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2010-05-18 HEX# 10-004 Exhibit KPreliminary Technical Information Report VILLAGE GREEN PHASE 11 d 111 Village Green Phases II & III (Cottages Vest) Prepared: November 18, 2008 DCI Project: 98480.2 Duncanson Company, Inc. 145 SW 155`h Street, Suite 102 RECEIVED Seattle, Washington 98166 (206) 244-4141 NOV 18 2008 CITY pE ERAL WAY EXH1 IT P'A E_LoF DO 98480 2 Table Of Contents 1. Project Overvic-w Figure 1.1 — Technical Information Report Worhsheet Figure 1? — Vicinity Map Figure 1.3.1 — Village Green Phases I & II Basin Map Figure 1.3 2 — Cottages \ est Phase III Basin Map Figure 1.4 — Soils Map 2. Preliminary Conditions and Requirements Summary 3. Offsite Analysis Offsite Analysis Drainage System Table Figure 3.1 — Offsite Analysis Map Figure 3.2 — Critical Area Map 4. Flow Control and Water Quality- Facility Analysis and Design Existing Area Calculations KCRTS Pre Developed Input Parameters Developed Area Calculations & Summary Calculations KCRTS Post Developed Input Parameters JF Conveyance System Analysis and Design SReports anal Ct��r��e� Special vr�- Geotechnical Report Trip Gelle 7. Other Per 8. CSNV Analysis and Design 9. id Quantities, Facility SumZanual ary nd Declaration of Covenant 10. Operations and Maintenance Note: Sections S through 10 are not prepared at the preliminary stage. The appropriate design information and supporting documentation will be prepared at the final engineering stage. E X 14 1 � 1 T-&-- n VILLAGE GREEN PHASE If 8 III DCl 98480 2 1. Project Overview Exiv rr PAGE 3 VILLAGE GREEN PHASE 11 & III DCI 98480 2 1. Project Overviety This project is titled Village Green Phases II and III. Village Green Phase It involves development of 5 apartment style buildings creating approximately 165 senior assisted living apartments. Village Green Phase If[ (also known as Cottages �k"est) includes approximately 40 independent senior homes configured in duplex and 4-plex buildings. Each phase is effectively served by separate existine, stormwater facilities in separate subbasins. Runoff separates into two flowpaths along the north -south ridge, creating two natural discharge locations. northwesterly and north easterly. The stormwater facilities were constructed with earlier phases and improvements under prior land use approvals. Village Green Phase II The proposed Village Green Phase II project is located in the northwest quadrant of the I" Avenue South and SW 356"' Street intersection in Federal Way, Washington. The subbasin area (Site) includes tax parcel 3021049017, which is approximately 4.357 acres in size_ Northerly of the site is the fully developed Village Green Phase I parcel; westerly is the partially developed Cottages West Phase III parcel. The site is bordered by 2"d Avenue SW along the west property line, SW 356`" Street along the southern property line, and I" Avenue South along the east property line within the Federal Way city limits_ The current -vegetation onsite consists of young to medium aged second growth deciduous and coniferous trees. Underbrush varies from dense to moderate. Portions of the site have also been cleared and improved as part of previous construction under prior land use approvals. Overall relief across the property is on the order of 25 feet south to north. Site topography is gently to moderately sloping. Site runoff is collected in existing catch basins, which were installed to serve the subject property. The Village Green Phase II project will access 2" d Avenue SW northerly of the Cottages West Phase III gated entrance. Site improvements will include sewer and water utility services, storm drain conveyance piping, dry utilities, roads, sidewalks and five buildings. Stormwater from this project, together with the stormwater from the Village Green Phase I parcel, will be conveyed to an existing combined detention/wetpond located in the northeastern corner of the Village Green Phase I parcel. The analysis contained in Section 4 of this report indicates that the existing ponds and swales can provide stormwater flow control to current Federal Way standards. EXHI IT PAu`E OF VILLAGE GREEN PELASE 11 & III DCI 88480 1 Village Green Phase [II — Cottages West The Village Green Phase I[1 —Cottages VVest project is an extension of the illa��e Green retirement communit} involving the development of 8.606 acres of land into 40 retirement cottage units consisting of single. duplex and 4-plex building eontigurations. Site improvements including grading, roadway. storm drainage_ sewer, water and dry utilities are completed and 8 of the 40 residential units are complete. Remaining �aork involves construction of the remaining residences, with associated driveways, side%%alks and landscaping_ Stormwater from this project, and from the adjacent plat of Tuscan,,, is conveyed to the existing presettling(wetpond pond prior to entering the existing infiltration pond: both installed ponds are located on the northwestern portion of the site. Complete water quality and infiltration analysis and sizing is contained in the TIR for the Plat of Tuscany (FW 01-103235-00-EN)_ These ponds were designed to current Federal Way standards. Included are Figures 1.1 — Technical Information Report Worksheet, 1.2 — Vicinity Map, 1.3.1 — Village Green Phases 18 II Basin Map. 1.3.2 — Cottages West Phase III Basin Map and 1.4 — Soils Map. This report is intended as a preliminary stage TIR including the required off -site analysis. It also contains a preliminary hydrologic analysis used to develop a conceptual drainage plan. This report does not include the design of all drainage components, however, it does contain sufficient detail for assessing the existing and proposed' drainage characteristics. E X,141 PAGE VILLAGE GREEN PHASE 11 d III DCI .)gag( King County Department of Development and Environmental Services FIGURE 1.1 - TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER & PROJECT ENGINEER Project Owner: Village Green of Federal Way, A Retirement Campus LLC Andress: P.O. Box 98309 Phone: Des Moines, WA 98198 Heidi Swartz i (206) 730-6933 I Project Engineer. Harold M. Duncanson, P-E. jCompany: Duncanson Company, Inc. Address/Phone: 145 SW 155" St., Suite 102 