APPLICATION OF RISK ANALYSIS IN MEETING EFFLUENT
STANDARDS
Carolyn H. Harvey, Environmental Engineer
Union Carbide Corporation
Texas City, Texas 77590
Richard C. Allison, Associate Professor
University of Houston at Clear Lake City
Houston, Texas 77058
INTRODUCTION
In the past fifteen years industrial wastewater pollution control has advanced to the
point where technology can meet almost any effluent criteria. The rapid technical advances
have been geared to the stringent environmental regulations enacted since the mid-sixties.
Prior to 1968, treated industrial wastewater was only 30.5% of the total volume discharged.
By 1973, the percent treated had risen to 43.5% of all industrial discharges. The chemical
industry has been even more advanced in its treatment rising from 7% to 52% by 1973
[ 1 ]. Capital investment for wastewater treatment facilities has also risen appreciably from
a level of 2.4% to more than 20% in 1976 [2].
Operation and maintenance of treatment facilities to ensure the effluent quality is being
promoted by the Environmental Protection Agency. This paper presents a method for performing a rigorous analysis of a treatment plant's processes and operations to determine
deficiencies. These deficiencies can be monitored to warn of failure in plant performance.
The analysis technique selected to determine these deficiencies is Fault Tree analysis, a
logic technique developed in the aerospace industry [3,4].
FAULT TREE ANALYSIS
Fault Tree analysis is a comprehensive and ordered method of breaking down some
undesirable occurrence into its various causes and displaying them in logic form. After
completion of the logic diagram, highly likely logic paths, called critical paths, which
may cause the occurrence of the top event are determined. After determination of
these critical paths with their accompanying events, changes in procedures or equipment can be proposed which can prevent the occurrence of an event in the critical
path and therefore will prevent the occurrence of the top event. This analysis technique has been used successfully in the evaluation of the Apollo moon landing program
and the safety systems of the Minuteman Launch Control System [3,4].
After application of the Fault Tree technique to the system, the resulting logic diagram
will probably not be the only possible logic flow even though most of the undesired events
may have been considered. This is in part due to the knowledge of the system and experience of the analyst in both the wastewater treatment and the Fault Tree technique. Another
analyst may take the same events and derive a completely different logic flow for the occurrence. This is an advantage of the Fault Tree technique and demonstrates the many ways
a system may be described in logic flow. The differences between the logic flows will become less pronounced as the Fault Tree is reduced to determine its critical paths. The
analysis of the system being examined should be performed by someone knowledgeable
about the operation of the system. This will also ensure that the proper questions are
asked at each branch point in the logic flow.
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