Assessing Distribution System Performance:

Sampling and Monitoring

Outline

Sampling Approach

Field Methods

Representative Sampling:

What, Why, Where

Critical Sites – identifying, sampling considerations, and the process

Optimization Monitoring:

What / Where, Frequency

Summary

Assessing Distribution System Performance

Objective: To develop an accurate “picture” of water quality in the distribution system.

Optimization Monitoring

Representa-tive Sample Sites

Sampling

Approach

Your Sampling Practices

How long do you flush a sample tap before you collect a sample?

Sampling Approach: Our Observations

Inconsistent practices for flushing a sample tap before sample collection:

Temperature: Note change by “feel.”

Time: All sites are considered “equal” (i.e., 5 to 15 minutes, 2 songs on the radio).

Flush until you get a “good” sample.

Practices vary by operator.

Who Cares?Regulatory vs. Optimization Sampling

For regulatory purposes: Frequently, the focus is on getting a “good” number to meet state regulations

For optimization purposes: The focus is on getting a “representative” number in order to: Accurately characterize distribution system water quality –

both spatially and temporally

Make important process control decisions in the distribution system

The sampling procedure used for optimization can be applied to regulatory sample locations (taps)

Calculated Flush Time Approach

A consistent & technically sound approach for sample collection.

Sample should represent water in the distribution system main immediately adjacent to the sample location.

Flush/waste the water in the service line before collecting a sample.

Avoid over-flushing, which may pull in water from another area of the distribution system.

Based on article: Collect Representative Distribution System Samples, Opflow, January 2009

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Key Elements of the Optimization Sampling Approach

Provides guidance for sample taps and hydrants.

Does not use temperature or chlorine residual as indicator of “adequate” flushing.

Time-based flushing approach using the volume of the service line length, diameter, and pre-determined flow rate.

General Sampling ApproachCan be applied to Taps or Hydrants

1. Estimate the length and diameter of the pipe that is to be flushed.

2. Determine flush time based on an estimated service pipe length, diameter, and flow-rate.

3. Slowly open the tap/hydrant At a tap: immediately start the timer and

verify that the flow is at the desired rate of 2 gpm if tap sampler is not used (e.g., by quickly timing the fill of a measuring cup)

At a hydrant: once the hydrant is fully open, open the flush valve and start the timer. The flow control valve will regulate the flow to 20 gpm

4. After twice the calculated flush time (CFT), or time specified by the rule of thumb, stop flushing and collect the water sample(s).

Tap Sampler

Step 1: Estimate Pipe Length and Diameter (Tap)

Service LineDiameter:Estimate based water system staff knowledge, a system/site map, and/or best judgment.

Length:Measure the distance from the meter/curb stop to building (at approximately where the service enters the building).

Premise PlumbingDiameter:(Ideally) go into the building to estimate the pipe diameter.

Length:(Ideally) go into the building to estimate the pipe length.

Note: If the tap is close to where the service line enters the building, the volume of premise plumbing may be negligible.

MainService Line

Estimating pipe lengthand diameter at tap sampleSites can be difficult. Hydrants are preferred for investigative sampling.

Premise Plumbing

Recommended approach for calculating flush time ~ especially for taps sampled on a routine basis (e.g., TCR).

• Table shows CFT in minutes

• Can be determined for any length and pipe diameter

• Assumes 2 gpm flushing rate

• Determine CFT from matrix

• Flush time = 2 times the CFT

(adjust if the flush rate ≠ 2 gpm)

Tap CFT Matrix

Step 2: Determine Flushing Time- Calculated Flush Time (CFT)

Tap Approach

Example

20’ of 3/4” Line

30’ of 1/2” Line

Premise Plumbing:Pipe Length = 30’, Diameter of Pipe = 1/2”CFT = 0.2 minutes

Distribution System Main

CFT = 0.2 + 0.2 = 0.4 minutes

Total flush time = 2* CFT

= 0.8 minutes or 48 seconds

Service Line:Pipe Length = 20’, Diameter of Pipe = 3/4”CFT = 0.2 minutes

Assumes the flush rate is 2 gpm

Step 3 and 4: Flush, Then Collect Water Quality Sample(s) and Record Data

Flush at ~ 2 gpm (verify flow-rate if needed) for total flush time (previous slide).

Measure chlorine residual, temperature and pH and record the results on a data collection sheet.

Also, record the characteristics of the site: Description of sample site (e.g., Chevron Station

600 Main St.).

CFT (*2) (it might be used in the future).

Type of customer demands (residential, commercial, rural area, old industrial area).

Pressure zone (if applicable).

Others (e.g., characteristics of water sample; site was recently flushed during seasonal flushing program, main pipe material and age).

Notes and Recommendations

The procedure provides a reasonable quick and easy estimate of flush time along with a controlled safety factor.

CFTs are only estimates because “precise” measurements of pipe length and diameter would be difficult to obtain.

Try to avoid sample locations where piping diameter/length are unknown.

Follow a Similar Approach When Sampling from Hydrants

Easier to estimate hydrant service pipe diameter and length than internal building plumbing.

Hydrant Sampler

https://www.youtube.com/watch?feature=player_detailpage&v=2u0rR9TTENw

Representative Sample Sites

What: Optimization sample sites that represent water quality throughout your distribution system.

Optimization Monitoring

Representa-tive Sample Sites

Sampling

Approach

Representative Sample Sites: Why

Sampling throughout the distribution system helps ensure that your disinfection barrier is in-place!

