Update: Performance-Based System for PCC at MSW Landfills

Transcription

1 Update: Performance-Based System for PCC at MSW Landfills A Procedure for Long-Term Stewardship Under RCRA Subtitle D Mike Houlihan., P.E. GeoSyntec Consultants, Columbia MD ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

2 Presentation Agenda 1. Background 2. Project Description 3. Methodology Basis 4. Methodology Description lite 5. Examples 6. Summary and EPCC Process Rollout 2

3 1. Background Update: Performance-Based System for PCC ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

4 Problem Statement What Defines the End of Post Closure Care (PCC)? Subtitle D prescriptive term for PCC of 30-years is founded in Subtitle C According to 40 CFR (b), the length of the post-closure care period may be Increased (or decreased) by the Director of an approved State if the Director of an approved State determines that the lengthened (or reduced) period is necessary to protect human health and the environment. 4

5 Current USEPA PCC Model Site Closure Implement Post-Closure Care Program Post-Closure Care Period Has duration of Post-Closure Care been 30 years, or a shorter/longer period allowed/required by the Director? No Yes End Post-Closure Care 5

6 Who is Pushing for Regulatory Change to the Subtitle D PCC Period? USEPA Inspector General (2001): most of the state agencies in our sample had not developed a policy and process to determine whether post-closure care should be extended beyond 30 years, and there is no EPA guidance on determining the appropriate length of PCC. 6

7 What are States doing in the Absence of Federal Guidance? Known activity: IN, VA Internal Draft Guidance WI, CA, WA, NJ, NY, AZ, NV, IA, Canada Regulation, Guidance, and Workshops MA, MN Local municipalities looking at Very Long Term Care/beginning to evaluate 7

8 Public Pressure for Perpetual Care Grass Roots Recycling Network (GRRN) Peter Anderson, spokesman G. Fred Lee & Associates G. Fred Lee and Ann Jones-Lee, spokespersons Proposed Solutions: Waste Stabilization or organic waste exclusion Funding for perpetual care using a fully funded cash instrument with a moving window of 30-years PLUS a funded Trust Fund for a future failure Bioreactors at every landfill 8

9 Waste Stabilization (e.g., WDNR Proposal) Organic stabilization does not provide a solution to the problem of whether a site is a potential threat to human health and the environment Does not provide realistic endpoints Results of solids analysis will not be uniform Anaerobic sites will always have elevated ammonia Will not provide guidance on appropriate monitoring during PCC Does not provide for optimization during PCC 9

10 2. Project Description Update: Performance-Based System for PCC ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

11 EREF Project Team Project Team Team Experts EREF EREF (Funder) GeoSyntec (Project Management and and Staffing) Tech. Tech. Advisory Panel Panel Industry Regulators Researchers Industry (Technical Resources and and Data) Data) 11 Other Other Resources: ITRC ITRC ASTSWMO SWANA Industry Leaders State State Regulators Trade Trade Associations

12 EREF PCC Project Objectives Develop a Performance-Based System to Answer the Question: How does PCC end? Intent of the EREF EPCC Process is to: Define site-specific stewardship in terms of threat More effectively manage existing PCC funds Maintain consistency with current regulations Build consensus (ASTSWMO; USEPA; Owner/Op) promote a more wide-spread application of proactive landfill technologies (e.g. bioreactor, alt. caps) 12

13 EREF PCC Project Objectives (Cont d) Prime objective of the PCC project/process is to provide a systematic approach to define when a landfill does not pose a threat to HH&E Optimize level of activity and financial resources during PCC Allow regulatory PCC to end The process is not designed to predict a total duration of PCC at this time. Intended for use at Subtitle D landfills only. 13

14 3. Methodology Basis Update: Performance-Based System for PCC ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

15 Subtitle D Systems Approach to Post- Closure Care (40 CFR ) 1. LCRS Operation and Maintenance 4. Cap Maintenance And Monitoring Gas Wells Gas Collection System 2. Gas Migration Control/Monitoring Leachate Recirculation Primary LCS and Secondary (if present) Liner System Gas Probes 3. Groundwater Monitoring 15 Other Factors: Surface Water Monitoring Perimeter Security Grounds Maintenance Groundwater Monitor Wells

16 Functional Stability - 16

17 Technical Basis Five Elements 1. Landfill source (i.e., leachate and landfill gas) can be characterized 2. Trends in concentrations and quantities at the source can be predicted and defined 3. The release of constituents can be evaluated for potential impacts to human health and the environment. 4. Changes to, or ending, PCC can be justified based on the outcome of these evaluations 5. We can monitor to confirm our predictions prior to going down a path of no return be conservative. 17

