Environmental Fate and Transport of Solvent-Stabilizer Compounds - Environmental Investigation and Remediation - page 168

TABLE 3.21
Initial Rates of 1,4-Dioxane, THF, and MTBE Oxidation by
Propane-, THF-, and Dextrose-Induced Mycelia of Graphium sp.

Induction Compound 1,4-Dioxane THF

Propane 3.8 ± 1 115 ± 3

THF

9.2 ± 5 123 ± 22

Dextrose

0 ± 6 20.4 ± 25

Source: Skinner, K.M., 2007, Graphium species. PhD Dissertation, Oregon State
University, Corvallis, OR.
Note: Units: nmol/h per milligram dry weight.

3.4 LABORATORY, FIELD, AND MODELING STUDIES OF
1,4-DIOXANE MOBILITY
The best evidence for 1,4-dioxane's high mobility comes from i eld studies. A growing number of
cleanup case studies have characterized the occurrence of 1,4-dioxane from which interpretations
of its mobility relative to solvents can be made. Laboratory column studies of 1,4-dioxane
breakthrough in soil columns are also informative. Modeling can also yield an understanding of
1,4-dioxane's high mobility relative to methyl chloroform, its host solvent. This section summarizes
laboratory and i eld studies and presents some screening-level modeling calculations of the relative
mobility of 1,4-dioxane at solvent release sites.

3.4.1 L ABORATORY S TUDIES
A common approach to establishing the retardation rates of contaminants migrating in the subsur-
face is to perform column tests on saturated soil columns. This approach generally involves steril-
izing a column containing a known mass of soil and saturating the soil with water, establishing a
pressure gradient and l ow rate for the water, then adding a solute to the water and measuring for its
presence in the column efl uent. Samples of column efl uent water are taken at regular intervals and
analyzed for the contaminant under study. Breakthrough occurs when the efl uent concentration
i rst yields a detection of the subject contaminant, and equilibrium is established when the efl uent
concentration equals the initial concentration.
Retardation factors ( R f —see Equation 3.32 in Section 3.3.2.3) vary with the l ow velocity in column
tests. In i eld tests, the duration of the observation period and the distance over which i eld measure-
ments are made also affect the retardation factor value. Retardation factors for 1,4-dioxane predicted
from i eld data were twice the values measured in laboratory tests of soil columns ( Table 3.22 ). The
difference was attributed to heterogeneities in the aquifer media encountered at the i eld scale. Highly
soluble and miscible compounds are more likely to migrate into low-permeability zones, thereby
increasing retardation values derived from i eld observations (Priddle and Jackson, 1991).

3.4.2 F IELD S TUDIES
In a study of 1,4-dioxane migration relative to other contaminants at the Gloucester Landi ll near
Ottawa, Canada, researchers found that the rate of contaminant migration was inversely proportional
to the octanol/water partition coefi cient ( K ow ). The retardation factors and relative mobilities of organic
compounds released at the landi ll were ascertained by using the ratio of the plume length for each