HomeMy WebLinkAboutFile Documents.COACH RD.0079.2018 (10).ARBK1
Drainage Report
BAR X RESIDENCE
110, 112 COACH ROAD
ASPEN, CO
Comment Response: 12/4/2018
Prepared by
Danny Stewart, P.E.
Roaring Fork Engineering
592 Highway 133
Carbondale, CO 81623
02/14/2019
Reviewed by Engineering
02/26/2019 5:26:04 PM
"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.
2
Drainage Report
BAR X RESIDENCE
110, 112 COACH ROAD
ASPEN, CO
I HEREBY AFFIRM THAT THIS REPORT FOR THE IMPROVEMENTS AT DOUBLE BAR X RANCH, LOT 7
WAS PREPARED BY ME FOR THE OWNERS THEREOF IN ACCORDANCE WITH THE PROVISIONS OF THE
CITY OF ASPEN (COA) URBAN RUNOFF MANAGEMENT PLAN (URMP) AND APPROVED
VARIANCES AND EXCEPTIONS LISTED THERETO. I UNDERSTAND THAT IT IS THE POLICY OF THE
CITY OF ASPEN THAT THE CITY OF ASPEN DOES NOT AND WILL NOT ASSUME LIABILITY FOR
DRAINAGE FACILITIES DESIGNED BY OTHERS.
DANNY STEWART, P.E.
RFE Project # 2017-30
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Contents
1.0 General .................................................................................................................................................... 4
1.1 Existing Site ......................................................................................................................................... 4
1.2 Proposed Conditions ........................................................................................................................... 4
1.3 Previous Drainage Studies .................................................................................................................. 4
1.4 Offsite Drainage & Constraints ........................................................................................................... 5
2.0 Drainage Basins ...................................................................................................................................... 5
2.1 Basin 1 ................................................................................................................................................. 5
2.2 Basin 2 ................................................................................................................................................. 5
2.3 Peak Discharge Calculations ................................................................................................................ 5
3.0 Low Impact Site Design .......................................................................................................................... 7
3.1 Principles ............................................................................................................................................. 7
4.0 Hydrological Criteria .............................................................................................................................. 9
4.1 Storm Recurrence and Rainfall ........................................................................................................... 9
4.2 Storage Volumes Methodology .......................................................................................................... 9
5.0 Hydraulic Criteria ................................................................................................................................... 9
5.1 Piping ................................................................................................................................................... 9
5.2 Inlet Sizing ......................................................................................................................................... 10
6.0 Proposed Facilities ................................................................................................................................ 11
6.1 Proposed Structures.......................................................................................................................... 11
7.0 Operation and Maintenance .................................................................................................................. 11
7.1 Drywell .............................................................................................................................................. 11
8.0 Appendices ............................................................................................................................................ 12
Drawings 11x17 ....................................................................................................................................... 12
FEMA FIRM Map ..................................................................................................................................... 12
Sopris Engineering Survey ....................................................................................................................... 12
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1.0 General
1.1 Existing Site
The site is located at Lot 7 within the Double Bar X Ranch of Aspen, Colorado. The address is 110 and
112 Coach Road. The site is currently a 155,641 square foot (sf) green field site with native vegetation of
sage brush and evergreens. There is a flat bench on the east side of the property that provides access to the
storm and sewer lines crossing the property. There are a couple paths that lead down to Maroon Creek
from this bench. Aspen trees are also scattered around the property. There are no ditches onsite. Coach
Road occupies the western portion of the lot. Storm drainage and sewer easements cross the lot and
border the east edge of the property. East of the property the grade drops down to Maroon Creek.
Conservation easements also occupy the western half of the property and the eastern side from the top of
bank to the Creek.
HP Geotech performed a field exploration on May 14, 2009. A sub-surface soils report was produced on
May 22, 2009. The soil profile consists of one to two feet of topsoil overlaying clayey silty sandy gravel
with cobbles and boulders. About two feet of gravelly fill was encountered above the topsoil in one area.
No ground water was encountered during the investigation. A percolation test was performed on February
23, 2018. Results from the percolation test was 5 minutes per inch. This is suitable for infiltration. Table
3.1 of the URMP indicates this is Soil Type A. The NRCS web soil survey indicates that the Soil is Type
B.
The property is on the upper banks of Maroon Creek within the un shaded Zone-X of the FEMA FIRM
map. The map is attached within the appendix.
