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HomeMy WebLinkAboutC_City_Response_Letter2_w_Enclosures_Walter_190930_v1 September 30, 2019 Karen Walter Muckleshoot Indian Tribe Fisheries Division Habitat Program 39015-A 172nd Ave SE Auburn, WA 98092 SUBJECT: 4th Dimension Building Comment Response Letter (2) LUA19-000153, SA-H, ECF, V-H Dear Ms. Walter: Thank you again for your initial comments related to 4th Dimension Building (received on July 31, 2019) wherein you raised concerns regarding the proposed project. Responses to your comments are enclosed. If you have any further questions or comments please feel free to contact me at 425-430-7289 or cclose@rentonwa.gov. Sincerely, Clark H. Close Senior Planner Enclosure(s): Response to City Comments, prepared by Raedeke Associates, Inc., dated August 27, 2019 Revised SEPA Environmental Checklist, received September 12, 2019 Upstream Flow / Water Routing Question, received September 12, 2019 Revised Preliminary Technical Information Report, prepared by Harmsen & Associates, Inc., dated September 11, 2019 cc: Fisher / Party of Record Wetland & Aquatic Sciences Wildlife Ecology Landscape Architecture 2111 N. Northgate Way, Ste. 219 Seattle, WA 98133 206-525-8122 www.raedeke.com Associates, Inc. Raedeke August 27, 2019 Mr. Martin Reimers Concept Architecture, LLC. 1712 Pacific Avenue, Suite 107 Everett, WA. 98201 RE: Response to City Comments R.A.I. Project #2019-052-002 Dear Mr. Reimers, The purpose of this letter is to respond to comments provided by the City of Renton (2019) planning department dated August 7, 2019 for the 4th Dimension Building, LUA19-000153. Specifically, this letter is intended to address comments received by the City of Renton from the Muckleshoot Tribe Fisheries Division dated July 31, 2019 regarding the 4th Dimension Building application. We have included specific comments from the Muckleshoot Tribe (2019) comments as they relate to critical areas followed by our comment responses, below. Comment: In short, the stream needs to be correctly classified before the project continues with environmental review and design. With the correct classification, the project needs to provide design details for the relocated/open stream channel particularly if it is to be located under a new building. The project also needs to evaluate the potential project impacts to stream functions. The checklist doesn’t even acknowledge the existence of a piped stream onsite. Finally, the City should check with WDFW to see if the proposal can be permitted under the State’s Hydraulic Code. Response: We reviewed the provided Cedarock Consultants, Inc. (2007) report included with the Muckleshoot comment letter. Based on our review of the report, it appears that natural fish-passage barriers are located downstream of the project site that would act to preclude fish passage. As part of our assessment we plotted approximate location of the information provided in the Cedarock Consultants, Inc. (2007) report onto an aerial image showing the location of the project site and the downstream location of natural fish passages barriers (see Figure 1, attached). In addition, Raedeke Associates, Inc. conducted a site meeting on August 16, 2019 with the City of Renton Planning staff, Mr. Larry Fisher of Washington Department of Fish and Wildlife, and Ms. Karen Walter Muckleshoot Tribe in order to confirm the stream classification. As a result of the site meeting, both Mr. Larry Fisher and Ms. Karen Walter agreed with Raedeke that onsite stream is correctly classified as a Type Ns (non-fish bearing) stream. During the site meeting, details of the proposed open stream channel located under the new building were discussed. The applicant’s architect indicated that a watershed analysis (TIR) report had been RECEIVED Clark Close 09/12/2019 PLANNING DIVISION Mr. Martin Reimers August 27, 2019 Page 2 prepared for the project site and was currently being reviewed by the City of Renton. The TIR demonstrates that current volumes and water quality standards would be maintained as part of the project. In addition, new stormwater generated from the construction of the new building would be detained and treated onsite before being released to the stormwater system downstream of the project site. As such, no adverse impacts to water storage, volume, or water quality are anticipated as part of the proposed site development application. As a result of the site meeting, Mr. Larry Fisher (WDFW) determined that the project would require a Hydraulic Permit Application (HPA) for removal of the piped stream segment and construction of an open channel located under the proposed building. The project will apply for an HPA after it completes the City of Renton SEPA review process. LIMITATIONS We have prepared this report for the exclusive use of the Mr. Martin Reimers and his consultants. No other person or agency may rely upon the information, analysis, or conclusions contained herein without permission from Mr. Martin Reimers. The determination of ecological system classifications, functions, values, and boundaries is an inexact science, and different individuals and agencies may reach different conclusions. With regard to wetlands and streams, the final determination of their boundaries for regulatory purposes is the responsibility of the various agencies that regulate development activities in wetlands. We cannot guarantee the outcome of such agency determinations. Therefore, the conclusions of this report should be reviewed by the appropriate regulatory agencies prior to any detailed site planning or construction activities. We warrant that the work performed conforms to standards generally accepted in our field, and has been prepared substantially in accordance with then-current technical guidelines and criteria. The conclusions of this report represent the results of our analysis of the information provided by the project proponent and their consultants, together with information gathered in the course of the study. No other warranty, expressed or implied, is made. If you have any questions or comments, or wish to discuss this issue further, please contact me at (206) 525-8122 or at kkosters@raedeke.com. Sincerely, RAEDEKE ASSOCIATES, INC. Kolten T. Kosters, MS, PWS Wetland Scientist Mr. Martin Reimers August 27, 2019 Page 3 LITERATURE CITED Cedarock Consultants, Inc. 2007. Fish Presence/Absence Surveys – West Fork Maplewood Creek. Dated June 4, 2007. Renton, City of. 2019. Subject: “On Hold” Notice 4th Dimension Building, LUA19-000153, SA-H, ECF, V-H. Received August 7, 2019. Muckleshoot Indian Tribe Fisheries Division. 2019. Subject: City of Renton LUA Acceptance: 4th Dimension Building, LUA19-000153, Notice of Application. Received July 31, 2019. First Migration Barrier identified by Cedarock Consultants, Inc. (2007) Piped stream segment Conservative extent of fish-bearing waters identified by Cedarock Consultants, Inc. (2007) West Fork Maplewood Creek Pictometry International Corp., Sources: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong Kong), Esri Korea, Esri (Thailand), NGCC, © OpenStreetMap contributors, and the GIS User Community I 4th Dimension Renton Fish Passage Map - Maplewood Creek RAI Project #: 2019-052-002 Note: Stream type and fish passage information depicted on map is dirived from Cedarock Consultants, Inc. (2007) Fish Presence/ Absence Surveys - West Fork Mapelwood Creek. Off-Site Stream (Type Ns) Off-Site Wetland (Category III) Project Site 00 920920 1,8401,840460460 FeetFeet Figure  SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 1 of 14 SEPA ENVIRONMENTAL CHECKLIST Purpose of checklist: Governmental agencies use this checklist to help determine whether the environmental impacts of your proposal are significant. This information is also helpful to determine if available avoidance, minimization or compensatory mitigation measures will address the probable significant impacts or if an environmental impact statement will be prepared to further analyze the proposal. Instructions for applicants: This environmental checklist asks you to describe some basic information about your proposal. Please answer each question accurately and carefully, to the best of your knowledge. You may need to consult with an agency specialist or private consultant for some questions. You may use “not applicable” or "does not apply" only when you can explain why it does not apply and not when the answer is unknown. You may also attach or incorporate by reference additional studies reports. Complete and accurate answers to these questions often avoid delays with the SEPA process as well as later in the decision- making process. The checklist questions apply to all parts of your proposal, even if you plan to do them over a period of time or on different parcels of land. Attach any additional information that will help describe your proposal or its environmental effects. The agency to which you submit this checklist may ask you to explain your answers or provide additional information reasonably related to determining if there may be significant adverse impact. Instructions for Lead Agencies: Please adjust the format of this template as needed. Additional information may be necessary to evaluate the existing environment, all interrelated aspects of the proposal and an analysis of adverse impacts. The checklist is considered the first but not necessarily the only source of information needed to make an adequate threshold determination. Once a threshold determination is made, the lead agency is responsible for the completeness and accuracy of the checklist and other supporting documents. Use of checklist for nonproject proposals: For nonproject proposals (such as ordinances, regulations, plans and programs), complete the applicable parts of sections A and B plus the SUPPLEMENTAL SHEET FOR NONPROJECT ACTIONS (part D). Please completely answer all questions that apply and note that the words "project," "applicant," and "property or site" should be read as "proposal," "proponent," and "affected geographic area," respectively. The lead agency may exclude (for non-projects) questions in Part B - Environmental Elements –that do not contribute meaningfully to the analysis of the proposal. A. Background [HELP] 1. Name of proposed project, if applicable: 4th Dimension Building 2. Name of applicant: 4th Creek Meadows, LLC 3. Address and phone number of applicant and contact person: RECEIVED Clark Close 09/12/2019 PLANNING DIVISION SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 2 of 14 12505 Bel Red Road, Suite 212, Bellevue, WA 98005, Attn. Hari Ghadia 4. Date checklist prepared: 17 July 2018, Rev. 5/2019 5. Agency requesting checklist: City of Renton 6. Proposed timing or schedule (including phasing, if applicable): Const. to begin 10/2019 or as soon as possible. 7. Do you have any plans for future additions, expansion, or further activity related to or connected with this proposal? If yes, explain. No Plans at this time. 8. List any environmental information you know about that has been prepared, or will be prepared, directly related to this proposal. Stormwater Site plan, Harmsen Assoc. 7/2018 Geotechnical Report, Geogroup Northwest, Inc., 5/14/2018 9. Do you know whether applications are pending for governmental approvals of other proposals directly affecting the property covered by your proposal? If yes, explain. City of Renton Building and Grading Permits 10. List any government approvals or permits that will be needed for your proposal, if known. Building Permit issued by City of Renton 11. Give brief, complete description of your proposal, including the proposed uses and the size of the project and site. There are several questions later in this checklist that ask you to describe certain aspects of your proposal. You do not need to repeat those answers on this page. (Lead agencies may modify this form to include additional specific information on project description.) The project is the construction of a new mixed use building at 4502 NE 4th Street, Renton, WA. The building will face 4th Street and Bremerton Ave. with pedestrican access from both streets and vehicle access from Bremerton. The building will house 51 parking spaces within the building, 34 in the basement and 17 on the ground level. Commercial space will also be at grade level (+-6,237 sf). The second third and fourth levels will feature 8 two bedroom living units each, for a total of 24 units. The building will form to the existing topography, utilizing the existing low spot for the basement parking except where clearance from water storage line is required. The site is 23,170 sf (0.55ac) 12. Location of the proposal. Give sufficient information for a person to understand the precise location of your proposed project, including a street address, if any, and section, township, and range, if known. If a proposal would occur over a range of area, provide the range or boundaries of the site(s). Provide a legal description, site plan, vicinity map, and topographic map, if reasonably available. While you should submit any plans required by the agency, you are not required to duplicate maps or detailed plans submitted with any permit applications related to this checklist. 4502 NE 4th Street, Renton, WA – APN: 1023059068 B. Environmental Elements [HELP] SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 3 of 14 1. Earth [help] a. General description of the site: Depression at the north-central portion of the lot w/ moderate to steep minor slopes at the north and south sides of the lot. There is an existing residence to the south with slopes descending towards the depression in the north There are also several retaining walls on the site (circle one): Flat, rolling, hilly, steep slopes, mountainous, other _____________ b. What is the steepest slope on the site (approximate percent slope)? There are several retaining walls on site with near vertical slopes. Steepest vegetated slope is approximately 57% and man made. c. What general types of soils are found on the site (for example, clay, sand, gravel, peat, muck)? If you know the classification of agricultural soils, specify them and note any agricultural land of long-term commercial significance and whether the proposal results in removing any of these soils. – Silty soils and fills overlaying apparent dense and competent till, gravelly sand and sandy gravel. d. Are there surface indications or history of unstable soils in the immediate vicinity? If so, describe. None Known. e. Describe the purpose, type, total area, and approximate quantities and total affected area of any filling, excavation, and grading proposed. Indicate source of fill. The purpose of grading will be to prepare building and access pads. Volumes will involve approximaely 3,500 cy of fill and 1,500 cy of cut. There is also an expectation that 2,000 cy of existing fill will need to be removed and replaced with structural material. f. Could erosion occur as a result of clearing, construction, or use? If so, generally describe. Any time that soils is exposed to weather, there is a chance for erosion. Best Management Practices will be used to limit the threat. g. About what percent of the site will be covered with impervious surfaces after project construction (for example, asphalt or buildings)? 89% h. Proposed measures to reduce or control erosion, or other impacts to the earth, if any: Best Management Practices for erosion control will be implemented to stabilize exposed soils, identify clearing areas, and prevent soil from moving off-site. 2. Air [help] a. What types of emissions to the air would result from the proposal during construction, operation, and maintenance when the project is completed? If any, generally describe and give approximate quantities if known. Automobiles and typical construction machines will be used during construction. Automobiles will be present during building operation b. Are there any off-site sources of emissions or odor that may affect your proposal? If so, generally describe. None Known SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 4 of 14 c. Proposed measures to reduce or control emissions or other impacts to air, if any: All engines will be properly maintained so full efficiencies are experienced and emissions minimized. 3. Water [help] a. Surface Water: [help] 1) Is there any surface water body on or in the immediate vicinity of the site (including year-round and seasonal streams, saltwater, lakes, ponds, wetlands)? If yes, describe type and provide names. If appropriate, state what stream or river it flows into. An upstream storm system flows through the site. This system continues west through adjacent development and discharges to Maplewood Creek approximately 850 feet from the site. See Raedeke Technical Memo, dated 25 June 2019. The piped system is considered a piped stream. 2) Will the project require any work over, in, or adjacent to (within 200 feet) the described waters? If yes, please describe and attach available plans. The project will require removal of the existing 24” pipe and a new open channel under the building, after which the 24” pipe will be upsized to 30” from the property line to the existing transition to 30”. 