Leak Detection for Landfill Liners Overview of Tools for Vadose Zone Monitoring Karen Hix Technology Status Report prepared for the U.S. E.P.A. Technology Innovation Office under a National Network of Environmental Management Studies Fellowship August 1998 NOTICE This document was prepared by a National Network of Environmental Management Studies grantee under a fellowship from the U.S. Environmental Protection Agency. This report was not subject to EPA peer review or technical review. The U.S. EPA makes no warranties, expressed or implied, including without limitation, warranty for completeness, accuracy, or usefulness of the information, warranties as to the merchantability, or fitness for a particular purpose. Moreover, the listing of any technology, corporation, company, person, or facility in this report does not constitute endorsement, approval, or recommendation by the U.S. EPA. FOREWORD Identifying leaks in landfill liners is an essential part of waste management. EPA’s Technology Innovation Office (TIO) provided a grant through the National Network for Environmental Management Studies (NNEMS) to prepare a technology assessment report on identifying leaks in landfill liners. This report was prepared by a senior undergraduate student from Virginia Tech during the summer of 1998. It has been reproduced to help provide federal agencies, states, consulting engineering firms, private industries, and technology developers with information on the current status of this technology. About the National Network for Environmental Management Studies (NNEMS) NNEMS is a comprehensive fellowship program managed by the Environmental Education Division of EPA. The purpose of the NNEMS Program is to provide students with practical research opportunities and experiences. Each participating headquarters or regional office develops and sponsors projects for student research. The projects are narrow in scope to allow the student to complete the research by working full-time during the summer or part-time during the school year. Research fellowships are available in Environmental Policy, Regulations, and Law; Environmental Management and Administration; Environmental Science; Public Relations and Communications; and Computer Programming and Development. NNEMS fellows receive a stipend determined by the student’s level of education and the duration of the research project. Fellowships are offered to undergraduate and graduate students. Students must meet certain eligibility criteria. About this Report This report is intended to provide a basic summary and current detection of leaks in landfill liners. It contains information gathered from a range of currently available sources, including project documents, reports, periodicals, Internet searches, and personal communication with involved parties. No attempts were made to independently confirm the resources used. While the original report included color images, this copy is printed in one color. Readers are directed to the electronic version of this report to view the color images; it is located at http://clu-in.org. TABLE OF CONTENTS Page 1. PURPOSE 3 1.1 Monitoring background 3 1.2 Overview of leak sensor options 4 1.3 Cost 5 1.4 Other types of leak detection 5 2. ESTABLISHED SENSORS 6 2.1 Electrical 6 2.1.1 Two electrode method 6 a. Advantages 7 b. Disadvantages 7 c. Example- Sandy Lane landfill 7 2.1.2 Electrode grid method 7 a. Advantages 7 b. Disadvantages 8 c. Example 1- Sandy Lane landfill 8 d. Example 2- WESTEC’s Electronic Leak Detection System 9 2.2 Diffusion hoses 9 a. Advantages 9 b. Disadvantages 9 c. Example- Siemens’ LEOS 10 2.3 Capacitance sensors 10 a. Advantages 11 b. Disadvantages 11 c. Example- Troxler’s Sentry 200 EMMS 11 2.4 Tracers 12 a. Advantages 12 b. Disadvantages 12 c. Example 1- Tracer Research Corporation’s Automatic Leak Detector 12 2.5 Electro-chemical sensing cables 13 a. Advantages 13 b. Disadvantages 13 c. Example 1- Noverflow’s SMART CABLE 13 d. Example 2- Raychem’s TraceTek 14 2.6 Other 15 a. Visual inspection 15 b. Wires in geotextiles 15 3 3. EMERGING TECHNOLOGIES 15 3.1 Geosynthetic Membrane Monitoring System 15 3.2 SEAtrace 17 3.3 FLUTe ideal system 18 3.4 Other 19 a. LIDAR 19 b. Acoustic monitoring 20 4. CONCLUSION 20 Appendix A- Overview grid 21 Appendix B- Contact information- available sensors 22 Appendix C- Contact information- emerging technologies 23 Appendix D- Web sites 24 References 25 4 1. PURPOSE Identifying leaks in landfill liners is an essential part of waste management. Several types of leak detection tools can be installed in addition to monitoring wells to identify leaks soon after they occur. This paper provides an overview of some tools for vadose zone monitoring, as well as the advantages, disadvantages, and costs associated with them. 1.1. Monitoring background Federal law requires all landfills to include a leak detection system above the bottom composite liner. The system must consist of a layer of granular drainage materials with a slope of at least one percent, so any leachate which passes through the top liner will drain into the sump at the bottom of the unit, where its volume is recorded.