Source Water Study Challenges Environmental Limitations

Problem

The Walker County Water and Sewerage Authority (WCWSA) in Georgia currently provides water to its distribution system using three different groundwater well fields. Two of the well fields are groundwater wells and only require disinfection, but the third well field is considered ground water under the influence of surface water and requires additional treatment to make it safe for consumption. WCWSA decided it was in the best interest of its customers to consolidate all the groundwater and surface water resources into one modern membrane water filtration facility centralized in Chickamauga to serve the entire distribution system. To meet the needs of the entire system and future demands, WCWSA wanted to expand the treatment plant capacity to a peak daily demand of 8.3MGD and peak instantaneous flow capacity of 12MGD, however, their total groundwater permits only allowed them to withdraw 8.3MGD total.

Solution

After receiving permission from the EPD, CTI and the County conducted a flow study to determine whether the wells and the surface water could sustain a 12MGD demand without impacting the groundwater levels or downstream water quality.

To begin the study, water was pumped from upstream just above a dam to the treatment plant and measured using the available raw water meters beginning at 2MGD and increasing in 2MGD increments. The flow was increased in stages from 2MGD to 4, 6, 8, 10 and 12 and finally once the flow reached 12.8MGD, it was held there for 30 days and continuously measured.

During 30 continuous days of drawing 12.8MGD, the withdrawal rate had no effect on the groundwater or perched water levels and was also not affecting lake or downstream water quantity. Since the study found there were no environmental or water quality concerns from withdrawing the necessary amount of water, the EPD removed the withdrawal limits at the plant and issued a revised permit to the County.