HomeMy WebLinkAboutStormwaterDesignReport_01-20-2021
INTRODUCTION
The Swiss Plaza Master Site Plan consists of 7 office/shop/two-bedroom dwelling unit duplexes,
located on Lot 3, Block 4 of Cattail Creek Subdivision, Phase 1 in Bozeman, Montana. A
combination of site grading, curb and gutter, curb inlets, area drains and underground R Tank
storage chambers will be used to manage stormwater runoff for the development of the site. The
lot currently has a 7,200 square foot Swiss Detail shop and associated parking lot. The Swiss Detail
shop was designed and built in 2016 and required the construction of a 1,095 cubic foot retention
pond. The retention pond is proposed to be removed with the proposed development of Phase 2 of
the Swiss Plaza Master Site Plan. The proposed two underground R Tank stormwater storage
systems will replace the existing pond and also provide stormwater storage for the rest of the site.
Supporting stormwater calculations are attached to this report. A Drainage Area Map is included
in Appendix A. Calculations for each individual drainage area are included in Appendix B. Pipe
sizing calculations are included in Appendix C. Groundwater depth information is included in
Appendix D. The original approved Swiss Detail Stormwater Report is included in Appendix E.
A Stormwater Facilities Inspection and Maintenance Plan is included in Appendix F.
DRAINAGE AREAS
Drainage Area 1
Drainage Area 1 consists of a portion of the existing parking lot, a portion of the existing shop,
and a small area of new landscaping between Building 1 and N. 27th Ave. Existing roof downspout
locations were field verified in October 2020. Runoff from Drainage Area 1 flows into the N. 27th
Ave Right of Way (R.O.W.). As discussed in the 2016 Swiss Detail Stormwater Report (see
Appendix E), the original Cattail Creek Subdivision stormwater calculations accounted for the
entirety of Lot 3, Block 4 to runoff into the R.O.W. (using a C coefficient of 0.8) and flow via curb
and gutter to the subdivision’s regional detention pond. The C value of Drainage Area 1 was
calculated to be 0.65 and comprises only 0.46 acres of the entire 2.39 acre lot. Therefore, it is
allowable to grade the site such that Drainage Area 1 contributes runoff to the N. 27th Ave. R.O.W.
and is not retained on site.
Drainage Area 2
Drainage Area 2 consists of the largest portion of the site including portions of the existing shop
and parking area, a portion of Building 7, the entirety of Buildings 1, 2 and 3 and a large portion
of the proposed parking area. Runoff from this drainage area flows via curb and gutter, valley
gutter, and underground storm drain piping to Underground Stormwater Retention System #1 near
the center of the site. This system was sized for the 10-year, 2-hour storm and was checked for the
half inch requirement. It was found that the 10-year, 2-hour storm governed the design and required
3,456 cubic feet of storage. 3,540 cubic feet of storage is provided in Retention System #1
including the surrounding washed rock using a porosity of 0.4.
Drainage Area 3
Drainage Area 3 consists of a small portion of the site including a portion of Building 7, the entirety
of Buildings 4, 5 and 6, and a portion of the proposed parking area. Runoff from this drainage area
flows via valley gutter, and underground storm drain piping to Underground Stormwater Retention
System #2 at the north end of the site. This system was sized for the 10-year, 2-hour storm and
was checked for the half inch requirement. It was found that the 10-year, 2-hour storm governed
the design and required 1,101 cubic feet of storage. 1,120 cubic feet of storage is provided in
Retention System #2 including the surrounding washed rock using a porosity of 0.4.
DEPTH TO GROUNDWATER
Groundwater was monitored at two locations on the subject property during the high groundwater
season in 2020. The wells were found to be dry throughout the entire monitoring period from April
10 through July 10, 2020. However, groundwater was encountered during test pit explorations for
the Swiss Detail project on March 8, 2016. Groundwater was found to be relatively deep
throughout the site. The three test pits encountered groundwater 9 to 11 feet below ground surface.
