For a reservoir that’s meant to hold water for a long period of time, or protect the local groundwater from toxins and chemicals, preventing seepage is a major concern. Water seeping into porous ground can lower the overall water-level quicker than your design has adjusted for. Subsequently, pumps or valves may not function properly if water falls too low. Additionally, basins that are used for retaining run-off, like municipal stormwater or agricultural tailwater, store large amounts of polluted water in one central location. Seepage from this highly concentrated water will carry more toxins, nutrients, and chemicals, as it trickles into the surrounding soil and groundwater.
Clay Liners
Clay liners, most often made of bentonite clay, are fairly popular for small, low-budget operations. Clay is easier to source than some liner materials, however, rolled or puddled clay is easily spread too thinly during application, resulting in a less than water-tight seal. Clay is also less likely to protect surrounding soil from chemical seepage, or the transfer of hard metals and nutrients.
PVC Liners (Polyvinyl Chloride)
For many years, almost every pond and reservoir was lined with PVC. However, these days, conventional PVC isn’t as durable as other liners, and usually has a lifespan of only 10 years. This material also lacks the UV-protection found in newer liner technology, meaning they need to be buried underneath a layer of dirt or other ballast to avoid brittleness and damage from sun and movement. Moving the liner for repairs is likely to cause further damage, making upkeep difficult.
EPDM Liners (Ethylene Propylene Diene Monomer)
EPDM liners are more durable, thicker, and heavier than PVC. This thicker, stronger liner is still somewhat flexible, but its weight and general unwieldiness makes shipping and installation more complex. EPDM liners are sealed using adhesive tape, and any mistakes during installation will have significant impacts on the liner’s permeability. EPDM is less sensitive to UV damage than PVC, but still needs to be protected from long-term sunlight and decay. Leaks are easier to locate and repair in EPDM liners than in clay or PVC, but installation is still the most likely time for damage to occur.
HDPE Liners (High-Density Polyethylene)
HDPE liners are thick, and stiffer than PVC or EPDM liners, and are incredibly resistant to UV degradation and tearing. Despite this toughness, HDPE is typically lighter than EPDM liners. However, the stiffness of the material means that any folds or creases are more common. Their seams are heat-welded, leaving their watertight seal virtually permanent; while new holes and damage are patchable, saving you the cost and trouble of choosing and installing entirely new liners.
RPE Liners (reinforced polyethylene)
RPE liners are light-weight, durable, and UV-resistant. These are welded using the same heat technology as HDPE liners, reducing the frequency and/or severity of damage from installation or wear-and-tear. RPE is also built to prevent leaching of internal chemicals, which is essential for water intended to be used on crops. The lightweight flexibility of RPE liners mean that even the largest panels can be factory-welded to be delivered installation-ready. RPE is also simpler to install, meaning that in all but the largest projects, manual installation is still possible.
Concrete Liners
Many times, reservoirs and retention ponds are built using precast or poured concrete. Concrete is porous and capillary action will quickly pull water through the material towards the earth below. Sealants will protect the concrete from permeation for a couple of years but aren't permanent or reliable. A geomembrane liner serving as an underlayment between the concrete and the soil will solve this issue. This will keep any water from soaking into the ground when it makes its way through cracks or pores. Additionally, this will protect the concrete from subterranean movement within the earth that could cause the material to bend or crack.
Retention Maintenance
While retention ponds at the smallest scale don’t require a massive amount of maintenance, leaving a reservoir completely to its own devices is guaranteed to result in less-than-ideal conditions in a matter of time. Regular monitoring will give you an indication of how well the pool is performing.
Things to check for include:
- Chemical content of the water: Are the toxins present the ones that you expected to find? Sudden increases or drops in certain chemicals can point to issues further upstream, or within your filtering system itself.
- Water levels within the pond: Sudden drops or increases in water level can mean that a pump or drain isn’t functioning properly, or that emergency spillways are no longer allowing water to escape.
- The health of wetland plants in and around the pond perimeter: These plants help to reduce the pollutants that are absorbed in the water, while also keeping the pond structurally secure. Sudden die-offs around the border of the pond can mean something is off within the water, like increased chemical contents, or anaerobic conditions.
- The condition of the land surrounding the pond. Specifically, indicators that any leakage has taken place, such as patches of newly saturated or destabilized earth.
Record and monitor the age and health of your installed equipment.
The pieces and structure of your retention pool were not designed to last forever. These should be replaced as they near their expected lifespan, before major damage occurs and allows consequences to expand. Keep a record of these expected lifespans, and make sure that retention pond maintenance includes policies of component replacement.
Respond to any traumatic or emergency events
Any significant damage to the pond itself, or any extreme weather conditions, can seriously affect the lifespan of the retention pond. Make sure to respond to these events in a timely and effective manner, and to consider whether repair or replacement is required to keep your pool well-maintained. (This is typically understood as inspecting the reservoir within 24 hours of the most recent extreme weather cycle).
