AES Indiana — Technical Presentation (September 2025)
56 slides from AES Indiana's technical presentation, Sep 16, 2025
Slide 1: Harding Street Station Corrective Measures Assessment
1 Harding Street Station Corrective Measures Assessment Public meeting September 16, 2025
Slide 2: Agenda and Introductions
Agenda and Introductions Stewart Ramsay Managing Executive, Vanry and Associates 2
Slide 3: Agenda
Agenda Topic AESI Overview Presenter Brandi Davis-Handy, AESI President, AES Indiana AESI Harding Street Greg Ellis, AESI Director of Generation Environmental Pilar Cuadra, AESI Regulations Environmental Manager Harding Street CMA Steve Putrich, Haley & Aldrich Report Professional Engineer Summary a
Slide 4: Welcome and Overview
Welcome and Overview Brandi Davis-Handy President, AES Indiana 4
Slide 5: Accelerating the future of energy, together.
Accelerating the future of energy, together. Reliable Resilient Cost-Effective Stable Sustainable 5
Slide 6: AES Indiana Harding Street Station
AES Indiana Harding Street Station Greg Ellis Director of Generation, AES Indiana 6
Slide 7: Harding Street Station
Harding Street Station → Located in Indianapolis, IN on ~400 acres → Stopped coal use and coal combustion residuals (CCR) production in February 2016 → HSS began operation in 1931 → Units 5, 6 and 7 repowered on natural 7 gas in 2015 and 2016
Slide 8: Environmental regulations
Environmental regulations Pilar Cuadra Environmental Manager, AES Indiana 8
Slide 9: What are coal combustion residuals (CCR)?
What are coal combustion residuals (CCR)? → Coal Combustion Residuals (CCR) are byproducts generated from the combustion of coal from coal-fired power plants → CCR contains trace metal elements, generally called CCR constituents 9
Slide 10: 2015 CCR Federal Rule
2015 CCR Federal Rule Rule overview – General requirements Establish groundwater Initiate and complete closure Publish compliance data and monitoring systems to of CCR units within a specific information to a public determine if there are impacts timeframe. website. to the groundwater above groundwa
Slide 11: 2015 CCR Federal Rule
2015 CCR Federal Rule Rule overview – Implementation Detection Assessment Corrective Measures → 8 Initial Events → Twice per Year → Assessment → Twice per Year → Nature & Extent → Selection of Remedy → Implementation 11
Slide 12: Harding Street CMA report
Harding Street CMA report Steve Putrich Engineer, Haley and Aldrich 12
Slide 13: Technical Agenda
Technical Agenda CCR Groundwater Program, Monitoring Results 1 and Groundwater Risk Evaluation Outcomes Corrective Measures Assessment (CMA): 2 Background & Process 3 CMA Analysis and Results 4 Conclusion & Next Steps 13
Slide 14: CCR Groundwater Program, Monitoring Results and Groundwater Risk Evaluation Outcomes
CCR Groundwater Program, Monitoring Results and Groundwater Risk Evaluation Outcomes
Slide 15: HSS Site Features
HSS Site Features • The HSS Ash Pond System includes Ponds 1, 2A, 2B, and 3 as well as Former Ponds 2 and 4. Together, these ponds cover approx. 72 acres. • Ponds 1, 2A, 2B, and 3 are CCR surface S. HARDING ST. POND 1 POND 3 impoundments subject to the CCR Rule. FORMER POND 2 2A 2B Former Ponds 2 an
Slide 16: Overview of the CCR Groundwater Monitoring Program
Overview of the CCR Groundwater Monitoring Program Groundwater Monitoring Background Monitoring Detection Monitoring Assessment Monitoring 16
Slide 17: CCR Compliance Groundwater Monitoring Wells
CCR Compliance Groundwater Monitoring Wells • AESI has been monitoring groundwater at HSS in compliance with the CCR Rule since 2016. • CCR monitoring wells include a total of 15 well locations installed immediately upgradient and at the downgradient edge of S. HARDING ST. POND 1 POND 3 the CCR unit
Slide 18: CCR Rule Groundwater Monitoring Program & CMA Development
