Blue Lakes Stream Gauge Improvement and Lake Level Stabilization Project: Summary of Dye Tracer Testing City of Twin Falls September 12, 2011

Brief Background Blue Lakes pumps operational 1994 Blue Lakes pumps operational 1994 Lower lake weir installed 1997 in an effort to stabilize lake level fluctuations Lower lake weir installed 1997 in an effort to stabilize lake level fluctuations Membrane liner placed upstream of weir, and later extended to about 50’ Membrane liner placed upstream of weir, and later extended to about 50’ Excessive seepage from bottom of lake prevents weir from operating effectively: Excessive seepage from bottom of lake prevents weir from operating effectively: The “orifice” – large hole The “orifice” – large hole Fissure(s) Fissure(s) Seepage around boulders upstream of weir Seepage around boulders upstream of weir

Brief Background Extensive computer modeling: must have at least 130 to 140 cfs net inflow to lower lake. Below this flow, level control is compromised Extensive computer modeling: must have at least 130 to 140 cfs net inflow to lower lake. Below this flow, level control is compromised Net inflow = Natural Spring Inflow – City Pumping Net inflow = Natural Spring Inflow – City Pumping Lake control problem aggravated by continuing declines in natural spring flow Lake control problem aggravated by continuing declines in natural spring flow

Where is it going? Statistically, the trend is still downward. Where is it going? Statistically, the trend is still downward.

Brief Background Current maximum day pumping: 25 cfs Current maximum day pumping: 25 cfs Down from a peak of 31 cfs in 2003 Down from a peak of 31 cfs in 2003 Maximum day typically occurs in July Maximum day typically occurs in July Springs have a seasonal pattern, low point typically in May, and have not recovered by July Springs have a seasonal pattern, low point typically in May, and have not recovered by July Natural spring inflow must be 155 to 165 cfs to achieve effective lower lake level control at current maximum day demand. Natural spring inflow must be 155 to 165 cfs to achieve effective lower lake level control at current maximum day demand. July natural flow, last 5 years: 120 to 140 cfs July natural flow, last 5 years: 120 to 140 cfs

Proposed Solution Component 1: Replace USGS gauging station with measuring device Component 1: Replace USGS gauging station with measuring device Rated section is highly inaccurate Rated section is highly inaccurate +/-30 cfs is not adequate to properly manage the lake system +/-30 cfs is not adequate to properly manage the lake system Trend in natural spring inflow (not the total Blue Lakes supply at the BL Trout weir) Trend in natural spring inflow (not the total Blue Lakes supply at the BL Trout weir) Daily value of spring inflow guides how much can be pumped Daily value of spring inflow guides how much can be pumped

Proposed Solution Reduce seepage from Lower Lake Reduce seepage from Lower Lake Attempt to find more cost effective ways other than controlling the orifice Attempt to find more cost effective ways other than controlling the orifice Other flow paths Other flow paths More flow passes over the lake control weir and sinks More flow passes over the lake control weir and sinks Question: Will changing the seepage pattern… Question: Will changing the seepage pattern… Reduce the flow in Alpheus Creek? Reduce the flow in Alpheus Creek? Change the distribution of outflow from the various springs in the Alpheus Spring complex? Change the distribution of outflow from the various springs in the Alpheus Spring complex?

Dye Tracer Test: Objectives Identify high seepage areas in lake bottom (other than orifice) Identify high seepage areas in lake bottom (other than orifice) Define flow paths, travel times, and mass balance Define flow paths, travel times, and mass balance Determine whether all water reaches Alpheus Springs, or if some bypasses the system Determine whether all water reaches Alpheus Springs, or if some bypasses the system Determine effect of seepage reduction actions on distribution of flow from Alpheus Springs Determine effect of seepage reduction actions on distribution of flow from Alpheus Springs BLCC allowed testing and permit applications BLCC allowed testing and permit applications

Preliminary Work Initial reconnaissance Initial reconnaissance Three dives Three dives Small amounts of dye used to identify seepage areas Small amounts of dye used to identify seepage areas Identified another major seepage location (fissure) Identified another major seepage location (fissure) Measured outflow of fissure and the orifice using current meter Measured outflow of fissure and the orifice using current meter Orifice: 24 cfs Orifice: 24 cfs Fissure: 14 cfs Fissure: 14 cfs No appreciable seepage from upper lake No appreciable seepage from upper lake Video Video