18 4. Methodology Description Update: Performance-Based System for PCC ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

19 Methodology Description The EPCC Methodology requires the Owner/Operator to: 1. Quantify source characteristics 2. Define trend of source characteristics over time 3. Evaluate future threat posed to human health and the environment by the source - and justify PCC changes on the outcome of this evaluation 4. Monitor to confirm evaluations or predictions 19

20 Master Diagram for EPCC Model M1 Start Leachate Module Figure 3 End-Use Strategy Evaluate Alternatives and Characterize / Define End-Use for WMU Data Requirements & Prerequisites Figure 2 M2 M3 Gas Module Figure 4 Prerequisite Modules M4 M5 Groundwater Module Figure 5 M6 Post-Closure Care Modules Cap Module Figure 6 M7 Final Outcome M8 20

21 Evaluation Philosophy: Overview 1. Can you evaluate change to PCC facility or activity? 2. Evaluate change. 3. Make change. 4. Monitor impacts of change. 5. Module completed. 21

22 Evaluation Philosophy: Details POST-CLOSURE CARE MAINTENANCE AND/OR MONITORING POST-CLOSURE CARE SURVEILLANCE MONITORING TAKE NECESSARY ACTION Undo Modification (if Necessary) and Re-define Approach High Trigger Failure High Trigger Failure Start Define Approach and Perform Evaluation(s) Acceptable? Yes Apply Modification Confirmation Monitoring Completed? Yes Surveillance Monitoring Completed? No 1. & Low Trigger Failure Low Trigger Failure Can change be evaluated? (prior eval.) 2. Evaluate change 3. Make change 4. Monitor impacts of change POST-CLOSURE CARE WITHIN MODULE COMPLETED WITH RESPECT TO REGULATORY FRAMEWORK. OPERATOR MUST CONTINUE TO MEET END-USE OBLIGATIONS. Yes Move to Next Module Complete 22

23 Requirements for Ending PCC Duration of PCC is based on performance criteria (HH&E) Performance criteria are site specific Performance criteria for ending PCC are very well defined in the EPCC Approach: Leachate Management System Quality meets GWPSs (Subtitle D/EPA SW Technical Guidance) at Source or POC Monitoring has been performed long enough to have detected an impacting release Build-up of leachate head addressed Landfill Gas System Satisfied all applicable NSPS and other non-subtitle D Requirements Current and future gas migration does not represent a threat to HHE Groundwater Monitoring In Detection Monitoring Monitoring has been performed long enough to have detected an impacting release Final Cover Cap predicated on other modules requirements Containment of waste addressed Provide post-regulatory custodial care as needed 23

24 Custodial Care The EREF EPCC reports defines the end of Regulatory PCC as Custodial Care, identified as: If the outcomes of all four modules indicate that no further regulatory PCC is needed for any module, then all PCC activities for the landfill in all modules have been completed. In this case, PCC under the jurisdiction of the State agency would be ended, although a de minimus level of care will invariably still be required for the cap and site. 24

25 M1 Start End-Use Strategy Evaluate Alternatives and Characterize / Define End-Use for WMU M2 Data Requirements & Prerequisites Figure 2 M3 Module Highlights Leachate Module Figure 3 Gas Module Figure 4 M4 M5 Groundwater Module Figure 5 M6 Cap Module Figure 6 M7 Final Outcome M8 25

26 Advantages of EPCC Approach Identifies and demonstrates how a site has reduced and eliminated threats to HH&E using technically defensible approaches Includes additional monitoring (i.e., confirmation and surveillance) as insurance for decisions that were based on analysis Develops a defensible approach to ending regulatory PCC Module-specific, independent outcomes Is consistent with requirements of the current regulations Provides a systematic approach to optimize PCC costs 26

27 5. Example Application Update: Performance-Based System for PCC ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

28 Example Site Landfill unit closed for 17 years, lined, soil/clay (not FML) cover, leachate and LFG management Currently in compliance with all permit conditions, relatively mild leachate, no impacts Low LFG generation, nearing end of NSPS obligations Assumed end-use is open field, controlled access Initially, check to see if any PCC element can be ended If not, see what we can do to optimize PCC program to more efficiently provide the level of care that is needed Leachate Module Groundwater Module 28

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30 6. Summary and EPCC Process Rollout Update: Performance-Based System for PCC ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