A conservative estimate of high groundwater was used in designing the underground retention
systems by adding two feet to the highest observed groundwater measurement. Therefore, high
groundwater was assumed to be 7 feet below ground surface for the purpose of designing the
underground stormwater system. The bottom elevation of Retention System #1 is 4,680.2 feet and
the high groundwater is 2.2 feet lower at 4,678 feet elevation. The bottom elevation of Retention
System #2 is 4,681.4 feet and the high groundwater is 3.9 feet lower at 4,677.5 feet elevation. See
Appendix D for more groundwater depth information.
PROPOSED STORMWATER DESIGN
Storm sewer pipes were sized to convey the 25-yr storm using Manning’s Equation. For each
drainage area, a weighted C factor, and time of concentration were calculated. These values were
input into Manning’s Equation to check capacity of the storm drain pipes. For simplicity a standard
worst case scenario pipe size and slope were determined for a given drainage area. Pipe sizing
calculations are included in Appendix C. The proposed Underground Retention systems are sized
according to City of Bozeman Design Standards to capture and retain the volume of the 10-year
2-hour storm event.
MASTER SITE PLAN PHASING
Phase 1
Phase 1 will include the installation of Retention System #1, two combination manhole/curb inlets,
170 linear feet of valley gutter, one 24” riser inlet, approximately 174 linear feet of 6” PVC storm
drain for roof downspouts to tie into, and approximately 161 linear feet of 12” PVC storm drain.
Phase 2
Phase 2 will include the installation of Retention System #2, one 36” storm drain inlet, 155 linear
feet of valley gutter, one 24” riser inlet, approximately 82 linear feet of 6” PVC storm drain for
roof downspouts to tie into, and approximately 3 linear feet of 12” PVC storm drain. Also, during
Phase 2, the existing retention pond will be filled in for the construction of Building 7.
Phase 3
Phase 3 will include the installation of approximately 255 linear feet of 6” PVC storm drain for
roof downspouts to tie into. The rest of the storm infrastructure will already be installed with
previous phases.
G:\C&H\20\200203\Design Reports\Stormwater\200203 Stormwater Design Report.Docx
APPENDIX A
DRAINAGE AREA MAP
APPENDIX B
DRAINAGE AREA AND RETENTION
SYSTEM SIZING CALCULATIONS
DRAINAGE AREA #1
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Hardscape 0.95 10571 10043
Landscape 0.20 8030 1606
Total 18601 11649
A = Area (acres)0.4270
C = Weighted C Factor 0.63
DRAINAGE AREA #2
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Hardscape 0.95 51092 48537
Landscape 0.20 13612 2722
Total 64704 51260
A = Area (acres)1.4854
C = Weighted C Factor 0.79
DRAINAGE AREA #3
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Hardscape 0.95 16227 15416
Landscape 0.20 4560 912
Total 20787 16328
A = Area (acres)0.4772
C = Weighted C Factor 0.79
RETENTION SYSTEM #1 - REQUIRED VOLUME
REQUIRED VOLUME (flood control per DSSP II.C.5)
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft2 )C * Area
Hardscape 0.95 51092 48537
Landscape 0.20 13612 2722
Total 64704 51260
C=Weighted C Factor 0.79
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.79
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres)1.49
Q = runoff (cfs)0.48
V = REQUIRED VOL (ft3)3456
REQUIRED VOLUME (1/2" runoff per DSSP II.A.4)
1. Determine Area of Hardscape within Drainage Area #2
Contributing Area Area (ft 2)
Hardscape 51092
2. Calculate 1/2" runoff volume over hardscape
(aka Runoff Reduction Volume [RRV] as calculated in Montana Post-
Construction Storwater BMP Manual - Equation 3-1)
RRV = [P*Rv*A]/12
P = Water quality rainfall depth 0.50 inches
Rv = Dimensionless runoff coefficient 0.76 0.05 + 0.9*I
I = Percent impvious cover (decimal)0.79 decimal
A = Entire drainage area 1.49 acres
RRV = Runoff Reduction Volume 0.047 acre-ft
RRV = Runoff Reduction Volume 2051 cubic feet
Because the runoff volume from the 10-yr, 2-hr storm (for flood
control) is greater than the runoff volume produced by the half inch
rainfall (for water quality) the proposed retention facility #1 is sized
to handle the larger volume (3456 cf).
