BIOAUGMENTATION CONSIDERATIONS - Bioaugmentation for Groundwater Remediation - page 150

the desired depth. A digital scale or other measuring device provided by vendors can be used to
determine the mass or volume of culture added to each well/drive point.
For injections requiring smaller volumes (0.3-1 L) of culture per well/drive point, metering
devices have been developed that allow for the accurate injection of a smaller target culture
volume. For deeper injections in direct-push points, anaerobic water can be used to push the
culture into the formation. In these cases, the tubing from the culture vessel is not positioned to
the desired depth in the drive point, but rather is connected at the surface to the tubing carrying
the anaerobic water to the desired depth.

5.3.5 Distribution Techniques

There are a number of techniques that can be used to distribute the culture in situ . The first
traditional approach is to “push” in or chase the culture with an electron donor solution to
distribute the culture further into the formation. While a small fraction of the culture may be
pushed further into the formation, it appears (based on column studies) that most of the culture
will stay close to the injection well initially (as discussed in Section 5.3.1 and Appendix A ). It is
unclear how much further the culture will be transported under this scenario versus injecting
the Dhc at the end of the electron donor injection, as most Dhc transport is expected to occur as
a result of in situ growth and cell detachment.
A similar approach, which has been used to distribute Dhc in an aquifer prior to it being
fully reduced, is to sandwich Dhc between electron donor additions by injecting reduced
anaerobic water before and after the Dhc . In other words, a portion of electron donor mixed
with aerobic water is injected, then anaerobic water, then culture, followed by more anaerobic
water and the remaining electron donor mixed with aerobic water (as illustrated in Figure 5.3 ).
This technique is referred to as the “donut” approach, and it was developed to permit
bioaugmentation and electron donor addition in one mobilization and to allow for a large
portion of the electron donor to be introduced with aerobic water from an easily-obtained
hydrant source. The disadvantage of this approach is the possibility of Dhc being exposed to
oxygen in the electron donor injectate or aquifer. Therefore, the onset of reductive dechlorina-
tion may be slower if a fraction of the Dhc is inactivated. However, bioaugmentation and
electron donor addition can be accomplished in one mobilization, lowering field labor costs.

Section View

1. Dono r 2. Anaerobic

water

3. Microbial
culture

4. Anaerobic
water

5. Remaining
donor

Plan View

Figure 5.3. Schematic of “donut” approach to bioaugmentation culture injection.