
"Holy f--k!" said Andrew Baxter, the mining supervisor at the quarry, who was video-recording the blast.
Slipy paused in painting his garage. Living in that neighborhood, he'd been through quarry blasts before. This one was different.
"I was like, 'What's that sound?'" Slipy said. "It was the rocks coming in. You could hear it flying through the trees. ... Small ones, big ones. You're talking 20, 30, maybe 50."
The big ones were very big. Mankato police found seven in the residential area weighing 10 pounds or more, including a 48-pounder, a 68-pounder and one that topped 82 pounds. The 82-pounder was 19 inches by 8 inches by 9 inches.
One of those large rocks sailed 570 feet from the blast site, nearly the length of two football fields, before sheering off the limb of a tree along Harper Street. And one slammed into the side of 601 Harper Street, putting a deep gouge in the side of the house just below the bedroom window of the Kreiselmeier girls and just above their parked bicycles.
MANKATO — A quarry that was accused in April of causing an earthquake-like tremor felt acros…
"I was with my kids at Grandma's," a relieved Kreiselmeier said that afternoon. "Seriously lucky, because my kids are always out here playing. Just shocked. We're just in shock now."
While no one in the neighborhood was struck by the barrage of stone, Kreiselmeier wasn't alone in her shocked reaction.
Baxter — the mining supervisor for Jordan Sands, which manages the quarry for the Coughlan Companies — was packing up the video camera when Brent Stoltz of Olson Explosives pulled up after evacuating the site for the blast.
"He asked me how the blast went, and I shook my head and said, 'Not good. We had shit everywhere,'" Baxter said, according to investigation records obtained by The Free Press. "I mean, excuse my language, but that's what I said."
Stoltz, who was the blaster-in-charge, pointed upward, questioningly.
"I said, 'No, out towards the north,'" Baxter said. "And he asked me if anything left the quarry. I said, 'I don't know,' because I couldn't see. I said, 'I have a feeling it did.'"
Following the rocks
Mankato police and fire officials descended on the neighborhood, and by about 11:15 a.m. Jeff Bengtson, the deputy director of Public Safety for fire operations, informed Baxter that he would be suspending the quarry's blasting license.
Bengtson also sought any early theories from Baxter and Stoltz about why the blast had gone so wrong.
"I asked them if they knew what had happened, and Mr. Stoltz described that there may have been a weak area in the limestone that allowed the explosive emulsion to accumulate or allow more energy to escape from the blast," Bengtson wrote in an Aug. 8 investigation report.
"I asked Mr. Baxter to describe the shot and he said it should have been a normal limestone shot," Bengtson wrote.
Baxter and Stoltz also threw some of the rocks back into the quarry that morning, stopping when some in the neighborhood accused them of attempting to eliminate evidence. Both denied that was their intent in later police interviews, with Stoltz saying it was "normal procedure" when rocks from a blast land on private property.
"It was more of just a trip hazard," Baxter said of his motivation for getting rid of some rocks, noting that he photographed everything he moved and that there were people, including Public Safety officers, in the area while he did it. "... It was more of one of those things, you know, do you leave it there?"
A criminal investigation
On the morning of Aug. 10, police investigators assigned to the case attempted to schedule formal interviews with officials from Jordan Sands and Olson Explosives. After interviewing residents of the neighborhood, Detective Thomas Rother contacted Baxter and told him a criminal investigation was underway.
"Baxter told me that he was not at work yet and that he believed an attorney would be assisting them in this case," Rother wrote in his report four days later. "I told Baxter to reach out to me when he and his attorney could meet with me. At the time of this report, I have not received any call back from Baxter."
Formal interviews eventually occurred, with company attorneys present, two weeks after the blast. By then, Jordan Sands officials said they didn't know why the blast showered their neighbors with rocks and boulders, known in the blasting industry as "flyrock," but suspected that Olson Explosives blasters had improperly loaded the ANFO in one of the 47 drill-holes involved in the blast, according to investigation reports and police interviews reviewed by The Free Press.
