[The Well] S and Sy in fracturated rocks
Carlos Eduardo Molano Cajigas
Hello,
I’m facing the determination of Storage Coefficient (S) and Specific Yield (Sy) in a crystalline fracturated rocks to estimate prelimar dewatering flow rates. This deposit is very heterogeneous with various types of fractures; some aquifer tests are available, but the observation wells behaves very diferent according to the depth and the fractures they intercept; therefore there is no general patern of time-drawdown curves, and changes in a very short distance, even some close observation wells behaves different for the same pumping well. I apreciatte if some one could advise on this issue for determining S and Sy.
Thank you,
Carlos E. Molano C.
Hidrogeocol Ltda
Carrera 70A No. 109-18 Bogotá, Colombia
Phone Bogota: (57) 1 6241973 / 2715284, ext 230
Movil Colombia: (57) 310 2620049
web : www.hidrogeocol.com.co
T
Mark W. Eisner
Dear Carlos:
The classical methods of storativity and specific storage determinations, presume radial flow from an equivalent porous media. Jenkins and Prentice (1982) postulated that a chevron-shaped flow-field exists in fractured bedrock more commonly, with flow orthogonally inward to a infinitely-transmissive single fracture. If your data appear linear when graphed as the square foot of time vs. water level, you have the Jenkins and Prentice linear flow field instead of the Theis / Cooper / Jacob radial one. Kruseman and deRidder (1994) published methods for analyzing data and determining coefficients from fractured bedrock pumping test data. Most of the techniques in this compendium build on the work of Gringarten and others. Key citations include:
q Gringarten, A.C. and P.A. Witherspoon, 1972, a Method of Analyzing Pump Test Data from Fractured Aquifers in Int. Soc. Rock Mechanics and Int. Ass. Eng. Geol., Proc. Symp. Rock Mechanics, Stuttgart, Vol. 3-B, pp. 1-9.
q Kruseman, G.P. and N.A. de Ridder, 1994, Analysis and Evaluation of Pumping Test Data, Second Edition, International Inst. For Land Reclamation and Improvement, Netherlands, 377 p.
q Jenkins, D.N. and J.K. Prentice., 1982. Theory for aquifer test analysis in fractured rocks using linear (non-radial) flow conditions. Groundwater., (20)1: 12-21.
I think you may find what you need. I hope this helps. Good luck.
Mark W. Eisner, P.G., President
Advanced Land and Water, Inc.
7540 Main Street, Suite 7
Sykesville, MD 21784
Tel: 410-795-4626
Fax: 410-795-4611
web: www.alwi.com
CONFIDENTIALITY NOTICE: This transmission (including any attachments) contains information which is confidential or may be subject to work product or other privilege, and is intended solely for the individual or entity named above. If you are not the intended recipient, any interception, copying, distribution, disclosure or use of this transmission or any information contained in it is strictly prohibited, and may be subject to criminal and civil penalties. If you have received this transmission in error, please call 410-795-4626 immediately, delete this transmission from all forms of electronic or other storage, and destroy all hard copies. Do not forward this transmission. Thank you.
From:
blmailer-thewell=ngwa.big...@biglist.com
[mailto:blmailer-thewell=ngwa.big...@biglist.com] On Behalf Of Carlos Eduardo Molano Cajigas
Sent: Thursday, August 20, 2009
12:04 PM
To: the...@ngwa.biglist.com
Subject: [The Well] S and Sy in
fracturated rocks
Hello,
I’m facing the determination of Storage Coefficient (S) and Specific Yield (Sy) in a crystalline fracturated rocks to estimate prelimar dewatering flow rates. This deposit is very heterogeneous with various types of fractures; some aquifer tests are available, but the observation wells behaves very diferent according to the depth and the fractures they intercept; therefore there is no general patern of time-drawdown curves, and changes in a very short distance, even some close observation wells behaves different for the same pumping well. I apreciatte if some one could advise on this issue for determining S and Sy.
Thank you,
Carlos E. Molano C.
