A survey of river versus lake water supplied to a drinking water treatment plant in Alabama

Abstract

Raw water quality, specifically total organic carbon (TOC) and chlorine demand, are of particular concern to the treatment process due to upcoming tightening regulations. To address this, the Birmingham Water Works Board developed the following study in an effort to further improve finished water quality. This year a survey was performed at Shades Mountain Filter Plant (SMFP) to monitor the influent water quality to the plant. The objective was to evaluate the difference in chlorine demand and TOC for the two primary source waters, Cahaba River and Lake Purdy. Initially sampling was performed at the following locations throughout the SMFP system: Upstream Cahaba River, Cahaba Pump Station, Lake Purdy, Bottom of Lake Purdy dam, Bridge located downstream from Lake Purdy, SMFP receiving basin, SMFP flume or rapid mix. These sites were chosen for their ability to provide information on each water source independently as well as information pertaining to their combination at SMFP. Sampling occurred during and/or after several weather events to capture all weather variations. Initial results suggested that Lake Purdy had higher TOC than the Cahaba River. Consequently, the Little Cahaba site was added approximately two miles downstream of Lake Purdy just before the junction of the two source waters. It will provide crucial information as to what the water quality of Lake Purdy is just before it is combined with the Cahaba River and sent to the plant as a blend. Evaluation of the water quality at this new site downstream from the lake is important because it will help determine if additional pre-treatment or reservoir treatment will be beneficial.