Monitoring for Phytoremediation of Groundwater Contamination - Introduction to Phytoremediation of Contaminated Groundwater - page 351

15

Monitoring for Phytoremediation
of Groundwater Contamination

In 1977, the Federal Water Pollution Control Act was
amended as the Clean Water Act (CWA). In general, the
CWA provides for the regulation of the release of
contaminants to water. This regulation is monitored by
the USEPA by effluent standards, and permits are required
to ensure the discharge of acceptable levels of wastes. The
CWA covers contaminant levels that affect aquatic life and
recreational standards, although the CWA affects drinking-
water quality by proxy. In 1974, the Safe Drinking Water
Act (SDWA) was enacted to regulate the quality of
drinking water, either existing or potential sources of sur-
face or groundwater. This regulation also is monitored
by the USEPA through water-quality standards, and
municipalities are required by law to treat drinking water
to these standards.
To track the manufacture, use, and disposal of potentially
hazardous wastes that could affect water quality, the
Resource Conservation and Recovery Act (RCRA) was
enacted. It is managed by the USEPA, or states if so directed.
It also addresses releases from underground storage tanks.
The Comprehensive Environmental Response, Compensa-
tion, and Liability Act (CERCLA), or Superfund, was
enacted to deal with those previously contaminated sites
not covered by RCRA.
Plants can be installed at sites characterized by
contaminated groundwater to achieve part or all of the site
remedial goals required by these various regulatory
programs. Although these goals will be site specific, they
have in common the requirement of establishing plant
growth. But it is not sufficient from a regulatory perspective
to simply plant a phytoremediation system and then walk
away. Part of most remedial programs requires monitoring
of the groundwater or remedial apparatus to verify that
remediation is occurring and to document its performance
over time. This chapter provides some basic approaches that
can be used to evaluate the success of phytoremediation
implemented at sites characterized by contaminated ground-
water.

15.1 Plant Physiologic Methods

A plant's survival depends on its interaction with the
various components of soil, microbes, water, and air. These
interactions provide the opportunity to evaluate the effect
of plants when applied to remediate

contaminated

groundwater.

15.1.1 Rhizospheric Community Analysis

Rhizospheric processes are important to monitor and
quantify at groundwater-contaminated sites because
contaminants completely mineralized or absorbed in the
rhizosphere are not available for plant uptake or potential
transfer to other parts of the immediate environment.
Rhizospheric processes can be monitored using a com-
bination of field and laboratory approaches. At the field
scale, soil material representative of the root zone for most
plants can be obtained with a stainless-steel hand auger.
In the laboratory, the biodegradation potential of these
sediment samples can be assessed using microcosm
studies, where sediment samples are amended either with
radiolabeled contaminants to track the appearance of
biodegradation end products such as 14 CO 2 or are amended
with nonradiolabeled contaminants to track their disap-
pearance. Microbial numbers can be quantified using the
most probable number (MPN) technique (Jordahl et al.
1997), which is based on the appearance of growth in serial
dilutions.
To further determine if this increase in growth translates
to an increase in the bacteria needed to degrade specific
contaminants, molecular approaches, such as fatty acid
methyl ester analysis (FAME), phospholipid fatty acid anal-
ysis (PLFA), and denaturing gradient gel electrophoresis