3.0 Affected Environment - Knik Arm Bridge and Toll Authority
3.0 Affected Environment - Knik Arm Bridge and Toll Authority
3.0 Affected Environment - Knik Arm Bridge and Toll Authority
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<strong>Knik</strong> <strong>Arm</strong> Crossing DraftFinal EIS<br />
<strong>Affected</strong> <strong>Environment</strong><br />
Table 3-19. Existing noise levels in selected Study Area locations<br />
Receiver<br />
identification<br />
Description or location<br />
Receiver<br />
type<br />
Existing<br />
L eq<br />
(dBA)<br />
3 Private driveway off Point MacKenzie Road residential 57<br />
4 Government Hill School school 51<br />
6 309 Harvard Avenue residential 59<br />
9 Sunset Park south of Vine Avenue recreational 60<br />
13 C Street <strong>and</strong> 3rd Avenue commercial 63<br />
14 A Street <strong>and</strong> 3rd Avenue commercial 66<br />
15 Gambell Street <strong>and</strong> 3rd Avenue residential 64<br />
16 Ingra Street <strong>and</strong> 3rd Avenue commercial 67<br />
3.5.3 Geology/Soils/Seismic Hazards<br />
This section summarizes the affected environment for geology, soils, <strong>and</strong> seismic hazards in<br />
the Study Area. Additional details on these resources can be found in the <strong>Knik</strong> <strong>Arm</strong> Crossing<br />
Geotechnical Memor<strong>and</strong>um (KABATA 2006j) <strong>and</strong> the <strong>Knik</strong> <strong>Arm</strong> Crossing Seismic Studies<br />
Technical Report (KABATA 2006k).<br />
3.5.3.1 Geology <strong>and</strong> soils<br />
3.5.3.1.1 Physiographic setting<br />
Onshore physiography<br />
<strong>Knik</strong> <strong>Arm</strong> lies in the Cook Inlet-Susitna Lowl<strong>and</strong> physiographic province. Numerous lakes,<br />
ponds, <strong>and</strong> wetl<strong>and</strong>s associated with glacial tills <strong>and</strong> outwash deposits are found throughout<br />
this gently sloping area. The lowl<strong>and</strong>s are fed by multiple drainages that originate in the<br />
surrounding mountains, several of which are large, glacially fed, braided rivers with heavy<br />
sediment loads that drain into <strong>Knik</strong> <strong>Arm</strong> (Nowacki et al. 2002; Wahrhaftig 1965).<br />
The shorelines of <strong>Knik</strong> <strong>Arm</strong> are characterized by large mud flats in the intertidal zones<br />
<strong>and</strong> 50- to 150-foot-high bluffs. Cairn Point on the eastern shore marks the southwestern<br />
extent of Elmendorf Moraine, which is an end moraine of the combined Matanuska <strong>and</strong> <strong>Knik</strong><br />
glaciers that advanced during the Naptowne Ice Age. This major geomorphic feature extends<br />
across <strong>Knik</strong> <strong>Arm</strong> to the Susitna Lowl<strong>and</strong>s, <strong>and</strong> was breached by rapid downcutting of<br />
outwash streams during a period of lowered sea level in the late Pleistocene. The waters of<br />
Cook Inlet then rose in response to a worldwide sea level increase, <strong>and</strong> melting glaciers<br />
flooded the valley, creating modern-day <strong>Knik</strong> <strong>Arm</strong>.<br />
Submerged l<strong>and</strong>forms<br />
L<strong>and</strong>forms beneath <strong>Knik</strong> <strong>Arm</strong> near the proposed project consist of shallow tidal flats <strong>and</strong><br />
gently sloping, hummocky benches that extend from shore to depths of about 20 to 30 feet<br />
below MLLW (see Figure 3.24). The deepest part of the channel in the middle of <strong>Knik</strong><br />
3-108 12/18/07
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