1.2 Proposed Conditions
This project is classified as a ‘Major Project’ in Table 1.1 of the Urban Runoff Management Plan
(URMP), as the proposed development is over 1000 square feet and disturbs an area greater than 25% of
the site. The intent of this report is to demonstrate compliance with the requirements of the City of Aspen
(COA) URMP. The Low Impact Design (LID) Principles in the introduction of the manual were used as a
guide throughout the design process.
The proposed development involves the construction of a new main residence and an accompanying
detached dwelling. Grading around the new structure will take place to accommodate the driveway, new
walkways, lawn area and patios. No changes to land use or soil types are planned. Cut depths of up to 25
feet will be made for the foundation excavation. Site grading cuts and fills are much less compared to the
foundation excavation.
The runoff from impervious surfaces will be collected in a system of roof drains, inlets and slot drains,
which will convey runoff to drywells. The drywells are sized for the WQCV of their tributary basin.
Overflow will be dispersed via rip rap before sheet flowing toward Maroon Creek.
A foundation drain system will collect runoff that seeps into the ground from around the building
foundation and will be piped to a drywell located just north of the structure.
1.3 Previous Drainage Studies
This property is located within the Maroon Creek Drainage Basin. The property is not within any
mudflow areas as defined by the COA Storm Drainage Master Plan. There is no master drainage plan for
the sub-division but there is a storm system running along the east side of the property that conveys
runoff from Stage Coach Rd. to Maroon Creek.
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1.4 Offsite Drainage & Constraints
We are unable to tie into this system due to a top of bank setback where disturbance is not allowed. This
storm drain has an accompanying drainage easement that leads toward Maroon Creek. The development’s
storm water overflows will discharge directly to Maroon Creek without impacting any downstream
properties. The URMP states that only WQCV is required if this is achievable.
The topography of the site slopes from the west down to the east toward Maroon Creek. Stage Coach Rd.
to the south and south west captures the drainage originating from the pastures and directs it into the road
side swale leading to the existing storm drain. All disturbance and drainage basins being mitigated
originate within the property boundaries.
2.0 Drainage Basins
There are two major basins with two separate points of concentration proposed for the onsite drainage
system. Both points of concentration are drywells. These major basins were established to calculate the
retention requirements. These Major basins were broken up into sub-basins for hydraulic calculation and
the sizing of piping and inlets.
2.1 Basin 1
Basin 1 is comprised of the gravel driveway, fire truck turn around, auto court and the south east portion
of the structures roof. This basin has an area of 22,240 sf, with 10,429 sf of that being impervious. This
area also includes the area surrounding the driveway that drains into the swales running along either side
of the driveway. These two swales lead to two separate inlets that are piped to the north drywell. Roof
drainage is collected and routed to a down spout that is also piped to the north drywell. The auto court
area is graded away from the structure to inlets set in depressions that are also piped to the north drywell.
2.2 Basin 2
Basin 2 is 14,209 sf with 3,026 sf of impervious area. It is made up of the area between Coach Rd. and
the structure, the detached dwelling, and a portion of the main structure’s eastern roof. An interceptor
drain will capture surface runoff from above the auto court wall while inlets downspouts and swales will
collect the rest of the uphill area and convey it to the south drywell. A down spout from the main structure
conveys a portion of roof drainage to the south drywell as-well.
Below is a summary of the basins and their areas.
2.3 Peak Discharge Calculations
Peak flows were calculated for 5-year and 100-year storm events. Rainfall intensity was calculated using
the Time of Concentrations (To) for each basin. The Over Land Flow Time Equation 3-4 of the URMP
𝑇 ൌ0.395ሺ1.1 െ 𝐶ሻඥ𝐿
𝑆 .ଷଷ
Onsite Basin Data Entry
Basin # Total Area Impervious Area Impervious
(ft2)(ft2)%
1 22240 10429 46.89%
2 14209 3026 21.30%
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was used to calculate the To for each major basin. The To calculations are shown below for the 5-year and
100-year storm events.
The 1-hour Rainfall depth (P1), given in Table 2.2 as 0.64 inches for the 5-year event and 1.23 inches for
the 100-year event. Equation 2.1 was referenced when solving for the rainfall intensity (I).
