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SWP272119(2)
CITY OF RENTON MEMORANDUM DATE: April 26, 1990 TO: Mary Lynne Myer, Planning Dept. FROM: Kim Scattarella, Stormwater Engineering Specialist SUBJECT: THE BLUFFS - DRAFT EIS �� There are still a number of concerns in the Draft EIS for the Bluffs. They are the following: L. On Page 3-8, the landslides of January 9, 1990 were briefly documented. It is mentioned that; "if the slough in the catchment area were removed on a regular , perhaps annual basis, it is unlikely that future slough debris would reach the road". Unless the slough is in the Right-of-way, what guarantee is there of it being removed annually? Some more definitive mitigation should be suggested here. According to the plans, no construction is planned here, nor should it be permitted in this area. How did freeze-thaw cycles contribute to the landslides? There were no extended periods of subfreezing weather for the winter of 1989-90 up to Jan 9. 2. On page 3-12, after the heading of Mitigating Measures, it was stated that a detailed geotechnical investigation to identify the potential problems and provide appropriate design solutions be performed. This needs to be made more specific, as to what problems will be examined. Additional soils tests need to be performed to provide concrete evidence of why the landslides took place. Specific grading limits shall be established, and vegetation to be saved shall be specifically identified. 3. Excavation and construction shall only be permitted between April I and Sept 30, which is the same as the time window for hydroseeding. 4. On page 3-17, proposed action for Surface Water mitigation is mentioned. This section needs to be more specific. Specific detention requirements shall be mentioned, which are abiding by the requirements of the 1990 King County Surface Water Design Manual, and using the SCS Hydrograph or Santa Barbara Hydrograph method to compute the detention volume. It shall also be emphasized that the release rate from the site shall not exceed the two-year design predeveloped release rate. The 100 year design storm will be analyzed, and a Level 1 Downstream Analysis (per 1990 King County Surface Water Design Manual) shall be performed. 5. From page 3-18, the use of Baffled Oil/Water Separators (per City design Standards), and biofiltration swales will be a requirement for the enhancement of water quality before the on-site system is connected to the existing downstream system. ® � DOODS ENGINEERS, INC. CIVIL ENGINEERING SURVEYING PLANNING March 26, 1990 DE:I Project No. 88139 Mr. Kim Scattarella City of Renton Public Works Department — Storm Drainage 200 Mill Avenue South Renton, WA 98055 Re: "The Bluffs" — Additional Erosion Control Input. Dear Kim: Per your March 13th request, I am providing you with some additional- narrative regarding potential erosion/sedimentation control implementation during construction of "The Bluffs" project. Attached for reference are my previous two documents regarding erosion control. The February 12th letter is actually quite complete and is difficult to expound upon without designing a specific erosion/sedimentation control system. I will attempt, however, to supply more detail. Construction of the project will proceed in a logical sequence, Construction will begin at the base of the slope and proceed upward, with the entry road development_.. The construction entrance will be armored with rock to reduce the tracking of mud into the public roadways. The cut/fill slopes of the entry road construction will be hydroseeded and/or covered with plastic sheeting to reduce the erosion of the exposed surfaces. The formal detention pond will be constructed at the base of the slope and will be fitted with erosion/sedimentation control features (i.e, silt fences, gravel filter cones, etc.) and maintained throughout construction. As construction proceeds up the hiil, so will the utility extensions. In particular, the storm drains will be extended tip the hill to intercept and convey the silt laden runoff to the detention pond, throughout construction. Once the entry road has been extended up to the site proper, protection of the area to be developed can begin. Limits of clearing and grading will be defined prior to any disruption. Filter fabrics fences can be constructed along these limit_.s to reduce the flow of silt laden runoff. Interceptor ditches can be constructed and maintained just uphill of the silt fences, These ditches will direct flow into the storm drain system which has been extended up the entry road. The ditches will be equipped with rock or straw bale check dams to aid in the entrapment of mud and the heavier soil particles. The ditches will either be earth—lined, grass—lined or rock—lined, depending upon the tributary flows, slopes and velocities. In essence, the lower perimeter of the developed area will he surrounded by ditches and fences In order to reduce the silt laden runoff over the hillside. The dense, existing vegetation downstream will be maintained, wherever possible, to provide additional filtration, 4205 148TH AVE. N.E., SUITE 200-BELLEVUE, WA 98007 [206] 8135-71377 OR 454-3743 FAX:[206]885-7963 Mr. Kim Scattarella March 26, 1990 Page Two Once the perimeter has been protected, onsite grading can occur. The site can be divided into logical "pods of construction", to minimize the amount of disturbed area at any one time. Each "pod" can be brought to subgrade elevation, the slopes can be hydroseeded or lined with plastic, the utilities (specially the storm drains) can be installed, the building pads can be poured and ATB paving can be placed. In essence, the exposed areas can be sealed and directed to the permanent storm drainage system for conveyance to the erosion/sedimentation control pond. Each "pod" can be developed in a logical sequence, so as to extend utilities in an efficient manner. This step by step procedure should minimize the exposure of disturbed surfaces and reduce the potential for erosion. There may be topographically isolated pockets, however, that will require special, remote erosion control facilities. These facilities might include small erosion/sedimentation control ponds, dispersal trenches, double filter fabric fences, etc., depending upon the sensitivity of the locale. In all cases, the sensitivity of the steep slopes will be respected and drainage will be routed away from the bluffs, where possible. I hope this brief (and preliminary) construction sequence supplies adequate detail for the EIS phase of this project. The next step would be the preparation of a formal plan, which cannot be justified at this time. If you have any additional questions, please call. Sincerely, DODDS ENGINEERS, INC. Roy E. Lewis, in, P.E. Associate/Project Engineer Attachments: February 12th Letter & Original EIS Narrative cc: Donald Erickson &. Mary Lynne Myer (City of Renton) Mike Blumen R_. Leslie Lloyd (The Ferris Company) Scott Springer &. Colin Quinn (Lincoln Property Company) John Phillips (Phillips & Wilson) n u � Golder Associates 1) CONSULTING GEOTECHNICAL AND MINING ENGINEERS MAR , rig, •+ TRANSMITTAL LETTER To City of Renton Date March 12, 1990 200 Mill Avenue South Renton, Washington 98055 Project No. 893-1160 Attn: Mary Lynn Meyer Sent by ER Mail ❑ Under Separate Cover ❑ Air Freight ❑ Enclosed ❑ Hand Carried Quantity Item Description 1 Test Pit Logs Draft Test Pit Logs The Bluffs Apartments Renton, Washington TP-1 thru TP-9 Remarks --- Per request of Leslie Lloyd. Per J. So uth r GOLDER ASSOCIATES INC.•4104 148th AVENUE NE,REDMOND,WASHINGTON 98052.U.S.A.•TELEPHONE(206)883-0777•TELEX 5106002944 OFFICES IN UNITED STATES•CANADA•UNITED KINGDOM•AUSTRALIA Unified Soil Classification System Component Definitions by Gradation Soil Classification Criteria for Assiqning Group Symbols and Names Generalized Component Size Range Group Descriptions Boulders Above 12 in. .COARSE-GRAINED SOILS GRAVELS CLEAN GRAVELS GW well-groded Gravels 'More then 50% More than 50% of Less than 5% fines Cobbles 3 in. to 12 in. retained on coarse froction GP Poorly-graded grovels No. 200 sieve retained on Gravel 3 in. to No. 4 (4.76mm) No. 4 Sieve GRAVELS WlTil FINES GM Grovel and Silt Mixtures Coarse gravel 3 in. to 3/4 in. More than 12% fines ravel and Cloy Fine grave: 3/4 in, to No. 4 (4.76mm) GC Mixtures Sand No. 4 (4.76mm) to No. 200 (0.074mm) SANDS CLEAN' SANDS SW Well-graded Sands 50% or more of Less than 5% fines Coarse sand No. 4 (4.76mm) to No. 10 (2.0mm) coarse froction SP Poorly-graded Sands Medium sand No. 10 (2.Omm) to No. 40 (0.42mm) passes No. 4 Sieve SANDS WITH FINES SM Sand and Sift Mixtures Fine sand No. 40 (0.42mm) to No. 200 (0.074mm) More than 12% fines Sift one Clay Smaller than No. 200 (0.074mm) SC Sand and Cloy Mixtures FINE-GRAINED SOILS SILTS AND CLAYS CL Low-plasticity Clays 50% or more passes Liquid limit INORGANIC the No. 200 sieve less than 50 ML Nontiplastic and Low- Non-ply Silts Non-pa sh Samples a and Low- ORGANIC OL Plasticity Organic Clays Non-plastic and Low- SS SPT Sampler (2ff OD) Plasticity Organic Sills HD Heavy Duty Split Spoon SILTS AND CLAYS CH High-pasticity Clays SH Shelby Tube Liquid limit INORGANIC greater than 50 P Pitcher Sampler - MH High-plasticity Silts B Bulk High-plasticity ORGANIC OH Organic Clays C Cored High-plasticity Organic Silts Unless otherwise noted, drive samples HIGHLY ORGANIC SOILS Primarily organic matter dark in color, and odvonced with 140 lb. hemmer with , organic