3) Estimate the amount of fill and dredge material that would be placed in or removed from surface water or wetlands and indicate the area of the site that would be affected. Indicate the source of fill material. None 4) Will the proposal require surface water withdrawals or diversions? Give general description, purpose, and approximate quantities if known. NO 5) Does the proposal lie within a 100-year floodplain? If so, note location on the site plan. No. 6) Does the proposal involve any discharges of waste materials to surface waters? If so, describe the type of waste and anticipated volume of discharge. No b. Ground Water: [help] 1) Will groundwater be withdrawn from a well for drinking water or other purposes? If so, give a general description of the well, proposed uses and approximate quantities withdrawn from the well. Will water be discharged to groundwater? Give general description, purpose, and approximate quantities if known. No. 2) Describe waste material that will be discharged into the ground from septic tanks or other sources, if any (for example: Domestic sewage; industrial, containing the following chemicals. . . ; agricultural; etc.). Describe the general size of the system, the SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 5 of 14 number of such systems, the number of houses to be served (if applicable), or the number of animals or humans the system(s) are expected to serve. None anticipated c. Water runoff (including stormwater): 1) Describe the source of runoff (including storm water) and method of collection and disposal, if any (include quantities, if known). Where will this water flow? Will this water flow into other waters? If so, describe. Source of site runoff is direct precipitation. Runoff will be collected, 20% of the site will be directed to a pair of raingardens, the remaining pollution generating runoff will flow through a pre- manufactured treatment system providing for enhanced treatment, and then all of the runoff will be detained in an underground vault below the lower parking level. Conceptual volumes are included in the preliminary Technical Information Report. 2) Could waste materials enter ground or surface waters? If so, generally describe. The proposed treatment measure will prevent the discharge of pollutants. 3) Does the proposal alter or otherwise affect drainage patterns in the vicinity of the site? If so, describe. The proposal will reroute enlarge an existing culvert that carries upstream flow through the site. However, the flow will discharge from the site in the same location it currently does. d. Proposed measures to reduce or control surface, ground, and runoff water, and drainage pattern impacts, if any: Storm drainage will follow the requirements of the 2017 City of Renton Surface Water Design Manual. 4. Plants [help] a. Check the types of vegetation found on the site: _X__deciduous tree: alder, maple, aspen, other ____evergreen tree: fir, cedar, pine, other _X__shrubs _X__grass ____pasture ____crop or grain ____ Orchards, vineyards or other permanent crops. ____ wet soil plants: cattail, buttercup, bullrush, skunk cabbage, other ____water plants: water lily, eelgrass, milfoil, other ____other types of vegetation b. What kind and amount of vegetation will be removed or altered? All vegetation will be removed and new will be installed. SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 6 of 14 c. List threatened and endangered species known to be on or near the site. None Known. d. Proposed landscaping, use of native plants, or other measures to preserve or enhance vegetation on the site, if any: Native plants will be utilized. A full landscape plan has been prepared which shows the extent of of the landscape proposal. e. List all noxious weeds and invasive species known to be on or near the site. The site has numberous blackberry plants. 5. Animals [help] a. List any birds and other animals which have been observed on or near the site or are known to be on or near the site. Examples include: birds: hawk, heron, eagle, songbirds, other: mammals: deer, bear, elk, beaver, other: fish: bass, salmon, trout, herring, shellfish, other ________ None Known b. List any threatened and endangered species known to be on or near the site. None Known. c. Is the site part of a migration route? If so, explain. No d. Proposed measures to preserve or enhance wildlife, if any: None proposed. e. List any invasive animal species known to be on or near the site. None known. 6. Energy and Natural Resources [help] a. What kinds of energy (electric, natural gas, oil, wood stove, solar) will be used to meet the completed project's energy needs? Describe whether it will be used for heating, manufacturing, etc. Electricity for power, heat and cooling. Possibly natural gas for heat. b. Would your project affect the potential use of solar energy by adjacent properties? If so, generally describe. Not anticipated. The building may create shade on adjacent site to east certain times of day / year. SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 7 of 14 c. What kinds of energy conservation features are included in the plans of this proposal? List other proposed measures to reduce or control energy impacts, if any: Full compliance with WA Energy Code. 7. Environmental Health [help] a. Are there any environmental health hazards, including exposure to toxic chemicals, risk of fire and explosion, spill, or hazardous waste, that could occur as a result of this proposal? If so, describe. None Anticipated 1) Describe any known or possible contamination at the site from present or past uses. None Known 2) Describe existing hazardous chemicals/conditions that might affect project development and design. This includes underground hazardous liquid and gas transmission pipelines located within the project area and in the vicinity. None Known. 3) Describe any toxic or hazardous chemicals that might be stored, used, or produced during the project's development or construction, or at any time during the operating life of the project. None Anticipated. A nominal amount of fuel will be on site to operate construction equipment. 4) Describe special emergency services that might be required. No special services should be necessary. 5) Proposed measures to reduce or control environmental health hazards, if any: Building Management will have operational measures to limit and control hazards. b. Noise 1) What types of noise exist in the area which may affect your project (for example: traffic, equipment, operation, other)? None 2) What types and levels of noise would be created by or associated with the project on a short-term or a long-term basis (for example: traffic, construction, operation, other)? Indi- cate what hours noise would come from the site. Construction equipment will be utilized during construction in conformance with Renton noise standards. 3) Proposed measures to reduce or control noise impacts, if any: The project will comply with all City of Renton ordinances and standards. 8. Land and Shoreline Use [help] SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 8 of 14 a. What is the current use of the site and adjacent properties? Will the proposal affect current land uses on nearby or adjacent properties? If so, describe. The site is currently unoccupied. One residence was previously occupied. The surrounding properties are either commercial or residential per zoning. The proposal is for the site to remain residential and have some commercial. The use will not impact neighbors. b. Has the project site been used as working farmlands or working forest lands? If so, describe. How much agricultural or forest land of long-term commercial significance will be converted to other uses as a result of the proposal, if any? If resource lands have not been designated, how many acres in farmland or forest land tax status will be converted to nonfarm or nonforest use? No 1) Will the proposal affect or be affected by surrounding working farm or forest land normal business operations, such as oversize equipment access, the application of pesticides, tilling, and harvesting? If so, how: The project will not be affected nor have and affect. c. Describe any structures on the site. Existing residence at south end of property. d. Will any structures be demolished? If so, what? Yes – existing residence. e. What is the current zoning classification of the site? CA f. What is the current comprehensive plan designation of the site? CMU g. If applicable, what is the current shoreline master program designation of the site? None h. Has any part of the site been classified as a critical area by the city or county? If so, specify. No i. Approximately how many people would reside or work in the completed project? Commercial – Work – 10+ people Residential – Reside – 24-60 people j. Approximately how many people would the completed project displace? Zero k. Proposed measures to avoid or reduce displacement impacts, if any: None, no displacement SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 9 of 14 L. Proposed measures to ensure the proposal is compatible with existing and projected land uses and plans, if any: The project is designed to be consistent with City requirements pertaining to land use. m. Proposed measures to reduce or control impacts to agricultural and forest lands of long -term commercial significance, if any: None. There are no agricultural or forest lands in the vicinity. 9. Housing [help] a. Approximately how many units would be provided, if any? Indicate whether high, mid- dle, or low-income housing. 24 - Middle b. Approximately how many units, if any, would be eliminated? Indicate whether high, middle, or low-income housing. – 1 - Middle c. Proposed measures to reduce or control housing impacts, if any: None, project improves housing. 10. Aesthetics [help] a. What is the tallest height of any proposed structure(s), not including antennas; what is the principal exterior building material(s) proposed? The highest point will be 60’ above average grade. The exterior will have cementitious siding and panels, exposed CMU and Concrete b. What views in the immediate vicinity would be altered or obstructed? None anticipated. b. Proposed measures to reduce or control aesthetic impacts, if any: The exterior design, finishes and color selection will be that of a high quality project. 11. Light and Glare [help] a. What type of light or glare will the proposal produce? What time of day would it mainly occur? Walkway lighting will light the ground at night. b. Could light or glare from the finished project be a safety hazard or interfere with views? No. All light will be directed toward the ground or building and be shielded to avoid spillage. c. What existing off-site sources of light or glare may affect your proposal? None Known SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 10 of 14 d. Proposed measures to reduce or control light and glare impacts, if any: Exterior lighting will be directed downward and be shielded to minimize offsite impacts. 12. Recreation [help] a. What designated and informal recreational opportunities are in the immediate vicinity? Heather Downs Park b. Would the proposed project displace any existing recreational uses? If so, describe. No c. Proposed measures to reduce or control impacts on recreation, including recreation opportunities to be provided by the project or applicant, if any: None proposed. 13. Historic and cultural preservation [help] a. Are there any buildings, structures, or sites, located on or near the site that are over 45 years old listed in or eligible for listing in national, state, or local preservation registers ? If so, specifically describe. No b. Are there any landmarks, features, or other evidence of Indian or historic use or occupation? This may include human burials or old cemeteries. Are there any material evidence, artifacts, or areas of cultural importance on or near the site? Please list any professional studies conducted at the site to identify such resources. None c. Describe the methods used to assess the potential impacts to cultural and historic resources on or near the project site. Examples include consultation with tribes and the department of archeology and historic preservation, archaeological surveys, historic maps, GIS data, etc. None Proposed. d. Proposed measures to avoid, minimize, or compensate for loss, changes to, and disturbance to resources. Please include plans for the above and any permits that may be required. No measures proposed. 14. Transportation [help] a. Identify public streets and highways serving the site or affected geographic area and describe proposed access to the existing street system. Show on site plans, if any. The site is served by NE 4th Street and Bremerton Ave NE. b. Is the site or affected geographic area currently served by public transit? If so, generally describe. If not, what is the approximate distance to the nearest transit stop? SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 11 of 14 There is a bus stop on NE 4th Street on the same block as the subject property. c. How many additional parking spaces would the completed project or non-project proposal have? How many would the project or proposal eliminate? The project will have 51 parking spaces. The existing residence has two spaces which will be eliminated. d. Will the proposal require any new or improvements to existing roads, streets, pedestrian, bicycle or state transportation facilities, not including driveways? If so, generally describe (indicate whether public or private). NE 4th Street and Bremerton Ave will receive new improvements where adjacent to property, including paving, curbs and gutters, sidewalks and landscaping e. Will the project or proposal use (or occur in the immediate vicinity of) water, rail, or air transportation? If so, generally describe. No f. How many vehicular trips per day would be generated by the completed project or proposal? If known, indicate when peak volumes would occur and what percentage of the volume would be trucks (such as commercial and nonpassenger vehicles). What data or transportation models were used to make these estimates? 277 Average Daily Trips. See TIA Report by Gibson Traffic g. Will the proposal interfere with, affect or be affected by the movement of agricultural and forest products on roads or streets in the area? If so, generally describe. No h. Proposed measures to reduce or control transportation impacts, if any: No measures have been taken. We do not expect any transportation related impacts from our project. 15. Public Services [help] a. Would the project result in an increased need for public services (for example: fire protection, police protection, public transit, health care, schools, other)? If so, generally describe. None Anticipated. b. Proposed measures to reduce or control direct impacts on public services, if any. The building will have fire sprinklers which will be an aid to the fire department. 16. Utilities [help] a. Circle utilities currently available at the site: electricity, natural gas, water, refuse service, telephone, sanitary sewer, septic system, other ___________ SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 12 of 14 c. Describe the utilities that are proposed for the project, the utility providing the service, and the general construction activities on the site or in the immediate vicinity which might be needed. Electricity, Gas, Water, Sewer, Telephone, Trash. C. Signature [HELP] The above answers are true and complete to the best of my knowledge. I understand that the lead agency is relying on them to make its decision. Signature: __ _________________________________________________ Name of signee ____Martin J. Reimers________________________________ Position and Agency/Organization ___Principal__________________________ Date Submitted: __5/28/2019___________ D. Supplemental sheet for nonproject actions [HELP] (IT IS NOT NECESSARY to use this sheet for project actions) Because these questions are very general, it may be helpful to read them in conjunction with the list of the elements of the environment. When answering these questions, be aware of the extent the proposal, or the types of activities likely to result from the proposal, would affect the item at a greater intensity or at a faster rate than if the proposal were not implemented. Respond briefly and in general terms. 