Seattle, WA 98166 (206)244-4141 Part 3 TYPE OF PERMIT APPLICATION Subdivision Short Subdivision C,rnrlinn Commercial X Other: Process IV (Hearing Examiner Approval) Part 2 PROJECT LOCATION & DESCRIPTION Project Name Village Green Phases II & III - Extension i Location Township Range Section 21N 4E 30 Part 4OTHER REVIEWS AND PERMITS ❑ DFW HPA _ Shoreline Management ❑ COE 404 Rockery i 1 DUE Dam Safety _ Structural Vaults FEMA-Floodplain J Other= Commercial COE Wetlands _ Other: Building Permit Part 5 SITE COMMUNITY AND DRAINAGE BASIN Community: Federal Way Drainage Basin: Hylebos Creek Part 6 SITE CHARACTERISTICS River Stream Critical Stream Reach Depressions/Swales Lake Steep Slopes ❑ Floodplain ❑ Wetlands ❑ Seeps/Springs ❑ High Groundwater Table ❑ Groundwater Recharge X Other: Critical Aquifer Recharge & Wellhead Protection Area 751T Part 7 SOILS Soil Type Slopes Everett Gravelly 0-5% Sandy Loam Additional Sheets Attached I Part 8 DEVELOPMENT LIMITATIONS REFERENCE X Section 3 — Offsite Analysis r Additional Sheets Attached Part 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Sedimentation Facilities Stabilized Construction Entrance Perimeter Runoff Control r, Clearing and Grading Limits Li Cover Practices Construction Sequence J Other: Silt Fence , Other: Catch Basin Inlet Protection Erosion Potential Erosive Velocities LIMITATION/SITE CONSTRAINT We recommend sediment be removed from specified components. MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION Stabilize Exposed Surface Remove and Restore Temporary ESC Facilities J Clean and Remove All Silt and Debris ;J Ensure Operation of Permanent Facilities Flag Limits of SAO and open space preservation areas L Other EXA H. I Rf PACE OFFS Part 10 SURFACE WATER SYSTEM Grass Lined Channel X Pipe System Open Channel �i Dry Pond X Wet Pond Tank Vault Energy Dissipater Wetland Stream Infiltration Method of Analysis — Depression KCRTS ' Flow Dispersal — Waiver Compensation ; -- Mitjgati.on of �. _. Regional Eliminated Site Detention Storage i f Brief Description of System Operation: Stormwater will be conveyed to an existing wetpond followed by an existing bioswale, both located in the northeastern corner of the Village Green Phase I parcel. Facility Related Site Limitations Reference Facility Limitation Part 11 STRUCTURAL ANALYSIS ❑. Cast in .Place Vault ❑ Retaining Wall Rockery > 4' High ❑ Structural on Steep Slope ❑ Other Part 12 EASEMENTS/TRACTS Drainage Easement Access Easement Native Growth Protection Easement Lj Tract Other Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site_ Actual site conditions as observed were incorporated into this worksheet and the attachments. To the best of my knowledge the information provided here is accurate. SignedlDate K pAGI-3-Y YL 4. SaiSif sr _- MST P4 o I Mott I Village Green-Phase1I Cottages West -Phase QI DUNCANSON COMPANY, INC. Cisil Engincc+mg - Sm,cying - land Pldmiug 145 SW 155th St, Suite 101 Seattle, Washington 98166 Phone 206.244.4141 Fox 206.244 4455 Figure 1.2 — Vicinity Map Site @ 1'` Avenue South & SW 356h Street Scale: N/A 1 Drawn: JMK I Job No: 98480.2 PAGE -r - w cn _ % Y d w - a ``) a LLJ L ; olti en p Om Q o 356TH -gF 4 ' PAGE OF e.� C7 Q� d 0 _• _ - s 1. L 0 w O W W �c nQ OO 'iM �Z �O lil M of a ]L O Q m p 11 Z 0 Z Q ' N !n W W Q cr C Om Q z .J 'J II J �I L � SW 356TH ST PAG-E: -LI Lui a r• .s_KA AD I -- ata DUNCANSON COMPANY, INC, Chil Engiuccring - Stmvcymw • Laud Planning 145 SW 155th .St• Suile 102 Seattle, Wadnnglon 96166 Phone 206.1Jd d141 Far 206.244.4455 Figure 1.4 — Soils Map EvB = Everett Gravelly Sandy Loam, 0-5% Slopes Scale: NTS I Drawn: KCF I Job No: 98480.2 PACE IZ ni zva 2. Preliminary Conditions and Requirements Summary \gLLAGE GREEN PHASE II d Ill ExHle P4GE Ii-,F_ 2. Preliminary Conditions and Requirements Summary The Citv of Federal Wa\ requires compliance with the 1998 King County Surface Water Design Nlanual (KCSk\'D1v,1) and the CitN of Federal Way Addendum to KCS\k'Dlv1_ This report follows the format specified in the manual_ This Section describes how the Prn7ect will meet the kla-ftual's Core and Special Requirements. King County Surface Water Design Manual Core Requirements: I. Discharee at the Natural Location The site runoff separates into two flowpaths (Basin 1 and Basin 2) along the north - south ridge, creating two natural discharge locations_ See Figure 3.1 — Offsite Analysis Map for more information. 2. Offsite Analvsis A Level 1 offsite analysis has been performed for this project. See Section 3 for more information. 3. Flow Control Level 1 Flow Control will be provided for this project. See Section 4 for more information. 4. Conveyance Svstem Appropriate --convevance--calculations—witt -be 'included Section 5-- at -the- final engineering stage. 5. Erosion and Sediment Control ESC measures will conform to the 1998 KCS WDM. ESC plans will be provided at the final engineering stage. 6. Maintenance and O eralions A maintenance and operations manual will be provided in Section 10 at the final engineering stage. 7. Financial G marantees and Liabilitv The project owner will provide appropriate financial guarantees and liability insurance prior to recording. 8. Water Quality The site is in the Resource Stream Protection Area_ See Section 4 for water quality calculations and design_ VILLAGE GREEN PHASE 11 d ❑1 King County- Surface Water Design Manual Special Requirements: 1 _ Other Adopted Area -Specific Requirements The site is in the Hvlebos Creek Basin_ The adopted area specific requirement consists of BW-2: Basinwide Onsite Detention Standard; which is Level 1 Flo« Control (KCRTS) — Match predeveloped 2- and 10- year peak flow rates. 2. Flood Hazard Area Delineation This site does not lie within the 100-year flood plain_ 3. Flood Protection Facilities This requirement does not apply. 4. Source Control This requirement does not apply. 5. Oil Control This requirement does not apply. VILLAGE GREEN PHASE II & III EX M. "15 r11 PACE I F 3. Offsite Analysis K. PA u E _d= VIII.AGE GREEN PHASE 11 8 111 DO 98480 2 3. Offsite Analysis Task l - Stud Area Definition & Maps The stud, area was defined b\ the site topography using City of Federal Way's G[S maps. The study area includes the site and downstream flow -paths. See Figure -'),I — Offsite Analysis Map for more information_ Task 2 - Resource Revie-tv 1. Adopted Basin Plan BVk'--': Basinwide Onsite Detention Standard. which is Level 1 Flo", Control (KCRTS) — Match predeveloped 2- and 10- year peak flow rates_ 2. Finalised Drainage Studies Not applicable. 