RETENTION SYSTEM #1 - PROPOSED VOLUME
PROPOSED VOLUME - R TANK CHAMBER
1. Define storage volume of one chamber (Double + mini)
Chamber volume (ft3)10.36
2. Define quantity of chambers
Number of rows (main east-west)4
Number of columns (main east-west)43
End chambers 48
Total 220
3. Define volume of gravel bedding and backfill
Length of one chamber (feet)2.35
Width of one chamber (feet)1.31
Height of one chamber (feet)3.54
Total area of chambers (ft2)677
Total area of excavation (ft2)967
Area of backfill (ft2)290
Volume of backfill (ft3)1025
Gravel base depth (feet)2.2
Gravel base volume (ft3)2127
Total volume of gravel bedding and backfill (ft3)3153
Porosity of gravel bedding and backfill 0.4
Storage volume within gravel (ft3)1261
4. Calculate total storage volume
Storage volume of chambers (ft3)2279 =220 chambers x 10.36 cf
Storage volume of bedding and base gravel (ft3)1261
Total volume of chamber system 3540
RETENTION SYSTEM #2 - REQUIRED VOLUME
REQUIRED VOLUME (flood control per DSSP II.C.5)
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft2 )C * Area
Hardscape 0.95 16227 15416
Landscape 0.20 4560 912
Total 20787 16328
C=Weighted C Factor 0.79
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.79
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres)0.48
Q = runoff (cfs)0.15
V = REQUIRED VOL (ft3)1101
REQUIRED VOLUME (1/2" runoff per DSSP II.A.4)
1. Determine Area of Hardscape within Drainage Area #2
Contributing Area Area (ft 2)
Hardscape 16227
2. Calculate 1/2" runoff volume over hardscape
(aka Runoff Reduction Volume [RRV] as calculated in Montana Post-
Construction Storwater BMP Manual - Equation 3-1)
RRV = [P*Rv*A]/12
P = Water quality rainfall depth 0.50 inches
Rv = Dimensionless runoff coefficient 0.75 0.05 + 0.9*I
I = Percent impvious cover (decimal)0.78 decimal
A = Entire drainage area 0.48 acres
RRV = Runoff Reduction Volume 0.015 acre-ft
RRV = Runoff Reduction Volume 652 cubic feet
Because the runoff volume from the 10-yr, 2-hr storm (for flood
control) is greater than the runoff volume produced by the half inch
rainfall (for water quality) the proposed retention facility #2 is sized
to handle the larger volume (1,101 cf).
RETENTION SYSTEM #2 - PROPOSED VOLUME
PROPOSED VOLUME - R TANK CHAMBER
1. Define storage volume of one chamber (Single + mini)
Chamber volume (ft3)6.33
2. Define quantity of chambers
Number of rows (main east-west)4
Number of columns (main east-west)16
End chambers 16
Total 80
3. Define volume of gravel bedding and backfill
Length of one chamber (feet)2.35
Width of one chamber (feet)1.31
Height of one chamber (feet)2.17
Total area of chambers (ft2)246
Total area of excavation (ft2)400
Area of backfill (ft2)154
Volume of backfill (ft3)334
Gravel base depth (feet)3
Gravel base volume (ft3)1200
Total volume of gravel bedding and backfill (ft3)1534
Porosity of gravel bedding and backfill 0.4
Storage volume within gravel (ft3)613
4. Calculate total storage volume
Storage volume of chambers (ft3)506 =80 chambers x 6.33 cf
Storage volume of bedding and base gravel (ft3)613
Total volume of chamber system 1120
APPENDIX C
PIPE SIZING CALCULATIONS
BLDG 1, 2 ROOF DRAINS
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 ) C * Area
Building 1 0.95 2700 2565
Building 2 0.95 2700 2565
Total 5400 5130
A = Area (acres) 0.1240
C = Weighted C Factor 0.95
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 25.0% Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 23 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)0.3
Tc Total = 5.0 (5 minute minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.95 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.12 (calculated above)
