HomeMy WebLinkAboutFile Documents.614 North St.0248.2017 (47).ARBK1
Drainage Report
614 W. NORTH STREET
ASPEN, CO 81611
September 6th, 2017
Updated February 15th, 2018
Updated April 30th , 2018
Prepared by
Richard Goulding, P.E.
Roaring Fork Engineering
592 Highway 82
Carbondale, CO 81623
5/4/2018
Reviewed by Engineering
05/16/2018 12:04:02 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
614 W. NORTH STREET
ASPEN, CO 81611
I HEREBY AFFIRM THAT THIS REPORT FOR THE IMPROVEMENTS AT 614 W. NORTH STREET,
ASPEN, CO WAS PREPARED BY ME FOR THE OWNERS THEREOF IN ACCORDANCE WITH THE
PROVISIONS OF THE CITY OF ASPEN URBAN RUNOFF MANAGEMENT PLAN 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.
RICHARD GOULDING, P.E.
RFE Project # 2017-33
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Table of Contents
1.0 General .................................................................................................................................................... 4
1.1 Existing Site ......................................................................................................................................... 4
1.2 Proposed Conditions ........................................................................................................................... 4
1.3 Previous Drainage Studies .................................................................................................................. 5
1.4 Offsite Drainage & Constraints ........................................................................................................... 5
2.0 Drainage Basins and Sub‐basins .............................................................................................................. 5
2.1 Drainage Basins ................................................................................................................................... 5
2.2 Peak Discharge Calculations ................................................................................................................ 5
3.0 Low Impact Site Design ........................................................................................................................... 7
3.1 Principles ............................................................................................................................................. 7
4.0 Hydrological Criteria ............................................................................................................................... 8
4.1 Storm Recurrence and Rainfall ........................................................................................................... 8
4.2 Peak Runoff Methodology .................................................................................................................. 8
5.0 Hydraulic Criteria .................................................................................................................................... 8
5.1 Inlets .................................................................................................................................................... 9
5.2 Pipes .................................................................................................................................................... 9
6.0 Proposed Facilities ................................................................................................................................ 12
6.1 Drywell .............................................................................................................................................. 12
6.2.1 Infiltration .................................................................................................................................. 12
7.0 Operation and Maintenance ................................................................................................................. 12
7.1 Drywell .............................................................................................................................................. 12
7.2 Pervious Paver Area .......................................................................................................................... 13
8.0 Appendices ............................................................................................................................................ 13
Drawings 11x17 ....................................................................................................................................... 13
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1.0 General
1.1 Existing Site
This report is an evaluation of a developed site located to the north of W. North Street, in the middle of
the block between North 5th and North 6th Street in the City of Aspen, Colorado. The property address is
614 W. North Street, and is located between two residential homes. To the north is the alley Right‐of‐
Way, and to the south is the North Street Right‐of‐Way. The lot is 4,064 square feet (sf.) and consists of a
3,800 sf. single‐family residence with a concrete driveway and flagstone patios. Large mature trees are
scattered along the southern half of the property and Right‐of‐Way, and large mature trees located near
the northeast property corner. No sidewalk or curb and gutter is installed in front of the residence on
North Street. All utilities are located in the alley, excluding the water line, which is located in North Street.
View of the site from North Street
A Geotechnical Report was produced on August 21, 2017. One exploratory bore was limited to 8 feet
below grade to perform the analysis due to auger refusal. The bore results are described as 0.5 feet of
organic, sandy clay and silt “topsoil”, over 6.5 feet of mixed clayey sand and gravel backfill material. The
final 1.5 feet of the boring consisted of gravel and cobbles where the practical auger refused at 8 feet
below the surface. No groundwater was encountered. A percolation test was conducted during this
analysis, with an average percolation rate of 4 minutes per inch, or 15 inches per hour.
1.2 Proposed Conditions
This project is classified as a ‘Major Project’ per Table 1.1 of the URMP. This is because the proposed
development is over 1,000 square feet (sf) and disturbs an area of approximately 2,707 sf., which is over
67% of the site. The intent of this report is to demonstrate compliance with the requirements of the
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URMP. The Low Impact Design (LID) Principles in the introduction of the manual were used as a guide
throughout the design process. Onsite storm infrastructure has been sized for conveyance and full
detention storage of a 100 year event.
The proposed residence to be remodeled is 4,369 square feet (sf). Patios will be located on the south
and east sides of the structure. An existing two car garage will be accessed from the alley. For drainage,
one drywell will capture all runoff from roofs and hardscape and is sized to have capacity for full
detention.
