Shock Chlorination by Udc4XK1S

VIEWS: 11 PAGES: 63

									Disinfecting Your System

  Advance Small Water System Course
                June 15, 2012
  City of Hillsboro Civic Center Complex
                Hillsboro, OR




       OFFICE OF ENVIRONMENTAL PUBLIC HEALTH
                 Drinking Water Program
              Why do we need to disinfect?
    •Community water system serving 35 residents
    • April 25th – 2 coliform samples E. coli positive
    • Boil water public notice sent to residents
    •Evaluated source of coliform (tested well water)
    •Chlorinated to correct problem




2
        Determining the Correct Approach
• What system components need to be disinfected?
    –   Sources (wells, springs)
    –   Storage facilities (reservoirs, pressure tanks)
    –   Distribution piping
    –   New or repairs to wetted system components
         • (i.e., pipes, storage chambers, fittings & valves, pumps)




3
         Determining the Correct Approach

    • Why do we disinfect?
      – To kill pathogens: protozoa, bacteria & viruses
        that may cause illness or effect human health
    • What type of event are you addressing?
      – Total coliform/E. coli in distribution system             Adenovirus photo credit:
                                                                     http://cronodon.com/

      – Total coliform in source water
      – Confirmed E. coli in source
    • How do we disinfect?
       – Use oxidizers to inactivate pathogens
                                                        E. Coli photo credit: photobucket




4
         Disinfectants - How They Work
         Disinfectants are most commonly oxidants*
Oxidants:
 • Either gain electron(s) or provide oxygen in a chemical
   reaction.
 • This reaction disrupts cell walls (bacteria) or protein coats
   (viruses).

           Oxidants do the same to our cells which
          is why our skin may feel slippery when in
            contact with bleach…the skin cells are
          breaking open and their contents spill out.



5
    Disinfectants - How They Work

                         Virus

      E. coli



           Oxidizer
            (chlorine)




6
             Disinfectants - How They Work

    In more detail, when we say “chlorine” disinfection:
    •   We usually mean 1 Chlorine (Cl) + 1 Oxygen
        atom (O)  is called hypochlorite (OCl-)
    •   When the Oxygen or Chlorine atom binds to
        other molecules, they no longer work the same
        way
    •   After enough of its molecules are transformed in
        this way the cell dies or cannot reproduce




OFFICE OF ENVIRONMENTAL PUBLIC HEALTH
Drinking Water Program
                                        Hypochlorite Ion Wikipedia

7
             What type of event requires
               disinfection of wells?
    Organisms may enter wells during
    major repairs or other instances.
    Chlorination is recommended after:
    • Construction of a new well
    • Maintenance activities (i.e.,
      broken pipe)
    • A positive coliform sample or
      other contamination event
    • As a preventative measure to kill
      biofilm that may have built up in
      the well casing

8
        Determining the Correct Approach
    • What level of chlorination should be achieved?
      – Shock chlorination
         • Approximately 50 mg/L for wells, levels vary for
           storage and distribution applications)
      – Low level chlorination (< MRDL of 4.0 mg/L)
         • A good strategy when total coliform is only concern
           (not E. coli)
         • Maintain service to customers during disinfection
           process

                          mg/L = milligrams per liter
                     MRDL = mean residual disinfectant level

9
         Resources Available on DWP Website
     http://public.health.oregon.gov/healthyenvironments/drinkingwater/operations/pages/shockchlorination.aspx




10
            Simple Well Shock Chlorination
                (Modified AWWA Standard C654-03)

     • To calculate the volume to be disinfected &
       dosage, you’ll need to know the static water level
       & total depth of the well.
     • How can SWL be determined?
                                                 Static Water
        – Take a current measurement              Level = 35’
        – Use the most recent measurement
                                                Length = 65’
        – Use value from well log (Note:
           water level varies seasonally)      Total Well Depth
                                                      = 100’


Example: 100 ft (TWD) – 35 ft (SWL)= 65 ft (Length)

