Advanced wastewater treatment facility designed to protect freshwater springs

April 2009 » Feature Articles
The Wakulla Springs, located near Tallahassee in the Florida Panhandle, is one of the world’s largest freshwater springs. But its shallow aquifer is particularly vulnerable to pollution from the chemicals used on lawns and in agriculture, stormwater runoff, and nitrates from wastewater treatment and septic systems. The city of Tallahassee’s main sewage and wastewater treatment plant, located adjacent to the springshed, is rated at 26.5 million gpd and uses an activated sludge process to produce secondary effluent. Most of the effluent is stored in onsite ponds and reused for spray irrigation on agricultural crops and pasture. Now, the city is investing more than $180 million to overhaul its wastewater facilities to advanced wastewater treatment standards.
Adam Strafaci and Sarah Hodges

Project
T.P. Smith Water Reclamation Facility, Tallahassee, Fla.
Participants
City of Tallahassee
Hazen and Sawyer, P.C.
Product application
Software solutions from Autodesk help design facility upgrades to advanced wastewater treatment standards within an abbreviated timeline.
The Wakulla Springs, located near Tallahassee in the Florida Panhandle, is one of the world’s largest freshwater springs. Its water "springs" from the longest and deepest known submerged freshwater cave system in the world and its springshed includes major portions of Tallahassee. On average, more than 250 million gallons per day (gpd) of water flow from Wakulla Springs. But its shallow aquifer is particularly vulnerable to pollution from the chemicals used on lawns and in agriculture, stormwater runoff, and nitrates from wastewater treatment and septic systems. Increased nitrogen concentrations have been observed in the Wakulla Springs discharge during the last several decades. Nutrients fuel invasive plant growth and can lead to degradation of the spring’s water quality.

The city of Tallahassee is investing more than $180 million to overhaul its main sewage and wastewater facility to reduce the flow of nutrients into the world-famous Wakulla Springs. (Photo: Hazen and Sawyer)


The city of Tallahassee’s main sewage and wastewater treatment plant—the Thomas P. Smith Water Reclamation Facility—is located adjacent to the springshed. The facility is rated at 26.5 million gpd and uses an activated sludge process to produce secondary effluent. Most of the effluent is stored in onsite ponds and pumped to the facility’s Southeast Farm and Southwest Sprayfields, where it is reused for spray irrigation on agricultural crops and pasture.

In 2002, the city began a study with the U.S. Geological Survey to track groundwater flow and characteristics near the sprayfields. The study demonstrated a link between the facility’s Southeast Farm effluent and the springs. In response, the city is investing more than $180 million to overhaul its wastewater facilities to advanced wastewater treatment standards. Its goal is to reduce the flow of nutrients into Wakulla Springs by 75 percent—improving the quality of reuse water and protecting the natural water quality in Wakulla Springs.

The wastewater treatment plant is located adjacent to the springshed of Wakulla Springs. The facility uses an activated sludge process to produce secondary effluent, which is used for spray irrigation on agricultural crops and pasture. (Photo: City of Tallahassee)

In the spring of 2008, the city hired environmental engineering firm Hazen and Sawyer to design upgrades to the existing wastewater treatment facility. The firm uses 3D model-based design software from Autodesk for its projects, including AutoCAD MEP and AutoCAD Civil 3D software. Both solutions use 3D models as the basis of the design, helping to keep the entire team coordinated. The combination of these AutoCAD-based solutions fits Hazen and Sawyer’s multidisciplinary needs. The firm currently has more than 60 designers and engineers working on this project.

The city hired environmental engineering firm Hazen and Sawyer to design upgrades to the existing wastewater treatment facility. The firm uses 3D model-based design software from Autodesk as the basis of its design. (Image: Hazen and Sawyer)

Existing facility
One of Hazen and Sawyer’s first challenges on the project began with the plant site, which has congested underground utilities (yard piping and electrical power distribution) that can’t be disrupted. Thankfully, the city had accurate 2D CAD files of the existing utilities. To supplement that, the Hazen and Sawyer team performed extensive subsurface utility exploration, using ground penetrating radar and vacuum excavation to physically locate existing utilities.

Based on those drawings and digital survey files, Hazen and Sawyer engineers modeled the yard piping in 3D using their Autodesk software. The result was an accurate, field-verified, as-built 3D model from which to start their design. As new utilities are designed in 3D, Hazen and Sawyer engineers merge their design models together using Autodesk Navisworks, which uses model aggregation technology to combine design information from multiple platforms into a single model. The team then uses Navisworks to perform clash detection to help identify conflicts or surprises to minimize project schedule delays. The project team knows where everything is, knows where everything needs to go, and can visualize and review it all in a 3D virtual environment.


The Autodesk software provides virtual walkthroughs of complicated areas, helping the project team to visualize and identify potential issues such as the clash detection shown here. (Image: Hazen and Sawyer)


Continuous operation
Another major challenge facing the project team is that the plant has to maintain continuous, full treatment throughout this project. In some areas, entire new treatment processes are being constructed and integrated into the existing plant, and then existing facilities are being demolished or taken off-line for upgrades. In other areas, portions of a specific process are being upgraded in a phased manner so as not to interrupt service completely. All of this means that the team has to sequence construction and startup of the new or upgraded facilities carefully, and therefore needs to understand what’s already there, what’s being built, what’s being demolished, and how all of that fits together during the next six-plus years (the length of the overall project).