I = 88.8P1/(10+To )1.052
The Runoff coefficients (C), a function of the hydrologic soil group in this case Soil Group B and the
percentage of impervious area within each sub-basin, were developed using Figure 3.3. The runoff
coefficient was then multiplied by the rainfall intensity (I) and the acreage of each major basin (A) to
determine the peak discharge for the Major Basin. Q allowable was calculated the same way, except the
basin was treated as undeveloped, or 100% pervious. The Peak Discharge (Qp) in cubic feet per second
lcfs) is given by equation 3.1 of the URMP.
Qp= CIA
Qp= Peak Discharge (cfs)
A= Area (acres)
I= Rainfall intensity (inches per hour)
C= Runoff Coefficient (unitless)
The tables below contain the peak flows for developed and undeveloped conditions for 5-year and 100-
year storm events.
5yr ‐ Time of Concentration ‐ Basin 1
Overland Flow Time (To)
Top Elevation 7797 ft.
Bottom Elevation 7781 ft.
Over Land Distance (Lo)213 ft.
Slope (So)0.075 ft./ft.
Runoff Coefficient, C 0.33 5‐yr
Overland Flow Time (To)10.43 Min.
5yr ‐ Time of Concentration ‐ Basin 2
Overland Flow Time (To)
Top Elevation 7797 ft.
Bottom Elevation 7787 ft.
Over Land Distance (Lo)175 ft.
Slope (So)0.057 ft./ft.
Runoff Coefficient, C 0.2
5‐yr
Overland Flow Time (To)12.09 Min.
100‐yr Time of Concentration ‐ Basin 1
Overland Flow Time (To)
Top Elevation 7797 ft.
Bottom Elevation 7781 ft.
Over Land Distance (Lo)213 ft.
Slope (So)0.075 ft./ft.
Runoff Coefficient, C 0.51 100‐yr
Overland Flow Time (To)7.99 Min.
100‐yr Time of Concentration ‐ Basin 2
Overland Flow Time (To)
Top Elevation 7797 ft.
Bottom Elevation 7787 ft.
Over Land Distance (Lo)175 ft.
Slope (So)0.057 ft./ft.
Runoff Coefficient, C 0.45
100‐yr
Overland Flow Time (To)8.73 Min.
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3.0 Low Impact Site Design
3.1 Principles
Principle 1: Consider storm water quality needs early in the design process.
The grading and drainage design was coordinated with the architects early in the design. Comments from
the City, architects and planners were considered and analyzed. Multiple site visits ensured proper
understanding of existing conditions.
Principle 2: Use the entire site when planning for storm water quality treatment.
Given the restrictive top of bank setbacks coupled with the conservation easements and vegetation, there
was limited area for storm water mitigation. All areas surrounding the proposed development were
5 Year Peak Discharge Developed Calculations
1 Hour(P1)0.64
Return Period 5
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 22240.13 10428.83 46.89% 0.330 10.43 2.38 0.40
2 14208.64 3026.37 21.30% 0.200 12.1 2.19 0.14
5 Year Peak Discharge Pre Development Calculations
1 Hour(P1)0.64
Return Period 5
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 22240 0.00 0.00% 0.080 10.43 2.38 0.10
2 14209 0.00 0.00% 0.080 12.1 2.19 0.06
100 Year Peak Discharge Developed Calculations
1 Hour(P1)1.23
Return Period 100
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 22240.13 10428.83 46.89% 0.510 8.0 5.22 1.36
2 14208.64 3026.37 21.30% 0.450 8.7 5.01 0.73
100 Year Peak Discharge Pre Development Calculations
1 Hour(P1)1.23
Return Period 100
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 22240 0.00 0.00% 0.350 8.0 5.22 0.93
2 14209 0.00 0.00% 0.350 8.7 5.01 0.57
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investigated to determine the best place for storm infrastructure. BMPS were placed in areas where
disturbance to existing trees could be limited.
Principle 3: Avoid unnecessary impervious area.
There is no unnecessary impervious area as all areas are either roof or facilitate pedestrian or vehicular
traffic.
Principle 4: Reduce runoff rates and volumes to more closely to match natural conditions.
All runoff from impervious surfaces will be initially collected and retained, reducing peak concentrated
discharges. Dispersion rip rap will be placed at overflows to return the flow to a more natural sheet flow
to eliminate channeling and erosion.