11
              Measuring Static Water Level

                                        Go very slow to avoid
                                        getting your water level
                                        meter stuck in the well




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       Methods to Measure Static Water Level
     • Borrow or rent the equipment (Ask Oregon
       Water Resources Dept, environmental
       consultants, or an analytical lab to find out)
     • If you cannot measure the static water
       level
        a) Use this level listed on the well log, or
        b) Many suggest using the total depth of
            the well to calculate volume (covers
            worst case scenario)
Oregon Department of Water Resources: http://www1.wrd.state.or.us/pdfs/NGWN/Water_Level_Booklet.pdf
  Oregon State University Extension Service: http://extension.oregonstate.edu/catalog/pdf/ec/ec1368.pdf

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     Finding the Well Log




     http://apps.wrd.state.or.us/apps/gw/well_log/

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                             Calculate Well Volume
     • Determine the volumes of components to be disinfected
       using the following formulas:




       http://public.health.oregon.gov/HealthyEnvironments/DrinkingWater/Operations/Documents/welldisinfection.pdf
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                        Calculate Well Volume
                  Determine the volume to be disinfected


        Example: You have a 6-inch
        diameter well that contains
        65 feet of water. What is the
        volume in gallons?




Formula to use:
(Total water depth)(# gallons of water per foot of well depth) = Gallons in well

       65 ft x 1.5 gal/ft of well depth = 97.5 gallons of water in well
  OFFICE OF ENVIRONMENTAL PUBLIC HEALTH
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  18
     Next: What Type and Source of Chlorine?
     • Decide whether to use bleach (sodium hypochlorite), or
       calcium hypochlorite.
        – Usually liquid sodium hypochlorite (5%, 6%, or 12.5% solution),
          but calcium hypochlorite can be useful for deep well applications.
        – If using over a few days (e.g., low level continuous chlorination),
          the product must be NSF approved (Standard 60); for shock
          chlorination, NSF is preferred but not required.
        – Avoid using stabilized chlorine (i.e. dichlor and trichlor) common
          in the pool and spa industry.




19
                           NSF Standard 60
• The National Sanitation Foundation certifies
  products and equipment for use in public
  drinking water systems.
• Look for this emblem.
  (Again, it’s not required if the system will be
  flushed again before people drink the water.)
• Although the “NSF” emblem is not on the package, the Water
  Quality Association certified that “Clorox® Regular Bleach,”
  and “Clorox® Ultra Bleach” meet NSF Standard 60. So they
  are certified for use in public water systems.
• For more info: The DWP Summer 2009 Pipeline article
  discusses bleach products and NSF 60 certification.

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                                        Half Life of 12.5% Sodium Hypochlorite
                                                at Various Temperatures




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                          Chlorine Dosing
• Commonly, wells are shock chlorinated to achieve 50 mg/L for 12 - 24
  hours
• Guideline: 50 mg/L = Approximately 1 cup of 5% bleach per 100 gallons
  of water
• Note: Solution concentration in “%” is not synonymous with mg/L

            Formula to determine cups of bleach needed =

     (16 cups/gal)(target concentration in mg/L)(volume to be disinfected in gal)
                    (bleach concentration as %)(10,000 mg/L/%)
                     Milligrams per Liter (mg/L) = Parts per million (ppm)




22
                           Chlorine Dosing
                Formula to determine cups of bleach needed =
     (16 cups/gal)(target concentration in mg/L)(volume to be disinfected in gal)
                    (bleach concentration as %)(10,000 mg/L/%)

            •Target Concentration = 50 mg/L
            •Volume = 100 gallons
            •Bleach concentration = 5% (Note: product strength varies)
            •Conversion factors
                  chlorine bleach = (16 cups/gal)(50 mg/L)(100 gal)
                                (5%)(10,000 mg/L/%)

                                    = 1.6 cups
23
                            Chlorine Dosing
     • If using calcium hypochlorite




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                            Chlorine Dosing
     • If using calcium hypochlorite:
Formula to calculate Chemical Feed (lbs or lbs/day of chlorine) =
      Volume (MG) or Flow (MGD) x 8.34 (lb/gal) x Target Residual (mg/L or ppm)