3. Basin Reconnaissance Summary Reports This project is in the Hylebos Creek Basin and contributes to Tributary 0014B. 4. Critical Drainage Area Maps See Figure 3.2 — Critical Areas Map for the offsite wetland location. 5 _ FEjVLA :Claps Not applicable. 6. Other Offsite Analyses The downstream analyses for the Village Green Phase I and Cottages West Phase III projects were consulted. These plats adjoin the site to the northwest and northeast. These downstream analyses did not reveal any problems or require any special mitigation. 7. Sensitive Areas Folio A map detailing King County's critical areas in the site vicinity is included as Figure 3.2. The figures shows that the downstream flowpaths re -combine downstream and then outlet into a city identified wetland. VILLAGE GREEN PHASE H S III PRGE OF .- 8. Drainage Complaints and Studies Drainage complaint summaries were obtained from ling Count\ . See Figure 3.1 - Offs1te analysis Map. The drainage complaint parcels are shaded orange and have been assigned a number (DC-2 for example). Two drainage complaints were found to be in the downstream flowpath_ Below is a description of how each drainage complaint has been addressed. DC-1- 1987-0727 Parcel + 292104-9029. This drainage complaint was regarding an old drainage pipe with constriction issues. This complaint is more than 10 years old. therefore it is not applicable_ DC-2: 1989-0448 Parcel R292104-9030. This drainage complaint was regarding drainage issues with the Sunrise Methodist Church construction. This complaint is more than 10 years old, therefore it is not applicable. 9. USDA Soils Survey See Figure 1.4 - Soils Map. Soils noted as EverettGravelly Sandy Loam. 10. Gf etlands Inventory No onsite wetlands. See Figure 3.2 for the locations of offsite wetlands. 1.1. A gratin-g-River-Studies Not applicable. XILLAGE GREEN PHASE If d IH 1:9: DCI°3K ��_�$ 0 57- Task 3 - Field Reconnaissance A field reconnaissance kvas conducted on October 28. 2008_ Weather conditions were overcast and dr- . The downstream flow paths were observed for !/a mile_ A description of the various downstream runoff system components is contained under Task 4 below_ Task 4 - Drainage Svstem Description And Problem Screening Basin I Com anent 1.4 --- Street Flow 015 Runoff appears to exit the site along the northeastern property line and sheet flows to the northeast over asphalt until it reaches the drainage system for Village Green Phase I. No problems were observed. Component IB — Pipe Flow 150'— 650' Runoff is collected by the drainage system for Village Green Phase L This drainage system consists of catch basins and ID to 18" CPEP with an average slope of 4%. Runoff is routed through this system until it reaches a detention pond. No problems were observed. Component 1 C — Detention Pond 650' — 825 ' Runoff outlets into a detention pond located in the northeast comer of the Village Green Phase I site_ Runoff is contained in the pond and is released from a control structure in the northern portion of the pond_ No problems were observed. Component ID — Pie Floit 825' —1 270' Runoff is released from the pond via control structure and is routed north to the drainage system along the western side of I" Avenue South. This drainage system consists of catch basins and IF CPEP with an average slope of 6%_ Runoff is routed north through this system until it reaches the sag location along I" Avenue South. No problems were observed. Component E -- Culvert 1 270'-1310' Basin 1 runoff recombines with Basin 2 runoff at this drainage component. Runoff from both basins are collected at the sag location by a culvert and is routed east under Is' Avenue South. The culvert is a 48" CMP with a slope of +2%_ Accumulation of sediment was observed at the inlet and outlet, which could potentially create an overtopping and/or ponding problem_ No other problems were observed_ Component F --- Sheet Flow (1310'--1,320'+) Runoff outlets east from the culvert and into a city identified wetland. A concentrated flowpath was observed for a few feet but then flows disperse into the heavily vegetated wetland. Heavy sediment accumulation was observed at the beginning of this drainage component, which could potentially plug the outlet of the 487' CMP culvert. No other problems were observed. VILLAGE GREEN PHASE [[d [[[ Basin 2 Component 1-1 - Pipe Flow (0' -- 625) Runoff appears to exit the site along the northwestern property line and collected by the drainage system of Village Green Phase III and is routed north. This drainage system consists of catch basins and 12" CPEP with an average slope of 3%. No problems were b --oserved: _ Component 2B -- Infiltration Pond (625' - 9 75 '1 Runoff outlets into an infiltration pond located in the northern portion of the Village Green Phase III site. No problems were observed. Directly north of the pond, an apartment complex was constructed in the mid 1980's under King County jurisdiction under the name of The Height on Viest Campus. At the time King County allowed the developer to build a retaining wall along the southern property line of The Height on West Campus. This retaining wall blocked the natural discharge point and created a manmade closed depression. If runoff were to leave the pond, approximately 10 feet of water would need to be in place for any runoff to discharge from the site. The remaining drainage components in this downstream analysis was performed under the premise that if runoff were to leave the pond. Component 2C - Channeled Flow (975 ' -1, 025' Runoff from the pond flows north onto a internal road for The Height on West Campus apartments. The runoff is routed north over asphalt and along the flowline of the internal road, which has an average slope of__21/o. No problems were observed. Component 2D - Pipe Flow (1,025'-1,725) Runoff is collected by the drainage system of The Height on West Campus and routed east; towards the I" Avenue South