Subject: Feasibility Assessment for 115-kV Underground Transmission Line Segment on Front Street

Transcription

1 1600 SW Western Blvd, Suite 100 Corvallis, OR (541) (desk) August 30, 2013 Robert White Power Services Manager Tillamook People s Utility District 1115 Pacific Avenue Tillamook, Oregon BWhite@TPUD.org Mr. White, Subject: Feasibility Assessment for 115-kV Underground Transmission Line Segment on Front Street Per our authorization and further discussion this report provides a brief independent feasibility assessment of a proposed 115-kV underground transmission concept along Front Street in Tillamook. The objective of this feasibility assessment is to describe and estimate the impacts of the most probable underground facility concept that may be permitted by various agencies, accepted by the PUD, and properly designed for construction on the planned alignment. Thanks again for asking us to help you with this effort. Please call if you have any questions. Sincerely, TriAxis Engineering, Inc. Gordon Ormsby, P.E. Project Engineer Tillamook 115kV UG Feasibility Assessment Cover Letter Cover Letter

2 The City of Tillamook requested Tillamook PUD to investigate placing a 0.5-mile-long segment of the proposed Oceanside overhead transmission line underground along Front Street in Tillamook. The underground portion would parallel the south side of Hoquarten Slough, cross under Oregon Highway 101 and would need to accommodate the future planned ODOT rearrangement of Highway 101 at the Hoquarten Bridge. In response to the City s request, TriAxis Engineering, Inc. completed the attached Feasibility Assessment for 115-kV Underground Transmission Line Segment on Front Street, dated August 30, Executive Summary Reliaibility A four-cable underground system would be required as the proposed Oceanside 115-kV Transmission Line would be the only 115-kV circuit serving the Netarts-Oceanside Area. Three of the cables would be normally energized. The fourth emergency cable would be terminated on a riser pole. If the underground segment along Front Street were constructed with only three cables, a failure of any component of the underground segment would cause an area-wide outage. Failure of an underground cable, splice, or riser component would require a minimum of several weeks or months to repair, compared to the repair time of overhead line, primarily due to the fact that high-voltage underground systems and individual components are specialized devices and require specialized technicians. Spare components would be warehoused at the PUD, but specialists to perform the work would need to be brought in to the area to make the repairs. Field installations would require building a climate-controlled room around termination sites or inside the splice vaults. Because repairs typically require weeks, transmission systems must mitigate the risk of a failure. The District plans to improve its existing 25-kV distribution line to the Oceanside area to serve as an emergency power supply in the case of a transmission outage. This planned emergency distribution tie line would be designed to serve the area for a few hours or days at a time, but would not be practical to design with enough efficiency and reliability for long-term (weeks or months) transmission line outages. 115-kV Cables Underground cables will be designed to match the thermal capacity of the overhead conductors of the transmission line. The size of the underground cable is calculated to keep the cable temperature under the manufacturer s maximum specified operating temperature. Depending on the required size of the copper conductor, the finished diameter is expected to be approximately 3.5 inches in diameter and weigh about 9.5 pounds per foot. Duct Bank A typical transmission line duct bank design has four large conduits placed in a square arrangement. Each of the transmission line cables must be placed in its own conduit to facilitate the pulling-in or replacement of the cables and to provide for heat dissipation. Two smaller conduits would also be

