In Situ Bioremediation at the Texas Gulf Coast Site, Houston, Texas

Site Name:

Texas Gulf Coast Site


Houston, Texas

Period of

Ongoing (data available from June 1995 to December 1998) Cleanup Type: Full scale Cleanup Authority: State of Texas Voluntary Cleanup Program; administered by TNRCC


Pilot and Full scale


Susan Tighe Litherland, P. E
David W. Anderson, P.E., P.G.
Roy F. Weston, Inc.
5300 Bee Caves Road, Suite 1-100
Austin, TX 78746
(512) 329-8399
fax: (512) 329-8348

In situ bioremediation
- An extraction-injection recirculation system, completed in May 1995, consists of an alternating series of four extraction (1,800 linear ft total) and four injection (1,100 linear ft total) trenches set at a spacing of approximately 100 ft
- The extraction trenches were completed to a depth of at least one foot into the bottom clay layer (20 - 22 ft bgs), and were sloped to a sump
- System operation consists of groundwater circulation and addition of methanol
- As of January 1999, the recirculation rate averages 6 to 8 gpm, and a total of 12 million gallons have been recirculated through the system (approximately 2.5 pore volumes)

Cleanup Authority:
State voluntary cleanup program

Site Contact:
Not identified
EPA Remedial Project Manager:
Eugene Dennis
U.S. EPA Region 3
1650 Arch Street (3HS21)
Philadelphia, PA 19103-2029
(215) 814- 3202

TCE, hexavalent chromium
- Concentrations of TCE reported as high as 12,000 µg/L

Waste Source:
Leaks and spills from manufacturing operations

Type/Quantity of Media Treated:
- The area of contaminated groundwater is approximately 600 ft by 700 ft in an unconsolidated water-bearing zone which occurs at a depth of approximately 12 - 20 ft bgs
- Hydraulic conductivity is 1 x 10-4 to 4 x 10-4 cm/sec
- Groundwater velocity is 4 - 18 ft/yr

Purpose/Significance of Application:
Groundwater recirculation system using trenches for extraction and injection Contaminants: TCE, cis-1,2-DCE, VC - TCE was present at approximately 50 mg/L

Regulatory Requirements/Cleanup Goals:
The primary objectives of the clean up are to actively remediate the contaminated groundwater at this site to a point that natural attenuation would prevent further migration of the plume, and to discontinue active treatment - No specific cleanup goals have been identified for groundwater at this site

- Excluding results from the one potential "source" area, the average decrease in TCE concentrations is approximately 99% (from an average of 12 to 0.12 mg/L) during a 3 1/2 year period
- TCE concentrations in portions of the plume have decreased to below the detection limit (0.005 mg/L).
- Accounting for dilution, the site contractor reported that TCE concentrations were reduced by approximately 2% per month during a period of nutrient-only addition, and approximately 10% per month during the period of methanol addition
- The ratio of cis-1,2-DCE to TCE increased from approximately 0.06:1 to 0.30:1 after addition of methanol, suggesting more active dechlorination associated with higher concentrations of substrate.

Cost Factors:
- Capital costs for construction of the extraction/injection trenches and control building were approximately $600,000
- Annual costs for operation, maintenance and monitoring are approximately $100,000

The Texas Gulf Coast site is an abandoned industrial manufacturing facility located near Houston, Texas that operated between 1952 and 1985. Trichloroethene was used at the facility and was found in the groundwater starting in 1986. In situ bioremediation is being used to clean up groundwater at the site under the State of Texas Voluntary Cleanup Program.

Methanol addition was found to increase the rate of biodegradation of TCE at this site, based on the reduction of TCE concentration and increase in the ratio of cis-1,2-DCE to TCE. This site is planning to stop using active bioremediation after four years of system operation (three years of methanol addition) to allow use of natural attenuation. According to the site contractor, natural attenuation will be used to prevent future migration of the plume, and to achieve stable or declining contaminant concentrations.

Excessive biomass formation, leading to a reduced flow rate, was found to be a concern for addition of methanol. Excess biomass was not noted during the period when nutrients alone were added; however, a significant increase in biomass formation was noted after addition of methanol. To remedy this, the site contractor modified their methanol addition to a batch system. The site contractor found that it was difficult to balance the system hydraulics between the extraction and infiltration trenches, and that it required approximately one year of operating time to achieve a balance. In addition, they found it difficult to interpret the treatment performance data because of the non-homogeneous nature of the initial groundwater quality, and dilution due to recharge of rainwater and clean water from beyond the planned treatment area.