Abstract

Background:

Groundwater quality in the Silurian dolomite aquifer in northeastern Wisconsin, USA, has become contentious as dairy farms and exurban development expand.

Objectives:

We investigated private household wells in the region, determining the extent, sources, and risk factors of nitrate and microbial contamination.

Methods:

Total coliforms, Escherichia coli, and nitrate were evaluated by synoptic sampling during groundwater recharge and no-recharge periods. Additional seasonal sampling measured genetic markers of human and bovine fecal-associated microbes and enteric zoonotic pathogens. We constructed multivariable regression models of detection probability (log-binomial) and concentration (gamma) for each contaminant to identify risk factors related to land use, precipitation, hydrogeology, and well construction.

Results:

Total coliforms and nitrate were strongly associated with depth-to-bedrock at well sites and nearby agricultural land use, but not septic systems. Both human wastewater and cattle manure contributed to well contamination. Rotavirus group A, Cryptosporidium, and Salmonella were the most frequently detected pathogens. Wells positive for human fecal markers were associated with depth-to-groundwater and number of septic system drainfield within $229\mathrm{m}$. Manure-contaminated wells were associated with groundwater recharge and the area size of nearby agricultural land. Wells positive for any fecal-associated microbe, regardless of source, were associated with septic system density and manure storage proximity modified by bedrock depth. Well construction was generally not related to contamination, indicating land use, groundwater recharge, and bedrock depth were the most important risk factors.

Discussion:

These findings may inform policies to minimize contamination of the Silurian dolomite aquifer, a major water supply for the U.S. and Canadian Great Lakes region. https://doi.org/10.1289/EHP7813

中文翻译：

---

威斯康星州东北部断裂白云岩含水层私人家庭水井硝酸盐和微生物污染的来源及危险因素

摘要

背景：

随着奶牛场和郊区开发的扩大，美国威斯康星州东北部志留纪白云岩含水层的地下水质量引起了争议。

目标：

我们调查了该地区的私人家庭水井，确定硝酸盐和微生物污染的程度、来源和风险因素。

方法：

在地下水补给和非补给期间通过天气取样评估总大肠菌群、大肠杆菌和硝酸盐。额外的季节性采样测量了人类和牛粪便相关微生物和肠道人畜共患病原体的遗传标记。我们构建了每种污染物的检测概率（对数二项式）和浓度（伽马）的多变量回归模型，以识别与土地利用、降水、水文地质和井建设相关的风险因素。

结果：

总大肠菌群和硝酸盐与井场和附近农业用地的基岩深度密切相关，但与化粪池系统无关。人类废水和牛粪都造成了油井污染。轮状病毒 A 群、隐孢子虫和沙门氏菌是最常检测到的病原体。人类粪便标记物阳性的水井与地下水深度和化粪池系统排水场数量相关$229\mathrm{米}$. 粪便污染的水井与地下水补给和附近农业用地的面积有关。对任何粪便相关微生物呈阳性反应的水井，无论来源如何，都与化粪池系统密度和基岩深度改变的粪便储存接近度有关。钻井一般与污染无关，表明土地利用、地下水补给和基岩深度是最重要的风险因素。

讨论：

这些发现可能会为尽量减少志留纪白云岩含水层污染的政策提供信息，志留纪白云岩含水层是美国和加拿大五大湖地区的主要供水系统。https://doi.org/10.1289/EHP7813