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HomeMy WebLinkAboutDrainage Reports - 06/01/2012TST 760 Whalers Way Bldg C, Suite 200 Fort Collins, CCI 80525 970.226.0557 main 303.595.9103 metro 970226.0204 fax ideas@tstinc.com vn Asffnc.com TST, INC. CONSULTING ENGINEERS City of Ft.:Collins prov Plans Approved By. May 16, 2012 Date Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80521 RE: Seven Lakes PUD Phase 11 Subdivision —Amended Site Plan (OCR Site) Supplemental Drainage Report PIN 0978.0010.00 Dear Wes: Please find included in this revised letter report a supplemental drainage analysis for the amended site plan for the Orthopedic Center of the Rockies (OCR) site. The amended site plan includes an addition to the exisfing building to allow additional exam rooms and administrative space, and an expansion of the parking lot in the northwest portion of the site. This report has been updated to include the information required for the Floodplain Use Permit. This supplemental report evaluates the drainage components for the proposed changes to the existing parking lot area and drainage facilities. Documents reviewed include the Final Drainage Report for the Seven Lakes PUD Phase II Subdivision, dated January 5, 1989; prepared by Stewart & Associates, Inc. Excerpts from that report are included here for reference. Floodplain This site lies within the FEMA 100-yr Spring Creek Floodplain as shown on the FIRM (Flood Insurance Rate Map), Panel 0983H, Map Number 08069C0983H, map revised May 2, 2012. A copy of the FIRMette is included within this report. The existing building and proposed building expansion finished floor elevations are above the base flood elevation by a minimum of 0.50'. The base flood elevation along the western edge of the building is 4901.02 and the finished floor elevation of the existing building and proposed building addition is 4901.86. An exhibit showing the base flood elevation interpolation is included in this report. Building Addition The proposed building addition is for additional exam rooms, administrative areas and the expansion of the physical therapy area. The foundation construction will consist of slab on grade construction and the elevation will match the finished floor elevation of the existing building of 4901.86. The finished floor elevation (lowest floor elevation) is above the regulatory flood protection elevation of 4901.52 and in compliance with Chapter 10 of the City Code. The table below summarizes the finished floor elevation and associated flood elevations. Description NGVD 29 NAVD 88 Proposed Finished Floor Elevation 4901.86 4904.86 FEMA 8FE at upstream end of structure 4901.02 4904.02 Regulatory Flood Protection Elevation 4901.52 4904.52 Lowest Floor Elevation 4901.86 4904.86 HVAC Equipment 4909.86 4912.86 OCR Supplemental Drainage Report Page 1 A Floodplain Use Permit will be submitted at the time of the building permit application and a FEMA Elevation Certificate shall be completed and approved prior to the certificate of occupancy is issued for the building addition. Existing Drainage Patterns Existing basin 1 is 3.35 acres and includes the western portion of the existing parking lot and OCR building. Stormwater runoff in this basin basically sheds from the OCR roof to the west, and then to the northeast via overland flow and across the parking lot. Runoff is intercepted in two 5' type R inlets located on the eastern edge of the existing parking lot. Runoff that is not taken into the inlets overtops the sidewalk and flows toward the wetand channel in existing basin 3. (The existing basin 1 is comprised of proposed basins 1, 1.1 and 1.2.) Existing basin 3 includes the wetland channel along the northern property line and a small portion of the OCR building on its northern side. This basin is 1.10 acres. Runoff from this basin sheds from the roof and overland flow on the north side of the OCR building into the wetland channel that drains