The International Information Center for Geotechnical Engineers

Soil Remediation Techniques: Examination of In Situ Chemical Oxidation

 

10. Case Studies

10.1 Case Study 1: Former Service Station Site; Southeastern PA

This project took place in Southeastern Pennsylvania (1999) and consisted of an out-of-service , former retail petroleum service property underlaid by a silty sand and fill material with a depth to groundwater table of approximately 10-12 feet (Interstate Technology and Regulatory Council, 2005). The site was underlid by soils and groundwater contaminated by LNAPL and high residual concentrations of petroleum hydrocarbons (BTEX, MTBE, and PATH (naphthalene)), and was very close to a large pet store which was one of the main receptors (Interstate Technology and Regulatory Council, 2005). Figure 12 shows the extent of contamination previous to site remediation.

Figure 11

Figure 12: Contamination extent before ISCO remediation (Interstate Technology and Regulatory Council, 2005)

 

The remedial design had as goal to remove all LNAPL from subsurface and to reduce hydrocarbons to levels at which natural attenuation could become a viable long-term approach to site cleanup (Interstate Technology and Regulatory Council, 2005). In situ oxidation via ozone sparging was used to remediate the site by the nine-month deadline. For eight months, ozone sparging was conducted through a series of six nested sparge points to reduce concentration of hydrocarbons in saturated and unsaturated soils and groundwater (Interstate Technology and Regulatory Council, 2005). Ozone sparging was complemented by soil vapor and groundwater extraction; the extracted and treated groundwater was then reinjected into the subsurface to further enhance remedial effectiveness (Interstate Technology and Regulatory Council, 2005).

In the months following culmination of the remediation process, several soil and groundwater samplings were conducted to corroborate effectiveness of technique. The resulting outcome was a decrease of 86%-99% in total BTEX, 97%-98% in total MTBE, and 52%-97% in total naphthalene across the site (Interstate Technology and Regulatory Council, 2005).  Furthermore, groundwater concentrations also continued to decrease after the implemented remediation, demonstrating that natural attenuation was indeed taking place (Interstate Technology and Regulatory Council, 2005). LNAPL at the site was removed and concentrations were below the PADEP cleanup standards. The total costs for remediation accounted for approximately $222,000, including a two-year period of post-remediation sampling, reporting, and site closure negotiation with PADEP (Interstate Technology and Regulatory Council, 2005). Figure 13 illustrates the contamination extent after ISCO remediation. 

 

Figure 12

Figure 13: Contamination extent after ISCO remediation (Interstate Technology and Regulatory Council, 2005)

 

 

10.2 Case Study 2: Anniston Army Depot, Anniston, AL

The project took place in Anniston, Alabama (1997) at a 2 acres site consisting of three industrial waste lagoons backfilled with clay in 1978 and with a water table fluctuating from 25-30 ft below the surface (EPA, 1998). The underlying lithography comprises over 43,125 yd. of contaminated soil containing up to 31% trichloroethene 3 (TCE), dichloroethene (DCE), methylene chloride, and benzene, toluene, ethylbenzene, and xylene (BTEX) (EPA, 1998). The majority of contaminants were found at depths of 8 ft and greater, while the highest concentrations of TCE are found at depths between 8 and 10 ft (maximum 20,100 mg/kg) (EPA, 1998). After fully characterizing the soil and contaminants present, hydrogen peroxide (H2O2) was chosen to remediate the site.

Three different types of injector wells were installed to target three distinct depth intervals (EPA, 1998):

  • Single shallow injectors screened (8-14 ft deep) were installed where contamination was shallower than 15 ft
  • Single intermediate injectors were installed where contamination was 15-20 ft deep
  • Paired shallow and deep injectors screened (20-26 ft deep) were installed where contamination was at both deep and shallow depths.

Also, 25 deep ground-water injector wells were used for monitoring and a vent flow balance system was installed to aid in ensuring an effective radial dispersion of catalyst and H2O2. The Geo-Cleanse┬« patented injection process was used to distribute H2O2 and track quantities of ferrous sulfate and acid into the contaminated soil (EPA, 1998). Chemical oxidation of the soil took place over a 120-day period during which 109,000 gallons of 50% H2O2  were injected through a total of 255 injectors (EPA, 1998).

Results of the areas treated with H2O2 indicate that the remediation technique was effective in reducing contaminant concentrations in clays to below SSLs (EPA, 1998). Soil concentrations of up to 1,760 mg/kg of TCE have been reduced to below detection. The approximate total cost of the project is $5.7M (EPA, 1998).

 

10.3 Case Study 3: Cape Canaveral Air Force Station, FL

Cape Canaveral Air Force Station contains waste contaminants of discharge from rocket engines and parts. The cleaning compounds used to clean these rocket parts were part of the waste generated which included chlorinated solvents (TCE) (Federal Remediation Technologies Roundtable, 2006).

Permanganate was implemented at Launch Complex 34, Cape Canaveral Air Force Station to test the technology of ISCO with the objective of destroying TCE present as DNAPL in the saturated zone. The test zone volume was 75 ft by 50 ft by 45 ft deep. A total of 842,985 gallons of permanganate solution was injected into this plot in 3 phases over the span of 8 months. Figure 14 depicts the implementation process for this project.

Figure 13

Figure 14: TCE Concentration before ISCO (Federal Remediation Technologies Roundtable, 2006) 

During the first phase 304,763 gallons was injected into the order as follows: upper unit, middle unit, and the lower unit for one month. The radius of influence for the first injection was about 10-12 feet; however heterogeneities of the soil limited oxidant distribution. The second and third phases focused on targeting oxidation of areas which had not had sufficient levels of oxidant to produce satisfactory results, or the destruction of the contaminant. A total of 87,483 and 450,739 gallons were injected in the second and third phases respectively (Federal Remediation Technologies Roundtable, 2006).

Results showed (Federal Remediation Technologies Roundtable, 2006):

  • Mass TCE and DNAPL levels decreased by 77% and 76% respectively and the topsoil demonstrated the highest levels of removal (indicating the oxidant was most efficient in coarser soils)
  • Decreased TCE levels were consistent, with most monitoring wells displaying  concentrations of less than 5 micrograms/liter which corresponds to the minimum concentration level
  • TCE and DNAPL removal pathways included destruction by oxidation, migration to the surrounding aquifer, and migration to the vadose zone and atmosphere

Figure 14

Figure 15: TCE Concentration after ISCO (Federal Remediation Technologies Roundtable, 2006)

The total cost of this project was about $1 million from design to finish. About 15% of this cost was estimated to be due to the fact this project was especially designed for demonstration purposes versus full scale applications (Federal Remediation Technologies Roundtable, 2006). 

 

 

 

 

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