Existing utilities servicing the residence will remain and will be used to service the remodeled residence.
1.3 Previous Drainage Studies
The City of Aspen updated their URMP in 2014 and the property is within the boundaries of the study.
The study indicates that the property is not within a Mudflow Area.
1.4 Offsite Drainage & Constraints
No offsite basins effect the site; no analysis was required.
2.0 Drainage Basins and Sub‐basins
The site was designed as one major drainage basin, which was then subdivided into smaller sub‐basins. A
Drainage Exhibit in the appendices illustrates the basin and sub‐basin delineations. It lists Impervious
Areas, Runoff Coefficients, and Peak Flows.
The sub‐basins were created to calculate the concentrated flow from each impervious area, including
patios, decks and roofs. These sub‐basin peak flows were then used to size the proposed infrastructure.
2.1 Drainage Basins
Basin 1 is 2,293 square feet (sf), 100% impervious, and consists of roof and deck areas, patios, and the
existing concrete driveway. Runoff from this basin is collected and conveyed to the drywell through a
series of downspouts, inlets, and trench drains. This drywell has capacity for full detention for the entire
basin.
2.2 Peak Discharge Calculations
The peak flows were calculated for each Major Basin for the 5 and 100 year storm events. Rainfall
intensity was calculated using a Time of Concentration (Td) of 5 minutes. Actual time of concentration
on the site is significantly less than 5 minutes, but according to the City of Aspen URMP, equations used
to calculate rainfall intensity are only valid for a Time of Concentration of greater than 5 minutes. So the
smallest valid Time of Concentration value was used. 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 = 88.8P1/(10+Td )1.052
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Runoff Coefficients (C), a function of the Soil Group (in this case B) and the percentage of impervious
area within each basin were developed using Figure 3.2. The Runoff Coefficient (C) was then multiplied
by the Rainfall Intensity (I) and the acreage of each Major Basin (A) to determine the peak discharge for
each Major Basin. Q allowable was calculated the same way except each basin was treated as
undeveloped or 100% pervious. The Peak Discharge (Qp) is given by equation 3.1.
Qp= CIA
Qp= Peak Discharge (cfs)
C= Runoff Coefficient (Unitless)
I= Rainfall intensity (inches per hour)
A= Area (Acres)
Peak flow values were used to calculate the size of the proposed detention and conveyance structures,
such as drywells, inlets and piping. The tables below contain the peak flows for developed and
undeveloped conditions for 5 and 100 year storm events.
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 CIntensityQ Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 2292.89 2292.89 100.00% 0.896 5 3.29 0.16
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 CIntensityQ Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 2292.89 0.00 0.00% 0.080 5 3.29 0.01
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 CIntensityQ Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 2292.89 2292.89 100.00% 0.950 5 6.33 0.32
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 CIntensityQ Max
See(D1) (ft
2)(ft2)(%)From Table (Td) I=88.8P1/(10+Td)1.052 (ft3/sec)
1 2292.89 0.00 0.00% 0.350 5 6.33 0.12
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3.0 Low Impact Site Design
Low Impact Development (LID) aims to mimic the natural pre‐development hydrologic pattern. The goal
is to manage storm water as close to its source as is possible. This entire developed site is approximately
57% impervious. The treatment train approach is used on all runoff to increase water quality and
percolation.
3.1 Principles
Principle 1: Consider storm water quality needs early in the design process.
The Grading and Drainage design was coordinated with the architect during the design phase. Due to
the lack of space for the project, coordination in the design process was key.
Principle 2: Use the entire site when planning for storm water quality treatment.
Because of the size and limitations of the parcel, it was necessary in the design process to use the site
efficiently. Grading away from the residence for the project was difficult to achieve with the flat site.
Principle 3: Avoid unnecessary impervious area.
Pervious paver patios are being implemented, which will reduce the impervious area of the site.
Principle 4: Reduce runoff rates and volumes to more closely match natural conditions.
The runoff will all be infiltrated into the ground, as the drywells are sized for full detention. There will be
no runoff leaving the site.
Principle 5: Integrate storm water quality management and flood control.
The Drywells are being used for water quality, which in itself increases flood control. The drywells will
eliminate the peak flow as there is no runoff leaving the site.
Principle 6: Develop storm water quality facilities that enhance the site, the community and the
environment.
The proposed design encourages replenishing groundwater, and does not introduce any runoff into the
city infrastructure. This reduces the flows being introduced to the Roaring Fork River.
Principle 7: Use treatment train approach.
