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A Generalized Water Quality Index Based on Multivariate Factor Analysis¹

ABSTRACT

Water quality indexes permit an evaluation of water quality conditions in comparative terms. This paper presents a methodology for derivation of a generalized water quality index based on factor analysis (a multivariate statistical technique), and examines the geographical applicability of such an index. Ten pollutant parameters from water quality data accumulated in the Carson Valley of Nevada during the 1974, 1975, and 1976 irrigation seasons provided the basis for two indexes: i) WQITN = f(temp., BOD, TP, EC, DODP); and ii) WQIPN = f(temp., BOD, PO₄-P, EC, DODP). Regression analysis of the indexes as functions of water quality variables from two river basins in Nevada indicated WQITN to be the better index (F-test 99%, R₂ = 0.9098). The WQITN formulation was then compared with index values suggested by water quality experts (WQIE). Regression coefficients were determined for WQIE and WQITN index regression equations as functions of water quality data from selected locations throughout the United States. The proposed WQITN appeared the most geographically acceptable index (F-test 99%, R² = 0.9754). The model estimated by factor analysis was shown to have good potential as a generalized water quality index. Use of the suggested methodology for the development of generalized, as well as specific-use water quality indexes, may enable better geographic identification of problem areas contributing to water pollution and the development of appropriate water quality standards. Standardization of the indexes in terms of a range of acceptability, e.g., light, moderate, or severe pollution, is suggested for further investigation.

Key Words: agricultural pollution • water pollution index • principal component analysis • irrigation return flows

¹ This paper is a contribution of the Nevada Agric. Exp. Stn. and the Nevada Coop. Ext. Serv., Max. C. Fleischmann College of Agric., Univ. of Nevada, Reno, NV 89557. Exp. Stn. J. Ser. no. 378. Financial support from the Nevada State Environ. Prot. Serv., Health Div., Dep. of Human Resour. is gratefully acknowledged.

² Lecturer and Water Chemist (currently Hydrologist, Army Corp. of Eng., Buffalo Dist.), Associate Professor of Soil and Water Science, Extension Irrigation Specialist, and Professor of Irrigation Engineering, respectively. This paper contains information to be submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Hydrology by H. M. Joung.

Received for publication May 26, 1977.