CCR Rule Groundwater Monitoring Program & CMA Development (40 CFR 257) Groundwater Exceedance of GWPS Monitoring Triggers Nature & Extent (N&E) Investigations and Corrective Measures Assessment Background Monitoring Detection Nature & Extent (N&E) Monitoring Investigations Assessment Monitoring GWPS
Slide 19: Nature & Extent Groundwater Monitoring Wells
Nature & Extent (N&E) Groundwater Monitoring Wells • Nature & Extent (N&E) monitoring wells include a total of 23 well locations installed south and west of the Ash Pond System. S. HARDING ST. POND 1 POND 3 FORMER 2A • The N&E wells are used to determine POND 2 2B the nature (i.e., to measure the CC
Slide 20: Generalized Groundwater Flow
Generalized Groundwater Flow • Groundwater levels are generally higher in the spring and lower in the fall. • While regional groundwater flow is typically toward the White River, S. HARDING ST. POND 1 2A POND 3 ongoing dewatering operations at the FORMER POND 2 2B quarry direct groundwater flow sout
Slide 21: Findings from N&E Investigation
Findings from N&E Investigation • The horizontal extent of groundwater impacts APPROX. LIMITS OF covers approx. 235 acres which encompasses GROUNDWATER the Ash Pond System and extends offsite on IMPACTS ABOVE GWPS the property to the south. • Ongoing dewatering operations at the quarry induce steep
Slide 22: CCR Constituent: Arsenic
CCR Constituent: Arsenic Arsenic N&E Summary • Arsenic is one of three (3) constituents above the Groundwater Protection Standard (GWPS). • Arsenic is the least mobile of the three S. HARDING ST. POND 1 POND 3 (3) constituents identified in this group. 2A • For that reason, arsenic concentrations FO
Slide 23: CCR Constituent: Lithium
CCR Constituent: Lithium Lithium N&E Summary • Lithium is relatively mobile in the environment and has been detected at concentrations above the Groundwater Protection Standard (GWPS) in each of the three flow S. HARDING ST. POND 1 POND 3 FORMER 2A zones, primarily south of the Ash POND 2 2B Pond Sy
Slide 24: CCR Constituent: Molybdenum
CCR Constituent: Molybdenum Molybdenum N&E Summary • Like Lithium, Molybdenum is relatively mobile in the environment and has been detected at concentrations above the Groundwater Protection Standard S. HARDING ST. POND 1 (GWPS) in each of the three flow POND 3 FORMER 2A zones, primarily south of th
Slide 25: Implications of N&E Findings
Implications of N&E Findings • Although groundwater results indicate levels above drinking water standards APPROX. LIMITS OF GROUNDWATER for arsenic, lithium, and molybdenum, IMPACTS ABOVE GWPS there is no use of groundwater for drinking water on or downgradient of the HSS site. S. HARDING ST. POND
Slide 26: Risk Evaluation Summary
Risk Evaluation Summary • What work was performed? – Reviewed the analytical data at the Site and Site vicinity using EPA tools; – Identified the pathways by which people and the environment could potentially come in contact with groundwater; – Evaluated if the pathways could cause an adverse impact
Slide 27: Corrective Measures Assessment (CMA): Background & Process
Corrective Measures Assessment (CMA): Background & Process
Slide 28: What is a Corrective Measures Assessment (CMA)?
What is a Corrective Measures Assessment (CMA)? • When levels of constituents in groundwater are found to be above the groundwater protection standards, the CCR Rule calls for corrective measures to be evaluated. • The Corrective Measures Assessment evaluates potential corrective measures that can b
Slide 29: Corrective Measures Assessment Process
CCR Rule Groundwater Monitoring Program & CMA Development (40 CFR 257) Corrective Measures Assessment Process Exceedance of GWPS Triggers N&E Investigations and Assemble List of Corrective Measures Viable Remedial Assessment Options Screen remedial options with CCR N&E CMA Rule Criteria Investigatio
Slide 30: Background - Why was the CMA updated?
