Groundwater Occurrence & Movement:

Transcription

1 Groundwater Occurrence & Movement: An Introductory Discussion with Application to East-Central Illinois East-Central Illinois Regional Water Supply Planning Committee July 27, 2007 Allen Wehrmann, P.E., P.H.(GW), D.WRE, Director Center for Groundwater Science, Illinois State Water Survey

2 Special thanks to: Ed Mehnert, Ph.D. Hydrogeology Section Illinois State Geological Survey Steve Burch & George Roadcap, Ph.D. Center for Groundwater Science Illinois State Water Survey

3 East-Central Illinois Water Supply Planning Area

4 Topical Presentation Outline Basic Concepts and Definitions The Hydrologic Cycle What is groundwater? Concepts & Definitions Porous Flow vs. Fractured Flow Aquifers vs. Aquitards Artesian vs. Water Table Conditions Regional Groundwater Flow Systems Well & Aquifer Hydraulics Groundwater Modeling

5 The Hydrologic og Cycle Climate, surface water, and groundwater are linked

6 Porous Systems Porosity = volume of pore space / total volume of porous material

7 Fractured Systems

8 Fractured Limestone or Dolomite

9 Porosity & Effective Porosity Ranges Material Porosity (%) Eff. Porosity (%) Silt Clay Sand/Gravel Limestone/dolomite Shale Sandstone

10 Aquifers vs. Aquitards An aquifer is a saturated bed, formation, or group of formations which yields water in sufficient quantity to be of consequence as a source of supply. An aquitard yields inappreciable quantities of water to wells compared to an aquifer but through which leakage of water is possible. Aquitards often act as confining beds.

11 Unconfined vs. Confined Groundwater An unconfined aquifer is one in which groundwater possesses a free surface open to the atmosphere. The upper surface of the zone of saturation is called the water table. A confined aquifer is one in which groundwater is confined under pressure by overlying and underlying aquitards or aquicludes and water levels in wells rise above the top of the aquifer. Also called an artesian aquifer.

12 Unconfined Aquifers Land Surface Unsaturated (Vadose) Zone Water Table Saturated Zone Unconfined Aquifer Bedrock

13 Confined Aquifers Land Surface Unsaturated (Vadose) Zone Water Table Unconfined Aquifer Saturated Zone Confining Layer - Aquitard Potentiometric Surface Confined Aquifer Bedrock

14 Confined Aquifers & Artesian Wells Flowing artesian well Land surface Water table Aquifer

15 Regional Groundwater Flow Systems 0.1 mile 20 miles Depth

16 Groundwater Stream Interaction Regional Flow Systems

17 Groundwater Stream Interaction Regional Flow Systems

18 Groundwater Stream Interaction Regional Flow Systems

19 Groundwater Stream Interaction Regional Flow Systems

20 Groundwater Flow Velocities Material Gravel Clean sand Clayey sand Clay Sandstone Highly fractured limestone Velocity 5-10 feet per day 1 5 feet per day feet per day < 0.1 feet per day < 0.5 feet per day s feet per day

21 Regional Bedrock Topography Green= higher elevations Light violet= lower elevations

22 The Mahomet Aquifer Region Peoria WOODFORD CO Watseka NORTH MILES Havana Morton Pekin TAZEWELL CO Normal Bloomington` MCLEAN CO FORD IROQUOIS CO CO Gibson City Hoopeston Paxton CHAMPAIGN CO VERMILION CO Rantoul MASON CO LOGAN CO DEWITT CO Mahomet Danville CASS CO Petersburg MENARD CO Lincoln Clinton Champaign Urbana PIATT CO MACON CO Monticello Springfield Decatur Bedrock high aquifer absent Proposed ethanol plants using Mahomet Aquifer as principal source

23 Illinois Geology: glacial materials

24 Glacial Depositional Processes

25 Major Sand & Gravel Aquifers

26 Geology of the Mahomet Aquifer

27 Withdrawals from Sand & Gravel Aquifers Total use ~ 400 mgd + ~200 mgd for irrigation

28 Regional Community Groundwater Use 2004 Water Use (gpd) Gibson City (not Mahomet Aquifer) 730, IL-American Water Co. 21,000,000 Mahomet 500, Monticello 700,000 Normal 4,100, Paxton 650,000 Rantoul 1,600,000 Stone Ridge Dairy (near Bellflower) ~1,200,000 White Heath 50,000

29 Well/Aquifer Interactions Cone of Depression

30 Overlapping Cones of Depression Well/Aquifer Interactions

31 Overlapping Cones of Depression: Well Interference Well/Aquifer Interactions

32 Overlapping Cones of Depression: Well Interference A B Well/Aquifer Interactions

33 Overlapping Cones of Depression: Well Interference A B Well/Aquifer Interactions

34 Overlapping Cones of Depression: Well Interference A B Well/Aquifer Interactions

35 Mahomet Aquifer Groundwater Levels foot conto r 10-foot contour Flow direction

36 Mahomet Water Levels by the Illinois River Land Surface = 485 MSL elevation Great Flood of aa Depth to water, fe eet Drought Year

37

38 Potentiometric Surface of Eastern Mahomet Aquifer, 2005 Rantoul Monticello Champaign- Urbana Danville

39 Mahomet Potentiometric Heads near Champaign Groundw water elevation, fe eet

40 Water Use Trend at Champaign paign, million gallons per day 12 8 Pumpage at Cham

41 Impacts of pumping on water levels (head) Mahomet aquifer nonpumping heads (artesian) head P Pump settings High-capacity well Low-capacity well Glacial till P P P Mahomet aquifer

42 Impact of pumping hydraulically linked aquifers Mahomet nonpumping Glasford nonpumping Mahomet pumping Glasford pumping Glacial Till P Glasford Aquifer P Glacial Till P Mahomet Aquifer

43 ISWS Regional Flow Model Predicted Heads

44 Model-Predicted Drawdown Q = 23 mgd at Champaign

45 Thanks! Visit us on the web for updates: Or Google: Illinois State Water Survey