Regular root control an important part of compliance initiative to reduce blockages and costs.

By Sheila Joy

Regular root control an important part of compliance initiative to reduce blockages and costs.

Virginia Beach, Va., has a land area of 249 square miles and a population of 248,000. To serve this growing city, the Virginia Beach Department of Public Utilities has over 400 pumping stations, nearly 1,800 miles of gravity pipe and 190 miles of force mains.

The city is located at the mouth of the Chesapeake Bay with little topographical relief, which results in design of shallow gravity sewers and a multitude of pumping stations to convey flow from its customers to the local treatment facilities.

Virginia Beach is also party to a Special Order by Consent, issued by the Virginia State Water Control Board to reduce SSOs, rehabilitate the sanitary sewer system, reduce inflow and infiltration, and make long-term improvements to provide adequate system capacity.

“In order to comply, we knew we needed to develop a Management, Operation, and Maintenance [MOM] program,” says Stephen Motley, regulatory compliance manager for the City of Virginia Beach. “In 2005 we hired Brown and Caldwell to assist us in the development of our MOM program. We quickly learned that we needed to be more proactive rather than reactive. A great example of this was our hotspot-cleaning program. Prior to MOM development, our crews would simply visually inspect through manholes and if the flow appeared to be impeded, we would clean the lines. We weren’t solving the problem before it happened — we were waiting until the problem had already developed. We modified this program to proactively clean the trouble lines at regular intervals of 30, 60 or 90 days. Today we clean about 70,000 feet per month as part of this program.”

Implementing a comprehensive MOM program and understanding the city’s main strategic goals was the first step, says Aaron K. Nelson, P.E., vice president of Brown and Caldwell in Virginia Beach. “Next came the analysis phase to determine the cause of stoppages and overflows, maintenance history, the work process and system characteristics, including condition assessment. Inspections and thorough analysis showed that grease and roots were the No. 1 and 2 listed causes of SSOs, respectively, so we started there.”

Upon discovery of these findings, the city started a FOG program, inspecting food establishments for compliance. “We did an educational inspection at first,” Motley says. “It was very informal, but we wanted to educate the establishments about the things they need to do to maintain grease control devices, help them understand the records they need to keep and make sure they understand what would be investigated during a compliance inspection. We changed our city ordinance to enforce compliance inspections and we now have a full-time city inspector dedicated to ensure compliance is met.”

In addition to the ongoing education and support of food establishments to minimize grease in the sewer system, the city also maintains a grease control program using Jet Power II, a grease liquefier that leaves pipes virtually grease-free.

To tackle root obstructions in the sewer pipes, Brown and Caldwell recommended a pilot program with Duke’s Root Control to kill live roots in the system. “Our recommendation of Duke’s was based on our personal experience seeing positive results on other projects and the fact that environmental concerns were minimized with Duke’s,” Nelson says.

In order to apply chemical root control products in Virginia Beach, approval must be granted by the Hampton Roads Sanitation District. The HRSD issues a permit dictating how much root control can be done on a given day to ensure treatment plant limits are not exceeded. “Duke’s uses a product called Razorooter II, which is the only diquat-based herbicide registered by the U.S. Environmental Protection Agency for controlling tree roots in sanitary sewer line collection systems,” Nelson says. “Last summer the EPA also lowered the signal word on Duke’s diquat dibromide labels from ‘warning’ to ‘caution,’ giving us even greater peace of mind.”

Results
The city documented an instantaneous return on its investment via reduced frequency of SSOs after implementation of the MOM program. It is also notable that after the first year of the formal root control program, the number of SSOs dropped over 30 percent and have continued to drop substantially every year since. Motley attributes this to regular maintenance.

“Once we saw the positive results from the pilot root control initiative, we increased the program and it is now part of our ongoing maintenance for the entire system. The best part is that Duke’s comes in and takes care of everything. Our guys don’t want to do it themselves. It’s not their job. They don’t want to deal with chemicals, and they shouldn’t have to. So the Duke’s crew comes in, applies the product and helps us keep track of treatment history and when and where maintenance is due.”
The continued drop in SSOs as a result of ongoing MOM program efforts and ramping up of the root control component is especially impressive considering the city experienced 100-year storm events from 2009 to 2013, including tropical storms Nicole, Irene and Sandy.

“This comprehensive MOM program, which includes a sizeable root control effort, is a prime example of a success story that can be shared with other similar communities,” Nelson says. “It documents capacity assurance results and reductions in SSOs, which was our primary goal, without high cost of implementing traditional I&I reduction efforts.

“Since the city was initially put under the consent order we began collecting flow data, paying close attention to the root program, hotspots, cleaning and FOG. We began plotting data, including wastewater flow, rainfall accumulation and specific MOM program elements. We anticipated that root control might contribute to an increase in wet-weather flows, and result in a need for the addition of I&I-reducing MOM program elements. However, we noted little change in flow even during substantially wetter periods. This contradicts industry expectations, but the results were pretty clear in the data.”

Financial impact
“We calculated that if we simply followed the consent decree outline, for a traditional comprehensive find-and-fix program to reduce I&I, the city would spend about $369 million and that program would take approximately 20 years to implement,” Nelson says. “But the MOM program we have implemented for the city, with refinements including ongoing root control, costs about $7.8 million per year, not including potential escalations in the economy. All things being equal, over 20 years, the cost would be about $157 million, significantly less than the nearly $400 million estimated for a traditional once-and-done solution that would likely require a reinvestment 20 years down the road.”

What’s next?
The MOM program was approved by the Department of Environmental Quality in August 2010, and the implementation has been executed with ongoing performance measurement assessments as well as prioritization and planning for a 50-year cycle.

“The next step for us is monitoring,” Motley says. “We now have a good, solid foundation, fewer environmental impacts and a process to continually get to the cause — grease and roots — instead of our previous reactionary approach to clean when the stoppages occurred. We have made great strides.

“Even with our many successes, there is still a lot of pressure to keep our MOM program effective and sustainable. For those areas where ongoing maintenance is required, such as root control, diligence is key. You don’t cut your grass once and then forget it the rest of the summer. You don’t brush your teeth once a week, or shave once a month. You need to be continually on top of maintaining the high levels of service our customers desire, and this MOM program and all of its key elements is an essential ingredient. The refinements to our existing program to include hotspot cleaning, a FOG program and root control really minimizes headaches for us and allows us to use our city resources to focus on other collection system areas of responsibility in the MOM program, including gravity sewer condition assessment, manhole condition assessment, force main condition assessment, right-of-way/easement maintenance, valve maintenance, private systems and vacuum systems.”