Application of In-Situ Porewater Technology at a Contaminated Sediment Site to Assess Recontamination. Impacted Groundwater

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1 Application of In-Situ Porewater Technology at a Contaminated Sediment Site to Assess Recontamination from VOC and PCB Impacted Groundwater

2 Acknowledgment of Authors AmyMarie Accardi-Dey, Len Warner, Ed Dudek, and Ken Goldstein The Louis Berger Group, Inc. Philip M. Gschwend& John MacFarlane Massachusetts Institute of Technology Coreen Hamilton & Georgina Brooks AXYS Analytical Services, Ltd Mark Austin USEPA Region 2 Ken Maas & Amy Darpinian USACE Kansas City District

3 Site Background and Things to Know Superfund Site: 8-mile stream with PCB and VOC contaminated sediments and surface water Wadable freshwater stream passes a former facility with a source area groundwater plume Groundwater head predicts that the stream is gaining near the former facility (RM6.1-RM6.6) Fractured bedrock exposed to the surface water. Sediment beds less than 30 cm thick VOC and PCB passive samplers were deployed to measure porewater and surface water

4 Lines of Evidence for Groundwater Discharge Measured elevation data indicate stream is gaining Surface water samples at 10 ug/l VOC next to former facility Total VOC in sediments next to former facility with no detections upstream

5 Lines of Evidence on Groundwater Discharge Shallow, turbulent surface water with detected VOC concentrations

6 Field Reconnaissance to Locate Groundwater Discharge Hydrodynamic Model Based on measured head data, model predicted groundwater discharge between RM Stream Flow Survey Ground-truth model and identify discharge points. Measured flow increase near RM6.6 Water Quality Survey Variations in conductivity and temperature adjacent to the former facility, where fractured bedrock is exposed

7 Rationale for Passive Samplers Represent the truly dissolved-phase Hydrophobic compounds require large volumes Time-integrated, colocated surface water and porewater VOC passive diffusion bags and PCB polyethylene strips selected because they allowed analyses with standard analytical methods.

8 Description of VOC Passive Sampler EON Products, Inc: polyethylene bag in mesh Bags housed in perforated PVC cylinders (30 cm) Bags deployed for two 2- week periods VOC samples were collected by inserting a discharge tube VOC analysis via Method 8260 Photograph credit: EON Products, Inc.

9 Description of VOC Passive Sampler PCB Sampler VOC Sampler Photograph credit: EON Products, Inc. Photograph credit: EON Products, Inc.

10 4500 Porewater Total VOC Concentration (ug/l) PorewaterTotal VOC not detected upstream or downstream Near former facility, porewatertotal VOC reached maximum Consistent VOC trends in two sampling events Consistent with field reconnaissance Porewater in Passive Samplers Total VOC Deployment 1 Total VOC Deployment River Mile

11 Description of PCB Passive Sampler Water Column Water Column Water-Sediment interface Water-Sediment interface Polyethylene: 5 cm wide by 50 cm long (exposed) or 22 cm long (exposed) by 25 µm thick Porewater PCB partitions into polyethylene sheet (represented by diagonal lines) Sediment Passive samplers prepared by Dr. Philip M. Gschwend s laboratory at MIT.

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13 Description of PCB Passive Sampler Porewater 0-5 cm Interval Surface Water Porewater

14 Description of PCB Passive Sampler Caqueous Cpolyethylene Kpartition coefficient Measured in laboratory by AXYS Analytical via Method 1668 to provide recovery-corrected concentrations Reported in literature or estimated with octanol/water partitioning coefficient Performance Recovery Compounds (PRCs) shortened deployments. Using MIT mass transfer model and knowing the fraction of PRClost, correct C polyethylene to equilibrium concentration.

15 Why This Program is Unique Calculated Total PCB by estimating concentration of each PCB congener Multiple PRCsprovide flexibility in the model to estimate fraction of PRCloss in different media 30-day deployment was not long enough to reach equilibrium for heavy PCB congeners Analytical challenges to report high level PCB concentrations without diluting PRC signal

16 Porewater in Passive Samplers Total VOC Deployment 1 Total VOC Deployment 2 Total PCB (30-day) 800 Two PCB porewater points coincide with VOC Porewater Total PCB Conc centration (ng/l) Porewater Total PCB due to sediment partitioning Porewater Total PCB coincides with Total VOC porewater (and groundwater discharge) Total PCB and Total VOC in porewater not detected upstream Porewater Total VOC Conc centration (ug/l) River Mile

17 Surface and Porewater in Passive Samplers Total VOC Deployment 1 (porewater) Total VOC Deployment 2 (porewater) Total PCB (30-day, surface water) Surface Water Total PCB Co oncentration (ng/l) Total PCB in surface water jumps by factor of 15 from background with sustained load Most PCB loading to water column occurs between RM6.6-RM Porewater Total VOC Concentration (ug/l) River Mile 0

18 Summary of Results Stream flow and water quality results were used to place samplers VOC and PCB passive samplers provided time-integrated concentrations VOC and PCB data provided strong evidence that groundwater was discharging Multiple PRCsprovided flexibility to model fraction loss Internal data consistency between field measurements and two samplers Porewater and surface water data supported risk assessment and FS