Scale (hard mineral coatings) and corrosion deposits are made up of solids and sediments that collect on or in the distribution system piping, storage reservoirs and household plumbing. Corrosion product solids can be:
- copper, and
- lead carbonates and oxides.
They form directly from the corroding metal pipe wall. The sediments consist of corrosion by-products and precipitated solids such as:
- manganese oxides,
- aluminum hydroxide, and
- calcium carbonate), as well as
- solids that carry over from water treatment plants.
The scale and corrosion deposits serve as sites for adsorption or coprecipitation, as well as for mineral growth for certain contaminants, such as:
- radium, and
Any changes in water chemistry or physical disturbances to distribution system materials can result in the rerelease of the contaminants into our water supply, sometimes in elevated amounts. When this happens, dangerous contaminant levels can end up at public taps.
EPA is currently conducting field and bench-scale projects to investigate different aspects of this issue. Activity and research in this subject cover several areas:
- Mineralogical characterization using in-house analytical techniques such as optical microscopy, powder X-ray diffraction, and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS)
- Absorption spectroscopy by X-ray absorption near edge structure (XANES), X-ray absorption fine structure (XAFS), and extended X-ray absorption fine structure (EXAFS) techniques for metal speciation, carried out in collaboration with EPA’s Land Remediation and Pollution Control Division and the Advanced Photon Source Research Facility at Argonne National Laboratory
- Collaborative interagency agreements and contracts to extend analytical capability
Results and Impacts
No regulations are currently in place to control the accumulation of scale and corrosion deposits within distribution systems. However, several solids and surface analyses are currently being used to understand the structure and content of scale and corrosion deposits