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City of Renton Heather -Downs Interceptor Improvements Feasibility Report August 2008 Prepared By Roth Hill Engineering Partners, LLC 2600 — 116'h Avenue NE #100 Bellevue, WA 98004 (425) 869-9448 Rich rd Hefti, P August Zoos TABLE OF CONTENTS ' Page No. INTRODUCTION AND PURPOSE......................................................................................1 GEOTECHNICAL REPORT.....................................................................................................2 ' POTENTIALPIPE ROUTES....................................................................................................2 SurfaceAlternative 2............................................................................................................. 3 Trenchless Alternative 1........................................................................................................3 ' Trenchless Alternative 2........................................................................................................3 TrenchlessAlternative 3........................................................................................................3 ' PERMIT REQUIREMENTS......................................................................................................4 SensitiveAreas..................................................................................................................... 4 King County Clearing and Grading Permit.............................................................................6 ' King County Wastewater Treatment Division Approval.........................................................6 OtherPotential Permits.........................................................................................................6 EASEMENTREQUIREMENTS...............................................................................................7 ' PRELIMINARY ENGINEERING ANALYSIS..........................................................................7 Hydraulic Consideration — Alternative B1..............................................................................7 Scenario No. 1 - Heather Downs 2001 Model.......................................................................9 ' Scenario No. 3 - The Heather Downs Ultimate Model with Mini -Basin U3A.........................10 Hydraulic Consideration — Moderately Surcharged Lines....................................................12 Geotechnical Considerations..............................................................................................13 ' PIPEMATERIAL OPTIONS...................................................................................................14 DuctileIron.........................................................................................................................14 PolyvinylChloride..............................................................................................................15 HighDensity Polyethylene.................................................................................................15 CONSTRUCTIONMETHODS...............................................................................................16 ' Ground Surface (On -Grade) Installation..............................................................................16 Hand -dug Shallow Trench Construction..............................................................................17 TrenchConstruction............................................................................................................17 ' Horizontal Directional Drilling..............................................................................................18 IDENTIFICATION AND SELECTION OF ALTERNATIVES................................................19 PipeMaterial Selection.......................................................................................................20 ConstructionCost Estimating.............................................................................................. 20 SurfaceAlternative 2...........................................................................................................21 Trench................................................................................................................................. 21 Trench and Ground Surface................................................................................................21 Trenchless Alternative 1......................................................................................................21 TrenchlessAlternative 2......................................................................................................22 ' Trenchless Alternative 3......................................................................................................22 PIPEREPLACEMENT...........................................................................................................22 ' CONCLUSION........................................................................................................................23 RECOMMENDATIONS..........................................................................................................24 City of Renton ' Heather Downs Interceptor Improvements Feasibility Report Page i August 2008 ' LIST OF TABLES Table 1 Construction Cost Estimate for Surface Alternative 2.............................................21 ' Table 2 Alternative Summary .............................................................................................23 Table 3 Estimated Project Cost..........................................................................................24 ' LIST OF FIGURES Figure A Interceptor Route and Discharge Point...................................................................2 Figure B Excerpt from City of Renton Landslide Hazard Area Map.......................................4 ' Figure C Excerpt from City of Renton Erosion Hazard Map...................................................5 Figure D Excerpt from City of Renton Aquifer Protection Map...............................................6 Figure E Scenario 1 (excerpt from Figure 2A — Updated in Appendix B) ..............................9 ' Figure F Scenario 3 (excerpt from Figure 3A Updated in Appendix B)...............................10 Figure G Recommended Improvements..............................................................................11 Figure H Existing Moderately Surcharged Pipe...................................................................22 APPENDICES Appendix A — Alternatives Map ' Appendix B — Hydraulic Analysis Results Appendix C — Shannon & Wilson Preliminary Geotechnical Report ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page ii August 2008 INTRODUCTION AND PURPOSE In 2006, the City of Renton requested that Roth Hill Engineering perform an analysis of the sewer system piping, within the Heather Downs area, in order to identify any capacity problems created by increased population density, infiltration and inflow (W), and added upstream flows associated with Ultimate design flows. The resulting Heather Downs Sewer System Analysis report dated December 2006 highlighted pipe segments of the existing interceptor sewer that will operate under moderate to severe surcharged conditions as the Basins served by the interceptor reach their planned density. Surcharging slows velocities, which allows sediment deposition and accumulation in the pipe. This in turn slows velocities more, allowing even more sediment accumulation that eventually can plug the pipe and create unwanted backups to the end user. Additionally, the system analysis report recommended the City address capacity issues in ' the existing Heather Downs interceptor sewer through various upgrades to the existing system. The recommended solution from the System Analysis Report was "Alternative B1 — Trenchless Construction". Roth Hill recommended constructing a 10-inch diameter relief ' sewer from the plateau to the valley floor and upsizing the existing sewers on the plateau using pipe bursting technology. Appendix A shows the proposed 10-inch diameter relief sewer alternatives that will re -direct upstream flows to an underused existing 15-inch ' diameter sanitary sewer within the Maplewood Golf Course. It also shows the proposed 12-inch diameter sewer line, which will replace existing 8-inch and 10-inch diameter sewer pipe that was identified as "highly surcharged" by the hydraulic model. ' The purpose of this feasibility study is to evaluate the most cost effective alignment and construction method to build the proposed 10-inch diameter relief sewer from the plateau to the existing sewer in the Maplewood Golf Course. This report will also identify relevant regulatory and easement issues along with implementation considerations for the project and includes estimates of probable construction costs. The report concludes with ' recommendations for pipe routes in order to proceed with the design and construction of the project. ' Figure A shows the Heather Downs Interceptor route and its discharge point into the King County Trunk at Manhole RE*CEDAR2.R10-26A near the intersection of SE 5ch Street and Maple Valley Highway (SR 169). The Heather Downs Interceptor serves Mini -Basin 25, a ' portion of Mini -Basin 46, and Mini -Basin U3A. City of Renton ' Heather Downs Interceptor Improvements Feasibility Report Page I Roth Hill Engineering Partners, LLC RothHill LETTER OF TRANSMITTAL To: Dave Christensen Planning/Building/Public Works Renton City Hall - 5th Floor 1055 South Grady Way Renton, WA 98055 Please find: ❑ Herewith via: UPS 2600 116`' Avenue NE, Suite 100 Bellevue, Washington 98004 Tel. 425.869.9448 800.835.0292 Fax 425.869.1190 Date: August 4, 2008 Client: City of Renton Contract No: Project No: 0015.00016.001 Subject: Heather Downs Interceptor Upgrade Feasibility Study COPIES DATE NO. DESCRIPTION 2 Aug2008 FINAL Heather Downs Interceptor Feasibility Stud THESE ARE TRANSMITTED as checked below: ❑ As requested ® For your file ❑ Approved as noted ❑ For review and comment ❑ For your information ❑ Returned for corrections ❑ For approval ❑ Approved as submitted ❑ Resubmit copies REMARKS: Included are two copies of the Feasibility Study for your files. Please let me know if you have any comments or questions. COPIES: file SIGNED: F.\0015\00016.001\Feasibility Study #28615\DC_e1w_080408_Transmtl_Final F_rik Waligors PE Feasibility Study doc August 2008 Figure A Interceptor Route and Discharge Point ••. n44 , 43 Heather Downs —� _ 4,= .. _"'• ,E,„ Interceptor Study Area Boundary 14�-- ' •f • • �,. • gE 1i „ W '+E VV i yy • • 2 Heather Downs _ ,• Interceptor -- �T .n ■onw ti_, t GEOTECHNICAL REPORT Roth Hill retained Shannon & Wilson as a geotechnical subconsultant to address issues associated with constructing a sanitary sewer pipeline down a steep slope. A copy of their preliminary geotechnical report is included as Appendix C. The Shannon & Wilson investigation was limited to field reconnaissance along with identification and review of available existing geological information. Their investigation did not include subsurface field explorations. As the proposed routes require traversing of steep slopes, the geotechnical considerations for this project are significant. For this reason, information provided by Shannon & Wilson has been incorporated directly into this report, and summarized or elaborated upon as appropriate. POTENTIAL PIPE ROUTES This analysis follows the nomenclature used in the Shannon & Wilson preliminary geotechnical report, with the exception of Surface Alternative 1, which has not been evaluated at this time. The four easterly alignments are included in this analysis as they provide the most direct route to the existing sanitary sewer in the Maplewood Golf Course. City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 2 August 2008 Those alignments shown in Appendix A are designated as Surface Alternative 2 and Trenchless Alternatives 1, 2, and 3. ' Each alternative of the steep slope sewer would tie into the existing 15-inch line within the Maplewood Golf Course constructed in 1988. ' Surface Alternative 2 Surface Alternative 2 alignment (B-B') was determined primarily by following an existing narrow ridge line along the plateau, then dropping perpendicularly down a steep slope to the valley below. The overriding geotechnical concern is to construct the pipe as ' perpendicular to the contours as possible. Alignment B-B' is entirely within the Maplewood Golf Course property. ' Trenchless Alternative 1 ' Trenchless Alternative 1 alignment (C-C') was dictated primarily by horizontal directional drilling (HDD) requirements. HDD pipe installation requires an exit and entrance pit. The entry pit area needs to be large enough to layout and assemble the pipe. In this case, the ' entry pit would be the square near C at the bottom of the slope; the exit pit would be C' on the top of the plateau. ' Alignment C-C' is entirely within the Maplewood Golf Course property. Trenchless Alternative 2 Trenchless Alternative 2 alignment (D-D') was determined primarily by extending the HDD under and past Maplewood Creek. Recent evaluation of City as-builts, however, has ' revealed an existing sanitary sewer under the creek. With no need for crossing the creek, this Alternative route will not be considered further. ' Trenchless Alternative 3 Trenchless Alternative 3 alignment (E-E') was determined by attempting a direct route ' from the valley floor to the top of the plateau. This alignment would allow a long, "straight shot" for pipe assembly along Union Avenue SE. A house, built in 2005 and located within King County's jurisdiction, was not shown on Shannon & Wilson's Figure 2 graphic in ' Appendix C. The home lies east of this proposed alignment, and just south of the SPU facility. An easterly alignment deviation could conflict with the house in this scenario. Additionally, the route straddles the property line, and would require an easement along the westerly 20+/- feet of the impacted parcel. ' Although all four alignments can potentially be adjusted and modified in a number of ways, they are not only representative of the practical route alternatives available; they also keep the analysis of alternatives to a manageable level. Some refinement of any of these ' alignments can be anticipated during design with any cost impacts of such adjustments relatively