Automated time-series measurement of microbial concentrations in groundwater-derived water supplies

Authors: OWENS, DAVID - Us Geological Survey (USGS); HUNT, RANDALL - Us Geological Survey (USGS); FIRNSTAHL, AARON - Us Geological Survey (USGS); MULDOON, MAUREEN - University Of Wisconsin; Borchardt, Mark

Submitted to: Groundwater
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2019
Publication Date: 3/1/2019
Citation: Owens, D.W., Hunt, R.J., Firnstahl, A.D., Muldoon, M.A., Borchardt, M.A. 2019. Automated time-series measurement of microbial concentrations in groundwater-derived water supplies. Groundwater. 57(2):329-336. https://doi.org/10.1111/gwat.12822.
DOI: https://doi.org/10.1111/gwat.12822

Interpretive Summary: Groundwater is often thought to be unchanging, moving slowly underground and staying constant in its chemical and biological composition. This popular perception is untrue, especially for groundwater in the type of aquifer known as fractured bedrock. In the fractures groundwater can move and change very quickly, behaving more like a river, with changes that happen over the course of hours instead of months. In this type of dynamic aquifer, a one-time sample from a well is not very informative. This paper reports how USDA-ARS and US Geological Survey scientists solved this problem by designing the first automated sampler for collecting groundwater samples from private wells. The sampler is controlled remotely by phone and can collect samples continuously over many days. In one private well with the auto-sampler installed, the scientists showed the concentration of some contaminant microorganisms, like coliform bacteria, can change 100-fold in one day. The auto-sampler will allow scientists to better characterize contamination levels and vulnerability of groundwater wells located in fractured bedrock and other dynamic aquifers.

Technical Abstract: Fecal contamination by human and animal pathogens, including viruses, bacteria, and protozoa, is a potential human health hazard, especially with regard 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 describe a sampler deployment used to characterize water quality from a household well tapping a shallow fractured bedrock in northeast Wisconsin. The sampler was deployed from January-April 2017, and monitored temperature, nitrate, chloride, specific conductance, and fluorescent dissolved organic matter on a minute timestep; water was directed to sequential microbial filters during 3 recharge periods ranging 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 1-2 orders of magnitudes during a single recharge event.