Q 25-yr Flow Rate (cfs)=0.45
MANNING'S EQUATION FOR PIPE FLOW (PROVIDED CAPACITY)
Pipe: worst case scenario Location: Roof Drain pipes (buildings 1, 2, 3)
INPUT
D= 6 inches
d= 5.63 inches
Mannings Formula n= 0.013 mannings
57.7 degrees
Q=(1.486/n)ARh2/3S1/2 S= 0.0075 slope in/in
R=A/P
A=cross sectional area
P=wetted perimeter V=(1.49/n)Rh2/3S1/2
S=slope of channel Q=V x A
n=Manning's roughness coefficient
Solution to Mannings Equation
Area,ft2 Wetted
Perimeter, ft
Hydraulic
Radius, ft velocity ft/s flow, cfs PVC 0.013
0.19 1.32 0.15 2.73 0.52 PE (<9"dia) 0.015
PE (>12"dia) 0.02
PE(9-12"dia) 0.017
CMP 0.025
ADS N12 0.012
HCMP 0.023
Conc 0.013
Manning's n-values
d
D
BLDG 4, 5, 6 ROOF DRAINS
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Building 4 0.95 2700 2565
Building 5 0.95 2700 2565
Building 6 0.95 2700 2565
Total 8100 7695
A = Area (acres) 0.1860
C = Weighted C Factor 0.95
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 25.0% Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 23 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)0.3
Tc Total = 5.0 (5 minute minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.95 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.19 (calculated above)
Q 25-yr Flow Rate (cfs)=0.68
MANNING'S EQUATION FOR PIPE FLOW (PROVIDED CAPACITY)
Pipe: worst case scenario Location: Roof Drain pipes (building 4, 5, 6)
INPUT
D= 6 inches
d= 5.63 inches
Mannings Formula n= 0.013 mannings
57.7 degrees
Q=(1.486/n)ARh2/3S1/2 S= 0.012 slope in/in
R=A/P
A=cross sectional area
P=wetted perimeter V=(1.49/n)Rh2/3S1/2
S=slope of channel Q=V x A
n=Manning's roughness coefficient
Solution to Mannings Equation
Area,ft2 Wetted
Perimeter, ft
Hydraulic
Radius, ft velocity ft/s flow, cfs PVC 0.013
0.19 1.32 0.15 3.59 0.69 PE (<9"dia) 0.015
PE (>12"dia) 0.02
PE(9-12"dia) 0.017
CMP 0.025
ADS N12 0.012
HCMP 0.023
Conc 0.013
Manning's n-values
d
D
DRAINAGE AREA #2 PIPE SIZING
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 ) C * Area
Hardscape 0.95 51092 48537
Landscape 0.20 13612 2722
Total 64704 51260
A = Area (acres) 1.4854
C = Weighted C Factor 0.79
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 1.1% Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.79 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 190 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)5.7
Tc Total = 5.7 (5 minute minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.79 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.52 (25-yr storm)
A = area (acres) 1.49 (calculated above)
Q 25-yr Flow Rate (cfs)=4.14
MANNING'S EQUATION FOR PIPE FLOW (PROVIDED CAPACITY)
Pipe: worst case scenario Location: PVC pipes in DA #2
INPUT
D= 12 inches
d= 11.26 inches
Mannings Formula n= 0.013 mannings
57.7 degrees
Q=(1.486/n)ARh2/3S1/2 S= 0.0125 slope in/in
R=A/P
A=cross sectional area
P=wetted perimeter V=(1.49/n)Rh2/3S1/2
S=slope of channel Q=V x A
n=Manning's roughness coefficient
Solution to Mannings Equation
Area,ft2 Wetted
Perimeter, ft
Hydraulic
Radius, ft velocity ft/s flow, cfs PVC 0.013
0.77 2.64 0.29 5.60 4.28 PE (<9"dia) 0.015
PE (>12"dia) 0.02
PE(9-12"dia) 0.017
CMP 0.025
ADS N12 0.012
HCMP 0.023
Conc 0.013
Manning's n-values
d
D
APPENDIX D
GROUNDWATER DEPTH INFORMATION
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APPENDIX E
ORIGINAL SWISS DETAIL STORMWATER
REPORT (2016)
APPENDIX F
STORMWATER FACILITIES INSPECTION
AND MAINTENANCE PLAN
INSPECTION AND MAINTENANCE FOR
STORMWATER MANAGEMENT FACILITIES
The Property Owners Association shall be responsible for the maintenance of the stormwater
drainage facilities within The Swiss Plaza development.
