Grantee Research Project Results
2003 Progress Report: Field Evaluation of Evapo-Transpiration (ET) Caps
EPA Grant Number: R830845Title: Field Evaluation of Evapo-Transpiration (ET) Caps
Investigators: Abichou, Tarek , Chan-Hilton, Amy , Tawfiq, Kamal , Abdelrazig, Yassir
Institution: Florida Agricultural and Mechanical University
EPA Project Officer: Hahn, Intaek
Project Period: April 1, 2003 through March 31, 2005 (Extended to June 30, 2006)
Project Period Covered by this Report: April 1, 2003 through March 31, 2004
Project Amount: $395,548
RFA: Superfund Minority Institutions Program: Hazardous Substance Research (2002) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Safer Chemicals , Hazardous Waste/Remediation
Objective:
The objective of this research project is to assess the field performance of evapo-transpiration (ET) caps through a field study. This project was developed to continue the effort led by the research team in designing ET caps in the State of Florida and beyond. The first two steps of this process have been started by two mini projects funded by the Florida Center for Hazardous Waste Management. Data from this study will be incorporated into Alternative Cover Assessment Program data to assist engineers and site owners in designing alternative covers, such as ET caps, and provide researchers with data to calibrate existing percolation models. The objective of this study will be achieved by constructing, instrumenting, and monitoring three types of lysimeters to evaluate the performance of ET caps. One lysimeter was constructed in accordance with Resource Conservation and Recovery Act (RCRA) Subtitle D requirements. One lysimeter has cottonwood trees with grass for vegetation, and the other has eucalyptus trees and grass.
Progress Summary:
The research program consists of four major tasks. Task 1 involves the preconstruction testing and design of ET caps and RCRA Subtitle D cap lysimeters. Task 2 consists of the construction of lysimeters using the same cap designs obtained in Task 1. Task 3 consists of monitoring the lysimeters constructed in Task 2 to assess the field performance of the cap designs developed in Task 1. Task 4 will consist of analyzing the data collected in Task 3 and calibrating existing water balance models that will be used as predictive tools.
Task 1–Preconstruction Testing and Cap Profile Design (100 percent completed)
ET Soil Thickness Design . This subtask consisted of collecting climate data, soil samples, and vegetation characteristics from Tallahassee, FL. Hydraulic properties of the soil samples, along with vegetation root density functions, were evaluated in the laboratory. The accumulated data was used as input into an unsaturated flow model (UNSAT-H) to simulate the water balance during peak weather events. Simulations were performed to estimate the soil thickness needed to construct an ET cap using different types of vegetation. Simulations of ET caps with trees and grasses having a thickness between 1.0 and 1.5 m had a balance of infiltration and evapo-transpiration resulting in neutralized percolation. The vegetation type, however, proved to have a significant effect on percolation.
ET Lysimeter Design . A modeling study using Windows program HYDRUS-2D was performed to investigate how lysimeter geometry and boundary conditions affect lateral diversion and percolation rates, which are measured using lysimeters. The break in texture that occurs at the interface between the base of the cover profile and the percolation collection layer at the base of the lysimeter was determined. Results of the modeling activities showed that cost-effective lysimeters can be 5 m wide, have sidewalls that are 0.35 m high, and be constructed on slopes not steeper than 5:1. Lysimeters constructed in accordance with these recommendations have a performance ratio greater than 0.80. That is, the percolation rate measured from such lysimeters underestimates the percolation through an actual cover by at most 20 percent. The recommended design also results in less overcompaction typically associated with lysimeter construction.
Task 2–Construction of ET Cap Lysimeters (90 percent completed)
Construction of lysimeters is in progress. Preparation of a firm foundation for the ET cap lysimeter involved the stripping of topsoil and proof rolling. Three lined test pads of 20 ' x 42 ' were prepared along the dominant slope in an east–west direction. Each of the constructed lysimeters consists of a system to collect percolation from the base, a system to collect surface runoff, and sensors to monitor the hydrologic variables. Each lysimeter consists of a “bath tub” lined with geomembrane and geocomposite. At the down slope, a drainage sump pump was installed and connected to a drainage monitoring system. A geocomposite drainage layer, followed by a thin gravel layer, was placed on top of the geomembrane to collect the percolating water from the cap soil and to rapidly transmit it to the sump area. This layer also acts as a cushion to protect the bottom geomembrane during soil placement. A root barrier was placed on top of the gravel layer. The root barrier was intended to prevent the roots from reaching the percolation collection system. The ET cap was subsequently placed in three lifts of soils. A thin layer of mulch was also added at each lift of soil to improve fertility to aid the growth of trees and grasses and to improve the water storage capacity of the soil. Fertilizer and lime were also added. The thickness of soil cover above the root barrier is approximately 4.5 ft.
Tasks 3 and 4–Data Collection and Analysis (0 percent completed)
There has been no progress on these two tasks.
Future Activities:
We are installing a weather station. The weather station and sensors will then be connected to the data logger for collection of the relevant data. The collected climatic conditions data, soil properties, and vegetation data will be used as input parameters for a water balance model such as UNSAT-H or HYDRUS-2D. The performance of these models will be compared to the observed results.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
landfill covers, landfill caps, evapo-transpiration, ET, lysimeters, percolation rates, alternative covers, barrier layers, water balance, vegetative cover, contaminated sediments, environmental chemistry, hazardous waste, waste treatment, bioremediation, chemical contaminants, chemical kinetics, contaminant transport models, contaminated marine sediment, leaching, remediation, risk assessment, sediment caps, sediment treatment., RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, TREATMENT/CONTROL, Ecosystem Protection/Environmental Exposure & Risk, Waste Treatment, Contaminated Sediments, Environmental Chemistry, Fate & Transport, Hazardous Waste, Ecology and Ecosystems, Environmental Engineering, Hazardous, fate and transport, environmental technology, sediment treatment, hazardous waste management, hazardous waste treatment, risk assessment, landfill caps, evapo-transpiration caps, contaminated marine sediment, soil and groundwater remediation, sediment caps, contaminated sediment, chemical contaminants, contaminated soil, chemical kinetics, remediation, control technologies, leaching, contaminant transport models, bioremediationProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.