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ORIGINAL RESEARCH

Field Performance of Three Compacted Clay Landfill Covers

^a Desert Research Inst., Nevada System of Higher Education, 2215 Raggio Parkway, Reno, NV 89512
^b Dep. Of Civil and Environmental Engineering, Univ. of Wisconsin-Madison, 1415 Engineering Dr., Madison, WI 53706
^c Battelle Pacific Northwest Laboratories, 3200 Q Ave., Richland, WA 99352
^d Dep. of Natural Resources and Environmental Sciences and Dep. of Geological Sciences and Engineering, MS 175, Univ. of Nevada, Reno, NV 89557
^e Dep. of Civil and Environmental Engineering, 2525 Pottsdamer St., Florida State Univ., Tallahassee, FL, 32310-6046
^f USEPA National Risk Management Research Laboratory, 5995 Center Hill Ave., Cincinnati, OH 45268
^* Corresponding author (bill{at}dri.edu)

Received 11 November 2005.

A study was conducted at sites in subtropical Georgia, seasonal and humid Iowa, and arid southeastern California to evaluate the field hydrology of compacted clay covers for final closure of landfills. Water balance of the covers was monitored with large (10 by 20 m), instrumented drainage lysimeters for 2 to 4 yr. Initial drainage at the Iowa and California sites was <32 mm yr^–1 (i.e., unit gradient flow for a hydraulic conductivity of 10^–7 cm s^–1, the regulatory standard for the clay barriers in this study); initial drainage rate at the Georgia site was about 80 mm yr^–1. The drainage rate at all sites increased by factors ranging from 100 to 750 during the monitoring periods and in each case the drainage rate exceeded 32 mm yr^–1 by the end of the monitoring period. The drainage rates developed a rapid response to precipitation events, suggesting that increases in drainage rate were the result of preferential flow. Although no direct observations of preferential flow paths were made, field measurements of water content and temperature at all three sites suggested that desiccation or freeze–thaw cycling probably resulted in formation of preferential flow paths through the barrier layers. Data from all three sites showed the effectiveness of all three covers as hydraulic barriers diminished during the 2 to 4 yr monitoring period, which was short compared with the required design life (often 30 yr) of most waste containment facilities.