Controlling Lead and Copper in Drinking Water

Lead and Copper – 90th Percentile Activity

Action Level for Lead 0.015 mg/L

Action Level for Copper 1.3 mg/L

“Action Level” means the concentration of lead or copper at which the supplier is required to comply with additional requirements, which may include public education, corrosion control treatment, source water treatment, and/or lead service line replacement. Being above the action level is not a violation, not taking action to fix it - could be!

The action level is calculated using 90th percentile.

Action level exercise

1. Fold Airplane

2. Each person fly plane, record distance

3. Calculate 90th percentile (see example left)

  1. Arrange results in order from lowest to highest.
  2. Rank each result: 1 = lowest result through highest result (i.e. 54)
  3. Multiply the number of total results by 0.9 = 90th percentile rank
  4. The sample result corresponding to the 90th percentile rank above is the 90th percentile level.

To calculate 90th percentile

Number of measurements X 0.9 =

53 X 0.9 = 47.7 (round to 48)

90th percentile = 0.0020 mg/L

Lead mg/L / "Rank"
<0.001 / 1
<0.001 / 2
<0.001 / 3
<0.001 / 4
<0.001 / 5
<0.001 / 6
<0.001 / 7
<0.001 / 8
<0.001 / 9
<0.001 / 10
<0.001 / 11
<0.001 / 12
<0.001 / 13
<0.001 / 14
<0.001 / 15
<0.001 / 16
<0.001 / 17
<0.001 / 18
<0.001 / 19
<0.001 / 20
<0.001 / 21
<0.001 / 22
<0.001 / 23
<0.001 / 24
<0.001 / 25
<0.001 / 26
<0.001 / 27
<0.001 / 28
<0.001 / 29
<0.001 / 30
<0.001 / 31
<0.001 / 32
<0.001 / 33
<0.001 / 34
<0.001 / 35
<0.001 / 36
0.0011 / 37
0.0011 / 38
0.0012 / 39
0.0013 / 40
0.0014 / 41
0.0016 / 42
0.0017 / 43
0.0018 / 44
0.0018 / 45
0.0019 / 46
0.0019 / 47
0.0020 / 48
0.0021 / 49
0.0026 / 50
0.0036 / 51
0.0120 / 52
0.0283 / 53