Analysis and Evaluation of Pumping Test Data Second Edition Background Two types Igneous Sedimentary Igneous dikes are formed when magma rises through the subsurface and intrudes or cuts through preexisting strata ID: 265117
Download Presentation The PPT/PDF document "Chapter 19: Single Vertical Dikes" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Chapter 19: Single Vertical Dikes
Analysis and Evaluation of Pumping Test Data
Second EditionSlide2
Background
Two types:
Igneous
SedimentaryIgneous dikes are formed when magma rises through the subsurface and intrudes, or cuts through, pre-existing strata.Igneous dikes are normally coarse-grained due to slow rate of cooling.Weathered material may form sedimentary dikes when sediment fills a pre-existing crack.Sedimentary dikes are not as common as igneous dikes. Both types have high aspect ratios.
2Slide3
3Slide4
4Slide5
5Slide6
6Slide7
7Slide8
Background
Dikes can be highly permeable.
If a single, permeable, vertical dike bisects an aquifer whose
transmissivity is several times less than that of the dike, a specific flow pattern will be created when the dike is pumped. “Trough of Depression” similar to cone of depression
8Slide9
9Slide10
Assumptions and Conditions
The dike is vertical and of infinite extent over the length influenced by the test.
The
width of the dike is uniform and does not exceed 10 mThe flow through the fracture system in the dike is laminar (Darcy!)The uniformly fractured part of the dike can be replaced by a representative continuum to which spatially defined hydraulic characteristics can be assigned
The fractured part of the dike
is bounded above and below by impermeable
weathered zone and solid rock, respectively.
The
well fully penetrates the fractured part
of the dike and is represented by a plane sink;
flow through the dike towards the well is parallel
The hydraulically connected country rock aquifer is confined, homogeneous, isotropic, and of infinite areal extent.
All water pumped from the well comes from storage within the composite system comprised by the dike and aquifer.
The ratio of hydraulic diffusivity of the dike to the aquifer is not less than 25.
Well-losses and well-bore storage are
negligibe
.
10Slide11
Methods for Observation Wells
Partial solutions for the drawdown in observation wells:
Boonstra
– Boehmer’s curve fitting methodBoehmer – Boonstra’s curve-fitting method11Slide12
Boonstra –
Boehmer’s
Curve Fitting Method
To analyze the drawdown behavior for early and medium times along the pumped dike:12Slide13
Boonstra –
Boehmer’s
Curve Fitting Method
13Slide14
Example: Observation Well in the Dike, p. 284
14Slide15
Example: Observation Well in the Dike, p. 284
W
d
Td = 2.6 x 104 m3/dWdSd = 4.3 x 10-4
m
S T = 3.2 x 10
-4
m
2
/d
15Slide16
Boehmer
–
Boonstra’s
Curve-Fitting MethodTo analyze early and medium time drawdown behavior in observation wells drilled in the aquifer along a line perpendicular to the dike and even with the pumped well:
16Slide17
Boehmer –
Boonstra’s
Curve-Fitting Method
17Slide18
Example: Observation Well in the Aquifer, p. 285
18Slide19
Example: Observation Well in the Aquifer, p. 285
T/S = 2.7 x 10
5
m2/dCombining results from observation wells in the dike and aquifer, we get separate values for transmissivity and storativity of the aquifer:T = 9.3 m2
/d
S = 3.4 x 10
-5
19Slide20
Methods for Pumped Wells
For early and medium pumping times
For late pumping times
20Slide21
Early and Medium Pumping Times
At
early times
, all the pumped water is from dike storage (no water from aquifer storage). At medium times, most of the drawdown is governed by parallel flow from the aquifer into the dike (no water from dike storage).21Slide22
Early and Medium Pumping Times
Early time
:
Medium time:22Slide23
Early and Medium Pumping Times
23Slide24
Late Pumping Times
At late times, the flow in the aquifer is no longer considered parallel, but rather pseudo-radial.
Solution for the drawdown in the pumped well during late time:
For a pumping test of usual duration, this method can only be applied to fractures or thin dike structures.
24Slide25
Late Pumping Times
25Slide26
Example: pumped well, p. 285 - 286
26Slide27
Example: pumped well, p. 285 - 286
(
W
dTd) √(ST) = 425 m4/d3/2Substituting the values of dike width and transmissivity (Wd
T
d
) and aquifer
storativity
and
transmissivity
(ST) obtained with
Boonstra
–
Boehmer’s
method into
(
W
d
T
d
) √(ST
), the value is 465.
27