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HomeMy WebLinkAboutFalse Pass Geotechical Wind Reconnaissance Report - June 2014 - REF Grant 7040051MIMI VFGolder Associates June 2, 2014 Maggie McKay Marsh Creek, LLC 2000 East 88th Avenue Anchorage, AK 99507 123-95824.01 RE: GEOTECIHNICAL RECONNASSIANCE FOR WiND TURBINE FEASIBILITY, FINAL FALSE PASS, ALASKA Dear Mrs. McKay: Golder Associates Inc. (Golder) is pleased to present the results of our geotechnical reconnaissance and conceptual level engineering recommendations for the feasibility study of wind turbine generation in False Pass, Alaska. This phase of the project is supported by the Alaska Energy Authority's (AEA's) Renewable Energy Fund Grant Program. We understand that the City of False Pass is considering the feasibility of installing one or more wind turbine generators (WTGs) near the community. We understand that the site of the current Meteorological (Met) Tower, installed collaboratively by AEA in 2005, is also the proposed site for the wind turbine(s), and this location was provided by you. The proposed site is located at the north end of the community, about 1.2 miles from the main townsite, and adjacent to the north and to the east of the landfill. The site is within the lower alluvial fan of Ungaman Creek, and about 0.2 miles Inland from Isanotski Straight / Bechevin Bay (as shown in Figures 1, 2, and 3). It is understood that the size, type, and number of wind turbine(s), and type of supporting tower(s), are still being determined. And therefore, foundation configuration and loads are unknown at this time. We understand from you that preliminary wind data suggests turbulence coming off the mountains, which will strongly influence the appropriate type of installation. For that reason, vertical axis wind turbines (VAWTs) are being considered as an alternative to the more conventional horizontal axis wind turbines (HAWTs), and associated metal tubular or lattice towers, that have typically been deployed in wester / southwestern Alaska (i.e., Northwind 100 or Vestas V20). In support of this feasibility study, our scope of work was to review readily available existing geotechnical data, conduct a reconnaissance walk-through of the site, advance two shallow hand -probes, and develop preliminary conceptual -level foundation options and other geotechnical considerations. A description of methods and findings of this effort is presented in the following sections of this report. Our services have been conducted in general accordance with our proposal to you dated March 29, 2012 and our ensuing Subcontract Agreement. Regional2.1 -• False Pass is located on Unimak island, at the far western end of the Alaska Peninsula, near the eastern margin of the Aleutian Islands. Unimak island is part of the East Aleutian Volcanic Arc, consisting of a chain of volcanic islands located along the crest of a submarine ridge. The Aleutian Trench is one of the False Pass Whd Turdne Feasibilit Golder Associates Inc. 2121 Abbott Road, Suite 100 Anchorage, AK 99607 USA Tel: (907) 344-6001 Fax: (907) 344-6011 www.goider.wm A J4 Golder Associates: operations in Africa, Asia, Australasia, Europe, North America and South America Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation Maggie McKay June 2, 2014 Marsh Creek, LLC 2 123-95824.01 world's most active tectonic plate boundary zones; where the Pacific Oceanic Plate is sub -ducting under the North American Continental Plate. As part of the Aleutian Islands Section of the Alaska -Aleutian Physiographic Province, the area is noted for its mix of recent volcanic terrain and Pleistocene glacial features. The landscape is generally rugged and steep; being shaped by volcanic activity, extensive glaciation, and subsequent glacial erosion. Terrain features are often stark and spectacular, such as dramatic U-shaped glacial valleys and steep cirques, stratovolcanic cones, calderas, and cliff -lined fjords. There are seven historically active volcanoes within a 100 mile radius of the site (ADGGS, 2014); with Shishaldin Volcano being the closest, located near the center of Unimak island, 24 miles to the west. Deposits of volcanic ash are found throughout the region. The city of False Pass, including the proposed wind site, however, is situated on a nearly level bench that was initially formed by tidal action and frost weathering of rock and has been expanded by the development of alluvial fans where streams break out of their steep mountain channels. In some areas, wind-blown silt and sand from active beaches are often mixed with volcanic ash to form a surface veneer. The proposed site is located on the broad alluvial fan of Ungaman Creek (USGS, 1998). Drainage is typically well defined on the mountain slopes above the site with steep, swift, high-energy stream flow. Low velocity, branching and recombining streams are typical over broad alluvial fan deposits at lower elevations, and toward the coastline. The region is mapped as "generally free of permafrost" (Ferrians, 1965) with a few small isolated masses of permafrost at higher elevations. Permafrost may be present under thicker peat or organic silt deposits or along windswept ridges and areas of topographic relief. Permafrost is not expected to be present at this site given its low elevation, moderate maritime climate, geologic history, proximity to the coast, and thin vegetative ground cover. 