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HomeMy WebLinkAboutFile Documents.320 N 7th St.0111-2021-BRES (13) 320 N. 7th Street-Variance Request May 3, 2021 Tricia Aragon, P.E. City of Aspen Engineer Aspen, CO 81611 Subject: 320 N. 7th Street Unit#2 Request for Variances from URMP SE Project No. 31016.01 Dear Mrs. Aragon, Per the requirements outlined within the City of Aspen's Urban Runoff Management Plan (URMP) this letter has been prepared to request a variance from providing water quality treatment for portions of the proposed impervious areas associated with the above referenced project. The City of Aspen's stormwater mitigation requirements are outlined within the Urban Runoff Management Plan, dated December 2014. This document states that any development that disturbs more than 1,000 square feet shall be classified as a "Major Design" project which requires water quality treatment for the disturbed and/or added impervious area. Due to site constraints the applicant is requesting a variance for providing water quality treatment for approximately 110 sf of proposed onsite impervious area as further outlined below and as identified on the civil building permit plan set: Driveway (88 sf): The proposed driveway comes off the alley and down towards the proposed garage addition. A trench drain is proposed at the bottom of the driveway however since the trench drain is below surrounding grades there is not an opportunity to route collected stormwater to either of the proposed rain gardens. Treating the driveway with permeable pavers was considered however given the proximity to the proposed garage addition an underdrain system would be required however the underdrain system would be too deep to connect into the proposed onsite drainage piping system. West Entrance Steps (17 sf): The steps leading down into the front west entryway will drain towards a proposed trench drain associated with the front porch. Given the elevation of the trench drain, in relationship to the surrounding area, collected runoff is unable to be directed to one of the proposed rain gardens. Instead, runoff will be conveyed directly to the City's storm system forgoing any opportunity for water quality treatment. South Patio (5 sf): There is a small portion of the south patio area that falls outside the limits of the existing southern gabled roof. Again, given some of the elevation challenges this impervious area cannot drain to a proposed rain garden and will therefore be collected in a trench drain and piped directly to the City's storm system without receiving water quality treatment. It should be noted that approximately 175 sf of existing gravel area located within the City's right-of-way will be removed and reclaimed as part of the improvements associated with this project. This reduction of impervious area is greater than the amount of impervious area being requested from water quality treatment. Furthermore, the proposed variance will not have any adverse impacts to downstream properties. 