3.0 Affected Environment - Knik Arm Bridge and Toll Authority

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Knik Arm Crossing DraftFinal EIS Affected Environment high as 1,430 milligrams per liter [mg/L]), iron (as high as 7.2 mg/L), chlorides (700 mg/L), sulfates (130 mg/L) and manganese (0.46 mg/L). Shallow ground water close to the northwestern portion of the Study Area is reportedly brackish or salty. The water quality problem occurs in the vicinity of Nancy Lake, at depths as shallow as 50 to 100 feet bgs, or nearly 180 feet above sea level. The cause for the salinity has not been determined; however, it is believed to be attributable either to connate water (water trapped in the sedimentary rock at the time of its deposit) or to inundation of the area by an ancestral Cook Inlet. In the Point MacKenzie portion of the Study Area, unconsolidated materials are known to provide potable water from unconfined as well as from confined aquifer sources. Unconfined aquifer yield in this portion of the Study Area is estimated by Glass (1983) to be 5 to 35 gpm, while the confined aquifer yield may range widely from less than 1 gpm to more than 300 gpm. Ground water quality in the Point MacKenzie area varies widely. High salinity was reported in a 300-foot-deep well west of Horseshoe Lake, close to the Little Susitna River. Water samples collected during test well drilling near Lake Lorraine indicate increasing chlorides with depth; however, concentrations meet drinking water quality standards. 3.5.6.1.2 Ground water quality concerns Arsenic Conditions favorable to the occurrence of arsenic in ground water are found throughout the Study Area. These include the presence of iron oxide and sulfide minerals in the aquifer materials and phosphates and organic carbon in alkaline (high pH) ground water. Several wells in the Study Area were identified with concentrations of arsenic between 10 micrograms per liter (µg/L) and 50 µg/L (USGS 2001a). USEPA’s maximum contaminant level for arsenic in drinking water is 10 µg/L. Contaminated sites The Alaska Department of Environmental Conservation (ADEC) on-line databases were searched for incidents of “open” leaking underground storage tank sites (ADEC 2005a) and “active” contaminated sites (ADEC 2005b) located in Big Lake, Houston, and Wasilla. No other location references from within the Study Area are used in the existing databases. The search resulted in the identification of seven sites in Big Lake, one site in Houston and 32 sites in Wasilla. The locations of the Wasilla sites were not researched to determine the number of sites situated within the Study Area. 3.5.6.1.3 Ground water recharge areas Regional hydrogeologic mapping has not previously been conducted for the Mat-Su. Based on general geological conditions in the Study Area, recharge to unconfined aquifers is through downward percolation of precipitation. Recharge to deeper aquifers is by infiltration of ground water through aquitards and “leaky” confining layers, by lateral migration from other aquifers, and/or by direct infiltration of precipitation where the till or other confining 3-132 12/18/07
Knik Arm Crossing DraftFinal EIS Affected Environment layers are absent. Ground water recharge occurs over most of the land surface, with discharge occurring locally to low-lying areas such as lakes, streams, and wetlands. 3.5.6.2 Anchorage The Anchorage portion of the Study Area is underlain by two primary freshwater aquifers within glacial outwash sands and gravel. The upper unconfined aquifer (0–50 feet bgs) is separated from the lower, confined aquifer (70–300 feet bgs) by impermeable clay deposits of the Bootlegger Cove Formation. These aquifers flow west and generally thicken with distance from the Chugach Mountains. Recharge of the Anchorage-area aquifers has been estimated at 75 mgd. Recharge primarily occurs from bedrock seepage (25 mgd); infiltration by perennial surface streams and seepage along the Chugach front and foothills (20 mgd); and through direct recharge of rainfall, snowmelt, and water body losses within the lowland areas (30 mgd) (Barnwell et al. 1972). Saltwater intrusion into the aquifers has been documented near Point Woronzof. Previous studies have used a value of 22 to 33 mgd for the ground water yield for the Anchorage Bowl. This number was originally obtained from a 1972 study (Barnwell et al.). It appears that the Barnwell study has been the basis for all Anchorage Bowl estimates of ground water yield since that time. Water quality is generally good; however, high arsenic levels have been found in some locations, Sand Lake area for example. 3.6 Cultural Environment 3.6.1 Archaeology and Historic Preservation 3.6.1.1 Section 106 of the National Historic Preservation Act consultation To conduct project consultation with SHPO, the Study Team combined compliance with NEPA regulations [43 C.F.R. § 1500.5(i)] with the process it used to comply with Section 106 of the National Historic Preservation Act (NHPA) (16 U.S.C. § 470f, as amended). Section 106 requires that: The head of any Federal agency having direct or indirect jurisdiction over a proposed Federal or federally assisted undertaking … take into account the effect of the undertaking on any district, site, building, structure, or object that is included in or eligible for inclusion in the National Register. The head of any such Federal agency shall afford the Advisory Council on Historic Preservation … a reasonable opportunity to comment with regard to such undertaking. As lead federal agency, FHWA is carrying out this responsibility for itself and on behalf of USACE, USCG, and any other cooperating federal agency with the same legal requirements [43 C.F.R. § 1500.5(h)], but not including Elmendorf, or BLM acting on Elmendorf’s behalf, as it relates to the Anchorage approach. [see 36 C.F.R.§ 800.2(2)]. The regulations implementing Section 106 are found at 36 C.F.R. Part 800, Protection of Historic Properties. 12/18/07 3-133
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3.0 Affected Environment - Knik Arm Bridge and Toll Authority

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