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Section 7 Environmental Effects of the Selected Plan

EAA Storage Reservoirs Revised Draft PIR and EIS February 2006

7-1

7.0 ENVIRONMENTAL EFFECTS OF THE SELECTED PLAN

This section documents the environmental impacts and benefits of the selected

plan (the preferred alternative). It presents detailed analysis on the

environmental effects including unavoidable adverse effects, irreversible and

irretrievable commitments of resources, cumulative effects, and environmental

commitments. Documentation also is provided for a comprehensive review of

water resources issues, including water supply, flood protection, threatened and

endangered species, and other natural system and habitat needs. In addition,

this section provides recommendations to minimize the potential impacts

identified for the preferred alternative.

7.1 GEOLOGY, TOPOGRAPHY, AND SOILS

7.1.1 Geology

Some caprock would be removed on site for use as construction material for

embankments. Most of this limestone caprock would be obtained from widening

of canals and during excavation of deep water refugia within the reservoir. The

underlying regional geology would not be affected.

7.1.2 Topography

The plan includes conversion of relatively flat, uniform agricultural lands to a

reservoir with deep water and embankments up to 23 feet above existing grade

(generally 12 ft NGVD). The seepage buffer on the east, west, and north of the

project site would have a 100 foot wide strip returned to existing grade, with the

remainder of the buffer contoured as an upland and wetland mosaic of

appropriate topography. Contouring of the STA component and canal littoral

shelves would lower existing topography to mimic suitable depths for long-

hydroperiod wetlands. These topographic changes, along with operations of the

reservoir, would significantly alter the current surface hydrology of the property.

7.1.3 Soils

Soils in the construction footprint will be redistributed by construction activities

and excavation for embankment materials. Soils that remain undisturbed

within the reservoir footprint would be impacted during operations of the

reservoir, as a layer of fine sediments containing a high level of organic debris

and nutrients will settle from the overlying water to coat the bottom. The low

oxygen environment that is expected at the bottom of the reservoir will act to

preserve organic material in the remaining soils and in the sediment.

Soils within the canals will also be removed during widening. Littoral shelves

constructed within the seepage canals would experience sediment deposition as

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