Characterizing Contaminant Flux at the Groundwater- Surface Water Interface Robert Ford USEPA Office of Research and Development Cincinnati, OH Collaborators: Steve Acree, Randall Ross, Bob Lien Office of Research and Development National Risk Management Research Laboratory, Cincinnati, OH USEPA Ground Water Forum Meeting, August 8, 2019
Disclaimer The findings and conclusions in this presentation have not been formally disseminated by the U.S. EPA and should not be construed to represent any agency determination or policy. 1 SHC 3.61.1 Contaminated Sites - Technical Support
Plan for Presentation • Context for evaluating water and contaminant flux from upland groundwater to downgradient surface water bodies (CSM) • Assessing hydraulic pathway from groundwater to surface water • Assessing factors controlling contaminant flux to surface water 2 SHC 3.61.1 Contaminated Sites - Technical Support
Conceptual Site Model Understand Interaction Between GW & SW • Water flux of GW and SW at interface will govern processes controlling contaminant fate • Dominant chemical processes will be governed by the mass of contaminant and reactive constituents delivered to and mixed at the interface • Net result of processes will likely vary in time (seasonal) and space (geology) 3 SHC 3.61.1 Contaminated Sites - Technical Support
Conceptual Site Model 4 SHC 3.61.1 Contaminated Sites - Technical Support
Conceptual Site Model Effective CSMs - Site Hydrology Issues • Hydraulic connection between contaminated GW and surface water body ‒ Does it exist? ‒ If so, is it continuous or episodic? ‒ When connected, does the direction of water exchange vary? • Questions need to be addressed to understand timing and location of contaminant discharge 5 SHC 3.61.1 Contaminated Sites - Technical Support
Conceptual Site Model • Site topography and stream morphology influence GW flow Stream n o i t GW Potentiometric Surface direction and magnitude a v e l • May need to E Aquifer characterize this spatial variability relative to GW plume dimension e d u t i • GW is not a static t a L system, but may respond more slowly to Longitude changes in water budget (continuous logging) 6 SHC 3.61.1 Contaminated Sites - Technical Support
Conceptual Site Model • An effective CSM depends on understanding contaminant transport from source area(s) to SW and dynamics at GW-SW interface • Contaminant non-detects that occur along some assumed flow path could mean two things: ‒ Contaminated GW does not reach SW ‒ Monitoring location is not in the flow path • Hydrologic & chemical measurements across the GW-SW interface bridge upland GW-to-SW transport pathway 7 SHC 3.61.1 Contaminated Sites - Technical Support
Assessing Hydrology • Site topography and stream morphology influence GW flow direction and magnitude adjacent to surface Recharge water body Discharge • Characterizing local flow field across GW-SW interface important for understanding dynamic processes governing water exchange & contaminant flux 8 SHC 3.61.1 Contaminated Sites - Technical Support
Assessing Hydrology • Hand-Deployed Devices ‒ Piezometer (P) ‒ Piezometer-Stilling Well (PS) Pm ‒ Temperature Profiler (TP) PS TP ‒ Permeameter (Pm) PS • Provide for assessment of the P direction and magnitude of P water exchange • Logging sensors allow assessment of variability over time 9 SHC 3.61.1 Contaminated Sites - Technical Support
Assessing Hydrology PS P TP TP PS Installation of Temperature Piezometer-Stilling Well Profile & Temperature Profiler Measurements Vertical Gradient Piezometer-Stilling Well 10 SHC 3.61.1 Contaminated Sites - Technical Support
Assessing Hydrology Develop Integrated Knowledge of GW-SW Interface • Localized monitoring network used to understand dynamics of flow system with time (seasonal) ‒ Horizontal gradient ‒ Vertical gradient ‒ Horizontal/vertical water flux • Basis for comprehending processes controlling contaminant flux and fate at GW-SW interface • Baseline analysis of system provides the basis for interpreting whether upgradient remedial actions are performing as desired 11 SHC 3.61.1 Contaminated Sites - Technical Support
Factors Affecting Contaminant Transport Inorganic Contaminant Properties & Mass Flux • Contaminant properties influence types of processes active in controlling fate (adsorption, precipitation, chemical speciation) • GW-SW interface is typically a zone with major changes in chemistry over distance due to mixing of reactive constituents delivered by GW and SW • Contaminants with chemical fate sensitive to changes in pH and redox may show changing patterns with season • Contaminants sequestered in sediments may become a secondary source of contaminant flux to SW 12 SHC 3.61.1 Contaminated Sites - Technical Support