3 installed above the transmission conduits. The entire duct bank is anchored to the floor of the trench with an initial placement of 3-4 of concrete, which is allowed to set. Then the entire duct bank assembly is encased with a high-strength, thermally-conductive concrete mix. Concrete encasement under city streets and highways include steel reinforcing bars on the corners of the duct bank to improve the strength of the encasement and control cracking. Construction of duct banks under roads is complex and the trench width must be increased. For protection against dig-ins, the top of the transmission line conduit is typically placed from grade; the trench will be about 6 feet deep. Under pavement, the roadway occupancy permit may allow the duct bank to be placed in a shallow trench. Shallow placement under roadways may be allowed due to the intrinsic protection against dig-ins. If a narrow trench is required, the top of the encasement could be just under the pavement material and the trench will be approximately 3 feet deep. If a 5-foot-wide trench is allowed, the conduits may be laid flat and a trench depth of 2 feet may be practical. A shallower trench along Front Street would interfere with fewer of the existing underground utilities. However, the wide-trench option to lay the conduits flat, would increase surfacing demolition and repair work. Riser Termination Poles At both ends of the underground run, all four cables must rise up a self-supporting tubular-steel pole. These steel poles are approximately 80 to 90 feet above grade. Foundations may consist of vibrahammer-installed steel caissons. Alternatively, if soils are corrosive, construction may require drilled-pier-type concrete foundations. Splice Vaults Splice Vaults for 115-kV underground circuits are made of prefabricated concrete sections with inside dimensions of approximately 20 feet long, 10 feet wide, and 7-6 floor to ceiling. The maximum distance between splice vaults is determined by the weight of the cable, the friction in the conduit, and the number and degree of bends. Due to bends in the typical trench route, the distance between vaults will normally be less than 2000 feet. Construction Method Underground construction becomes unconventional when special conditions are encountered for the excavation and placement of splice vaults and duct banks. The Front Street trench route presents a list of unconventional situations that will cause design and construction impacts: a. Wider trench and shoring required by saturated soils and possible lack of soil stability b. Trench de-watering and proper disposal of the seepage water c. Special Mitigation of subsurface discoveries during trenching, such as environmental hazards, or archeological finds d. Asphalt pavement cuts and repairs e. Concrete pavement cuts and repairs f. Salty ground water requires that all reinforcing steel in duct bank encasement and splice vaults be coated for corrosion protection. g. Special Civil/Structural design to mitigate construction problems due to the proximity to building foundations, or the crossing of water, sewer, storm sewer, communication lines, and other power lines on the line route

4 h. Directional Boring: This method requires the directional bore of a pilot hole followed by a series of passes to ream the hole as necessary for the pulling-in of a 24 diameter steel pipe for the length of the bore. The PVC Duct bank with special spacers is pulled into the 24 pipe. Slurry thermal concrete is then pumped into the spaces between conduits to fill the pipe. Operation and Maintenance Requirements. Two manhole access covers would be required. Manhole access holes must be large enough to apply active ventilation pipes for people entering and working in the vaults. Splice vaults under Front Street would generate special design features. Vaults along Hoquarten Slough would be subject to relatively frequent flooding and the continual ingress of brackish ground water. Salty water will inevitably enter the vaults due to the water table level, and floods will fill the vaults and cover them by several feet. The PUD must have plans and equipment in place for dewatering and cleaning. In addition, PUD operation and maintenance staff may require primary and backup sump pumps constructed into the vault. Reliable electric service to these pumps would need to be provided and maintained. Flood or seepage water removed from the vault, as well as vault cleaning water must be disposed of in compliance with City requirements. Proper connections to the City storm or sanitary sewer may be required for these purposes. Vaults must be designed with coated reinforcing steel and a specific concrete mix. Interior vault fittings, fasteners, racks, and ladders must be designed to resist salt water corrosion in a humid atmosphere. Vault design will require special specification and sourcing of stainless steel, plastics, and fiberglass fasteners and equipment. FRONT STREET 115-KV UNDERGROUND CONSTRUCTION COST ESTIMATES Estimated costs are ballpark amounts and are the professional opinion of the engineer. l project costs might be if based on numerous best guess assumptions. If the PUD proceeded with an underground option a stepwise approach to confirm the technical feasibility: starting with the geotechnical engineering exploration, and then preliminary design development for the purpose of ODOT permitting. 1. Probable Front Street Design and Construction The estimate is based on a 0.5-mile-long underground 115-kV transmission line project consisting of four 115-kV cables in the alignment described in the foregoing discussion. The construction assumes: 2 Terminal/Riser Poles 3 Splice Vaults with special water handling provisions (sump pumps and/or City plumbing connections 2640 feet of reinforced concrete-encased duct bank at typical depth, with special design accommodations for crossing utilities and adjacent building foundations It is assumed that the Oregon Department of Transportation will Permit the Tillamook PUD transmission line duct bank crossing, and will construct the PUD duct bank as part of its proposed re-construction of the Hoquarten Slough Bridge and Highway 101 work. This configuration of construction is judged by us to be the most probable configuration