Storm Water Facilities:
1. Underground R Tank Stormwater Retention Systems collect storm water runoff and store
the water until it infiltrates into the ground.
2. Pipe Networks convey storm water to different discharge locations underground.
3. Inlets are facilities where storm water runoff enters a pipe network. Inlets include storm
water manholes and drains.
4. Catch Basins are sumps typically located directly below storm water inlets and allow
sediment to settle before storm water enters the pipe network.
5. Outlets are points where storm water exits a pipe network.
Post Construction Inspection:
1. Use the attached R Tank Operation, Inspection & Maintenance manual to determine if
maintenance is required on the system after construction is completed.
2. Observe that catch basins are clear of any material or obstructions in the drainage slots.
Inspect these structures to insure proper drainage following a storm event. Immediately
identify and remove objects responsible for clogging if not draining properly.
Semi-Annual Inspection:
1. Use the attached R Tank Operation, Inspection & Maintenance manual to determine if
maintenance is required on the system semi-annually.
2. Check for grass clippings, litter, sediment, and/or debris in inlets and catch basins. Flush
and/or vacuum storm water pipes if excessive material is observed in the facilities.
Standard Maintenance:
1. Inspect and remove debris from catch basins. Use a vacuum truck to clean catch basins and R
Tank system.
2. Inspect for the following issues: differential accumulation of sediment, drain time, signs of
petroleum hydrocarbon contamination (odors, oil sheen in pond water), standing water, trash
and debris.
Sediment accumulation:
In most cases, sediment in a catch basin or a retention system does not contain toxins at levels posing
a hazardous concern. However, sediments should be tested for toxicants in compliance with current
disposal requirements and if land uses in the drainage area include commercial or industrial zones, or
if visual or olfactory indications of pollution are noticed. Sediments containing high levels of
pollutants should be disposed of in accordance with applicable regulations and the potential sources of
contamination should be investigated and contamination practices terminated.
Cost Estimate:
Depending on the amount of rainfall in the given year, the cost to maintain the stormwater
infrastructure will vary. The underground R Tank system will need to be cleaned according to the
attached R Tank Operation, Inspection & Maintenance manual. Cost of maintenance will be
dependent on the frequency and estimates should be obtained from a local vacuum truck company.
The applicant will be responsible for financing the maintenance of the stormwater infrastructure.
Operation
Your ACF R-Tank System has been designed to function in conjunction with the engineered drainage system on your
site, the existing municipal infrastructure, and/or the existing soils and geography of the receiving watershed. Unless
your site included certain unique and rare features, the operation of your R-Tank System will be driven by naturally
occurring systems and will function autonomously. However, upholding a proper schedule of Inspection & Maintenance
is critical to ensuring continued functionality and optimum performance of the system.
Inspection
Both the R-Tank and all stormwater pre-treatment features incorporated into your site must be inspected regularly.
Inspection frequency for your system must be determined based on the contributing drainage area, but should never
exceed one year between inspections (six months during the first year of operation).
Inspections may be required more frequently for pre-treatment systems. You should refer to the manufacturer
requirements for the proper inspection schedule.
With the right equipment your inspection and measurements can be accomplished from the surface without physically
entering any confined spaces. If your inspection does require confined space entry, you MUST follow all local/regional
requirements as well as OSHA standards.
R-Tank Systems may incorporate Inspection Ports, Maintenance Ports, and/or adjoining manholes. Each of these
features are easily accessed by removing the lid at the surface. With the cover removed, a visual inspection can be
performed to identify sediment deposits within the structure. Using a flashlight, ALL access points should be examined
to complete a thorough inspection.
Inspection Ports
Usually located centrally in the R-Tank System, these perforated columns are designed to give the user a base-line sediment depth across the system floor.
Maintenance Ports
Usually located near the inlet and outlet connections, you’ll likely find deeper deposits of heavier sediments when compared to the Inspection Ports.