                   •Volume = 5,000 gallons/1 million = 0.005 MG
                   •Conversion factor
                   •Target Residual = 2 mg/L
                   •Available chlorine = 45% (or 0.45)

         Lbs or lbs/days of chlorine = (0.005 MG x 8.34 lb/gal x 2 mg/L)/0.45
                        = 0.185 lbs or ~ 3 ounces
            Don’t forget to consider the available chlorine in the product…


25
     Formulas / Conversion Tables




26
          Helpful Tools – Conversions Online
     • Use any number of online conversion tools by doing a search on
       “unit conversion.”
     • Or, just type the value to be converted into the Google search bar
       (e.g. “25 tablespoons to cups” yields a result of “25 US tablespoons
       = 1.5625 US cups”).




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           Solution Mixing – General Rules
     • When mixing chemicals it is suggested that you always
       add the water first, and then the chemicals.




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                             Solution Mixing
     • Many chemicals require a designated mix time before
       injecting into the water system. Mixing may be done
       manually with an inert paddle or automatically using a
       propeller mixer.




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     • Adding extreme amounts of chlorine to a well is not a
       good idea. High doses of chlorine may actually prevent
       effective disinfection by causing hardening of the surface
       of bacterial colonies, preventing the chlorine from
       penetrating & possibly damaging equipment.




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              Preparing Chemical Solutions
     •Preparing chemical solutions for disinfection
     involves:
                    Safety
                    Sanitation
                    Dilution
                    Delivery
     • Handle solutions carefully (oxidants are
       powerful chemicals at high concentrations
       and can cause permanent damage).
     • Be sure the equipment used to handle the
       chemicals is sanitary and safe.
     • Plan your dilution steps, write out the math.
     • Deliver solution properly (always add
       product  water! Not water  product!).

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                Simple Well Shock Chlorination
                      “Bottom Up Injection” – Option 1

Ideal Method - More likely to achieve 50 ppm throughout the
water column:
• If possible, run a tube through the casing vent to the bottom of
  the well. Then withdraw the tube while injecting the chlorine
  solution.
• Surge/run the well pump three times and then let solution sit for
  12-24 hours.
• After 12-24 hours, use a throttled discharge valve (flow splitter)
  to re-circulate half the water down the casing while pumping half
  to waste until there is no residual chlorine.

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                                                                                Use
                                                                               nearby
                                                                              hose bib
     Example of how to
     recirculation water
        down a well




     University of Nebraska, Institute of Agriculture and Natural Resources
     http://infohouse.p2ric.org/ref/20/19703.htm#SHOCKCHLORINATE
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                 Simple Well Shock Chlorination
     Steps after Chlorinating:
     •   Pump to waste for 15 more minutes after verifying zero residual
         chlorine.
     •   Collect at least 2 coliform samples a minimum of 30 minutes apart
     •   If any come back positive, pump to waste for another 15 minutes
         and collect at least 2 more samples a minimum of 30 minutes
         apart.
     •   If any are still positive, either repeat chlorination and retest, or take
         other corrective action in consultation with a well professional.
     •   Note: For newly constructed wells, AWWA Standard A100-06 calls
         for solution strengths of up to 100 ppm for 24 hours (versus 50 ppm
         to shock chlorinate preexisting wells).


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                 Simple Well Shock Chlorination
                      Simplified Procedure – Option 2
     If bottom-up chlorine injection method is not feasible, dilute bleach into
        at least 5 gallons of (warm) water, mix together, and pour into well
     through a plug or casing vent hole at the top of the sanitary seal (make
                 sure bleach mixes thoroughly with dilution water).




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                Simple Well Shock Chlorination
                      Simplified Procedure – Option 2

     • You will need a funnel and a tube. Direct the tube against the
       casing walls while pouring in the solution to disinfect the walls
       as well.
     • To mix the solution within the well, attach a hose to the
       nearest downstream tap (prior to any unpressurized storage
       tanks) and recirculate the water from the tap back into the well
       for at least 15 minutes.
     • Note: When you restrict the pump’s outflow to one hose
       (during recirculation), back pressure on the pump could
       damage it or trip it off. If necessary, use a buffer tank and
       siphon it back into the well in batches.

