NID Regional Water Supply Project Technical Memorandum

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2 NID Regional Water Supply Project Technical Memorandum Cross River Penstock Predesign January 2011 Prepared for Nevada Irrigation District City of Lincoln Prepared by Stantec Consulting Services Inc Atherton Road Rocklin, CA Tel: (916) Fax: (916)

3 Contents NID Regional Water Supply Project - Technical Memorandum Cross River Penstock Predesign 1.0 INTRODUCTION Background Purpose and Scope PIPELINE CORRIDOR HYDRAULIC DESIGN Design Flows Pipeline Diameter, Length, and Design Velocity Hydraulic Control Points (HCP) and Hydraulic Grade Line (HGL) Internal Working Pressure Surge Control PROJECT COMPONENTS Pipeline Materials Design Conditions Methods of Pipeline Support Pipeline Design Span Lengths and Stresses External Loads Pier Supports Concrete Anchors Pipeline Joints Pipeline Appurtenances Air and Vacuum Valves Isolation Valves CONSTRUCTION ZONES AND CONSIDERATIONS Aerial Truss Crossing- Reach A River Bank Crossing- Reach B Tie-In to the Combie North Penstock - Combie North Tie-In Tie-In to the Combie South Penstock - Combie South Tie-In ENGINEER'S OPINION OF PROBABLE PROJECT COSTS CONCLUSIONS AND RECOMMENDATIONS Conclusions Recommendations Stantec Consulting Services Inc i Regional Water Supply Project

4 Cross River Penstock Predesign Tables Table 1 Engineer s Opinion of Probable Project Costs Drawings Drawing C90 Cross River Penstock Predesign Plan and Profile... 4 Drawing C91 Cross River Penstock Predesign Details... 9 Drawing C92 Cross River Penstock Predesign Details Appendices Appendix A Cross River Penstock Alternatives Evaluation TM Stantec Consulting Services Inc ii Regional Water Supply Project

5 NID Regional Water Supply Project Technical Memorandum Cross River Penstock Predesign Prepared For: Prepared By: Reviewed By: Nevada Irrigation District and City of Lincoln Shawn Labanowski, P.E. Todd Kotey, P.E. Date: January INTRODUCTION This section provides information about the overall NID Regional Water Supply Project (Project) as it relates specifically to the background, purpose, and scope of the intertie between the North and South Combie penstocks across the Bear River just downstream of the Combie Dam. The Project team as it relates to this technical memorandum (TM) includes key staff from the Nevada Irrigation District (NID), the City of Lincoln (City), and the consultant team including, McCall Engineering (NID representative), C.F. Bradham Consulting Engineer (City representative), ECO:LOGIC Engineering now Stantec Consulting Services Inc., Ray Toney & Associates (RTA), Blackburn Consulting, Inc. (BCI), James C. Hanson, Bender Rosenthal, Inc (BRI), Andregg Geomatics, and J. Harrison Public Relations Group. 1.1 BACKGROUND To address the projected demand for treated water in the City and within the NID service area, NID and the City joined in a cooperative study to identify a site for a new regional water treatment plant. ECO:LOGIC Engineering prepared the initial engineering study for the water treatment plant site evaluation and selection. Robertson-Bryan, Inc. prepared an environmental constraints analysis to screen the various sites to identify potential constraints or fatal flaws that would prevent or jeopardize the construction of the facilities. The results were presented in the Lincoln Area Water Treatment Plant Planning and Site Study by ECO:LOGIC Engineering, August 2005 (2005 Site Study). Subsequent to the 2005 Site Study, ECO:LOGIC Engineering was selected to prepare a planning and predesign study for the Project. This study was commissioned by NID to further investigate the feasibility of the Project, and to recommend the location, size, and configuration of Project components. The purpose of the Planning and Predesign Study is to recommend feasible alternatives to the Project as a whole, as well as alternatives for individual Project components, and then incorporate these recommendations into a proposed Project Description for use in the Draft Environmental Impact Report (Draft EIR). Stantec Consulting Services Inc Regional Water Supply Project

6 Cross River Penstock Predesign To prepare the Planning and Predesign Study, a series of TM s were developed to discuss the specific project criteria and components. 1.2 PURPOSE AND SCOPE Currently, there are two existing outlet pipes (penstocks) from the 700-foot long concrete gravity arch dam constructed across the Bear River, the Combie Dam; one on the north side of the Bear River and the other on the south side. These penstocks convey flow to the Combie North hydroelectric power generation (HPG) facility, and the Combie South HPG, also known as the Combie North and Combie South Powerhouses (CNP) and (CSP), respectively. The recommended Project pipeline corridor, includes a crossing of the Bear River just downstream of the dam. This element of the Project is called the Cross River Penstock (CRP). The CRP connects the 60-inch diameter Combie South (CS) Penstock to the 60-inch diameter Combie North (CN) Penstock and is necessary to provide additional capacity to serve the Project service area. In the Cross River Penstock Alternatives Evaluation TM, included in Appendix A, feasible alternatives for connecting the two penstocks across the Bear River were identified and evaluated. Because the alternatives available for an above grade installation are different for certain portions of the CRP corridor, it was divided into two distinct reaches: Reach A and Reach B. The alternatives for each reach were evaluated with both economic and noneconomic criteria. The detailed evaluation concluded that the best method for installing the pipeline in Reach A is to use a truss supported aerial pipe installation, and in Reach B to use an above grade shallow pier supported pipe installation. The purpose of this TM is to discuss the preliminary pipeline and facility design considerations, and to provide preliminary layouts and details for both reaches of the CRP within the recommended proposed corridor. The scope of work to accomplish this purpose is to: Provide 10% predesign plan and profile drawings, Discuss the hydraulic parameters for the anticipated Project demands, Recommend viable pipeline materials and appurtenances, Provide predesign drawings of the pipeline tie-ins and pipeline support details, Provide predesign drawings of the truss crossing and abutment supports, Discuss construction considerations, and Provide a planning level opinion of probable construction costs. Tasks required to complete this scope include: Review of supplementary Project TM s to verify predesign compatibility with other Project facilities. Stantec Consulting Services Inc Regional Water Supply Project

