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HomeMy WebLinkAboutICE Critical Areas Report Report Geotechnical Engineering Services Critical Areas Report Merlino Short Plat Proposed 7-Lot Residential Development Renton, Washington April 23, 2014 ICE File No. 0864-002 Prepared For: Merlino Land Development Co., Inc. Prepared By: Icicle Creek Engineers, Inc. April 23, 2014 Merlino Land Development Co., Inc. Attn: Gary Merlino 5050 1st Ave S, Suite 102 Seattle, Washington 98134-2400 Report Geotechnical Engineering Services Critical Areas Report Merlino Short Plat Proposed 7-Lot Residential Development Renton, Washington ICE File No. 0864-002 1.0 INTRODUCTION This report summarizes the results of Icicle Creek Engineers’ (ICE’s) geotechnical engineering services for a Critical Areas Report related to our evaluation of the Merlino Short Plat (referred to as the Merlino Property in this report) 7-Lot Residential Development located southwest of the intersection of South 7th Street and Cedar Avenue South in Renton, Washington. The Merlino Property is shown relative to nearby physical features on the Vicinity Map, Figure 1. The general layout of the Merlino Property is shown on the Site Plan, Figure 2. Our services were completed in general accordance with our Proposal dated January 31, 2014 and were authorized in writing by Gary Merlino of the Merlino Land Development Co., Inc. (MLDC) on January 31, 2014. 2.0 SCOPE OF SERVICES The purpose of our services was to review available geologic and geotechnical information and complete a site visit as a basis for evaluating Critical Areas (Geologic Hazards) consistent with the City of Renton Municipal Code (RMC) 4-3-050 (Critical Areas Regulations). Our evaluation of Critical Areas provides recommendations for mitigation, as appropriate, for these areas. Specifically, our services included the following:  Review readily available information concerning project site topography, geology, soil conditions and other relevant site characteristics. Published materials include geologic maps prepared by the US Geological Survey and the Washington State Department of Natural Resources, and geotechnical reports prepared for the I-405 widening project.  Complete a geologic reconnaissance of the property, with particular emphasis on Steep Slope (Protected Slope) areas.  Evaluate the presence of Geologic Hazards including Steep Slopes (Protected and Sensitive Slopes), Coal Mine Hazards, Landslide Hazards, Erosion Hazards, Seismic Hazards, and Volcanic Hazards, as defined by the RMC. Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 2 I c i c l e C r e e k E n g i n e e r s 0864002/042314  Provide recommendations for the width(s) of a building setback from the top edge of the Protected Slope area, as appropriate.  Provide recommendations for the mitigation for design of structures in Geologic Hazard areas (primarily Protected Slope), as appropriate.  Evaluate risk associated with Geologic Hazards and the proposed development pursuant to RMC 4- 3-050J.2 3.0 BACKGROUND INFORMATION ICE previously completed coal mine hazard assessments of the subject property for a previous property owner, GWC, Inc. (GWC); the results of those assessments are presented in our reports dated January 17, 2005 and June 10, 2005. Those reports included what is currently the Merlino Property as well as additional property that GWC owned to the east and south of the southerly part of what is currently the Merlino Property. ICE also completed a hydrogeologic report for GWC dated March 24, 2006 and a geotechnical report for GWC dated September 30, 2005. In addition, ICE completed a coal mine hazard assessment of the Merlino Property; the results of that assessment are summarized in our report dated April 23, 2014. We understand that, subsequent to the reports we prepared in 2005 and 2006, GWC sold the portion of the GWC property that lies between Cedar Avenue South (and its southerly extension) and Interstate 405 (I-405) to the Washington State Department of Transportation (WSDOT) because preliminary plans for I-405 widening indicated encroachment into this property depending on final I-405 roadway configuration and the need for slope support measures. Thereafter, as part of the I-405 widening project, WSDOT’s design-build team for the I-405 widening project, I-405 Corridor Design Builders (CDB), placed excess soil that was excavated from an adjacent portion of the I-405 project onto what is now the Merlino Property (property that at the time was owned by WSDOT). The fill was designed as a Reinforced Soil Slope (RSS – the RSS is referred to as the “Engineered Fill” in the remainder of this report) by CDB (with CDB joint venturer CH2M Hill providing the I-405 project’s geotechnical engineering). David Halinen, attorney for MLDC, forwarded to ICE a copy of the CDB report entitled Technical Memorandum, I-405 Renton Stage 2 Design/Build Project, WSDOT Exchange Property Reinforced Soil Slope, Geotechnical Design Recommendations Memorandum, dated August 14, 2009, a technical memorandum that was prepared specifically for that Engineered Fill. That technical memorandum is attached to this report (Attachment A). Page 6 of the CDB Technical Memorandum states an assumption that “structures (e.g., residences) will be constructed on the Engineered Fill in the future” and noted that the factors of safety (FOS) used in the CDB Technical Memorandum were based on that assumption. For that purpose, CDB evaluated the stability of the Engineered Fill for sliding, global stability, compound failure, internal stability, and seismic stability. The final design of the Engineered Fill required a minimum FOS of at least 1.5 for all the factors evaluated. Mr. Halinen also arranged for ICE to review electronic copies of construction monitoring reports that were obtained by Chad Webley of Gary Merlino Construction Co., Inc. Based on our review of the construction monitoring reports, the construction monitoring was completed on a full-time basis by Mayes Testing Engineers, Inc. (Mayes) of Tacoma, Washington. We reviewed 39 Daily Field Reports (DFRs) that were prepared by Mayes dating from August 22 through October 19, 2009. Field density tests (FDTs) are included with 34 of the DFRs. Based on our review of the FDTs, a total of 109 in-situ field tests using a nuclear densometer were completed by Dan Quelhl of Mayes. It appears that T. Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 3 I c i c l e C r e e k E n g i n e e r s 0864002/042314 Bergstorm and Tom Robinson of Mayes filled-in for Mr. Quehl on at least three days. According to the FDT summary sheets, the fill that was placed on each specified day “meets compaction specifications” and/or “generally meets specifications as indicated by the test numbers.” Based on our review of the DFRs, Mayes was also checking to “assure that the proper type of Geogrid reinforcing was being used and was not damaged; assure the minimum embedment depth was attained according to approved plans & specs; and check that Geogrid was attached together with the subcontractor using twist ties” at the appropriate spacing. Mayes submitted a construction summary letter dated April 23, 2014 (signed and stamped by Michael S. Dolder, PE) for the Engineered Fill construction monitoring; that letter is included in this report as Attachment B. The Mayes summary letter states that “all work inspected was either (1) performed in accordance with or (2) corrected to conform to the I-405 Corridor Design Builder’s Geotechnical Design Recommendations Memorandum dated 8/14/09.” Based on information in the DFRs, it appears that the Engineered Fill mass was substantially completed by October 12, 2009. Based on (1) five Mayes DFRs that were completed after October 12, 2009 and (2) review of 108 date-stamped photographs from October 7 through November 3, 2009, final grading, cutting in and establishing ditchlines, and placement of erosion control fabric on slopes was being completed during that time period. In ICE’s June 2005 coal mine hazard assessment completed for GWC (an assessment that included 12 test pits and three test borings in the area of what is now the Merlino Property), we concluded that a “High Coal Mine Hazard Area” as defined in the RMC exists at the south end of Cedar Avenue South. Additional subsurface evaluation (seven test borings completed during 2009 and used for our current coal mine hazard assessment for the Merlino Property) targeted the High Coal Mine Hazard Area at the south end of Cedar Avenue South consistent with RMC 4-3-050J.1 (Geologic Hazards--Applicability) and RMC 4-3-050J.2 (Geologic Hazards--Special Studies Required). 4.0 PROJECT DESCRIPTION We understand that Core Design, Inc. has prepared a conceptual development plan of the Merlino Property dated March 19, 2014 that includes seven residential lots that are proposed to abut Cedar Avenue South’s west edge. The lots are positioned within the level, upper area (plateau) of the Engineered Fill. The west edge of all of the proposed lots is approximately located at the crest of the Engineered Fill. As part of the conceptual development plan, Cedar Avenue South is proposed to be widened along its west edge, with the widening to include construction of a cul-de-sac bulb at the south end. To construct the cul-de-sac bulb, a “sliver fill” and retaining wall up to about 6-feet thick/high will be required as shown on Figure 2. The sliver fill is to consist of a tapered thickness of soil fill (up to 6- feet thick) along the downhill side of the cul-de-sac where additional space is needed to provide the required radius for the cul-de-sac. An underground concrete stormwater vault is planned within the cul- de-sac bulb area. Water discharge from the stormwater vault will be to an existing rock-lined ditch that runs parallel to and along the north edge of a portion of the existing WSDOT gravel access road that extends toward WSDOT’s stream mitigation area on State-owned property to the south of the Merlino Property. 5.0 REGULATORY ISSUES 5.1 GENERAL Based on regional Critical Areas mapping by the City of Renton (City of Renton Map Gallery – Sensitive Areas) the Merlino Property contains Geologic Hazards including Steep Slopes (Protected and Sensitive Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 4 I c i c l e C r e e k E n g i n e e r s 0864002/042314 Slopes – 08/13/12)), Coal Mine Hazards (08/07/12), Landslide Hazards (08/12/12) and Erosion Hazards (08/13/12). No Seismic Hazards (RMC 4-3-050J.1.d) or Volcanic Hazards (RMC 4-11-220; USGS, 1998, Volcano Hazards from Mount Rainier, Washington, Open-File Report 98-428)are present within the Merlino Property based on the cited references. According to RMC 4-3-050J.2, special geotechnical studies by qualified professionals are required to be prepared when Geologic Hazards are present on a site. 5.2 STEEP SLOPES 5.2.1 Protected Slopes RMC 4-11-190 defines “Protected Slopes” as follows: “A hillside, or portion thereof, with an average slope, as identified in the City of Renton Steep Slope Atlas or in a method approved by the City, of forty percent (40%) or greater grade and having a minimum vertical rise of fifteen feet (15 feet).” Protected Slopes within the Merlino Property are currently present as shown on Figure 2. According to RMC 4-3-050J.5.a, generally “Development is prohibited on protected slopes.” However, an exception to the prohibition may be granted by the City of Renton under various subsections of RMC 4- 3-050J.5, including RMC 4-3-050J.5.d, which is a subsection that states: d. Exceptions through Waiver: Exceptions to the prohibition may be granted for installation of public utilities which are needed to protect slope stability, and public road widening where all the following provisions have been demonstrated: i. The utility or road improvement is consistent with the Renton Comprehensive Plan, adopted utility plans, and the Transportation Improvement Program where applicable. ii. Alternative locations have been determined to be economically or functionally infeasible. iii. A geotechnical evaluation indicates that the proposal will not increase the risk of occurrence of a geologic hazard, and measures are identified to eliminate or reduce risks. iv. The plan for the improvement is based on consideration of the best available science as described in WAC 365-195-905; or where there is an absence of valid scientific information, the steps in RMC 4-9-250F are followed. SubsectIon L (Top and Toe Setbacks) of RMC 4-4-060 (Grading, Excavation and Mining Regulations) addresses setbacks from the top and toe of cut and fill slopes. Subsection L states: 1. Setbacks – Minimum: The tops and toes of cut and fill slopes shall be set back from setback lines as far as necessary to preserve the setback for the safety and benefit of adjacent properties, the adequacy of foundations, and to prevent damage as a result of water runoff or erosion of the slopes. Setbacks shall be no less than the following: a. Tops of Slopes: Distance to the setback line for the top of slopes shall be a minimum of ten feet (10'). Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 5 I c i c l e C r e e k E n g i n e e r s 0864002/042314 b. Structures: Distance to structures, if any structures on the site shall be as follows: Slope Height Top Toe Less than 11’ 5’ 3’ 11 – 30.9’ 7’ Height/2’ 31’ and over 10’ 15’ (Ord. 5526, 2-1-2010) 5.2.1 Sensitive Slopes RMC 4-11-190 defines “Sensitive Slopes” as follows: “A hillside, or portion thereof, characterized by: (1) an average slope, as identified in the City of Renton Steep Slope Atlas or in a method approved by the City, of twenty five percent (25%) to less than forty percent (40%); or (2) an average slope, as identified in the City of Renton Steep Slope Atlas or in a method approved by the City, of forty percent (40%) or greater with a vertical rise of less than fifteen feet (15'), abutting an average slope, as identified in the City of Renton Steep Slope Atlas or in a method approved by the City, of twenty five percent (25%) to forty percent (40%). This definition excludes engineered retaining walls. Sensitive Slopes occurred over much of the Merlino Property prior to placement of the Engineered Fill. However, because of the Engineered Fill, no Sensitive Slopes currently exist within the Merlino Property. 5.3 COAL MINE HAZARDS High and Low Coal Mine Hazards exist within the Merlino Property according to Critical Areas mapping by the City of Renton (Map Gallery – Sensitive Areas) and previous studies of the Merlino Property and adjacent areas by ICE. Coal Mine Hazards are addressed in a separate ICE report dated April 23, 2014. 5.4 LANDSLIDE HAZARDS Prior to placement of the Engineered Fill, the Merlino Property was within a Moderate Landslide Hazard area according to regional Critical Areas mapping by the City of Renton (Map Gallery – Sensitive Areas). Because of the Engineered Fill, the designation of a Moderate Landslide Hazard area should be removed for the Merlino Property. 5.5 EROSION HAZARDS Prior to placement of the Engineered Fill, the Merlino Property was within an Erosion Hazard area according to regional Critical Areas mapping by the City of Renton (Map Gallery – Sensitive Areas). During a recent phone discussion with Steve Lee, Development Engineering Manager of the City of Renton’s Community & Economic Development Department’s Planning Division, Mr. Lee advised that the Erosion Hazard area designation on the Merlino Property now applies to the slope created by the Engineered Fill. This is reflected on Figure 2. 5.6 SEISMIC AND VOLCANIC HAZARDS No Seismic or Volcanic hazards have been regionally mapped by the City of Renton (Map Gallery – Sensitive Areas) or field identified by ICE within the Merlino Property. 6.0 GEOLOGIC SETTING The surficial geology at the site prior to the placement of the Engineered Fill was mapped by the US Geological Survey (USGS - D. R. Mullineaux, 1965, “Geologic Map of the Renton Quadrangle, King Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 6 I c i c l e C r e e k E n g i n e e r s 0864002/042314 County, Washington,” Geologic Quadrangle Map GQ-405) as “undifferentiated glacial sediments” underlain by “Renton Formation” bedrock. Undifferentiated glacial sediments are described by the USGS as consisting of layers of glacial till (ice-deposited silty sand with gravel), glacial outwash (stream- deposited sand and gravel), glaciolacustrine deposits (lake-deposited clay and sand), and nonglacial sand and clay. Renton Formation bedrock is described by the USGS as interbedded (layered) sedimentary rock consisting of sandstone, siltstone, shale, claystone, carbonaceous shale and coal beds. Structurally, the bedrock has been uplifted, folded and faulted over time. This structural deformation of the bedrock has caused the “bedding” of the rock to be tilted about 10 to 14 degrees down to the east in the Merlino Property area. 7.0 SITE CONDITIONS 7.1 SURFACE CONDITIONS Surface reconnaissance of the Merlino Property was completed by Brian Beaman of ICE on April 27, 2009 and again on February 2, 2014. The Merlino Property is located on a west-facing hillside overlooking the City of Renton and is bordered by Cedar Avenue South to the east, the Cedar Crest Condominiums to the north, I-405 to the west, and undeveloped WSDOT-owned forest land and a Puget Sound Energy (PSE) transmission line easement to the south. Before placement of the Engineered Fill, the portion of the subject property immediately west of Cedar Avenue South was characterized by a steep (60 percent grade) road embankment long-ago-created for Cedar Avenue South, an embankment that was about 5- to 15-feet high and that transitioned to a natural slope inclined downward to the west at about a 20 to 30 percent grade. The natural slope flattened gradually to the west. Mine Rock Fill (Coal Spoils) consisting of broken rock and coal fines were observed during our 2005 field reconnaissance and in Test Pits TP-8, TP-14 and TP-16 that were completed for our 2005 study for GWC. Presently, the Engineered Fill has created a nearly-level plateau area that ranges from about 112 feet to 122 feet east-west abutting the west edge of Cedar Avenue South. This plateau area is where the seven residential lots are planned. From the west edge of the plateau, a slope that ICE field-measured as being about 30 degrees (about 1.75H:1V – horizontal to vertical) extends down to the west toward the I-405 right-of-way. The plateau area is vegetated with grass. The bordering slope to the north, west and south of the plateau area (the Engineered Fill slope) is generally vegetated with Douglas-fir trees that are about 8-feet high and shrubs. No surface water was observed within the Merlino Property at the time of our 2009 and 2014 site reconnaissance efforts; these efforts included observation of the ground surface before and after the placement of the Engineered Fill. No surface evidence of landsliding was observed within the Merlino Property at the time of our 2009 and 2014 site reconnaissance efforts. 