to the east. (Proposed basin 3 is a small portion at the very upstream stretch of existing basin 3.) The existing basins are illustrated on the Drainage Plan prepared by Stewart & Associates that is included with this report. Proposed Drainage Patterns The proposed parking lot addition, shown in proposed basins 1.1 and 1.2 will redirect the drainage pattern in the existing basin 1. Proposed basin 1.2 redirects stornwater runoff toward the north to a proposed rain garden. The amount of developed runoff in the 100-yr storm directed into the rain garden is 4.97 cfs. This runoff is intended to infiltrate in the rain garden. However, there is a weir overflow at the east end of the rain garden to accept and direct runoff toward the existing 8" storm pipe and wetland channel in basin 3. Runoff that does not infiltrate at the rain garden will follow the existing drainage patterns and into the wetland channel. Proposed basin 1.1 is still directing runoff toward the existing parking lot and storm inlets. The amount of area now draining to the existing lot is reduced by 0.48 acres. The amount of developed runoff (attenuated flow from basins 1 and 1.1) at design point 1 is 21.9 cfs for the 100-yr storm. This is an overall reduction of 1.4 cfs in this basin, as -the existing basin 1 generated 23.3 cfs for the 100-yr storm (according to Stewart & Associates calculations). Inlets There is an existing type 13 inlet located at the western side of basin 1, and two existing 5' type R inlets located in basin 1 on the eastern edge of the existing parking lot. These inlets intercept a portion of the minor storm, while the remaining runoff flows to the east and north in the parking lot and overtops the sidewalk to follow existing drainage patterns and spill into the wetland channel located north of the building. As stated earlier, the proposed condition reduces the amount of runoff toward these inlets slightly; however, runoff will still overtop the sidewalk at design point 1. The amount of runoff anticipated to be intercepted in each of the type R inlets is 4.9 cfs in the 100-yr condition. Since this area is within the 1O0-yr floodplain, the amount of runoff that will overtop the curb and sidewalk at design point 1 was not calculated at this time. Storm Sewer There is an existing 8" diameter storm pipe located below the sidewalk at design point 3. This storm pipe accepts approximately 1.73 cfs. Additional runoff in this area overtops the pipe and sidewalk. Rain Garden The proposed rain garden provided at the north end of the new parking lot is intended to accept stormwater runoff for infiltration into the granular sub -base and to provide the water quality capture volume (WQCV) sufficiently sized for the basin draining to it. An emergency overflow weir will be provided at the east end of the rain garden to allow for overtopping directed toward the wetland channel in the event that infiltration in the rain garden fails. The tributary area for the rain garden is 100% impervious and approximately 21,000 sq. ft. Thus the required WQCV for a 12-hour OCR Supplemental Drainage Report Page 2 drain time is 700 cu. ft. The provided rain garden size exceeds the requirement and is approximately 1258 cu. ft. in volume. The base elevation of the rain garden is 4899.25 and the top elevation is 4900.25. A detail of the rain garden is provided in the construction drawing plan set. A Subsurface Exploration and soil percolation evaluation was completed by Earth Engineering Consultants, Inc. (EEC) for the rain garden concept and the results of this evaluation have been included,in this report. The overflow weir elevation is also set at elevation 4900.25. The width of the weir is 5' with a crest length of 3'. The weir calculations show that this size of weir will sufficiently pass the 100-yr developed flow from basin 1.2 of 4.97 cfs to the downstream channel. Summary The stormwater runoff from the amended site plan at OCR has met the