Inside a New Sewage Lift Station: Construction of San Antonio River Authority’s Wet Well and Redundant Pump System

Overview

Practical Engineering takes viewers to a fast-growing area outside San Antonio where a new wastewater lift station is under construction. The video follows the project from initial dirt scoops through shoring, precast wet-well segments, backfill, piping, manholes, electrical shelters, and final pump testing, highlighting how a modern lift station integrates with an existing system to handle increasing demand and provide maintenance redundancy.

Introduction and Project Imperatives

Outside San Antonio, Texas, a construction crew begins a significant expansion of wastewater infrastructure to keep pace with a rapidly developing region. The host Grady Hillhouse collaborates with the San Antonio River Authority to take viewers through the end-to-end process of building a new pumping station that will work in tandem with an existing lift station. The goal is twofold: increase system capacity to meet growing demand and introduce redundancy that enables maintenance without service interruptions during low-flow periods. This project also emphasizes forward-thinking planning; the new wet well is upsized relative to its neighbor so future upgrades can be achieved by adding pumps rather than excavating anew.

Groundbreaking and Site Constraints

The excavators, dumps, and trucks arrive on site, revealing the constraints of a narrow construction area. The bottom of the hole is planned to sit roughly 30 feet (9 meters) below the surface, which presents unique safety challenges. Safety regs require sloped sides in deep excavations to prevent collapse, yet slopes consume valuable space on a confined site. To address this, the crew stages the work in two parts: the shallow 10-foot depth uses slope sides, while deeper sections rely on a slotted shoring system—the blue panels and rails we see unloading from trucks—that keeps the walls from caving in as the excavation proceeds. The reference corner panel sets the geometry for the entire shoring system, underscoring the critical role of precise alignment in complex earthworks.

Excavation, Sloping, and Shoring Techniques

The workers progressively lower the hole while a loader continuously removes soil. The shoring system comprises outer panels that stay fixed and inner panels that slide downward as the hole deepens. The process requires careful measurement and squared placement; any misalignment could jeopardize the entire wall system. The crew uses a combination of mechanical assistance and hand signaling to coordinate the shoring installation in the constrained space. Throughout the process, the team negotiates adverse weather, spacing, and the need to keep the site safe for workers while still advancing toward final depth.

Surveying, Subgrade, and the Mud Slab

Once the hole reaches its final depth, surveyors descend to verify elevation. The subgrade needs to be compacted to provide a stable foundation for the wet well. A remote-controlled compacting roller is used to densify the bottom, minimizing the risk of settlement and enabling the concrete bottom to sit evenly. Because native clay is problematic for backfill due to shrinkage and settling, the crew specifies alternative backfill materials that will be brought in as needed. A mud slab, or working slab, is created to protect the clay and prevent it from turning into a muddy mess during rain, ensuring a clean, stable interface for the subsequent concrete placement.

Working Slab and Early Concrete Pour

The working slab is formed using boards placed inside the excavation, with a reference rod ensuring precise elevation for the concrete that follows. A concrete pump truck is set up with outriggers and a boom, enabling controlled placement of concrete exactly where needed rather than relying on a chute. The primer of the pump and the waste from primer disposal demonstrate the practical considerations of maintaining clean operations on a busy job site. The mud slab cures and becomes a stable foundation for the wet well and future concrete elements of the lift station.

The Wet Well: Precautionary Measures for Large-Scale Concrete Work

With the bottom reference in place, the project moves to the most dramatic component: the wet well. A 300-ton all-terrain crane arrives, accompanied by a convoy of trucks carrying outrigger pads and counterweights. The crane's outriggers distribute its weight across reinforced pads to prevent ground damage and ensure stability during heavy lifts. The first precast bottom segment is positioned and connected with a gasketed joint, then the interior of the joint is lubricated to ensure a watertight seal. The blue shoring panels continue to provide lateral support as more segments are added to form a large cylindrical watertight vessel that will hold the raw sewage. The crane, sling configuration, and rigging caution illustrate the complexity and risk of assembling the wet well from precast components in a restricted space, with spotters and signal persons coordinating every move to minimize the chance of a mislift or a collision with the shoring system.

Segment-by-Segment Wet Well Assembly

Each precast segment weighs approximately 15 tons, comparable to a city bus, underscoring the scale and risk of the operation. The crew sequentially offloads segments, cleans mating surfaces, coats gaskets with lubricant, and seats each ring on the previous one. The use of a spreader bar prevents horizontal forces that could crack the concrete during hoisting. The process requires meticulous measurement and alignment; even a seemingly small misalignment could compromise watertight seals or the structural integrity of the entire tank. As the penultimate and final segments are installed, scissor lifts and mobile boom lifts are used to reach the higher joints. The wet well now takes shape as a stacked cylinder that will act as the primary collection and storage basin for incoming wastewater before pumping it to the treatment facility uphill.

Sealants, Leak Testing, and Final Wet Well Readiness

After assembly, grout is hand-applied inside the joints to further seal the precast connections, and epoxy coatings are applied to improve corrosion resistance in the harsh wastewater environment. A leak test is mandatory: the wet well is filled with water and allowed to sit for several days. The presence of any leakage or evaporation-based loss would trigger corrective actions. The team injects epoxy into minor cracks as a precaution during the leak test, which demonstrates a proactive approach to long-term integrity. Once certified leak-free, the wet well is backfilled in stages and prepared for backfill around the perimeter with flowable fill to avoid differential settlement once the site is completed.