insignificant. City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 3 August 2008 PERMIT REQUIREMENTS Sensitive Areas A review of the City of Renton's sensitive area maps (available via City of Renton's website) indicate this project is located within landslide hazard, erosion hazard and aquifer protection sensitive areas. The Alternative alignments are located entirely within the City limits and will require permit coordination between the City's Public Works and Planning departments. In Figure B, the orange banded area represents the high landslide hazard area; the brown represents moderate potential and the red represents very high potential of a landslide. The preliminary geologic report addresses the stability of this area and will be investigated further during the pre -design phase, once a route has been selected. Figure B Excerpt from City of Renton Landslide Hazard Area Map w _)E _. Approximate project impact area 60. Srh St SF Soh PI City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 4 August 2008 ' Figure C illustrates the erosion hazard area. The area consists of the steeper slopes between the valley and the top of the plateau. The preliminary geologic report addresses ' the need to stabilize this area after construction. A design for mitigating erosion concerns will be included with the preliminary design report for the Alternative selected. Figure C Excerpt from City of Renton Erosion Hazard Map In Figure D, the blue shaded area represents the Zone 2 protection area and the green diagonally hatched area represents Zone 1 — Modified protection area. The significance of ' the Zone 2 area is that it is the zone of potential groundwater capture for the City's water supply system. Areas within the Zone 2 boundary are generally protected by overlying geologic strata. The preliminary geologic report validates this. ' Zone 1 — Modified areas are designated to protect aquifers that are partially protected by overlying geologic strata. The only impact to this zone from this project will be near the ' connection to the City's existing sanitary sewer. City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 5 August 2008 Figure D Excerpt from City of Renton Aquifer Protection Map Approximate project impact area 1 I w,a ' King Count Clearing and Grading Permit Y g g Trenchless Alternative 3 alignment straddles the west boundary of a privately held parcel located within King County. For any land disturbed within King County, a King County grading permit and restoration plan will be required. Depending upon the type and amount ' of disturbance, King County may require a mitigation plan. The City would prefer to keep all construction within the city limits, making Trenchless Alternative 3 less desirable. Application fees for a King County grading permit are calculated based on the amount of land disturbed. Permit approval typically takes twelve weeks. King County Wastewater Treatment Division (KCWTD) Approval A KCWTD permit is required for any connection to the King County sewer system. This ' approval typically takes approximately 4-6 weeks. There are no application fees for this permit. Other Potential Permits The point where this project ties into the existing City sanitary sewer is fairly close to Maplewood Creek and most likely within the creek buffer area. Working within the buffer area will require a permit from the City of Renton. According to City Renton Municipal Code, a Class 2 stream minimum buffer width is 100 feet and a Class 3 stream minimum buffer width is 75 feet. The stream class and buffer area determination may require field verification by a qualified professional. ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 6 August 2008 Land disturbance activities within City limits require a grading permit if project modifies existing grade and exceeds specified volumes of excavated materials. As this project ' does not modify grades, the City will not require a grading permit. This project will require a SEPA Checklist, with a Determination of Significance ' anticipated, as well as an approved Temporary Erosion and Sediment Control Plan. Permit conditions may possibly include limiting construction to the `dry season' between April and October. ' In addition, if this project disturbs one acre or more of land, it will require a NPDES Construction Stormwater permit. EASEMENT REQUIREMENTS ' Neither permanent nor temporary easements will be required for Surface Alternative 2 or Trenchless Alternative 1. These pipe alignments are within the Maplewood Golf Course property, which the City owns. ' Trenchless Alternative 3 will require permanent and possible temporary easements as its northerly alignment encroaches onto private property. PRELIMINARY ENGINEERING ANALYSIS ' The preliminary engineering analysis for this project consists of examining the following: • Hydraulic Consideration — Alternative B1 ' • Geotechnical Considerations ' • Pipe Material Options • Construction Methods ' Hydraulic Consideration — Alternative 131 As part of the Heather Downs Sewer System Analysis, Roth Hill performed a hydraulic analysis of the Heather Downs interceptor in late 2006. For that analysis, we separated the model from the Renton 2001 model and Ultimate Model, and used with the November ' 24, 1990 storm to identify existing capacity issues. The 2006 report analyzed four scenarios, including an existing conditions scenario and three different ultimate conditions scenarios. Results of that analysis are further described in the Heather Downs Sewer ' System Analysis report, December 2006. During the development of the Renton 2001 model, there were numerous issues and complications in creating the model from the City's database. These issues were described in detail in the September 2006 Sanitary ' Sewer Model Development and Analysis Summary Report. Generally, it was determined the database included many inaccuracies that could potentially generate flawed or incorrect model results. a City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 7 August 2008 In order to address these inaccuracies, the City contracted with Roth Hill, as part of this project, to survey the Heather Downs Interceptor. The survey area extended from Manhole 5315192 to the connection with the King County trunk sewer in State Route 169. The collected survey information was limited to manhole locations with rim and invert elevations. As part of this project, the Heather Downs model was updated using the newly collected survey data. A few of the manholes were buried and could not be located during the survey. In these cases we used the manhole data from the original Renton model. Scenario No. 1 (existing conditions) and Scenario No.3 (ultimate conditions plus U3A), as described in the Heather Downs Sewer System Analysis report, were re-evaluated using the updated physical model. All other population assignments, flow rates, and I&I parameters where kept consistent with those used in the original Heather Downs analysis. Figure E, representing Scenario 1, and Figure F, representing Scenario 3, graphically summarize the results of the analysis of each scenario. Refer to Appendix B for more detailed results, including color -coded maps and profiles. The pipes on each map were color -coded based on modeled peak flows divided by maximum pipe capacity (Qpeak/Qf,„). This color -coding scheme is consistent with the previous results from the various analyses provided to the City and is summarized below: QFeak/QFull Color Greater than 1.2 Red 1.0 to 1.2 0.8 to 1.0 Green 0.6 to 0.8 Blue 0.0 to 0.6 Gray All pipes with ratios greater than 0.8 (color -coded green, orange, or red) are considered to be exceeding their capacity. Significantly surcharging pipes with ratios larger than 1.2 are coded red. Moderately surcharging pipes are represented by ratios of 1.0 to 1.2 and are color -coded orange. Green colored pipes have flows that exceed the pipes capacity without surcharging. Pipes colored blue are close to, yet not exceeding, the capacity standard. Although the color -coding identifies most of the problem areas, some surcharging may occur in adjacent mains upstream from the identified problem areas due to backwater effects. The actual level of surcharging may not be as pronounced as shown in the model results. This analysis did not identify the pipes that were surcharging due to backwater affects, since alleviating the downstream capacity restrictions in those instances eliminated the surcharging. In addition to the color -coded maps, we generated profiles for each of the problem areas. The profiles are useful in analyzing the severity of the surcharging and are attached in Appendix B. The following paragraphs summarize the issues identified for each scenario. ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 8 August 2008 Figure E Scenario 1 (excerpt from Figure 2A — Updated in Appendix B) 441, sr. 43 .� •� -t■ N b 1 � i w•+: � t 4 E 2n4 Sf •l. ''`1, ' y'• =_r, • _ • ,M .� — -1� `J�•s� Blue (0.60 to 0.80) -:a�► in original analysis •-` ��' ,., , ■ i SE9 '• 2 Blue (0.60 to 0.80) in r original analysis Scenario No. 1 - Heather Downs 2001 Model Results of the revised Heather Downs 2001 Model vary slightly from the original analysis. Most changes resulted in either moving up or down one surcharging level. This corresponded to the effect of the revised pipe slope based off the new and updated data. Where the new data resulted in flatter pipe slopes than determined from the original database, then surcharging would increase. Likewise, where new data resulted in steeper pipe slopes than from the original database, then surcharging would decrease. Two locations, noted in Figure E, went from blue, satisfactory, to red, significantly surcharging; an increase of three levels. Another area of interest for this report includes the change in a pipe segment in Chelan Avenue SE and SE 4" Place. Each pipe segment increased from green (0.8 to 1.00), exceeding their capacity, to yellow (1.00 to 1.20), moderately surcharging. The map and profiles for these results are included in Appendix B. City of Renton Heather Downs Interceptor Improvements Feasibility Report page 9 August 2008 Figure F Scenario 3 (excerpt from Figure 3A Updated in Appendix B) Gray (<0.60) in original analysis4 6 • + ... y �' • ' •. tir'! . Yellow (1.00 to 1.20) in ` 'L, , • > '' ; •� f, 1 - - • �I�• . a • original analysis ' . ;.. • - :► �• ' VV cf. s... " ' . Yellow (1.00 to .• 1.20) in original f I• ' F analysis P Blue (0.60 to 0.80) .r in original analysis r .��sF�r► a sT • ; Scenario No. 3 - The Heather Downs Ultimate Model with Mini -Basin U3A Results of the revised Heather Downs Ultimate Model with Mini -Basin U3A also vary slightly from the original model. The number of pipe sections with capacity issues changes slightly based on the updated pipe information; however, the level of capacity issue varies from the original analysis in many locations. Updated results indicate moderate to significant surcharging throughout the Heather Downs Interceptor along SE 6th Street between the King County Trunk line and Manhole No. 5316017 (intersection of SE 6`h Street and Pierce Avenue SE), with three short exceptions. Significant surcharging, shown in red, continues along Pierce Avenue SE and SE 5th Street and in the first upstream pipe segment from the northeast. A short segment near the intersection of SE 5th Street and Pierce Avenue SE increased from green, exceeding capacity, to red, significantly surcharging. Other segments changing from the original analysis are noted on Figure F. The map and profiles for these results are included in Appendix B. City of Renton Heather Downs Interceptor Improvements Feasibility Report Page to August 2008 The main impact resulting from our revised analysis is a reduction of pipe replacement within SE 4`h Street. This occurs within the first segment downstream of the intersection of SE 4" Street and Anacortes Avenue SE as shown in Figure G. The overall outcome reiterates our original findings and recommendations. Figure G Recommended Improvements SE 1st P1 R4' i Evc, groer) Planned for replacement 41SE 2nd q in original analysis _ - ? A - r on r F r$rG Rosewood Df a s r r �. }' r m •M si•- r T_ Replace pipeline r • • 2 Conceptual Alignment of New 10-Inch Sewer 10/ �f r: � ' d 4 lJ Y • To alleviate the pipe surcharging within the entire Heather Downs Interceptor sewer, Roth Hill recommends a two-phase approach. The first phase would be redirecting flow off the plateau to the south. This will alleviate pipe surcharging along SE 5`h Street, Pierce Avenue SE and SE 6"' Street. The second phase would be upsizing some of the existing pipe on top of the plateau. This will alleviate pipe surcharging along the south end of Union Avenue SE and along SE 4" Avenue, Chelan Avenue SE. SE 2nd Place and north to Bremerton Avenue SE. Redirecting flow to the south can be achieved via a new 10-inch diameter pipe extending south off the end of Union Avenue SE and connecting to the existing 15-inch diameter City sanitary sewer within the Maplewood Golf Course. This redirects approximately 760 gpm City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 11 August 2008 of ultimate flow from the upper portion of Basin 25 and mini -basin U3A. The 10-inch pipe at a minimum 0.5% slope provides 900 gpm flow capacity. The 15-inch sanitary sewer pipe downstream connection for the new 10-inch line has a capacity of over 4,900 gpm. The existing interceptor pipeline recommended for upsizing, shown in red, is depicted in Figure G. The existing 10-inch diameter pipe needs to be increased to 12-inch diameter ' pipe in the following areas: • The most southerly manhole on Union Avenue SE (No. 5315002) to the manhole at the intersection of Union Avenue SE and SE 4th Street (No. 5315001). • Along SE 41h Street from the intersection of SE 41h Street and Anacortes Avenue SE ' (No. 5315013) to the intersection of Chelan Avenue SE (No. 5315011). The existing 8-inch pipeline needs to be increased to 12-inch in the following area: • From the intersection of Chelan Avenue SE and SE 41h Street (No. 5315011) to Chelan and SE 2 1 d Place (No. 5315023) to the next manhole west (No. 5315024), then north two manholes where the interceptor intersects with Bremerton Avenue SE (No. 5315046). Solids deposition could be a potential problem in the steep slope pipe. The high velocities could cause the solids to separate from the liquid and remain behind. Estimated