Background - Why was the CMA updated? • The CMA and associated report were updated to account for the supplemental information collected since 2019. That supplemental information is sourced from: – additional monitoring data and groundwater N&E investigations, – conceptual site model development and
Slide 31: Groundwater Corrective Measures/Remedy Diagram
Groundwater Corrective Measures/Remedy Diagram Source Control Groundwater (GW) Measures Treatment Measures Remedial Source Control will minimize Groundwater Treatment will Alternatives infiltration into the CCR address areas of impacted material and restrict groundwater to reduce potential for leach
Slide 32: Source Control (Closure) Measures
Source Control (Closure) Measures Source Control will minimize infiltration into the CCR material and restrict potential for leaching Hybrid Closure in Place Closure in Place with Slurry Wall Closure by Removal • Removal of CCR in potential contact • Regrade CCR within the pond(s) • Excavate CCR and
Slide 33: Source Control Measure: Hybrid Closure in Place
Ash Pond System Source Control Measure Hybrid Closure in Place Hybrid CIP Hybrid CIP Source control measures to address ponded CCR material are considered POND 1 individually based on each pond’s PONDSPOND 1, 3 2A, 2B, 3 2A unique characteristics. FORMER FORMER POND 2 2B POND 2 Hybrid Closure in Pla
Slide 34: Source Control Measure: Closure in Place with Slurry Wall
Ash Pond System Source Control Measure Closure in Place with Slurry Wall CIP with Source control measures to address Slurry Wall ponded CCR material are considered POND 1 individually based on each pond’s 2A POND 3 unique characteristics. FORMER FORMER POND 2 2B POND 2 CIP with Closure in Place (CIP
Slide 35: Source Control Measure: Closure by Removal
Ash Pond System Source Control Measure Closure by Removal CBR Source control measures to address CBR ponded CCR material are considered PONDS 1, individually based on each pond’s FORMER FORMER 2A, 2B, 3 unique characteristics. POND 2 POND 2 Closure by Removal (CBR): FORMER FORMER CBR • Considered fo
Slide 36: Ash Pond System Source Control Measures
Ash Pond System Source Control Measures Source control measures to address Hybrid CIP Hybrid CIP ponded CCR material are considered CIP with CBR individually based on each pond’s Slurry Wall unique characteristics. CBR PONDS 1, 2A, 2B, 3 FORMER FORMER POND 2 POND 2 Hybrid Closure in Place (Hybrid CI
Slide 37: Groundwater Treatment Measures
Groundwater Treatment Measures Ex-situ (above ground) Hydraulic Controls In-situ (treatment in the ground) • Pump • Monitored Natural Attenuation • Pump & Treat (e.g., reverse osmosis) • Redox Manipulation (e.g., reagent injection, air sparging) • Water Infiltration (e.g., injection wells) Biodegrad
Slide 38: Impacted Groundwater Areas of Interest (AOIs)
Impacted Groundwater Areas of Interest (AOIs) APPROX. LIMITS OF Areas of Interest (AOIs) are used to GROUNDWATER designate portions of the impacted IMPACTS ABOVE GWPS groundwater based on the CCR constituents above the GWPS [Arsenic, AOI D Lithium, Molybdenum] and the POND 1 location on the site. AO
Slide 39: Summary of Remedial Alternatives
Summary of Remedial Alternatives AOI = Area of interest CIP = Closure in place CBR = Closure by removal CBR Hybrid CIP with Capping, Groundwater Groundwater MNA = CBR Monitored natural attenuation CIP with Slurry Wall, Pumping and Pumping, 1A Groundwater Pumping, in-ground in-ground in-ground Treatm
Slide 40: Summary of Remedial Alternatives
Summary of Remedial Alternatives Source Control Hybrid Hybrid CIP Hybrid CIP with Capping, Groundwater Groundwater CIP CIP with Slurry Wall, Pumping and Pumping, 1A Groundwater Pumping, in-ground in-ground CIP w/ in-ground Treatment, Treatment Slurry and MNA CIP Treatment Wall Slurry Wall and MNA Hy
Slide 41: Summary of Remedial Alternatives
Summary of Remedial Alternatives Source Control Hybrid Hybrid CIP Hybrid CIP with Capping, Groundwater Groundwater CIP CIP with Slurry Wall, Pumping and Pumping, in- 1A Groundwater Treatment, in-ground ground CIP w/ in-ground Treatment, Treatment Slurry and MNA CIP Treatment Wall Slurry Wall and MNA
Slide 42: Summary of Remedial Alternatives
