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

Outline

Problem Statement

Research Objectives

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.

• 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

Problem Statement

Research Objectives

Study Area

Methodology

Results

Conclusions

Santa Rita

Study Area

Regional Geology

Tpc - Coyol Group

Fractured ignimbrites,

tuff, andesite, basalt

X XX

X

Source: INETER

Rope-pump well

60’

Outline

Problem Statement

Research Objectives

Study Area

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

• Allow well to recover for an hour or more

• Triplicate tests

Well 2 - 2/10/07

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

0 20 40 60 80 100 120 140 160 180 200

Elapsed time (min)

Dra

wd

ow

n (

ft)

Well 2 - 2/10/07

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

0 20 40 60 80 100 120 140 160 180 200

Elapsed time (min)

Dra

wd

ow

n (

ft)

Recuperation

Eq

uili

briu

m

dra

wd

ow

n

Pumping

ExplanationWell 2: 1/11/07

-6.00

-5.00

-4.00

-3.00

-2.00

-1.00

0.00

0 500 1000 1500 2000 2500 3000 3500

Elapsed Time (sec)

Dra

wd

ow

n (

ft) Test 1 levelogger

Test 2 levelogger

Test 3 levelogger

Test 3 sounder

Test 2 sounder

Test 1 sounder

Equilibrium drawdown Data analysis method

Pump and recovery curves Data analysis methods

SrTt

TsQ

2

3.0log264

Cooper-Jacob Approximation in “Conventional” Units:

Log Log

JSL: T=264 Q/Δs JSL: T=264 Q/Δs’

Δs Δs’

Outline

Problem Statement

Research Objectives

Study Area

Methodology

Results

Conclusions

Change in static water level

Static Water Levels (Dec '06 - Oct '07)0

5

10

15

20

25

30

35

40

45

5010/22/06 12/11/06 1/30/07 3/21/07 5/10/07 6/29/07 8/18/07 10/7/07 11/26/07

Time

Sta

tic

Wate

r Level (

ft b

tc)

Well 1

Well 2

Well 3

Well 4

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

Average dry season drop = 6 ftAverage dry season drop = 6 ft

DRY RAINY

Specific Capacity Changes

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

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

-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

Sp

ecif

ic c

apac

ity

(gp

m/f

t)

Well 1

Well 2

Well 4

Linear(Well 4)Linear(Well 2)Linear(Well 1)

Specific capacity (attained from recovery data) vs. SWL

Well 1

0.0

0.5

1.0

1.5

2.0

2.5

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

Sp

ec

ific

Ca

pa

cit

y (

gp

m/f

t)

Non-equilibriumrecoverycurveEquilibriumapprox

Linear (Non-equilibriumrecoverycurve)

Analysis method comparison

Prueba perfil

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0 500 1000 1500 2000 2500

Prueba perfil

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0 500 1000 1500 2000 2500

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

Static Water Level (ft btc)

Sp

ec

ific

ca

pa

cit

y (

gp

m/f

t)

Equilibriumapprox

Non-equilibriummethod -recoverycurveNon-equilibriummethod -pump curve

Linear(Equilibriumapprox)

Linear (Non-equilibriummethod -pump curve)

Linear (Non-equilibriummethod -recoverycurve)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)

Sp

ec

ific

ca

pa

cit

y (

gp

m/f

t)

Equilibriumapprox

Non-equilibriummethod -recovery curve

Non-equilibriummethod - pumpcurve

Linear (Non-equilibriummethod -recovery curve)Linear(Equilibriumapprox)

Linear (Non-equilibriummethod - pumpcurve)

Factorof 2

Factorof 2

Factorof 2

Spec. cap values calculated from :

equilibrium approx

recovery curve

pump curve

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)

Sp

ec

ific

ca

pa

cit

y (

gp

m/f

t)

Equilibriumapprox

Non-equilibriummethod -recovery curve

Non-equilibriummethod - pumpcurve

Trad Equilibriumapprox

Trad Non-equilibrium-pumpcurve

Trad Non-equilibrium-recovery curve

Linear (Non-equilibriummethod -recovery curve)Linear(Equilibriumapprox)

Linear (Non-equilibriummethod - pumpcurve)

Prueba perfil

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0 500 1000 1500 2000 2500

Prueba perfil

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0 500 1000 1500 2000 2500

Spec. cap values calculated from manual tests:

equilibrium approx

recovery curve

pump curve

Spec. cap values calculated from conventional test:

equilibrium approx

recovery curve

pump curve

Conventional pump test comparison

Outline

Problem Statement

Research Objectives

Study Area

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 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.

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

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

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