11: Groundwater

1. 11: Groundwater • Water resources • Geologic Agent

2. Hydrogeology Defined Water Earth Earth materials • Rock • Sediment (Soil) • Fluids (Water) Geologic processes • Form, • Transform and • Distribute (redistribute) Earth materials  Water is a primary agent of many (all?) geologic processes

3. Hydrogeology DefinedWater Earth Interactions  Interactions go both ways • GeologyGroundwater • Geology controls flow and availability of groundwater because • Groundwater flows through the pore spaces and/or fractures • Groundwater  geologic processes.

4. Shale Sandstone Shale Hydrogeology DefinedWaterEarth Interactions Geology controls groundwater flow • Permeable pathways are controlled by distributions of geological materials. • E.g., Artesian (confined) aquifer

5. Hydrogeology DefinedWaterEarth Interactions Geology controls groundwater flow • Permeable pathways are controlled by distributions of geological materials. • Groundwater availability is controlled by geology.

6. Hydrogeology DefinedWaterEarth Interactions Geology controls groundwater flow • Permeable pathways are controlled by distributions of geological materials. • Groundwater availability is controlled by geology. • Subsurface contaminant transport in is controlled by geology.

7. Hydrogeology DefinedWaterEarth Interactions Groundwater controls geologic processes • Igneous Rocks: Groundwater controls water content of magmas. • Metamorphic Rocks: Metasomatism (change in composition) is controlled by superheated pore fluids. • Volcanism: Geysers are an example of volcanic activity interacting with groundwater.

8. Hydrogeology DefinedWaterEarth Interactions Groundwater controls geologic processes • Landforms: Valley development and karst topography are examples of groundwater geomorphology. • Landslides: Groundwater controls slope failure. • Earthquakes: Fluids control fracturing, fault movement, lubrication and pressures.

9. Hydrogeology Subdisciplines • Water resource evaluation • What controls how much groundwater is stored and can be safely extracted? • What controls where groundwater comes from and where it flows? • What controls natural water quality: natural interactions with geological materials control the chemistry of groundwater? • How can we protect groundwater recharge areas and groundwater reservoirs from contamination and depletion?

10. Hydrogeology Subdisciplines • Contaminant Hydrogeology • Anthropogenic effects: degradation of water quality due to human influences (contamination) • How fast are dissolved contaminants carried by groundwater? • Transport pathways of contaminants: Where are sources of contamination impacting the groundwater, where are the going and what are the destinations? • Remediation (clean-up) of contaminants dissolved in the groundwater.

11. Potentiometric Surface Darcy’s Law Answers the fundamental questions of hydrogeology. • What controls: • How much groundwater flows? • How fast groundwater flows? • Where groundwater flows?

12. Darcy’s Law Henry Darcy’s Experiment (Dijon, France 1856) h1 h2 Dh : Hydraulic Gradient h Slope = Dh/Dx ~ dh/dx h1 Dh h2 Dx x x1 x2 Darcy investigated ground water flow under controlled conditions A Q:Volumetric flow rate [L3/T] A:Cross Sectional Area (Perp. to flow) Dx Q K: The proportionality constant is added to form the following equation: Kunits [L/T]

13. Calculating Velocity with Darcy’s Law • Q= Vw/t • Q: volumetric flow rate in m3/sec • Vw: Is the volume of water passing through area “a” during • t: the period of measurement (or unit time). • Q= Vw/t = H∙W∙D/t = a∙v • a: the area available to flow • D: the distance traveled during t • v : Average linear velocity • In a porous medium: a = A∙n • A: cross sectional area (perpendicular to flow) • n: porous For media of porosity • Q = A∙n∙v • v = Q/(n∙A)=q/n v Vw a H w D

14. Darcy’s Law (cont.) • Other useful forms of Darcy’s Law Used for calculating Volumes of groundwater flowing during period of time Volumetric Flow Rate Volumetric Flux (a.k.a. Darcy Flux or Specific discharge) Used for calculating Q given A Q = A Ave. Linear Velocity Used for calculating average velocity of groundwater transport (e.g., contaminant transport Q q = = A.n n Assumptions: Laminar, saturated flow

15. Pond 2 Pond 1 658 652 N 0 5000 ft Darcy’s Law Application • Settling Pond Example* • A company has installed two settling ponds to: • Settle suspended solids from effluent • Filter water before it discharges to stream • Damp flow surges • Questions to be addressed: • How much flow can Pond 1 receive without overflowing? Q? • How long will water (contamination) take to reach Pond 2 on average?v? • How much contaminant mass will enter Pond 2 (per unit time)? M? *This is a hypothetical example based on a composite of a few real cases

16. Q? v? M? Dh=6.51 ft K W b=8.56 ft Contaminated Pond Dx =186 ft b Clay Dx Not to scale Application(cont.) Water flows between ponds through the saturated fine sand barrier driven by the head difference Pond 1 Pond 2 W 1510 ft Outfall Overflow Elev.= 658.74 ft Elev.= 652.23 ft Dx =186 Sand

17. Application(cont.) • Develop your mathematical representation (i.e., convert your conceptual model into a mathematical model) • Formulate reasonable assumptions • Saturated flow (constant hydraulic conductivity) • Laminar flow (a fundamental Darcy’s Law assumption) • Parallel flow (so you can use 1-D Darcy’s law) • Formulate a mathematical representation of your conceptual model that: • Meets the assumptions and • Addresses the objectives Q? v? M? M = Q C

18. Application(cont.) • Collect data to complete your Conceptual Model and to Set up your Mathematical Model • The model determines the data to be collected • Cross sectional area (A = w b) • w: length perpendicular to flow • b: thickness of the permeable unit • Hydraulic gradient (Dh/Dx) • Dh: difference in water level in ponds • Dx: flow path length, width of barrier • Hydraulic Parameters • K: hydraulic tests and/or laboratory tests • n: estimated from grainsize and/or laboratory tests • Sensitivity analysis • Which parameters influence the results most strongly? • Which parameter uncertainty lead to the most uncertainty in the results? Q? v? M = Q C M?

