The Long-Term Environmental Risks of Subtitle D Landfills. Jeremy K. O Brien, P.E. Director of Applied Research SWANA

Transcription

1 The Long-Term Environmental Risks of Subtitle D Landfills Jeremy K. O Brien, P.E. Director of Applied Research SWANA 1

2 ARF Landfill Research Date November 2004 December 2008 December 2010 June 2011 Publication The Effectiveness of Municipal Solid Waste Landfills in Controlling Releases of Heavy Metals to the Environment The Long-Term Environmental Risks of Subtitle D Landfills The Long-Term Management and Care of Closed Subtitle D Landfills The Long-Term Environmental Risks of Subtitle D Landfills (Peer-Reviewed Version) 2

3 Overview of Presentation Project Background Performance of Sub D Environmental Systems Long-Term Environmental Risks Management Strategies to Mitigate Long- Term Risks 3

4 Background Subtitle D landfill regulations promulgated in 1991 Some Sub D landfills now closing 30-year post closure period can be extended or shortened by states. 4

5 Perspective of Certain Environmental Groups Closed Sub D Landfills constitute major environmental risk Ticking Time Bombs Post-closure care period should never end 5

6 Purpose of Project Document what is known about short-term and long-term environmental risks Identify long-term alternatives to manage and minimize these risks 6

7 Four Key Publications 1. Assessment of the Performance of Engineered Waste Containment Barriers (2007) Major study conducted by National Research Council 119-page report published in Assessment and Recommendations for Improving the Performance of Waste Containment Systems (2002) Comprehensive study conducted by three renowned researchers (Drs. Bonaparte, Koerner, and Daniel) Report over 1,000 pages in length published in Present and Long-Term Composition of MSW Leachate: A Review (2002) Summary of research on MSW leachate conducted by Dr. Mort Barlaz and Dr. T. Christensen Article published in technical journal in Performance-Based System For Post-Closure Care at MSW Landfills: A Procedure For Providing Long-Term Stewardship under RCRA Subtitle D (2006) Developed in 2006 by Geosyntec in collaboration with leading researchers and technical experts for EREF. 7

8 Report Peer Review Dr. Debra R. Reinhart, PE, BCEE Pegasus Professor Assistant Vice President for Research and Commercialization University of Central Florida Dr. Craig H. Benson, PE, DGE Chair, Geological Engineering Wisconsin Distinguished Professor University of Wisconsin-Madison. 8

9 CURRENT PERFORMANCE OF SUBTITLE D ENVIRONMENTAL PROTECTION SYSTEMS 9

10 Subtitle D Environmental Protection Systems Bottom Liner System Leachate Collection and Removal System Landfill Gas Collection and Control System Final Cover System Stormwater Management System 10

11 Subtitle D Environmental Protection Systems Current Performance Bottom Liner Systems Substantially prevent leachate/pollutants from exiting waste containment area. Life of bottom liner system can be substantially shortened by high landfill temperatures above the liner. VOC migration remains an issue that needs additional study. 11

12 Impact of Temperature on Geomembrane Service Life Temperature Service Life Centigrade Fahrenheit Years

13 VOC Migration Issue NRC Report (2007) Geomembranes offer little, if any, resistance to the migration of several types of Volatile Organic Compounds (VOCs) Kjeldsen Paper (2002) VOCs are affected by volatilization and degradation as well as leaching and are in most cases not believed to be a long-term problem Unpublished MS thesis VOC concentrations in lysimeters below geomembrane and composite liners to be similar. 13

14 Subtitle D Environmental Protection Systems Current Performance Leachate Collection Systems Generally are performing well and are collecting over 99% of leachate. Clogging problems in small number of landfills. Landfill Gas Collection Systems Collection efficiencies of over 97% reported for landfills with active LFG collection systems and final cover systems. Additional methane oxidation achieved in cover soils. Final Cover Systems Perform satisfactorily and can effectively isolate waste from the environment. 14

15 Overall Performance of Subtitle D Environmental Protection Systems Based on as much as 20 years of observations, the committee concluded that most engineered waste containment barrier systems that have been designed, constructed, operated, and maintained in accordance with current statutory regulations and requirements have thus far provided environmental protection at or above specified levels. (2007 NRC Study) 15

16 LONG-TERM PERFORMANCE OF SUBTITLE D ENVIRONMENTAL PROTECTION SYSTEMS 16

17 Post-Closure of Sub D Landfills 30-year period unless changed by State Allows landfill owner to determine if final cover system is functioning properly LFG should drop to very low levels Leachate should drop to very low levels Waste mass essentially becomes dormant If all other systems look good (groundwater, stormwater) looks good, post-closure care could end. However, we can t walk away from the site why? 17

