The Monroe City Board of Alderman reviewed the Initial Findings Report on March 19, at the City Council meeting. Representatives Ben Frese and Karen Dietze, of Black & Veatch, were present via video to discuss the report with council members.
The recommendations from the initial findings report included several points. One recommendation was the option of wholesale water. The report advised the alternatives for improving plant performance should be compared to the costs and benefits for switching to a wholesale water supply.
These alternatives should be evaluated for effectiveness in the treatment process, along with considering the cost. The recommended alternatives for further evaluation and proposed testing approach of each of the alternatives were as follows. Concerning chlorine dioxide, the company recommended the chlorine dioxide pilot study should continue to evaluate effectiveness of chlorine dioxide as an alternative oxidant. Historical data for TTHM and HAAS prior to implementation of the chlorine dioxide pilot should be evaluated to validate merits of chlorine dioxide application. Additional bench-scale testing should be conducted to establish a baseline of existing plant THM formation with and without chlorine dioxide to provide a better evaluation of chlorine dioxide performance. Costs should be developed to implement a permanent chlorine dioxide system.
Recommendations for enhanced coagulation included additional testing to be done of ferric sulfate as an alternative coagulant. This will determine whether success in initial bench-scale testing can be repeated consistently under seasonal water quality conditions. The report stated pH control was a challenge during bench-scale testing.
The report recommended implementation of chloramine as a secondary disinfectant demonstrated significant reduction in TTHM formation and should be considered as a viable DBP control strategy.
In terms of aeration, the report recommended the implementation of aeration in the finished water reservoir to be considered a viable alternative if partnered with another DBP control strategy that address TTHM formation.
Treatment alternatives were eliminated from further evaluation if they either did not result in significant improvements for reduction of disinfection byproduct (DBP) precursors or DBPs (total trihalomethanes and haloacetic acids) compared to current operating conditions (baseline), or if the expected cost of implementation was high, relative to the anticipated performance benefits.
Based on the criteria the following alternatives are not recommended for further evaluation at this time: Modifications to powered activated carbon (PAC); Implementation of MIEX; Further evaluation of granular activated carbon (GAC) through pilot testing; and Further evaluation of RO technologies.
Black & Veatch shared the Route J Lake is very challenging water to treat from a DBP perspective. Water is very high in total organic carbon (TOC) and very high in ammonia. Ammonia will raise the demand for chlorine, resulting in subsequent formation of DBPs. TOC is a strong indicator of DBP formation comprised of total trihalomethanes and haloacetic acids which are the two chlorinated DPBs that are regulated.
The study has mostly focused on treatment methods that either address the removal of TOC or oxidize the organics so that they are less likely to produce disinfection byproducts. The water plant achieved a very high percentage of TOC removal in the range of 60-75 percent which is well above the required percentage removal by EPA.
Moving forward, Black & Veatch will continue their study of bench-scale testing during more challenging raw water conditions. The anticipated timeframe to conduct these tests will be May or June of this year.
A final report should be prepared which includes the finding from the second round of bench scale testing, additional pilot data from the chlorine dioxide system, and additional analysis to confirm water quality goals can be met. For each viable alternative conceptual layouts and capital and operational cost will be prepared to compare the alternatives and select the best long-term approach for the City.