5 that may be eventually permitted and constructed along Front Street. The following is a listing of major cost items and the expected Order-of-Magnitude cost for each line item. Pre-Design Plan and Profile Survey and Mapping: $20,000 Pre-Design Sub-Surface City Record Investigation and Ground-Penetrating RadSurveys: $40,000 Tillamook 115kV UG Feasibility Assessment Page 13 of 14 Design Development and Permit Engineering Underground 115-kV System $80,000 Structural/Civil Design $20,000 Final Design Engineering Underground 115-kV System $200,000 Structural/Civil Design $30,000 Engineering Services during Construction Underground 115-kV System $50,000 Structural/Civil Design $50,000 Total Engineering Cost: $430,000 Subtotal Surveys and Engineering: $490,000 Labor and Material Construction Contractor Compensation: $2,360,000 Subtotal: $2,850,000 Design and Construction Contingency (25% rounded up): $750,000 Tillamook PUD Administrative and Financing (4%-5% of Subtotal): $150,000 Tillamook PUD Cost to Obtain New Conditional Use Permit: $150,000 (PUD Estimate based on Original CUP Cost) Grand Total: $3,900,000 CONSTRUCTION OPTIONS 1. Shallow Trench Construction In Paved Areas: If the City and the PUD can permit and accept a shallow trench under paved areas, the structural mitigations due to the adjacent building foundations and waterline crossings may be totally avoided. In this case, the expected cost may be reduced. Expected Cost Reduction: $370, Design Without Vaults: During the design development process, it may be found possible and preferable to design the system without vaults. Because the trench is very straight and the length of the project is about 2500 feet, it seems technically possible to install the four cables in a continuous duct bank without a splice vault between the two terminal riser poles. To provide for this no-vault design, the first 100 feet from the termination/riser poles would have the cables placed in a sand bed in a wide trench without conduits. In these two areas, the cables would be laid flat in sand bedding, separated by 3 feet or so, and snaked to allow some slack. The cables would be protected with removable concrete slabs that would be covered with sufficient topsoil to allow some native grasses or vines. If this design was acceptable to the City and the PUD, the construction cost could be reduced. Expected Cost Reduction: $350,000Concrete Roadway Cuts and Repairs for Highway 101 New Bridge Approach: If ODOT does not construct the duct bank as part of the Bridge project, cost to install the duct bank later will involve concrete cuts, special repair designs, special construction schedules, and traffic flagging costs. Expected Cost Increase: $250,000

6 4. Directional Boring: Directional boring for may not be technically possible. Vertical geotechnical test borings along the line route would be necessary to determine feasibility and provide the basis of a better cost estimate. Directional bores can cost 3 to 5 times (or more) the cost of conventional construction. Subtract trenching and related costs:$1,000,000 Add Boring and Pipe installation: $4,000,000 Expected Cost Addition: $3,000,000 EXPECTED PROJECT SCHEDULE FOR THE DESCRIBED PROJECT Pre-Design Surveys: 2 months Design, PUD Reviews, Rural Utility Service Financing Reviews, and Permitting:12 months Construction Bidding: 2 months Contract Selection, Negotiation, and Execution: 1 month Material Procurement and Delivery: 12 months (Cable and steel riser poles are the longlead items) Construction: 3 months (street use may be disrupted for 5 weeks) Total Schedule Requirement: 32 months

7

8 115-kV UNDERGROUND CONSTRUCTION ALONG FRONT STREET LOCATION AND ALIGNMENT Tillamook PUD plans to construct a 115-kV overhead transmission line between the Bonneville Power Administration Tillamook Substation east of the City of Tillamook and a proposed PUD substation between the towns of Netarts and Oceanside. The City has asked Tillamook PUD to investigate the concept of placing a 0.5-mile-long segment of the alignment underground along Front Street in Tillamook. The underground portion would parallel the south side of Hoquarten Slough. The underground facility would cross under Oregon Highway 101 and would need to accommodate the future planned rearrangement of Highway 101 at the Hoquarten Bridge. The following map indicates the location of the alignment and the end points of the underground segment. Project location SYSTEM CONFIGURATION The system configuration is determined by the following criteria: 1. Reliability Requires a 4-Cable System. The Oceanside 115-kV Transmission Line will be the only 115-kV circuit serving the Netarts-Oceanside Area. This circuit is composed of three energized wires. If the underground segment along Front Street were constructed with three cables, a failure of any component of the underground segment would cause an area-wide outage in the area served by the new Netarts/Oceanside substation. Repair of an overhead transmission line is usually accomplished in a matter of hours with the PUD s linemen, equipment, spare conductor, and hardware. However, failure of an underground cable, splice, or riser terminator will require a minimum of several weeks or months to repair the failed components. This Tillamook 115kV UG Feasibility Assessment Page 1 of 14

