On a muggy summer morning, hydrogeologist Bill Simpkins has just finished raising pressure transducers from seven wells hugging the west bank of the South Skunk River in Ames. Tethered to black Kevlar rope, the transducers – narrow, weighted brass cylinders about seven inches long – and dataloggers inside the cylinders have recorded the past eight months of groundwater levels and temperatures. The data is sent through an optical interface to a laptop propped open on top of a black plastic milk crate in the back of Simpkins’ car.
“Low-cost transducer technology has revolutionized the monitoring of water levels and temperature,” Simpkins said. “At this location, transducer data show that the water level (stage) in the river is higher than that in the wells, indicating groundwater flow from the river into the aquifer.”
In addition to water level data, temperature data show it takes about five months for the river water to arrive in this part of the aquifer. Then, groundwater flows from this site southwestward in the Ames aquifer toward the downtown well field.
Simpkins, professor in the Department of Geological and Atmospheric Sciences and Smith Family Foundation Departmental Chair in Geology, has been researching the physical and geochemical interactions of groundwater with lakes and streams in Iowa’s glacial materials for nearly three decades. His work is unique because it combines the physics and geochemistry of groundwater to understand and model groundwater flow.
He said the process of groundwater flow can be described mathematically, thus allowing groundwater systems to be modeled on computers that solve these equations, producing values of the water level, or “hydraulic head,” on a grid in three dimensions.
“Think of the grid as a large Rubik’s Cube with each block having a hydraulic head value at its center,” he said. “We contour those values to interpret the direction of groundwater flow, both at the water table near the surface, and three-dimensionally in the subsurface. To demonstrate confidence in our model results, we match known water levels in wells to the model-generated ones to create a calibration curve.
“If there is a good match, we can use the model to predict, for example, groundwater flow patterns in the future; to identify drawdown effects of new municipal wells; to predict the spread of contaminants from a spill; to simulate aquifer sustainability under the effects of global climate change; and to estimate the age of groundwater at any point in the aquifer.”
“If there is a good match, we can use the model to predict, for example, groundwater flow patterns in the future; to identify drawdown effects of new municipal wells; to predict the spread of contaminants from a spill; to simulate aquifer sustainability under the effects of global climate change; and to estimate the age of groundwater at any point in the aquifer.”
For more than 10 years, officials at the Ames Water and Pollution Control Department have relied on Simpkins’ groundwater flow models and geochemical analysis to provide safe and sustainable drinking water to Ames citizens. His modeling of the Ames aquifer has led directly to siting the construction of a new municipal well field that will start next year, and his geochemical analysis of groundwater has provided evidence for implementing more frequent rehabilitation of municipal wells in the aquifer.
Simpkins’ research goes beyond the city limits, though. Data collected by Simpkins’ Hydrogeology Research Group is raising awareness of contaminants lurking in groundwater and the need for vigilance in disinfecting and treating our drinking water.
Beyond bacteria and nitrate
Water quality is a big issue in Iowa. Nitrate, phosphorus, pesticides, bacteria — as well as viruses, personal care products and pharmaceuticals – have all been found in Iowa rivers, lakes and groundwater. In Ames and other cities throughout Iowa, only bacteria and viruses from that list are eliminated through disinfection at water treatment plants before it pours from our tap.
“We are fortunate in Ames that naturally occurring bacteria in the aquifer remove nitrate in groundwater prior to entering our production wells,” Simpkins said.
But, not all towns are so lucky. Most do not have the facilities, or the knowledge, to remove all contaminants from drinking water, particularly emerging contaminants such as personal care products and pharmaceuticals.
“The water saga in Flint, Mich. illustrates why it’s important for consumers to understand how their city treats drinking water,” Simpkins said, also citing the state of Wisconsin as an example where each city — not the state — determines whether or not to disinfect their drinking water. “This is not sound public health policy. Published epidemiological studies in that state by one of my collaborators have shown that people have become sick from drinking non-disinfected water that contained human enteric viruses.”
Simpkins’ Hydrogeology Research Group joined the hunt for viruses in groundwater in 2011 through a grant from the Center for Health Effects of Environmental Contamination (CHEEC) at the University of Iowa. They looked for four common human enteric viruses — Adenovirus, Enterovirus, Norovirus and Rotavirus, which all emanate from human waste — in the aforementioned seven wells tapping groundwater near the South Skunk River, in the Ames aquifer below the Ames Municipal Cemetery, and in the Ames downtown well field. They also sampled Ames' sewage.
They also studied the Hepatitis-E virus (HEV), which can have human or animal origins. Because viruses are very small and travel easily through sand and gravel aquifers, Simpkins was convinced that viruses would be found in the Ames aquifer. But, his group found the sampling very difficult.
“We pumped 1,000 liters of water through a glass wool filter for four hours to collect enough sample on the filter to analyze in a laboratory about 350 miles away,” Simpkins said. “My graduate student, Adam Davison, experienced some very long days in the back of a cargo van.”
Simpkins’ group uses cutting-edge PCR analysis – the standard for criminal investigations – to identify the virus type and its subgroups present in the water and to quantify the virus concentration. PCR showed virus material was likely present – probably within the last two years.
Then, they used DNA sequencing to further define the viruses present by determining the serotype of the Adenovirus and genotype of the HEV. The results showed Adenovirus serotype 31 may enter the aquifer either from the South Skunk River or Ames’ leaky sewer system, but HEV genotype 3 – of animal origin – could only come into the aquifer from the South Skunk River.
Considering the two-year lifespan of virus material in groundwater coupled with water isotope and hydraulic head data collected previously, the research suggests contaminants originating from the South Skunk River can travel to the downtown well field (about one mile away) in two years or less.
“We demonstrated the vulnerability of the Ames aquifer to contamination and why cities need to be vigilant about treating drinking water extracted from rivers and groundwater,” Simpkins said. His group's virus research is currently under review in the journal of Environmental Science and Technology and is on track to be published next year.