As the population of Johnson County, Kan., grew, turning it into the most densely populated county in the Kansas City metropolitan area, its main wastewater treatment facility, the Tomahawk Creek Wastewater Treatment Facility in Leawood, failed to grow alongside it.
The plant, built in 1955, was able to treat up to only 19 million gallons a day, forcing burgeoning Johnson County to send most of its 450,000 citizens’ wastewater to neighboring Kansas City, Mo., (KCMo) for costly treatment. Tomahawk Creek could only treat about 150,000 local flushes.
“They had to do an economic event analysis,” says John Keller, project manager at engineer Black & Veatch. “Is it cheaper to build a new facility or continue to have KCMo treat our flow? That was the first phase of the project. If we built a new facility, how much would it cost? Then we compared that to if the flow went to KCMo. We did a life-cycle cost analysis, and it was cheaper to build the brand new facility—with the new permit and discharge into the Tomahawk Creek versus continuing flowing to KCMo.”
35年来,分析表明,约翰逊有限公司unty would save $785 million by investing in a new plant rather than sending its waste to Kansas City. During the plant’s three-and-a-half-year construction timeline that began in 2018, Johnson County will send all its flow to Kansas City. Sewer rate charges will rise for residents during that time, but by 2022, rates will drop. The average sewer bill is around $35 a year.
3.35亿美元的扩张和重建不仅将使战斧溪废水处理设施现代化，并将其治疗能力提高到每天1.72亿加仑的潮湿和干燥天气流量，还将增加洪水保护措施，以帮助该工厂越来越多否则可能会导致下水道备用和溢出的雨季和夏季，这可能会威胁到供水。19 MGD是新设施的平均每日设计处理能力。先前的治疗设施只能治疗平均流量为7 mGD。
“现有工厂是为一百年洪水活动而设计的，”工程师HDR副总裁兼水科经理Michael Kalis说。“植物被洪水泛滥时。我们将整个地点提升到了500年的洪泛区高程，以满足当前的法规。通过这样做，我们必须进入[Tomahawk Creek]的渠道，该渠道将减轻我们通过增加洪泛区而可能造成的任何其他径流或洪水。”
Construction Management
Because of the complexity and tight schedule, and the fact that continuing costs for treatment in Kansas City would inflate the project’s overall cost if work wasn’t completed on time, Johnson County chose the construction manager at-risk delivery method and hired the Kansas City division of McCarthy Building Cos. as its CM, while Black & Veatch and HDR kept their engineering design team roles that predate the county’s decision to build.
该项目包括Aqua-Aerobic Disc过滤系统的安装，在网站上构建30多个新结构（比以前的工厂都要大30％ - 安装了130多个泵，放置50,000立方米的混凝土和放置超过9英里的地下公用设施基础设施。
麦卡锡（McCarthy）正在建设进水连接和流量控制结构，一个新的峰值流动泵站，新的Headworks建筑物，主要澄清板，生物营养清除盆以及最终的澄清池及其相关的泵站和分离器结构。结构还包括第三级泵站，过滤络合物，化学消毒复合物，废水重新结构，重力增稠剂，包括增厚和脱水的固体过程建筑，固体消化和气体储存结构，废气燃料以及新的给药和新的给药和新的给药维护建筑。原始建筑群的几乎没有，麦卡锡正在使用三台塔架来管理复杂的混凝土结构，该建筑将持续该项目的大部分时间。
麦卡锡的全资子公司,城堡的合同ing, is providing concrete services, making the project’s concrete all self-performed. The job required several high-strength mixtures for the facility’s new disc filtration tanks and carefully monitored curing for both the base placements and the tanks’ walls. Testing of all of the tanks for seepage is required later in the process.
“The key to self-performing is it allows us to control schedule as well as quality,” says B.J. Peterson, McCarthy’s project manager. “The mix design is extremely technical. It’s important that you get the proper consolidation, especially as it relates to the hydro testing that we have to do on all of the tanks. They have to hold water. So it’s incredibly important for us to be able to control all of those measures, curing and others, that go into that.
他说：“这最终会影响时间表，因为如果有任何问题，您会增加时间尝试调查并弄清楚这笔交易是什么。”“我们为建立一个治疗厂而感到自豪，并觉得能够控制这种风险很重要。”
技术协助
McCarthy is using other measures to keep to the schedule such as regular drone flights to take real-time construction photos and measure progress and coordination. Trimble SX10 is being used to scan for accurate layout and Earthworks is being used for GPS-enabled heavy equipment placement and excavation measurement with sloping and location specificity. A 3D Autodesk Navisworks model of the entire site is being used to facilitate construction coordination and eliminate conflicts. The three tower cranes on site are operating a coordinated dance every day of construction. The CMAR method is allowing the engineering team to plan ahead for the project’s target completion in early 2022.
“The contractor schedule shows them that they’re on schedule, so we’ve switched to starting to develop the start-up plans for the project,” Kalis says. “We have the contractor getting in their operation maintenance manuals, and we are, right now, developing start-up plans of how we’re going to actually bring the treatment plant online because we’re starting the whole treatment plan up from ground zero.”
Heavy Rain … Then a Pandemic
One thing the design and construction team could not plan for, however, was the COVID-19 pandemic. Kansas never stopped construction on essential infrastructure such as the Tomahawk Wastewater Treatment Facility, so the schedule has not been impacted. McCarthy did, however, have to install new social distancing and monitoring protocols on the 60-acre site.
“We had over 300 workers on site, and they were already practicing the 6-foot social distancing,” Peterson says. “So the key is just making sure that everybody can come to work, they feel safe and keeping everybody 6 feet apart as much as possible on top of just additional cleaning measures and protective measures to make sure that we’re practicing the CDC guidelines around proper hygiene.”
A project with so much concrete placements made some work-arounds necessary for tasks such as monitoring the placement of concrete for the eight disc filter tanks with 24 filtration discs per tank.
彼得森说：“那里的关键是密切关注它，并尽可能使人们相距6英尺。”“如果有人必须在6英尺范围内工作，那就是我们将这些额外措施（无论是面罩还是口罩）结合起来的时候，只是为了确保我们正在保护人们。因此，如果您今天要在那里倒入那里，您会发现每个人都有额外的PPE，只是为了确保每个人都保持安全。”
The project keeps moving forward and is on schedule for 2022 despite the many challenges the last two years have brought.
“Last year we had the wettest year in Kansas from October to October,” Keller says. “We had almost 60 inches of rain. McCarthy dealt with the wettest year and when we continue on forward, it’s a pandemic this year. This is a lot of challenges.”
