At the onset of the project the Burns & McDonnell team evaluated multiple alternatives to improve the plant’s raw water intake, water treatment processes, finished water storage, high-service pumping and site configuration. Evaluations considered whether the best option was to rehabilitate existing infrastructure, build new, or create a combination of new and existing infrastructure solutions.
Members of the city’s project team had a long list of needs they wanted to address within the fixed $31 million budget. By weighing key factors such as project funding, operations, energy consumption, maintenance requirements and reliability, Burns & McDonnell identified improvements to meet the city’s needs. This consisted of a mix of rehabilitation and new construction, and included: improving existing water intake, installing a parallel raw water pipeline, rehabilitating and expanding the treatment system, and improving the high-service pump station.
The design-build delivery method was an ideal option for the project, bringing together design, construction and owner personnel to efficiently develop creative solutions that would offer cost certainty. Further, working inside an operating water treatment facility required close design and construction coordination to see that disruptions to plant operations were minimized.
No large capital project is executed without challenges. For Siloam Springs, one of the biggest issues was starting the construction phase of the project during the COVID-19 pandemic. The health of the population was uncertain, travel was restricted, virtual meeting technology tools were in their infancy, supply chains were severely disrupted, and cost-escalation was at an all-time high. By ramping up communication and adhering to our robust procedures and protocols, the project was successfully delivered on budget and on schedule, despite pandemic-related challenges.
Handling Old Problems in New Ways With Design-Build
By utilizing a design-build approach, the City of Siloam Springs gained several benefits in terms of cost, schedule, efficiency and coordination.
This was the first design-build contract in the city government’s history. It also marked the first time that design-build was used to deliver a municipal drinking water facility in Arkansas, and it was the first time the state of Arkansas funded a design-build project through the State Revolving Fund, triggering additional federal provisions and permitting requirements that our permitting team helped the city navigate. These additional provisions included environmental permitting, good-faith efforts to use disadvantaged businesses as subcontractors, and American Iron and Steel compliance.
The design-build delivery method generated confidence in construction quality throughout the process. This approach enabled the Burns & McDonnell team to select subcontractors and suppliers who met our standards for safety and quality without being constrained to using the lowest bidder. This approach also provided Siloam Springs with the flexibility to evaluate and implement minor changes as needed, without significantly impacting the budget or schedule. For example, six months into construction, the city’s team elected to upgrade lighting in the filter gallery. This was easily accommodated through coordination with the electrical subcontractor. With additional self-performing capabilities, Burns & McDonnell was able to manage and execute critical-path construction elements with ease.
Early on, it was concluded that the plant’s existing 9 MGD capacity would be adequate to meet the city’s near-future needs. While many plant assets would require retrofits or replacements, the major concrete structures at the existing plant were generously sized and in good physical condition. The team identified a construction sequence that would allow for the replacement of equipment within the existing basins, while keeping the plant in service and meeting peak summer water demand. Therefore, new treatment basins were deemed unnecessary, resulting in substantial cost savings. The team’s design included increasing the capacity of individual basins for increased redundancy so that the plant’s capacity might later be expanded to 12 MGD without major structural changes, if needed.
In addition to treatment improvements, one of the top priorities was to improve the raw water intake and conveyance from the Illinois River. The solution was to install 2.3 miles of new raw water conveyance pipeline to back up the aging raw waterline. The existing raw water pipeline was 65 years old, so a second pipeline that provides redundancy was a necessity for reliability of the city’s water supply. The proposed pipeline route was chosen with care to minimize impacts to the scenic forested hills, which stretched from the intake on the Illinois River to the water treatment facility at the city’s edge. The existing pipeline easement was already kept mown and clear, so the team opted to route the new pipeline immediately adjacent, cutting by 40% the amount of new easement area required and greatly reducing environmental impacts compared to other available alignments.
Making Safety and Sustainability a Priority
The project’s design and construction incorporated several features to improve safety and sustainability. One priority was to upgrade the treatment plant’s disinfection system. The existing chlorine gas storage and feed system was replaced with one using sodium hypochlorite, an alternative disinfectant that greatly reduces public safety risk. This change helped reduce operators’ occupational exposure to disinfection chemicals.
Additionally, high-service backwash pumps were modified so that they can be removed for inspection and maintenance without the need for a diver to enter the clear wells (a confined space) to unbolt pipe connections. Plus, turbidimeters in the filter gallery were relocated so that operators were no longer required to climb over the 36-inch backwash pipe to read them, eliminating fall hazards.
From a sustainability standpoint, the project team took special care when choosing the brick that was utilized, confirming that it was regionally sourced and that the new structures aesthetically matched the existing plant. To reduce energy consumption, continuous insulation was utilized in all the buildings and new, high-efficiency pumps were installed. Plus, white roofs were selected to limit the heat island effect and increase reflectance at the building; and overhead doors that were used were partially made from recycled materials.