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Water Quality Index. Torrey Lindbo, Jan Miller, SWRP Clean Water Services. Role of the Water Quality Index. WQI numerically summarizes the information from multiple water quality parameters into a single value The single value can be used to compare data from several sites
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Water Quality Index Torrey Lindbo, Jan Miller, SWRP Clean Water Services
Role of the Water Quality Index • WQI numerically summarizes the information from multiple water quality parameters into a single value • The single value can be used to compare data from several sites • It can be used to look at trends over time on a single site
Parts of the Water Quality Index • Q-Value - indication of water quality relative to 100 of one parameter • Weighting Factor - sets the relative importance of the parameter to overall water quality
Q = 50 Medium Q = 25 Q = 75 Very Good Very Bad Q = 0 Q = 100 Q Value • The Q-Value is an indication of how good (or bad) the water quality is relative to one parameter. • 100 = Very Good • 1 = Very Bad
pH Q-Graph and Q-Table pH Q-Value • 6.6 81 • 6.8 88 • 7.0 94 • 7.2 98 • 7.4 100 • 7.6 98 • 7.8 94 • 8.0 88 • 8.2 80 • 8.4 72
E.coli Q-Graph & Q-Table E. coli Q-Value • 0 100 • 1 99 • 2 94 • 5 89 • 10 84 • 20 80 • 50 74 • 100 69 • 200 65 • 500 27 • 1000 30
Adjusting for Missing Data • When a parameter is missing, the sum of the weighting factors that have data can be used to adjust the WQI • Sum of the Parametric Index Values is divided by the sum of the weighting factors that have data.
