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 [email protected]
