Water Quality Index of Natural Streams: A Case Study of Five Headwater Streams in Bald Eagle State Forest, Pennsylvania

Abstract

Water quality index (WQI) uses many weighted, measurable parameters to give one number that reflects the quality of the water. WQI is a standard approach to evaluate and compare results of different streams because of its concise form. The correct WQI expression for a specific stream can be challenging and requires a good stream water quality knowledge. In this study, five Penns Creek headwater streams located in the Bald Eagle State Forrest, PA were selected and assessed with five different Water Quality Indices and a new specific WQI expression was identified and implemented to simplify a water quality index value. The water quality data used for the five WQI and the specific WQI expressions was collected from the summer months of June and July from 2015 to 2017. Using these five different WQI expressions, revealed a range of values from 80 to 100 making these streams ranked between good and excellent quality. Since the WQI is meant for drinking water, the normalization factors of some parameters such as pH, temperature, and Biochemical Oxygen Demand (BOD5), are excessively lowered and limits the application on natural headwater streams, where some parameters should not be weighted. Using this experimental site that is known to have a good water quality, with little to no human impact, the WQI has been rearranged taking in consideration the following steps: 1) the range of the pH has been expanded to more acidic and basic water 2) the range of temperature lowered for colder water 3) excess parameters, like BOD5 and other ion concentration were removed.