design requirements set forth by the City of Fort Collins and has incorporated water quality measures prior to the runoff entering the existing wetland channel, thus achieving betterstonnwater quality than existed prior to the building and parking lot additions. Please refer to supporting exhibits, calculations and the proposed drainage plan included in this report. TST, INC. CONSULTING ENGINEERS Sincerely, 016��4 Heather McDowell, P.E. Cc: Mr. Brian Varella, CFC Utilities ha ene A. Sh6deowZen, P.E. OCR Supplemental Drainage Report Page 3 '' �CITYOF FORT�COLLINS� r a, ,�€� , a�x080102� 4E AH 9e' MAP SCALE 1"=500' .Y' $ 9' $)IEL49D41 ppp 60 0 500 1 FEEi METE ,„'y�' b��o- '•04 ra ¢.'P;. r+i fD in) "R > u91°°°°iN "Am 'lot �, .� v /� �A 4 1 � � r �331 -� y �x*msbsa[f` r° o �a SQIv!S_ "ZONE AE C p G+ ZONEAE EAST PRowEcr ROAD FLOODING EF L0487 r xfL">'. CACHE LA POI i �..� Spring Creek 20 P C 1 PROSPECT PARKL TION>-' ZONE AE ZONE AE S R �( MIDPDINT OR/YE 4900 NUALCHANCE D DISCHARGE USED IN CULVERT TY.Mm[Atl�[©'a.P.[ua>n..md�wd.[.e.om m.P. k ' WpPYRgnUn. llW mpp[YMryIM CIy�N.. d xmNnae• MI[tl m.y Nd [� mM.ib.WdO bb. WI. m b. Etl. tlmk. Fd1N 1Y..IdWe[IlbmNpn.pTX NWafY FqM IWI�PY. PiadBn.wl m.P cMck Iln FEM4 floaO M.p $IM.1 wvA'.m.c.Mn.. pn' - rAntL uuwn FIRM FLOOD INSURANCE RATE MAP LARIMER COUNTY, m COLORADO m I AND INCORPORATED AREAS PANEL W70F WD I a 19E! MM INpE. iCq FqM PNEL UYITJII I 0 fONMIN� MltIODI VREI SIIF&Y w[uum/wacmd Wd w x ® . of ,,...,........w..w. rAPxurRER m I ao�cweR+ YAP REV64ED MArzmu Pedenl F:me[gnq MuugdnevlAgivq E N X i YY� i 1 ♦� II- �1 SCAU: r - my � 1 y i R. la7TI17TRi — 1 nVI PE ti � - --- 1 EXHIBIT BFE DETERMINATION SEVEN LAKES PUD PHASE II AMENDED PLAN m ftO ''. Bmg. C SWI9 m Fw CeRr, COIwaEo OCR BUILDING ADDITION Plw 9)9.]Z9.9997 M\919\W19v1L99PVM 115E PPA191v109wP m O!lIC890 r m \ M r�Atsx`, I I I I I X DRAINAGE PLAN ssvex vx¢ ruo vxnu n sumnnox - ur[xomsirtnuxlansnEl w-c-wiw�v �fY — 11pa® MM nwwv NO® 4Y1M -- Deno sor ce. — riw om�or I Li eru cia ® ��rnsc �.•e nor.. ro. nr�t Nr eo �e n. menm re. ie. mmioao nr.�. x:Ve�eoWHeinwx�.a.o U U g m m o m y U o 0 0 c v a U 0 O N m 7 U O G C C a w aQ N O r N r m f0 O N QU o c c o m lL U N o w e r r w n n E 00 o c o 0 0 U U c V O YI O h O N O h O U 0 c U N pp�J d Q v d 0 3 0 ti o m o a c w g y y o o Q v K v m K m J J J J U o m a m Q J (n ✓ � m N W W N m m U O G =�f /\E 0> f/z //« !;a■� (J !y}§f\ \ k�' C U O C ^ m ^ N w R Y _ R O U ^ N r D✓ R p� O U i N N �D OHO N O ^ Y R N r a c m e w e N m } m m a ,-.o ma aim c Z � 0 _m^ n e < a c m R Y m m m o N N N N N C d E T r �n inn U O � O o� A R C T � hYfW $ o C ^ O U `om F F N N R C W Q1 T m Ot O t0 O ai0 U r m o R C R o N m o J T r r 4-1 1A �O O ^ Q C � P T On r w N R O O O O LL N R N O yy C N O O m ^NO00 R 6] C ^ M ^ N m W W G m o. c 0 ®l c c o m U m c a' y C U � @ 5 o a n1th WgksllNt PTalecte0 DESIGN PEAK FLOW FOR ONE-HALF OF STREET BY THE RATIONAL METHOD Proled: OCR We ID: etlsBTlp - wutMm type R ITIM DeaIgn Flow• Gutter Flow+ GnTo FNw r OVERL1 S1 I0VERIp y FLOVPN0 Y I + RE SIWET ♦ I ♦ FLWMI (GUTTER FLOW RUS CNRRY-OVER FLOW ♦GUTTER FLOW $Opv Owama INLET INLET _ _I/2 STREET — 0c,.1MRllow WF lR d aMal plw M.Y bM.ibIl upMam auOUMlmanb): •G• T.3 31.8 cia FILL IN THIS SECTION •N anbntla.1. Mn aRIP lM Wald tMa aNNlantl roeNtl bRMatOA9pw R... aopnp a orma r m w FILL IN THE SECTIONS SUMa .MMa.L'11'���a 7P'..t�-'_' BELOW. PwwnlWpaniauwaa •L.�J` — NRC5561Tkpa•— Bib Tyln: SWIw (IW4 wq%N Owl•ntl ® SRe k UWn M. • O 9v k IbMIhM Gutlw M. Daalyn SWnn RFWm PWW. UN.