<p>Nitrate is one of the most common groundwater contaminants, with levels commonly exceeding established drinking water limits. In areas of high agricultural or industrial nitrate use, nitrate contaminated groundwater poses a potential health risk. In situ denitrification is the microbially mediated reduction of nitrate to innocuous nitrogen gas compounds and is the principal process for nitrate removal in contaminated aquifers. This process is becoming increasingly recognized for its ability to reduce or eliminate nitrate concentrations in groundwater with minimal site disturbance and cost. Predicting the extent to which denitrification occurs in aquifers as well as the rate, therefore, has become the focus of numerous mathematical models. However, the predictive capabilities of numerical models are constrained because knowledge of the biological processes implicated in denitrification is limited.</p> <p>This report examines the microbial processes involved in <i>in situ</i> denitrification, and then applies this knowledge to assess the capability of a two-dimensional numerical model, NBI02D. NBI02D is a variation of a code, SEAM2D, developed by Widdowson (1988,1992).</p> <p>Model development and model application are presented. The model development overview provides insight to the mathematical methods used to simulate the microbial processes. The model application compares model predictions with data received from a USGS research site on Cape Cod, Massachusetts. Data are derived from a natural gradient experiment in which formate was injected into a carbon-limited aquifer in order to stimulate and accelerate denitrification. NBI02D simulations for the Cape Cod site are developed for model verification and model applicability.</p> / Master of Science