An Analysis of Nitrate Groundwater Sample Preservation and Storage Methods

Many Minnesotans receive their drinking water directly from underlying aquifers through private wells. Certain aquifers can be susceptible to nitrate leaching from surface activities, including feedlots, fertilizer use, septic systems, among others. The federal maximum contaminant limit (MCL) and state Health Risk Limit (HRL) for nitrate as nitrogen (N) are 10 mg/L, which provides reasonable protection against the negative health effects of nitrate (MDH, 2015). There are many private drinking water wells in Minnesota with nitrate levels that exceed these standards. In recent years, quantifying the degree of nitrate contamination in groundwater has become an increasing priority for Minnesota. Due to the immensity of such a task, some groundwater samples will inevitably exceed recommended storage times and/or lack recommended preservation techniques. In this study, the effects of various preservation and storage methods on measured nitrate + nitrite as N concentrations were evaluated for groundwater samples collected from three different wells in Minnesota. Nitrogen in groundwater is primarily in the forms of nitrite and nitrate (Warner and Arnold, 2010). Measurements of nitrate + nitrite as N in this report will hereafter be referred to as nitrate.""