7 Cross River Penstock Predesign Perform predesign calculations for each major component. Prepare predesign drawings and details, and Prepare a planning level opinion of probable construction costs. References used in preparation of this Predesign TM include TM s prepared as part of the Project including: Nevada Irrigation District Combie South Pipeline Project Alternatives Evaluation Report, Black and Veatch Corporation, June Environmental Constraints Analysis, ECO:LOGIC, October Land Use and Water Demands - Revised, ECO:LOGIC, October Raw and Treated Water Pipelines Corridor Evaluation, ECO:LOGIC, January Cross River Penstock Alternatives Evaluation, ECO:LOGIC, September 2010, see Appendix A of the TM. Backup Water Supply Alternatives Evaluation, Stantec, November Pipeline and Related Facilities Predesign, Stantec, January American Iron and Steel Institute, Steel Plate Engineering Data - Volume 4, Steel Penstocks and Tunnel Liners. NID Combie South Hydroelectric Project As-Built Drawings. 2.0 PIPELINE CORRIDOR As discussed in the Cross River Penstock Alternatives Evaluation TM, the most evident and economical source of providing additional flows to the Combie conveyance system is making a connection between the 60-inch CS penstock which feeds the CSP, and the 60-inch penstock feeding the CNP. The CS penstock is owned and operated by NID and is only used seasonally for hydroelectric power generation when the run-of-the-river flows exist. The output of a run-ofthe-river HPG facility is highly dependent on natural run-off. Spring melts will create a lot of energy while dry seasons will create relatively little energy. The dry season, generally the summer and fall months, is when demands for raw water increase. During that time, both 60-inch penstocks, if tied together, could be utilized to provide additional flow to the Combie Phase I Canal. By combining the flow from the south and north penstocks, NID can convey projected demands within the service area. To make the connection between the CS and CN penstocks, the Bear River must be crossed. The proposed river crossing pipeline will connect to the existing penstocks downstream of Combie Dam and upstream of the Combie Powerhouses somewhere within the corridor shown on Drawing C90. It is the recommended proposed CRP raw water pipeline corridor, upon which the preliminary design herein is based. Stantec Consulting Services Inc Regional Water Supply Project

8 A B C D E F G H REVISION DESCRIPTION BY APP CITY DATE DATUM ELEVATION DATUM ELEVATION SCALE DATE DESIGNED DRAWN CHECKED ECO:LOGIC Consulting Engineers Rocklin, California NEVADA IRRIGATION DISTRICT 1036 WEST MAIN STREET GRASS VALLEY, CALIFORNIA NID REGIONAL WATER SUPPLY PROJECT CROSS RIVER PENSTOCK PREDESIGN DRAWING NUMBER PLAN AND PROFILE STA to STA 12+99± C90 1 SHEET NUMBER OF 3

9 Cross River Penstock Predesign 3.0 HYDRAULIC DESIGN 3.1 DESIGN FLOWS A detailed hydraulic analysis of the two existing penstocks and the proposed intertie pipeline has not been completed at this time. Following CEQA compliance and during Project design, a thorough analysis will be performed to determine the optimum diameter of the CRP given pipeline structural properties, system hydraulics, and the economics of power generation and construction. 3.2 PIPELINE DIAMETER, LENGTH, AND DESIGN VELOCITY This section provides a discussion of the pipeline diameters and design velocities required to deliver raw water given the anticipated Project demands, pipeline length, and recommended maximum velocity. In this element of the Project there were two distinct segments of the corridor: 1) outside the 100-year floodplain and 2) within the 100-year floodplain. The potential methods for above grade installation of the pipeline along the river banks outside of the 100-year floodplain elevation were different and significantly less complex than the potential methods for installing the pipeline across and within the limits of the 100-year floodplain and/or the OHWM of the Bear River. For the purposes of evaluating the installation alternatives within the Project corridor, the corridor was divided into the following areas: Reach A: the river crossing at or within the limits of the 100-year floodplain Reach B: the river banks outside of the limits of the 100-year floodplain As previously discussed in the Cross River Penstock Alternatives Evaluation TM, the 100-year floodplain has been approximated at elevation 1544-feet in elevation and the OHWM has been approximated at elevation feet. Both of these elevations should be verified in detailed design to ensure that permit and prudent engineering requirements are met. Plan and profile views of the CRP corridor, including the approximate locations of the reaches and the 100-year floodplain and the OHWM described above are shown on Drawing C90. The recommended maximum velocity for the raw water pipeline is 7-feet per second (fps) to minimize the degree of deterioration of the pipe lining. As previously mentioned, a detailed hydraulic analysis of the two existing penstocks and the proposed CRP has not been completed at this time. However, based upon knowledge of the existing facilities, it is estimated that the size of the proposed pipeline will be between 48 and 60 inches in diameter. The raw water pipeline from the CS penstock to the CN penstock is approximately 320-feet in length. In maintaining a design velocity of 7 fps, a 60-inch diameter pipe is suitable for maximum day demands of 89 MGD (137 cfs), and a pipe size of 48-inch diameter is suitable for maximum day demands of 57 MGD (88 cfs). Following CEQA compliance and during CRP design, a thorough analysis will be performed to determine the optimum diameter given pipeline Stantec Consulting Services Inc Regional Water Supply Project

10 Cross River Penstock Predesign structural properties, system hydraulics, and the economics of power generation and construction. In order to provide a predesign for the Project of maximum impact, the following elements of the predesign, including the cost estimate will assume that the CRP will be a 60-inch diameter penstock. The existing CN and CS penstocks are epoxy lined steel pipeline. The CN penstock is above grade with a paint coating, and in the area of the intertie, the CS penstock is partially buried with a tape wrap coating. Given the materials of the connecting penstocks, steel pipe was considered the most likely material to be selected for the relatively short CRP at this time. Although other pipe types could be considered during final design, it is anticipated that the above grade installation of the CRP will be epoxy lined and polyurethane coated C200 pipeline, with some buried or semi-buried sections having cement mortar or tape wrapped coating. This pipe material and others are described in further detail in the Pipeline and Related Facilities Predesign TM. 3.3 HYDRAULIC CONTROL POINTS (HCP) AND HYDRAULIC GRADE LINE (HGL) Hydraulic control points (HCP), such as existing open water surface elevations and existing high point elevations in the topography along the pipeline corridor, are discussed herein. The design hydraulic grade line (HGL) elevation for the CRP is the high water elevation of Combie Reservoir, which is 1,605-feet. A predesign pipeline plan and profile drawing is included on Drawing C90. The dynamic HGL is not shown on the drawings, because the hydraulic analysis has not been performed on this segment of pipeline. The pipeline alignment will be finalized during detailed design; therefore, for the purposes of the predesign drawings, the profile is typically represented along the centerline of the corridor, which is approximately 100-feet in width. 3.4 INTERNAL WORKING PRESSURE The internal working pressure in the raw water pipeline corridor is greatest when there is little flow or when there is only static pressure. Based on the Combie Reservoir maximum spill elevation HGL of 1,607-feet and assuming an aerial crossing above the 100-year floodplain elevation of 1544 feet, the internal predesign pressures within the CRP corridor range from approximately 18 psi to 26 psi. 3.5 SURGE CONTROL Due to the preliminary nature of this report, a surge analysis was not performed on the CRP. A detailed surge analysis is recommended during the final design to determine if the calculated surge pressures are within the allowable range. Results from the surge analysis may dictate the surge pressures in pipe design are higher than maximum static pressures. High surge pressures may also result in the addition of a surge tank(s), anticipator valves, or a combination thereof. Stantec Consulting Services Inc Regional Water Supply Project

