Extending our Lengths

Several of our Dealers have requested that we increase the length of our standard rolls. Longer rolls will provide less down time by deploying fewer rolls and therefore will allow for fewer cross seams, less seam testing and patching. Following is a chart comparing the current lengths with the new lengths. The new lengths were engineered to produce a roll of approximately 3,500 pounds. As soon as our current inventory is depleted, all rolls will be the new lengths.

Field Performance of HDPE Liners
by George Yazdani, P.E.

How long are HDPE liners going to last in the field when they are exposed to landfill leachate, gases, and field loading conditions? This is one of the most frequently asked questions in our business. There have also been questions regarding long term integrity of HDPE folds as liners may be folded during the placement of cover soils. The "liner fold" topic has been and continues to be a controversial issue. Some believe that folds cannot be completely avoided during construction of HDPE lined facilities due to expansion and contraction properties of the liner and that the liner is not detrimentally affected at the folds. Others are concerned with long term integrity of folds and other side effects which may be created as a result of folds. Technical papers which dealt with these issues were presented at the 10th GRI Conference, held December 10-11, 1996, in Philadelphia. The first paper¹ provided data on performance of an eight (8) year old HDPE liner in service and revealed some real answers to the long asked questions regarding long term performance of HDPE liners and folds. As part of the reconstruction of several sumps in a landfill, several sections of a 60 mil HDPE double liner system were uncovered in October 1996. The municipal waste landfill, located in the Mid-Atlantic Region of the U.S., was constructed in 1988 and has been in service since. Two types of samples were extracted and tested in a laboratory. Samples that were exposed to leachate and those that were not exposed to leachate. The unexposed samples were extracted from a large area under a cap strip repair. The test results indicated that after eight (8) years of exposure to leachate, landfill gases, and loading, the liner properties were within the range of data obtained from the original testing in 1988. In the process of uncovering the liner, a number of folds were noticed in the uncovered area. Some folds had been positioned vertically, as high as 3 - 4 inches. Others had completely collapsed during placement of the cover soils. The folds were visually inspected and showed no signs of tears or cracks after eight (8) years. Samples were obtained from the folds for further evaluation in the laboratory. The study of folds is ongoing and should be completed in 1997. The final results will most likely be presented in another paper. I will keep you posted of any new development.

A second paper², related to field performance of geomembranes, was presented at the conference. The author provided information on subsidence of landfills and condition of a HDPE geomembrane after three (3) years of service in a landfill closure. Before the introduction of VLDPE and LLDPE geomembranes to the market, most projects used HDPE or other non-polyethylene flexible liners for landfill closures. Presently, VFPE geomembranes (i.e. LLDPE, or polyethylene liners with maximum sheet density of 0.940 g/cc) are the desired products for landfill closures. This is due to the extra deformation characteristics of VFPE geomembranes as compared to HDPE liners. The paper presented a study in which a 40 mil HDPE geomembrane was uncovered after three (3) years of service in a landfill closure. The subsidence in this landfill varied up to ten (10) percent of the landfill height in the three (3) years post-closure period. The HDPE geomembrane showed no visual signs of subsidence related stresses or strains. The study also indicates that landfill settlements are not uniform (i.e. not all points on the landfill settle at the same rate), but the overall deformed profile of the final cover is often a smooth surface. In conclusion, although VFPE geomembranes are desired, the HDPE geomembranes are capable of providing a satisfactory performance in landfill closures.

1. Anthony W. Eith, P.E., Rust, Inc. and George R. Koerner, Ph.D., P.E., Geosynthetic Research Institute "ASSESSMENT OF HDPE GEOMEMBRANE PERFORMANCE IN A MUNICIPAL WASTE LANDFILL DOUBLE LINER SYSTEM AFTER EIGHT YEARS OF SERVICE", pp. 97 - 109, Proceedings of the 10th GRI Conference.
2. Daniel R. Spikula, Browning-Ferris Industries "SUBSIDENCE OF LANDFILLS", pp. 211 - 218, Proceedings of the 10th GRI Conference.