Summary of Remedial Alternatives Source Control Hybrid CIP w/ CIP Hybrid CIP with Capping, Groundwater Groundwater Slurry Wall CIP with Slurry Wall, Pumping and Pumping, 1A Groundwater Pumping, in-ground in-ground CIP w/ in-ground Treatment and Treatment Slurry MNA CIP Treatment Wall Slurry Wall and
Slide 43: Summary of Remedial Alternatives
Summary of Remedial Alternatives Source Control CBR Hybrid CIP with Capping, Groundwater Groundwater CBR CIP with Slurry Wall, Pumping and Pumping, 1A Groundwater Pumping, in-ground in-ground in-ground Treatment and CBR Treatment Treatment MNA CIP Slurry Wall and MNA Hybrid Hybrid with MNA Hybrid CI
Slide 44: Summary of Remedial Alternatives
Summary of Remedial Alternatives Source Control CBR Hybrid CIP with Capping, Groundwater Groundwater CBR CIP with Slurry Wall, Pumping and Pumping, 1A Groundwater Pumping, in-ground in-ground in-ground Treatment and CBR Treatment Treatment MNA CIP Slurry Wall and MNA Hybrid Hybrid with MNA Hybrid CI
Slide 45: Summary of Remedial Alternatives
Summary of Remedial Alternatives CBR Hybrid CIP with Capping, Groundwater Groundwater CBR CIP with Slurry Wall, Pumping and Pumping, 1A Groundwater Pumping, in-ground in-ground in-ground Treatment CBR Treatment Treatment and MNA CIP Slurry Wall and MNA Hybrid Hybrid with MNA Hybrid CIP with Capping,
Slide 46: Corrective Measures Assessment (CMA): Analysis and Results
Corrective Measures Assessment (CMA): Analysis and Results
Slide 47: How are the Remedial Alternatives Evaluated? Threshold Criteria
How are the Remedial Alternatives Evaluated? Threshold Criteria (Minimum Requirements) Remedies must: (1) Be protective of human health and the environment; STEP 1: Potential (2) Attain the groundwater protection standard as specified remedial alternatives pursuant to §257.95(h); are then screened a
Slide 48: How are the Remedial Alternatives Evaluated? Threshold Criteria
How are the Remedial Alternatives Evaluated? Threshold Criteria (Minimum Requirements) Remedies must: (1) Be protective of human health and the environment; STEP 1: Potential (2) Attain the groundwater protection standard as specified All five of the remedial alternatives pursuant to §257.95(h); Thr
Slide 49: How are Remedial Alternatives Evaluated? Balancing Criteria
How are Remedial Alternatives Evaluated? Balancing Criteria (Effectiveness and Performance) (1) The long- and short-term effectiveness and STEP 2: Once these protectiveness of the potential remedy(s), along remedial alternatives with the degree of certainty that the remedy will are demonstrated to p
Slide 50: How are Remedial Alternatives Evaluated? Balancing Criteria
How are Remedial Alternatives Evaluated? Balancing Criteria (Effectiveness and Performance) (1) The long- and short-term effectiveness and STEP 2: Once these protectiveness of the potential remedy(s), along remedial The fivealternatives Remedial with the degree of certainty that the remedy will are
Slide 51: Summary of CMA Balancing Criteria Analysis
Summary of CMA Balancing Criteria Analysis Balancing Criteria #1 - The long- and short-term effectiveness and protectiveness of the remedy(s), along with the degree of certainty that the remedy will prove successful. • All alternatives are effective and protective of human health and the environment
Slide 52: Summary of CMA Balancing Criteria Analysis
Summary of CMA Balancing Criteria Analysis Balancing Criteria #2 - The effectiveness of the remedy in controlling the source to reduce further releases. • Hybrid Closure in Place, Closure in Place with a slurry wall, and Closure by Removal all effectively minimize the risk of further releases either
Slide 53: Conclusion & Next Steps
Conclusion & Next Steps HACBRICH
Slide 54: What is the process to move from completion of the CMA to Selection of Remedy?
What is the process to move from completion of the CMA to Selection of Remedy? Selection of Remedy Process Selection of Remedy 54
Slide 55: Next steps
Next steps The comment period Comments can be Public comments for the CMA will be submitted via the will be considered, open for 30 days. public meeting per the CCR Rule, in website. the Selection of Remedy process. https://www.aesindiana.com/ harding-street-cma-meeting 55
Slide 56: Comments and Discussion
56 Comments and Discussion https://www.aesindiana.com/harding-street-cma-meeting September 16, 2025
AES Indiana — Technical Presentation (September 2025) on 6ix