Steve Hubbs & Tiffany Caldwell University of Louisville

1. Clogging in Louisville Steve Hubbs & Tiffany Caldwell University of Louisville

2. This presentation: • Provide some slope data from US Rivers. • Present calculations for Specific Capacity and decrease with time at Louisville (clogging). • Analyze Pump Test data from 1999 and 2004 for indications of Riverbed compression at Louisville. • Analyze field data for flux and head • Review calculations of riverbed hydraulic conductivity (K) for 1999 and 2004 at Louisville.

3. Typical RBF systems in US • Smaller system capacity (5,000 m3/day) • Recent tendency for large systems (100,000 m3/day) and larger • Located very close to streams (30 meters from bank) • Laterals extend under riverbed

4. Sites with RBF Systems • Louisville, 20 MGD (45 MGD planned), Ohio River • Cincinnati, 30 MGD, Great Miami River • Somoma, CA. 45 MGD, Russian River • Lincoln NE, xx MGD, Platte R • Des Moines, KC, • Considering: St.Louis, New York, others

7. RIVERBANK FILTRATIONAn effective technique for public water supply • An ancient technology…documented in the Bible! • Exodus 7:24 “…dug around the Nile for water to drink.  Filtered through sandy soil near the river bank, the polluted water would become safe to drink.” • Modern installations in Germany over 140 years old • Extensive development in US since the 1950s • Recent interest as a treatment technique for Disinfection By-Product and Pathogen Regulations

8. Indications of Clogging • Louisville capacity decreases to 67% of original level over 4 years, hardpan present. • Cincinnati “hardpan” forms when pumping at high levels under low-stream flow conditions • Sonoma infiltration beds hard to penetrate and unsaturated below surface. • Initial capacity of collector wells decrease after several years of operation.

9. Factors Impacting Yield • Temperature (River, Aquifer, Well) • Time (used as a surrogate for plugging) • Pumping Rate and Driving Head • Aquifer Characteristics (at riverbed, through bulk of aquifer, near wellscreen) • Water Quality

10. Factors Restoring Yield • Riverbed shear stress and scouring • Biological “Grazing” (Rhine River) • Mechanical Intervention (Llobregat River)

11. Sustainable Yield • The long-range sustainable yield is a balance between all yield-limiting factors and all yield-restoring factors • The question is: How do we measure and predict all of these factors? • Focus of this part of the presentation: looking at the composite of plugging factors, and the impact of shear stress on sustainable yield.

12. Predicting Sustainable Yield • Use a combined stochastic/deterministic approach. • Specific Capacity = Flow/(river head - well head) • Cs = a*(river temp) + b*(well temp) + c*(time)

15. Raw Data for Regression Model

16. Model with Temperature only

18. RegressionModel, “cleaned data”

19. Projection of Model-20 years

20. September 9, 2004

21. Impact of 4 month layoff, 2004 • Pump failures resulted in long downtime • Pumps off during high flow events of spring 2004 • Pumps restarted July 28, 2004 • Pump test of 1999 repeated

22. Projection with Jumps-capacity in MGD Specific Capacity: Measured: 0.545 MGD/ft Predicted: 0.36 MGD/ft August 2004 (predicted) measured

23. Specific Yield Calculations • Adjusting for temperature, the calculated specific capacity for 2004 is 0.645 MGD/ft at week 4 of pump test. • A similar calculation for specific yield was 0.848 for 1999 after week 4 of pumping. • Current capacity approximately 76% of original after layoff and scouring event. • Previous measurements indicated that capacity was approximately 67% of original.

24. Pump Tests at LWC • 1999 Pump test • 2004 Pump test • Direct measures of infiltration

25. 20 MGD Collector Well: Ohio River at Louisville

28. Measured 2 feet below riverbed

29. 1999 P39 The aquifer velocity q is measured at the mid-point of curve at W1 (P39) at 1.08 hours for the 2 foot distance or 2 feet/hour The measured head loss at P39 was 10 feet across the 2 foot vertical distance yielding a riverbed K value of: K=(2’/10’)(2ft/hour)=0.4 ft/hr (0.12m/hr)

32. 2004 pump test repeat

33. 0.6 meter below surface

34. 3 meters below surface

36. What’s going on?

37. Ohio River Geokon Probe P39 t=20 min t=2 days Geokon Probe P37 Sand and Gravel Aquifer Lateral L-4 BEDROCK Piezometric surface

38. Compressed Riverbed Ohio River t=20 min Geokon Probe P37 Sand and Gravel Aquifer Several months Lateral L-4 BEDROCK Piezometric Surface

39. Interpretation of 2004 Temp data • Pump test starts with aquifer saturated to 420’. • As head increases, vertical velocity increases and piezometric surface drops. • After 8 hours, the piezometric surface intersects and drops below the riverbed. Riverbed conductivity reduces sharply, and the flow path shifts from vertical to horizontal. • The piezometric surface continues to extend, increasing the distance of flow and bringing in cooler aquifer water. Minimal flow is passing P39. • The piezometric surface stabilizes, and temperature increases to river temperatures.

41. Direct Measure of Riverbed Flux Rate • Seepage meter procedure modified for deep river use • Heavy “can” 1 sq. foot surface (0.093 sq meter) • Flexible connection to surface • Stilling well at river surface • Camera to observe riverbed conditions

42. Problems with flux measurement • Wind, Waves, and Current are enemies • Unable to work when river velocity exceeds 1 mph (1.6 km/hour) due to erosion of seal • Wind/waves make boat and stilling well pitch • It takes near-perfect conditions to get repeatable data

45. Hose to Attach to Bladder In Stilling Well Seepage meter “can”

47. Stilling Well

48. Ohio River t=20 min No flux Area of high flux measurement Geokon Probe P37 Sand and Gravel Aquifer Several months Lateral L-4 BEDROCK Piezometric Surface

49. Calculating Riverbed K from direct measurement of infiltration rate • Approach Velocity measured at .3 to 1 meter/hour • Porosity assumed at 0.2 • Aquifer velocity q = (.3/0.2) = 1.5 m/hour • Head loss across riverbed at 0.6 meter depth is 6 meters • K=(L/hL)(q)= (0.6/6)1.5m/hour = 0.15 m/hr • Measured range based on approach velocities was 0.15 to 0.45 m/hour

50. Summary of Measured Riverbed K values • At identical points (P39, 0.6m depth) • 1999 temperature-derived value = 0.12 m/hr • 2004 temperature-derived value = 0.03 m/hr • From direct measure of flux across riverbed • Max 2003 flux-derived value = 0.45 m/hr • Typical 2004 flux-derived value = 0.15 m/hr • Max 2004 flux-derived value = 0.38 m/hr