Read the blast report from Olson Explosives' Aug. 8 quarry blast at the Jordan Sands quarry in Mankato.
Olson Explosives workers said the blast was handled according to Jordan Sands' specifications and the flyrock was just an unfortunate result of a hidden weakness in the limestone, according to police investigation records.
A long history, a rough 2017
Bordered by the Minnesota River bike trail on the west, Highway 14 on the north, commercial properties on the northeast, and houses and apartments on the east and south, the Jefferson Quarry has been mined for decades for limestone, gravel and sand.
The 127-year-old Coughlan Companies revealed nearly two years ago that operations would wrap up at the quarry in two or three years and their tapped-out quarries in the city would be redeveloped, possibly partly as public parkland.
But even with the quarry operations winding down, the company's blasting activity has received more public attention in the past six months than it had in the previous six years.
Jordan Sands had its permit suspended for 60 days after an April 25 blast was immediately followed by a temblor strong enough to be felt in buildings across the Minnesota River valley — one that prompted damage reports from more than two dozen homeowners and registered 2.8 on the Richter scale. An investigation followed, but the city allowed blasting to resume after determining that "there was no negligent discharge of explosives in the quarry on April 25."
The company conducted an investigation of its own, hiring an engineering firm that company officials said had determined a natural earthquake — not an explosion at the quarry — caused the tremor. Because earthquakes are extremely rare in Mankato and because the alleged earthquake happened virtually simultaneously with a blast at the quarry, the report was met with widespread skepticism in the community.
The U.S. Geological Survey said seismological data suggested that the temblor was likely caused by a quarry blast, and several other geologists contacted by The Free Press agreed that the raw data indicated an explosion — not an earthquake — caused the city to shake.
The police investigation of the Aug. 8 blast also revealed another, more isolated, instance of flyrock from the quarry. Company officials described a mortar-like incident where a rock was ejected from a drill-hole when the explosives were detonated.
"We had a hole-eject where we had, you know, a single rock that hit the roof of someone's house. The closest structure," Jordan Sands Vice President Brett Skilbred told investigators. "... That was earlier this year."
Skilbred said that incident prompted changes in the use of stemming material, which is put at the top of blast holes to minimize ejections of rock and better concentrate the force of the blast.
The April 25 blast with the accompanying tremor prompted the company to audit its blasting procedures, and operational changes were made to better reflect recommended standards for operating an urban quarry, Skilbred told investigators. Tighter documentation of the various steps involved in conducting a blast was also put in place.
The new steps seemed to be working, he said. Then came Aug. 8.
What was supposed to happen
The detonation was intended to fracture a shelf of limestone in a narrow arm of the quarry that juts into the residential neighborhood off of Third Avenue, breaking it up enough that it could be hauled away so the sand underneath could be mined. The pattern of 47 holes were drilled 22 feet into the rock, each nine feet apart, according to the blast report from Olson Explosives.
The ANFO explosives were intended to fill roughly the bottom half of each drill hole with the non-explosive stemming material — made up of rocks less than 1 inch in size — placed on top. By design, there was 9 feet of rock — known as "burden" — between the explosives and the vertical face of the rock shelf being blasted. And 8 feet of rock, which is called "stemming," was left above the explosives.
The presence of proper amounts of burden and stemming typically concentrates the force of the blast on fragmenting the rock and eliminates the threat of flyrock.
Stoltz, the blaster-in-charge that day, actually saw too much burden on one section of the rock.
"I had the driller add a couple of holes on because there was an excessive burden on the east end of the shot," he told investigators. "So I had him add two more holes on there to break that up."
Bengtson, who oversees Mankato's fire department, asked Skilbred and Baxter on the day of the blast to show him the video and immediately noticed that the blast didn't behave as intended. Engineered explosions of the type executed on Aug. 8 are supposed to be powerful but also tightly concentrated within the earth.
