Statistical Modeling

In situations where drought flows are rare events, the typical permit derivation conditions (pairing the facility design flow with the drought stream flow to derive permit limits) result in effluent limitations that are unnecessary to meet the return frequency assumptions inherent in the water quality standards (i.e., one exceedance every three years on average). Under these circumstances, H&A develops statistical models to derive effluent limits that match the allowable exceedance frequency.