31 EPCC Approach Summary A Performance-Based Approach to Post-Closure Care Offers a Well-Defined Process For Managing Post-Closure Care Periods at Landfill Facilities Provides Purpose to, and Enhances Control Over, PCC Duration Encourages Owners to Focus Landfill Design and Operations on Reducing Post-Closure Risk and Impacts Quantifies Ability of Design to Protect the Environment Based on Conservative Technical Evaluation of Risks Basis in Existing Guidance and Regulations 31

32 Key Conclusion Regarding the Current 30- Year PCC Benchmark The EREF EPCC Report concludes: The extensive data review performed for this project indicates steady or decreasing trends in leachate quality and LFG generation occurring in much less than 30 years. Based on this information, the current 30-year benchmark period for PCC under Subtitle D appears reasonable for financial planning purposes. 32

33 Project Progress and Schedule Approach outline finalized 4Q 2002 Test Application of EPCC Model, Oct 2003 Nov 2004 Draft text and applications currently in process Final Draft Issued on 24 August 2005 Final review by experts (Ongoing now) Fine-tuning procedural steps (September and October) Final report to EREF 4Q

34 Implementation Preparation of Guidance Documents ITRC has included elements of the approach in the Technical/Regulatory Guidance document on Alternative Landfill Covers (Published in 2004) ITRC to produce initial EPCC-Approach Guidance Document in 2006 Approach to be considered in RCRA/CERCLA Final Cover Document USEPA considering including approach in revision to Subtitle D Guidance, but needs ASTSWMO support (this is different than the ITRC document and a very important EPCC need) Workshops ITRC in 2006, others planned General work towards getting regulatory endorsement, funding, and leadership 34

35 Thank You! Questions? If you have questions later, please call us: Mike Houlihan or Jeremy Morris (410) Or: Charles Johnson, Colorado DPH&E

36 M1 Start End-Use Strategy Evaluate Alternatives and Characterize / Define End-Use for WMU M2 Data Requirements & Prerequisites Figure 2 M3 Module Highlights Leachate Module Figure 3 Gas Module Figure 4 M4 M5 Groundwater Module Figure 5 M6 Cap Module Figure 6 M7 Final Outcome M8 36

37 37 First General Prerequisite: End-Use Setting Definition: The characteristics of the landfill and the surrounding area that determine potential of a threat Considerations: Characteristics include the proximity of receptors, the pathways of exposure, local regulations. The characteristics assumed for the EPCC evaluations must always be met after the change is made. If the characteristics change then the outcomes of the EPCC evaluations need to be reconsidered End-Use Setting Involves Defining: Post-closure use of the property Long-term use of properties that could be exposed to a future release Local regulations and obligations Deed restrictions (current or recommended) Engineering Controls

38 Second General Prerequisite - Obtain Data Landfill Design and Construction Details Site Development History Hydrogeology and Meteorology Characteristics of Receiving Waterbodies Surrounding Area Details (Receptor Info.) Leachate Quality Leachate Flow Rates Landfill Gas Quantity Landfill Gas Quality Groundwater Quality (Water Quality Indicators, VOC, metals, etc.) Surface-Water Quality Many sites already have the data Implementing the EREF Process requires proper planning and forward thinking 38

39 Step 1: Module-Specific Prerequisites Mohawk Valley, Up State NY Leachate BOD - East Tank Leachate BOD conc. (mg/l) BOD (mg/l) BOD load (g) 4 per. Mov. Avg. (BOD load (g)) Clear Trend Dec-88 May-90 Sep-91 Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Date 4.5E E E E E E E E E E+00 Leachate BOD load (g) Leachate Module: Steady or Decreasing Trend in Leachate Quality Landfill Gas Module Compliance with NSPS Obligations and other non-subtitle D regs Groundwater Module In Detection Monitoring Cap Module Other modules have been evaluated Landfill is closed 39

40 Step 2, Evaluate: Leachate Module Must have pre-determined strategy for 40 long-term leachate management and/or release scenarios at the landfill Step-Up Evaluation of Change Step 1: Compare source to standards Step 2: Evaluate dilution/attenuation at the point of compliance (POC) Step 3: Asses risk at the point of exposure (POE) Evaluate whether criteria are met (indication that potential threat is acceptable) Identify Opportunities to Optimize LCRS Operation Modify PCC Plan as Appropriate 2. Evaluate change.

