Quality and Age of Water in the Madison Aquifer, Cascade County, Montana John LaFave Montana Ground-Water Assessment Program Madison Limestone Great Falls Madison Limestone – Structural Setting Kevin-Sunburst Dome Poplar Dome Great Falls Porcupine Dome Madison outcrop Madison Limestone – Economic Geology Kevin-Sunburst Dome Poplar Dome Great Falls Porcupine Dome Madison outcrop Madison - Petroleum well Metal, cement, burnt lime mine Madison Limestone – Springs Giant Springs Great Falls Blaine Springs Big Spring Layout Snowflake Springs LaDuke Spring Spring Madison Limestone – Aquifer Cascade Co. other counties 15 % Cascade Co. Madison water well 85 % Madison major spring Madison Aquifer – Geologic Setting 5 mi N N Line of section Giant Sp. Sunburst mbr. Sun Riv. Highwood Mtns. Great Falls Kootenai Fm Belt Pyrite Coal Mines Cut Bank mbr. Coal Mines coal Mm Morrison Fm S Madison Limestone Mm Little Belt Mtns. N S Madison Ls (Mm) Madison Aquifer – Cascade County 5 mi N Number of wells Well depth (ft) Well 4 % - Madison Aquifer well 5 % Well Use 85 % Madison Aquifer – Porosity 1 - Bedding Madison Aquifer – Porosity 2 - Fracture Madison Aquifer – Porosity 3 - Solution Madison Aquifer – Porosity Heterogeneous Madison Aquifer – Water Quality Data 1 – GWCP Samples 5 mi N Field SC – 120 wells Sampled – 50 wells Madison Aquifer – Water Quality Data 2 – Tritium 5 mi N Field SC – 120 wells Sampled – 50 wells Tritium – 14 wells Madison Aquifer – Water Quality Data 3 – Other samples 5 mi N Field SC – 120 wells Sampled – 50 wells Tritium – 14 wells Other samples – 35 wells Abandoned coal mines With AMD Madison Aquifer – Water Quality Estimated and measured total dissolved solids 5 mi N SC uS/cm TDS mg/L TDS mg/L Abandoned coal mines With AMD 1400 1000 600 500 200 < 500 mg/L Meas. TDS Est. TDS 500 – 1,000 mg/L (n=85) (n=70) > 1,000 mg/L Madison Aquifer – Water Quality Measured total dissolved solids 80 80 5 mi > = 60 60 4 O < N S = C + a Cl + 40 40 M g 20 20 Mg SO4 80 80 60 60 40 40 20 20 8 6 4 2 0 0 0 0 0 0 0 0 2 4 6 8 Ca Na HCO3+CO3 Cl TDS mg/L 1400 1000 600 500 200 < 500 mg/L Meas. TDS Est. TDS 500 – 1,000 mg/L (n=85) (n=70) > 1,000 mg/L Madison Aquifer – Water Quality 80 80 5 mi > = 60 60 O4 < S = N C + l a C + 40 40 M g Ca-HCO3 20 20 low TDS Mg SO4 80 80 60 60 40 40 20 20 8 6 4 2 0 0 0 0 0 0 0 0 Ca Na HCO3+CO32 4 6 8 Cl TDS mg/L 2000 1500 1000 500 500 HCO3 type (n=35) Madison Aquifer – Water Quality Ca-SO4 high TDS 80 80 5 mi > = 60 60 O4 < S = N C + l a C + 40 40 M g Ca-HCO3 20 20 low TDS Mg SO4 80 80 60 60 40 40 20 20 8 6 4 2 0 0 0 0 0 0 0 0 Ca Na HCO3+CO32 4 6 8 Cl TDS mg/L 2000 1500 1000 500 500 HCO3 type SO4 type (n=35) (n=40) Madison Aquifer – Water Quality Ca-SO4 high TDS 80 80 5 mi > = 60 60 O4 < S = N C + l a C + 40 40 M g Ca-HCO3 20 20 low TDS Mg SO4 80 80 60 60 40 40 20 20 8 6 4 2 0 0 0 0 0 0 0 0 Ca Na HCO3+CO32 4 6 8 Cl 4 Fe mg/L 3 2 1 0.3 0 HCO3 type SO4 type (n=35) (n=40) Madison Aquifer – Water Quality Pyrite Oxidation Madison wells drilled by Byrne Drilling 5 mi N FeS2 + 7/2 O2 + H2O 2+ + Fe + 2SO4 + 2H Madison Aquifer – Water Quality Pyrite Oxidation wells with pyrite note in the log 5 mi N FeS2 + 7/2 O2 + H2O 2+ + Fe + 2SO4 + 2H Madison Aquifer – Tritium concentrations Concentrations of CFC’s in air and tritium in precipitation 5 mi N Tritium CFC-12 ND ND CFC-11 CFC-113 1940 1960 1980 2000 20 sub- modern modern Tritium (TU) < 1.5 (or ND) 4.5 – 10 10 – 20 Tritium (TU) Madison Aquifer – CFC age dating Giant Springs A A’ Well 216851: 470 ft deep Madison Aquifer – CFC age dating samples collected in 2005 Recharge yr CFC-11 – 1974 CFC-12 – 1982 Apparent Age = 24 yrs ∆ A’ 3H = 10.2 TU Formation Kootenai Giant Well A Springs 216851 ~ 440ft Morrison Fm ~ 1,400 ft Madison Limestone Recharge yr CFC-11 – 1975 CFC-12 – 1979 Apparent Age = 26 yrs 3H = 10.1 TU Madison Aquifer – Groundwater Velocity 5 mi N Giant Sp. Groundwater is moving at a rate of: Sun Riv. Highwood Mtns. ~ 1 mile/year, or 25 – 30miles ~ 14 – 15 ft/day (In this part o f the aquifer) Mm Little Belt Mtns. Distance ~ 25 – 30 miles Madison Ls (Mm) Madison Aquifer – 14C dating PMC 14C age BP 49.38 5,668 d13C: -7.1 ∆ A’ 3H = 10.2 TU Formation Kootenai Giant Well A Springs 216851 ~ 440ft Morrison Fm ~ 1,400 ft Madison Limestone PMC 14C age BP 1) CO2 + H2O H2CO3 CO2 dissolves in water and hydrates to carbonic acid 47.48 5,920 2) H CO + CaCO 2HCO - + Ca2+ d13C: -7.2 2 3 3 3 3H = 10.1 TU ½ HCO3 from CO2 (modern) and ½ from limestone (dead) Conclusions – Madison Aquifer 1)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 LaFave Ground Water Assessment Program Montana Bureau of Mines and Geology [email protected].