velocities are between 19.5 and 25 fps. ' In addition, the high velocities translate into shallow depth of flow that may not be enough to move solids. For example, assuming low flow is approximately 40% of design peak flow, resulting in flows between 270 to 360 gpm. Their corresponding depths would be 0.12 to 0.15 feet, or roughly 1.5 inches deep at the pipe bottom. Since the pipe is round, the depth decreases rapidly moving away from the pipe centerline. Projected peak flow conditions, Qp=760 gpm, may flush debris as flow depth will be approximately 0.2 feet (2%2 inches). At this depth, solids would be kept in suspension and existing debris would also be picked up by the flow. However, peak flow rates are not anticipated to occur frequently. Therefore City staff may need to occasionally flush this steep slope pipeline. Hydraulic Consideration - Moderately Surcharged Lines (Figure 7 - HDSSA) ' The December 2006 analysis identified a portion of the interceptor within SE 4th Street as being moderately surcharged. Our revised hydraulic analysis, based on updated field data, determined a smaller segment in this area is moderately surcharged. Specifically, the moderately surcharging segment is the 10-inch diameter pipeline from the intersection of Anacortes Avenue SE to the intersection of Chelan Avenue SE. This segment is shown in yellow highlights in Figure G. City staff requested that we identify segments classified as moderately surcharging to allow some decision based flexibility with respect to available funding. As a result, the existing 10-inch diameter pipeline segment on SE 4th Street between Anacortes Avenue SE and Chelan Avenue SE (No. 5315014 to No. 5315013) could be left in place. The ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 12 August 2008 remainder of the pipe upstream of the intersection of SE 4tn Street between Anacortes Avenue SE would be upsized to a 12-inch diameter pipeline. ' The existing 10-inch line will remain moderately surcharged. Under maximum flow conditions, these pipes will operate at or slightly above their capacity. As a result, this portion of the system may require more frequent cleaning. Geotechnical Considerations ' The importance of the site geology comes into play in evaluating the construction methods available to install the proposed 10-inch relief sewer pipe. To assist with estimating the ' current site geology and its anticipated construction impacts for constructing a sewer pipeline down steep slopes, Roth Hill Engineering Partners contracted with the geotechnical consulting firm of Shannon & Wilson. The complete geotechnical report is ' contained in Appendix C. The following summarizes their findings: Site Geology Site generally consists of upland plateau geology. The top of the plateau is made up of low density silty or gravely sand with abundant cobbles and boulders. The likely thickness ranges from 5 to 15 feet. Till underlies the top layer and consists of very dense silty, gravelly sand along with cobbles and boulders. This combination makes excavation difficult and will likely require larger mechanical equipment to perform any excavations. The likely till thickness is 20 to 30 feet. Silty to gravely sand and sandy gravel layers with some silt underlie the till. These layers are very dense as result of glacier overriding. Also, cobbles are likely within the gravely ' layers and boulders are also possible. This layer lies roughly above the 270 foot elevation and below the till. Finally, below approximately the 270-foot elevation there exists finer graded deposits of ' slightly clayey, fine sandy silts with scattered gravelly layers. ' Groundwater Groundwater may be present perched above less permeable, finer graded soils. Prior to final design, further investigation will be required to determine the degree of de -watering that may be required. ' Slope Stability The slopes appear fairly stable. The soil consultants did not observe any fresh landsliding; however, they noted the steep slopes along proposed routes appear to be at or above the limit of stability for near -surface slide failures. City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 13 August 2008 ' PIPE MATERIAL OPTIONS Three types of pipe materials are considered for the proposed steep sewer construction: ' • Ductile iron ' • Polyvinyl chloride • High density polyethylene ' An overview of each type of pipe with their advantages/ disadvantages with specific reference to the steep slope portion of the project is given below. We believe that, ' regardless of the pipe material and construction methodology used, it would be prudent to use some type of restrained joint, and not to rely solely on pipe anchors, to prevent pipe joints from pulling apart on the steep slopes. Those portions of the project outside of the steep slope areas (i.e., upstream and downstream thereof) can probably be constructed of conventional sewer pipe materials per the City's standards. Ductile Iron Ductile iron (DI) pipe is classified as a 'rigid pipe' and has excellent strength characteristics. Using restrained joints with this pipe will hold itself together under many circumstances even without pipe support (such as may occur if the pipe trench backfill material fails). The simplest and least costly type of restrained joint uses locking gaskets with the standard push -on joints. For a sanitary sewer application, DI pipe should have an epoxy or calcium aluminate mortar type of interior liner instead of the standard cement mortar lining used for water mains. Besides providing corrosion protection, these linings are superior to cement mortar in terms of scour resistance that will occur due to the high fluid velocity and presence of solid materials in the sewage as it flows down the steep slopes. Due to potential corrosion problems, the City does not normally use DI pipe in sanitary sewer applications. ' Ductile iron pipe is readily available and is the most expensive of the three pipe materials in terms of per foot material costs. Ductile iron pipe is also the heaviest of the three pipe materials and this extra weight would add to the difficulty of installing the pipe on the steep slopes. An advantage of DI pipe for above -grade installation would be its toughness, making it ' more resistant to acts of vandalism. However, the DI pipe would be more susceptible to long-term corrosion effects from weathering. Thermal expansion effects in DI pipe are not usually of concern because of its low coefficient of thermal expansion. In addition, the small amount of expansion and contraction which does occur can be absorbed by the joints. ' Class 52 DI pipe is the most commonly used pressure classification. Although hydraulic pressure is not a consideration for this application, Class 52 pipe provides a reasonable intermediate wall thickness and pipe strength. Therefore Class 52 is the basis for evaluating DI pipe in this report. If selected for this project, the use of a different class City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 14 IAugust 2008 may be considered during design. The price differences between Class 52 and the other pressure classes are relatively insignificant. Polyvinyl Chloride (PVC) ' PVC pipe is considered a 'flexible pipe' and is made for both gravity sewer and pressure flow applications. Although this application is hydraulically gravity flow, we do not recommend standard SDR 35 PVC gravity sewer pipe on the steep slopes for two reasons: • It is has a relatively thin wall compared to PVC pressure pipe. • Joint restraints are not standard and pipe collars would have to be relied upon ' solely to protect against joint separation. PVC pressure pipe, on the other hand, has a thicker wall and joint restraint methods are readily available. We would recommend AWWA C9O0 PVC pipe for this application. This is the highest standard pressure class available in the 10-inch diameter size and would provide the greatest wall thickness. ' When compared to DI pipe, PVC pipe is not as strong, although it has inherently excellent corrosion resistance and requires no special lining. Its material price per foot is lower than DI and its lighter weight would ease installation under the difficult steep slope conditions. PVC also has excellent scour -resistant characteristics and, unlike DI pipe, does not have an interior lining potentially subject to wear. ' Although not a major consideration for the steep slope application, PVC pipe has excellent hydraulic flow characteristics. We do not recommend PVC pipe for above -ground installation primarily because it is subject to ultraviolet degradation. Furthermore, as compared to DI pipe, it would not be as resistant to vandalism. High Density Polyethylene (HDPE) HDPE pipe is another type of 'flexible pipe'. HDPE is the most versatile of the three pipe materials in terms of its potential use for this application. While DI and PVC pipe is delivered in 20 foot lengths, 10-inch diameter HDPE pipe is manufactured in 40-foot lengths. For longer runs of pipe this translates into fewer pipe joints. In buried pipe applications taking advantage of the extra pipe length requires the ability to keep open a longer trench excavation. Depending upon the soil conditions, this ' may be difficult on a steep slope. HDPE lengths are joined together by a heat butt fusion technique that inherently constitutes a restrained joint. ' HDPE pipe has outstanding scour -resistant properties, allowing its common use in slurry applications. It has excellent hydraulic flow characteristics even with its inside diameter being slightly less than either DI or PVC pipe. As noted previously, hydraulic capacity should not be an issue on the steep slopes based on the information we have available at this time. The ultraviolet component in sunlight can be harmful to polyethylene unless the material is sufficiently protected with a minimum 2% concentration of carbon black. Pipe that is City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 15 August 2008 ■ protected with carbon black is the principal polyethylene material selected for above- ground installations. With this protection, we consider HDPE pipe to be a viable ' consideration for installation above ground even though it would be more susceptible to vandalism than DI pipe. ' Of more concern for direct installation on grade is that HDPE has a high coefficient of thermal expansion (approximately 10 times that of metal or concrete) and therefore is subject to considerable expansion and contraction due to ambient temperature fluctuations. This is usually not a concern when the pipe is buried. This is not the case when subject to atmospheric conditions and especially to direct sunlight when the surface temperature of an empty black HDPE pipe can be raised by 40 to 50 degrees F. ' The thermal expansion/contraction effects need to be taken into account during design. The easiest method to account for this effect is to `snake' the pipe above the ground. This ' allows the pipe to move when expanding and contracting. Snaking the pipe on a steep slope would not be as easily accomplished as on flatter terrain. The bending radius for 10-inch diameter HDPE pipe is approximately 30 feet. The other method of controlling thermal expansion effects is to anchor the pipe. In this case, the anchor spacing must be such that excessive strain does not build up in the pipe wall. Finally, HDPE pipe is the most viable material for use in conjunction with horizontal directional drilling (HDD) pipeline installation. That being the case, it is our recommendation to use HDPE pipe for the proposed steep sewer construction. I CONSTRUCTION METHODS There are four steep slope construction methods under consideration for this project: 1 • Laying the pipe on the ground surface ' • Shallow, hand -dug trench and backfill • Conventional trench excavation and backfill (i.e., buried pipe) • Horizontal directional drilling (HDD) These methods pertain to the steep slope portions of the project. The upstream and downstream pipe runs will be buried pipes installed by trench excavation and backfill. Some of the information in this section is taken from the Shannon & Wilson Preliminary ' Geotechnical Report (see Appendix C). ' Ground Surface (On -Grade) Installation This is perhaps the simplest method of steep slope construction and is therefore also the least expensive. Pipe collars and intermediate anchors would be used to restrain lateral pand down -slope displacements. City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 16 August 2008 Pipe installation on grade has the disadvantage of being exposed to both vandalism and to the elements. However, it does mitigate having to restore ground surface of the areas disturbed using trench construction methods. These restored areas can potentially create slope stability problems. With regard to potential vandalism, the Surface Alternative 2 (B-B') alignment may not be ' as susceptible to vandalism as the slope has heavier vegetation and it is at the back of the city owned golf course and out of view from any public roads. The heavier vegetation would provide more shade to the exposed pipe from the direct sunlight thereby mitigating UV degradation concerns. The alignment for on -grade pipe installation on the steep slope should be as perpendicular to the contours as possible. As compared to trench construction, this method would contribute less to instability of the soils on the steep slope and would cause fewer disturbances to the ground and vegetation. 