1. How would the proposal be likely to increase discharge to water; emissions to air; pro- duction, storage, or release of toxic or hazardous substances; or production of noise? Proposed measures to avoid or reduce such increases are: SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 13 of 14 2. How would the proposal be likely to affect plants, animals, fish, or marine life? Proposed measures to protect or conserve plants, animals, fish, or marine life are: 3. How would the proposal be likely to deplete energy or natural resources? Proposed measures to protect or conserve energy and natural resources are: 4. How would the proposal be likely to use or affect environmentally sensitive areas or areas designated (or eligible or under study) for governmental protection; such as parks, wilderness, wild and scenic rivers, threatened or endangered species habitat, historic or cultural sites, wetlands, floodplains, or prime farmlands? Proposed measures to protect such resources or to avoid or reduce impacts are: 5. How would the proposal be likely to affect land and shoreline use, including whether it would allow or encourage land or shoreline uses incompatible with existing plans? Proposed measures to avoid or reduce shoreline and land use impacts are: 6. How would the proposal be likely to increase demands on transportation or public services and utilities? Proposed measures to reduce or respond to such demand(s) are: SEPA Environmental checklist (WAC 197-11-960) July 2016 Page 14 of 14 7. Identify, if possible, whether the proposal may conflict with local, state, or federal laws or requirements for the protection of the environment. CONCEPT ARCHITECTURE, LLC 1712 Pacific Avenue Suite 107, Everett, WA 98201 1005 Terminal Way Suite 245 Reno, NV 89502 ConceptArchitecture.com UPSTREAM FLOW / WATER ROUTING QUESTION Project: 4th Dimension Building Site Location: 4502 NE 4th Street, Renton, WA APN 1023059068 Item A – The upstream basin has been analyzed using the Renton GIS to determine tributary areas. The calculation of upstream flows was performed in accordance with standard practice and by direction provided by the City for modeling upstream detention systems. This is all documented in the TIR. We feel the numbers generated are suitable for the flow calculations performed for the TIR in regards to backwater and flood storage. We reviewed the site and its immediate vicinity for critical areas (wetlands, streams, and their associated buffers) per the City of Renton Code Requirements. We have also prepared a TIR analysis to model if anticipated development of the project site would significantly alter downstream flow regimes. As part of the TIR model, an assessment of land use cover was assessed for the watershed basin. It was determined that no adverse impacts to stream flows would result from the project. Additional stormwater generated from site development would be directed to stormwater facilities where it would be treated and discharged accordingly. Any additional study would seem to be informational only and not necessary to the analysis and design of the project from an engineering or wetland stand point. RECEIVED Clark Close 09/12/2019 PLANNING DIVISION SNOHOMISH COUNTY 125 E Main Street, Suite 104 Monroe, Washington 98272 tel: 360. 794.7811 | fax: 360.805.9732 ISLAND COUNTY 840 SE 8th Avenue, Suite 102 Oak Harbor, Washington 98277 tel: 360. 675.5973 | fax: 360.675.7255 www.HarmsenInc.com SKAGIT COUNTY 603 South First Street Mount Vernon, Washington 98273 tel: 360. 336.9199 | fax: 360.982.2637 PRELIMINARY TECHNICAL INFORMATION REPORT FOR THE 4TH DIMENSION MIXED USE BUILDING RENTON, WASHINGTON JUNE 11, 2019 REV SEPTEMBER 11, 2019 9/11/19 RECEIVED Clark Close 09/25/2019 PLANNING DIVISION PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 1 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh I. PROJECT OVERVIEW PROJECT DESCRIPTION This technical information report and has been prepared for the 4 th Dimension Mixed Use Building project located at the City of Renton. The developer is proposing to construct a 12,370 sf mixed use building on the 0.55 acre site. After dedication of right-of-way the site contains 0.44 acres. The site currently contains a single family home. The property is surrounded by multi family housing to the north and west, across Bremerton Avenue NE and by commercial uses to the east and south, across NE 4th Street. PREDEVELOPED CONDITIONS The site located at the northeast corner of the intersection of NE 4th Street and Bremerton Avenue NE. The property currently contains a 1,053 sf single family residence, 665 sf walkways and concrete on the southern end of the site. The remainder of the southern portion of the site is lawn, 0.16 ac, and the northern 0.24 ac is trees and brush. There is a 24” storm pipe that crosses through the center of the site. It is proposed as part of this project to remove that pipe and provide for an open flow path under the building. A review of King County iMAP and City of Renton mapping show the site is does not contain any critical areas or lay within a hazard area, see mapping in Appendix C. DEVELOPED CONDITIONS 4th Dimension Mixed Use project has proposed to construct a 12,370 sf mixed use building, and underground parking access drive on the site. The building will include 3 stories of residential units with a portion of the first floor being commercial and parking. An additional level of parking lays below that. A stormwater detention vault will be constructed below the lowest parking level and discharge to the storm system that existing on the site. SITE AREA: 0.44 acres PROJECT SITE AREA: 0.44 acres SIZE OF IMPROVEMENTS Roof Area: 0.28 ac Walks: 0.02 Asphalt: 0.07 ac Landscaping: 0.07 ac DISPOSITION OF RUNOFF BEFORE/AFTER DEVELOPMENT Runoff currently leaves the site in the 24” storm system that flows through the site. After development detained and treated runoff will flow to the 24” storm system that flows through the site. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 2 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh DIFFICULT SITE PARAMETERS The project geoptechnical engineer observed 2.5-9 feet of fill soils on the site and groundwater at a depths of 5-7 feet in two test pits. NATURAL DRAINAGE SYSTEM The topography of the site shows that most of the rainfall that falls on the site flows to a catch basin located centrally along the western edge of the site. ADJACENT PROPERTY DRAINAGE The site and surrounding properties are developed and do not contribute significant surface runoff to the site. There is an existing 24” storm main that crosses through the site. It will be relocated as part of the site work. A discussion of the upstream basin is included in Section III of this report. BYPASS FLOWS There is no portion of the proposed improvements that can not be collected and conveyed to the detention facility. DRAINAGE BASIN ANALYSIS The entire site drains to the north and is within one drainage basin. The 0.76 acres basin used for calculations consists of the street frontages and the 0.44 acre property. SOIL DESCRIPTION GEO Group Northwest explored the soil and groundwater conditions at the subject parcel by excavating five test pits by mini-excavator at the site. The test pits were excavated to depths of up to 9-feet 8-inches below ground surface. Soils observed at the test pits generally consist of variable density silty soils and fills which include brick, wood, organic material, concrete and asphalt debris overlying apparent dense and competent till and gravelly SAND and sandy GRAVEL. The depth of fills ranged from 2.5-feet at the test pit TP-5 to around 9-feet at the test pit TP-3. Groundwater seepage was not encountered at the test pits TP-1 through TP-3. Significant groundwater seepage was encountered at a depth of 7-feet bgs at the test pit TP-4 and 5-feet bgs at the test pit TP-5. Based on the fill soils revealed in the geotechnical report, Till soil parameters have been used in WWHM2012. See GEO Group Northwest report in Section IV, Special Reports and Studies on page 18, for additional information. The observed underlying soils appear to match the USDA SCS soil description for Alderwood gravelly sandy loam (AgC) at the uplands and Everett very gravelly sandy loam (EvB) at the depression as shown the SCS Soil Map, see Appendix A. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 3 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh II. PRELIMINARY CONDITIONS SUMMARY CONDITIONS OF APPROVAL There are currently no project specific conditions of approval for the project other than those from the 2017 RSWDM as adopted by the City of Renton. The site is subject to Full Drainage Review, including all 9 Core Requirements and all 6 Special Requirements. SURFACE WATER MANAGEMENT DESIGN MANUAL CORE REQUIREMENTS: 1. Discharge at Natural Location: Runoff currently leaves the site in the 24” storm system that flows through the site. After development, that pipe will be removed and a new extension made to the storm system in Bremerton using 30” pipe. An open channel will be extended under the building. Site runoff, after it is detained and treated, will flow to a new 30” pipe to replace the existing 24” storm system. 2. Off-site Analysis: This is covered in Section III of this report. 3. Flow Control: The site will use a detention vault to meet the Flow Control Duration – Forested Condition Area requirement. See Section IV of this report. 4. Conveyance System: A backwater analysis will be prepared for the project and will be included in the final TIR in Section V of that report. 5. Erosion and Sedimentation Control: The project will construct a series of sedimentation controls to address the specific site conditions. See Section IX of this report. 6. Maintenance and Operations: The proposed onsite storm system will be owned, operated and maintained by the owner. A Maintenance and Operation Manual will be included in the final TIR in Section X of that report. 7. Financial Guarantees and Liability: The owner and contractor will obtain all necessary permits prior to beginning of construction. The owner will be responsible for any bonds. 8. Water Quality: The site is located within a Basic Water Quality Treatment Area. Though being a commercial project it is required to meet the Enhanced Basic Water Quality standard. The Filterra Treatment System has been chosen to meet the runoff treatment requirements for the site runoff. See Section IV of this report for the design of the treatment systems. 9. Onsite BMPs: In addition to the required detention facility, the RSWDM also requires the implementation of Flow Control BMPs to a portion of the impervious surfaces on the site. The intent of this requirement is to lessen the impact of the runoff from the proposed impervious surfaces. For this 19,166 sf site, a Rain Garden is proposed, see page 12 for more information. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 4 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh SPECIAL REQUIRMENTS 1. Other Adopted Area-Specific Requirements: a. Critical Drainage Areas: The site is not within a CDA. b. Master Drainage Plans: The site is not within a MDP. c. Basin Plan: The site is not within a BP. d. Salmon Conservation Plan: The site is not within a SCP. e. Stormwater Compliance Plan: The site is not within a SWCP. f. Lake Management Plan: The site is not within a LMP. g. Flood Hazard Reduction Plan Update: The site is not within a FHRP. h. Shared Facility Drainage Plan: The site is not within a SFDP. 2. Flood Hazard Area Delineation: This site not within the 100-year flood plain per the City of Renton Flood Hazard Area Map in Appendix C. The site has been determined to have an infrastructure induced floodplain to elevation 394.87. The 24” culvert exiting the site is not adequate to pass runoff through the site with out a backwater effect, both inlet controlled and a backwater from the downstream storm system. This was originally determined in a report by Coughlin-Porter-Lundeen (CPL) and the City has mandataed that compensatory storage be provided for any reduction in storage volume. See page 7 for additional information. 3. Flood Protection Facilities: The site does not rely on an existing flood protection facility or modify or construct a new flood protection facility. 4. Source Control: The project is considered a commercial project and therefore is required to have source control measures, see Section IV of this report for more information. 5. Oil Control: The site does not meet the criteria for a high-use site, see Section IV of this report for more information. 6. Aquifer Protection: The site is not within a critical aquifer recharge area and is shown in the low groundwater contamination suseptability area, see maps in Appendic C. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 5 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh III: OFFSITE ANALYSIS Task 1: Study Area Definition and Maps See Figures 3, 3a, 3b and 4 in Appendix A for sub basins and downstream analysis map. Task 2: Resource Review a. Adopted Drainage Plans – The site is within the Maplewood Drainage Basin per the City of Renton Drainage Basin Map in Appendix C. There is no specific adopted drainage plan for this area. b. FEMA maps – the site is not within Flood Hazard Zone per the City of Renton Flood Hazard Area Map in Appendix C. c. Sensitive Areas Folio – the site is not within a shoreline, erosion hazard, coal mine hazard, channel migration hazard or seismic hazard area. see King County SAO and CAO Basin Condition Maps in Appendix C. d. DNRP Drainage Complaints and studies – see Appendix B. e. Wetland Inventory Maps – none per the City of Renton online mapping, see Appendix C. f. Community Plan – None g. Review of the 303d Listings – see Appendix B and Task 4, below. Task 3: Field Investigation Runoff leaves the site in the 24” storm piping that conveys flow through the site. This piped storm system continues to the west across Bremerton Avenue, through the apartment complex and into the shopping center. At a distance of about 850 feet from the site the storm system bends to the south, across NE 4th Street, then back to the west, outfalling at the headwater for the west fork of Maplewood Creek. The creek meanders in a southerly direction through wooded tracts of several residential developments. At a distance of 3,160 feet from the site a culvert conveys the stream under Bremerton Place NE. The stream continues to a distance of about 5,760 feet from the site where it joins the east fork of Maplewood Creek. At this point a deep gulley has formed where the creek drops down to the valley floor. At about 8,000 feet from the site the creek enters the Maplewood Golf Course. The channel continues through both open and wooded stretches of the golf course, bending to the west, then back to the south where it crosses under Highway 169 and into the Cedar River about 9,860 feet from the site. Cedar creek flows westerly an additional 3.3 miles to Lake Washington. Task 4: Drainage System Description and Problem Descriptions There are no known drainage problems along the downstream drainage route. Beyond the initial 1000 feet an opened unnamed stream. A review of the drainage complaint data revealed the closest two drainage complaints, both over 30 years old and located about 2,650 feet from the site. One was related to water on the adjacent roadway and is unrelated to the stream system. The second was regarding diversion of the stream onto filled land. There are no other known drainage issues along the downstream flowpath within the area of study. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 6 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh The City’s Lower Cedar River Habitat Study list several restoration projects within Reach 3 of the river see Herrera figure in Appendix B. These projects are to be implemented by the City using grant and other public funding. Review of the 303d Listings The Washington State Department of Ecology Water Quality Atlas Map has been reviewed for any 303d listings associated with the downstream drainage system. A portion of the Maplewood Creek, at a distance of about 7,000 feet from the site, is listed as Category 5 for Bioassesment. Further downstream the Cedar River is listed as Category 5 for pH, temperature and dissolved oxygen levels. See figures in Appendix B. Task 5: Mitigation of Existing or Potential Problems Downstream Flooding Issues To be included with full TIR Conclusions To be included with full TIR UPSTREAM BASIN The 24" culvert that crosses the property collects a significant upstream drainage basin. The culvert needs to be rerouted to clear the proposed building construction. Based on City of Renton GIS for storm systems and Lidar contours, a basin boundary has been estimated that encompasses 140 acres of mostly developed property, see Figure in Appendix B. Complicating a calculation of upstream runoff rates are the approximately 11 existing detention systems that have been constructed in the basin over the years and designed over several drainage manual iterations. In working with City Staff, Rohini Nair, Engineer for the City of Renton provided the following guidance: “The City of Renton will allow a modified Level 2 Offsite Analysis to be conducted to meet the City's requirements, which include the following: a. Perform a hydrologic analysis comparing the existing condition and developed condition at the 25-year and 100-year peak flow per Core requirement #4. The intent of the comparison is to show that the developed conditions will not adversely impact the existing and future conveyance system. i. This analysis will compare the existing and developed condition under the following tailwater conditions: 1. The downstream pipe at the point of compliance is empty 2. The downstream pipe at the point of compliance is full 3. The downstream pipe at the point of compliance is 1/2 full 4. The downstream pipe at the point of compliance is near full with 1" of freeboard from top of pipe PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 7 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh *Note: The POC of the site is the catch basin with the Facility ID No. 131550 per COR maps ii. To determine the upstream land-use designation the City of Renton will allow the following options: 1. All upstream land-use shall be existing unless shown to have a detention facility. If there is a detention facility the associated land-use can be designated as pasture. 