11 Cross River Penstock Predesign 4.0 PROJECT COMPONENTS The following sections provide information on the predesign considerations for major components such as the pipeline, pipeline appurtenances, tie-ins, anchor blocks, supports, and truss supported aerial crossing. 4.1 PIPELINE MATERIALS The recommended pipeline material for the CRP is AWWA C200 (Steel Pipe) - epoxy lined and polyurethane coated or tape wrapped pipe. However, other pipeline materials may be considered during final design. Since the recommended alternative, per the Cross River Penstock Alternatives Evaluation TM, is an above grade installation, the depth of cover over the pipeline is not a primary design consideration. If any pipe is buried or semi-buried it may require an external protective coating or cathodic protection, which should be analyzed during the final design. It may be prudent to isolate the new CRP from the existing CS penstock, which is partially buried, if the CS penstock is not currently cathodically protected. The most efficient combination of pipeline coating and cathodic protection should consider the other facilities connected to the new pipeline and will be addressed during final design. AWWA C200 (Steel Pipe) is a flexible pipe manufactured in a wide variety of standard sizes, with a variety of different linings and coatings, and wall thicknesses making it suitable for the above grade installation and varying operating conditions on this element of the Project. An epoxy lining in accordance with AWWA C210, is recommended, since it is light weight and durable; it protects the steel core from corrosion, and is easily applied to joints and repair sections in the field. The minimum steel shell thickness will be at least 0.20-inches, which is the recommended minimum wall thickness for handling. However, there are other criteria to be address during final design of this above grade pipeline. They include determining the thickness required for: Longitudinal stresses, Circumferential (hoop) stress, Beam-bending stresses, Transverse earthquake loads, External pressures and vacuum conditions, Span length, i.e. the design distance between supports, and The use of stiffener rings of the required thickness. Each of these criteria are discussed in further detail in the following sections. However, final locations of the supports and the pipeline shell and stiffener ring (if required) design will require a detailed analysis, which will be completed during final design. Stantec Consulting Services Inc Regional Water Supply Project

12 Cross River Penstock Predesign 4.2 DESIGN CONDITIONS In designing an above grade, exposed, or non-embedded penstock there are multiple design conditions and corresponding allowable stresses to be considered. These conditions and the appropriate above grade design differs from the design of a buried penstock, with the exception of the internal pressure considerations. For internal pressures, above grade penstocks are designed in the same manner as buried penstocks. For the shell of an above grade penstock the following design conditions and their corresponding allowable stresses must be considered during final design: Normal Condition: This occurs when the penstock is under the maximum static head condition Intermittent Condition: This occurs during draining and filling of the penstock, or during an earthquake under normal operations. Emergency Condition: This occurs when the pipeline is under maximum surge pressures. Exceptional Condition: Generally speaking, this occurs during a malfunctioning of control equipment in the most adverse manner. This condition should not be used as the basis of design. It should, however, be analyzed to ensure the maximum stress does not exceed the specified minimum tensile strength. It is also important to consider the external loads associated with a vacuum condition. Vacuum relief valves and other appurtenances are discussed in Section 4.9. In most cases, the potential of a vacuum is eliminated by proper design of vacuum release valves; therefore, the design of exposed penstocks is governed by the allowable stress under the normal condition of loading. 4.3 METHODS OF PIPELINE SUPPORT The penstock installed above grade can be supported in several different ways depending upon site conditions, size, and economics. The exposed or above grade penstock is usually supported by either concrete saddles or ring girders. Concrete anchor blocks support the pipeline at points of horizontal and vertical deflection. When it is installed on concrete piers placed relatively close together the top of the pier is formed into a saddle support whose contact angle is usually 120 degrees and has a rubberized polyester fabric pad placed between the pipe and concrete surface of the saddle. When spans increase, ring girders or support rings are provided to prevent excess deflection of the pipe cross section over the pier. Rocker assemblies, roller assemblies, or bearing plates are provided to prevent the transfer of bending or lateral forces to the piers. The CRP predesign includes details of ring girder and anchor block type supports. The details of the pier supports are shown on Drawings C91 and C92. Stantec Consulting Services Inc Regional Water Supply Project

13 A B C D E F G H REVISION DESCRIPTION BY APP CITY DATE COMBIE SOUTH TIE-IN DETAIL COMBIE NORTH TIE-IN DETAIL TYPICAL ANCHOR BLOCK DETAIL TYPICAL BRIDGE ABUTMENT DETAIL TYPICAL BRIDGE SECTION SCALE DATE DESIGNED DRAWN CHECKED ECO:LOGIC Consulting Engineers Rocklin, California NEVADA IRRIGATION DISTRICT 1036 WEST MAIN STREET GRASS VALLEY, CALIFORNIA NID REGIONAL WATER SUPPLY PROJECT CROSS RIVER PENSTOCK PREDESIGN DRAWING NUMBER DETAILS C91 2 SHEET NUMBER OF 3

14 A B C D E F G H REVISION DESCRIPTION BY APP CITY DATE TYPICAL STEEL PIPE SUPPORT DETAIL TYPICAL CONCRETE PIPE SUPPORT DETAIL TYPICAL CONCRETE ANCHOR BLOCK DETAIL SCALE DATE DESIGNED DRAWN CHECKED ECO:LOGIC Consulting Engineers Rocklin, California NEVADA IRRIGATION DISTRICT 1036 WEST MAIN STREET GRASS VALLEY, CALIFORNIA NID REGIONAL WATER SUPPLY PROJECT CROSS RIVER PENSTOCK PREDESIGN DRAWING NUMBER DETAILS C92 3 SHEET NUMBER OF 3

15 Cross River Penstock Predesign In using either saddles or ring girders to support the pipeline, there are two generally accepted methods of integrating the support and pipeline design. The first method is to support the penstock on intermediate concrete saddles or piers between concrete anchors with field welded girth joints. In order to accommodate longitudinal movements, an expansion joint is provided between anchor points. A second method consists of shop fabricated 40-foot sections that are field installed using sleeve-type coupled field joints. One end of the section is anchored to a concrete saddle or pier and the opposite end is designed to slide on the saddle or pier. The longitudinal movements of the penstock are accommodated by movement within the coupling. Locations of the anchors and expansion joints are identified on Drawing C90 and details of the supports and anchors are shown on Drawings C91 and C PIPELINE DESIGN SPAN LENGTHS AND STRESSES Span length varies with the method of installation. In the first method, the span length usually ranges from 60 to 120 feet. However the actual length is largely dictated by economics. Longer spans result in few piers, but may require substantially heavier support rings or ring girders or a greater pipeline shell thickness over the supports and at mid span. These factors combined with any required anchor points due to change in direction or slope or by other field conditions and the selection of optimum plate widths, will have an direct impact on the span length. With the second method of installation the span lengths are limited to a maximum of 40-feet between the sleeve type couplings. The maximum allowable longitudinal movement within a sleeve-type coupling is set by the coupling manufacturers as 3/8-inches, which is the maximum movement anticipated for a 40-foot length of pipe allowing for thermal expansion/contraction through 100ºF of temperature change. In designing the pipeline, stresses in the pipeline must be analyzed at the supports as well as between the supports. Both locations must consider equivalent stress based on the Hencky-Mises theory of failure. Stresses considered at the supports include: Circumferential (hoop) stress in the supporting ring girder due to bending and direct stresses and tensile stress due to internal pressure. Circumferential stress in support rings at saddle supports. Longitudinal stresses in the shell at support due to beam bending, and stresses in the shell due to longitudinal movement of the shell under temperature changes and internal pressure. Bending stresses imposed by the ring girder. Stresses considered between the supports include: Longitudinal stresses due to beam bending. Longitudinal stresses due to longitudinal movement under temperature changes and internal pressure. Stantec Consulting Services Inc Regional Water Supply Project

