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alluvium is shown on Plate 7A. Plate 7B shows only water level data for the San Gabriel
Formation, and therefore depicts groundwater flow direction for most of the area that would
be overlain by the landfill footprint.

Based on static measurements from monitoring wells (Janes, 1991, Meredith/Boli &

Associates, 1992a and 1992b), the groundwater potentiometric surface at the project
property generally appears to follow the overall topography of the ground surface (Plates 7A
and 7B). Groundwater levels are highest along the East Firebreak Road ridgeline at
approximately 2,700 to 2,800 feet above mean sea level (msl), and are less than 1,500 feet
above msl along the lower drainages of Elsmere Canyon in the northwest portion of the

project property. In general, groundwater occurs at greatest depths below ground surface
along the main ridgeline. Groundwater is also deeper at topographically higher areas
surrounding the Elsmere Canyon drainage on the north, south and west, and is usually
shallow in the lower portions of the Elsmere Canyon drainage where local seeps and springs
may be present. Groundwater is near surface and also flows at the surface as springs and

seeps at several other locations at the project property, and a few groundwater monitoring
wells experience continuous flowing or near-flowing conditions (C-l, MW-3, C-3 and MW-S).
These areas generally are located within small drainages on crystalline basement about
500 to 600 feet topographically below the East Firebreak Road ridgeline.

Groundwater flow direction at the project property is predominately to the northwest, from
higher areas along East Firebreak Road ridgeline toward the lower portion of Elsmere

Canyon (Plate 7A). However, groundwater flows to the southwest in a localized southern
portion of the property. Groundwater contours defined by wells and well pairs drilled along
the ridgeline and supplemented by springs/seeps mapping information, indicate that East
Firebreak Road ridgeline is a major groundwater divide in the area. Northwest and
downslope of this divide in the central portion of the project property, the groundwater I

gradient is relatively uniform toward the northwest at about 0.25 (ft/ft) or 1,320 ft/mile, and
with a similar gradient to the southwest along the southern end of the divide. Downgradient
of the north and south Elsmere Canyon confluence, groundwater contours bend into a more
constricted U-shaped configuration that approximates the topographic relief surrounding the
lower canyon reach (Plate 7A). This localized basin is defined to the north by well control

along Whitney Ridge and to the south by an interpreted groundwater divide in the area of
wells C-8, C-9, and C-10. The overall gradient within the lower canyon reach is still to the

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