Liner Installation – Measure for Payment

There continue to be a number of instances where there is a misunderstanding
between installer and contractor or contractor and owner about the amount of
geomembrane that should be paid for in a lining system. This should be
clearly spelled out in the project specifications.
The installer should be paid for all material used to make the installation,
including seam overlaps, anchor trench material, repair patches, penetration
boots, destructive samples and patches, and trial seaming material. The
easiest way to do this is to determine the amount of material delivered to
the site and to subtract the amount of useful material removed from the
site. The next simplest is to measure the accumulated length of each panel
removed from a roll. The CQA firm can keep such records in conjunction
with the installer.
However the most common method is to reference the area of the horizontal
projection at a specific level of the facility, typically the top of slope.
It then is the responsibility of the installer to incorporate factors for
the anchor trench and the other items. The horizontal projection should be
surveyed at the start of the project for initial estimates of cost. A final
survey of the installed liner would also be appropriate.
The anchor trench material can easily be calculated with material from the
top of slope to the front of the trench, down the trench, and across the
bottom. Material should not be folded in the bottom of the trench. The
CQA firm should ensure that material is not billed up the back of the trench
but only installed to the bottom of the trench. The anchorage of the liner
in the trench is a critical part of a properly designed lining system.
A waste factor of 10 to 12% might be allowed for a typical rectangular
facility with slopes of 10%. Both anchor trench and seam overlaps will
account for about 3% each, slope gain for 1 to 3% and 2 to 5% for the
remainder. More complex shapes will require larger waste factors. If
horizontal seams are not allowed on slopes the waste factor could be as high
as 20 to 30%.
Clearly, the answer to the problem is make sure that all parties understand
the basis of measurement, so that an appropriate bid can be placed by the
installer, and so that all understand on what area payment will finally be
made. Installers should not assume that if they put qualifying statements
in their bid others will take note of them. Confirm that a statement such
as “area of material laid” does or does not include overlap and patches etc.
Remember, the person who wrote the specifications or the contract probably
does not appreciate the finer details of liner installation.