"The blast appeared to have projected energy outward from right to left rather than being contained within the blast rock as I have observed in previous blasts," Bengtson wrote.
One measure sometimes used when detonating explosives near homes and other sensitive neighboring property — blasting mats — were not in place. Numerous mats, which are often constructed of hundreds of strips of used tires cabled together and weigh well over a ton, can reduce noise and dust as well as the chance of flyrock if they're placed over the blast site.
Jordan Sands CEO Scott Sustacek, in an interview with The Free Press last week, said the company determined that blasting mats weren't feasible because of the volume of rock being removed at the Jefferson Quarry.
"It's just the amount of area we're trying to blast," Sustacek said.
What went wrong
In preparing for the blast, several workers noticed that something unexpected was happening with one of the 47 holes — hole A8 — drilled into the rock. The driller, the two blasters from Olson Explosives and Baxter from Jordan Sands all noticed that A8 wasn't necessarily a solid 3.5-inch by 22-foot cylindrical hole in solid rock. The blasters had doubts about hole A9 as well.
Driller Scott Lewis of Falcon Drilling lost air pressure on his drill at 15 feet on hole A8, indicating soft rock or some sort of a seam or cavity in the limestone. Lewis said he made notes and highlighted the issues on his drilling report.
The police record doesn't indicate whether Stoltz reviewed the drilling report, but Stoltz and fellow blaster Allen Renken told police they noticed when adding the explosive emulsion that — rather than filling the hole to the desired height and staying put — it seemed to be disappearing somewhere.
And when Baxter came to top off hole A8 with stemming material, the hole consumed twice as many shovelfuls of stemming material as the other holes.
"So that's when I stuck the pole down there — and this pole was 16 feet long — and I didn't hit anything," Baxter told Detective Rother.
If the explosives were quickly leaking out of the hole, Rother wondered about the possibility that the Olson Explosives workers might have pumped more ANFO than intended into hole A8 as they waited for the emulsion to reach the elevation in the tube called for in the blast design.
"Do you think they added more explosives than they should have?" Rother asked.
"I have no idea," Baxter replied.
He brought the issue to Stoltz's attention, Baxter told Rother.
"We talked. OK, what are we going to do? Is this going to be OK?" Baxter said.
The explosives weren't leaking out the vertical face of the rock, so Stoltz concluded they were pooled near the bottom of the hole and shouldn't be a problem.
Baxter said he thought about the daunting task of trying to remove the stemming rocks, the other components of the blast hole and all of the explosive material.
"I've had plenty of experience digging stuff out after a misfire, and it sucked," he told police.
Ultimately, they decided to go ahead with the detonation, including hole A8.
Baxter never expected the result to be anything like what he witnessed and recorded, he told Rother.
"My opinion would be that it was loaded improperly by the time I came across it," Baxter said in his recorded police interview.
Blaster: It didn't happen that way
There was no extra explosive added to the holes, Stoltz told the detective. Renken, the second Olson Explosives blaster, was running the pump that sent the ANFO into the hole, watching the meter and ensuring that the maximum of 90 pounds per hole was not exceeded, Stoltz told police.
Stoltz was measuring the height of the explosives in the hole. The ANFO reached the targeted height 8 feet below the top of holes A8 and A9.
"And then they were rechecked within a few minutes and they were dropping," Stoltz told Rother. "So I monitored them. They dropped down to 10 feet. And that's all they got. So, instead of adding more product to it, they settled out at 10 feet, and that's as much (ANFO) as they got."
Skilbred said in his police interview that a review of the drilling log should have prompted the blasters to take a different approach.
The drilling log warned of the potential seam in the rock and indicated it was between a depth of 15 feet and the bottom of the 21-foot hole, Skilbred said. Seeing that, a blaster would have two choices: Don't put any ANFO in that hole, or fill the bottom six feet of the hole with stemming rocks to ensure that the explosives were above the seam and wouldn't leak.