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                Simple Well Shock Chlorination
                      Simplified Procedure – Option 2

     • After recirculation, test the well water to verify the target
       concentration has been achieved (Note: This is ideal,
       but most will not have a chlorine meter for that range.)
     • Let the chlorinated water stand in the well casing for 12-
       24 hours.
     • Follow the same flushing and coliform sampling
       procedure as described previously and repeat process if
       necessary.




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                 Chlorine Sampling Methods
     • Must use DPD (or other EPA approved) method, unless doing a
       gross evaluation of shock chlorination levels.
                                                   Unapproved methods
                                 Drinking water     for drinking water
                                approved methods




                                                              Restaurant
                                                           inspector’s Tape

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 Disinfecting through
      Well Caps
     • Three common types
     • You will need to have
       the right tools




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     Disposing of Chlorinated Water Correctly
• DEQ has requirements for disposal of super-chlorinated
  water
  (> 4 mg/L total residual chlorine).
• Regardless of volume, super-chlorinated water must not be
  discharged to surface waters or storm sewers.
• Non-discharge alternatives: sanitary sewer disposal (either
  by connecting to a sanitary sewer or by hauling to a sewage
  treatment plant), land disposal or irrigation.
• Visit the DEQ guide for disposal of super-chlorinated water
  here:
  http://www.deq.state.or.us/wq/pubs/bmps/chlorwaterdisp.pdf
• Do not flush any chlorinated water into on-site septic
  systems.


40
              Disinfect the Whole Water System
                                (No Storage Tank)
     Main difference: pump the chlorine solution throughout the
     distribution system, then dose the well for its own
     disinfection.
     1. Estimate total system volume (distribution piping and
     pressure tanks).
     2. Determine the amount of bleach solution that will be
     needed to achieve 25 ppm throughout the entire
     distribution system.
     3. Chlorinate one well volume to 25 ppm by previously
     described methods. Once mixed, pump this well volume
     into the distribution by opening taps.
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              Disinfect the Whole Water System
                       (No Storage Tank - continued)

     4. Repeat chlorination and pumping of well volumes into
     system until 25 ppm is achieved at all distribution taps.
     5. Finally, chlorinate the well(s) to 50 ppm as previously
     described and let the entire system (well and distribution)
     sit for 12-24 hours.
     6. Flush the entire system by opening all distribution taps
     until no chlorine residual is detected (which may need to
     be done in phases depending on well yield and distribution
     volume).


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           Disinfect the Whole Water System
                  (No Storage Tank - continued)
 NOTES:
 • Think through the timing of events before you start (this process can
   take many hours).
 • This is not an exact science. Inevitably, there are technical
   considerations in each system that require variations of the theme.
 • One option: a temporary NSF-approved storage tank could be set up to
   pump or gravity-feed batches of chlorinated water into the distribution
   (as opposed to mixing batches in the well).
 • Many unknowns (including how much bacteria is in the system), but
   shock chlorination procedures are designed to handle worst case
   scenarios.
 • See AWWA Standard C651-05, Disinfecting Water Mains.
 • Share your experiences and technical solutions.


43
     Full-System Shock Chlorination with Storage

 • Disinfecting the well(s) and piping to the storage tank(s)
 are considered separate phases of the project.
 • Coordinate timing for the storage and distribution disinfection.
 • Calculate the volume of water in the reservoir (this should be on
   file). If not, use the tank dimensions in feet.
     – If the tank is rectangular, the volume (gals) is:
       = length X width X height of the overflow port
       (use the top, to be conservative) X 7.48 gallons per cubic foot.
     – If the tank is circular, the volume (gals) is:
       = the radius (i.e., half the diameter) squared X
       π (i.e., 3.1416) X height of the overflow port X
       7.48 gallons per cubic foot.