7.2 ABANDONED UNDERGROUND COAL MINES As previously described, abandoned underground coal mines and related coal mine hazards at the Merlino Property are described in a separate Coal Mine Hazard Assessment report by ICE dated April 23, 2014. This report does not duplicate the description of the abandoned coal mines and coal mine hazards set forth in the separate Coal Mine Hazard Assessment report or the results of subsurface explorations (test pits and test borings) that were set forth in reports completed in 2005 and 2009. Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 7 I c i c l e C r e e k E n g i n e e r s 0864002/042314 However, site data from those reports was used to supplement our understanding of the site subsurface conditions and was used, in part, as a basis for some of the conclusions in this report. 8.0 CONCLUSIONS AND RECOMMENDATIONS 8.1 GENERAL As previously noted, page 6 of the CDB 2009 Technical Memorandum indicated that the Engineered Fill was designed such that residences could be constructed on this fill. CH2M Hill evaluated the stability of the Engineered Fill for sliding, global stability, compound failure, internal stability, and seismic stability. The final design of the Engineered Fill slope required a minimum factor of safety (FOS) of at least 1.5 for all the factors evaluated. 8.2 STEEP SLOPES 8.2.1 Protected Slopes 8.2.1.1 Engineered Fill Slope Most of the Engineered Fill slope that borders the plateau area of the Merlino Property is a Protected Slope according our site observations and the City’s Protected Slope definition in RMC 4-11-190. In view of both (1) above-quoted subsectIon L (Top and Toe Setbacks) of RMC 4-4-060 (Grading, Excavation and Mining Regulations) and (2) our overall assessment of the Engineered Fill, we recommend (a) a building setback of 25 feet from the Engineered Protected Slope area along the west side of all seven of the proposed lots, (b) a building setback of 10 feet from the portion of the Engineered Fill slope area to the north of Lot 1, and (c) a building setback of 10 feet from the portion of the Engineered Fill slope area to the south of Lot 7, as shown on Figure 2. Our above-stated setback distance recommendations are contingent on vegetation in the Protected Slope areas (other than in the general area of the above-noted proposed sliver fill and/or retaining wall to the south and southwest of the southwest edge of the cul-de-sac) not being cut down or otherwise removed. ICE should be contacted to review tree removal plans if selected trees are to be cut down or otherwise removed from the Protected Slope area (other than in the specific area described above for the proposed sliver fill and retaining wall). We recommend that the west edge of the plateau at the crest of the Engineered Slope be slightly bermed/graded to prevent surface water runoff onto the slope from the plateau. Roof downspout drains and footing drains should discharge to a tightline system that discharges away from the Engineered Slope. 8.2.1.2 Protected Slope – Cedar Avenue South In our opinion, the portion(s) of the sliver fill and/or retaining wall proposed to be installed within the Protected Slope area to the south and southwest of the proposed cul-de-sac at the south end of Cedar Avenue South should be approved by the City pursuant to an “exception through waiver” under RMC 4- 3-050J.5.d, provided the following design and construction practices are followed in regard to the sliver fill and retaining wall:  The surface of the applicable portion of the Engineered Fill should be stripped of topsoil and sod, with care taken to not damage the reinforcement fabric in the Engineered Fill.  An Ecology block or similar (gravity-type) retaining wall should be used along the south side of the sliver fill where the wall height exceeds 2.5 feet, otherwise a rockery or modular block wall may be Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 8 I c i c l e C r e e k E n g i n e e r s 0864002/042314 used. Ecology blocks and Ultra Blocks are typically about 2.5- to 3-feet high and 5- or 6-feet long. ICE can provide design criteria for a gravity-type retaining wall system, if requested.  The proposed retaining wall system, once the final design is known, should be evaluated by ICE for overall stability.  Proper surface and subsurface drainage should be installed to reduce the potential for accumulation of ground water and to reduce the risk of erosion.  New fill should be compacted as Structural Fill. Structural Fill should be compacted to at least 95 percent of the maximum dry density obtained using ASTM Test Method D 1557.  Construction of the retaining wall and fills should be completed during an extended period of dry weather.  ICE should be retained to review the construction plan for the cul-de-sac at the south end of Cedar Avenue South once the design details are available.  ICE should be retained to observe and document the construction of the retaining wall and placement of Structural Fill for the retaining wall at the south end of Cedar Avenue South. 8.2.2 Sensitive Slopes As previously described, all Sensitive Slope areas within the Merlino Property have been eliminated by the Engineered Fill. No recommendations for mitigation are needed. 8.3 COAL MINE HAZARDS High and Low Coal Mine Hazards exist within portions of the Merlino Property. Coal Mine Hazards are addressed in a separate ICE report dated April 23, 2014. 8.4 LANDSLIDE HAZARDS The designation of a Moderate Landslide Hazard area should be removed because the Engineered Fill has mitigated this hazard designation. No recommendations for mitigation are needed. 8.5 EROSION HAZARDS As described above, the Erosion Hazard area designation applies to the slope created by the Engineered Fill as shown on Figure 2. Except as noted in the next paragraph, the Engineered Slope will not be disturbed by the development process. For this reason, no special erosion control measures are required other than assuring that the no stormwater runoff is allowed to flow to the slope area (other than the planned discharge from the proposed stormwater detention vault into the existing rock-lined ditch that runs parallel to and along the north edge of the existing gravel access road. We recommend that Core Design evaluate planned flow from the stormwater vault and the ability of the existing rock- lined ditch to accommodate this flow. Construction of the cul-de-sac bulb area will require disturbance of (1) the portion of the Erosion Hazard area underlying part of the southwesterly quadrant of the proposed cul-de-sac bulb and (2) the abutting sliver fill area. Proper temporary erosion and sediment control measures in accordance with local regulations should be provided within the project plans for these areas. 