. 2021 Jun 23;129(6):067004. doi: 10.1289/EHP7813

Table 1.

Estimated contamination rates (percent positive wells) for total coliform bacteria, Escherichia coli, or $nitrate-N > 10 mg / L$ .

Sampling period or reference data	Region or depth-to-bedrock category^a	Number of wells sampled	Percent positive wells (95% confidence interval)
Sampling period or reference data	Region or depth-to-bedrock category^a	Number of wells sampled	Total coliforms	E. coli	$Nitrate-N > 10 mg / L$	Total coliforms or nitrate- $N > 10 mg / L$
Groundwater recharge	$< 1.5 m$ to bedrock	26	46 (30, 63)	4 (0, 9)	7 (0, 15)	50 (34, 66)
	$1.5 - 6.1 m$ to bedrock	120	28 (18, 37)	1 (0, 2)	20 (7, 33)	42 (28, 55)
	$> 6.1 m$ to bedrock	167	19 (11, 26)	0.3 (0, 0.6)	6 (1, 10)	23 (15, 31)
	Kewaunee County	313^b^,^c 316^c^,^d	21 (14, 27)	0.4 (0.1, 0.7)	7 (3, 11)	26 (19, 34)
No groundwater recharge	$< 1.5 m$ to bedrock	24	23 (6, 39)	7 (0, 15)	10 (0, 20)	33 (12, 53)
	$1.5 - 6.1 m$ to bedrock	122	29 (16, 41)	1 (0, 3)	19 (9, 28)	40 (28, 53)
	$> 6.1 m$ to bedrock	252	21 (15, 27)	1 (0, 2)	5 (2, 8)	26 (19, 32)
	Kewaunee County	396^b^,^c 400^c^,^d	22 (17, 28)	1 (0.1, 2)	7 (4, 10)	28 (22, 33)
Reference data	Wisconsin^e	534	23	3	7	—
Reference data	Wisconsin^f	3,838	18	—	10	—

Note: —, no data available. Estimates and corresponding 95% confidence intervals account for the stratified random sampling design employed in the study.

^{^a}

The estimated number of wells in each bedrock depth category are 76, 575, and 4,156 wells at $< 1.5$ , 1.5–6.1, and $> 6.1 m$ , respectively, totaling 4,807 wells in Kewaunee County. Our final estimates of the number of wells in each bedrock depth category are different than the initial estimates at the study beginning using the bedrock map created by Sherrill (1979).

^{^b}

n for coliforms and E. coli.

^{^c}

The n’s do not equal the number of samples analyzed (see Figure S1) because some wells had missing depth-to-bedrock values (six wells for the groundwater recharge period and one well for the no recharge period) for which analytic weights could not be generated.

^{^d}

n for nitrate.

^{^e}

Data for private wells; U.S. General Accounting Office 1997.

^{^f}

Knobeloch et al. 2013.