Meter Testing Update

Gwinnett County DWR

Gwinnett County Water Resources

• Approximately 30 miles northeast of

Atlanta

• Population of approximately 800,000

• 437 square miles

• 15 cities

Just the Facts

WATER 3,665 miles

239,146 accounts 150 MGD

2 Filter Plants SEWER

2,900 miles 150,000 accounts

98 MGD 3 WRFs

STORM WATER

1,300 miles 13 Cat 1 Dams

Flow Meters at Water Production

Volume From Own Sources

Water Balance

• SCADA history showed an imbalance

between withdrawals and water

produced

• Reported to EPD in MOR

• More water was produced than

withdrawn

• Especially concerning because of

known in-plant losses of over 300,000

gallons per day

In-Plant Losses

Water Balance

Water Balance

GAZINTA < GAZOUTA

Water Gain

Where is the water coming from?

Water Gain

Water Gain

More likely – it’s meter inaccuracies

Testing vs. Calibration

Testing:

Drawdown

Draw-Up

Redundant Meter

Testing vs. Calibration

Calibration:

Manufacturer’s PMs

“Zeroing”

SCADA Validation

Clearwell Overview

High Service Venturi Meter

Draw-down Test

Clearwell Levels During Test

Accounting for Valve Leakage

Low Flow LFP Central HSP Test Results (Not adjusted for leakage)

Parameter Value Notes

Draw-down Flow (MGD) 29.17 Based on change in SCADA Clearwell 4 level

Existing Meter Flow (MGD) 35.27 SCADA reported flow rate for Central HS

Existing Meter Difference (%) 20.89% Over-registering, not adjusted for leakage

Low Flow LFP Central HSP Test Results (Adjusted for leakage)

SCFP Transfer Flow (MGD) 0.00 SCADA reported flow rate for SCFP Transfer

Sum of Clearwells 1, 2, 3 Flow (MGD) 16.20 Based on change in SCADA clearwell levels

North HSP Flow (MGD) 12.15 SCADA reported flow rate for North HS

Plant Water Flow (gpm) 125.56 SCADA reported flow rate for LFP

Leakage from Clearwells 1, 2, 3 into Clearwell 5 (MGD) 0.10 Based on change in SCADA clearwell level

Valve Leakage Flow into Clearwell 4 (MGD) 3.77 Estimated leakage through closed valves

Adjusted Draw-down Flow (MGD) 32.94

Existing Meter Flow (MGD) 35.27 SCADA reported flow rate

Existing Meter Difference (%) 7.07% Over-registering,adjusted for estimated leakage

Replacement Meter

Calibration Certificate – 60”

Calibration Certificate – 30”

Error Adjustment

Water Balance Dashboard

• Raw Water Withdrawals

• Plant Water Usage (Domestic usage,

Washdown, Other?)

• Production Metering

• Redundant Metering

Redundant Metering

Discussion – Meter Testing

• Draw-up & Draw-down Drawbacks

– Valve Leakage

– Precision of Level Indicators

• Redundant Metering Drawbacks

– Meter Accuracy Less Than Main

Meters

• Redundant Metering Advantages

– Can be Continuous

– Create Dashboard for Water Balance

Next Steps

• Install downstream metering

• Create SCADA dashboard

• Trend results

• Report on Water Audit