Comment

The proposed BNR system will not have the capacity to achieve target nutrient levels of 3 mg/L total nitrogen and 0.03 mg/L total phosphorus as required by Montana DEQ standards (Circular DEQ-12A)

Response

The comment confuses the nutrient criteria for the Gallatin River (0.3 mg/L TN and 0.03 mg/L TP) with the eventual permit for plant effluent quality (i.e., it ignores dilution credits from a mixing zone). The proposed treatment process will be capable of achieving less than 5.0 mg/L TN, and less than 0.1 mg/L TP, with sufficient chemical addition. Year-round performance at this level is difficult without additional downstream treatment processes, such as ion exchange, reverse osmosis, etc (this is discussed in Chapter 6). These processes are not justifiable from an environmental impact standpoint and do not appear warranted for compliance with the eventual discharge permit, but the Gallatin River provides more than enough dilution to enable compliance at the end of a mixing zone.