41 Step 2, Evaluate: Landfill Gas Module Focuses on effect of eliminating/modifying existing level of LFG control on LFG migration, emissions, and odor Approach is based on screening criteria Primary: extent of modification proposed, site environs Secondary: more detailed screening Go to risk assessment if simple screening unsatisfactory Emphasis is on Confirmation Monitoring to demonstrate that change was appropriate Develop intensive, post-modification monitoring plan 2. Evaluate change. Duration and frequency based on predicted time-of travel for a LFG plume to move in vadose zone to migration-monitoring POC 41

42 Step 2, Evaluate: Groundwater Module Basis must be no existing impacts 2. Evaluate change. USEPA has good guidance for Assessment and Corr. Action Monitoring In the absence of impacts, GW Monitoring Duration must be as long as it takes hypothetical plume to migrate to POC: Lined site with LCRS: assume plume started migrating just before pass condition Unlined site: no liner to degrade, no leachate data - so assume plume started migrating at closure While LFG control remains active, GW must be monitored Identify Opportunities to Optimize Groundwater Monitoring Program Modify PCC Plan as Appropriate 42

43 Step 2, Evaluate: Cap Module Define Post-Closure Requirements 2. Evaluate change. Regulatory requirements Requirements established by outcomes of other modules Performance requirements Evaluate compliance with Cap Post-Closure requirements Identify Opportunities to Optimize Cap Maintenance and Monitoring Modify PCC Plan as Appropriate 43

44 Step 3: Make Change Change existing system to match system evaluated in Step 2 Implement changes in PCC operation and maintenance Implement changes in PCC monitoring program 44

45 Step 4: Monitoring 1. Confirmation Monitoring: Monitoring to confirm that a change produced the predicted outcome: Indicators of release (leachate, gas) or containment (cap) Completion of CM leads to SM, during which no maintenance is required other than Custodial Care (i.e., PCC may be ended). Otherwise, continue at new level of PCC. 2. Surveillance Monitoring: Monitoring only for an extended period after ending PCC for a module to further validate the decision to end PCC: No maintenance may be specified Geometrically reducing frequency for monitoring 45

46 Step 5, Module Completed PCC Level 3 (Post-Closure Care Completed): All PCC monitoring and maintenance has been eliminated (i.e., the Surveillance Monitoring Program has been completed) and PCC may be certified completed. If all modules achieve PCC Level 3 status, then only de minimus custodial care of the cap is required WMU can be considered functionally stable in the absence of PCC. 46

47 Step 5, Other Outcomes PCC Level 1 (Continue Regulated Post-Closure Care): Significant PCC systems and/or activities are still required because the WMU could potentially cause impacts to HH&E if PCC were to cease. Optimize Proactive operations (in-situ / ex-situ) PCC Level 2 (Surveillance Monitoring): Only monitoring is required (i.e., potential source impact controls have been eliminated, and no maintenance is scheduled. 47

48 Advantages of EPCC Approach Identifies and demonstrates how a site has reduced and eliminated threats to HH&E using technically defensible approaches Includes additional monitoring (i.e., confirmation and surveillance) as insurance for decisions that were based on analysis Develops a defensible approach to ending regulatory PCC Module-specific, independent outcomes Is consistent with requirements of the current regulations Provides a systematic approach to optimize PCC costs 48

49 5. Example Application Update: Performance-Based System for PCC ASTSWMO State Solid Waste Managers Conference Phoenix, Arizona 13 September

50 Example Site Landfill unit closed for 17 years, lined, soil/clay (not FML) cover, leachate and LFG management Currently in compliance with all permit conditions, relatively mild leachate, no impacts Low LFG generation, nearing end of NSPS obligations Assumed end-use is open field, controlled access Initially, check to see if any PCC element can be ended If not, see what we can do to optimize PCC program to more efficiently provide the level of care that is needed Leachate Module Groundwater Module 50

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52 Evaluation Steps: This Site Satisfy Prerequisites. Collect Data, Confirm Trends, Define End Use 2. Evaluate Compliance of Changed PCC Program with Post-Closure Requirements. Can we end PCC Care of any module? If not, can changes be made that allow facility to meet still PCC requirements? 3. Make Change. Implement changes that evaluation shows should meet PCC requirements. 4. Monitor for Impacts of Change. Confirmation and/or Surveillance Monitoring. 5. Determine Outcome. If results of monitoring indicate Pass, then change is acceptable.