"We don't know whether the blaster ever saw the drill log or whether he considered what he saw," Skilbred said. "And the other thing we don't know is how the hole loaded."
Asked by Rother if he thought the hole might have been overloaded with ANFO because the drillers didn't immediately recognize it was leaking into a seam, Skilbred said he couldn't speculate. Jordan Sands checked the amount of explosives arriving at the quarry for the blast, but the audit includes some margin of error.
"It was within normal error," Skilbred said. "With that being said, all you need is 20 more pounds or 40 more pounds (in a hole) and it can cause a big problem."
Stoltz told Rother the flyrock was not an indication of a fault with the blast but instead of a fault in the rock — that the force of the explosion took the path of least resistance through that area of stone.
"It found a weakness and exploited it," Stoltz said.
No criminal charges
With the investigation report detailing conflicting theories about who — or what — was to blame for the incident, Blue Earth County Attorney Pat McDermott told The Free Press Oct. 11 that he would not pursue criminal charges.
McDermott said he and two other attorneys in his office determined they couldn't meet the burden of proof to charge anyone with negligent discharge. A criminal charge requires evidence that someone “negligently causes an explosive or blasting agent to be discharged” in a manner that is in “gross disregard for human life or property.”
Sustacek was pleased with the county attorney's conclusion, saying a company review of the incident found no evidence of criminal negligence.
Even before McDermott's decision to not prosecute the case, Public Safety Director Todd Miller informed Jordan Sands he wouldn't be renewing the quarry's blasting permit, according to a letter from Miller to Sustacek obtained by The Free Press. If the company wishes to resume quarry operations, an appeal of Miller's decision would have to be taken to the City Council.
Sustacek said there would be no more blasting at the Jefferson Quarry in the immediate future.
"We have switched blasting to our northern quarry," he said of the Jordan Sands property in Lime Township. "Part of it was to let this situation play out. We thought that was appropriate."
The company is also no longer contracting with Olson Explosives. "They were new to our operations starting this mining season," Sustacek said.
The company will have conversations with the city in coming months regarding future redevelopment of the Jefferson Quarry.
"The next life of that particular quarry is of great interest to the city and to a number of people," he said. "And it's a valuable property."
Whether that redevelopment will be preceded by more mining, with a different blasting company, could be part of the conversation, according to Sustacek.
"That has yet to be determined," he said, adding that any further extraction of minerals would require blasting. "There's no other reasonable way to mine the sand."
But Sustacek pledged that safety has been, and will continue to be, a primary focus of the company.
The final say
Council members' attitude about future blasts might hinge on their reading of the police investigation — which version of events seems more credible. The Jordan Sands officials, in police interviews, suspected a human error by the blaster, something that presumably could be avoided in the future and ensure the Germania Park neighborhood doesn't receive a second shower of bowling ball-sized rocks.
Stoltz, the blaster in charge, suggested to Detective Rother that the rocks soaring into the neighborhood were a fluke and a rarity but something that can't be completely eliminated in quarry blasting.
"In my experience, it happens from time to time," Stoltz said. (At least one expert disputes this theory. See related story.)
For an explosives engineer, flyrock should never be seen as an unfortunate but sometimes-una…
Baxter, who shot the video of the blast, told the detective he's seen flyrock repeatedly the past two and a half months — in his dreams.
"I've had nightmares ever since," he said.
And at 601 Harper Street, where the crater in the siding remains, the rock that crashed into the Kreiselmeiers' home on Aug. 8 carried a silver lining — the suspension of the blasting license.
"It's been quiet," Dave Kreiselmeier said Friday afternoon. "My house doesn't shake all the time now."
Calls Thursday and Friday by The Free Press requesting comment from Baxter, Skilbred, Stoltz and from Olson Explosives executives were not returned.