odor PT Peat 30 in. drop. Relative Density or Consistency Laboratory Tests Utilizing Standard Penetration Test Values Test Designation Cohesionless Soils(a) Cohesive Soils (b) Moisture (1) Density D (c) (c) Relative (c) Undrained (d) Groin Size G Density N, blows/ft. Density Consistency N, blows/ft. Shear Strength (7) (psf) Hydrometer H Atterberg Limits (1) Very loose 0 to 4 0 - 15 Very soft 0 to 2 <250 Consolidation C Loose 4 to 10 15 - 35 Soft 2 to 4 250-500 Unconfined U Compact 10 to 30 35 - 65 Firm 4 to 8 500-1000 UU Triax UU Dense 30 to 50 65 - 85 Stiff 8 to 15 1000-2DOO CU Triax Cu Very Dense over 50 >85 Very Stiff 15 to 30 2000-4000 CD Triax CD Hord over 30 >4000 Permeability P (a) Soils consisting of gravel, send, and silt, either separately or in combination, possessing no characteristics (1) Moisture and Atterberg Limits of plasticity, and exhibiting drained behavior. -plotted on log. (b) Soils possessing the characteristics of plasticity, and exhibiting undrained behavior. (c) Refer to text of ASTM D 1586-84 for a definition of N; in normally consolidated cohesionless soils Relative Density terms ore based on N values corrected for overburden pressures. (d) Undrained shear strength - 1/2 unconfined compression strength. Silt and Clay Descriptions Description Typical Unified Designation_ Descriptive Terminology Denoting Component Proportions silt ML (non-plastic) Clayey Silt CL-ML (low plasticity) Descriptive Terms Range of Proportion Silty Clay CL Clay CH Trace 0-5z Plastic Silt MM Little 5-12% Some or Adjective(0) 12-30% Organic Soils OL. OH. Pt And 30-505 (a) Use Gravely, Sandy or Silty as appropriate. Golder Associates SOIL CLASSIFICATION/LEGEND 773-1064/FORM 573 --� ---� -_ BIRAFT TEST PIT LOGS Test Pit 1 Approximate ground surface elevation 55 feet. 0.0 - 0.4 ft. Forest litter 0.4 - 1 .8 ft. Compact, pale yellowish brown, fine silty SAND, little rounded gravel , roots and organics present (SM) (TOPSOIL) 1.8 - 4.5 ft. Dense, dark yellowish brown, fine to medium SAND, some rounded medium to coarse gravel , roots to 2.4 ft. (SW) (OUTWASH) 4.5 - 4.9 ft. Very dense, light brownish gray to brownish gray, fine to medium SAND, little rounded gravel and cobbles (SW) (OUTWASH) 4.9 - 6.8 ft. Dense, dark yellowish brown and brownish gray, medium SAND, some rounded gravel , trace rounded cobbles (SW) (OUTWASH) 6.8 - 9.0 ft. Dense to very dense, dark yellowish brown and brownish gray, medium SAND, some rounded gravel , little rounded cobbles, trace silt (SW) (OUTWASH) 9.0 - 11 .0 ft. Dense, dark yellowish brown, medium SAND, some rounded gravel , trace rounded cobbles (SW) (OUTWASH) 11 .0 - 12.0 ft. Compact, olive gray and dark gray, silty SAND, some rounded gravel , trace rounded cobbles (SM) (OUTWASH) 12.0 - '14.5 ft. Firm to stiff, greenish black and dark gray, sandy SILT, little clay, trace rounded gravel (ML) (OUTWASH?) 14.5 - 19.0 ft. Compact to dense, dark gray, olive gray, and greenish gray, silty fine to medium SAND, some rounded gravel , little rounded cobbles, roots present (SM) (OUTWASH) No caving observed. No groundwater observed. Test pit terminated at 19.0 feet. 9/21/89 Test Pit 2 Approximate ground surface elevation: 165 feet. 0.0 - 1 .4 ft. Dense to very dense, pale to dark yellowish brown, fine to medium SAND, some rounded gravel , little rounded cobbles, roots to 0.5 ft. (SW) (OUTWASH) 1 .4 - 2.9 ft. Very dense, pale yellowish brown, and yellowish gray, fine SAND (SP) (OUTWASH) F T 2.9 - 6.2 ft. Very dense, pale to dark yellowish brown, fine to medium SAND, some rounded gravel , little rounded cobbles (SW) (OUTWASH) No caving observed. No groundwater observed. Test pit terminated at 6.2 feet. 9/21/89 Test Pit 3 Approximate ground surface elevation: 160 feet. 0.0 - 1 .5 ft. Very loose, grayish brown and black, FILL, composed primarily of cinders, roots present 1 .5 - 2.5 ft. Loose, dark yellowish brown and pale brown, medium to coarse SAND, some rounded gravel , roots present (SW) (FILL) 2.5 - 3.0 ft. Loose, pale to dark yellowish brown, medium to coarse SAND, roots present (SP) (FILL) 3.0 - 6.0 ft. Loose, pale to dark yellowish brown and medium dark gray, medium to coarse SAND, some rounded gravel , roots present (SW) (FILL) Extensive caving throughout excavation. No groundwater observed. Test pit terminated at 6.0 feet (due to caving) . 9/21/89 Test Pit 4 Approximate ground surface elevation : 165 feet. 0.0 - 0.5 ft. Forest litter 0.5 - 1 .0 ft. Very loose, pale to dark yellowish brown, fine SAND, trace rounded fine to medium gravel , roots and organics present (SP) (TOPSOIL) 1 .0 - 4.5 ft. Compact, light olive gray, fine to medium SAND, some rounded gravel , roots to 2.5 ft. (SW) (OUTWASH) 4.5 - 7.4 ft. Dense to very dense, light olive gray, fine to medium SAND, some rounded gravel , trace rounded cobbles (SW) (OUTWASH) 7.4 - 8.0 ft. Very dense, pale to dark yellowish brown, SAND, little rounded gravel (SW) (OUTWASH?) 8.0 - 9.4 ft. Compact to dense, moderate to dark yellowish brown, medium to coarse SAND, some rounded gravel , trace rounded cobbles (SW) (OUTWASH) No caving observed. No groundwater observed. Test pit terminated at 9.4 feet. 9/21/89 Test Pit 5 Approximate ground surface elevation 155 feet. 0.0 - 0.4 ft. Very loose, pale yellowish brown and light olive gray, SAND, roots and organics prsent (SW) (TOPSOIL) 0.4 - 5.4 ft. Compact, moderate yellowish brown, fine to medium sand, little rounded gravel , roots present to 3.7 ft. (SW) (OUTWASH) 5.4 - 9.8 ft. Dense, pale to moderate yellowish brown, fine to medium sand, trace rounded gravel (SW) (OUTWASH) No caving observed. No groundwater observed. Test pit terminated at 9.8 feet. 9/21/89 Test Pit 6 Approximate ground surface elevation : 135 feet. 0.0 - 1 .6 ft. Very loose, dark brownish gray, fine SAND, little silt, trace rounded gravel , roots and organics present (SW) (TOPSOIL) 1.6 - 3.8 ft. Compact to dense, light olive gray and dark yellowish orange, mottled, medium SAND, some rounded fine to medium gravel (SP) (OUTWASH) 3.8 - 4.3 ft. Compact, dark greenish gray, medium SAND, some rounded fine to medium rounded gravel , trace rounded cobbles (SW) (OUTWASH) 4.3 - 6.5 ft. Compact to dense, medium dark gray and light olive gray, fine SAND, little silt, trace rounded fine to medium gravel and cobbles (SP) (OUTWASH) 6.5 - 10.6 ft. Dense to very dense, medium dark gray fine silty sand, trace rounded gravel and cobbles (SM) (OUTWASH?) No caving observed. No groundwater observed. Test pit terminated at 10.6 feet. 9/21/89 DRAFT Test Pit 7 Approximate ground surface elevation : 175 feet. 0.0 - 0.5 ft. Forest litter 0.5 - 3.2 ft. Compact to dense, pale yellowish brown, fine to medium SAND, some rounded medium to coarse gravel , little rounded cobbles, roots present (SW) (OUTWASH) 3.2 - 8.0 ft. Compact, pale yellowish brown, fine to medium SAND, some rounded medium to coarse gravel , little rounded cobbles, roots present to 6.2 ft. (SW) (TILL? OUTWASH) 8.0 - 10.5 ft. Compact to dense, pale yellowish brown, SAND, some rounded gravel , some rounded cobbles (SW) (OUTWASH) No caving observed. No groundwater observed. Test pit terminated at 10.5 feet. 9/21/89 Test Pit 8 Approximate ground surface elevation : 155 feet. 0.0 - 0.5 ft. Forest litter 0.5 - 1 .4 ft. Very loose, dark yellowish brown, fine SAND, little rounded gravel , trace rounded cobbles, roots and organics present (SP) (TOPSOIL) 1 .4 - 3.5 ft. Loose to compact, pale yellowish brown, fine SAND, little rounded gravel , trace rounded cobbles, rotted wood 2.6-3.5 ft. (SP) (FILL) 3.5 - 6.5 ft. Compact to dense, light brown and pale yellowish brown, fine to medium SAND, some rounded gravel , trace rounded cobbles (SW) (OUTWASH) 6. 5 - 8. 5 ft. Dense to very dense, light olive gray, fine to medium SAND, some rounded gravel , some rounded cobbles (SW) (OUTWASH) 8.5 - 10.5 ft. Very dense, light brown and pale yellowish brown, motled, SAND, some rounded fine to medium gravel , trace rounded cobbles (SW) (OUTWASH) No caving observed. No groundwater observed. Test pit terminated at 10.5 feet. 9/21/89 DRAFT Test Pit 9 Approximate ground surface elevation : 165 feet. 0.0 - 1 . 1 ft. Loose, pale yellowish brown, fine SAND, little rounded gravel ,roots and organics present (SP) (TOPSOIL) 1 . 