Environmental Engineering Reference
In-Depth Information
A positive response will require structuring implementation procedures and strategies
in combination with a competent monitoring scheme to track progress. A very necessary
part of the implementation scheme is the speciication or prescription of success indicators
shown in the ellipse at the bottom right-hand corner of Figure 10.18. These indicators also
serve as markers for performance assessment of the impact mitigation scheme. We have
shown the requirements in terms of intermediate stage indicators and inal success indica-
tors. Since the time required for processes contributing to the natural attenuation to fully
complete their functions, it is necessary to prescribe intermediate indicators as tracking
indicators and as performance assessment markers. Note that we have used italicized nota-
tion for indicators when we mean them as markers and have left them without italicization
when we discuss them as general items.
Monitoring and sampling of porewater and soils are needed in the contaminant attenu-
ation zone. The choice of type of monitoring wells and sampling devices and their spatial
distribution and/or location will depend on the purpose for the wells and devices. At least
three separate and distinct monitoring-sampling schemes need to be considered:
1. Initial site characterization studies . Site characterization monitoring and sampling
provide information on site subsoil properties and hydrogeology. Subsurface
low delineation provides one with the information necessary to anticipate
transport direction and extent of contaminant plume propagation. With a proper
knowledge of the requirements of the veriication and long-term monitoring-
sampling schemes, a judicious distribution of monitoring wells and sampling
devices up- and down-gradient can be made such that the information obtained
can be used to service the requirements for all the three monitoring-sampling
schemes.
2. Veriication monitoring . This requires placement of monitoring wells and soil sam-
pling devices within the heart of the contaminant plume and also at positions
beyond the plume. Figure 10.14 gives an example of the distribution of the wells
and devices. Obviously, assuming that the wells and devices are properly located,
the more monitoring and sampling devices there are, the better one is able to
properly characterize the nature of the contaminant plume. Monitoring wells
and sampling devices placed outside the anticipated contaminant plume will
also serve as monitoring wells and sampling devices for long-term conformance
assessment.
3. Long-term conformance monitoring . This is essential to verify success of mitigation
scheme and for long-term management of the potential impact.
Analyses of samples retrieved from monitoring wells will inform one about the concen-
tration, composition, and toxicity of the target contaminant. A knowledge of the partition
coeficients and solubilities of the various contaminants, together with the monitoring well
information will provide one with the opportunity to check the accuracy of predictions
from transport-fate models. For organic chemicals detected in the monitoring-sampling
program, laboratory research may be required to determine the long-term fate of the
transformed or intermediate products. This is not a necessary requirement if modeling
predictions and especially if the indicators for the intermediate show good accord with
the sampling values of contaminant concentrations. Tests on recovered soil samples from
the sampling program should determine the environmental mobility of the contaminants
and also the nature and concentration of contaminants sorbed onto the soil particles (soil
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