WATERSHED MANAGEMENT APPROACH TO EFFLUENT DISCHARGE LIMITS ADVANCED WASTEWATER TREATMENT ASSESSMENT: A CASE STUDY

For small island communities, protection of the limited fresh water resources is of critical importance. In order to comply with all the established NPDES permits limits and conditions; and to protect the water quality of their inland rivers and streams, the Puerto Rico Aqueduct and Sewer Authority (PRASA) has undertaken an essential program which was designed to identify the upgrade requirements for all inland wastewater treatment plants (WWTPs) and used a watershed management approach. The application of this watershed management approach requires the development of Waste Load Allocation (WLA) and Total Maximum Daily Loadings (TMDLs) based on the assimilative capacity of the rivers and streams. This approach represents a significant shift from the present way of specifying discharge limits for facilities based on generic or process capabilities. This in essence is moving from a technology based discharge limits to water quality based limits in order to identify Advanced Wastewater Treatment (AWT) requirements for individual facilities. This project, which covered a total of 20 watersheds (approximately 2,500 sq mi) and included 40 WWTPs, is the first application of a watershed management approach on the island of Puerto Rico. The implementation of this watershed management program includes three main phases: (I)Study and evaluation (II)Determination of WLAs and (III)Identification and implementation of control strategies or treatment options.At this time, Phase I of the program has been completed, and the specific investigations and finding are presented here. This phase of the project was designed to provide the data necessary to develop WLAs for the WWTPs, and included a watershed characterization through screening analyses, field studies and plant WLA prioritization.