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The National Pollutant Discharge Elimination System (NPDES) is utilized when a discharge is made to
any surface water. The NPDES program provides for a non-degradation analysis of the receiving
stream water quality analysis, and a review of the parameters of concern to determine the appropriate
limits and monitoring requirements. Permit limits are derived from the more stringent applicable water
quality standards, technology based effluent limits, and federal categorical limitations (not applicable in
this case).
Air Strippers are part of the selected remedy for Source Areas 4 & 7 and have been determined by the
Illinois EPA Bureau of Water to be an appropriate effective technology for the removal of VOCs.
VOCs in both areas are the primary contaminants of concern, however, the effectiveness of the air-stripping
system will be deferred until the design is completed and submitted.
A permeable reactive barrier wall was the proposed remedy for remediation of the leachate in Source
Area 9/10. The Illinois EPA, however, modified the remedy used for leachate control in this area,
based on additional data and analysis of the potential sources of contamination and public comment.
The remedy will be designed to meet regulations of Public Water Supplies and 35 Ill. Adm. Code Part
620 Class I Groundwater Standards for potable water supplies.
Sampling requirements vary from site to site, however, a protocol that has worked well for remediation
systems is to require more frequent initial monitoring. Once consistency is established, the frequency of
sampling may be reduced. One method frequently used is to require weekly sampling during the first
two months of operation, twice a month sampling during the next two months and finally monthly
sampling thereafter. A shutdown of the system would require a return to weekly sampling for a period
of time, before returning to the previous sampling frequency. Situations may call for a variance in the
frequency of sampling, requiring more sampling following a period of shutdown. The additional
sampling will allow for adjustments to be made in the establishment of system equilibrium.
Discharge Limits are based upon the most up-to-date information gathered for the parameters of
concern. Table 34 includes both aquatic toxicity and human-health-based criteria. In most cases, the
AATC (acute criteria) is used as the daily maximum quality-based limit. In some rare cases, a human-health-
based limit may be used as the monthly average limit, depending on the potential for longer-term
exposure. Discharge would be to a storm ditch, which would most likely be a zero low flow stream and
therefore, water quality criteria would apply at the end of the pipe and would be the permit limits.
Table 34. Discharge Limits
Parameter Acute Criteria Chronic Criteria Human Health
1,1 dichloroethylene 3000 ug/l 240 ug/l 0.95 ug/l
1,2-dichloroethylene 14 mg/l 1.1 mg/ -
ethyl benzene 210 ug/l 17 ug/l 9.3 mg/l
tetrachloroethylene 1.2 mg/l 0.15 mg/l 2.8 ug/l
toluene 2000 ug/l 230 ug/l 62 mg/l
