Oklahoma Administrative Code › Title 252 - Department of Environmental Quality › Chapter 690 - Water Quality Standards Implementation › Subchapter 3 - Point Source Discharges › Section 252:690-3-62 - Modeling procedures for the implementation of dissolved oxygen criteria to protect the Fish and Wildlife Propagation beneficial use

Current through Vol. 41, No. 20, July 1, 2024
Additional technical guidance for modeling procedures may be
				  found in the CPP.
(1)
Model
				types.
Many types of water quality models for DO are available. Some are
				extremely complex, some are extremely simple. Professional judgment is
				exercised to determine the appropriate modeling strategy for a particular
				situation. A simple model requires little or no field data but its applications
				are limited. A simple model should only be used for small, non-complex systems
				with discharge flows under 1 MGD or as an initial screening tool for larger
				systems. Typical simple models include desktop or spreadsheet-based formulae. A
				complex model requires a large amount of field data and should be calibrated
				and/or verified with observed conditions and then used to make predictive
				decisions. Complex models are appropriate for complex systems, multiple
				discharges, or large systems involving point source discharges of 1.0 MGD or
				more. Typical models include various versions of QUAL2, RIVERMOD, HSPF, and the
				BASINS system.
(2)
Target DO
				concentrations.
Some of the DO criteria in the OWQS are minimum values
				while others allow for a 1.0 mg/l excursion from the criterion for up to 8
				hours during any 24 hour period. Dynamic models can predict these
				time-dependent conditions and the OWQS criteria may be used directly. Since
				steady state water quality models cannot represent such a time-based excursion,
				appropriate average DO target values are used to protect the minimum DO
				criteria. The following average DO target concentrations will be used for
				steady state models when the numerical criteria apply: for streams designated
				HLAC, 5 mg/l for the early life stage season, 4 mg/l for the summer season, and
				4 mg/l for the winter season; for streams designated WWAC, 6 mg/l for the early
				life stage season, 5 mg/l for the summer season, and 6 mg/l for the winter
				season; for streams designated CWAC, 7 mg/l for the early life stage season, 6
				mg/l for the summer season, and 7 mg/l for the winter season. When site
				specific data are available, the target concentrations shall be adjusted to
				account for the magnitude of the actual diurnal variation. When numerical
				criteria do not apply, the OWQS require that DO concentrations be maintained at
				a level to prevent "nuisance conditions". A target average DO concentration of
				2 mg/l will be utilized to prevent nuisance conditions.
(3)
Margin of safety.
To
				compensate for uncertainty, a margin of safety is required for all models. The
				CPP provides guidance for recommended margins of safety for various types of
				models. As model complexity and use of actual data increase, the recommended
				margin of safety decreases. The margin of safety is determined by comparing the
				unallocated load to the maximum assimilative capacity of the system as
				predicted by the water quality model.
Added at 19 Ok Reg 1721,
				  eff 6-13-02; Amended at 28 Ok Reg 1316, eff
				  7-1-11