16 Cross River Penstock Predesign Circumferential stress due to internal pressure. Circumferential stress in support rings at saddle supports. Longitudinal stresses in the shell at support due to beam bending, and stresses in the shell due to longitudinal movement of the shell under temperature changes and internal pressure. Bending stresses imposed by the ring girder. Equivalent stress, based on the Hencky-Mises theory of failure. Installing stiffener rings can significantly increase the strength of the pipe shell and therefore reduce the shell thickness required. 4.5 EXTERNAL LOADS The exposed CRP should be designed to withstand external loads with a 1.5 load factor, such as the anticipated external pressures in a vacuum condition, maintenance live loads, and dynamic loads due to wind or seismic loads. An exposed pipe shell s ability to resist external pressures depends upon the thickness/diameter ratio, yield point of the steel, and the length/diameter ratio between stiffener rings, if present. 4.6 PIER SUPPORTS The piers should be designed for the vertical reactions at the support, longitudinal forces resulting from frictional resistance due to longitudinal strain and temperature movements, and lateral forces caused by wind and earthquake forces. 4.7 CONCRETE ANCHORS Concrete anchors are required at all points of changes in slope or alignment in an above grade penstock that has expansion joints or sleeve-type couplings, which is the case for the CRP. The size of the anchor required is determined by the thrust forces at that anchor. It is preferable that the base of the anchor be placed on a rock foundation and below the frost line. It is common practice to provide a nominal size anchor even at points where computations indicate a balance of forces. 4.8 PIPELINE JOINTS The typical joint type used for exposed steel pipe should be lap-welded bell and spigot along with flexible couplings and expansion joints. In a buried pipeline, welded joints are required where thrust restraint is necessary and where pressures are above 250 psi. However for an above grade penstock the thrust restraint is resolved in the concrete anchors. In order to accommodate longitudinal movement of the pipeline due to temperature changes and circumferential strains due to internal pressure, to allow for vertical movements due to any anticipated differential settlements or deflections between two structures, and to provide moment release at the joint; sleeve type couplings are included between anchors in the CRP predesign. Stantec Consulting Services Inc Regional Water Supply Project

17 Cross River Penstock Predesign Welded butt strap joints are the recommended joint type at the Combie South and Combie North Tie-Ins. These tie-ins are shown in detail on Drawing C90 and discussed in Section 5.3 and 5.4. Joint types should be confirmed during the final design. 4.9 PIPELINE APPURTENANCES Pipeline appurtenances are necessary to properly maintain and operate water pipelines. Appurtenances include combination air valves (CAV s), air and vacuum release valves, blowoff valves (BOV s), access manways, and isolation valves. The ideal design will minimize the use of these appurtenances and use them only as necessary. Approximate sizing and location of these appurtenances are included in the CRP predesign drawings, but exact sizes and locations will be determined during final design Air and Vacuum Valves The above grade penstock must be protected from the potential for vacuum conditions, which can occur during emergency closure of the gate at the upstream end of the penstock or during normal draining operations. The existing CS penstock has a venting system on the downstream side of the Combie South penetration. During final design, calculations should be made to ensure that the existing venting system will have sufficient capacity to supply the full air requirement for the slide gate during the closing cycle without decreasing the pressure on the inside of the CRP to more than 2 or 3 psi below atmospheric pressure. By maintaining a consistently positive or negative slope, wherever possible, the need for additional air relief valves can be minimized. An additional combination air and vacuum relief valve is recommended on the upstream side of the new isolation valve at the Combie North Tie-In, along with a new blowoff valve on the upstream side of the truss bridge crossing Isolation Valves The CRP predesign includes two new isolation valves. One valve is required along the existing 60-inch diameter CS penstock, just downstream of the new CRP tie-in. This isolation valve is required to bypass the CSP and provide NID with the ability to route all of the desired flow through the CRP to the CNP or to the CN penstock and the Combie Ophir 1 canal. This valve could be placed anywhere along the CS penstock between the Combie South Tie-In and the CSP. However, it is recommended that the valve be installed just downstream of the new CRP to minimize any additional excavation and limit demolition of the existing CS penstock to one area. A second isolation valve is required on the CRP to isolate the Combie North Facilities from the CRP and the Combie South Facilities, providing NID with the ability to route all of the flow through the CS penstock, if desired. In order to provide NID with the ability to dewater the CRP without the need to shut off the CN penstock, it is recommended that this isolation valve be located at the north end of the CRP just south of the Combie North Tie-In. Stantec Consulting Services Inc Regional Water Supply Project

18 Cross River Penstock Predesign 5.0 CONSTRUCTION ZONES AND CONSIDERATIONS There are several areas along the proposed pipeline corridor that require unique methods of construction due to the terrain and physical barriers. The corridor is broken into the following zones: Reach A: the river crossing at or within the limits of the 100-year floodplain Reach B: the river banks outside of the limits of the 100-year floodplain, The Combie North Tie-In, and The Combie South Tie-In. Construction considerations for each of these construction zones are discussed in the following subsections. 5.1 AERIAL TRUSS CROSSING- REACH A An above grade installation with the pipeline above the elevation of 1544-feet necessitates that the river crossing span the Bear River. There are several ways to aerially span this segment of the CRP. Due to its ability to avoid the US Army CORPS permits and probably avoid the CDFG permit, as well as its simplicity, availability, stability, and the ease of access it would provide; the truss supported alternative is the most desirable of the three aerial crossing alternatives evaluated in the Cross River Penstock Alternatives Evaluation TM. The primary reasons for using this type of crossing are that the truss supported crossing: Can be designed, prefabricated, and delivered to the job site, by a fabricator. Has the simplest of the three alternative foundation supports to design. Avoids the OHWM and the 100-year floodplain elevation, so the CWA 404 permit can be avoided and the CDFG Code Section 1602, and the CWA 401 permits can probably be avoided. Provides a high level of stability, and Can easily include an access way along side the pipeline to provide NID and authorized staff access and to facilitate maintenance activities. The Cross River Penstock Alternatives Evaluation TM recommends the truss supported bridge crossing as the primary proposed method of installing pipeline and the column supported bridge crossing as the secondary method of installing pipeline above the limits of the 100-year floodplain (Reach A) of the Bear River within the CRP corridor. As a result, the truss supported bridge crossing is described, herein, for Reach A. A predesign of the secondary method could be further evaluated during final design, but is not included in this TM. The following information was obtained from Big R Manufacturing LLC, which is one of the leading manufacturers of the truss supported bridge crossings in the United States. Of the truss Stantec Consulting Services Inc Regional Water Supply Project

