Section 14. LAWS AND REGULATIONS
CATEGORICAL PRETREATMENT STANDARDS: THE FORECASTING
OF POTW REMOVALS OF POLLUTANTS AS A BASIS FOR REVISION
OF STANDARDS
John R. Milne, Project Engineer
Leslie D. Rose, Supervision Civil Engineer
Robert P. Miele, Head, Technical Services Department
County Sanitation Districts of Los Angeles County
Whittier, CA 90607
Untd a few years ago, each publicly owned treatment works (POTW) was permitted
by state regulatory authorities to treat industrial wastewater only to the extent necessary
to protect receiving waters. The Clean Water Act has now become the basis for categorical
pretreatment standards for industry and these standards must be enforced by the POTW
which serves the industry [ 1 ].
A new twist has been added to the rules, which adows, but does not require, a POTW
to give allowances to industries for the discharge of poUutants which are removed in part
by the POTW. The idea is simple in principle and apparently reasonable: If, for instance,
a discharger is limited by a pretreatment standard to a concentration of 1 mg/1 of copper
in the effluent which he discharges to the sewer, and if the POTW removes 80% of the
copper entering its plant, then the POTW may adow the firm to discharge as much as 5
mg/1.
Application of the principle, as pointed out by Lordi [2] and others, turns out to be
neither simple nor equitable. There are three problems: reliably predicting so-called
"consistent removals," imperfect knowledge about the relationship between influent and
effluent podutant concentrations, and vagueness in the regulations.
SCOPE OF THE STUDY
The present study was undertaken with the aim of determining the removals of trace
constituents in the Los Angeles County Sanitation Districts' Joint OutfaU System, determining the variabdity of removals between treatment plants, developing methods for predicting
them, and evaluating the desirability of requesting authority to grant allowances for removing them under the current regulations.
The Joint Outfall System is comprised of five biological treatment plants ranging in
capacity from 10-40 MGD each, and a primary plant to which they are tributary with a
capacity of about 400 MGD. Because the primary plant is being upgraded with 200 MGD of
secondary treatment capacity, the prediction of removals at it in the future is uncertain.
However, it is hoped that a study of existing plants wdl enable a better evaluation of future
options.
Because alternative methods of calculating removals may be allowed with EPA approval,
four different procedures were studied. In addition to evaluating removals themselves, an
effort was made to evaluate their reliabdity as well in order to provide assurances that
commitments to industry and regulatory authorities wdl be met.
The prediction of removals is equivalent to predicting effluent concentrations when
influent concentrations are known. Consequently, an effort was made to determine whether
effluent concentrations are, in fact, dependent on influent concentrations. If there does
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