Pond Liners: Does My Pond Need a Liner?

The liner is stretched, then overlapped into a peripheral trench. The trench is backfilled with pulverized clay to securely hold the liner in place.

By Bob Lusk

Eastern Tennessee, Missouri and the Texas Hill Country. What do these places have in common besides their beauty? Rocky soils, that’s what.

Not ideal places to build a pond…unless due diligence is duly done. Soils with rock, when it comes to pond-building, aren’t exactly what pond builders prefer.

Pond builders prefer clay mixed with moderately good soils, spread in lifts and tamped down with big, heavy machines, so that soil is compacted forever and ever.

There are plenty of places around this nation where the soils are unforgiving. Those soils drain well…too well. While that’s great for a septic tank or for a good garden, these porous soils aren’t the choice to have a pond. Sandy soils, rock and gravel do not a pond make.

Pond Boss magazine founding editor, Mark McDonald, while living in the Texas Hill Country town of Boerne, decided to help a buddy design a pond in that hardscrabble part of the nation. They found a reputable bulldozer operator, a fellow who cut his teeth on the rocky hillsides and fertile creek beds northwest of San Antonio. He forewarned the eager men. “The only way to guarantee a pond won’t leak is to install a liner.” The two men were ready to learn. The salty veteran of local pond building explained it even further. “We project the costs of building a pond like this in two ways. First, we figure out roughly how much it will cost to prepare the site for a liner. Second, we figure the cost of the liner and installing it in square feet.”

Square feet? That’s like building a house, not a proverbial pond.

The two men scratched their heads together and then went to work to figure out their best option.

So, how do you decide if your pond needs a liner?

You need a liner if your soils are so suspect that you and most every expert you speak with describes your soils as too rocky, too sandy…or basically that you don’t have enough clay to seal the pond and keep water from escaping through the soils faster than it comes in…and the cost of bringing in clay or other amendments such as bentonite are prohibitive.

Just like any project, do your homework. Make sure that you don’t have adequate clay close by. Dig test holes around the property to find out what you have. Study local soil surveys to see your prospects of finding good soils that can be compacted.

That’s just what McDonald and his landowner buddy did. They brought in soil scientists, worked with the Natural Resources Conservation Services and the local earthmover. Collectively, they decided a liner was the best choice.

Choosing the best liner was a chore itself. That’s where McDonald called on Colorado Lining’s Houston office to assist with engineering and design. Yes, engineering and design. If you need a liner, you don’t go to the local lumber yard, into the garden department and buy a roll of plastic. Your liner needs to be a certain thickness with a certain pliability and then be the proper size to be sure you don’t have issues after installation, when water begins to flow.

A team was being assembled for that Hill Country project.

As the liner was ordered, work began to prepare the site. Thank goodness the rocks in that rocky, leaky soil was mostly limestone. That’s because limestone can be fairly soft, as this stuff was, and can be pulverized with heavy equipment. As the bulldozer shaped the pond with gentle slopes, the operator made sure the rocks were pulverized into the smallest pieces possible. Then, he added sandy soils as a top dressing. Liners are made from a small variety of plastic-type materials, but they have one thing in common…they can be punctured. So, no sharp rocks, no sticks…nothing that can poke a hole in your high-dollar liner.

Rocky soils must be amended. Liners need a smooth bottom so as not to be punctured.

After the site was prepared, the crew brought in as many people as they could find. The liner showed up in big rolls on the back of a tractor trailer rig. A track hoe gently lifted the sections of the liner and placed them strategically along the shore. Heavy on the word “strategically”. That’s because, once the roll is unrolled and put into place, it’s not like a bed sheet. You can’t just pull it over into place. It’s too heavy. The different sections were rolled out and stretched and then the edges stitched together with a hand-held machine designed just for that purpose.

After the liner was draped across the pond bottom, it was secured around the entire edge of the pond by digging a trench, pulling the liner edge into the trench and then refilling with good soils. That maneuver ensures the liner won’t pull free as the pond fills with water.

Part of the planning phase was discussion about deer. Yes, deer. White-tailed deer are abundant in that part of the world. Deer have sharp hooves. Sharp hooves cut pond liners.

The decision was made to add 18 inches of dirt on top of the liner after it was installed. That had to be done with care, because bulldozers cut pond liners, too. So, a rubber-tired front end loader was brought in and soil was added from the sides downward to the desired thickness.

Preparing the site is crucial to the process.

A well was turned on, care was taken that the soils weren’t washed down the liner, and soon the pond was on its way. Today, that may be the only pond within miles that doesn’t leak.

Was it worth it? Site prep for this ¾ acre pond was almost $7,500. The liner cost almost $.65 per square foot and another $.35 per square foot to install it. That tallied to $35,000. Add the dirt they had to buy, the select sand to mix with existing soils and to cover the liner and this showcase pond that doesn’t leak cost almost $50,000. It’s not cheap, but a liner is the only guarantee that a pond won’t leak.

Here are the take-home points.

• Be sure your local soils won’t work to build a pond.
• Investigate the cost of bringing clay to your prospective pond site.
• Quantify site preparation costs to install a liner.
• Shop for the best (not cheapest) liner for your project.
• Most of all, find a contractor who’s “been there, done that.”

After the fact, McDonald and his friend were pretty happy with the way the project ended. It cost considerably more than they hoped, but now this little pond is a gathering pond for a variety of wildlife. They’ve seen plenty of deer, turkey, waterfowl and abundant small game and the pond is alive with fish. The landowner justified the expense because he “did it right the first time” and will never have to deal with typical leaky-pond issues in that part of the country. In his mind, if that pond lasts 25 years, it cost him $2,000 per year. He saves that much money by not having to run his well to keep an otherwise leaky pond full of water.

Is a liner for you? That’s a choice you, your contractor, your experts and your soils need to make.