Site Assessment and Characterization - Introduction to Phytoremediation of Contaminated Groundwater - page 137

(RI/FS) required by RCRA and CERCLA regulations. The
types of plants to be used may require some oversight by
local officials concerned with invasive species or plants that
are perceived to create aesthetic concerns.

proposed to achieve hydrologic control. A site visit also
permits the opportunity to interview others involved or
neighboring residents; a 5-min conversation with a long-
time resident near the site often reveals more information
than contained in a site report.
A visit also can reveal areas within the property boundary
of a contaminated site that cannot be used for
phytoremediation. The presence of buildings or parking
lots or other inaccessible areas may preclude the installation
of a phytoremediation system. Also, areas that receive high
foot or automotive traffic may have areas of reduced soil
permeability because of compaction. Airports or other
businesses may require specific lines-of-sight to remain
unobstructed to ensure safe business operation, thus
preventing the installation of a phytoremediation system in
those areas. Moreover, the presence of buildings on site may
negatively affect the amount of solar radiation available to
grow and sustain the phytoremediation system.
A site visit also can permit a conceptual model of ground-
water flow to be visualized. The local topography can be
used to approximate the direction of groundwater flow and
where recharge may occur. Steep topography often results in
steep hydraulic gradients and fast rates of groundwater flow,
which may limit the uptake of groundwater by plants at rates
high enough to affect groundwater flow and contaminant
transport. Conversely, low-lying areas that contain surface
water throughout the year or during certain periods indicate
groundwater discharge, which can potentially limit the flow
of contaminated groundwater to off-site areas. Areas of
standing water at high elevations, particularly for a short
time after precipitation events, can indicate areas of ground-
water recharge. For limitations to this approach, however,
see Chap. 4 and Haitjema and Mitchell-Bruker (2005).
Regardless of how much information can be gleaned about
the depth to water table from reports and site visits, however,
it still is useful to collect depth to groundwater data if only to
confirm or refute the data previously collected by others or to
establish the range of seasonal fluctuations that occur.
Finally, perhaps the most important reason to justify a site
visit is to examine the presence and extent of existing vege-
tation. The existence of vegetation indicates that the mini-
mum requirements for plant life are provided. The type of
plant also may provide a proxy on the depth to groundwater
or soil moisture content in the unsaturated zone as was
described in Part I.

6.3 Site Visit

The amount of information that is available about the con-
taminant release and delineation history at a particular site
will vary considerably. For some sites, a lot of information
may be available, but it may not apply to the areas that
require phytoremediation. Alternatively, the contamination
may be delineated in the source areas at some sites, because
the release event may be apparent, as with a ruptured pipe-
line, but contaminant delineation may not be as comprehen-
sive in downgradient areas.
Such site information often can be found at the state or
federal regulatory agency that oversees initial site-assessment
activities that follow a known or suspected release. The
amount of information available may vary from state to
state and from contaminant to contaminant, such as fuels
released by USTs, fuels released from aboveground storage
tanks (ASTs), or solvents released by various industries; each
type may be covered by separate assessment and corrective-
action programs. Assessment data often are generated by a
private consulting firm if a responsible party exists or by state
or federal agencies if the responsible party cannot be deter-
mined. Data generated is available through the Freedom of
Information Act (FOIA). Alternatively, discussions with state
or federal project managers offer a more direct route to this
type of site information, with the added benefit of initiating a
discussion about a potential phytoremediation project.
After perusal of existing site data, a visit to the site is
warranted. A site visit pays dividends by revealing much that
cannot be observed simply by going over files of data. Prior
to the investment of limited time and resources commensu-
rate with any proposed phytoremediation project, a site visit
may reveal that conditions of demographic issues, human or
wildlife receptors, and extent of the source area are not
conducive to phytoremediation. For example, consider the
scenario in which a UST leak from a gasoline station is
characterized by a large volume of gasoline floating on the
water table that is also located upgradient from a reservoir
used as a sole-source of drinking water. Because of the large
volume of gasoline in the subsurface and the short distance
to a surface-water receptor, more aggressive remedial
actions other than phytoremediation likely will be needed.
If the reservoir were not a source of drinking-water supply,
such a scenario could be acceptable for hydrologic control
by phytoremediation. In any event, a site visit helps to more
rapidly form remedial hypotheses and make informed
decisions on whether or not phytoremediation should be

6.4 Plant Hydroecology Assessment

and Characterization

Visits to contaminated sites around the world generally
would lead to observations of some type of plant growth,
even in arid desert areas. Plants, after all, represent more