In Situ Remediation of MTBE Contaminated Aquifers Using Propane Biosparging at the National Environmental Technology Test Site, Port Hueneme, CA

Site Name:

National Environmental Technology Test Site

Location:

Port Hueneme, CA

Period of
Operation:

May 2001 to March 2002

Cleanup
Type:

Field Demonstration µg/L

Technology:
In Situ Bioremediation (Propane Biosparging)
- Test plot and control plot (90 ft by 60 ft)
- Test plot - network of 8 oxygen injection points (OIP), 7 propane injection points (PIPs), and 7 bacteria injection points (BIPs) installed along a line perpendicular to groundwater flow; groundwater monitoring network of 15 dual-level (shallow and deep), nested wells
- Control plot - 8 OIPs installed along a line perpendicular to groundwater flow; no PIPs or BIPs; groundwater monitoring network of 10 dual-level (shallow and deep), nested wells
-2 oxygen cylinders per plot; oxygen delivery - 40-60 psig; one propane cylinder for test plot; propane delivery - 20-30 psig; oxygen and propane control manifold assemblies, and a control panel
- Oxygen system - operated for four, 6-minute cycles per day, yielding approximately 5 lb/day of
oxygen in the test and control plots
- Propane system operated for four, 10-minute cycles per day and yielded approximately 0.5 lb/day of propane at the test plot; after several months of operation and a review of the geochemical data, the propane flow was decreased from 1 scfh to between 0.3 and 0.4 scfh (yield of approximately 0.17 to 0.2 lb/day of propane)

Cleanup Authority:
State

Contacts:
Navy
Commanding Officer (specific name not provided)
Naval Facilities Engineering Service Center
1100 23rd Avenue
Port Hueneme, CA 93043

Contaminants:
MTBE and TBA
- Groundwater contaminant concentrations as high as - 6,300 µg/L for MTBE; TBA detected in one well only at 470 µg/L

Waste Source:
Leaks from a gasoline distribution system

Type/Quantity of Media Treated:
Groundwater
- Unconsolidated sediments composed of sands, silts, clays, and small amounts of gravel and fill material
- Upper-most water-bearing unit - shallow, semi-perched, unconfined aquifer (upper silty sand, underlain by fine to coarse grain sand, and a basal clay layer)
- Depth to groundwater - 6 to 8 ft bgs; saturated aquifer thickness - 16 to 18 ft

Purpose/Significance of Application:
Field demonstration of propane biosparging to treat MTBE-contaminated groundwater

Regulatory Requirements/Cleanup Goals:
- Treatment goal for the demonstration was to reduce MTBE and TBA concentrations to <5 µg/L for MTBE (California secondary MCL) and <12 µg/L for TBA (California Action Level)
- Primary objectives of the demonstration were to: (1) demonstrate the safe application of propane biosparging for in situ remediation of MTBE and (2) evaluate the ability of this technology in reducing MTBE concentrations in groundwater to below 5 µg/L

Results:
- MTBE concentrations were reduced in both the test plot and the control plot, as expected based on the results of microcosm studies and previous demonstrations at the site; however, MTBE concentrations were reduced to <5 µg/L in only 3 of the 30 monitoring wells in the test plot; in the control plot, MTBE concentrations remained above 5 µg/L in all wells; most active MTBE degradation appeared to occur near the oxygen injection points
- MTBE concentrations - in test plot, in shallow wells decreased 62-88% and in deep wells decreased 86-97%; in control plot, decreased 86-97% and in deep wells decreased 88-90%; results indicate that indigenous bacteria at this site are capable of aerobically degrading MTBE
- TBA concentrations - in test plot, generally <25 µg/L in shallow and deep wells; reduced to below 12 µg/L in some wells

Cost Factors:
- Costs for the demonstration were $333,288, including $122,311 in capital costs, $184,647 in O&M costs, and $26,329 for treatability studies
- Projected full scale costs are $145,600, reflecting improved efficiencies of technology implementation and reduced monitoring and reporting requirements than those required for a demonstration project

Description:
The National Environmental Technology Test Site, Port Hueneme, CA was the location of a field demonstration of propane biosparging to (1) demonstrate the safe application of propane biosparging for in situ remediation of MTBE and (2) evaluate the ability of this technology in reducing MTBE concentrations in groundwater to below the California secondary MCL of 5 µg/L. Leaks from a gasoline distribution system resulted in the groundwater at the site being contaminated with MTBE and its degradation product , TBA. BTEX was present at low levels only. The demonstration, conducted from May 2001 to March 2002, included a test plot and a control plot, with oxygen injected in both. The technology was also evaluated under the EPA SITE Program.

MTBE concentrations were reduced in both the test plot and the control plot. This was expected based on the results of microcosm studies and previous demonstrations at the site. However, in the test plot, MTBE concentrations were reduced to <5 µg/L in only 3 of the 30 monitoring wells and were not reduced below this level in any wells in the control plot. The most active MTBE degradation appeared to occur near the oxygen injection points. The results of a cost assessment indicated that full-scale application would be up to 44% less costly than the demonstration project, reflecting improved efficiencies of technology implementation and reduced monitoring and reporting requirements than those required for a demonstration project. Observations and lessons learned from the demonstration included: propane biosparging can be applied safely and economically; system designs must ensure sufficient delivery of oxygen; indigenous microbes in some aquifers can effectively degrade MTBE if supplied the appropriate nutrient or oxygen; and propane biosparging can support the growth or activity of indigenous or added propane oxidizing bacteria.