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54 Leachate Data Requirements and Availability at Site A Applicable Standard Number of Parameters Federal Groundwater Appendix I 62 MCLs 73 (41) Additional State Groundwater 15 Total Groundwater 118 Federal Surface Water 9 (4) Additional State Surface Water 7 (4) Total Surface Water (incl. MCLs) 83 TOTAL 126 Data Available at Site A

55 Leachate BOD 100,000 Sump #B1 Area A drain 10,000 1,000 BOD (mg/l) Oct-80 Oct-82 Oct-84 Oct-86 Oct-88 Oct-90 Oct-92 Oct-94 Oct-96 Oct-98 Oct-00 Oct-02 Oct-04 Date 55

56 Step 2: Evaluation of Ending PCC Component of Post-Closure Care (PCC) New Approach (i.e., Change ) to be Evaluated Evaluati on Approach Evaluation Outcome Leachate Collection and Recovery System (LCRS) End Leachate Management Check resulting potential for flux to groundwater Evaluate general slope stability impacts Determine dependence on cap hydraulic barrier Evaluation fails second tier due to presence of ammonia Owner didn t want to do Tier 3 (i.e., Risk Assessment) Change is Not Acceptable Landfill Gas Management System End Landfill Gas Management Evaluate Future LFG Generation Potential Evaluate potential for migration of LFG to structures or off-site Evaluate dependence of outcome on performance of the landfill cap LFG generation potential is very low. Even without passive gas vents, landfill gas migration problems are not expected. Low gas generation rate depends on performance of current cap system. Change is Acceptable Leachate impacts would have been detected from a release during operations, but current leachate quality exceeds standards (NH 4 ) LFG impacts would have been detected and quality does not exceed standards Change is not acceptable, but reducing monitoring frequency and list of parameters is appropriate Alternative design meets project PCC Regulatory and Performance Requirements. Outcomes of Leachate and LFG Modules depend on the cap limiting leachate generation to a certain level. Change is not acceptable LFG Module outcome depends on presence of cap Groundwater Monitoring System End Groundwater Monitoring. Evaluate characteristics of leachate source and evaluate time required for potential leachate impacts to have been detected at POC Evaluate characteristics of landfill gas source and evaluate time required for potential LFG impacts to have been detected at POC Cap System End Cap Maintenance and Monitoring Evaluate compliance with PCC Requirements: o Regulatory o Consistency with Other Module Outcomes o Performance

57 Step 2 (again): Evaluation of Modified PCC Would like to evaluate these changes to Current PCC: Passive leachate management No LFG management No GW Monitoring Change Cap to E/T for PC Use Evaluate anticipated performance of changed system Develop any needed changes to PCC Plan Develop Confirmation and Surveillance monitoring plans as needed Example results follow: 57

58 58 Leachate Module

59 Trend Analysis & Data Evaluation Purpose of the evaluations in this sub-module: Establish whether there exists a steady or downward trend in the pollution potential of leachate indicator parameter (BOD) under existing conditions at the WMU downward trend confirmed for both sumps at Site A Generate representative (statistical) current and maximum values for concentrations of regulated leachate constituents to be used in the evaluation process Verify consistency between composite and sump-specific data all data consistent (only two sumps) 59

60 Leachate Management Strategy Let s assume: No Migration Demonstration will not be successful Leachate will continue to be collected using the existing LCRS, thereafter gravity discharge/drainage No accumulation of leachate in landfill Cap properties will not be modified Direct contact with raw leachate will be prevented Current quantity of leachate (10,000 gal/day) must continue to be managed in some way 60

61 Future Leachate Management Strategies Two future leachate management strategies were evaluated: 1. Direct discharge of all leachate to surface water: Only pathway for leachate to groundwater is through leakage from the bottom liner. 2. Direct discharge of all leachate to groundwater. 61

62 Case 1: Leachate Discharge to Surface-Water POC Evaluation The State regulations for Site A allow for mixing and dilution prior to meeting surface water discharge standards Mass load to receiving stream is small: Ammonia-N = kg/day, BOD = 1-10 kg/day Required flow of receiving stream to achieve required dilution to meet regulatory standards for remaining 11 parameters is small, e.g.: BOD: req. flow = 0.1 cfs (standard = 37 mg/l monthly average) Ammonia: req. flow = 2.6 cfs (standard = 4.9 mg/l monthly av.) Antimony: req. flow = cfs (MCL = 6 ppb) 62 Alternatively, a passive treatment system for ammonia, BOD (e.g., constructed wetland system) could be designed. this would require some performance monitoring

