The Process and Water Quality Specialists

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Correcting the Standard Methods Langelier Saturation Index calculation

We are pleased to announce the publication of a Trussell Tech article, "Technical Note: Calculation of the Langelier Index at High pH," in the March issue of the Journal of American Water Works Association (AWWA). The article describes an error that Trussell Tech identified in the Standard Methods' (SM) calculation of the Langelier Saturation Index (LSI), and provides equations for correcting the error. Trussell Tech has updated its corrosion model and its blending worksheet to use the corrected calculation. Trussell Tech has also taken this opportunity to simplify the corrosion model and update the mineral analysis model and the blending worksheet. Total dissolved solids (TDS), rather than a complete mineral analysis, is now used to estimate ionic strength in the corrosion model, which simplifies the water quality analyses that are required to use the model. John Kenny is chairing the AWWA SM Joint Task Group on updating the LSI calculation method.