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Index for Determining Water Quality

E. coli (Bacteria)

You can average all the E. coli values for each site, or for a higher grade, calculate individual E. coli values for each site.

[90-100 = Excellent] [70-90 = Good] [50-70 = Medium] [25-50 = Bad] [0-25 = Very Bad]

E. coli value (CFU/100 mL)	Q-Value
0	100
1	99
2	94
5	89
10	84
20	80
50	74
100	69
200	65
300	62
400	60
500	53
600	47
700	42
800	37
900	34
1000	30
2000	22

pH

You can average all the pH values from all your visits, or for a higher grade, rank the pH quality for each visit.

[90-100 = Excellent] [70-90 = Good] [50-70 = Medium] [25-50 = Bad] [0-25 = Very Bad]

pH	Water Quality Value
< 2.0	0
2.0	2
3.0	4
4.0	8
5.0	24
6.0	55
7.0	90
7.5	92 (maximum)
8.0	85
9.0	50
10.0	50
11.0	22
12.0	7
> 12.0	2

Temperature Change

Organisms need a stable temperature (although cooler is usually better). Rapid variation in temperature stresses sensitive stream animals, which often kills them.

[90-100 = Excellent] [70-90 = Good] [50-70 = Medium] [25-50 = Bad] [0-25 = Very Bad]

Change in Temp (deg C)	Water Quality Value
-10.0	50
-7.5	65
-5.0	77
-2.5	85
0.0	93 (maximum)
2.5	85
5.0	72
7.5	57
10.0	44
12.5	36
15.0	28
17.5	23
20.0	18
22.5	16
25.0	14
27.5	12
30	10

Dissolved Oxygen

For this water quality determination, change your group's oxygen reading to % oxygen saturation. This requires the water temperature for the day, and that someone in your group fills out the dissolved oxygen sheet.

[90-100 = Excellent] [70-90 = Good] [50-70 = Medium] [25-50 = Bad] [0-25 = Very Bad]

Percent Saturation (% Oxygen)	Water Quality Value
0	0
10	8
20	13
30	20
40	30
50	43
60	56
70	77
80	88
90	95
100	100
110	95
120	90
130	85
140	78
>140	50

Nitrate Nitrogen

Nitrogen enters a stream as a result of animal wastes and also as over application of fertilizers.

[90-100 = Excellent] [70-90 = Good] [50-70 = Medium] [25-50 = Bad] [0-25 = Very Bad]

Nitrate Nitrogen (mg/L NO3-N)	Water Quality Index
0.00	98
0.25	95
0.5	90
0.75	80
1.0	73
1.5	63
2.0	53
3.0	44
5.0	36
10.0	15
15.0	6
20.0	2

Phosphate Phosphorus

Phosphorus sources include soaps (like washing your car near a storm drain!) and decomposition of dead plants and animals.

[90-100 = Excellent] [70-90 = Good] [50-70 = Medium] [25-50 = Bad] [0-25 = Very Bad]

Phosphate Phosphorus (mg/L P)	Water Quality Value
<0.5	98
0.5	92
1.0	80
1.5	64
2.0	50
2.5	37
3.0	24
>3.0	14

Turbidity

Turbidity is a measure of the clarity/cloudiness of the water. Cloudiness results from erosion, decomposition, and growth of algae among other things. As the turbidity increases, less light travels through the water, and algae and plants begin to lack light for photosynthesis. Thus the food chain is heavily impacted by turbidity. Animals also find it difficult to navigate and find food.

[90-100 = Excellent] [70-90 = Good] [50-70 = Medium] [25-50 = Bad] [0-25 = Very Bad]

Turbidity (NTU)	Water Quality Value
0	97
10	76
20	62
30	53
40	45
50	39
60	34
70	28
80	25
90	22
100	17
>100	5

Slichter