Don’t Let Your Water Quality

Tank

Thomas F. Clark, P.E.

Monroe County Water Authority

Outline

• Past water quality problems

• Inspection of critical tank features

• How can diving and ROV assist with tank maintenance

• Ten State Standards & AWWA C 652-11

Water Storage Tanks and Water Quality

• Water treatment is a critical component in the process of delivering high quality water.

• After the water leaves the plant, but prior to reaching the customer, it must be adequately and safely stored.

• The best treatment process is negated if water storage tanks allow for degradation of the water contained in them.

The Role of Storage tanks

• Historically, storage tanks were installed to

▫ allow for flow equalization

▫ maintain pressure

▫ fire reserve

▫ emergency storage

• But in recent years, there has been additional recognition of the role tanks can play in water quality degradation.

Photo source: MCWA

Water Quality Issues

• Loss of Disinfectant Residual

• Bacterial Regrowth

• Disinfection By-Product Formation

• Nitrification

• Sedimentation

• VOC’s

• Contamination due to poor sanitary safeguards

Storage Facility Case Study

Utility A, MO• This town in MO

experienced an outbreak of Salmonella.

Photo source:wikipedia

Storage Facility Case StudyUtility A, Missouri

System Description

▫ A small mid-west town serving 1,100

▫ Ground water with disinfection waiver

▫ Two deep wells…….two water storage tanks of 50,000 and 100,000 gallons

In early November, there were taste and odor complaints that resulted in an extensive system flushing.

Storage Facility Case StudyUtility A, Missouri

Within several days, routine bacteriological samples showed the presence of total and fecal coliform.

Subsequent sickness told hold with stool samples taken from sick residents positive for Salmonella typhimurium.

The health department conducted an investigation which implicated the water serving the town.

Storage Facility Case StudyUtility A, Missouri

Inspection showed one tank had severe sanitary defects in the hatch, vent and overflow including holes that had been drilled in the tank dome.

These holes were used by painting contractors to rig scaffolding and had been left open (or duct taped) after the job was complete.

Underwater Solutions, Inc

Storage Facility Case StudyUtility A, Missouri

The presence of feathers in the tank and open holes in the dome led investigators to conclude that fecal matter from pigeons had contaminated the tank and entered the system as the water tank level dropped during the extensive flushing effort in November.

Final count…….650 people sick (> 50 % of the population), 15 hospitalized and 7 deaths.

Storage Facility Case Study

Utility B, CO

System Description

▫ Serves 8,900 plus 1,000 through purchase systems

▫ Ground water with

disinfection waiver.

▫ Three storage tanks

(1 ground level)

Storage Facility Case Study

Utility B, CO• The first illness due to Salmonella was reported

and was thought to be a food event.

• After additional cases are reported, the state determines that the source of the Salmonella is waterborne.

• Well water samples were not contaminated, implicating the water system.

Storage Facility Case Study

Utility B, CO

Physical contamination of a ground storage tank:

o Cracks and holes could allow small animal or water (snow melt?) to contaminate the tank

o Evidence of wildlife near (but not inside) in the tank

Photo source: Colorado DOH report

Storage Facility Case Study

Utility B, CO• In a second elevated tank, they

found a significant amount of bird droppings on the top in the general proximity of gaps in seams on the dome where bolts (holding plates together) were missing.

• Some vent issues were noted as well.

Storage Facility Case Study

Utility B, COImpacts of the outbreak…….

Public Health:

▫ 442 illness reported (as many as 1,300 sick?);

20 hospitalized, 1 death

Costs estimated around $1 Million to City,

County and State

Storage Facility Case Study

Utility B, COIt doesn’t take much to impact an entire system. They suspect just one bird may have been involved.

The water supply was deemed unsafe for three weeks.

Photo Source: Colorado DOH Report

The Bacteria : Salmonella

Salmonella is a primary pathogen.

Generally is a cause of bacterial

food poisoning.

Is also a cause of typhoid fever

and gastroenteritis.

Easy to inactivate with chlorine.Photo source: University of Rochester

The Bacteria : Salmonella

Detection in water is not easy.

• It does not react with m-Endo agar or enzymatic tests.

• Coliform definition……Aerobic, facultative anaerobic, gram negative non-spore forming rod that ferments lactose @ 35 ° C utilizing galactosidase.

• Salmonella does not ferment lactose

Disease Outbreak Prevention

• Both of these outbreaks were with utilities that did not disinfect . But are these situations really different from a water system that can’t maintain a chlorine residual in its tanks ?

