green city, clean waters...green city, clean waters. dan o’rourke, cdm smith. ... (distribution...
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GREEN CITY, CLEAN WATERS
Dan O’Rourke, CDM SmithJason Cruz, Philadelphia Water
Chris Bergerson, Philadelphia WaterStephen White, Philadelphia Water
Taylor Heffernan, Philadelphia WaterMatthew Gamache, CDM Smith
Laurie Kellndorfer, CDM Smith
Investigation of Infiltration in Unsaturated Urban Fill MaterialVUSP Pennsylvania Stormwater SymposiumOctober 15, 2015
Philadelphia or Fill-adelphia?
• Urban fill covers much of Philadelphia
• Often exceeds the depth of green stormwater infrastructure
• What happens when we infiltrate into it?
Fill Areas
3from USGS OFR 224 (2000)
The Importance of Over-Excavation
Contact between fill and silty clay (orange)
Poor Fill Quality
• Brick fill
Groundwater Flow Modeling
• 3D regional and site scale models (DYNFLOW; www.dynsystem.com)
• Mounding analysis by USGS (1D, using Hantush equation)
• Saturated zone
8after Gamache et al (2015)
SWMS 2D
• USDA Code (finite element)• Solves Richards equation for saturated
and unsaturated groundwater flow• Requires:
– Saturated hydraulic conductivity (Ks)– Residual saturation (θr)– Maximum saturation (θs) = porosity (φ)– Coefficient in soil water retention
equation (α)– Exponent in soil water retention
equation (η)
9after Gamache et al (2015)
Applications of 2D Modeling
• Provide guidance on siting GSI– Evaluate how infiltrated water migrates within the
subsurface• risk of lateral flow to adjacent infrastructure
– Evaluate extent of water table mounding
10
Tree Trench 2D Simulations
• Test 3 scenarios:– General tree trench– General tree trench with a liner– Conduits
• Very permeable areas within fill– Gravel, brick fill, etc.
• Set-up based on actual tree trench
11
10’
7’Trench GravelKh = Kv = 1000 ft/day
FillKh = Kv = 16 ft/day
Native Aquifer Sediments Kh = 10 ft/dayKv = 1 ft/day
6’ 5’
Tree Trench
Length of Trench = 137 ftDrainage Area = 15,500 ft2
8’
Bedrock (assumed to be impermeable)
Model Set-Up (Tree Trench)
13
Fixed head at lateral boundaries
No-flow along bottom
Infiltration at set of nodes (distribution pipe)
after Gamache et al (2015)
Scenarios
14
BuildingFoundation
Tree Trench
Water Table
Tree Trench with Liner
BuildingFoundation
Tree Trench, No Liner, Gravel Patch
BuildingFoundation
after Gamache et al (2015)
Tree Trench
15
BuildingFoundation
Under baseline conditions, the tree trench
drains twice the design flow without excessive mounding or basement infiltration. Increases in water content/saturation is simulated around the trench in all directions.
after Gamache et al (2015)
Tree Trench with Liner
16
With a liner in place, the tree trench retains water and lateral increases in water content/saturation are minimized. However, infiltration is restricted,
relative to the base case.
BuildingFoundation
after Gamache et al (2015)
17
In this instance, the simulated gravel patch acts as a conduit for flow to the building foundation. Brick fill would produce the
same effect.BuildingFoundation
Tree Trench, No Liner, Gravel Patch
18
This conduit effect is exacerbated with lower
permeability soils
BuildingFoundation
after Gamache et al (2015)
Calibration Check
• Use observation wells within GSI
• Approximately 50 systems are actively being continuously monitored by Philadelphia Water
19
Monitoring Data: April 2014 Event
• Compare observation well data from 6 different tree trenches
20
N
after Gamache et al (2015)
Rain Event
21
0
Cum
ulat
ive
Rai
nfal
l (in
)
2
3
4
5
6
1
4/28/2014 4/29/2014 4/30/2014 5/1/2014 5/2/2014 5/3/2014 5/4/2014 5/5/2014
after Gamache et al (2015)
22
0
2
3
4
5
6
1
4/28/2014 4/29/2014 4/30/2014 5/1/2014 5/2/2014 5/3/2014 5/4/2014 5/5/20140
Cum
ulat
ive
Rai
nfal
l (in
)
2
3
4
5
6
1
Wat
er L
evel
(ft)
Observed Data
23
0
2
3
4
5
6
1
Wat
er L
evel
(ft)
4/28/2014 4/29/2014 4/30/2014 5/1/2014 5/2/2014 5/3/2014 5/4/2014 5/5/20140
Cum
ulat
ive
Rai
nfal
l (in
)
2
3
4
5
6
1
Observed Data
Observed Data
24after Gamache et al (2015)
0
2
3
4
5
6
1
4/28/2014 4/29/2014 4/30/2014 5/1/2014 5/2/2014 5/3/2014 5/4/2014 5/5/20140
Cum
ulat
ive
Rai
nfal
l (in
)
2
3
4
5
6
1
Wat
er L
evel
(ft)
15’
4’
Tree Trench
10’
Length of Trench = 100 ftDrainage Area = 15,000 ft2
9’
Trench GravelKh = Kv = 1000 ft/d
FillKh = 0.50 ft/dKv = 0.25 ft/d
Native Aquifer Sediments Kh = 10 ft/dayKv = 1 ft/day
26
Simulation Results
27
Simulation Results
Summary & Next Steps
• Two dimensional modeling can be used for GSI siting, particular in areas of shallow water table or poor fill quality– Can also be used for design to determine infiltrated volume
• Permeable conduits can be problematic– Need good characterization
• Reasonable match to measured observation well data• Need to correlate with:
– Residual saturation – Simulated run-off testing– Groundwater monitoring wells
28
Water Table Mounding
29
Green City, Clean Waters
www.phillywatersheds.org
www.phillywatersheds.org/ltcpu
Dan O’Rourke, P.G.CDM Smith110 Fieldcrest Ave, #8, 6th Fl.Edison, New Jersey [email protected]