USGS NAWQA Transport of Anthropogenic and Natural Contaminants to Supply Wells Study
Framework for Identifying Predominant Redox Conditions in Groundwater from a Well
The framework for assessing redox conditions in groundwater from a well (see table below) uses threshold concentrations of six water-quality constituents
that are relatively inexpensive and easy to measure: dissolved oxygen, nitrate, manganese, iron, sulfate,
and hydrogen sulfide. This systematic and generalized approach can be applied to diverse aquifer settings.
The calculator (below) below is an interactive version of the redox framework. It provides the redox conditions for a
well when known values of water quality constituents are provided. Enter values for each constituent and click
"Calculate" to obtain the general redox category, predominant redox process, and the iron/sulfide mass ratio.
The iron/sulfide mass ratio will only be calculated when these two values are provided. An "Unknown" Process
indicates additional constituent values are necessary to complete the calculation. Note that units for all constituents are milligrams/liter.
One limitation of this method is that dissolved iron and manganese are subject to precipitation,
so measured concentrations may underestimate the extent of iron or manganese reduction. Nonetheless,
the redox framework has proven to be useful for documenting redox conditions. The redox framework
is available as a Microsoft Excel® Workbook (Jurgens and others, 2009)
for estimating redox conditions for very large datasets. The workbook also allows threshold concentrations to be modified and the user can assign qualified
redox codes for samples with incomplete data sets.