HDD is a trenchless method of installing pipelines in areas where traditional open cut excavations are not feasible due to sensitive resource areas or logistical reasons. The greatest advantage of the HDD crossing technique is that open cut trenching and equipment disturbance within sensitive resource areas are not necessary, and, as a result, environmental impacts on sensitive resource areas are minimized. However, a greater amount of equipment staging is required for HDD than for the open cut crossing method, and typical installation of an HDD segment generally occurs at durations two to three times slower than a conventional open cut crossing.
A minimum workspace footprint of 200 feet wide by 250 feet long is required at the entry and exit points to support the drilling operation. The amount of workspace required can vary significantly from site to site based on site-specific conditions. The entry-side equipment and operations typically will include the drilling rig and entry hole, control cab, drill string pipe storage, site office, tool storage trailers, power generators, bentonite storage, bentonite slurry mixing equipment, slurry pump, cuttings separation equipment, cuttings return/settlement pit, water trucks and water storage, and the heavy construction equipment necessary to support the operation.
Environmental Report Northeast Energy Direct Project Resource Report 1 General Project Description
1-87 Exit-side equipment and operations typically will include the exit point and slurry containment pit, cuttings return/settlement pit, cuttings separation and slurry reclamation equipment, drilling string pipe storage, and the heavy construction equipment necessary to support the operation. In addition to the drilling operations to be conducted within this workspace footprint, ATWS, will be required along the working side ROW. ATWS in the form of a “false” ROWs may be required to provide a straight corridor for handling pipe at HDD locations where the ROW changes direction, in which to prefabricate the pipeline into one continuous section in preparation for the pull-back. Because this “false” ROW must be relatively straight to accommodate a long section of pipe before it is pulled through the annulus, a significant area of ATWS will be required outside of the standard pipeline construction workspace. Once assembled, the pipeline will be placed on pipe rollers so that it may be conveyed into the drill hole during the pull-back operation.
Locations of proposed HDDs, are included in Table 1.3-2. There are risks associated with HDD, including inadvertent returns during drilling operations and inaccessibility for visual inspection of the pipe and repairs post-construction. Tennessee has developed an HDD Contingency P lan as part of the Project-specific ECPs for each state. This Plan outlines protocols for handling unanticipated releases of drilling mud.
Each proposed HDD crossing will be analyzed to confirm feasibility, including geotechnical core borings at proposed locations. At this time, Tennessee is evaluating each proposed HDD crossing. Geotechnical investigation must be completed for each HDD, however, for some locations, lack of landowner access has hindered the geotechnical investigations. Therefore, the crossing designs for each HDD have not been finalized to determine the need for false ROWs for pullback sections. For crossings where an HDD is determined to not be feasible, Tennessee will propose an alternative construction method at those crossings.
Pennsylvania
Loop 317-3 Bradford Asylum / Wyalusing A 24.70 Avoidance of Susquehanna River, Norfolk Southern Railway 1,900
Pennsylvania Subtotal 1,900 New York
Pennsylvania to Wright Pipeline Segment Schoharie Schoharie E 46.40 Avoidance of Karker Road, Schoharie Creek, Park Place Holiday Way 2,400 Wright to Dracut Pipeline Segment Albany / Rensselaer Bethlehem / Schodack F 28.10 Avoidance of the Hudson River, Amtrak Railroad, River Road 4,800 New York Subtotal 7,200 Massachusetts
Wright to Dracut Pipeline Segment Franklin Conway / Shelburne H 5.00 Avoidance of Bardwells Road, Western Mass Electric Powerline, Deerfield River, Pan Am Railway, Unknown Road 4,400
Wright to Dracut Pipeline Segment Franklin Deerfield H 8.10 Avoidance of Upper Road, Pan Am Railway, I-91, Lower Road, Article 97 Property, Deerfield River, Pogues Hole Road 4,100
Wright to Dracut Pipeline Segment Franklin Deerfield / Montague H 11.50 Avoidance of Pan Am Railway, McClelland Farm Road, Connecticut River, Greenfield Road, Greenfield Cross Road 3,200 Lynnfield Lateral Middlesex / Essex Dracut / Andover N 2.70 Avoidance of Merrimack Ave (SR-110), Merrimack River, River Road 2,700
Haverhill Lateral4 Essex Methuen P 5.40 Avoidance of Hampshire Road, I-93, Spicket River,
Existing TGP Pipeline 1,200
Fitchburg Lateral Extension Worcester Lunenburg Q 13.70 Avoidance of Electric Ave (SR-13), Electrical Infrastructure 800
Massachusetts Subtotal 16,400 New Hampshire
Wright to Dracut Pipeline Segment Hillsborough Amherst J 20.70 Avoidance of Souhegan River 1,600
Wright to Dracut Pipeline Segment Hillsborough Amherst J 21.20 Avoidance of Souhegan River, Simeon Wilson Road 3,200
Wright to Dracut Pipeline Segment Hillsborough Merrimack / Litchfield J 26.20 Avoidance of Pan Am Railways, Merrimack River 2,300 New Hampshire Subtotal 7,100 Connecticut
300 Line CT Loop Hartford Windsor S 11.70 Avoidance of Farmington River, Connecticut Light & Power Powerlines 2,000
Connecticut Subtotal 2,000 Project Total 34,600 1Each segment is associated with its own set of mileposts beginning at M P 0.00.
2Nearest M P is the approximate midpoint of the proposed HDD.
3Horizontal lengths are approximate (nearest 100 ft) and subject to field verification.