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                Full-System Shock Chlorination
                    with Storage - continued

     • Determine the time-frame or “Method Exposure Time”: There
       are three official AWWA exposure timeframes : 3, 6, and 24
       hours.
     • The method exposure time depends on the chlorine
       concentration and whether the chlorine can be added
       simultaneously with the filling of the reservoir (improves
       mixing).
     • The paired time and concentration is referred to as a “Method”
       per the AWWA Standard (C652-02). Longer periods of
       exposure are more conservative (i.e., they generally result in
       better disinfection).

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                Full-System Shock Chlorination
                    with Storage - continued

     • To determine amount of disinfectant: Use the spreadsheet on
       our webpage (Shock Chlorination calc.xls). Tank volume goes
       into “Volume to be disinfected =”. When you change that
       volume, it automatically changes the amount of chlorine
       needed under “Chlorine Source Material…” to achieve the
       target dose. The volume or weight of chlorine needed desired
       dose (given at the head of the column, cells are highlighted).
     • The desired dose is either 10 or 50 mg/L (unless the “method”
       is spray application – 200 ppm).
     • Wait for the disinfection to occur: Wait the full duration of the
       “Method Exposure Time” listed in the spreadsheet.



46
                     Storage Tank Chlorination Tool
     http://public.health.oregon.gov/HealthyEnvironments/DrinkingWater/Documents/ShockChloroCalc.xls




47
                Full-System Shock Chlorination
                    with Storage - continued
     • For Example: The tank water volume is 10,000 gallons. There is no
       other storage for the system and we need to get water production
       back online as soon as possible. Thus, use the 6 hour time-frame
       (Method B). How much normal household bleach do I need to add in
       order to disinfect my tank? When does the Method Exposure Time
       start?
     • Answer: Based on the spreadsheet, add 10 gallons of normal
       household (5%) bleach to disinfect the tank. Measure the chlorine
       concentration. If well mixed in the tank and measures a bit low (e.g.,
       45 mg/L), add about 10% of the original dose, or 1 gallon of bleach
       and mix again. If the concentration is now > than 50 mg/L, start the
       clock on the 3-hour interval.
     • Mix by recirculating water in the tank. Note that chlorine demand is
       not usually so high that Method B would require 50% more dose
       than calculated in the corresponding spreadsheet.

48
                 Full-System Shock Chlorination
                     with Storage - continued

     • Flush the volume of the storage reservoir through the distribution
       system until the maximum residual achieved in the storage reservoir
       is detected at all distribution taps.
     • Once the prescribed contact time has been achieved in the
       distribution (12-24 hours) begin flushing the entire system. May
       need to flush in multiple phases depending on source yield and
       distribution volume (might also want to haul in water to refill the
       reservoir).
     • After zero chlorine residual is detected at all distribution taps, collect
       a representative number of coliform samples (use sites designated
       in the Coliform Sampling Plan).
     • Repeat the disinfection process as necessary if any samples are
       coliform positive.


49
     Verifying Detectable Chlorine Residual




50
     Chlorine Residuals & Testing: DPD Test
                     WE USE THE DPD TEST BECAUSE…


        • Accuracy of
          measurements at
          the range needed
        • Speed of use
        • Calibration


              Beware
             of fading
           color wheels

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       Full-System Low Level Residual Chlorination

     • This procedure may not work if there is extensive bacteria and/or
       biofilm. It may not be enough to break through biofilm protecting
       bacteria growth.
     • This method may be a good choice if bacteria levels (total coliform
       only) are thought to be low, and/or it is important to maintain service
       during the disinfection process.
     • Chlorine residual must be kept below 4.0 mg/L – maximum for
       human consumption.
     • The amount of time to maintain residual is a guessing game.
     • Mechanics: A continuous feed pump is ideal, batch dosing into a
       storage tank can work with good math.
     • Frequent distribution residual monitoring is critical!

