Riverbank Filtration A Ground-Water Perspective

Transcription

1 Riverbank Filtration A Ground-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 GWUDISW and RBF GWUDISW-The potential for surface water containing pathogenic protozoa (Giardia & Cryptosporidium) to enter a ground-water collection device 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

3 Definition of GWUDISW Any water beneath the surface of the ground with significant occurrence of: insects or other macroorganisms, algae or large diameter pathogens such as Giardia lamblia or Cryptosporidium; or significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or ph that closely correlates to climatological or surface water conditions. (40 CFR 141.2) States must determine criteria Microscopic Particulate Analysis (MPA) developed to identify algae in ground waters

4 GWUDISW/RBF Background AWWARF to develop a protocol for determining Ground Water under the Direct Influence of Surface Water (GWUDISW) GWUDISW evaluation in Casper, WY arguing that the well field was not GWUDISW due to natural filtration of pathogenic protozoa via the aquifer matrix (sand & fine gravel) Concept rejected by USEPA because of a lack of a protocol to evaluate natural filtration ; Classified the source as GWUDISW and required the utility to install filtration

5 Log Removal of Algae (MPA*) Nov, 1997 Published first paper on Reduction of Microscopic Particulates by Aquifers in the Journal AWWA MPA samples from North Platte River, treatment plant filter effluents, and each of the ground water collection devices (wells, caissons & infiltration gallery) CWRWS-Casper, WY Conventional Treatment vs Riverbank Filtration SW Treatment Plant Wellfield Collection Devices Filter Log Device Log Caisson Morad Morad 6 > Caspar Caspar 14 > Caspar * Microscopic Particulate Analysis

6 Log Diatoms Log Algae Treatment Plant Efficiency Evaluations - MPA 12 Raw water Finished water 12 Raw water Finished water

7 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

8 RBF Background Cincinnati Water Works GWUDISW evaluation for Bolton well field Flowpath Study Natural Filtration became Riverbank Filtration Casper, WY developed a formal protocol for RBF demonstration of performance acceptable to the USEPA; demonstrated 2.0 log credit for Crypto removal RBF demonstration of performance study in Kennewick, WA; collector well received 2.0 log credit Sonoma County Water Agency, CA - Review of hydrogeologic data combined with fifteen years of waterquality data used to maintain a ground-water source classification

9 How do you determine GWUDISW? Federal SWTR Guidance Manual AWWARF GWUDISW project report Ohio EPA source classification protocol The term GWUDISW is not formally defined Definition of groundwater -.not under the influence of surface water Source is either a ground water or surface water

10 OEPA Source Water Designation Summary of OEPA Rules-OAC Chapt Source Water Designation : Well obtains water from rapid pathways or compromised hydrogeologic barriers Cased <15 in depth Casing depth+horizontal distance to surface water <40 Horizontal collector/infiltration gallery<25 deep Collector lateral depth+distance from lateral end to SW<50 OAC Chapt Ground water rule microbial monitoring Mean annual E. coli concentration 10 colonies/100 ml

11 Recommended Way to Determine GWUDISW Hydrogeology Size & shape of the aquifer Matrix-sand & gravel, fractured rock, karst limestone, etc. Confined or unconfined aquifer Where does recharge come from; and how quickly? precipitation surface water Water quality Temperature Turbidity Coliform bacteria Microscopic particulate analysis (algae, diatoms, etc.) Is there hydraulic communication with the river? How effective is natural filtration?

