2014-05-16_HYDROLOGY - C1981025 - Laserfiche WebLink

Home Browse Search

Minrec, Incorporated Water Quality Assessment CO- 0048233 Introduction to the Antidegradation Process The antidegradation process conducted as part of this water quality assessment is designed to determine if an antidegradation review is necessary and if necessary, to complete the required calculations to determine the limits that can be selected as the antidegradation -based effluent limit (ADBEL), absent further analyses that must be conducted by the facility. As outlined in the Antidegradation Significance Determination for New or Increased Water Quality Impacts, Procedural Guidance (AD Guidance), the first consideration of an antidegradation evaluation is to determine if new or increased impacts are expected to occur. This is determined by a comparison ofthe newly calculated WQBELs verses the existing permit limitations in place as of September 30, 2000, and is described in more detail in the analysis. Note that the AD Guidance refers to the permit limitations as of September 30, 2000 as the existing limits. If a new or increased impact is found to occur, then the next step of the antidegradation process is to go through the significance determination tests. These tests include: 1) bioaccumulative toxic pollutant test; 2) temporary impacts test; 3) dilution test (100:1 dilution at low flow) and; 4) a concentration test. As the determination of new or increased impacts, and the bioaccumulative and concentration significance determination tests require more extensive calculations, the Division will begin the antidegradation evaluation with the dilution and temporary impact significance determination tests. These two significance tests may exempt a facility from further AD review without the additional calculations. Note that the antidegradation requirements outlined in The Basic Standards and Methodologies for Surface Water specify that chronic numeric standards should be used in the antidegradation review; however, where there is only an acute standard, the acute standard should be used. The appropriate standards are used in the following antidegradation analysis. Significance Tests for Temporary Impacts and Dilution This is not a temporary discharge and therefore exclusion based on a temporary discharge cannot be granted and the AD evaluation must continue. The ratio of the chronic (30E3) low flow to the design flow is 2:1, and is less than the 100:1 significance criteria. Therefore this facility is not exempt from an AD evaluation based on the dilution significance determination test, and the AD evaluation must continue. For the determination of a new or increased impact and for the remaining significance determination tests, additional calculations are necessary. Therefore, at this point in the antidegradation evaluation, the Division will go back to the new or increased impacts test. If there is a new or increased impact, the last two significance tests will be evaluated. New or Increased Impact and Non Impact Limitations (NILs) To determine if there is a new or increased impact to the receiving water, a comparison of the new WQBEL concentrations and loadings verses the concentrations and loadings as of September 30, 2000, Appendix A (WQa v 7.0) Page 16 of 25 Last Revised Sept 14, 2009 /ES