Using Systematic Sampling and Automatic Monitoring Data to Evaluate and Modify Water Quality Criteria in an Urban Estuary

Edward D. Santoro, M.S. & Patricia McSparran

Delaware River Basin Commission

Since the Delaware River Compact was signed into law in the 1960s the Delaware River Basin Commission has been effective working with its Federal and State partners to regulate activities in the Delaware River Basin in a consistent manner. For many years during the 1960s and 1970s the River suffered from severe depletion of dissolved oxygen preventing fish passage and propagation. The DRBC helped raise the dissolved oxygen in the river and estuary by determining the waste assimilative capacity of the estuary for 20-day carbonaceous biochemical oxygen demand and allocating it among individual dischargers.

In support of these efforts, the DRBC has provided consistent monitoring of the main stem of the River and Bay to assess attainment of water quality standards. The DRBC also provides funding support for 5 automatic monitors in the estuary.

The current average summer dissolved oxygen concentrations in the center channel of the Estuary indicate that present-day oxygen levels are at or near water quality standards for the entire length of the Estuary. However in an effort to reach the Clean Water Act goal of fishable and swimable in all portions of the estuary, DRBC has proposed raising the 24-hour average DO criteria in three zones in the urban area of the river. Discreet monitoring data collected by DRBC and data from continuous monitors were used to create absolute minimum DO criteria that reflect existing water quality and were also used to evaluate the impact of raising the 24-hour average criteria on dischargers. Upon adoption of the revised criteria, the monitoring program will continue to be used to evaluate compliance with the criteria. In this way, the monitoring data has been a tool for both modifying and evaluating water quality criteria used to protect fish passage and propagation in an urban estuary.

Keywords: Dissolved Oxygen, Automatic Monitors, Water Quality Criteria