Expansion and Update of the City of Spokane and SAJB Spokane
Valley Rathdrum Prairie Aquifer Model
Doug GreenlundCity of SpokaneMarch 26, 2013
2013 Spokane River Conference
Made Possible by
• Grant Funding from the Washington State Department of Health
Source Water Protection Program
• Funding from the Spokane Aquifer Joint Board
• City of Spokane Utilities Division
• GSI Water Solutions: John Porcello (hydrogeology and modeling lead), Matt Kohlbecker (stormwater and pollutant transport), Ari Petrides (modeling, GIS)
Outline
• Description of MicroFEM®
• Similarities and differences with the Bi-State Model
• Similarities and differences with the previous model
• Examples of outputs
The Model
• MicroFEM®
• Steady State
• Finite Element mesh
• Uses annual averages for pumping, recharge, boundary conditions
Model Development History
• 1994 City of Spokane worked with CH2MHill to develop Wellhead Protection and finite element model
• 2000 SAJB version of the model
The Project
• Expand the Model to avoid truncation of capture zones at the state line
• Update the model with current information
New Aquifer Boundary
• Original model ended at the state line. Key element of entire project
• New model based on Bi-State boundary but includes Hoodoo Valley and lower Hangman Creek
• Removed Green Street Knoll
Model Boundary Comparison
Developed New Grid
• Mesh on 550 foot centers
• 80 to 100 nodes per square mile
• Bi-State model is 16 grids per square mile
• Original model has about 25 nodes per square mile
• 44,703 nodes in model
• Tighter spacing around wells
Comparison of Grid and Mesh near Consolidated Irrigation District Well 2
Bi-State Model Square Grid Cells (Black) MODFLOW
Finite Difference
¼ mile
City/ SAJB ModelFlexible mesh (Blue)( Micro FEM®)Finite Element
2C 2A
2B
Aquifer Base and Aquifer Level
• Developed the base of the aquifer and assigned a value to each node
• Used contour maps to develop the aquifer surface elevation
Model Groundwater Elevations
Aquifer Thickness
• This is the difference between the base elevation and the average surface level
• Model has three layers– First layer down to 100 feet
– Second layer 100 to 200 feet
– Third layer below 200 feet
Thickness and Bedrock
• Uses three layers to simulate groundwater flow
– The USGS Bi-State model used just one layer, except in Hillyard Trough (3 layers north of Spokane city limits)
– Pain-staking effort to resolve issues with Bi-State model files
• Electronic files: Too thick just east of state line,
and too thin between state line and City of Spokane
• Published maps: Found internal inconsistencies
(saturated thickness did not match water table and basement)
• Localized change to USGS representation of basement bedrock and SVRP thickness near downtown Spokane (per City and Ecology)
Transmissivity and Vertical Resistivity
• Used original data on the Washington portion
• Bi-State model in Idaho
• Transmissivity used to define internal boundaries such as Pines Road Knoll
• Vertical Resistivity used to create layers
Boundary Conditions• Annual Averages
• Set a fixed groundwater elevation for Long Lake based on the average from the Bi-State Model
• Tributary inflow from 37 areas in Washington and 37 in Idaho
• Stage elevations for Spokane River from the original MicroFEM model.
• Stage elevations for the Little Spokane River and Lake Pend Oreille are from the Bi-State Model
Pumping Rates
• Used existing model data for Washington with updates from purveyors
• Extracted data from Bi-State model and information from USGS for certain wells in Idaho
• Idaho well locations provided by Idaho DEQ
Pumpage and Recharge
Pumping and areal recharge are now separated!– Lumped together into single term in Bi-State model
Bi-State model pumping =(1) Actual pumping minus(2) Septic system infiltration minus(3) 40% of outdoor-applied water in urban areas minus(4) 40% of outdoor-applied water on irrigated fields
– Difficult to change pumping in Bi-State model: requires decisions about whether (and how) to change recharge– Difficult and time-consuming to separate, but GSI Water Solutions did it!