8.6 SEISMIC AND VOLCANIC HAZARDS No Seismic or Volcanic Hazards have been regionally mapped by the City of Renton or field identified by ICE within the Merlino Property. Thus, no recommendations for mitigation are needed. Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 9 I c i c l e C r e e k E n g i n e e r s 0864002/042314 9.0 RISK EVALUATION 9.1 COMMENTS RELATING TO SUBSECTIONS (iii) AND (iv) OF RMC 4-3-050J.5.d The above-stated design and construction practices are recommended to reduce risks. If these design and construction practices are implemented, in our opinion the proposal to modify the Engineered Slope in the area near the cul-de-sac with a sliver fill and retaining wall should not increase the risk of slope failure to an unacceptable level (FOS less than 1.5). In addition, the planned sliver fill and retaining wall improvement within the Protected Slope in the cul-de-sac bulb area is being designed using locally accepted current standards of engineering practice (“best available science” as described in WAC 365-195-905). 9.2 COMMENTS RELATING TO RMC 4-3-050J.2 Consistent with RMC 4-3-050J.2, (1) the project should not increase the risk of Geologic Hazards to adjacent or abutting properties beyond pre-development conditions, (2) the project should not adversely impact other Geologic Hazards, and (3) the development can be safely accommodated on the site with careful planning by the design team. 10.0 USE OF THIS REPORT We have prepared this report for use by Merlino Land Development Co., Inc. The data and report should be used for land use planning, but our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. There are probable variations in subsurface conditions between the explorations completed for other studies; variation in subsurface conditions also may occur over time. A contingency for unanticipated conditions should be included in the short plat infrastructure’s construction budget and schedule. During construction, sufficient observation, testing and consultation by our firm should be provided to (1) evaluate whether the conditions encountered are consistent with those indicated by the explorations, (2) provide recommendations for design changes if the conditions encountered during construction differ from those anticipated, and (3) evaluate whether earthwork activities comply with contract plans and specifications. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in this area at the time the report was prepared. No warranty or other conditions, express or implied, should be understood. ******************* Merlino Land Development Co., Inc. Attn: Gary Merlino April 23, 2014 Page 10 I c i c l e C r e e k E n g i n e e r s 0864002/042314 We trust this information meets your present needs. If you have any questions or if we can be of further assistance to you, please call. Yours very truly, Icicle Creek Engineers, Inc. Brian R. Beaman, PE, LEG, LHG Principal Engineer/Geologist/Hydrogeologist Kathy S. Killman, LEG Principal Engineering Geologist Document ID: 0864002.REP Attachments: Vicinity Map – Figure 1 Site Plan – Figure 2 Attachment A – I-405 CDB Technical Memorandum, August 14, 2009 Attachment B – Mayes Testing Engineers, Inc. Construction Summary Letter, April 23, 2014 Submitted via surface mail (three original copies) cc: David Halinen, Halinen Law (email as pdf, surface mail – one original copy) I c i c l e C r e e k E n g i n e e r s 0864002/042314 FIGURES 0 ICE FILE NUMBERIcicle Creek Engineers, Inc. 29335 NE 20th Street Carnation, Washington 98014 (425) 333-0093 FigureCHECKED: KSK DRAWN: BRB DESIGNED: --- SCALE: As Shown DATE: April 23, 2014 MERLINO SHORT PLAT - PROPOSED 7-LOT RESIDENTIAL DEVELOPMENT RENTON, WASHINGTON VICINITY MAP 1 0864-002 2,0000 4,000BensonRoadBensonRoadMerlino Property Approximate Scale in Feet ICE FILE NUMBERIcicle Creek Engineers, Inc. 29335 NE 20th Street Carnation, Washington 98014 (425) 333-0093 Figure 0864-002 CHECKED: KSK DRAWN: BRB DESIGNED: --- SCALE: 1 inch - 100 feet DATE: April 23, 2014 MERLINO SHORT PLAT - PROPOSED 7-LOT RESIDENTIAL DEVELOPMENT RENTON, WASHINGTON 2 SITE PLAN EXPLANATION Protected Slope Area (RMC 4-11-190) Building Setback (RMC 4-4-060L)South 7th StreetBase map reference: Core Design, March 19, 2014, Merlino Short Plat, Renton, Washington, Preliminary Site Plan. 25 feet10 feet10 feetCedar Avenue SouthCedar Avenue South Approximate Scale in Feet 0 100 200 Retaining Wall Sliver Fill WSDOT Property Merlino Property Proposed Right-of-Way Line Existing Right-of-Way Line Erosion Hazard Area (RMC 4-3-050Q.3.b) I c i c l e C r e e k E n g i n e e r s 0864002/042314 ATTACHMENT A I-405 CORRIDOR DESIGN BUILDERS TECHNICAL MEMORANDUM DATED AUGUST 14, 2009 I-405 RENTON STAGE 2 DESIGN/BUILD PROJECT WSDOT EXCHANGE PROPERTY REINFORCED SOIL SLOPE GEOTECHNICAL DESIGN RECOMMENDATIONS MEMORANDUM REV 0 RTN/RS2_EXCHANGEPOPERTY_RSS_DESIGNRECOMMENDATIONS_REV0_081409.DOC 2 COPYRIGHT 2009 BY I-405 CORRIDOR DESIGN BUILDERS • COMPANY CONFIDENTIAL Subsurface Conditions Geotechnical conditions for the WSDOT Exchange Property area were established on the basis of existing geotechnical explorations supplemented by 3 new explorations advanced by Icicle Creek Engineers in support of the Renton Stage 2 Project. The new boring logs were used with the existing site soil information to develop geotechnical parameters for analysis and design of RSS slope. Geotechnical Explorations The following exploration locations were used in the evaluation of the site conditions and in the creation of soil profiles beneath the RSS. The boring and test pit logs were also used to develop geotechnical parameters for analysis and design of the RSS. The source of the exploration information is summarized in Table 1. Figure 2 shows the approximate locations of