This document summarizes a case study of installing an impervious cap at a former manufactured gas plant site along a river in Ann Arbor, Michigan to control residual non-aqueous phase liquid (NAPL) migration. The cap was constructed using AquaBlok, a composite particle material that can be coated with treatment materials. At the site, layers were placed including a gas transmission layer, low permeability AquaBlok layer, and cover layers to trap and isolate NAPL migrating from contaminated sediments. Monitoring showed the cap was effective at providing an isolation barrier and reducing contaminant releases from the river sediments.

1. April 2014
Authors: John A. Collins4, Gary Loveland3, Howard
Evans3, John Rice2, Katherine Vater2and Shayne A.
Wiesemann 1
1 DTE Energy
2 TRC Environmental
3 Terra Contracting Services, LLC
4 AquaBlok, Ltd.
Installation of an Impervious Cap for Control of
Residual NAPL Migration:
Construction Issues and Solutions

2. 2
Presentation Outline
I. Overview of Material Technology Utilized
II. The Problem – Ebullition – Shoreline Seeps
III. Case Study – DTE Energy Ann Arbor Site
IV. Summary/Q & A

3. powder coating AquaBlok “composite particle”
+
aggregate core
=
Key Technical Advantages:
¤ Efficient delivery of high-value
materials at low concentrations
¤ No field mixing or blending
¤ Low cost handling & installation
¤ Unique geotechnical attributes:
self-compacting; shear strength
¤ Highly versatile: custom-
formulate for project-specific need
Allows a particle to be uniformly coated with fine-grained (i.e. powdered) materials
For efficient/effective placement in both freshwater and saltwater environments
Variables:
¤ Coating composition:
- AquaGate™ for treatment;
- AquaBlok® for isolation/sealing
¤ Coating to aggregate ration
¤ Permeability:
1 x 10-2 to 5 x 10-9 cm/s
(dependent on composition)
¤ Particle size: -1/4” to -3/4”
Coating
Core
Overview of Technology

4. Low-Permeability for Sub-
Aqueous Capping & Lining
Applied through
standing water
or in the dry
MGP Sites
PAH / PCBs
Landfill Cap
Refinery/PAH Sites
Metals/DDT

5. 5
Demonstrating Compliance
in a Dynamic Environment
Split-core from Section A
(2.5 yrs after placement)
New sediment
Deposits
AquaBlok Clean Cap Layer
Discrete boundary
Contaminated Sediment

6. Permeable Materials for In-Situ
Treatment & Remediation Applications
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
0 20 40 60 80 100
Residence Time ( hrs )
Concentration(µg/L)
As
Cr
+Sorbster®+ORGANOCLAYAquaGate+PAC

7. not to scale
Organoclay Treatment Layer
Water
Column
Clean Backfill
Residual Contamination
Armoring Layer
Example: Use of Permeable
AquaGate+ORGANOCLAY
Layer to Protect from Sheen
Must Vary Thickness to
Provide for Adequate
Residence Time for Adsorption
AND Capacity
Must Have Adsorption
Capacity to Protect from Higher
Concentration Areas of an
Isolated Seep Zone
Granular Organoclay will Swell
and Reduce Permeability as
Oleophilic Clay Adsorbs NAPL
– Can Cause “Blinding-Off” of
Unused Adsorptive Capacity
Treatment of Groundwater Through
A Permeable Treatment Layer

8. Conceptual Model - Gas Carries Coal Tar from Sediment to
Water Surface (modified from McLinn & Stolzenburg, 2009)
The Problem: Ebullition – Shoreline Seeps

9. Conceptual Design - NAPL Trapping Cap
A sediment capping system made of geological materials (clay,
sand, gravel, boulders ) that can be used to capture NAPL
permanently and predictably as it migrates from sediments
* NAPL Trapping Cap was designed by TRC
Patent Nos: US 8,419,314 and US 8,651,768

10. 10
Site Location: U.S. EPA Region 5
MGP Impacted River – Ann Arbor, MI

11. 11
Overview of Site

12. 12
Overall Project Details

13. 13
Cap Cross-Section / Layers

14. Initial Survey and Removal Area
Significant Effort was placed on protection of the
river – a soil berm and boom system was employed

15. Removal of Impacted Sediments
15

16. AquaBlok - Bulk Transport and Loading

17. Placement of Gas Transmission Layer
– Formation of the Base of the Cap
17

18. AquaBlok Low Permeability Layer
18

19. Cover Layers & Armor
19

20. View of Cap Layers – As Placed
20

21. Cap Completion and Restoration
21

22. View of Site

23. 23
• All Natural Clay Material Provides Low Hydraulic Conductivity for
Effective Contaminant Isolation (Addresses Food Chain Uptake Issues)
• Serves as a Delivery System for a Wide Range of Treatment Materials
• Easy to Handle and Install
• Provides Ability to Perform Low Cost Post-Cap Monitoring
• Implementable in Connection with Either MNA or Dredge/Cap Strategy
• Highly Cost-Effective Alternative and Less Invasive than Dredging
Engineered Thin Capping Materials Provide
Remediation Alternative for Sub Aqueous Treatment
and Sequestration of Contaminants at MGP Sites
Summary – Q&A