1 Hand -dug Shallow Trench Construction ' Hand -dug shallow trench construction on the steep slope would be shallower than typical trench construction and allow the sewer pipe to be buried in the topsoil layer and out of site. The trench would need to be just deep enough to allow four to six inches of topsoil cover and just wide enough to allow the pipe placement and hand tamping around the pipe. This method would keep the sewer pipe out of site for vandals and harm from UV degradation. Also, the area disturbed would be kept to a minimum resulting in a much better chance to establish vegetation cover for stabilizing the disruption to the steep slope. Still, stabilizing disturbed areas on steep slopes can be difficult. It doesn't take a lot of runoff to erode the disturbed areas. Also, using hand construction methods makes it ' difficult to evenly backfill and compact the hand -dug trench. The looser backfilled material will be even more susceptible to erosion rills. Even when re -vegetation is finally achieved, the surface soils will be exposed to downhill creep. The Shannon & Wilson preliminary ' report alludes to this. Finally, this construction method is extremely labor intensive. As a result this method most likely will not see any cost advantage over the ground surface installation. For these reasons, we will not be pursuing this option in any further detail in this report. Trench Construction Trench construction on the steep slope would be shallow, yet would need to extend below the looser surficial soils subject to downhill creep. Near -surface trenching (nominally 4 feet of cover) for a pipeline would most likely encounter the recessional outwash (sand and gravel with cobbles and boulders), till (dense gravelly sand with cobbles and ' boulders), sandy gravel in the upper half of the slope, and the finely sandy silt in the lower part of the slope. The upper sand and gravel would be easily excavated but would slough to slopes of 30 degrees or flatter where water -bearing. The till would be difficult for a ' small backhoe to excavate although relatively easy for a larger track -hoe with a toothed ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 17 August 2008 bucket and hoe -ram attachment. Perched water is likely on top of the till and in sandy lenses within the till. Trench sides in the till will hold near vertical; however, shoring would be required by safety regulations if greater than 4 feet deep. Deep gravity sewers (> 15 feet) might be required near the upstream (north) end of Surface Alternative 2 alignment. This is where the 10-inch relief sewer would connect to the existing Heather Downs Interceptor. Trench construction on steep slopes requires the use of backhoes attached by cables and winches to the top of the slope or the use of specialized equipment with hydraulic support attachments (spider backhoe). The slope for Surface Alternative 2 is approximately 40 degrees, which is near the maximum limit for trench installation. In general, the native materials should be suitable for backfill if they do not become wet. Special backfill procedures would be needed to keep the fill stable. The hillsides in the vicinity of the trench installations would be subject to increased risk of land sliding because of the disturbed soils and the potential collection of groundwater with the trench serving as a flow conduit. As with on -grade installation, the pipe trench alignments on the steep slope should be as perpendicular to the contours as possible. Of the three construction methods, trench construction would cause the most disturbances to the soils, ground, and vegetation requiring more re -vegetation and restoration. The City has found on previous projects that steep slopes disturbed by construction are difficult to restore, a problem aggravated by the fact that such areas tend to become pathways and play areas for children. Trench installation will be required at the top and bottom of the slopes regardless of the conveyance method on the slopes themselves. Horizontal Directional Drilling ' As explained in the Shannon & Wilson geotechnical report, the elevation difference between the top and toe of the plateau makes horizontal directional drilling (HDD) the preferred trenchless construction technique for underground construction for this project. An obvious advantage to HDD is that it avoids construction directly on the steep slopes and creates minimal surface disruption. Another advantage is that the alignment need not ' be limited to traversing directly down the slope. HDD consists of drilling a pilot hole from the bottom of the slope upward to the top. The initial hole, approximately 3-inch diameter, is drilled carefully with the drill path controlled using a walk -along sonde system that monitors the depth and location of the drill head. After the drilling, the pilot hole is reamed to a larger diameter. For a 10-inch HDPE pipe, ' the hole needs to be enlarged to about 16-inches. The sewer pipe is pulled back from the top through the hole. HDD pipe installation requires staging areas at both ends of the pipe. Instead of drilling from the bottom of the slope, it is also possible to drill from the top. For this project, drilling from the top has some advantages. First, there is more physical ' space at the top of both slopes. Second, the elevation at the top is more critical than at the bottom of the slopes. By drilling from the top, the more critical elevation can be ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 18 IAugust 2008 ■ established with more certainty than by drilling from the bottom. The biggest disadvantage of drilling from the top is that the full pressure of the slurry fluid is brought to bear on the ■ bottom of the hole which could lead to a ground fracture. As discussed previously, the plateau slopes are underlain by fine-grained soils in the ■ lower half of the slope and more granular soils in the upper half. The fine-grained soils consist of sandy silt to silty fine sand and the granular soils consist of sandy gravel, gravelly sand, and gravel. Cobbles and boulders are expected in the recessional outwash and till deposits. These would be obstacles for the HDD method. The drill head will not be able to drill through ■ boulders and the cobbles will hinder reaming operations. Should a boulder be encountered, the drill would have to be retracted and steered deeper into the slope to go around the obstacle. In this scenario, there would need to be flexibility to relocate the exit ■ point at the top of the slope, if the drill path must be altered. In general, HDD is most successful in soft or silty and clayey soils and even rock because stable boreholes are formed. In non -cohesive soils (e.g., sand and gravel laced with ■ cobbles and boulders), HDD projects have experienced serious problems with caving holes and jammed and lost drill bits. These holes require more time and preparation procedures. ' Other drilling risks include hydraulically fracturing the soil, resulting in a spill. The bore may drill into a perched water table in a granular deposit. The sudden release of perched ■ groundwater can destabilize the surrounding soil, causing soil flow into the bore annulus so that the drill steel becomes locked. Although a final bore diameter of 12 inches is well within current technology, the lack of a stable cake in gravelly ground would promote caving and collapse of the hole. (The cake helps to stabilize the opening and is formed from bentonite slurry used during drilling). The problematic soils for this installation are near the top of the slopes. After the pilot hole is drilled and reamed (assuming the drilling is from the bottom), an approximately 15- foot-long casing pipe may be installed from the top to prevent caving of the recessional outwash. If a boulder is encountered in the upper 15-feet, it should be possible to excavate it and backfill with select material. On the other hand, if the drilling is from the top, it would be possible to excavate down through some or all of this material before commencing the drilling. Regardless of which drilling approach is used, selection of an experienced HDD contractor who has worked in the Seattle area is important for this project. ■ Another disadvantage is that HDD is less common than the other two construction methods and could be undertaken only by a limited number of specialty contractors, ■ potentially limiting competition and thereby raising prices. ■ IDENTIFICATION AND SELECTION OF ALTERNATIVES This section evaluates the previously presented information as it pertains to the three ■ identified pipe alignments: Surface Alternative 2, Trenchless Alternative 1 and Trenchless Alternative 3. These alternatives are shown on Appendix A. ■ City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 19 August 2008 Common to all the alternatives would be the proposed 12-inch pipe upsizing on the plateau. These costs are not considered as part of this alternative comparison and selection because they would be the same in each case. Pipe Material Selection ' In order to simplify the identification and comparison of the alternatives, the following pipe materials will be used for the three types of construction methods along with the reasons and assumptions for making these selections. This simplification is justified in part because, in our opinion, the pipe material costs are a relatively small variable for this project. ' HDD Installation: By default, this would be HDPE. Above Ground Installation: The City preference is for HDPE pipe. This material is easier to install and less expensive than DI pipe and has excellent corrosion and scour resistance characteristics. Being much lighter in weight, it would be much easier to install ' than DI. One disadvantage of HDPE pipe is the effects of thermal expansion and contraction must be taken into consideration during design but there are a number of techniques for addressing this concern as previously described. Buried Installation on Steep Slopes: For the reasons discussed in the previous paragraph, we believe that HDPE pipe would be the best choice here as well; although, AWWA C900 would be a viable option. Our price research indicates the base material price per foot for ' HDPE is higher than for C900. However, HDPE has fewer pipe joints thus making installation easier. As a result, we believe the installation costs for HDPE would be similar to C900. Also, the C900 pipe joints would have to be provided with some type of joint restraint that would add to the cost. Buried Pipe on the Top and Bottom of the Slopes: Based on our present knowledge, these could be constructed of conventional gravity sewer pipe materials. We have assumed SDR 35 PVC pipe. ' Construction Cost Estimating For the comparing the various construction methods for each of the three alignments we tdeveloped planning level construction cost factors. The costs do not include construction contingency, sales tax, survey, engineering, permits, easements or other allied project costs. These allied costs will be estimated for the final selected alternative(s). In other ' words, for the purposes of these estimates, we have assumed that the allied project costs would be similar for each alternative. tThe following cost factors are used: • 10-inch PVC in easement (10'-15' deep) $150/LF • 10-inch PVC in easement (15'-20' deep) $170/LF I • 10-inch HDPE on steep slope (above grade) $140/1-F City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 20 August 2008 • 10-inch HDPE in steep slope (average 4-foot bury) $280/LF • 10-inch HDPE installed by HDD $450/LF It is important to note these are planning -level costs for budget estimating purposes with an estimated accuracy of approximately 20%. A planning -level cost is not a definitive estimate of Opinion of Probable Construction Cost based on detailed design and quantity takeoffs. The cost factors were based on past project experience by Roth Hill and research of available reference materials. Surface Alternative 2 This Alternative can be installed using conventional trench construction, or limit the conventional trench construction to the flatter slopes and use ground surface construction methods over the steep slopes. Table 1 indicates estimated construction cost for each option. Besides being less costly, the ground surface option also has the following advantages over trenching on the steep slopes: • Does not require attaching cables and winches to backhoe, or use of specialized equipment with hydraulic supports to stabilize the digging equipment • Does not introduce potential slope stability problems due to granular backfill acting as groundwater conduit Due to lower cost and easier constructability we recommend using the trench and ground surface construction method for Surface Alternative 2. Table 1 Construction Cost Estimate for Surface Alternative 2 Construction Method Length (If) Construction Cost Trench 1,400 $311,500 ......._.._... ....-...__..............................._..._.........._............... .........................._........._........................ ..._................................................. ........_......................_....... _............. ......__ .............._.._.._...._ ..........._..._................ .............. ...... ___ ..................................... ................. .................._ _.... Trench and Ground Surface 1,400 $234,500 Construction cost include, as applicable: mobilization, pipe materials and installation, excavation and backfill, gravels, drilling, manholes, pipe anchors, temporary erosion controls, slope stabilization, and surface restoration. Construction cost does not include contingency, sales tax and other allied project costs such as design surveying, design, easements, permits, construction staking, construction administration, and construction field observation. Trenchless Alternative 1 HDD pipeline installation techniques require a significant target area at each end of the ' HDD alignment. This Alternative would provide large enough target areas on top and bottom. Refer to section C-C' on Appendix A for the approximate alignment. ' This Alternative still requires some conventional trench construction at each end of the HDD installation to connect to existing sewers. ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 21 August 2008 The construction cost estimate for this Alternative is $512,000. Trenchless Alternative 2 Since it is not necessary to cross Maplewood Creek. this Alternative is not considered further. Trenchless Alternative 3 As with Trenchless Alternative 1, this Alternative requires significant target areas at each end of the HDD alignment. While there is adequate room in the golf course for the bottom target, the top target is relatively narrow. The top target area consists of a driveway extension off Union Avenue SE and is approximately 20 feet wide. Refer to section D-D' on Appendix A for the approximate alignment. The construction cost estimate for this Alternative is $610,000. PIPE REPLACEMENT This project proposes to upsize existing 10-inch and 8-inch pipes to 12-inch diameter along the red route shown in Figure H. Pipe bursting is a trenchless technology construction method preferred in performing this work. It minimizes street disruption and repair cost. Still, the final decision on whether to use pipe bursting technology or not will be based on the presence of all existing underground utilities. That will not be known until a full field survey can be accomplished during the preliminary design phase. Assuming pipe bursting is feasible, the estimated cost for this work is approximately $485,200. Figure H Existing Moderately Surcharged Pipe ro ♦ . _ l `D f �J S E 22Moderately e• u surcharged 10- t*d° inch pipe that l: could be left in _ T =9 place. rWf�I .;.i v JL 'y is - r -- N mr City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 22 August 2008 In addition, this report discusses on page 12 that a portion of this alignment is only ' moderately surcharged and could be left in place. Leaving the moderately surcharged line would save approximately $94,500 of capital construction cost. Annual maintenance cost ' would potentially increase as the City would need to clean these segments more often. CONCLUSION Providing a relief sanitary sewer to the existing Heather Downs Interceptor is feasible. Table 2 lists the feasible Alternatives along with their advantages and disadvantages. The Alternatives are ranked in order of preference. Table 2 Alternative Summary Alternative Advantages Disadvantages 1 Surface Alternative 2 Lower cost Slight potential for Easily accessible for vandalism maintenance and future Tree removal repairs No easement required 2 Trenchless Alternative 1 No potential for vandalism High cost Limited tree removal Installation requires Limited restoration higher degree of No easement required difficulty and risk Difficult accessibility for maintenance and future ...._._..................................... - .. ..................... repairs 3 Trenchless Alternative 3 No potential for vandalism High cost Limited tree removal Installation requires Limited restoration higher degree of difficulty and risk Difficult accessibility for maintenance and future repairs Requires easement As Surface Alternative 2 is the preferred Alternative, an estimated project cost has been ' provided: Table 3 illustrates the project cost estimate for Surface Alternative 2 and all recommended ' 12-inch replacement pipe is approximately $1,069,700. ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 23 August 2008 The project cost estimate for Surface Alternative 2 as presented below assumes Roth Hill and its subconsultant team performs engineering -related services. The project costs do ' not include easement acquisition, legal, and City administration costs nor do they include construction phase services by the City. The design phase engineering permit costs include estimated application fees, required ' supporting documentation and time to prepare the applications. Not included are costs for addressing, in detail, any concerns that might be expressed by King County regarding ' odor and corrosion control (for the Wastewater Treatment Division Approval), unusual mitigation measures on the steep slopes (for a Clearing and Grading Permit), or other non- typical responses resulting from the application submittals. RECOMMENDATIONS Upon evaluating all information and existing data discussed within this report, we recommend the City pursue Surface Alternative 2 for the installation of the 10-inch relief sewer line to the Heather Downs Interceptor. In addition, we recommend upsizing the total length of existing 10-inch pipe within SE 41h Street. However, if capital funding is an issue and the City is willing to perform more frequent pipe cleaning operations on that segment, then the moderately surcharging segment within SE 4 t h Street could be left as is. ' City of Renton Heather Downs Interceptor Improvements Feasibility Report Page 24 Appendix A August 2008 APPENDIX A Alternatives Maps City of Renton Heather Downs Interceptor Improvements Feasibility Report • ,. r ere t _ .- .. *, O O w f.. MH#46 I. QAVA D• • . O O O O D� O Q O— 'MH#24 MH#23 .,.. O MH#22 �Z . Q O O O 0- 0 `�► O W t - r MH#11 6 ' O'•?s' 0. •.v I� .p— - — O rW ""r1 • .L • p O MH#12 r ; .O. .0 `• Q -Q O i '_� p+ Qom— _ — ' �CJ�Q`� �• %' A p �}" " O p i ~ MH#2 MH#3 I MH#14 \y tj _ +ley O - Q O 0. MH#3�&H#35- MH#34 MH#33 MH#32 MH#1 O !. �MH#37 n Azs-}+• �� . wgrr•'..n �' . ''_ �• . �1['�t. �lr •:- � � .tk.. ..+'� � sae' -� t w Jr � .: S, . �� � ♦y .,. ,yew• • .• •yAN,K• ' 7 an Pap. O rr-.& y w ys p 'w ►t T , y a `,r r • * ��M��Mi `'` v''.r;•r it ti �+ • .. < • Legend 46 O cy� ' • + MAPLEWOOD • •. .GOLF COURSE• , Q Existing Manhole , i Existing Sewer Heather Downs Interceptor �• _ i Proposed 12-inch Upsizing _ Trenchless Alternate 1 Surface Alternate 2 :�. Trenchless Alternate 3 HEATHER DOWNS t `• t4 �• 1 INTERCEPTOR UPGRADE l(+ ,� •� N APPENDIX A N-- ALTERNATIVES Rot h H i l l Appendix B m m m m m m it m m m m m its m m m m m it August 2008 APPENDIX B Hydraulic Analysis Results City of Renton Heather Downs Interceptor Improvements Feasibility Report J Q c c c c pp '< r 0 w D m t)D W �o L v m CD � (D CDc v _ 0 0 o ,y �_ a v v v v 1n fl Q Q N o 00 o N dim 4% ro r I' A, 0 r -- i Edmonds Ave. E p � r Zi y w 14' V1 yj - Y •I / y 0 W �_ Z A RR y LA R R R Y � w H C 1 IY 02, R rk TW O e N i Monroe Ave NE 1z - QCO- -_- _=fill q� rt m 7 FAN 4,' al -- ---- - - N ' �t Ln T 0 � N �---•ti g l0' SC � rn a n� +� r s < o m c� �ET r r T. a 1r IV 4IR j R ffi 1n 03 = �r � m a N 4 - = m �' m 1Y 1r 1s a A a - 4 — Is, ` 1.P � 4 S =A � � v � r to 13O$1 Ave SE remertop Avq S 4 4 D _ r r 8' ti r 140th Ave m � , Q. C 'N W Cn m � r 142nd Ave SE 142 Ave E w ml Na �s a �1z m C F143rd Ave SE rd A ve m w 144th Ave SE : 144th Ave SE R s ericho Ate NE W City of Renton Roth Hill Engineering Partners, LLC. Heather Downs 2600 116th Avenue NE #100 z Alternate B1 -Feasibility Report � ®� � �' RTel425.869.9448 I I Bellevue, Washington 98004 Figure 2A - Updated From %ft.I 2001 Model Results - Scenario 1 Fax425.869.1190 °PD< 75' .g �i- i I I' 128 •" -779 2v 102 103 121 120 24• 0.\ 076 zo2 9B ..-•' g �� 1 Itt jr 109 6, 110 IF ve `.`-029 - " 810 29 51 V i, 74 31 9 L. 11 801 gq Q 25 a t ' Z yJ 270152 �271 R. 112 73 7 13/ 307 3015 314 ; 53 r NE r b - U 3A t.. 321 r 24• 44Q I 55 9 -- 87 �B I I �7I�' - 57 r 110 139 386 �f830 828 �+ 0 4 e 86 W 170 8. 111 W ' 24' • 319 •� CO ■ 3 �� 59 b 56 h in 314 3 4827 L - • 84 -179 •� �i 320 ♦ 308 0. g•5 Q• 177 175 200 ,�4 325 72 E 2nd St "ItI r �e3 Zvi �- i i ap 326 1 2{Z7 • 213 boA 93 r Ak fYi 162 8. -^817 95 164 % " _ f • f 1d 802 r 92 }191 'r W 179 17 'H2 s r 285 10 10' 6 Ir 88 2 21 p T 819 2 66 W816 W 163, T 2B6 °e 281 w R ° 6+ 59 fA L H3 2t' l I l' 803 89 (� -----® �,1c i 63 189 I88 j 17] IM i 7 282 203 7/ 6• I 93 92 i 76 NE 9 1st 62 i 00 9' -� � 145 1283 �' •f a 804 91 ' r 471 a• < 1 i 1B2 r 70 284 BD 171 175* i� �y 6' 11; 2 227 I° 61 O . 82 205 75 .2 4N. - E 170 176 79 S E 1st PI 56 185 I } I81 309 4 ,4 E 1 r W 169 177 I, 6 206 76 228 0.5 51 50 r 12 r 5 IB 168 4t Ev ree i I n 82A 174 t � 96 � 814 -- 55 1 7 '_♦94 B29 _ i 190 Pf. 312 311 46 77 232 • 222 38 r 48 1. i g" � ' 178 179 310 ° SSE 2nd PI g• lam- - � 3 z9s C' • � „B 14 32' r 332 161 7B 235 (P 280 ed 2% 283 287 ] H9 •� 1 333 339 168 02' 162 1c r 31 r 33 r 801 r r 29 rf �y 286 r •i • ' R %6 65 291 29 ' 316 3 3 �. Q LJf 271 216 26 R 4p 39 447 0 3 75 2 28_. �281{ �8'150 R' \ 330 34 r 159 257 1 27 1i< �.. 2 87 7 81 i 34 341 2" 2 r 29 It E J 86 Y a`2 R 2': 151 344 r31357 .0 158 258 824 241 i 42 S 115I52383 rr 1 1 827 2 819+d6 R I' 262 255 44 821 24 17 c �� 1 299 256 16 r `�� 10 i 1 5 d -17 �� 251r r yr �y 15_ i T 16 252 31 2 14 302 RIO-I8 1:j4 4 48 ar 303 825 247 W 155 a 0 6 4 305 R 9 RIO-23 10-2/ 94 8 36 W 269 .. _.. 248 q RIG-25 4 S C/Y�] 37 \� 306\IO 20 RIO_ RIO-22 R10- 2 27 IV 12' 5 7 6 r V l� % . a Rlo- F 9 10 t1tYU n 06 24 1' 23 39 4125 Conceptual Alignment of \ R10 2 41 a 0. " 114 New 10-Inch Sewer x� 16 �♦ v 19 70 IB LEGEND Study Area Boundary Mini -Basin Boundaries Upsize to 12-inch Diameter Pipes New 10-inch Diameter Pipe R10 2 a 76 .6, 20 12 79 r 13 IS. B 17� 14 b R 4'' 16 • ENSINGTON CREST RIO-30 e} 2" r � LIFT STATION �.�809 y 3 L-33 256 r 255 Rto-. R 251 10-32 250 r 25` 1249 244 216 r 247 yt • 91 243 242 b 239 240 241 B R10- RIO " •4. 9 1 • 2,. -- 218 20' 200 / ...�2n _ 216 •6 • 9 gam•. 17 ®202 �203 H' �^ •2207 215 40 6 if Its. 1 c 3 V \-A I % 85 a - f ....8I9 "'62 107 i 1 169 101 :4810 06 95 i 168 815 143 144 w 813 yy Z 148 m 149 174 O 147 173 C SE 132 d St 806 i U � NTS w U) ♦ 805 IBI U 3 B Q SE 136th St O V O O J # m0 Z c 0 fn r - T ny' L > N J Q3 L ID [D C D 00 °D _ LO 'n L L O N N V Co a-N m I.- 1i o0 c � N • � C SE �g1st St c W MC SE 142nd St = U) W (/1 0 f 7 � Q Q -C O C 2 04 co n U7 RIO-41 RID-42 o 0Li a,m� NNc O t m i U Q = _ 0 _ Q [feet] 181000.0 180500.0 180000.0 179500.0 179000.0 178500.0 178000.0 177500.0 177000.0 176500.0 176000.0 I ■ 1.20 < a 1.00 1.20 V 0.80 1.00 0.60 0.80 < 0.60 1307000.0 Q / Q-manning - Maximum Heather Downs 2001 -Surveyed. PRF Y _ v A�✓� 1308000.0 1309000.0 1310000.0 1311000.0 1312000.0 1313000.0 [feet] 1b Link Water Level - 24-11-1990 12:33:53 Heather Downs 2001-Surveyed.PRF Discharge 087 �.� 2.066 1.964 1.943 1.922 1.905 11.8871 1.869 11.77311.755 1 1 1.719 1 1.696 1.650 1.606 1.600 1.598 cfs t��Po 0`t' O� `L� �L�O rL� rL�` `L`� `L�' ti� ,tio ,�� �� �'l rbC, t�, (d �O �O rd � rO rd 60 �O N �O �O �O qO �O �O roO [feet]� � �� � � � 69.0 68.0 67.0 66.0 65.0 64.0 63.0 62.0 61.0 60.0 59.0 58.0 57.0 56.0 0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0 1800.0 2000.0 2200.0 2400.0 2600.0 2800.0 3000.0 3200.0 3400.0 3600.0 1:0 [feet] NT (D N OD N N N N N N CD CO N (D p f� Ground Lev. U� tD M N h Cp N (9 (D N (n N O O) N N M N N M et M M M M U1 (D (� [m] C.(D (D CD (D (D CD CD CD CD (D (D (D CD CD CD CD Cn p CO 0) r- 0 p M (D p CO p N It 00 � Invert lev. r N ? r,17 p N M U? O V: Cn � p [m] LO Cn (O W Il- Il- 00 CO CO CO CA p M p J CA Ul) (n Cn (n (n V) Cn (n (n U) (n (n CD uO (D CD Length 229.91 391.38 337.82 184.50 262.59 231.86 294.66 216.78 229.49 201.52 219.87 [m] Diameter 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.00 1.00 1.00 0.83 [m] Slope o/oo 2.86 0.83 0.56 1.23 1.15 1.73 0.85 0.91 0.17 0.25 1.51 1.38 1.05 2.08 2.35 2.68 3.87 Link Water Level - 24-11-1990 12:24:53 Heather Downs 2001-Surveyed.PRF Discharge 1.614 1.613 1.602 1.167 1.151 1.140 1.130 cfs �ro1z,�� �1b��� ���roll'�� [feet] 4�1 365.0 360.0 355.0 350.0 345.0 340.0 335.0 330.0 325.0 320.0 315.0 310.0 305.0 300.0 295.0 Ground Lev Invert lev. Length Diameter Slope o/oo 0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0 900.0 1000.0 1100.0 1200.0 1300.0 1400.0 1500.0 1:0 O O CAD O M CNO co O O ca M co LO M M M co M co Cl) O U? IR N V: CV Cl? O O O O N N N M M M M M M 250.76 119.98 256.04 190.69 354.78 251.87 178.10 0.83 0.83 0.83 0.83 0.83 0.83 0.83 43.71 4.17 4.34 4.20 33.18 26.28 172.38 1600.0 [feet] [m] [m] [m] [m] Link Water Level - 24-11-1990 12:24:53 Heather Downs 2001-Surveyed.PRF Discharge 1.119 0.730 0.683 0.669 f 0.654 0.639 0.578 0.541 1 0.527 1 0.502 10.4901 1 1 10.38410.034 0.023 cfs 00 b` O �`� �`1' �N �`f' �"� `l,� �'1 fir° ph p,D� p`� h�O tot 4lb 3 h0 O O O O O O O O O O O O O O O O O O N� �� �� �� �� �� �h �h [feet] �`� �`� �'� hO hO �� hO h� 00 h� 4O 4 �� hO 4� hO 4P 4 hO 390.0 388.0 386.0 384.0 382.0 380.0 378.0 376.0 374.0 372.0 370.0 368.0 --�� 366.0 364.0 362.0 360.0 358.0 0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0 1:0 Ground Lev. O Cl? CA 7 O °' N °0 (D "i M O 'T rn M O O M CO O O rn v N M t_ C4 IT (D O 00 O O 't 00 r• (V r` N r-- •-- 00 'T rl- CO O n r__ O O r• CO CM (M CO M M M M M Cl) M M CO M M M Invert lev. N O N 7 CM f- M CD O O 9 CD � - 00 M (D (M O O � O 00 O O O O CD - (D N CD M CD CD CD CD COD CD (OD (OD �O OI- ti M M M (M Cl) M ('r1 M CV) M M M M M CO Length 300.35 272.73 257.37 478.04 450.24 345.20 291.02 216.35 221.94 358.15 Diameter 0.83 0.83 0.83 I 0.83 0.83 0.83 0.67 0.67 0.67 0.67 0.67 0.67 Slope o/oo 2.83 4.33 3.15 3.08 2.00 1.10 4.47 1.80 5.00 3.49 7.19 6.68 4000.0 [feet] � � CC) O � [m] O0i C I M M M h (V ( [m] N M M M M 279.45 [m] 0.67 0.67 0.67 [m] 2.71 5.56 3.44 [feet] 181000.0 180500.0 180000.0 179500.0 179000.0 178500.0 178000.0 177500.0 177000.0 176500.0 176000.0 [] ■ 1.20 < ■ 1.00 1.20 ■ 0.80 1.00 ■ 0.60 0.80 < 0.60 1307000.0 Q / Q-manning - Maximum Heather Downs Ultimate-surveyed.PRF c Pv 1 1308000.0 1309000.0 1310000.0 1311000.0 1312000.0 1313000.0 1314000.0 [feet] ,lb" Link Water Level - 24-11-1990 12:17:22 Heather Downs Ultimate-surveyed.PRF Discharge 1 P.62 2.487 2.468 1 2.451 12.4i4 2.417 12.32212.306 1 1 2.272 1 2.253 1 2.215 2.179 2.214 2.278 cfs p`5 `L�` `Lp CO, 1L1 `f, NCB 'gyp �.