Manholes
Most systems will include at least two manholes - one at the inlet and another at the outlet. There may be more than one location where stormwater enters the system, which would result in additional manholes to inspect.
Bear in mind that these manholes often include a sump below the invert of the pipe connecting to the R-Tank.
These sumps are designed to capture sediment before it reaches the R-Tank, and they should be kept clean to ensure they function properly. However, existence of sediment in the sump does NOT necessarily mean sediment
has accumulated in the R-Tank.
After inspecting the bottom of the structure, use a mirror on a pole (or some other device) to check for sediment
or debris in the pipe connecting to the R-Tank.
R-TANK OPERATION, INSPECTION& MAINTENANCE
TECHNICALSTORMWATER MANAGEMENT
For more information about our products, contact Inside Sales at 800.448.3636
or email at info@acfenv.com
If sediment or debris is observed in any of these structures, you should determine the depth of the
material. This is typically accomplished with a stadia rod, but you should determine the best way to
obtain the measurement.
All observations and measurements should be recorded on an Inspection Log kept on file. We’ve included a form you can use at the end of this guideline.
MaintenanceThe R-Tank System should be back-flushed once sediment accumulation has reached 6” or 15% of the
total system height. Use the chart below as a guideline to determine the point at which maintenance
is required on your system.
Before any maintenance is performed on your system, be sure to plug the outlet pipe to prevent contamination of the adjacent systems.
To back-flush the R-Tank, water is pumped into the system through the Maintenance Ports as rapidly
as possible. Water should be pumped into ALL Maintenance Ports. The turbulent action of the water
moving through the R-Tank will suspend sediments which may then be pumped out.
If your system includes an Outlet Structure, this will be the ideal location to pump contaminated water out of the system. However, removal of back-flush water may be accomplished through the
Maintenance Ports, as well.
For systems with large footprints that would require extensive volumes of water to properly flush the system, you should consider performing your maintenance within 24 hours of a rain event. Stormwater entering the system will aid in the suspension of sediments and reduce the volume of
water required to properly flush the system.
Once removed, sediment-laden water may be captured for disposal or pumped through a DirtbagTM (if permitted by the locality).
R-Tank Unit Height Max Sediment Dept
Mini 9.5” 1.5”
Single 17” 3”
Double 34” 5”
Triple 50” 6”
Quad 67” 6”
Pent 84” 6”
R-TANK OPERATION INSPECTION & MAINTENANCE
2831 Cardwell Road
Richmond, Virginia, 23234
800.448.3636
FAX 804.743.7779
acfenvironmental.com
Step-By-Step Inspection & Maintenance Routine
1) Inspection
a. Inspection Port
i. Remove Cap
ii. Use flashlight to detect sediment deposits
iii. If present, measure sediment depth with stadia rod
iv. Record results on Maintenance Log
v. Replace Cap
b. Maintenance Port/s
i. Remove Cap
ii. Use flashlight to detect sediment deposits
iii. If present, measure sediment depth with stadia rod
iv. Record results on Maintenance Log
v. Replace Cap
vi. Repeat for ALL Maintenance Ports
c. Adjacent Manholes
i. Remove Cover
ii. Use flashlight to detect sediment deposits
iii. If present, measure sediment depth with stadia rod, accounting for depth
of sump (if present)
iv. Inspect pipes connecting to R-Tank
v. Record results on Maintenance Log
vi. Replace Cover
vii. Repeat for ALL Manholes that connect to the R-Tank
2) Maintenance
a. Plug system outlet to prevent discharge of back-flush water
b. Determine best location to pump out back-flush water
c. Remove Cap from Maintenance Port
d. Pump water as rapidly as possible (without over-topping port) into system until at least
1”
of water covers system bottom
e. Replace Cap
f. Repeat at ALL Maintenance Ports
g. Pump out back-flush water to complete back-flushing
h. Vacuum all adjacent structures and any other structures or stormwater pre-treatment
systems that require attention
i. Sediment-laden water may be captured for disposal or pumped through a DirtbagTM.
j. Replace any remaining Caps or Covers
k. Record the back-flushing event in your Maintenance Log with any relevant specifics
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