63 Summary of Results (Case 1) Site A Category Surface Water Groundwater Total Parameters Missing Analytes 0 0 Starting Parameters All ND Pass Source Maximum - 11 Pass Source Current Pass POC Maximum - 11 Pass POC Current Remaining Parameters

64 Groundwater Evaluation POC Evaluation (simple DF calculation only): DF = Q GW Q + Q LEACHATE LEACHATE average potential leakage rate through single geomembrane liner assumed to be 1 gallon per acre per day (gpad). For a 27-acre cell, this equates to 27 gpd. DF = 380 (limited by very slow-moving GW) The only parameter not passing an evaluation at any level at this stage was ammonia. 64

65 Case 2: Leachate Discharge to Groundwater No need to evaluate, we know that direct discharge to groundwater will not be viable because: Source concentrations exceed standards for a number of parameters. It would have to be assumed that all leachate will migrate to the groundwater POC rather than just the 27 gpd of leachate that could leak from the base of the WMU (as evaluated for Case I). The derived DF would be roughly equal to one, because the volume of leachate in the DF expression would be as significant as the volume of groundwater. 65

66 66 Groundwater Module

67 Groundwater Monitoring Requirements Must continue monitoring GW while an active LFG control system is being operated From previous Case 1, GW monitoring for potential leachate impacts cannot be eliminated, but the analyte list can be significantly reduced/optimized Could GW monitoring frequency be optimized based on the time of travel for groundwater through the site (i.e., a high frequency of monitoring will not be useful where groundwater moves very slowly)? 67

68 Groundwater Monitoring Time of Travel and GW CM Condition Site A TOT MIN TOT MAX Frequency of GW CM Duration of GW CM 25 days 6 years 13 weeks 6 years The duration of GW CM is calculated from TOT MAX, the maximum time it would take leachate to travel from the most upstream sump to the POC. 68

69 GW Module Outcome Once ammonia can pass evaluation, the required remaining duration of GW CM at Site A would be 6 years. SM on geometrically reducing schedule would be required: Initial event = 13 weeks after completion of CM 6 months later 1 year later 2 years later 4 years later DONE Total CM + SM = 10 years NOTE: At sites with long TOT MAX, the most common course of action to reduce GW CM would be to relocate the groundwater POC closer to the WMU, thus eliminating some of the groundwater travel time upon which the GW CM duration is based. 69

70 Component of Post-Closure Care (PCC) New Approach (i.e., Change ) to be Evaluated Evaluation Approach Evaluation Outcome Leachate Collection and Recovery System (LCRS) Landfill Gas Management System Groundwater Monitoring System Cap System Treat Leachate Passively (Wetlands Leachate Treatment System). Discontinue Passive Landfill Gas Management. Eliminate Groundwater Monitoring. Convert Cap to Vegetated, ET Cap. Design passive system o Estimate discharge quality o Compare to discharge limitations (SPDES) o Develop O&M and Monitoring Plan Evaluate leachate generation potential o Check resulting potential for flux to groundwater o Evaluate General Slope Stability impacts o Determine dependence on cap hydraulic barrier Evaluate Future LFG Generation Potential Evaluate potential for migration of LFG to structures or off-site Evaluate dependence of outcome on performance of the landfill cap Evaluate characteristics of leachate source and evaluate time required for potential leachate impacts to have been detected at POC Evaluate characteristics of landfill gas source and evaluate time required for potential LFG impacts to have been detected at POC Design alternative cap. o Estimate infiltration through cap o Evaluate water balance o Evaluate stability under Maintained State Evaluate compliance with PCC Requirements: o Regulatory o Consistency with Other Module Outcomes o Performance Nearly all constituents meet discharge limitations pass DC evaluation Remaining pass only after treatment No stability or flux issues since system works by gravity flow Change is Acceptable System performance depends on cap limiting leachate generation rate LFG generation potential is very low. Even without passive gas vents, landfill gas migration problems are not expected. Low gas generation rate depends on performance of current cap system. Change is Acceptable Leachate impacts would have been detected from a release during operations, but current leachate quality exceeds standards (NH 4 ) LFG impacts would have been detected and quality does not exceed standards Change is not acceptable, but reducing monitoring frequency and list of parameters is appropriate Alternative design meets project PCC Regulatory and Performance Requirements. Outcomes of Leachate and LFG Modules depend on the cap limiting leachate generation to a certain level. Change is acceptable note that outcome of LCRS and LFG Modules depend on it. New CMMP required. Duration of PCC period likely a function of remaining degradation potential of LF and rate of decomposition.