� �h �`l. ,�b ,�. pp 'd p0 p0 pp Cd p0 pp pR p0 pp pp p0 p0 p0 pp p0 �,N 60 p0 [feet] �� 4 5N4 5� p� 4p1 4p� 4`5� �p� �p,�p� 4p)N �pN 4N p� 4;5 �p� �p� �p� �pN 69.0 68.0 67.0 66.0 65.0 64.0 63.0 62.0 61.0 60.0 59.0 58.0 57.0 56.0 0.0 200.0 400.0 600.0 800.0 Ground Lev. � v (D 17 1- Un N cD N (D M (D N (D N (D Invert lev. U) cq M a? CO 1 a) N U) � � LO Length 229.91 391.38 Diameter 1.25 1.25 1.25 1.25 Slope o/oo 2.86 0.83 0.56 1.23 CO M M (D to LO 1000.0 1200.0 1400.0 1600.0 1800.0 2000.0 2200.0 2400.0 2600.0 2800.0 3000.0 3200.0 3400.0 3600.0 1:0 [feet] N N N N N N (O N U) (D N CO U? N N (D O O O I� N [m] ct CD M (D CO (D (D M CD Cl) U) (D (D (D (D (D CD M O (D v (n r� O rn M N (D M O M v Un (D O N v rn CO v I� o [m] (n (n LO 00 (n CO U') CO 00 (n U) a) U') rn (n a) In O (D (D 337.82 184.50 262.59 231.86 294.66 216.78 229.49 201.52 219.87 [m] 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.00 1.00 1.00 0.83 [m] 1.15 1.73 0.85 1 0.91 0.17 0.25 1.51 1.38 1.05 2.08 2.35 2.68 3.87 Link Water Level - 24-11-1990 11:53:22 Heather Downs Ultimate-surveyed.PRF Discharge 2.291 2.291 2.278 1.702 1.689 1.676 1.664 cfs �60�1 ��� ��� �6O�R rOZ ti N [feet] 365.0 360.0 355.0 350.0 345.0 340.0 335.0 330.0 325.0 320.0 315.0 310.0 -- - 305.0 300.0 295.0 0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0 900.0 1000.0 1100.0 1200.0 1300.0 1400.0 1500.0 1600.0 1:0 [feet] Ground Lev. o c° 0 Cl? C° ry o to _M Sri v M co co 0 [m] M co M co M M co Invert lev. a0 °' `Q `o `: M rn O 0 O 0 N N [m] (V M M M co CO M Length 250.76 119.98 256.04 190.69 354.78 251.87 178.10 [m] Diameter 0.83 0.83 0.83 0.83 0.83 0.83 0.83 [m] Slope o/oo 43.71 4.17 4.34 4.20 33.18 26.28 172.38 Link Water Level - 24-11-1990 11:53:22 Heather Downs Ultimate-surveyed.PRF Discharge 1.651 1.135 1.075 1.061 1.046 1.031 0.956 0.910 I 0.896 I 0.866 10.8511 I I 10.7181 10.2821 0.271 I cf ix tl N1 N tx O h h O h h 00 00 Oo O� OHO O�� O�� O� 00 O 0o O� O 00 0o 0o 00 [feet] ta`� �,`� �`� �`� h'S ho �'� �� �'� �h�� h0 �h 390.0 388.0 386.0 384.0 382.0 380.0 378.0 376.0 374.0 372.0 370.0 368.0 366.0 364.0 -- 362.0 -- --- 360.0 - 358.0 0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0 4000.0 1:0 [feet] Ground Lev. °' a) 17 w r It °) N 0D LD M M o rn M o a) M CO CO N M rl- Ln rn v r` (p o LO r-: a) U? v cD It r` v rl- o ao M CO It CO It r- c i N rl- - oo v ao a) ai o ai r` rl- ti r` CO rl- CO r-- I- F1- [m] M M CO CO M M CO M M M CO M M CO CO CO CO M Invert lev. N N M `° a) Ln r` 17 CD CO Ln o CO CO O in r- N N rIt ao Ln ai Ln o LD LD �i co CO LD v cD Lri CD 0 cD cD ao ai o o CD cD r` rl- r- t` [m] M CM M M M M M M M M CO CO CO CO M M M CO Length 300.35 272.73 257.37 478.04 450.24 345.20 291.02 216.35 221.94 358.15 279.45 [m] Diameter 0.83 0.83 0.83 0.83 0.83 0.83 0.67 0.67 0.67 0.67 0.67 0.67 0.67 0.67 0.67 [m] Slope o/oo 2.83 4.33 3.15 3.08 2.00 1.10 4.47 1.80 5.00 3.49 7.19 6.68 2.71 5.56 3.44 Appendix C August 2008 APPENDIX C Shannon & Wilson Preliminary Geotechnical Report City of Renton Heather Downs Interceptor Improvements Feasibility Report Preliminary Geotech Report Preliminary Geotechnical Report Heather Downs Interceptor Upgrade King County, Washington May 29, 2008 Submitted To: Mr. Erik Waligorski Roth Hill Engineering Partners 2600 116th Avenue NE, Suite 100 Bellevue, Washington 98004 By: Shannon & Wilson, Inc. 400 N 34th Street, Suite 100 Seattle, Washington 98103 21-1-20730-001 Revised 5/30/08 Appendix C TABLE OF CONTENTS SHANNON 6WILSON, INC. Page 1.0 INTRODUCTION.................................................................................................................1 2.0 SITE AND PROJECT DESCRIPTION.................................................................................1 2.1 Site Description..........................................................................................................1 2.2 Project Description.....................................................................................................2 3.0 GEOLOGY ............................................................................................................................2 3.1 Regional Geology.......................................................................................................2 3.2 Site Geology...............................................................................................................3 3.3 Groundwater...............................................................................................................4 3.4 Slope Stability............................................................................................................5 4.0 CONSTRUCTION METHOD ALTERNATIVES................................................................5 4.1 Trench and Ground Surface Construction..................................................................6 4.2 Trench Construction...................................................................................................6 4.3 Trench and Trenchless Construction..........................................................................7 5.0 ALTERNATIVE CONSIDERATIONS..............................................................................10 5.1 Anticipated Benefits and Difficulties.......................................................................10 5.2 Opinion of Probable Costs.......................................................................................11 6.0 LIMITATIONS....................................................................................................................12 LIST OF FIGURES Figure No. 1 Vicinity Map 2 Site Plan 3 Profile A -A' Surface Alternative 1 4 Profile B-B' Surface Alternative 2 5 Profile C-C' Trenchless Alternative 1 6 Profile D-D' Trenchless Alternative 2 7 Profile E-E' Trenchless Alternative 3 APPENDIX Important Information About Your Geotechnical Report 21-1-20730-001-R l.dodwp/EET 21-1-20730-001 1 Preliminary Geotech Report Appendix C - 3 SHANNON &WILSON, INC. PRELIMINARY GEOTECHNICAL REPORT HEATHER DOWNS INTERCEPTOR UPGRADE KING COUNTY, WASHINGTON 1.0 INTRODUCTION This report presents the results of a feasibility study of alternatives for construction of a 10-inch- diameter sanitary sewer main as part of the Heather Downs Interceptor Upgrade Project, located in Renton, King County, Washington. The project will increase the capacity of the existing sewer system by constructing a new sewer main from the top of the plateau down the steep slope of the northern wall of the Cedar River valley to the valley floor. Evaluation of alternatives is the first phase of this project, after which detailed studies of the chosen alternative would need to be accomplished. The scope of Shannon & Wilson's services for this phase of the project included: P. Identification and review of existing available geotechnical and geologic information in the vicinity of the project, including geologic and Light Detection and Ranging (LIDAR) maps, logs of borings and wells, and aerial photographs. P. Performance of a geologic reconnaissance of the slope in the vicinity of the proposed alternatives to identify surface geology and features such as unstable soils, landslides, springs and seepage, and other surface information. ► Evaluation of construction alternatives and development of an opinion of probable construction costs. Our services for this project were authorized by a contract between Shannon & Wilson, Inc. and Roth Hill Engineering Partners, LLC, dated April 10, 2007. 2.0 SITE AND PROJECT DESCRIPTION 2.1 Site Description The proposed project is located in City of Renton (City), King County, on the northern side of the Cedar River valley, as shown in Figure 1. The proposed 10-inch sewer main would descend from the top of the plateau, down the steep slope of the north valley wall to the floor of the Cedar River valley. This steep -slope portion of the project is anticipated to extend from the southern 21-1-20730-001-RLdodwp/EET 21-1-20730-001 1 Preliminary Geotech Report Appendix C- 5 SHANNON 6WILSON, INC. end of Union Avenue SE down to the Maplewood Golf Course below. Potential construction alternativesthat were considered include surface -mounted, open -cut trenching and trenchless construction methods such as horizontal directional drilling. The pipeline alternative alignments we evaluated, provided by Mr. Tony Fisher, Roth Hill Engineering Partners, are shown in the Site Plan, Figure 2. The upland plateau is relatively flat but gently undulating, sloping to the south toward the Cedar River. A small stream has formed a deeply incised, northeast -trending valley into the plateau. The hillside in the vicinity of the proposed surface alternatives is approximately 200 to 240 feet high. The upper 100 feet of the hillside tends to slope at 20 to 25 degrees from the horizontal, while the lower 50 to 100 feet is more steeply inclined at 35 to 40 degrees. 1 2.2 Project Description The Heather Downs Interceptor Upgrade project involves increasing the capacity of the existing sewer system by constructing a new sewer main and upsizing existing sewer pipe in the residential area above the north valley slope. The new sewer main will collect and convey sewer flow from the upland area down to one of the existing sewer mains located along the valley floor. Our evaluation addresses only alternatives for constructing the new pipeline down the steep hillside. It is our understanding that the proposed sewer main will be continuous, fuse -welded, high - density polyethylene (HDPE) pipe 10 inches in outside diameter. Alternatives that we consider appropriate for constructing the sewer mains at the proposed steep location include: (a) placing the pipe on the ground surface, (b) placing the pipe in a trench excavated down the steep slope, ' and (c) using trenchless construction methods, such as horizontal directional drilling (HDD). Each of these construction alternatives offers advantages and disadvantages. Other than the steep slopes, many of the difficulties associated with these construction method alternatives are related to the underlying geology. ' 3.0 GEOLOGY 3.1 Regional Geology The site is located in the central portion of the Puget Lowland, an elongated topographic and structural depression filled with a complex sequence of glacial and nonglacial sediments that unconformably overlie bedrock. The area has been glaciated six or more times in the past 21-1-20730-001-R1.doc/wp/EET 21-1-20730-001 ' 2 Preliminary Geotech Report Appendix C - 6 SHANNON 6WILSON, INC. 2 million years. The distribution of the sediments is complex because each glacial advance deposited new sediments and partially eroded previous sediments. Between glacial episodes, the complete or partial erosion or the reworking of deposits, as well as the local deposition of other sediments, took place. During the last glacial advance, known as the Vashon, the ice was about 3,000 feet thick in the Seattle area. The Vashon ice sheet receded from the area about 13,500 ' I years ago, leaving topography characterized by low -rolling relief to about 500 feet above sea level, with some deeply cut ravines and broad valleys. Since then, present-day geologic processes, such as erosion and deposition by streams and landsliding, have modified the ground surface and further complicated the geology. 3.2 Site Geology Our understanding of the geology at the site is based on scattered exposures of soils observed in old road cuts and along the sidewalls of the Maplewood Creek valley, the logs of several borings located over 1 mile to the east previously drilled in 2006 for the Central Plateau Interceptor, the logs of borings previously drilled for the Maplewood Creek Sedimentation Basin and the Maplewood Treatment Facility, logs of water wells located more than 2,000 feet from the site, and on our general understanding of the geologic history and stratigraphy of the region. Our interpretation of the geologic conditions at the site is depicted in the generalized subsurface profiles shown in Figures 3 through 7. These profiles were constructed at approximate locations of alignments proposed by the City from topographic contours generated from King County LIDAR data. The geologic deposits that underlie the site consist largely of Vashon and pre-Vashon glacial and nonglacial sediments that have been overridden by glacial ice one or more times and are very dense or hard. These deposits are generally overlain at the ground surface by a thin layer of Vashon or post-Vashon (Holocene) deposits that have not been glacially overridden. The geologic deposits that compose the upper portion of the hillside are very coarse, as indicated by the abundant gravel and scattered cobbles that litter the ground surface and are exposed in the sidewalls of a former, nearby gravel pit situated at about the same elevation. Generally, finer - grained deposits comprise the lower portions of the hillside. Geologic maps indicate that deposits of recessional outwash exist as a thin blanket of variable I , thickness across most of the upland plateau in the vicinity of the proposed project. These outwash deposits are expected to be on the order of 5 to 15 feet thick and to consist of clean to Isilty sand or gravelly sand with abundant cobbles and boulders. These sediments have not been glacially overridden and are commonly loose to medium dense. The steep hillside has a surficial 21-1-20730-001-RLdoc/wp/EET 21-1-2073 0-001 Preliminary Geotech Report Appendix C - 7 SHANNON &WILSON, INC. of seepage was observed on the hillside at an approximate elevation of 270 feet, approximately corresponding to the top of the finer -grained deposits. Seepage may also be expected to occur, at least seasonally, at the contact between the surficial layer of recessional outwash and the underlying till, just below the top of the plateau surface. 3.4 Slope Stability The scars of several shallow landslides were observed in the vicinity of the steep -slope portion of the project on stereo -pair, aerial photographs taken as far back as 1936. The majority of ' landslide scars were located on the deeply incised slopes facing Maplewood Creek. Most of the landslides observed on the photos were small, surficial failures resulting from undercutting by Maplewood Creek. Only a few landslides were observed on the hillsides facing the Cedar River, and most were located to the east of the project area. No evidence of fresh landsliding was observed in the field except along Maplewood Creek, approximately 600 feet upstream of the lower portion of proposed surface alternative 2, where stream erosion had undercut the stream bank or oversteepened the sideslope. No active, large, or deep-seated landslides were observed or indicated by the aerial photographs; however, the presence of jack-strawed trees and thicker colluvium on the lower hillsides facing the Cedar ' River and along Maplewood Creek, suggests minor but steady soil creep has occurred over the last 50 years or more. In general, the slopes on the hillsides appear near the limit of stability for near -surface slide failures. Disturbance of the slope soils could contribute to instability unless ' mitigation measures are utilized. 