By Glenn Eckert, manager of engineering business development at Layfield Group, and Prabeen Joshi, engineering business manager at Layfield Group
Experienced geomembrane liner installation crews ensure that strict quality assurance/quality control (QA/QC) guidelines and procedures are in place during installation. Details such as time of installation, destructive and nondestructive test results, as-installed drawings, etc., are recorded and usually provided to the clients (upon request or contract dependent). The installation crew carries out a detailed final inspection (often includes a leak detection survey) and addresses any identified issues before handover and leaving the site. In other words, when the installation crew leaves the site, the installed geomembrane is certified to be as per the final design.
Once the geomembrane is in operation (exposed or covered), several external factors occur that can influence the service life of the geomembrane and thereby the integrity of the overall containment system. Factors such as temperature, ultraviolet rays, chemicals, local or global strains, etc., can all impact primary and secondary geomembranes. It becomes essential for the owners/operators to ensure that these (and potentially other) factors are well understood, and a timely health-check exercise is integrated into their asset management plan.
As hinted in the short answer above, good QC, regular inspection and preventive maintenance are the only ways to identify and address potential issues. They are necessary to meet/exceed the expected service life, reduce the risk of significant failures and help stay compliant with applicable environmental regulations. This is where Layfield can help.
Inspection and maintenance
Layfield Geosynthetics offers inspection and maintenance services for existing secondary containment systems and exposed geomembrane liners. Layfield’s technicians will review your containment for existing or potential concerns and address all requiring attention.
Inspection and maintenance services may include:
- Correct subgrade deficiencies along the containment wall
- Redistribute backfill and geotextile to ensure proper geomembrane protection
- Confirm geomembrane liner clamp reliability
- Detect signs of liner distress or mechanical damage
- Identify subgrade settlement, slope slumping or failure
- Redistribute geomembrane slack as required
- Destructive and/or nondestructive tests to assure seam integrity
A written report can be provided detailing the location and the corrective actions required to bring your containment system to compliance. Issues that require immediate action are highlighted and can often be dealt with at this time. Less pressing matters are also identified and may require additional labor from a third party such as an earthworks contractor to complete.
Leak location survey
Layfield can also help check the integrity of the geomembrane inside a primary or secondary containment system. This can be done in several different ways. Two plausible scenarios are discussed below.
- For a containment system without a conductive geotextile installed beneath the liner:
A water truck is brought to the site to flood the containment system, or this can be done directly after a rain event. Once the containment is filled above the level of the liner clamp and pile penetrations, the perimeter of the containment is then monitored for any leaks running out from under the geomembrane liner or from the attachment between the geomembrane and the containment wall.
2. For a containment system with conductive geotextile installed beneath the liner:
In this method, the conductive geotextile that is installed beneath the geomembrane is electrically charged through a preinstalled electrical cable, and an electrical leak location survey is conducted.
Scenario 1 has several moving parts and is generally much more time-consuming with far less certainty in detecting small leaks. On the other hand, Scenario 2 requires minimal resources and is independent of the geomembrane type, subgrade/cover material, moisture content of the subgrade/cover, temperature, etc. The only way to ensure Scenario 2 on your containment facility is to integrate a conductive geotextile in the original installation.
Service life expectancy
Once any physical damage to the geomembrane is identified and fixed, your asset management team may also be interested to know how much longer the geomembrane will last.
Layfield offers an evaluation service that will give you a realistic indication of the longevity of the exposed or backfilled geomembrane. Layfield’s technicians visit your site to extract the liners’ representative sample(s) (then immediately repair the opening caused by the sample recovery). Layfield then submits these samples for a laboratory evaluation; by comparing the performance of the recovered samples against the original material specification, we can provide an estimate of the remaining service life. This estimate can help you with the asset management plan by predicting when a complete liner replacement will be needed.
This article first appeared in the Layfield Group’s Knowledge Center, www.layfieldgroup.com/knowledge-center.aspx.