the explorations. Figure 3 shows the interpreted typical subsurface. Copies of the exploration logs are included in Attachment B. TABLE 1: WSDOT EXCHANGE PROPERTY EXPLORATION LOCATIONS Exploration Location Type Source B-1 Boring Icicle Creek Engineers, Inc., 2005 B-2 Boring Icicle Creek Engineers, Inc., 2005 B-3 Boring Icicle Creek Engineers, Inc., 2005 TP-1 Test pit Icicle Creek Engineers, Inc., 2005 TP-2 Test pit Icicle Creek Engineers, Inc., 2005 TP-3 Test pit Icicle Creek Engineers, Inc., 2005 TP-4 Test pit Icicle Creek Engineers, Inc., 2005 TP-5 Test pit Icicle Creek Engineers, Inc., 2005 TP-6 Test pit Icicle Creek Engineers, Inc., 2005 TP-7 Test pit Icicle Creek Engineers, Inc., 2005 TP-8 Test pit Icicle Creek Engineers, Inc., 2005 TP-12 Test pit Icicle Creek Engineers, Inc., 2005 TP-13 Test pit Icicle Creek Engineers, Inc., 2005 TP-14 Test pit Icicle Creek Engineers, Inc., 2005 TP-15 Test pit Icicle Creek Engineers, Inc., 2005 TP-16 Test pit Icicle Creek Engineers, Inc., 2005 515-4-06 Boring Geoengineers, 2007 CDB-6p-08 Boring Geoengineers, 2007 SRX-20-05 Boring Geoengineers, 2007 REV 0 RTN/RS2_EXCHANGEPOPERTY_RSS_DESIGNRECOMMENDATIONS_REV0_081409.DOC 3 COPYRIGHT 2009 BY I-405 CORRIDOR DESIGN BUILDERS • COMPANY CONFIDENTIAL TABLE 1: WSDOT EXCHANGE PROPERTY EXPLORATION LOCATIONS Exploration Location Type Source 515-6-06 Boring Geoengineers, 2007 515-7-06 Boring Geoengineers, 2007 B-5 Boring Icicle Creek Engineers, Inc., 2009 B-10 Boring Icicle Creek Engineers, Inc., 2009 B-11 Boring Icicle Creek Engineers, Inc., 2009 Icicle Creek Engineers, Inc., “Report- Coal Mine Hazard Assessment and Preliminary Geotechnical Evaluation, Renton Hill Property, King County Parcel Nos. 2023059085 and 0007200194/196, Renton, Washington,” June 10, 2005. GeoEngineers, 2007, “Geotechnical Baseline Report I-405/1-5 to SR 169 Stage 2 – Widening and SR 515 Interchange, Renton, Washington,” September 7, 2007. Icicle Creek Engineers, Inc., “Report, Geological Engineering Services, Coal Mine Hazard Assessment, WSDOT Property, Renton, Washington,” May 11, 2009. Interpreted Geotechnical Conditions and Groundwater Location The existing WSDOT Exchange property is an undeveloped parcel of land located on the hillside between I-405 and Cedar Avenue. Slopes vary from 5 to over 90 percent, with slope lengths varying from 25 to over 100 feet. The site elevation varies from approximately 140 feet to 230 feet. The general subsurface profile consists of colluvium/fill overlying residual soils weathered from the Renton Formation overlying the Renton Formation. The colluvium/fill/residual soils are difficult to distinguish from each other and are considered as one unit for the analysis. The site is underlain by the Renton Formation sandstone bedrock. In the southwest portion of the site there are deposits of materials consisting of mine tailings and old municipal waste that are associated with the abandoned Renton Civic Dump site. The general characteristics of the predominant geologic units are as follows: • The colluvium/fill/residual soils vary from ~1 foot to 10 feet thick over the site. These soils are generally medium dense and consist primarily of silty sand. • The tailings/municipal waste thickness varies from a thin veneer to over 25 feet thick. These soils are loose to medium dense and contain a wide variety of materials including silt, sand, slag, ashes, glass, metal, debris, and other materials associated with municipal waste disposal. Mine tailings may also be incorporated in this material, either as cover soils, or as a result of previous mining activities that occurred in the same area. • The Renton Formation consists of weak sandstone bedrock with occasional siltstone layers and extends below the depth explored with borings at the site. Boring log information indicates that groundwater was found generally in the Renton Formation, below elevation 100 feet. REV 0 RTN/RS2_EXCHANGEPOPERTY_RSS_DESIGNRECOMMENDATIONS_REV0_081409.DOC 4 COPYRIGHT 2009 BY I-405 CORRIDOR DESIGN BUILDERS • COMPANY CONFIDENTIAL Seismicity and Ground Motions The Renton Stage 2 Project is being designed in accordance with WSDOT’s current seismic design requirements. These requirements include use of a design earthquake that has a 7 percent probability of exceedance in a 75-year exposure period. The seismic ground motions and liquefaction potential for this design earthquake are summarized below. Seismic Ground Motions Design peak ground acceleration (PGA) of 0.44g is used in analysis. This ground motion was determined using the AASHTO ground motions hazard map and a site coefficient for peak ground acceleration (Fpga) of 1.0 based on Site Class C site classification. Per the WSDOT GDM (2008), a horizontal pseudo-static acceleration coefficient, kh = 0.22 (F*PBA/2) was used in the global stability analysis. Use of this reduced seismic coefficient implies that several inches of permanent slope displacement is acceptable during the design seismic event. Liquefaction Potential Soils at the project site below the water table are the sandstone bedrock; therefore, liquefaction potential of site soils is very low. Surface water will be routed from the RSS and fill to prevent infiltration and possible ponding of water within the compacted fill layers and RSS. Geotechnical Design The design of RSS follows the steps outlined in Chapter 7 of FHWA Publication FHWA- NHI-00-043, “Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines,” by Elias, et al. (2001). General Design Considerations The general design considerations for this project are listed below. • Traffic Surcharge assumed equivalent to 2.0 feet of soil surcharge (surcharge unit weight = 125 pcf) = 125 pcf x 2 feet = 250 psf. • Extensible (geosynthetic geogrid) reinforcement is to be used. • A wrapped face is not required because the slope is shallower than 1.2(H):1(V) (GDM, 2008). • Minimum length of reinforcing is 6 feet (GDM, 2008). • Primary reinforcing shall be vertically spaced at 3 feet or less (GDM, 2008). • Minimum long-term allowable strength of primary reinforcing = 1,250 lb/ft. REV 0 RTN/RS2_EXCHANGEPOPERTY_RSS_DESIGNRECOMMENDATIONS_REV0_081409.DOC 5 COPYRIGHT 2009 BY I-405 CORRIDOR DESIGN BUILDERS • COMPANY CONFIDENTIAL • Secondary reinforcing between layers of primary reinforcing shall be at a maximum vertical spacing