9 is because high-voltage underground systems and the individual components are specialized devices, carefully matched with each other, and requiring technicians of carefully maintained training and certification. The PUD would store spare components, but with no underground transmission technicians on staff, the PUD would need to schedule a specialist to mobilize to Tillamook with the proper equipment to make the repairs. Although cable rated 35 kv and below is common, cable for transmission voltages is rarely justified, and is therefore rarely installed. Because transmission line outages can affect thousands of consumers, transmission cables are manufactured to higher dimensional and purity standards than the common underground distribution cable. To reduce deterioration due to the high voltage stress, 115-kV transmission cable incorporates a welded copper or lead moisture barrier to preclude any water molecules from the insulation. As a result, the terminations and splices must be installed in clean room laboratory conditions. Consequently, field installations require building a climate-controlled room around termination sites or inside the splice vaults. The cable ends must be prepared to exacting tolerances and cleanliness. It is typical to expect that the installation of each high-voltage terminal or splice will require one 8-hour shift by a skilled technician. Even with the best of transmission cable installations, there remains a probability of an equipment failure due to manufacturer or installation defect. An underground transmission system has an expected life of about 50 years, and the failure probability tends to increase with age. In addition, there is always the risk of damage due to severe storm, vehicle accident, fire, or vandalism. Because repairs typically require weeks, owners of transmission systems must mitigate the risk of a failure. Usually, the risk is covered by constructing a redundant circuit on a separate alignment. These looped systems are typical in metropolitan transmission networks. The PUD s plan for the proposed Oceanside 115-kV overhead transmission line does not include a second 115-kV transmission source to the proposed Oceanside Substation. Instead, the PUD plans to improve its existing 25-kV distribution line to the Netarts-Oceanside area so that it can serve as an emergency power supply in the case of a brief transmission outage. However, a failure in the 115-kV underground segment would take weeks or months to correct. The planned emergency distribution tie line to the Netarts/Oceanside area will be designed to serve the area for a few hours or days at a time, but it will not be practical to design this tie line with enough efficiency and reliability for long-term (weeks or months) transmission line outages. Therefore, in my opinion, because a single-component 115-kV underground failure is the is most likely mode of failure, the PUD should install four, terminated, and tested cables; this way, the failure of any one of the three normally-energized cables can be by-passed with the fourth (spare) cable to restore service. With the spare 115-kV cable operating, The PUD can order parts and arrange for qualified repair personnel and equipment. When finally ready for the permanent repairs to the failed component, the 115-kV transmission would be de-energized and the emergency distribution tie line would be used to carry the load. With the fourth cable in place, the emergency tie will only operate during the several days that the 115-kV line is actually shut down for repairs. Tillamook 115kV UG Feasibility Assessment Page 2 of 14

10 115-kV CABLES Three of the 115-kV cables would be normally energized. The fourth (emergency) cable will be terminated on the side of the riser pole where the overhead conductors are deadended. The spare cable termination would be positioned between the overhead conductors so that it can be jumpered to take the place of the failed cable or terminator. This process can be done with a man-lift truck and with the system de-energized and grounded. The design and planning of the permanent repair must begin as soon as possible. The nature and cost of the repair will depend on the extent of damage. Replacement cable, terminators, and additional underground splice vaults may be required. The cables specified for this system will have a stranded copper conductor at its core and insulated with cross-linked polyethylene. The cable construction will include a conductor shield material, an insulation shield material, an impervious copper or lead inner jacket and a tough plastic outer jacket. The underground cables will be designed to match the thermal capacity of the overhead conductors of this transmission line. Given the thermal properties of the duct bank and concrete encasement, the size of the stranded copper conductor of the underground cable is calculated to keep the cable temperature under the manufacturer s maximum specified operating temperature. Depending on the required size of the copper conductor, the finished diameter is expected to be approximately 3.5 inches in diameter and weigh about 9.5 pounds per foot. Tillamook 115kV UG Feasibility Assessment Page 3 of 14