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704 E' 3', SOPRIS ENGINEERING • LLC civil coQap(tZa/2022 ASPEN BUILDING DEPARTMENT Thank you for your consideration with the above requested variance. Sincerely, Ittiv 4 787 s • • Sopris Engineering, LLC Jesse K. Swann, PE Encl: C-4: Water Quality Basin Plan 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 ED SOPRIS ENGINEERING • LLC civil consultants 05/23/2022 ASPEN BUILDING DEPARTMENT S OPRIS ENGINEERING,LLC. I CIVIL CONSULTANTS I I B cAN zsz BONDALE,C00 IB]e 3 )]oaaizz POST DEVELOPMENT DRAINAGE BASIN PEAK RUNOFF SUMMARY TABLE AK:,0)7050 0313 f 10•YR PEAK POST ONSITE BASINS 10•YR PEAK POST ONSITE BASINS P. BASIN Cy Tc Iy AREA Q. BASIN Csy Tc Ins AREA Qt■ LJ I.D. (min) (in/hr) (acres) (cf) I.D. (min) IlnPoE) (acres) Ids) c,'.'.�,H x ay',•:-e> \ Q BASIN 1 0.76 S.0 3.72 0.029 0.08 _ BASIN 1 0.84 5.0 6.32 0.029 0.16 : 4 787\1 \ BASIN 2 0.70 S.0 3.72 0.041 0.11 BASIN 2 0.8 5.0 6.32 0.041 0.21 _ _ _ _ _ _ _ BASIN 3 0.53 5.0 3.72 0.005 0.01 BASIN 3 0.7 5.0 6.32 0.005 0.02 \ rl r NOTE:THEHA CHED'OOFAREAFOR731W.F'•NCISWAS P P BASIN4 0.26 5.0 3.72 0.003 0.002 BASIN4 0.54 5.0 6.32 0.003 0.009 Sj ALg'A J9 INCLUDED IN THE WATER QUALITY DESIGN OF RG#2 r� BASIN 5 0.86 5.0 3.72 0.005 0.02 BASIN 5 0.89 5.0 6.32 0.005 0.03 £ 1 HOWEVER INSTALLATION OF GUTTERS,DOWNSPOUTS AND ' BASIN 6 0.86 5.0 3.72 0.0003 0.001 BASIN 6 0.89 5.0 6.32 0.0E03 0.002 ROUTING TO RG#21S OUTSIDE THE SCOPE OF THIS PROJECT :SH•LLB PR VID€DBYOTHERSINT E F URE FKESI' D / WATER QUALITY TREATMENT SUMMARY TABLE 731 W.FRANCA $I• WQ SUB-BASIN AREA IMPERV % WQCV REQUIRED FOOTPRINT DEPN PROVIDED i / . I.D. I.D. S.F. S.F. IMPERV (in) WQCV(d) I ) (hl WOCV kJ) DATE: 5-3-2021 _ RG 41 BASIN 1 1272 1135.2 WA Q21 223 70 0.33 23.1_ JOB NO. 31016.01 I'�' RG R2 BASIN2 1777 1424.5 80% Q17 252 200 0.17 33.d 1 ® , RG 43 BASIN3 2D4 119.5 59% 0.12 2.0 17 0.21 iliLi Al'�j,4I ��,I r od libilik \ EX.SHED ut-',-.=;=ss-'r_"-sue;.;; - ,;,,;'sr =z,_.,.;';,,s,s„y!n 729 W.FRANCIS STREET 4v4441T° LI \ A i w poi.IiCi 1. _ INLETS&TRENCHDRAINSUMMARYTABLE ��_ _ �m+Jr( t L'_ ERG #,- _;I �� INIFT CONTRIBUTNG Qsae CLOGG QwJ CIOGG OPEN AYAl1ABlf RKOMMFNDED .„„,p. INIEF / `�.���NA�.- -1 • _ 4iM �"' -- _ - ;' '�_ II 1.0. BASWS �. - \' III■ \ (CFS) FACTOR (CFS) AREA(Sf) NGD(IN) INLET GPACRY(CFSJ O H / ay �I 1-o���� II(� `'7 ' r^ -- ___ �� \ _ _ _ _ ORIFICE DESIGN(EQ.2) _ _- _ Q w // I.4� -J Iw,� {' 7 '"i I ' Y - - - --� RG fl BASIN 1 0.16 50% 0-31 0.23 2.0 Nyloplast 10'Standad Grate Q45 J c - •. III OOFT ?PLANTER-I ttQOF1.OP PLANTER I RG112 BASIN 1 0.21 50% 041 0.23 2.0 Nyloplast 10'Standard Grate Q45 CC a / �, 'iI. FLOWS FROM 6A8�D ROOF I AG BASIN 3 0.01 50% 0 Oi 0.03 2.0 NOS 4"Round Grate 0.05 WEIR