Long‐Term Trends in Chloride Concentrations in Shallow Aquifers near Chicago

Abstract

The rapid expansion of major cities throughout the world is resulting in the degradation of water quality in local aquifers. Increased use of road deicers since the middle of the 20th century in cities in the northern United States, Canada, and Europe has been linked to degraded ground water quality. In this article, Chicago, Illinois, and its outlying suburban areas are used as an example of the effects of urbanization in a historical context. A statistical study of historical water quality data was undertaken to determine how urbanization activities have affected shallow (<60 m) ground water quality. Chloride (Cl(-)) concentrations have been increasing, particularly in counties west and south of Chicago. In the majority of shallow public supply wells in the western and southern counties, Cl(-) concentrations have been increasing since the 1960s. About 43% of the wells in these counties have rate increases greater than 1 mg/L/year, and 15% have increases greater than 4 mg/L/year. Approximately 24% of the samples collected from public supply wells in the Chicago area in the 1990s had Cl(-) concentrations greater than 100 mg/L (35% in the western and southern counties); median values were less than 10 mg/L before 1960. The greater increase in Cl(-) concentrations in the outer counties is most likely due to both natural and anthropogenic factors, including the presence of more significant and shallower sand and gravel deposits, less curbing of major highways and streets, and less development in some parts of these counties.

River chloride trends in snow-affected urban watersheds: increasing concentrations outpace urban growth rate and are common among all seasons

“…Since baseline concentrations increased with time over the course of the study, less additional road salt runoff was needed to reach concentrations of concern in the later years of the study than in the early years, effectively changing the slope of the chloride to urban land cover relation. With baseline concentrations governed by groundwater discharges in many instances, this finding is consistent with other research that has observed elevated chloride concentrations in groundwater which has caused elevated stream concentrations (Kelly, 2008;Eyles et al, 2013).…”

“…A similar year-round influence has been noted multiple times in previous research (Williams et al, 2000;Kelly, 2008;Perera et al, 2013). This non-deicing season effect has been attributed to salt infiltrating into the shallow groundwater system thereby serving as a "reservoir" of salt that is slowly discharged into streams as baseflow.…”

“…Increasing trends in chloride concentrations have been observed in water bodies of the U.S. and attributed, at least in part, to road salt influence. These trends have included rivers (Godwin et al, 2003;Interlandi and Crockett, 2003;Thunqvist, 2004;Kaushal et al, 2005;Kelly et al, 2012a), groundwater (Reisch and Toran, 2013;Kelly, 2008;Perera et al, 2009;Cassanelli and Robbins, 2013), inland lakes (Ramstack et al, 2004;Novotny and Stefan, 2010;Müller and Gächter, 2012), and even water bodies as large as the Laurentian Great Lakes (Chapra et al, 2009(Chapra et al, , 2012.…”

Increasing chloride concentrations in Lake Constance: characterization of sources and estimation of loads

“…Degradation of groundwater resources is a major concern in growing urban areas, as elevated chloride concentrations are indicative of anthropogenic impact (Kelly 2008), and even approach the limits of drinking water quality standards (Howard and Maier 2007). Surveys in the Greater Toronto Area documented a strong relationship between increasing chloride concentration in the groundwater and urbanization (Williams et al 1999;Howard and Maier 2007).…”

Análise dos sistemas hidroquímicos dos campos de captação de abastecimento público, para identificação dos padrões de qualidade da água e definição das massas de água subterrânea: Holanda

“…The ratio is less reliable than δ 18 O, due to more complications. On the one hand, raised levels in autochthonous groundwater are encountered in urbanized areas, because of leaky sewer systems and/or road de-icing salt (Kelly 2008). On the other hand, levels in RBF can be lower, mainly by the release of Br from organic rich muds that accumulate where river flow is reduced , and by abstraction of old RBF with a Cl/Br ratio ≤300 because it infiltrated before the salt mining industry started.…”