OBJECTIVES :

      The proposed project is a modeling study that will investigate how lysimeter geometry and boundary conditions affect lateral diversion and percolation rates measured using lysimeters.  Results of the modeling study will be used, to develop design guidelines for cost effective lysimeters to be used for alternative landfill cover demonstrations.

Methodology :

      A review of the different concerns about the use of lysimeters will be conducted.  Based on the concerns sited in the literature on the use of lysimeters in landfill cover demonstrations, a modeling plan will be developed to address the different concerns in addition to the following:

      Use of sidewall: How high should the sidewalls be?  Are they a function of   climate conditions?

       Effect of slope of lysimeter on sidewall height

       Minimum areal extent of a lysimeter  should be investigated.  Does it depend on climatic conditions? Does depend on slope of lysimeter?

       Existence of artificial break caused by lysimeter bottom

      Presence of no-flow boundary caused by FML at bottom of lysimeter

       Use of percolation collection layer on top of FML, usually geonet-geotextile composite

     Computer simulations of virtual lysimeters will be performed using the computer code HYDRUS 2D.  The upper boundary of these lysimeters will be climatic data obtained from actual weather stations.    The percolation of water through these lysimeters will be monitored.  Factors such as the geometry of the lysimeter, the type of boundary conditions such as the no-flow boundary, and the use of a percolation collection layer at the base, will be considered.

Rationale:

    Before the acceptance of alternative landfill covers by the regulatory agencies, and the full-scale implementation of alternative covers can be achieved, field studies are needed to verify the effectiveness of the designs. In most cases, alternative landfill covers used in place of a prescriptive cover are required to be “equivalent” to the prescriptive cover; that is, percolation from the alternative cover must be less than that from the prescriptive cover. 

     Lysimetry, which is defined here as the use of buried containers with open tops that collect and measure soil water, provides a direct measurement of percolation rate from an AEFC.  Since lysimetry consists of collecting percolating water from the base of a test section, it provides the most precise estimates of percolation rate and is often recommended in equivalency demonstrations.  However, guidelines do not exist to assist engineers and regulators regarding proper design of lysimeters.  Factors such as the geometry of the lysimeter, the presence of no-flow boundary, and the use of a percolation collection layer at the base, can have significant effects on the performance of these lysimeters and thus can affect the outcome of equivalency demonstrations.

Status: Finished

Update: 07/03/2004

Final Reports