To the editor:
I read the “2010 ICOLD Bulletin on geomembrane sealing systems for dams” article with great interest (April/May, 2012).
Good article to have presented, but I was a little surprised by the low numbers of geomembrane-lined earth- and rock-fill dams listed [in] the 2010 ICOLD Bulletin.
ICOLD defines “large dams” as more than 20m high, and there are numerous exposed GSS (geomembrane-lined) water and tailings fill dams that meet that description in the mining industry worldwide but [they] are not making the list. The reason I think there are many more lined fill dams than listed comes from reading a footnote to Table 4 that said “The table includes 43 dams in China and 5 tailings dams.” I know of five GSS geomembrane-lined tailings dams that I was involved with just in the state of Nevada alone in the 1980s.
Outside of the U.S., [such as] in South America, there are quite a few mines with geomembrane lined water or tailings storage dams existing or coming on line and very likely will not show up on the ICOLD listing … To incorporate all geomembrane-lined, large-fill dams, I would also argue that we should expand the list to include the large GSS valley leach dams constructed along the toe of high stacked ore heap fills, as these fill structures retain ponds inside the heap that are sometimes more than 50m deep! An infamous example of a GSS valley leach dam is the 75ft- (23m-) high Summitville Valley leach dam in southern Colorado (60-mil HDPE in 1986) that nearly overflowed and [subsequently] became a Superfund site. A more recent example of a large lined fill valley leach dam of similar size is the Carlota dam in Arizona (double-lined HDPE and LLDPE liners in 2009 and, again, not on the list).
I am proud to say that, many years ago, I was the CQA Resident Engineer in Nevada on the construction of the first internal geomembrane-lined water storage dam that used the geomembrane liner as the low permeability core of an earth fill-dam (composite 2.5mm VLDPE and Claymax GCL in 1989). However, this dam did not make the ICOLD list! … the geomembrane liner industry is not giving itself enough credit on GSS fill dam liners for sure!
Allan J. Breitenbach, P.E.
Littleton, Colo., USA
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