When is the use of a geotextile under/overlayment appropriate?

 As touched on earlier, use of a geotextile underlayment (under the liner) with the PPL-24 is rare (see Question 2). It is always a judgment call, but we don't require the underlayment unless it is impossible or impractical (cost ineffective) to get an acceptable subgrade any other way. The "other way" is usually to haul in and spread clean fill over the entire area to be lined. Often it is cheaper and faster to spread an underlayment over angular rock subgrades than the "other way". Use of the geotextile as an overlayment (over the liner) is normally for having a separation between the liner and any type of fill, rock, gravel, rip-rap, etc. that is to be placed on top of the liner for various reasons. As an option, we often sell a "ribbon" of geotextile overlayment (typically 8oz. per square yard non-woven needle-punched polypropylene, whew!) usually simply referred to as "geo", which is installed over the liner on the upper perimeter and keyed into the anchor trench or shelf right along with the liner itself. This "ribbon" is normally the roll width of either 12.5 or 15 feet. Prior to filling a pond, some minimal amount of fill must be placed over the entire ribbon so that is not prone to floating. Again, this is an option and not mandatory. However, it is becoming increasingly popular for a number of reasons. We know from experience that any form of physical damage (from deer, kids with rocks, mechanical equipment, UV degradation, etc.) is by far the most likely to occur on the upper edges of the pond liner, not out in the depths of the pond. Also, an added degree of safety is introduced when doing this option. The upper edges are made less slippery so kids, dogs, deer, etc. can get out more easily. So while "necessary" this option is a relatively cheap form of "insurance" in a number of ways.

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