Receiving water characterization for the implementation of dissolved oxygen

criteria to protect the Fish and Wildlife Propagation beneficial use DO modeling will be performed under conditions that are most critical with respect to processes that determine instream concentration of DO as outlined below. (1) Flow. Background flow for models shall be set at the higher of the seven-day, two-year low flow for the study area or 1 cfs. When a daily flow record of ten years or more exists, a seasonal 7Q2 may be calculated and applied for streams designated as HLAC or WWAC. Also see OAC 252:740. (2) Temperature. The seasonal regulatory temperatures specified in the WQS shall be modeled as background conditions unless site-specific data is available. If at least one year of average daily stream temperature values is available, the upper 90th percentile value calculated from the dataset for the season will be used. (3) Water quality constituents. Where available, the long-term average of measured values will be used to establish receiving water conditions. For seasonal analyses, values calculated from the dataset for the season shall be used. For simple models, assumed conditions estimated from similar streams in the area may be used.