11 Tillamook 115kV UG Feasibility Assessment Page 4 of 14

12 DUCT BANK A typical transmission line duct bank design has four large PVC pipes (conduits or ducts) placed in a square arrangement using plastic spacer devices. Each of the transmission line cables must be placed in its own conduit to facilitate the pulling-in, or replacement, of the cables, and to provide for heat dissipation. Two smaller conduits would also be installed above the transmission conduits: usually one for a transmission line protective relay communication cable, and another conduit used as a spare or for substation data acquisition and control. The entire duct bank is anchored to the floor of the trench with an initial placement of 3-4 of concrete, which is allowed to set. Then the entire duct bank assembly is encased with a high-strength, thermally-conductive concrete mix, which is designed and tested for this purpose. Concrete encasement under city streets and highways include steel reinforcing bars on the corners of the duct bank to improve the strength of the encasement and control cracking. Because steel reinforcement rods must have at least 3 of concrete around them, construction of duct banks under roads is more complex, and the trench width must be increased. For protection against dig-ins, the top of the transmission line conduit is typically placed from grade; the trench will be about 6 feet deep. However, power cables generate heat and soil acts as insulation that causes the cable temperature to rise. Engineers test the soil thermal characteristic and use this value in the design of the optimum duct bank depth and encasement. The design objective is to economically limit the maximum cable temperature to the manufacturer s specification. Under pavement, the roadway occupancy permit may allow the duct bank to be placed in a shallow trench. Shallow placement under roadways may be allowed due to the intrinsic protection against dig-ins. If a narrow trench is required, the top of the encasement could be just under the pavement material and the trench will be approximately 3 feet deep. If a 5-foot-wide trench is allowed, the conduits may be laid flat and a trench depth of 2 feet may be practical. A shallower trench along Front Street would interfere with fewer of the existing underground utilities. However, the wide-trench option to lay the conduits flat, would increase surfacing demolition and repair work. Tillamook 115kV UG Feasibility Assessment Page 5 of 14

13 Typical Duct Bank under soil (under roadway, excavation will be shallower) Note: This illustration does not include the fiber optic conduit. Typical construction in an asphalt roadway: Pavement cuts, trenching in road base, and duct bank construction Tillamook 115kV UG Feasibility Assessment Page 6 of 14

14 Placing concrete encasement around and over a duct bank Note: The Front Street duct bank will require pavement cuts, shoring, and coated-steel reinforcing bars. RISER TERMINATION POLES At both ends of the underground run, all four cables must rise up a self-supporting tubular-steel pole. The pole-top assembly includes four cable termination devices that provide an electrical transition from insulated cable to the bare overhead conductor (wire). These steel poles are approximately 80 to 90 feet above grade and capable of holding the full tension of the adjacent overhead transmission line span. Foundations may consist of vibrahammer-installed steel caissons. Alternatively, if soils are corrosive, construction may require drilled-pier-type concrete foundations. The Front Street project would require all four cables to rise up the outside of the poles with cable clamps, and be protected by steel shrouds up to 18 feet from the ground. Tillamook 115kV UG Feasibility Assessment Page 7 of 14

15 Spare cable Three normally energized cables (spare cable on back) Rural Example 115-kV Riser Pole with Four Underground Cables (TriAxis Design, Bend, Oregon) Tillamook 115kV UG Feasibility Assessment Page 8 of 14

16 Urban Street Example 115-kV Riser Pole with Four Underground Cables (TriAxis Design, Portland, Oregon) SPLICE VAULTS Splice Vaults for 115-kV underground circuits are made of prefabricated concrete sections with inside dimensions of approximately 20 feet long, 10 feet wide, and 7-6 floor to ceiling. The maximum distance between splice vaults is determined by the weight of the cable, the friction in the conduit, and the number and degree of bends. Experience indicates that the calculated maximum pulling length of a 115-kV cable in a straight duct bank is approximately 2500 feet. This distance correlates well with practical cable reel sizes for shipment, and handling at the job site. Due to bends in the typical trench route, the distance between vaults will normally be less than 2000 feet. Tillamook 115kV UG Feasibility Assessment Page 9 of 14

