There is an extensive body of research documenting that nitrate from nitrogen fertilizer can leach below the root zone and migrate to groundwater.
While contributions from soil organic matter, manure applications and legume crops do occur, fertilizer inputs are recognized as the most important in terms of management options. Nitrogen fertilizer sales have increased dramatically since the 1960s and corresponding increases in nitrate concentrations in vulnerable regions of the Midwestern states are well documented.
Rather than repeating the science, this document provides a short list of useful references for some of this research. While there is a wealth of information in the scientific journals, many articles are not publicly available without a subscription. For purposes of this document we will provide references that are accessible on the web and a separate list of articles that are only accessible through academic journals.
Of particular relevance is ongoing work in the state of Nebraska which clearly documents nitrate impacts to groundwater from fertilizer, work by the United States Geologic Survey (USGS) on sources of nitrate in wells, and work by numerous researchers on the leaching potential for nitrate under various cropping systems and practices in Minnesota.
The Township Testing Program (TTP) helps to identify areas with elevated nitrate and at the same time informs well owners of the potential health risk from nitrate and pesticides in their well. Nitrate in wells can come from non-fertilizer sources such as feedlots, septic systems and overland flow into damaged well casings. Therefore the TTP applies a rigorous protocol using trained technical staff to inspect the well and its location for potential contaminant sources and removes wells that fail the inspection from the data set. The MDA will not make regulatory decisions based on TTP data. MDA will develop and use a local groundwater monitoring network or public water supply well(s) for assessing local water quality.
These are other references, however they are not publicly available. They are only available through journal subscription.