2. All upstream land-use shall be existing unless shown to have a detention facility with an available recorded TIR. *Note: The upstream flows shall be modeled assuming that there are no upstream conveyance systems beyond the property line.” Based on this guidance the upstream basin has been analyzed using the following land uses: Impervious roads, parking, and roofs 22.01 ac Pasture (sites with existing detention) 75.67 ac Lawn and landscaping 19.25 ac Native vegetation areas 25.67 ac The upstream basin has the following current 25 year and 100 year flow frequency runoff rates, see Appendix D: Storm Event Rate 25 Year 26.50 cfs 100 Year 35.52 cfs The project site itself has the following existing and mitigated 25 year and 100 year flow frequency runoff rates: Storm Event Existing Mitigated 25 Year 0.14 cfs 0.08 cfs 100 Year 0.17 cfs 0.10 cfs Note: The tailwater conditions in the original requirements no longer apply as a larger study of the downstream has been performed to obtain tailwater conditions per the floodplain calculations below. FLOODPLAIN CALCULATIONS The site has been determined to have an infrastructure induced floodplain. The 24” culvert is not adequate to pass runoff through the site with out a backwater effect, both inlet controlled and a backwater from the downstream storm system. This was originally determined in a report by Coughlin-Porter-Lundeen (CPL) and the City has mandataed that compensatory storage be provided for any reduction in storage volume. Therefore, to account for the development, it is proposed to have the flow system run under the building with the building constructed on columns, leaving space for water storage. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 8 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh CPL has assumed that the downstream system had no backwater onto the site. Harmsen has determined that there is a backwater. Since the elevation of the backwater has a direct impact through storage on how much water flows through the culvert and the amount of flow through the culvert determines the elevation of the backwater, an iterative calculation needed to be made that matched those two elevations. The intial step is to determine the flood plain stage storage. This was calculated by creating a surface model in Autocad Civil 3D using the following three topographic sources. First the topographic survey for the project has been used, modified to include the proposed compensatory storage under the building. The second source of information is the proposed flood plain compensatory storage plan by Coughlin-Porter- Lundeen for the Renton Highlands project. The proposed grading contours shown on this plan have been used to create a ground surface model. It was found that this would create a more accurate map than using available lidar as the area is heavily vegetated. Lastly, available lidar topographic information, obtained from the Lidar Consortium, has been used to fill between the two primary flood plain sources. Using Autocad Civil 3D, the flood plain storage volume was calculated in one foot increments to prepare a stage – storage – discharge table for input into WWHM2012. The table is as follows: Elevation (ft) Area (ac) Volume (ac-ft) Discharge (cfs) 388 0.00 0.00 varies 389 0.15 0.14 390 0.16 0.28 391 0.17 0.45 392 0.24 0.61 393 0.70 1.16 394 1.02 2.00 395 1.50 3.47 396 1.88 5.10 397 2.05 7.12 398 2.16 9.04 399 2.20 11.39 400 2.30 13.59 To get outflow rates for a variety of storage depths, the upstream runoff was routed through the ‘pond’ with a spread of different orifice sizes to force the flow to reach various depths and thus give various outflows. Then these flows would be used in the downstream backwater calculations to determine backwater elevations. Once the two models match, that would be the storage elevation. The discharge values for 13 different orifice sizes (10”, 12”, 14”, 15”, 16”, 17”, 18”, 19”, 20”, 21”, 22”, 24” and 26”) were calculated using the orifice equation for elevations between 388 and 400. Each of these stage – storage – discharge tables were input into WWHM2012 to calculate the 100 year discharge from the flood plain. The cooresponding 100 year ponding PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 9 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh elevation could then be interpolated from the stage – storage – discharge table for each orifice size creating a data point. These data points are as follows: Orifice Size 100yr Discharge (cfs) 100yr Elevation (feet) 10” 8.52 397.73 12” 11.53 396.79 14” 14.62 395.56 15” 16.20 395.00 16” 17.38 394.23 17” 18.75 393.73 18” 20.20 393.27 19” 22.55 392.84 20” 23.33 392.64 21” 24.70 392.25 22” 25.90 391.89 24” 28.41 391.32 26” 29.86 390.67 These data points were then graphed: DOWNSTREAM BACKWATER CALCULATIONS Backwater calculations have been prepared for the removal of the culvert through the site. The downstream system is based on the CPL report and the flows therein with the addition of the upstream flow calculated above. The Hydraflow Storm Sewer Extension for Autodesk Civil 3D was used perform the backwater calculations. A 30” smooth-walled pipe was proposed to replace the 24” cmp. An open channel will be used under the building with a special inlet in the west wall of the facility per plan detail. Below is a graph showing the elevation and flow rate PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 10 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh where the backwater and upstream floodplain calcalutions match up. This is at 16.7 cfs and elevation 394.82, see Hydraflow output in Appendix D. This then indicates that the artificial floodplain is expected to have a 100 year elevation of 394.81 and compensatory calculations and building clearances are calculated from that elevation. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 11 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh IV: RETENTION/DETENTION ANALYSIS AND DESIGN PART A: EXISTING SITE HYDROLOGY The site located at the northeast corner of the intersection of NE 4th Street and Bremerton Avenue NE. The property currently contains a 1,053 sf single family residence, 665 sf walkways and concrete on the southern end of the site. The remainder of the southern portion of the site is lawn, 0.16 ac, and the northern 0.24 ac is trees and brush, see Figure 3A: Existing Drainage Basin Map in Appendix A. There is a 24” storm pipe that crosses through the center of the site. This pipe will be removed, replaced with an open channel under the building, and a 30” connection to the storm system in Bremerton. Existing Basin The basin for the existing condition contains 0.76 acres including 0.32 ac of existing and future right or way. There is currently 0.15 acres of the right-of-way that is paved and is included in the basin. The remainder of the basin, the portion being redeveloped has been modeled as forest. Based on the geotechnical report the site is underlain with till soils so the appropriate parameters have been used in WWHM2012. The existing basin has the following land uses and areas: Land Use Area(ac) Impervious 0.15 Forest 0.61 The existing basin has the following flow frequency runoff rates: 2 Year 0.08 10 Year 0.12 50 Year 0.16 100 Year 0.17 PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 12 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh PART B: DEVELOPED SITE HYDROLOGY Developed Basin The 0.76 acre basin includes the frontage street, access drive, walkways and landscaping and the proposed building, see Figure 3B: Developed Drainage Basin Map in Appendix A. The runoff from the road, walkways, landscaping and access will be collected and treated, then will be routed to the proposed detention vault to be located under the building. The building roof will flow directly to the vault. The impervious areas have been calculated for the access, parking areas, walkways and building using AutoCAD by constructing a polyline around the specific area. The developed basin has the following land uses and areas: Land Use Area(ac) Impervious (roof) 0.28 Impervious (paving) 0.39 Landscaping 0.09 The developed basin has the following flow frequency runoff rates: 2 Year 0.28 10 Year 0.42 50 Year 0.54 100 Year 0.60 ONSITE FLOW CONTROL BMP’S In addition to the required detention facility, the RSWDM also requires the implementation of Flow Control BMPs to a portion of the impervious surfaces on the site. The intent of this requirement is to lessen the impact of the runoff from the proposed impervious surfaces. The site area is 0.44 ac or 19,166 sf which is less than 22,000 sf so the Small Lot BMP Requirement applies. The BMP must be applied to a minimum of 20% of the site area in this case an area of atleast 3,850 sf. Per Section 1.2.9.2.1 Small Lot BMP Requirements, there are 12 possible ways to meet this requirement. They are addressed below: Full Dispersion Full Dispersion is not a feasible Flow Control BMP for this project. Per Section C.2.1.1.1.3 in the RSWDM: “A native vegetated flowpath segment of at least 100 feet in length (25 feet for sheet flow from a nonnative pervious surface) must be available along the flowpath”. There is no native vegetation on the site, nor is there a vegetated flowpath longer than 5 feet from the proposed improvements to a property line. Therefore Full Dispersion is not a feasible for this site. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 13 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh Full infiltration GEO Group Northwest explored the soil and groundwater conditions at the subject parcel and documented their findings in their report titled Geotechnical Report With Infiltration Evaluation, dated May 18, 2018. From pages 2 and 3 of their report: “The soils observed at the uplands, overlying much of the site consist of silty soils which are relatively impermeable. The soils observed at the depression (lowland) portion of the site include where located below silty fills may have relatively high permeability, however, the groundwater level at this area is also relatively high, thereby reducing the effectiveness for an infiltration system. Groundwater seepage ranged in depth at test pits TP-4 and TP-5 from 5 to 7-feet below ground surface. This level may vary dependent upon the time of year, precipitation amounts and changed land use in the area. Due to the presence of silty soils overlying much of the site and the relatively high groundwater conditions we do not recommend attempting to infiltrate stormwater at the subject site.” Per Section C.2.2.2.1.a in the RSWDM: “Existing soils must be coarse sands or cobbles or medium sands and cannot be comprised of fill materials where the infiltration device will be located.” The site soils are silty sands and fill, therefore full infiltration is not feasible on the site. Limited infiltration Limited Infiltration is similar to Full Infiltration except that per Section C.2.2.2.1.a in the RSWDM: “The minimum design requirements for limited infiltration are the same as those for full infiltration, except infiltration depressions are excluded and existing soils in the location of the infiltration device may be fine sands, loamy sands, sandy loams, or loams as opposed to only medium sands or better.” And: “Silt and clay loams, and cemented till (hardpan) are not suitable for limited infiltration systems.” The GEO Group Northwest report titled Geotechnical Report With Infiltration Evaluation, dated May 18, 2018. From pages 2 and 3 of their report: “Soils observed at the test pits generally consist of variable density silty soils and fills which include brick, wood, organic material, concrete and asphalt debris overlying apparent dense and competent till and gravelly SAND and sandy GRAVEL. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 14 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh “Due to the presence of silty soils overlying much of the site and the relatively high groundwater conditions we do not recommend attempting to infiltrate stormwater at the subject site.” The site soils are silty sands and fill with more pervious soils below, however groundwater encroaches into the pervious soils, therefore limited infiltration is not feasible on the site. Rain Garden For this 19,166 sf site, a Rain Garden is proposed. With this BMP being applied to 20% of the targeted surfaces, a raingarden is required for an area of about 3,850 sf. Per Appendix C, Section C.2.1.2, rain gardens must have a minimum horizontal projected surface area below the overflow that is at least 5% of the area draining to it. With a maximum ponding depth of 12 inches, the required raingarden would have an overflow area of atleast 193 sf. Two rain gardens are proposed to be located in planting areas along the southern side of the building with a combined area of about 200 sf. For this preliminary TIR no Flow Control credits have been applied in the design of the detention system based on the reduction in runoff that will result from use of the raingarden. The final TIR will incorporate the reduction by modeling 50% of the roof surface area draining to the raingarden as grass. With 3,850 sf, 0.088 ac, 0.044 ac will be modeled as grass and 0.044 ac will be modeled as impervious in the Developed Basin. This will be incorporated in the final TIR and WWHM2012 design calculations. Bioretention With less than 5,000 sf of contributing area, a Rain Garden is proposed to meet the Flow Control BMP requirement. Permeable Pavement Full Dispersion is not a feasible Flow Control BMP for this project. Per Section C.2.7.24 in the RSWDM: “24. Where appropriate field testing indicates soils have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.3 inches per hour.” Initial unfactored infiltration rates were calculated by GEO Group Northwest. Page 4 of their report states: “From Darcy’s Law for permeability and using the D10 grain size correlation we calculate that the initial infiltration rate for the soils at the TP-4 2’ and TP-5 2’- 8”sampled depths is 0.14 to 1.3 inches/hour. These rates are relatively low, highly variable and subject to correction due to the potential for groundwater mounding and possible groundwater movement. “ PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 15 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh “If stormwater infiltration is to occur for the subject development then we recommend that the designer apply appropriate correction factors to account for site variability, the test methodology and siltation/maintenance.” The Washington State Department of Ecology Stormwater Management Manual, DOE Manual, was reviewed to determine the appropriate correction factors to determine a design infiltration rate. From Section 3.3.6 of the DOE Manual, Table 3.3.1, the following factors have been applied: Correction Factor for Site Variability, CFv = 0.40 Correction Factor for Testing Procedure, CFt = 0.40 Correction Factor for Influent Control, CFm = 0.90 Therefore CFT = CFv x CFt x CFm = 0.144. After applying the correction factor the resulting design infiltration rates would be 0.02 to 0.18 inches per hour. This is significantly less than the minimum rate of 0.3 inches per hour so the use of permeable pavement is not feasible. Basic Dispersion With a possible maximum vegetated flow length of 5 feet the use of Basic Dispersion is not feasible for this site. The minimum required vegetated flow path for each dispersion device is addesssed below: USE OF SPLASH BLOCKS FOR BASIC DISPERSION Per Section C.2.4.2.2 in the RSWDM: “2. A “vegetated flowpath segment” of at least 50 feet in length must be available along the flowpath that runoff would follow upon discharge from the splash block.” USE OF ROCK PADS FOR BASIC DISPERSION Per Section C.2.4.3.2 in the RSWDM: “2. A “vegetated flowpath segment” of at least 50 feet in length as illustrated in Figure C.2.4.C must be available along the flowpath that runoff would follow upon discharge from the rock pad.” C.2.4.4 USE OF GRAVEL FILLED TRENCHES FOR BASIC DISPERSION Per Section C.2.4.4.2 in the RSWDM: “2. A “vegetated flowpath segment” of at least 25 feet in length must be available along the flowpath that runoff would follow upon discharge from a dispersion trench. This length must be increased to 50 feet if the discharge is toward a steep slope hazard area or a landslide hazard steeper than 15%. All or a portion of the vegetated flowpath segment may be within the buffer for the steep slope hazard area or landslide hazard.” PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 16 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh USE OF SHEET FLOW FOR BASIC DISPERSION Per Section C.2.4.5.3 in the RSWDM: “3. A “vegetated flowpath segment” of at least 10 feet in length must be available along the flowpath that runoff would follow upon discharge from the strip of crushed rock.” Reduced Impervious Surface Credit As it is possible that a Rain Garden BMPs can be installed, it is not necessary to utilize this BMP option. Native Growth Retention Credit There is no native growth areas on the site. Tree Retention Credit There are no significant trees on the site. Soil Amendment This BMP will be used in the planter beds and other landscaped areas on site and disturbed areas adjacent to the site. Perforated Stubout Connection Other than the portion of the roof that will flow to the rain gardens, the roof drains for the building will flow directly through the building and into the detention vault directly below the building. PART C: PERFORMANCE STANDARDS 1. The drainage design for the site was prepared using the requirements of the 2009 City of Renton Surface Water Design Manual, (RSWDM Manual). WWHM2012, by the Department of Ecology, has been used to calculate basin runoff and for retention/detention facility sizing. 2. The Flow Control Duration Standard – Forested Conditions, has been applied for sizing of the detention facilities. 3. The site is subject to Flow Control BMPs per Section 5.2.1.3 Large Lot High Impervious BMP Requirements. 4. The conveyance system is subject to the design standards applicable to “Conveyance Requirements for New Systems”. 