Method to characterize aquitards above leaky aquifers with water supply wells

Ostendorf, David W.; DeGroot, Don J.; Judge, Aaron I.; LaMesa, Daniel F.

Method to characterize aquitards above leaky aquifers with water supply wells | Une méthode pour caractériser les épontes des aquifères semi-captifs à l’aide de puits de production Un método para caracterizar acuitardos por encima de acuíferos filtrantes con pozos de abastecimiento de agua 利用供水井刻画越流含水层上覆弱透水层参数的方法 Um método para caracterizar aquitardos sobrejacentes a aquíferos semi-confinados utilizando furos de abastecimento de água

2010

Ostendorf, David W. | DeGroot, Don J. | Judge, Aaron I. | LaMesa, Daniel F.

Leaky aquifers provide protected drinking water since the aquifer is overlain by an aquitard, and this study develops a method to estimate hydraulic properties of the latter deposit. Steady pumping, supply well shutdowns, and slug tests generate data in adjacent monitoring well clusters that characterize the aquitard. An existing steady model estimates a site-averaged value of the aquitard permeability k if its thickness is known, and this site-averaged estimate may be compared with local k estimates from conventional and extended slug tests. A shutdown attenuation model estimates a local value of the consolidation coefficient CV, which combines with the local k value to specify the compressibility α of the aquitard. The method is illustrated for the Fowl Meadow Aquifer, a stratified drift deposit used as a drinking water supply in eastern Massachusetts (USA), with an overlying silt aquitard of 10 m thickness. Steady data and theory suggest a site-averaged k of 2.3 × 10–¹⁷ m²for the aquitard, while the shutdown attenuation model generates local CVvalues that vary from 10–⁵to 10–³ m²/s. The slug tests yield a local k variation (10–¹⁷–10–¹³ m²) that brackets the site-averaged value, and an α range of 10–⁹–10–⁷ Pa–¹.

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