Section 323.1207. Total maximum daily loads.

(1) The following general principles are applicable to establishing total maximum daily loads (TMDLs) for toxic substances in the surface waters of the state, with the exception of whole effluent toxicity:

(a)     TMDLs shall ensure attainment of applicable water quality standards for the toxic substances for which they are established and shall, at a minimum, be developed in accordance with the listing and priority setting  process established in section 303(d) of the clean water act and 40 C.F.R.§130.7. Where water quality standards cannot be attained immediately, TMDLs shall reflect reasonable assurances that water quality standards will be attained in a reasonable period of time, with specific controls on individual sources being implemented in stages. Determining the reasonable period of time in which water quality standards will be met  is  a case- specific determination considering a number of factors, including all of the following factors:

(i)       Receiving water characteristics.

(ii)     Persistence, behavior, and ubiquity of toxic substance of concern.

(iii)   Type of remediation activities necessary.

(iv)     Available regulatory and nonregulatory controls.

(v)       Department requirements for attainment of water quality standards.

(vi)     Technical and economic feasibility of attainment.

(b)   TMDLs shall include wasteload allocations (WLAs) for point sources addressed by these rules and load allocations (LAs) for nonpoint sources, including background, such that the sum of the allocations plus a specified margin of safety (MOS) is not greater than the loading capacity of the water for the toxic substance addressed by  the   TMDL.  TMDL   allocations  are as follows:

(i)       Nonpoint source LAs shall be based on all of the following factors:

(A)            Existing toxic substance loadings if changes in loadings are not reasonably anticipated to occur.

(B)      Increases in toxic substance loadings that are reasonably anticipated tooccur.

(C)            Anticipated decreases in toxic substance loadings if the decreased loadings are technically feasible and are  reasonably  anticipated  to   occur within a reasonable time  period  as a result of  implementation  of   best management practices  or   other  load  reduction  measures. In determining whether anticipated decreases in toxic substance loadings are technically feasible and can be expected to occur within a reasonable period of time, technical and institutional factors shall be considered. These decisions are case-specific and shall reflect the particular TMDL under consideration.

(ii)      The sum of the WLAs is the portion of the loading capacity that is not assigned to an MOS or to nonpoint sources including background.National pollutant discharge elimination system (NPDES) permits for the point sources shall include effluent limitations consistent with WLAs in TMDLs.

(c)       If separate TMDLs are prepared for different, but overlapping, segments of the same watershed and the separate TMDLs each include WLAs for the same toxic substances for 1 or more of the same point sources, then WQBELs for that toxic substance for the point source or sources shall be consistent with the most stringent of the WLAs to ensure attainment of all applicable water quality standards.

(d)       Each TMDL shall include an MOS sufficient to account for technical uncertainties in establishing the TMDL and shall describe the manner in which the MOS is determined and incorporated into the TMDL. The MOS may be provided by leaving a portion of the loading capacity unallocated or by using conservative modeling assumptions to establish WLAs and LAs. The MOS  may also include reserved allocation for future growth.

(e)        Where appropriate and where sufficient data or sediment criteria are available, TMDLs shall prevent the accumulation of the toxic substance in the sediment to levels injurious to designated or existing uses and shall reflect contributions to the water column from the sediments.

(f)          Where appropriate and where sufficient data are available, TMDLs shall reflect loadings of toxic  substance discharges resulting from wet- weather events

(g)         The representative background concentration of toxic substances to develop TMDLs and WLAs calculated in the absence of a TMDL shall be established as follows:

(i)       "Background" represents all toxic substance loadings as specified by the following:

(A)         Flow from upstream waters into the specified watershed, water body, or water body segment for which a TMDL or WLA in the absence of a TMDL is being developed.

(B)            Enter the specified watershed, water body, or water body  segment  through atmospheric deposition, chemical reaction, or sediment release or resuspension.

(ii)         When determining what available data are acceptable for use in calculating background, the department   shall  use  its  best  professional judgment,  including   consideration of the sampling location and the reliability of the data through comparison, in part,  to detection and quantification levels. When data in more than 1 of the data sets or categories described in paragraph (iii) of this  subdivision   exists,  best professional judgment shall be used to select the data that most accurately reflects or estimates background concentrations. Toxic substance degradation and  transport   information  may  be   considered  when  using   toxic substance loading data to estimate a water column concentration.

(iii)     The representative background concentration for a toxic substance in the specified watershed, water body, or water body segment shall be established as the geometric mean of acceptable water column data or water column concentrations estimated through the use of acceptable or projected toxic substance loading data. When determining the  geometric   mean  of the data for a toxic substance that includes values both above and below the detection level, values less than the detection level shall be assumed to be present at 1/2 of the detection level if the detection level is less than the lowest water quality value for that substance. If all of the acceptable data in a data set are below the detection level for a toxic substance, then all the data for the toxic substance in that data set shall be assumed to be zero. If the detection level of the available data is greater than the lowest water quality value for the substance, then the background concentration will be determined by the department on a case-by-case basis after considering all representative data, including acceptable fish tissue data.

(h)           If the margin of safety does not include a reserved allocation, then any increased loadings of the toxic substance for which the TMDL was developed that are due to a new or expanded discharge shall not be allowed unless the TMDL is revised in accordance with these procedures to include an allocation for the new or expanded discharge.

(2)         If the department develops an alternative type of assessment   and remediation plan that meets the requirements of this rule and public participation requirements applicable to TMDLs, then the assessment and remediation plan may be used instead of a TMDL. The assessment and remediation plans may include lakewide management plans, remedial action plans for the areas of concern designated by the  international   joint commission, and state water quality management plans. Also, any part of an assessment and remediation plan that satisfies 1 or more requirements under section 303(d) of the clean water act or implementing regulations may be incorporated by reference into a TMDL as appropriate. Assessment and remediation plans under this subrule shall be tailored to the level of detail and magnitude for the watershed and toxic substance being assessed.

(3)     Design flows for establishing TMDLs in lotic waters are given in R 323.1090.

(4)     If a TMDL has been established for a water body receiving the direct discharge of point sources, then the chronic WLA for each point source shall equal a fraction of the loading capacity assigned to point sources that discharge to the water body, but shall not be greater than the chronic WLA established by the procedures in R 323.1209, unless the TMDL reflects anticipated decreases in nonpoint source loadings through a phased approach to water quality standards attainment. Acute WLAs shall be established in accordance with R 323.1209.

(5)      It is not necessary to establish a TMDL for all waters that may be affected by a point source or nonpoint source before establishing a WLA or LA for the respective sources.

(6)     TMDLs and WLAs in the absence of a TMDL shall be based on the assumption that environmental fate or other physical, chemical, or biological factors do not affect the concentration of the toxic substances in the water column, unless both of the following occur:

(a)        Scientifically valid field studies or other relevant information demonstrate that degradation of the toxic substance is expected to occur during typical environmental conditions expected to be encountered.

(b)     Scientifically valid field studies or other information address other factors that affect the level  of  toxic substance in  the water column including:

(i)       Sediment release or resuspension.

(ii)     Chemical speciation.

(iii)   Biological and chemical transformation.

History: 1997 AACS.