5. The Enhanced Basic Water Quality Treatment standard has been used for design of the treatment facilities. 6. The site has been evaluated in respect to the Enhanced Basic Treatment requirement, see Part E of this Section. 7. The site has been evaluated in respect to Special Requirement #4 – Source Controls and Special Requirement #5 – Oil Controls, see Part E of this Section. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 17 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh PART D: FLOW CONTROL SYSTEM Flow Control Design The site is located within the Flow Control Duration Standard – Forested Condition Area. Storm water detention will be accomplished through the use of an “L” shaped detention vault located along the north and east sides of the building. WWHM2012 has been used to size the detention pond. The required vault contains a ‘live’ storage volume of 8,780 cf, see Appendix D. The proposed “L” shaped detention vault has the following dimensions: Vault Length 58 feet Vault Width 18 feet “L” Vault Length 50 feet “L” Vault Width 8 feet Bottom of ‘Live’ Elevation 100.00 feet (assumed) Top of ‘Live’ Elevation 106.10 feet Release from the vault will be controlled by a three orifice flow control riser with the following dimensions: Riser Diameter 12 Outlet Elevation 100.00 feet 1st Orifice Elevation 98.00 feet 1st Orifice Diameter 0.88” 2nd Orifice Elevation 103.80 feet 2nd Orifice Diameter 0.88” 3rd Orifice Elevation 105.00 feet 3rd Orifice Diameter 0.80” Top of Riser Elevation 106.10 feet The existing and mitigated flow frequency runoff rates are: Storm Event Existing Mitigated 2 Year 0.08 cfs 0.04 cfs 10 Year 0.12 cfs 0.06 cfs 50 Year 0.16 cfs 0.09 cfs 100 Year 0.17 cfs 0.10 cfs An emergency overflow will be installed along the west edge of the vault to allow for a safe discharge of rogue storm events. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 18 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh PART E: WATER QUALITY SYSTEM Water Quality Facility The site is located within the Basic Water Quality Treatment Area. As runoff to the facility is from roadway and the development is considered a commercial land use, it is necessary to meet the Enhanced Basic Water Quality Treatment standards. The Filterra Treatment System has been chosen to meet the runoff treatment requirements for the site runoff. The system has Department of Ecology GULD and City of Renton approval for enhanced treatment. The treatment basin includes the roadway, planters and sidewalks as well as the rain garden runoff. FILTERRA OPERATION Stormwater runoff enters the Filterra bioretention system through a curb-inlet opening and flows through a specially designed filter media mixture contained in a landscaped concrete container. The filter media captures and immobilizes pollutants; those pollutants are then decomposed, volatilized and incorporated into the biomass of the Filterra system’s micro/macro fauna and flora. Stormwater runoff flows through the media and into an underdrain system at the bottom of the container, where the treated water is discharged. FILTERRA SIZING Treatment facility has been performed using WWHM2012 with the parameters based on Contech’s approved media, see output in Appendix B. For this site a Filterra Facility with a 4’x6’ filter bed will provide treatment of 92.3% of the treatment basin runoff. This exceeds the required treatment level of 91% of the total runoff record. The facility will be located in the northwest corner of the site near the access drive and will drain to the detention vault. See WWHM2012 report for sizing calculations in Appendix D. ROOF AREA The building roof is not subject to any vehicular traffic and therefore does not require treatment. Special Requirement #4 – Source Controls Structural Source Controls Structural source controls will include covered garbage and recycle areas. Additionally, vehicle washing will not be permitted on the site. Non-Structural Source Controls See Section VIII of this report for the Construction Stormwater Pollution Prevention Plan. This includes Erosion and Sedimentation Control Plan design where the minimum requirements of Core Requirement #5: Temporary Erosion and Sedimentation Control are discussed. The section also includes discussion of the Construction Stormwater Pollution Prevention where the BMPs contained in Volume II of the current DOE Manual will be used to control pollution from sources other than sedimentation. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 19 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh Special Requirement #5 – Oil Controls The site does not qualify as a high use site as it is does not meet the three criteria of a high use site per Section 1.3.5 of the RSWDM. The site is does not contain an open parking lot as the parking is under the structure and will discharge any runoff to the sewer. Petroleum storage or transfer will not occur on the site. The site is not subject to use, storage or maintenance of 25 or more 10 ton diesel vehicles. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 20 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN Site conveyance calculations to be included with full TIR. The upstream storm system re-routing conveyance calculations are included in Section III of this report. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 21 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh VI. SPECIAL REPORTS AND STUDIES The geotechnical report prepared by GEO Group Northwest for the project follows. No other special reports or studies have been prepared at this time. 13705 Bel-Red Rd – Bellevue, WA 98005 Phone: 425/649-8757 – Fax: 425/649-8758 GEO Geotechnical Engineers, Geologists, & Environmental Scientists Group Northwest, Inc. May 14, 2018 G-4661 Hari Ghadia 12505 Bel-Red Rd, Suite 212 Bellevue, WA 98005-2510 Send via: ghadia_hari@hotmail.com Subject: GEOTECHNICAL REPORT WITH INFILTRATION EVALUATION PROPOSED DEVELOPMENT 4502 NE 4TH ST RENTON, WASHINGTON Dear Hari Ghadia: In accordance with our March 8, 2018 contract with you we have investigated the soil and groundwater conditions at the subject property and prepared the following geotechnical report for the proposed commercial/residential development. SITE AND PROJECT DESCRIPTION The subject site consists of a developed parcel containing one building which is located at the south side of the lot as shown on the attached Plate 2 – Topographic Map. The existing building is a 1-story building with daylight basement which daylights toward the north. The property has an approximate area of 0.55 acres. There is an ecology block retaining wall which is located at the west side of the lot or at the adjacent west right-of-way which has an estimated height of around 12-feet and retains Bremerton Ave NE. The site topography includes a relative depression at the north-central portion of the lot with moderate to steep relatively minor slopes at the north and south sides of the lot. Based upon plans provided by Kaul Design Associates the subject site is proposed to be developed with a mixed-use building containing parking as shown on the attached Plate 2 – Site Plan. We understand that the development will consist of the following: May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 2 GEO Group Northwest, Inc. 1. The building and garage lowest level is roughly at the existing grade at the depression near the center of the lot. 2. At the "6600 sf commercial" portion of the building there will be main floor level (above the garage) which roughly matches the adjacent existing grades at the south side of the lot and then will have 3-stories of apartments above this level. 3. At the "structured garage" section we understand that the top of the garage roughly matches existing grade at the adjacent Bremerton Ave NE (also main floor level for the "6600 sf commercial" building). A ramp goes down to the lower garage level at the east side of the garage building. A detention or infiltration system may be constructed below the lowest level in the garage although depth/elevation information for this structure has not been provided. GEOLOGIC CONDITIONS The USGS geologic map 1 for the site vicinity indicates that the soils at the subject lot consist of Quaternary-age Ground Moraine deposits. These soils consist of ablation till overlying lodgement till. Till soils are generally described as a mixture of silt, sand and gravel which was both deposited and overridden by glacial ice at least 14,000 years ago. SUBSURFACE CONDITIONS On April 18, 2018 GEO Group Northwest explored the soil and groundwater conditions at the subject parcel by excavating five test pits by mini-excavator at the Test Pit locations noted on the attached Plate 2 – Site Plan. The test pits were excavated to depths of up to 9-feet 8-inches below ground surface (bgs). Soils observed at the test pits generally consist of variable density silty soils and fills which include brick, wood, organic material, concrete and asphalt debris overlying apparent dense and competent till and gravelly SAND and sandy GRAVEL. The depth of fills ranged from 2.5-feet at the test pit TP-5 to around 9-feet at the test pit TP-3. The observed underlying soils appear to match the USDA SCS soil description for Alderwood gravelly sandy loam (AgC) at the uplands and Everett very gravelly sandy loam (EvB) at the depression as shown on the attached Plate 4 – SCS Soil Map. 1 “Geologic Map of the Renton Quadrangle, King County, Washington”, USGS, D.R. Mullineaux, 1965. May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 3 GEO Group Northwest, Inc. Groundwater seepage was not encountered at the test pits TP-1 through TP-3. Significant groundwater seepage was encountered at a depth of 7-feet bgs at the test pit TP-4 and 5-feet bgs at the test pit TP-5. The results of our subsurface investigation are shown on the attached Appendix A - Test Pit Logs and USCS Soil Legend. GRADATIONAL ANALYSES We performed gradational analyses for soil samples collected at a depth of 2-feet at the test pit TP-4 and a depth of 2-feet 8-inches at the test pit TP-5. These analyses confirmed the soil descriptions at these levels as being gravelly silty SAND. The results of these analyses are attached as Plates 5 and 6 – Gradational Analysis. Extrapolation of the gradation curves indicates that the D10 value for the sampled soils at TP-4 and TP-5 to be 0.01 mm and 0.03 mm, respectively. INFILTRATION EVALUATION The USDA NRCS maps the site soils as Alderwood gravelly sandy loam AgC) and Everett very gravelly sandy loam (EvB) which appear to match the observed conditions at our test pits. The USDA NRCS online data indicates that for the AgC soil unit the capacity of the most limiting layer to transmit water (Ksat): very low to moderately low. Per NRCS for the EvB soil unit the capacity of the most limiting layer to transmit water (Ksat): is high. The soils observed at the uplands, overlying much of the site consist of silty soils which are relatively impermeable. The soils observed at the depression (lowland) portion of the site include where located below silty fills may have relatively high permeability, however, the groundwater level at this area is also relatively high, thereby reducing the effectiveness for an infiltration system. Groundwater seepage ranged in depth at test pits TP-4 and TP-5 from 5 to 7- feet below ground surface. This level may vary dependent upon the time of year, precipitation amounts and changed land use in the area. Due to the presence of silty soils overlying much of the site and the relatively high groundwater conditions we do not recommend attempting to infiltrate stormwater at the subject site. If site stormwater must be infiltrated then we recommend that infiltration rate testing be performed at the infiltration location and it may also May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 4 GEO Group Northwest, Inc. be necessary to install a monitoring well to determine the groundwater level conditions throughout the year. INFILTRATION RATE From Darcy’s Law for permeability and using the D10 grain size correlation we calculate that the initial infiltration rate for the soils at the TP-4 2’ and TP-5 2’-8”sampled depths is 0.14 to 1.3 inches/hour. These rates are relatively low, highly variable and subject to correction due to the potential for groundwater mounding and possible groundwater movement. As noted above we recommend performing infiltration rate testing at the infiltration rate location and depth if it is determined that infiltration must occur at the site. If stormwater infiltration is to occur for the subject development then we recommend that the designer apply appropriate correction factors to account for site variability, the test methodology and siltation/maintenance. Catchbasins with sump pits should be installed between the stormwater collection system and the infiltration system(s) and periodic maintenance should be required to clean-out the catchbasin sump pit(s). The infiltration system may eventually clog due to siltation and require replacement construction. This reason may also make it difficult to maintain an infiltration system below the proposed structure as currently proposed. SEISMIC DESIGN CRITERIA Based upon our subsurface investigation the project site has Site Class D soil (Stiff Soil) per the IBC based upon the observed subsurface soil conditions and provided that the buildings are constructed to bear on the competent soils as described herein. CONCLUSIONS AND RECOMMENDATIONS General Based upon the results of our study, it is our professional opinion that the site is geotechnically suitable for the proposed development. The primary geotechnical concern with regard to the design for the proposed building is the presence of loose and unacceptable fill soils which present risks of damage due to soil settlement, if not properly over-excavated and filled with compacted structural fill. It is our opinion that these risks can be mitigated by implementing a building pad improvement program. Building foundations should not be constructed to bear May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 5 GEO Group Northwest, Inc. directly on top of the loose fill soils or fill debris. An alternative to the building pad improvement program would be to construct the building on top of a pile foundation system. In the final recommendations section of this report we provide recommendations for an augercast pile foundation which may be used as an alternative to the recommended building pad improvement. It may also be an option for a portion of the building to be supported on a spread footing foundation, such as at the south side of the property, with the remainder of the building supported on a pile foundation, provided that competent soils are encountered at the foundation subgrades at the proposed spread footing areas. Site Preparation and General Earthwork The building pad areas should be stripped and cleared of surface vegetation and organic soils (forest duff). Silt fences should be installed around areas disturbed by construction activity to prevent sediment-laden surface runoff from being discharged off-site. Exposed soils that are subject to erosion should be compacted and covered with plastic sheeting. Temporary Excavation Slopes Under no circumstances should temporary excavation slopes be greater than the limits specified in local, state and national government safety regulations. Temporary cuts greater than four feet in height should be sloped at an inclination no steeper than 1H:1V (Horizontal:Vertical) in the overlying loose site soils. If seepage is encountered at the excavation slopes should have inclinations of no steeper than 2H:1V for the temporary construction time period. If excavations with the aforementioned slope inclinations encroach upon the adjacent properties or remove support for the existing ecology block wall at the west side of the site than shoring may be required. Structural Fill All fill material used to achieve design site elevations below the building areas and below non- structurally supported slabs, parking lots, sidewalks, driveways, and patios, should meet the requirements for structural fill. During wet weather conditions, material to be used as structural fill should have the following specifications: May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 6 GEO Group Northwest, Inc. 1. Be free draining, granular material containing no more than five (5) percent fines (silt and clay-size particles passing the No. 200 mesh sieve); 2. Be free of organic material and other deleterious substances, such as construction debris and garbage; 3. Have a maximum size of three (3) inches in diameter. All fill material should be placed at or near the optimum moisture content. The optimum moisture content is the water content in soil that enables the soil to be compacted to the highest dry density for a given compaction effort. Based upon our subsurface investigation the overlying apparent fill site soils consist of sandy SILT and silty SAND with some organic soils and debris. These soils are relatively silty and may be difficult to compact to meet the minimum structural fill compaction requirements. If work occurs during a period of wet weather it is likely that the native site soils may become too wet to achieve the compaction criteria. We recommend that the contractor take measures to protect the site soils from wet weather impacts such as using plastic sheeting to cover stockpiles. Additionally