Minnesota Water Resources Conference · Minnesota Stormwater Manual: “… [to] manage stormwater...
Transcript of Minnesota Water Resources Conference · Minnesota Stormwater Manual: “… [to] manage stormwater...
Cottage Grove: A Case Study in Wellhead
Protection and Stormwater BMPs
October 16, 2012 Steve Robertson – MN Department of Health
Brad Schleeter – Stantec
Minnesota Water Resources Conference
Wellhead Protection Goal
• Safeguard drinking water supplies through managing potential sources of contamination in recharge areas
Goal of Stormwater Management
Minnesota Stormwater Manual: “… [to] manage stormwater in a way that conserves, enhances, and
restores high-quality water in our rivers, lakes, streams, wetlands, and ground water.”
Summary
• Infiltration is a good stormwater management tool • Use common sense in siting infiltration devices, especially in
wellhead protection areas
MDH Guidance on Infiltration of Stormwater in Vulnerable WHPAs
• Advisory, not mandatory • For PWS/municipal staff • Process is stepwise (6 steps) • Flow chart is available
(http://www.health.state.mn.us/divs/eh/water/factsheet/index.html#swp)
Main MDH Approaches
• Avoid stormwater infiltration in Emergency Response Areas
Main MDH Approaches
• Avoid stormwater infiltration in Emergency Response Areas • Avoid infiltration in certain sensitive WHPAs (e.g., fractured,
solution weathered bedrock)
Wellhead Management Areas in Minnesota • Total Land Area in
Minnesota:~218,505 km2
• WHPA total: 2787 km2 (1.3%)
• Vulnerable WHPA: 899 km2 (0.4 %)
Wellhead Management Areas, Twin Cities Metro Area
Main MDH Approaches
• Avoid stormwater infiltration in Emergency Response Areas • Avoid infiltration in certain sensitive WHPAs (e.g., fractured,
solution weathered bedrock) • Infiltration of runoff from any stormwater hotspot (see Minnesota
Stormwater Manual)
Different Source Areas Yield Different Contaminants
Take home message
• Infiltration is not a panacea • Your stormwater is someone else’s water • Use common sense in managing it
Resources
• MDH guidance – (http://www.health.state.mn.us/divs/eh/water/fs.htm)
• MDH SWP hydrologist (651-201-4700) • Minnesota Stormwater Manual
– (http://www.pca.state.mn.us/water/stormwater/stormwater-manual.html) • MPCA
– (http://www.pca.state.mn.us)
Case Study: City of Cottage Grove
• MDH Infiltration Guidance • Physical Characteristics of Cottage Grove • Wellhead Protection • Project Examples
Cottage Grove Location Map
MDH Infiltration Guidance Flow Chart
Bedrock Geology
*Source: South Washington Watershed District 2007 Watershed Management Plan – Map 8.4
Wellhead Protection Areas
Wellhead Protection Area: Well #10
New Pond Construction Project: Hamlet Park Pond Expansion
Historic Flow Pattern Current Flow Pattern
New Development
*Source: Google Images
Pond Retrofit Project: Pine Tree Valley Park Pond Improvements
*Source: Google Images
Pond Retrofit Project: Pond C-P6 Improvements
Pond Retrofit Project: Pond C-P6 Improvements
Pond Retrofit Project: Pond C-P6 Improvements
Pond Retrofit Project: Pond C-P6 Improvements
Pond Retrofit Project: Pond C-P6 Improvements
Pond Retrofit Project: Pond C-P6 Improvements
Pond Retrofit Project: Woodridge Park Pond Improvements
Pond Retrofit Project: Woodridge Park Pond Improvements
Pond Retrofit Project: Pond ED-P5 Water Quality Improvements
Final Thoughts: • Wellhead protection concerns are real • When designing infiltration features,
knowledge of both surface water and ground water impediments is necessary
• Err on the side of caution when it comes to a stormwater management approach that places a priority on drinking water protection
Can stream baseflow be augmented
through stormwater infiltration? The case of the Minnehaha Creek Watershed
Trisha Moore
University of Minnesota – St. Anthony Falls Laboratory
Minnesota Water Resources Conference, October 16 2012
Stormwater to baseflow? John Gulliver (Civil Eng./SAFL), John Nieber (Bioproducts and
Biosystems Eng.) and Joe Magner (Bioproducts and Biosystems Eng.)
