Pinellas Plant

After evaluating the different methods available for treating the source of contamination at the Northeast Site, DOE selected a combination of electrical heating and steam injection. In electrical heating, an electrical current is applied to electrodes inserted into the subsurface, and as the current passes through the soil between the electrodes, electrical resistance heats the soil. Steam injection involves injecting steam from a boiler into the subsurface through injection wells or generating steam when hot water is injected around the heating electrodes. The electrical current and steam travel through the subsurface, heating the soil, the groundwater, and the waste material. As the temperature of the soil rises, the volatile organic contaminants are converted to vapor, which is captured and pumped to the surface through vacuum extraction wells. The recovered vapor is then treated at the surface. This interim action to remove contaminant source material was completed in September 2006.

Subsequent groundwater monitoring demonstrated that a small amount of contaminant source material remained in the subsurface. Therefore, in 2008 and 2009, approximately 3,700 cubic yards of contaminated soil were excavated using the large-diameter auger method and disposed of off site.

Currently, all remediation activities are complete and DOE is conducting closure monitoring of groundwater under the FDEP’s risk-based corrective action (RBCA) regulations.

Building 100 Area

Building 100, the largest building at the STAR Center, covers approximately 11 acres. During the period of DOE ownership, the building was used for offices, laboratories, and production facilities. Groundwater contamination at the Building 100 Area resulted from historical leaks of underground drain lines located beneath the building and from leaks or spills at the former drum storage pad near the northwest corner of the building. The drum storage pad was removed in 1983, and use of the underground drain lines was discontinued in 1989. The major groundwater contaminants of concern are trichloroethene, dichloroethene, vinyl chloride, and 1,4-dioxane.

A groundwater extraction and treatment system operated at the Building 100 Area from 1997 to 2005. Contaminated groundwater was extracted through two recovery wells located at the northwest corner of the building, and treated at the surface using an air-stripper treatment system.

The Building 100 Area was evaluated for potential closure under global RBCA, but it was concluded that long-term monitoring is currently the best solution. During the course of monitoring, DOE discovered two groundwater contaminant plumes that extend beyond the property boundaries, one to the south and one to the east. Therefore, DOE is evaluating options for plume management while continuing long-term groundwater monitoring to verify that the contaminant plume is stable.

Wastewater Neutralization Area

The Wastewater Neutralization Area includes the area south of Building 200, near the industrial wastewater neutralization facility. The industrial wastewater neutralization facility currently receives sanitary and industrial wastewater from the STAR Center industrial operations, neutralizes the water, and discharges it to the publicly owned treatment works.

In 1997, arsenic, trichloroethene, and vinyl chloride were detected in the groundwater at concentrations above federal and state regulatory limits. Arsenic is the principal contaminant of concern; trichloroethene and vinyl chloride concentrations are at low levels. The origin of the contamination in this area is not known.

Groundwater cleanup at the Wastewater Neutralization Area began in 1997 and continued into 2005. Contaminated groundwater was pumped from the subsurface and piped to the industrial wastewater neutralization facility, where the water was discharged to the publicly owned treatment works. Discharge from the industrial wastewater neutralization facility is sampled regularly to confirm that contaminant concentrations in the wastewater are below regulatory limits.

Extensive soil sampling was conducted at the Wastewater Neutralization Area in 1998 to identify areas of soil with elevated arsenic contamination. In 1999, approximately 22 cubic yards of soil was removed from the areas with the highest arsenic concentrations. This action removed the source of arsenic contamination.

FDEP issued written approval to proceed with the closure of the Wastewater Neutralization Area in May 2007. Currently, DOE is working with FDEP and the STAR Center to establish institutional controls at the STAR Center. Institutional controls will ensure the protection of human health and the environment by restricting access to shallow soil and groundwater. Site closure will proceed once these controls are in place.

4.5 Acre Site

The 4.5 Acre Site was sold to a private landowner in 1972, and DOE currently leases the site while groundwater remediation is ongoing.

During the period of DOE ownership, the 4.5 Acre Site was used for the disposal of drums containing waste resins and solvents. This practice resulted in the contamination of groundwater in the shallow surficial aquifer. The main contaminants of concern are trichlorethene, dichloroethene, vinyl chloride, and benzene. The drums and the contaminated soil were removed in 1985.

In 1990, a groundwater extraction and treatment system was put into operation at the 4.5 Acre Site. Contaminated groundwater was extracted through seven recovery wells at the site, treated with an air stripper to remove the volatile organic contaminants, and discharged to a publicly owned water treatment system. For several years, this treatment reduced the mass of the contaminant plume and contained it within the boundaries of the site. By 1997, however, the treatment system no longer effectively reduced concentrations of groundwater contaminants.

A dual-phase extraction system was installed at the site in 1997 to replace the groundwater extraction system. The dual-phase system consisted of a vacuum pump linked to 22 extraction wells. The dual-phase aspect of the system referred to the system’s capability to recover both contaminated water and contaminant vapors from the subsurface. The dual-phase system was an improvement over the groundwater extraction system because it used a vacuum to help move the groundwater and recover vapor from subsurface areas not reached by the groundwater extraction system.

By the end of 1998, the dual-phase system had treated approximately 9.45 million gallons of contaminated groundwater. This system was effective at removing high concentrations of contaminants, but it became less effective as contaminant concentrations decreased.

To treat the remaining lower concentrations of contaminants, DOE selected a type of enhanced bioremediation called biosparging. Bioremediation helps naturally occurring subsurface microorganisms break down organic contaminants into non-toxic compounds. A biosparging system, consisting of three horizontal wells 500 feet long, was installed at the site in late 1999 to enhance aerobic bioremediation. Aerobic bioremediation takes place in the presence of oxygen. The system injects air into the subsurface; the air passes through the groundwater and provides an oxygen-rich environment for the aerobic microorganisms, increasing their ability to break down organic compounds. The effectiveness of the biosparging system was limited by preferential pathways in the subsurface, which caused the injected air to contact only a small portion of the aquifer. Also, high chemical-oxygen demand in the aquifer material used up most or all of the oxygen in the injected air before aerobic conditions could be attained. The biosparging system was shut down in May 2003.

Subsequent groundwater monitoring showed that elevated contaminant concentrations remained in the subsurface. In response, DOE conducted an investigation in the summer of 2007 to determine if a source of contaminants was present in soil. Nearly 1,200 soil samples were collected and analyzed to characterize a 1-acre area of the site, and results indicated that a contaminant source was present.

In 2008 and 2009, approximately 2,500 cubic yards of contaminated soil were excavated using the large- diameter auger method and disposed of off site, thereby removing the source of contamination.

Currently, all remediation activities are complete and DOE is conducting closure monitoring of groundwater under the FDEP’s RBCA regulations.

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