Table 3

Agreement* between nitrate measures, overall and by type of water source

Radius (maximum distance between residence and water source, miles)

0.5

1

2

3

4

5

6

7

8

9

10

All residences (N = 105)

% with monitoring data in radius

50

72

87

92

94

98

100

100

100

100

100

Agreement*

All sources in radius

Mean

0.49

0.44

0.39

0.34

0.34

0.30

0.32

0.32

0.31

0.32

0.34

Maximum

0.37

0.37

0.27

0.26

0.28

0.28

0.33

0.29

0.29

0.29

0.25

Most recent

0.38

0.17

0.31

0.32

0.25

0.27

0.31

0.30

0.28

0.21

0.18

Closest source only

Mean

0.34

0.32

0.25

0.25

0.25

0.24

0.25

0.25

0.25

0.25

0.25

Maximum

0.19

0.26

0.19

0.20

0.19

0.21

0.20

0.20

0.20

0.20

0.20

Most recent

0.35

0.33

0.24

0.24

0.23

0.22

0.21

0.21

0.21

0.21

0.21

Residences on a public system† (N = 87)

% with monitoring

data in radius

47

72

87

92

94

99

100

100

100

100

100

Agreement* (mean, all sources in radius)

0.49

0.39

0.35

0.29

0.29

0.24

0.29

0.30

0.28

0.31

0.35

Residences with a private well‡(N = 18)

% with monitoring data in radius

61

72

83

94

94

94

100

100

100

100

100

Agreement* (mean, all sources in radius)

0.14

0.60

0.40

0.51

0.47

0.44

0.47

0.46

0.43

0.41

0.40

* Correlation (Spearman's rho) between nitrate levels measured in tap water of individual residences and selected summary measures for that home estimated using public water quality monitoring data and geographic information systems (GIS).

^† Water system served by wells, surface sources or other sources with federally-mandated monitoring.

‡ Individual or shared private well, not subject to federally-mandated monitoring.

Searles Nielsen et al. Environmental Health 2010 9:4   doi:10.1186/1476-069X-9-4