(40 CFR 264.301) This system establishes what volume of leachate has leaked through the top liner, but it does not indicate whether or not leachate is leaking through the bottom liner. In addition, all landfills are required to install a groundwater monitoring system. The system must consist of both up gradient and down gradient wells which allow sampling of the groundwater in the uppermost aquifer, as shown in figure 1. The number, spacing, and depths of the required wells are dependant on the geologic and hydrologic properties of the area. (40 CFR 258.51) Figure 1: 5 Cross section of a traditional groundwater monitoring system. (GAO, 1995) By collecting groundwater samples and analyzing them, landfill operators can usually detect contaminant plumes caused by leaks in the landfill liner. One limitation of this method is that it does not prevent the groundwater from becoming contaminated. Another limitation is the expense of comprehensive monitoring for all groundwater which comes in contact with a landfill. Because most landfills are lined with geomembranes, most leaks are point sources, not widespread. If there is no monitoring well in the path of a plume, it is possible for the front of the plume to pass by the line of wells at the point of compliance without being detected. Installing enough monitoring wells to be sure of intercepting a narrow plume in any position can be prohibitively expensive. (Godfrey, 1987) California has especially rigorous monitoring requirements. State law requires testing for leakage in the vadose zone under waste disposal sites. (CA Code) The two most common ways to comply with this requirement are lysimeters, which collect pore water for later removal and testing, and soil core sampling. Both of these methods require laboratory testing and neither can easily pinpoint the location of the leak. (Daniel, 1987) 1.2 Overview of leak detection options In addition to the monitoring methods required by law, some landfill owners are choosing to install systems of leak detection sensors. These sensors permit early leak detection without laboratory analysis, and often locate the leak. Several different types of sensors provide these benefits. Some work by electrical methods, measuring the resistivity or dielectric constant of the soil. Others work by chemical methods, either analyzing soil vapor or reacting directly to leachate. These sensors are often dependant on the composition of the leachate. Still others use tracer chemicals to detect leaks. Use of these technologies is not widespread, mainly because of cost. Most must be installed during construction and are not applicable to existing landfills. Each of the leak detection systems available has different advantages and disadvantages. The perfect vadose zone monitoring system has not yet been designed, but the ideal system would: - Be affordable - Be durable enough to last through the life of the landfill and the 30 year post-closure period - Locate leaks and determine their sizes - Be automated - Be applicable to all types of landfills and all types of leachate - Provide full spacial monitoring for the entire area below the landfill Research on new sensors for leak detection at landfills is ongoing, but it is also limited because the market for this optional extra level of detection is extremely small. 6 7 1.3 Cost The main reason leak detection sensors are not more widely used at landfills is the cost. By law, sensors may only be used in addition to monitoring wells, not in place of them. Therefore, it is uncommon for a landfill owner to choose to install leak detection sensors. The owner has no way of knowing whether or not a major leak will ever occur, so the benefits of detecting a hypothetical future leak earlier do not outweigh the immediate costs of installing a vadose zone leak detection system. A comparison compiled by Inyang (Rumer, 1995) of monitoring costs for a hypothetical landfill showed that sensors can be less expensive than monitoring wells. Inyang compared the cost of monitoring a 20,000 ft2 area for 20 years with monitoring wells to the cost of monitoring the same area with the Raychem system for electro-chemical monitoring. (see section 2.5 d) The costs are broken down in the following table: Cost comparison for monitoring wells vs. electro-chemical sensing Monitoring technique Unit cost ($) Number required Total item cost Groundwater monitoring wells CWell installation 5,000 3 15,000 CChemical analyses 18,000 per well 3 54,000 COperation and management 100,000 - 100,000 Total cost 169,000 Electro-chemical sensing CCentral electronic unit 5,000 1 5,000 CSensing cables 1,200 3 3,600 CConnecting cables 300 3 900 CSensor installation 400 3 1,200 COperation and management 120,000 - 120,000 Total cost 130,700 (Rumer, 1995) Although the cost of the electro-chemical system is lower than that of the monitoring wells, the entire system would cost $299,700, which is substantially more than the wells alone.