Site Assessment and Characterization - Introduction to Phytoremediation of Contaminated Groundwater - page 151

Table 6.3 Decision-making list modified from Introduction to Phytoremediation (U.S. Environmental Protection Agency 2000a).
Decision Task

Define problem Conduct site characterization

Identify contaminant and media
Identify regulatory needs
Identify remedial objectives
Establish success criteria

Evaluate site for phytoremediation Perform site characterization to include data for phytoremediation

Identify phytotechnology that addresses site need
Review all available information
Select plants

Conduct preliminary studies Screening studies

Optimization studies
Conduct field plot trials
Reevaluate plant selection, if needed

Evaluate full-scale system Design system

Install system
Maintain and operate system
Evaluate system

Achieve objectives Take quantitative measurements

Meet criteria for success

Three separate frameworks are specific to the source of
contamination—groundwater, soils, or sediments. In the
groundwater flowchart, it is realized that hydrologic control
is a form of contaminant containment, as previously stated
earlier in this chapter. However, the flowchart provides only
two courses of action: (1) hydrologic control by prevention
of recharge through the contaminated area, similar to the
goal of a vegetative cover at a landfill; and (2) the
contaminated groundwater potentially being mechanically
pumped and re-applied back to the planted area as irrigation
water. Although hydrologic control can be defined as the
reduction of leachate formation by reducing recharge to the
water table, hydrologic control also can be used to capture
plumes in downgradient areas prior to transport off site.
This application is not included in this version of the ITRC
groundwater decision tree. However, the groundwater
decision flowchart supports the reduced feasibility of
phytoremediation of contaminated groundwater at sites
where the depth to groundwater is greater than about 20 ft
(6 m). This is not to say that plants cannot use groundwater
at depths greater than 20 ft, but that deep-planting methods
usually increase the installation cost and(or) remediation
time.
The ITRC released a second document that more com-
prehensively addresses the issue of hydrologic control by
phytoremediation and the processes for proceeding from site
assessment to site closure (Interstate Technology and Regu-
latory Council 2001). This document restates the importance
of plants in reducing recharge to groundwater. It extends the
previous document by acknowledging that plants can be
used to create hydrologic barriers to prevent groundwater

flow and contaminant transport off site. This ITRC docu-
ment addresses some of the potential limitations of a pro-
posed phytoremediation system, such as the potential lack of
performance during periods of presumed plant dormancy.
The ITRC document acknowledges that a conventional
pump-and-treat system could be used during dormancy. Of
course, the concern regarding the effect of dormancy on
groundwater can be answered only if the rate of groundwater
flow is known to enable predictions of groundwater move-
ment downgradient during dormancy to be estimated.
The 2001 ITRC document includes a section on the
technical requirements for phytoremediation to assist in
determining if a site is appropriate for hydrologic control
by phytoremediation. The process begins with assembling
members of a phytoremediation team and generating a
checklist, similar to Table 6.3 , that includes the following:
baseline site characterization, review of existing site
data, agronomic site assessment, site visit, definition of
remedial objectives, and answers to the question of how
phytoremediation can be used to meet the objectives at the
site. Once these data have been collected, a proposal that
outlines the goals is drafted and submitted to various
stakeholders for review, comment, and approval.
The document acknowledges a common problem at sites
being analyzed for phytoremediation—plant physiologists
can be concerned solely with plants, and hydrogeologists
can be concerned only with groundwater. These specialized
interests can result in little interaction between the scientists.
This indicates that other specialists should be involved, such
as risk assessors, environmental engineers, etc., if resources
permit. The document continues with other activities, such