Principle 5: Integrate storm water quality management and flood control.
All inlets and piping are sized to accommodate the 100-year peak flows. Pipes were sized to ensure
100-year flows do not exceed 80% of the pipe capacity. Flow paths are directed away from the structure
so large events don’t present a problem.
Principle 6: Develop storm water quality facilities that enhance the site, the community and the
environment.
Inlets have 6-inch sumps to help trap sediment. All runoff from impervious surfaces are routed to one of
two drywells reducing any stress on the surrounding areas. Given the property’s proximity to Maroon
Creek and the good percolation rates, runoff from the property will have no impact on any downstream
neighbors.
Principle 7: Use treatment train approach.
Many impervious surfaces discharge into lawn or landscaped areas before inlets collect and convey the
runoff to the BMPs. Inlets are also equipped with six-inch-deep sumps to help trap any debris or sediment
before entering the BMPs.
Principle 8: Design sustainable facilities that can be safely maintained.
Inlets and piping will be vacuumed or flushed periodically to maintain adequate flow. Proper grading
reduces dangerous slopes and proper drainage reduces ice buildup. Drywells will have two chambers with
perforated snout wrapped in filter fabric. The filter fabric can easily be replaced prolonging the life of the
perforations within the lower chamber of the drywell. All facilities are easily accessible and are installed
with cleanouts when applicable.
Principle 9: Design and maintain facilities with public safety in mind.
Walkways and the auto court will be snowmelted to provide a dry surface for foot and vehicle traffic.
Grading was also done in such a way as to not develop hazardous slopes in walking areas.
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4.0 Hydrological Criteria
4.1 Storm Recurrence and Rainfall
The 5-year and 100-year 24-hour rainfall events were analyzed due to the property’s location. No City
storm infrastructure is within the area and the site cannot discharge into a City storm system. Basins one
and two are able to over flow into the lawn and disperse through the surrounding vegetated areas before
flowing directly down to Maroon Creek.
4.2 Storage Volumes Methodology
Here are the storage calculations for Basins 1 and 2. The required WQCV is multiplied by a factor of
safety (F.O.S.) of 1.5 because drywells are being utilized as the BMPs.
5.0 Hydraulic Criteria
5.1 Piping
Pipes used in all drainage systems will be standard dimension ratio (SDR) 35 PVC with a Manning’s
coefficient (n) of 0.01. The pipes were sized to accommodate peak flows for a 100-year event at 80%
full. If the water level in the pipe exceeds the 80% full criteria, then the pipe is deemed inadequate. Sub-
basins where delineated to isolate specific peak flows being directed to individual pipes and inlets. Below
is a table of sub-basin peak flows.
Water Quality Capture Volume Storage
Basin Total Area Impervious Area Impervious WQCV Table Value WQCV Storage F.O.S. Required Storage BMP
(#) (ft
2)(ft2) (%) (in) (ft
3)(ft3)
1 22240 10429 46.89% 0.089 164.9 1.5 247.4 North Drywell
2 14209 3026 21.30% 0.048 56.8 1.5 85.3 South Drywell
100 Year Sub Basin Peak Discharge Developed Calculations
1 Hour(P1)1.23
Return Period 100
Sub Basin Total Area Imp. Area Impervious C Value Time of C Intensity Sub Basin Flow Rate
(Name)At (ft2)Ai (ft2)Ai/At (%) From Table (Td)I=88.8P1/(10+Td)01.052 Qsub (ft3/sec)
1.1 3150 0 0.00% 0.350 5 6.33 0.16
1.2 11395 4933 43.29% 0.500 5 6.33 0.83
1.3 1570 1570 100.00% 0.950 5 6.33 0.22
1.4 896 658 73.42% 0.620 5 6.33 0.08
1.5 5229 3268 62.50% 0.570 5 6.33 0.43
2.1 419 419 100.00% 0.950 5 6.33 0.06
2.2 11345 641 5.65% 0.380 5 6.33 0.63
2.3 1072 1072 100.00% 0.950 5 6.33 0.15
2.4 713 448 62.79% 0.570 5 6.33 0.06
2.5 208 102 49.01% 0.510 5 6.33 0.02
2.6 452 345 76.28% 0.650 5 6.33 0.04
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Separate systems were established to convey storm water to the two points of concentration. Below is a
table showing which sub-basins contribute runoff to each pipe and the total flow (Q) accumulated during
a 100-year peak flow event.