2.2 Regional Climate Information As a result of its coastal location, False Pass lies in the maritime climate zone. According to the Community Database (DCED, 2014), temperatures range from 11 to 55 °F and annual snowfall averages 56 inches, with total annual precipitation of 33 inches. Prevailing winds come from the north and south; however, large gusts of often turbulent wind come from the west off of the mountains (YourCleanEnergy LLC, 2010), and are often strong during winter. Fog is common during summer months. The freezing index for False Pass is about 500°F-days, and many freeze -thaw cycles occur each winter. 3.0 SITE SURFACE CONDITIONS The ground surface at the proposed site is relatively flat with slight undulations, and has a low down - gradient toward the coast (see site photos in Appendix A). Site elevation ranges between 30 and 50 feet above sea level (DCED, 2014), and is approximately 8 to 12 feet or more above the level of the creek. The current channel of Ungaman Creek is a little over 200 feet south of the site, and is incised into the alluvial fan. There is also a drainage path, located within 60 to 80 feet north of the site, that drains westward and flows intermittently. No standing water was noted on the surface of the site, but occurrence of wetlands would need to be verified by others. Near the site, vegetation consists of a mixture of relatively open tundra, tall grass, and salmonberry brush with discontinuous, dense stands of alder. Hillsides rising away from the beach are typically thick with mature alder and chest -high brush. Vehicle access to the site is via the road to the landfill, and travel over the site is by ATV or tracked - vehicle, not suitable for regular rubber -tired cars or trucks. The guyed Met Tower is currently on the site, and there is a two foot deep trench surrounding the tower in an approximate 100 foot square. False Aass wind Turbine Feasibility lNf.` StCS. Maggie McKay June 2, 2014 Marsh Creek, LLC 3 123-95824.01 We reviewed geotechnical data near the proposed wind turbine site, which is summarized below. • Proposed Landfill, 2002 Investigation: In September of 2002, HDR Alaska, Inc. and Duane Miller & Associates (DMA) conducted subsurface test pit excavations for the then proposed landfill. • Four test pits (named TH-1 thru TH-4) were completed in the general vicinity of the proposed wind turbine site, including one (TH-11) within the current landfill tract, two down gradient of the landfill near the proposed wind site (TH-2 and TH-3), and one (TH-4) at the cut bank of Ungaman Creek downstream. • in general, the test pits encountered half to a foot of organics at the surface, underlain by mostly sandy silt to 5 to 6 foot depths, underlain by a mixture of sand, silt, and occasional gravel inclusions, but mostly sand. Some of the upper silt can be interpreted as possible volcanic ash. Cobbles were also noted. • Groundwater was not noted within the depth of excavation (typically 11 foot depth) of test pits TH-1 thru TH-3. The cut bank at TH-4 was 8.5 feet higher than the water level in the creek. • A copy of the report is included in Appendix B, including a map showing the investigations and records of test pit logs. • Proposed Landfill, 2004 Investigation: Additional investigations were completed by DMA in September of 2004 for the proposed landfill and access road. Four test boreholes (named FP-11 thru FP-14) were drilled within and near the current landfill tract. • Organics near the surface was commonly less than a foot thick. Below that, soils in the upper 11 to 25 feet of these holes were variable, and contained a mixture of sand, silty sand, and trace to some gravel and cobbles, but mostly silty sand. Below 11 to 25 foot depths, to the depths of explorations of 21 to 31 feet, soils were more consistent containing relatively clean sand and gravel with cobbles and boulders. • Two samples were collected from the City Pit located in the floodplain of Round Top Valley Creek. Both an unprocessed "pit run' sample and a sample that had been run through the "grizzly" screener were obtained. The material consisted of mostly gravel, with cobbles and sand, and has less than 6% fines content, classifying