1 - 4.5 ft. Compact to dense, pale yellowish brown, fine to medium SAND, some rounded gravel , trace silt roots present to 2.0 ft. (SW) (OUTWASH) 4.5 - 7.0 ft. Dense to very dense, pale yellowish brown and light olive gray, medium SAND, little rounded gravel , trace rounded cobbles (SW) (OUTWASH) 7.0 - 9.2 ft. Very dense, light olive gray and light brown, mottled, medium SAND, some rounded fine to medium gravel (SW) (OUTWASH) 9.2 - 9.7 ft. Very dense, pale yellowish brown and light olive gray, fine to medium SAND, little rounded gravel , trace rounded cobbles, lenses light olive gray fine SAND (SP) in coarser matrix (SW) (OUTWASH) No caving observed. No groundwater observed. Test pit terminated at 9.7 feet. 9/21/89 CITY OF RENTON Community Development Department Earl Clymer, Mayor Kenneth E.Nyberg,Director March 12 , 1990 Roy E. Lewis Jr. Dodds Engineering Inc. 4205 148th Ave N.E. Suite 200 Bellevue, Washington 98007 Dear Roy; Per our telephone conversation on Friday, March 9 , 1990, I am sending you the City's Public Works comments on your February 12 , 1990 letter and the drainage basin map, the sanitary sewer exhibit and the water systems exhibit. The following changes should be made before the DEIS is finalized. WATER UTILITY COMMENTS The exhibits omitted the placement of hydrants. Where will they be located? Please show these on the exhibits. Also, please state the fire flow requirements for this project. As part of this project, 12" watermain must be installed on Lake Washington Boulevard, as previously stated by the Public Works staff. It was not shown on the water utility exhibit. Please include it in both text and maps for the DEIS. The PDEIS states that a 16" main could be placed on the I-405 right of way. This should be corrected to read that the main would be located on the access road to the development and should connect back to the 12" main on Lake Washington Boulevard. STORM WATER COMMENTS The DEIS should include a temporary erosion/sedimentation control plan. This site is sensitive and all due precaution should be taken to prevent erosion and further landslides. In light of ^- cis, this, an updated soils study for more of the site should be included, rather than just the test pits for selected parts of the site. of particular interest are the 40% slopes and �tS especially the landslide areas along the southeastern portion of the site adjacent to Lake Washington Boulevard N. The DEIS should include an analysis of what caused the recent Winter landslides r!" in this area and identify mitigation measures for prevention of future occurrence. 200 Mill Avenue South - Renton, Washington 98055 At the request of Kim Scattarella, Stormwater Engineering Specialist, more detail in the storm drainage calculations, for detention, and conforming to the King County Surface Water Design Manual, and utilizing the SCS Hydrograph methods, for 25 year design storage and 2 year design release rate, should be included by the Plan Review phase of the project. More information on the plans (i.e. Detention facility volume/dimensions, elevations for pipes, catch basins, and supporting calculations) should also be included during Plan Review phase. This information is not necessary for the DEIS, however. Please call me at 235-2550 if you have questions. Sincerely, Mary Lynne Myer Senior Environmental Planner Current Planning Community Development Department cc: Kim Scattarella, Storm Water Utility Ron Olson, Water Utility Leslie Lloyd, The Ferris Company CITY OF RENTON MEMORANDUM DATE: March 6, 1990 TO: Mary Lynne Myer, Current Planning FROM: Kim Scattarella, Stormwater Engineering Specialises SUBJECT: THE BLUFFS- STORM DRAINAGE EXHIBIT The following comment applies to the most recent submittal of the enclosed Storm Drainage Plans; More information on the plans (i.e. Detention facility volume/dimensions, elevations for pipes, catch basins, and supporting calculations). These comments are not necessarily pertinent to the DEIS review. The initial comments from the DEIS review need to be addressed in a resubmittal of the EIS, which will then be reviewed. The previously enclosed comments regarding revisions of the DEIS from Roy Lewis have been reviewed, and the following concerns are; 1) More detail in the storm drainage calculations, for detention, and conforming to the King County Surface Water Design Manual, and utilizing the SCS Hydrograph method, for a 25 year design storage and 2 year design release rate. 2) Providing an updated soils study to incorporate an analysis of the landslide areas along the southeastern portion of the site that boundaries Lake Washington Blvd. N , and mitigation measures for prevention of a future occurrence. This shall also include an analysis of what caused the landslides. 3) A Temporary Erosion/Sedimentation Control Plan shall be outlined in the EIS, with more detail added in the Plan Review phase. If there are any other questions or comments, please don't hesitate to calls cc: Paul Lumbert a - DODDS ENGINEERS, INC. C I VIL E N GIN EERING S U R V E Y I N G P L A N N I N G February 12, 1990 DEI Project No. 88139 Mr. Kim Scattarella City of Renton Public Works Department - Storm Drainage 200 Mill Avenue South Renton, WA 98055 Re: "The Bluffs" - Response to your comments to the Preliminary DEIS Dear Kim: At the request of The Ferris Company, I have reviewed your comments to the Preliminary Draft Environmental Impact Statement for "The Bluffs". Response to your concerns will be provided by Golder Associates (the soils engineer) and me (grading, storm drainage & utilities). The information presented in the Preliminary DEIS is a synopsis of the extensive work completed to date. It was presented in a format quite typical of Environmental Impact Statements prepared today. To aid in your review, I will attach the more detailed support documentation that was utilized to generate the Preliminary DEIS narrative. In addition, I will provide the specific input you requested below. Item A- Erosion/Landslide and Item B. Seismicity will be addressed by Golder Associates. Both Craig Lavielle (Golder Associates) and I have visited the site since the sloughing of the bluffs along Lake Washington Boulevard. Item C. Surface Water will be addressed below. Erosion/Sedimentation is a special concern when working with steep slopes and working in areas close to streams and lakes. The final Erosion/Sedimentation Control design will incorporate a combination of the most effective and economical methods of erosion control. Some of the common practices utilized today that will most likely be employed at "The Bluffs" are; 1. Phased Construction: By developing and "sealing" portions of the site at a time, the exposed areas, most sensitive to erosion, are minimized. 2. Temporary Erosion Control Ponds: Quiescent conditions are optimal for settling of silt laden water. Pond construction requires space and flat slopes, however, so site selection will be critical. A relatively large pond can be constructed at the toe of the slope, south of the proposed entry road (as shown on the Preliminary Storm Drainage Plan). The large pond will provide much needed settling time. 3. Temporary Interceptor Swales: Temporary interceptor swales can be constructed at the downstream edge of disturbance. These swales would intercept and safely convey interim drainage to erosion control facilities. The swales would either be rock-lined, grass-lined or lined with an erosion-resistant fabric, depending 4205 14E7-TH AVE. N.E., SUITE 200-SELLEVUE, WA 98007 (2061 8e5-7877 OR 454-3743 FAX:(206]835-7963 Mr. Scattarella February 12, 1990 Page Two upon the flows and slopes. Rock or straw bale check dams can be installed at a uniform spacing to provide interim locations for settlement of the larger soil particles. 4. Filte:r Fabric Fences: These fences can be constructed in locations which would best protect existing roadways or sensitive natural areas. These fences prove effective in reducing transport of silt-laden overland flow. These fences can also be utilized to induce serpentine flow in the larger sedimentation ponds. 5. Temporary Ground Cover: Hydroseeding, mulching, sodding, and plastic sheeting can be utilized on the exposed cut slopes. The methodology most effective depends on the time of year, area of disturbance, slope of disturbance and eventual treatment of the area. 6. Natural Vegetation: Dense natural vegetation sometimes proves to be our best ally in erosion control. Slopes and a uniform dispersal of flow are design criteria that must be reviewed. Stormwater Detention was another point that you mentioned. As the Preliminary DEIS narrative mentioned, this project will be designed to satisfy current City of Renton Development Standards, including stormwater detention. Typically, if it can be shown that "adequate" conveyance is provided from the site to Lake Washington, stormwater detention will not be required. We can demonstrate that the downstream storm drainage facilities have the hydraulic capacity to convey our developed, undetained flows to Lake Washington, but, the cumulative effects of other developments may combine to create erosive conditions in the existing swale in Gene Coulon Park. Because of this possibility and the desire to provide water quality enhancement and an entry amenity, stormwater detention will be provided in an ornamental (yet functional) pond, just south of the proposed entry road (refer to the Preliminary Storm Drainage Plan). This pond will be designed for the 5-25 SCS conditions you have quoted and will be equipped with the standard flow restrictor and oil/water separator facilities. In addition to these facilities, a biofiltration swale will be incorporated into the outfall from this pond. Special grasses and wetlands plantings will line this swale for maximum performance. I trust this response and attached exhibits/analyses satisfy your concerns. If not, please give me a call, it's been a while since I've visited your department. Sincerely, a ENFJr., P.E. NC. ewi Associate/Project Engineer Enclosures: Full size preliminary engineering drawings. cc: Donald Erickson & Lenora Blauman (City of Renton) Mike Blumen & Leslie Lloyd (The Ferris Company) Scott Springer & Colin Quinn (Lincoln Property Company) John Phillips (Phillips & Wilson) STORM DRAINAGE Attached for reference is an exhibit which delineates the various drainage basins associated with development of The Bluffs. The total drainage basin under analysis consists of 65.90 acres; 41.40 acres offsite and 24.50 acres onsite. The ridges and valleys clearly delineate eight major sub-basins which combine at three separate discharge points. I-405 and Jones Ave. N.E. (further to the east) intercept and divert to the south, a portion of