Factors Affecting Contaminant Transport Reduced GW Plume • SW body with varying water depth in which oxygen reaches sediments in shallow locations but not deep • Oxidation & attenuation of Fe and As in sediments for shallow depths • Unhindered transport of As into SW for deeper depths 13 SHC 3.61.1 Contaminated Sites - Technical Support
Case Study N • Arsenic plume flowing from landfill toward cove • Nested piezometers used to evaluate magnitude & distribution of arsenic flux 14 SHC 3.61.1 Contaminated Sites - Technical Support EPA-600-R-09-063
Case Study Picture at central Picture of cove from north shore cove from boat next to contaminated seepage area April 2007 April 2007 15 SHC 3.61.1 Contaminated Sites - Technical Support
Case Study What influences SW concentrations? • Sediment arsenic concentrations variable 218 MC SW02B SW04 within cove – correlate 216 with iron 214 Contaminated Sediment • PZ5 location shows RCTW 4 RCTW 9 PZ13 212 9 sustained discharge PZ5 210 9 with plume chemistry RCTW 10 208 signature in deep SW 192215 192220 192225 192230 192235 GW Discharge • PZ13 in location of low High As, Fe, K Low DO discharge & no plume chemistry signature in Sediment Recycling High As, Fe – Low K deep SW Variable DO 16 SHC 3.61.1 Contaminated Sites - Technical Support EPA-600-R-09-063
Case Study Upland GW Median Flux Reduction Factors Flow 2.9 Barium 7.6 Arsenic 4.3 Ammonium 12.8 N 0.20 150 Barrier Wall 125 0.16 100 0.12 75 0.08 50 0.04 25 0.00 0 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Calendar Year Groundwater Flux, m / d GW Arsenic Flux, mg / d-m 2 Measured Interpolated 17 SHC 3.61.1 Contaminated Sites - Technical Support
Case Study GW-SW Middle of Cove ( June - August ) 20 Calculated Seepage Flux (cm/d) Pre-Installation ( 2008 ) Interface Post-Installation ( 2014 ) Sediment Upland GW Flux 15 Temperature Profile 10 Method 5 0 170 180 190 200 210 220 230 240 Calendar Day 25 Comparison GW Flux Water Flux, cm/d Seepage Flux 20 over entire 15 monitoring 10 period… 5 0 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 Calendar Year 18 SHC 3.61.1 Contaminated Sites - Technical Support
Case Study Interpolated GW Arsenic Flux, mg / d-m 2 Measured Cove Arsenic Flux, mg / d-m 2 150 125 100 75 50 25 0 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Calendar Year 19 SHC 3.61.1 Contaminated Sites - Technical Support
Case Study BEFORE Outcome • GW plume diverted away from cove by hydraulic barrier • Performance metric of GW contaminant flux reduction was realized and could be assessed in multiple ways AFTER • Episodic exceedances of AWQC (As) during late Summer / early Fall, but… • Spring fish nest building observed immediately after remedy and continues (2014- 2018) 20 SHC 3.61.1 Contaminated Sites - Technical Support
Closing Remarks • Methods to assess GW flow and seepage flux are relatively easy to implement and provide flexibility to monitor the GW-SW interface • Knowledge of water flux dynamics improves understanding of processes controlling contaminant fate • Comprehension of baseline contaminant flux dynamics across the GW-SW interface are critical to assessing response to upland remediation 21 SHC 3.61.1 Contaminated Sites - Technical Support
Acknowledgements Engineering Technical Support Center John McKernan, mckernan.john@eda.gov Ed Barth (Acting), barth.edwin@epa.gov Groundwater Technical Support Center David Burden, burden.david@epa.gov EPA Region 1 – Carol Keating, Bill Brandon, Ginny Lombardo, Jerry Keefe, Dan Boudreau, Tim Bridges, Rick Sugatt, David Chaffin (State of Massachusetts) Workbook Beta Testing – Region 1 (Bill Brandon, Marcel Belaval, Jan Szaro), Region 4 (Richard Hall, Becky Allenbach), Region 7 (Kurt Limesand, Robert Weber), Region 10 (Lee Thomas, Kira Lynch, Bruce Duncan, Piper Peterson, Ted Repasky), Henning Larsen and Erin McDonnell (State of Oregon) EPA ORD – Jonathon Ricketts, Patrick Clark (retired!), Kirk Scheckel, Todd Luxton, Mark White, Lynda Callaway, Cherri Adair, Barbara Butler, Alice Gilliland US Army – Robert Simeone Don Rosenberry (USGS – Lakewood, CO) – verification studies at Shingobee Headwaters Aquatic Ecosystems Project 22 SHC 3.61.1 Contaminated Sites - Technical Support
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