Drones Aid in Evaluation of Public Water-System Construction
The identification of a trichloroethylene (TCE) plume impacting groundwater in a village within the “Amish Country” of Pennsylvania pressed the need for immediate investigation and action. Residents in this local tourist and commercial hub relied on groundwater as their sole source of potable water.
consultant for the Commonwealth of Pennsylvania, was tasked with rapidly investigating the chlorinated plume in a fractured bedrock setting, and managing the design and construction of a new public water-supply system to connect 443 properties and allow for further expansion.
After the $7.3M distribution system construction was completed in December 2017, 13 months ahead of schedule, the client issued the “Notice of Award” for the construction of the water treatment plant, water tower, water supply wellhead modifications, and water service connections for $10.1M in February 2018.
As part of the treatment plant and water tower construction oversight activities, GES implemented the use of unmanned aircraft systems (UAS), or drones, to assist in the day-to-day documentation and inspection of the project. Flights were conducted to confirm that the contractor had laid out the various project components properly. These included building foundations, subsurface clearwell and wastewater tanks, roads, fencing, trenches for piping, and erosion control.
During water tower construction, the drone was used to inspect and document welding work on the water tank (up to 50 feet above ground surface). Performing these inspections with the drone eliminated the health and safety hazard of construction oversight personnel working at heights.
Drone-derived data were also used to determine proper construction of the wastewater tank in the water treatment plant footprint, as the contractor had misaligned the building footer/pad excavation and the wastewater tank pad excavation, which would have caused significant problems when pouring the concrete for the foundation. The aerial photograph taken from the drone confirmed that the base slabs were approximately 2.33 feet out of square with each other, and while there was some room for adjustment in the final placement of the tank walls (about 3 inches either way), it was not enough to cover the 2.33-foot deviation. The wastewater tank would have been too close to the building footer for proper backfilling between the tank wall and the building foundation wall. As a result, GES directed the contractor to correct the error in the tank orientation. Prior to drone technology, an issue like this may not have been realized before the building foundation was installed, which could have meant over $400,000 in costs incurred for the required rework by the contractor.
This technology has allowed GES to access normally inaccessible areas, oversee simultaneous site activities remotely, survey and measure site features, lay out property boundaries, document locations of fiber-optic lines, inspect water tower construction work without the health and safety issues of construction oversight personnel working at heights, and produce orthomosaic images for documentation, all of which are an integral component of GES’ obligations on this project. By using this innovative approach, goals were met with greater scope accuracy and fewer losses in time and capital.
GES’ senior construction manager, an FAA-licensed drone pilot, logged 250 flights (nearly 37 hours of flight time) during this phase of construction that was completed in August 2019.
GES’ rapid deployment and use of innovative data-gathering methods protected local residents and reduced both time and effort for the state, ultimately resulting in taxpayer cost savings. The new public water supply system will provide a permanent, high-quality community water source while delivering greater treatment effectiveness and operational efficiencies.