19 Cross River Penstock Predesign bridge crossings that they manufacture, the most cost effective design for the Reach A crossing is the Half-Through (H-Section), which is Available in spans between 80 and 240 feet, Commonly used when clearance below the deck is not a critical issue, and Shipped in multiple sections for field bolting Big R Bridges include the following standard features: weathering steel, Douglas Fir wood decking, 54-inch high hand rail, and a 4-inch opening in safety railing, which is the maximum opening allowed by the State of California for the safety railing systems on pedestrian bridges. Optional features include: painted or galvanized steel, Ipe hardwood decking, concrete deck forms, decorative railings, vinyl coated chain link, and Ipe hardwood or galvanized steel pipe rub rails. Predesign details of the truss supported crossing are shown on Drawing C91. The crossing is approximately 200-feet in length, 10-feet x 14-feet: a 200 x 10 x 14 pipe bridge. These types of bridges are typically designed with 40-foot segments, which mean that it will likely be constructed in five spans. Predesign details of the bridge supports are shown on Drawing C RIVER BANK CROSSING- REACH B There are several ways to install pipeline within this segment of the CRP. An above grade installation is preferred in this reach for the following reasons: It requires less excavation and less potential blasting than open cutting or using trenchless methods to install the pipeline. It minimizes the potential risk to the other infrastructures, especially the existing Combie Dam. It is the simplest and most cost effective method of installation for Reach B of the CRP. The Cross River Penstock Alternatives Evaluation TM recommends shallow pier supports as the proposed method of installing pipeline outside the limits of the 100-year floodplain of the Bear River (Reach B) within the CRP corridor. The piers should be designed as described in Section TIE-IN TO THE COMBIE NORTH PENSTOCK - COMBIE NORTH TIE-IN Under current operating conditions, the Combie conveyance system is fed entirely by the flow diverted to the CNP (i.e. the headworks for the Combie conveyance system). A 34-inch diameter penetration through the north abutment of the dam provides these flows. It is anticipated that this penetration will remain in its current condition. During the recent CNP upgrade, the CN penstock was increased to 60-inches in diameter immediately downstream of the dam penetration to minimize headlosses and accommodate higher flows. The new 60-inch diameter penstock bifurcates into a 60-inch turbine feed/intake and a 60-inch bypass pipeline. Stantec Consulting Services Inc Regional Water Supply Project

20 Cross River Penstock Predesign The proposed Combie North Tie-In will be located at the 60-inch penstock upstream of the newly installed 60-inch by 60-inch wye and the two existing 60-inch butterfly valves. Because the Combie conveyance system is fed entirely by the flow diverted to the CN penstock (i.e. the headworks for the Combie conveyance system), construction of the tie-in will result in a temporary shut down of the Combie North Dam penetration, causing temporary outages in the system. The Combie North Tie-In details are shown on Drawing C TIE-IN TO THE COMBIE SOUTH PENSTOCK - COMBIE SOUTH TIE-IN Under current operating conditions, the CSP is not operated full-time and is only run during the winter and spring months when there is excess flow that would be spilled to the Bear River. This water is discharged to the river once it passes through the CSP. The CS penstock is owned and operated by NID and is only used seasonally and purely for hydroelectric power generation when the run-of-the-river flows exist. The output of a run-of-the-river HPG facility is highly dependent on natural run-off. Spring melts will create a lot of energy while dry seasons will create relatively little energy. The dry season, generally the summer and fall months, is when demands for raw water increase. If the Combie South Tie-In is constructed during the dry season, it will not result in any changes to current operations of the CS penstock nor the CSP. However, if the tie-in is constructed when run-of-the river flows exist and system demands are low, the CSP would experience a temporary disruption to service during the construction of the tie-in. The Combie South Tie-In details are shown on Drawing C ENGINEER'S OPINION OF PROBABLE PROJECT COSTS This section provides information on how the engineer s opinion of probable costs for the CRP were determined. All costs are conceptual level estimates, based on 10 percent pipeline and related facilities design, which assumes the pipeline diameter of 60-inches. A substantial contingency of 25 percent is included at this conceptual level estimate and can be reduced after more detail allows quantity and unit price estimates to be refined. Probable costs are based on contemporary prices and do not contain provisions for inflation of construction costs in the future. A summary of the engineer s opinion of planning level probable project costs, assuming a truss bridge span of 200 and a soffit elevation of 1,544-feet, is presented in Table 1. Stantec Consulting Services Inc Regional Water Supply Project

21 Cross River Penstock Predesign Table 1 Engineer s Opinion of Probable Project Costs Project Component Opinion of Probable Cost (a) Mobilization/Demobilization $70,000 Clearing and Grubbing $3,000 Shoring and Bracing $5,000 Project Schedule $1,000 Miscellaneous Excavation and Soils Stabilization $2,000 Corrosion Control $5, inch Diameter Welded Steel Pipeline $135,000 Steel Truss Bridge (c) $545,000 Setting the Steel Truss Bridge and Pipe on Bridge In Place $113,000 Bridge Approach Stairs $30,000 Concrete Bridge Abutments $55,000 Reinforced Concrete Anchor Blocks including Pier Supports as needed $118,000 Rock Anchors (10 feet deep) $32,000 Bolted Flexible Couplings and Ring Girder Supports $198, inch Diameter Butterfly Valves $100,000 Flanged Coupling Adapters $40,000 Combie North Tie-In $10,000 Combie South Tie-In $5,000 Additional Rock Excavation $2,000 Additional Slurry Backfill $1,000 Subtotal $1,470,000 Electrical/Instrumentation $5,000 Subtotal $1,475,000 Engineering, Legal, Administration, and CM Costs (20%) $295,000 Subtotal $1,770,000 Land Purchase/Easements (b) $0 Subtotal $1,770,000 Contingency (25%) $442,500 Total Project Construction Cost $2,212,500 (a) At the time of these cost estimates, the ENR 20 Cities CCI was 8,865 (July 2010). (b) It is assumed that NID already has all of the land required for this element of the Project. (c) All costs are based upon crossing the Bear River at elevation 1,544-feet. Stantec Consulting Services Inc Regional Water Supply Project

22 Cross River Penstock Predesign 7.0 CONCLUSIONS AND RECOMMENDATIONS Conclusions and recommendations for the CRP predesign are included in this section. 7.1 CONCLUSIONS During the final design process, the preliminary findings that are summarized within this TM and the Cross River Penstock Alternatives Evaluation TM, will need to be refined and confirmed. Items identified in this report as requiring further analysis during final design include: 1. Conformance of design with findings in Project Final Environmental Impact Report (Final EIR). 2. Finalize pipeline alignment within the identified corridor. 3. Perform design-level survey; including utility identification. 4. Perform design-level geotechnical investigations, including a seismic study. 5. Perform design-level corrosion control study and develop a detailed corrosion control plan. 6. Perform design-level surveys and analysis to determine the actual elevation of the 100-year floodplain and OHWM. 7. Confirm hydraulic parameters and pipeline sizes for design. 8. Confirm ultimate HGL elevation. 9. Confirm the minimum bridge elevation and length. 10. Confirm that the design conforms to the State of California Division of Safety of Dams, Army Corps of Engineers, and/or Federal Emergency Management Agency (FEMA) regulations, if necessary. 11. Complete final pipeline design; including selection of pipeline material(s), appurtenance sizes and locations, and confirm permanent and temporary construction easements, and additional staging locations. 12. Perform design-level surge control analysis and determine surge control methods. 13. Analyze construction and project funding phasing. 14. Complete final plans and specifications for construction. 15. Identify and acquire permits as required by NID. 16. Acquire all right of way required for the Project, if necessary. 17. Provide engineer s opinion of probable construction cost based on the final plans and specifications for construction. Stantec Consulting Services Inc Regional Water Supply Project