sag location. This drainage system consists of catch basins and 12" pipes with an average slope of 5%. No problems were observed. Com onent E : Culvert (1,.725' -1, 765'� Basin 2 runoff recombines with Basin 1 runoff at this drainage component. Runoff from both basins are collected at the sag location by a culvert and is routed east under I" Avenue South. The culvert is a 48" CMP with a slope of f2%. Accumulation of sediment was observed at the inlet and outlet, which could potentially create an overtopping and/or ponding problem. No other problems were observed_ Component F -- Sh eet Flom, 1, 765 '+ Runoff outlets east from the culvert and into a city identified wetland. A concentrated flowpath was observed for a few feet but then flows disperse into the heavily vegetated wetland. Heavy sediment accumulation was observed at the beginning of this drainage component, which could potentially plug the outlet of the 48" CMP culvert. No other problems were observed. VILLAGE GREEN PFL-kSE Q 3 III r .,- W-M-0i Iowa SOUND ri "4 W mitt Wy . 224M Wr CRE, I ) f 1A RIVER Salle: 0 112 I Hy*bc4i Crack tWsia Whdo P4%W a"m U)WW GWfv Pdftr Basn LwwWWe HU" AMU Lowm Pug* Smnd ftsfn a 92 1 W C-eek as* eDUNCANSON COMPANY, INC. Civil EngmCang - Surmying - UM Planning 145 SW 1551h Sr, Suite 102 Seatde, MaduqgM 98166 Phmie 206.244.4141 Far 206.244.4455 Figure 3.2 — Critical Areas Map Scale: Shown Above I Drawn9Y r- TJ ri O_ LU O N O L o rr J f e) IE IA 4) O O p L 0 L I ♦ d co Co � CL i Q ca co a. m O :1� O lC U) o v v v i c d y .� _ �' o_Cc: O O O O O yr, y r O L a s .0 L 'Cul O =0 C co O — �2 �°'_ N -0 C _ i U N 7 «• 0 L 07 cc«^. Q N ul o Q m U >~ O O O O o r. N t rn wa �o�,� v O U 0 U C ¢ O ~" ^1 C/) d F O O cn N Cl co O N 00 CV M M lC +•+ O O cn O � � O l� O ONC N M � N Q. o o o 01 � .o o� N N p o 00 llzt O � + -H -H �CD cri I4) � o - tu T> p o__ 0 �� o � a U� 4) Y n n Q- (L) Vl 00 00 00 Qy > O O N cccu _ G� T 2! IZ = iu d lV O U 3 n� o = 2 4)Z _4D 0 3 3 0 � >Z C N a) a) a) a) EE co 0 7., ER a) coa 3 O O w 0 (0 U cn N (D Y O L=o O @ff o �- � ° i m 3caEQ �N n a)-0To O� �a L E X O u1 L a z I{ - I > O aj co � f v i v v op CD G G ~ v z z � > o r. ca v G _� •:J U !n � I o � E 01 O L w `n v N in �O L. N U U N� _- m 13 a O o (r -H + (V -H kn I a) a)o Now°' cc d-/ CO Qa)) N >O orw C C) 0 U U U po�L10 y > N P -o N_ m c- C N ca Q- C i6 EN V E O � CD z � � E � cc 3 v 3 c �La o v O Q SUN w � w a O_ v v > o Q E E W N N N N W X H PAIN Task 5 — Conclusion It is recommended that the sediment be removed from Components E and F. It is Duncanson Company's opinion from the available information that the developed site will not create or aggravate any downstream conditions. AA'GE 25 O VILLAGE GREEN PFLASE 11 d W DCi 98a60 2 4. Flow Control and Water Quality Facility Analysis and Design VILLAGE GREEN PHASE 11 B III EXHIBIT PACE 26 OF � 4. Flow Control and Water Quality Facility Analysis and Design Village Green Phase 111—Cottages West Stormwater from the Cottages West site is collected in catch basins and routed through an existing presettling wet pond to an infiltration pond located in the northwestern corner of the Cottages Nk est site — see Figure 1.3.2 — Cottages West Phase III Basin Map. Complete water quality and infiltration analysis and slZtngT is contained in the TIR for the Plat of Tuscany (FVa' 01-103235-00-EN)_ The Cottages West water quality and infiltration facilities meets all current and anticipated future standards for the existing and planned impervious areas and development_ The remainder of this section will focus on the Village Green Phase II site_ Village Green Phase Il—Buildings E - J Part A — Existing Village Green Site Hvdrolog2� Stormwater from the Village Green Phase I1 site is and will be collected in catch basins and routed through an existing detention/wet pond and bioswale located in the northeastern corner of the Village Green site — see Figure 1.3.1 — Village Green Phases I & II Basin Map_ While Village Green Phase I is not part of the current proposal, it was necessary to model the hydrology of that existing development since it also contributes to the same detention pond that Phase I1 will use. The Village Green Phase I impervious areas will remain; are not being redeveloped; are mitigated by an existing facility; and are not target impervious surfaces. The combined onsite area is 13.047 acres. No additional impervious areas are anticipated in the surrounding right -of -ways - The existing, or predeveloped site, impervious areas include eight existing cottages, five existing buildings; concrete, asphalt and gravel. The current vegetation onsite consists of landscaping, young to medium aged second growth deciduous and coniferous trees; underbrush varies from dense to moderate_ Overall relief across the property is on the order of 25 feet south to north. Site topography is gently to moderately sloping_ Runoff separates into two flowpaths along the north -south ridge, creating two natural discharge locations, northwesterly and north easterly. Geotechnical investigation revealed ouovash surface soils and till soils at less than 5' below the surface — soils modeled as till. The various cover types occur in the following proportions: Model Predevelope& Till Forest: 2.900 acres Till Pasture: 1.457 acres Till Grass: 4.528 acres Impervious: 4.162 acres Total: 13.047 acres VILLAGE GREEN PHASE 11 d In XIA V�3 ' PAGE 7F 0- A complete KCRTS input summary sheet is included on the following page_ The predeveloped model "EXIST" yields the following peaks: _D-v. _ requency --.._�lvsi s i-m_ Se__es =--c_exist _tsf ---=knnuai e_k Flow Rates--- _71ow Raze Rank Time of Peak 1.66 2109/01 2:00 1.22 7 1/05102 16:00 1.97 2 2/27/03 7:00 1. 17 8 8 /26/ 34 2: 00 1.43 6 10/26/04 16:00 1.76 3 1/18/06 16:00 1.70 4 10/26/06 0:00 3.40 1 1/09/08 6:00 Computed Peaks VILLAGE GREEN PHASE U d IR -----Flow __ Yuen 'y" _'' naiy'sis------- - - Peaks - - Rank Return Prob iCrS? Period 3.40 - 100.00 0.990 1.97 2 25.00 0.96 1. 