Shoring System Removal and Flowable Fill Backfill

Backfilling begins with loosening the shoring panels and gradually removing inner components while maintaining stability. The soil is disturbed by limited access to the panels, so crews employ hydraulic pullers and heavy equipment to free the inner rails. Because traditional backfill would be impractical in this narrow excavation, controlled low-strength material, flowable fill, is introduced to fill hollow spaces and irregular zones that would be difficult to compact. Flowable fill is pumped into the excavation with a pump truck and allowed to cure, creating a stable base while preserving the ability to excavate later for additional work. After the flowable fill sets, further backfill uses conventional soil, and a density gauge verifies proper compaction. The site becomes progressively tidier as the shoring system is removed and the backfill solidifies around the wet well perimeter, culminating in a stabilized base for the next construction phases.

Pipe Bedding, Trenching, and Conduits

Three sewer lines connect the wet well to the upstream lines and the downstream network. Bedding gravel is deployed to support each pipe, and lynx seals and flexible couplings ensure that movement and settlement do not stress the joints. The team drills penetrations into the wet well for pipe connections, using a core drill with water cooling to prevent dust and maintain sanitary conditions. The first pipe is lowered into the wet well and connected to the discharge system, with subsequent lines installed in a similar fashion. The pipes pass through the trench with careful bedding, and the backfill around the pipes uses a mixture of gravel bedding and soil, carefully avoiding the crush of the ducts. A tape warning is placed overhead to indicate buried utilities and reduce the chance of accidental damage during future digging work. The final sections are connected to the existing lift station and to a phase three plan to link to the upstream plant as demand grows, with some lines temporarily capped until they’re needed in future work.

Thrust Blocks, Aboveground Piping, and Thrust Management

As the pipes curve and connect to elbows that turn corners, thrust blocks are poured to distribute pressure into the surrounding soil and prevent movement over time. The underground piping is wrapped in protective plastic to shield it during backfill. Aboveground piping is anchored to the concrete pad with drilled anchors and epoxy, and flanges are bolted with gaskets to ensure leaks are kept out. A dedicated line runs from the wet well to an above-ground discharge manifold with pressure gauges that allow operators to monitor flow and pressure in real time. The system also includes a valve arrangement to isolate lines for maintenance while continuing to operate the rest of the facility.

Electrical, Control, and Redundancy Architecture

The project features robust electrical infrastructure to ensure reliability during peak demand and emergencies. Grid power is delivered through 480-volt transformers with disconnects, fuses, and a transfer switch for mobile generator integration. The control shelter houses pump control panels with soft-start and auto-shutdown protections. A remote terminal unit (RTU) and SCADA network enable centralized monitoring, data logging, and remote operation. The grounding system includes deep copper rods and a test to verify its integrity. A dedicated ground ensures personnel safety and rapid fault detection in a chlorinated, corrosive environment typical of wastewater facilities. The electric and control systems are designed with redundancy in mind so that if one pump fails, the others can continue to move wastewater uphill without risking an overflow or a system-wide shutdown.

Wet Well Epoxy Lining and Confined-Space Safety

The interior of the wet well receives epoxy lining to mitigate hydrogen sulfide corrosion and to extend the life of the concrete. The walls and floor receive an epoxy coat to reduce corrosion and leakage paths. Workers must enter confined spaces, so safety protocols include gas monitoring, ventilation, a rescue winch, and a dedicated observer to ensure continuous safety. After the lining cures, the team conducts leak testing and confirms there are no leaks before proceeding to final backfill and backfilling around the tops of the joints. The epoxy lining, sealant application, and leak testing are crucial steps to guarantee that the structure can handle raw sewage while remaining watertight and resistant to chemical attack.

Commissioning and System Integration

With the wet well in place, the project proceeds to integrate the new system with the existing lift station. Three new discharge lines are connected to an above-ground manifold, and the entire arrangement is pressure-tested. The system later ties into the upstream treatment plant, with plan for a potential third lift station to handle future growth. Workers verify elevations and align the pipe connections to the wet well precisely, ensuring gravity-fed segments align properly with the wet well’s inlets and outlets. The project team also adds a diesel backup pump for power outages, enabling the system to continue moving wastewater if electrical power is interrupted. A bypass pumping setup is used to divert flows during valve installations so that the downstream lift station remains in operation during construction. The final elements include a control shelter, an electrical rack, venting, and a secure access hatch integrated into the wet well cover slab. The team completes final backfill, installs bollards to protect the structure from vehicle impacts, and closes the site for commissioning testing.

Final Testing, Commissioning, and Reflection

The first pump test uses city water and a hose to fill the wet well to a set level, observing how quickly the leading pump reduces the level. The flow meter and pressure gauges are checked to confirm that they reflect accurate flow and pressure. After the primary pumps pass their tests, the emergency diesel pump is tested to verify reliability. The on-site team, including a pump manufacturer representative, validates that the system meets design specifications and operates as intended. The host closes with reflections on how the completed lift station will enable growth in the surrounding area while remaining largely invisible to residents because the pumping system operates underground and behind secure shelter structures. The episode emphasizes the important but often unseen work of civil infrastructure that keeps modern life functioning, while acknowledging the teams, engineers, and utility partners who make such projects possible. Grady and the San Antonio River Authority staff express gratitude to the contractor and subs who contributed to the project and invite feedback from viewers who want to learn more about the process. The video ends with a nod to the project’s partners and a teaser for future installments that will cover the remaining components of the lift station installation, including final testing, commissioning, and integration with the broader sewer network.