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REVIEWED BLD2023-1134+Geotechnical_Report+1.9.2024_1.46.51_PM+3990881SHANNON 6WILSON, INC. GEOTECHNICAL AND ENVIHONMENTAL CONSULTANTS March 30, 2018 Snohomish County Parks & Recreation 6705 Puget Park Drive Snohomish, WA 98296 Attn: Ms. Logan Daniels, PE RE: GEOLOGICALLY HAZARDOUS AREAS, MEADOWDALE BEACH PARK ESTUARY RESTORATION PROJECT, SNOHOMISH COUNTY, WASHINGTON This letter report presents our site observations, review of publicly available information, and opinions regarding geologically hazardous areas as part of the proposed Meadowdale Beach Park and Estuary Restoration Project in Snohomish County, Washington. The purpose for this letter is to address Snohomish County Code (SCC) Critical Areas Regulations (Snohomish County Planning and Development Services, 2017), Chapter 30.62B — Geologically Hazardous Areas (GHA) and the Edmonds City Code and Community Development Code (ECDC) Geologically Hazardous Areas, Chapter 23.80 (Edmonds, 2018) as part of the project State Environmental Policy Act (SEPA) checklist. The scope of our work for this aspect of the project included the following: ■ Preparation of Light Detection and Ranging (LiDAR) maps for field use and analysis. ■ Site reconnaissance on November 9, 2016. ■ Analysis of information and site classification to satisfy GHA requirements. ■ Preparation of this letter report. SITE DESCRIPTION AND CLASSIFICATION The project site is located on the north boundary of Edmonds, Washington, as shown in the Vicinity Map, Figure 1. The southwestern portion of the site, including the access road and much of the grassy park area, is within the Edmonds city limits. The park areas north and east of those approximate boundaries are in unincorporated Snohomish County. 400 NORTH 34TH STREET, SUITE 100 P.O. BOX 300303 SEATTLE, WASHINGTON 98103-8636 206-632-8020 FAX: 206-695-6777 www.shannonwilson.com 21-1-22288-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 2 of 14 The park is accessible via a gated road (Figure 2), which extends north from 75th Place West. North of the park entrance gate, the road continues in a northern direction, paralleling Puget Sound shoreline and a west -facing coastal bluff for about 400 feet before turning sharply to the east and descending the north -facing slope of Lund's Gulch. At the toe of this steep hillside is a hairpin turn sharply to the west to a parking lot. The park ranger's residence and a grass -covered playfield with picnic shelters are located west of the parking lot. The western edge of the playfield is bounded by an approximately 10-foot-high BNSF embankment. Impervious surfaces at the site include the access road, asphalt -paved walking paths in the lower park area, and associated paved surfaces (Figure 2). Buried utilities, such as fiber optics and electrical power, are located on the inboard side of the entrance road, beneath the drainage ditch. Based on review of existing LiDAR topography (Figures 3 and 4), SCC 30.91L.040, and ECDC 23.80.020, most of the slopes forming both the north and south flanks of Lund's Gulch are classified as Landslide Hazard Areas (LHA): ■ As defined in SCC 30.91L.040 because they have: — Vertical height greater than 10 feet. Areas of historic and active landslides. — Most of the slope areas are steeper than 33 percent. Slopes intersect geologic contacts between relatively permeable sediment overlying relatively impermeable sediment. — Slopes contain springs and groundwater seeps. ■ As defined in ECDC 23.80.020 because they have: — Areas of ancient or historic failures. — Coastal areas mapped as u (unstable), uos (unstable old slides) in the Department of Ecology Washington Coastal Atlas. — Most of the slope areas are steeper than 40 percent with a vertical height of over 10 feet. — Slopes intersect geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment. — Slopes contain springs or groundwater seepage. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 3 of 14 Additionally, the relatively flat valley bottom is classified as a LHA as defined in SCC 30.91L.040 because: ■ It is in a canyon and an active alluvial fan, susceptible to inundation by debris flows or catastrophic flooding. ■ It is entirely encompassed within the boundaries defined as twice the valley wall steep slope height measured from the toe of the slope. The park and stream areas qualify as GHA as defined in both SCC 30.91L.040 and ECDC 23.80.020 because they have: ■ An area potentially unstable as a result of rapid stream incision or stream bank erosion. ■ They are on an alluvial fan, presently potentially subject to inundation by debris flow or deposition of stream -transported sediments. Based on this site classification, Chapter 30.62B SCC and Chapter 23.04090 ECDC requires a geotechnical report for any site development activity. This report describes site conditions and features specific to the GHA report requirements. Design recommendations to address geologic hazards are presented in the project geotechnical report. PROPOSED IMPROVEMENTS Proposed improvement details will be presented in the project SEPA checklist and are beyond the scope of this report. In summary form, proposed improvements include: ■ Constructing a 130-foot-long, four -span railroad bridge to replace the existing concrete culvert that serves as passage for Lund's Gulch Creek through the BNSF embankment. ■ Site grading to widen the Lund's Gulch Creek channel meander zone, restore the former brackish wetland area, and restore the natural intertidal and delta reaches of Lund's Creek. ■ Constructing an Americans with Disabilities Act, width -compliant walking path beneath the proposed bridge for pedestrian access between the park and beach areas. ■ Constructing a pedestrian bridge across Lund's Gulch Creek near the upper reach of the proposed widened channel meander zone. ■ Constructing a new restroom enclosure near the picnic shelter. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 4 of 14 To construct the proposed bridge and site grading activities, it is anticipated that heavy equipment and materials ingress and egress would be via the existing access road. Based on the access road assessment provided during the project feasibility study (Shannon & Wilson, Inc., 2016), we anticipate road improvements will be required to support construction traffic. Anticipated improvements include road widening, particularly at the sharp curves, and stabilization measures along the outside shoulder of the road where longitudinal pavement cracks have been observed and low -strength, non -engineered fill is present. GEOLOGIC CONDITIONS Geologists generally agree that the Puget Sound area was subjected to six or more major glacial events. Each glaciation deposited new sediment and partially eroded previous sediments. During the intervening periods when glacial ice was not present, normal stream processes, wave action, weathering, and landsliding eroded and reworked some of the glacially -derived sediment, further complicating the geologic setting. During the Vashon Stade of the Fraser Glaciation (most recent ice incursion) that covered the central Puget Lowland, approximately 18,000 to 16,000 years before present (Porter and Swanson, 1998), the glacial ice is estimated to have been about 3,000 feet thick in the project area (Thorson, 1989). The weight of the glacial ice resulted in compaction of the glacial and nonglacial soils beneath the ice. The glacial and nonglacial deposits are overlain by younger (Holocene Epoch), relatively loose and soft, post -glacial soils that include peat, beach, colluvial, and fill deposits. Lund's Gulch incises through glacial and nonglacial soils from uplands of greater than 300 feet elevation to Puget Sound along a west-northwest trend in south Snohomish County (Figure 1, Vicinity Map). Meadowdale Beach Park encompasses the lower part of Lund's Gulch. Lund's Gulch was carved by glacial meltwater after Vashon ice retreated and the land was uncovered (Applied Geotechnology, Inc., 1986). During the time of ice retreat, the steep slopes along the sides of the meltwater channels (the gulch and Puget Sound) became destabilized. On the creek side of the park, the slopes remain largely set in their position (Applied Geotechnology Inc., 1986). On the Puget Sound side of the park, the shoreline slopes retreated many hundreds of feet following deglaciation owing to upland instability, wave action, and soil erosion by longshore drift. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 5 of 14 Lund's Gulch Creek flows through an approximately 6-foot-wide by 9-foot-high by 55-foot-long concrete box culvert through the BNSF embankment. A delta has formed in the intertidal zone between the culvert outlet and Puget Sound shoreline. The stream outlets on the north side of the delta as influenced by northward littoral drift. Existing Geologic Information According to geologic maps of the area (Washington State Department of Natural Resources, 2016; Minard, 1982; Smith, 1976), we have interpreted the stratigraphic layers along the park entrance road as follows (Hf) Fill — Materials placed in locations other than their original native locations. The engineering properties of such deposits vary widely with soil density and composition. Slope stability will be negatively affected where loose fill soils are present, and positively affected where dense fill soils are present. Older fills, such as along the outside edge of the park entrance road, are commonly very loose to loose, because they were not compacted during original construction. They were likely excavated from the inboard side of the road prism and dumped on the outboard side. Permeability of these soils ranges from highly pervious to relatively impervious, depending on their source and the amount of compaction during construction. (Qls/Hc) Landslide Debris/Colluvium — Loose or soft landslide debris/colluvium deposits cover nearly of the slopes, except for those that are too steep to maintain a colluvial cover. These deposits generally reflect the soils that are uphill from them. They may be relatively pervious, but within close proximity, the soil may have a low permeability. Landslide debris and colluvium is generally loose to medium dense, with density increasing with depth. Engineering properties of such deposits vary widely with soil density and composition. On steep slopes, such soils are susceptible to failure, particularly at the contact with underlying undisturbed formations. (Qvt) Vashon Till — Very dense, low permeability diamict that blankets much of upland to the east of the project area, but does not outcrop near the proposed improvements. Till is very dense, has a low permeability, and has high shear strength properties because it is poorly sorted, contains 20 to 50 percent fine-grained particles and has been overridden by glacial ice. As a foundation material, it can support heavy loads. Slopes in this material generally exhibit stable behavior. Surface water commonly ponds on top of this layer. (Qva) Advance Outwash Sand — Very dense, glaciofluvial, advance outwash consisting of sand and/or gravel with relatively few fine-grained particles. It has a relatively high permeability and can support heavy loads where it is undisturbed. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 6 of 14 This soil type generally exhibits high shear strength due to its density and granular composition. Where exposed in slopes, it can exhibit both stable and unstable behavior. In locations where it is underlain by lower permeability Transitional Beds, groundwater commonly perches on the finer -grained soil and forms seeps or springs where exposed. This seepage can cause slope instability. (Qtb) Transitional Beds — Interbedded glacial and nonglacial fine sand, silt, and clay in the exposed cut slopes along the southern end of the entrance road. The fine sand and silt are dense to very dense and clay is commonly very stiff to hard. The silt and clay have a very low to low permeability, except where they have been fractured, and water is able to move in the cracks. The fine sand is commonly wet. Where undisturbed, these soils support moderate loads. These soils typically exhibit moderate to high shear strength values, and in slopes exhibit both stable and unstable behavior. Along the park entrance road, fractured and jointed silt, clay, and fine sand are exposed and have a history of small failures. ■ (Qog) Olympia Gravel — Very dense, nonglacial, relatively pervious sand and gravel deposit lying at and below the entrance road level. The gravel is very dense, where undisturbed, exhibits high shear strength, and can support heavy loads. It is locally cemented and can stand vertically for years. Where cemented and containing fine- grained particles in the matrix, it has a low permeability. (Qw) Whidbey Formation — Very dense, nonglacial, fluvial, interbedded fine to medium sand with fine gravel interbedded with silt and clay exposed in the vertical bluff along the BNSF tracks to the west of the entrance road. No seepage was observed. The exposure was blocky, and colluvium at the toe of the slope contained small soil blocks. Due to its compaction by ice and fine-grained particles in its matrix, it exhibits high shear strength and low permeability at this site. The Natural Resources Conservation Service map (Debose and Klungland, 1983) of soils indicates three soil types within the park boundaries: The lawn and parking areas, and other predominantly flat areas of the lower park are underlain by Alderwood gravelly, sandy loam on 2 to 8 percent slopes. The erosion potential for this soil type is classified as slight. The southern end of the entrance road is underlain by Alderwood gravelly, sandy loam on 15 to 30 percent slopes. The erosion potential for this soil type is classified as moderate. ■ The remainder of the entrance road and park areas that are on steep slopes are underlain by Alderwood-Everett gravelly, sandy loam on 25 to 70 percent slopes. The erosion potential for this soil type is classified as high. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 7 of 14 GEOLOGIC HAZARDS Geologic hazards at the site include erosion hazards, seismic hazards, and landslide hazards. Erosion Hazard Vegetation consists mainly of deciduous trees, namely red alder and big -leaf maple, with moderate to thick undergrowth. Large -diameter conifers, such as Douglas fir, western hemlock, and western red cedar, are scattered throughout the site. Erosion will occur naturally and in response to construction. The site is well vegetated for the most part; however, some of the cut slopes are bare, exposing soil to rain and entrainment. They provide little sediment, except infrequently when the slope soils fail and fill the drainage ditch. During construction, sediment will be created during excavation and filling, but Best Management Practices will control sediment so it does not reach Lund's Gulch Creek or Puget Sound. Landslide Hazard Landslide Hazard — Natural Slopes Landslides at the site are both deep-seated and shallow. No active or dormant deep- seated landslides were identified on slopes along the entrance road or near the proposed structures. Proposed structures are outside of the North Edmonds Earth Subsidence and Landslide Hazard Area. Three moderately sized bowls are on the slope above the road on the north -facing slope of the road corridor, as shown in Figure 2, but there are no signs of active or recent deep-seated instability. These bowls are relict remains of past instability. The colluvium-filled slopes above and below the entrance road are susceptible to shallow instability. Figure 2 indicates locations at which scars of landslides and evidence of recent instability were observed. A very large bowl breaks the otherwise uniform, south -facing slope (north side of Lund's Gulch Creek) to the north of the proposed site improvements. Based on reconnaissance of the lower part of the bowl, there is no seepage and no defined channel that carries water. Therefore, this bowl is also considered to be relict. