Description
Historical activity that resulted
in contamination.
| From approximately 1948 to 1984 petroleum based dry-cleaning solvents
were used during cleaning operations. From approximately 1984 to present, Brock's Cleaners has utilized tetrachloroethene (PCE) as the dry-cleaning solvent. There was a significant release from the machine in the mid 90's. Soil impacts appear to be localized beneath the dry cleaner. Depth to bedrock ranges from 0-8' at the site. Grondwater is contaminated at concentrations indicative of DNAPL presence and the plume has caused significant surface water impacts approximately 500' from teh site. Also Vapor Intrusion occurring at moderate levels in two off property residences. Remediation Status: In groundwater monitoring |
Contaminants
Contaminants present and the highest amount
detected in both soil and groundwater.
| Contaminant |
Media |
Concentration (ppb) |
Nondetect |
| Benzene |
groundwater |
|
|
| cis-1,2-Dichloroethene |
groundwater |
|
|
| cis-1,2-Dichloroethene |
soil |
|
|
| 1,1-Dichloroethene |
groundwater |
|
|
| Tetrachloroethene (PCE) |
groundwater |
|
|
| Tetrachloroethene (PCE) |
soil |
|
|
| naphthalene |
groundwater |
|
|
| naphthalene |
soil |
|
|
| Trichloroethene (TCE) |
groundwater |
|
|
| Trichloroethene (TCE) |
soil |
|
|
| trans-1,2-Dichloroethene |
groundwater |
|
|
Site Hydrology
| Deepest Significant
Groundwater Contamination: |
|
80ft bgs |
| Plume Size: |
|
Plume Length: 700ft
Plume Width: 600ft
Plume Thickness: 80ft |
| Average Depth
to Groundwater: |
|
10.73ft |
Lithology and Subsurface Geology
|
|
yellowish-orange, coarse to medium micaceous sandy silt saprolite and partially weathered rock (PWR) regolith
Depth: 0-8ft bgs
8ft thick
Conductivity: 0.000286299ft/day
Gradient: 0.11ft/ft
|
Pathways and DNAPL Presence
 Groundwater
Sediments
Soil
 Presumptive 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
|
Results of VI evaluation: |
|
A completed VI pathway has been indentified |
Has a vapor mitigation system been installed? |
|
No |
Remediation Scenario
Cleanup
Goals: |
|
To stabilize the plume in order to decrease concentrations leaving the site thereby reducing VI potential and impacts to the surface water body 500 feet away. Furhtermore, decrease the overall advancement of a large plume.
|
Remedy Level: |
|
Interim Action |
Technologies
In Situ Bioremediation |
|
Why the technology was selected:
Bench scale studies indicated that activated persulfate did not perform well and permanganate daylighting issues were a concern. With the presence of daughter products, the measured presence of dehalococcoides, and absence of electron competitors, reductive dechlorination and in situ chemical reduction vial ZVI were selected. Also the viscosity of the mixture was important because much the top of bedrock was very shallow and we were aiming for maximal contaminant/reagent contact.
Date implemented:
April 11, 2011
Final remediation design:
Prior to the injection, four monitoring
wells (PZ-4 through PZ-7) were installed and seven injection wells (IW-14 through IW-20) and a
baseline groundwater sampling event was conducted between April 1 and 15, 2011. The injection
activities were conducted between April 11 and 16, 2011. The solution (consisting of
ABC+, ZVI, and water) was injected into the subsurface through 26 temporary injection points
(IP-1 through IP-26) and 20 injection wells (IW-1 through IW-20). Injection depths ranged from
approximately 3.5 ft below ground surface (bgs) to 8 ft bgs. A total of approximately 1,768
gallons of ABC+ solution was injected into the subsurface.
Results to date:
Groundwater elevation data indicate that groundwater flow in the shallow aquifer is to the northeast towards an unnamed tributary of Vaughn Creek.