-0 ,R tl Stml RUMR Coen peen IN. blank Wa i Utar-DefinE ti-w. Rube Coe id.m Mm tlIM Nan, b.0 a BypaM (Gmy-0varl Fbw Inm uWtnam Total Daaipn PMk Flow, O - 13 Y RTa I In I woo Qioo. ()PI UD-Mbt_WS OlZealpn Point tale, G?aek 2111¢012, 12:17 PM Wc 11 ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm) 11 Project: OCR Inlet ID: existing - southern type R inlet �`—Tn.oi_ YCROW sx —Y T. r,,.T y d Allowable Width for Spread Behind Curb f Behind Curb (leave blank for no conveyance credit behind curb) Roughness Behind Curb of Curb a; Gutter Flaw Line :e from Curb Face to Steel Crown Transverse Slope Longitudinal Slope - Enter 0 for sump condition 1g a Roughness for Street Section T_Tacx= 160 fl c ` 0.020 n. vart. / n, hertz nOxCR' 0,020 Nano= 6.00 inch.. Tcsown ` 58.0 ft a = 2.00 In W = 2.00 fl Sx = 0 U20 fl. vart. / n. hertz So. 0 005 It vart. / It horiz namEET =1 0,018 Minor Stonn Major Storm Max. Allowable Water Spread for Minor B Major Storm T. 752 162 fl Warning 02 Max. Allowable Depth at Gutter Flow Lane for Minor B Major Storm d. = 12.0 12.0 inches Allow Flow Depth at Street Crown (leave dank for no) Li Li check = yes Minor Storm Major Storm Max. Allowable Outhr CaRacitsrBased on Minimum of Q, or Q, Q.. - 6.1 8.1 of$ WARNING: MINOR STORM max. allowable capacity is leas than now given on shast'Q-Peak' Warning 02: Minor Storm Is Overtopping the Curb. UD-Inlet_v301-Design Point 1.xls, O-Allow 2/172012. 12:17 PM INLET IN A SUMP OR SAG LOCATION Inle�s Project • OCR Inlet to / aaiapng wulnam lyq R Inlet ,_._. �� KVerl wP u(c) ip MAN Inlet Tyq I Demotion (a00inonelbro".. pi bpn.Ye,n'/Intent 'O-AbM) ems' iparelUMlNeN tor., ar LUN Openiq) Meg D"th eu,i0e a taW Dwnwian alhap i OpT e Inhunnstinn - 0 of a Unit Grets hale Unn Ora, W. Ogbng Rut. is• Grab n iulymu O.1SO.W) A—• phq FW for a Shp, Gnb(ryumal vale 0.30-o.W) Q(G) s WACoaeidmt gYPlvl wlua 2.15400) 4 (G) e Oi commit (typical new 0.60- 0.60) C. (G) � OgnNp Infeme,lien N G • UMI Cbb Opening L. (C) - MpV.Nu1CUTOgXphl An N,.a• MpCUN� T,aphlnpAsa Nr• e NTlrwl (we USOCM Flyun aT5) TMb Mi far Depnasbn Pan(WMg3y he gutter vA01F of 2 Na0 I a lip Faifer a Si Cut OpeNnp (typical value, 0,10) c,(c) OpeNp Werr coel00er, natal vane 2.3 6) 4(c) OgnNO OMn C.6 M(Ovlul vpu. 0.50-030) C.(c)• II Inlet Interception Capacity (assurnas clogged condition) O.r W.m,p 3: Otpyn, hi 1. net In the....n&d W. I., Met net. a neUI1M. CpOTTrolit hOeemp 3.00 linclue, 1 1 a0 I so Joni MINOR MAJOR NIA N/A lee, fee WA WA WA WA WA WA N/A N/A WA N/A MINOR Abi 500 Sao e00 6.00 6.00 600 63.e0 1 2.OD 2W 0.10 150 3.60 067 0.57 M nabs nines mpere. Np UD-In v3 01-0ami Pohl l.ti Man In Sump 2/1)2012, 12:11 PM 61tc s INLET IN A SUMP OR SAG LOCATION proles • OCR Inlw ID existing-noMein type R Won at D..lgn Pclnt,t� f 1� H{up MVm \1 WIG) )emn. (.tlG00nel Wwbenuou. g.M-wpnwbn'i horn'O-Aaery) N.10na NMla(G -Curb Opening) Mp6� o W itle a laY Oeprwvon M INM w.nnetian Op.nNp Ra0o I -a Gr.W (lypk.l whro. 0.154 90) lisp F. We 9ryM G.W (pgiwl valw OW -W v Camffic'am(typl-Al vale 2.15-3.60) O0ha Cwlhci.nl(MM+Iv 0W-0.e0) a. Wit ad, op.rmg mvwcvC n,opwftnI . acemO n.Fl-Nw A .W(.w OSDCMFipun ST-5) W%t-D.p wn P.n It Ope W. guX-'wWlb a 2 W.Q g Fa=r l-a Single Cum CpwWg (lyGiwl v.hW 0.10) wnhp WW CwMd.n1(typkal wle 2.S3 6) penhp Gnaw Gw6rJea (Wand wue 0 W -GT0) Inlet Intemop0on Capacity (assume Clogged condition) Wamirp J: Cbp0in91aa-W na In iM.ecomnvMa6 wlw I- Wn ryw apwYaY. L.(G)- W.. AW• T.(G) C. (G)• 0.(G)• MINOR MAIOR COOT Type R Cum Op , J.W 300 1 6o Co WRnR W R NIA WA NIA WA WA WA WA WA WA NIA WA N!A nch . eel wl N UD-Inlet 0 01-0eaign Pain 2.Ms, Inlet In Sump 2/1712012. 12:19 PM :1 a' Storm P1PC/ Ex. 8" Pipe Calculation at DP 3 PTiect'Description Friction Method Manning Formula ' Solve For Full Flow Capacity Input Data _J Roughness Coefficient 0.013 Channel Slope 0.02000 ft/ft Normal Depth 0.67 ft Diameter 0.67 ft Discharge 1.73 fN/s Resu[tsr Discharge 1.73 fV/s Normal Depth Flow Area 0.67 0.35 ft ft= -basin 1.2 Wetted Perimeter 2.10 It Top Width 0.00 it Critical Depth 0.60 it Percent Full 100.0 % Critical Slope 0.01759 fVft Velocity 4.91 ft/s Velocity Head 0.37 It Specific Energy 1.04 ft Froude Number 0.00 Maximum Discharge 1.86 ft'/s Discharge Full 1.73 ft•/s Slope Full 0.02000 fVft Flow Type SubCrilical GVF InputData Downstream Depth 0.00 it Length 0.00 It Number Of Steps 0 'GVF'Output Data _.... - _ _ Upstream Depth 0.00 It .Profile Description Profile Headloss 0.00 It Average End Depth Over Rise 0.00 % Normal Depth Over Rise 100.00 % Bentley Systems, Inc. Haested Methods Solution Center Bentley FlowMaster [08.01.071.00] 2/17/2012 12:12:53 PM 27 Siemens Company Drive Suite 200 W Watertown, CT 06795 USA +1.203.756.1666 Page 1 of 2 Rain 6ar4en Design Procedure Form: Rain Garden(RG) Shoat I of 2 - Designer. HEM Company: TST Date: February 16, 2012 project OCR Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, 1. 