I'm John Torek. And I'm Danny Sullivan. And you're listening to Speaking of Design, stories and sounds from the world of engineering, engineering, architecture, and beyond. We're here to bring to life stories behind some of the industry's most innovative design projects. In more than a decade working with engineers and architects, we've been witness to exciting breakthroughs in the way communities are designed. We wanna share our best stories with you.
Mommy, look at that big green spaceship down there. What do you see? I see a diamond shape and squares for the windows. Why do you think it's down there? If you find yourself flying into Atlanta, you two might ask what that bright green mountain is in here urban skyline. Quite literally, it's greener than grass, but in the environmental and economic sense. What you're seeing is the Hickory Ridge Landfill.
It was there that an environmental engineer with a love for garbage teamed up with a landfill owner committed to environmental change. And together, they implemented an idea that's changing how we think about landfills. Engineers have a way of thinking differently. I kinda followed the garbage trucks around on my bike when I was a kid. So I think there must have been some gene there early on that I didn't, quite
get. But, yeah, you know, my Matchbox toys seem to have a preponderance of garbage trucks in them too, so I don't know. But when I first realized it, it was, it was in college when I saw this big landfill, down in Alachua County, Florida, getting constructed. That's Mark Roberts. He's an environmental engineer with HDR. Now when we said he liked garbage, he does. He actually made a career out of it. More than twenty five years working in solid waste engineering.
I caught the garbage bug, I guess, when I was an undergraduate civil engineer, and I went out to see a landfill, and I saw this massive construction project and structure being built and with different layers of materials and that sort of thing. And I just I you know, building something the size of the Superdome out of dirt, and garbage was something that appealed to me, and I've been working on landfill design ever since. That's something I felt just from writing about landfills.
It's not just a pile of trash. The planning, engineering, and technology that goes into them is actually pretty interesting. You're right. I it's it's amazing how, everything in the world goes into landfills. So you have the opportunity to capture that stuff or dispose of it properly. And so as an engineer, it's very interesting to work out systems that can that are improved with each generation for environmental protection and, and cost.
Everything we throw away, ever used Kleenex, plastic wrapper, styrofoam, gets carted to one spot in town. What happens to that spot when it's full? This popular place to play fetch in West Omaha is on top of a landfill. You'll find Huttlinger Park near A Hundred And Twentieth in West Maple. Omaha's First off leash dog park is also home to lots of garbage. You can't see the waste, but it's easy to
see what it's doing to the park. Deep underground or maybe not deep enough, garbage continues to decompose and compress under the weight of time. This is where Douglas County put its waste from 1967 to 1973. Back then, crews dug out trenches and threw the garbage inside. When a hole filled up, it was covered with dirt. Four decades later, the trenches are reappearing as the ground subsides.
So you heard about how Hefflinger Park transformed from Omaha, Nebraska city dump into a present day dog park. But in between, it spent about twenty years as a baseball complex. When I was a kid, I remember going to my dad's slow pitch softball games, and it was your typical softball complex with four fields facing out from a central area with bleachers and a concession stand. But as the garbage underneath decomposed, the park started to sink, but not evenly.
The flat outfield grass became rolling hills, and the level fences took on a cartoonish wave like they were made out of rope. Eventually, the park just wasn't safe for baseball, but the large fenced in areas with green grass were perfect for dogs and dog owners alike. So we tell the Hefflinger story for a reason. You see, there are a lot more regulations to properly close a landfill today than they were back in the seventies, but we'll let Mark explain.
The old landfills were kinda a lot of times were kinda dug in in low parts of a piece of property. It would be a trench and fill method where they would dig trenches and fill it with garbage and then cover it up. So not very efficient filling or utilization of that footprint of the landfill. A lot of burning dunks were around and you'll still see this around the world kind of how we were thirty, forty years ago.
When time came to close, they just put a a couple feet of soil on it and tried to get the grass to grow and and kinda moved on. What has happened, we're we're still monitoring some of these old landfills. They had, contamination and trying to, remediate those or address those issues somehow. So that that's kind of where they are now. That's right. It used to be that when you finished filling your landfill with trash, you just poured dirt on top of it, planted some grass, packed up, moved along.
It wasn't like anything could go on top of it. You wouldn't have seen houses or, say, a skyscraper, but you didn't have nearly the same obligation to monitor the site after it closed. Since that time, the EPA established the Resource Conservation and Recovery Act, which updated the laws for how we dispose of solid waste and
hazardous waste in The US. The landfills we're talking about fall under subtitle d, which refers to what you'd normally think of in landfills, typical household waste, construction debris, agricultural waste, and even sludge from wastewater treatment plants, anything nonhazardous. So there's more to it when you close a landfill today.
