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Both high-angle and low-angle fractures have been documented in outcrop and in subsurface
cores. The available data suggest that most fractures appear to be open, although some
fractures have been cemented by secondary mineralization, or partially infilled by tar and/or

clay. Hydraulic conductivities and transrnissivity calculated from in-situ packer testing are
relatively consistent, and suggest that fractures are generally interconnected and capable of
effectively transmitting groundwater. On a small scale within the fracture system, water
level fluctuations observed in the monitoring wells (See section 9.2.3) have indicated that
groundwater flow within the saturated portion of the San Gabriel Formation likely occurs

under heterogeneous, anisotropic conditions, similar to that observed in other fractured rock
aquifers (Freeze and Cherry, 1977; after Snow, 1968; 1969). On a larger scale that covers
the area of the project property, groundwater flow within San Gabriel Formation rocks
follows the steep topography at the property, under hydraulicgradients exerted by this relief
(Plate 7B).

Eocene Rocks: Eocene sedimentary rocks, although indurated and moderately cemented,

contain groundwater within both primary intergranular- porosity and secondary fracture
porosity. Fracture density within these rocks increases in the vicinity of local faults.
Hydraulic conductivities and transmissivities are similar to those of the San Gabriel
Formation. Based on available data including water level measurements, Eocene strata
juxtaposed against San Gabriel Formation rocks along the Whitney Canyon fault exist under

a single hydraulic regime. However, local influence on groundwater flow along the fault
plane may be possible.

9.4.2 001011103

The Towsley Formation, comprised predominantly of siltstone, claystone and fine-grained

sandstone, has extremely low hydraulic conductivities based on in-situ packer testing. The
upper member, dominantly a siltstone and claystone, is interpreted to be an aquitard.
Groundwater occurring in the Towsley is either present as localized saturated zones within
sandstone lenses and layers in the upper member, or within coarse-grained deposits of the
lower member, which typically contains naturally occurring petroleum hydrocarbons.

Overall, the formation, which occurs stratigraphically above both the San Gabriel Formation
and Eocene rocks, may act as a barrier to any significant upward flow into overlying units
at the project property. This relationship is shown in geologic cross-sections on Plate 2 and
diagrammatically depicted in Figure 13.

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