Four-year performance evaluation of a pilot-scale evapotranspiration landfill cover in Southcentral Alaska

Alternative landfill covers utilizing evapotranspiration (ET) as the primary mechanism for protecting the waste layer from aerial moisture represent promising tools for cold region solid waste management. However, ET covers have not been evaluated for use in subarctic climates. As the functionality of an ET cover is driven primarily by climactic variables, climate-specific field tests are required prior to widespread implementation. The objective of this study was to evaluate the four-year performance of two competing pilot-scale landfill covers built atop drainage lysimeters near Anchorage, AK. The compacted soil cover (CSC) was designed and constructed according to standards prescribed by Alaska solid waste regulations. The alternative ET cover design was based upon a preliminary modeling study. After four years, the two adjacent lysimeters had each received a total of 1636 mm precipitation. Over that period, 201 mm moisture drained from the ET lysimeter, compared to 292 mm in the CSC lysimeter. The difference in drainage rates between the two covers was most apparent during the autumn season, when the drainage rates for both covers were at their annual maximum. The lower autumn and annual drainage rates observed in the ET lysimeter after the first year were potentially due to higher moisture storage capacity in the ET cover soils and/or formation of preferential flow paths in the CSC soils. Analysis of soil temperature, precipitation, and drainage data indicated that negligible amounts of winter precipitation infiltrated the ET cover during winter, and that the frozen soils promoted runoff over drainage during the spring melt. These results indicate that similar ET cover designs merit consideration for broader use in subarctic conditions.