DESIGN(EQ.31 w O 1- or �� ROUTED TO RG#2 ( J L u 2 ., ','O, , I/", ROOF DRAIN SCUPP Ft TO XI ``®�I I LENGTH ft -• CC CO O Z l%x/al DIRECT FLOWS TO RGn l^� - TRENCH RI BASIN 4 0.009 50% 0.017 11.50 0.01 Turn P4.11PP Grate / c 1 .S I TRENOIP2 BASINS 0.02B 50% 0.057 16.00 0.01 gum P658G Grate I , if �1 9 E �. II .I!!iii {------ TRENCH 43 BASIN 6 0.002 50% 0.004 11.50 0.02 Zum P4NPP Grateili; N V ' ip_ q .6.. ■ - �� ROOFTOP DECK / z C or v. / o C ■ 1 1 1 6 C ..1 r I 320 N.7TH STREET / N• d ow od yf ■ E : .LIP / z Q IP� a o� , lif �I . I-0 go BASIN 1 Z©© FLOWS FROM GABLED ROOF, O LL merit iir ©©4© � NOSED TRENCH l i r ROOFTOP DECK&FLAT ROOF OF I PROPOSED LEGEND EXISTING LEGEND m - I ©� 0© H DRAI C' i ADDITION ROUTED TO RG:1 O __ m "_ _ •.•LOOP ANOP r� a EXISTING 5-FTPROPERTYTBACKE e Y r �� p3 B.III PROPOSED CONCRETE -x- x EXISTING 5-FT SETBACK RQPFTDP3lA l-� :..�. 11 - EXISTING CONTOUR I 1 Y,. ; PROPOSED:u,NGARDEN „Do - E%ISTING CONTOURINTERVAL V • ��' +f--, a4' I /,'y' ' EXISTING 10 Ff SETBACK Jo Y Y y �,(/y B.•OPOSEDTRENCH Y r 'B.' t i 1 � a\C'�c y L '• �%/Ir/2 D AIN tt1 - PROPOSED CRUSHER FINES EXISTING ROCK WALLS / I r EX Mr LB y ��L. y � ^, E \ I �'��'�� E C EXISTING ELECTRIC METER l r y 5 i y i y y W y y y ry 1 I +, W" . "W + PROPOSED LANDSCAPING / I y { Cy ,.�( u / r1 ,� LI ■I��� J9 I m EXISTING TELEPHONE PEDESTAL ., R; _ Y . Y ` y - ; DG 1 '" y V © EXISTING CAN PEDESTAL // I i-4,y Y ■ r ` y , , , 54-1, y�y�/� WATER OUAUTY VARIANCE AREA 71 EXISTING STORM INLET 0. / I I ('\ ,`/ / W pan r 0 ,Y R y� - `/\`/",� / / \ -ma y yr a 7«DITI FLATR =rY )_ W y BASIN W ' I PROPOSED CONCRETE WALL EXISTING ASPHALT \ \ ,I 'I . / 1 UPPER LEVEL LANDSCAPE AREA ROUTED \ \ 1"I. / a i - ' I �+� TO PATIO TRENCH DRAT I j J I PROPOSED DRY STACK STONE WALL { E ���� EXISTING GRAVEL \ \ ' .+I r II / Y_ --f,.' :,k_ : }Ar- •/ P.. SCUPPER .• �� a4IIIIP �p m PROPOSED STORM PIPE "l� I yl' Yi yYr 1 /� �Y-r PROPOSED CONTOUR I A- ,■' . ^� '//, &CALI S' H Pno I I k I Y I. / Y� RI/,�yy OR COBRL 1•GRAD �s 4 III ]900- PROPOSED CONTOURINTERVAL L4L �SSSS3PROPOSEDSWALEI - _ (LOWER LEVEL) -{ B� r I (r L II i I B - PROPOSED TR N -- #3 ` ■BE � � � ■BE POST DEVELOPMENT DRAINAGE BASIN ,I ` I _ _ pRAIN p2 . \\ �' �� ��' HARDSCAPE 8 I \ 11 \ .y ,� ■ _ - IR• IMRPOVEMENTS&FLAT \ o` / - CANOPY ROOF ROUTED TO O il , 7 _,._i_ ..,,,....,. ., .... • .A E i''AAKL,A a tt V_ii4lm_Ae_i-P0z42r447i7Av4..,.0#.4-l.i-.6i.-1 \\; \ II// L :ASI 3 ` � , 1 a-lbI" l---.;.4,.„goia ..4.., mo\ DATE REVISION \\ \ III .�a `� \ _ . i.,� ik _rii _a_.r 4 4 'f.-_--g....* -"or Ap,.,i j r�. I / ��� 44* �� ioi.' (t •_., ot 41/ �.cl 1-'). '-III_ill �� i-AP. •� At I g0 z 3 2 i 1 Z TITLE k 8 110 WBASINPLANATER �'Iv ED GRAPHIC SCALE '' r n e Know what's below. DRAWINGO Call before you dig. O5/23/2022 (IN FEET) 2.1,BUSINESS DAYS IN ADVANCE3 1 inch=5 ft. fOfl PIE LARKING OF UNDERGROUND IMES ASP FN BUILDING DEPARTMENT