Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 389

Inl uent concentrations in various pilot-test coni gurations ranged from 250 to 900 μg/L 1,4-dioxane and
2800-10,000 μg/L trichloroethylene. The corresponding rate constant for TCE, averaged from both
the upper- and lower-aquifer pilot tests, was 36.8 (L/min)/kW and for 1,4-dioxane, 24.9 (L/min)/kW.
The lower aquifer has higher chloride concentration, which also scavenges hydroxides and affects
TCE destruction, but has less impact on the destruction of 1,4-dioxane (Powell, 2005).
By modeling different extraction and contaminant migration scenarios, the timeframe to achieve
90% overall mass removal in approximately 30 years was estimated; however, the time to achieve
FDEP's groundwater target level, 3.2 ppb for 1,4-dioxane, may be greater than 100 years. A screen-
ing-level analysis was performed for ISCO and enhanced biological degradation to eliminate
1,4-dioxane in the source zone; this analysis determined that these technologies would have limited
effectiveness at the Tallevast site. As of April 2008, nearly 6 million gallons of groundwater have
been pumped and treated. The expanded extraction system with trenches, extraction wells, and
large-capacity treatment is expected to be fully operational by March 2009 (Arcadis-BBL, 2007c).

8.4.3.2 Ozone and Peroxide Oxidation Pilot Study
Samples of contaminated site groundwater were sent to Applied Process Technology, Inc. (APT) in
California to evaluate treatability of 1,4-dioxane and chlorinated solvents using APT's HiPOx™
technology. HiPOx, described further in Chapter 7, uses a continuous, in-line, at-pressure AOP to
destroy VOCs and 1,4-dioxane. The HiPOx process employs ozone (O 3 ) and hydrogen peroxide
(H 2 O 2 ) chemistry in a uniquely designed oxidation reactor. These reactants are injected under high
pressure directly into the treatment water stream at specii ed ratios and locations, generating
hydroxyl radicals that attack the bonds in organic molecules, progressively oxidizing contaminants
and their by-products into carbon dioxide, water, and salts. Table 8.2 summarizes inl uent and efl u-
ent concentrations for Tallevast groundwater treated with the HiPOx process and the corresponding
ozone demand (Herlihy and Bowman, 2005).
The reasons for selecting Photo-Cat instead of HiPOx are not stated in the consultant reports, but
the HiPOx system generally has a higher capital cost, but lower long-term operating and mainte-
nance costs, and the higher capital cost may have inl uenced the decision. Both appear to be effec-
tive at removing 1,4-dioxane and chlorinated solvents, and both require the use of hazardous
chemicals (sulfuric acid for Photo-Cat and hydrogen peroxide for HiPOx). Systems dependent on
UV light may be impeded where nitrate, colloids, or other light-blockers are present, whereas sys-
tems using ozone may form undesirable bromates where bromide is present.

8.4.3.3 In Situ Biostimulation and Bioaugmentation Treatability Study
Primary and secondary evidence was established for reductive dechlorination of chlorinated
solvents, but it was concluded that biodegradation of 1,4-dioxane through biostimulation or bioaug-
mentation was unlikely to be effective. The primary positive evidence includes the presence of
reductive dechlorination by-products, including cis -1,2-DCE, 1,1-DCE, 1,1-DCA, and ethene in
some groundwater samples; secondary evidence includes reducing geochemical conditions,

TABLE 8.2
Ozone Demand for HiPOx Treatment of 1,4-Dioxane and Trichloroethylene

Infl uent TCE
(μg/L)

Effl uent TCE
(μg/L)

Infl uent 1,4-Dioxane
(μg/L)

Effl uent 1,4-Dioxane
(μg/L)

Applied Ozone
(mg/L)

2700 2 500 3.2 15.2

2700 4.2 300 3.2 13.6

2700 3 300 2.5 14.3

Source: Herlihy, P. and Bowman, R., 2005, HiPOX-TM Technology Lab Testing, Former American Beryllium site, Tallevast,

Florida. Pleasant Hill, CA: Applied Process Technologies Inc.