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Sylmar Basin Subarea: The major portion of the land area within the Sylmar Basin lies
within corporate limits of the City of Los Angeles. Water supply for the City of

Los Angeles, Sylmar District is obtained from the Owens River Aqueduct. All of the
pumpage from the City’s Mission well field is exported from the Sylmar Basin Subarea to
the San Fernando Basin Subarea (Brown, 1975).

In water year 1987-1988, a total of 5,937 acre-feet of groundwater was produced from the

Sylmar Basin, with about 5,685 acre-feet of this amount delivered to the San Fernando Basin
Subarea. Of the total production, approximately 3,134 acre-feet were pumped from the City
of Los Angeles Mission well field, and 2,804 acre-feet were extracted at the City of
San Fernando well field near Hubbard Street. The subarea received approximately
11,281 acre-feet of imported water from the Owens River aqueduct (Blevins, 1989).

9.0 CAL HYDRO EO I E'I'I‘IN

The following discussion of the hydrogeologic setting of the project property is based
on: 1) geologic and hydrogeologic data obtained as a result of site investigation in 1991

(Janes, 1991); and 2) additional hydrogeologic data collected in 1992, as contained in
Appendices C through E to this report.

Hydrogeologic investigation performed in 1991 included the following major tasks:
1) drilling, coring and installation of 36 monitoring wells including 13 well pairs (shallow and
deep); 2) open-hole packer testing (constant head and pressure decay); 3) slug testing in

completed wells (falling and rising head); 4) laboratory core permeability testing (horizontal
and vertical); 5) water level monitoring in wells; and 6) groundwater and surface spring
sampling and analytical testing. Boring logs, well-completion diagrams, testing methods, and
data obtained are presented in the 1991 database report (Janes, 1991).

Additional hydrogeologic investigation performed in 1992 included: 1) springs/seeps
mapping to supplement 1991 data; 2) drilling, coring and installation of five groundwater
monitoring wells at the project property (wells C-17A, C-18A, MW-23B, MW-24, and
MW-25; Plate 7A); 3) open-hole packer testing; 4) slug testing of one well; 5) bi-weekly and
monthly water level measurements in all monitoring wells at the property; and 6) two
periods of groundwater/surface spring sampling and analytical testing.

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