the offsite drainage. The undiverted drainage is processed by the I-405 drainage system and discharged into The Bluffs' natural valley areas, as shown on the provided exhibit. Drainage apparently filters to the valley floor and is conveyed westerly towards Lake Washington. After close (late summer) review of each valley, it was difficult to locate a well-defined drainage flow path. Small drainage basins, porous soils and well vegetated slopes appear to reduce the potential for concentrated flows. There is no evidence of erosion in the upper valley floors. The valleys are characterized by a uniform, undisturbed covering of forest litter. Apparently, the valley floors can easily handle the existing tributary flows. Lake Washington Boulevard acts as a lower drainage interceptor. A roadside ditch conveys intercepted flows to the north and the south, from a high point just north of the proposed Bluffs entrance road. This ditch also shows little sign of erosion. The northerly flows are intercepted by the recently completed Marina Landing Apartments storm drainage system. This system drains beneath Lake Washington Boulevard via three pre-Marina Landing culverts. Drainage is then PAGE 5 culverted beneath the Burlington Northern Railroad tracks, into the Gene Coulon Park storm drainage system. The park's system then conveys drainage directly into Lake Washington. A recent inspection of these downstream systems showed well armored channels with little sign of erosion or capacity problems. The drainage which flows south along Lake Washington Boulevard is eventually intercepted by a 12" concrete culvert located just north of the N. 14th St. right-of-way. This culvert discharges into a swale along the east side of the Burlington Northern Railroad. Shortly downstream, this swale is intercepted by a 24" concrete culvert which extends beneath the Burlington Northern Railroad and ties directly into the Gene Coulon Park 24" CMP storm drainage system. This park system discharges, a short distance away, into a natural, well maintained stream, which gently meanders into Lake Washington. The stream bottom is lined with cobbles and shows little evidence of erosion. The stream banks are lined with dense, tall grasses which appear to protect the channel well. An exhibit of this downstream system is provided on the next page. In summary, existing onsite and downstream storm drainage systems appear to be well suited for the tributary flows. There is little evidence of erosion or capacity problems in these storm drainage conveyance systems. Development of The Bluffs will alter existing drainage conditions. Buildings and paved surfaces will be constructed, replacing existing ground cover with impervious surfaces. Other areas of natural vegetation will be removed during grading operations and replaced with urban-like landscaping. These alterations will increase the rate of surface runoff and decrease the uniform rate of groundwater recharge. The approximate magnitude of these disturbances is tabulated in the pages PAGE 6 that follow. For the preferred alternative, approximately 8.3 acres of the site will be disturbed during development. This 8.3 acres represents 33.9% of the 24.5 acre site or only 12.6% of the 65.9 acre drainage basin. Only 4.2 acres of this disturbance will be converted into impervious surfaces; the remaining 4.1 acres will be landscaped or restored to pre-developed conditions. As shown on the attached "24-Hour Storm Runoff Estimates" table (for the preferred 165 unit alternative), developed stormwater runoff will average 167% of the existing runoff rate. A comparison of peak developed flows of all of the alternatives is also provided. The existing conveyance systems can hydraulically handle this minor increase in flow, but concentration of flows, at the increased rates, may increase the probability of erosion in the steeper slopes. To reduce the potential for erosion and help mitigate the impacts of increased stormwater discharge rates, several standard design practices can be implemented. Conveying developed storm drainage runoff through tight-lined systems minimizes the potential for erosion of the natural channels. Offsite flows will continue in the natural ravines, but developed flows will be intercepted by tight-lined systems which will be designed to convey the developed 25-year stormwater runoff. The 135 unit and 165 unit alternatives will convey developed drainage down the proposed entrance road to the toe of the bluffs. Here, where grades are gentle, the flows can be safely directed to the existing conveyance systems, which have adequate capacity for the nominal increase in flows. Though not required for the 135 unit or 165 unit alternatives, stormwater detention systems can be constructed to help maintain the existing rates of stormwater runoff and provide settling time for water quality enhancement. (The 95 unit and 240 unit alternatives will require multiple stormwater detention facilities due to the topographic isolation of several areas of PAGE 7 development. These two alternatives may also require storm drainage discharge over the steep slopes.) By maintaining existing drainage basin boundaries, flows will be directed to the locations that have historically proven to have adequate capacity. Subsurface flow dispersion trenches will help return the stormwater runoff to a less erosive interflow condition. A planting of dense, hardy grasses, downstream of discharge points, will help in flow attenuation, distribution and filtering. The use of oil/water separator vaults (prior to discharge), the use of dense vegetation just below the discharge points and the maintenance of existing vegetation in the natural valley floors will aid in water quality enhancement. The ultimate receiving waters should notice little water quality degradation due to construction of The Bluffs. It is important to plan for good water quality management, especially during the construction period. Noticeable cuts and fills will have to be accomplished in order to access and develop The Bluffs. These exposed cut and fill slopes will need to be protected from erosion due to rainfall. Hydroseeding or permanent revegetation should be in place as soon as practical. Mulching and plastic sheeting may be required in areas of special sensitivity. If grading operations are quickly performed and/or completed in small phases, the potential for erosion will be reduced. In any case, providing sedimentation ponds and maintaining dense vegetation, where practical, will aid in the entrapment of eroded soils, minimizing the potential for siltation of downstream streams and Lake Washington. PAGE 8 THE BLUFFS . ESTIMATION OF SITE DISTURBANCE ALTERNATIVE PREFERRED ................................... .................................... #OF UNITS 95 135 .165 240 TOTAL AREA OF 12.6 AC 8.9 AC 8.3 AC 12.6 AC DEVELOPMENT IMPERVIOUS AREA 4.5 AC 4.1 AC 4.2 AC �6.4 AC PERVIOUS AREA 8.1 AC 4.8 AC 4 1`AC 6.2 AC APPROXIMATE 73,000 CY 66,000 CY 81,4700 CY.... 77,000 CY VOLUME OF CUT APPROXIMATE 36,000 CY 31,000 CY 21,000 CY 32,000 CY VOLUME OF FILL * THE AREAS OF DEVELOPMENT, IMPERVIOUS AREAS AND PERVIOUS AREAS HAVE BEEN OBTAINED FROM TABLES PREPARED BY MILBRANDT ARCHITECTS. ® � DODDS ENGINE S, IN � J l CIVIL ENGINEERING SU FIVE YING -r L I N G CITY OF RU4TON February 12, 1990 Engineering Dept. DEI Project No. 88139 Mr. Kim Scattarella City of Renton Public Works Department - Storm Drainage 200 Mill Avenue South Renton, WA 98055 Re: "The Bluffs" - Response to your comments to the Preliminary DEIS Dear Kim: At the request of The Ferris Company, I have reviewed your comments to the Preliminary Draft Environmental Impact Statement for "The Bluffs". Response to your concerns will be provided by Golder Associates (the soils engineer) and me (grading, storm drainage & utilities). The information presented in the Preliminary DEIS is a synopsis of the extensive work completed to date. It was presented in a format quite typical of Environmental Impact Statements prepared today. To aid in your review, I will attach the more detailed support documentation that was utilized to generate the Preliminary DEIS narrative. In addition, I will provide the specific input you requested below. Item A. Erosion/Landslide and Item B. Seismicity will be addressed by Golder Associates. Both Craig Lavielle (Golder Associates) and I have visited the site since the sloughing of the bluffs along Lake Washington Boulevard. Item C. Surface Water will be addressed below. Erosion/Sedimentation is a special concern when working with steep slopes and working in areas close to streams and lakes. The final Erosion/Sedimentation Control design will incorporate a combination of the most effective and economical methods of erosion control. Some of the common practices utilized today that will most likely be employed at "The Bluffs" are; 1. Phased Construction: By developing and "sealing" portions of the site at a time, the exposed areas, most sensitive to erosion, are minimized. 