12 Recommended Protocol Well in porous media evaluated for GWUDISW- Is there hydraulic communication? Yes No Provide engineered treatment or Perform RBF Demonstration Study Ground water - Provide disinfection under GWR 0 to 1 log treatment 2 to 3 log treatment Add additional treatment using UV or ozone disinfection 4.0 or > log treatment

13 Typical Ohio River Ground Water System Multiple wells located in a glacial outwash/river alluvium terrace adjacent to river Each well pumps 350 to 800 gallons per minute (GPM) with total design production of million gallons per day (MGD) Wells are submersible GW treated for Fe/Mn removal Filtration with no coagulant

14 Wooded area with small stream transversing the length of the well field Well field is at the base of this hill (bedrock)

15 Conceptual Drawing of Aquifer Profile Line Fe/Mn Treatment Plant Bedrock? Edge of Hill (Bedrock) Creek Channel Wells Ohio River Not to Scale

16 Elevation (Feet) Ohio Ohio River Aquifer Profile Kentucky 540 Creek Channel 520 Road Well Field Ohio River Channel 500 Approx top of aquifer Meander Scar Range of River Stage Typical Well Bedrock Wall Approx Screened Intervals Estimated Bedrock Elevation Distance (Feet) Land Surface Profile River Stage Bedrock

17 Hydrogeologic System Aquifer dimensions: 7,000 x 1,000 x 20 x 25% 261 million gallons of water Maximum pumping 14 mgd Time to dewater 19 days Wellhead Protection Modeling Flowpath travel time 1 month to 1 year Ninety-five percent of the water comes from the river

18 Stage (Ft above MSL) Turbidity (NTU) Ohio River Stage vs GW Turbidity SW Turbidity Limit /7/08 12:00 AM 5/2/08 12:00 AM 4/27/08 12:00 AM 4/22/08 12:00 AM 4/17/08 12:00 AM 4/12/08 12:00 AM 4/7/08 12:00 AM 4/2/08 12:00 AM 3/28/08 12:00 AM 3/23/08 12:00 AM 3/18/08 12:00 AM 3/13/08 12:00 AM 3/8/08 12:00 AM 3/3/08 12:00 AM 2/27/08 12:00 AM 2/22/08 12:00 AM 2/17/08 12:00 AM 2/12/08 12:00 AM 2/7/08 12:00 AM 2/2/08 12:00 AM 1/28/08 12:00 AM 1/23/08 12:00 AM 1/18/08 12:00 AM 1/13/08 12:00 AM 1/8/08 12:00 AM 1/3/08 12:00 AM 12/29/07 12:00 AM 12/24/07 12:00 AM 12/19/07 12:00 AM 12/14/07 12:00 AM 12/9/07 12:00 AM 12/4/07 12:00 AM Time (Days-Hours) River stage Raw Turbidity Finished Turbidity

19 Well Bacteriological Data Collected After Multiple Flood Events Number of Positive Samples Well Total Coliform E. coli

20 Signs of Potential Risk for Protozoa Contamination (GWUDISW) - Hydrogeology Boundary conditions on north side, bottom (bedrock) and semi-confined top sediments River channel penetrates >60% of the aquifer; water likely enters primarily on river side Estimated river recharge ranges from 75% to 95% River stage can increase to over 50 feet in 1 to 3 days Anecdotal information supports water entering quickly (air rushing from monitoring wells) Travel time from river to closest wells can be hours, days or weeks depending on head conditions

21 Signs of Potential Risk for Protozoa Contamination (GWUDISW) Water Quality Turbidity spikes (over 0.3 ntu) occur during and after high river stage events If 3/day grab samples detect turbidity spikes it is likely that high turbidity is more prolonged Total and E coli hits indicate a potential fecal problem Is there hydraulic communication Yes How effective is natural filtration -?

22 What Should Be done?-collect More Data! Is there much natural filtration? Install water level recorders in two monitoring wells to verify rapid recharge of aquifer Install a continuously monitoring turbidimeter Collect weekly coliform and E coli samples from the combined influence to the plant Collect microscopic particulate analysis (MPA) samples after high stage events (identify algae, diatoms & other microbes)

23 Source Classification Change?-Utility Options Source should be reclassified as a surface water if: Water table data shows rapid recharge Majority of water quality data show limited natural filtration The utility would then have two options: Modify treatment plant to incorporate a coagulant; or Perform a Demonstration of Performance evaluation under the LT2ESWTR to quantify Cryptosporidium removal

