The secondary treatment system at a western integrated bleached kraft mill was evaluated for its ability to meet the proposed Cluster Rule. Long term performance data were reviewed and compared to the proposed effluent criteria. A lack of COD data prompted studies to be conducted at the mill to evaluate wastewater characteristics as well as in-mill process changes that might be required to reduce the non-biodegradable COD loading to the treatment plant. Wastewater treatment plant investigations focused upon process improvements that could be implemented to achieve the overall goal of complying with the proposed regulations. pH fluctuations were measured to determine the sizing of spill protection and pH correction/mixing chambers. Temperature data were reviewed to assess the need for cooling so as to minimize thermal shocks to the biological treatment system. BOD, COD, and TSS data were collected to establish process criteria for a biological treatment system. Alternative design approaches were developed to facilitate a cost-benefit analysis.