Helena Valley Ground Water Monitoring Program

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1 Helena Valley Ground Water Monitoring Program James Swierc Lewis & Clark County Water Quality Protection District October 6, 2011

2 WQPD Sampling Program Overview Helena Area Water Related Issues Nutrient Loading to Lake Helena TMDL Interaction of Surface and Ground Water Source Identification Agriculture, Wastewater, Natural? Onsite Wastewater Treatment Septic Systems Impacts to Ground Water (Site Scale vs. Valley Scale) Ground Water Depletion Trace Elements Arsenic, Uranium, Selenium Data Needs Water Quality Related (This Talk) Characterize changes/impacts to water quality Compilation of Historical and Current Data Characterize spatial distribution of different water types Fate and Transport of Nutrients Monitoring Program Results Presentation Overview Water Quality Map of Helena Valley Different Water Quality Types (major ions) present Review of different areas Observations on ground water temperature from specific sites

3 Regional Hydrogeology Overview Helena Valley Aquifer Combined upper Tertiary and Quaternary Sediments Unconfined Recharge Stream Loss at valley margins Stream Loss from Helena Valley Irrigation Canal and Ditch Network Bedrock Flow in subsurface Direct Infiltration of Precipitation Discharge Upwelling to Lake Helena Surface flowing artesian wells near center of valley Upwelling to tributary streams Valley drain network Wells Bedrock Aquifers Various pre Tertiary Bedrock units defining valley Unconfined/Confined in Areas Fracture Flow system(s) Recharge Direct Infiltration of Precipitation Discharge Direct to Valley Aquifer in subsurface Discharge to streams outside of valley Wells Scratch Gravel Hills North Hills Asarco Potentiometric Surface from Briar & Madison (1992) (Developed from numerical gw flow model)

4 Helena Valley Water Quality Map Methods Stiff Diagrams Data Sources WQPD Data MBMG Data USGS Data Consultant Project Data Asarco Helena Sand & Gravel Helena Landfill GIS data management Water quality types based on major ions Map ongoing project updated as more data becomes available Basemap shows Geology

5 Water Quality Type Differentiation Multiple Samples on same diagram Generally Stable both seasonally and over time

6 Assessment Example East Helena Seaver Park/Lamping Field Surface/Ground Water Interaction Tertiary Flow and Water Quality Impacts to Water Quality Seaver Park Location

7 Water Quality Types Based on relative proportions of major ions, as milliequivalents Breaks identified to highlight changes in water quality Cations Primarily Calcium (Ca) and Magnesium (Mg) increasing Sodium (Na) and Potassium (K) Anion Primarily Bicarbonate (HCO 3 ) Increasing Sulfate (SO4) Concentrations Note some minor exceptions in Mg Ca Bicarbonate and Mixed Anion Water Types

8 Water Quality Generalizations Mg Ca Bicarbonate in Helena Formation wells Dolomite source of Mg Distinct water type Outliers Na+K Mixed east valley Hot Springs Anthropogenic Impacts Very high TDS High Chloride Ca Mg Bicarbonate in shallow wells Central part of valley, near streams Bedrock areas primary recharge from precipitation See increase in Sulfate Surface Water / Ground Water Interaction

9 Sodium (Na) Potassium (K) Waters East North Hills Broadwater Hot Springs Marysville Thermal Anomaly Emerald Ridge Green Meadow CC Shallow 100 well Deep 358 well Significant ground water depletion Initial wells ft bgs Replacement wells 600 feet or more Tertiary Aquifer Initial High Yield; Dewatered Water bearing units well below Lake Helena All associated with ground water temperatures above geothermal gradient

10 Ground Water Temperature Background Conservative Tracer of mixing waters Average water temperature1 2 C above mean annual temperature Can seasonally fluctuate several degrees near surface Ground water temperature increases with depth at Geothermal Gradient 1.8 C/100 m ( C/ft) in normal sedimentary basins 3.6 C/100 m (0.011 C/ft) in volcanic areas Geothermal Gradient Temperature with depth April 2010 Sampling (Heath, 1983)

11 Noticable Warm Waters Temperature > 14 C (57 F) From recent sampling data Temperature with depth

12 Thermal Sources Helena Valley Deep Basin 6000 feet of Tertiary Valley Fill Geothermal gradient range maximum temperatures C/ft x 6000 ft = 33 C (91 F) C/ft x 6000 ft = 66 C (151 F) Upwelling of Heated Waters Helena Sedimentary Basin Outline Based on Gravity Survey Data Know warm water is present What about cool water at normal geothermal gradient?

13 Cool Waters Temperature normal geothermal gradient Bedrock west of valley Shallow wells central valley Temperature with depth

14 Conclusions Water Quality Map Preliminary Form Need to incorporate well depths Work in progress will add additional data as becomes available Ca Mg Bicarbonate (with Sulfate) waters simplest water type Local Recharge from Precipitation and Stream Loss Associated with cool water temperatures Na+K Waters associated with warm waters May also be derived from anthropogenic sources High Chloride/Mixed ion wells reflect localized problems/issues Warm waters are present along margins of Helena Valley Bedrock areas in Scratch Gravel Hills and western North Hills area show normal geothermal gradient STILL MUCH WORK TO BE DONE Mapping Method with Stiff Diagrams Useful for delineating water quality trends spatially Data Need Piper Diagrams for each water quality type

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