18 Reasons For Concern: 2002 Bonaparte Study A partial stabilization of waste will probably occur by the end of the post-closure period, although this process will be incomplete due to a deficit of moisture in the landfill. The waste will retain a latent capacity to generate leachate and gas and release pollutants should moisture be reintroduced into the landfill in the future. 18

19 Timeframe For Concern: 2007 NRC Study Overall, the period during which a large landfill will potentially release contaminants at unacceptably high levels may be on the order of hundreds of years for municipal solid wastes. 19

20 Long-Term Risk Scenarios 1. Functional Final Cover System 2. Minor Breaches in Final Cover System 3. Major Breaches/Deterioration of the Final Cover System at the End of its Service Life 20

21 Scenario #1 Functional Final Cover System 2007 NRC Study Properly designed and constructed cover systems at MSW landfills can effectively isolate waste from the environment. Good performance of cover systems requires periodic maintenance to repair erosion or other forms of cover distress Most engineered cover systems rely on regular maintenance to maintain their integrity. Conclusion Environmental risk is minimal if cover integrity is maintained through regular maintenance. 21

22 Scenario #2 Minor Breaches in Final Cover System Would result in small quantities of water entering the landfill. As a result, small quantities of leachate and LFG would be generated. LFG most likely would exit breach and dissipate. 22

23 Scenario #2 Minor Breaches in Final Cover System Leachate Could be absorbed in waste mass If not, would drain through bottom portion of landfill Could potentially exit landfill through holes in bottom liner. What is the level of environmental risk? 23

24 Reasons that Environmental Risks of Scenario #2 Are Low Internal landfill biochemical environment Low concentrations of pollutants in mature leachate Dilution and attenuation capacity of soil and groundwater beneath landfill. 24

25 Internal Landfill Biochemical Environment Anaerobic, reducing chemical environment Partially saturated and decomposed waste mass Little or no leachate or landfill gas production Mature leachate characteristics Bottom portion of waste mass tends to act as an Anaerobic Trickling Filter 25

26 Reasons that Environmental Risks of Scenario #2 Are Low Low concentrations of pollutants in mature leachate Dilution and attenuation capacity of soil and groundwater beneath landfill. 26

27 Groundwater Maximum Contaminant Levels (MCLs) Established for MSW Landfills with performance-based liner designs. MCLs must not be exceeded at the relevant point of compliance i.e., at 150 meters from waste unit boundary. MCLs are identical to drinking water standards. A dilution and attenuation factor of 100 has been assumed by the EPA in the past for groundwater impacts of landfill leachate. In other words, pollutant concentrations were expected to be diluted by a factor of 100 before reaching the relevant point of compliance. 27

28 Concentrations of Mature Leachate Constituents Constituents That Don t Have Groundwater MCLs Dissolved Organic Compounds Inorganic Macrocomponents Constituents With Groundwater MCLs Heavy Metals Xenobiotic (Man-made) Organic Compounds 28

29 Table 4. Concentrations of Xenobiotic Compounds in Mature Landfill Leachate and Comparisons to Regulatory Standards All Concentrations Reported in Milligrams Per Liter Groundwater Maximum High Median Diluted Contaminant Chemical Concentration Concentration Level 3 Xenobiotic Compounds Benzene Carbon Tetrachloride ,2- Dichloroethane (Ethylene Dichloride) ,1,1-Trichloromethane (Chloroform) Trichloroethylene Vinyl Chloride

30 Table 5. Published Concentrations of Heavy Metals in Mature Landfill Leachate and Comparisons to Regulatory Standards All Concentrations Reported in Milligrams Per Liter Groundwater Maximum Methanogenic High Median Diluted Contaminant Chemical Average Concentration Concentration Level Heavy Metals Arsenic Barium Cadmium Chromium Lead Mercury Selenium Silver

31 Scenario #2 Minor Breaches in Final Cover System Xenobiotic Compounds and Heavy Metals Relatively low concentrations in mature leachate. Likely to be absorbed in waste mass and/or diluted to below groundwater MCLs in the case of leakage due to small breaches/tears in top and/or bottom liner systems. Landfill Gas Minor quantities escape through breaches Conclusion Low level of environmental risk 31

32 Scenario #3: Major Breaches/Deterioration of the Final Cover System at the End of its Service Life Waste decomposition process could restart Landfill s internal chemical environment could change Anaerobic to Aerobic Reducing to oxidizing Basic to acidic Metals could be remobilized in leachate Leachate strength and quantities could grow Bottom of Landfill Still acts as anaerobic trickling filter Potentially removes metals and organics 32