The emergency overflow from the drywell will release into a grass field, which will treat the water
before entering the city storm system.
Principle 8: Design sustainable facilities that can be safely maintained.
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Screens will be placed over downspouts to provide a barrier against vermin and debris. Drainage
systems were simply designed so maintenance is minimized. Infrastructure will be just below grade
providing little labor for maintenance. The Owner will sign a maintenance agreement as part of their
Certificate of Occupancy.
Principle 9: Design and maintain facilities with public safety in mind.
Proper drainage and grading of the driveway and walkways reduces ice buildup and dangerous icy
conditions. All grading was done with safety as the priority.
4.0 Hydrological Criteria
4.1 Storm Recurrence and Rainfall
The property is not in the commercial core and is not served by any city curb and gutter so this property
classifies as a “Sub‐urban area not analyzed or served by public storm sewer”. The 5 and 100‐year events
were analyzed for this designation.
4.2 Peak Runoff Methodology
Since the site is not serviced by public storm infrastructure, full detention is necessary. To determine these
capacities, the rainfall from a 100 year storm that is collected on all impervious areas must be detained.
No detention is required for pervious areas. Below is a summary of the required storage.
5.0 Hydraulic Criteria
Sub‐basins were delineated per the design points of concentrations created by roof drains and inlets.
Pipe networks were then created connecting the sub‐basins and conveying the flows to the overall point
of concentration for the basin. The 100‐year peak flow for each sub‐basin was calculated.
Full Detention Storage
Basin Total Area Impervious Area Impervious Full Detention Depth Factor of Safety Required Storage BMP
(ft2)(ft2) (%) (in) F.O.S. (ft
3)
1 2292.89 2292.89 100.00% 1.23 1 235 Drywell
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5.1 Inlets
The 100 year peak flows were used in the sizing of inlets. Equations 4‐17 to 4‐20 from the URMP were
used in the analysis. They incorporate a 50% clogging factor and 40% opening in the grates. A water
depth of 0.04’ was assumed and all the inlets were treated as sumps as they will be set a minimum of
.04‘(½ Inch) below the flow lines. Below is a summary of each square inlet being tested for capacity
against their tributary basin.
5.2 Pipes
The pipes were analyzed by calculating the flow from the sub basins entering them. Below is table which
groups what sub basins are conveyed in each pipe. The TOC is below 5 minutes for all sub‐basins, so a
reduction was not taken for the intensity. They were tested for hydraulic capacity at 80% of pipe
diameter. Depth of flow was also calculated in the tables below. The pipes are all SDR 35 PVC with a
Manning’s coefficient of 0.01.
Design Q design / Q full charts were downloaded from FHWA. The equations in Section 4.8.4 was used as
the basis for these calculations.
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 CIntensitySub Basin Flow Rate
(Name) At (ft2)Ai (ft2)Ai/At (%) From Table (Td) I=88.8P1/(10+Td)01.052 Qsub (ft3/sec)
1.1 494.32 494.32 100.00% 0.950 5 6.33 0.07
1.2 180.27 180.27 100.00% 0.950 5 6.33 0.02
1.3 155.56 155.56 100.00% 0.950 5 6.33 0.02
1.4 465.98 465.98 100.00% 0.950 5 6.33 0.06
