Field Hydrologic Performance of Water Balance Cover in North Texas: Fid-Bau Portal

Field Hydrologic Performance of Water Balance Cover in North Texas

Alam, Md. Jobair Bin / DeVries, Brett / Rahman, Naima / Hossain, Md. Sahadat

Performance assessment of water balance cover or evapotranspiration (ET) cover is critical for waste containment as its performance largely depends on the site-specific condition. Post construction changes in the soils’ hydraulic properties, as a consequence of wetting-drying cycles, frost action, ingress of plant root, etc. may affect the cover performance. The objective of this study was to evaluate the water balance performance of ET cover in the semi-humid region of North Texas. As part of the study, a large-scale test section was constructed with drainage lysimeter (12 m×12 m) in the City of Denton landfill for continuous and direct monitoring of the water balance. The test section was constructed with 0.9 m (3 ft.) of a compacted fine-grained soil layer and 0.3 m (1 ft.) of a vegetated surface layer. Cover soil was placed over a geomembrane and a geocomposite drainage layer. An extensive field instrumentation program was implemented in the field to monitor the water balance components of the drainage lysimeter. Moisture sensors and tensiometers were installed at the site to monitor the change in soil water storage. Surface runoff and percolation collection tanks, connected to the lysimeter through HDPE pipes, were placed at the site to monitor these two components. A weather station was also installed to monitor the overall climatic condition. Based on the monitoring results accumulated after two years, drainage from the bottom of the cover soil (percolation) was recorded to be 42 mm/year and 49 mm/year (2.8% and 3.7% of precipitation) respectively. Annual percolation was identified to be significantly influenced by annul precipitation and water storage capacity of the cover soil.