1. = 100.0 % (100% 9 a0 paved mtl =led areas upstream of rain garden) B) Tdbdary Area's Impervloua a ss Ratio (I - U100) I = 1.000 C) Water Quality Capture Volume(WQCV)for a l2-hour Drain Time WQCV= 0.40 watershed inches (WQCV=0.8' (0.91' i- 1.19 - IR- 0.78 - R D) ConmLuling Watershed! Area (Including rain garden area) Area = 21.000 sq If E) Walter Quality Capture Volume (WQCV) Design Volume t 1 yer V 1i -e� LI D I Vol - (WQGV / 12) - Ana F F) For Watersheds OulsMe of the Denier Region, Depth of Q = N Average Runoff producing Storm G) For Watersheds Outside of me Denver Region, V. arks = 0.0 cu R { Water Quality Capture Volume (WQCV) Design Volume p H) User Input of Water Quality Capture Volume (WQCV)Design Volume Vwocivass= cuR (Only d a different WQCV Design Volume Is deWmd) 2. Basin Geometry A) WQCV Depth (12-Inchmaximum) 0.. 12 N 1 B) Rain Garden Side Slopes (Z - 4 min., hods- list per unit vertical) Z = 3.00 R / R Z <4:1 (Use -0- 0 rain garden has vertical walla) 11 C) Mimimum Flat Surface Area 3 Aa„ _ 487 eq R D) Actual Fla] Surface Area A, - 903 sq R ry E) Area M Design Depth (Top Surface Area) Arm = 1813 sq It I F) Rain Garden Total Vdume V i 238 Y (VT=((Arm' A....) 12)' Depth) 1 1 3. Growing Media Qnoos, One IV Rain Garden Gmvsng Dealer 1 O Other (E�laln): 4. Underdmin System A) Are un h rdrans provided? Choose One O yF5 (A)NO B) Underdmin system orifice diameter for 121our drain time ) Distance From Lowest Elevation of the Storage y= N/A A Volume to the Center of the Orifice e) Volume to Drain In 12 Hours Vdrr - WA cu R Ili) Orifice Diameter, 318' Minimum De - N/A In '9 Copy of UD-BMP_v3_01.xis, RG 2116/2012, 4:37 PM ill Weir Calculation at DP 2 Project Description^ . .. - _ll Solve For Discharge lnput,Data - Headwater Elevation Crest Elevation Taiwater Elevation Crest Surface Type Gravel Crest Breadth Crest Length Re'sUjis� Discharge Headwater Height Above Crest Taitwater Height Above Crest Weir Coefficient Submergence Factor Adjusted Weir Coefficient Flow Area Velocity Wetted Perimeter Top Width 4900.75 ft 4900.25 It 4899.36 ft 3.00 ft 5.00 ft . C,522 T/�:D 0.50 ft -0.89 ft 2.96 US 1.00 2.96 US 2.50 It- 2.09 ft/s 6.00 It 5.00 ft Bonney Systems, Inc. Hassled Methods Solution Center Bentley FlowMaster [08.01.071.001 2117/2012 12:15:24 PM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1.203.755-1666 Page 1 of 11 ggrwl Channel A -A Calculation Friction Method Manning Formula Solve For Normal Depth - Roughness Coefficient 0.060 Channel Slope 0.90000 ft/ft Left Side Slope 4-06 nlft (H:V) Right Side Slope. 4.00 ft/ft (H:V) Bottom Width 8.00 It - Discharge 28.10 ft-Is -- I Normal Depth Flow Area Wetted Perimeter 2.86 r 10.55 ft' It `vl Top Width 10.47 it (� t G(A•�' G`�IJ I �1, Critical Depth Critical Slope 0.65 0.06626 ft Rift �� \ 111 Velocity 9.83 ft/s G Velocity Head 1.50 It Specific Energy 1.81 ft Froude Number 3.32 Flow Type Supercritical GVFI pUV%ta,f Upstream Depth 0.00 ft Length 0.00 It Number Of Steps 0 GVF Output Data Downstream Depth 0.00 ft Profile Description Profile Headloss 0.0o ft Downstream Velocity Infinity file Upstream Velocity Infinity ft/s Normal Depth 0.31 It Critical Depth 0.65 ft Channel Slope 0.90000 Nft Critical Slope 0.06626 Nft ' Bentley Systems, Inc. Haestad Methods Solution Center Bentley FlowMaster (08.01.071.061 2 I612012 4:42:31 PM 27 Siemens Company Drive Suite 200 W Watertown, CT 06795 USA N-203-755-1666 Page 1 of 1 we+ect _Scx✓LL dCG��I/D_ n,... t' w.e—�s(eJ IB As/+/.1L AReA '6,33 A, C-086 'I- i Qhyp= 0. 