GIS ARCMAP COST DISTANCE TOOL USED TO DETERMINE PUBLIC WATER SUPPLY RELATIVE RISK METALS SAMPLING SITES IN LEXINGTON, KENTUCKY

This study developed an approach to determine relative risk metals monitoring sampling sites within a public water supply (PWS) system that complied with Code of Federal Regulations (CFR) §141.86, Lead and Copper Monitoring and emulated management practices. Goals were to use existing PWS GIS data and ArcMap’s 10.3.1 cost distance tool to rank drinking water distribution lines based on recognized human health risks (HHRs) associated with metals leaching and determine placement for metals sampling sites within a PWS.

KY American Water GIS data was obtained from KY American Infrastructure and filtered to water lines servicing Lexington, KY. Then, pipe materials were assigned relative risk values on a scale 1 to 5 (low to high) based on HHRs. Unknown materials and those in the CFR (copper, lead and galvanized) were assigned a value 5. Materials with no HHRs (PVC, PE and concrete) were valued 1 and iron-based 3. Thereafter, risk-valued materials were multiplied by respective pipe diameters to account for varying contact times. Finally, ArcMap’s cost distance tool was run from the treatment plant across the system. Resulting cost distance map (Map 1) ranks the system showing areas of high (value 5) to low (value 1) risk for leaching metals. Using ArcMap’s map algebra tool, Map 1 was evaluated for effects of buildings constructed pre-1989 using 2010 Block Group Census data. Map 2, percentage of buildings per block group, and Map 3, density of buildings per acre within each block group, were generated by adding to Map 1.

The three maps depicted areas downtown and northwest Lexington with high (value 5) risk. Southwest to southeast, in southern Lexington, pose little (value 2-3) to no risk (value 1). To verify interpretations and advance the study, it is recommended to analyze ten water samples from areas identified as high, moderate, and low risk for leaching metals regulated by EPA’s primary and secondary drinking water standards. An observed positive correlation between risk values and metals concentrations would support the maps’ validity.

If employed at PWS, this approach may prevent future drinking water crises similar to Flint, MI by improving evaluation and selection of metals monitoring sampling sites. Use of ArcMap’s cost distance tool allows for efficient updates and evaluation of sites as systems evolve to meet water demands.