Tunnels

For years, the Hultman Aqueduct was the only supply route bringing water from the Quabbin Reservoir to Boston. By the 1980s, with the Hultman in need of repair, the Massachusetts Water Resources Authority (MWRA) rekindled the idea of a second water supply route, which had been thwarted by World War II delays and funding problems. A 17.6-mile tunnel, bored between 200 to 400 feet below ground, not only would safeguard Boston's water supply, but tunnel construction would have little impact on the heavily populated MetroWest region. Nitsch Engineering performed a myriad of land surveying and civil engineering tasks as a subconsultant to different firms during the design and construction phases of this multi-million dollar project.

 

• Our residential and industrial subdivision plans and cost estimates determined the future build-out of the properties taken by eminent domain for shaft sites.
• We performed a topographic and location survey at each of the shaft sites and community connections, and property line surveys of 400 parcels. Nitsch Engineering prepared 50 topographic and 86 taking plans for the project.
• We verified the tunnel's ongoing alignment during construction and monitored the Fayville Dam for deformation during construction of one of the shafts. Nitsch Engineering set a first-order control network using the Global Positioning System with traversing and leveling observations, to which all verification surveys were connected. We carried out shaft transfers using high-precision optical methods, and surveyed tunnel cross-sections using a reflectorless electronic total station. Nitsch Engineering maintained accuracy well within the contract limits and the hole-throughs were within tolerance.

Despite unforeseen conditions of tunnel excavation, Nitsch Engineering's surveys were completed on time and within the final established budget.

The Narragansett Bay Commission (NBC), under Phase I of its Combined Sewer Overflow (CSO) Abatement Plan, is constructing a deep earth tunnel. The main spine tunnel, which will be 30 feet in diameter, three-and-a-half miles long, and bored 250 feet below ground, will serve as the centerpiece of the NBC’s efforts to end sewage discharges into Narragansett Bay and comply with the federal Clean Water Act. The tunnel will capture and store the combined sewage discharges that occur during heavy rain storms and then transport the flow to the NBC’s Field’s Point Wastewater Treatment Facility for treatment. A 30-foot diameter shaft at each end for tunnel boring machine installation and recovery; seven intermediate vertical drop shafts with connecting adits; and a large circular shaft at the southern end to house the Field’s Point Tunnel Pump Station will be constructed. The pump station will reside 300 feet below ground in a chamber 72 feet high by 72 feet wide by 125 to 160 feet long, and connect to the surface by a 33-foot diameter utility shaft and an 11.5-foot diameter access shaft.

Nitsch Engineering provided survey control for construction and verified the construction survey and as-built locations of the constructed tunnel, adits, shafts, and chambers for the Contract Manager.

The Chattahoochee Tunnel project was designed to meet East Cobb County's long-term wastewater capacity needs and to provide flow equalization to the R.L. Sutton Water Reclamation Facility. Nitsch Engineering provided hands-on technical and field training to perform the traverse, azimuth, and shaft transfer surveys in tunneling. 

The tunnel alignment began at the confluence of Sope Creek and Sewell Mill Creeks in Indian Hills Country Club and extended 9.5 miles to the R.L. Sutton Water Reclamation Facility. The excavated diameter was 18 feet, and the depth of the tunnel averaged 200 feet below the ground surface. The entire tunnel, with the exception of a very small portion near the Sutton plant, was constructed using tunnel boring machines (TBM). The bored portion of the tunnel was constructed in two segments using two machines working simultaneously. Each TBM was launched from a 30-foot diameter construction shaft. Another construction shaft about 100 feet in diameter was built at the southern terminus of the tunnel. This shaft became the influent pump station for the treatment plant. Four 6-foot diameter shafts were also constructed to connect the existing sewer lines to the tunnel.

This $113.6-million construction project was the largest project that the water system had ever undertaken, and it was completed in May 2004.

The $73-million contract provided for the construction of a 2.8-mile-long, 11.5-foot diameter, deep rock tunnel stretching from the Fore River Ship Yard to the Inter-Island Tunnel at Nut Island in Quincy. The project was the centerpiece of an MWRA $150-million sewer relief project that was in the planning stages for two decades.

Nitsch Engineering provided subsurface survey verification of the alignment of the tunnel. These services included verifying the surface control network, establishing shaft control, and transferring the surface data to the tunnel invert. During construction, Nitsch Engineering verified the azimuth of the tunnel at the shaft and at the point of curvature near the tunnel terminus at Nut Island.

The tunnel was mined at depths in excess of 200 feet. In addition to supporting a new 42-inch wastewater pipe, the tunnel also contains two 14-inch diameter sludge lines running from Nut Island to MWRA's fertilizer plant at Fore River, eliminating the barging of sludge across Boston Harbor; two 12-inch pipes to transport wastewater from the fertilizer plant to the tunnel, eliminating two million gallons of wastewater per day from the local Quincy sewer system; and a 12-inch water pipe from the fertilizer plant to support a new Intermediate Pump station on Sithe Energy property in North Weymouth.

The tunnel is part of an overall South System improvement program that includes a new 60-million-gallon-per-day North Weymouth pump station, the new 13-mgd Braintree-Weymouth pump station, and 7,700 feet of new sewers and siphons.