Construction of Facilities Dan Cloak Environmental Consulting Construction Workshop, May 2, 2012 Low Impact Development: What it is, what it does Runoff dispersal (“self-retaining.
Download
Report
Transcript Construction of Facilities Dan Cloak Environmental Consulting Construction Workshop, May 2, 2012 Low Impact Development: What it is, what it does Runoff dispersal (“self-retaining.
Construction of Facilities
Dan Cloak
Environmental Consulting
Construction Workshop, May 2, 2012
Low Impact Development: What it is, what it does
Runoff dispersal (“self-retaining areas”)
Pervious pavements
Bioretention
How facilities work and how they are sized
What to watch for during construction
Features
Impervious surfaces:
roofs and pavement
Catch basins and
piped drainage
“Collect and
convey” design
objective
Site Scale
Watershed and Stream Scale
Higher peak flows
Flooding and scouring of stream beds
Lower time of concentration
Flash flows
Runoff from small storms
Discharge when runoff did not previously occur
Increased runoff durations
Stream erosion at moderate stream flow rates
Greater runoff volumes
Higher pollutant loading
Greater runoff energy
Conveys trash and gross pollutants to streams
Decreased infiltration
Lower and less frequent stream base flow
Dry weather discharges
High pollutant concentrations during low flows
Watershed and Stream Scale
Site scale
Reduce peak flows
Detain runoff on site
Increase time of concentration
Slow runoff from leaving site
No runoff from small storms
Infiltrate, evapotranspirate and reuse
Reduce duration of moderate flows
Let runoff seep away very slowly
Reduce runoff volume
Infiltrate and reuse where possible
Reduce runoff energy
Detain and slow flows
Increase groundwater storage and
stream base flows
Facilitate infiltration
Reduce pollutants in runoff
Detain and filter runoff
Protect against spills and dumping
Disconnect drainage and filter runoff
Instead of “collect and convey,”
“slow it, spread it, sink it.”
Avoid concentrating flows
Keep drainage areas small
Promote infiltration
Detain
Treat
Optimize the site
layout
Optimize the site
layout
Use pervious
surfaces and green
roofs where possible
Optimize the site
layout
Use pervious
surfaces and green
roofs where possible
Disperse runoff to
landscaping
Optimize the site
layout
Use pervious
surfaces and green
roofs where possible
Disperse runoff to
landscaping
Direct drainage from
impervious surfaces
to bioretention
facilities
Rationale
Produce no runoff from
“small” storms
Also called “zero discharge”
areas
Criteria
Bermed or graded concave
Slopes do not exceed 4%
Amended soils and
vegetation to maintain soil
stability and permeability
Inlets of area drains, if any,
3" minimum above
surrounding grade
Rationale
Self-retaining areas are
capable of ponding and
infiltrating some additional
runoff
Criteria
Ratio is not greater than 2:1
if treatment-only
requirements apply
Ratio is not greater than 1:1
if flow-control requirements
apply
Provide sufficient
ponding/storage depth
Facilitate infiltration
Variations
Pervious concrete
Porous asphalt
Porous pavers
Gravel
Open pavers
Solid unit pavers set on sand/gravel
Artificial turf
Common Characteristics
Require a base course
Base course depth varies with soil type
More costly than conventional concrete or asphalt
Installation on slopes requires careful design
Minimal compaction of underlying soil
Check base course depth
4 to 12 inches or more, depending on competence of
underlying soils
Base course underdrains
Consider omitting the underdrain and relying on
infiltration and lateral flow
Perforated SDR 35 or equivalent
Outlet elevation minimum 3" above bottom of base course
Underdrain may be routed to storm drain
Pavers
Rigid edge required
Solid pavers require 3/8" minimum gap
Joints filled with open-graded aggregate free of fines
Permeable concrete and pervious asphalt
Installed by industry-certified professionals according to
vendor’s recommendations.
