Environmental Engineering Reference
In-Depth Information
9.2.2 Contaminants and Geoenvironment Indicators
An example of impacts from the discharge of liquid waste and/or sludge and solid waste is
shown in Figure 9.2. Not all the indicators shown in the diagram (depicted by the shaded
ovals) are sustainability indicators (SIs). These indicators have several functions. In the top
right-hand corner, the various pieces of information from the wastewater discharge from
the industrial plant, which are wastewater chemistry indicators, tell us whether the waste-
water discharge meets the regulatory requirements permitting discharge into the sewer
system or receiving waters. The wastewater chemistry indicators, which are material indi-
cators, could include, for example, suspended solids, alkalinity, metals, fats, oils, grease,
organic chemicals, etc. Failure of the wastewater chemistry to meet discharge standards
will require a re-engineering of the treatment system.
Information obtained from analyses of the sludge being discharged (from the discharge
end of the sludge pipe, i.e., the sludge discharge indicators) can be used to determine
whether the toxicity and sludge characteristics meet lagoon (holding pond) capabilities
or whether the sludge should be contained in a secure landill. This assumes that lagoons
and holding ponds do not generally have the same type of secure impervious barrier-liner
systems that are required for landills. In this instance, the sludge discharge indicators are
not sustainability indicators but are status indicators that provide one with the informa-
tion required to make the necessary judgment for disposal of the sludge.
The contaminant indicators located below the lagoon and the landill serve several pur-
poses. In the lagoon case, assuming that the barrier-liner system for the lagoon is not as
secure as the landill system, the contaminant indicators will tell us whether the contami-
nants escaping from the lagoon are in the range of acceptable concentrations. One needs
to rely on the attenuation characteristics and properties of the subsoil strata to further
ameliorate the concentration of contaminants as the contaminant plume travels further
into the soil substratum. If the contaminant indicators show unacceptably high concentra-
tions of contaminants immediately under the lagoon, regulations would require corrective
action to be taken.
The same situation applies to the contaminant indicators immediately adjacent to or
under the barrier-liner system of the landill. Corrective action is needed if the contami-
nant indicators exceed speciied concentration trigger levels. Acceptable concentration lev-
els reported by the contaminant indicators immediately under the barrier-liner system
do not mean that the other contaminant indicators located further away from the landill
would report favorably. Much depends on the nature of the contaminants and the trans-
port processes. Contaminant transport modeling, using the information from the irst set
of indicators under the barrier-liner system, can be useful. Predicted transport values
can be used to compare with the second set of contaminant indicators. The contaminant
indicators are seen to be markers that show progress of the contaminant front (i.e., track-
ers of transport), and if design speciications and expectations of attenuation are correct,
the indicators should accord well with predictions, provided that the transport models
accurately predict performance. The transport of contaminants has been briely discussed
in Chapter 2. A further detailed discussion of these transport and fate processes will be
found in Section 9.3.
9.2.3 Prescribing Indicators
Where and how are indicators prescribed? To a large degree, material performance and
system status indicators are speciied or determined on the basis of how or what one needs
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