Graduation Semester and Year

2018

Language

English

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering

Department

Civil Engineering

First Advisor

Sahadat Hossain

Abstract

The purpose of landfill cover systems is to minimize, and if possible prevent the interaction of the environment with the buried waste mass. In this effort, one of the most prevalent parameters to control is the percolation of rainfall through the cover system into the waste mass. In addition to this, if the cover system utilizes an evapotranspiration or water balance cover, understanding this parameter becomes especially important. This type of system relies on the ability of the soil to retain moisture and the natural process through which vegetation transports water from its roots to the atmosphere. Consequently, the percolation rate is directly influenced by the type of vegetation, the type of soil, the compaction level of the soil, and the environment. Environmental loading conditions can change drastically throughout the seasons, which in turn can substantially alter the hydraulic conductivity of the cover soil. Directly affecting the percolation rate, and the performance of the cover. Therefore, the objective of this study was to monitor the hydraulic conductivity of an existing ET cover system on the city of Irving landfill at variable environmental conditions. By doing so, the seasonal performance of the cover system could be evaluated and eventually improved. To develop a better understanding of the hydraulic performance of the cover system, soil samples were collected from depths of 12 to 30 inches in both slopes and were fully characterized. Later, the selected sites were monitored monthly with the Guelph Permeameter at variable depths.Additionally, electrical resistivity imagining was conducted on both slopes seasonally, in an effort to corroborate the results obtained with Guelph Permeameter. By evaluating the hydraulic conductivity of the cover system at the three selected depths throughout the changing seasons, the influence of the root system and compaction level could be studied. It was observed that the average hydraulic conductivity decreased directly proportionally to an increase in the investigated depth. Furthermore, it was observed that the hydraulic conductivity of the cover system at all of the investigated depths, varied in a cyclical pattern in accordance to the changing seasons. The highest values were registered during the summer seasons, whereas the lowest values were observed in the winter season. Moreover, during the course of the investigation it was observed that the hydraulic conductivity changed in response to periods of heavy rain. Measurements that were taken shortly after rainfall events were significantly lower than those that were taken during periods of relatively low precipitation. The exception to this pattern were the measurements taken during the spring of 2017. The hydraulic conductivity increased despite the precipitation events. However, Bermuda grass has shown to experience its fastest growth phase during this season. During this phase water demand greatly increases, ultimately improving its evapotranspirative properties. Finally, the longest saturation times were observed during the summer when the soil is comparatively dryer than winter. This observation and all of the additional cyclical patterns observed during the in-situ investigation, suggest that the cover system was at its critical hydraulic performance during the summer months.

Keywords

Hydraulic conductivity, Landfill cover

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

Download

Share

COinS