as non -frost susceptible with USCS class (GW-GM) to (GP). • Cobbles and boulders were noted lining the creek bed and bank at the bridge crossing of Ungaman Creek that serves as access to the landfill. This bridge is more than 1,000 feet up -gradient of the proposed site. It was also noted that clast sizes of bank and channel deposits decrease gradually downstream. • A copy of the report is included in Appendix B, including a map showing the investigations, records of test pit logs, and grain size distributions of the borrow source. The Alaska Department of Natural Resource's database of domestic and public water well logs, available on-line through the Well Log Tracking System (WELTS), did not reveal any water wells located in the area of the project site. A geotechnical field reconnaissance was conducted by Golder's geologist, Mr. Daniel Willman, on May 23, 2012. The reconnaissance in False Pass was completed consecutively with trips to prospective wind False Pass Wind Turbine Feasibility 1, : Maggie McKay June 2, 2014 Marsh Creek, LLC 4 123-96824,01 sites in Cold Bay and Nelson Lagoon. The field effort entailed visually observing and walking the proposed wind site, completing two shallow hand probes, and visiting local borrow sources. During the reconnaissance, the field effort entailed hand excavating and sampling two hand test probes, identified as KFP-1 and KFP-2, as shown in Figure 2. The hand probe locations were selected in the field based on our understanding of the prospective site (i.e. proximity to the Met Tower), information regarding property boundaries, existing geologic reports, and site considerations. Mr. Willman performed the excavation in part with a shovel and advanced a hand probe while maintaining a log of samples and subsurface conditions. Soils encountered were visually classified in the field according to the Unified Soils Classification System (USCS), presented on Figure 4. Conditions encountered in the test probes are summarized in Table 1 below, and shown on the site photos in Appendix A. Representative soil samples were collected from each test probe. The recovered samples were visually classified in the field before being individually sealed in plastic bags and transported to our Anchorage laboratory for further examination and classification. Table 1: Summary of Hand Test Probes Probe Location Hand Probe # Description of Soils Latitude Longitude KFP 1 Surface vegetation: Tall grass. N 54.873920° W 163.4107700 0 to 1 feet: Brown, Silty SAND with Organics (SM w/ Org.) 1 to 1.5 feet: Gray, SAND, trace fines, with little Gravel (SP), medium grained sand 1.5 to 4.5 feet: Moist, brown to dark brown, Sandy SILT to Silty SAND (ML to SM) 4.5 to 7.5 feet: Moist, brown/gray, poorly -graded SAND, trace to little silt, trace gravel, (SP-SM) Bottom of Hole 7.5 feet. No Groundwater encountered. KFP 2 Surface vegetation: Tall grass and shrub. N 54.8742200 W 163.410860° 0 to 1.5 feet: Brown, Silty SAND with Organics (SM w/ Org.) 1.5 to 3 feet: Gray, SAND, trace to little silt, with little Gravel (SP-SM), 3 to 6 feet: Brown, Silty SAND, (SM) 6 to 7 feet: Moist, brown, poorly -graded SAND, trace to little silt, trace gravel, (SP to SP-SM) Bottom of Hale 7 feet. No Groundwater encountered. Notes: 1) Probe coordinates were acquired using hand-held GPS with navigational accuracy, using horizontaE datum WGS84. 2) The location of the Met Tower was recorded as N 54.87406° W 163.41075°. Shallow bedrock was not observed during this test probe program or during the previous investigations at the landfill, and is not anticipated to be near the surface at the proposed site. Volcanic ash was not specifically noted in the test probes, but could potentially be present on -site and intermixed with the sediments and overburden. False Pass Wind Turbine Feasibility Maggie McKay June 2, 2014 Marsh Creek, LLC 5 123-5824.01 5.2 Borrow Stockpiles Two stockpiles of borrow material were noted in the community. Tne first source is reported to be extracted from the active channel of the Round Top Valley Creek, and comprised mostly of relatively clean sand, gravel, and cobbles. Material is screened and stockpiled in an area between the Round Top Valley Creek and isanotski Drive. This material site is reported to be owned and operated by the lsanotski Corporation. Samples of this material source were collected and tested during the 2004 investigation by DMA, indicating sandy gravel with cobbles (GW-GM) to (GP) USCS classification (see Section 4 and Appendix B for further details). The second borrow stockpile is located closer to the proposed site at the Crab Pot Storage Site, and is owned by the City of False Pass. The source of this material is unknown, but the stockpile appears to be comprised of relatively clean sand and gravel with