Code of Maine Rules
06 - DEPARTMENT OF ENVIRONMENTAL PROTECTION
096 - DEPARTMENT OF ENVIRONMENTAL PROTECTION - GENERAL
Chapter 586 - RULES PERTAINING TO DISCHARGES TO CLASS A WATERS

SUMMARY: This rule establishes criteria to define what constitutes effluent quality necessary to ensure the standards for class A waters are met.

BASIS STATEMENT

These criteria provide a definition of effluent quality that is equal to or better than the receiving water which can be measured and evaluated for the purpose of permitting discharge facilities. The section of law ( 38 M.R.S.A. Section465(2)(C) which contains the equal to or better than language creates certain regulatory ambiguities. While the phrase 'equal to' has an empirical basis which can readily expressed, the phrase 'better than' implies an allowance for change, but does not assign where any benefit can be placed. Certain human benefits may have negative ecological consequences or vice versa. This regulation, therefore, relies on criteria equal to measured ambient values in the receiving water and allows for variation from these measured equivalencies only to account for natural or analytical variances and where these variances are known or expected not to cause any negative impacts either to the ecological balance or to human values. Certain criteria rely on a seasonal time span to specify the period of equivalency. Because water chemistry can vary from moment to moment, this regulation allows the Department to designate appropriate seasonal periods within which data are gathered.

The pH of the water may affect biological communities by either increases or decreases. pH is known to fluctuate, sometimes substantially over brief periods. A sustained variation of + 0.2 pH units from the seasonal median concentrations is not significant and is not expected to have any measurable effect on the biotic community. A measure of central tendency, the median, is used to define what is equal. By using a seasonal median value, the criteria is not strongly affected by widely outlying values. The allowed variation is consistent with natural variations which occur.

This rule limits the discharge of nutrients to the seasonal median concentrations. It is recognized however that impacts from nutrients are dependent on Liebig's Law of the Minimum, that productivity is limited as long as the limiting nutrient is controlled. This rule allows the discharger to exceed the seasonal median concentration for any nutrient if it is demonstrated that a better condition can occur and that the biological community will still be as naturally occurs. A further constraint is placed on the discharger which prohibits significant alterations of the particle size of algae or other organic growths which can create a negative impact on the community.

Temperature of the effluent is limited to a variation of no more 0.5[DEGREE]F from the temperature of the receiving water. This value is consistent with natural daily fluctuations and is a condition to which the biotic community is well adapted.

The dissolved oxygen content of the effluent shall be equal or exceed that of the receiving water at all times but shall never be less than 7 parts per million or 75% saturation as expressed in Section 465(2)(B) of the statute.

Discharge of all other substances of concern is controlled by Section 6. The concentration in the effluent shall not exceed the seasonal median concentration for any of these constituents in the receiving water. The seasonal median value is chosen for those reasons stated in the above discussion for pH.

AUTHORITY: 38 M.R.S.A., Section343-A, 464(5) , and 465(2)