Hidrogeocol Ltda
Carrera 70A No. 109-18 Bogotá, Colombia
Phone Bogota: (57) 1 6241973 / 2715284, ext 230
Movil Colombia: (57) 310 2620049
web : www.hidrogeocol.com.co
T
Guy Swenson
If your long term focus is on dewatering with unconfined conditions,
then the specific yield may play a bigger role in determining the amount
of water you produce than the storage coefficient. That is because Sy is
likely to be an order of magnitude or more larger than the S value. So
for a unit decline in head Sy will release more water.
You might want to recognize that you may have a range in S and Sy
values in your fractured rock situation and you will probably be forced
to assume an average value for S and Sy.
Then consider how long you might expect the S value to dominate your
flow estimates before you truly begin to dewater the system and the Sy
value becomes dominate your flow estimates. If S will dominate only for
a short time you may want to focus your dewatering estimates on
calculations using Sy.
Another option is to calculate a range in dewatering flows for both the
semi-confined and unconfined conditions to reflect a range in S and Sy
values.
Hope this helps.
Guy
Guy Swenson
Sr. Technical Director
O'BRIEN & GERE
PO Box 4873
5000 Brittonfield Parkway
Syracuse, NY 13221
315 437-6100
fax 315 463-7554
cell 315 506-3063
swen...@obg.com
www.obg.com
>>> Carlos Eduardo Molano Cajigas <cmo...@uniandes.edu.co> 8/20/2009
12:03 PM >>>
Hello,
I*m facing the determination of Storage Coefficient (S) and Specific
Yield
(Sy) in a crystalline fracturated rocks to estimate prelimar dewatering
flow
rates. This deposit is very heterogeneous with various types of
fractures;
some aquifer tests are available, but the observation wells behaves
very
diferent according to the depth and the fractures they intercept;
therefore
there is no general patern of time-drawdown curves, and changes in a
very
short distance, even some close observation wells behaves different for
the
same pumping well. I apreciatte if some one could advise on this issue
for
determining S and Sy.
Thank you,
Carlos E. Molano C.
Hidrogeocol Ltda
Carrera 70A No. 109-18 Bogotá, Colombia
Phone Bogota: (57) 1 6241973 / 2715284, ext 230
Movil Colombia: (57) 310 2620049
web : www.hidrogeocol.com.co
T
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Walker, Doug
Challenging stuff, to be sure. My first question is: what conceptual model is suggested by the diagnostic plot? See
Philippe Renard & Damian Glenz & Miguel Mejias, 2009. Understanding diagnostic plots for well-test interpretation, Hydrogeol J. 17, p589-600.
I mention this because the slope of the Bourdet derivative is the key to picking the interpretive model, which, as Mark Eisner already pointed out, is not necessarily radial. There are hydraulic test interpretation software that include the derivative as a tool for interpreting tests. The derivative isn’t too hard to compute the derivative using a spreadsheet.
Hope that helps,
Doug Walker
=========
Illinois State Water Survey
From:
blmailer-thewell=ngwa.big...@biglist.com
[mailto:blmailer-thewell=ngwa.big...@biglist.com] On Behalf Of Carlos Eduardo Molano Cajigas
Sent: Thursday, August 20, 2009
11:04 AM
To: the...@ngwa.biglist.com
Subject: [The Well] S and Sy in
fracturated rocks
Hello,
I’m facing the determination of Storage Coefficient (S) and Specific Yield (Sy) in a crystalline fracturated rocks to estimate prelimar dewatering flow rates. This deposit is very heterogeneous with various types of fractures; some aquifer tests are available, but the observation wells behaves very diferent according to the depth and the fractures they intercept; therefore there is no general patern of time-drawdown curves, and changes in a very short distance, even some close observation wells behaves different for the same pumping well. I apreciatte if some one could advise on this issue for determining S and Sy.
Thank you,
Carlos E. Molano C.
Hidrogeocol Ltda
Carrera 70A No. 109-18 Bogotá, Colombia
Phone Bogota: (57) 1 6241973 / 2715284, ext 230
Movil Colombia: (57) 310 2620049
web : www.hidrogeocol.com.co
T