cobbles. Photos are shown of the stockpiles in Appendix A. Apparently, based on discussion with personnel from the City of False Pass (2014), the material is good quality, and is utilized both for local projects and as export to other nearby communities, and has been utilized by contractors in the past as concrete aggregate. The screening plant is available for rent, along with heavy equipment. Therefore, the material is considered suitable for constructing access roads and pads for this project, and is likely suitable for use as structural fill and concrete aggregate, but may have to be screened or otherwise processed for those purposes. No samples were collected for testing, and quality and composition will need to be verified during the next phase of the project. FOUNDATION6.0 GEOTECHNICAL CONSIDERATIONS AND CONCEPTUAL -LEVEL O 6.1 Summary of Expected Conditions Based on the findings of this report, subsurface conditions are inferred to be comprised of shallow organics and a stratum of sandy silty material that is underlain by granular sandy and/or gravelly material. Based on the available information, the organic and silty materials extend down to 5 to 8 feet depths below the ground surface. Shallow groundwater, within the upper 11 feet, is not expected. Shallow bedrock is not expected. Large - dimensioned materials (cobbles and boulders) could impact installation of a deep foundation. As stated, the size, type, location, and number of wind turbines, and associated supporting towers, have yet to be determined in this phase of the project. And therefore, no foundation configuration or loads are known at this time. However, for foundation design of wind turbines, overturning moments at the base of the towers is most often the controlling loading scenario, Dynamic loading from the structures, including vibration and resonance frequencies, may also be a foundation design consideration. From this preliminary understanding of conditions, the wind turbine site is considered suitable for both shallow concrete gravity foundations and deep foundations, such as helical or driven steel piles, or concrete caissons. Alternatives to these conventional foundations may be appropriate for smaller -sized turbines that are being considered here. Once more detailed selection of wind turbine type, tower, and exact location(s) are known, it is recommended that additional site -specific geotechnical subsurface investigation and detailed foundation engineering be conducted at that time. False Pass Wind Turbine Feasibility Maggie McKay June 2, 2014 Marsh Creek, LLC 6 123-95824.01 6.2.1 Shallow Foundations In the case of a shallow concrete foundation, it would be advisable to remove the organic, silty, and otherwise deleterious materials from the foundation footprint, including any volcanic ash, if present. The foundation should be placed bearing within the underlying granular materials. Preliminarily, the organic and silty materials are expected to extend down to 5 to 6 feet depths below the ground surface. Depending upon the condition and relative density of the underlying granular materials in which the foundation bears, and the bearing pressures exerted from the foundation, the in -situ material may need to be densified by compaction, or otherwise improved or replaced with a layer of compacted structural fill. The exposed subgrade must be proof compacted, and any soft or yielding surfaces removed and replaced. If the in -place soils at the expected shallow foundation depth range are frost susceptible, frost protection measures would be needed to reduce the potential for seasonal frost penetration under the tower foundation. Based on the information, groundwater is expected to be greater than 11 feet deep, but should be verified, and may change seasonally and with precipitation events. The foundation should be designed to avoid excavating below the ground water level in order to reduce/eliminate the need for dewatering. Either cast -in -place reinforced concrete foundation or post tensioned, pre -cast foundation systems can be used. 6.2.2 Deep Foundations Various types of deep foundations are also considered viable at this site. First, larger diameter helical pile foundation systems are considered feasible, but not without installation risk due to the potential to encounter larger dimensioned subsurface materials (cobbles and boulders). Helical piles would require sufficient embedment to develop axial and lateral capacity for the wind turbine units being considered. Large dimensioned materials, including cobbles and boulders, were noted frequently in the creek channel and cut bank up -gradient of the site, and should be expected, but to a lesser extent, at this proposed site. Material this large can impact helical pile installation, and could severely damage