- Agency Interest Number 81438
- Location Plaquemine, LA
- Media of Concern Groundwater
- LDEQ Contact Laurie Peacock
Site Background and Activities
On November 5, 1997 and September 30, 1998, the Louisiana Department of Health and Hospitals (LDHH) sampled water wells at the Myrtle Grove Trailer Park in Plaquemine, Louisiana, and detected levels of vinyl chloride and cis-1,2-dichloroethylene, exceeding Maximum Contaminant Levels (MCLs) established for Drinking Water under the Federal Safe Drinking Water Act. The two chemicals were detected again during a February 26, 2001 sampling event and verified on March 13, 2001. LDHH notified the Louisiana Department of Environmental Quality (LDEQ) on March 29, 2001.
The LDEQ began a groundwater investigation April 2, 2001. The initial objectives for the investigation were to: identify the source and extent of groundwater contamination and determine if additional exposure was occurring; identify potential sampling locations; perform a survey of water wells, irrigation wells and petroleum production wells; review and investigate potential sources listed in the Source Water Protection Plan for the City of Plaquemine supply wells and the Myrtle Grove Trailer Park; review historical land use and potential sources using aerial photos; discuss historical activities and potential sampling locations with local citizens; and investigate reports from citizens of potential hazardous activity.
The initial sampling program centered in the area nearest to the Myrtle Grove trailer park. A number of private wells, used primarily for irrigation and pond supply, were identified during the well survey. Contamination was found to be highest north of the trailer park. The Dow Chemical Company, approximately one mile north, was informed of the investigation and both the DEQ and Dow reviewed the status of known shallow groundwater contamination at the plant. Dow has several wells at the depth of the Plaquemine aquifer that are used to determine if the shallow contamination at the plant has moved deeper and away from the facility. None of these wells indicated contamination.
Dow entered into the investigation by beginning a soil boring program within the greenbelt south of the main plant entrance, sampling three different levels of the Plaquemine Aquifer to aid in the determination of the location and source of the contamination. Combining Dow’s data with the DEQ’s, over 120 sample points were used to delineate the extent of the plume. The investigation revealed that the area of contamination exists at approximately 120 – 200 feet below land surface (bls) and is approximately 1 mile wide by 2 miles long from just south of the Dow chemical plant to north of the City of Plaquemine supply wells. Use of the aquifer by the City of Plaquemine for drinking water and The Island Country Club for pond supply and irrigation have increased the movement of the plume southward.
The Louisiana Geological Survey Water Resources Bulletin No. 16 “Ground Water in the Plaquemine-White Castle Area, Iberville Parish” refers to the contaminated aquifer as the Mississippi River Alluvial Aquifer, which is known locally as the Plaquemine Aquifer. It is encountered at approximately 100 feet bls and is approximately 100 feet thick. The water is of poor quality, is hard and has high levels of naturally occurring iron and arsenic. The City of Plaquemine supplements its primary source of drinking water (wells located in Port Allen at approximately 2000 ft. deep in the Southern Hills Aquifer System) with treated water from this aquifer. Drinking water in Plaquemine is currently (2008) supplied equally from the two sources.
DEQ first requested assistance on June 14, 2001 from the Environmental Protection Agency’s (EPA) nationally known experts at the National Risk Management Research Laboratory Subsurface Protection and Remediation Division in Ada, Oklahoma. The national laboratory provided expertise in evaluation the fate and transport of contaminants in the aquifer. Additionally, EPA Region 6 in Dallas provided assistance with installation of monitor wells and expertise in modeling both potential sources and movement of the contaminants in the subsurface.
Due to the probable age and nature of the contamination, the exact location of the source of contamination is not likely to be determined. However, modeling performed by EPA Region 6 suggests a source area at and south of the former Lighthouse Road disposal site, owned by the Dow Chemical Company. This site, used in the 1960’s and 1970’s as an alternative location for disposal of waste, was remediated under the purview of the LDEQ and EPA in 2004 and 2005.
In October 2004, the LDEQ, EPA and Dow entered into a Cooperative Agreement wherein Dow committed to conduct a study of the current capability of the City of Plaquemine’s (“the City”) water treatment facility to treat contaminants, should they reach the City’s system. Dow also agreed to perform semi-annual sampling of 18 wells in the Plaquemine area to observe and track the contaminant plume. The final requirement of the Agreement was for Dow to perform a Remediation Study to evaluate the long-term need for remediation, and to evaluate options for remediation for the protection of human health and the environment. Dow submitted a final Remediation Study to both the LDEQ and EPA, dated April 27, 2007. This Study was approved by both agencies in correspondence dated July 24, 2007.
The Final Basis of Decision for the Final Remedy for Contamination of the Plaquemine Aquifer was issued July 9, 2008. The public has been kept informed of investigation activities and the Final Basis of Decision through various public meetings and public hearings. A new cooperative agreement between Dow, DEQ and EPA is being prepared wherein Dow will be required to submit various work plans and reports regarding the implementation of the preferred remedy. A Community Relations Plan will be required to describe how the community will be informed of monitoring results and progress of the remedy.
Sentinel wells near the City of Plaquemine drinking water supply wells are sampled quarterly to determine if the plume is nearing the city’s water supply. Eighteen wells in and around the plume are monitored semi-annually. Upon review and approval of a new sampling plan that will be required in the new Cooperative Agreement, the number, location of wells and sampling parameters for the monitoring system may be modified.
Map of Location of Myrtle Grove Sampling for source investigation
One drinking water supply in Myrtle Piezometer installed by Dow Chemical
Grove Trailer Park to aid in determining flow direction
in Plaquemine Aquifer
Documents and Reports
None at this time