24 Demonstration of Performance Allowed under the LT2ESWTR and OAC Chapter Filtration of Water from Surface Water Sources, (Section) C Applies to alternative filtration technology (e.g. methods other than rapid sand filtration and slow sand filtration) Must demonstrate 2 log removal of Cryptosporidium; 3 log removal/inactivation of Giardia and 4 log removal/inactivation of viruses

25 RBF Demonstration of Performance Studies General Summary-Hydrogeologic Data Identify the aquifer hydrogeologic characteristics Shape and aerial extent Sources of recharge (proximity to surface water) Aquifer permeability Pumping periods and rates Estimate time to dewater aquifer (time of travel of SW) USE ground water models if available Source Water (Wellhead) Protection material can be very helpful Identify conditions when SW recharges the aquifer at high rates (typically low water table due to high pumping prior to a high river stage event)

26 RBF Demonstration of Performance Studies General Summary-Water Quality Data Sample surface water and ground water in order to determine reduction Use multiple filtration surrogates Turbidity Algae (MPA) Diatoms (MPA) Particle counts Spores Coliform bacteria Giardia and Cryptosporidium Concentrate sampling during and after high recharge rate events

27 Successful Demonstration of Performance Studies Central Wyoming Regional Water System Successful two-year demonstration of 2-log reduction of multiple surrogates therefore receiving Cryptosporidium removal credit from USEPA under the IESWTR Cost of the DOP evaluation <$1 million Cost to expand the surface water treatment plant >$20 million

28 Central Wyoming Regional Water System General Layout of Caspar & Morad Well Fields RBF Demo Study Test Sites M9 Morad Field

29 North Platte River & Recharge Basins

30 Basis for Crypto Removal Credit Aquifer matrix is fine grained - >80% sand, silt & clay On average >30% of grain sizes are 1mm or smaller (>10% required by LT2) Shortest flowpaths are >20 in length as compared to 3-5 for engineered systems Many of the flowpaths are in excess of 1,000 Range of estimated infiltration rates are less than engineered systems No detections of G/C in any ground water samples RBF turbidities are well below 0.3 NTU All devices achieve a minimum geomean of 2.1 log reduction of all surrogates; 66% (4/6) are conservative in that they are smaller than Crypto; Results also conservative due to use of detection limits when no detects were found

31 Successful Demonstration of Performance Studies Cincinnati Water Works-Bolton Well Field Two-year Flow Path Study demonstrated 4-log reduction of multiple surrogates even during high stage events; therefore well field should retain its ground water classification Production Well

32

33 Successful Demonstration of Performance Studies Kennewick Washington

34 Successful Demonstration of Performance Studies Kennewick Washington

35 Successful Demonstration of Performance Studies Kennewick Washington

36 Riverbank Filtration DOP Evaluation Summary Summary of Surrogate Removal at RBF Sites Parameter Cincinnati-Bolton CWRWS-Casper Kennewick Louisville Well #1 Well #8 Caspar Well Morad Well Caisson Caisson Caissons Turbidity <0.1 NTU <0.1 NTU <0.1 NTU < 0.1 NTU < 0.1 NTU <0.1 NTU 0.5 to 0.69 NTU Total coliform ND ND 2.15 log 2.35 log 2.15 log >2.9 log 3.2 log E coli log 2.05 log 1.9 log >1.4 log - Enterococci log 1.95 log 2.05 log >1.6 - HPC log Particle counts 7-10 µm 3.8 log 3.7 log Particle counts 3-5 µm 3.6 log 3.6 log Spores 5 log 4.9 log 2 log 1.5 log 2.1 log 2.9 log 3.3 log MPA-algae 4.8 log 6.2 log 5.4 log 3.7 log 5.5 log 7 log > 7.1 log MPA-diatoms log 6.7 log 7.1 log 8 log > 6.7 log Giardia ND ND ND ND ND ND ND Cryptosporidium ND ND ND ND ND ND ND

37 Recommendation Existing primacy agency protocols should incorporate riverbank filtration demonstration of performance studies as an alternative filtration technology This will provide utilities an option other than engineered treatment which can save the utility money

38 Thank you! Questions? William D. Gollnitz