85u dRO% L.=3 'De+! Qioyz'= 0.6SX�32 ,Pe.. Qlooyq= 633+0. Es%S4 4�33= 3YA c.r'L iI1 1 I �BASJh. .. DFl. Q/4p�v.. /. ['.SX().dSK/.);10 Q./$�./l. I. H'nsiu .]Y AIeAC.oaa .. 'Tc= h57 (I. I-0. 3)sao'h ZS!•.�I. t '06 d. D6v. Q/oyq 0.31 Dcv. Qiaey�/.zSX0.3)r./G'r'1.::.=.0.%7c./(. 0 No Text April 5, 2012 EARTH ENGINEERING CONSULTANTS, Irac. Gateway Medical Services c/o Mr. Michael Bergerson 2500 East Prospect Road Fort Collins, Colorado 80525 Attn: Mr. Michael Bergerson (tuber eg rson(c�orthohealth.com) Re: Subsurface Exploration —Addendum Report Proposed Rain Garden Concept Adjacent to Pavement Area Improvements Orthopaedic Center of the Rockies 2500 East Prospect Road Fort Collins, Colorado EEC Project No. 1122002 Mr. Bergerson: Enclosed, herewith, are the results of the supplemental subsurface exploration/soil percolation evaluation completed by Earth Engineering Consultants, Inc. (EEC) personnel for the rain garden concept planned along the north side of the proposed on -site pavement improvement area, (please refer to the enclosed site diagrams) at the Orthopaedic Center of Rockies (OCR) facility at 2500 East Prospect Road in Fort Collins, Colorado. For this phase of the project three (3) soil percolation borings were located and drilled within the proposed rain garden concept as shown on the enclosed site diagram, created from civil drawings provided to us by TST, Inc. —Consulting Engineers. This supplemental study was completed in general accordance with our electronic proposal dated March 27, 2012. EXPLORATION AND TESTING PROCEDURES The supplemental rain garden/soil percolation borings were located in the field by representatives of Earth Engineering Consultants, Inc. (EEC) by pacing and/or estimating locations relative to identifiable site features. The approximate boring locations are indicated on the attached boring location diagram. The locations of the borings should be considered accurate only to the degree implied by the methods used to make the field measurements. 4396 GREENFIELD DRIVE WINDSOR, COLORADO 80550 (970) 545-3908 FAX (970) 663-0282 www.earth-engineering.com F�nh Engineering Consultants, Inc. EEC Project No. 1122002 April 5, 2012 Page 2 The borings were completed using a truck mounted, CME-45 drill rig equipped with a hydraulic head employed in drilling and sampling operations. For this study, as shown on the enclosed site diagram, soil percolation borings P-1 and P-3 were extended to depths of approximately 5-feet below existing site grades, while soil percolation boring P-2 was extended to a depth of approximately 8-feet below site grades. Upon completion of the drilling operations, the borings were filled with water, saturated for an approximate 24-hours period and in -situ infiltration/soil percolation characteristics were performed the following day at each boring location. SUBSURFACE CONDITIONS In summary, a sparse vegetated/topsoil layer was encountered at the surface of each soil percolation boring and was underlain by a zone of cohesive sandy lean clay subsoils, which was either fill of native overburden material. The cohesive zone extended to the native granular subsoils below, which were encountered at an approximate depth of 4- feet below existing site grades. The native granular fine to course silty sand with gravel and intermittent cobbles extended to the depths explored in the soil percolation borings, approximately 5 to 8-feet below site grades. Groundwater was encountered within the deeper profile boring P-2 at an approximate depth of 5-feet below site grades during the initial drilling operations. The subsurface conditions encountered within the rain garden/soil percolation borings were very similar/consistent with those described in our "Subsurface Exploration Report" completed for the site on January 17, 2012, EEC Project No. 1122002. ANALYSIS AND RECOMMENDATIONS We understand a rain garden concept is planned along the north