Nitrogen Drives $25M Harwich Sewer Program
The Nitrogen Threat: Major Sewer Construction Underway in Cape Cod Community to Reverse Impacts to Vulnerable Water Resources
The popular Cape Cod resort community of Harwich, Massachusetts, has embarked on a $25 million sewer construction program to help counter the negative impacts of 50 years of nitrogen leaching from septic systems.
Harwich-based contractor Robert B. Our Company was awarded the first contract for sewer and pumping station construction with a bid of $11.4 million. This contract is one of several included in Phase 2 of an overall eight-phase, $240 million project spread out over 40 years. The huge project is driven by the need to protect the community’s environmentally sensitive water resources including 11 miles of tidal shoreline, four harbors, 22 freshwater ponds, two reservoirs, and two river corridors.
While atmospheric air containing 78 percent nitrogen is harmless, the gas can cause harmful environmental impacts when excessive amounts of it interact with water and soil. Septic systems are a case in point.
Designed to treat solids, pathogens, and organics in human waste, septic systems also contain bacteria that consume ammonium in human waste and convert it to nitrate in the leeching field. This produces highly nitrified effluent that flows through soil and eventually into groundwater and various water bodies.
Within certain limits, nitrogen in the forms of nitrate, nitrite, or ammonium, is a nutrient needed for normal plant growth, but too much of it can lead to extreme proliferation of aquatic plants and algae. When this happens vital dissolved oxygen in the water body is depleted as the plants decompose, and essential light is prevented from reaching deeper waters. This devastating cycle continues, sometimes leading to lake or pond eutrophication, and termination of such recreational activities as fishing, swimming, and boating.
According to “Comprehensive Wastewater Management Plan and Single Environmental Impact Report (SEIR),” a comprehensive report published March 2016 by Boston consultant CDM Smith Inc., the significant growth of the Harwich population over the past 50 years and its reliance on the use of septic systems for wastewater management have yielded excessive amounts of nitrogen leaching into groundwater. This has negatively impacted the town’s valuable saltwater estuaries and embayments, those areas at the mouths of freshwater rivers and streams where they join the ocean. These locations provide essential habitat for a variety of fish, birds, crabs, and mollusks. They also support many recreational activities. In recognizing the seriousness of the nitrogen threat, the Massachusetts Department of Environmental Protection has established enforceable nitrogen threshold limits for these critical areas.
The CDM Smith report indicates that excessive nitrification is affecting the quality of life of Harwich residents and also the tourist economy on which the town relies. Thus, the need to address the nitrogen issue was a key driver in the town’s voting to adopt a Comprehensive Wastewater Management Plan (CWMP) based on the recommendations of the CDM Smith report. Simply stated, the solution to the nitrogen problem is abandoning the use of individual septic tanks in Harwich and building a sewer system to collect all wastewater and convey it to an existing treatment plant in neighboring Chatham (for a usage fee negotiated with Chatham). Harwich officials signed a contract with the consultant to prepare the sewer design documents for public bidding and to represent the community as resident engineer during construction.
The focus of the CWMP is Pleasant Bay, the community’s largest watershed area, which has the highest percentage of septic system nitrogen removal required. The Town’s long-term sewerage project tentatively proposes the following construction, but these are preliminary approximations that are subject to change over the years:
- 61,000 linear feet (11.5 miles) of gravity sewer
- 6,200 linear feet (1.2 miles) of force main
- 6 pumping stations
- 400 linear feet of pressure sewer
- 690 parcels served (639 developed parcels)
Two Years of Construction
Robert B. Our began work in September 2019 as the first construction contractor of the ambitious long-term wastewater management program, with Abigail Our serving as Project Manager, Bill McMahon as Chief Estimating Officer and Bradley Yochum as Project Superintendent. John DeSimone of CDM Smith is the town’s Resident Engineer. The work is concentrated along Route 137 in East Harwich, the most populous of seven villages comprising the Town of Harwich.
The general contractor is installing the main sewer together with connection stubs. When the sewer is completed private homeowners will have one year to connect to the new system. Licensed contractors must install new lateral sewers on residents’ properties and connect them to the main line sewer stubs. Homeowners also must have these licensed contractors crush or fill in their septic tanks.
Construction is expected to take two years. Street detours and one-way traffic passage sometimes occur, but emergency vehicle access is always maintained. Trenches are backfilled daily and temporary paving is done on a regular basis. After trenches have been compacted and paved a final overlay of the full road width will be done. Subcontractors John H. Canto & Son, and Lawrence Lynch, are installing 54,600 square yards of temporary pavement and 93,000 square yards of final pavement.
