Code of Maine Rules
06 - DEPARTMENT OF ENVIRONMENTAL PROTECTION
096 - DEPARTMENT OF ENVIRONMENTAL PROTECTION - GENERAL
Chapter 530 - SURFACE WATERS TOXICS CONTROL PROGRAM
Section 096-530-3 - Water Quality-based Effluent Limits for Waste Discharge Licenses

Universal Citation: 06 ME Code Rules ยง 096-530-3

Current through 2024-38, September 18, 2024

The Department shall establish appropriate discharge prohibitions, effluent limits and monitoring requirements in waste discharge licenses if a discharge contains pollutants that are or may be discharged at levels that cause, have reasonable potential to cause, or contribute to an ambient excursion in excess of a numeric or narrative water quality criteria or that may impair existing or designated uses. The licensee must also control whole effluent toxicity (WET) when discharges cause, have a reasonable potential to cause, or contribute to an ambient excursion above the narrative water quality criteria. In determining if effluent limits are required, the Department shall consider all information on file and effluent testing conducted during the preceding 60 months. However, testing done in the performance of a Toxicity Reduction Evaluation (TRE) approved by the Department may be excluded from such evaluations.

A. Specific pollutant approach. When specific toxic pollutants of known action and interaction are identified in a discharge or potential discharge, the water quality-based effluent limit is determined by use of the applicable numerical water quality criteria for the pollutants to protect aquatic life and human health and using the appropriate dilution described in section 4(A) below.

NOTE: See section 4(F) for procedures to address multiple discharges into a common receiving water.

B. Whole effluent approach. When the existing or proposed discharge contains two or more pollutants whose actions or interactions are unknown or when toxic components cannot be identified, WET effluent limits may be required for the protection of aquatic life. Whole effluent toxicity limits are the "acute no observed effect level" (A-NOEL) and the "chronic no observed effect level" (C-NOEL), expressed as percent effluent (the mathematical inverse of the applicable dilution factor), and must be greater than the actual receiving water concentrations (percent of effluent in receiving water at the appropriate dilution pursuant to section 4(A)).

C. Determination of Exceedence of Criteria. The results of all testing required by this rule must be submitted to the Department not later than the next discharge monitoring report required by the discharger's license, provided, however, that the discharger may review the toxicity reports for up to 10 business days of their availability before submitting them. Using information and guidance provided by the Department, dischargers shall evaluate test results being submitted and identify to the Department possible exceedences of applicable water quality criteria. The Department shall review all testing data as received. If these data indicate that the discharge is causing an exceedence of applicable water quality criteria, then: (1) the licensee must, within 45 days of becoming aware of an exceedence, submit a TRE plan for review and approval and implement the TRE after Department approval; and (2) the Department must, within 180 days of the Department's written approval of the TRE plan, modify the waste discharge license to specify effluent limits and monitoring requirements necessary to control the level of pollutants and meet receiving water classification standards. Evaluations of the reasonable potential for exceedence of criteria must be conducted upon any license action, following the provisions of section 3(E). The Department shall utilize mass discharge criteria for evaluating individual exceedences of specific chemical pollutants.

When considering the need for license limits, the Department may exclude from evaluations tests in a series done for an individual pollutant or WET test during five years only if the discharger satisfactorily demonstrates through implementation of a TRE pursuant to this subsection that the cause(s) for a high result have been identified and corrected. Additionally, tests subsequent to the high test(s) must not show reasonable potential for exceedence of water quality criteria. In making these determinations, the Department shall not exclude tests solely because the values are higher than other values obtained by the discharger.The Department shall issue a license limit in situations where an exceedence is recorded due to a valid test and a cause for the exceedence cannot be identified and corrected.

D. Expression of effluent limits. Where the need for effluent limits has been determined, limits derived from acute water quality criteria must be expressed as daily maximum values. Limits derived from chronic or human health criteria must be expressed as monthly average values.

(1) For specific chemicals, effluent limits must be expressed in total quantity that may be discharged. Unless required by an applicable effluent limitation guideline adopted by the Department, all permit limitations for metals shall be expressed only as mass-based limits. If required, in establishing concentration, the Department may increase allowable values to reflect actual flows that are lower than permitted flows and/or provide opportunities for flow reductions and pollution prevention provided water quality criteria are not exceeded. With regard to concentration limits, the Department may review past and projected flows and set limits to reflect proper operation of the treatment facilities that will keep the discharge of pollutants to the minimum level practicable.

(2) WET test effluent limits must be expressed as the maximum percent effluent that will not cause observable adverse effects on test organisms.

E. Determination of Reasonable Potential to Exceed Receiving Water Quality Criteria. For effluent monitoring data and the variability of the pollutant in the effluent, the Department shall apply the statistical approach in Section 3.3.2 and Table 3-2 of USEPA's "Technical Support Document for Water Quality-Based Toxics Control" (USEPA Publication 505/2-90-001, March, 1991, EPA, Office of Water, Washington, D.C.) to data to determine whether water-quality based effluent limits must be included in a waste discharge license. Where it is determined through this approach that a discharge contains pollutants or WET at levels that have a reasonable potential to cause or contribute to an exceedence of water quality criteria, appropriate water quality-based limits must be established in any licensing action.

F. Procedures for data analysis and effluent limit calculations

(1) When a test result for a specific chemical is reported as not found in concentrations at a detection level specified by the Department pursuant to section 2(C)(6), the compound must be considered to be not present for the purposes of determining exceedences of water quality criteria.

NOTE: Concentrations of compounds detected below levels specified by the Department must still be reported.

(2) When the no observed effect level in a WET test is reported as being below the lowest dilution of effluent tested, the effluent is considered to be in exceedence of water quality criteria.

(3) When all results are reported as below a detection level specified by the Department, the compound must be considered to have no reasonable potential to exceed water quality criteria. For the purposes of determining the coefficient of variation in calculating reasonable potential to exceed water quality criteria pursuant to section 3(E), when some results are reported as below a detectable amount, those values must be considered to be present at a level of one half of the detection level specified by the Department.

(4) Flows used in calculations are to be governed by the following. For exceedence determinations with specific chemicals, calculations must be based on the facility's flow on the day the sample was collected for acute criteria and the monthly average flow for the chronic and human health criteria. Allowable discharge quantities must be calculated based on the facility's licensed flow and the appropriate design stream flow and water quality criteria. In situations where a discharger's flow augments the stream flow (as is the case with most POTW's), the Department's calculation of allowable mass limits must reflect the differences in dilution factors resulting from actual flows being less than the facility's full license amount. For determination of WET test exceedences and all reasonable potential determinations, the discharger's licensed flow must be used.

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