Expansion and Update of the City of Spokane and SAJB Spokane Valley Rathdrum Prairie Aquifer Model Doug Greenlund City of Spokane March 26, 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 Model Flexible mesh (Blue) ( Micro FEM®) Finite Element 2C2A 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 20 th & 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 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 Years 25-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 Years 25-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 Years 25-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 Years 25-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 Years 25-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 Years 25-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 9 th 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