Comparative Demonstration of Active and Semi-Passive In Situ Bioremediation Approaches for Perchlorate-Impacted Groundwater at Longhorn Army Ammunitions Plant

Site Name:

Longhorn Army Ammunitions Plant (LHAAP), Site 16

Location:

LHAAP, Texas

Period of
Operation:

  • First amendment cycle: March 25 to April 14, 2004
  • Second amendment cycle: December 3 to December 28, 2004
  • Third amendment cycle: November 7 to November 30, 2005

Cleanup
Type:

Field-scale

Technology:
The demonstration evaluated the performance of semi-passive enhanced in situ bioremediation (EISB) of perchlorate through the addition of an electron donor on a periodic basis to stimulate natural microorganisms. For this semi-passive approach, groundwater was recirculated for an "active phase" for a limited duration to distribute the electron donor, and then the recirculation system was shut off for a "passive phase" of longer duration.

The design of the system is detailed below:

  • The semi-passive electron donor system included a series of five recirculation wells installed in a line perpendicular to the direction of groundwater flow.
  • The distance between the recirculation wells was 35 feet (ft).
  • Groundwater was periodically extracted, amended with a sodium lactate solution (electron donor), and recharged to the aquifer. Once the electron donor was delivered, recirculation was stopped and the electron donor remained in the groundwater to promote in situ biodegradation of perchlorate and prevent migration of perchlorate beyond the biobarrier.
  • There were a total of three amendment cycles, as described below:
    • First and second amendment cycles: Groundwater was extracted at a rate of about 0.9 gallons per minute (gpm). A total of 273 gallons of a 60% sodium lactate solution (electron donor) was added.
    • Second amendment cycle: Groundwater was extracted at a rate of 1.7 gpm. A total of 443 gallons of a 60% sodium lactate solution (electron donor) was added.
    • Third Amendment cycle: Groundwater was extracted at a rate of 1.7 gpm. A total of 1105 gallons of 60% sodium lactate solution was added.

Cleanup Authority:
Contacts:

USACE Project Manager
Andy Obrochta
U.S. Army Corps of Engineer
1645 South 101 East Avenue
Tulsa, OK 74128
Phone: 918-669-7155
Email: andy.obrochta@usace.army.mil

USACE Technical Advisor
Cliff Murray
U.S. Army Corps of Engineer
1645 South 101 East Avenue
Tulsa, OK 74128
Phone: 918-669-7573
Email: cliff.murray@usace.army.mil

LHAPP Representative
Rose Zeiler
U.S. Army
P.O. Box 23610
Barling, Arkansas 72923
Phone: 479-484-2516
Email: zeilerr@sill.army.mil

Principal Investigator
Evan Cox
Geosyntec Consultants
130 Research Lane, Suite 2
Guelp, ON NIG 5G3 Canada
Phone: 519-822-2230
Email: ecox@geosyntec.com

Co-Principal Investigator
Tom Krug
Geosyntec Consultants
130 Research Lane, Suite 2
Guelp, ON NIG 5G3 Canada
Phone: 519-822-3151
Email: tkrug@geosyntec.com

Contaminants:
Perchlorate and volatile organic compounds (VOCs) (TCE, cis-1,2-Dichloroethene (cis- 1,2-DCE) and vinyl chloride (VC))

Waste Source:
Site 16 at LHAAP was used for the disposal of various types of soil and industrial waste until the 1980s. These disposal activities resulted in the release of perchlorate and various VOCs in groundwater in the vicinity of the Site 16 landfill.

Type/Quantity of Media Treated:
Groundwater (quantity not documented)

Purpose/Significance of Application:
The overall objective was to demonstrate the efficacy of the semi-passive approach to enhanced in situ bioremediation to generate accurate full-scale design and cost information for widespread technology consideration and application. The demonstration was designed to evaluate the following performance objectives:

  • Ease of installation of system components,
  • Ease of electron donor delivery events,
  • Enhancement of microbiological activity and the reduction in perchlorate concentrations,
  • Ease of performance monitoring and validation,
  • Reduction in perchlorate concentration, and
  • Radius of influence and distance for degradation.