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                  Complications of the Process
     • Shock chlorination is not an exact science
     • Dosing values address a worst case scenario (often not the case).
       Sometimes chlorination is not even needed
     • High-volume flushing alone may solve the problem. But there is
       usually no way to know the extent of bacteria colonization.
     • Each scenario can have mechanical and electrical nuances:
        – Overloading well pumps
        – “Tricking” float switches in the storage tank
        – Manual overrides (to turn the pump on)
        – Inadequate valves for effectively recirculation
        – Other issues?


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       Calculating Volume of Rectangular Basin
A reservoir is 60 feet long by 40 feet wide and 10 feet deep at the overflow.
               What is the volume in cubic feet that it can hold ?


         L × W × H = Volume
         60 × 40 × 10 = 24,000 cubic feet


       Convert cubic feet to gallons:
         24,000 ft3 × 7.48 gal/ft3 =
               179,520 gallons




  56
            Volume Calculations in Cubic
                  Feet & Gallons
 A tank has a diameter of 40 feet and is 10 feet deep at the overflow.
                 How many gallons can the tank hold?


 Calculate the volume:
 d2 × 0.785 × h = Volume (ft3)
 40' × 40' × 0.785 × 10' = 12,560 ft3

 Convert cubic feet to gallons:
 12,560 ft3 × 7.48 gal/ft3 = 93,949 gallons




57
                  Volume of Pipe or Well
Area of a Circle = “π r2” …OR… 3.1416  (radius2);
                                                   Cylinder Volume
Can also be written… 0.7854  (diameter      2)
                                                   Diameter per Foot
Volume of cylinder (e.g., pipe, well, tank) =         (in)    (gal)
        Area x Length                                   2     0.16
                                                        3     0.37
 Area of the circle opening as shown above (e.g.,
                                                        4     0.65
   for a 2-inch pipe: 3.14  1 in 2 = 3.14 in2, or
             2)
                                                        6      1.5
   0.0218 ft                                            8      2.6
 Length is the water-filled length.                    10      4.1
                                                       12      5.9
So, a 250-ft length of 2-inch pipe can hold:           16      10.5
 0.0218 ft2  250 ft = 5.45 ft3 of water               20      16.5
In a more common unit of volume:                       24      23.5
 5.45 ft3  7.48 gal/ft3 = 40.8 gallons                36      53.0
(A table of volumes per foot for common pipe or
well casing diameters is shown at right.)
58
                 Links To Disinfection Guides
     •   How to Disinfect a Well:
         http://public.health.oregon.gov/HealthyEnvironments/DrinkingWater/Docum
         ents/pn/WellDisinfection.pdf
     •   Shock Chlorination for Storage Tank; Well and Distribution System -
         Procedure and Volume Calculation:
         http://public.health.oregon.gov/HealthyEnvironments/DrinkingWater/Pages/s
         hockchlorination.aspx
     •   Shock Chlorination Calculation Tool:
         http://public.health.oregon.gov/HealthyEnvironments/DrinkingWater/Docum
         ents/ShockChloroCalc.xls
     •   AWWA Standards:
         http://www.awwa.org/Resources/Standards.cfm?ItemNumber=33777&navIt
         emNumber=33778



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                    Questions & Discussion

                                  Michelle Byrd
                            Oregon Health Authority
                            Drinking Water Services
                           michelle.p.byrd@state.or.us


                                Adapted from Presentation by:
                                    Daniel Hough, REHS
                                 Natural Resource Specialist
                                  Oregon Health Authority
                                  Drinking Water Services
                                 daniel.l.hough@state.or.us




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            Class Exercise (Part 1):
Calculate System Volumes For Your Own System

Determine well volume




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62
                 Class Exercise (Part 2):
           Design Your Own Shock Chlorination

     • Determine quantities of chlorine product needed based
       on the system volumes.
     • Develop strategy in steps (e.g. add chlorine to well and
       then batch dose into distribution, etc.).
     • Plan the public notification process. Users must be
       informed of timelines and water use restrictions to
       protect their health (dishes and household cleaning are
       about the only things you can do with 50 ppm water).



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