Pumping Tests and Hydrogeologic Data -...

Pumping Tests andHydrogeologic Data

Daniel O. Niemela P.G.

Topics

• Well and aquifer basics• Pumping tests• Data analysis• Projecting well performance

Water Well 101

• Water level in wellis lower than waterlevel in aquifer

• Greater welldrawdown results ingreater flow

• Well yield anddrawdown can bepredictable

Static Water Level

Pumping Water Level

Hydrogeologic Terms

• Static Water Level(SWL)

• Pumping Water Level(PWL)

• Drawdown(PWL) – (SWL) = s

• Available Drawdown(Max PWL) – (SWL)

s

SWL

PWL

Principal Types of Aquifers• Alluvial

– Unconsolidated– Type III

• Bedrock– Consolidated– Type II

• Confined– Frequently consolidated– Type I

• Measure flow rate and water level• Determine yield for permanent pump

setting• Collect aquifer data• Pumping development (remove fines)• Water rights (document use rate)

Pumping Test Objectives

Manners of Well Testing

• Pumping (submersible, turbine, etc.)• Airlift (Baski)• Bailer (Low flow rate)• “Slug” (only for aquifer properties)

Pumping Test Field Measurements

• Flow rates– Totalizing flow meter, instantaneous flow meter,

orifice, flume/weir, 5-gallon bucket– Stop watch– Redundant

• Water levels– M-Scope, pressure transducer, airline, sounder– Redundant– 1” PVC tube(s) for easy access downhole

Dan’s Six Pump Test Essentials

1. M-Scope2. 5-gallon bucket3. Stopwatch4. 2 pens5. Notepad6. Calculator

Graduated Bucket

M-Scope

Measurements and Observations• Well construction

– Borehole depth, diameter– Casing and screen size diameter– Screened interval

• SWL, PWL’s• Recovery WL’s *** especially for low yield wells ***• Observation well WL’s (Nearby Wells)• Total well depth before and after testing• Flow rates• Sand production• Color of discharge• Location of discharge• Water quality• Temperature• Weather• Time, date• Nearby streams, ditches, etc.

You only get onechance todocument apumping test!

Constant-Discharge Pumping Test

• Easiest to data to evaluate because only WL’s change• Constant flow during duration of test (<10% change)• Most water level change occurs early in test• Measure flow rate and water levels at specific intervals

– 1 to 10 minutes : Every 1 minute– 10 to 20 minutes: Every 2 minutes– 20 to 50 minutes: Every 5 minutes– 50 to 90 minutes: Every 10 minutes– 1.5 to 4 hours: Every ½ hour– 4 to 24 hours: Every 1 hour

• Most important: Write down WHEN the measurement iscollected, even if it is late

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Constant Discharge Pumping TestLinear Graph (24 – hours)

675 gpmArapahoe Aquifer

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Transducer Theis Type-Curve

Constant Discharge Pumping TestSemi-Log Graph (24 – hours)


Constant Discharge Pumping TestLog-Log Graph (24 – hours)


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Transducer T heis Type-Curve

Theis -Curve

Consistent Response for LongerPumping Periods (7 – days)

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MiniT roll Dat a Match P oint T heis Type-Curve


Step Pumping Test

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40 gpm, 70 gpm, 100 gpmLower Arapahoe Aquifer

Water Level Recovery

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T im e ( mi n)

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Ideal Aquifer Trend• Gradual increase in drawdown

Recharge Trend• Water level stabilizes

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Draw

down

(ft)

Fractured Rock Aquifer Trend• Water level does not stabilize

Constant Discharge Pumping Test(80 – minutes)

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Transducer Match Point Theis Type-Curve

25 gpmMountain Alluvial Aquifer

Plot Data in the Field

• Identify for trends• Watch out for changes in trends

Plot Data in the Field (cont.)