Typically, when a landfill has reached its permitted capacity, it, it is then time to close it with an impermeable liner system that is capable of lasting for many years so as to protect the waste inside and also to contain anything that may be coming out of it such as landfill gas and that sort of thing. Once the landfill has reached full capacity, the entirety of the hill, the mound, must be properly closed according to EPA rule.
Do you have a thirty year post closure care obligation to that site as the owner of the landfill. So you now you have groundwater monitoring wells. You're you're doing air, inspections to make sure that you're not leaking gas. So you have to maintain your landfill. You have to monitor for environmental monitoring of surface water and groundwater and that sort of thing and take financial responsibility for that landfill for at least thirty years.
Whether you think of land as an investment or a resource, thirty years is a long time. Marty, you've gotta come back with me. Where? Back to the Future. A lot can change in thirty years. In '85, Madonna had the number one song. Back to the Future was a top grossing movie at the box office, and environmental regulations looked a lot different than they do today. The problem is, while everything else changes, there's not much you can do with that closed
landfill during those thirty years. You have many less options for any sort of beneficial reuse of the side at that point because you've got this geomembrane liner that is basically laid over the waste and then with several feet of soil on top of that. So you have to be really careful because you don't want to hurt that geomembrane underneath there. So doing activities like that, you don't see it that
much. The other thing is because we've gotten better at landfilling, we have now very good side slopes, three to one side slopes and that sort of thing. They can't really do very many activities with something of that steepness. We've talked about walking trails and we've done things like that, model airplane, clubs, we've talked about ski runs and things like that too. So there are options that you can do, but there aren't that many and it's particularly
revenue generating option. But before turning a landfill into a source of revenue, there were some innovations designed to lower maintenance costs during that thirty year post closure period. Part of that maintenance starts with rain. Landfills are capped with a liner that prevents the water from running through the trash, picking up contaminants, and then reentering the water supply as leachate. But sometimes, those liners
get punctured. And it's not as easy to do maintenance if you have to dig up a layer of grass and soil to find the tear. In the steep slopes of the landfill, they're highly susceptible to erosion. But what if you capture landfill and skip the extra layers of dirt and grass on top? Think a less is more approach.
We started to realize if we anchored geomembrane, instead of putting it over a landfill and using the soil as ballast, if we just anchored that geomembrane directly into the landfill itself, it makes for a very stable surface. And we were doing designing, letdown channels so that stormwater could go down the side slope of the landfill without creating erosion. So that's one of the big problems with the landfill is you have this three to one side slope with all this grass and
soil on it. And, you know, you get a big rainfall and it takes a lot of that soil with it. So if they can reduce that amount of stormwater that gets into the waste and trickles down through the garbage and becomes leachate that they collect at the bottom and then have to haul off to a wastewater treatment plant, that's a huge cost saving. These were kind of a a low maintenance alternative that were also cost effective.
So without that layer of soil and grass on top, they needed a way to secure the geomembrane to the ground so the wind wouldn't rip it off the landfill. What they came up with was essentially like tucking in a bed sheet. So we kinda get the geomembrane, which is typically a 40 or 60 mil thickness, and we bend it down into a trench and then backfill that trench and then weld the next panel over the trench as the trench isn't exposed. So it's
like a series of bedsheets. That's a good comparison shot. But it gives us that flexibility compared to the old sod roof where you couldn't have it too flat or all the water is gonna get sink in and you're gonna your roof is gonna collapse. And you didn't want it too steep or all the water run off and the grass wouldn't have a chance to collect that water and grow.
So there was and that's kind of the problem with landfills is you become like a turf person trying to keep this grass established on on all these different types of slopes. And then you have the problem like what Danny told about the ballpark where you get little subsidence in specific spots, and then you have these low points where water collects. And it just becomes a much harder maintenance issue.
This idea sounded like it had a lot of built in advantages, but we wondered if there were drawbacks. After all, that bright green geomembrane covered mountain still isn't a common sight. The number one drawback is that it's not protected. So you need to inspect it frequently like you would a roof. We've had alligators on them. We've had deer running across them. So that sort of thing is is okay.