23 Cross River Penstock Predesign 7.2 RECOMMENDATIONS The following recommendations are based on the preliminary analysis of the pipeline and may change during the final design as more detailed information is gathered. A summary of the pipeline design recommendations as discussed within this TM are as follows: 1. Pipeline diameter to be carried forward through the EIR is 60-inches. 2. Design should be based on the preferred material, as determined by NID and the engineer in final design. For purposes of preparing the cost opinions, AWWA C200 was assumed as the proposed pipeline material as called out on the drawings. 3. Maximum operating and test pressures not to exceed 150 psi to maintain use of AWWA 150 fittings, valves, and other pipeline appurtenances. 4. Design the penstock and supports in accordance with USBR Design Standards for exposed steel penstocks. 5. Pipeline Appurtenances: Install standard CAV s within the corridor at high points or changes from positive to negative slopes, and on the downstream side of isolation valves Install BOV s at defined low points and on the uphill side of isolation valves located on a slope to allow dewatering of the pipeline; Install an access manway within the CRP at least 10-feet from either side of an isolation valve to allow access into the pipeline; Install isolation valves, i.e. butterfly valves, at the locations shown on the drawings. 6. Install anchor blocks at all locations of change in horizontal or vertical alignment. 7. Install expansion joints to permit longitudinal movement and transverse deflection, at a maximum of 40 foot intervals. 8. Verify that the existing venting system(s) can provide the sufficient capacity to supply the full air requirement for the slide gate during the closing cycle without decreasing the pressure on the inside of the CRP to more than 2 or 3 psi below atmospheric pressure. 9. Install fiber optic cable within as needed to provide transmission of telemetry data to and from the supervisory control and data acquisition (SCADA) instrumentation. Stantec Consulting Services Inc Regional Water Supply Project

24 Appendix A Cross River Penstock Alternatives Evaluation TM

25 NID Regional Water Supply Project Technical Memorandum Cross River Penstock Alternatives Evaluation September 2010 Prepared for Nevada Irrigation District City of Lincoln Prepared by ECO:LOGIC

26 Contents NID Regional Water Supply Project - Technical Memorandum Cross River Penstock Alternatives Evaluation 1.0 INTRODUCTION Background Purpose and Scope INITIAL ALTERNATIVES EVALUATION Geotechnical Considerations Engineering Considerations Environmental Considerations Operation and Maintenance Considerations ABOVE GRADE INSTALLATION EVALUATION Reach A (Aerial River Crossing) Reach B (River Bank Crossing) PRELIMINARY COST COMPARISONS CONCLUSIONS AND RECOMMENDATIONS Conclusions Recommendations Tables Table 1 Non-Economic Considerations Table 2 Reach A Alternative Preliminary Cost Comparisons (a) Table 3 Reach B Alternative Preliminary Cost Comparisons (a) Figures Figure 1 Existing Facilities... 3 Figure 2 Cross River Penstock Corridor Preliminary Plan and Profile... 9 ECO:LOGIC Engineering NVID i Regional Water Supply Project

27 NID Regional Water Supply Project Technical Memorandum Cross River Penstock Alternatives Evaluation Prepared For: Prepared By: Reviewed By: Nevada Irrigation District and City of Lincoln Mariska Chuse, E.I.T. Shawn Labanowski, P.E. Todd Kotey, P.E. Gerry LaBudde, P.E. Date: September INTRODUCTION This section provides information about the overall NID Regional Water Supply Project (Project) as it relates specifically to the background, purpose, and scope of the intertie between the Combie North (CN) and Combie South (CS) penstocks across the Bear River just downstream of the Combie Dam. The Project team as it relates to this technical memorandum (TM) includes key staff from the Nevada Irrigation District (NID), the City of Lincoln (City), and the consultant team including, McCall Engineering (NID representative), C.F. Bradham Consulting Engineer (City representative), ECO:LOGIC Engineering, Ray Toney & Associates (RTA), Blackburn Consulting, Inc. (BCI), James C. Hanson, Bender Rosenthal, Inc (BRI), Andregg Geomatics, and J. Harrison Public Relations Group. 1.1 BACKGROUND To address the projected demand for treated water in the City and within the NID service area, NID and the City joined in a cooperative study to identify a site for a new regional water treatment plant. ECO:LOGIC Engineering prepared the initial engineering study for the water treatment plant site evaluation and selection. Robertson-Bryan, Inc. prepared an environmental constraints analysis to screen the various sites to identify potential constraints or fatal flaws that would prevent or jeopardize the construction of the facilities. The results were presented in the Lincoln Area Water Treatment Plant Planning and Site Study by ECO:LOGIC Engineering, August 2005 (2005 Site Study). ECO:LOGIC Engineering NVID Regional Water Supply Project

28 Cross River Penstock Alternatives Evaluation Subsequent to the 2005 Site Study, ECO:LOGIC was selected to prepare a planning and predesign study for the Project. This study was commissioned by NID to further investigate the feasibility of the Project, and to recommend the location, size, and configuration of Project components. The purpose of the Planning and Predesign Study is to recommend feasible alternatives to the Project as a whole, as well as alternatives for individual Project components, and then incorporate these recommendations into a proposed Project Description for use in the Draft Environmental Impact Report (Draft EIR). To prepare the Planning and Predesign Study, a series of TM s were developed to discuss the specific project criteria and components. 1.2 PURPOSE AND SCOPE Currently, there are two existing outlet pipes (penstocks) from the 700 foot long concrete gravity arch dam constructed across the Bear River, the Combie Dam; one on the north side of the Bear River and the other on the south side. These penstocks convey flow to the Combie North hydroelectric power generation (HPG) facility, and the Combie South HPG, also known as the Combie North and Combie South Powerhouses (CNP) and (CSP), respectively. The recommended Project pipeline corridor, includes a crossing of the Bear River just downstream of the dam. This element of the Project is called the Cross River Penstock (CRP). The CRP connects the 60-inch diameter CS penstock to the 60-inch CN penstock and is necessary to provide additional capacity to serve the Project service area. The purpose of this TM is to first identify and evaluate the feasible alternatives for the connecting the two penstocks across the Bear River; and second to recommend a component of the proposed Project to be considered during the Project Draft EIR development. A preliminary design of the recommended alternative shall be included in the Cross River Penstock Predesign TM. The CNP serves as the headworks for the Combie Phase I Canal and was just recently upgraded. The flow diverted through the CNP is either conveyed to the Combie Phase I Canal and/or is spilled into the Bear River. The CSP is not operated full-time and is only run during the winter and spring months when there is excess flow that would be spilled to the Bear River. This water is discharged to the river once it passes through the CSP. The current design maximum flow of the Combie Phase I Canal is 200 cfs. The canal infrastructure is in need of improvements or replacement due to age, which is addressed in the Draft Combie South Pipeline Project Alternatives Report (Black and Veatch, June 2008). As stated in this report, the desired ultimate design flow is 265 cfs, which includes 65 cfs for the Project demands. The main purpose of the CRP is to provide additional capacity, which cannot be provided through the 34-inch penetration (outlet) on the north side of the Combie Dam. Figure 1, shows the existing facilities in the area of the Project, immediately downstream the Combie Dam. Additionally, the CRP will improve system reliability and flexibility, and improve efficiencies at the CNP. ECO:LOGIC Engineering NVID Regional Water Supply Project

