FLOOD09522

• County: Logan
• Community: Sterling, Atwood
• Basin: South Platte
• Title: Pawnee Creek Flood Mitigation, City of Sterling, Town of Atwood and Logan County
• Date: 7/1/1999
• Prepared For: Logan County
• Prepared By: URS Greiner Woodward Clyde
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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SECTIONTHREE AUected Environments and Environmental Consequences

during the 1997 flood, this alternative would have prevented floodwaters from entering Sterling
and flood elevations would have been reduced by 4 to 6 feet upstream of the Highway 6 and
UPRR bridges, and by 3 to 6 feet upstreanl of the UPRR embankment at Atwood (URS Greiner
Woodward Clyde 1999). It is estimated that the alternative would have prevented over
$10 million in damage to residential, commercial, and infrastructure in Sterling; and reduced
flood damage to residential structures, agriculture land, and transportation infrastructure in
Logan County by approximately $1 million. In addition, Alternative 2 would have a small,
short-term beneficial effect on the local economy associated with the purchase of goods and
services during the construction of the project.

3.5.3 Alternative 3 . Pawnee Creek Overflow Cutoff

Other than the conversion of agricultural land to flood control facilities as discussed in
Section 3.2.3, impacts associated with this alternative are beneficial. Therefore, this alternative
would not have a disproportional adverse impact on any minority or low-income population. All
lands would be purchased on a "willing" seller basis as no land would be condemned with this
alternative. Flood protection would be provided only to Sterling. If this alternative had been in
place during the 1997 flood, it would have prevented over $10 million in damages to residential,
commercial, and infrastructure properties in Sterling. In addition, Alternative 3 would have a
small, short-term beneficial effect on the local economy associated with the purchase of goods
and services during the construction of the project.

3.6 AIR QUALITY

The National Ambient Air Quality Standards (NAAQS) established by the U.S. Environmental
Protection Agency define the allowable concentrations of pollutants that may be reached but not
exceeded in a given time period to protect human health (primary standard) and welfare
(secondary standard) with a reasonable margin of safety. The standards include maximum
concentrations for ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, lead, and
particulate matter with a diameter of 10 microns. Logan County is classified as a NAAQS
Attainment Area (C. Dann, Public Information Officer, Colorado Department of Public Health
and the Environment, Air Quality Division, personal communication 1999), which indicates
existing concentrations of air pollutants are below the established standard(s), and limited
emissions are allowable.

3.6.1 Alternative 1 . No Action

The No Action Alternative would not impact air quality in the project vicinity or surrounding
areas because no construction would occur.

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