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 8 of 14 A near -vertical cliff of cemented sand and gravel with silt interbeds is about 20 to 30 feet high for a length of about 110 feet along the BNSF. A large block of fallen soil at the toe of the slope is indicative of the type of instability that could be expected from this bluff. However, due to the slope orientation, such an event would not affect park facilities. Landslide Hazard — Constructed Slopes The southern 400 feet of the entrance road is located on a steep, west -facing slope and northern 900 feet of the road is north -facing, as indicated in Figure 2. The asphalt -paved road appears to have been constructed by cut -and -fill methods, with a paved drainage ditch on the inboard side. A guard rail protects the outboard edge of the road. Linear cracks were observed on the outside half of the road in several places, and repairs have been made at two locations along the road, the result of road prism failures. The cut slopes in the southern 400 feet of the entrance road were excavated to very steep inclinations, the result of which are periodic failures of blocks of soil into the ditch or onto the pavement. The slopes immediately downslope from the road are very steep (65 to 130 percent), and downhill bowing of the guard rail in two locations indicates slow failure of those slopes along the outboard edge of the road. Mounds of colluvium form a mostly continuous apron at the toe of the north -facing slope. Two walls have been constructed on the outboard side of the north -facing segment of the entrance road at the locations indicated in Figure 2. The date of construction of the wooden soldier pile wall is unknown. This wall is about 80 feet long and a maximum 12 feet high. No as -built plans are available for this wall. The mechanically stabilized earth wall is about 10 feet (maximum) high and 100 feet long. It was built in 2008 by the Snohomish County Public Works Department to repair the failure of the outside shoulder of the road that crossed a steep, but shallow ravine. Excavation for the repair extended to 23 feet below the inside edge of pavement, and backfill consisted of quarry rock and geogrids. Presently, no distress was observed on the road at this site and the face of the wall appeared to be in good condition. Landslide Hazard — Setback and Buffer Requirements As stated previously, the entire valley bottom is classified as a LHA as defined in SCC 30.91L.040. Based on this condition, proposed structures within the project area will, by definition, fall within the LHA boundary, and no setback or buffer dimension will mitigate this 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 9 of 14 condition. Consequently, SCC 30.62B.340 allows development within LHA when: ■ There is no alternate location for the proposed structure. ■ The project geotechnical report demonstrates that the design will provide protection commensurate to being located outside of the landslide area. ■ The design satisfies the provisions of SCC 30.62B.320, including: — Utilizes best management practices. — Prevent collection, concentration, or discharge of water within a landslide area. — Minimize impervious surfaces and retain vegetation. Do not increase risk of property damage, death, or injury. — Do not cause or increase erosion or landslide hazard risk. Do not increase surface water discharge, sedimentation, slope instability, erosion or landslide potential to adjacent or downstream and down -drift properties beyond pre -development conditions. Do not adversely impact wetlands, fish and wildlife habitat conservation areas or their buffers. ECDC 23.80 contains several requirements for development within LHA, including: ECDC 23.80.050 defines the special study and report requirements for development within GHA, including a requirement for minimum setback recommendation for avoiding landslide or erosion hazard, and other recommendations for site development so that the frequency or magnitude of landsliding or erosion on or off the site is not altered. ■ ECDC 23.80.060 provides general development standards for GHA, including a requirement that the development be designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than the predevelopment conditions. ECDC 23.80.070 provides development standards specific to erosion and landslide hazard areas, and specifies minimum buffer requirements, which include a requirement to eliminate or minimize the risk of property damage, death or injury resulting from landslides caused in whole or in part by activities within the buffer area. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 10 of 14 Seismic Hazards The Meadowdale Beach Park is located near a seismically active zone; the Southern Whidbey Island Fault Zone. As shown in Figure 5, the park is about I mile south of the active fault zone, and is about halfway between two other geophysical lineaments of unknown age. The potential effects of an earthquake and faulting on the site included ground rupture, liquefaction, and seismically induced landslides. Seismic liquefaction is the loss of soil strength caused by ground shaking during an earthquake in areas with loose sand and silt and a high groundwater table. The liquefaction susceptibility map of Snohomish County (Palmer and others, 2004) indicates the project site has low to very low susceptibility. The alluvial and colluvial soils in the parking area and the picnic area to the west may be liquefiable, but we have no site -specific soil density and consistency data on which to evaluate their susceptibility. Strong shaking could also engender landslides on the steep slopes along the south entrance road, particularly during the wet winter season. WATER WELLS We searched the Washington State Department of Ecology well log database and found 68 records on file within the same township, range, section, and quarter -section as the project site. Of