2. Temporary Erosion Control Ponds: Quiescent conditions are optimal for settling of silt laden water. Pond construction requires space and flat slopes, however, so site selection will be critical. A relatively large pond can be constructed at the toe of the slope, south of the proposed entry road (as shown on the Preliminary Storm Drainage Plan). The large pond will provide much needed settling time. 3. Temporary Interceptor Swales: Temporary interceptor swales can be constructed at the downstream edge of disturbance. These swales would intercept and safely convey interim drainage to erosion control facilities. The swales would either be rock-lined, grass-lined or lined with an erosion-resistant fabric, depending 4205 14BTH AVE. N.E., SUITE 200-BELLEVUE, WA 9B007 [206) 8B5-7877 OR 454-3743 FAX:(206)B85-7963 Mr. Scattarella February 12, 1990 Page Two upon the flows and slopes. Rock or straw bale check dams can be installed at a uniform spacing to provide interim locations for settlement of the larger soil particles. 4. Filter Fabric Fences: These fences can be constructed in locations which would best protect existing roadways or sensitive natural areas. These fences prove effective in reducing transport of silt-laden overland flow. These fences can also be utilized to induce serpentine flow in the larger sedimentation ponds. 5. Temporary Ground Cover: Hydroseeding, mulching, sodding, and plastic sheeting can be utilized on the exposed cut slopes. The methodology most effective depends on the time of year, area of disturbance, slope of disturbance and eventual treatment of the area. 6. Natural Vegetation: Dense natural vegetation sometimes proves to be our best ally in erosion control. Slopes and a uniform dispersal of flow are design criteria that must be reviewed. Stormwater Detention was another point that you mentioned. As the Preliminary DEIS narrative mentioned, this project will be designed to satisfy current City of Renton Development Standards, including stormwater detention. Typically, if it can be shown that "adequate" conveyance is provided from the site to Lake Washington, stormwater detention will not be required. We can demonstrate that the downstream storm drainage facilities have the hydraulic capacity to convey our developed, undetained flows to Lake Washington, but, the cumulative effects of other developments may combine to create erosive conditions in the existing swale in Gene Coulon Park. Because of this possibility and the desire to provide water quality enhancement and an entry amenity, stormwater detention will be provided in an ornamental (yet functional) pond, just south of the proposed entry road (refer to the Preliminary Storm Drainage Plan). This pond will be designed for the 5-25 SCS conditions you have quoted and will be equipped with the standard flow restrictor and oil/water separator facilities. In addition to these facilities, a biofiltration swale will be incorporated into the outfall from this pond. Special grasses and wetlands plantings will line this swale for maximum performance. I trust this response and attached exhibits/analyses satisfy your concerns. If not, please give me a call, it's been a while since I've visited your department. Sincerely, ENFJr., P.E. NC. Lw ,Associate/Project Engineer Enclosures: Full size preliminary engineering drawings. cc: Donald Erickson & Lenora Blauman (City of Renton) Mike Blumen & Leslie Lloyd (The Ferris Company) Scott Springer & Colin Quinn (Lincoln Property Company) John Phillips (Phillips & Wilson) ® � DDDDS ENGINEERS, INC. C IVIL ENGIN EERING S U R V E Y I N G P L A N N I N G February 12, 1990 DEI Project No. 88139 Mr. Donald K. Erickson,AICP Ms. Lenora Blauman City of Renton Current Planning 200 Mill Avenue South Renton, WA 98055 Re: "The Bluffs" - Response to the City of Renton's comments to the Preliminary DEIS Dear Mr. Erickson & Ms. Blauman: At the request of The Ferris Company, I have reviewed the City of Renton's comments on the Preliminary Draft Environmental Impact Statement for "The Bluffs". In the following pages I will respond to those items which relate to my civil engineering input. If additional information or explanation is needed, I'll be glad to meet with you and/or staff to further discuss these issues. There are three items in your January 31, 1990 letter which request additional civil engineering input. Items 17, 19 and 31 will be addressed in the following paragraphs. ITEM 17 Can the natural ravines (valley areas) on site continue to contain storm water runoff after development, how much? If not, how will we compensate? There appears to be a need [for] more discussion concerning percolation factors. (3-13) My first three site visits occurred during the dry late summer months of 1989. A close review of each major ravine showed no evidence of erosion or instability. In fact, in many cases, I couldn't even identify the natural flowpath. My last two site visits were during the recent very wet weather conditions. Again, it was very difficult to find any erosion or swale instability, though some of the very steep "bluffs" had sloughed. Many of the ravine bottoms were still densely vegetated and covered with forest litter. In those areas where flows could be observed, it was well-contained within its channels and was relatively"clean". These favorable drainage conditions may be the result of the porous soil conditions found onsite. Golder Associates excavated nine test pits to analyze existing soil conditions. The depths of these pits ranged from 6.0 feet to 19.0 feet, averaging around 10.0 feet. No groundwater was encountered in any of these test pits. The soils consisted primarily of sands and gravels,with some silts and clays. 4205 14BTH AVE. N.E., SUITE 200-BELLEVUE, WA 98007 [208] 885-7877 OR 454-3743 FAX:[208]885-7883 Mr. Erickson Ms. Blauman February 12, 1990 Page Two Development of the Preferred Alternative will respect the existing drainage conditions and the recommendations in the Golder Associates Soils Report. It is proposed that all development runoff be collected by a tight-lined storm drainage system and conveyed through the site, down the access road, to a stormwater detention/water quality enhancement pond, located in the flat area adjacent to Lake Washington Boulevard. The impacts of development on these natural ravines should be minimal, if not beneficial. A copy of the Preliminary Grading & Utility Plans is attached for your reference. Details of the design will be established at a later date, during the Building Permit process. ITEM 19 The "Water" section talks about "higher" and "lower" levels of ground water but is not specific; some better definitions or greater specificity would be desirable. (3-15, 3-16) I've touched on what was found during the preliminary soils investigation. I believe Golder Associates will expound on this issue. ITEM 31 Public Works Department staff indicates that site characteristics (sloped terrain, location, etc.) pose some substantial challenges for utilities service connection. It would seem useful to have some discussion about these problems, and the ways in which they can be addressed. (3-68 + +) Agreed, the site is steep and has undulating terrain. Construction access will be challenging but is far from impossible. Taken in a logical sequence, construction of this preferred alternative will be no more difficult than the "typical" site being developed today. This first step in the construction process will be establishing site access and erosion control. The site access road will be carefully serpentined up the slope to the main development level. Once on the plateau, building pads and parking grades will be carved into place. Once the site is rough graded, utility construction can begin. Storm drainage, water and sanitary sewer facilities will be designed to follow the newly achieved site grades. Based upon the preliminary designs provided, sanitary sewer depth will not exceed fifteen feet and storm drainage depths will not exceed twelve feet, approximately. These depths are well within standard construction tolerances. Water main construction will require a little out-of-the-ordinary work. The westerly connection to the existing 16" main will require construction of a cross-country access road. This access/maintenance road is depicted on the preliminary Water Plan. Grades on this maintenance road are designed not to exceed 20%, with most of the roadway not exceeding 15%. Again, construction may be a little elaborate for a simple water main, but it is not impossible. Mr. Erickson Ms. Blauman February 12, 1990 Page Three Construction of utilities for some of the other alternatives, as discussed in the Draft EIS, may be more difficult. In particular, sanitary sewer construction for any development directly above (east of) Marina Landing will require sewer extensions down some fairly steep slopes. Again, preliminary analyses indicate that these proposals are feasible, but more detailed design will be required during the Building Permit phase. This concludes my responses to your comments. I have attached copies of my responses to the other Public Works Department comments. If you have awn y questions, please call me. We can talk over the phone or meet in your office. Sincerely, DODDS ENGINEERS, INC. Roy . Lewis, Jr., P.E. Associate/Project Engineer Enclosures: Responses to Abdoul Gafour, Kim Scattarella and David M. Christensen cc: Mike Blumen & Leslie Lloyd (The Ferris Company) Scott Springer & Colin Quinn (Lincoln Property Company) John Phillips (Phillips &Wilson) F , - DODDS ENGINEERS, INC. CIVIL ENGINEERING S U R V E Y I N G P L A N N I N G CIVIL ENGINEERING INPUT INTO THE DRAFT ENVIRONMENTAL IMPACT STATEMENT FOR: "THE BLUFFS" RENTON, WASHINGTON Prepared By: Roy E. Lewis, Jr., P.E. •=y E• w/s�'% DEI Project No. 88139 i @ h�� November 17, 1989 . • ''ti9fC/STEF�r g�• 4205 14BTH AVE. N.E., SUITE 200-BELLEVUE. WA 96007 (20B) B135-7877 OR 454-3743 FAX:(206]BB5-79B3 Y TABLE OF CONTENTS BOUNDARY & TOPOGRAPHIC SURVEY EXHIBIT LAND USE MAP SLOPE ANALYSIS WATER SUPPLY NARRATIVE PAGES 1 - 2 POPULATION ESTIMATE AND WATER DEMAND TABLES WATER SYSTEM EXHIBIT SANITARY SEWER NARRATIVE PAGES 3 - 4 SANITARY SEWER EXHIBIT SANITARY SEWER ANALYSIS (RH2 ENGINEERING) STORM DRAINAGE NARRATIVE PAGES 5 - 8 ESTIMATION OF SITE DISTURBANCE TABLE 24-HOUR STORM RUNOFF ESTIMATES TABLE COMPARISON OF DEVELOPED RAINFALL RUNOFF TABLE DRAINAGE BASIN MAP STORM DRAINAGE EXHIBIT DOWNSTREAM STORM DRAINAGE SYSTEM EXHIBIT 1 - t i r \ I Y \ �\Az� 1 Ic `\ 31 •� � - �. ��� r i�f�'� ice_I J c, � D,•� � _ � I, I II 1 � z ,r! `•, i -� I 11. P Lk IZZ 1 rl — �cn�0� r ( y, �Oooa�$z mu cn 1 ono �p OATE AUGUST 1989 •••lfW/ No v L)Ar BOUNDARY B TOPOGRAPHIC SURVEY D O D D S ENGINEERS , I N C . j-�c• ;'•, _ m or=scNEO k.Lh'WI$ CIVIL ENGINEERING SURVEYING PLANN,NG f`p THE BLUFFS BORAWN ELLEVUBTHAVE N.E.