17 115-kV Splice Vault Interior Prior to Cable Pulling. (splice racks partially assembled) (Eugene Water and Electric Board) 2. Construction Methods. Conventional Underground Construction: Typical cross country construction involves a wide trench approximately 6 feet deep. A duct bank consisting of four 6 PVC conduits and two 2 PVC conduits would be placed at the bottom of the trench and then encased in concrete as described earlier. The duct bank would run between splice vaults located at the termination riser poles and otherwise spaced every 2000 to Unconventional Underground Construction Underground construction becomes unconventional when special conditions are encountered for the excavation and placement of splice vaults and duct banks. The Front Street trench route presents a list of unconventional situations that will cause design and construction impacts: a. Wider trench and shoring required by saturated soils and possible lack of soil stability at trench depth b. Trench de-watering and proper disposal of the seepage water c. Special Mitigation of subsurface discoveries during trenching, such as environmental hazards, or archeological finds d. Asphalt pavement cuts and repairs e. Concrete pavement cuts and repairs Tillamook 115kV UG Feasibility Assessment Page 10 of 14

18 f. Salty ground water requires that all reinforcing steel in duct bank encasement and splice vaults be coated for corrosion protection. g. Special Civil/Structural design to mitigate construction problems due to the proximity to building foundations, or the crossing of water, sewer, storm sewer, communication lines, and other power lines on the line route h. Directional Boring: This method requires the directional bore of a pilot hole followed by a series of passes to ream the hole as necessary for the pulling-in of a 24 diameter steel pipe for the length of the bore. The PVC Duct bank with special spacers is pulled into the 24 pipe. Slurry thermal concrete is then pumped into the spaces between conduits to fill the pipe. 3. Operation and Maintenance Requirements. Due to the size of the splice vaults, two manhole access covers are required along with ladders. Where vaults are subject to ground or surface water intrusion, effective drains, or sump pumps are required. Manhole access holes must be large enough to apply active ventilation pipes for people entering and working in the vaults. Splice vaults under Front Street would generate special design features: Vaults along Hoquarten Slough would be subject to relatively frequent flooding and the continual ingress of brackish ground water. The floor of the vaults in this area would be below the average water table, which is influenced by the tides. Salty water will inevitably enter the vaults to the water table level, and floods will fill the vaults and cover them by several feet. The PUD must have plans and equipment in place for dewatering and cleaning. In addition, PUD operation and maintenance staff may require primary and backup sump pumps constructed into the vault. Reliable electric service to these pumps would need to be provided and maintained. Flood or seepage water removed from the vault, as well as vault cleaning water must be disposed of in compliance with City requirements. Proper connections to the City storm or sanitary sewer may be required for these purposes. Vaults must be designed with coated reinforcing steel and a specific concrete mix. Interior vault fittings, fasteners, racks, and ladders must be designed to resist salt water corrosion in a humid atmosphere. Vault design will require special specification and sourcing of stainless steel, plastics, and fiberglass fasteners and equipment. Tillamook 115kV UG Feasibility Assessment Page 11 of 14

