In situ Chemical Oxidation Using Fenton's Reagent at Naval Air Station Pensacola, Florida

Site Name:

Naval Air Station Pensacola

Location:

Pensacola, FL

Period of
Operation:

11/98 – 5/99 (for oxidation)

Cleanup
Type:

Full Scale

Technology:
Chemical Oxidation Using Fenton’s Reagent

Chemical oxidation using Fenton’s Reagent involved pressurized injection of concentrated hydrogen peroxide and ferrous iron catalyst to oxidize organic compounds in groundwater.

A two-phase treatment was performed – in the first phase, 6 injectors were installed in the former sludge drying bed from 11 – 31 ft bgs, and 8 injectors were installed at 35 – 40 ft bgs down-gradient of the bed; a total of 4,089 gallons of 50% hydrogen peroxide and a similar volume of ferrous iron catalyst were injected over 5 days in December 1998.

In the second phase, 6,038 gallons of 50% hydrogen peroxide and a similar volume of catalyst, along with phosphoric acid, were injected over 6 days in May 1999.

A pump and treat system had been ongoing at the site since February 1987; in 1995, a review of available data showed that contamination was limited to around monitoring well GM-66, at an intermediate depth, and the number of recovery wells was reduced from 7 to 3, focused in the area near GM-66; as of 2000, the Florida DEP was allowing the pump and treat system to be discontinued and a Monitored Natural Attenuation (MNA) remedy to be used for the site.

Cleanup Authority:
RCRA Corrective Action

Navy Contacts:
Maxie Keisler
SOUTHDIV
Phone: (843) 820-7322
Fax: (843) 820-7465
E-mail: keislermr@efdsouth.navfac.navy.mil

Mike Maughon
SOUTHDIV
Phone: (843) 820-7422
Fax: (843) 820-7465
E-mail: maughonml@efdsouth.navfac.navy.mil

Doug Zillmer
NFESC
Phone: (805) 982-1556
Fax: (805) 982-4304
E-mail: zillmerda@nfesc.navy.mil

Contaminants:
Chlorinated Solvents
Maximum concentrations – 3,600 ug/L for TCE, 520 ug/L for DCE, and 63 ug/L for VC

Waste Source:
Unlined sludge drying beds and surge pond

Type/Quantity of Media Treated:
- Geology characterized as relatively homogeneous fine to medium grained; a clay layer is located at 40 – 60 ft bgs.
- Depth to groundwater is generally less than 5 ft, with a flow direction of generally east.

Purpose/Significance of Application:
Use of Fenton's Reagent to remediate chlorinated solvents in groundwater

Regulatory Requirements/Cleanup Goals:
- Evaluate effectiveness of in situ chemical oxidation technology.
- No specific cleanup goals were identified.

Results:
The groundwater monitoring network for the site consists of 8 point of compliance wells, 10 assessment wells, and 1 background well.

The results from the first phase of treatment showed that an 81% reduction in concentrations of chlorinated solvents was achieved in GM-66, and that there was rebound in other wells.

The results from the second phase of treatment showed reduction in concentrations of chlorinated solvents, including the wells that had rebound after Phase 1, and that there had been substantial source reduction

Cost Factors:
The cost for two phases of in situ chemical oxidation and subsequent MNA was $250,000 for treatment and $100,000 per year for monitoring; the total cost of this approach was projected as $750,000 over a five year period

The pump and treat system had a cost of $70,000 per year for operations and $100,000 per year for monitoring; the total cost of the pump and treat remedy was projected to be $3.4 million over a 20 year period

The use of in situ chemical oxidation was projected to save several million dollars compared with the continued use of pump and treat

Description:
Naval Air Station (NAS) Pensacola is a 5,800-acre naval facility located in the western portion of the Florida panhandle. The former Industrial Wastewater Treatment Plant (IWWTP) at the site treated wastewater from operations such as painting and electroplating, as well as organic solvents and acids, and included an unlined sludge drying bed and surge pond. A groundwater recovery system had been operated for more than 10 years under a RCRA corrective action program to control migration of contaminated groundwater. In situ chemical oxidation using Fenton’s Reagent was evaluated for its ability to reduce concentrations of chlorinated solvents in the source area, such that natural attenuation would be an effective remedy for down-gradient groundwater.

In situ oxidation was conducted in two phases, and included a total of 10,127 gallons of hydrogen peroxide and similar volumes of reagents injected under pressure at a depth of 10-40 ft bgs. Over the two phases, the concentration of TCE was reduced substantially. Elevated concentrations of ferrous iron in the groundwater, limited the effectiveness of the first phase of injections. In the second phase, phosphoric acid was added to the reagent mix to help stabilize the hydrogen peroxide in the presence of elevated ferrous iron concentrations. The use of in situ chemical oxidation was projected to save several million dollars compared with the continued use of pump and treat at this site.