29 Combie Phase I Canal Combie North Powerhouse New 60 0 Combie North Penstock u:project-graphics/nevada Irrigation District/NVID07-001/Combie Reservoir/NVID Aerial Combie.ai 10/13/10 cms Bear River Combie South Powerhouse 54 0 Combie South Penstock 100-foot wide Cross River Penstock Pipeline Corridor Combie Dam (Spill El. 1,600 ) South Penetration (48 0, Inv. El. 1,586 ) North Penetration (34 0, Inv. El. 1,545 ) Combie Reservoir Figure 1 Existing Facilities

30 Cross River Penstock Alternatives Evaluation Under current operating conditions, the Combie conveyance system is fed entirely by the flow diverted to the CNP (i.e. the headworks for the Combie conveyance system). A 34-inch diameter penetration through the north abutment of the dam provides these flows. It is anticipated that this penetration will remain in its current condition. Water flow velocities in the 34-inch penetration can reach 24 feet per second under existing demands of 150 cfs. Velocity will reach 42 feet per second at ultimate design flow of 265 cfs. Current and anticipated velocities exceed generally accepted criteria for this type of installation. During the recent CNP upgrade, the CN penstock was increased to 60-inches in diameter immediately downstream of the dam penetration to minimize headlosses and accommodate higher flows. The new 60-inch diameter penstock bifurcates into a 60-inch turbine feed/intake and a 60-inch bypass pipeline. With these recent upgrades, the CN penstock and turbine will accommodate the designed capacity of 265 cfs; however, the 34-inch penetration remains undersized. The most evident and economical source of providing additional flows to the Combie conveyance system is making a connection between the 60-inch CS penstock that feeds the CSP and the 60-inch penstock that feeds the CNP. The CS penstock is owned and operated by NID and is only used seasonally and purely for hydroelectric power generation when the run-of-theriver flows exist. The output of a run-of-the-river HPG facility is highly dependent on natural run-off. Spring melts will create a lot of energy, while dry seasons will create relatively little energy. The dry season, generally the summer and fall months, is when demands for raw water increase. During that time, the two 60-inch penstocks, if tied together, would compensate for the undersized 34-inch penetration; thereby providing additional flow to the Combie Phase I Canal. By combining the flow from the south and north penstocks, NID can convey projected demands within the service area. To make the connection between the CN and CS penstocks, the Bear River must be crossed. The proposed river crossing pipeline will connect to the existing penstocks downstream of Combie Dam and upstream of the powerhouses somewhere within the corridor shown on Figure 1. A detailed hydraulic analysis of the two existing penstocks and the proposed intertie pipeline has not been completed at this time. However, based upon knowledge of the existing facilities, it is estimated that the size of the proposed pipeline will be between 48 and 60 inches in diameter. Following CEQA compliance and during Project design, a thorough analysis will be performed to determine the optimum diameter given pipeline structural properties, system hydraulics, and the economics of power generation and construction. There is access to both the north and south ends of the Project site via existing roads currently used to access the powerhouses and the dam. However, due to the rough and confined terrain there is little room for equipment and construction staging areas. Ground and aerial crossings will both be challenging due to the confined workspace, existing infrastructure, and environmental issues. The tie-in location on the south side will be between the dam and the existing powerhouse. The tie-in location on the north side is upstream of the 60-inch wye just ECO:LOGIC Engineering NVID Regional Water Supply Project

31 Cross River Penstock Alternatives Evaluation upstream of the CNP. The total cross-river distance between the CN penstock to the CS penstock is approximately 320 feet. This TM includes: Identification of alternative methods of constructing the CRP, Evaluation of these alternatives, and Recommendation of the alternative method of constructing the CRP for which a preliminary design shall be established in the Cross River Penstock Predesign TM. 2.0 INITIAL ALTERNATIVES EVALUATION There are two fundamental alternatives for installing the CRP. Those options are to either install it above ground or underground, and there are multiple construction methods to consider for each basic methodology. The three alternatives initially identified for installing the CRP are: open cut installation, trenchless installation, and above grade/aerial installation. The criteria identified for the initial evaluation are: Geotechnical Engineering, Environmental, and Operation and Maintenance Each criteria and the specific considerations used to identify the recommended alternative(s) to be carried forward for further evaluation are as follows: 2.1 GEOTECHNICAL CONSIDERATIONS The surface soils in the area appear to be fairly weathered rock underlain by bedrock a few feet below. Excavating the hard soils and rock in this area could require blasting and/or more powerful equipment for excavation. Considering the proximity of the new CRP to the existing dam structure and powerhouses, blasting is not ideal. These types of soil and rock make an open cut or trenchless installation more difficult and costly than conventional cut-and-cover installation. The hard soils and rock provide an ideal foundation for shallow above grade supports. ECO:LOGIC Engineering NVID Regional Water Supply Project

32 Cross River Penstock Alternatives Evaluation 2.2 ENGINEERING CONSIDERATIONS Trenchless installation and open cut excavation in hard soils at the base of a 700-foot long concrete dam is not ideal and has the potential to be unacceptable to or trigger scrutiny from the California Department of Water Resources Division of Safety of Dams (DSOD). In addition, the location of this element of the Project is difficult to access with major equipment. Therefore, a method of construction requiring a minimal mobilization effort is desirable. Compared to open cut or trenchless construction, above grade construction requires relatively shallow excavation, which will require smaller equipment. Trenchless excavation requires larger specialize equipment capable of trenching hard rock and blasting large volumes of rock for the deep boring and receiving pits. 2.3 ENVIRONMENTAL CONSIDERATIONS The highest potential for environmental impacts from this Project is within the limits of the 100-year floodplain which includes the Ordinary High Water Mark (OHWM) of the Bear River. From an environmental perspective, the alternative that would require fewer permits, has the least costs relative to permits, and has the least impact to the Bear River is preferred. In order to establish the recommended method for installing the penstock across the river, potential impacts to the following should be considered: water quality, fisheries, riverine habitat, special-status species, cultural resources, streambed, riparian area, and floodplain. The Bear River is a US Army CORPS jurisdictional waters of the US and is regulated under CWA Section 404. The US Army CORPS CWA 404 permit requires the following three prerequisite permits. Regional Water Quality Control Board (RWQCB) 401 Certification (CWA 401). National Historic Preservation Act (NHPA) Section 106 Compliance Federal Endangered Species Act (FESA) Section 7 Consultation The California Department of Fish and Game (CDFG) Streambed Alteration Permit (CDFG Code Section 1602) is required for any open cut or trenchless installation within the 100-year floodplain. Of the potential permits required, the CWA 404 permit takes the most time and is the most costly to acquire. However, the CWA 404 permit is required only if the Project is located below the OHWM or entails a federal action, such as federal permit or federal funding. There are costs associated with obtaining these permits, but the timeline and ultimately the hours required to obtain these permits from federal and state regulatory agencies can vary greatly from project to project. In comparing the three alternatives, an open cut buried installation has the highest overall environmental impact, such as water quality impacts, fisheries, riverine habitat, endangered species, and potential cultural resource impacts. It would also require all permits to be acquired, including the US Army CORPS Section 404 permit; because there would be disturbance below the OHWM elevation. Although its impacts are high, they are likely considered temporary; because after construction the river bed will be restored to pre-existing conditions. ECO:LOGIC Engineering NVID Regional Water Supply Project