19 FRONT STREET 115-KV UNDERGROUND CONSTRUCTION COST ESTIMATES The cost of any project is determined by the design. In this case a final design concept is not available. The design criteria can only be listed after requirements of the State, County, City, and the PUD are completely determined, soils are tested, and all surveys complete. The design process requires initial investigations, the development of design proposals, and then revisions to address review comments. Meetings with all stakeholders may be needed to resolve conflicting requirements. Therefore, cost estimating at this time can be no more than order-of magnitude (ballpark) accuracy. Due to the lack of geotechnical information and other archeological or hazardous trenching finds that may be present, I judged that a minimum of 25% design and construction contingency must be added to these estimates. The estimates that follow are my professional opinion of what competitive final project costs might be if based on numerous best guess assumptions, and caveats. If the PUD proceeded with an underground option, I would advise that the approach be stepwise to confirm the technical feasibility: starting with the geotechnical engineering exploration, and then preliminary design development for the purpose of ODOT permitting. The construction estimating developed here is based on recent bidding experience for 115-kV construction, and then adapted with my professional judgment to the project envisioned along Front Street. 1. Probable Front Street Design and Construction The estimate is based on a 0.5-mile-long underground 115-kV transmission line project consisting of four 115-kV cables in the alignment described in the foregoing discussion. The construction assumes: 2 Terminal/Riser Poles 3 Splice Vaults with special water handling provisions (sump pumps and/or City plumbing connections 2640 feet of reinforced concrete-encased duct bank at typical depth, with special design accommodations for crossing utilities and adjacent building foundations It is assumed that the Oregon Department of Transportation will Permit the Tillamook PUD transmission line duct bank crossing, and will construct the PUD duct bank as part of its proposed re-construction of the Hoquarten Slough Bridge and Highway 101 work. This configuration of construction is judged by us to be the most probable configuration that may be eventually permitted and constructed along Front Street. The following is a listing of major cost items and the expected Order-of-Magnitude cost for each line item. Pre-Design Plan and Profile Survey and Mapping: $20,000 Pre-Design Sub-Surface City Record Investigation and Ground-Penetrating Radar Surveys: $40,000 Tillamook 115kV UG Feasibility Assessment Page 12 of 14

20 Design Development and Permit Engineering Underground 115-kV System $80,000 Structural/Civil Design $20,000 Final Design Engineering Underground 115-kV System $200,000 Structural/Civil Design $30,000 Engineering Services during Construction Underground 115-kV System $50,000 Structural/Civil Design $50,000 Total Engineering Cost: $430,000 Subtotal Surveys and Engineering: $490,000 Labor and Material Construction Contractor Compensation: $2,360,000 Subtotal: $2,850,000 Design and Construction Contingency (25% rounded up): $750,000 Tillamook PUD Administrative and Financing (4%-5% of Subtotal): $150,000 Tillamook PUD Cost to Obtain New Conditional Use Permit: $150,000 (PUD Estimate based on Original CUP Cost) Grand Total: $3,900,000 CONSTRUCTION OPTIONS 1. Shallow Trench Construction In Paved Areas: If the City and the PUD can permit and accept a shallow trench under paved areas, the structural mitigations due to the adjacent building foundations and waterline crossings may be totally avoided. In this case, the expected cost may be reduced. Expected Cost Reduction: $370, Design Without Vaults: During the design development process, it may be found possible and preferable to design the system without vaults. Because the trench is very straight and the length of the project is about 2500 feet, it seems technically possible to install the four cables in a continuous duct bank without a splice vault between the two terminal riser poles. To provide for this no-vault design, the first 100 feet from the termination/riser poles would have the cables placed in a sand bed in a wide trench without conduits. In these two areas, the cables would be laid flat in sand bedding, separated by 3 feet or so, and snaked to allow some slack. The cables would be protected with removable concrete slabs that would be covered with sufficient topsoil to allow some native grasses or vines. If this design was acceptable to the City and the PUD, the construction cost could be reduced. Expected Cost Reduction: $350,000 Tillamook 115kV UG Feasibility Assessment Page 13 of 14

21 3. Concrete Roadway Cuts and Repairs for Highway 101 New Bridge Approach: If ODOT does not construct the duct bank as part of the Bridge project, cost to install the duct bank later will involve concrete cuts, special repair designs, special construction schedules, and traffic flagging costs. Expected Cost Increase: $250, Directional Boring: Directional boring for may not be technically possible. Vertical geotechnical test borings along the line route would be necessary to determine feasibility and provide the basis of a better cost estimate. Directional bores can cost 3 to 5 times (or more) the cost of conventional construction. Subtract trenching and related costs:$1,000,000 Add Boring and Pipe installation: $4,000,000 Expected Cost Addition: $3,000,000 EXPECTED PROJECT SCHEDULE FOR THE DESCRIBED PROJECT Pre-Design Surveys: 2 months Design, PUD Reviews, Rural Utility Service Financing Reviews, and Permitting:12 months Construction Bidding: 2 months Contract Selection, Negotiation, and Execution: 1 month Material Procurement and Delivery: 12 months (Cable and steel riser poles are the longlead items) Construction: 3 months (street use may be disrupted for 5 weeks) Total Schedule Requirement: 32 months Tillamook 115kV UG Feasibility Assessment Page 14 of 14