HomeMy WebLinkAboutFile Documents.533 W Hallam St.0058-2020-BCHO (9)
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GLENWOOD SPRINGS 118 West Sixth St, Suite 200 | Glenwood Springs, CO 81601 | 970.945.1004
Page | 1
October 13, 2020
Duncan Skihaus
533 W Hallam Street
Aspen, Colorado 81611
RE: Drainage Memo for Updated Tree Removal
Expansion of Pavers / Green Roof
This memo addresses Civil Engineering aspects of the proposed exterior remodel of the Duncan Skihaus
along W Hallam Street in the City of Aspen and is intended to meet the review requirements for the City
of Aspen Engineering Department. Through the workings of this project, Tree R, a Spruce was removed
from the site allowing an expansion of the pervious paver patio.
The removal of Tree R reduced the tree canopy credits and the expansion of the pervious paver patio also
reduced the grass/mulch buffer that was used to treat runoff from the residence. However, the pervious
paver patio is being utilized as a green roof since some of the pavers are over the substructure of the
basement. The green roof aspect of the patio is based off the grass strips between pavers and the growing
substrate of the grass consisting of partly sand mixture. This sand is intended to treat the runoff of silt,
sediment, and debris collected during a storm event.
After adjusting the WQCV calculations, it came to our attention that the originally prescribed composition
of sand in the substrate at 35% was too little for sub-basin 5. It is our recommendation that the sand
composition be of 50% for sub-basin 5 to provide the necessary water quality treatment. See the attached drainage drawings showing the adjusted tree canopy credits, grass/mulch buffer, and green roof space. Also attached are the updated water quality calculations for reference.
We hope this drainage memo is enough for the modifications to the major project for the development of
this site. Please feel free to contact us if we may provide further information or clarification.
Respectfully,
Rick L Barth, P.E.
Senior Engineer
Civil Services Sector
SGM
12/17/202012/22/2020
Reviewed by Engineering
01/21/2021 9:49:24 AM
"It should be known that this review shall not
relieve the applicant of their responsibility to
comply with the requirements of the City of
Aspen. The review and approval by the City is
offered only to assist the applicant's
understanding of the applicable Engineering
requirements." The issuance of a permit based
on construction documents and other data shall
not prevent the City of Aspen from requiring the
correction of errors in the construction
documents and other data.
Engineering 1 - 533 W Hallam - 0058.2020.BCHO
Page: [6] C3 Utility Plan
File Name: 0285.2018.ARBK_533 W HALLAM CIVIL.pdf Provide a drainage memo that
shows the WQCV is met with the
added impervious area and tree
removal. Per the paver detail
F-10 on sheet A801 of the
issued architectural plan set the
pavers are not pervious. The
grass buffer BMP seems to be
maxed out treating other
impervious area. An additional
tree is proposed to be removed.
This results in less tree canopy
credit for runoff treatment.
Update the tree credits with the
removal of the tree. Please show
the WQCV is met with required
BMPs.
0285.2018.ARBK_533 W HALLAM CIVIL.pdf (1)
Provide a drainage memo that shows the WQCV is met
with the added impervious area and tree removal. Per the
paver detail F-10 on sheet A801 of the issued architectural
plan set the pavers are not pervious. The grass buffer BMP
seems to be maxed out treating other impervious area. An
additional tree is proposed to be removed. This results inless tree canopy credit for runoff treatment. Update the tree
credits with the removal of the tree. Please show theWQCV is met with required BMPs.
WQCV is met with the
added impervious area.
The added pavers will be
counted as green roof as
a portion of them are
above the basement. The
sand composition was
revised to satisfy the
WQCV treatment for the
added area.
12/17/202012/22/2020
Input
Calculation
Sub Basin Basin
Name Total Area Imp.
Area
Imperv-
iousness
Req'd WQCV
(depth)
Req'd WQCV
(vol.)Decid. Area Conif. Area
Green Roof
Area
Green Roof
Substrate
Sand
Grass Buffer
Area
No Inf.
Paver Area
No Inf. Paver
Depth
No Inf.
Paver Void
Vol.
Green Roof
Volume
Rain
Garden
Vol.
Perv.
Paver
Ratio
Grass
Buffer
Ratio
Canopy
Credit
Grass Buffer
Credit
Eff. Imp.
Area
Eff. Imperv-
iousness
Eff. WQCV
(depth)
Net
WQCV
(vol.)
(#)(sq. ft.)(sq. ft.)(%)(in)(cu. ft.)(sq. ft.)(sq. ft.)(sq. ft.)(%)(sq. ft.)(sq. ft.)(ft)(cu. ft.)(cu. ft.)(cu. ft.)(sq. ft.)(sq. ft.)(sq. ft.)(%)(in)(cu. ft.)
