WATER CORROSIVITY ANALYSIS FOR THE PUBLIC WATER SUPPLY SYSTEM OF LEXINGTON, KENTUCKY

The Flint, Michigan water crisis highlighted the importance of drinking-water quality and health impacts of insufficiently treated water. In spring 2016, eight tap water samples were analyzed from the public water supply (PWS) system of Lexington, Kentucky. Samples did not exceed EPA’s maximum contaminant level for lead (15 µg/L), but had higher corrosivity (2.9) than Flint (1.6) based on the chloride-sulfate mass ratio (CSMR).

A follow-up study was conducted to determine if: 1) CSMR values exhibit seasonal variability; 2) low lead levels, despite high CSMR values, are due to the addition of corrosion inhibitors (phosphate and/or silica) during treatment; and 3) pipe material and other factors pose corrosivity risk. An ArcMap GIS model was developed to select sample locations. By assigning health risk values to pipe materials and combining with diameter and distance, the risk of leaching metals was calculated using the ArcGIS Cost Distance tool. The resulting model rated the PWS network, showing areas of leaching metals risk (high to low) under corrosive conditions. Samples were collected in spring and fall 2017 from taps at 11 sites and from near the PWS intake in the Kentucky River. Samples were collected in accordance with the EPA Lead and Copper Rule and analyzed for field parameters, metals, major ions, phosphate, and silica.

Results showed that water corrosivity values were low (spring 0.184 and fall 0.417) in 2017. Presence of phosphate-based corrosion inhibitors lessens the risk of metals leaching, which may explain the high corrosivity but low lead concentration in spring 2016. This study also showed metal concentrations (copper, iron) increased with pipe distance, revealing areas with high risk of leaching metals and demonstrating that the ArcGIS model is useful in locating areas of concern.