the 68 records, 15 were listed as water wells, 15 were listed as resource protection wells, and 36 were listed as well abandonments. The 15 water wells were registered to Alderwood Water District, and each water well log had a corresponding abandonment log. The location stated in the well logs for the 15 water wells is the Alderwood Water and Wastewater District Water Treatment Plant address, 6315 Picnic Point Road, Edmonds, Washington 98026. That address is more than one mile from the project site. Based on available water well records, it appears there are no water wells within the project site. DRAINAGE Drainage at the site is surface and subsurface. No surface channels were observed on, below, or above the access road. A paved drainage ditch is located on the inboard side of the road. From the high point at the curve about 400 feet north of the entrance gate, the ditch water flows south and east. Most of the subsurface water in the park appears to be intercepted by the deep valley of Lund's Gulch, on the slopes to the north and south of the creek. The result of that seepage is a plethora of small to very large landslides along the gulch sidewalls. On the slope facing 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 11 of 14 westward, above the BNSF tracks, no seeps were observed. Minor seepage was observed in the locations indicated in Figure 2, in the project area. Two small seeps were observed on the uphill side of the road on the north -facing slope: (1) behind an electrical service box at the bottom of the slope where the road bends sharply to the west and (2) from a topographic bowl uphill from the road, as indicated in Figure 2. SUMMARY The project area and entrance road are underlain by competent overconsolidated glacial soils, alluvial deposits, and weak colluvial deposits. The latter are the result of past slope instability and erosion on the steep slopes. Only two seeps were observed, both on the north -facing slope of the road. Three types of geologic hazard exist within the project area: erosion, landslides, and seismic. Potential landslide hazards are both deep-seated and shallow, and may be natural or the result of past disturbance of the natural conditions. The deep-seated landslides are relict, and very unlikely to reactivate naturally or as the result of the proposed site improvements. There are many instances of shallow landsliding: The cut slope of the road is too steep to maintain a stable condition. This slope has failed many times in the past, and can be expected to fail in discrete small areas (on the order of 5 to 100 cubic yards) in the future. The trees on this slope will also fall of their own volition or along with a soil mass. The trees constitute a particular danger to the walking and driving public. Sudden shallow landslides and tree falls are likely, but not exclusively, to occur during the winter months. 2. The outside edge of the roadway is loose sidecast fill for perhaps as much as 80 percent of the road alignment length. Where there are signs of distress in the pavement or the guard rail, measures need to be taken to remediate the road; however, other sidecast fill areas are still susceptible to failure or settlement in the future. Such failures could endanger drivers if failure of soils beneath the existing roadway occurred and a void developed suddenly, and was undetected. 3. The bluff along the BNSF tracks is exposed and vertical, and fails periodically in blocks defined by joints in the glacially overridden soil. The soil comes to rest in the railroad drainage ditch. Failures of this type will not affect the project area, and the BNSF has posted no trespassing signs, making access off limits. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 12 of 14 To comply with SCC 30.6213.340, structures in LHA must be designed to provide protection commensurate to being located outside of the LHA. This condition applies to the proposed restroom enclosure. A retaining wall structure, located immediately south of the asphalt walking path and between the proposed restroom enclosure and steep slope south of the structure, will be included in the project design to provide protection from landslide runout. Recommendations for the retaining wall structure will be included in the project geotechnical report. To comply with ECDC 23.40.280 structures in LHA buffer zones must not cause landslides. In our opinion, the proposed restroom enclosure will not cause landslides, and will not increase the potential for landslides on the slope above the proposed structure. The south entrance road stability improvements will increase slope stability within the footprint of those features and will not, in our opinion, increase the risk of property damage, injury or death. Nor will the improvements increase similar risks to neighboring properties. Liquefaction is not likely along the access road because groundwater is low or non-existent. However, in the parking lot and in the open field and picnic area to the west of the Ranger's house, the groundwater level is high and the soils may be very loose to medium dense, making them susceptible to liquefaction and damage under seismic shaking. This hazard could potentially heighten the risk for structures in this area, such as the proposed restroom enclosure and pedestrian bridge across Lund's Gulch Creek. Mitigative measures have been recommended as appropriate in the project geotechnical report. In the parking lot, it may be more economical in the long-term to repair damaged pavement due to liquefaction. So as to maintain stability and prevent erosion along the entrance road, existing surface grades should be maintained such that surface water and groundwater continue to flow toward ditches, and ditches should be regularly cleared. Impervious surfaces will be minimized to the extent possible and native vegetation will be retained. The exception to this is the cutting of leaning trees along the entrance road that could fall with or without slope movement. Evaluation of the trees could be provided by a professional forester. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON bWILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 13 of 14 CLOSURE This letter report was prepared for the exclusive use of Snohomish County and their representatives for their evaluation of the Geologically Hazardous Areas on and adjacent to the proposed project. Our evaluation was performed solely to address the Geologically Hazardous Areas on and adjacent to the proposed project, and should not be used for design or construction. Explorations will be performed to support engineering recommendations for this project. Our assessment of geologically hazardous areas for this letter report is based on: ■ The limitations of our approved scope, schedule, and budget. ■ Our understanding of the project and information provided by Snohomish County. For any site located on or near a slope, there are slope instability risks that present and future owners have to accept, including, but not limited to: Natural factors: soil and groundwater conditions, steep topography, heavy rainfall events, erosion, and vegetation conditions. Human -related factors: water leaks, pipe breaks, improper drainage, lack of maintenance of vegetation or drainage facilities, fill or debris placement, excavation, and/or removal of trees/vegetation. Similar circumstances or other unknown conditions may also affect slope stability. Our evaluation and recommendations described herein are not a guarantee or warranty of future stability. 21-1-22288-040-L4/wp/lkn 21-1-2228 8-040 Snohomish County Parks & Recreation SHANNON 6WILSON, INC. Attn: Ms. Logan Daniels, PE March 30, 2018 Page 14 of 14 We have prepared the enclosed document, "Important Information About Your Geotechnical/ Environmental Report," to assist you and others in understanding the use and limitations of this report. Please read this document to learn how you can lower your risks for this project. Sincerely, SHANNON & WILSON, INC. Tyler J. Stephens, PE Associate e'\\ Enaineering GedogW r 1736 000 C Nc c,l D. J. M oCulloofi Neal D McCulloch, PE, LEG Vice President TJS :NDM/tj s Enc: References Figure 1 — Vicinity Map Figure 2 — Site Plan — Observed Landslide Features Figure 3 — Site Plan - City of Edmonds Landslide Hazard Areas and Mapped Landslides Figure 4 — Site Plan — Snohomish County Landslide Hazards Figure 5 — Seismic Features Important Information About Your Geotechnical/Environmental Report 21-1-22288-040-L4iwpntn 21-1-22288-040 SHANNON WALSON, INC. REFERENCES Applied Geotechnology, Inc., 1986, Geotechnical engineering study, Meadowdale Beach Park, Snohomish County, Washington: Report prepared by Applied Geotechnology, Inc., Bellevue, Wash., 14,845.004, for Snohomish County Parks and Recreation, August 28. Debose, Alfonso, and Klungland, M. W. 1983, Soil survey of Snohomish County, Washington: Washington, D.C, U. S. Soil Conservation Service, 197 p., 65 maps. Edmonds, Washington, 2018, Edmonds City Code and Community Development Code: Edmonds, Wash., March 30, available: http://www.codepublishing.coin/WA/Edmonds/, Accessed March, 2018. Minard, J. P., 1982, Geologic map of the Mukilteo quadrangle, Washington: U.S. Geological Survey Miscellaneous Field Studies Map MF-1438, scale 1:24,000. Palmer, S. P.; Magsino, S. L.; Bilderback, E. L.; and others, 2004, Liquefaction susceptibility map of Snohomish County, Washington, in Liquefaction susceptibility and site class maps for Washington State, by county: Washington State Department of Geology and Earth Resources, Open File Report 2004-20, sheet 61, scale 1:150,000. Porter, S. C., and Swanson, T. W., 1998, Radiocarbon age constraints on rates of advance and retreat of the Puget Lobe of the Cordilleran ice sheet during the last glaciation: Quaternary Research, v. 50, p. 205-213. Smith, Mackey, 1976, Preliminary surficial geologic map of the Mukilteo and Everett quadrangles, Snohomish County, Washington: Washington State Division of Geology and Earth Resources Geologic Map GM-20, scale 1:24,000. Shannon & Wilson, Inc. (S&W), 2016, Meadowdale Beach Park feasibility study, preliminary geotechnical assessment addendum, south Snohomish County, Washington: Report prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-22034-001, for Anchor QEA, LLC, Seattle, Wash., February 3. Snohomish County, Wash., Planning and Developments Services, 2017, Critical areas regulations update: Available: http:Hsnohomishcountywa.gov/2183/Critical-Areas- Regulations-Update, accessed April, 2017. Thorson, R. M., 1989, Glacio-isostatic response of the Puget Sound area, Washington: Geological Society of America Bulletin, v. 101, no. 9, p. 1163-1174. Washington State Division of Geology and Earth Resources, 2016, Washington interactive geologic map: Available: http://www.dnr.wa.gov/geologyportal, accessed December, 2016. 