Remediation Technologies - Environmental Investigation and Remediation - page 336

(2002) concluded that the model effectively simulated the removal rates and distribution of 1,4-diox-
ane in the plant material that have been documented by others in laboratory experiments. The CTSPAC
model could therefore be used to estimate removal rates from contaminated sites.
In a second modeling study, Ying (2008) developed a dynamic model for the uptake and trans-
location of contaminants from a soil-plant ecosystem (UTCSP) using the STELLA ® modeling tool
(isee systems, inc., Lebanon, New Hampshire) UTCSP assesses simultaneous transport, accumula-
tion, and transpiration of water and contaminants in plant systems. The model was calibrated with
experimental data and then used to predict 1,4-dioxane phytoremediation from a sandy soil by a
poplar tree. Results indicated ~20% 1,4-dioxane removal from the soil in 90 days. Ying (2008)
identii ed a steadily increasing mass of 1,4-dioxane in the plant material over time, as well as a typi-
cal diurnal distribution pattern in the uptake and translocation in the plant system, resulting from
daily variations of plant leaf transpiration. The study concluded that the UTCSP model could be
useful for estimating 1,4-dioxane phytoremediation in soil-plant systems.
7.5.3 G REENHOUSE AND F IELD S TUDIES
Ferro et al. (2005) performed greenhouse and i eld pilot studies toward the design of a full-scale
1,4-dioxane phytoremediation project at an industrial site in North Carolina. Greenhouse studies
were utilized to identify candidate species of both deciduous and coniferous trees to employ in the
full-scale design. The study concluded that the full-scale project should go forward with both types
of trees in use for continuous groundwater phytoremediation. In this scenario, the coniferous trees
address the contaminants during the winter when the deciduous trees, which are the major water-
extraction plants, are dormant.
Documented i eld application of phytoremediation of 1,4-dioxane has been limited to a single
study by Chiang et al. (2007a). A phytoremediation i eld pilot study was performed in an area of
approximately 8000 ft 2 to address a groundwater seep with the potential to impact surface water.
Over 100 poplar trees were planted in 12 rows perpendicular to the groundwater l ow direction.
Later, an additional 100 hybrid poplar cuttings were planted between the trees to increase the imme-
diate water uptake capacity. Seep sample locations were not able to be sampled the following
summer because they were dry, which was interpreted to be a direct result of the dewatering (i.e.,
water uptake) capacity of the trees. Thus, although the specii c removal of 1,4-dioxane could not be
documented, the removal of impacted groundwater was deemed a successful outcome.
7.5.4 S UMMARY
Phytoremediation to remove 1,4-dioxane from soil and groundwater has been repeatedly demon-
strated in bench-scale studies, predominantly through the use of hybrid poplars. The primary
removal mechanism includes uptake into the plant and transpiration of the 1,4-dioxane out of the
leaves to the atmosphere. Because of the short half-life of 1,4-dioxane in the atmosphere, this process
could be considered an effective long-term method for the removal and destruction of 1,4-dioxane.
Climatic (i.e., growing season) and hydrogeologic (i.e., depth to groundwater) limitations are impor-
tant factors when considering phytoremediation of 1,4-dioxane.
7.6 BIOREMEDIATION
Bioremediation of common organic contaminants such as chlorinated solvents and petroleum
hydrocarbons has been demonstrated to be effective at many project sites, such that it is now con-
sidered a presumptive remedy for certain contaminants. In general, bioremediation is implemented
by providing amendments to the existing biocommunity in the form of nutrients, food, or oxygen.
In some cases, the native bacterial community is not robust enough to effectively address the con-
taminants present. In these cases, bioaugmentation with specialized bacteria is often performed.