all unsuitable debris such as concrete, wood, organic soil, plastic sheeting and other deleterious materials must be removed from the site soils if they are to be used as structural fill. An imported granular fill material may provide more uniformity and be easier to compact to the required structural fill specification, especially if work occurs during periods of wet weather. Structural fill should be placed in thin horizontal lifts not exceeding ten inches in loose thickness. Structural fill under building areas (including foundation and slab areas), should be compacted to at least 95 percent of the maximum dry density, as determined by ASTM Test Designation D- 1557-91 (Modified Proctor). Structural fill under driveways, parking lots and sidewalks should be compacted to at least 90 percent maximum dry density, as determined by ASTM Test Designation D-1557-91 (Modified Proctor). Fill placed within 12-inches of finish grade should meet the 95% requirement. We recommend that GEO Group Northwest, Inc., be retained to evaluate the suitability of structural fill material and to monitor the compaction work during construction for quality assurance of the earthwork. May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 7 GEO Group Northwest, Inc. Building Pad Improvement The observed overlying loose soils and fills observed at the test pits present risks of soil settlement related damage to proposed building if the building is constructed to bear on top of these soils. Consequently we recommend that the building pad areas on which foundations and any building slabs are to be constructed be over-excavated to remove loose fills, organic soils and deleterious debris to a depth where the underlying medium dense to dense soils are encountered and then replaced with compacted structural fill as required, dependent upon the proposed building/floor elevations. These fills and unacceptable loose soils were observed at depths as deep as 9-feet below the existing ground surface at the test pit TP-3. Following removal of the unsuitable loose soils and debris fills the base of the excavation should be compacted by vibratory equipment to a firm and unyielding condition, approved by GEO Group Northwest and then backfilled with compacted structural fill placed in accordance with the Structural Fill section of this report. The over-excavation and fill placement at the building pad area is expected to require a significant amount of earthwork and may also present difficulties if loose and unsuitable fills are encountered at the base of the existing block wall at the west side of the site since this would necessitate shoring for the adjacent right-of-way. New building foundations and slabs may be constructed to bear on the compacted structural fill which is in turn placed on top of the competent medium dense to dense underlying soils. Spread Footing Foundations The proposed buildings can be supported on conventional spread footings bearing on top of an improved building pad constructed per our recommendations noted above and which has been approved by GEO Group Northwest, Inc., at the time of construction. Individual spread footings may be used for supporting columns and strip footings for bearing walls. Our recommended minimum design criteria for foundations bearing on improved building pad or on compacted structural fill placed on top of the improved building pad are as follows: - Allowable bearing pressure, including all dead and live loads Medium dense to dense native soils (competent soils) = 2,000 psf Compacted structural fill on top of competent soil (improved building pad) = 2,000 psf - Minimum depth to bottom of perimeter footing below adjacent final exterior grade = 18 inches May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 8 GEO Group Northwest, Inc. - Minimum depth to bottom of interior footings below top of floor slab = 18 inches - Minimum width of wall footings = 16 inches - Minimum lateral dimension of column footings = 24 inches - Estimated post-construction settlement = 1/4 inch - Estimated post-construction differential settlement; across building width = 1/4 inch A one-third increase in the above allowable bearing pressures can be used when considering short-term transitory wind or seismic loads. Lateral loads can also be resisted by friction between the foundation and the supporting compacted fill subgrade or by passive earth pressure acting on the buried portions of the foundations. For the latter, the foundations must be poured "neat" against the existing undisturbed soil or be backfilled with a compacted fill meeting the requirements for structural fill. Our recommended parameters are as follows: - Passive Pressure (Lateral Resistance) • 350 pcf equivalent fluid weight for compacted structural fill • 350 pcf equivalent fluid weight for native dense soil. - Coefficient of Friction (Friction Factor) • 0.35 for compacted structural fill • 0.35 for native dense soil We recommend that footing drains be placed around all perimeter footings. More specific details of perimeter foundation drains are provided below in the section titled: Subsurface Drainage. Conventional Retaining Walls and Basement Walls Based upon the preliminary plans we understand that conventional concrete retaining walls are proposed for the below-grade portions of the building and this may be at the lower level at the May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 9 GEO Group Northwest, Inc. south side of the site. These walls should be constructed on top of footings which bear on the building pad improvement discussed above or on top of augercast concrete piles. Permanent retaining walls restrained horizontally on top (such as basement walls) are considered unyielding and should be designed for a lateral soil pressure under the at-rest condition; while conventional reinforced concrete walls free to rotate on top should be designed for an active lateral soil pressure. Active Earth Pressure Conventional reinforced concrete walls that are designed to yield an amount equal to 0.002 times the wall height, should be designed to resist the lateral earth pressure imposed by an equivalent fluid with a unit weight of 35 pcf for level backfill; At-Rest Earth Pressure Walls supported horizontally by floor slabs are considered unyielding and should be designed for lateral soil pressure under the at-rest condition. The design lateral soil pressure should have an equivalent fluid pressure of 40 pcf for level backfill; Seismic Surcharge For the anticipated 100 year seismic event a horizontal surcharge load of 8H psf should be applied; Passive Earth Pressure 350 pcf equivalent fluid weight for compacted structural fill and native undisturbed soil; Base Coefficient of Friction 0.35 for compacted structural fill and native undisturbed soil; To prevent the buildup of hydrostatic pressure behind permanent concrete basement or conventional retaining walls, we recommend that a vertical drain mat, such as Miradrain 6000 or equivalent, be used to facilitate drainage behind such walls. The drain mat core should be placed against the wall(s) with the filter fabric side facing the backfill. The drain mat should extend from near the finished surface grade down to the footing drain system. Additionally all backfill placed between the excavation slopes or temporary shoring and the new basement/retaining walls should consist of free-draining fills having less than 5% passing the No. 200 sieve. Also, a May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 10 GEO Group Northwest, Inc. waterproofing layer should be placed between the drainage mat layer and the concrete wall, for moisture protection at all basement wall locations. The top 12 inches of backfill behind retaining or basement walls should consist of compacted and relatively impermeable soil. This cap material can be separated from the underlying more granular drainage material by a geotextile fabric, if desired. Alternatively, the surface can be sealed with asphalt or concrete paving. Where possible the ground surface should be sloped to drain away from the wall. GEO Group Northwest, Inc., recommends that backfill material which will support structures or improvements (such as patios, sidewalks, driveways, etc.) behind permanent concrete retaining walls and basement walls be placed and compacted consistent with the structural fill specifications in the Structural Fill section of this report. Slab-on-Grade Concrete Floors Slab-on-grade concrete floors may be constructed directly on top of the native medium dense to dense site soils or on top of compacted structural fills placed on top of the medium dense to dense site soils (building pad improvement). If structural fills are to be placed at these areas then they should be compacted in accordance with the specifications in the section titled: Structural Fill. To avoid moisture build-up on the subgrade, slab-on-grade concrete floors should be placed on a capillary break, which is in turn placed on the prepared subgrade. The capillary break should consist of a minimum of a six (6) inch thick layer of free-draining crushed rock or gravel containing no more than five (5) percent finer than the No. 4 sieve. A vapor barrier, such as a 10-mil plastic membrane, is recommended to be placed over the capillary break beneath the slab to reduce water vapor transmission through the slab. Two to four inches of sand may be placed over the barrier membrane for protection during construction. Subsurface Drainage We recommend that subsurface drains, footing drains, be installed around the perimeter of the foundation footings. The drains should consist of a four (4) inch minimum diameter perforated rigid drain pipe laid at or near the bottom of the footing with a gradient sufficient to generate flow. The drain line should be bedded on, surrounded by, and covered with a free-draining rock, May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 11 GEO Group Northwest, Inc. pea gravel, or other free-draining granular material. The drain rock and drain line should be completely surrounded by a geotextile filter fabric, Mirafi 140N or equivalent. Once the drains are installed, the excavation should be backfilled with a compacted fill material. The footing drains should be tightlined to discharge to the stormwater collection system. Under no circumstances should roof downspout drain lines be connected to the footing drainage system. All roof downspouts must be separately tightlined to discharge into the stormwater collection system. We recommend that sufficient cleanouts be installed at strategic locations to allow for periodic maintenance of the footing drains and downspout tightline systems. Augercast Concrete Pile Foundations An alternative to implementing the building pad improvement noted above the new building may be supported on augercast concrete piles that are embedded at least 10-feet into the underlying dense native soils which are anticipated at a depth of around 10-feet below the ground surface. Implementing this option may allow for less excavation at the site and may reduce the risk that temporary shoring will be necessary. Concrete grade beams should be used to connect the pile foundations and distribute the building loads. A structural concrete slab may be designed and constructed to support the slab loads and transfer these loads to the piling. Based upon the depth to competent soils at the test pits we estimate pile lengths may be on the order of 20-feet with 10- foot embedment into the competent dense soil. The piles should be designed with a minimum diameter of 14 inches. For concrete piles 14 to 18 inches in diameter embedded 10 feet into the underlying dense soils, the following allowable bearing capacities may be used: AUGERCAST CONCRETE PILE CAPACITIES Pile Diameter (Inches) Pile Embedment (Feet) Allowable Bearing (Tons) Allowable Uplift (Tons) 14 10 13 6.5 16 10 16 8 18 10 19 9.5 Note: Pile embedment length is based on the embedment depth below the top of the dense, native soil. May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 12 GEO Group Northwest, Inc. No reduction in pile capacity is required if the pile spacing is at least three times the pile diameter. A one-third increase in the above allowable pile capacities can be used when considering short-term transitory wind or seismic loads. Lateral forces can also be resisted by the passive earth pressures acting on the grade beams and friction with the subgrade. To fully mobilize the passive pressure resistance, the grade beams must be poured “neat” against compacted fill. Our recommended allowable passive soil pressure for lateral resistance is 350 pcf (pounds per cubic foot) equivalent fluid weight. A coefficient of friction of 0.35 may be used between the subgrade and the grade beams. We estimate that the maximum total post-construction settlement should be one-half (1/2) inch or less, and the differential settlement across building width should be one-quarter (1/4) inch or less. The performance of piles depends on how and to what bearing stratum the piles are installed. It is critical that judgement and experience be used as a basis for determining the embedment length and acceptability of a pile. Therefore, we recommend that GEO Group Northwest, Inc., be retained to monitor the pile installation operation, collect and interpret installation data, and verify suitable bearing stratum. We also suggest that the contractor’s equipment and installation procedure be reviewed by GEO Group Northwest, Inc., prior to pile installation to help mitigate problems which may delay work progress. ADDITIONAL SERVICES GEO Group Northwest, Inc., can provide additional exploration and testing services for the project such as infiltration rate testing if it is determined to be necessary. We recommend that GEO Group Northwest Inc. be retained to perform a general plan review of the final design and specifications for the proposed development to verify that the earthwork and foundation recommendations have been properly interpreted and implemented in the design and in the construction documents. We also recommend that GEO Group Northwest Inc. be retained to provide monitoring and testing services for geotechnically-related work during construction. This is to observe compliance with the design concepts, specifications or recommendations and to allow design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. We anticipate the following construction monitoring inspections may be necessary: May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 13 GEO Group Northwest, Inc. 1. Site clearing and grubbing; 2. Grading of temporary excavation slopes; 3. Preparation of building foundation subgrades; 4. Over-excavation and structural fill placement at building pad improvement areas, removal of unsuitable fill soils; 5. Permanent subsurface drainage installation; 6. Installation of augercast piling, if implemented; LIMITATIONS This report has been prepared for the specific application to this site for the exclusive use of 4th Creek Meadows LLC and their authorized representatives. Any use of this report by other parties is solely at that party’s own risk. We recommend that this report be included in its entirety in the project contract documents for reference during construction. Our findings and recommendations stated herein are based on field observations, our experience and judgement. The recommendations are our professional opinion derived in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in this area and within the budget constraint. No warranty is expressed or implied. In the event that soil conditions not anticipated in this report are encountered during site development, GEO Group Northwest, Inc., should be notified and the above recommendations should be re-evaluated. If you have any questions, or if we may be of further service, please do not hesitate to contact us. May 14, 2018 G-4661 Geotechnical Report – 4502 NE 4th St, Renton, Washington Page 14 GEO Group Northwest, Inc. Sincerely, GEO GROUP NORTHWEST, INC. Adam Gaston Project Engineer William Chang, P.E. Principal Attachments: Plate 1 – Vicinity Map Plate 2 – Site Plan Plate 3 – Topographic Map Plate 4 – SCS Soil Map Plates 5 – 6 – Gradational Analyses Appendix A – USCS Soil Legend and Test Pit Logs cc: Mr. Martin Reimer – Kaul Design Associates APPENDIX A TEST PIT LOGS AND USCS SOIL LEGEND G-4661 CLEAN GRAVELS GW (little or no fines)GP DIRTY GRAVELS GM (with some fines)GC CLEAN SANDS SW (little or no fines)SP < 5% Fine Grained: GW, GP, SW, SP DIRTY SANDS SM > 12% Fine Grained: GM, GC, SM, SC (with some fines)SC 5 to 12% Fine Grained: use dual symbols Liquid Limit < 50%ML Liquid Limit > 50%MH Liquid Limit < 30%CL Liquid Limit > 50%CH Liquid Limit < 50%OL Liquid Limit > 50%OH Pt Sieve Size (mm)Sieve Size (mm) SILT / CLAY #200 0.075 SAND 0 - 4 0 -15 Very Loose < 2 < 0.25 Very soft FINE #40 0.425 #200 0.075 4 - 10 15 - 35 26 - 30 Loose 2 - 4 0.25 - 0.50 Soft MEDIUM #10 2 #40 0.425 10 - 30 35 - 65 28 - 35 Medium Dense 4 - 8 0.50 - 1.00 Medium Stiff COARSE #4 4.75 #10 2 30 - 50 65 - 85 35 - 42 Dense 8 - 15 1.00 - 2.00 Stiff GRAVEL > 50 85 - 100 38 - 46 Very Dense 15 - 30 2.00 - 4.00 Very Stiff FINE 19 #4 4.75 > 30 > 4.00 Hard COARSE 76 19 COBBLES BOULDERS ROCK FRAGMENTS ROCK PLATE A1 CONTENT OF FINES EXCEEDS 12% Cu = (D60 / D10) greater than 6 Cc = (D302 ) / (D10 * D60) between 1 and 3 Cu = (D60 / D10) greater than 4 Cc = (D302 ) / (D10 * D60) between 1 and 3 SILTY & CLAYEY SOILS Blow Counts N Unconfined Strength qu, tsf Description Bellevue, WA 98005 NOT MEETING ABOVE REQUIREMENTS Fax (425) 649-8758Phone (425) 649-8757 Blow Counts N Relative Density % Friction Angle N, degree Description > 76 mm >0.76 cubic meter in volume 13240 NE 20th Street, Suite 10 DETERMINE PERCENTAGES OF GRAVEL AND SAND FROM GRAIN SIZE DISTRIBUTION CURVE COARSE GRAINED SOILS ARE CLASSIFIED AS FOLLOWS:SANDS (More Than Half Coarse Grains Smaller Than No. 4 Sieve) SILTS (Below A-Line on Plasticity Chart, Negligible Organic) CLAYS (Above A-Line on Placticity Chart, Negligible Organic) HIGHLY ORGANIC SOILS NOT MEETING ABOVE REQUIREMENTS UNIFIED SOIL CLASSIFICATION SYSTEM (USCS) LEGEND OF SOIL CLASSIFICATION AND PENETRATION TEST CONTENT OF FINES EXCEEDS 12% ATTERBERG LIMITS BELOW "A" LINE. or P.I. LESS THAN 4 ATTERBERG LIMITS ABOVE "A" LINE. or P.I. MORE THAN 7 CLAYEY GRAVELS, GRAVEL-SAND-CLAY MIXTURES TYPICAL DESCRIPTION LABORATORY CLASSIFICATION CRITERIA ATTERBERG LIMITS BELOW "A" LINE with P.I. LESS THAN 4 ATTERBERG LIMITS ABOVE "A" LINE with P.I. MORE THAN 7 U.S. STANDARD SIEVE SOIL PARTICLE SIZE FRACTION Passing Retained GENERAL GUIDANCE OF SOIL ENGINEERING PROPERTIES FROM STANDARD PENETRATION TEST (SPT) SANDY SOILS INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY ORGANIC CLAYS OF HIGH PLASTICITY PEAT AND OTHER HIGHLY ORGANIC SOILS CLAYEY SANDS, SAND-CLAY MIXTURES INORGANIC SILTS, ROCK FLOUR, SANDY SILTS OF SLIGHT PLASTICITY INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS, FINE SANDY OR SILTY SOIL INORGANIC CLAYS OF LOW PLASTICITY, GRAVELLY, SANDY, OR SILTY CLAYS, CLEAN CLAYS WELL GRADED SANDS, GRAVELLY SANDS, LIITLE OR NO FINES POORLY GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES SILTY SANDS, SAND-SILT MIXTURES WELL GRADED GRAVELS, GRAVEL-SAND MIXTURE, LITTLE OR NO FINES POORLY GRADED GRAVELS, AND GRAVEL- SAND MIXTURES LITTLE OR NO FINES SILTY GRAVELS, GRAVEL-SAND-SILT MIXTURES > 203 mm FINE-GRAINED SOILS More Than Half by Weight Smaller Than No. 200 Sieve MAJOR DIVISION GROUP SYMBOL 76 mm to 203 mm ORGANIC SILTS & CLAYS (Below A-Line on Placticity Chart) More Than Half by Weight Larger Than No. 200 Sieve COARSE- GRAINED SOILS GRAVELS (More Than Half Coarse Grains Larger Than No. 4 Sieve) 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 100 110PLASTICITY INDEX (%)LIQUID LIMIT (%) CL-ML CL or OL MH or OH OL or ML A-LinePLASTICITY CHART FOR SOIL PASSING NO. 40 SIEVE 7 4 CH or OH Geotechnical Engineers, Geologists, & Environmental Scientists GEO Group Northwest, Inc. TEST PIT NO. TP-1 LOGGED BY AG TEST PIT DATE:04/18/2018 DEPTH SAMPLE Water OTHER TESTS/ ft.USCS SOIL DESCRIPTION No.