1.5 232.55 232.55 100.00% 0.950 5 6.33 0.03
1.6 397.08 397.08 100.00% 0.950 5 6.33 0.05
1.7 49.84 49.84 100.00% 0.950 5 6.33 0.01
1.8 317.29 317.29 100.00% 0.950 5 6.33 0.04
Sub Basin and Rectangular Inlet Calculations
1 Hour(P1)1.23 m=40% Ys=.04 (Depress inlet by 0.04')
Return Period 100 Cg=50% Co=0.65
Inlet ID Basin ID Total Area Imp. Area Impervious C Value Time of Concentration Intensity Q Max Inlet Type Inlet Width Inlet Length Effective Open 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) Rectangular Wo (inches) Lo (inches) Ae=(1‐Cg)mWoLo Q=CoAe√2gYs (Yes/No)
A5‐TRENCH DRAIN 1.3 155.56 155.56 100.00% 0.950 5 6.33 0.021 6" x 11.5' 6 138 1.150 1.154 Yes
A16‐TRENCH DRAIN 1.7 49.84 49.84 100.00% 0.950 5 6.33 0.007 6" x 4' 6 48 0.400 0.401 Yes
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Storm System Pipes
Pipe System Pipe Contibuting Sub‐Basins Design Flow Rate
Qdes
A1 1.1 0.07
A2 1.1 0.07
A3 1.1 0.07
A4 1.1, 1.2 0.09
A5 1.1‐1.3 0.11
A6 1.1‐1.3 0.11
A7 1.4 0.06
A8 1.1‐1.4 0.18
A9 1.5 0.03
A10 1.1‐1.5 0.21
A11 1.1‐1.5 0.21
A12 1.1‐1.5 0.21
A13 1.1‐1.6 0.27
A14 1.1‐1.6 0.27
A15 1.1‐1.6 0.27
A16 1.7 0.01
A17 1.7 0.01
A18 1.7 0.01
A19 1.1‐1.7 0.27
A20 1.8 0.04
A
K=0.462
Pipe Design Flow
Rate
Proposed
Slope
Manning
Coefficient
Required Pipe Diameter
Equation 4‐31
Required Pipe
Diameter
Proposed Pipe
Diameter
Qdes (ft3/sec) S (%) n d (ft) = {nQdes/K√S}3/8 Dreq (in) Dpro (in)
A1 0.07 2.00% 0.01 0.18 2.17 4.0
A2 0.07 2.00% 0.01 0.18 2.17 4.0
A3 0.07 2.00% 0.01 0.18 2.17 4.0
A4 0.09 2.00% 0.01 0.20 2.44 4.0
A5 0.11 2.00% 0.01 0.22 2.63 4.0
A6 0.11 2.00% 0.01 0.22 2.63 4.0
A7 0.06 2.00% 0.01 0.18 2.12 4.0
A8 0.18 2.00% 0.01 0.26 3.11 4.0
A9 0.03 2.00% 0.01 0.14 1.63 4.0
A10 0.21 2.00% 0.01 0.28 3.31 4.0
A11 0.21 2.00% 0.01 0.28 3.31 4.0
A12 0.21 2.00% 0.01 0.28 3.31 4.0
A13 0.27 2.00% 0.01 0.30 3.61 4.0
A14 0.27 2.00% 0.01 0.30 3.61 4.0
A15 0.27 2.00% 0.01 0.30 3.61 4.0
A16 0.01 2.00% 0.01 0.08 0.92 4.0
A17 0.01 2.00% 0.01 0.08 0.92 4.0
A18 0.01 2.00% 0.01 0.08 0.92 4.0
A19 0.27 2.00% 0.01 0.30 3.65 4.0
A20 0.04 2.00% 0.01 0.15 1.84 4.0
Pipe Sizing
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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)
A1 0.07 4.0 2.00% 3.2 0.01 0.087 0.351 0.19 0.34 1.34 Yes
A2 0.07 4.0 2.00% 3.2 0.01 0.087 0.351 0.19 0.34 1.34 Yes
A3 0.07 4.0 2.00% 3.2 0.01 0.087 0.351 0.19 0.34 1.34 Yes
A4 0.09 4.0 2.00% 3.2 0.01 0.087 0.351 0.27 0.38 1.52 Yes
A5 0.11 4.0 2.00% 3.2 0.01 0.087 0.351 0.33 0.45 1.80 Yes
A6 0.11 4.0 2.00% 3.2 0.01 0.087 0.351 0.33 0.45 1.80 Yes
A7 0.06 4.0 2.00% 3.2 0.01 0.087 0.351 0.18 0.33 1.30 Yes
A8 0.18 4.0 2.00% 3.2 0.01 0.087 0.351 0.51 0.57 2.28 Yes
A9 0.03 4.0 2.00% 3.2 0.01 0.087 0.351 0.09 0.24 0.94 Yes
A10 0.21 4.0 2.00% 3.2 0.01 0.087 0.351 0.60 0.63 2.52 Yes
A11 0.21 4.0 2.00% 3.2 0.01 0.087 0.351 0.60 0.63 2.52 Yes
A12 0.21 4.0 2.00% 3.2 0.01 0.087 0.351 0.60 0.63 2.52 Yes
A13 0.27 4.0 2.00% 3.2 0.01 0.087 0.351 0.76 0.73 2.90 Yes
A14 0.27 4.0 2.00% 3.2 0.01 0.087 0.351 0.76 0.73 2.90 Yes
A15 0.27 4.0 2.00% 3.2 0.01 0.087 0.351 0.76 0.73 2.90 Yes
A16 0.01 4.0 2.00% 3.2 0.01 0.087 0.351 0.02 0.08 0.32 Yes
A17 0.01 4.0 2.00% 3.2 0.01 0.087 0.351 0.02 0.08 0.32 Yes
A18 0.01 4.0 2.00% 3.2 0.01 0.087 0.351 0.02 0.08 0.32 Yes
A19 0.27 4.0 2.00% 3.2 0.01 0.087 0.351 0.78 0.74 2.95 Yes
A20 0.04 4.0 2.00% 3.2 0.01 0.087 0.351 0.12 0.26 1.05 Yes
Hydraulic Grade Line and Pipe Capacity
Pipe Design Flow
Rate
