## Civil Engineering Graduate Theses & Dissertations

#### Title

Solute Age and Groundwater Well Contamination

Spring 1-1-2014

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Roseanna M. Neupauer

Janet S. Herman

Shemin Ge

Diane M. McKnight

Joseph N. Ryan

#### Abstract

Solute age is a measure of the amount of time that a solute has been in an aquifer. A water sample that contains solute will represent a distribution of solute ages, accounting for the different travel times and paths from recharge points to the sampling location. This research introduces the concept of solute age as a tool to assess groundwater well contamination. We show that solute age for a sorbing solute is older than groundwater age because sorbing solutes move more slowly than groundwater. This implies that a pumping well contaminated by a sorbing solute would remain contaminated for longer after source removal than what would be expected based on groundwater age. In this work, we develop the adjoint equation of solute age. Using forward equations to calculate solute age under transient flow conditions, a separate forward simulation is needed for each possible release time. This is computationally burdensome and the results are limited to only the preselected set of release times. We show that an adjoint equation of solute age, however, can be used to solve for the solute age distribution at a particular observation location and time with a single simulation to account for all possible release times. This more efficient adjoint equation provides comparable results to those found using the forward equation. In addition, in this work we use solute age to evaluate the effectiveness of a riverbank filtration (RBF) system. We use the adjoint equation of solute age to calculate the spatial and temporal distribution of travel times between a river and an RBF well (equivalent to solute age) where the river water level fluctuates. Successful filtration in an RBF system will require that the travel time is long enough to achieve sufficient contaminant degradation, so the distribution of travel times can be used to evaluate the effectiveness of an RBF system.

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