The Effect of Fractures on the Reclamation ofNAPL
55
1 Introduction
This study originates from recent field observations and laboratory measurements
(Rubin and Braester 2000) performed in a portion of the Coastal Plain Aquifer of
Israel. This water supply aquifer is composed of sandstone with minor quantities
of sandy silt and sandy clay lenses. Pump tests (Averbach 1988) have measured
very high transmissivity and hydraulic conductivity values in the formation.
Together this information indicates that the formation is comprised of fractured
sandstone, even though the pump test results have not exhibited features of double
porosity (Barenblatt et al. 1960).
Subsurface aquifers that exhibit significant transmittance through both a
primary porosity and secondary fracture porosity are termed fractured permeable
formations by Birkholzer et al. (1993a). In such formations the fracture porosity
typically amounts to no more than a few percent but can contribute substantially to
the effective conductivity (pettijohn et al. 1987). Thus, a primary characteristic of
fractured permeable formations is the so-called mobility number, NM, defined as
the ratio of flow through the primary porosity (permeable block flow) to the flow
through the fracture network (Birkholzer et al. 1993a). Examples of permeable
fractured formations described in the literature are listed in Table 1 and indicate
that mobility numbers can range between 10-4 and 25. Fractured permeable
formations may also be important economically as water supply aquifers,
particularly sandstone aquifers like those found in Germany (Andres and
Georgotas 1978) and along the coastal plain of Israel (Kanfi 1986). In the latter
case, Gvirtzman et al. (1988) documented evidence of slow flow through the
porous matrix and fast flow through the fractures, using environmental tritium as a
natural tracer. They found that about 25% of the total rain-flow infiltration occurs
through the fissures, and about 75% occurs through the permeable blocks.
Table 1: Examples of fractured permeable formations
Reference
Andres and
Georgotas
(1978)
Gvirtzman et al.
(1988)
Berkowitz et al.
(1988)
Haldeman et al.
(1991)
Objectives/System
Survey of sandstone aquifers
Investigation of flow paths
through calcareous sandstone
Summary of 20 numerical
experiments
Experimental investigation of
unsaturated water flow
through a fractured porous tuff
Summary of findings
Conductivity of core samples
ranged between 10. 8 and 10. 5 mls
Effective conductivity ranged
between 10. 5 and 5xl0-4 m S·1
75% flow through primary
porosity, 25% flow through
fissures (NM== 3)
NMranged from 10. 7 to 10 3
50% flow through primary
porosity, 50% flow through the
fracture (NM == 3)
55
1 Introduction
This study originates from recent field observations and laboratory measurements
(Rubin and Braester 2000) performed in a portion of the Coastal Plain Aquifer of
Israel. This water supply aquifer is composed of sandstone with minor quantities
of sandy silt and sandy clay lenses. Pump tests (Averbach 1988) have measured
very high transmissivity and hydraulic conductivity values in the formation.
Together this information indicates that the formation is comprised of fractured
sandstone, even though the pump test results have not exhibited features of double
porosity (Barenblatt et al. 1960).
Subsurface aquifers that exhibit significant transmittance through both a
primary porosity and secondary fracture porosity are termed fractured permeable
formations by Birkholzer et al. (1993a). In such formations the fracture porosity
typically amounts to no more than a few percent but can contribute substantially to
the effective conductivity (pettijohn et al. 1987). Thus, a primary characteristic of
fractured permeable formations is the so-called mobility number, NM, defined as
the ratio of flow through the primary porosity (permeable block flow) to the flow
through the fracture network (Birkholzer et al. 1993a). Examples of permeable
fractured formations described in the literature are listed in Table 1 and indicate
that mobility numbers can range between 10-4 and 25. Fractured permeable
formations may also be important economically as water supply aquifers,
particularly sandstone aquifers like those found in Germany (Andres and
Georgotas 1978) and along the coastal plain of Israel (Kanfi 1986). In the latter
case, Gvirtzman et al. (1988) documented evidence of slow flow through the
porous matrix and fast flow through the fractures, using environmental tritium as a
natural tracer. They found that about 25% of the total rain-flow infiltration occurs
through the fissures, and about 75% occurs through the permeable blocks.
Table 1: Examples of fractured permeable formations
Reference
Andres and
Georgotas
(1978)
Gvirtzman et al.
(1988)
Berkowitz et al.
(1988)
Haldeman et al.
(1991)
Objectives/System
Survey of sandstone aquifers
Investigation of flow paths
through calcareous sandstone
Summary of 20 numerical
experiments
Experimental investigation of
unsaturated water flow
through a fractured porous tuff
Summary of findings
Conductivity of core samples
ranged between 10. 8 and 10. 5 mls
Effective conductivity ranged
between 10. 5 and 5xl0-4 m S·1
75% flow through primary
porosity, 25% flow through
fissures (NM== 3)
NMranged from 10. 7 to 10 3
50% flow through primary
porosity, 50% flow through the
fracture (NM == 3)