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Rocks, Towsley Formation, and alluvial sediments. Detailed lithologic descriptions of these

units are presented in Section 5.0. Information presented below pertains to the
hydrogeologic characteristics of the above-mentioned units.

Groundwater was not encountered in the Pico Formation during investigation conducted at
the project property, possibly due in part to its topographic position. Therefore, the Pico

is not considered to represent a significant water-bearing hydrogeologic unit at the property.

San Gabriel Formation: The San Gabriel Formation consists of dense, crystalline basement
rocks of igneous and metamorphic origin which underlie the topographically steep rugged
eastern portion of the project property, including the ridgeline traversed by East Firebreak
Road (Plates 7A and 7B). Nearly all of the proposed landfill footprint will be underlain by

these rocks. Based on surface mapping and subsurface drilling information, San Gabriel
Formation rocks are very hard and the weathered zone is typically a few feet thick. For all
practical purposes, the San Gabriel Formation contains little primary porosity, if any, based
on appearance and hydraulic testing data. However, these basement rocks have been
moderately to highly fractured, resulting in secondary fracture porosity and likely, highly

variable water-bearing characteristics. In addition, some minor porosity may exist within
foliation and schistosity planes in gneissic (metamorphic) rocks.

A total of 21 groundwater monitoring wells ranging in-depth from 23 feet to 500 feet bgs
were drilled and installed in San Gabriel Formation rocks. Included within this well group
are 5 well pairs (Table 5). Groundwater was encountered as deep as 450 feet bgs in one
well (C-17A) and flowing to the surface in three of these basement wells (G1, G3 and

MW-S, Plates 7A and 7B). Mapping performed in May 1992, approximately two months
after a period of significant precipitation, documented the presence of springs and seeps
within San Gabriel Formation rocks exposed in upper drainages flanking the East Firebreak
Road ridgeline area.

Eocene Rocks: Eocene rocks occurring at the project property are well-indurated and
cemented medium to coarse-grained sandstone with minor siltstone and conglomerate
interbeds. A total of 6 groundwater monitoring wells were completed within Eocene rocks,
and groundwater was encountered at depths ranging from 10 feet to 215 feet bgs. Included
in this group are one well pair (MW-1/MW-2), and a second well pair with a deep Eocene
completion (C-13) and a shallow alluvium completion (C-14) (Table 5). Groundwater

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