side of the proposed on - site improvement parking area as shown herein as part of the storm water run- off/drainage plan. Based on our review of the rain garden design concepts prepared by TST, Inc. - Consulting Engineers, the existing grade in the general vicinity of the proposed rain garden is between approximate elevations 4900 to 4902. The bottom of the proposed rain garden, as shown herein will be at an approximate elevation of 4899.25. It appears as part of the rain garden concept the upper 18-inches will consist of a sand/peat Earth Engineering Consultants, Inc. EEC Project No. 1122002 April 5, 2012 Page 3 mixture of approximately 25% ASTM C33 concrete sand and approximately 75% peat mix. We also understand the current rain garden concept does not have an underdrain system or outlet structure designed. In essence the proposed rain garden concept as currently planned is a simple rain garden that will infiltrate into the underlying subsoils with no underdrain system and will have an overflow weir without an outlet structure. The review comments from the City of Fort Collins' Stormwater Department indicated the following: "The City requires underdrains and the standard urban drainage outlet structure for rain gardens/bioretention ponds. If soil sampling shows A or B soils and a high percolation rate, underdrains can be omitted from the design. " For this project, we conducted a series of three (3) soil percolation tests at approximate depths of near surface grades to about 4-feet below grades at boring locations P-1 and P- 3, and from about 3-feet to about 8-fet below site grades at the boring P-2 locations. Again, based on our review of the rain garden concepts it appears the majority of cohesive materials would be removed to establish the design grades, which would also include the upper 18-inches being replaced with a sand/peat mixture. Soil percolation testing within the proposed location of the rain garden, conducted for a period of approximately 70 minutes after an initial "24-hour soaking period", is summarized below, and a spreadsheet is also included.with this report. Percolation Test Results Test Hole Depth (feet) Soil Classification Percolation Rate (minutes/inch) P-1 4 Sandy Lean Clay transitioning toward Sand with Gravel 16 P-2 8 Silty Sand with Gravel 4 P-2 4 Sandy Lean Clay transitioning toward Sand with Gravel 22 Based on the soil percolation rates presented herein for the underlying fine to course granular subsoils, (i.e., in essence less than 5 minutes per inch), the relatively shallow depth to the groundwater table in this area, which is approximately 5-feet below site grades, and the understanding that the majority of the upper cohesive subsoils will be Ennh Enswocnag Conmhann, Inc. EEC Project No. 1122002 April 5, 2012 Page 4 removed, it is our opinion an underdrain system along with an outlet structure would not be necessary for the proposed rain garden planned as part of the site improvements at the referenced site. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we can be of further service to you in any other way, please do not hesitate to contact us. Very truly yours, onsultants, Inc. David A. Richer, P.E. Senior Geotechnical Engineer cc: Wm. T. Welch LLC — Mr. Will Welch: wwelch(a),wmtwelch.com TST, Inc. — Ms. Sharlene Shadowen, P.E.:sshadowen(a)tstinc.com The Neenan Company - Mr. Bill Pigg: bill.pie¢na,neenan.com Mr. Jake Courts iake.coutts(o)neenan.com Mr. Bob Mooney: bob.moonev(a,neenan.com Legend .D Approximate Locations for 3 Sdi Percolation Borings xenn w r ar. y� pAMO Bona c '� RCORR /casmc m¢ wv - o.'