Calculated pipe sizes were tested for hydraulic capacity at 80%. Values for depth of flow for each pipe
were calculated. Design charts giving Q design / Q full were downloaded from Federal Highway
Administration (FHWA) and the equations in Section 4.8.4 of the URMP were used as the basis for these
calculations. Calculated pipe sizes and internal depth of flow within the pipes are shown below.
5.2 Inlet Sizing
Inlets were sized to accommodate the 100-year peak flow conditions for each basin. Equations 4-17
through 4-20 were used to size inlets, which incorporate a 50% clogging factor (Cg) and a 40% opening in
grates (m). A water depth of 0.25 feet was assumed and all the inlets were treated as sumps as they will
be set a minimum of 0.25 feet below the flow lines. The inlets are set in swales or depressed areas to
facilitate this. The slot drain in front of the garage is an auxiliary drain to prevent runoff from flowing
completely across the auto court. Inlets set in landscaping will be circular. Below are the sump
calculations for circular inlets.
Storm System Pipes
POC Pipe Contibuting Sub‐Basins Design Flow Rate
Qdes
N1 1.1 0.16
N2 1.2 0.83
N3 1.3 0.22
N4 1.1‐1.4 1.28
N5 1.5 0.43
WALL DRAIN CONNECTION 2.2 0.63
SOUTH DOWNSPOUT 2.3 0.15
S1 2.1‐2.3 0.83
S2 2.4 0.06
S3 2.1‐2.5 0.91
S4 2.1‐2.5 0.91
S5 2.1‐2.6 0.95
North Drywell
South Drywell
Pipe Design Flow
Rate
Proposed Pipe
Diameter Slope 80% of Proposed
Pipe Diameter
Manning
Coefficient
Full Pipe Cross
Sectional Area Full Pipe Flow Rate Q Design /
Q Full d/D Hydraulic Grade Line
(Depth of Flow)
Depth of Flow Less Than
80% of Pipe Diameter
Qdes (ft3/sec) Dpro(in) S (%) Dpro*.8 (in) n A (ft) = π (Dpro/2)2 Qfull (ft3/s) = A(1.49/n)((Dpro/48)2/3)S1/2 Qdes/Qfull (from Chart) d (in) = (d/D)*Dpro (Yes/No)
N1 0.16 4.0 6.66% 3.2 0.01 0.087 0.640 0.25 0.38 1.52 Yes
N2 0.83 6.0 2.89% 4.8 0.01 0.196 1.243 0.67 0.66 3.96 Yes
N3 0.22 6.0 1.72% 4.8 0.01 0.196 0.959 0.23 0.37 2.19 Yes
N4 1.28 8.0 2.00% 6.4 0.01 0.349 2.226 0.58 0.62 4.92 Yes
N5 0.43 6.0 2.00% 4.8 0.01 0.196 1.034 0.42 0.50 3.00 Yes
WALL DRAIN CONNECTION 0.63 6.0 2.00% 4.8 0.01 0.196 1.034 0.61 0.63 3.78 Yes
SOUTH DOWNSPOUT 0.15 6.0 1.00% 4.8 0.01 0.196 0.731 0.20 0.35 2.10 Yes
S1 0.83 6.0 32.38% 4.8 0.01 0.196 4.160 0.20 0.34 2.01 Yes
S2 0.06 6.0 26.23% 4.8 0.01 0.196 3.744 0.02 0.08 0.48 Yes
S3 0.91 6.0 26.23% 4.8 0.01 0.196 3.744 0.24 0.37 2.19 Yes
S4 0.91 6.0 3.00% 4.8 0.01 0.196 1.266 0.72 0.69 4.14 Yes
S5 0.95 6.0 3.00% 4.8 0.01 0.196 1.266 0.75 0.70 4.22 Yes
Hydraulic Grade Line and Pipe Capacity
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6.0 Proposed Facilities
6.1 Proposed Structures
There are two drywells proposed. They are sized to capture the WQCV. Over flows will be dispersed via
rip rap into the surrounding vegetated areas.
The North Drywell is sized for the WQCV for Basin 1. The South Drywell is sized for the WQCV for
Basin 2. If these drywells are to overflow through the grated lids, rip rap will disperse overflows. The
percolation rate is 5 minutes per inch so this soil is desirable for infiltration and drywells are acceptable.