1 A 684 254 37%0.0761 4.33 309.09 0.00 0 0.35 0 0.0 0.00 0.0 6.50 6.50 2 1 46.4 0 207 30.3%0.0651 -2.79
2 A 672 234 35%0.0724 4.05 0.00 478.30 0 0.35 150 0.0 0.00 0.0 0.00 0.00 2 1 143.5 150 -60 -8.9%0.0000 0.00
3 B 1262 970 77%0.161 16.93 75.06 0.00 0 0.35 0 126.5 0.50 21.1 0.00 0.00 2 1 11.3 0 959 76%0.1582 -4.44
4 C 796 539 68%0.135 8.97 108.60 345.77 350 0.35 200 0.0 0.00 0.0 5.02 0.00 2 1 120.0 200 219 28%0.0605 -1.00
5 D 1312 882 67%0.134 14.65 857.63 0.00 320 0.49 404 0.0 0.00 0.0 6.46 0.00 2 1 128.6 404 349 27%0.0591 0.00
6 B 442 327 74%0.152 5.60 0.00 0.00 0 0.35 0 112.2 0.50 18.7 0.00 0.00 2 1 0.0 0 327 74%0.1522 -13.10
7 B 834 624 75%0.155 10.76 29.23 0.00 0 0.35 0 39.8 0.50 6.6 0.00 0.00 2 1 4.4 0 620 74%0.1533 4.01
Total 6000 3830 64%0.9 65.3 1379.6 824.1 670 0.37 754.0 278.5 1.5 46.4 18.0 6.5 454.2 754 2621.5 43%0.65 -17.3
Basin
Name Total Area Imp.
Area
% Imperv-
iousness
Req'd WQCV
(depth)
Req. WQCV
(vol.)Decid. Area Conif. Area
Green Roof
Area
Green Roof
Substrate
Sand
Grass Buffer
Area
No Inf. Perv.
Paver Area
No Inf. Paver
Depth
No Inf.
Paver Void
Vol.
Green Roof
Volume
Rain
Garden
Vol.
Perv.
Paver
Ratio
Grass
Buffer
Ratio
Canopy Area
Credit
Gras Buffer
Area Credit
Eff.
Imperv.
Area
Eff. Imperv-
iousness
Net WQCV
Depth (in)
Net
WQCV
(cu. ft.)
Available
WQCV
(cu. ft.)
1,2 A 1356 488 36%0.074 8.39 309 478 0 0.35 150 0.00 0.00 0.00 0.00 6.50 2 1 190 150.0 148 10.9%0.030 -3.1 11.5
3,6,7 B 2537 1921 76%0.157 33.27 104 0 0 0.35 0 278.5 0.50 46.4 0.0 0.00 2 1 15.6 0.0 1905 75%0.156 -13.5 46.8
4 C 796 539 68%0.135 8.97 109 346 350 0.35 200 0.00 0.00 0.00 5.02 0.00 2 1 120.0 200.0 219 28%0.061 -1.0 10.0
5 D 1312 882 67%0.134 14.65 858 0 320 0.35 404 0.00 0.00 0.00 4.58 0.00 2 1 129 404.0 349 27%0.059 1.9 12.8
6000 3830 64%0.5 65 1380 824 670 0.35 754 278 0.5 46.4 9.6 6.5 454 754 2621 35%0.31 -15.8 81.1
Basin WQCV Calculations Duncan
Legend
12/17/202012/22/2020
7 (B)
834 10.76
Sub-basin (Basin)
Area WQCV
sqft cuft
5 (D)
1312 14.65
6 (B)
442 5.60
3 (B)
1262 16.93
2 (A)
672 4.05
1 (A)
684 4.33
4 (C)
796 8.97
Title:
Basins & WQCV
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Job No.
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Date:
File:
PE:QC:
2018-292.001
JAK
09.17.2020
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APPENDIX
A 2Of :
Graphic Scale
In Feet: 1" = 10'
0 5 10 20
12/17/202012/22/2020
7 (B)
834 10.76
Sub-basin (Basin)
Area WQCV
sqft cuft
5 (D)
1312 14.65
6 (B)
442 5.60
3 (B)
1262 16.93
2 (A)
672 4.05
1 (A)
684 4.33
4 (C)
796 8.97
Title:
Tree Canopy Credit
Re
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Dwg No.
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Date:
File:
PE:QC:
2018-292.001
JAK
09.17.2020
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APPENDIX
B 2Of :
Graphic Scale
In Feet: 1" = 10'
0 5 10 20
12/17/202012/22/2020