Consider your system… Do you think your current sample sites represent

water quality throughout the system?

Do you have data to confirm that you have a disinfection barrier throughout your entire system?

Do you think some investigative sampling could help you better understand your system?

This System Thought Their Disinfection Barrier was Robust, Based on Their Historical Data

Chlorine Performance (TCR Sites Only)

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Monitoring at Critical Sites Showed Something Different…

Your system’s representative sample sites should include some combination of: Plant effluent and/or master meter

Your regulatory sites (i.e., for TCR and DBP sampling)

Critical sites Areas in your system that have poor water

quality

These are determined (confirmed) by investigative sampling in your system

Representative Sample Sites: Where

Areas influenced by (draining) tanks: With high turnover time (confirmed or suspected)

Operated in series

Standpipes (generally are poorly mixed)

Hydraulic “problem areas”:

On dead-ends ~ actual and looped (subdivisions)

Towards the “extremities” of the distribution system (hydraulically far from the treatment plant)

Near pressure zone boundaries (i.e., closed valve creates a “hydraulic” dead-end)

Areas where water from different sources is blended

Critical Sites Might Include…

Areas with aging pipes (old cast iron lines) Low demand, low flow, stagnant areas Water quality problem areas:

At TCR / DBP sites with historically low chlorine residual, high DBPs, coliform occurrences

Areas with persistent customer complaints In general,

These criteria should be considered when selecting potentially critical sites (i.e., have low chlorine residual); however, water quality data is needed to confirm.

Critical Sites (cont.)

Low chlorine residual = Critical site(high DBPs, high water age, microbiological risk)

Critical SitesOther Considerations

When conducting investigative sampling in your system for optimization, you may measure a free chlorine residual < 0.2 mg/L (especially at a critical sample location!)

Measure total chlorine to assess relative to the regulatory requirement

Write-down the data to determine whether this is a critical site, or a one-time incident

If the residual is extremely low, respond to increase the residual.

Document (write down) what is done in this area!

Identification of Critical Sites: Final Thoughts

Flexibility to sample at as many investigative sampling sites as you want to identify water quality problem areas in your system

Based on your investigative sampling results, select a minimum of ten potential sites to monitor on a routine basis (consider monthly during warmer months)

Review your sampling results to identify which sites will become part of your routine optimization monitoring program

What could you do with your data?

Assess whether you are meeting the:

disinfection optimization goals

DBP optimization goals (and Stage 2 compliance

requirements)

Longer-term, ongoing monitoring data helps tell us

whether process adjustments (operational changes) are

needed to improve water quality

Assess the impacts of your distribution system

optimization efforts.

However - it is difficult to do the above if the data is not

collected or lost!!

Data Collection SheetSample

Site Name(Lat & Long)

Date TimeFree

Chlorine(mg/L)

Temp.(C)

CFT*2 (min)

CFT Notes

Comments(street location, sample location [faucet, hose, hydrant], description of sample site [i.e., remote, high demand, dead-end, residential, etc.], pipe material, pipe age, pipe diameter, pressure zone, and influence of which tank)

EXAMPLE:121 Main St.36.5042 Lat-80.674754

Long

7/31/84 14:35 2.10 22.4 2.2

Hydrant Site – 6’ of 6” hydrant lead +9’ of 6’’ line = 15’ of 6’’ line = 1.1*2 = 2.2

flush time (@ 20gpm)

Site located in a remote area off of main transmission line, old 6” cast-iron pipe, in low-pressure zone, likely influenced by Tank A

               

               

               

               

               

               

Optimization Monitoring:Where are we heading?

What: Long-term, routine sampling at representative sites throughout your distribution system, using the optimization sampling approach, to generate water quality data!

Optimization Monitoring

Representa-tive Sample Sites

Sampling

Approach

Field Methods Used for Optimization Monitoring

Objectives of Optimization Monitoring

To characterize water quality throughout all areas of the distribution system

Hopefully… ensures that the water quality goals (chlorine residual, DBPs) are consistently met

May… identify areas of poor water quality

Definitely… raises system’s awareness of issues in the distribution system!

Ensures integrity of the distribution system (disinfection) barrier is maintained.

Field Methods Used For optimization work, parameter(s) should be:

Useful for process monitoring (i.e., can be used to assess impact of process/operational changes).

Easy to measure and provide relatively quick results.

A surrogate for the parameter of interest (e.g., chlorine).

Primary Parameters: Free chlorine as surrogate for water age and DBP formation.

Total chlorine, pH, and temperature also measured (to support/verify the primary parameters).

Secondary Parameters: TTHM and HAA5 (at regulatory sites and entry point to the

distribution system).

Optimization Monitoring Routine sampling at representative sites

helps us to: Develop water quality data and trends over time

Have a basis for assessing performance relative to water quality goals

Have data needed before process control is implemented

Confirm that your distribution system barrier is in-place

Steps to Assure Data Integrity

Collect representative samples (i.e., using the CFT approach throughout your distribution system)

Be familiar with the field test equipment and test methods

Routinely calibrate (or check) field instruments

Use clean glassware Use reagents within the expiration date

Summary

Establishing a consistent and technically sound sampling approach is the foundation for distribution system optimization

Free chlorine residual is a surrogate for bacteriological water quality, DBPs, and water age. pH, temperature, total chlorine (and DBPs, less frequently) are also useful parameters to assess distribution system water quality

Sample at representative sites (system influent + compliance + critical sites)

Consider determining the CFT and utilizing for your routine sample locations (for TCR, DBPs, etc.)