Roof area will be collected via roof drains that will then be internally piped through the structure.
Hardscape will be graded away from the structure toward landscaping where the inlets are placed. The
BMPs were designed and confirmed to be adequately sized for the required storage volumes.
Drywell volumes were calculated using the geometric equations shown in the spreadsheet below. The 18”
thick layer of screened rock surrounding the drywells was also taken into account. The North Drywell is
five feet in diameter and ten feet deep while the South Drywell is four feet in dimeter and ten feet deep.
Both drywells have a four-foot perforated section.
The infiltration capacities of each drywell were also tested. Given the drywell dimensions, the amount of
perforated area and the soil percolation rate, the 24-hour infiltration volume can be derived.
7.0 Operation and Maintenance
7.1 Drywell
Drywells must be inspected and maintained quarterly to remove sediment and debris that has washed into
them. A maintenance plan shall be submitted to the City in the Drainage Report describing the
Sub Basin and Circular Inlet Calculations
1 Hour(P1)1.23 m=40% Ys=.33 (Head on inlet 4")
Return Period 100 Cg=50% Co=0.65
Inlet ID Basin ID Total Area Imp. Area Impervious C Value Concentration Intensity Q Max Inlet Type Diameter Area(EQ. 4‐20) Inlet Capacity (EQ 4‐19) Has Capacity
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 ft3/sec Wo (inches) Ae=(1‐Cg)mA Q=CoAe√2gYs (Yes/No)
INLET‐N1 1.1 3150 0 0.00% 0.350 5 6.33 0.160 8" Round 8 0.070 0.209 Yes
INLET‐N2 1.2 11395 4933 43.29% 0.500 5 6.33 0.827 18" Round 18 0.353 1.059 Yes
INLET‐N3 1.4 896 658 73.42% 0.620 5 6.33 0.081 8" Round 8 0.070 0.209 Yes
NORTH DRYWELL 1.5 5229 3268 62.50% 0.570 5 6.33 0.433 24" Round 24 0.628 1.882 Yes
INLET‐S1 2.4 713 448 62.79% 0.570 5 6.33 0.059 8" Round 8 0.070 0.209 Yes
INLET‐S2 2.5 208 102 49.01% 0.510 5 6.33 0.015 8" Round 8 0.070 0.209 Yes
INLET‐S3 2.6 452 345 76.28% 0.650 5 6.33 0.043 8" Round 8 0.070 0.209 Yes
Drywell Storage
Drywell Basins Diameter Storage Depth Internal Volume External (18" of Screened Rock) Volume Total Capacity Required Capacity
(Name) (#) D (ft) H (ft) π*H*(D/2)
2) (ft3) 0.3*π*H(perf)*((D/2)+1.5)
2 ‐ (D/2)2) (ft3)(ft3)(ft3)
North Drywell 1 5 10 196 55 251 247
South Drywell 2 4 10 126 31 157 85
Drywell Infiltration
Name Diameter Perforation Height Perforated Area Total Capacity Infiltration Rate Infiltration Time Volume Infiltrated in 24 Hours
(Name) D (ft) H (ft)
A (ft2) = 3.14*D*H V (ft3)I (in/hr) T (hr) = V/(A*I/12) Vtotal (ft3) = V*T
North Drywell 5 4 62.83 251.48 12 4.00 1006.57
South Drywell 4 4 50.27 156.77 12 3.12 488.91
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maintenance schedule that will be undertaken by the owners of the new residence or building. Minimum
inspection and maintenance requirements include the following:
Inspect drywells at least four times a year and after every storm exceeding 0.5 inches.
Dispose of sediment, debris/trash, and any other waste material removed from a drywell at suitable
disposal sites and in compliance with local, state, and federal waste regulations.
Routinely evaluate the drain-down time of the drywell to ensure the maximum time of 24 hours is
not being exceeded. If drain-down times are exceeding the maximum, drain the drywell via pumping
and clean out the percolation area (the percolation barrel may be jetted to remove sediment
accumulated in perforations. If slow drainage persists, the system may need to be replaced.
Inspect the 6-inch perforated pipe to ensure the surrounding filter fabric has not become clogged.
8.0 Appendices
Drawings 11x17
FEMA FIRM Map
Sopris Engineering Survey
02/14/2019