Proposed Pipe
Diameter Slope d/D Manning
Coefficient Rh/D Hydraulic Radius Exit Velocity
(ID)Qdes (ft3/sec) Dpro(in) (%) (from Chart) n (from Chart) Rh (ft) = (Rh/D) Dpro V (ft/sec) = [1.49/n] Rh
2/3 √S
A1 0.068 4.0 2.00% 0.34 0.01 0.18 0.18 6.84
A2 0.068 4.0 2.00% 0.34 0.01 0.18 0.18 6.84
A3 0.068 4.0 2.00% 0.34 0.01 0.18 0.18 6.84
A4 0.093 4.0 2.00% 0.38 0.01 0.21 0.21 7.35
A5 0.115 4.0 2.00% 0.45 0.01 0.23 0.23 7.98
A6 0.115 4.0 2.00% 0.45 0.01 0.23 0.23 7.98
A7 0.064 4.0 2.00% 0.33 0.01 0.18 0.18 6.72
A8 0.179 4.0 2.00% 0.57 0.01 0.27 0.27 8.81
A9 0.032 4.0 2.00% 0.24 0.01 0.14 0.14 5.58
A10 0.211 4.0 2.00% 0.63 0.01 0.28 0.28 9.10
A11 0.211 4.0 2.00% 0.63 0.01 0.28 0.28 9.10
A12 0.211 4.0 2.00% 0.63 0.01 0.28 0.28 9.10
A13 0.266 4.0 2.00% 0.73 0.01 0.30 0.30 9.41
A14 0.266 4.0 2.00% 0.73 0.01 0.30 0.30 9.41
A15 0.266 4.0 2.00% 0.73 0.01 0.30 0.30 9.41
A16 0.007 4.0 2.00% 0.08 0.01 0.05 0.05 2.91
A17 0.007 4.0 2.00% 0.08 0.01 0.05 0.05 2.91
A18 0.007 4.0 2.00% 0.08 0.01 0.05 0.05 2.91
A19 0.273 4.0 2.00% 0.74 0.01 0.30 0.30 9.43
A20 0.044 4.0 2.00% 0.26 0.01 0.15 0.15 5.99
Exit Velocities
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6.0 Proposed Facilities
6.1 Drywell
The proposed drywell collects all runoff from the site and is designed to have capacity for full detention.
Five feet of perforations are proposed for the drywell, rather than the standard 4 feet. The drywell is 5
feet in diameter and 16 feet deep, with 10 feet of storage capacity. It is 3.4 feet away from a structural
column and 2.9 feet from the property line that borders the Waters Avenue ROW. An impermeable liner
is proposed on half of the outside of the drywell that faces the residence to allow infiltration only
towards the ROW so that it will not affect the structure. If the system were to backup during a storm
event, the additional 6 feet of drywell capacity will allow it to not overflow. Below is a summary of the
drywell storage capacity.
6.2.1 Infiltration
Part of the analysis is to ensure that the drainage structures can completely drain within 24 hours. The
minimum depth of perforation a drywell must have is 4 feet, however 5 feet of perforations is proposed
for this specific drywell. Below is a calculation showing that there is enough perforation area for the
drywell to drain within 24 hours using the percolation rate determined from H‐P Kumar’s Subsoil Study.
The determined percolation rate of 15 inches per hour for the entire site. Section 8.5.4.2 was
referenced for these calculations. The perforated area was reduced by half due to the impermeable liner
being proposed on the outer half of the drywell facing the structure.
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
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
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*5*((D/2)+1.5)2 ‐ (D/2)2) (ft3)(ft3)(ft3)
Drywell 1 5 10 196 46 242 235
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)/2 V (ft3)I (in/hr) T (hr) = V/(A*I/12) Vtotal (ft3) = V*T
Drywell 5 5 39.27 242.30 15 4.936 1195.97
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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.
7.2 Pervious Paver Area
As per section 8.5.3.1 of the URMP, the following schedule will be undertaken by the owners of the
property to achieve long term performance of the BMP’s.
8.0 Appendices
Drawings 11x17
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