What you find is sometimes the welding that went on initially sometimes starts coming apart a little bit, and that needs to be repaired with the flap and rewelded over that and that sort of thing. But those are the same sorts of problems that are gonna occur whether it's covered with soil or not. You'd think it would be greener or more environmentally friendly to have grass instead of an artificial cover, and yet geomembrane is actually a more sustainable choice than grass. That's right.
Yes. One of the things, think about all those two stroke motors emitting their carbon footprints from just mowing huge acreages continually, you're just mowing and mowing to maintain the grass in order to keep the soil kind of stuck on the side slopes. So think of the fertilizer that's needed sometimes too and what happens if your grass starts to die and all the energy taken to do that.
So it's probably a tenth of the cost of maintenance, and that includes what I was talking about earlier with the inspections and repairs and that sort of thing. That's over thirty years, so it adds up. The exposed geomembrane design lowers maintenance costs and delivers environmental benefits, but further innovation brought even more eyes to the industry. Within view of planes landing at the world's busiest airport in Atlanta, Georgia sits Hickory Ridge Landfill.
Once a mountain of trash sitting idle, it is now covered with 10 acres of solar panels. The idea, give an old landfill a new, greener life. Mark partnered with Republic Services, the owner of Atlanta's Hickory Ridge Landfill. Together, they turned that thirty year closure period into a revenue stream by creating green energy at the landfill. They previously worked on a pilot project in Texas that tested the concept on a partial closure of the Tesman Road landfill,
then they expanded the concept in Atlanta. We really wanted to find a way to provide a beneficial reuse for landfill. I mean, one of the things that happens is they get capped and everyone drives by and says there's Mount Trashmore or something like that. So this was a great way to say, hey. Look. We're gonna use this site. You know, its primary use is now finished, and we found a secondary use where the side slope can kind
of come in handy here. Instead of trying to mow it and maintain it, we're now affixing solar panels to it, and we're going to derive clean energy from it. That to me seemed like a win win situation. The issue was finding the right kinds of materials that can go out there. You probably haven't seen a whole lot of landfills with solar panels, and it's a lot different than you
might picture. Instead of putting solar panels on a base angled toward the sun, the designers used really thin panels that roll up, almost like giant rolls of film, and those are applied directly to the geomembrane. This takes advantage of the steep slopes of the landfill, and also offers more flexibility as trash decomposes and the landfill settles. That's right. Those are the crystalline panels that
need that base to support them. And what we're using on a lot of the ones are these laminate ones that basically you can roll them up almost like geomembrane liner itself. One of the things that we do at HDR is we don't specify any particular brand or anything like that. So it's an open specification so that people can bid on it and we can get the lowest cost for our clients. And that goes with the geomembrane too.
That's a big deal. With that first partial solar landfill closure in Texas, Mark had to make sure this new technique would still meet all the EPA requirements we talked about a bit earlier. And, of course, that it would stand up to the weather. But what happens, EPA has in their subtitle d rule, has an option for landfills to provide designs that are equivalent in performance and longevity
to subtitle d, traditional subtitle the cover. So we had to show that this landfill cap design had equivalent safeguards for both percolation, not allowing stormwater into the waste and also erosion control. And because we're not having any grass, we could address that right away. Really, what this did, it was an amazing project for them because it was down in South Texas. It was windy all the time, and it was hard to get grass to grow, and then they would have big Texas kinda storms.
So this sort of thing worked really well because now the landfill didn't have to try growing grass. They put down the exposed to your membrane. We put down the solar. So now it lowered their dust. It made clean stormwater that ran off and then generated electricity that they could then use on-site. So they could use those 250 kilowatts for their at their maintenance facility and their office building on-site there. The grass is made to withstand more extreme
weather. How would the geomembrane cover and solar panels hold up to hail or hurricanes? And I'm Mike Bettis in Destin, Florida. There's severe storms out there. Chief Inter Officer Rick Mitchell. That tornado warning for the top. Have a live snake. I think that hail Again, that is probably the number one drawback of that is not protected.
The other side of the thing on whether it is like down in tropical regions where you have hurricanes and that sort of thing, that exposed geomembrane works much better than the soil because you don't get these kind of landslides of soil as kind of the veneer stability of the cap itself is put in with saturated conditions, a lot of rain, a lot of wind, and all of a sudden, these soils start sliding down off of on top of the geomembrane.