33 Cross River Penstock Alternatives Evaluation For a trenchless installation, the environmental impacts would be slightly less than those for the open cut installation, including fewer water quality impacts, fewer impacts to special-status species, and an avoidance of an US Army CORP CWA 404 permit. However, there are still potential impacts to cultural resources and potential for seepage of bentonite through fractures in rock, known as frac outs, during the drilling process. A CDFG streambed alteration permit is, therefore, still required. For an aerial crossing that avoids the placement of dredge or fill material within the limits of the OHWM of the Bear River, a US Army CORPS CWA 404 permit would not be required. If the aerial crossing is above the 100-year floodplain elevation, there is potential to avoid a CDFG streambed alteration permit, so long as the riparian habitat is avoided. An aerial crossing also reduces impacts to both water quality and cultural resources. The area is relatively devoid of riparian vegetation, so placement of structural elements above or below the OHWM will have minimal impacts to the riparian habitat. One disadvantage to the aerial crossing is the aesthetic impacts. However, due to the numerous other structures in the vicinity, these impacts would likely be considered negligible. Including a pedestrian crossing with the aerial pipe crossing would eliminate the need for an additional pedestrian crossing and provide the potential to remove the existing pedestrian bridge crossing near the SCP and downstream of the proposed CRP. Abandoning the existing pedestrian bridge and combining the two crossings into a single crossing would minimize aesthetic impacts; as well as reduce future costs associated with maintaining the existing pedestrian walkway, such as repairs and painting. 2.4 OPERATION AND MAINTENANCE CONSIDERATIONS An above grade pipeline has operational and maintenance advantages and disadvantages compared to buried pipeline. The primary advantage is that the pipeline, joints, and appurtenances are easy to access, may be visually inspected, and are less difficult to maintain. The primary disadvantage is that because it is exposed, there is greater opportunity for it to be damaged, either intentionally or unintentionally. Although the initial criteria did not include costs, excavation and backfill costs typically make up about half of overall pipeline construction costs for a typical open cut installation. Generally, trenchless installation is typically four times the cost of open cut installation per linear foot, exclusive of the jacking and receiving pits. There is less excavation and backfill efforts required for an above ground or semi-buried installation, compared to a typical buried or trenchless installation. However, the reinforced concrete anchor blocks used to provide thrust restraint in an above grade or semi buried installation can be a significant element of the cost. In addition, an above grade installation in the section of the CRP that crosses the Bear River will require a relatively expensive supporting structure. Therefore, pipeline installation costs are highly dependent upon the specific type of crossing considered, above grade or below grade, and the economic climate at the time of construction. In an effort to identify the potential cost advantages to the various alternatives evaluated, an engineer s opinion of preliminary comparative construction costs is included in Section 4.0. ECO:LOGIC Engineering NVID Regional Water Supply Project

34 Cross River Penstock Alternatives Evaluation Based upon the non-economic criteria above, all three methods of installation are viable alternatives. Due to the environmental impacts and the potential impacts to the other structures in the vicinity, the above grade alternative is considered superior to the open cut, semi-buried, and trenchless installation alternatives. Therefore, the initial evaluation resulted in the recommendation of further evaluation and identification of specific above grade installation alternatives. 3.0 ABOVE GRADE INSTALLATION EVALUATION In evaluating the specific method of above grade installation of the CRP, it was evident that there were two distinct segments of the corridor in this element of the Project: 1) outside the 100-year floodplain and 2) within the 100-year floodplain. The potential methods for above grade installation of the pipeline along the river banks outside of the 100-year floodplain elevation were different and significantly less complex than the potential methods for installing the pipeline across and within the limits of the 100-year floodplain and/or the OHWM of the Bear River. For the purposes of evaluating the installation alternative for this area of the Project, the corridor was divided into the following areas: Reach A: the river crossing at or within the limits of the 100-year floodplain Reach B: the river banks outside of the limits of the 100-year floodplain Before comparing above grade alternatives, it was important to identify the total span of the crossing, by establishing the 100-year floodplain elevation. FEMA maps delineate the area below the Combie Dam as Zone A, which is the 100-year inundation area. However, the maps do not indicate the specific elevation of the Zone A boundary. Therefore, the clearance of the 100-year floodplain elevation was determined based upon conversations with NID staff and field visits. The SC HPG facility turbines are mounted on a slab at approximately 1544-feet in elevation. NID staff indicated that when the water surface elevation in the Combie Reservoir exceeded the maximum height of the Combie Dam in 1986, 1997, and 2005; the turbines in the SC HPG facility turbines remained above the high water mark. Therefore, it was concluded that the bottom of the structure, be it pipeline or truss, should remain at or above that same elevation of 1544-feet. The pipeline would need to span approximately 200-feet to be at or above elevation 1544-feet. Based upon the location of the scour lines, water staining, lower edge of the vegetative layer along the channel, and the location of the lower edge of the riparian tree zone; the OHWM was identified by Project environmental staff to be approximately feet. Plan and profile views of the CRP corridor, including the approximate locations of the reaches and the 100-year floodplain and the OHWM described above are shown on Figure 2. ECO:LOGIC Engineering NVID Regional Water Supply Project

35 Approximate 100-Year Flood High-Water Mark A B C D E F G H South Combie Powerhouse 5 North Combie Powerhouse 54 Penstock (E) Bear River 60 Penstock (E) 4 Combie Dam 100 Foot Wide Pipeline Corridor Combie Dam DATUM ELEVATION Approximate Ordinary High-Water Mark (OHWM) DATUM ELEVATION Reach B Reach A Approximate 100-Year Floodplain Reach B 3 u:project-graphics/nevada Irrigation District/NVID07-001/Combie Reservoir/Figure 2 Cross River Penstock.ai 6/8/10 cms SCALE DATE DESIGNED DRAWN CHECKED ECO:LOGIC Combie Dam Spill El 1600 Consulting Engineers Rocklin, California OHWM NEVADA IRRIGATION DISTRICT 1036 WEST MAIN STREET GRASS VALLEY, CALIFORNIA NID REGIONAL WATER SUPPLY PROJECT Approximate Original Grade at Centerline of Corridor Cross River Penstock Corridor Preliminary Plan and Profile Figure 2 2 1