°�.10m°Damumw n :mi w y1y umn ' I t ✓ten rC� r t1M3 i;r, ` I __-_-___-EMI Boring Location Diagram Orthopaedic Center of the Rockies - Proposed Addition Fort Collins, Colorado EEC Project #: 1122002 Date: March 2012 FARTN FNrINFFRINr.. MMU 11 TANT A - BOTTOM OF POND 4899.25 — VERTICAL & GUTTER CONCRETE PAN 2' CURB — OPENING PAVEMENT TRANSITION INTO A V—SHAPED CONCRETE RUNDOWN INTO A SECTTON AT BOTTOM THAT HAS 3—INCH RIVER ROCK INBEDDED 1.5—INCHES INTO THE CONCRETE. POND WATER SURFACE 4900.25 + J^ r OVERFLOW WIER 1 TURF REINFORCEMENT MAT xIS PROPEX GEOSYNTHETTCS LANDLOK 450 OR EQUAL 24" CURB CUT TO BE INSTALLED PER W/ V—SHAPED VERTICAL CURB MANUFACTURER'S CONCRETE & GUTTER SPECIFICATIONS. RUNDOWN ELEV. 4899.75 PLAN VIEW DRYLAND GRASSES AND WILD FLOWERS SEEDED IN ACCORDANCE WITH SECT. 5.6 OF VOL 3. DO NOT USE SOD. REFER TO LANDSCAPE PLAN FOR PLANTINGS & LANDSCAPING iB" SAND/PEAT LAYER 25% ASTM C-33 SAND 75% PEAT MIX ALL SIDE SLOPES 2:1 OR FLATTER WRAP ALL GEOTEXTTLE FABRIC AND IMPERMEABLE UNERS TO TOP OF SOIL ATTACH ALL LINERS FIRMLY TO WALLS OR TRENCH SIDES. OVERFLOW Woven geotextile fabric meeting: ASTM D4751—AOS US Std. Sieve #50 to f70, ASTM D4633 min. trapezoidal tear strength 100 x 60 Ibs, Minimum COE specified open area of 4% SECTION " Orthopaedic Center of The Rockies .2500 East Prospect Road - Fort Collins, Colorado EEC Project No. 1122002 Soil Boring No. Depth of Boring, Ft. Zone of Soil Percolation, Range in ft. Time Difference in Tlme, Minutes Inches Measured Difference in Inches between readings, Minutes Soil Percolation Rate, Minutes/inch P 1 3.5 0.0-5.0 0:00 17,375 0:10 10 18.375 1 10.00 0:20 10 19.125 0.75 13.33 0:30 10 19.75 0.625 16.00 0:40 10 20.375 0.625 16.00 0:50 10 21.0625 0.6875 14.55 1:00 30 21.5 0.4375 22.86 1:10 10 22 0.5 20.00 Average Soil Percolation Rate minutes/inch 36.11 P-2 10 3.0-8.0 0:01 34.625 0:11 10 47.5 12.875 0.78 0:21 10 50.25 2.75 3.64 0:31 10 51 0.75 13.33 Refill 30.75 0:41 SO 44 13.25 0.75 0:51 10 49.75 5.75 1.74 1:01 10 51 7 1.43 1.11 30 52.5 1.5 6.67 Average Soil Percolation Rate minutes/inch 445 P-3 3.5 aD-5.0 0:02 26.625 -- 0:12 30 27.25 0.625 16.00 0:22 10 27.75 0.5 20.00 0:32 10 28.25 0.5 20.00 0:42 10 28.75 0.5 20.00 0:52 10 29.125 0.375 26.67 102 10 29.5 0.375 26.67 1:12 10 29.875 0.375 26.67 AwragaSoll Percolation Rate minutes/Inch 22.29 Legend __ 1`B-1 thm B-0: Approximate '' Locations for 4 Foundation Q46- ---- ---- --- Related Borings --�' T` - - t_ 0 B-5 S BL Approximate t -- o Locations for 2 Pavement Related Borings Proposed Boring Location Diagram Orthopaedic Center of the Rockies Fort Collins, Colorado Hon Date: December 2011 ri_i?iff INC ORTHOPAEDIC CENTER OF THE ROCKIES EXPANSION FORT COLLINS, COLORADO PROJECT NO: 1122002 DATE: JANUARY 2012 LOG OF BORING B.6 RIG TYPE: CME46 SHEET 1 OF 1 WATER DEPTH FOREMAN: DG START DATE 111=12 WHILE DRILLING 7.0' AUGER TYPE: P CFA FINISH DATE 1112121112 AFTER DRILLING WA SPT HAMMER: MANUAL SURFACE ELEV NIA 24HOUR NIA SOIL DESCRIPTION 0Iou MIC oo ALNITS .0 SWELL LL PI PRESSURE % at so PSF TYPE (FEET) (PSF) Sit IPCFI 1%1 APPARENT FILL MATERIAL 1 Sandy Lean Clay (CL) I Clayey Sand (SC) _ _ dark brown, mast varying amounts of gravel 2 memum so _ _ x lm P.r 12.4 122.E ease Pay, 4.6% CB 39000* 4 ss 6 B 22 13A SILTY SAND entb GRAVEL(SMSW) bmwn, grey moiel to wet 7 medium dense to dense 6 'Inlermiaent COBBLES with Indmeeetl dea61 9 FSS 10 11 34 13.1 BOTTOM OF BORING DEPTH 10.5' 12 13 14 16 1E 17 16 19 20 21 22 23 24 7a Earth Engineering Consultants ORTHOPAEDIC CENTER OF THE ROCKIES EXPANSION FORT COLLINS, COLORADO PROJECT NO: 1122002 DATE: JANUARY 2012 LOG OF BORING S-6 RIG TYPE: CME45 SHEET 1 OF 1 WATER DEPTH FOREMAN: OG START DATE 1/12/2012 WHILE DRILLING It AUGER TYPE: 4" CFA FINISH DATE IN22012 AFTER DRILLING NIA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA SOIL DESCRIPTION 0 a W MC OD A -LIMITS -200 SWELL LL Pi PRESSURE % 6 $ad PSF TYPE IFEETI (BLOWSs'T1 IPSFI M) IPCFI 1%1 APPARENT FILL MATERIAL. 1 Sandy Lean Clay (Q) I Clayey Sand (SC) dark drown, mina. varying amounts o/ gravel 2 medium atiff _ _ 50 9.9 132.0 1100 1.6% CS 3 4 SS 6 6 12 4000 27.6 SILTY SAND with GRAVEL(SM-SW) bmwn, grey moist to wet, i medium dense to dense 8 SS 10 11 10 14.1 BOTTOM OF BORING DEPTH 10 5 12 13 14 15 16 12 18 19 20 21 22 23 24 25 Earth Engineering Consultants