•SUITE d00 APPROVED ii.LI:IVIti -�'® t ----- -- - --- -�--�� BELLEVUE,WASHINGTON 96007 � ; �� '•'• `� 7 Id1Y El.1.11., Jlt.,I'.I!. •, ^�i��t _�_._.__._.___ __ D �'�+DJE C7 MANAGERRI•:NTON WASIIING'1'ON _;,. 120BIee5-7e77OR454{37n3 titi ,1+�?: ---- ----- . ,_ ,,ot!I71fiI8 lilt • \\••����\\\��\CNN\\\��� NNN\NNNNN\•\N`\��t�• f tt \ ';Xnzt:...\\\ i Ili \.,..\.\\\\\.\\.\.\\\.\. �•ij�;,�iJ�4J;;!►�IiilJllhi i� ;:�::�;:�:;::;:;: ;:.:_ ;Ilhjl I li►��Iil�I i. I(I� i III - !!,,,�f L,fI,►I,�I•� Jl ,Ii, \.\..\\.......\........\.. ......\.\.\\\.\........\.\.\....\.... JII NNNNNNNNNNNN\NNNNN, I!!� � � ' �iNnmw l \\\N\NN,N,\\\NNN\\,\\ i IJ�IIIlllllidllllllll�f(IJ�IIIIIII!II NNN\\\N• NNNNNNN\NN; li I I�!�� I \NNE\\?\•'-��\N\• li I Ii�IJh�►fi;�!ri;l'�I(,�III� I� I �'�IJf II I i ly,l lilliliJ�IIII�+I II I I1(' I t, + I'IilIlIIiII! illl I'i• : I , i+++IIIIIIigIi�'IlihllilllipJ�Jii � �I f i°��I�,I II li �f:lll►�,i,,�,+il�Jill I 1 .I i II,I , _ II,� �Iil,lj�ill I;(1i► li,,f J If ��,,JI IJI _ � I► I, (i I� +' I � ,I��i�llilll1111.�,�1� glil,;IallU,ll(((�+�i( I���! , �i 7 ►I !II�� ►� ' I Nilll,lir�:l � i �!I� II II �� ll►d► I!i(ul�,lifl�(Ilhl.flf�I�Ili�l il,� �I!I!I lit I,I:I I ir(�I:r!JiJ l�ll.I _ ► • . re r►�®er��rrrr►�w � veer s�arrrr►er . : � ;:�irw�re►vrrr�►�r� _ -• r • � w�®rw�irovrrrrrr� _ ' - • � ��r'��ir�ic �lreri► _ � r�irrw�rra�rrrrr rrrr�►r�er�►r►�wrcws � • e rr, w� W. �,w►,ir►�r� � �Nii� e r'ee�asi VrrAA Navin CIVIL ENGINEERING SURVEYING PLANNING 4205 ,- FA © • -- - OR 454-3743 O \ � r ,� � , \,1i•II Rt pp� ti w o5 � i 7 a\° oP 7. * 11 F Stil`t��'``�t��`(S1� '.,\ `(� • ,...}i �I i i� I i 1 �I i � "`('Sttt�,.t(5t5`l�5'`�� , � Z\4 �I I I� I`II •'�` t, r I1 '• r �41t `;SSlir"'"t��``` ;,,II ;. �I ' •1 1�;;• _. I ,r�i,''j}�5r I ll�j�r i� � / %`�� .f 'ri i, '.• ��1;tSi`�r�}```;�rtt'ttrtt4r4S��1 5�0 7- � \ ! •� p `�/ \ ::�• .; WWI N— 5 �� y I I —� 1}tti'y}';'•'`,`i�il��}1StyS' C' � Z ` I� m � ,',' \ I"`'tt1 1 I ,r `yt4t tttt z- !,�}i1'�S'Str S5S5 �S`Stl�1l11r,}t � Z �.;, I, l •`•' � �, 5`t} I i1�1'�rl}y'S'} C1 Z k", `y. �.... �111i,'i5�;51''4SFSr�4Ft�t�• �� � ,�� 5 �. .••: �. ,' J. ,51'r'1f1t 111'(llr,l � ' \ xJ 4`�;s'ti5tslc,`11c�5'��1`11�i •• �. l ' i i tits`,ir`,�5'''S11r.. �..• ••tt l.': , 'r�',,5ltt'SyrS1';SStt, I t •''••''•• V'',j;'�1. �IA r r ,t�r1t�'s;ti�'i,stl'ttittl�;dt ��'. �'. ,• •�. , ' , bd vj� O •S,,1itrrSt�t t�l'`Qli1i`t' 3 � ', ? •'\ ` q7� L-t O o 'er to r•I r5trl}`SSt� tb 30 o /r C S'itt y OZ mo - ��•• � ��� ° GATE AUGUST E_989 SLOPE ANALYSIS DODDS ENOINEERS " INC . �rVIEM�� pp rt1 OESIGNE0 P-LMS CIVIL ENGINEERING SURVEYING PLANNING �� d DRAWN R.LEWES 4205-14'BTH AVE.N.E.-SLATE 200 , APPROVEO R.E.Wpi THE BLUFFS Q30 12061885-7B77 OR 454.3743BELLEVUE,WAS'h1INGTON DOM7ROY E.L1iW18,JK.,P.L.c,d�r_innn�,ncEa RF,NTnN WASHMGTON -- 9- WATER SUPPLY Water supply is available from a recently extended water system north of The Bluffs. This existing 16" water system is strong, providing over 3920 GPM at the nearby Marina Landing Apartments. The supply of this water system lies within the 435 Pressure Zone. The pressure is reduced to the 320 Pressure Zone, to serve the Marina Landing Apartments, which lie north and west (below) The Bluffs. Pressure is reduced once again to the 196 Pressure Zone,just prior to the connection to the Gene Coulon Park water system. This interconnection completes a major City loop. The Bluffs' water system will extend from the existing 16" main, which parallels I-405, on the hillside above Marina Landing. A 16" extension may be required since it is a single source providing over 3500 GPM. Construction of the first 600' of this extension may be challenging. The existing topography is somewhat steep and undulating, requiring noticeable grading for construction access and permanent access for maintenance. Route selection will be important to minimize construction impacts. Once the main reaches the developed area of The Bluffs, construction will easily conform to the final grades of the site. Pressure must be reduced from the 435 Pressure Zone to the 320 Pressure Zone to serve the site. This will yield onsite static pressures of 60 to 70 PSI, which are optimal. The extension will continue through the site, down the proposed Bluffs entrance road, to Lake Washington Boulevard. Here, pressure will be reduced to the 196 Pressure Zone and connected to an existing 12" main in Lake Washington Boulevard, approximately 300' south of the proposed entrance road. This will PAGE 1 complete another valuable loop for the City's water system. A loop is required for all sites with required fire flows over 2500 GPM. At this time it is estimated that the required fire flow for the site will be approximately 3000 - 4000 GPM. Sprinklered buildings (as proposed), fire resistive building materials and/or fire walls can significantly reduce (50% +/-) the fire flow requirement. Consumptive water demands are determined by domestic and irrigation uses. Domestic uses can be approximated at 100 Gal/Person/Day and summer time irrigation uses can be approximated at 600 Gal/Acre/Day. The table on the next page indicates consumptive water demands of 31,380 Gal/Day (or 21.79 GPM) to 54,120 Gal/Day (or 37.58 GPM) for the four alternatives. The consumptive requirements are insignificant when compared to the required fire flows. The proposed system improvements will satisfy both needs while providing a more robust regional system. A schematic of the existing and proposed water systems is provided for reference. PAGE 2 THE BLUFFS POPULATION ESTIMATE ALTERNATIVE PREFERRED #OF UNITS 95 135 165 240 1 BEDROOM UNITS 0 67 82 120 2 BEDROOM UNITS 65 54 66 96 3 BEDROOM UNITS 30 14 17 24 ESTIMATED 268 285 348 504 POPULATION ............... * BASED UPON 1.5 PERSONS PER ONE BEDROOM, 2.5 PERSONS PER TWO BEDROOM AND 3.5 PERSONS PER THREE BEDROOM. WATER DEMAND ALTERNATIVE PREFERRED #OF UNITS 95 135 165 240 DOMESTIC FLOW (GAL/DAY) 26,800 28,500 34,800 50,400 (GALIMIN) 18.61 19.79 24.17 35.00 * BASED UPON 100 GAL/PERSON/DAY. LANDSCAPED AREA 8.1 AC 4.8 AC 4.1 AC 6.2 AC IRRIGATION FLOW (GAL/DAY) 4860 2880 2460 3720 (GAL/MIN) 3.38 2.00 1.71 2.58 * BASED UPON 600 GAL/ACRE/DAY. TOTAL FLOW (GALIDAY) 31,660 31,380 37.260 54,120 (GAL/MIIN) 21.99 21.79 25;88 37.58 W + PROPOSED W47£R"M(TYPJ PROPOSED PRV _ Q 435 iWESSURE T6 _ ----- -- l 320 PRESSURE ZONE --- -' - - r EVS74w W47ER F/R£HYA94M./TYPJ SYSTEM lrYP/ \• ;v . /NTERSTATE 405 JAI- _ � I 40 _ uj ur - ZZ u r road /'mil ^� __ ` \— Wa m 3 m ' ,'1✓ I�5 Ex�sr a4v % �— /' �r4s AVEssurE zavE zrn,C ss�E mnE s..W O ,� .\ ,\ O oz t e w Io�1N /�� /=" ou e ac o 9'w MAR/N4 \ �r !!!`i` 0 D „w srsrEu mPJ z LAND/NG _-1 AP4RTMENTS ✓ 1ZjLA e,w tN RA1 \ zW pR PRK Ns a� gt;RoNCjCN' REACH A - k F� Pro CDULnN GENE ✓;. _ _ 1._- ;✓ _ -LO W .r_r"=fir`_? ✓'�`^;^=;:'ram_::1 .._sue-"�^'__=-'.`�� =✓f- ON REDUCED SCALE ,�.- .ter.--_:. __;.r1:.--="` WA ri,r z �. . r r- ✓ �AKt _ � W = NORTH 1"=100, �� d jj d d d y a O /00 200 300 400 I -1 u a uj tj BOUNDARY INFORMATION HAS BEEN OBTAINED FROM A r 7/15/86 UPDATE OF THE KING COUNTY ASSESSOR'S s MAP. TOPOGRAPHIC INFORMATION HAS BEEN OBTAINED I FROM 1962 CITY OF RENTON AERIAL PHOTOS. I405 STORM DRAINAGE INFORMATION HAS BEEN OBTAINED ^.BEET OF FROM 1983 WSDOT AS-BUILTS. LAKE WASHINGTON BLVD.STORM DRAINAGE INFORMATION HAS BEEN OBTAINED FROM 1986 MARINA LANDING AS-BUILTS. .,. ... .. 88139 SANITARY SEWER The ultimate discharge point for all sanitary sewers in this area is a 96" METRO trunk line which is parallel to and westerly of the Burlington Northern Railroad. There are two nearby 8" taps into this METRO main. One is the recently completed Marina Landing Apartments tap, which is located near the main entrance to the Gene Coulon Park. The service area of this tap is very small and ultimate capacity problems are not anticipated. The second tap is located near the south entrance to the Gene Coulon Park, approximately 450' south of the proposed Bluffs entrance road. This tap serves a rather large area, yet the City of Renton (per an analysis provided by RH2 Engineering, attached) indicates that there are no anticipated capacity problems for the pipe segments downstream of the proposed connection point for The Bluffs. This location will be the likely connection point for The Bluffs' sanitary sewer. Due to the terrain, the sanitary sewer alignment will have to closely follow a uniform contour line along the westerly (downhill) limits of development. This will minimize the depth of the sewer and keep the sewer within the developed area, where it will be easier to maintain. The 135 unit & 165 unit (preferred) alternatives will be sewered from north to south, then down the proposed Bluffs entrance road, to the existing southerly sewer stub in Lake Washington Boulevard. The 95 unit and 240 unit alternatives will require additional, more difficult construction for the developed areas due east (above) the Marina Landing Apartments. Either gravity sewers must be constructed down the steep slopes above the Marina Landing Apartments, or a small sewage pump station must be installed. PAGE 3 As estimated in the section on Water Supply, the average daily sewage flows will probably be around 100 Gal/Person/Day. The tabulated flows of 26,800 Gal/Day (or 18.61 GPM) to 50,400 Gal/Day (or 35.00 GPM) are well within the capacity of the downstream systems. A schematic of the existing and proposed sanitary sewer systems is provided for reference. PAGE 4 i -` - I Hill /NTERSTA TE 405 AVVaW / t, un �� �\ Z Q v Q > U) `` .,�J J'../ -P,O f ,/ / �. �s;' `•,.