21-1-22288-040-L4-Refwp/lkn 21-1-2228 8-040 11 0 IN at m iu Vancouver Vict«ia Seattle Irk— s µA SHI NC T,- N OlymlH a I:enntw�<k .Portland N Mukilteo � "s 112u,stsw; u m y 4 Q 1 e Q Project Location 1481h SISW� y o a Mill Credo a J o v rc I g 164th Sw 0 168MSlSW z r,brlh # c ` 6 u Cteek ` Dr j ' € �iy�o P Park o 1 } ° City of Edmonds ;' `i Lynnwood s P N9 ev, �1' 1961h St Sw Q '^ Ed �ionds Main St Yo st {_-�© v 4 3 0 < 7/Mlh SW m ~ a228 th St s9WBrler 228th StSE EsplYance 'Nlou ntlke _j f Terrace ------------------`\ ay Q Q v ym Lake Bothell • Both•II W Kenmore Forest Shoreline = NE NE < atnst Park ° Hamlin y� ETt r k. < Park — N s 7 f / � P / NE 145thSt Saint = 'NE Edavd i I Stale park a °' i a 1 W � I NE 125th 31 NE 2nd z / • z y Ct ? / Catkeek Q qi / q = � � Qt z NE 1161hSt � 6 • -; I/ �oep6 N1 05th St ,ra 522 S� NW 85th St= N�lNA z d q NW 80th S tQ N 801h S 4 w i i z m 3 N NE 75th St 4 L i ` `Kirkland N Green z b NNW 65th StQ La� ¢ NE 65wh SIQ m r = z H f, II 'h NW Market St z Q' = � < N 45th St a r f - Meadowdale Beach Park Estuary Restoration Project Snohomish County, WA VICINITY MAP March 2018 21-1-22288-040 SHMNON 6WILSON, INC. FIG. 1 GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS uocurnent rain: I:\Y"1-"1\ZZU34 MeaoOWoalevw MXo\r U-Z ULS.MXo � I MP 21.9 ` LEGEND ' I ` Spring O Impervious Surface - Landslide Scar -- Lunds Gulch Creek 7 Impervious Surface H g Raner House \ - \ - ,•� \ rl Parking Lot ---- ---- - - ` 4.0- -- -- -- •• , - _ _ - - Guard Rail - --- `- MSE Wall - _ =_= - -- _ - _7; �_ - - T- _ ---- - - Undermined - ----- --- -- --_ _ --=a- -- _ ----- ` and Displaced _--- -- - �i ------------ -- - --- - -___- „+ ---_-_=_ - --- -I-------=i=- X' _-- - --- - _ _ _ _ - - r ' ` LiDAR and Topographic Contours derived ► __ - �` - from data provided by Puget Sound Exposed Bluff I '�', �,+•,";�„I'I'''I ; � __ -_ __ -- � - - _,� �- _' �_ -_ � � --- _---- LiDAR Consortium. 1 , - _ _ _ - - `` -!Y -_ = i` _ _ _ _ _ _ - - http://pugetsoundlidar.ess.washington.edu/ IN Soldier Pile Wall _ r = - _r _ _ - - - - - - -------- IN `L N PUGET SOUND S Entrance Road's / I- - -- Relict Feet Meadowdale Beach Park BNSF Railwa 1 1 ► , _ / _ - - _ _- _ _ _ _ _ Estuary Restoration Project y `' ' - Snohomish County, WA . + , I 1 l ' SITE PLAN Gate OBSERVED LANDSLIDE FEATURES March 2018 21-1-22288-040 SHANNON 6WILSON, INC. FIG. 2 J �t � 1,62nd�St SW�• 1 Access Rtl .- a �� 164th St SW ••��'"'. 164th-PI SW —Access-Rd 4 b 165th PI SW / f > e I � ♦r� l - � I y I AMC. "I N 00,1 4w lS�thP,•/SW � 1 156th-PI SW\ 160th.St SW I t 160-PI' 3rd-A1 0 1, - 16r4th-Pt_SW� J -A/ I - AMTi:d 1 � �-• 4 ., - J0 .0 u LEGEND Edmonds City Limits Meadowdale Beach Park Project Location City of Edmonds Landslide Areas L Earth Subsidence J Hazard Area Earth Subsidence Landslide Area Earth Subsidence Minimum Buffer to Landslide Hazard Washington Department of Natural Resources Landslides City of Edmonds Hazardous Slopes LiDAR Slope Percent Rise -� Over 40% SOURCES 1. 'City of Edmonds Landslide Areas' provided by City Of Edmonds, GIS Webmap, available: http://maps.edmondswa.gov/Html5Viewer/?viewer=html 2. 'Landslides' provided by Washington Department of Natural Resources - Geologic Information Portal available: https://www.dnr.wa.gov/geologyportal N 0 250 500 W E Feet S Meadowdale Beach Park Estuary Restoration Project Snohomish County, WA SITE PLAN CITY OF EDMONDS LANDSLIDE HAZARD AREASAND MAPPED LANDSLIDES March 2018 21-1-22288-040 SHANNON 6WILSON, INC. FIG. 3 a I Project Location Southwest Sourh: i County Park County Park 184th St SW �tl n Hutt _ nl Jk : G F�aor Fo Harbour Points OoHClub b 5�ti 90 Holip 4 Hatno Jt e � _r G\ h 3 y s o �,0/ - _ Ly P1 Serene aY Lake Serene s/t./ 6,Rd 148th St S'JJ <45 fi 0 \` O Ebey I.,. I I O II . / O Port Gamble O O O FAdI Creek — O / O O ;� 1 \ // Project Location Lvnnwood O Edmo S O O O h, ntla ke O I E�. _ ra Te ce O O t O p O O Lake O \ ofest BO II O O \ Shof 71' rk--K ore ;io inville O O r` Poulsbo O O O �7 O O. Port Madison Puget Sound O O ngsgate Indian O Reservation O / O O O I / Kirkland 0 Redn Lake O Bridle Q- tvlry 1 O -Trails O F' 1 Pwit ark O 520 I O Bainbridge 1 O O Island l O --0 \ O O O O l O ellevvue O I Seattle O O; O ° sland— Brem �\ O O� O N W E 0 S 3.5 Miles SOURCES: LEGEND 1. U.S. Geological Survey and California Geological Survey, 2018 Earthquakes (20yr History) Accessed: March, 2018 O 2.0 to 2.9 Magnitude Quaternary fault and fold database of the United States: Quarternary Faults Available: http://usgs.maps.arcgis.com/apps/ O 3.0 to 3.9 Magnitude webappviewer/index.html? 2014 1 Hazard Faults id=db287853794f4555b8e93e42290e9716 O3.9 to 4.9 Magnitude 2. Czajkowski, J. L. and Bowman, J. D., 2014, Faults and earthquakes in Washington State: Washington Division of Geology and Earth Resources Open File Report 2014-05, 1 plate, scale 1:750,000. - SHANNON & WILSON, INC. Attachment to and part of Report 21-1-22288-040 - Geotechnical and Environmental Consultants Date: March 30, 2018 - To: Snohomish County Parks & Recreation Attn: Ms. Logan Daniels, PE IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL •. CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS. Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may not be adequate for a construction contractor or even another civil engineer. Unless indicated otherwise, your consultant prepared your report expressly for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended purpose without first conferring with the consultant. No party should apply this report for any purpose other than that originally contemplated without first conferring with the consultant. THE CONSULTANT'S REPORT IS BASED ON PROJECT -SPECIFIC FACTORS. A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of project -specific factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as access roads, parking lots, and underground utilities; and the additional risk created by scope -of -service limitations imposed by the client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report may affect the recommendations. Unless your consultant indicates otherwise, your report should not be used: (1) when the nature of the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a refrigerated warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation, or configuration of the proposed project is altered; (3) when the location or orientation of the proposed project is modified; (4) when there is a change of ownership; or (5) for application to an adjacent site. Consultants cannot accept responsibility for problems that may occur if they are not consulted after factors which were considered in the development of the report have changed. SUBSURFACE CONDITIONS CAN CHANGE. Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a report whose adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for example, groundwater conditions commonly vary seasonally. Construction operations at or adjacent to the site and natural events such as floods, earthquakes, or groundwater fluctuations may also affect subsurface conditions and, thus, the continuing adequacy of a geotechnical/environmental report. The consultant should be kept apprised of any such events, and should be consulted to determine if additional tests are necessary. MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS. Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data were extrapolated by your consultant, who then applied judgment to render an opinion about overall subsurface conditions. The actual interface between materials may be far more gradual or abrupt than your report indicates. Actual conditions in areas not sampled may differ from those predicted in your report. While nothing can be done to prevent such situations, you and your consultant can work together to help reduce their impacts. Retaining your consultant to observe subsurface construction operations can be particularly beneficial in this respect. Page 1 of 1/2018 A REPORT'S CONCLUSIONS ARE PRELIMINARY. The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can be discerned only during earthwork; therefore, you should retain your consultant to observe actual conditions and to provide conclusions. Only the consultant who prepared the report is fully familiar with the background information needed to determine whether or not the report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by applicable recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of the report's recommendations if another party is retained to observe construction. THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION. Costly problems can occur when other design professionals develop their plans based on misinterpretation of a geotechnical/environmental report. To help avoid these problems, the consultant should be retained to work with other project design professionals to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and to review the adequacy of their plans and specifications relative to these issues. BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT. Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results, and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in geotechnical/environmental reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or other design drawings, because drafters may commit errors or omissions in the transfer process. To reduce the likelihood of boring log or monitoring well misinterpretation, contractors should be given ready access to the complete geotechnical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared for you, you should advise contractors of the report's limitations, assuming that a contractor was not one of the specific persons for whom the report was prepared, and that developing construction cost estimates was not one of the specific purposes for which it was prepared. While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with your consultant and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy of subsurface information always insulates them from attendant liability. Providing the best available information to contractors helps prevent costly construction problems and the adversarial attitudes that aggravate them to a disproportionate scale. READ RESPONSIBILITY CLAUSES CLOSELY. Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design disciplines. This situation has resulted in wholly unwarranted claims being lodged against consultants. To help prevent this problem, consultants have developed a number of clauses for use in their contracts, reports, and other documents. These responsibility clauses are not exculpatory clauses designed to transfer the consultant's liabilities to other parties; rather, they are definitive clauses that identify where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities and take appropriate action. Some of these definitive clauses are likely to appear in your report, and you are encouraged to read them closely. Your consultant will be pleased to give full and frank answers to your questions. The preceding paragraphs are based on information provided by the ASFE/Association of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland Page 2 of 2 1/2018