Swansboro Dry Cleaner
Project Year
2012-2015
Project Duration
3 years (Multi-phase)
Contaminants of Concern
Remediation Technologies Used
- • Enhanced Reductive Dechlorination
- • Biostimulation & Bioaugmentation
- • Multi-Phase Treatment
- • Adaptive Management
Key Results
- ✓Over 80% source area PCE reduction
- ✓Plume-wide contaminant mass reduction
- ✓Complete dechlorination in multiple zones
- ✓Sustained biological activity
- ✓Significant plume contraction
Target Contaminants
Site Background
The Swansboro site is a former dry cleaning facility where decades of PCE usage resulted in extensive soil and groundwater contamination. The site presented unique challenges due to complex geology and a large dissolved-phase contaminant plume extending downgradient.
The contamination required a comprehensive, multi-phase approach to address both source areas and the extensive plume.
Remediation Strategy
IET designed a multi-phase remediation approach combining several treatment technologies:
- Source zone treatment with enhanced reductive dechlorination
- Plume treatment using biostimulation and bioaugmentation
- Multiple injection events over several years
- Adaptive management based on monitoring results
- Strategic targeting of high-concentration areas
This phased approach allowed for optimization of treatment effectiveness while managing project costs.
Implementation
The remediation program was implemented in multiple phases over several years. Each phase included:
- Pre-injection characterization and monitoring
- Targeted injection of treatment reagents
- Post-injection monitoring to assess effectiveness
- Adjustment of subsequent phases based on results
IET's field team maintained close coordination with the client throughout the multi-year program.
Results
The multi-phase remediation approach achieved progressive improvements:
- Source area PCE concentrations reduced by over 80%
- Plume-wide contaminant mass reduction documented
- Evidence of complete dechlorination in multiple zones
- Sustained biological activity throughout treatment areas
- Significant plume contraction observed
This case study demonstrates IET's ability to manage complex, long-term remediation programs with sustained results.
Technical Approach & Multi-Phase ERD Strategy
This Swansboro project demonstrates IET's multi-phase enhanced reductive dechlorination (ERD) approach for complex dry cleaner sites with extensive dissolved-phase plumes. The multi-phase design — source zone treatment with ERD followed by plume treatment with biostimulation and bioaugmentation — addresses the dual challenge of destroying source mass while simultaneously controlling the down-gradient plume.
The adaptive management approach — adjusting subsequent phases based on monitoring results — is a hallmark of IET's remediation philosophy. Rather than designing a single static treatment program, IET's multi-phase approach uses performance monitoring data from each phase to optimize reagent dosing, injection point spacing, and treatment targeting for subsequent phases. This data-driven approach maximizes treatment effectiveness while managing project costs.
The 80%+ source area PCE reduction, plume-wide contaminant mass reduction, and evidence of complete dechlorination in multiple zones demonstrate the effectiveness of this phased approach. The sustained biological activity throughout treatment areas confirms that the ERD program successfully established self-sustaining dechlorinating microbial communities — the key to long-term treatment without repeated mobilizations.
Swansboro Site Context & Coastal North Carolina Geology
Swansboro, North Carolina is located in Onslow County along the Atlantic coast within the Coastal Plain physiographic province. The shallow geology consists of Quaternary-age barrier island and back-barrier deposits — predominantly sand, silt, and shell hash — overlying Tertiary-age marine sediments. The sandy, high-permeability soils in this area create conditions where contaminant plumes can spread rapidly, but also where in-situ remediation can achieve effective reagent distribution.
The complex geology and large dissolved-phase plume noted in the site background are characteristic of coastal North Carolina dry cleaner sites, where decades of PCE use have created extensive contamination in the sandy aquifer system. The multi-phase approach — with multiple injection events over several years — is specifically designed to address the challenge of treating both the source zone and the extensive down-gradient plume that has migrated through the high-permeability coastal sediments.