4.0 CONSTRUCTION METHOD ALTERNATIVES Laying the pipe on the ground surface with anchors, trenching, and trenchless methods (HDD) ' are all feasible options to traverse the steep slopes in the project area, as shown in Figure 2. On the western portion of the hillside, we considered a single surface or trench alignment to traverse the steep slope along the power transmission corridor down to SE 5th Street, as shown in Surface ' Alternative 1 (Figure 3). The slope has been modified for the Williams pipeline at this location and is approximately 20 degrees at the top and 35 to 40 degrees at the base of the slope. For the eastern portion of the hillside, in the vicinity of Maplewood Creek, we have considered four alternative alignments to reach the valley floor. The second surface or trench alternative ' (Surface Alternative 2, Figure 4) utilizes the knife-edge ridge that separates the north wall of the Cedar River valley from the northwest side of the incised Maplewood Creek valley cut into the 1 21- I-20730-001-Rl.doclwp/EET 21-1-2073 0-001 ' S Preliminary Geotech Report Appendix C - 9 ' SHANNON &WILSON, INC. plateau. The last 100 feet of this alternative falls steeply (approximately 40 degrees) down the ' incised valley wall near the entrance of Maplewood Creek to the Cedar River floodplain. ' The first trenchless alternative (Trenchless Alternative 1, Figure 5) has the entry pit on the west side of Maplewood Creek, just within the confines of the creek valley. The exit pit for this alternative would be located on the top of the plateau, southwest of Union Avenue SE within the forest. Trenchless Alternative 2 (Figure 6) also has the exit pit southwest of Union Avenue SE; however, the entry pit would be located east of Maplewood Creek, in the vicinity of the Maplewood Treatment Facility. This alternative has the advantage of accomplishing the creek crossing with HDD construction. Trenchless Alternative 3 (Figure 7) places the entry pit on the west side of Maplewood Creek, as in Alternative 1, and the exit pit at the south end of Union Avenue SE. 4.1 Ground Surface Construction ■ Proposed alternatives for trenching and ground surface installations are shown in Figure 2. Perhaps the simplest method of constructing the pipelines down the hillside is to place the pipe in ' a trench along relatively level ground and, where the ground is steep, lay the 10-inch pipe on the slope with intermediate anchors and pipe collars to restrain lateral and downslope displacements. On the west portion of the hillside, surface Alternative 1 may not be appealing because the pipe would be partially visible from the roadway. At Alternative 2, within dense tree cover, a surface installation would be more obscured. The pipeline would need to be restrained by helical or similar anchors on the slope and collars or cradles on the pipe. The lower portion of this alignment lies along a narrow ridge that is as little as 25 feet wide in places. Instability on the slope facing Maplewood Creek could encroach upon the pipeline, requiring pile or other support. This possibility would be evaluated further in future studies if the alternative were selected. 4.2 Trench Construction Proposed alternatives for trenching are also shown in Figure 2. The two alternatives follow the ' same alignments as the surface installation options. We anticipate that trenching on the slopes would be shallow, but trenches would need to extend below looser, surficial soils subject to downhill creep. Depending on the required grade of the pipeline, a trench extending southwestward from the southern end of the utility right-of-way may need to be relatively deep until reaching the edge of the plateau. All trenches would be backfilled with granular material. ' Since the trenches can be a source for groundwater accumulation and direct flow toward the bottom of the slope that may cause slope instability, the steep slope trenches would have to be 21-1-20730-001-RI rev.doc/wp/EET 21-1-20730-001 Revised 5/30/08 Preliminary Geotech Report Appendix C - 10 1 SHANNON 6WILSON, INC. drained. A perforated pipe would need to be installed along the bottom of the trench that transitions into a tightline with a cut-off dam. The steep -slope portions of the trench should be aligned directly along the fall line. Trench construction on steep slopes can usually be performed on slopes as steep as 45 degrees. Steep slope construction, however, would require the use of backhoes attached by cables and winches to the top of the slope or the use of specialized equipment with hydraulic support attachments (spider backhoe). At the base of the hillside, the existing slope is approximately 40 degrees, which will make the trench excavation very difficult. Near -surface trenching for a pipeline would most likely encounter recessional outwash (sand and gravel with cobbles and boulders), till (dense gravelly sand with cobbles and boulders), sandy gravel in the upper half of the slope, and the fine sandy silt in the lower part of the slope. The upper sand and gravel would be easily excavated, but trench sidewalls may cave to slopes of 30 degrees or flatter where they are water bearing. The till would be difficult for a small backhoe to excavate but relatively easy for a larger track -hoe with a toothed bucket and hoe -ram attachment. Perched water is likely on top of the till and in sandy lenses within the till, but neither source is likely to be recharged. Trench sides in the till will be nearly vertical but will need to be shored for safety purposes if depths are greater than 4 feet and if they will be occupied by construction workers. It would be possible to reuse the silty sand and the gravelly sand for backfill during dry weather. During wet weather, native soils could be used as backfill provided the fines (soil particles finer than the No. 200 sieve) do not exceed 5 percent, based on the minus 3/-inch fraction of the soil. Where wet, the soils would probably not be suitable for reuse at any time of the year. The till is not suitable for reuse during wet conditions, and in some cases, its natural moisture content is already sufficiently over the optimum moisture content to preclude its use as a backfill material. 4.3 Trenchless Construction ' The proposed alternatives for using trenchless construction are shown in Figure 2. Because of difficulties explained below, the target location of the pipe at the top of the slope needs to be flexible to allow variances of the drill path. The elevation difference between the start and end points(approximately 200 feet) makes the use ' of HDD methods for installing the 10-inch-diameter pipe preferable to tunneling methods. Tunneling methods, such as auger boring, would require that a deep shaft (almost to the elevation of the lower end of the pipe) be constructed at the top of the slope, because typical 21-1-20730-001-R1.dodwp/EET 21-1-20730-001 Preliminary Geotech Report Appendix C - 11 SHANNON 6WILSON, INC. tunneling installations are installed at a grade of less than 10 percent and not at the steep slopes required for this installation. HDD consists of drilling a pilot hole from the bottom of the slope upward to the top of the slope and then pulling back the sewer pipe through the enlarged pilot hole. The initial, approximately 3-inch-diameter hole is drilled while the drill path is controlled with a walk -along, location - tracking system that monitors the depth and location of the drill head. After the pilot hole is drilled, the hole is reamed to a larger diameter. In this case, to install a 10-inch HDPE pipe, the hole needs to be enlarged to about 16 inches. Once the hole is enlarged, the pipe is pulled back through the hole. Bentonite slurry is used during the drilling and reaming operations to remove the drill cuttings from the hole. This slurry circulates through the drill steel to the drilling bit and returns with the cuttings in the annular space between the drill steel and the open hole. The bentonite slurry also forms a cake around the borehole to help stabilize the opening. Drilling typically starts at the toe of the slope, and bentonite slurry is collected in a pit, located at the toe of the slope, and then re -circulated. The slope of the drill path starts at about 10 degrees below horizontal and gradually increases upward, following a large -radius arch until it reaches a constant slope to reach the top of the hillside. The radius of the vertical curve is typically between 800 to 1,200 feet; the minimum radius is a function of the drill steel diameter and the pipe diameter. A longer radius will facilitate installation and result in lower pullback loads. As discussed in Section 3, the Heather Downs Interceptor slopes are underlain by fine-grained soils in the lower half of the slope (up to about elevation 270 feet) and more granular soils in the upper portion. The fine-grained soils consist of sandy silt to silty fine sand, and the granular soils consist of sandy gravel, gravelly sand, sand, and gravel. Cobbles (3 to 12 inches in diameter) and boulders (12 inches to 3 feet in diameter or larger) are present in the recessional outwash and till deposits, which would be obstacles for the installation of pipe by the HDD method. The drill head will not be capable of drilling through boulders, and the presence of cobbles will hinder the reaming operation. In the event of encountering a boulder, the drill path will have to be modified to reach the top of the slope. The drill steel would have to be retracted for about 15 feet and steered deeper into the slope to avoid the boulder. For the anticipated conditions, there needs to be flexibility for the exit point at the top of the slope since the drill path may have to be modified if boulders are encountered. Possible targets for the exit point include Union Avenue SE and the yard surrounding Seattle Public Utilities' (SPU's) pump station. 21-1-20730.001-R I.doc/wp/EET 21-1-20730-001 8 Preliminary Geotech Report Appendix C- 12 SHANNON 8WILSON, INC. In general, HDD is most successful in medium hard to hard, silty, and clayey soils and even rock, all of which form relatively stable boreholes. In non -cohesive soils, such as sand and gravel laced with cobbles and boulders, HDD projects have experienced serious problems with caving holes and jammed and lost drill bits and rods. These holes usually require additional time and preparation procedures, such as pulling hole compactors through the completed bore. The drilling fluid serves to return the cuttings and also to stabilize the circumference of the hole and prevent collapse, particularly in granular soils. However, the drilling fluid generally establishes a more capable "cake" of mud -impregnated soil around the periphery of the drilled hole in silt and sand. Gravel layers may be too coarse to rapidly establish a stabilizing cake, particularly where groundwater is flowing into the drill hole. HDD pipe installation requires two staging areas. A staging area at the bottom of the slope would be required for the drilling machine and a mud pit. A temporary pipe assembly area is required at the opposite end of the hole from the drilling machine. Generally, contractors prefer an area with a length equal to the total hole length with a width of approximately 12 to 15 feet to lay out and pre -assemble pipe sections for rapid installation of the completed pipe as soon as the hole is drilled. Pipe installation involves a rapid and continuous pull to reduce the risk of collapsing the hole. ' Sidehill bores are typically drilled uphill, where possible, to reduce the chance of hydraulically fracturing the soil, which could result in a spill. Mud cakes can be developed by using hole ' compactors as the bore fluid runs by gravity out of the hole as fast as it is injected. The highest risk for these types of bores is the chance that the bore will drill up and into perched water in a granular deposit. The sudden release of perched groundwater into the bore can destabilize the ' surrounding ground and result in soil flowing into the bore annulus rapidly enough that the drill steel becomes locked. This problem often results in loss of both the bore and the drill tools. Although a final bore diameter of 16 inches is well within the capabilities of current drilling ' techniques, the lack of a stable cake in gravelly ground will likely promote caving and collapse of the hole. Collapse of gravelly soils during pulling of the pipe into the hole, behind the ' reaming tool, could result in locking of the casing in the hole. Although, the HDD method may experience difficulties for this installation, the problematic soils are located near the top of the slope. After the pilot hole is drilled and reamed, an approximately 15-foot or longer casing pipe may be installed from the top of the hole to prevent caving of the ' recessional outwash. If a boulder is found within 15 feet of the top of the slope, it could be excavated with a backhoe and backfilled with select material. Selection of an experienced HDD 21-1-20730.001-R1.doc/wp/EET 21-1-20730-001 9 Preliminary Geotech Report Appendix C - 13 SHANNON &WILSON, INC. contractor who has worked in the Seattle area in similar geologic conditions is important for this installation. 5.0 ALTERNATIVE CONSIDERATIONS 5.1 Anticipated Benefits and Difficulties Each of the construction alternatives has potential benefits and difficulties, which should be considered in deciding which construction alternative or combination of alternatives is appropriate for the project. Some factors that may need to be considered were not included in our evaluation. Such factors were not known to us and include ability or ease in obtaining necessary right-of-way, public preference or opposition to certain alignments or design elements, and specific design constraints such as required depth and grade of the pipeline at the top of the hillside. Ground Surface Installation — A ground surface installation is likely to have the least expensive construction cost. However, HDPE may be subject to degradation from ultraviolet (UV) light and vandalism. These may be less of an issue for surface alternative 2, which is farther from the road and has heavier vegetation. At -grade construction would be less likely to contribute to instability of the soils on the steep slopes and less likely to disturb the ground and vegetation than trench construction and surface restoration. ' The alignment should be limited to traversing the steep -slope portions of the hillside directly downslope. Trench installation would still be required at the top and bottom of the slopes. In ' areas where the ridge is too narrow along Surface Alternative 2, support of the ground or the pipe, using piles or other methods, may be required. Surface Alternative 1 appears to be more straightforward, with less risk of instability than Surface Alternative 2. Trench Installation — Installation of the pipeline in a trench is the more conventional approach to constructing a pipeline down a slope. As with an at -grade installation, potential alignments should be limited to traversing the hillsides directly downslope. Like the other below -grade alternatives, the pipeline would not be subject to UV degradation or vandalism. Construction of a trench on the steep slopes would be difficult, particularly for the lower portions of both Surface Alternatives 1 and 2. The excavation would disturb the soils, and special backfill requirements would be needed to keep the fill stable on such steep slopes. Restoration and revegetation would be more difficult than for other construction methods. The hillside in the 21-1-20730-001-R1.doc/wp/EET 21-1-20730-001 10 Preliminary Geotech Report Appendix C - 14 SHANNON WILSON, INC. vicinity of the trench installations would be subject to increased risk of landsliding because of the disturbed soils and the potential collection or