Specifying Performance Over Equipment Quickly Reduces THMs In The Colorado Springs' Distribution System

Colorado Springs, Colorado, enjoys some of the highest quality drinking water in the country, with most of its water coming from high country snowmelt. Despite its pristine origin in the mountains, the water at the far end of the distribution system is prone to developing trihalomethanes (THMs) due to low turnover and high water age. Armed with water quality lab results, the staff at Colorado Springs Utilities graphed the data to pinpoint the precise location of the highest occurrence of THMs in the distribution system in an effort to be proactive in reducing THM levels. The utility staff had developed numerous disinfection by-product (DBP) mitigation strategies over the years, including an annual distribution system flushing program, treatment process modifications, reduced tank storage levels, and on-site chlorine boosting to allow for reduced chlorine dosing at the water treatment plant itself. None of these strategies reduced the THMs to an acceptable level.

The utility staff then turned to THM aeration – a technology that removes THMs from finished water by volatilization. They determined that the quickest way to achieve their reduction targets was to create a specification for a design-build project that was based on an exact performance range, as opposed to specific equipment. The specification was written to require a reduction in THMs of at least 25% as measured in two different sampling locations. Critically, the specification called for the tank, located at an elevation of approximately 7,500 feet, to remain in operation during installation, which had to be completed within a short window of less than two months during the winter.