11: Groundwater Water resources Geologic Agent

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

Hydrogeology Defined Water 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.

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

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

Hydrogeology Defined Water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.

Hydrogeology Defined Water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.

Hydrogeology Defined Water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.

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?

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.

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

Henry Darcy’s Experiment (Dijon, France 1856) Darcy’s Law Henry Darcy’s Experiment (Dijon, France 1856) Darcy investigated ground water flow under controlled conditions h1 h2 A Dh Q: Volumetric flow rate [L3/T] h x h1 A: Cross Sectional Area (Perp. to flow) Dx Q K: The proportionality constant is added to form the following equation: Controlled laboratory experiment designed to investigate what controls the flow rate (e.g. through a dam) Experiment A saturated porous medium is placed in a “column” (this could just as easily be vertical and was in Darcy’s experiment but this orientation, horizontal flow, is more familiar to us hydrogeologists) A method of measuring the dependent variable, volumetric flow rate, Q A method of individually changing the variables that were hypothesized to control flow (the dependant variable) Manometers can be thought of as wells (but you know that you need more than two wells to calculate groundwater flow rates and directions) discuss proportionalities Introduce hydraulic gradient as the slope of head with distance, Slope at a point is the derivative of the functional relationship between h and x In reality we use delta h/delta x Negative sign results from the fact that head decreases in the direction of flow, I.e. when the slope (hydraulic gradient is negative flow id in the positive x direction) Dimensional analysis shows that the units of K are [L/T] (this is not a velocity but can be thought as a quantitative measure of how easily water flows through the porous media : Hydraulic Gradient Slope = Dh/Dx ~ dh/dx Dh Dx h2 x1 x2 K units [L/T]

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 a Vw H w D

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) Q Used for calculating Q given A = A Volumetric Flux: Volumetric flow per unit area (e.g. Rainfall depth is a volumetric flux, R*A=Q) q*A The volumetric flux is easy to calculate once you have measured (or approximated) the hydraulic gradient and measured or estimated q In order to calculate velocity you need to account for porosity because the same flow is squeezed through the percentage of pore space represented by the porosity therefor the velocity is greater than the volumetric flux by a factor of 1/n Once you’ve calculated q you cal calculate Q by multiplying by the cross sectional area (A: the area perpendicular to the flow vector) and you can calculate v by dividing by n (measured or approximated) Ave. Linear Velocity Q q Used for calculating average velocity of groundwater transport (e.g., contaminant transport = = A.n n Assumptions: Laminar, saturated flow

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? 5000 ft 652 658 N Pond 1 Pond 2 The company wanted to discharge sediment laden water into Pond 1 and have the water filter through a sand dike before it discharges into the stream This brings up the first question: How much water could they discharge without overflowing Pond 2? The upper settling pond is separated from the lower pond by 186 ft of sand The maximum elevation of Pond 1 is 658 ft and the outlet of Pond 2 is at an elevation of 652 If Pond 1 becomes contaminated with a dissolved contaminant it will flow towards Pond 2 at a rate roughly equivalent to the average groundwater velocity Once we figure out this velocity (given the distance of travel) it can be used to get a worst case calculation of the time of arrival of the advective front Once the contamination reaches Pond 2 the volumetric flow rate of the groundwater *This is a hypothetical example based on a composite of a few real cases

Application (cont.) W Q? v? M? Dh=6.51 ft K Water flows between ponds through the saturated fine sand barrier driven by the head difference Pond 1 Pond 2 Outfall 1510 ft W Overflow Elev.= 658.74 ft Elev.= 652.23 ft Sand Dx =186 Q? v? M? K Dx =186 ft b=8.56 ft W Two settling ponds were dug in 10 ft of sand, bottomed on low permeability clay. Two settling ponds, different levels, separated by an earthen barrier Start with conceptual model Clay Dh=6.51 ft Contaminated Pond b Dx Not to scale

Application (cont.) Develop your mathematical representation Q? v? M? (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 Any mathimatical model requires assumptions in order to represent an infinitely complex natural system with a set of mathematical equations This is a bit of an art because technically you need to develop a more complex model and demonstrate that the simplifications do not significantly effect the results If you understand the limits of the model you can make more appropriate assumptions Q? v? M? M = Q C

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? The mathematical model is helpful in that it will dictate what information you need to collect Cross sectional area (perpendicular to flow): A=b*w Hydraulic gradient: Dh: head difference between ponds, Dx flow pathlength Discuss sensitivity analysis The accuracy of the model results depends on 1) how well your assumptions represent reality and 2) how accurately you have determined the parameters of the model. M = Q C M?

Ground Water Zones Degree of saturation defines different soil water zones

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

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

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

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%

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

Porosity and Permeability Permeability is not proportional to porosity. 30% Table 11.1 5% 1%

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

Ground-Water Flow Precipitation Infiltration Ground-water recharge Ground-water discharge to Springs Streams and Wells

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)

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

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

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

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

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

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

Confined Aquifers

Confined Aquifers

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

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

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

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

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

1861: Frazier v. Brown English Rule in Ohio Ohio Groundwater Law 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. Brown English Rule in Ohio Groundwater is “…occult and concealed…” and legislation of its use is “…practically impossible.”

Wisconsin Groundwater Law 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. Michels Pipeline Constructors 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.”

English Rule Overturned in Ohio 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.