Overflow
Underdrain
i = 0.2 inches/hour
BMP Area/Impervious Area =
0.2/5 = 0.04
Surface Loading Rate
i = 5 inches/hour
1.00
Impervious
Mitigated Post-Project Site
Pre-Project Site
Q10
0.1Q2
0.90
0.80
Flow (cfs)
0.70
0.60
0.50
IMP Reduces Impervious Runoff
to Less Than Pre-Project Levels
0.40
0.30
0.20
0.10
0.00
0.00
0.05
0.10
0.15
0.20
0.25
% Time Exceeded
0.30
0.35
0.40
A
V1
V2
0.04
Overflow
2"
4"
Soil Mix
18"
Gravel
12"
Φ = 0.4
Facility
Design
Soil Group
A
Bioretention
B
Facility
C
D
A
FlowB
through
C
Planter
D
A
B
Dry Well
C
D
A
Cistern +
B
Bioretention
C
D
A
Bioretention
B
+ Vault
C
D
Area
Volume
A
V1
(ft2/ft2)
(ft3/ft2)
0.07
0.11
0.06
0.05
0.058
0.092
0.050
0.042
0.06
0.05
0.05
0.06
0.050
0.042
0.130
0.204
0.020
0.009
0.013
0.017
0.04
0.04
0.04
0.04
0.193
0.210
0.105
0.063
N/A
N/A
N/A
N/A
Volume
Rainfall
Adjustment
2
for Surface
3
(ft /ft2)
Area
No min.
Eq. 4-6
No min.
Eq. 4-7
0.066
Eq. 4-8
0.055
Eq. 4-9*
Not permitted in “A” soils
Not permitted in “B” soils
0.066
Eq. 4-8
0.055
Eq. 4-9*
N/A
Eq. 4-6
N/A
Eq. 4-7
Not permitted in “C” soils
Not permitted in “D” soils
N/A
Eq. 4-13
N/A
Eq. 4-14
N/A
Eq. 4-15
N/A
Eq. 4-16
0.096
N/A
0.220
N/A
0.152
N/A
0.064
N/A
V
Rainfall
Adjustment
for Storage
Volume
Eq. 4-6
Eq. 4-7
Eq. 4-8
Eq. 4-9
Maximum
Release
Rate
No orifice
No orifice
Eq. 4-10
Eq. 4-11
Eq. 4-8
Eq. 4-9
Eq. 4-6
Eq. 4-7
Eq. 4-10
Eq. 4-11
No release
No release
Eq. 4-6
Eq. 4-7
Eq. 4-8
Eq. 4-9
Eq. 4-6
Eq. 4-7
Eq. 4-8
Eq. 4-9
Eq. 4-17
Eq. 4-12
Eq. 4-10
Eq. 4-11
No release
Eq. 4-12
Eq. 4-10
Eq. 4-11
Drainage
area
includes
portions of
roof and of
parking lot
Runoff may
enter by sheet
flow or be
piped.
Roof leaders
can be piped
directly or spill
across
pavement
Ensure is
consistent with
DMA
delineation
Outlet structure
Top of overflow grate
Underdrain connection
Inlet
Flow line at inlet
Top of curb
Top of adjacent paving
Soil layers
Top of soil layer
Bottom of gravel layer
Bottom of soil layer
15"
Overflow
elevation
Class 2 permeable
Caltrans spec 68-1.025
Typical to be slightly off
gradation spec on delivery
No filter fabric
Underdrain
Near top of gravel layer
PVC SDR 35 or equivalent; holes facing down
Solid pipe for 2' closest to outlet structure
Cleanout
Now included in NPDES Permit
60-70% Sand
ASTM C33 for fine aggregate
30-40% Compost
Certified through US Composting
Council Seal of Testing Assurance
Program
Submittal per Guidebook
Option to accept test results for a
“brand-name” mix if volume is
less than 100 cubic yards
Install in 8"-12" lifts
Do not compact
Do not overfill
Leave room for mulch
Maintain design
top of soil
elevation
Trees
Incorporate into
bioretention
facility
Account for
surface roots
Inspect each new facility within 45 days of
installation
Inspect 20% of all facilities each year
Inspect every facility at least once every
five years
Stormwater C.3 Guidebook, 6th Edition
www.cccleanwater.org/c3.html
Or search “Contra Costa Stormwater”
See in particular:
Chapter 5, Construction Checklist
Design sheets at end of Chapter 4
Appendix B, Soils/Plantings/Irrigation
for Bioretention Facilities