Site Assessment and Characterization - Introduction to Phytoremediation of Contaminated Groundwater - page 132

indicate that plants can be used to control groundwater and
site hydrology to contain a plume of dissolved-phase con-
taminants, then the complete remediation of recalcitrant
contaminants by phytoremediation or other technologies
may not be warranted. In this case, the influence of plants
on the hydrology of contaminated groundwater can be con-
sidered to be a contaminant-independent process, as long as
the contaminant concentrations are below levels toxic to
plants. Finally, site assessment activities may reveal that
existing or native vegetation may be appropriate to meet
site-specific hydrologic goals and an engineered phytore-
mediation system need not be installed.
In Part II, methods and approaches are presented for
phytoremediation evaluation that can be used during typical
site-assessment and characterization activities at con-
taminated sites. These methods and approaches can help to
determine the viability of a particular site for hydrologic
containment or control by phytoremediation, either by
uptake of groundwater or through a decrease in recharge.
Such approaches are logical extensions of work conducted
by early researchers as documented in Part I. The selection
of plants, correct site characterization, design, installation,
and monitoring of a phytoremediation system to achieve the
three hydrologic goals also is discussed. In many cases, the
burden of proof that phytoremediation will achieve the
hydrologic goals is the responsibility of those proposing to
use phytoremediation, and this proof can be achieved
through proper site monitoring. Planting trees at a site typi-
cally does not require regulatory approval. However, the
application of plants to achieve site-remedial goals within
a regulatory context does require regulatory sanction and
approval.
Chapter 6 provides techniques used to investigate sites
with known or potential groundwater contamination. Some
of this information will be a review for hydrogeologists
who implement such techniques in their daily work. These
same hydrogeologists, however, may be surprised to dis-
cover how commonly collected groundwater data can be
used to assess plant and groundwater interactions. To
others, this information will provide a starting point
from which investigations can precede at individual
groundwater contamination sites where the application of
phytoremediation to achieve hydrologic goals is being
considered as one of many remedial options, for instance,
as part of feasibility studies. Chapter 6, however, does not
compare costs of different phytoremediation approaches, or
advocate a particular approach in order to realize cost
savings; this is left to the individual project manager.
Thus, no recommendations are given, for example, regard-
ing the amount or type of fertilizer to use or which would be
more cost effective.
Chapter 6 can be used by the following, depending on
site-specific needs:

• Environmental consultants or others involved in site restora-
tion to determine the range of remedial options for a particu-
lar site, including hydrologic control by phytoremediation;
• Environmental regulators who review proposals for
projects in which phytoremediation would be used for
hydrologic control;
• Environmental professionals and educators interested in
the interaction between plants and groundwater.

The first two users often are at cross purposes regarding
the fate of a particular site as a consequence of, in part, a lack
of defensible published data on the effectiveness of
phytoremediation of contaminated groundwater. Hopefully,
Chap. 6 will provide common ground between these two
users for discussion of phytoremediation for hydrologic con-
trol at specific sites to answer the general question, “Can
phytoremediation be used successfully at a site to decrease
the risks associated with contaminated groundwater?”

6.1 Site History of Contaminant Release,

Assessment, and Characterization

To comply with federal laws, state regulatory agencies
typically compile an annual list, or inventory, of sites
where regulated compounds have been detected. States are
given this responsibility pursuant to 40 Code of Federal
Regulations (CFR), part of the Clean Water Act legislation
passed in the 1970s. Based on the types of contaminants
found or the type of contaminated source area, the sites
are categorized under various laws. Recent spills or releases
within the workplace are regulated under the Occupational
Safety and Health Act (OSHA) under 29 CFR 1910.
The USEPA regulates spills or releases to the environment
under laws outlined in the Resource Conservation and
Recovery Act (RCRA) and Comprehensive Environmental
Response, Compensation and Liability Act (CERCLA, or
Superfund). Most sites inventoried in the United States
require an assessment of the contaminant distribution in
groundwater, the groundwater-flow rate, and potential
effects on human or ecological receptors, as well as a plan
and eventual implementation of corrective action(s) to meet
remedial goals.
The restoration of contaminated groundwater to compli-
ance levels is documented in two general types of legal
documents—a Corrective Action Plan (CAP) for sites
regulated under RCRA, or a Record of Decision (ROD) for
sites regulated under CERCLA. As part of the verbage in
each of these documents, regulatory agencies hold responsi-
ble parties to the two following goals at a minimum, regard-
less of the site-specific contaminant:

1. Hydrologic containment and(or) control of the

contaminant(s), and