After the successful pilot project in Texas, Republic Services decided they were ready to take the idea to Atlanta and bring the innovation on a larger scale at Hickory Ridge. That's correct. So we kinda took the success and what we learned from our design at Tesman Road in San Antonio and moved to Atlanta to implement something with different types of materials, but, the same general design criteria. This was a complete final closure for a
landfill. So instead of just a partial closure as we did at Tustin Road, this capped the entire hill with exposed geomembrane and over 7,000 solar panels. It was so it was one megawatt of energy created and then put on the grid and used by Georgia Power. So in this case, it's not just producing enough power to operate the facility. It's enough
power to put back on the grid. In fact, that one megawatt of energy is enough to power 224 homes, and that's not the only energy being created at Hickory Ridge. The other thing that it does is one thing here with landfills is they generate a lot of landfill gas. So you can augment your landfill gas, which is then converted at least at Hickory Ridge into electricity. So you're you're converting the landfill gas to electricity, and now you're also converting
solar to electricity. So you can develop a a a very kind of wide, range of different types of renewable portfolios from energy from landfills. While it's clear that generating solar energy creates some revenue, we wondered if the installation cost was a barrier to doing this type of project. EGC is generally lower than the cost of the traditional Subtitle D landfill. And you can use the difference in that cost to put
in your solar panels at that point. So I don't know exactly where it was, but it came out somewhat equal to the price of doing a traditional landfill closure.
I believe very strongly that this will be one of many ribbons for the future, Bob, with your technology and your innovation and your capital and your vision for where you wanna go as a company and demonstrating, sustainability along with renewable energy sources, I'm confident that we'll be this will be a standard not only for Georgia but also for the nation. That was Georgia Lieutenant Governor Casey Cagle at the Project Ribbon Cutting Ceremony. You may be
thinking what we were at this point. This groundbreaking idea has so many benefits. It cuts maintenance costs for mowing and soil replacement. It helps protect the groundwater. It creates green energy, and it pays for itself over the life of the landfill closure. So is it catching on? The environmental benefits are it opens shut. You realize it right
away. The problem is the solar benefits have not been, as obvious here because when you sell that electricity back to the energy company in that region. We have been seeing some falling prices over the last five or six years on that. Some states are starting to come back a little bit with this incentive for renewables. There are grants available, that sort of thing, for this incentives for the solar aspect, then you're good
to go. And though solar energy covers haven't become commonplace, people are talking inside the industry, but also people who've seen them, including people flying into Atlanta. Is that a spaceship? You know, when you fly into Hartsfield, Jackson, and Atlanta and it's right in the flight path as you're landing, it's kinda you'll see it, like, thirty seconds, twenty seconds before you
the wheels hit the ground there. So if you look out the window and you see this kinda brighter than grass green, I would say, with these kinda black strip that aren't uniform in in their shape as far as the patterns they make. That is the Hickory Ridge Solar Energy, landfill. People were kind of very inquisitive about what that is. I've heard things you know, a lot of people in Atlanta are kinda saying, hey. You know, this is part of our skyline now, and this is something that identifies us,
kinda welcoming you into Atlanta. So, you know, here we are trying to do something with the the landfill, that's closed and didn't have very many reuse options, and here we are generating solar electricity and putting it on the grid and, and helping energize our city. Wait a minute. What are you doing, doc? I need fuel. Go ahead, quick, get the car. Who knows where we'll be thirty years down the road? Will we have cars running on trash? Will there even be landfills?
The post closure period will be over at Hickory Ridge. What will the future hold for that? Hey, doc. You better back up. We don't have enough road to get up to 88. Roads, where we're going, we don't need roads. So what it does, it gives them this thirty year period now of they save money from the installation. They're they're saving money on the maintenance. They're generating some revenue from the solar. And when that time period is up, let's see where we are and let's make
a decision at that time. In a way, that's really what we're trying to do here. I mean, why spend all this money and energy constructing these very complicated engineered caps when you can do something much less costly, much more efficiently, and be more sensitive to the environment. And then in thirty years, I mean, this world the world of garbage never changes I mean, never ceases to change. So So it's changing all the time. So let's see where we are in thirty years and
determine what to do at that point. And by that time, we've saved enough money from all this, savings, from the construction savings and the post closure savings and the energy revenue. Let's see what we do then. That's kind of my thought. What will landfills look like in the future? It used to be a closed landfill might become Mount Trashmore or a sinking ballpark. But today, at least at Hickory Ridge Landfill, it has a bright green place in Atlanta skyline.
We'd like to thank you for joining us. You can find out more about the Hickory Ridge Landfill And HDR at hdrinc.com.