Riverbank Filtration A Surface-Water Perspective

Transcription

1 Riverbank Filtration A Surface-Water Perspective W I L L I A M D. G O L L N I T Z S U P E R I N T E N D E N T O F W A T E R P U R I F I C A T I O N C I T Y O F L O R A I N, O H E A R T H W O R K S W A T E R R E S O U R C E T E C H N I C A L C O N S U L T I N G S H E F F I E L D V I L L A G E, O H

2 Using these? You have to remove or kill these!

3 Surface Water Treatment Rules Surface Water Treatment Rule (SWTR) Protects against-giardia, Bacteria, Viruses Requires disinfection; and possible filtration Interim Enhanced Surface Water Treatment Rule (IESWTR) Adds Cryptosporidium Requires coagulation & filtration for 2-log removal Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) Applies IESWTR to small systems (serving <10,000) Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) Requires SW monitoring for Crypto concentrations Requires additional treatment if Crypto conc. is high

4 Poor Source Water Quality?

5 Requirements of the LT2ESWTR Monitor source for Cryptosporidium once per month for 24 months Add additional treatment if needed Mean Cryptosporidium Concentration Bin Classification < oocysts/l Bin to < 1.0 oocysts/l Bin to < 3.0 oocysts/l Bin oocysts/l Bin 4 Bin Classification Conventional Treatment (including softening) Direct Filtration Slow Sand or Diatomaceous Earth Alternative Filtration Technology Bin 1 No additional treatment No additional treatment No additional treatment No additional treatment Bin 2 1-log treatment 1.5-log treatment 1-log treatment Demonstrate 4.0-log Bin 3 2-log treatment 2.5-log treatment 2-log treatment Demonstrate 5.0-log Bin 4 3-log treatment 3-log treatment 2.5-log treatment Demonstrate 5.5-log

6 SWTRs also apply to GWUDISW Typical examples: Well River Well Till Stream Bedrock Karst Limestone Pumping Well Fractured Interface Silt & Clay Sand & Gravel Water Table Alluvial Aquifer Pumping Water Table Bedrock Regional Ground-water Flow

7 LT2 Tools in the Toolbox Watershed control Alternative source/intake management Presedimentation Tw0-stage lime softening Riverbank filtration Combined filter performance Individual filter performance Demonstration of performance Bag/cartridge filters Membrane filtration Second stage filtration Slow sand filters Chlorine dioxide Ozone UV

8 Riverbank Filtration (RBF) RBF-The removal of particles & pathogens by filtration thru the porous matrix of the streambed & aquifer Pumping Well Silt & Clay Sand & Gravel Water Table Pumping Water Table Bedrock Regional Ground-water Flow

9 Log Diatoms Log Algae Treatment Plant Efficiency Evaluations- MPA* 12 Raw water Finished water 12 Raw water Finished water * Microscopic Particulate Analysis

10 11/09/04 02/17/05 05/28/05 09/05/05 12/14/05 11/09/04 02/17/05 05/28/05 09/05/05 12/14/05 Log Diatoms Log Algae Riverbank Filtration DOP Evaluations - MPA 1.0E E E E E E E E E E E E E+03 SW RBF 1.0E E E+03 SW RBF 1.0E E E E E E E E-01

11 RBF as a Pretreatment Tool Conventional Engineered Treatment Disinfection (chlorine) Coagulant Addition & Rapid Intake Mix & Pumphouse Flocculation & Coagulation Sedimentation Filtration with Backwash Storage RBF Conventional Engineered Treatment with RBF Disinfection (chlorine, Ozone, UV) Coagulant Addition & Rapid Mix Flocculation & Coagulation Sedimentation Filtration with Backwash Storage

12 Riverbank Filtration Guidance Long Term 2 Enhanced Surface Water Treatment Rule Guidance Manual cfm Chapter 4 Riverbank Filtration LT2 compliance requirements for receiving automatic credit Toolbox selection considerations Site selection and aquifer requirements Design and construction Demonstration of performance (Based upon Casper, WY DOP)

13 Automatic 0.5 or 1.0 Log Credit Criteria RBF can be used as a pre-filtration toolbox option for presumptive credit Vertical & horizontal wells only Granular aquifers only Credit based upon shortest flowpath distance 25 feet 0.5-log 50 feet 1.0 log Monitor turbidity every 4 hours; monthly avg <1 NTU Must be followed by engineered filtration

