“Elimination of Chronic Total Coliform Presence in a Gravel Packed Well Through Enhanced Well Redevelopment” Rebecca McEnroe, P.E., Superintendent, Sudbury Water District, Sudbury, MA. Savas Danos, General Manager, Panton-McLeod – Americas, Groton, MA
Sudbury Water District
Sudbury Water District • Population 18,300 • Average Day = 1.8 MGD • 9 wells, flow range = 300-600 GPM • Wells 2A, 7 and 9 treated at the Raymond Rd WTP. • RRWTP, Mn and Fe removal, corrosion control, fluoride addition and disinfection
Well 9 Water Quality • Hardness 140 mg/l • Mn 1.5 mg/l • Fe 1.75 mg/l • TOC 2.5 mg/l • UV 0.22 cm -1 • Turbidity = 0.55 NTU
Well 9 • 75 ft deep X 24” diameter gravel pack well • Drilled in 1989 • Total Coliform present in intermittent samples starting around 2010 • MaDEP approved Ground Water Rule CT for RRWTP • 2014-15 19 of 24 sample were TC present (79% present)
Well 9 • Researched well design and installation to determine if there were any structural issues causing the total coliform presents within the well • Met with two different well installers to visually inspect the well • Could not determine if there were any structural issues with the well
Well 9 • Original specific capacity = 125 gpm/ft • Specific capacity prior to cleaning = 83.3 gpm/ft (33% reduction in capacity) • Records were not available for the last well cleaning but antidotal evidence indicated the last well cleaning was before issues with total coliform presents
Well Redevelopment • Scheduled a well rehabilitation for January 2016 • Typical acid redevelopment was specified • Decided to use Pantonite tm PM77after acid redevelopment to see if it would help with TC issue. • Well went back on-line February 2016
Well screen before cleaning
Well screen after cleaning
Results • February – October 2016 (9) All sample absent for TC • November 2016 – January 2017 (3) TC present • February – March 2017 (2) All TC samples absent • 3 of 14 samples present for TC (22% present) • Positive samples may be a result of very dry soils due to the drought followed by very heavy rains in October
Signs of Well Degradation Decrease in Wire- to-Water Efficiency Decrease in Specific Capacity (gal/ft) Water Quality Degradation Decrease in Output (gal/minute)
Causes of Well Output Reduction • Lower Water Table due to Drought or Aquifer Depletion • Reduced Pump Efficiency due to worn, corroded and/or plugged pumping parts • Mineral Plugging (Iron, Manganese, Calcium Carbonate) • Microbial Corrosion (Sulfate-Reducing Bacteria) • Mud, sand and/or silt fouling • Slime Formation (bio-fouling) caused by iron and slime forming bacteria
Typical Signs of Fe/Mn Plugging
Typical Well Rehabilitation Methods for Iron/Manganese Removal • Pre & Post Bore Hole Video • Mechanical Pre-Cleaning/Brushing • Acid Treatment/Injection (pH 3 or below for 24-48 hours) • Surging • Discharge/Neutralization • Chlorination/Disinfection
Well Screen – New vs. Used!!!!
Typical Disinfection/Acid Treatments • Chlorine: • Most effective as disinfectant after chemical treatment – polishing. • Ineffective at removing biofilm • Mineral Acids • Hydrochloric (muriatic): mineral build-up, inexpensive, dangerous (fuming) • Phosphoric: mineral build-up, non-harmful vapors, slow reacting, phosphates? • Sulfamic: slow reacting w/ mineral buildup, dry form non-dangerous • Organic Acids • Glycolic (hydroxyacetic): some effectiveness on bio-film, non-corrosive • Glacial Acetic (Vinegar): sulfate removal, organics, very corrosive • Oxalic : some effectiveness on bio-film. • Citric: mn/fe removal • Concerns: NSF Certified?; Are Minerals the only problem/concern?
When Typical Treatment(s) Stops Working Specific Capacity Evaluation 0.98 mg/l Mn 0.50 mg/l Fe 140 Acid Blend 120 Acid Blend Enhanced Treatment Specific Capacity (g/ft) 100 80 60 40 Time For Enhanced Redevelopment! 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Months After Treatment
Why Typical Treatments loose Effectiveness: • Reduction Process for Iron/Manganese Dissolution is/are not the target mineral(s) • Pumping Component(s) Failure • Well Screen/Gravel Pack Compromise • Biofilm/Bio-Fouling Build-up • Generally Associated with Excessive Fe & Mn Concentrations
What is Biofilm? A biofilm is made up of aggregates of microorganisms, such as bacteria, fungi, diatoms, protozoa, algae and any exogenous materials, which are embedded in a hydrated extracellular matrix and attached to a solid surface (well screen, pipes, ship’s hull, teeth, lungs, etc) Young Seo , 2012. “Biofilm Formation and Control in Drinking Water Distribution Systems”
Examples of Biofilm:
Biofilm Formation on Well Pump
Iron – oxidizing bacteria use oxygen (when de-oxygenated water reaches a source of oxygen) and convert soluble ferrous iron back into an insoluble reddish precipitate of ferric iron Thiobacillus ferrooxidans & Leptospirillum ferrooxidans
Biofilm Matrix
Biofilm Formation
Biofilm Formation in Water
Enhanced Treatment Techniques for Biofilm Elimination: • Proprietary Blends: • Pantonite tm PM77 (NSF 60 certified - complex mixture) • Johnson – NU 310/400, etc …. • Cotey Dry Acid/Liquid Descaler • Laval Boresaver BLS • Bariod AquaClear AE • Wire Charge Methods: • Sonar-Jet • Shock Blast • Prima Cord
Enhanced Treatment Techniques for Biofilm Elimination (continued): • Fluid Precussive Methods: • Airburst • Airshock • Nitroburst/Nitro-pulse • Jetting • CO 2 Injection: • COMBINATION of physical and chemical!
Enhance Redevelopment Needed -When : • Other typical methods fail and/or: – Video taping of bore hole finds no structural failure – Pump components intact – Chronic Total Coliform Bacteria problem and/or background bacteria presence (if membrane filtration TC testing methodology utilized). – Excessive Heterotrophic Bacteria counts when plated on agar media.
Biofilm Analysis Methods: • Advanced Laboratory Methods: • Electron Microscopy: • Immunofluorescence Microscopy: » MPN Testing • Field Analyses: • Biological Activity Reaction Analysis (BART Assay) • Adenosine Triphosphate Analysis (ATP Assay)
Biological Activity Reaction Analysis (BART) • A simple yet effective method for monitoring the population size and/or activity of specific groups of bacteria. Results are obtained by observation after 2-8 days of room temperature incubation. • With BART, you can monitor for Iron Related Bacteria (IRB), Sulfate Reducing Bacteria (SRB) and Heterotrophic Aerobic Bacteria (HAB) - the three most important agents involved in biofouling:
Adenosine Triphosphate Analysis (ATP) • ATP is a molecule found in and around living cells, and as such it gives a direct measure of biological concentration and health. ATP is quantified by measuring the light produced through its reaction with the naturally occurring firefly enzyme luciferase using a luminometer. The amount of light produced is directly proportional to the amount of ATP present in the sample.
Conclusions: • IF: Well Yield and Specific Capacity are Decreasing &/or there is an increase in Chronic Microorganism Concentrations & – Typical Acid Redevelopment Has Lost Its Effectiveness &/or – Well Mechanical and Physical Components are Intact: • TIME FOR an ENHANCE REDEVELOPMENT APPROACH !
Acknowledgements
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