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For Daphne, pipeline assessment surveys not without peril

Some pipeline inspections are more daunting than others, as Daphne Utilities recently found out. Not only was the planned condition assessment on a critical pipeline hampered by non-existent plans, there were also obstacles in the pipeline path that included urban development atop the pipe and an alligator-infested swamp.

In the end, to map and assess their pipeline, Daphne Utilities opted for the Sahara® leak and gas pocket detection platform, which includes the ability to determine pipeline alignment with sub-meter accuracy.  With the Sahara platform, Daphne Utilities could not only determine the exact pipeline location, but also assess its operation and condition.

Daphne’s Story

Affectionately known as the “Jubilee City”, Daphne was incorporated in 1953 and due to its location, serves as a suburb of Mobile, Alabama. Daphne is located along the eastern shore of Mobile Bay, an area served by Daphne Utilities, which provides water, wastewater, and natural gas services to approximately 25,000 residents.

In 1985 the City purchased the Lake Forest Utility, and in doing so, Daphne Utilities took over their existing wastewater treatment plant, which was built in the 1970s.  The facility discharges through the Daphne Outfall, a 6,000-foot, 18-inch ductile iron effluent pipeline that discharges treated wastewater into Mobile Bay. Although the main was critical to the City, little information about it was transferred when Daphne Utilities acquired the facility.  Daphne Utilities later officially named the facility the Water Reclamation Facility.

For many years after Daphne Utilities took over the Water Reclamation Facility the outfall line operated as a gravity discharge line. As the population grew and flows to the plant increased, Daphne Utilities installed pumps to occasionally increase the volume of treated wastewater passing through the discharge line. As development expanded, the situation progressed from a time when the pumps occasionally ran, to the point where the pumps ran almost continuously.

Satellite view with sewer location

Over the years the gravity main transformed into a force main

Now, a pipe designed as a gravity main had transformed into a force main, pumping under pressure at all times, with its location and condition unknown – and with no redundancy.

To proactively manage this critical asset, Daphne Utilities retained the services of Pure Technologies for a one-day Sahara® leak and gas pocket detection inspection of the Daphne Outfall, with a mapping deliverable.

The primary purpose of the inspection was to determine the pipeline alignment, since you can’t maintain what you can’t locate.  Since the 18-inch outfall was built, the terrain had changed markedly.  The original shoreline had been extended by hundreds of feet to accommodate the construction of a major highway and several hotels and restaurants.

In fact, based on best guesses and poor drawings, Daphne Utilities suspected that a five-story Hampton Inn had been built on top of the 18-inch outfall!

In short, Daphne Utilities didn’t know the exact pipeline location or its operational conditions.

Bridges over a river

Section of the outfall traverses area known as “Gator Alley”

To ascertain the alignment and condition of the 18-inch outfall, Daphne Utilities engaged Pure Technologies for a single day inspection. In addition to the challenge of not knowing the exact pipeline alignment, it also appeared that the pipeline traversed under a swamp sanctuary for hundreds of alligators and other wildlife, in an area known as “Gator Alley.”

Due to the location that the line traverses, extra safety precautions were needed for the inspection crews. Project planning included the deployment of an alligator watchman to watch specifically for a notorious 14-foot alligator known to inhabit the area in the vicinity of the 18-inch outfall.

Sahara inspection technology chosen for accuracy at pinpointing leaks and gas pockets

To conduct the mapping and assessment survey, Pure recommended the Sahara leak and gas pocket detection platform. Sahara is an inline tethered tool that can assess pipelines 6 inches and larger, without any disruption to service.

Because the sensor tool is tethered, an operator can stop and reverse the tool to investigate acoustic events such as leaks, gas pockets and visual anomalies. At the same time, an above-ground operator locates the sensor above ground, marking the exact location of the pipeline at any point along the pipe with sub-meter accuracy.

The mapping capability of Sahara allows utility owners to determine the exact location of their pipeline at any point, as well as the location of any leaks or gas pockets.

Results give Daphne jubilant confidence moving forward

Analysis of the acoustic data identified zero (0) leaks and eight (8) air pockets, which were impacting the efficiency of the line, as gas pockets occupy space within the already maxed-out pipeline. During the inspection, the alignment of the pipeline was determined and recorded from the treatment plant to the edge of the marsh where Mobile Bay starts, confirming the pipeline does indeed pass underneath the Hampton Inn.

Not bad for a day’s work

In a single day, the Sahara crew determined flow velocity, inserted the tethered tool, inspected 1,000 feet, determined the pipeline alignment, and confirmed its location and the location of 8 gas pockets.  As a result, Daphne now knows they have gas pockets and they now know the line location in order to execute a plan to deal with the gas pockets.

As for dealing with alligators, that’s unnecessary now.

Alligator watching to the cammera