7 iC.00 0- 900 1.70 4 5.00 0.800 1.66 5 3.00 0.657 1.43 6 2.00 0.500 1.22 7 1.30 0.231 1.17 8 1.10 0.091 2.92 50.00 0.980 EXIMIMMMT r-11 MI MPL VILLAGE GREEN EXISTING AREA CALCULATIONS (All cottages, buildings A-E. associated paving and sidewalks.) TOTAL ONSITE AREA: Area (SF) Area (Acres) Entire Lot C Area 378,538 8.690 Entire Lot D Area 189,774 4.357 EXISTING IMPERVIOUS AREAS LOT C IMPERVIOUS AREA Cottage 2 2,552 0.059 Cottage 3 2,552 0.059 Cottage 4 2,552 0.059 Cottage 5 2,552 0.059 Cottage 6 2,552 0.059 Cottage 7 2,552 0.059 Cottage 8 2,552 0.059 Cottage 7 2,552 0.059 Building A, B and C 34,916 0.802 Building D and E 24,512 0.563 Sidewalks and Curbs 19,657 0.451 Asphalt 70,841 1.626 Gravel 11481 0.034 TOTAL IMPERVIOUS AREA 171,821 3.944 LOT D IMPERVIOUS AREA: Sidewalks and Curbs 346 0.008 Asohalt 9,144 0.210 TOTAL IMPERVIOUS AREA 9,491 0218 EXISTING PERVIOUS AREAS ONSITE PERVIOUS AREA Native Forest - Retained 126,324 2.900 Native Forest - Cleared 63,450 1.457 Landscaping 197,226 4.528 TOTAL PERVIOUS AREA 387,000 8.884 98480.2 11 /612008 JMK parcel 3021049024 . parcel 3021049017 " Directly connected to pond = non -targeted. Porte-cochere duplicated: bldg & asphalt. Porte-cochere duplicated: bldg & asphalt. MODEL AS 100% EFFECTIVE Directly connected to pond = non -targeted MODEL AS 100% EFFECTIVE MODEL AS TILL FOREST MODEL AS TILL PASTURE MODEL AS TILL GRASS E MENT PAGAN ?®7._ KCRTS Data Entry & Computation Sheet Project: 98480.2 Village Green Process IV page 1 of 1 Comp by: JMK Date: 11/6/2008 Basin Name: 1998_ KCSWDM - Existing _ File Name: EXIST Region: Seatac Scale Factor: 1.02 Time Step: Hourly Record Length: Reduced Total Acreage: 13.047 Pervious Land Types Land Use KCRTS Soil Group Cover Group Area (sf) Acreage Retained Forest Till Forest 126,324 2.900 Cleared Forest Till Pasture 63,450 1.457 Landscaping Till Grass 197,226 4.528 Outwash Forest Outwash Pasture Outwash Grass Wetland -- Impervious Land Types Land Use Acreage EIF EIA Non Effective Area Reverts to: Cottage 2 0.059 1.00 0.059 0.000 N/A Cottage 3 0.059 1.00 0.059 0.000 N/A Cottage 4 0.059 1.00 0.059 0.000 N/A Cottage 5 0.059 1.00 0.059 0.000 N/A Cottage 6 0.059 1.00 0.059 0.000 N/A Cottage 7 0.059 1.00 0.059 0.000 N/A Cottage 8 0.059 1.00 0.059 0.000 N/A Cottage 7 0.059 1.00 0.059 0.000 N/A Building A, B & C 0.802 1.00 0.802 0.000 NIA Building D & E 0.563 1.00 0.563 0.000 NIA Sidewalks & Curbs 0.459 1.00 0.459 0.000 N/A Asphalt 1.836 1.00 1.836 0.000 N/A Gravel 0.034 1.00 0.034 0.000 NIA Adjusted Land Use Areas Based on OF Calculations KCRTS Soil Group Cover Group Added Acrea e Computed Acreage for Model Till Forest 0.000 2.900 Till Pasture 0.000 1.457 Till Grass 0.000 4.528 Outwash Forest Outwash Pasture Outwash Grass Wetland -- - Effective Impervious -- - 4.162 Total Area Check 13.047 n� PAWEA-0_OF 45~ Part R — Developed Village Green Site tivdrolo�r_. See Fwures Figure 1.3.1 — Village Green Phases I & I[ Basin Map and 1.3.2 — Cottages West Phase [[1 Basin Map. Site improvements for Village Green Phase II will include sewer and water utility services. storm drain conveyance piping, dry utilities, roads; sidewalks and five buildings. The Cully developed site conditions will have approximately 6.394 acres of impervious surface including the existing Phase I areas_ The remainder of the site was modeled as forest (retained significant trees), pasture and grass; landscaping will be in the form of grass, groundcover, shrubs and trees. The various cover types occur in the following proportions: Model Postdeveloped Till Forest: 0.075 acres Till Pasture: 181-5 acres Till Grass: 3.753 acres Impervious: 6.394.acres Total: 13.047 acres A complete KCRTS input sununary sheet is included on the following page. The postdeveloped model "DEV" yields the following peaks: 10s'i F requance --na1'_vsis TiT.e _es _'_ie: dev_ tsf P~c ent Laca:�ion:Sea-Tac ---nnaal °aak =iow Ra es--- -----Flow Frequency Anaivsis------- F.ow Rank Time o` Peak - - Peaks - - Rank Return Prob (1-Fs) ;CFS) Period 2.06 2/09/Ol 4.20 1 100.00 0.990 1.62 8 1/05/02 16:00 2.47 2 25.00 0.960 2.4, 2 2/2? 03 7,00 2.42 3 10.00 0.900 1.67 7 9/26/0, 2:00 2.19 4 5.00 0.800 2.02 6 10/28/04 16'.00 2.06 5 3_:00 0.667 2.19 4 i/"1L8/06 _i`€00 2.02 6 2.00 0.500 2.42 3 10/26/06 0t_:00 1.67 7 1.30 0.231 4.20 1 1/09/08 6:00 1_62 8 1.10 0.091 Commuted Peaks 3.62 50.00 0.980 Part C — Performance Standards The City of Federal Way has specified Level 1 Flow Control and the Resource Stream Protection Area as required performance standards. Facility sizing calculations showing compliance with these standards are included in the following subsections_ VILLAGE GREEN PHASE 11 B III EHMZMTV1. PA%2_4� F 115- VILLAGE GREEN PROPOSED AREA CALCULATIONS (Fully developed site.) PROPOSED IMPERVIOUS AREAS LOT C IMPERVIOUS AREA: Area (SF) Area (Acres) Cottage 2 2,552 0.059 Cottage 3 2,552 0.059 Cottage 4 2,552 0.059 Cottage 5 2,552 0.059 Cottage 6 2,552 0.059 Cottage 7 2,552 0.059 Cottage 8 2,552 0.059 Cottage 7 2,552 0.059 Building A, B and C 34,916 0.802 Building D and E 24,512 0.563 Sidewalks and Curbs 19,657 0.451 Asphalt 70,841 1.626 Gravel 1.481 0,034 TOTAL IMPERVIOUS AREA 171,821 3.944 LOT D IMPERVIOUS AREA Building F (located on lots C & D) 20,861 0.479 -Building-G- 10,469 0.240 Building H 7,547 0.173 Building 1 10,005 0.230 Building J 12,024 0.276 Sidewalks and Curbs 6,388 0.147 Asphalt 39,411 0.905 TOTAL IMPERVIOUS AREA 106,706 2.450 PROPOSED PERVIOUS AREAS 98480.2 11 /6/2008 JMK * Directly connected to pond = non -targeted * Porte-cochere duplicated: bldg & asphalt * Porte-cochere duplicated: bldg & asphalt. MODEL AS 100% EFFECTIVE Directly connected to pond = non -targeted. * Porte-cochere duplicated: bldg & asphalt. Porte-cochere duplicated: bldg & asphalt. * Porte-cochere duplicated: bldg & asphalt. * Porte-cochere duplicated_ bldg & asphalt_ MODEL AS 100% EFFECTIVE ❑NSITE PERVIOUS AREA. Native Forest - Retain "Significant' 3,267 0.075 MODEL AS TILL FOREST Native Forest - Cleared 123,057 2.825 MODEL AS TILL PASTURE Landscaping 163,461 3.753 MODEL AS TILL GRASS TOTAL PERVIOUS AREA 289,785 6.653 EY(. !