Graduation Semester and Year

2016

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Unknown

Abstract

Although alternative covers such as the evapotranspiration (ET) landfill cover system promise to provide equivalent or greater performance than conventional cover systems, uncertainties remain on the performance of these type of cover systems. The uncertainties associated with performance may derive from the relative newness of these covers (when compared to conventional landfill cover systems); and their dependency on relatively site-specific factors such as: climatic, vegetation, and soil conditions. As a results, the Texas Commission on Environmental Quality (TCEQ) requires a landfill facility to design and then verify the design and performance through site specific field scale testing (TCEQ 2012). Utilizing field scale lysimeters [having dimensions greater than 10 x 10-m (30 x 30-feet)] coupled with in-situ soil instrumentation is the preferred method of field verification by TCEQ (TCEQ 2012). Therefore; the motivation of this study was to develop an understanding of the short-term hydraulic performance and vegetation mix assessment of ET cover systems at the City of Denton, Texas Municipal Solid Waste Landfill utilizing six (6) 40-ft by 40-ft lysimeters. A plethora of sensors, instrumentation, and monitoring methods were utilized in an effort to effectively measure and analysis critical parameters of the ET cover systems such as: climatic conditions, surface runoff, soil water storage, soil water potential, vegetation, surface conditions, and percolation. Construction of six (6) 40-ft by 40-ft lysimeters was a time-consuming process which required a number of tasks (with multiple steps associated with each task) to be completed. Construction of the lysimeters started June 17th, 2014 and was completed November 1st, 2014 [a span of four (4) and a half months]. The tasks which were completed during the construction of the lysimeters are provided as follows: (1) embankment construction; (2) embankment excavation; (3) geomembrane placement; (4) geomembrane boot construction; (5) percolation collection system construction; (6) geocomposite drain placement; (7) 3-ft compacted clay placement; (8) topsoil sidewall and bentonite placement; (9) berm construction; (10) 1-ft of topsoil placement; (11) collection tank placement and installation; (12) instrumentation; (13) vegetation and erosion mat placement; and (14) clean-up activities. Preliminary results for the six (6) ET cover systems are generally characterized by large quantities of runoff, percolation, and soil water storage. The least amount of percolation was measured from the ET cover systems sodded and seeded with Bermuda, indicative of the best performance. These preliminary percolation results do not appear to be encouraging for the performance of the cover, with all the ET cover systems producing substantial amounts of percolation. However, it is important to note the following: (1) the results are from the short-term performance of the ET cover systems; (2) there has been a large amount of precipitation that has occurred during the monitoring period, much greater than the historic average; (3) vegetation appears to be established; however, the roots have not been observed to extend to a great depth within the cover systems; and (4) desiccation cracking and rodent burrows have been observed in the cover systems which may result in preferential flow pathways. The ET cover systems will continue to be monitored and their performance evaluated over a greater amount of time.

Keywords

ET Landfill Cover, Lysimeter

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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