ProjectedDrawdown

Well Performance Projections

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Transducer Theis T ype-Curve 200 gpm 400 gpm

Estimate drawdown for different pumping rates usingcalculated transmissivity and storativity

675 gpm

400 gpm

200 gpm

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Transducer Theis Type-Curve 200 gpm 400 gpm


Same data graphed semi-log

675 gpm

400 gpm

200 gpm

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Transducer 600 gpm 200 gpm 400 gpm


Estimate drawdown for different pumping periodsusing calculated transmissivity and storativity

600 gpm

400 gpm

200 gpm

Specific CapacitySimple Measure of Well Efficiency

• (Pumping Rate) / (Drawdown) = Q/s• Compare pumping tests at different pumping rates• Evaluate changes in well efficiency• Forecast drawdown at different pumping rates

– Pump sizing• Limitation: need to compare Q/s at same time after

pumping begins– E.g. Q/s at 4 hours– E.g. Q/s at 12 hours

Specific Capacity

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Pumping Rate = 100 gpm

Q/s = 0.83

Q/s = 0.71Q/s = 0.67 Q/s = 0.63

40min 6hrs 12hrs 24hrs

Specific Capacity

• Say well test at 15 gpm with 100 ft drawdown after4 hours: (15 gpm) / (100 ft) = 0.15 gpm/ft

Then, how much drawdown at 5 gpm after 4 hours?(5 gpm) / (0.15 gpm/ft) = 33 ft drawdown

Say only 70 ft drawdown acceptable?(70 ft) x (0.15 gpm/ft) = 10.5 gpm

Mountain Domestic Well• Estimate well yield in gallons per day

– Recovery data is crucial (how long to recover to swl?)

• Compare yield with demand– 50 to 100 gallons per day per person demand– 150 to 350 gallons per day demand for a family– Lawn/garden irrigation at 0.1 gallons per day per

square foot (conservative)

• Storage to accommodate peak demand

• Consider seasonal WL changes

SWL Changes

• Alluvial aquifers & fractured rock aquifers– Seasonal changes– Wet year vs. dry year

• Aquifers with limited recharge (DenverBasin & High Plains)– Regional decline– Irrigation season well-to-well impact

Jefferson County Mountain WaterWell Water Levels

Thanks to Roy Laws

100 ft

120 ft

• Large seasonalWL changes

• Wet year vs. dryyear

Wet

Wet

Dry

Dry

Denver Basin Water Level Decline

Appx. 38 ft/yr

Declining Denver Basin WaterLevels (cont.)

AvailableDrawdown

SWL2000 - 100 gpm

AvailableDrawdown

SWL

pump

PWL

AvailableDrawdown

SWL

2015 – 50 gpm

PWL

PWL

2010 - 75 gpm

pump

•Pumping water levelabove well screens•Well is efficient

•Pumping water level topwell screens•Well efficiencycompromised

pump

•Pumping water levelbelow most well screens•Well efficiencysignificantly compromised

Confined AquiferWell-to-Well Interference

700

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Dep

th to

Wat

er L

evel

(ft)

Static Water Level (ft) Pumping Water Level (ft) Top S creen (ft) Bottom of Well (ft) Pump (ft)

• Non-Pumping (Static) water level declinesduring summer due to well-to-well interferenceand recovers during winter and spring

• 175.5 ft irrigation season decline, in example

• Value to frequent water level data collection

1100

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1700

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Dep

th t

o W

ater

Lev

el (ft

)

Static Water Level (ft) Pumping Water Level (ft) Top Screen (ft ) Bottom of Well (ft) Pump (ft)

175 ft

Rules of Thumb• Maximum drawdown

– Alluvial and Unconfined Bedrock: 2/3 water column inwell

– Confined: 1/2 water column in well– Keep PWL above principal well production zone

• (Max 24-hour rate during testing) x (60%) = SafeWell Yield

• Test well at greater rate than plannedpermanent equipment

• Consider water level recovery

Summary• Aquifers are predictable (not all wells are

predictable!)• Consider future static water levels• Prepare for a successful test

– Redundant water level and flow rate measurements• Collect data and note the time• Plot data by hand to understand water level

trends• There are simple ways to forecast drawdown

and pumping rates

Pumping Tests and Hydrogeologic Data -...

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