Water Well Journal Q&A

RICHARD THRON, MGWC, NGWAF
The president of Mantyla Well Drilling Inc. in Lakeland, Minnesota, discusses sealing wells contaminated by PFAS.

By Mike Price

Richard Thron, MGWC, NGWAF, opened his Groundwater Week 2022 workshop on water well decommissioning/sealing by asking attendees if their respective state requires grouting of wells.

There were quite a few hands in the air, which Thron was thankful to see.

“It’s the most important thing we as an industry can do,” says Thron, president of Mantyla Well Drilling Inc. in Lakeland, Minnesota.

The sealing of wells in Minnesota has become essential as the state addresses the fallout of PFAS (per- and polyfluoroalkyl substances) contamination from 3M waste disposal sites. In 2019 alone, the state sealed more wells (6500) than it drilled (about 5900). From 1990-2019, Minnesota has sealed more than 300,000 wells.

“[Proper grouting] is very important because these old wells are direct conduits to our most absolute perfect well we could ever drill being useless if there’s a well nearby that has garbage [contamination] going into it or coming from it down below,” he says.

Thron, who serves on the Washington County Groundwater Advisory Committee and 3M PFOS Technical Group, works in East Metro, a suburban area east of St. Paul. Investigations there have identified an area of groundwater contamination covering more than 150 square miles, affecting the drinking water supplies of more than 140,000 Minnesotans.

By the end of 2021, more than 3800 wells had been sampled and 1451 private well advisories issued to East Metro homeowners with elevated PFAS in their well water.

Homes where wells are issued drinking water advisories are either connected to city water or provided with whole-house granular activated carbon (GAC) filters, which are maintained by the state. The Minnesota Department of Health also has undertaken testing of point-of-use water treatment devices to provide residents of affected communities with information regarding options available to them for PFAS removal from their water.

“It’s a dirty, tough job that a lot of people don’t want to do, and so we get a lot of sealing projects throughout the East Metro area,” says Thron, who has two GAC filters treating his well water at home.

With April’s issue focusing on water quality and water treatment, Water Well Journal sat down with Thron at Groundwater Week 2022 to learn more about the sealing of PFAS wells. The 2015 president of the National Ground Water Association and 2017 Robert Storm Intersectional Cooperation Award recipient also shares tips to be efficient in this line of work.

Water Well Journal: How busy has your company been with sealing PFAS wells?
Richard Thron, MGWC, NGWAF: In Lake Elmo where we’ve been working a lot this summer [2022], I think at one time my son [Jeffrey] had 100 wells on the books in those subdivisions. The wells are from the 1940s to present day, so they have different construction standards—limited casings, double casings, cement grouted wells—so we may have quite a variety of pump systems. In some cases where there’s a concern, we run a camera down the well to see if there’s any debris in the well to clean out.

We also try to search out any and all records that we can from old well drillers’ records. We want to get a history of the depth and the casings and basic formations that those wells were completed in.

Literally in one area where I live, about two miles down the road on one side of the street, there are 89-foot screened wells and just across the street—probably less than 150 feet away—the wells are 240 feet deep in sand rock. We have two glacial lobes that came through our area that collided and spun going out to the northeast, so you can have exposed limestone in one spot where they’re mining the limestone just north of our shop, and a half-mile away you got 350 feet of sand that was deposited by the glacier fronts. So, we have to do a lot of research on the wells to do the best we can to seal the wells properly per the state code.

WWJ: How often do you drill new wells in the special well construction areas where PFAS have been identified?
Thron: It varies on the wells as most of those subdivisions are sold out, but I would say around four to six wells a year are drilled on individual lots.

WWJ: Can you walk us through how you go about sealing a well?
Thron: After we do our research on any history of the well at that address, we then have to determine how we’re going to seal that well. In these subdivisions, what we do after the city water has been hooked up is we bring our service truck in, and we may pull three to four pumps out [in consecutive fashion down the street] and capping the lines in the homes. Then we bring our grout trailer in with a 400-foot hose reel, and we can sit it in the street as many wells are real close [most all wells are in the front yard of these subdivisions].