Minnehaha Creek Watershed District
Mississippi Watershed Management Organization
Presentation outline
Project background
What are the sources of flow in Minnehaha Creek?
Isotope analysis – identify flow sources
What is the direction of groundwater flow in the vicinity of the creek?
Overview of watershed geology and hydraulic characteristics
Seepage meters – measure groundwater fluxes
Piezometers – establish hydraulic gradients
Temperature – thermal profiles as groundwater tracer
Minnehaha Creek Watershed
Upper Watershed:
123 mi2
Lower Watershed:
47 mi2
Lake Minnetonka
Minnehaha Creek
Hydrologic alterations:
Urban runoff management
Stormwater outfalls
− Stormwater pipes
Hydrologic alterations:
Headwaters Regulation
Weirs operated to maintain Lake
Minnetonka elevation > 928.6 ft
Hydrologic alterations:
Resulting flashy hydrology
A waterfall with no flow?
Photo credit: Star Tribune, 1964
6 million gallons of municipal
water, released from fire hydrants
Can stormwater runoff be
infiltrated to augment baseflow?
What are the sources of flow in Minnehaha Creek?
What is the relative contribution of each?
What is the direction of groundwater flow in the
vicinity of the creek?
What is the potential to capture, store, and redistribute
stormwater runoff to contribute to baseflow?
Surface and groundwater features
Lake Harriet
Lake Hiawatha
(Barr, 2010)
What are the sources of flow in the Creek?
Flow source tracking with Isotopes
Isotope (18O and 2H)
sampling points
-80
-70
-60
-50
-40
-30
-20
-10
0
10
-11 -9 -7 -5 -3 -1
δ2H
δ18O
Lake Harriet
mean isotopic ratio central MN precip
5/25 and 5/27 MNPL precip
Lake Minnetonka
What are the sources of flow in the Creek?
Preliminary isotope results
Δ Creek Lakes Groundwater
-80
-70
-60
-50
-40
-30
-20
-10
0
10
-11 -9 -7 -5 -3 -1
δ2H
δ18O
Lake Harriet
mean isotopic ratio central MN precip
5/25 and 5/27 MNPL precip
Lake Minnetonka
What are the sources of flow in the Creek?
Preliminary isotope results
Δ Creek Lakes Groundwater
Groundwater
Creek isotopic signature ≠ Groundwater isotopic signature
Direction of groundwater flow
Watershed wide: downward
Rapid vertical transit through sand-gravel
quaternary deposits
Median vertical travel time from surface to bedrock
< 0.5 years (Tipping, 2011)
Relatively small contributing groundwatershed
< 0.1% of surficial watershed area based on
approach of Brutsaert and Nieber (1977)
Direction of groundwater flow
In creek riparian area: it depends
Preliminary field results
Corroborating seepage meter,
temperature, and piezometer data
Groundwater flow direction?