%COMMENTS 5 10 15 TEST PIT NO. TP-2 LOGGED BY AG TEST PIT DATE:04/18/2018 DEPTH SAMPLE Water OTHER TESTS/ ft.USCS SOIL DESCRIPTION No.%COMMENTS 5 10 15 TEST PIT LOGS PROPOSED DEVELOPMENT 4502 NE 4TH ST RENTON, WA DATE 4/19/18 PLATE A2JOB NO. G-4661 Total depth of test pit = 7 feet bgs No groundwater seepage Competent dense soils below 4-feet bgs SCS Classification: AgC Geotechnical Engineers, Geologists, & Environmental Scientists GEO Group Northwest, Inc. S-1 Total depth of test pit = 6.5 bgs No groundwater seepage Mottled soils from 5 to 6-feet bgs Competent dense soils below 5-feet bgs SCS Classification: AgC Dark brown to tan silty SAND with gravel and gravelly silty SAND, moist, variable density - dense to loose, also containing trace debris, bone, ceramics and spoon (FILL) SM Brown to tan gravelly silty SAND to gravelly sandy SILT, moist, Brown silty SAND with brick debris, moist, loose (FILL) SM/ ML SM Gray and mottled gravelly sandy SILT and gravelly silty SAND, cemented, moist, dense (TILL) S-2 Tan gravelly silty SAND to gravelly sandy SILT, moist, dense, cemented below 5.5-ft bgs (TILL) SM/ ML S-1 10.5 10.8 S-3 S-2 23.8 14.1 11.5 SM/ ML TEST PIT NO. TP-3 LOGGED BY AG TEST PIT DATE:04/18/2018 DEPTH SAMPLE Water OTHER TESTS/ ft.USCS SOIL DESCRIPTION No.%COMMENTS 5 10 15 TEST PIT NO. TP-4 LOGGED BY AG TEST PIT DATE:04/18/2018 DEPTH SAMPLE Water OTHER TESTS/ ft.USCS SOIL DESCRIPTION No.%COMMENTS 5 10 15 TEST PIT LOGS PROPOSED DEVELOPMENT 4502 NE 4TH ST RENTON, WA DATE 4/19/18 PLATE A3JOB NO. G-4661 Total depth of test pit = 9-ft - 8-inches bgs (max excavator depth) No groundwater seepage Competent dense soils below 9-ft bgs SCS Classification: EgB (below fill) Geotechnical Engineers, Geologists, & Environmental Scientists GEO Group Northwest, Inc. S-1 Total depth of test pit = 8-ft - 3-inches bgs Significant groundwater seepage at 7-ft bgs - prevented further exploration due to caving gravels Competent dense soils below 8-ft bgs SCS Classification: EgB (below fill) Brown and gray gravelly sandy SILT, SILT and silty SAND with plastic sheeting, organic material and debris, moist, variable dense to loose (FILL), fill includes concrete and asphalt debris observed at a depth of 8-feet bgs SM/ ML Gray gravelly sandy SILT, moist, dense (FILL) Brown gravelly fine silty SAND and drain rock zones, moist, loose (FILL) ML SM Gravelly SAND and sandy GRAVEL with some cobbles, wet, apparent dense soil at 8-ft bgs S-2 Brown fine to medium SAND with some silt, moist, dense S-1 9.7 23.1 S-3 S-2 10.9 21.0 12.6 SP/ GP S-4 13.5 SP- SM Brown gravelly SAND with some silt and occasional cobbles, moist, loose (APPARENT FILL) SP- SM TEST PIT NO. TP-5 LOGGED BY AG TEST PIT DATE:04/18/2018 DEPTH SAMPLE Water OTHER TESTS/ ft.USCS SOIL DESCRIPTION No.%COMMENTS 5 10 15 TEST PIT NO. LOGGED BY TEST PIT DATE: DEPTH SAMPLE Water OTHER TESTS/ ft.USCS SOIL DESCRIPTION No.%COMMENTS 5 10 15 TEST PIT LOGS PROPOSED DEVELOPMENT 4502 NE 4TH ST RENTON, WA DATE 4/24/18 PLATE A4JOB NO. G-4661 Total depth of test pit = 7-ft bgs Groundwater seepage at 5-ft bgs Competent dense soils below 3.5-ft bgs SCS Classification: EgB (below fill) Geotechnical Engineers, Geologists, & Environmental Scientists GEO Group Northwest, Inc. S-1 Tan cobbly and gravelly silty SAND, moist, medium dense (FILL) SM S-2 Dark brown gravelly silty SAND, moist, medium dense 18.5 S-3 16.6 19.9 SM Gray gravelly sandy SILT, moist, dense (FILL) SM Dark brown silty SAND grading to gravelly SAND / sandy GRAVEL with some cobbles, moist to wet, dense SM/ SP- GP PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 22 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh VII. OTHER PERMITS No other special storm drainage permits are required for the proposed work. Clearing and Grading and Utility permits will be required for the infrastructure installation. Sewer and water infrastructure permits will be required for the utility connections. NPDES Permit will not be required from the Department of Ecology, as the site is less than 1 acre in size. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 23 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh VIII. CSWPPP ANALYSIS AND DESIGN PART A: ESC PLAN DESIGN AND ANALYSIS The minimum requirements of Core Requirement #5: Temporary Erosion and Sedimentation Control are as follows: CLEARING LIMITS D.3.1.1, Plastic Clearing Limits Fencing. The clearing limits and trees to be saved will be marked in the field with orange clearing limits fencing prior to any construction activities. COVER MEASURES Temporary cover will be provided for all areas to remain unworked for more than 7 days during the dry season and more than 2 days during the wet season. Any areas to remain unworked for more than 30 days will be seeded. Specific cover measures are listed below: D.3.2.1, Slope Roughening. This will be used on slopes greater than 3:1 and greater than 5 feet in height. It will reduce flow velocities until vegetation becomes established. This is commonly accomplished by tracking equipment un and down the slope to leave horizontal depressions in the soil. D.3.2.2, Mulching. During construction, mulch can be placed to prevent raindrops from impacting exposed soils causing erosion. Straw is the most common method of mulching. This BMP is one of the options that can be employed to meet the temporary cover requirements: D.3.2.4, Plastic Covering: This involves covering a bare area with clear plastic that provides immediate protection, especially of uncompacted soils such as stockpiles. This BMP will be used on this site for areas requiring immediate protection and for stockpiles. This BMP is employed to meet the temporary cover requirements: D.3.2.6, Temporary & Permanent Seeding. Temporary seeding of topsoil stockpiles and other stripped areas will be necessary during construction depending on weather conditions and the use of other temporary cover BMP’s. All exposed surfaces will be final seeded or landscaped when construction is completed. This BMP will be employed to meet the temporary cover requirements as well as supplying permanent cover upon completion of the project. PERIMETER PROTECTION D.3.3.1, Silt Fence. Filter fabric fencing will be installed, where necessary, downslope of all disturbed areas to filter runoff before it leaves the site. Filter fabric inserts will also be placed in the catch basins along the fronting streets as additional sediment collection. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 24 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh TRAFFIC AREA STABILIZATION D.3.4.1, Stabilized Construction Entrance. The existing gravel site access drive will be used for the construction entrance. This will help to prevent vehicle tires from transporting sediment off-site. D3.4.2, Construction Road Stabilization. Construction road stabilization will be used on this site. This involves covering the road with crushed rock, gravel base or crushed surfacing base course to protect exposed erosion sensitive soil from rainfall. Much of the parking area is gravel and already stabilized. Dust Control will be used on this site during construction activities when dry weather causes loose soil to be transported by the wind. The soil will be moistened with water to hold down the dust. This BMP will be performed routinely during dry weather construction. SEDIMENT RETENTION D.3.5.2, Sediment Pond. With the site being less than one acre of disturbed area it should not be necessary to construct a sediment pond. In addition much of the area will be stabilized with temporary gravel paving and the building slab itself once construction commences. If necessary the detention vault can be configured as a sedimentation pond. D.3.5.3, Storm Drain Inlet Protection. Silt sacks will be installed in the existing catch basins on and near the site and in the new catch basins as they are installed. This will trap coarse sediment; preventing it from being conveyed downstream. SURFACE WATER CONTROL The site currently contains a storm drainage system that collects site runoff. Clean construction runoff will be directed to this system. DE-WATERING CONTROL Generally, de-watering is not expected to be needed on the site. If pumping is necessary, the discharge will be directed to a portable sediment tanks, such as a Baker tank prior to discharge from the site. DUST CONTROL The proposed timing, during the dry months, will increase the chance of wind born material to leave the site. The application of water to bare and dry soil will occur as conditions dictate. FLOW CONTROL With installation of the detention facility early in construction and by directing site runoff to the vault, the increases in runoff due to the changing site cover characteristics will be mitigated. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 25 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh WET SEASON CONSTRUCTION The site work for this project is expected to occur during the Summer of 2018. However if delays occur the completion date may extend into the wet season (October 1 through April 30). No soil shall remain exposed for more than 2 consecutive working days. In addition any exposed soils shall be stabilized at the end of the workday prior to a weekend, holiday or predicted rain event. During wet season construction, additional erosion control measures may be required. These include but are not limited to additional filter fabric fencing, rock and straw bale check dams, mulching and plastic sheeting. CRITICAL AREA RESTRICTIONS There are no critical areas on or adjacent to the site. POLLUTION PREVENTION & SPILL PREVENTION AND CLEANUP REPORT For additional information see the Pollution Prevention & Spill Prevention and Cleanup Report. CERTIFIED EROSION CONTROL SPECIALIST The project will result in less than 1 acre of disturbance. As such a Certified Professional in Erosion and Sediment Control or a Certified Erosion and Sediment Control Lead is not required. TURBIDITY REQUIREMENTS The ESC supervisor or the County may determine at any time during construction that the approved ESC measures are not sufficient and that additional action is required based on one of the following criteria: 1. IF a turbidity test of surface and storm water discharges leaving the project site is greater than the benchmark value of 25 NTU (nephelometric turbidity units) set by the Washington State Department of Ecology, but less than 250 NTU, the ESC Supervisor shall do all of the following: a) Review the ESC plan for compliance and make appropriate revisions within 7 days of the discharge that exceeded the benchmark of 25 NTU, AND b) Fully implement and maintain appropriate ESC measures as soon as possible but no later than 10 days after the discharge that exceeded the benchmark, AND c) Document ESC implementation and maintenance in the site log book. 2. IF a turbidity test of surface or storm water entering onsite wetlands, streams, or lakes indicates a turbidity level greater than 5 NTU above background when the background turbidity is 50 NTU or less, or 10% above background when the background turbidity is greater than 50 NTU, then corrective actions and/or additional measures beyond those specified in Section 1.2.5.1 shall be implemented as deemed necessary by the County inspector or onsite ESC supervisor. 3. IF discharge turbidity is 250 NTU or greater, the ESC Supervisor shall do all of the following: a) Notify the County by telephone, AND PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 26 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh b) Review the ESC plan for compliance and make appropriate revisions within 7 days of the discharge that exceeded the benchmark of 25 NTU, AND c) Fully implement and maintain appropriate ESC measures as soon as possible but no later than 10 days after the discharge that exceeded the benchmark, AND d) Document ESC implementation and maintenance in the site log book. AND e) Continue to sample discharges until turbidity is 25 NTU or lower, or the turbidity is no more than 10% over background turbidity. 4. IF the County determines that the condition of the construction site poses a hazard to adjacent property or may adversely impact drainage facilities or water resources, THEN additional measures beyond those specified in Section 1.2.5.1 may be required by the County. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 27 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh PART B: SWPPS PLAN DESIGN Those BMPs contained in Volume II of the current DOE Manual will be used to control pollution from sources other than sedimentation. Volume II of the DOE Manual shall also be reviewed during construction if any other BMPs become relevant. STORAGE AND HANDLING OF LIQUIDS Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, solvents, detergents, paint, pesticides, concrete admixtures and non-inert wastes present on the site (see Chapter 173-304 WAC for the definition of inert waste). Secondary containment systems shall be sized to adequately provide for containment of all liquids on site. STORAGE AND STOCKPILING OF CONSTRUCTION MATERIALS AND WASTES All pollutants, including waste materials and demolition debris, that occur on site during construction shall be handled and disposed of in a manner that does not cause contamination of stormwater. Woody debris may be chopped and spread on site. FUELING Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, and non-inert wastes present on the site (see Chapter 173-304 WAC for the definition of inert waste). MAINTENANCE, REPAIRS AND STORAGE OF VEHICLES AND EQUIPMENT Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge or spillage of pollutants to the ground or into stormwater runoff must be conducted using spill prevention measures, such as drip pans. Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Emergency repairs may be performed on-site using temporary plastic placed beneath and, if raining, over the vehicle. CONCRETE SAW CUTTING, SLURRY AND WASHWATER DISPOSAL Concrete saw water, wheel wash or tire bath wastewater shall be discharged to a separate on- site treatment system or to the sanitary sewer. HANDLING OF Ph ELEVATED WATER BMP’s shall be used to prevent or treat contamination of stormwater runoff by pH modifying sources. These sources include bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, and concrete pumping and mixer washout waters. Stormwater runoff shall not cause a violation of the water quality standard for pH in the receiving water. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 28 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh APPLICATION OF CHEMICALS INCLUDING PECTICIDES AND FERTILIZERS Application of agricultural chemicals including fertilizers and pesticides shall be conducted in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Manufacturers’ recommendations for application rates and procedures shall be followed. 