Seen in a landfill liner specification recently:
- Liner shall be checked with leak detection methodology (per ASTM D7002) by ENGINEER or its representative after installation....
Elsewhere it states:
- ...leak detection testing shall be conducted by ENGINEER or its representative in accordance with ASTM D7002. CONTRACTOR shall furnish mobile water supply and any hoses needed to conduct the testing. Installer shall arrange for training of ENGINEER'S technician at no extra cost....
So, who is going to train the installer to do integrity surveys before the Installer trains the Engineer/Technician!? Who will provide the survey equipment for training!? Who will provide the survey equipment for the survey!? And if an Installer, who has never done a survey, attempts to train the Engineer, how effective will the final survey be? Could the Owner have confidence in it? This arrangement is surely fraught with potential problems.
Specifying a water lance/puddle survey on exposed sheet is fine, but this sheet will eventually be covered by soil. Statistics show that 74% of leak damage in a geomembrane occurs when it is covered. So, in fact, a survey performed prior to coverage will be the final stage of CQC for the installer, but only a survey performed after geomembrane covering will be the final stage of CQA for the Owner/Engineer. If a survey is only performed before covering there will undoubtedly by significant damage in the final covered liner.
Example: A decorative pond was surveyed before the geomembrane was covered with soil. Four small leaks were found. They were repaired. The soil then placed on top of the liner contained many large (4 in., 100 mm) pieces of glass!! I can't guess how many holes would have been made in the liner!
Quite simply, in the interests of the Owner/Engineer, a geoelectric survey should be required to be performed by an independent, experienced surveyor under contract to the Engineer/Owner after the cover soil been placed. A survey before covering with soil will clearly cover the backside of the Installer, but will not guarantee the Owner an undamaged liner after soil has been placed.
And, when soil is placed on a single liner, the survey should be done before the liner at the crests of the slope is covered--the soil above the liner should not be in electrical contact with the soil below the liner.
Ian D. Peggs, Ph.D., P.E., P.Eng., is president of I-CORP INTERNATIONAL Inc. He can be reached at icorp@geosynthetic.com.
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