of 1 foot (GDM, 2008). Secondary reinforcing shall not be included in the internal stability analysis of the RSS. • Minimum long-term allowable strength of secondary reinforcing = 115 lb/in. • Backfill within the reinforced zone of the RSS shall consist of Common Borrow, meeting the requirements of WSDOT Standard Specifications Section 9-03.14(3), as modified in the Project Technical Specification drafted for the RSS. As follows: Sieve Size Percent Passing 3-inch 100 No. 4 100 - 20 No. 200 0 - 35 Geotechnical Material Properties The following properties were used in the design of the RSS: New Fill: • Unit weight = 130 pcf • Internal angle of friction = 36 degrees • Cohesion (static case) = 0 psf • Internal angle of friction (seismic case) = 34 degrees • Apparent cohesion (seismic case) = 200 psf Residual soil/colluvium/fill: • Unit weight = 130 pcf • Internal angle of friction = 36 degrees • Cohesion (static case) = 0 psf • Apparent cohesion (seismic case) = 200 psf Renton Formation: • Uniaxial compressive strength = 300 psi (43.2 ksf) • Geologic strength index (GSI) = 40 • Intact rock constant (mi) for sandstone = 17 • Disturbance factor (D) for good quality excavation = 0.0 • Mohr-Coulomb fit (Hoek-Brown Criteria), internal angle of friction = 32 degrees • Mohr-Coulomb fit (Hoek-Brown Criteria), cohesion (seismic and static cases) = 2100 psf Municipal Waste: • Unit weight = 115 pcf • Internal angle of friction = 28 degrees • Cohesion (static case) = 300 psf • Apparent cohesion (seismic case) = 300 psf REV 0 RTN/RS2_EXCHANGEPOPERTY_RSS_DESIGNRECOMMENDATIONS_REV0_081409.DOC 6 COPYRIGHT 2009 BY I-405 CORRIDOR DESIGN BUILDERS • COMPANY CONFIDENTIAL Reinforcement Length Requirements Analyses were conducted at selected sections along the RSS to evaluate the minimum reinforcement lengths (Lmin) required to satisfy stability requirements. The analytical results were compared to GDM minimum acceptable criteria shown below. • Sliding FS 1.5 • Global Stability (outside of reinforced zone) FS 1.5 • Compound Failure (through face of RSS) FS 1.5 • Internal Slope Stability (through the reinforcing) FS 1.5 • Lateral Squeeze (bearing failure) FS 1.5 • Seismic Stability FS 1.1 The above factors of safety assume that structures (e.g., residences) will be constructed on the RSS fill in the future. For sliding, global stability, compound failure, internal stability, and seismic stability evaluations, the computer program SLIDE (Rocscience, 2008) was used. Lateral squeeze does not apply because the RSS is founded on competent bearing materials. To achieve the required FS, a geogrid with minimum long-term design strength of 1,250 lb/ft, coupled with the reinforcement lengths summarized in Table 2, is required. The length of reinforcing was generally controlled by a combination of static and seismic stability. The approximate station extents for the different Lmin are summarized in Table 2. All stations are based on a construction reference alignment CEDAR RW Line. For a given embankment location, all reinforcing lengths are constant for the entire embankment height. TABLE 2: REINFORCEMENT TABLE Beginning Station Ending Station Minimum Reinforcement Length (Lmin) Bottom Reinforcing Elevation (ft) Top Reinforcing Elevation (ft) 10+35 10+75 25 200 Varies, max 220 10+75 11+50 40 194 220 11+50 11+75 40 182 220 11+75 12+50 50 172 222 12+50 13+00 45 172 222 13+00 13+75 40 176 222 13+75 14+50 40 172 224 14+50 15+45 40 172 226 15+45 15+95 40 172 Varies, max 226 REV 0 RTN/RS2_EXCHANGEPOPERTY_RSS_DESIGNRECOMMENDATIONS_REV0_081409.DOC 7 COPYRIGHT 2009 BY I-405 CORRIDOR DESIGN BUILDERS • COMPANY CONFIDENTIAL Settlement Due to the granular consistency and/or heavily overconsolidated nature of the existing soils and bedrock, settlement is anticipated to be elastic in nature and is expected to occur during embankment construction. Construction Requirements The construction of the RSS and backfill require careful planning and construction control, including oversight by the project geotechnical engineer, to assure that the slope is constructed in such a manner that short- and long-term stability requirements are met. The following subsection summarizes key construction requirements. Specific requirements for construction of the RSS are included in the technical specification Reinforced Soil Slope, I.5:1 (Horizontal to Vertical) Slopes, included as Attachment C to this memorandum. Subgrade Preparation and Ground Improvement Before placement of fill or backfill for the RSS, all surface vegetation, topsoil, trash, construction debris, or other deleterious materials shall be removed from beneath the reinforced soil zone and properly disposed of offsite. Loose, soft, or wet material should also be removed and replaced with competent backfill. All sharp stone protrusions that could damage the reinforcing should also be removed. The subgrade within the footprint of the reinforced soil volume should be graded level as required for construction, proof rolled, and compacted to 95% of Standard Proctor Density (ASTM D698, AASHTO T99). Fill shall be keyed into the existing slope following Section 2- 03.3(14) “Hillside Terraces” of the Standard Specifications. Because of the variable nature of the site fill, field review and approval of the RSS subgrade and construction site preparation below the RSS by the project geotechnical engineer is required. Overexcavation may be required in areas where actual subgrade conditions do not meet the design recommendations. Depth and extent of overexcavation will be as directed by the geotechnical engineer. Fill and Backfill Requirements Backfill within the reinforced zone of the RSS shall consist of Common Borrow, meeting the requirements the RSS Project Technical Specification. The borrow source is expected to be the Renton Formation that is excavated to construct other project elements. The backfill material must be free of organics and other deleterious materials. The maximum particle size should be 3 inches. If wet-weather construction makes it difficult to achieve the required moisture and compaction density, Select Borrow (Section 9-03.14(2)) or Gravel Borrow (Section 9-03.14(1)) shall be used in lieu of Common Borrow. Backfill in the reinforced zone shall be placed in loose lifts of maximum 12-inch thickness and compacted to 95% of maximum