-, . P��E % VILLAGE GREEN AREA CALCULATION SUMMARIES TOTALS SUMMARY 984802 11 /6 /2008 JMK Area (SF) Area (Acres) TOTAL ONSITE AREA 568,311 13.047 TOTAL OFFSITE AREA 11,929 0.274 * Not including proposed asphalt in ROWs TOTAL AREA 580,240 13.320 EXISTING ONSITE SUMMARY TOTAL IMPERVIOUS AREA TOTAL PERVIOUS AREA IMPERVIOUS LOT COVERAGE PROPOSED ONSITE SUMMARY 181,312 4.162 387,000 8.884 32% TOTAL IMPERVIOUS AREA 278,526 6.394 TOTAL PERVIOUS AREA 289,785 6.653 IMPERVIOUS LOT COVERAGE 49% SAGE_„ �- KCRTS Data Entry & Computation Sheet Project: 98480.2 Village Green Process 1V page 1 of 1 Comp by: JMK Date: 11 /6/2008 Basin Name: 1998 KCSWDM - Developed File Name: DEV Region: Seatac Scale Factor: 1.02 Time Step: Hourly Record Length: Reduced Total Acreage: 13.047 Pervious Land Types Land Use KCRTS_ Soil Group Cover Group Area (sf) Acreage Retained "Sig." i'ree Till Forest 3,267 0.075 Cleared Forest Till Pasture 123,057 2.825 Landscaping Till Grass 163,461 3.753 Outwash Forest Outwash Pasture Outwash Grass Wetland Impervious Land Types Land Use Acreage EIF EIA Non Effective Area Reverts to Cottage 2 0.059 1.00 0.059 0.000 N/A Cottage 3 0.059 1.00 0.059 0.000 N/A Cottage 4 0.059 1.00 0.059 0.000 N/A Cottage 5 0.059 1.00 0.059 0.000 N/A Cottage 6 0.059 1M 0.059. 0,000 NIA, Cottage 7 0.059 1.00 0.059 0.000 N/A Cottage 8 0.059 1.00 0.059 0.000 N/A Cottage 7 0.059 1.00 0.059 0.000 N/A Building A, B & C 0.802 1.00 0.802 0.000 N/A Building D & E 0.563 1.00 0.563 0.000 N/A Building F 0.479 1.00 0.479 0.000 N/A Building G 0.240 1.00 0.240 0.000 N/A Building H 0.173 1.00 0.173 0.000 N/A Building 1 0.230 1.00 0.230 0.000 N/A Building J 0.276 1.00 0.276 0.000 N/A Sidewalks & Curbs 0.598 1.00 0.598 0.000 N/A Asphalt 2.531 1.00 2.531 0.000 N/A Gravel 0.034 1.00 0.034 0.000 N/A Adjusted Land Use Areas Based on EIF Calculations for Model KCRTS Soil Group Cover Group Added Acreage' Computed Acreage Till Forest 0.000 0.075 Till Pasture 0.000 2.825 Till Grass 0.000 3.753 Outwash Forest Outwash Pasture Outwash Grass Wetland -- Effective Impervious -- - 6.394 Total Area Check 13.047 MIT Part D — Village Green Flow Control Systems Flow control will be provided through the use of an existing combined detention!wetpond located in the northeastern corner of the Village Green Phase I parcel_ This existing wetpond was modeled using the --existing" conditions. and multiple length and width configurations were analyzed in order to match the asbuilted pond volume, by AHBL_ The existing pond was designed to control the runoff from both Village Green Phases I and II. While the pond was originally sized using the single event SBUH method_ It was sized to the more restrictive 100-year, 7-day storm event. Due to the more restrictive standard used at the time and since Phase II has not been completed, the pond is currently oversized. Following are the results of a KCRTS analysis showing the stage and release rates of the pond under current conditions- Retention/Detention Facilit Type o7 Facility: .,ode S'ope: Pond Bottom Length: Dona' Bot_om Width: Pond Bc:tom Area: Too Area at 1 ft. FB: Errec.ive Storage Depth. - stage _ Elelv'a--ion: Sto-ag %73 Lume: Ris--.- Head: Rise- Diameter: Number Orifice Height ,fr) 1 0.00 2 4.60 Existing Wetpond 3.00 H:1V 150.00 _t 80.00 ft 12000. sq. ft 22565. sq. ft 0.319 acres . 54 f t 225.26 ft 89698. cu. ft 2.039 ac-tft 5.54 fi- 18.00 inches 2 Full Head Pipe Diameter Discharge Diameter 2.77 J 0.510 3.13 0.314 6.0 Route Time Series zhrough Facility Inflow Time Series Fiie:exist.tsf Outflow Time Series File:EXISTrdout Inflow/Outflow Anaivsis Peak Inflow Discharge:: 3.40 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.672 CFS_ at 17:00 on Jan 9 in Year 8 Peak Reservoir Stage: 5.16 Ft Peal: Reservoir E1ev: 230.42 Ft Peak Reservoir Storage: 81964. Cu-Ft 1.882 Ac-Ft VILLAGE GREEN BLASE 11 d M PAGE D20i" =Lte __ ___=:existrdout.tsf =Jar;s Ra 0.2-7 1 __.2 w_ _ :OG 0.66C '� 2 -75. 0 0 0.55C 0. 20 _ =_'13 2=:0: 0.420 --i.Iy3 1000 09G0 �. = .. _� .. I_� D. l C! . 4 16 Z J G 4 O 0.4083 _ 1= c �.0 0.338 2.65 6 2.00 3.50C 0.416 _-,%: n - _00 _.= 1.69 _.3u 0.23'' i 0.6'2 _ _ _!� 1 ..00 0__ - '_.33 8 __10 0_091 Compu-ed ?>;.;s 0.0"65 14 -0.00 0.9^ c0 The resulting _2 and 10-year peak release rates are the target release rates that must be matched in order to achieve Level 1 flow control. The -developed" conditions were run through the existing pond model. The pond geometry and volume were held constant, while the control structure configuration was modified to achieve the desired performance. Following is the resulting KCRTS analysis. Retention/Detentio Facility ,ype Developed Wetpond iae Slope: 3.00 i:'�" Pond Bo_t= teenyt:h: 150.00 =_ Pond Bottom 'vJldt: : 80.00 ft - P--n d 3 a- t-m-Ar- -a - - Top Area at _ it. FB: 22565. SQ. 0. 18 acres Effective "rah= Dep-._- 5.54 �t Stage J Eieva_io`: 225.26 tt Storage 89698. Cu. ft 2.059 ac-=- Riser H e a a: 5.54 _ t Riser Diameter: 18.00 es Number of orifices: 2 Full Head Orifice Height Diameter Discharge (ft) (in) !^FSj 1 0.00 2.57 0.420 2 3.59 0.56 3_0_2 Route Time Series through Facilitv Inflow Time Series File:dev.tsf Outflow Time Series File:DEVrdout Inflow/Outflow Analvsis Peak Inflow Discharge: 4.20 FS at Peak Outflow Discharge: 2.86 C-PS a -- Peak Reservoir Stage: 5.84 - Peak Reservoir Elev: 231.10 Ft Peak Reservoir Storage: 96028_ 2.205 Ac--7 VILLAGE GREEN PHASE 11 d f0 Pipe Diameter (in) 4.0 6:00 on Jan 9 in Year 8 i0:'0D on Jan 9 in Year 8 -.-me Ser-es F_-e:devrdout.tsf _ear _ iow _,a -_es--- .. ___ _ _------- ilow Raze Ra.^.}_ Titre of `-lea 0.286 12,120/0l 18.00 0.�'_2 2/28-03 20:'00 0.420 -6 3 io_00 .yD'' 0.233 8 8/26.'04 6:C0 5.0- 0.338 6 1 / 0 5 / 0 5 _6:OC- 0.4CY 4.8; 5 _ 0_404 5 1/19/06 2:00 0.338 3.59 6 2.00 0.420 3 11/24/06 10:0-3 0.2S6 2.55 7 1.30 G.231 2.86 - i/09/08 10:00 0.233 1.:70 8 -. G 0.:9' COMPU:e0 Leans z: 8v The following downstream peaks table shows that the 2 and 10-year peak wetpond release rates are equal to the corresponding target peaks, which demonstrates that the Level 1 performance criteria are also satisfied: Return Period Target Release Rate Developed Wetpond Release Rate (year) (cfs) (cfs) 2 0.420 0.420 10 0.338 0.338 Part E — Village Green Water ualits- System Resource Stream Protection Area water quality is provided through the existing two - treatment train configuration of the existing combined detention/'wetpond followed by a biofiltration swale. VQ-LAGE GREEN PHASE 11 B RI EXHir „.,.. _ Preliminary Technical Information ADDENDUM Alit Rze, 40 �" Ott) P'��li'c� Village Green Phases II & Ill (Cottages West) Prepared: August 3, 2009 Revised: December 21, 2009 DC[ Project: 