characterization of seasonal effects on the specific ...pages.mtu.edu/~elgross/presentations/awra...

Characterization of seasonal effects on

the specific capacity of rope-pump

wells in a fractured rock-aquifer in

Nicaragua

Essa L. Gross and John S. GierkeDepartment of Geological Eng. & Sciences

Michigan Technological University

Antoinette KomeSNV Nicaragua

E.L.Gross, "Characterization of seasonal effects on the specific capacity of rope-pump wells in a fractured rock-aquifer in Nicaragua” AWRA conference, Alb, NM 2007

Outline

� Problem Statement

� Research Objectives

� Study Area� Study Area

� Methodology

� Results

� Conclusions


Problem Statement

• Practically no information exists on the productivity of rural wells in developing countries.

• Policy makers have no information to base decisions or to develop water management plans.water management plans.

• The lack of technical and economic resources prevents the collection of performance and monitoring data.


Design and test a method to characterize

the productivity of existing rope-pump

wells in rural areas of developing countries

Research Objectives

Monitor seasonal changes in SWLs

and specific capacities of rope-pump

wells in an area that experiences

distinct rainy and dry seasons.


Outline




� Methodology

� Results

� Conclusions

E.L.Gross, "Characterization of seasonal effects on the specific capacity of rope-pump wells in a fractured rock-

aquifer in Nicaragua” AWRA

Study Area

Santa Rita


Regional Geology

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Tpc - Coyol GroupFractured ignimbrites,

tuff, andesite, basalt

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Source: INETER


Rope-pump well

60’


Outline




� Methodology

� Results

� Conclusions


Testing and Monitoring Approaches

• Monthly manual pump tests in triplicate at 3 wells

• Each test conducted to attain pumping, equilibrium, and recovery phases

• A conventional step-drawdown test performed in one well


Pump test regime

• Pump 60 – 90 gal

• Approximate rate of 5 gpm

Well 2 - 2/10/07

-0.5

0.0

0.5

0 20 40 60 80 100 120 140 160 180 200

Elapsed time (min)

of 5 gpm

• Allow well to recover for an hour or more

• Triplicate tests

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

Dra

wd

ow

n (f

t)


Recuperation

Pumping

ExplanationWell 2: 1/11/07

-3.00

-2.00

-1.00

0.00

Dra

wd

ow

n (f

t)

Test 1 levelogger

Test 2 levelogger

Test 3 levelogger

Test 3 sounder

Equ

ilibr

ium

dr

awdo

wn

-6.00

-5.00

-4.00

-3.00

0 500 1000 1500 2000 2500 3000 3500

Elapsed Time (sec)

Dra

wd

ow

n (f

t)

Test 3 sounder

Test 2 sounder

Test 1 sounder


Equilibrium drawdown Data analysis method


Pump and recovery curves Data analysis methods

Log Log

s s’

SrTt

TsQ

2

3.0log264

=Cooper-Jacob Approximation in “Conventional” Units:

JSL: T=264 Q/ s JSL: T=264 Q/ s’


Outline




� Methodology

� Results

� Conclusions


Change in static water level

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Average dry season drop = 6 ft

DRY RAINY

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�

�

�

��

��

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10/22/06 12/11/06 1/30/07 3/21/07 5/10/07 6/29/07 8/18/07 10/7/07 11/26/07

DRY RAINY


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Specific Capacity Changes

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0Well 1

Well 2

Well 4

Specific capacity (attained from recovery data) vs. SWL

WellChange SWL (ft)

Change SWL (% available

water column)*

% Change Specific Capacity

1 6.6 4 % 15 %

2 4.4 2.5 % 26 %

3 6.3 3.5 % --

4 7.9 4.8 % 81 % *Assuming 200’ well

0.0

0.2

0.4

-1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

Feet below SWL Dec 06


Well 1

0.0

0.5

1.0

1.5

2.0

2.5

Non-equilibriumrecoverycurveEquilibriumapprox

Linear (Non-

Analysis method comparison

Well 2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

25.5 26.5 27.5 28.5 29.5 30.5 31.5

Equilibriumapprox

Non-equilibriummethod -recoverycurveNon-equilibriummethod -pump curve

Linear

Factorof 2

Factorof 2

36.0 38.0 40.0 42.0 44.0Static Water level (ft btc)

25.5 26.5 27.5 28.5 29.5 30.5 31.5

Static Water Level (ft btc)

Well 4

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

35 36 37 38 39 40 41 42 43 44

SWL (ft btc)

Equilibriumapprox

Non-equilibriummethod -recovery curve

Non-equilibriummethod - pumpcurve

Linear (Non-

Factorof 2

Spec. cap values calculated from :

equilibrium approx

recovery curve

pump curve


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Well 4

2.0

2.5

3.0

3.5

4.0 Equilibriumapprox

Non-equilibriummethod -recovery curve

Non-equilibriummethod - pumpcurve

Spec. cap values calculated from manual tests:

equilibrium approx

recovery curve

pump curve

Conventional pump test comparison

0.0

0.5

1.0

1.5

2.0

35 36 37 38 39 40 41 42 43 44

SWL (ft btc)

curve

Trad Equilibriumapprox

Trad Non-equilibrium-pumpcurve

Trad Non-equilibrium-recovery curve

Spec. cap values calculated from conventional test:

equilibrium approx

recovery curve

pump curve


Outline




� Methodology

� Results

� Conclusions


Conclusions (1 of 2)

On method:

� Manual test pump rate low, but results are representative of well behavior at high rates (in this case 7 times higher).

� Recovery data easiest to collect and yields � Recovery data easiest to collect and yields accurate specific capacity values.

�Overestimated specific capacity of wells as determined by equilibrium drawdown method maybe caused by lack of understanding of geology.

� Modifications to well for manual pump test minor, economical.


Conclusions (2 of 2)

On seasonal effects:

� Current water demands not affected by seasonal change in the static water level.level.

� Method determined that max capacity of wells to be at least 10X greater than what rope pump well delivers.

� Observed changes in productivity with even slight changes in SWL.


Thank You

Financial Support:• National Science Foundation PIRE 0530109• DeVlieg Foundation• SNV Nicaragua• U.S. Peace Corps

We would like to acknowledge the following people for their assistance in this study:

Gregg Bluth, Fernando Flores, Luis Meza, Denia Acuña, Evelio Lopez , Ivan Palacios, Elisena Medrano, Luis Palacios, Beth Myre,

and the Families of Santa Rita


characterization of seasonal effects on the specific ...pages.mtu.edu/~elgross/presentations/awra...

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