• That’s why routine inspection of sanitary safeguards is so important !!! (States such as Ohio, New Hampshire, Wisconsin, Florida and Texas require tank inspection now…..)

• AWWA recommends inspections every 3 – 5 years.

Solids Within the Tank

• . • .Tank A

aluminum

arsenic

calcium

chromium

copper

iron

Tank B

aluminum

arsenic

calcium

chromium

copper

iron

Microbiological Content

• Serratia marcescens

• Pantoea agglomerans

• Enterobacter cloacae

• Enterobacter vulneris

• Citrobacter feundii

• Klebsiella oxytoca and

• Aeromonas species

Photo source: drainunblockers.co.nz

Wildlife in a Tank

This is not what you want to have in your tank !!!!

To prevent this, routine sanitary inspections are needed.

Photo source: AWWA

Tank Inspections

When inspecting a tank, you will want to look at such items as……

▫ the foundation

▫ supporting rods

▫ coatings

▫ cathodic protection system

▫ and sanitary safeguards

Sanitary Safeguards

Sanitary safeguards include

▫ vent

▫ overflow pipes

▫ screens

▫ hatches

▫ domes

Routine Inspection- Tank Exterior

This involves getting on your climbing shoes, obtaining proper climbing and safety gear, and going for a climb !!!

Or, contract for the inspection.

On the tank exterior, you are looking for sanitary breaches in the integrity of the tank, especially…..

Photo source: MCWA

Routine Inspection - Tank Exterior

Inspection of vent screens and vent structures

Checking for missing, corroded or collapsed vent screens

Photo Source: Utility Services Group

Photo Source: AWWA

Vent Screens

Proper screen material per Ten States Standards

Four mesh non-corrodible screen for elevated tanks, or finer mesh non-corrodible screen in combination with an automatically resetting pressure-vacuum relief mechanism.

Photo source: Government of Newfoundland

Photo Source: Government of Newfoundland

Avoid This !!!

Tanks can implode under the proper conditions!!!

Photo Source: WaltBeattie.com

Hatches

Hatches▫ Curbed with 4” – 6 “ rise

above the tank dome

▫ Hatch that overlaps the riser to exclude animals down to spider size.

▫ And they need to be kept closed and locked !!

Photo source: AWWA

Photo source: Government of Newfoundland

Holes in the Dome

There may be holes cut into a tank’s dome from which anodes can be suspended as part of the tank’s corrosion protection.

Photo source: AWWA

Avoid This

Contractors may cut riggers holes into the tank dome.

This topic needs to be addressed in the project specs.

Verify that if installed, the holes are properly closed prior to sealing the tank and refilling !!!!

Photo source: Underwater Solutions

Proper Drainage from Dome

Photo source: Government of Newfoundland

Overflows

Overflows MUST be screened to protect against animals getting up and into the tank.

Photo source: Government of Newfoundland

Photo source: Government of Newfoundland

Overflow Pipes

The overflow for an elevated tank shall open downward and be screened with a four mesh, non-corrodible screen or mechanical device, such as a flap valve or duckbill valve.*

The overflow for a ground-level storage reservoir shall open downward and be screened with twenty-four mesh non-corrodible screen.

Photo source: Government of Newfoundland

Routine Inspection & Cleaning- Tank

InteriorThis can be accomplished by one of three methods:

▫ Dry tank with washout and inspection

▫ Diver inspection and cleaning

▫ ROV inspection and cleaning

Dry Tank Inspection & Washout – Pro’s

vs Con’sPro’s Con’s

Once the tank is drained and cleaned, the exposed surfaces (including the floor where corrosion is found) can be thoroughly evaluated.

Repairs can be undertaken quickly and easily.

Either a second tank or pressure relief valve need to be set up to continue operation.

Lockout/tagout and confined space.

Some loss of water will be incurred.

Chlorine residual neutralization?

Dry Tank Washout

When you enter a tank, you need to be using equipment dedicated to tank interiors and follow “best practices” for disinfection. (AWWA C652-11)

And remember, a tank is a confined space !

Vacuum Trailer

• To be purchased in 2016 to assist in tank cleaning.

• Very efficient way to pick up

water and solids

remaining after tank

is empty.

Dewatering Silt Bag

Photo Source – BMP Supplies

Diver Inspection – Pro’s vs Con’s

Pro’s Con’s

Can be done in a few hours instead of a few days.