�. - _� -� _ �' WER (7m'PJ_- \. ^� j6� \ G/ — \ �_* r— ZD W> 3 - ML� z 0 Q mGAMAMMbC£ P Y 4 _ shun/OF N/4M sr Lu z 13ol W NPROPOSED oo f .SEWER \ SAKE Rpi D �" z � sr SERER �SAWAar / 90- �RtN RE k a 3 �IN�t° W w � � ..-:'-. -'- =_`'��✓_'-''"`,-.-'".-ccf.✓"'�.�^'�.�'✓..:-'ram-,� _ �. REDUCED SCALE -'-•fir=�~= `- - i� r - LA a NORTH 1 =100' 4a d d d yF 3 O A70 200 300 400 w BOUNDARY INFORMATION HAS BEEN OBTAINED FROM A Z 0 4'_'V86 UPDATE OF THE RING COUNTY ASSESSOR'S w 3 s MAP. TOPOGRAPHIC INFORMATION HAS BEEN OBTAINED o FROM 1962 CITY OF RENTON AERIAL PHOTOS. I405 S CET OF- STORM DRAINAGE INFORMATION HAS BEEN OBTAINED FROM 1983 WSDOT AS-BUILTS. LAKE WASHINGTON BLVD.STORM DRAINAGE INFORMATION HAS BEEN OBTAINED FROM 1986 MARINA LANDING AS-BUILT& A 88139 Engineering S1292.00(.243) November 1, 1989 Mr. Colin Quinn Lincoln Properties 1745-114th Avenue SE, Suite 100 Bellevue, WA 98004 SUBJECT: SANITARY SEWER ANALYSIS FOR 'THE BLUFFS" PROPOSED APARTMENT COMPLEX Dear Mr. Quinn: An analysis of the City of Renton's sanitary sewer system was performed for the purpose of determining the available capacity of the existing sewers in the vicinity of the proposed apartment complex called The Bluffs, located on the east side of Lake Washington Boulevard North. This letter summarizes the available capacity of the City's sanitary sewer system based on results of a computer analysis simulating wastewater flows in this location. The analysis was based on the existing sanitary sewer system without adding any new sewer extensions proposed for this project. The existing system consists of two manholes before the sanitary sewer discharges to the METRO Interceptor. The first manhole is MH 12-149 and is approximately 6 feet deep. At this time, no wastewater flows are entering this manhole. An 8-inch steel sewer pipe extends from manhole 12-149 to manhole 12- 148 as it crosses under the railroad tracks. The depth of manhole 12-148 is approximately 17 feet. A summary of the physical data for this section of the sanitary sewer is presented below: Pipe Size: 8-inch Pipe Length: 121 Feet Average Pipe Slope: 2.83% Mann;ngs Coefficient: 0.013 Maximum Ratio of Depth to Diameter: 0.70 The results of this analysis indicate that the maximum capacity for this section the existing system is approximately 760 gpm. The City is proposing in the update of its Comprehensive Sewer Plan that the estimated peak, wet weather flow should not exceed 70% of the sanitary sewers maximum design capacity based on the above criteria. Using this criteria the maximum allowable flow in this section of sanitary sewer would be 535 gpm. There is a limited amount of available data regarding the section of sanitary sewer between MH 12-148 and the METRO Interceptor. The only information known is that 1410 Market Street, P.O. Box 1180, Kirkland, Washington 98033 (206) 827-6400 the sanitary sewer is 8-inches in diameter. The combined estimated saturation wastewater flowrate entering MH 12-148 from MH 12-147 and MH 12-150 is 530 gpm. The minimum slope to accommodate this 530 gpm from MH 12-148 to the METRO Interceptor is 2.8%. A slope greater than 2.8% or replacement with a larger diameter sanitary sewer would be necessary to accommodate any additional wastewater from MH 12-149. The figure showing the location of this section of the City's sanitary sewer system is attached for your reference. A copy of the computer analysis has been retained in this office for future reference. If you have any questions or need additional information, please contact me. Sincerely, RH2 Engineering, P.S. Mark L. Semrau, P.E. Enclosures: Sanitary Sewer Node Diagram cc: Mr. Roy Lewis, Dodd's Engineers }.� NV .I . >~313 :•� _. J p.. ................................ f it 8... IV LJ ,.�` / •:; ; t '; t ,':i 1 , (r _._............... 112 ' i .'f•'.�,} •,..•',` �[.� .5;;, �`......._.................... .�»...:..;:,......_...•.«_...._! t.....,.. i tj ..........».. zo �.._.._.._ : j •� �.. ....... �:.'.'.... f f �•.t , rt 5] ii ..t ,j 60 Bob i n g t` ;•:�.,: JJS. ,... • ..� ,\�\1 �;I ; -:� Lilt- tionSta � � � ``t ! ;�,� �• l.: ,` �:�� � ,, .�_.Y.. t r... O17 .�. ............... STORM DRAINAGE Attached for reference is an exhibit which delineates the various drainage basins associated with development of The Bluffs. The total drainage basin under analysis consists of 65.90 acres; 41.40 acres offsite and 24.50 acres onsite. The ridges and valleys clearly delineate eight major sub-basins which combine at three separate discharge points. I-405 and Jones Ave. N.E. (further to the east) intercept and divert to the south, a portion of the offsite drainage. The undiverted drainage is processed by the I-405 drainage system and discharged into The Bluffs' natural valley areas, as shown on the provided exhibit. Drainage apparently filters to the valley floor and is conveyed westerly towards Lake Washington. After close (late summer) review of each valley, it was difficult to locate a well-defined drainage flow path. Small drainage basins, porous soils and well vegetated slopes appear to reduce the potential for concentrated flows. There is no evidence of erosion in the upper valley floors. The valleys are characterized by a uniform, undisturbed covering of forest litter. Apparently, the valley floors can easily handle the existing tributary flows. Lake Washington Boulevard acts as a lower drainage interceptor. A roadside ditch conveys intercepted flows to the north and the south, from a high point just north of the proposed Bluffs entrance road. This ditch also shows little sign of erosion. The northerly flows are intercepted by the recently completed Marina Landing Apartments storm drainage system. This system drains beneath Lake Washington Boulevard via three pre-Marina Landing culverts. Drainage is then PAGE 5 culverted beneath the Burlington Northern Railroad tracks, into the Gene Coulon Park storm drainage system. The park's system then conveys drainage directly into Lake Washington. A recent inspection of these downstream systems showed well armored channels with little sign of erosion or capacity problems. The drainage which flows south along Lake Washington Boulevard is eventually intercepted by a 12" concrete culvert located just north of the N. 14th St. right-of-way. This culvert discharges into a swale along the east side of the Burlington Northern Railroad. Shortly downstream, this swale is intercepted by a 24" concrete culvert which extends beneath the Burlington Northern Railroad and ties directly into the Gene Coulon Park 24" CMP storm drainage system. This park system discharges, a short distance away, into a natural, well maintained stream, which gently meanders into Lake Washington. The stream bottom is lined with cobbles and shows little evidence of erosion. The stream banks are lined with dense, tall grasses which appear to protect the channel well. An exhibit of this downstream system is provided on the next page. In summary, existing onsite and downstream storm drainage systems appear to be well suited for the tributary flows. There is little evidence of erosion or capacity problems in these storm drainage conveyance systems. Development of The Bluffs will alter existing drainage conditions. Buildings and paved surfaces will be constructed, replacing existing ground cover with impervious surfaces. Other areas of natural vegetation will be removed during grading operations and replaced with urban-like landscaping. These alterations will increase the rate of surface runoff and decrease the uniform rate of groundwater recharge. The approximate magnitude of these disturbances is tabulated in the pages PAGE 6 that follow. For the preferred alternative, approximately 8.3 acres of the site will be disturbed during development. This 8.3 acres represents 33.9% of the 24.5 acre site or only 12.6% of the 65.9 acre drainage basin. Only 4.2 acres of this disturbance will be converted into impervious surfaces; the remaining 4.1 acres will be landscaped or restored to pre-developed conditions. As shown on the attached "24-Hour Storm Runoff Estimates" table (for the preferred 165 unit alternative), developed stormwater runoff will average 167% of the existing runoff rate. A comparison of peak developed flows of all of the alternatives is also provided. The existing conveyance systems can hydraulically handle this minor increase in flow, but concentration of flows, at the increased rates, may increase the probability of erosion in the steeper slopes. To reduce the potential for erosion and help mitigate the impacts of increased stormwater discharge rates, several