From The Editor | June 9, 2016

Choosing A Corrosion Control Treatment Strategy

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By Kevin Westerling,
@KevinOnWater

InThePipe

Here in the post-Flint era of municipal water operations, and for the foreseeable future, the loudest mandate for utilities will be to "get the lead out" of our distribution systems. Until such time that all lead lines are replaced, control strategies will need to be employed to meet and exceed the standards of the U.S. EPA Lead and Copper Rule (LCR), which is currently being reconsidered to include stronger protections.

In March of this year, at the height of the Flint scandal, the EPA issued Optimal Corrosion Control Treatment Evaluation Technical Recommendations for Primacy Agencies and Public Water Systems to set the record straight on best practices. The document indirectly references the main failure of Flint — lack of consideration for source water quality — by guiding utilities on the right balance of pH, alkalinity, and dissolved inorganic carbon (DIC) necessary to build up protective scale in the pipe, thus creating a barrier to lead release. This basic method of corrosion control treatment (CCT) can also be buoyed by the addition of a corrosion inhibitor, typically orthophosphate.

Step one, however, is to know your water. As interrelated as the three key parameters are, learning the value of any two can reveal the value of the third. The EPA provides this handy chart to determine DIC from known measurements of alkalinity and pH, which are commonly acquired through instrumentation. Once all three parameters are determined, a corrosion control treatment (CCT) strategy can be undertaken.

To easily present the options, the EPA created the following flow charts using pH value as the starting point. Because iron and manganese are known to interfere with CCT, there are separate charts for finished water that contains either of these constituents. The next four flow charts apply to lead only or lead and copper together (but not to copper alone), without the interference of iron and manganese in the water.

Selecting Treatment for Lead only or Lead and Copper with pH < 7.2

 

Selecting Treatment for Lead only or Lead and Copper with pH from 7.2 to 7.8

 

Selecting Treatment for Lead only or Lead and Copper with pH > 7.8 to 9.5

 

Selecting Treatment for Lead only or Lead and Copper with pH > 9.5

The following charts apply to lead and/or copper, while also accounting for the presence of iron and manganese.

Selecting Treatment for Lead and/or Copper with Iron and Manganese in Finished Water and pH < 7.2

 

Selecting Treatment for Lead and/or Copper with Iron and Manganese in Finished Water and pH ≥ 7.2

Further reading:

Optimal Corrosion Control Treatment Evaluation Technical Recommendations for Primacy Agencies and Public Water Systems (full document)

Lead and Copper Corrosion:  An Overview of WRF Research (via the Water Research Foundation, published January 2016)

Image credit: "In The Pipe," Anders Sandberg © 2007, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by-nc-nd/2.0/