Environmental assessment of the lower reach of Pittman Wash
In compliance with the federal Clean Water Act, the City obtained a 404 Permit from the US Army Corps of Engineers (Corps) for construction of the concrete channel. An environmental consultant was hired to evaluate environmental effects associated with the proposed project, and to determine the extent of the Corps’ jurisdictional authority within the project area.
The process of obtaining the permit includes a survey of the project site to assess the hydrology, soils, and vegetative community located there. The results of this survey are presented in the Jurisdictional Determination which was submitted to the Corps as part of the 404 Permit application. As presented in the Jurisdictional Determination, the proposed project would affect 0.35 acres of “waters of the United States”. No wetlands are present within the project site.
“Waters of the United States” (WOUS) have been defined in the Clean Water Act (and subsequent court rulings and regulatory agency guidelines) to include a wide range of water bodies including the territorial seas, lakes, rivers, streams and wetlands. Because Pittman Wash is directly connected to the Colorado River by way of Duck Creek and the Las Vegas Wash, it is regarded as a WOUS under the Corps’ regulatory authority. The Corps’ regulatory authority is limited to that part of the water-body below the “ordinary high water line”. The proposed project would affect 0.35 acres of “waters of the United States”.
Wetlands are a particular type of WOUS. Wetlands possess three essential characteristics: 1) hydrophytic vegetation, 2) hydric soils, and 3) wetland hydrology. These characteristics and the technical criteria for their identification are presented in Federal manuals. All three of the essential characteristics must be present for an area to be identified as a wetland. No wetlands are present within the project site.
Because the proposed project would unavoidably affect 0.35 acres of WOUS, the 404 Permit includes a stipulation requiring the payment of compensatory mitigation. As required by the Permit, payment was made to The Nature Conservancy for activities associated with the Eglington Preserve In Lieu Fee Mitigation Site. The stipulation requiring payment to the in lieu fee program is consistent with other permits issued for projects in the Las Vegas Valley. To date, the Regional Flood Control District and its member entities have contributed more than $5,600,000 to the Clark County Wetland Parks In Lieu Fee program and the Eglington Preserve In Lieu Fee program.
An applicant for a 404 permit must demonstrate to the Corps that the proposed project is the least environmentally damaging practicable alternative (LEDPA) to achieve the project's purpose. The engineering analysis for this project included an evaluation of several alternatives including concrete lining, rip-rap lining, and placement of drop structures. Due to the erosive nature of the soils, the high velocities of the design flood flows, right-of-way limitations, maintenance access considerations, and desire to create usable areas for recreation and to minimize disturbance areas, the rip-rap lining and drop structure alternatives were eliminated as not being able to fulfill the project purpose.
Another component of the environmental analysis process was the preparation of a Section 8 environmental analysis report. The Section 8 report is essentially an Environmental Assessment, tiered off of the Regional Flood Control District’s Supplemental Programmatic Environmental Impact Statement (SEIS). The SEIS was prepared for the Bureau of Land Management in cooperation with the Corps, and presents the effects anticipated to be associated with flood control facilities identified in the Flood Control District Master Plan for the Las Vegas Valley at a programmatic level. Section 8 of the SEIS presents a procedure that provides for a site- and project-specific analysis of anticipated project impacts. The Record of Decision for the SEIS stipulates in part that the Section 8 analysis will be conducted for all Flood Control District Master Plan projects as a condition of funding a project. This analysis includes an assessment of the effects of the project to cultural resources, biological resources, surface and groundwater, geology and soils, air quality, recreation, paleontology, visual resources, hazardous materials, and land use.
The Section 8 report presents the anticipated project impacts to these resources, as well as mitigation measures to minimize those effects. Field reconnaissance did not reveal evidence of the presence of any protected plant or animal species. No sensitive cultural or paleontologic resources are present. The project site is a highly disturbed existing drainage channel, and there will be no significant adverse changes to the land use, recreation or visual resources. The construction contractor will be required to comply with all mitigation measures stipulated in the construction permits issued by the Clark County Department of Air Quality and Environmental Management. Impacts associated with geology, soils and groundwater will be adequately addressed through standard engineering design and construction practices.