Water quality monitoring records for estimating tap water arsenic and nitrate: a validation study

Table 2 Agreement* between arsenic 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 = 107)
% with monitoring data in radius	30	58	78	89	92	93	98	99	100	100	100
Agreement*
All sources in radius
Mean	0.49	0.30	0.32	0.20	0.18	0.15	0.12	0.04	0.05	0.08	0.09
Maximum	0.51	0.26	0.26	0.21	0.24	0.20	0.16	0.12	0.15	0.16	0.17
Most recent	0.49	0.33	0.13	0.10	0.17	0.07	0.20	0.17	0.24	0.25	0.31
Closest source only
Mean	0.49	0.35	0.19	0.11	0.10	0.09	0.11	0.11	0.13	0.13	0.13
Maximum	0.47	0.36	0.19	0.11	0.10	0.09	0.10	0.10	0.12	0.12	0.12
Most recent	0.49	0.35	0.17	0.09	0.08	0.08	0.09	0.09	0.11	0.11	0.11
Residences on a public system† (N = 89)
% with monitoring data in radius	31	60	81	89	91	93	98	99	100	100	100
Agreement* (mean, all sources in radius)	0.41	0.21	0.29	0.24	0.22	0.15	0.09	0.02	0.03	0.08	0.09
Residences with a private well‡(N = 18)
% with monitoring data in radius	22	50	61	89	94	94	100	100	100	100	100
Agreement* (mean, all sources in radius)	1.0	0.68	0.67	0.22	0.32	0.32	0.35	0.25	0.27	0.29	0.32

* Correlation (Spearman's rho) between arsenic levels measured in tap water of individual residences and selected summary measures estimated for that home 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.

ISSN: 1476-069X