98490.2 Duncanson Company, Inc. 145 SW ISS'h Street, Suite 102 Seattle, Washington 98166 (206) 2444141 Vff- ACE GREEN PHASE II8 m DC[95-30? f\ EXHIT1 1� PME�� The Cit\ of Federal Wa% plans to adopt the 2009 Ding County Surface Water Design V[anual, with a corresponding, Federal Wa\ ,-addendum (2009 Manual) in January 2010. Since adoption of these new standards mat preclude the final land use approval. this FIR Addendum and the revised Prelinunan Drainage. Grading, and Right-of-�k'a% Plan (Cl) identit'v ho" the Villagie Green project can meet the anticipated requirements. Flow Control The projected flow control standard tier this site will be Conservation Flow Control. In addition to this more restrictive tlow control standard. the 2009 klanual also requires application of flow control best management practices (BMPs)_ Flow control will be provided through the use of an existing combined detention; wetpond located in the northeastern corner of the Village Green Phase I parcel_ The combined onsite area is 13.047 acres_ The fully developed site conditions will have approximately 7.486 acres of impervious surface including the existing Phase I areas. The remainder of the site will be modeled as forest (retained significant trees), pasture and grass_ Landscaping will be in the form of grass, groundcover, shrubs and trees_ We anticipate the BMP requirements will be met through the use of infiltration, dispersal and permeable pavement_ The Full Dispersion and Full Infiltration BRfPs are not feasible due to till soil conditions. Limited Infiltration is proposed in the form of Gravel Filled Trenches_ Basic Dispersion is proposed in the forms of a Gravel Filled Dispersal Trenches w;/ Notch Board and Sheet Flow. Permeable Pavement is also proposed. In general these BMPs work to slow down runoff, recharge stormwater back into the ground as close as practical to where it falls and help reduce pollutants through settling. filtration and other processes. In addition to these environmental benefits.. BMPs help reduce the size of --end of the line" stonnwater storage and treatment facilities. The proposed impervious surface area that is required to be mitigated with BMPs, per the 2009 Manual Section 52.1.3 "Large Lot High Impervious", is at least 20% of the site/lot area or 40% of the target impervious surface, whichever is less. This equates to 37,955 SF of impervious area that must be drained to a Flow Control BMP either instead of or prior to draining to the detention pond. Refer to the Village Green Flow Control BMP Calculations on the following page_ With Conservation Flow Control and appropriate BMPs, preliminary calculations indicate that an additional 44,191 CF of storage volume is needed or approximately 1.42 times bigger than the existing pond. This can be achieved via the followrimi: 0.46' (5.52") depth increase via higher berms or a wall to protect existing mature vegetation rooted in berms, and increased pond coverage area near easternmost existing cottage via o" vertical pond walls_ We have shown the possible pond area change and proposed BMP locations on C 1. VILLAGE GREEN PHASE 0 d ID EX141P. IT-K.- 7/16/2009 JMK The site falls under the 2009 KCSWDM Section 5.2.1.3: Large Lot High Impervious BMP requirements. LOT D AREA LOT D IMPERVIOUS COVERAGE 189,774 sf 4.357 acres TOTAL VILLAGE GREEN SITE IMPERVIOUS COVERAGE 20% OF LOT D AREA 37,955 sf 40% OF LOT D IMPERVIOUS AREA 81% 57% 0.871 acres 61,713 sf 1.417 acres ` For projects that will result in an impervious surface coverage of more than 45% up to 65%, flow control BMPs must be applied to an impervious area equal to at least 20% of the site/lot area or 40% of the target impervious surface, whichever is less_ Application of Flow Control BMPs Limited infiltration Gravel Filled Infiltration Trench Back parking lot: 5 trenches @ 62.5 LF each yield East of bldgs I & J: 5 trenches @ 75 LF each yield Basic Dispersion 50' Gravel Filled Dispersal Trench wl Notch Board Bldg F: 3 trenches yield Bldg H: 2 trenches yield Bldg I: 1 trench yields Bldg 1: 1 trench @ 25 LF yields Sheet Flow 20' wide parking stalls into median, 1 /5 LF of sheet flow yields Permeable Pavement Permeable Pavers Back parking lot stalls only yield Other parking stalls separate from sheet flow stalls Total Impervious Area Mitigated by BMPs = 2,500 sf credit 5,000 sf credit 10,500 sf credit 7,000 sf credit 3,500 sf credit 1,750 sf credit 3,504 sf credit 3,727 sf credit 1,723 sf credit 39,203 sf credit > required area above (`) EXHIBIT �Ko PAGE `� GF `� Water Quality Currently the site is 1xithin an area of the City requiring the Resource Stream Protection Standard for stonn water quality treatment. This is anticipated to correspond to the Enhanced Basic Standard specified in the 2009 Manual. The exact implications of the Enhanced Basic Standard and how the requirements may be implemented through Federal Way's adoption of the 2009 Manual are still under consideration. Stormwater treatment is currently provided through a combined detentionlwet pond followed by a biofiltration swale_ The wet pond provides considerable treatment capacity- and meets at least the Basic Water Quality Standard. The Village Green project can meet the Resource Stream Protection and the Enhanced Basic Water Quality treatment criteria by using a StormFilter media treatment system. The existing detention/wet pond provides the required pre -settling function for use of the StomiFilter. The StormFilter can be installed in the location of the existing biofiltration Swale_ Preliminary StormFilter sizing worksheets and a cost estimate are included on the following pages. VIl1AGE GREEN PHASE Q & m r]f 19UaA U., EXHI S IT J��+�� WGEALOF. Determining Number of Cartridges for Systems STORMWATER g y soLUT�oNsINC. Downstream of Detention CONTECH Stormwater Solutions Inc. Engineer: KET Blue Cells = Input Date 9/29/2009 Black Cells = Calculation Site Information Project Name Village Green Project State Washington Project Location Federal Way Drainage Area, Ad 13.05 ac Impervious Area, Ai 6.39 ac Pervious Area, Ap 6.65 % Impervious 49% Runoff Coefficient, Rc 0.49 Upstream Detention System Peak release rate From detention, Qreleasepeak 1.70 cfs Treatment release rate from