Wellhead Protection Areas
• Backward Particle tracking
• Based on Purveyor supplied pumping rates
• Times of travel provided by purveyors
• There are Special Wellhead Protection Areas for 115 wells
Flowline Input Box
City of Spokane Ray Street 2 Month Time of Travel
Interstate 90
Thor Freya
City of Spokane Ray Street 2 Year Time of Travel in Blue
Argonne
Special Wellhead Protection Areas in ArcGIS
Infiltration
• MicroFEM®
is well suited to analyze infiltration such as stormwater
• Forward particle tracking
• The model has areas with nodes spaced with infiltration in mind
SAJB and Bi-State Model Grids at Chester Creek
27
Chester Creek Recharge Basins
Model ID #3
Model ID #7
WD#3 Browns Park
Modern Electric #9
Model ID #5
Model ID #1 and #6
WD#3 20th & Balfour
Influence of 25-Year Infiltration Events at the Chester Creek And Saltese Recharge Basins
Saltese Flats / Shelly Lake Recharge Basin
Chester Creek Recharge Basins
25-Year Event Infiltration Rates
42,941 gpm (95.7 cfs) Chester Creek
65,045 gpm (144.9 cfs)Saltese Flats / Shelly Lake
28
1 Year1 Year
Influence of 25-Year Infiltration Events at the Chester Creek And Saltese Recharge Basins
Saltese Flats / Shelly Lake Recharge Basin
Chester Creek Recharge Basins
29
2 Years2 Years25-Year Event
Infiltration Rates
42,941 gpm (95.7 cfs) Chester Creek
65,045 gpm (144.9 cfs)Saltese Flats / Shelly Lake
Influence of 25-Year Infiltration Events at the Chester Creek And Saltese Recharge Basins
Saltese Flats / Shelly Lake Recharge Basin
Chester Creek Recharge Basins
30
3 Years3 Years25-Year Event
Infiltration Rates
42,941 gpm (95.7 cfs) Chester Creek
65,045 gpm (144.9 cfs)Saltese Flats / Shelly Lake
Influence of 25-Year Infiltration Events at the Chester Creek And Saltese Recharge Basins
Saltese Flats / Shelly Lake Recharge Basin
Chester Creek Recharge Basins
31
5 Years5 Years25-Year Event
Infiltration Rates
42,941 gpm (95.7 cfs) Chester Creek
65,045 gpm (144.9 cfs)Saltese Flats / Shelly Lake
Influence of 25-Year Infiltration Events at the Chester Creek And Saltese Recharge Basins
Saltese Flats / Shelly Lake Recharge Basin
Chester Creek Recharge Basins
32
7 Years7 Years25-Year Event
Infiltration Rates
42,941 gpm (95.7 cfs) Chester Creek
65,045 gpm (144.9 cfs)Saltese Flats / Shelly Lake
Influence of 25-Year Infiltration Events at the Chester Creek And Saltese Recharge Basins
Saltese Flats / Shelly Lake Recharge Basin
Chester Creek Recharge Basins
33
8 Years8 Years25-Year Event
Infiltration Rates
42,941 gpm (95.7 cfs) Chester Creek
65,045 gpm (144.9 cfs)Saltese Flats / Shelly Lake
Influence of 25-Year Infiltration Events at the Chester Creek And Saltese Recharge Basins
Saltese Flats / Shelly Lake Recharge Basin
Chester Creek Recharge Basins
34
10 Years10 Years25-Year Event
Infiltration Rates
42,941 gpm (95.7 cfs) Chester Creek
65,045 gpm (144.9 cfs)Saltese Flats / Shelly Lake
Resources
• Technical Memorandums for the entire project are on line at greenspokane.org
• John Porcello will be presenting at the 9th Washington Hydrogeology Symposium “Wellhead Protection and Stormwater Recharge in the Washington Portion of the Spokane Valley - Rathdrum Prairie Sole Source Aquifer”
Conclusions• Differs Functionally from Bi-State Model– Steady State
– Pumping and Recharge are Separate
– Finer grid
• Improvements from 2000 version– Expanded Boundary
– Finer mesh
– Different Boundary Conditions
Doug Greenlund
March 26, 2013
Thank You
Expansion and Update of the City of Spokane and SAJB Spokane
Valley Rathdrum Prairie Aquifer Model