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Water Quality Index

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

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  1. Water Quality Index Torrey Lindbo, Jan Miller, SWRP Clean Water Services

  2. 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

  3. Parameters used for WQI

  4. 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

  5. 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

  6. 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

  7. 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

  8. Weighting Factors

  9. WQI Interpretation

  10. Example WQI Calculation

  11. 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.

  12. Calculation with Missing Parameter

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