Oregon Water Quality Index
Water resource professionals generally communicate water quality status and trends in terms of the evaluation of individual water quality variables. While this technical language is readily understood within the water resources community, it does not readily translate to communities having profound influence on water resources policy: the general public and the policy makers. Increasingly, these communities expect a comprehensible response to their right to know about the status of their environment. An example of this response is the annual Consumer Confidence Report provided by drinking water suppliers as required by the 1996 amendments to the Safe Drinking Water Act (USEPA, 1998). The purpose of the Oregon Water Quality Index (OWQI) is to improve understanding of water quality issues by integrating complex data and generating a score that describes water quality status and evaluates water quality trends. Although some information is lost when integrating multiple water quality variables, this loss is outweighed by the gain in understanding of water quality issues by the public and policy makers. Improved understanding is very important to water resource managers in terms of increased support for water resource improvement efforts.
The science of water quality has improved markedly since the introduction of the OWQI in the 1970s (Dunnette, 1979). The OWQI was improved in 1995 to reflect advances in the knowledge of water quality and in the design of water quality indices. The primary purpose of this report is to describe the historical basis and define the improved design of the OWQI. The improved OWQI is widely used and maintained by Oregon Department of Environmental Quality (DEQ). The OWQI has been used to report water quality status and trends in Oregon to state legislators and other water resource policy makers via presentations and to the public through reports accessible on the internet (http://www.deq.state.or.us/ lab/WQM/WQI/wqimain.htm). The OWQI has been used as a supplement to more traditional reporting formats, such as the Water Quality Status Assessment (305(b)) Report (Oregon DEQ, 1998a) and the annual McKenzie Watershed Water Quality Report (Cude, 1999). The OWQI has been incorporated intolarger sets of environmental indicators for the Oregon Benchmarks Report (Oregon Progress Board, 1999), the Oregon State of the Environment Report (Oregon Progress Board, 2000), the Performance Partnership Agreement between Oregon DEQ and U.S. Environmental Protection Agency Region 10 (Oregon DEQ, 1998b), and the Salmon Habitat Indicators Workshop (Green Mountain Institute of Environmental Democracy, 1997, “Report of the Pacific Northwest Environmental Indicators Work Group Salmon Habitat Indicators Workshop,” unpublished report). The OWQI has also been adopted and modified or borrowed from for construction of other water quality indices in Australia (A. M. Richardson, 1997, “Development of an Estuarine Water Quality Index (eWQI) for New South Wales,” unpublished dissertation, The University of Sydney), the Tualatin Basin of Oregon (Aroner, 1999), and Idaho (Idaho Division of Environmental Quality, “Idaho Rivers Ecological Framework,” Boise, Idaho, draft report). The OWQI has been recognized as an important contribution to the lexicon of environmental communications. The secondary purpose of this report is to demonstrate how the OWQI is utilized to communicate water quality information.
Uses and Limitation:
The present OWQI was developed to provide a simple and concise method for expressing the significance of data regularly generated from Oregon DEQ’s Ambient River Water Quality Monitoring Network. The OWQI aids in the assessment of water quality for general recreational uses (i.e., fishing and swimming). The OWQI cannot determine the quality of water for specific uses, nor can it be used to provide definitive information about water quality without considering all appropriate chemical, biological, and physical data. The OWQI cannot evaluate all health hazards. The OWQI was designed for Oregon’s streams, and its application to other geographic regions or waterbody types should be approached with caution.
Categorization Table
The OWQI classification scheme was derived as follows:
Standards Required
Any regional water quality standards for drinking purpose could be used for this model
Variables Selection
As the name of this model clearly indicates that this refers to the heavy metal toxicity, any possible heavy metal could be considered for this pollution index. For instance: Fe, Co, Ni, Cu, Ni, Zn etc.
Calculation of Oregon Water Quality Index:
The original Oregon Water Quality Index OWQI used a weighted arithmetic mean function
Where, SIi is the sub-index of the ith parameter and n is the number of parameters considered.
Case Studies based on Oregon Water Quality Index (The Talar River- Iran)
The qualitative investigation of the Talar river was done according to Oregon Water Quality Index (OWQI), National Sanitation Foundation Water Quality Index (NSFWQI) and Wilcox indicators during 2011–2012 years at upstream, midstream and downstream of the river in two periods of wet and dry seasons. According to the results of OWQI, all of the values at 3 stations and both periods are placed at very bad quality category and the water is not acceptable for drinking purposes. According to NSFWQI, the best condition was related to the upstream station at wet season period (58, medium quality) and the worst condition was related to the downstream in wet season period (46, very bad quality). Also the results of Wilcox showed that in both periods of wet season and dry season, the water quality is getting better from upstream station to the downstream station, and according to the index classifi cation, the downstream water quality has shown good quality and it is suitable for agriculture.
References
Gholamreza Darvishi, Farshad Golbabaei Kootenaei, Maedeh Ramezani, Eissa Lotfi, Hosseinali Asgharnia (2016). Comparative Investigation of River Water Quality by OWQI, NSFWQI and Wilcox Indexes (Case study: The Talar River – IRAN). Archives of Environmental Protection, 42(1): 41–48.