Applied Ecosystem Services, LLC

The Environmental Issues Doctor

Photo of Maximum Concentration Limits

Estimated reading time: 2 minutes

Much has changed since the Clean Water Act (CWA) was passed in 1972, but not how water quality is regulated. Existing environmental data analyzed with advanced statistical models can bring CWA regulatory compliance into the 21st century. With global warming, and societal concerns about sustainability, modernizing regulatory compliance benefits everyone.

The use of maximum concentration limits (MCLs) on individual chemical ions or collections such as total dissolved solids (TDS) applied to all water bodies regardless of type or geographic location is similar to the way medicine was practiced centuries ago when we did not understand human physiology and variability.

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MCLs have three critical shortcomings: geochemical constituents are predominantly compounds, not ions; there is no context to separate natural variability from anthropogenic effects; and there is no ecological cause-and-effect inkage between a specific concentration and the status of a beneficial use at a defined location and time.

Consider calcium. It is present as calcium carbonate, calcium sulfate, and other compounds. Calcium carbonate forms shells of fresh water mussels and snails as long as the pH is between 7.0 and 8.4. Below pH 6.8 calcium carbonate dissociates and the mollusks die. Knowing calcium ion concentrations without he context of pH, hardness (alkalinity), and other variables reveals nothing about the state of the aquatic ecosystem.

Avoiding environmental issues is critical to permitted operations.

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 Introduction to Wetlands

    Introduction to Wetlands


    Estimated reading time: 1 minutes

    Wetlands are difficult to understand by non-specialists, and by many specialists, too. There are differences among the general public perception of what is a wetland, the definitions used by wetland scientists, and the definitions used by regulators on jurisdictional wetlands. This post is designed to introduce wetland definitions. Wetland water quality is regulated under Section 404 of the Clean Water Act. The definition of wetland used by wetland scientists may not be the same as that used by the wetland regulator.

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