The ABC+ injection effectively reduced PCE and TCE concentrations in the vicinity and downgradient of the injection area with reductions up to 93% in MW-1 and 99% in MW-10s between April 2011 and October 2011. Similarly, TCE concentrations decreased
significantly in the performance monitoring wells with reductions up to 69% in MW-1 and 62% in PZ-6. Increased concentrations of cis-1,2-DCE, trans-1,2-DCE, and VC (PCE and TCE
breakdown products) were generally observed in the performance monitoring wells within the first two months after the April 2011 injection. Subsequently, cis-1,2-DCE,trans-1,2-DCE, and VC concentrations were varied during the August and October 2011
sampling events. These results indicate the ABC+ injection is effectively stimulating reductive dechlorination of PCE and TCE in the injection area.The ABC+ injection successfully created anaerobic conditions conducive to reductive dechlorination as indicated by reductions in DO and ORP and increases in methane.Increased concentrations of chloride (a by-product) and ethene and ethane (end products)
provide further evidence that the ABC+ injection has successfully stimulated reductive dechlorination.The ABC+ solution was effectively distributed within the injection area and remains
present to continue stimulating reductive dechlorination as evidenced by increases in TOC, VFAs, and iron.
Microorganisms and functional genes responsible for reductive dechlorination are present
within the injection area at the site.
Next Steps:
Monitor the site for performance of the injection, the aquifer's return to preinjection geochemical status, and evaluate a second injection.
Cost to Design and Implement:
~$98,105.00
|
In Situ Zero Valent Iron |
|
Why the technology was selected:
Bench scale studies indicated that activated persulfate did not perform well and permanganate daylighting issues were a concern. With the presence of daughter products, the measured presence of dehalococcoides, and absence of electron competitors, reductive dechlorination and in situ chemical reduction vial ZVI were selected. Also the viscosity of the mixture was important because much the top of bedrock was very shallow and we were aiming for maximal contaminant/reagent contact.
Date implemented:
April 11, 2011
Final remediation design:
Prior to the injection, four monitoring
wells (PZ-4 through PZ-7) were installed and seven injection wells (IW-14 through IW-20) and a
baseline groundwater sampling event was conducted between April 1 and 15, 2011. The injection
activities were conducted between April 11 and 16, 2011. The solution (consisting of
ABC+, ZVI, and water) was injected into the subsurface through 26 temporary injection points
(IP-1 through IP-26) and 20 injection wells (IW-1 through IW-20). Injection depths ranged from
approximately 3.5 ft below ground surface (bgs) to 8 ft bgs. A total of approximately 1,768
gallons of ABC+ solution was injected into the subsurface.
Results to date:
Groundwater elevation data indicate that groundwater flow in the shallow aquifer is to the northeast towards an unnamed tributary of Vaughn Creek.
The ABC+ injection effectively reduced PCE and TCE concentrations in the vicinity and downgradient of the injection area with reductions up to 93% in MW-1 and 99% in MW-10s between April 2011 and October 2011. Similarly, TCE concentrations decreased
significantly in the performance monitoring wells with reductions up to 69% in MW-1 and 62% in PZ-6. Increased concentrations of cis-1,2-DCE, trans-1,2-DCE, and VC (PCE and TCE
breakdown products) were generally observed in the performance monitoring wells within the first two months after the April 2011 injection. Subsequently, cis-1,2-DCE,trans-1,2-DCE, and VC concentrations were varied during the August and October 2011
sampling events. These results indicate the ABC+ injection is effectively stimulating reductive dechlorination of PCE and TCE in the injection area.The ABC+ injection successfully created anaerobic conditions conducive to reductive dechlorination as indicated by reductions in DO and ORP and increases in methane.Increased concentrations of chloride (a by-product) and ethene and ethane (end products)
provide further evidence that the ABC+ injection has successfully stimulated reductive dechlorination.The ABC+ solution was effectively distributed within the injection area and remains
present to continue stimulating reductive dechlorination as evidenced by increases in TOC, VFAs, and iron.
Microorganisms and functional genes responsible for reductive dechlorination are present
within the injection area at the site.
Next Steps:
Monitor the site for performance of the injection, the aquifer's return to preinjection geochemical status, and evaluate a second injection.
Cost to Design and Implement:
~$98,105.00
|
Costs
Cost
for Assessment:
|
|
~$304,911.92 |
Cost
for Operation and Maintenance:
|
|
~$50,000 |
Total
Costs for Cleanup:
|
|
|
Lessons Learned
|
In this case a bench scale study completely changed the reagent to be used in the remediation. Had we used activated persulfate, the remediation would likely have been a failure.
|
Contacts
Billy Meyer
919-707-8366
217 W. Jones Street, Raleigh, NC 27603
Contractors:
AECOM
Hart and Hickman
|
Site Specific References
ABC+ Injection
Final Project Evaluation Report
April 17, 2012
|
|