density in accordance with the requirements of Section 2-03.3(14)C, Method C, of the WSDOT Standard Specifications and the project-specific technical specification (see Attachment C). REV 0 RTN/RS2_EXCHANGEPOPERTY_RSS_DESIGNRECOMMENDATIONS_REV0_081409.DOC 8 COPYRIGHT 2009 BY I-405 CORRIDOR DESIGN BUILDERS • COMPANY CONFIDENTIAL Backfill behind the reinforced zone shall be Common Borrow in accordance with the requirements of Section 9-03.14(3) of the Standard Specifications, provided that the material can be compacted in accordance with the requirements of Sections 2-03.3(14)C and 2- 03.3(14)D of the Standard Specifications. If wet-weather construction makes it difficult to achieve the required moisture and compaction density, Select Borrow (Section 9-03.14(2)) or Gravel Borrow (Section 9-03.14(1)) may be used in lieu of Common Borrow. Temporary Excavation Limited excavation may be required in order to construct the reinforced soil slope. Temporary excavations sloped to 1:1 should perform adequately during construction. If the Renton Formation bedrock is encountered in temporary excavations needed to place reinforcing grids, the lengths of the geogrid may be reduced, provided the project geotechnical engineer is notified in advance to verify subsurface conditions. In no case shall the reduced length of reinforcing be keyed into the Renton Formation less than 5 feet. Existing Utilities No known utilities cross beneath the proposed the RSS footprint. If any are encountered during construction, they should be brought to the attention of the project geotechnical engineer. In no case should the arrangement of slope reinforcing by modified to accommodate utilities without the approval of the project geotechnical engineer. Drainage and Erosion Control Temporary construction slopes shall direct water away from the RSS slope face to prevent erosion. The face of the RSS shall be stabilized following project temporary erosion and sediment control procedures and shall be planted with permanent vegetation in accordance with the project landscaping plans. References AASHTO (2002). Standard Specifications for Highway Bridges, 17th Edition (2002) – Allowable Stress Design. American Association of State Highway and Transportation Officials, 2002. AASHTO (2007). AASHTO LRFD Bridge Design Specifications, Fourth Edition. American Association of State Highway and Transportation Officials, 2007. FHWA (2001). Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines. U.S. Department of Transportation, Federal Highway Administration. FHWA-NHI-00-043. March 2001. RocScience (2008). SLIDE Version 5.0 - User’s Manual. WSDOT (2008). Geotechnical Design Manual. Washington State Department of Transportation. WSDOT (2008). Standard Specifications for Road, Bridge, and Municipal Construction. Washington State Department of Transportation. M41-10. 90100100 100 100100100 110110 110 110 110110 120120 120120120120 130 130 13 0 130 130 130 130140140140 140140140 150150 150 150 150 1 5 0 160160160 160 160 160 170 170 170 170 170 170 170180180 180 180 180180 190190 190 190 190 19020 0 200 200 200 200 200210 210 210 210 210210220 220 220 220 220 220230230230 230 230 230 240240240240 ROW CLF CLF 200 NO. Washington State Department of Transportation ISSUE DATE ISSUE RECORD - DESCRIPTION DESIGNED BY ENTERED BY CHECKED BY WASH10 NO. DESIGN MANAGER: DESIGN TASK LEAD: PACKAGE: REGION STATE CONTRACT NO. P.E. STAMP BOX DATE B 07/29/09 K. LORENTSONFINAL DESIGN - 1B M. ROHILAC. HERMOGENES 08/14/09 K. LORENTSON M. ROHILAC. HERMOGENES0RELEASE FOR CONSTRUCTION - 1B WSDOT EXCHANGE PROPI-405 AND SR 515 INTERCHANGE STAGE 2 - WIDENING I-5 TO SR 169 SHEET OF SHEETS 7624_04_CG_1_01.dlv2:48:56 PM8/12/20097624150160 160 170170 170 180 180 180 190 190 190200 200 200210 210 220220 230 230230 1110 12 13 14 15 16 9 100101102103EE R.J NO RTHBOUND I-405 SOUTHBOUND I-405 J. BAUMAN K. LORENTSON SCALE IN FEET 0 30 60 A T. 23N. R. 5E. W.M. CG-0-02 CG-0-02 CEDAR RW LINE A S. FORMAN C. HERMOGENES CEDAR AVE S 1230 1230 B 06/19/09 PRELIMINARY DESIGN NB405 LINE SB405 LINE LEGEND 200 1.5:1CUT LINE CG-0-01 NOTES:2:12:11.5:11.5:12:1FILL LINE1.5:12:1 1.5:1 2:1 1.5:12:1 1 .5 :1 2:11.5:12:1 1.5:1 CEDAR RW 10+91.62, 113.77’ RT ELEV 228.00 CEDAR RW 11+63.35, 113.00’ RT ELEV 230.00 CEDAR RW 12+86.86, 8.00’ LT ELEV 232.00 CEDAR RW 11+89.62, 8.00’ LT ELEV 230.00’ CEDAR RW 13+74.52, 114.82’ RT ELEV 234.00 CEDAR RW 14+69.96, 115.25’ RT ELEV 236.00 CEDAR RW 14+00.63, 8.00’ LT ELEV 234.00 CEDAR RW 15+39.28, 118.95’ RT ELEV 236.00 CEDAR RW 15+99.89, 0.00’ RT ELEV 238.00 CEDAR RW 14+97.08, 8.00’ LT ELEV 236.00 CONTOUR GRADING WSDOT EXCHANGE PROPERTY2:1CEDAR RW 12+60.26, 113.59’ RT ELEV 232.00 CEDAR RW 10+97.21, 10.78’ LT ELEV 228.00’ N1^26’53.75"E 2:1 A. BASTASCH DITCH, SEE DRAINAGE PLANS VARIES 2:1 MAX STREAM BUFFER THUNDER HILLS CREEK EXISTING MAJOR CONTOUR EXISTING MINOR CONTOUR PROPOSED MAJOR CONTOUR PROPOSED MINOR CONTOUR STREAM/ WETLAND BUFFER SLOPE ARROW LIMITED ACCESS WSDOT ROW AR LI NE 1. 2. 3. 4. ACCESS SEE CG-0-05 1.5:1 629 CEDAR AVE S CONDOMINIUMS FOR DITCH PROFILES, SEE DRAINAGE PLAN AND PROFILES. FOR SLOPE ROUNDING, SEE DLS-0-02. FOR REINFORCED SOIL SLOPE DETAILS, SEE SHEET CG-0-04. FOR EXISTING UTILITIES, SEE UTILITY PLANS. RFC - 1B E405 L INE LIMITS OF FILL WITHIN WSDOT RIGHT-OF-WAY NOT TO EXCEED SIX (6) FEET IN HEIGHT AND NOT TO ENCROACH OVER FILL LINE SHOWN Dense BrushTreesTreesTreesDense BrushBrushBrushBrushSSSSSSSSRandomSIGN Request 140780TR_SN_OverheadSignTR_SN_OverheadSignUTILITY Request 1TP_MM_UnknownObjectTP_MM_UnknownObjectRD_BR_BarrierFaceRD_BR_BarrierFace31379Copy of GEOTECH Request 1Random"EXIT 4""900 WEST""169 SOUTH"100100110110120120120130130130140140140 150150150160160160170170170180180180190190190200200200210210210220220220230230230240240240250250BL_LN_BreaklineGenericBL_LN_BreaklineGeneric1000Book 1BreaklineWSDOT EXCHANGE PROP!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>!>CEDAR AVENB I-405B-5B-3B-2B-1B-11B-10TP-8TP-7TP-6TP-5TP-4TP-3TP-2TP-1TP-16TP-15TP-14TP-13TP-12515-7-06515-6-06515-4-06SRX-20-05CDB-6p-08050 100 150 20025Feet³Figure 2: WSDOT Exchange PropertySubsurface Investigation Locations I c i c l e C r e e k E n g i n e e r s 0864002/042314 ATTACHMENT B MAYES TESTING ENGINEERS, INC. CONSTRUCTION SUMMARY LETTER DATED APRIL 23, 2014 REINFORCED SOIL SLOPE AT WSDOT EXCHANGE PROPERTY