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## Re:[gwmodel] Minimum permissible distance between bore holes in hard rock aquifers

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• Dear Subrata, Thank you for clarifying Hard Rock aquifer system so clearly. Do you have the details of reference UNESCO 1972. Was ir developed through
Message 1 of 10 , Nov 11, 2012
Dear Subrata,

Thank you for clarifying Hard Rock aquifer system so clearly. Do you
have the details of reference UNESCO 1972. Was ir developed through
observation or through some theoretical analysis?. If the original paper
is available in soft I will like to have a copy of the same.Most of the
equations in Step 1 are developed for Homogeneous isotropic aquifer. For
double porosity I will like to know for what value(range) of porosity
these equations are valid and what is the range of Reynold number for
these porosity values. Huntleys equation is an Empirical Equation based
on observation from field data. However, Huntley takes care of the
turbulent flow part by introducing Specific Capacity ( S = AQ + BQ^n).
Again in Step 3 we are using an Equation which is developed for Laminar
Flow. Dr. Singhal has written a book of Hydrogeology of Fractured Rocks .
I have not seen that book. I am sure you have gone through the book. I
will like to know whether Dr. Singhal has included study of Anisotropic
Aquifer Heterogeneous Aquifer with partial laminar flow and partial
turbulent flow .

subrata halder <shalder_2007@...>
11/11/2012 11:56 PM

To
gwmodel@yahoogroups.com
Subject
Re: Fw: RE: [gwmodel] Minimum permissible distance between bore holes in
hard rock aquifers

Dear Mr. Veranis,

Radius of Influence (R) in fissured Granite/gneisses rocks (UNESCO, 1972):

1000-1500 m (in confined aquifer)
500-1000 m (in unconfined aquifer)

Therefore, safe spacing of bore holes in interconnected fissured
Granite/gneisses rocks may be maintained as follows-

Safe Spacing (Ss) >= 2 x R >= 2000-3000 m (in confined aquifer)
>= 1000-2000 m (in
unconfined aquifer)

If u want to calculate safe spacing precisely u have to do pumping test in
bore hole intercepted interconnected fissured Granite/gneisses rocks
aquifer and then

Step 1
1) For unconfined aquifer match Field Data Curve with Boulton's type
curves
2)For leaky aquifer match Field Data Curve with Hantush type curve
3) For double porosity leaky confined aquifer (involved delayed yield from
block to fissures)) match Field Data Curve with Streltsova-Adams Type
curve.
4) For double porosity matrix confined aquifer (involved delayed yield
from block to fissures)) match Field Data Curve with Bourdet-Gringarten's
Type curve.
Find out Transmissivity (T) value.

Step 2
Put T, Q, Sw values in Huntley's Equation (for fissured rocks) and
find coefficient 'A' :
T=A(Q/Sw)1.18
T- Transmissivity (m2/day)
Q- Discharge (m3/day)
Sw- Drawdown (m)
A- Coefficient = (2.3*log R/rw)/2π
Step3
Find rad of Influence 'R' from
A = (2.3*log R/rw)/2π
rw - radious of bore hole
Step 4
Calculate Safe Spacing (Ss) >= 2 x R

Thanks

Subrata Halder
Executive Engineer (Agri-Irrigation)
State Water Investigation Directorate
Department of Water Resources Investigation & Development
Govt. of West Bengal
• To Dr. A.K. Ghosh Dear Sir, 1) Dr. BBS Singhal has used the ref of UNESCO 1972 for rad of Influence in fissured rocks.  2) In double porosity model, best
Message 2 of 10 , Nov 12, 2012
To Dr. A.K. Ghosh

Dear Sir,

1) Dr. BBS Singhal has used the ref of UNESCO 1972 for rad of Influence in fissured rocks.
2) In double porosity model, best match with type curve has been achieved with porosity=10 %. Double porosity model is more representative of uniformly fractured aquifer.
3) Equations in connection with pumping Test are developed based on the assumptions of homogeneous & isotropic aquifers with laminar flow during pumping...well is 100% efficient and effective diameter is the same as the diameter of the well. But in reality aquifers are heterogeneous, anisotropic with non-laminar flow during pumping...pumping well is not 100% efficient and effective dia is usually more than dia. of screen mainly, in case of unconsolidated sediments. Considering the above reality, pumping well & observation wells are installed into closely spaced & inter-connected fractures and also, nested observation wells at different depth horizon in different direction are installed to get reading of water level at different depth & in different direction and an av. T value is computed. With a view to get  as much as radial,horizontal & laminar flow pattern, pumping well should be put in lower  1/2 or 1/3 rd of aquifer thickness and Observation
wells should be located at dist. 1.5 times the saturated thickness of interconnected fractured aquifer. Considering the above reality, Huntley used the Specific Capacity(Q/Sw) as (Q/Sw)1.18and he modifed Thiem's Eq for fractured aquifer as T=A(Q/Sw)1.18   using the coefficient A=(2.3*log R/rw)/2π  (as in Thiem's Eq.) Thus Huntley's Eq holds good for  i) small dia 100% efficient pumping well and ii) nested observation wells in different & different direction installed in closely spaced interconnected fracture zone.  Therefore, I think earlier steps may be quite O.K. for finding out Rad of Influence (R).
4) Dr. BBS Singhal has not included the study of Anisotropic Aquifer Heterogeneous Aquifer with partial laminar flow and partial turbulent flow in his book.
Thanks
Regards
Subrata HalderExecutive Engineer (Agri-Irrigation)
State Water Investigation Directorate
Department of Water Resources Investigation & Development
Govt. of West Bengal

--- On Mon, 12/11/12, asokg@... <asokg@...> wrote:

From: asokg@... <asokg@...>
Subject: Re:[gwmodel] Minimum permissible distance between bore holes in hard rock aquifers
To: "subrata halder" <shalder_2007@...>
Date: Monday, 12 November, 2012, 9:54 AM

Dear Subrata,

Thank you for clarifying Hard Rock aquifer system so clearly. Do you

have the details of reference UNESCO 1972. Was ir developed through

observation or through some theoretical analysis?. If the original paper

is available in soft I will like to have a copy of the same.Most of the

equations in Step 1 are developed for Homogeneous isotropic aquifer. For

double porosity I will like to know for what value(range) of porosity

these equations are valid and what is the range of Reynold number for

these porosity values. Huntleys equation is an Empirical Equation based

on observation from field data. However, Huntley takes care of the

turbulent flow part by introducing Specific Capacity ( S = AQ + BQ^n).

Again in Step 3 we are using an Equation which is developed for Laminar

Flow. Dr. Singhal has written a book of Hydrogeology of Fractured Rocks .

I have not seen that book. I am sure you have gone through the book. I

will like to know whether Dr. Singhal has included study of Anisotropic

Aquifer Heterogeneous Aquifer with partial laminar flow and partial

turbulent flow .
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