CE 394K.2 Hydrology

Homework 6

Effect of Best Management Practices on Water Quality

 

Two Austin watersheds, Jollyville and Far West, have Best Management Practices that improve their water quality.  Jollyville has a sand filter and Far West has an extended detention basin (has water ponded in it continuously).   The purpose of this exercise is to determine how to compare one set of water quality data with another and see if there are significant differences between them.   The attached spreadsheet WaterQuality.xls shows inflow and outflow data for storm events at these two facilities.  In some cases, only inflow data or outflow data is shown, while in other cases, both are shown.  Sometimes water quality sampling equipment fails to function.   It would be ideal to compare inflow and outflow for the same events at the two watersheds but the data don’t support doing that for all events, so we’ll use a more general approach to defining the differences.

The data following show the inflow and outflow of Total Suspended Solids (TSS) measured in mg/liter, for various storm events whose date of occurrence is imbedded in the EventID field.  

Jolleyville Sand Filter

Far West Pond

TSS (MG/L)

TSS (MG/L)

EventID

Inflow

Outflow

EventID

Inflow

Outflow

19880520A

 

136.92

19970617A

99.54

 

19880529A

990.12

34.55

19970807A

100.11

139.74

19880601A

204.19

25.39

19970922A

 

157.28

19880602A

422.99

21.81

19970922B

135.95

 

19880602B

230.69

 

19970923A

 

203.58

19880811A

269.11

288.03

19971007A

107.18

 

19880930A

122.86

 

19971008A

56.96

 

19881031A

52.68

16.61

19971009A

70.98

 

19890129A

151.81

 

19971219A

65.00

 

19890328A

668.27

 

19971220A

 

22.87

19890413A

138.94

10.85

19971220B

64.65

 

19890419A

13.70

19980106A

76.19

30.15

19890505A

121.75

6.20

19980131A

40.34

48.30

19890510A

120.04

7.89

19980214A

72.08

38.37

19890513A

135.35

2.31

19980221A

135.16

53.69

19890516A

145.00

 

19980225A

 

49.31

19890517A

122.34

 

19980330A

99.80

64.67

19890520A

111.26

 

19980704A

213.34

 

19890611A

909.11

40.96

19980910A

85.56

 

19890613A

258.62

17.30

19980911A

 

14.67

19890801A

29.35

mean

94.86

74.79

19890815A

658.64

41.21

std dev

42.52

62.56

19891007A

860.26

33.15

count

15.00

11.00

19891030A

396.65

 

std err

10.98

18.86

19891122A

227.71

24.86

Confidence

31.03

18.06

19900218A

139.95

6.39

19900314A

9.25

19900426A

9.64

19900604A

18.51

19941104A

116.52

 

19950112A

3.00

19950312A

142.26

 

19950313A

4.29

19950404A

257.52

1.27

19950405A

146.56

 

19950508A

10.39

19950518A

10.53

19950531A

39.89

 

19950611A

68.51

9.38

19950730A

187.76

13.17

19950731B

1.31

19951117A

146.26

2.94

19960422A

8.58

19970425A

110.38

0.50

19970426A

107.78

0.25

19970509A

115.39

1.05

mean

261.68

25.34

std dev

253.39

52.31

count

34.00

34.00

std err

43.46

8.97

Confidence

71.48

14.76

 

The Confidence function in Excel is here used with a = 0.10

A table of t-statistic values are shown below

Source: http://espse.educ.psu.edu/edpsych/faculty/rhale/statistics/Tables/tvalue.html

 

Assignment

Complete the table for the comparisons shown below for watersheds and BMP’s.

 

Watershed Comparison

Constituent

Jollyville Watershed

Far West Watershed

Likelihood that the concentrations are the same for the two watersheds (p value)

Cd

 

 

 

COD

 

 

 

Cu

 

 

 

Diss P

 

 

 

Fecal Coliform

 

 

 

Fecal Strep

 

 

 

NH3

 

 

 

NO2+3

 

 

 

Pb

 

 

 

TKN

 

 

 

Total P

 

 

 

TSS

262 ± 71

95± 18

p<0.001 (not paired)

VSS

 

 

 

Zn

 

 

 

 

Jollyville Sand Filter Performance

Constituent

Jollyville Influent

Jollyville Effluent

Likelihood that the concentrations are the same (p value) (i.e., no reduction for this pollutant)

Cd

 

 

 

COD

 

 

 

Cu

 

 

 

Diss P

 

 

 

Fecal Coliform

 

 

 

Fecal Strep

 

 

 

NH3

 

 

 

NO2+3

 

 

 

Pb

 

 

 

TKN

 

 

 

Total P

 

 

 

TSS

262 ± 71

25 ± 15

p <0.001

VSS

 

 

 

Zn

 

 

 

 

Far West Extended Detention Basin Performance

Constituent

Far West Influent

Far West Effluent

Likelihood that the concentrations are the same (p value) (i.e., no reduction for this pollutant)

Cd

 

 

 

COD

 

 

 

Cu

 

 

 

Diss P

 

 

 

Fecal Coliform

 

 

 

Fecal Strep

 

 

 

NH3

 

 

 

NO2+3

 

 

 

Pb

 

 

 

TKN

 

 

 

Total P

 

 

 

TSS

95± 18

75 ± 31

p = 0.21 (paired test)

VSS

 

 

 

Zn