the helices even with predrilling. Of particular concern is the requirement to maintain precise location for the helical piles within the foundation system. If a helical pile is able to penetrate the cobbles and boulders, the larger dimensioned material may deflect and force the helical pile from the desired target location. The amount of deflection can be considerable and may not meet the design tolerances. The occurrence of cobbles and boulders should be evaluated during the site -specific geotechnical investigation, detailed foundation design, and planning for installation. Driven pile is another deep foundation option for the wind turbine(s). As stated above, the presence of cobbles and boulders may impact installation of driven piles with the potential to damage the piles during driving or pre -mature refusal. The larger dimensioned materials will prohibit use of displacement (closed end) piles, thus H-Piles or open end pipe piles will most likely be required. Predrilling and other methods may be required to achieve embedment through the larger dimensioned materials where present, but this is often difficult and may be costly to mobilize equipment. Driven piles would need to be embedded deeper comparatively to helical piles, in order to develop the same axial resistance, particularly in uplift. However, driven piles pose somewhat less risk in terms of installation difficulties in large -dimensioned material compared to helical piles. Deep concrete cassion or pier foundations may also be viable, but are not preferred over helical or driven piles. With any deep foundation, the lateral resistance from soils in the upper portion of the foundation have a higher proportional influence on the overall lateral performance. With this in mind, and with the expectation of sandy silty material close to the surface that may provide limited lateral resistance, the deep foundation option may have to be augmented with compacted structural fill to improve that lateral performance. Structural fill can either be placed on top of the silty material, or in partial replacement of it. in this scenario, the addition of non -frost susceptible structural fill (defined on Figure 5) could also reduce frost heave forces on the foundation. (R=Iates kr False Pass Wind TurW ne Feasibility Maggie McKay June 2, 2014 Marsh Creek, LLC 7 123-95824.01 If a deep pile option is being considered, we advise conducting deep geotechnical soil borings at the proposed pile locations to determine the nature and extent of subsurface materials for a pile foundation design. 6.Z3 Other Foundation Options for Smaller turbines If smaller sized turbines and towers are selected, alternate foundation options may also be viable to resist the smaller loads, in lieu of the conventional shallow and deep foundations listed above. Concrete caissons or piers may be viable foundation options. The embedment depth and size needed for these foundations will depend upon the turbine / tower structure and resulting loads, and these factors will greatly influence the practicality of this type of foundation and the necessary installation methods. It would be beneficial to the cost of the project if a caisson or pier foundation system could be designed such that construction could be accomplished with excavation and heavy equipment that is available in the community, rather than requiring specialized drilling equipment for installation. Hybrid foundation systems, such as a shallow concrete base with uplift screw anchors, may also warrant consideration. The advantage of this type system over a concrete gravity foundation is that the uplift anchors are useful in counterbalancing overturning loads, and thus could potentially reduce the overall size of the concrete, comparatively. However, the advantage of this type of system over a concrete gravity foundation is reduced since it would still be advisable to remove the organic and silty material. As stated above, large -dimensioned materials, if present on site, may impact installation of the screw anchors. According to YourCleanEnergy LLC (2010), Aleutian Pribilof Island Community Development Association (APICDA) installed a Sky Stream 1.8kW wind turbine with a 33 foot monopole tower located next to the City Office. The type of foundation that supports this wind system, and the performance thereof, will be researched and information included for the final version of this report. A road and pad may be needed to access the proposed wind site(s) extending from the existing Landfill site. The surface organic material should be stripped before an embankment is constructed. Removal of the relatively thin organics will generally expose a silty sand I sandy silt that will provide firmer support for the roadway section than if the organics were overlaid. Otherwise, a