Regulatory Requirements/Cleanup Goals:
One of the primary objectives of the study was to demonstrate that perchlorate can be biodegraded in situ to acceptable levels (i.e., the practical quantitation limit [PQL]) using in situ bioremediation with a semi-passive electron donor delivery methodology. For this demonstration, the remediation target was to reduce perchlorate concentrations to the current common PQL for groundwater, which is 4 micrograms/liter (µg/L) in most jurisdictions.

Results:
Groundwater monitoring and tracer testing was conducted before and after the addition of electron amendments. Final groundwater samples collected in June 2006 were compared to baseline samples collected in June 2003 and March 2004.

The groundwater monitoring data demonstrated that significant reductions in perchlorate concentrations were achieved across the line of recirculation wells in the semi-passive biobarrier. Following the third and final injection of the electron donor, perchlorate concentrations were reduced to less than 4 µg/L in 10 shallow wells, within and downgradient of the biobarrier, and the concentrations in three wells ranged from 7 to 10 µg/L. The average concentration of perchlorate in shallow wells within and downgradient of the biobarrier following the third addition of electron donor was 3.4 µg/L.

In addition, groundwater sampling of performance monitoring wells during the tracer test and following electron donor addition demonstrated that the radius of influence for electron donor addition extended between injection and extraction wells. This indicated that the electron donor was applied effectively across the entire biobarrier. Additionally, the perchlorate in the groundwater was degraded before the groundwater reached downgradient performance monitoring wells.

Cost Factors:
The net present value (NPV) of 30 Years of Total Remedy (semi-passive biobarrier) Costs is estimated to be $1,560,000. A breakdown of these costs is provided below:

  • The capital cost, including design, installation of wells, installation of the groundwater recirculation and amendment system, and system start-up and testing for the semi-passive bioremediation system is estimated as $430,000.
  • The O&M cost is estimated to be $38,700 per year. The net present value of the O&M cost represents an additional $780,000 of costs over a 30-year life.
  • The NPV of the long-term monitoring cost is estimated to be $350,000.


The cross sectional area of the plume for this scenario is 1080 square meter (m2) or 12,000 square foot (ft2). The NPV unit costs for the capital and annual O&M are estimated to be $398/ m2 ($36/ft2) and $36/ m2 ($3/ft2), respectively.

Description:
LHAAP is located in central east Texas in the northeastern corner of Harrison County. LHAAP occupies nearly 8,500 acres between State Highway 43 at Karnack, Texas, and the western shore of Caddo Lake. From 1942 to 1956, the plant was used to produce Trinitrotoluene (TNT) flake and pyrotechnic ammunition. The plant was also used as a rocket motor facility that operated from 1955 to 1965. Site 16 at LHAAP was used for the disposal of various types of soil and industrial waste until the 1980s. These disposal activities resulted in the release of perchlorate and various VOCs to groundwater in the vicinity of the Site 16 landfill. Perchlorate analyses were conducted on groundwater samples collected in May 2000, September 2000, and January 2001. Samples indicated the presence of perchlorate in the shallow and intermediate aquifers at the site.

A field scale study was conducted to demonstrate the efficacy of a semi-passive approach to enhanced in situ bioremediation to generate accurate full-scale design and cost information for widespread technology consideration and application. The semi-passive electron donor system included a series of five recirculation wells used to distribute sodium lactate solution (electron donor) in the groundwater treatment area. The first and second amendment cycles were conducted from March 25 to April 14, 2004, and December 3 to December 28, 2004. The third amendment cycle was conducted between November 7 and November 30, 2005. During each amendment cycle, the electron donor was added in batches. At the conclusion of each electron donor delivery cycle, the recirculation system was shut off and the passive phase of operation was initiated. Groundwater monitoring and tracer testing was conducted before and after the electron amendments to evaluate the performance of the semi-passive bioremediation system. Sampling results indicated that the semi-passive bioremediation system effectively achieved all program objectives and reduced average perchlorate concentrations to less than 4 µg /L.