Dye Tracer Test Four injection locations, “slug” injections Four injection locations, “slug” injections Measured dye concentration curve at four locations: Measured dye concentration curve at four locations: Alpheus Springs, Alpheus Creek at BL Trout weir Alpheus Springs, Alpheus Creek at BL Trout weir Measured presence/absence of dye in Snake River Measured presence/absence of dye in Snake River Dye: Rhodamine WT Dye: Rhodamine WT Acknowledgements Acknowledgements IDWR and Idaho Power Co. – fluorometer equipment and expertise IDWR and Idaho Power Co. – fluorometer equipment and expertise IDEQ – discrete sampler IDEQ – discrete sampler Ozark Underground Laboratories, Missouri Ozark Underground Laboratories, Missouri

Overall map

Map of lake and injection points

Map of sample locations

Breakthrough Curve Elapsed Time Concentration Time to peak Arrival time

Test 1: Orifice Test 2: Fissure Test 3: Boulder Field Test 4: Pool below Weir Test 5: Orifice

Overall Mass Balance at BL Trout Weir Integrate Q x C under breakthrough curve Integrate Q x C under breakthrough curve All tests - mass injected: 30 lb All tests - mass injected: 30 lb Mass recovered: 25.7 lb (86%) Mass recovered: 25.7 lb (86%) Some adsorption and other degradation of dye is expected Some adsorption and other degradation of dye is expected No dye detected in any charcoal packet in Snake River No dye detected in any charcoal packet in Snake River Margin of error in mass balance may be +/- 10 to 15% Margin of error in mass balance may be +/- 10 to 15% Conclude: no significant mass loss Conclude: no significant mass loss

Mass Balance – Individual Springs

Seepage Reduction Action Scenarios Scenario 1: 15 cfs eliminated from fissure, infiltrates in pool below weir Scenario 1: 15 cfs eliminated from fissure, infiltrates in pool below weir Scenario 2: 20 cfs eliminated from boulder field, infiltrates in pool below weir Scenario 2: 20 cfs eliminated from boulder field, infiltrates in pool below weir Scenario 3 (Preferred): 15 cfs eliminated from fissure, 20 cfs eliminated from boulder field, infiltrates in pool below weir Scenario 3 (Preferred): 15 cfs eliminated from fissure, 20 cfs eliminated from boulder field, infiltrates in pool below weir Scenario 4: 20 cfs eliminated from orifice, infiltrates in pool below weir Scenario 4: 20 cfs eliminated from orifice, infiltrates in pool below weir Scenario 5: 15 cfs eliminated from fissue, 20 cfs from boulder field, 20 cfs from orifice, infiltrates in pool below weir Scenario 5: 15 cfs eliminated from fissue, 20 cfs from boulder field, 20 cfs from orifice, infiltrates in pool below weir

Predicted Flow Changes Flow change in absolute CFS: Flow change in absolute CFS:

Basic Findings and Conclusions All water seeping from the Lower Lake emerges at one or more springs in the Alpheus complex All water seeping from the Lower Lake emerges at one or more springs in the Alpheus complex 81% of the flow emerges from the City Spring / Main Spring complex; 19% of the flow emerges from the Clubhouse Spring 81% of the flow emerges from the City Spring / Main Spring complex; 19% of the flow emerges from the Clubhouse Spring Significantly different response curves depending on seepage location Significantly different response curves depending on seepage location Proposed seepage reduction actions will not decrease the flow in Alpheus Creek Proposed seepage reduction actions will not decrease the flow in Alpheus Creek Proposed seepage reduction actions will not significantly change spring flow distribution. Proposed seepage reduction actions will not significantly change spring flow distribution.

Proposed Plan Install measuring device at USGS gauge Install measuring device at USGS gauge Reduce or eliminate seepage in fissure and boulder field Reduce or eliminate seepage in fissure and boulder field Natural gravel pack Natural gravel pack Potential for membrane liner if needed Potential for membrane liner if needed Target 35 cfs seepage reduction Target 35 cfs seepage reduction Target minimum inflow to lower lake would be reduced from cfs to about cfs Target minimum inflow to lower lake would be reduced from cfs to about cfs Spring inflow would need to be: Spring inflow would need to be: cfs to allow City to pump current 25 cfs max day cfs to allow City to pump current 25 cfs max day cfs to allow City to pump full 52 cfs water right cfs to allow City to pump full 52 cfs water right

Proposed Plan Mitigate for roadside creek flow Mitigate for roadside creek flow Hydraulic fix Hydraulic fix Options for pumping Options for pumping