geotextile could be placed on the ground surface prior to fill in lieu of excavating the thin organics. The silty sand subgrade material is frost susceptible, and therefore the roadway section should be thick enough to reduce the effects of frost boils on the surface material. Preliminarily, a minimum fill embankment section would be 18 to 24 inches thick. Generally a thicker section will provide better performance and long term service; however, the embankment thickness could potentially be minimized considering the expected light use of the road. The thickness of the road embankment would also have to consider the equipment and wheel loads needed for construction. If the overburden material along a proposed access road is ash -rich, care must be taken to avoid disturbing the surface organic cover (DMA, 2004). The ash -rich material is likely to be weak and difficult to work with when wet. This report has been prepared for the use by Marsh Creek, LLC for conceptual -level feasibility study for the proposed wind turbines near False Pass, Alaska. As the project progresses, and civil and structural engineering designs are advanced, we must be contacted to verify or modify our conceptual -level geotechnical recommendations presented in this submittal. If there are significant changes in nature, design, or location of the facility, we should be notified so that we may review our conclusions and recommendations in light of the proposed changes and provide written modification or verification of the changes. False Pass Wind Turbine Feasibility a1��. Maggie McKay June 2, 2014 Marsh Creek, LLC 8 123-95824.01 There are possible variations in subsurface conditions between explorations and also with time. Therefore, inspection and testing by a qualified geotechnical engineer should be included during construction to provide corrective recommendations adapted to the conditions revealed during the work. Unanticipated soil conditions are commonly encountered that cannot be determined by a limited number of explorations or soil samples. Such unexpected conditions frequently result in additional project costs in order to build the project as designed. Therefore, a contingency for unanticipated conditions should be included in the construction budget and schedule. The work program followed the standard of care expected of professionals undertaking similar work in the State of Alaska under similar conditions. No warranty expressed or implied is made. 8.0 CLOSING It has been a pleasure to assist you with this interesting project. As the project proceeds, please feel free to contact us with any questions or concerns. We look forward to our continued involvement with Marsh Creek on this and future projects. Sincerely, GOLDER ASSOCIATES INC. ravis E. Ross, PE Senior Geotechnical Engineer Attachments: References Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Appendix A Appendix B TER/TGKImlp Project Vicinity Plan Project Location Map Site Map Soil Classification Legend Frozen Soil Classification Legend Site Photos — Geotechnical Reconnaissance Historic Geotechnical Data False Pass Wind Turbine Feasibility s REFERENCES City of False Pass, April 4, 2014, telephone discussion with City Staff regarding borrow sources. Department of Commerce, Community, and Economic Development (DCED). Community Database Online, accessed 03/2014 (http:/Icommerce.alaska.gov/cra/DCRAExternal). State of Alaska, Division of Community and Regional Affairs, Detterman, R.I., Wilson, F.H., Weber, F.R,, Dochat, T.M_, and Miller, T.P., 1998, Revised Geologic Map of the Cold Bay and False Pass Quadrangles, Alaska Peninsula, Alaska. Prepared for the United States Department of the Interior, U.S. Geologic Survey, Open -File Report 97-866. Duane Miller & Associates (DM&A), September 5, 2002, Geotechnical Consultation, Proposed Landfill, False Pass, Alaska, DM&A Job No. 4086.44 Duane Miller & Associates (DM&A), March 30, 2004, Geotechnical Exploration, Proposed Solid Waste Landfill, False Pass, Alaska, DM&A Job No. 4086.047. Ferrians, O.J., Jr., 1965, Permafrost Map of Alaska: U.S. Geological Survey Miscellaneous Geological Investigations Map 1-445, Scale 1:2,500,000. Schaefer, J_R., Cameron, C.E., and Nye, C.J., 2014, Historically active volcanoes of Alaska, in Schaefer, J.R., Cameron, C.E., and Nye, C.J., Historically active volcanoes of Alaska: Alaska Division of Geological & Geophysical Surveys Miscellaneous Publication 133 v. 1.2, 1 sheet, scale 1:3,000,000. YourCleanEnergy LLC, May 2010, by Andy Baker, P.E. and Lee Bolling, E.I.T. Renewable Energy Resource Assessment for the Communities of Cold Bay, False Pass, and Nelson Lagoon, report for Aleutians East Borough, funded by a grant from the Alaska Energy Authority, Project No. 407051. False Pau Wind Turbine Feasibility ASS Stes