19. Ground Water Zones • Degree of saturation defines different soil water zones

20. Soil and Groundwater Zones Unsaturated Zone: Water in pendular saturation Caplillary Fringe: Water is pulled above the water table by capilary suction Water Table: where fluid pressure is equal to atmospheric pressure Saturated Zone: Where all pores are completely filled with water. Phreatic Zone: Saturated zone below the water table

21. Ground water and the Water cycle • Infiltration • Infiltration capacity • Overland flow • Ground water recharge • GW flow • GW discharge

22. Hydraulic Conductivity of bedrock is controlled by Size of fracture openings Spacing of fractures Interconnectedness of fractures Bedrock Hydrogeology

23. Porosity and Permeability • Porosity: Percent of volume that is void space. • Sediment: Determined by how tightly packed and how clean (silt and clay), (usually between 20 and 40%) • Rock: Determined by size and number of fractures (most often very low, <5%) 30% 5% 1%

24. Porosity and Permeability • Permeability: Ease with which water will flow through a porous material • Sediment: Proportional to sediment size • GravelExcellent • SandGood • SiltModerate • ClayPoor • Rock: Proportional to fracture size and number. Can be good to excellent Excellent Poor

25. Porosity and Permeability • Permeability is notproportional to porosity. 30% Table 11.1 5% 1%

26. The Water Table • Water table: the surface separating the vadose zone from the saturated zone. • Measured using water level in well Fig. 11.1

27. Ground-Water Flow • Precipitation • Infiltration • Ground-water recharge • Ground-water flow • Ground-water discharge to • Springs • Streams and • Wells

28. Ground-Water Flow • Velocity is proportional to • Permeability • Slope of the water table • Inversely Proportional to • porosity Fast (e.g., cm per day) Slow (e.g., mm per day)

29. Natural Water Table Fluctuations • Infiltration • Recharges ground water • Raises water table • Provides water to springs, streams and wells • Reduction of infiltration causes water table to drop

30. Natural Water Table Fluctuations • Reduction of infiltration causes water table to drop • Wells go dry • Springs go dry • Discharge of rivers drops • Artificial causes • Pavement • Drainage

31. Effects of Pumping Wells • Pumping wells • Accelerates flow near well • May reverse ground-water flow • Causes water table drawdown • Forms a cone of depression

32. Effects of Pumping Wells • Pumping wells • Accelerate flow • Reverse flow • Cause water table drawdown • Form cones of depression Gaining Stream Water Table Drawdown Low well Dry Spring Cone of Depression Gaining Stream Low well Low river Pumping well

33. Effects of Pumping Wells Dry well • Continued water-table drawdown • May dry up springs and wells • May reverse flow of rivers (and may contaminate aquifer) • May dry up rivers and wetlands Losing Stream Dry well Dry well Dry river

34. Ground-Water/ Surface-Water Interactions • Gaining streams • Humid regions • Wet season • Loosing streams • Humid regions, smaller streams, dry season • Arid regions • Dry stream bed

35. Confined Aquifers

36. Confined Aquifers

37. Dissolved contamination travels with ground water flow Contamination can be transported to water supply aquifers down flow Pumping will draw contamination into water supply Ground-Water Contamination

38. Ground-Water Contamination • Leaking Gasoline • Floats on water table • Dissolves in ground water • Transported by ground water • Contaminates shallow aquifers

39. Ground-Water Contamination • Dense solvents • E.g., dry cleaning fluid (TCE) • Sinks past water table • Flows down the slope of an impermeable layer • Contaminates deeper portions of aquifers

40. Ground-Water Contamination • Effects of pumping • Accelerates ground water flow toward well • Captures contamination within cone of depression • May reverse ground water flow • Can draw contamination up hill • Will cause saltwater intrusion

41. Ground Water Action • Ground water chemically weathers bedrock • E.g., slightly acidic ground water dissolves limestone • Caves are formed • Permeability is increased • Caves drain • Speleothems form

42. Karst Topography Caves Sink holes Karst valleys Disappearing streams Giant springs Ground Water Action

43. 1843: Acton v. Blundell“English Rule” The landowner can pump groundwater at any rate even if an adjoining property owner were harmed. 1861: Frazier v. BrownEnglish Rule in Ohio Groundwater is “…occult and concealed…” and legislation of its use is “…practically impossible.” Ohio Groundwater Law

44. 1903:Huber v. Merkel English Rule in Wisconsin A property owner can pump unlimited amounts of groundwater, even with malicious harm to a neighbor. 1974:Wisconsin v. MichelsPipelineConstructors Inc. English Rule Overturned Landowners no longer have “an absolute right to use with impunity all water that can be pumped from the subsoil underneath.” Wisconsin Groundwater Law

45. 1984: Cline v. American Aggregates English Rule overturned in Ohio Justice Holmes: “Scientific knowledge in the field of hydrology has advanced in the past decade…” so it “…can establish the cause and effect relationship of the tapping of underground water to the existing water level.” Today: Lingering effects of English Rule It is very difficult to prove cause and effect to be defensible in court. English Rule Overturned in Ohio