Applied Ecosystem Services, LLC

The Environmental Issues Doctor

Photo of Nondetected Chemical Analysis


Estimated reading time: 1 minutes

Toxic metals and organics commonly occur in very low concentrations in water, sediments, soils, and rocks. These concentrations are so low they cannot be quantified by analytical chemists and today’s instruments. Censored data are commonly mis-analyzed with potential costly, unnecessary, or harmful results. EPA regulations and guidelines often tell data analysts to ignore (drop) censored data or substitute an arbitrary value. The results of dropping or substituting arbitrary values are wrong. Policies and regulations based on these wrong analyses can result in environmental and economic harm.

Statistical methods to correctly analyze data sets containing censored values are readily available. These methods are used to describe and summarize data sets, compare 2 or more temporal or spatial data sets, evaluate associations (correlations), quantify cause and effect (regression), and determine trends over time. Correctly analyzed, the results are technically sound and legally defensible. There is no reason not to apply these statistical models to all data types: binary, ordinal, or measured concentrations.

Understanding how to identify valid from invalid geochemical data analyses is explained in non-technical language (no math or environmental science involved) in the white paper, “Censored Geochemical Data Analysis for Non- Scientists” available for downloading and reading from the downloads section of this web site.

This work was originally published on the Applied Ecosystem Services, LLC web site at

It is offered under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International license. In short, you may copy and redistribute the material in any medium or format as long as you credit Dr. Richard Shepard as the author. You may not use the material for commercial purposes, and you may not distribute modified versions.

Keep reading

  1. Photo of Nepa Compliance Howto

    Nepa Compliance Howto


    Estimated reading time: 2 minutes

    When complying with NEPA requirements you benefit from submitting technically sound, legally defensible documents to regulators. NEPA, CEQ regulations, and agency directives describe in detail what is to be done in preparing an EA or EIS that is compliant with the law and all regulations. It does not direct staff or external contractors how each requirement is to be met. This blog post presents specific requirements and explains how using a quantitative approximate reasoning model, fulfills these requirements so that the results are demonstrably technically sound and legally defensible.
  2. Photo of Standards for Non-Potable Water Quality

    Standards for Non-Potable Water Quality


    Estimated reading time: 2 minutes

    Chemical standards are appropriate for human drinking water sources, but generally not for non-potable waters supporting fish and wildlife. This is because water chemistry is highly variable, measurements are isolated in time and space, and point measures are difficult to interpret as suitable for fish and wildlife. Biological-based standards of water quality are more appropriate because the presence of aquatic organisms reflect water quality integrated over time and space. Biological water quality measures have been of interest to environmental scientists and regulators for about 40 years.

Contact me when your data must be correctly analyzed.