standard design practices can be implemented. Conveying developed storm drainage runoff through tight-lined systems minimizes the potential for erosion of the natural channels. Offsite flows will continue in the natural ravines, but developed flows will be intercepted by tight-lined systems which will be designed to convey the developed 25-year stormwater runoff. The 135 unit and 165 unit alternatives will convey developed drainage down the proposed entrance road to the toe of the bluffs. Here, where grades are gentle, the flows can be safely directed to the existing conveyance systems, which have adequate capacity for the nominal increase in flows. Though not required for the 135 unit or 165 unit alternatives, stormwater detention systems can be constructed to help maintain the existing rates of stormwater runoff and provide settling time for water quality enhancement. (The 95 unit and 240 unit alternatives will require multiple stormwater detention facilities due to the topographic isolation of several areas of PAGE 7 development. These two alternatives may also require storm drainage discharge over the steep slopes.) By maintaining existing drainage basin boundaries, flows will be directed to the locations that have historically proven to have adequate capacity. Subsurface flow dispersion trenches will help return the stormwater runoff to a less erosive interflow condition. A planting of dense, hardy grasses, downstream of discharge points, will help in flow attenuation, distribution and filtering. The use of oil/water separator vaults (prior to discharge), the use of dense vegetation just below the discharge points and the maintenance of existing vegetation in the natural valley floors will aid in water quality enhancement. The ultimate receiving waters should notice little water quality degradation due to construction of The Bluffs. It is important to plan for good water quality management, especially during the construction period. Noticeable cuts and fills will have to be accomplished in order to access and develop The Bluffs. These exposed cut and fill slopes will need to be protected from erosion due to rainfall. Hydroseeding or permanent revegetation should be in place as soon as practical. Mulching and plastic sheeting may be required in areas of special sensitivity. If grading operations are quickly performed and/or completed in small phases, the potential for erosion will be reduced. In any case, providing sedimentation ponds and maintaining dense vegetation, where practical, will aid in the entrapment of eroded soils, minimizing the potential for siltation of downstream streams and Lake Washington. PAGE 8 THE BLUFFS ESTIMATION OF SITE DISTURBANCE ALTERNATIVE PREFERRED' #OF UNITS 95 135 165 240 TOTAL AREA OF 12.6 AC 8.9 AC 8.3 AC 12.6 AC DEVELOPMENT IMPERVIOUS AREA 4.5 AC 4.1 AC 4.2 AC 6.4 AC PERVIOUS AREA 8.1 AC 4.8 AC 4.1 AC 6.2 AC APPROXIMATE 73,000 CY 66,000 CY 81,000 CY 77,000 CY VOLUME OF CUT APPROXIMATE 36,000 CY 31,000 CY 21,000 CY 32,000 CY VOLUME OF FILL * THE AREAS OF DEVELOPMENT, IMPERVIOUS AREAS AND PERVIOUS AREAS HAVE BEEN OBTAINED FROM TABLES PREPARED BY MILBRANDT ARCHITECTS. THE BLUFFS 24-HOUR STORM RUNOFF ESTIMATES TIME OF 2-YEAR 5-YEAR 10-YEAR 25-YEAR 50-YEAR 100-YEAR AREA CURVE CONC. RUNOFF RUNOFF RUNOFF RUNOFF RUNOFF RUNOFF BASIN# (ACRES) NUMBER (MINUTES) (CFS) (CFS) (CFS) (CFS) (CFS) (CFS) EXISTING CONDITIONS 1 16.40 71 18.1 0.16 0.62 1.38 2.33 2.85 3.41 2 14.50 72 21.9 0.15 0.61 1.30 2.14 2.59 3.06 3 14.30 68 24.5 0.10 0.42 0.70 1.29 1.66 2.06 4 3.16 55 18.3 0.00 0.03 0.06 0.10 0.11 0.13 5 2.31 55 16.9 0.00 0.02 0.04 0.07 0.08 0.10 6 3.93 55 23.1 0.00 0.04 0.07 0.12 0.14 0.16 7 2.52 55 15.4 0.00 0.03 0.05 0.08 0.09 0.11 8 8.78 86 15.2 0.65 2.08 2.89 3.74 4.18 4.62 2+3+4 31.96 68 24.5 0.21 0.93 1.56 2.88 3.71 4.60 5+6+7+8 17.54 71 28.3 0.16 0.63 1.22 2.11 2.61 3.12 DEVELOPED CONDITIONS 1 16.40 71 18.1 0.16 0.62 1.38 2.33 2.85 3.41 2+3+4 31.96 73 24.5 0.36 1.50 3.10 4.96 5.96 7.01 5+6+7+8 17.54 76 28.3 0.26 1.25 2.22 3.31 3.89 4.50 * BASED UPON THE SANTA BARBARA UNIT HYDROGRAPH METHODOLOGY. *24-HOUR RAINFALL AMOUNTS ARE BASED UPON THE FOLLOWING TABLE. YEAR INCHES 2 1.50 5 2.50 10 3.00 *OBTAINED FROM THE NOAA ATLAS. 25 3.50 50 3.75 100 4.00 THE BLUFFS COMPARISON OF DEVELOPED RAINFALL RUNOFF 2-YEAR 5-YEAR 10-YEAR 25-YEAR 50-YEAR 100-YEAR ALTERNATIVE RUNOFF RUNOFF RUNOFF RUNOFF RUNOFF RUNOFF #OF UNITS (CFS) (CFS) (CFS) (CFS) (CFS) (CFS) 95 0.80 3.45 6.88 10.83 12.95 15.19 135 0.77 3.34 6.64 10.52 12.62 14.83 165 0.78 3.37 6.70 10.60 12 70 14.92, 240 0.91 3.99 8.03 12.32 14.55 16.91 * BASED UPON "TOTAL" SITE FLOWS IN THE DEVELOPED CONDITION. 24-HOUR RAINFALL EVENT, UTILIZING THE SANTA BARBARA UNIT HYDROGRAPH METHODOLOGY. 6 , a Lin Y/ �a.✓C... f1I j f oc r j 1 co e (W7 ra; dl'IJ ( \\` 1 11 ', �`_J '[_! ' o-j I ■- - , ET ' 1q _�-'_Y_ _• �� I •k. 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I••' \::��\ ( NCN.ND I , , \ 1 y r r P P Y P P P PA P P Ito 0�9f2�RdBAAd y \ �\ » I \ � , eN II'� 4�I,�('4J�1���yI I�. 1 •1 II. ask kid aHalteSk� "' $" 11 \ li ° f ) I �+ �I++ � I[►1�-']f J xRusN �xtl ~F'Y'�pscitrtl �Vl � � \ \ 111 -- _ � P Q)„'� 1� �•;II ., II ° ih w� ....� 11 � 'S' \Ni �� •I I all ' �cI i , ' •+Y Y!lP PPPYHtY�- -�i /E 1 ' I \_ _ 1l I' 'j li `._..._ IW' , roll D -�- orP-��' toe yC3O �z L A K E W A SH INGTON C7��y `�' Nd0 Z1717 P A R K rl• ' 7 p o () i i Z Al...��� H� � SNUr rI[7xx NO I R NO 2 "7+dOy�o�y0 0 Icy I�1.�.� N __ _ _ —_ ___ _—_ ■ O . �������� >o• m p R o 0o F-+ xz = � " zz� x o � N D �A p � O r edz� n $ m rod o C � � C � DATE Aucusr 1,vav CIATE D O D D S E N G I N E E R S ,PLI N C U ulvi� v � DEBK3fVED R.I.KWIS DRAINAGE BASIN MAP CIVIL ENGINEERING SRVEYING ANNING 1 t� d � _ DRAWN IL Lfi'WIS THE BLUFFS - 42D6-146TH AVE.N.E.-SUITE 2D0 �� Appgp,, p IL I.N•WIS - ® � BELLEVUE,WASHINGTON 'J0007 � Y ROY L LEWIS,1N.,P.E. r �MnP•°Ate. — n PRrkkCTMZ4AcFa — R1?NT'nN WASIIINCTnN I I�g7©77oRns4-a7n3 Hill- PROPOSED STOH/A - _—• OHA/N/TYP/ INTERSTATE 405 e / �5 ./ '. /I3 A� ps �y /\\ �• ANO FLOW n l-CATCH BASIN � ,uev ^ !P \\ W L i ZQ N f e Lu ZZ _ J .- \ __- — - - �. JJ_ \. - Z Z Q m IC,UJ .� -cc` � "� FAC/L/TY A ER Lu� ; = - - =_ 1 / Z.\_ &ss .` �' pnJALf/o-nc NFk1NCEM£NT, ' /b5 �— �a O� RCGreRr trnl , AnfOVITr y� I Oz / ) ` '~!� Cn � / � . .�.. SEE OOWNSTRfAM O I tl 'E. SED VOW _ / STORM CRAMC-F J EXH/BIT a> R /L ORt E R Z 3 �N PARK k IAL BEACNs`--� r =- Mof? / -I'- �_.r• _.- _ -_.may^� -. "r �- , TON REDUCED SCALE � r VV/A F —=t -- /o AKE NORTH 1"= 100' ut y �Iz O Kx0 ZOO 300 400 iu BOUNDARY INFORMATION HAS BEEN OBTAINED FROM A Z I p 7/15/86 UPDATE OF THE KING COUNTYASSESSOR'S MAP. TOPOGRAPHIC INFORMATION HAS BEEN OBTAINED c; c S, a FROM 1962 CITY OF RENTON AERIAL PHOTOS. I405 s EEr o� STORM DRAINAGE INFORMATION HAS BEEN OBTAINED FROM 1983 WSDOT AS-BUILTS. LAKE WASHINGTON BLVD.STORM DRAINAGE INFORMATION HAS BEEN OBTAINED FROM 1986 MARINA LANDING AS-BUILTS. 88139 Willi f 06 12" CONC. CUL VERT ��- /•E.=45.2/ 60LF@ 0. 1320 _ / GENE COULON I.E.=37.30 •O Z r MEMORIAL BEACH PARK C� N (SOUTH ENTRANCE) -� / *�� Z Q � Z m 7 J ANGLE POINT IN � O •�- Q 4 CHANNEL. EL.=33. / I (n C9 w rl aJu} Ili Z Q m I O � 3 n �m m ui TO LAKE.WASH/NGTON DRA/NAGS 0 > m CHANNEL ZZ N J (D cu CREEK 'I m N0 0w 24"CMP OUTFACE=/S.B/ 0J TYPE B 24"GWP R/A4=26/53 O U /56LFO 0.00/9 TOP OF STANDP/PE=/9. 1/ I z I 24"/.E. IN=/9.39(CUP) C _ 24"/.E. OUT=l6. //(CUP) F \ PIPE MATERIAL I z i f CHANGES 24"GNP O W 3 \ \ 53LF6 0.05/0 — rT _ Q W 24"G4/P V 24" CONC. 0 /6L FO 0.2856 CUL VERT 1�_ Q tN Z Z W.S.O.O. T. INLET Q 24-I.E. IN =23.98(CNP) L�/7 24-I.E. OUT-23.93(CUP) E"'r Rift J' O fzr a L ui J a J g ul >. 3r A Z N Q 0 G NORTH 1 " =2W > Z Z 0 W g 0 W Q 3 CCg Q w Q d 0 0 0 Q O /0 x 30 40 50 SHEET OF REDUCED SCALE 1 1 PgOJECT NU"3ER 88139 m N � { I \ N \ l r c rr i v \ o \ \ \ l \ f r , �\ m O ;i ! I I \ \ E \ � 8 K\' t i 1 iT7 r>i ti ;�'7Y77�{Is 1 � `,• I ; i i I ! I � i r Vy' (�� i `t ` l ''I '} ', tr I 1 \ ` y ,�r�� tit • ' l??(v�'y • trti t���7 ' � l `<, � - ,,�//i'' ___ i 4 : 7 7 , ti �y`��(77,7�`7\ti1!7,t ,y ��\,( tr'Ytt�tr��y,•T'� C _ __.\__ �-_-_ / /// 3 '` VI'( y �{i a, t o vit'� r( >1fT>7�''bi> t �'�r��t � , .:»^"°"" � �/ � �" /""`!"'",- •/ g� i t ( ; �t 1 ' Q) o '� •O 7 I t O 'I - 7 7Z d � ! o Cr 44 �' C t •r'1y7��.li ,��f r�y= \ � 1 l� � � f % i. j( �;,1 Syr \ti�f >i e`.?`. ,Y• `i ��►►� � /' Vt y � 1 I j S . SY4 Y 1(3 t ?ir;f y>> tF Yt>7 L� s s ti\ \• 4 I I YII }>tr 'Y�L 1.1 > ' E r l'la •�` '\ 7 > t , < � t 1 � i�- Y7'Yti7• >' >??c'..'>�7lvy{� C • � -..-.-__ CT m t 1 \ ' -, � 7 •y�� i= r{ y Y s i?'r m qt v 1 / dp I A � � � { i e T tt \ ep 7 1.ry EtrpT 414 � Y :Z i 135 <r16 :{> 115 �� ,0, . ✓ M� � Z �rj >(' tyrt'i'`:1�=r> .� �QQ _ Y /� /S \\ 4` \° o MCI O. Y;r7�`y7b>y�ti `\Sy` ► � \ �.� l II \\ t �.► � � Y.� M+•1 '1J O j:, _,y y�77.�. L�p\i: •- _ B6 •,: l , `* � 1� I =} ,1J M� `fit, r>'+;Z{ (a' ( �.`• / - � ')//t :1 '� I .,} i �.y ICI O O I1 Z x a R \" �e Oil VN I I i r--+ O you �► , i 1 tl t *.4 t 0-4 1 Nl 100 o� _ t (� DATE AUGUST 1989 .•+•���� NO. REVISIONS DATE o I — DODDS ENGINEERS , INC . Milo*; �Ewr �' m SA NI TA R Y SEWER EXH181 T ; CIVIL ENGINEERING SURVEYING PLANNING q� m m DESIGNED R. LEWIS ' yo � DRAWN R. LEWIS 4205 - 14BTH AVE. N.E. - SUITE 200 • s R. LEWIS Ilk. BELLEVUE, WAS B HINGTON 9007 c f C APPROVED T E BLUFFS ® • '�°s A� • rn ROY E. LEWIS, JR., F.E. [20Bi BB5-7B77 OR 454-3743 tih t I] PROJECT MANAGER RENTON WASHINGTON ••.,,,..-• , m W 1 ` m C rr z I V N N ( 1 , N .,.._..,.. 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