Repairing, Rehabbing And Replacing Infrastructure In Maryland

Rockville, Maryland, is aggressively renewing its pipe infrastructure to handle increasing population density.
Repairing, Rehabbing And Replacing Infrastructure In Maryland
Civil engineer James Woods and Deputy Director of Utilities Judy Ding, outside Rockville City Hall in Rockville, Maryland.

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Built to its borders, Rockville, Maryland, is growing up, not out. The city’s Department of Public Works (DPW) is paving the way for growth by repairing, rehabbing and replacing its pipe infrastructure at an aggressive pace, while establishing a reputation for investing public funds to produce tangible results. 

Rockville is located a half-hour north of Washington, D.C., and is ringed by the Washington Suburban Sanitary District (WSSD). Judy Ding, deputy director of utilities at the DPW, calls it “a doughnut hole in the middle of a large doughnut.” The city draws water from the Potomac River through a 24-inch pipe, 8 miles in length, which cuts through the doughnut. The city operates its own water treatment plant, supervised by Ding, while the WSSD provides wastewater treatment and supplies water to about 30 percent of Rockville residents. 

The DPW wears a number of hats, including water, sewer, stormwater, recycling and refuse, transportation, environment and right-of-way management. It also offers an active in-house engineering department.

“Our engineers do a hell of a job,” Ding says. “They act as program managers for our infrastructure projects and provide input on reports of outside engineering consultants.” 

The DPW maintains an aggressive program targeting the health and renewal of its water and wastewater systems. All of the pipes in both systems have been GIS mapped by in-house personnel using Esri ArcGIS software.

Working on water

The city’s water system is composed of 175 miles of pipe ranging from 6 to 24 inches in diameter. The oldest sections predate World War I and are made of unlined cast iron, with newer replacement pipes made of polyvinyl chloride and ductile iron.

The water transmission main from the Potomac is made of prestressed concrete cylinder pipe.  

“The wire in the PCCP is beginning to fail as it nears the limits of its service life,” says James D. Woods, P.E., PMP, a civil engineer II with the DPW. “We’re keeping the transmission main under constant surveillance and inspection, repairing and rehabilitating as necessary.” 

System leakage averages less than 10 percent. However, stress inflicted by the necessarily high pressure from the transmission main appears to cause the greatest number of leaks. Ongoing improvements to the city’s SCADA system are helping the department optimize a network of pressure-reducing valves.

Maintaining fire flows

The oldest unlined sections of the cast iron system are significantly tuberculated. Following an assessment in 2008, the department proposed the current replacement rate of 1 percent of the system per year. 

“Water quality is a driver for replacing the pipes, but in this case the tuberculation reduced the diameter of the pipe to the point where we were getting substandard fire flows from some hydrants,” says Ding. “However, we knew that the rate increases we needed to support that program might be tough to swallow.” 

The City Council unanimously backed four successive rate increases of 25 percent per year before increases leveled off in 2012. By targeting the most tuberculated sections first, the program is paying off.

“We’re pretty close to meeting our target of having every hydrant producing 500 gpm by 2018,” Ding says. 

The engineering department designs most water main replacement projects. In-house crews perform the majority of water pipe repairs and short line replacements, while outside contractors take on larger jobs.

Sustaining the sewers

The city’s sewer system measures 148 miles, and the oldest pipe also dates back to World War I. The largest pipes are 24 inches in diameter.

“A lot of the older sections are clay with a minority of Orangeburg pipe,” says Woods. “We prefer to replace any pipe with PVC.” 

The wastewater system is also being replaced and rehabbed at a rate of 1 percent per year. The DPW employs the Pipeline Assessment and Certification Program from the National Association of Sewer Service Companies to prioritize replacement.

“Whichever pipes rate a ‘5’ get priority attention, although some years we wind up with more ‘5s’ than money to spend on them,” Woods says. “However, we also take into consideration maintenance history at that location, a level of risk analysis and the consequences of not doing work immediately.” 

Pipeline assessments are based on results from the DPW’s ambitious in-house inspection program. Every inch of the system is inspected every 10 years. The DPW fields two CCTV vans, one a dedicated CUES system and another a combination flusher and camera truck. 

“The second truck uses a camera retrofitted to the back of the flusher,” Woods says. “It was an innovative technique in 2009 when we installed it, but it has some limitations. You can’t pan and scan like you can with a typical camera, and if you want to stop and look at something, you’re also holding up the flusher. It’s a great system for flushing something that you know needs flushing and then inspecting it, but it’s not something you’d use for miles of inspection.” 

The city has also adopted the Sewer Line-Rapid Assessment Tool (InfoSense) as a cost-effective tool for rapid analysis of sewer line blockages (see sidebar). 

Rockville has achieved Tree City USA status from the National Arbor Day Foundation. An abundance of roots and associated dirt is responsible for about 80 percent of system blockages. Inflow and infiltration are well under control, with much of the problem stemming from basement backups and sewer lateral leaks on the property owners’ side. 

In-house crews handle smaller repair jobs, including manhole-to-manhole segments. Crews also rehabilitate brick manholes, replacing covers and frames, repairing brick and parging the structure. Large construction projects are contracted out, while cured-in-place pipeline rehabilitation is covered by an outside specialist on a five-year standing contract. 

Sewer and water crews share personnel and equipment. Each group has its own utility truck and excavator, while the sewer crews operate a Vac-Con combo unit that does double duty cleaning storm drains.

Piggybacks cut costs

“We try to piggyback a lot of the work on existing projects ranging from road work to water main construction to valley stream restoration,” says Woods. “That’s less complicated than it might seem — we just poke our head out of the cubicle and ask each other what’s going on.” 

The DPW is essential to the city’s growth. Downtown development is seeing older commercial buildings replaced by high-rise residential and mixed-use development, placing strains on the collections system. 

Funded in part by developers, the $1.9 million Rock Creek Sanitary Sewer Capacity Improvement project is central to the city’s development plans. City engineers completed hydraulic modeling of the project in-house using InfoSWMM and InfoSewer software by Innovyze. 

“The city has three sewer sheds — Cabin John, Rock Creek and Watts Branch,” says Woods. “The capacity constraint is in Cabin John, but that’s the most difficult of the three areas to access and to mitigate effects of construction. Our hydraulic modeling showed that we could move the flow to Rock Creek and make the improvements there, benefiting both sewer sheds. Still, it’s a complex project involving 4,000 feet of upsized pipe with the new pipe and manholes to be constructed in roadways and within easements that cross private property.” 

As the city moves forward on improvements to the sewer and water system, the primary constraint is funding. 

Ding notes, however, that Rockville ratepayers value the results achieved by the department. In the 2014 City of Rockville Community Survey, eight in 10 residents rated water and sewer services as “excellent” or “good” — considerably higher than national benchmarks.

“Establishing that there’s a clear relationship between rates and resulting service levels is half the battle.”



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