Can document the condition of walls and support columns from floor to waterline w/o erecting scaffolding.

No facility downtime.

No water loss.

Video and audio quality may be questionable.

A detailed structural assessment of cracks and spalling may be lacking.

Suits and dive equipment need to be dedicated to use in potable water

Does the tank have a manhole of sufficient diameter?

ROV Inspection

Pro’s Con’s

• No tank down time.

• No water loss.

• No lockout/tagout procedures or confined space worries.

• A good way to assess the general condition and cleanliness of the tank interior.

• The ROV can only see those areas that it can reach.

• Can’t help with repairs.

Conrady Consultants

Diver/ROV Sanitary Considerations

Sanitary and other considerations include

- divers need to be completely encapsulated

- divers need to be certified for commercial work

- disinfection of equipment and divers w/ 200 ppm solution per AWWA C652-11

Photo source: underwatersolutionsinc.com

Diver/ROV Sanitary Considerations

Sanitary and other considerations include

• Establish chlorine residuals and turbidity in the water prior to entering.

• Daily tests for coliform, chlorine and turbidity if the tank remains in service during cleaning.

Photo Source: Texaswatertankinspection.info

Return to Service Samples

AWWA Standard C-652 – 11 “Disinfection of Water Storage Facilities”

Before the storage tank is placed into service, satisfactory bacteriological results and chlorine residuals are required. They need to be representative of water within the tank. They can be taken from a tap on the outlet piping, or a sample tap connected to the facility or taken through the hatch.

Water Quality Sampling

If sampling from the hatch is required, a Van Dorn sampler may be needed.

Proper disinfection of the sampler is also required. It then needs to be bagged in a clean plastic bag for transport to the top of the tank.

Closing Thoughts

• “EPA is also looking at distribution system storage tanks to learn more about whether or not sanitary surveys are a sufficient tool for monitoring tank sanitation and maintenance. While the recent Revised Total Coliform Rule does not include mandatory standards for inspection and maintenance of storage tanks, Grevatt told AWWA that EPA intends to ensure tanks are properly cleaned and maintained.” AWWA Water Utility Insider April 11, 2014

Summary

• Every tank periodically needs to be inspected and cleaned.

• Inspect your tank’s safeguards NOW !!

• Such defects as holes in tank domes and unscreened vents and overflow pipes put a utilities customers at risk.

• If you are not inspecting your tanks, start laying plans to do so. EPA will some day require it !!!

Thank You !!!

200 PPM Solution

• C 652-11 refers to use of a 200 ppm chlorine solution to disinfect equipment and divers.

• To make this solution requires 11 teaspoons of 5.25 % hypo for every 4 gallons of solution that you are preparing.

• 11 teaspoons is about ½ cup or 50 ml.

Summary of Tank Disinfection Methods

Method # 1Full Storage

Method # 2Spray

Method # 3Chlorinate and Fill

Chlorine Dose and Residual

10 mg/l dose 10 mg/l

residual

Spray 200 mg/l dose(10 mg/l residual for drains)

50 mg/l dose2 mg/l residual

Volume of Water toDechlorinate

Most volume –water drained from tank to reduce residuals

Minimal volume –only water from drains

Minimal volume –only water fromdrains

Holding Times 6 hrs or 24 hours, depending on chlorine feed used

30 minutes 6 hrs + 24 hrs(30 hrs total)

Photo Source- KLM Engineering

Photo Source- Underwater Solutions Inc

Riggers Holes

• Then there are rigger’s holes…..

Photo source: Underwater Solutions

The rTCR

• The revised Total Coliform Rule has just arrived due to an uptick in water related disease outbreaks due to factors in the distribution system.

Routine Inspection- Tank Exterior

• Inspection of vent screens and vent structures

• Checking for missing or collapsed vent screens

• Photo source: AWWA

Photo source: AWWA

Photo source: Utility Service Group

Verification of Water Quality

Check the chlorine residual and turbidity of water in the tank plus coliform bacteria level.

If coliform is present, isolate the tank, boost chlorine residual to 1.5 mg/l – 2 mg/l and resample for coliform content.

Vent Screens

Per Ten States Standards:

On ground-level structures, vents will open downwards with the opening at least 24 inches above the roof or ground and covered with 24 mesh

non-corrodible screen .Photo Source: Government of Newfoundland

24 Mesh Screen

Photo source:ebay.com