Volunteer Sampling of Privately-Owned
Groundwater Wells to Assess and Display

Groundwater Quality in Six Colorado Western Slope Counties

Holly Miller
2017 Harlan erker memorial scholarship recipient
CU Boulder

Wednesday, September 19th, 2018 @ 12:00pm

**Please note NEW location**

Golder Associates, Inc
44 Union Boulevard, 6th Floor
Lakewood, CO 80228


Lunch orders must be received by end of day Monday prior to the event.

Unfortunately we are no longer able to accept payment for lunches at the door.

Please prepay for your lunch or feel free to bring your own.



Golder Associates, Inc.

44 Union Blvd, 6th Floor

Lakewood, CO 80228



Many residents in six counties on Colorado's Western Slope rely on privately-owned groundwater wells for drinking water. Because the water quality from these privately-owned wells is unregulated, these sources are often untested, which constitutes a risk to public health. Water quality sampling from private homeowner volunteers within this region yields a more complete dataset that is analyzed for hazardous contaminants in the source aquifers, which ultimately helps to educate communities and alert public health authorities to areas of concern.

We present the results from a groundwater quality assessment using samples obtained from private well owners and a comparison of interpolation techniques to visualize water quality across the six counties. Sample volunteers were recruited via local media and provided with a prepaid sample kit for analysis from a national testing laboratory. The well locations and water quality parameters were compiled into a database. The private well water concentrations were compared to the following primary regulated drinking water standards: arsenic, barium, cadmium, chromium, copper, lead, nitrate, selenium, and uranium. Ten percent of the wells sampled contained arsenic concentrations above maximum contaminant level (MCL), which constitutes the highest exceedance. The remaining contaminants were only found in five percent or less of the wells. Geographical information system (GIS) was used to determine that 70% of the private groundwater wells tested in the Burro Canyon geologic formation have arsenic concentrations above the MCL. The mobilization of arsenic is likely from the groundwater having a negative reduction potential causing desorption from iron oxides. To assess and display arsenic concentrations across the six counties, GIS was used to compare the following interpolation methods: inverse distance weighting, regularized spline function, and ordinary kriging. The ordinary kriging interpolation method out-performed the other methods as determined by the lowest cross-validation error.

This study provides a model for using citizen scientists to help study groundwater quality to convey the health risks of groundwater contamination to homeowners as well as provide public health authorities with information about existing hazards.


Holly Miller is an environmental engineering graduate student at the University of Colorado Boulder with a keen interest in groundwater and hydrology. In her graduate work, Holly uses Geographical Information System (GIS) to visualize groundwater chemistry data and educate public audiences about the groundwater quality of private drinking water wells. In addition to her local study areas, she has had the opportunity to take her expertise abroad, developing the methods and installing advanced precision instruments while providing researcher training for the first-ever water chemistry laboratory in Bhutan. Holly brings over 7 years of experience as an environmental chemistry laboratory manager where she assisted in source water determination and quantification projects, long-term ecological research, and mine hydrology initiatives.