Minnesota Water Resources Conference · Minnesota Stormwater Manual: “… [to] manage stormwater...

transcript

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: 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

Questions?

Steve Robertson: steve.robertson@state.mn.us

Brad Schleeter: brad.schleeter@stantec.com

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

Headwaters Regulation

Weirs operated to maintain Lake

Minnetonka elevation > 928.6 ft

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

-11 -9 -7 -5 -3 -1

Lake Harriet

mean isotopic ratio central MN precip

5/25 and 5/27 MNPL precip

Lake Minnetonka

Preliminary isotope results

Δ Creek Lakes Groundwater

-11 -9 -7 -5 -3 -1

Lake Harriet

mean isotopic ratio central MN precip

5/25 and 5/27 MNPL precip

Lake Minnetonka

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

8/23 8/28 9/2 9/7 9/12

Blake Cold Storage Site, Right Bank

Precip

Meter 1

Meter 2

Meter 31.25

Corroborating with piezometer data

8/17/12 8/24/12 8/31/12 9/7/12 9/14/12 9/21/12

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:

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

10 15 20 25 30

Temperature (C)

Right Bank

Thalweg

Left Bank

Avg. gw temp. in piezometers = 15 C

Corroborating temperature…

10 12 14 16 18 20 22 24 26

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

1 10 100

Discharge, Q (cfs)

dQ/dt aQb 0.002Q32

Inferring aquifer characteristics

through streamflow analysis

α = fraction contributing aquifer < 1% of watershed area

0 2 4 6 8 10 12 14 16 18 20

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

Avg. seepage rate 32 cm d-1

Avg. discharge rate 12 cfs

Minnehaha Creek wetland inventory

Minnesota Water Resources Conference · Minnesota Stormwater Manual: “… [to] manage stormwater...

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