8.25 Miles of Pipe
According to spokesman Robbie Our, a third generation member of the family-owned company, their contract calls for the construction of 36,550 linear feet of main line sewer. Sewer pipe is either ductile iron or PVC SDR35 pipe. The 4-inch to 18-inch-diameter ductile iron pipe is manufactured by McWane Inc. and supplied in 18-foot lengths by Ferguson Enterprises. Ferguson is also supplying the 8-inch to 12-inch diameter PVC pipe for the job. In addition to the main line sewer, Our is installing connecting stubs for 275 residents’ homes and 7,000 linear feet of 6-inch-diameter PVC lateral sewers running from the connecting stubs to the homeowners’ property lines.
A local precast manufacturer, Acme-Shorey of Harwich and Carver, Massachusetts, is providing approximately 130 precast concrete sewer manholes, while United Concrete Products of Wallingford, Connecticut. is supplying precast concrete wet wells and control buildings for the project’s two pump stations.
The contractor is employing a varying number of crews as the job progresses. For example, they are using a double crew for the main line pipe installation, one crew on side street installations, a pipe testing crew from time to time, and a crew installing lateral sewers from the main line to homeowner’s property lines.
Trench excavation is exceptionally deep. The designers wanted to collect sewage by gravity from as many homeowners as possible, to preclude their having to install their own expensive individual pumping systems. The average digging depth was 15 feet, but the deepest cuts were more than 27 feet, said Robbie Our.
An American Shoring Slide Rail System is providing support for these extraordinary cuts. This system employs vertical sheeting trench support technology, and replaces conventional wood or steel sheeting. It allows excavation to be shored from ground level to sub grade without soil movement, and is often used in areas having unfavorable ground conditions, where an existing underground infrastructure would pose difficulties, or in especially deep excavations. The system is designed by professional engineers to meet OSHA requirements that any excavation over 20 feet deep requires engineering. The standards also mandate that shielding systems be installed and removed in a manner that protects employees from cave-ins, structural collapses, or from being struck by any part of the support system, and furthermore, that shielding systems restrict lateral or other hazardous movement of the shield in the event of a sudden collapse.
The American Shoring system is a “dig and push,” system that is assembled and disassembled using a medium sized excavator. Side panels are inserted in four vertical steel posts, creating a four-sided pit configuration, while rolling struts keep the rails apart and parallel to one another. Using the bucket of an excavator, the panels and posts are pushed gradually into the pit as the trench is being dug.
Our’s main line digging machine is a Komatsu PC 750 Excavator. They are also using a Komatsu PC600 that is working in the rear pulling apart the shoring system as necessary.
A Caterpillar 345 with compactor attachment is used for backfilling and trench compaction and a Caterpillar 950 Wheel Loader is supporting crews, bringing in material, aiding in backfilling, and performing cleanup.
Deep Cuts Pose Challenge
As of early November, crews had not encountered any ledge or problematic groundwater, nor did they expect to, Our said.
“The type of soil has been mostly sand,” he said. “The greatest challenge on this project is the preparation and sourcing of the machines to excavate for the deep section,” he said.
“Excavating down to 27 feet plus is difficult in more than one way. Going that deep requires large equipment. It can be tough working around overhead wires and underground utilities. (According to OSHA, all excavating must maintain a minimum of 10 feet from overhead power lines of 50 kilovolt or less, with 0.4 inches of clearance added for every kilovolt over 50.)
“Safety is the number one priority and digging this deep presents challenges. We have trained our employees thoroughly and always monitor the safety aspects of the jobs.
“Robert B. Our has put a great deal of time and planning into getting this project off the ground. Planning allows us to be prepared for complications and items that we need to take precautions with,” said Our.
Our indicated that using the American Shoring slide rail trench protection system has helped move the job along:
“Mark Dusseault and his team at American Shoring have really helped us understand what would work best and be the most efficient. They were very responsive and easy to work with,” Our said.
Cape Cod to See Major Construction
In the past few years, the negative impact of excess nitrogen has become the driving force for other Cape Cod towns to begin implementing wastewater programs of their own or taking part in regional solutions. Chatham has had a sewage collection program ongoing for the past few years and is reportedly going to continue the program for an additional 20 years, while treating a negotiated amount of sewage from Harwich in the existing Chatham facility. What’s more, a wastewater treatment plant slated for the Harwich landfill location (Area HR-12) under a future phase of the CWMP, may be replaced by a regional facility. Harwich has been participating in discussions with the Towns of Dennis and Yarmouth to consider a single shared wastewater treatment facility to be located in Dennis.
Ultimately, Cape Cod is expected to experience the construction of hundreds of million dollars’ worth of wastewater collection and treatment facilities over the next several decades to counteract the impacts of nitrogen leaching from septic systems.