Drycleaner Site Profiles

Sno-White Cleners, Charlotte, North Carolina

Description
Historical activity that resulted in contamination.

Prior assessment activities indicated that a release at the former drycleaning facility resulted in impacted soil and groundwater. The PCE plume in groundwater extends appproximately 1,500 feet to the northwest and off-site in the downgradient direction. Soil excavation was performed in 2008 and an AS/SVE system was installed in May 2009 and to remediate the source area. The remediation efforts were successful in significantly reducing source area concentrations. The AS/SVE system was shutdown in May 2010 and four groundwater monitoring events were conducted to evaluate plume stability. Based on the results of the monitoring events, the plume associated with the site appears adequately defined, generally stable, and concentrations are reducing. A TIER II risk assessment has been performed using the RAM RBCA toolkit and, additionally a site-wide TIER III risk assessment was performed using GSI's RBCA toolkit to specifcally address groundwater concentrations marginally exceeding the GW>IA screening levels. The site passed the risk asssessement and a Risk Management Plan has been written with on-site land use restrictions for: groundwater, vapor intrusion, and residential use. Off-site contamination is being controlled through notices placed on the survey plat that the property is impacted by tetrachloroethylene, and a "NOTICE OF DRY CLEANING SOLVENT REMEDIATION" documented with the county register of deeds which prohibits the use of groundwater on the property in accordance with 15A North Carolina Administrative Code 02C .0107(b)(1), (t)he source of water for any water supply well shall not be from a water bearing zone or aquifer that is contaminated.

Remediation Status: Site closed


Contaminants
Contaminants present and the highest amount detected in both soil and groundwater.


Contaminant Media Concentration (ppb) Nondetect
Tetrachloroethene (PCE) groundwater
Tetrachloroethene (PCE) soil
Trichloroethene (TCE) groundwater
Trichloroethene (TCE) soil

Site Hydrology

Deepest Significant Groundwater Contamination:   50ft bgs
Plume Size:   Plume Length: 1,500ft
Plume Width: 300ft
Plume Thickness: 50ft
Average Depth to Groundwater:   13.5ft

Lithology and Subsurface Geology

 
  Silty clay to fine sandy silt coarsening with depth to saprolite

Conductivity: 1.66ft/day
Gradient: 0.02ft/ft
Metagabbro of the Charlotte Belt
  bedrock

Pathways and DNAPL Presence

Groundwater
Sediments
Soil
checkPresumptive Evidence of DNAPL

Vapor Intrusion Pathway

Has the potential for vapor intrusion (VI) been evaluated?
  Yes
How was the site evaluated?
  Soil vapor and/or Sub-slab vapor sampling,Indoor air sampling,Groundwater sampling,Compared sample concentration to screening criteria,Used an exposure screening model
Results of VI evaluation:
  A completed VI pathway has been indentified,A potential VI pathway has been indentified
Has a vapor mitigation system been installed?
  Yes 
Type of Vapor Mitigation System(s):
  Soil Vapor Extraction
Additional VI Information:
  Environmental media exceeding VI screening levels were primarily contained to a small soil and groundwater source beneath the building. An excavation within the footprint of the former cleaner, followed by installation of an SVE/Air Sparge system in the source area, reduced Indoor Air concentrations below a Target Risk Level of 1.0 E -05 and HI of 1.0. Off property grounwater concentrations slightly exceeded NCDSCA GW>IA screening levels, therefore the GSI RBCA toolkit was used to perform a site wide ris assessment, and specifically evaluate off-property VI potential. The site wide risk assessment met closure criteria.

Remediation Scenario

Cleanup Goals:
  Achieve overall sitewide cumulative risk level of less than 1.0E-05 for all exposure pathways (combined) for each exposure unit evaluated through a risk assessment. Pathways evaluated were: Non-Residential Worker - Surficial SoilCombined Pathway; Non-Residential Worke Subsurface Soil - Vapor Emissions to Indoor Air; Non-Residential Worker Groundwater - Vapor Emissions to Indoor Air; and Protection of Groundwater (assuming point of exposure at the downgradient property
boundary).
Remedy Level:
  Interim Action

Technologies

In Situ Air Sparging
 

Why the technology was selected:
Air sparging was selected because the source groundwater concentrations appeared to be confined to the shallow water table aquifer and likely contributing to exceedances of 1.04E-04 indoor air risk.

Date implemented:
Sept 2008

Final remediation design:
Sept 2008

Results to date:
Air Sparge/SVE system shut down May 2010. 61.88 tons of soil were excavated. 21.705 lbs of vapor phase PCE was removed via SVE. 99% source GW concentration reduction.

Next Steps:
Site is in closure. Risk Management Plan is being signed.

Cost to Design and Implement:
$252,405.70 (all technologies)

In Situ Soil Vapor Extraction
 

Why the technology was selected:
Soil vapor extraction was chosen to remediate soil unable to be excavated while providing a significant vapor barrier from VOC's liberated from the air sparging.

Date implemented:
Sept 2008

Final remediation design:
Sept 2008

Results to date:
Air Sparge/SVE system shut down May 2010. 61.88 tons of soil were excavated. 21.705 lbs of vapor phase PCE was removed via SVE. 99% source GW concentration reduction.

Next Steps:
Site is in closure. Risk Management Plan is being signed.

Cost to Design and Implement:
$252,405.70 (all technologies)

Ex Situ Soil Removal
 

Why the technology was selected:
Soil Excavation was chosen becasue source concentrations were likely contributing to an expanding plume and therefore the goal was to stabilize or equilibrate the plume.

Date implemented:
Sept 2008

Final remediation design:
Sept 2008

Results to date:
Air Sparge/SVE system shut down May 2010. 61.88 tons of soil were excavated. 21.705 lbs of vapor phase PCE was removed via SVE. 99% source GW concentration reduction.

Next Steps:
Site is in closure. Risk Management Plan is being signed.

Cost to Design and Implement:
$252,405.70 (all technologies)

Costs

Cost for Assessment:
  $166,187.13 (including risk assessment) $170,204.13
Cost for Operation and Maintenance:
  ~$7,000.00 over approx 3 years
Total Costs for Cleanup:
  $420,019.16

Lessons Learned

Source removal was very effective at reducing indoor air concentrations. It appears that soil and groundwater must be addressed simultaneously in order to adequately reduce vapor intursion and reduce indoor air concentrations. This strategy is being used at an almost identical site. The only problems were O&M of the SVE/Air sparge blower. This remedial approach was optimal for these specific conditions and in hind site the same remedial approach would likely be used again with little modification.

Contacts

Billy Meyer, NCDSCA Project Manager
217 W. Jones Street, Raleigh, NC
919-707-8366
billy.meyer@ncdenr.gov

Site Specific References

2/26/10: "Interim Building Assessment and Remediation"
4/28/10: "Assessment Report"
3/9/11: "Remediation System Operation and Maintenance adn POst-Remediation Air Sampling Report"
7/27/11: Groundwater Montoring (Plume Stability Documentation) Report
10/12/11: TIER 3 Risk Assessment
2/14/12: Risk Management Plan