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Pump and Treat and In Situ Chemical Treatment of Contaminated Groundwater at the Odessa Chromium II South Superfund Site, Operable Unit 2, Odessa, Texas

Site Name:

Odessa Chromium II Superfund Site – South Plume, OU2


Odessa, Ector County, Texas

Period of

- Electrochemical Groundwater Pump and Treat – December 1993 to December 1997
- In Situ Chemical Treatment – December 1998 to April 1999


Full-scale cleanup

-- Pump and treat (P&T) with electrochemical precipitation of chromium using ferrous ion
o The extraction system consisted of four recovery wells at a depth of 70 feet and six recovery wells at a depth of 165 feet.
o Extracted groundwater was treated using ferrous ions (produced on site in an electrochemical cell) followed by pH adjustment, flocculation, precipitation, and multimedia and cartridge filtration.
o Treated water was injected using nine injection wells.
o 121 million gallons of groundwater treated.
o 141 pounds of chromium removed from groundwater.
-- In situ ferrous sulfate addition
o Two wells that did not meet cleanup goals using P&T were treated using ferrous sulfate.

Cleanup Authority:
CERCLA Remedial
-- ROD Date: 3/18/88
-- First ESD (October 25, 1999) added in situ chemical treatment to address residual contamination at the site.
-- Second ESD (September 10, 2003) eliminated the 30-year monitoring of site after completion of the remedial action

EPA Contact:
Ernest Franke, RPM
U.S. EPA Region 6
1445 Ross Avenue
12th Floor, Suite 1200
Dallas, TX 75202-2733
Telephone: (214) 655-8521

State Contact:
David Hastings
Texas Natural Resources Conservation
Commission (TNRCC)
P.O. Box 13087
Austin, TX 78711
Telephone: (512) 239-2030

Heavy Metals (Chromium)
Maximum concentration of chromium detected during 1986 sampling event was greater than 50 mg/L (perched zone aquifer)

Waste Source:
Unlined wastewater-holding ponds and waste drum burial

Type/Quantity of Media Treated:
-- Groundwater is found at 30-45 ft bgs.
-- Extraction wells are located in 2 aquifers, which are influenced by production wells in the area.
-- Hydraulic conductivity ranges from 1.6 to 5.1 ft/day.
-- 121 million gallons treated as of December 1997.

Purpose/Significance of Application:
Includes on-site treatment for chromium; relatively low groundwater flow; contamination in two aquifers.

Regulatory Requirements/Cleanup Goals:
-- Remediate groundwater so that chromium levels are less than the maximum contaminant level (MCL) or primary drinking water standard.
-- Prior to 1990, the drinking water standard for chromium was 0.05 mg/L; in 1990, EPA revised the drinking water standard to 0.10 mg/L.
-- Treated effluent that is injected into the aquifer must have a chromium level of less than 0.10 mg/L.
-- The remedial system was required to create an inward gradient toward the site to contain the plume.

Groundwater P&T
-- As of December 1997, all six wells in the Trinity Aquifer and two wells in the Perched Zone had achieved chromium concentration less than 0.10 mg/L.
-- The P&T system removed a total of 141 pounds of chromium from the groundwater.
-- Effluent chromium levels met the required performance standard of 0.1 mg/L. Therefore, injection of effluent occurred throughout system operation.
-- The site operators concluded that the plume had been contained in both aquifers.

In Situ Ferrous Sulfate Treatment

-- The two wells, PRW-20 and PRW-28 that did not meet cleanup goals using P&T were treated with two rounds of ferrous sulfate. The ferrous sulfate treatment reduced chromium concentrations to below the cleanup goal in both wells.

Cost Factors:
Groundwater P&T

-- The capital costs of remedial construction were $1,927,502. Remediation system construction was from January 1992 to August 1993.
-- Operation and maintenance costs from 1993 to 1996 were $560,232.

In Situ Ferrous Sulfate Treatment

-- The combined cost of two treatments with ferrous sulfate and plat operations for three months was approximately $42,600 (cost in 1999 dollars).

Basin Radiator & Supply operated a radiator repair facility at this site from 1960 to the early 1970s. Wastewater containing chromium was discharged to unlined ponds, and waste radiator sludge containing chromium corrosion inhibitors was buried on the site. In 1977, the TNRCC discovered elevated levels of chromium in the groundwater during investigations conducted in response to citizen complaints of contaminated well water. This site later became known as the Odessa II South (S) site. The Odessa IIS site was placed on the NPL in June 1986, and a ROD was signed for the site in March 1988.

The extraction system used at this site consisted of six extraction wells constructed in the Trinity Sand Aquifer and four extraction wells in the Ogallala Formation. Extracted groundwater was treated with ferrous iron (produced on site in an electrochemical cell), pH adjustment and aeration, clarification, and multi-media and cartridge filtration. By December 1997, all of the recovery wells had met the cleanup goal with the exception of PRW-20 and PRW-28, located in the Perched Zone.
Ferrous sulfate was injected into PRW-20 and PRW-28 on December 4, 1998. The wells were restarted on December 10, 1998, and sampled on a regular basis. Based on the results of the samples showing chromium concentrations below the cleanup goal, well PRW-20 was shut off on February 20, 1999. After 90 days of data showed chromium concentrations remained below the cleanup goal, the well was treated with ferrous sulfate a second time, then plugged and abandoned.

In Well PRW-28, chromium concentrations initially decreased to levels below the cleanup goal then increased to levels above the cleanup goal. On April 30, 1999, the well was treated a second time with ferrous sulfate. On December 10, 1999, after all wells in the Perched Zone and Trinity Aquifer had met the cleanup goals, the Closure Phase began. This phase included decommissioning and pressure washing the treatment building; plugging the remaining wells, and disconnecting the utilities.
There were several startup problems that delayed full-scale operation of the P&T system at this site, including clogging of injection wells and encrustation of the multimedia filter by iron and calcium. These problems were solved by modifying the P&T system.