Lavaca Bay, Point Comfort, TX

A.35 Lavaca Bay, Point Comfort, TX

A.35.1 Contacts

Regulatory Contact: USEPA

A.35.2 Summary

Environment:	Estuarine embayment
Scale:	Full
Contaminants of Concern:	Mercury, PAHs, methylmercury
Source Control Achieved Prior to Remedy Selection?	Yes
Final Remedy:	MNR (1700 acres), dredging (280,000 yd³)
Expected Recovery Time:	10-15 years
MNR viewed as a success?	Not yet determined

A.35.3 Site Description

The Lavaca Bay site is part of the larger Matagorda Bay system located in southeastern Texas, adjacent to the Gulf of Mexico. It is a shallow bay with an average depth of about 4 ft and covers approximately 60 square miles. Dredge Island is a 420 acre area located within the bay made up of dredge materials. The area surrounding this island is known as the "Closed Area." The primary sources of contamination at this site include past direct discharges and releases from metal refining and chlor-alkali processes.

Aluminum smelting was begun by the Aluminum Company of America (Alcoa) in 1948 and shut down in 1980. Bauxite refining began there in 1958 and continues to this day. Additional past operations have included cryolite processing, chlor-alkali production of sodium hydroxide and chlorine (1966-1979), and coal tar processing (by Witco Chemical Corporation, 1964-1985).

An offshore gypsum lagoon located on Dredge Island was used to hold mercury-containing wastewater from the chlor-alkali process. The overflow was then discharged to Lavaca Bay after a settling period. The Texas Water Quality Board ordered Alcoa to limit its mercury levels in wastewater discharges after it found elevated levels of mercury in crabs during the 1970s. In 1980, fishing was banned in the Closed Area. In 2000, this area was reduced following a decrease in concentrations of mercury in fish tissue.

This site was added to the National Priorities List in 1994. An ROD was issued for the site by the USEPA in 2001. A Consent Decree was signed by Alcoa with USEPA in 2005.

CSM summary: The primary natural recovery processes at the Lavaca Bay site is physical isolation. Two primary lines of evidencePieces of evidence are organized to show relationships among multiple hypotheses or complex interactions among agent, events, or processes. A weight of evidence approach includes the assignment of a numeric weight to each line of evidence. were collected to support this. A radiochemistry study was conducted to estimate the vertical extent of mercury contamination in sediments and sedimentation rates. Sedimentation rates vary between 0.3 and 2.0 cm per year. Hurricane scour modeling was conducted to determine the risk of sediment transport and the subsequent redistribution of mercury during future hurricane events. It was found that high-energy events would have negligible effects on mercury redistribution.

A.35.4 Remedial Objectives

The risk assessment showed unacceptable risks to human and ecological receptors from PAHs and mercury.

The RAOs for the site target a reduction in mercury levels in fish tissue to create the same risk level throughout the bay that would have existed without the Point Comfort Operations Plant. RAOs include:

Eliminate or reduce mercury and PAH loading from ongoing unpermitted sources to Lavaca Bay to the maximum extent practical.
Reduce mercury concentrations in surface sediments of sensitive habitats to an appropriate level.
Reduce mercury concentrations in open-water surface sediments that serve as a pathway for introducing mercury into the food web to an appropriate level. Reduce PAH concentrations in sediments to below 44.8 mg/kg total PAHs, the effects range median benchmark established by the National Oceanic and Atmospheric Administration.

Cleanup levels for mercury in sediments are as follows:

0.5 mg/kg mercury for sediments in open-water habitats
0.5 mg/kg mercury for sediments in marsh habitats

A.35.5 Remedial Approach

Final selected remedy: MNR (1700 acres), dredging (280,000 yd³)

Components of the remedy included:

Dredging of the most highly contaminated sediments and installation of a DNAPL collection or containment system (Witco Area).
Extraction and treatment of chlor-alkali process area groundwater and monitoring of surface water to evaluate the effectiveness of the hydraulic containment system.
MNR of remaining affected areas (aerial extent not available).
Institutional controls to manage human exposure to fish and shellfish.
Long-term annual monitoring of mercury in surface sediments, fish, and shellfish of the bay to confirm the natural recovery of sediment and fish tissue to acceptable levels.

The initial remedy for this site had called for EMNR (with thin-layer cappingTechnology which covers contaminated sediment with material to isolate the contaminants from the surrounding environment.) for sediments north of Dredge Island to eliminate an ongoing source of PAHs to the bay. Monitoring determined that natural recovery processes alone were sufficient. Currently MNR has been implemented in approximately 1700 acres of the Closed Area.

Primary lines of evidence collected to support physical isolation include radioisotope analysis and sediment age dating to document sedimentation rates. In addition, modeling was used to predict sediment stability during a hurricane.

A.35.6 Monitoring

Monitoring elements: Monitoring activities focused on analyzing risk reduction and includes monitoring of mercury in fish tissue as well as surface sediment chemistry.

RAOs/project objectives achieved? Mercury concentrations in sediments are reaching desired cleanup levels. Five marshes have met cleanup levels since 2005. There remains some localized open water sediment areas that are not recovering as expected, as well as locally elevated mercury concentrations in some marshes. In addition, while mercury concentrations in fish and crab tissue experience yearly fluctuations they are still elevated compared to the reference area.

Expected recovery time: 10-15 years

Projected monitoring costs: $1,660,000

RAOs/project objectives achieved? Overall, it is not yet determined if MNR is viewed as a success.

A.35.7 References

EPA Superfund Record of Decision. Alcoa (Point Comfort)/Lavaca Bay EPA ID: TXD008123168 OU 01. Dec 2001. http://www.epa.gov/superfund/sites/rods/fulltext/r0602001.pdf.

Record of Decision. Alcoa (Point Comfort)/Lavaca Bay Site CERCLIS# TXD 008123168. Dec 2001.http://www.epa.gov/region6/6sf/pdffiles/alcoa_lavaca_final_rod.pdf.

Five-Year Review Report. Alcoa (Point Comfort)/Lavaca Bay Superfund Site EPA ID# TXD 008123168. June 2011. http://www.epa.gov/superfund/sites/fiveyear/f2011060004079.pdf.

Major Contaminated Sediment Sites Database; Sept. 2004 as updated 2008. http://www.smwg.org/MCSS_Database/MCSS_Database_Docs.html.

Global Restoration Network, Case Study Detail. http://www.globalrestorationnetwork.org/database/case-study/?id=287.

Publication Date: August 2014

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