Maureen A. Muldoon

Stratigraphic controls on vertical fracture patterns in Silurian dolomite, northeastern Wisconsin

Vertical opening-mode fractures are mapped on quarry walls to assess the stratigraphic controls on fracture patterns in the relatively undeformed Silurian dolomite of northeastern Wisconsin. Our two-stage study uses maps of vertical fractures to assess the effectiveness of various types of stratigraphic horizons (e.g., organic partings or cycle-bounding mud horizons) in terminating opening-mode fractures. First, the mechanical stratigraphy of the exposures is interpreted from the observed fracture pattern. Both visual inspection and a newly developed quantitative method are employed to identify effective mechanical interfaces. The two methods show similar results, confirming the validity of qualitative visual inspection. The second stage of our study stochastically predicts mechanical stratigraphy and subsequent fracture pattern from empirical relationships between the observed sedimentary stratigraphy and the interpreted mechanical stratigraphy. For example, 63% of cycle-bounding mud horizons within the inner-middle and middle shelf facies associations serve as mechanical interfaces. These empirical percentages are input to a Monte Carlo analysis of 50 stochastic realizations of mechanical stratigraphy. Comparisons of the stochastically predicted and interpreted mechanical stratigraphy yield errors ranging from 13 to 33%. This method yields far better results than assuming that all stratigraphic horizons act as mechanical interfaces. The methodology presented in this article demonstrates an improved prediction of fracture pattern within relatively undeformed strata from both complete characterization of sedimentary stratigraphy and understanding mechanical controls on fracturing.

Hydraulic Conductivity Determinations in Unlithified Glacial and Fluvial Materials

Experiences with many measurements of the hydraulic conductivity of unlithified glacial and fluvial materials in Wisconsin suggest that hydraulic conductivity must be viewed in terms of the operational scale of measurement, based on the scale of the problem at hand and the volume of the materials of interest. Frequently, the hydraulic conductivity of a given lithostratigraphic unit appears to increase as the operational scale of measurement increases. In particular, laboratory methods can yield hydraulic conductivities one to two orders of magnitude lower than conductivities determined in field tests on the same materials. The operational scale of most laboratory methods is much smaller than the operational scale of most field problems, and laboratory tests, although often logistically and financially attractive, may be of little value in characterizing the hydraulic conductivity of Pleistocene and recent deposits at working field scales.

Using Enteric Pathogens to Assess Sources of Fecal Contamination in the Silurian Dolomite Aquifer: Preliminary Results

The fractured Silurian dolomite aquifer is an important, but vulnerable, source of drinking water in northeast Wisconsin (Sherrill in Geology and ground water in Door County, Wisconsin, with emphasis on contamination potential in the Silurian dolomite, 1978; Bradbury and Muldoon in Hydrogeology and groundwater monitoring of fractured dolomite in the Upper Door Priority Watershed, Door County, Wisconsin, 1992; Muldoon and Bradbury in Assessing seasonal variations in recharge and water quality in the Silurian aquifer in areas with thicker soil cover. p 45, 2010). Areas underlain by the Silurian dolomite aquifer are extremely vulnerable to groundwater contamination from various land-use activities, especially the disposal of human wastewater and dairy manure. Currently there is no consensus as to which source of wastewater generates the greater impact to the aquifer.

Automated Time Series Measurement of Microbial Concentrations in Groundwater-Derived Water Supplies: Automated Time Series Measurement of Microbial Concentrations in Groundwater-Derived Water Supplies

Abstract Fecal contamination by human and animal pathogens, including viruses, bacteria, and protozoa, is a potential human health hazard, especially with regards to drinking water. Pathogen occurrence in groundwater varies considerably in space and time, which can be difficult to characterize as sampling typically requires hundreds of liters of water to be passed through a filter. Here we describe the design and deployment of an automated sampler suited for hydrogeologically and chemically dynamic groundwater systems. Our design focused on a compact form to facilitate transport and quick deployment to municipal and domestic water supplies. We deployed a sampler to characterize water quality from a household well tapping a shallow fractured dolomite aquifer in northeast Wisconsin. The sampler was deployed from January to April 2017, and monitored temperature, nitrate, chloride, specific conductance, and fluorescent dissolved organic matter on a minute time step; water was directed to sequential microbial filters during three recharge periods that ranged from 5 to 20 days. Results from the automated sampler demonstrate the dynamic nature of the household water quality, especially with regard to microbial targets, which were shown to vary 1 to 2 orders of magnitude during a single sampling event. We believe assessments of pathogen occurrence and concentration, and related assessments of drinking well vulnerability, would be improved by the time‐integrated characterization provided by this sampler.