33 Bonaparte (2002) Ultimate degradation of any individual waste containment system component of a landfill at the end of its service life may or may not lead to a release of leachate or gas or contamination of groundwater May or may not result in a significant environmental impact 33

34 Long-Term Risk Scenarios Functional Final Cover System Negligible environmental risk Minor Breaches in Final Cover System Minimal environmental risk Major Breaches/Deterioration of the Final Cover System at the End of its Service Life May or may not result in a significant environmental impact. 34

35 Conclusions In general, Subtitle D landfills are meeting environmental regulations providing environmental protection at or above specified levels. A small percentage of existing Subtitle D landfills have experienced problems with: Pollution of groundwater by LFG escaping through the side slope edges of the bottom liner system, Clogging of the leachate collection and removal system, and Leakage of leachate through punctures or tears in bottom liner system. The potential for groundwater contamination from VOC migration remains an issue that needs additional study. 35

36 Conclusions (Cont.) Final cover systems with composite barriers have been shown to be effective at isolating waste as long as periodic maintenance is performed. Overall, the period during which a Subtitle D landfill could potentially release contaminants may be on the order of hundreds of years. The threat of leakage can be mitigated through long-term cap maintenance to minimize the migration of liquid into the landfill. 36

37 Conclusions (Cont.) Risks posed by closed Subtitle D landfills consist of possible leaking of a leachate of: moderate biological strength high inorganic macro-components varying concentrations of xenobiotic compounds low concentrations of heavy metals. The top and bottom liner systems in Subtitle D landfills are composite systems that provide multiple layers of environmental protection The discharge of significant quantities of leachate from a closed Subtitle D landfill is unlikely. 37

38 Conclusions (Cont) If a discharge occurs, the environmental and public health impacts will depend on the capability of the receiving groundwater body to dilute and attenuate the pollutants in the leachate. Based on current leachate concentrates and reasonable dilution assumptions (factor of 100), groundwater at landfill boundary will meet drinking water standards even if a discharge occurs. For a closed landfill with a fully functional final cover system or one where only minor breaches have occurred, the environmental and public health concerns are likely to be relatively minor. 38

39 Subtitle D Landfills: Long-Term Management Options Continuation of Post- Closure Monitoring/Planning for Corrective Action (Environmental Groups) Custodial Care (EREF) Perpetual Care (State of Minnesota) Post-Closure Management (State of California) 39

40 Continuation of Post-Closure Care/Planning for Corrective Action Advocated by some environmental groups Same level of care as PCC period Continuation of State regulatory oversight Funding for perpetual care and corrective action (assumed needed) should be built into landfill tipping fee. 40

41 Custodial Care Advocated by Environmental Research and Education Foundation (EREF) and Interstate Technology and Regulatory Council (ITRC) EPCC methodology used to determined long term care requirements Major strategy maintain integrity of final cover system Requirements included in deed for site PCC regulatory oversight by state ends. 41

42 Perpetual Care Advocated by State of Minnesota for medium to large landfills Activities include: Continued site maintenance Monitoring of gas/groundwater Maintaining integrity of final cover Groundwater monitoring 6 wells sampled yearly into perpetuity Assumed 3 acres of final cap would need replacement Perpetual care trust fund needed Continued State regulatory oversight 42

43 Post-Closure Management (PCM) New regulations promulgated by State of California in July 2010 PCM must continue until the waste no longer poses a threat to public health/safety and the environment. Landfill owners must provide financial assurance for PCM and reasonably forseeable corrective action activities, including replacement of final cover. State regulatory oversight continues after PCC. 43

44 Comparison of Long-Term Care Options All options rely on proper functioning and perpetual maintenance of final cover system. All options require some type of site care following PCC period. Financial assurance required for eventual replacement of final cover system (CA) or 3 acres of final cover (MN). PCC monitoring activities reduced in some options but not in others. Both states require continued state regulatory oversight while EREF approach ends state oversight. 44

45 Conclusions Long-term care beyond the current 30-year minimum post-closure care is likely, but the type and level of care needed is not clear. Funding to support the long term monitoring and maintenance of the final cover system, is not being accrued by Subtitle D landfill owners in most states Long term care strategies include: Continuation of PCC and planning for corrective action; Perpetual maintenance of final cover system Reduced monitoring/limited final cover system replacement Complete replacement of final cover system (CA). It is unclear whether or not States will continue regulatory oversight of closed sites once PCC ends. SWANA and its Landfill Technical Division should play a leadership role in addressing the long-term care issue. 45