14 Toolbox Selection Considerations Adjacent to rivers with consistent water quality Important to know type of streambed and aquifer material Dynamics of ground-water flow Potential for scouring of the streambed and bank Identify potential periods of poor removal

15 Site Selection & Aquifer Requirements Only unconsolidated granular aquifers Aquifer characterization Coring Sieve analysis Occurrence of scour Process of stream channel erosion

16 Aquifer Recharge Variation

17 Design & Construction Well types (only) Vertical Horizontal collector (Ranney) Distance between surface water and well screen Min 25 = automatic 0.5 log credit Min 50 =automatic 1.0 log credit Greater distances are preferred for additional removal Delineation of edge of surface water Edge of the 100 year flood zone

18 Low Infiltration Rates

19 High Infiltration Rates

20 Operational Considerations Continuously monitor turbidity High river stage decrease pumping Implications for scour Potential increase of streambed permeability Anticipate high flood events Response to spill events Floaters don t worry Sinkers shut the system down Monitor water levels to track streambed permeability changes

21 Do you need more credit? Riverbank Filtration (RBF) Pumping Well Streambed Sand & Gravel Aquifer Induced Infiltration Most well designed RBF systems can achieve > 2.0 log removal of pathogenic protozoa; but utility must demonstrate it.

22 Demonstration of Performance State approved protocol Collect hydrogeologic data related to system operation Collect Cryptosporidium and surrogate removal data Samples collected from: surface water intermediate monitoring well installed along the shortest flow path production well Data collected during full range of operating conditions Long-term performance monitoring

23 Hydrogeologic Data Streambed characteristics Thickness Permeability Aquifer characteristics Thickness Permeability Induced infiltration rates during variations in river stage Length of flow paths and their time of travel Ambient ground-water dilution

24 Cryptosporidium Removal Surrogates RBF turbidity - <1.0 NTU; prefer 0.3 NTU Log removal: surface water, monitoring well and groundwater collector Protozoa (Method 1623) Bacteria - smaller than Crypto Total coliform/e coli Heterotrophic plate counts Enterococci Particle counts - Giardia size range (7-10 µm) Particle counts Crypto size range (3-5 µm) Endospores similar size as protozoa Algae smaller and larger than protozoa Diatoms smaller and larger protozoa

25 RBF in Kentucky Louisville Water Co

26 The First Collector Well

27 The Biggest Problem The neighbors along the river didn t want to look at these!!

28 The Alternative-Keep Everything Under Ground! Caisson Ohio River Alluvial Aquifer Sand & Gravel Lateral Collector Shale Bedrock Tunnel

29 Basic Design of Louisville s RBF System

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31 Let s Watch the Movie!

32 RBF Performance RBF Microbial Removal at Louisville Water Parameters Ohio River RBF System Log Removal Turbidity (NTU) <5 to > to 0.69 NC Total Coliform (MPN/100 ml 9 to 165,200 0 to HPC (CFU/ml) 10 to 8,820 0 to Spores (CFU/ml) 30 to to MPA-Algae (No/100 L) 0.53 to 65x to 66 >7.1 MPA-Diatoms (no/100 L) 1.3 to 91x105 0 to 0.26 >6.7 Cryptosporidium (oocysts/l) 0 to NC NC = not calculated

33 The Advantages of Riverbank Filtration Removes pathogenic microorganisms (typically better than engineered filtration) Removes inorganic compounds Removes organic compounds Less engineered treatment required Produces a constant temperature water Not impacted by river spills Not impacted by ice flows Drought resistant

34 The Disadvantages of Riverbank Filtration Utility may have to change the treatment regime Ground water may contain higher levels of hardness and must be softened ph may have to be lowered using recarbonation Reduce alum sludge/increase lime sludge disposal Iron and manganese may be higher depending upon aquifer geochemistry

35 The Best Combination? Riverbank Filtration (RBF) Pumping Well Disinfection (UV) Disinfection (Cl2) Streambed Induced Infiltration Sand & Gravel Aquifer

36 Remember: A utility needs the RIGHT geology to do this! Site hydrogeologic evaluation is critical This is NOT a good RBF site!

37 Thank you! Questions? William D. Gollnitz