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Fractured San Gabriel Formation igneous/metamorphic basement and Eocene sedimentary
bedrock comprising the principal water bearing units at the project property are overlain by
relatively impermeable strata of the Towsley Formation. Based on order of magnitude

differences in hydraulic conductivities between Towsley deposits and San Gabriel
Formation/Eocene rocks, there is likely very limited lateral flow of groundwater into
Towsley strata. Because flow is confined beneath the Towsley aquitard, groundwater would
be expected to mound up at the subsurface contact between San Gabriel Formation/Eocene
rocks and overlying Towsley Formation. However, at Elsmere Canyon, stream drainages
have eroded through confining Towsley beds, allowing discharge to occur from surface

springs/seeps and subsurface fractures within canyon slopes where fractured bedrock is
exposed. Discharging groundwater then flows into stream bed alluvium and continues as
subsurface flow during low discharge‘periods or may contribute to surface flow during and
after significant precipitation.

Further to the northwest in lower Elsmere Canyon, stream bed alluvium directly overlies
and is in hydraulic communication with the coarse-grained Pico Formation. Some downward
groundwater flow may occur from alluvial deposits into the underlying Pico, but likely would
be limited because of the cemented and moderately indurated nature of Pico deposits.

At the southern portion of the project property, continuity of the Towsley Formation is not

as well defined (Shields, 1977; Janes, 1991), and Pico Formation is in fault contact with
San Gabriel Formation (Plate 1). In this area, groundwater has a southwest-directed
component (Plate 7A), and may flow from water-bearing portions of the San Gabriel
Formation into coarse-grained Pico deposits. However, the San Gabriel Formation/Pico
Formation fault contact is located generally upgradient of the project property, including the

southern part of the landfill footprint where groundwater flow is predominantly to the west
and northwest. Also noteworthy is the presence of clayey siltstone and fine-grained
sandstone belonging to the Sunshine Member of the Saugus Formation that occurs along
the southern flank of the San Gabriel Mountains adjacent to San Fernando Valley. In the
area south of the project property, the Sunshine Member is several hundred feet thick
(CDMG, 1975) and could also impede groundwater flow and act as an aquitard much like

the Towsley does to the northwest.

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