Drilling down to the site scale… Future MCWD stormwater management &
stream restoration site
Seepage Measurements Allows direct measurement of groundwater fluxes in
streambed
Preliminary seepage results:
Decline with time during dry period,
but upward groundwater discharge
0
0.05
0.10
2
4
6
8
10
12
14
8/23 8/28 9/2 9/7 9/12
Pre
cip
itati
on
(m
m)
Seep
age r
ate
, cm
/d
ay
Blake Cold Storage Site, Right Bank
Precip
Meter 1
Meter 2
Meter 31.25
2.5
Corroborating with piezometer data
0
1
2
3
4
5
694.8
95
95.2
95.4
95.6
95.8
8/17/12 8/24/12 8/31/12 9/7/12 9/14/12 9/21/12
Pre
cip
itati
on
(m
m)
Ele
vati
on
[ft
]
2012 Water Elevations at Blake and Precipitation
precip Stream surface
Well 3 (2 m from channel) Well 2 (6 m from channel)
Well 1 (8 m from channel)
Piezometric head groundwater to stream
Streambed temperature profiles
to estimate groundwater flux
1D, steady-state heat transfer:
qzT
zk fs
C f2T
z2
Where kfs = thermal conductivity streambed materials
Cf = fluid heat capacity
ρ = fluid density
T = temperature
z = profile depth
Vertical groundwater flux
Streambed temperature profiles to
estimate groundwater flux
0
10
20
30
40
10 15 20 25 30
Dep
th b
elo
w s
tream
bed
(cm
)
Temperature (C)
Right Bank
Thalweg
Left Bank
Avg. gw temp. in piezometers = 15 C
Corroborating temperature…
0
10
20
30
40
10 12 14 16 18 20 22 24 26
Dep
th b
elo
w s
tream
bed
(cm
)
Temperature (C)
Right Bank
Thalweg
Left Bank
3 cm d-1 UPWARD 4 cm d-1 DOWNWARD NUETRAL
Preliminary temperature data as
indicator of losing and gaining reaches
Upward groundwater flux
Downward groundwater flux
MetroModel
Can stormwater runoff be
infiltrated to augment baseflow in
Minnehaha Creek?
It depends.
Summary and future work
Sustained baseflow during drought periods likely
limited by rapid vertical transit
Vertical travel time calculations by Tipping (2011)
Contributing aquifer fraction very small by Brutsaert
and Nieber (1977) approach
Drought flow isotope signature reflects surface water
origin
UPWARD discharging groundwater to creek has been
observed BUT magnitude and direction varies by
reach and across channel
Summary and future work
Continue temperature and seepage measurements at
more locations along stream use to identify areas
with highest potential for stormwater infiltration
Develop model to evaluate impact of total integration
of infiltration practices on potential stream baseflow
Thank you!
Special thanks to:
John Gulliver, John Nieber, and Joe Magner (U of M)
Laina Breidenbach, Tom Dietrich, Jess DeGennero & Lauren Sampedro (U of M)
Perry Jones & Mike Menheer (USGS)
Minnehaha Creek Watershed District and Mississippi Watershed Management Organization
Isotope analysis:
Continuing work
Sampling from riparian wells and during drought flow
Apply mixing model
Is isotopic signature of groundwater different
from that of creek and its surface water
sources?
Does isotopic signature of creek reflect that of
groundwater during low flow periods?
Summary – streamflow
and geologic data Groundwater contributions to Minnehaha Creek likely
small (~ 1.5 cm yr-1, or average daily flow 5 cfs)
Sustained baseflow during drought periods likely
limited by rapid vertical transit
Contributing aquifer fraction of Brutsaert and Nieber
approach
Vertical travel time calculations by Tipping (2011)
Watershed geology
Watershed geology : Rapid vertical
transit through quaternary aquifer
Data from Tipping, 2011
Inferring aquifer characteristics
through streamflow analysis
Brutsaert and Nieber (1977) approach:
Relates ΔQ/Δt with watershed and aquifer parameters
dQ /dt aQb
a 4.8k 2L / f (A)32
k = hydraulic conductivity
f = drainable porosity
α = fraction contributing aquifer
L = total stream length
A = watershed area
0.1
1
10
1 10 100
-dQ
/dt
(cfs
day
-1)
Discharge, Q (cfs)
dQ/dt aQb 0.002Q32
Inferring aquifer characteristics
through streamflow analysis
α = fraction contributing aquifer < 1% of watershed area
88
90
92
94
96
98
100
0 2 4 6 8 10 12 14 16 18 20
ele
va
tio
n [
ft]
ground elevation
water elevation
creek surface
Creek cross section
Distance from stream bank (m)
Piezometer installation at headwaters wetland site
Screened interval
Coarse
sand/gravel/
cobble
Organic soils
Seepage measurements –
past work Groundwater seepage measured by Lundy and Ferrey
(2004) at Schloff Chemical Superfund site in St. Louis
Park
Avg. seepage rate 32 cm d-1
Avg. discharge rate 12 cfs
Minnehaha Creek wetland inventory