Technical Bulletin No. 0355: A Review of Variability in Effluent Quality Discharged by Selected Pulp and Paper Industry Sources

Selection of the appropriate relationship between the annual average, maximum 30 day, or maximum daily effluent quality limitations for BOD and total suspended solids was of particular interest to the pulp and paper industry, since these values were commonly incorporated into discharge permits. The subject was addressed extensively by the National Council staff in the development of existing effluent guidelines, and continues to be an important element of the technical studies program.

This technical bulletin is a review of the methods used by EPA, and described in the Development Document for the Phase III Effluent Guidelines. The bulletin contents include a review and description of the methodology used by EPA to arrive at maximum 30 day and maximum daily limits, as well as alternate methods used by the Council staff. The database draws upon a 33 mill "verification phase" database common in part with that used by EPA but excluding a significant number in this total group of about 55 where the data were judged for one or more reasons to be inadequate for use in this study. It also draws upon, and uses extensively information in the Council's continuing treatment plant performance data collection program from 34 mills. In total about 75 years of data were examined.

The study suggested several modifications in the EPA methodology for developing maximum day and maximum 30 day averages that would more nearly reflect the variability in treatment plant performance for BOD and total suspended solids over the life span of permits. Among these were, (a) a change in the percentile selected for use in non-parametric statistical analysis, (b) the use of additional test procedures for goodness of fit, (c) statistical distributions capable of more nearly characterizing performance over the five year permit span from one year of data or a more extensive database, and (d) the development of variability factors reflecting a probability of occurrence.