detention, Qrelease treat 0.42 cfs Detention pretreatment credit 60% (from removal efficiency calcs) Mass loading calculations Mean Annual Rainfall, P 38 in Agency required % removal 80% Percent Runoff Capture 90% Mean Annual Runoff,V, 795,397 ft' Event Mean Concentration of Pollutant, EMC 60 mg/I AnnuaLMass_Load, M,o,a, 2977.50 Ibs Filter System Filtration brand StormFilter Cartridge height 18 in Specific Flow Rate 1.0 gpm/ft2 Number of cartridges - mass loading Mass removed by pretreatment system, Mpre 1786.50 Ibs Mass load to filters after pretreatment, Mpassl 1191.00 Ibs Estimate the required filter efficiency, Erilter 0.50 Mass to be captured by filters, Mflter 595.50 Ibs Allowable Cartridge Flow rate, Qcan 7.50 Mass load per cartridge, Min (Ibs) 36.00 Ibs Number of Cartridges required, Nmass 17 Treatment Capacity 0.28 cfs Determine Critical Sizing Value Number of Cartridges using Qrelease [real, Nllow 26 Method to Use: HYDRAULIC SUMMARY reatment Flow Rate, cfs 04 artridge Flow Rate, gpm F 7 umber of Cartridges 'K EXHISIT-1 of1 FAGS 57 OFF �, ��I%►�TCAu CONSTRUCTION PRODUCTS INC_ Size a n d Cost Estimate Prepared by Kathryn Thomason on September 29, 2009 Village Green — Stormwater Treatment System Federal Way, WA Information provided: • Total contributing area = 13.047 acre • Impervious area = 6.394 acre • Detention release rate, Q1ed1 = 0.420 cfs • Presiding agency = City of Federal Way, WA Assumptions: • Media = ZPG cartridges • Cartridge Height = 18" • Per cartridge flow rate = 7.5 gpm • Drop required from inlet to outlet = 2.3' minimum Size and cost estimates: The StormFilter is a flow -based system, and therefore, is sized by calculating the peak water quality flow rate associated with the design storm_ However, when the StormFilter is placed downstream of detention the qow rate generated at the water quality storm is not always representative of the total volume of water that will go through the system or type of pollutant -loading the system may experience in one year - For this site, CONTECH Stormwater Solutions Inc. recommends using an 8'x16' StormFilter with 26 cartridges (see attached detail). The estimated cost of this system is $57,200, complete and delivered to the job site_ This estimate assumes that the vault is 6 feet deep_ The final system cost will depend on the actual depth of the unit and whether extras like doors rather than castings are specified. The contractor is responsible for setting the StormFilter and all external plumbing. Typically, precast StormFilters have internal bypass capacities of 1.8 cfs. If the peak discharge off the site is expected to exceed this rate, we recommend placing a high -flow bypass upstream of the StormFilter system. CONTECH Stormwater Solutions could provide our high -flow bypass, the StormGate, which provides a combination weir -orifice control structure to limit the flow to the StormFilter. The estimated cost of this structure is $4,000. The final cost would depend on the actual depth and size of the unit. @2008 CONTECH Construction Products Inc 11835 NE Glenn Widing Dr., Portland OR 97220 www contech-cpi.com Toll -free 800 548 4667 Fax: 800.561.1271 Page 1 of `j�� TS-P022 RAGE-0 O C x G Z c DUNCANSON Com.pauy; Inc. December 21, 2009 Ms_ Deb Barker City of Federal Way P.O. Box 9718 Federal Way, WA 99063-9718 Subject: Resubmittal of Village Green Phase fi File # 08-105555-UP Dear Deb: DC198430.I ES("E30TTED DEC 2 'GGq CITY OF FEDERAL W4y BUILDING DEPT. We have completed revisions of our plan and TIR addendum per your additional information request letter dated September 15, 2009 and the associated Lakehaven Utility District Memorandum dated August 26, 2009. Following are responses to each item included in these letters: DiduleC ii�uriw trit�isteering I. The applicants engineer shall determine how the project site will mee-1 the Enhanced Basic Water Quality treatment criteria This shall he determined prior to scheduling the Hearing Examiner meeting_ The Village Green project can meet the Enhanced Basic Water Quality treatment criteria by using a Storm Filter media treatment system. The existing detention/wetpond provides the required pre -settling function for use of the Storm.Filter system. preliminary sizing information is included in the enclosed revised TER Addendam. The Storm Filter can he installed in the location of the existing bio�iltration swale and is conceptually shown on revised plan sheet C1. 2. Add a legend for the different hatch patterns on Sheet Cl of the civil drawings_ A legend has been added to plan sheet C1 accordingly. 145 SW 155tb Street - Suite 102 - Seatde. Wasbington 98166 Pbone 206..244.4141 - Fax 206.244.4455 - Web wune.duncangonca.cone ICIVIL ENGINEEP.ING X 1EXHrm K PAGE Tq0F 416-- Ms_ Deb Barker 12/04 t09 Pa,2e Informational only: (a) Due to the proximity of the proposed pond retaining wall to the existing northeast cottage, the applicant shall provide documentation that excavation and construction of the pond retaining wall does not impact the 1-1 gone below- the footing for the existing cottage_ (bj At the time ofperrnit application for construction of the pond retaining walls, the applicant shall submit structural plans, details, calculations, and copies of the geotech report, along with a S2 500. 00 review deposit, to pay for third party review of the retaining wall_ The survey, geotech, structural and review requirements for future pond wall permitting and construction are noted. Lakehaven Refer to the O&Q6/09 Lakehaven memorandum and accompanying map. Nate that item #2 in the inamo states that there is an existing water main that dissects the property frotrt SW 336`h Sheet to the north that appears to be in coti- lict with Building F and relocation is required We have obtained new Water and Sewer Availability Certificates, enclosed. We are aware of the Building F conflict with the existing water main; the final configuration for relocating this water main will be determined in conjunction with Lalcehaveu prior to any conflicting construction. A note to this affect has been added to plan sheet Cf. Please give me a call if you have any questions or comments. Sincerely, Duncanson Company, Inc. Harold ❑uncanson President Enclosures EXHl�IT� PAGE}�Gr.