A.12 Formosa Plastics, TX

A.12.1 Summary

Environment:	Marine
Scale:	Full
Contaminants of Concern:	Ethylene dichloride
Final Remedy:	Site was partially dewatered by cofferdam. Partially dewatered sediment was placed on barges and mixed with 10% cement to off-load and dispose. Disposal at 2 hazardous waste landfills. One was 264 miles away; the other was 105 miles away.

A.12.2 Site Description

The site is located in Texas, and contaminated sediments consisted of 6–12 ft of soft, silty bay floor underlain by thick, high plasticity clay.

Year: 1992

Water Depth: 25–30 ft

Target Volume: 3,300 yd³

Actual Volume Removed: 7,500 yd³

A.12.3 Remedial Objectives

Ethylene dichloride: 500 ppm

Remedial area: Area of 150 by 350 ft in corner of an active turning basin, 1.1 acre.

A.12.4 Remedial Approach

Wet hydraulic dredgingDredging by use of a large suction pipe mounted on a hull and supported and moved about by a boom, a mechanical agitator, or cutter head which churns up earth in front of the pipe, and centrifugal pumps mounted on a dredge which suck up water and loose solids. did not work. The site was excavated with a barge- mounted crane and environmental bucket. Hydraulic dredging was the planned method of excavation, but due to severe water capacity limitations on land, mechanical dredging was performed. Concern over dredging causing even more erosion to channel stabilization. Active dredging periodically halted due to traffic.

Soft silty sediments kept "running into" the hot spot from the surrounding areas. Surface-to-bottom silt curtains with anchors on bottom were installed, and anchor cages were added to hold top of curtain in place.

Two passes were required because the first pass, using the hydraulic method, did not work effectively.

A.12.5 Monitoring

RAOs/project objectives achieved?: Project met all goals at all locations. No cappingTechnology which covers contaminated sediment with material to isolate the contaminants from the surrounding environment. or backfill was needed at this site for residuals.

A.12.6 References

Agency for Toxic Substances & Disease Registry as updated Oct 2009. Preliminary Public Health Assessment Alcoa (Point Comfort)/Lavaca Bay. http://www.atsdr.cdc.gov/HAC/pha/pha.asp?docid=46&pg=3.

U.S. EPA. Performance-Based Remedy Decision Document. Oct 2009. http://www.epa.gov/region6/6pd/rcra_c/pd-o/final_dd-fpctx100909.pdf.

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

Publication Date: August 2014