The model-based design environments of AutoCAD MEP and Civil 3D are critical in this regard, as the 3D design models from both of those solutions are merged in Navisworks for project coordination. This project is a collaborative effort between Hazen and Sawyer, the city’s program management team, and the city’s construction manager. This extended team uses Autodesk Navisworks regularly at design workshops and reviews, enabling them to "walk" around and through the design model, turn systems on and off to reduce visual clutter, and color-code systems based on criteria such as "existing," "to be demolished," and "proposed." This technology provides a venue for visualizing (and better understanding) how the newly designed components will tie into existing facilities and processes. In addition, when construction begins, this combined design data can be integrated with construction logistics models and project schedules, enabling 4D modeling—where time is the fourth dimension—for improved project sequencing and construction simulation.

Tight schedules
The city has established an aggressive timeline for this project to satisfy re-permitting criteria, but more importantly because time is critical for avoiding further environmental impact on the Wakulla Springs and the local aquifer. The model-based approach is a key component for time savings on this project. The software dynamically connects the design model and project documentation. This means that project drawings and material quantities are automatically updated as the design changes, helping to save time that would have been spent on manual documentation coordination.

Design workshops and reviews are also vital for keeping the project schedule on track. The 3D visualization features of Autodesk Navisworks are used to enhance collaboration among all project stakeholders including the city’s project managers, engineers, and operators. Instead of reviewing standard orthogonal plan and section drawings, virtual walkthroughs of complicated areas such as a control room or a dewatering building enable the team to better see, thus assisting them in identifying potential issues. The time needed for the traditional review-comment-response process is minimized; everyone is in the room together, making design decisions in real time. These collaborative sessions are particularly useful for getting input from the plant’s operators. For example, they can comment on placement of a valve that they’ll need to access during operation, or the accessibility of a piece of equipment that will need routine maintenance. This type of feedback leads to better decisions that will positively impact project construction and facility operations.

Hazen and Sawyer has many offices working on this job, as well as three subconsultants. Web-based Autodesk Buzzsaw software is used to help centralize and manage design- and construction-related documents, facilitating collaboration so project team members can make timely decisions based on accurate information. Buzzsaw is also critical for the production of drawings on such a tight schedule. The project has eleven 3D structures; each with 15 to 20 subassemblies for all of the engineering disciplines, including mechanical, architectural, structural, and electrical. On a bi-weekly basis, the design models and drawings for those subassembly designs, as well as the yard piping, are downloaded from a Buzzsaw site and brought together into a master site model. Hazen and Sawyer then creates digital sheet sets for the entire project (more than 1,200 projected) and uploads them back to Buzzsaw. This approach streamlines coordination and improves project quality because everyone is looking at up-to-date information.

The project has eleven 3D structures; each with 15 to 20 subassemblies for all of the engineering disciplines, including mechanical, architectural, structural, and electrical. On a routine basis, the models for those subassembly designs, as well as the yard piping, are brought together into a master site model. (Image: Hazen and Sawyer)

Flight paths
This treatment facility is located next to the Tallahassee Regional Airport, which adds another interesting twist to the project. With two large runways, the airport has an average of 275 aircraft operations per day, including commercial jet service. All structures in the facility must meet strict guidelines regarding flight ceilings. During construction, the contractor will need to limit crane reaches and construction equipment so as not to impact flight paths.
In fact, these flight ceiling restrictions were one of the reasons that the city added a requirement for drawings that contained 3D views—such as isometrics and perspectives—in its contract with Hazen and Sawyer. The drawings ensure that the construction manager and airport officials have the information needed to formulate and approve a construction safety plan.

Using AutoCAD Civil 3D, Hazen and Sawyer engineers modeled the flight ceiling in 3D, creating a wedge— called a glide slope—that tapers along the site based on the path of aircraft taking-off and landing. They then used that model in combination with the terrain represented in AutoCAD Civil 3D to guide their design of the new structures needed for the facility. With the 3D model, they could cut sections and profiles, making sure that individual structures and the equipment anticipated for their construction didn’t violate the height restrictions. As a result, early on in the design process they were able to set building dimensions and clearances. Autodesk Navisworks is also being used to demonstrate to both airport officials and the Federal Aviation Administration that the proposed facilities are being purposely located to maximize the buffer between the structures, the construction manager’s equipment, and the flight paths.

The treatment facility is located next to the Tallahassee Regional Airport. Using Autodesk software, Hazen and Sawyer engineers even modeled the flight ceiling in 3D to make sure that individual structures and the equipment anticipated for construction didn’t violate height restrictions. (Photo: City of Tallahassee)

Summary
Design of the upgrades for the Thomas P. Smith Water Reclamation Facility is 60-percent complete. The project team is well on its way to making this wastewater treatment system produce among the cleanest water in the state and restoring the water quality at Wakulla Springs. The project is on budget and on schedule, a testament to the dedication and engineering expertise of the entire project team, as well as their innovative use of collaborative design technology.


Adam Strafaci is the senior industry marketing manager for Land Development and Environmental Engineering for Autodesk. He can be contacted at adam.strafaci@autodesk.com. Sarah Hodges is the industry marketing manager for Building Engineering for Autodesk. She can be contacted at sarah.hodges@autodesk.com. Contributors to this article include Harold Litzenberger, corporate CAD coordinator, Hazen and Sawyer, Raleigh, N.C.; Josh Farmer, P.E., principal engineer, Hazen and Sawyer, Raleigh, N.C.; Kurt Pfeffer, P.E., consultant project manager, Hazen and Sawyer, Boca Raton, Fla.; and Sondra Lee, P.E., municipal project manager, city of Tallahassee, Fla.

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