Environmental Engineering Reference
In-Depth Information
Nest of
monitoring
wells
Nest of treatment wells
Leaky underground storage
tanks
Groundwater table
is near surface
water table
r surface
Direction of
groundwater flow
Direction of
undwater flow
Present
contaminant
plume
Present
contaminant
plume
Anticipated longer term
contaminant plume
Enhanced NA treatment zone
FIGURE 10.20
Use of treatment wells and ENA treatment zone in combination with permeable reactive barrier to mitigate and
manage impact from leaky underground storage tanks. Treatments for enhancement can be any or all of the
following: geochemical intervention, biostimulation, and bioaugmentation. Treatment occurs in the pollutant
plume and down-gradient from the plume.
designed to collect leachates draining down from the waste pile. If the system functions
well—i.e., as designed—there should be very little leachate reaching the HDPE barrier. If,
however, leachate does collect at the HDPE barrier, and if this barrier is somehow breached,
the underlying synthetic membrane (most likely another HDPE) is designed to prevent the
leachate from escaping. Above this synthetic membrane there is a leak detection system
that will alert the managers of the landill that the irst HDPE has been breached and that
the leachate collection system is most likely malfunctioning. If the second membrane fails,
the underlying soil subbase can be designed as an attenuation barrier using NA principles.
10.10.1 Remediation as Control-Management
Technically speaking, remediation of sites and regions contaminated with noxious sub-
stances and contaminants belongs to a category separate from contaminant impact miti-
gation. We have included this here because the treatment wells shown in Figures 10.19 and
10.20 are in fact wells or devices that introduce remediation aids. In addition, it can be
legitimately argued that remediation of a contaminated site in effect removes the contami-
nant source—assuming of course that the remediation-treatment process is successful.
The priority requirement in remediation-treatment of a contaminated site is to eliminate
the health and environmental threats posed by the presence of contaminants in the affected
site. Traditionally, this objective is met with the dig and dump technique. Replacement with
clean ill material will now ensure that all the contaminants have been removed from the
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