Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 387

8.4.3 R EGULATORY R ESPONSE : R EMEDIATION AND W ATER S UPPLY R EPLACEMENT
The record for the Tallevast site rel ects signii cant effort by the responsible party to delineate the
contamination, report i ndings to the regulatory agencies, and initiate voluntary remedial actions.
Although not required under environmental regulations to communicate directly with the commu-
nity, the responsible party made signii cant attempts to keep them informed, address their concerns,
and provide i nancial recompense to the affected community. Substantial additional effort by FDEP,
FDOH, and Manatee County Environmental Management was required to oversee the investiga-
tion, engage an active and concerned community, address health issues, and respond to a heavy
involvement by local, state, and federal elected ofi cials, as well as intensive coverage by the local
media. FDEP worked with the responsible party to aggressively investigate the extent of contamina-
tion, which was accomplished by installation and sampling of 250 monitoring wells in the space of
only a few years. A soil removal action and construction and operation of an interim remedial action
were also used to remove contaminants from the source area. 1,4-Dioxane turned out to be the most
widespread contaminant. This i nding greatly expanded the scope of the investigation and presented
a challenge to both analysis and remediation.
The primary remedial strategy is groundwater extraction and treatment for removal of trichloro-
ethylene, perchloroethylene, cis -1,2-dichloroethylene, 1,1-dichloroethylene, 1,1-dichloroethane, and
1,4-dioxane. The groundwater extraction plans include on-site extraction wells, six extraction trenches
in the upper aquifer totaling more than 1 mile of linear trenching to a depth of approximately 25 ft
bgs, and 50 off-site extraction wells in several lower-aquifer units (Arcadis-BBL, 2007c). Figure 8.5
shows the coni guration of extraction trenches at the former American Beryllium site.
Pilot testing was performed to evaluate treatment technologies—including photo-oxidation, ozone-
peroxide oxidation, and biostimulation—to remove 1,4-dioxane and chlorinated solvents. Pilot-test
outcomes are described in the following sections. The treatment technology selected at that time for
the on-site Interim Remedial Action was the Photo-Cat™ advanced oxidation system coupled with an
iron oxidation pretreatment system consisting of a 20,000-gallon inl uent tank to facilitate contact
time with a coagulant and precipitation of iron. A series of bag and cartridge i lters provides second-
ary i ltration for removal of iron hydroxide precipitate. Efl uent from the Photo-Cat system is further
treated by two larger GAC canisters installed in series in a lead/lag fashion that remove any remain-
ing 1,1-DCA and polish the treated groundwater. Following GAC treatment, the groundwater is dis-
charged to the Manatee County wastewater treatment plant (Arcadis-BBL, 2007c).
The Photo-Cat water treatment system destroys VOCs and 1,4-dioxane by mixing titanium diox-
ide (TiO 2 ) catalyst with the groundwater and exposing it to UV light in a reactor; the contaminants
are converted to carbon dioxide, water, and salts. Pilot testing (described further in the next section)
coni rmed that the Photo-Cat system reliably treats trichloroethylene (TCE) and 1,4-dioxane to less
than 3 μg/L, which is at or below the anticipated discharge limits to be established by Manatee
County (Arcadis-BBL, 2007c).
8.4.3.1 UV Oxidation Pilot Treatability Study
Purii cs ES, Inc. conducted an on-site pilot test using the Photo-Cat UVOx treatment process, a
patented closed-loop TiO 2 slurry-based photocatalytic process to remove 1,4-dioxane and VOCs
from groundwater at the former ABC facility. * Bicarbonate ions, abundant in the carbonate aquifers
at the Tallevast site, scavenge the hydroxyl radicals generated by the Photo-Cat process and can
limit the effectiveness of the photocatalytically generated hydroxyl radicals. Bicarbonate is con-
trolled by lowering pH with sulfuric acid, nominally to 4.6, where bicarbonate is converted to CO 2 ;
however, to control formation of iron hydroxide precipitates from dissolved iron present in the upper
aquifer, pH must be further lowered to 3.0 (Powell, 2005).
* In United States, Photo-CAT is sold under licenses from Purii cs ES by Basin Water; the technology is NSF-61 certii ed
for drinking water systems.