303d LISTINGS REVIEW The Washington State Department of Ecology Water Quality Atlas Map has been reviewed for any 303d listings associated with the downstream drainage system. A portion of the Maplewood Creek, at a distance of about 7,000 feet from the site, is listed as Category 5 for Bioassesment. Further downstream the Cedar River is listed as Category 5 for pH, temperature and dissolved oxygen levels. See figures in Appendix B. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 29 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh IX. BOND QUANTITIES WORKSHEET, RETENTION/ DETENTION FACILITY SUMMARY SHEET King County’s Bond Quantity worksheet for the site and storm drainage improvements to be included with full TIR. The Flow Control and Water Quality Facility Summary Sheets to be included with full TIR. The Declaration of Covenant and Grant of Easement will be provided prior to final approval. The standard County forms follow. PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 11, 2019 4TH DIMENSION MIXED USE PAGE 30 P:\Work\Projects\2018\18-196 Concept Arch\CE\DOCS\18-196 TIR-PRELIMINARY.doc SRM/dwh X. MAINTENANCE AND OPERATIONS MANUAL Following are the applicable Maintenance and Operations Guidelines taken from Appendix A of the RSWDM. To be included with full TIR             APPENDIX A    FIGURES & MAPS          FIGURE 2: VICINITY MAP    FIGURE 3A: EXISTING DRAINAGE BASIN MAP                                                            FIGURE 3B: DEVELOPED DRAINAGE BASIN MAP      FIGURE 4: SOILS MAP                APPENDIX B    DOWNSTREAM MAPS   DOWNSTREAM ANALYSIS MAP  DRAINAGE COMPLAINT MAP        DEPARTMENT OF ECOLOGY 303d LISTING                  DEPARTMENT OF ECOLOGY 303d LISTING CONT.      © 2018 Microsoft Corporation © 2018 DigitalGlobe ©CNES (2018) Distribution Airbus UPSTREAM DRAINAGE BASIN MAPSITELEGEND MODELED AS: PASTURE AREA DUE TO EXISTING DETENTION SYSTEM IMPERVIOUS AREA UNDEVELOPED AREA SITE AREA BASIN BOUNDARY             APPENDIX C    SITE CRITICAL AREAS & HAZARD MAPS  DRAINAGE BASIN MAP   FLOOD HAZARD AREA MAP WETLAND LOCATION MAP    CAO BASIN CONDITION MAP    SHORELINE CONDITION SAO MAP  LANDSLIDE HAZARD SAO MAP  EROSION HAZARD SAO MAP    SEISMIC HAZARD SAO MAP            COAL MINE HAZARD SAO MAP    CHANNEL MIGRATION HAZARD SAO MAP    CRITICAL AQUIFER RECHARGE AREA MAP     GROUNDWATER CONTAMINATION SUSEPTABILITY MAP                  APPENDIX D    WWHM2012 BASIN & DETENTION   FACILITY SIZING     UPSTREAM BASIN CALCULATIONS  WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Renton Site Name: Site Address: City : Report Date: 7/24/2018 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2017/04/14 Version : 4.2.13 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .61 Pervious Total 0.61 Impervious Land Use acre ROADS MOD 0.15 Impervious Total 0.15 Basin Total 0.76 Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .09 Pervious Total 0.09 Impervious Land Use acre ROADS MOD 0.39 ROOF TOPS FLAT 0.28 Impervious Total 0.67 Basin Total 0.76 Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 ___________________________________________________________________ Name : Vault 1 Width : 20 ft. Length : 72 ft. Depth: 7 ft. Discharge Structure Riser Height: 6.1 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 0.88 in. Elevation: 0 ft. Orifice 2 Diameter: 0.88 in. Elevation: 3.8 ft. Orifice 3 Diameter: 0.8 in. Elevation: 5 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.033 0.000 0.000 0.000 0.0778 0.033 0.002 0.005 0.000 0.1556 0.033 0.005 0.008 0.000 0.2333 0.033 0.007 0.010 0.000 0.3111 0.033 0.010 0.011 0.000 0.3889 0.033 0.012 0.013 0.000 0.4667 0.033 0.015 0.014 0.000 0.5444 0.033 0.018 0.015 0.000 0.6222 0.033 0.020 0.016 0.000 0.7000 0.033 0.023 0.017 0.000 0.7778 0.033 0.025 0.018 0.000 0.8556 0.033 0.028 0.019 0.000 0.9333 0.033 0.030 0.020 0.000 1.0111 0.033 0.033 0.021 0.000 1.0889 0.033 0.036 0.021 0.000 1.1667 0.033 0.038 0.022 0.000 1.2444 0.033 0.041 0.023 0.000 1.3222 0.033 0.043 0.024 0.000 1.4000 0.033 0.046 0.024 0.000 1.4778 0.033 0.048 0.025 0.000 1.5556 0.033 0.051 0.026 0.000 1.6333 0.033 0.054 0.026 0.000 1.7111 0.033 0.056 0.027 0.000 1.7889 0.033 0.059 0.028 0.000 1.8667 0.033 0.061 0.028 0.000 1.9444 0.033 0.064 0.029 0.000 2.0222 0.033 0.066 0.029 0.000 2.1000 0.033 0.069 0.030 0.000 2.1778 0.033 0.072 0.031 0.000 2.2556 0.033 0.074 0.031 0.000 2.3333 0.033 0.077 0.032 0.000 2.4111 0.033 0.079 0.032 0.000 2.4889 0.033 0.082 0.033 0.000 2.5667 0.033 0.084 0.033 0.000 2.6444 0.033 0.087 0.034 0.000 2.7222 0.033 0.090 0.034 0.000 2.8000 0.033 0.092 0.035 0.000 2.8778 0.033 0.095 0.035 0.000 2.9556 0.033 0.097 0.036 0.000 3.0333 0.033 0.100 0.036 0.000 3.1111 0.033 0.102 0.037 0.000 3.1889 0.033 0.105 0.037 0.000 3.2667 0.033 0.108 0.038 0.000 3.3444 0.033 0.110 0.038 0.000 3.4222 0.033 0.113 0.038 0.000 3.5000 0.033 0.115 0.039 0.000 3.5778 0.033 0.118 0.039 0.000 3.6556 0.033 0.120 0.040 0.000 3.7333 0.033 0.123 0.040 0.000 3.8111 0.033 0.126 0.043 0.000 3.8889 0.033 0.128 0.047 0.000 3.9667 0.033 0.131 0.050 0.000 4.0444 0.033 0.133 0.052 0.000 4.1222 0.033 0.136 0.054 0.000 4.2000 0.033 0.138 0.056 0.000 4.2778 0.033 0.141 0.058 0.000 4.3556 0.033 0.144 0.059 0.000 4.4333 0.033 0.146 0.061 0.000 4.5111 0.033 0.149 0.062 0.000 4.5889 0.033 0.151 0.063 0.000 4.6667 0.033 0.154 0.065 0.000 4.7444 0.033 0.156 0.066 0.000 4.8222 0.033 0.159 0.067 0.000 4.9000 0.033 0.162 0.068 0.000 4.9778 0.033 0.164 0.069 0.000 5.0556 0.033 0.167 0.074 0.000 5.1333 0.033 0.169 0.078 0.000 5.2111 0.033 0.172 0.080 0.000 5.2889 0.033 0.174 0.083 0.000 5.3667 0.033 0.177 0.085 0.000 5.4444 0.033 0.180 0.087 0.000 5.5222 0.033 0.182 0.089 0.000 5.6000 0.033 0.185 0.091 0.000 5.6778 0.033 0.187 0.093 0.000 5.7556 0.033 0.190 0.094 0.000 5.8333 0.033 0.192 0.096 0.000 5.9111 0.033 0.195 0.098 0.000 5.9889 0.033 0.198 0.099 0.000 6.0667 0.033 0.200 0.101 0.000 6.1444 0.033 0.203 0.202 0.000 6.2222 0.033 0.205 0.553 0.000 6.3000 0.033 0.208 1.013 0.000 6.3778 0.033 0.210 1.490 0.000 6.4556 0.033 0.213 1.895 0.000 6.5333 0.033 0.216 2.170 0.000 6.6111 0.033 0.218 2.363 0.000 6.6889 0.033 0.221 2.529 0.000 6.7667 0.033 0.223 2.685 0.000 6.8444 0.033 0.226 2.832 0.000 6.9222 0.033 0.228 2.972 0.000 7.0000 0.033 0.231 3.105 0.000 7.0778 0.033 0.234 3.233 0.000 7.1556 0.000 0.000 3.356 0.000 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.61 Total Impervious Area:0.15 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.09 Total Impervious Area:0.67 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.076519 5 year 0.099559 10 year 0.115906 25 year 0.13785 50 year 0.155162 100 year 0.173326 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.035519 5 year 0.049592 10 year 0.060574 25 year 0.076505 50 year 0.089974 100 year 0.104914 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.105 0.031 1950 0.091 0.034 1951 0.073 0.066 1952 0.052 0.028 1953 0.052 0.030 1954 0.063 0.030 1955 0.064 0.038 1956 0.067 0.034 1957 0.078 0.034 1958 0.060 0.031 1959 0.060 0.032 1960 0.085 0.061 1961 0.067 0.033 1962 0.048 0.025 1963 0.068 0.032 1964 0.067 0.031 1965 0.077 0.034 1966 0.057 0.027 1967 0.103 0.036 1968 0.102 0.029 1969 0.064 0.031 1970 0.072 0.031 1971 0.080 0.033 1972 0.087 0.040 1973 0.049 0.028 1974 0.080 0.028 1975 0.083 0.037 1976 0.070 0.031 1977 0.056 0.026 1978 0.082 0.033 1979 0.098 0.026 1980 0.137 0.042 1981 0.068 0.029 1982 0.106 0.064 1983 0.076 0.034 1984 0.056 0.027 1985 0.063 0.032 1986 0.079 0.054 1987 0.086 0.060 1988 0.058 0.028 1989 0.090 0.025 1990 0.171 0.058 1991 0.128 0.063 1992 0.063 0.029 1993 0.063 0.030 1994 0.054 0.023 1995 0.062 0.034 1996 0.115 0.064 1997 0.081 0.068 1998 0.069 0.031 1999 0.133 0.040 2000 0.072 0.033 2001 0.077 0.027 2002 0.084 0.058 2003 0.103 0.026 2004 0.132 0.128 2005 0.068 0.035 2006 0.066 0.033 2007 0.147 0.092 2008 0.144 0.097 2009 0.095 0.041 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.1712 0.1285 2 0.1472 0.0970 3 0.1438 0.0916 4 0.1373 0.0680 5 0.1333 0.0659 6 0.1317 0.0641 7 0.1280 0.0637 8 0.1149 0.0634 9 0.1060 0.0608 10 0.1052 0.0601 11 0.1030 0.0581 12 0.1030 0.0580 13 0.1024 0.0543 14 0.0984 0.0422 15 0.0948 0.0405 16 0.0913 0.0403 17 0.0900 0.0397 18 0.0872 0.0376 19 0.0863 0.0366 20 0.0845 0.0359 21 0.0841 0.0350 22 0.0828 0.0345 23 0.0817 0.0342 24 0.0807 0.0341 25 0.0803 0.0339 26 0.0798 0.0338 27 0.0794 0.0336 28 0.0785 0.0334 29 0.0773 0.0334 30 0.0767 0.0333 31 0.0759 0.0329 32 0.0729 0.0327 33 0.0716 0.0325 34 0.0716 0.0322 35 0.0700 0.0319 36 0.0695 0.0314 37 0.0680 0.0313 38 0.0678 0.0313 39 0.0678 0.0309 40 0.0671 0.0308 41 0.0668 0.0305 42 0.0667 0.0305 43 0.0660 0.0305 44 0.0639 0.0305 45 0.0638 0.0299 46 0.0633 0.0294 47 0.0630 0.0289 48 0.0629 0.0287 49 0.0627 0.0285 50 0.0624 0.0284 51 0.0602 0.0282 52 0.0595 0.0276 53 0.0575 0.0273 54 0.0568 0.0271 55 0.0564 0.0269 56 0.0564 0.0264 57 0.0543 0.0261 58 0.0523 0.0258 59 0.0520 0.0252 60 0.0488 0.0245 61 0.0482 0.0230 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0383 2184 1798 82 Pass 0.0394 1959 1389 70 Pass 0.0406 1761 1036 58 Pass 0.0418 1585 976 61 Pass 0.0430 1435 936 65 Pass 0.0442 1314 902 68 Pass 0.0453 1194 878 73 Pass 0.0465 1101 861 78 Pass 0.0477 1005 834 82 Pass 0.0489 925 803 86 Pass 0.0501 853 772 90 Pass 0.0512 770 732 95 Pass 0.0524 712 681 95 Pass 0.0536 652 628 96 Pass 0.0548 599 575 95 Pass 0.0560 552 534 96 Pass 0.0572 491 484 98 Pass 0.0583 438 425 97 Pass 0.0595 393 378 96 Pass 0.0607 354 322 90 Pass 0.0619 318 278 87 Pass 0.0631 293 238 81 Pass 0.0642 278 200 71 Pass 0.0654 258 177 68 Pass 0.0666 240 157 65 Pass 0.0678 224 143 63 Pass 0.0690 211 131 62 Pass 0.0701 190 124 65 Pass 0.0713 180 122 67 Pass 0.0725 170 118 69 Pass 0.0737 155 116 74 Pass 0.0749 143 113 79 Pass 0.0760 131 110 83 Pass 0.0772 120 106 88 Pass 0.0784 115 102 88 Pass 0.0796 107 99 92 Pass 0.0808 97 96 98 Pass 0.0820 88 92 104 Pass 0.0831 82 88 107 Pass 0.0843 80 83 103 Pass 0.0855 74 79 106 Pass 0.0867 69 74 107 Pass 0.0879 62 68 109 Pass 0.0890 56 61 108 Pass 0.0902 51 52 101 Pass 0.0914 46 45 97 Pass 0.0926 43 38 88 Pass 0.0938 39 34 87 Pass 0.0949 37 30 81 Pass 0.0961 37 23 62 Pass 0.0973 36 13 36 Pass 0.0985 33 11 33 Pass 0.0997 32 8 25 Pass 0.1008 30 6 20 Pass 0.1020 27 5 18 Pass 0.1032 24 5 20 Pass 0.1044 24 5 20 Pass 0.1056 21 4 19 Pass 0.1067 20 4 20 Pass 0.1079 20 4 20 Pass 0.1091 19 4 21 Pass 0.1103 18 3 16 Pass 0.1115 18 3 16 Pass 0.1127 17 3 17 Pass 0.1138 17 3 17 Pass 0.1150 15 3 20 Pass 0.1162 15 3 20 Pass 0.1174 15 3 20 Pass 0.1186 14 3 21 Pass 0.1197 14 3 21 Pass 0.1209 14 3 21 Pass 0.1221 14 2 14 Pass 0.1233 13 2 15 Pass 0.1245 12 2 16 Pass 0.1256 11 2 18 Pass 0.1268 10 2 20 Pass 0.1280 9 2 22 Pass 0.1292 8 1 12 Pass 0.1304 8 1 12 Pass 0.1315 8 1 12 Pass 0.1327 7 1 14 Pass 0.1339 6 1 16 Pass 0.1351 6 1 16 Pass 0.1363 6 0 0 Pass 0.1374 5 0 0 Pass 0.1386 5 0 0 Pass 0.1398 5 0 0 Pass 0.1410 5 0 0 Pass 0.1422 4 0 0 Pass 0.1434 4 0 0 Pass 0.1445 3 0 0 Pass 0.1457 3 0 0 Pass 0.1469 3 0 0 Pass 0.1481 2 0 0 Pass 0.1493 2 0 0 Pass 0.1504 2 0 0 Pass 0.1516 2 0 0 Pass 0.1528 2 0 0 Pass 0.1540 2 0 0 Pass 0.1552 2 0 0 Pass _____________________________________________________ TREATMENT FACILITY SIZING Name : Treatment Basin Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .09 Pervious Total 0.09 Impervious Land Use acre ROADS MOD 0.39 ROOF TOPS FLAT 0.09 Impervious Total 0.48 Basin Total 0.57 Element Flows To: Surface Interflow Groundwater Sand Filter 1 Sand Filter 1 ___________________________________________________________________ Name : Sand Filter 1 Bottom Length: 6.00 ft. Bottom Width: 4.00 ft. Depth: 0.85 ft. Side slope 1: 0 To 1 Side slope 2: 0 To 1 Side slope 3: 0 To 1 Side slope 4: 0 To 1 Filtration On Hydraulic conductivity: 70.92 Depth of filter medium: 1.8 Total Volume Infiltrated (ac-ft.): 72.952 Total Volume Through Riser (ac-ft.): 6.09 Total Volume Through Facility (ac-ft.): 79.042 Percent Infiltrated: 92.3 Total Precip Applied to Facility: 0 Total Evap From Facility: 0 Discharge Structure Riser Height: 0.7 ft. Riser Diameter: 100 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Sand Filter Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.000551 0.000000 0.000 0.000 0.0094 0.000551 0.000005 0.000 0.039 0.0189 0.000551 0.000010 0.000 0.039 0.0283 0.000551 0.000016 0.000 0.040 0.0378 0.000551 0.000021 0.000 0.040 0.0472 0.000551 0.000026 0.000 0.040 0.0567 0.000551 0.000031 0.000 0.040 0.0661 0.000551 0.000036 0.000 0.040 0.0756 0.000551 0.000042 0.000 0.041 0.0850 0.000551 0.000047 0.000 0.041 0.0944 0.000551 0.000052 0.000 0.041 0.1039 0.000551 0.000057 0.000 0.041 0.1133 0.000551 0.000062 0.000 0.041 0.1228 0.000551 0.000068 0.000 0.042 0.1322 0.000551 0.000073 0.000 0.042 0.1417 0.000551 0.000078 0.000 0.042 0.1511 0.000551 0.000083 0.000 0.042 0.1606 0.000551 0.000088 0.000 0.042 0.1700 0.000551 0.000094 0.000 0.043 0.1794 0.000551 0.000099 0.000 0.043 0.1889 0.000551 0.000104 0.000 0.043 0.1983 0.000551 0.000109 0.000 0.043 0.2078 0.000551 0.000114 0.000 0.043 0.2172 0.000551 0.000120 0.000 0.044 0.2267 0.000551 0.000125 0.000 0.044 0.2361 0.000551 0.000130 0.000 0.044 0.2456 0.000551 0.000135 0.000 0.044 0.2550 0.000551 0.000140 0.000 0.045 0.2644 0.000551 0.000146 0.000 0.045 0.2739 0.000551 0.000151 0.000 0.045 0.2833 0.000551 0.000156 0.000 0.045 0.2928 0.000551 0.000161 0.000 0.045 0.3022 0.000551 0.000167 0.000 0.046 0.3117 0.000551 0.000172 0.000 0.046 0.3211 0.000551 0.000177 0.000 0.046 0.3306 0.000551 0.000182 0.000 0.046 0.3400 0.000551 0.000187 0.000 0.046 0.3494 0.000551 0.000193 0.000 0.047 0.3589 0.000551 0.000198 0.000 0.047 0.3683 0.000551 0.000203 0.000 0.047 0.3778 0.000551 0.000208 0.000 0.047 0.3872 0.000551 0.000213 0.000 0.047 0.3967 0.000551 0.000219 0.000 0.048 0.4061 0.000551 0.000224 0.000 0.048 0.4156 0.000551 0.000229 0.000 0.048 0.4250 0.000551 0.000234 0.000 0.048 0.4344 0.000551 0.000239 0.000 0.048 0.4439 0.000551 0.000245 0.000 0.049 0.4533 0.000551 0.000250 0.000 0.049 0.4628 0.000551 0.000255 0.000 0.049 0.4722 0.000551 0.000260 0.000 0.049 0.4817 0.000551 0.000265 0.000 0.049 0.4911 0.000551 0.000271 0.000 0.050 0.5006 0.000551 0.000276 0.000 0.050 0.5100 0.000551 0.000281 0.000 0.050 0.5194 0.000551 0.000286 0.000 0.050 0.5289 0.000551 0.000291 0.000 0.051 0.5383 0.000551 0.000297 0.000 0.051 0.5478 0.000551 0.000302 0.000 0.051 0.5572 0.000551 0.000307 0.000 0.051 0.5667 0.000551 0.000312 0.000 0.051 0.5761 0.000551 0.000317 0.000 0.052 0.5856 0.000551 0.000323 0.000 0.052 0.5950 0.000551 0.000328 0.000 0.052 0.6044 0.000551 0.000333 0.000 0.052 0.6139 0.000551 0.000338 0.000 0.052 0.6233 0.000551 0.000343 0.000 0.053 0.6328 0.000551 0.000349 0.000 0.053 0.6422 0.000551 0.000354 0.000 0.053 0.6517 0.000551 0.000359 0.000 0.053 0.6611 0.000551 0.000364 0.000 0.053 0.6706 0.000551 0.000369 0.000 0.054 0.6800 0.000551 0.000375 0.000 0.054 0.6894 0.000551 0.000380 0.000 0.054 0.6989 0.000551 0.000385 0.000 0.054 0.7083 0.000551 0.000390 0.067 0.054 0.7178 0.000551 0.000395 0.209 0.055 0.7272 0.000551 0.000401 0.397 0.055 0.7367 0.000551 0.000406 0.621 0.055 0.7461 0.000551 0.000411 0.876 0.055 0.7556 0.000551 0.000416 1.158 0.055 0.7650 0.000551 0.000421 1.466 0.056 0.7744 0.000551 0.000427 1.797 0.056 0.7839 0.000551 0.000432 2.149 0.056 0.7933 0.000551 0.000437 2.522 0.056 0.8028 0.000551 0.000442 2.914 0.057 0.8122 0.000551 0.000448 3.325 0.057 0.8217 0.000551 0.000453 3.753 0.057 0.8311 0.000551 0.000458 4.198 0.057 0.8406 0.000551 0.000463 4.660 0.057 0.8500 0.000551 0.000468 5.137 0.058 ___________________________________________________________________   UPSTREAM BASIN ANALYSIS  & BACKWATER CALCULATIONS WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: RENTON UPSTREAM Site Name: Site Address: City : Report Date: 5/21/2019 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2017/04/14 Version : 4.2.13 ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Flat 140.6 Pervious Total 140.6 Impervious Land Use acre Impervious Total 0 Basin Total 140.6 Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Flat 25.67 C, Pasture, Flat 73.67 C, Lawn, Flat 19.25 Pervious Total 118.59 Impervious Land Use acre ROADS MOD 10.65 PARKING FLAT 11.36 Impervious Total 22.01 Basin Total 140.6 Element Flows To: Surface Interflow Groundwater SSD Table 1 SSD Table 1 ___________________________________________________________________ Name : SSD Table 1 Depth: 400 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ SSD Table Hydraulic Table Stage Area Volume Discharge (feet) (ac.) (ac-ft.) (cfs.) NotUsed NotUsed NotUsed NotUsed 388.0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 389.0 0.150 0.140 3.906 0.000 0.000 0.000 0.000 390.0 0.160 0.280 5.524 0.000 0.000 0.000 0.000 391.0 0.170 0.450 6.765 0.000 0.000 0.000 0.000 392.0 0.240 0.610 7.811 0.000 0.000 0.000 0.000 393.0 0.700 1.160 8.734 0.000 0.000 0.000 0.000 394.0 1.020 2.000 9.567 0.000 0.000 0.000 0.000 395.0 1.500 3.470 10.33 0.000 0.000 0.000 0.000 396.0 1.880 5.100 11.05 0.000 0.000 0.000 0.000 397.0 2.050 7.120 11.72 0.000 0.000 0.000 0.000 398.0 2.160 9.040 12.35 0.000 0.000 0.000 0.000 399.0 2.200 11.39 12.95 0.000 0.000 0.000 0.000 400.0 2.300 13.59 13.53 0.000 0.000 0.000 0.000 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:140.6 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:118.59 Total Impervious Area:22.01 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 4.133758 5 year 6.492226 10 year 7.828811 25 year 9.244806 50 year 10.121029 100 year 10.866296 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 7.14541 5 year 8.495664 10 year 9.300155 25 year 10.242169 50 year 10.900842 100 year 11.529425 ___________________________________________________________________