Quality and Age of Water in the Madison Aquifer, Cascade County, Montana

John LaFaveMontana Ground-Water Assessment Program

Madison Limestone

Great Falls

Kevin-SunburstDome

Madison outcrop

Madison Limestone – Structural Setting

Great Falls

Porcupine Dome

Poplar Dome

Kevin-SunburstDome

Madison outcropMadison - Petroleum wellMetal, cement, burnt lime mine

Madison Limestone – Economic Geology

Great Falls

Porcupine Dome

Poplar Dome

Giant Springs

Blaine Springs

Snowflake Springs LaDuke Spring

Big Spring

Layout Spring

Madison Limestone – Springs

Great Falls

Cascade Co.85 %

Cascade Co.

Madison water wellMadison major spring

other counties

15 %

Madison Limestone – Aquifer

Madison Aquifer – Geologic Setting

Cut Bank mbr.

Sunburst mbr.

coal

MadisonLimestone

Mm

Koo

tena

i Fm

Mor

rison

Fm

Pyrite

Line of section

N

S

Madison Ls (Mm)

N S

Sun Riv.Giant Sp.

Little Belt Mtns.

HighwoodMtns.

Great Falls

Belt

Coal MinesCoal Mines

Mm

5 miN

85 %

5 %4 %

Num

ber o

f wel

lsW

ell d

epth

(ft)

Well Use

Madison Aquifer – Cascade County5 mi

N

- Madison Aquifer well

Madison Aquifer – Porosity1 - Bedding

Madison Aquifer – Porosity2 - Fracture

Madison Aquifer – Porosity3 - Solution

Madison Aquifer – PorosityHeterogeneous

Madison Aquifer – Water Quality Data1 – GWCP Samples

Field SC – 120 wellsSampled – 50 wells

5 miN

Madison Aquifer – Water Quality Data2 – Tritium

Field SC – 120 wellsSampled – 50 wellsTritium – 14 wells

5 miN

Madison Aquifer – Water Quality Data3 – Other samples

Field SC – 120 wellsSampled – 50 wells

Tritium – 14 wellsOther samples – 35 wells

Abandoned coal minesWith AMD

5 miN

Abandoned coal minesWith AMD

< 500 mg/L500 – 1,000 mg/L> 1,000 mg/L

TDS mg/L

SC

uS

/cm

200

600

1000

1400

500

Est. TDS(n=70)

Meas. TDS(n=85)

TDS mg/L

5 miN

Madison Aquifer – Water QualityEstimated and measured total dissolved solids

Madison Aquifer – Water QualityMeasured total dissolved solids

80

20

40

60

80

60

Mg

Cl+

SO4=

>

60

20

40

60

80

20

40

SO4

<=Ca+

Mg

80 40 20 20 40 60 80

20

40

60

80

Ca Na HCO3+CO3 Cl

< 500 mg/L500 – 1,000 mg/L> 1,000 mg/L

200

600

1000

1400

500

Est. TDS(n=70)

Meas. TDS(n=85)

TDS mg/L

5 miN

20

40

60

80

60

80

Cl+

SO4=

>

20

40

<=Ca+

Mg

80 60 40 20 20 40 60 80

20

40

60

80

60

80

Ca Na HCO3+CO3

Mg SO4

20

40

Cl

500

1000

1500

2000

500

HCO3 type(n=35)

Madison Aquifer – Water Quality

Ca-HCO3low TDS

TDS mg/L

5 miN

20

40

60

80

60

80

Cl+

SO4=

>

20

40

<=Ca+

Mg

80 60 40 20 20 40 60 80

20

40

60

80

60

80

Ca Na HCO3+CO3

Mg SO4

20

40

Cl

500

1000

1500

2000

500

SO4 type(n=40)

HCO3 type(n=35)

Madison Aquifer – Water Quality

Ca-HCO3low TDS

Ca-SO4high TDS

TDS mg/L

5 miN

20

40

60

80

60

80

Cl+

SO4=

>

20

40

<=Ca+

Mg

80 60 40 20 20 40 60 80

20

40

60

80

60

80

Ca Na HCO3+CO3

Mg SO4

20

40

Cl

0

1

2

3

0.3

SO4 type(n=40)

HCO3 type(n=35)

Madison Aquifer – Water Quality

Ca-HCO3low TDS

Ca-SO4high TDS

4 Fe mg/L

5 miN

FeS2 + 7/2 O2 + H2O

Fe2+ + 2SO4 + 2H+

Pyrite Oxidation

Madison Aquifer – Water QualityMadison wells drilled by Byrne Drilling

5 miN

Madison Aquifer – Water Quality

FeS2 + 7/2 O2 + H2O

Fe2+ + 2SO4 + 2H+

Pyrite Oxidation wells with pyrite note in the log

5 miN

1940 1960 1980 2000

CFC-12

CFC-11

CFC-113

Tritium

Concentrations of CFC’s in air and tritium in precipitation

5 miN

< 1.5 (or ND)4.5 – 1010 – 20

Tritium (TU)

ND

ND

20

Madison Aquifer – Tritium concentrations

Tritium (TU)

sub-modern modern

Well 216851: 470 ft deep

Giant SpringsA

A’

Madison Aquifer – CFC age dating

Morrison Fm

~ 440 ftWell

216851Giant

Springs

Madison Limestone

~ 1,400 ft

Kootenai

Formation

∆

A

A’

Madison Aquifer – CFC age datingsamples collected in 2005

Recharge yrCFC-11 – 1975CFC-12 – 1979Apparent Age = 26 yrs

Recharge yrCFC-11 – 1974CFC-12 – 1982Apparent Age = 24 yrs

3H = 10.1 TU

3H = 10.2 TU

Madison Aquifer – Groundwater Velocity

Madison Ls (Mm)

Sun Riv.

Giant Sp.

Little Belt Mtns.

HighwoodMtns.

Mm

5 miN

Distance ~ 25 – 30 miles

25 –30 m

iles

Groundwater is moving at a rate of:

~ 1 mile/year, or~ 14 – 15 ft/day

(In this part o f the aquifer)

Morrison Fm

~ 440 ftWell

216851Giant

Springs

Madison Limestone

~ 1,400 ft

Kootenai

Formation

∆

A

A’

Madison Aquifer – 14C dating

PMC 14C age BP47.48 5,920d13C: -7.23H = 10.1 TU

3H = 10.2 TU

PMC 14C age BP49.38 5,668d13C: -7.1

1) CO2 + H2O H2CO3CO2 dissolves in water and hydrates to carbonic acid2) H2CO3 + CaCO3 2HCO3

- + Ca2+

½ HCO3 from CO2 (modern) and ½ from limestone (dead)

Conclusions – Madison Aquifer1)Most utilized in Cascade Co.

2)Water quality variable: • Ca-Mg-HCO3 (low TDS) – Ca-Mg-SO4 (high TDS)

3)Pyrite oxidation – controls?

4)Tritium –modern to sub-modern– variable porosity

5)Giant Springs: Young water

John LaFaveGround Water Assessment ProgramMontana Bureau of Mines and Geologyjlafave@mtech.edu