conduction of groundwater in the trench. Surface Alternative 1 appears to be more straightforward, with less risk of instability than Surface Alternative 2. HDD Installation — Potential benefits of this method include the lack of disturbance of vegetation and surficial soils on the steep hillside and the greater flexibility of a horizontal alignment. Hillside alignments are not limited to traverses that are directly downslope. A disadvantage of this method is that a relatively large layout area and a large target area are needed at the top of the slope. For the Trenchless Alternatives 1 and 2, the pipe would need to extend along the utility right-of-way that runs along the top of the hillside behind the houses west of Union Avenue SE. For Trenchless Alternative 3, the assembled pipe would need to be laid out along Union Avenue SE. If the HDD-portion of these alignments was drilled starting from the top of the slope, or if the HDD drill switches to the top of the hill after drilling the hole, then the layout area would run along the golf course road for all three alternatives. Another disadvantage is the fact that this construction method, although not uncommon, is less common than other construction methods. Construction of the HDD portion of the alignment would be limited to fewer specialty contractors than construction using other methods. Ground conditions are likely to be somewhat unfavorable for HDD in the upper one-third to one- half of the hillside because of the potential presence of cobbles, boulders, and perched water. Their presence could cause difficulties, add to construction costs, and reduce the probability of success. For Trenchless Alternative 2, there may be a greater risk of drill mud blowout or encountering cobbles and boulders at the base of the slope than for the Trenchless Alternatives 1 and 3. Drilling from below, the target area at the top of the slope would be near a large water main and ' other utilities that lie along Union Avenue SE or along the utility right-of-way that lies behind the houses along the top of the hillside. The least -encumbered target area may be in the fenced ' area that surrounds the SPU pump station, just east of the Union Avenue SE southern terminus. 5.2 Opinion of Probable Costs ' Probable construction costs for the alignments and construction methods discussed in this report are based on preliminary development of pipeline routes. Ranges of estimated unit costs for each of these construction methods are presented in the table below. These estimated construction costs are based on construction estimates previously compiled for the Fairwood Interceptor ' 21-1-20730-001-RI.dodwp/EET 21-1-20730-001 ' 11 Preliminary Geotech Report Appendix C - 15 1 SHANNON 6WILSON. INC. project, recent bids for construction of the Central Plateau Interceptor, data from a survey of 2003 bid prices conducted by the Trenchless Technology Center, and on our experience. Experienced contractors could likely provide estimates that are more accurate for each of these construction methods. A greater contingency percentage of estimated construction cost should be planned for HDD construction to accommodate greater uncertainty of potential costs at this level of study. The indicated costs do not include such things as manholes, revegetation, etc. ESTIMATED CONSTRUCTION COSTS Construction Method Estimated Costs (per lineal foot) At -grade $60 to 120 Trench $60 to 120 Trench on slope $100 to 160 Horizontal directional drilling (HDD) $250 to 400 A more -detailed geotechnical investigation would be needed prior to design, once construction methods and alignments are chosen. At -grade and trench construction would require the least costly geotechnical investigation, because only relatively shallow explorations would be needed. The geotechnical investigation for HDD construction would be much more costly because of the need for one or more deep borings. 6.0 LIMITATIONS This report was prepared for the exclusive use of Roth Hill Engineering Partners and the City for specific application to this project. The discussions of subsurface conditions included in this report are not a warranty of subsurface conditions. Our evaluation was prepared in accordance with generally accepted professional geotechnical engineering principles and practice in this area at the time this report was prepared. We make no other warranty, either express or implied. These conclusions and recommendations are based on our understanding of the project as described in this report and on site conditions inferred from existing information. Additional design studies that include subsurface explorations and engineering analyses are needed prior to design of the project. The presence of unanticipated subsurface conditions could alter our conclusions and impact the potential cost of the project. 21a-20730-00 i-R I .doc/wassT 21-1-2073 0-001 12 Preliminary Geotech Report Appendix C - 16 SHANNON &WILSON, INC. The scope of our services for this -project did not include any environmental assessment or evaluation regarding the presence or absence of wetlands or hazardous or toxic materials in the soil, surface water, groundwater, or air, on or below or around the site, or any evaluation regarding disposal of contaminated soils or groundwater, should any be encountered. However, we will be glad to provide such services on request. Shannon & Wilson has prepared and included in the Appendix, "Important Information About Your Geotechnical Report," to assist you and others in understanding the use and limitations of our reports. SHANNON & WILSON, INC. t4, / �( 26086 GIsrc:� (0:))NAL EN .©(WRES 10/5 zoo Theodor W. Hopkins, L.E.G. Roberto J. Guardia, P.E. Associate Vice President TWH:RJG:WTUtwh Geologic interpretations and investigations were prepared by or under the direct supervision of Theodor W. Hopkins, L.E.G. Geotechnical design recommendations were prepared by or under the direct supervision of Roberto J. Guardia, P.E. 21-1-20730-001-Rl.doe/wp/EET 13 21-1-20730-001 Preliminary Geotech Report Appendix C - 17 U Q O Washington W'\ " Project `% Location CEDAR RIVER Jf � S tiF T„ { %Y n }SA •Ir i iFTF. 4E 5TH T P.l G I I iAL J-.� :_r�r,i>GGr" `y =t�i .•L „� Nr Ky' Y�!t ':r NER -W *�. 4TH ". s ST ;�„ : t•, , z < 119RIAL NI WD:'r;y Iw _ =meal SE 129THjF - rA0m PL PARK co- Aw � ` } _ Turn t�ND PL t Cl STn Y ULS' lND S� ! hME J Y y �i 2ND _ s a.3 ST i =. CTH s l i; y y 11p t t 1[ lk!t' d i% STWSW < 7 t' SSE W ESTATES f ft V tt �V stsy - r SE 2t0 PL 136TH r -am i O _ F II� 4 1R� „ v PAW a .. '9AMM8rtf = Y - < f7 t i "" SE >< o PROJECT � �� 13ff,,, R; S1 5E 4�4 q1N �" T LOCATION flLa �,= SE EM'lfrb P �' — JAIST b ` : UT, AST N +F 142ND ST s SE 14200 ST Y 6rr�. , h � rf ,;• �` Y ti � � a 14414j ST r l nML ZONE WV — — - - - ` ,�• Q. a sE 14srH A� °c Rf pq I� 1 1 t 0 D 4 Tna CdNiSE Ue R Nov VIP o MAPS ITm C li 44 S�taF i�a ."SE 19rNt6sN SE «T - al _ ` Sir H s 5156 M r IF( ^ �;T - - " FAI RWOOL R`Si WI ' a SF 161ST x ST �1r t ' Sf i. ` y VL ' Y ` t MIST Pt. 1 CIM -- S. •6t1S SE 163KD St y � �51 ✓r �, � _ - r � � _s `v� 1sf d'X: tiA, • y �6rsr� SE 164TH ST - ry rt � 3 09 1! sl 165TH ST 3 N. 16..rN sA SE gcY�'`�i+sr xr� 'nTM f?}rt L 1 ? FAlgyp% � :66L 5.. :4 /-H ,} 16 S DARLE5 A i 1A11WR(W HS .. S. .n £ ST l6BTH c 0 1/4 1/2 1 � I 1 Scale in Miles NOTE Reproduced with permission granted by THOMAS BROS. MAPS . This map is copyrighted by Rand McNally R.L. 08-S-34. It is unlawful to copy or reproduce all or any part thereof, whether for personal use or resale, without permission. All rights reserved. PaiiiII - a'� •" � 14 r� `�" t Fslh sr • J / y MaA/e k. -lip ySR /69 Q Cedar River aY- g i4 -S rr � is • � - 't � ��-•� �� C r �„, I Alli TRENCHLESS ALT. 3 ALT..; FA A1,T 11 1 1 1 I 1 , i I TRENCHLESS ALT. 1 eAA.5° 1 II TRENCH�ESS ALT. 2 1 1 , 1 ; � 1I , Maplewood Golf Course 'MYO • 1 -.wf 7 +ail : LL1 0 200 400 Approximate Scale in Feet Preliminary Geotech Report SL& PL LEGEND S Surface Alternatives '-y _ _ — _ _ - Trenchless Alternatives 150 Topographic Contour (10-Foot Interval) ® Jacking/Recieving Pit or Shaft Location A A' Generalized Subsurface Designation and tProfile � Approximate Location Heather Downs Interceptor Upgrade Renton. Washington SITE PLAN May 2008 21-1-20730-001 SHANNON & WILSON, INC. FIG. Y Geoledw icel and Environmental consultants Appe dix C - 20 U Q U c 0 0 J CO O O N m N N O N CO 0 300 - - -- -__ __ _ - .. _ _ _ _ .-- — . _ - _ - D and GRAVEL with cobbles and boulders Sandy GRAVEL to gravely SAND (Recessional Outwash) 300 LL SZ (Advanc%Outwash) m LL o Silly fine SAND to fine sandy SILT, trace of day c YAM scattered layers of sand and gravel g > (Non -Glacial Fluvial Deposits) 16 w 200 - - -- ---- ... - - - - - -ZZt 200 m w SE 5th St m edium denseo -D and GRAVEL- - — -- - X CL lluvium) n100 ---- --- - — --- R911ra This subsurface profile is generalized from materials observed in surface exposures and from published geologic maps. No soil borings were used to produce this profile. Variations may exist between profile and actual conditions. 0 _� SAND and GRAVEL with scattered SILT interbeds and wood debris (Alluvium) 0 100 200 Scale in Feet Horizontal = Vertical LEGEND Location of Inferred Seepage Approximate Groundwater Elevation 0 Preliminary Geotech Report B B. South North 400 - _ _. _ _ _ _. _ -. _. _. _ _ _ _ _ _____ _ - 00 Existing Ground Surface and GRAVEL with cobble sand boulders (Recessional Oulwash) 300 - - - - - - - - - - -- - -- - Silly, gravely SAND with cobbles and boulders (Till)-- - _ - - ---- - - - - 300 m ? Sandy GRAVEL to gravelly m LL SAND (Advanced Outwash) a) - - - - - - Silty fine SAND to fine sandy o SILT, trace of day with scattered o m layers of sand and gravel lL 200 ? (Non -Glacial Fluvial Deposits) _- -- _ _ _ -- .- - 200 w m Ca Loose to medium dense E SILT, SAND and GRAVEL E x- — - -- -- -- -- - - - - - 0 a 100 -- --- - - - -- ---- - --- - - - - - - 100 0 i SAND and GRAVEL with scafferedSILTntertiedsand - --__-.-----------------_-_-----..-.-- ------__ wood debris (Alluvium) J[6]tr9 This subsurface profile is generalized from materials observed in surface exposures and from published geologic maps. No soil borings were used to produce this profile. Variations may exist between profile and actual conditions. 0 100 200 Scale in Feet Horizontal = Vertical LEGEND ? Location of Inferred Seepage Approximate Groundwater Elevation 0 Preliminary Geotech Report U Q C 0 O J oo O O N 0) N u) O N l6 0 C South 400 r— Existing Ground Surface C' North 400 SAND and GRAVEL with cobbles and boulders (Recessional Outwash) Silty, gravelly / SAND with cobbles and boulders (Till) 300 �? Sanay GRAVEL to gravelty SAND (Advanceo Oulwash) LL c Loose to medium dense c SILT, SAND and GRAVEL ? Silly fine SAND to fine sandy SILT, trace of day with scattered layers of sand and gravel / (Non -Glacial Fluvial Deposits) w 200 ? rn C13 / E X / `OCL / ? / / PROPOSED HORIZONTAL DIRECTIONAL DRILL (HDD) PATH 100 0 NOTE SAND and GRAVEL with scattered SILT interbeds and wood debris (Alluvium) This subsurface profile is generalized from materials observed in surface exposures and from published geologic maps. No soil borings were used to produce this profile. Variations may exist between profile and actual conditions. 0 100 200 Scale in Feet Horizontal = Vertical LEGEND Location of Inferred Seepage Approximate Groundwater Elevation 300 m LL c c 0 200 w 100 0 U Q c 0 0 J 00 O O N N cD O N m 0 D' South Existing Ground Surface North 400 4 00 _. -SAND and GRAVEL wfth cobbles i i -- ' boulders (Recessions Oulwash) 9 Silly, SAND with 300 - - -- - - - - _ . - - - - - - and gravelly oulders (Till) - - - / / - - - - - - - _ _._ .. - 0 Approximate Centerline ? 3 0 m of Maplewood Creek Loose to medium dense QSandy RAVEL to gravelly SAND (Advanced Outwash) / LL SILT, SAND and GRAVEL / - ._ .. c LL _ ? Si fine SAND to fine y / p o ny sandy SILT, trace of da to scattered erFluvialsan and ravel o _. - - - - with w200 -(Non-Glacial- --Posi�j- / -- -- - - - - - 200 w m ? / d E � m cx- - -- - _. _ _. - - -- - - - . _ - - _ _ X - - / - -- - _ a 0. Q — — ? ? — PROPOSED HORIZONTAL DIRECTIONAL DRILL (HDD) PATH 100 - ----------- - -- and GRAVEL with - - . - - - - - -- - 00 SAND scattered SILT interbeds and wood debris (Alluvium) 0 NOTE This subsurface profile is generalized from materials observed in surface exposures and from published geologic maps. No soil borings were used to produce this profile. Variations may exist between profile and actual conditions. 0 100 200 Scale in Feet Horizontal = Vertical LEGEND ILocation of Inferred Seepage Q Approximate Groundwater Elevation Preliminary Geotech Report E Ev South North 400 400 Loose to medium dense SILT, SAND and GRAVEL - - - (Colluvium) Sandy GRAVEL to gravely Existing Ground Surface SAND (Advanced Qutwash) / Silty, gravely SANG'with cobbles / 300—_._..__ . ---- ----- — ---- --- -- -------_.._._.------- - --- --- — ----- - - -- - -- ----- ---� andboulders.(�Iq_. - _ _ � - - -- 300 ri ' ' Sandy GRAVEL' to grave D Advanced Outwash / SAND and GRAVEL with Loose to medium dense ? / cobbles and boulders UL i • _. �. _ _ - - - ___- -- . - ---(Recessional _Outwash) — SILT, SAND and GRAVEL ( ) Siltyfine SAND to fine sandy SILT, trace of day / o Colluwum with sca ered layers of sand and gravel > (Non-Gladal Fluvial Deposits) / m w 200 -- -- -- - - - -- -- - -- -- ._ __ .. - ---- - -- - -- -- - - - - --- - - -- -- - -- - - - m SAND and GRAVEL with / -- - - - -- - - - _ 200 w m scattered SILT mterbeds and / wood debris (Alluvium) / io X / - -- - a / PROPOSED HORIZONTAL DIRECTIONAL DRILL (HDD) PATH Q 100 100 0 NOTE This subsurface profile is generalized from materials observed in surface exposures and from published geologic maps. No soil borings were used to produce this profile. Variations may exist between profile and actual conditions. 0 100 200 Scale in Feet Horizontal = Vertical LEGEND Location of Inferred Seepage S Approximate Groundwater Elevation 11 I — x MEMO n to aw-P--, MEN x NO Mr-l"Oh, ,OAOFA 1.011 Mp Mil 29 v l W MI ox M NII a 1 x r/// �\�� ����� ��l�l"�� �� \`\���\�\`XN� � ��\�\ ������ �.�-rs � \� ���\\�� \� I: � I� ill ����/� I I I \� � ( I\�\�:� �`��\\�\ � �` \ \ ' � , i � � � it l �I Ili ���\\ � �� � (�i �i III \ 1�;� ..��� � ��\��� � � .� ���� �� u��ii��(1��� �\�:: �, ,; ' ice% ✓ C� x V\A\ A 00 \ , n 0? (/Z / o o6 (f) x x 00 00 cdfC CD r- 00 Ci CY) 00 CID ■ 130 OR a6 OR M x CID rn x UQ ,3) . 00 (D CD x (I�If N / To x 00 r- to 00 T';�► I "oh., 0 a MJIL ql �310. a