Then we bring in a cement mixer full of grout and we go down the street on three or four wells pumping them full of neat cement grout. In some areas where there’s fractured limestone on the older wells that aren’t cased all the way to the aquifer, they can consume a large amount of cement. The code requires us to pump 150 percent of the calculated volume of that borehole before we can stop. In many cases we pump that 150 percent, and it only comes up to the crevices, then what happens is we cease pumping and come back the next day. We then pump again and can then add pea rock in to bridge those crevices and complete the sealing of the well. So you can see there’s a fair amount of work involved in preparation and research prior to starting the job.

WWJ: How long does it typically take to seal a PFAS well?
Thron: In Lake Elmo, from start to finish with a lot of those pumps set at 220 feet to 240 feet, it’d take you an hour and a half to pull it out, another half-hour or so to maybe check other things with the capping of the water line in the home, taking the pressure tank out, and then if you video it, you probably figure another hour for that. The grouting part would probably take two and a half, three hours, maybe four hours, so we figure about eight hours on each job. If it’s an older well, then the research might get more labor intensive in doing the videoing and perforation and possibly gamma logging or other state requirements.

Each one is kind of like a human being; they have their little inconsistencies and you got to deal with that on a case-by-case basis. But usually those newer areas recently developed, it’s a fairly cut and dried situation, and occasionally you may hit a surprise where one well will take more cement than the other but there’s a built-in addendum on the bid for extra charges for the hourly rate and the extra bags of cement. A yard of cement grout would be around 23 bags of cement, and so that’s how we calculate the cost of materials and labor in the sealing bid. Make sure you’re charging enough for your work too.

WWJ: What’s the workload look like in 2023 and beyond?
Thron: Actually, in the Lake Elmo project that my son is working on, we’ve won 90 percent of the bids because other companies don’t want to deal with it, but again they don’t set up an economical system of progress—how to start and finish the projects—so they come in and do a onesie-twosie. They pull the pump and then wait for the cement truck, or they mix the cement and they gotta come back. Most of our work is within 40 miles of our shop. It appears we have another three to five years of work ahead of us.

WWJ: How do you cement grout in an efficient manner?
Thron: Don’t pump too fast if there’s a good head of water in the well that will float the tremie line out. Start out slow because the cement has to go down there slow to displace the water, which is 8 pounds a gallon, and the cement is 15 pounds a gallon. Sometimes you will pump 150 percent of the volume in one day, come back the next day or two later, and then pump cement again and it could still settle. Thankfully this is not real common.

We had one well that settled four times, so you need to top it off, and then once it’s topped off, the code requires the casing be cut off 2 feet below grade. What that means is that if you’re in a farm field, hopefully the plows won’t hit it preparing for crops.

But again, we try to do it in a series, so one day we’re removing pumps, then another day we’re grouting, and then maybe while we go down the street to remove another three, four pumps, we can check those wells to see if they’ve settled, and if they have not, we can dig around them with a shovel and we’ve got a portable torch in a carrying case [suitcase torch system] so we can torch those casings off to finish that well and keep on going down the street in a progression. It’s called efficiency. You try to keep the cost as low as you can but be as efficient as you can as well.

WWJ: How does Minnesota’s diverse geology affect this type of work?
Thron: We’ve been told that we have some of the most diverse geology in the nation in such a small area, and it’s very difficult to deal with. There’s been a study by the University of Wisconsin–River Falls that’s a good read because it tells you of all the geological changes and conditions that there are in those 50 miles. As a matter of fact, that granite that’s sticking out up there is about as close as we could have gotten to a volcano. When you’ve got such a mixture of geology like that, how do you deal with it? Especially when it changes so quickly over such a short horizontal distance. This makes our job not only quite challenging but very interesting.

WWJ: Lastly, how do you view PFAS in your state?
Thron: Quite frankly, all our aquifers have PFAS in them now. We’re just going to have to deal with it, but we don’t want a migration of other products in there. We have VOCs [volatile organic compounds] from other dump sites. We have that as well, so some of the wells could have a combination of different contaminants and they could come from different sources—land surfaces, crevices, aquifers—so we got to make sure that we seal these wells the best we can for now and the future.

Mike Price is the senior editor of Water Well Journal. In addition to his WWJ responsibilities, Price contributes to the Association’s scientific publications. He can be reached at mprice@ngwa.org, or at (800) 551-7379, ext. 1541.