RAINBOW CANYON DEBRIS FLOW DIVERSION STRUCTURE Mt
Total Page:16
File Type:pdf, Size:1020Kb
RAINBOW CANYON DEBRIS FLOW DIVERSION STRUCTURE Mt. Charleston, Clark County, Nevada Final Environmental Assessment Prepared by U.S. Army Corps of Engineers Los Angeles District U.S. Forest Service Humboldt-Toiyabe National Forest October 2014 Table of Contents 1.0 INTRODUCTION ................................................................................ 2 1.1 LOCATION ....................................................................................................... 2 1.2 BACKGROUND ................................................................................................. 2 1.3 FEDERAL ACTIONS ........................................................................................... 2 1.4 PUBLIC SPONSOR ............................................................................................ 3 1.5 PURPOSE AND NEED ........................................................................................ 3 2.0 ALTERNATIVES ................................................................................ 4 3.0 AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES ....................................................................................... 6 3.1 LAND USE..................................................................................................... 7 3.2 SOILS AND SUBSTRATE ............................................................................. 8 3.3 WATER QUALITY ....................................................................................... 10 3.4 AIR QUALITY .............................................................................................. 12 3.5 NOISE ......................................................................................................... 16 3.6 BIOLOGICAL RESOURCES ....................................................................... 18 3.7 CULTURAL RESOURCES .......................................................................... 23 3.8 SOCIOECONOMICS AND ENVIRONMENTAL JUSTICE ........................... 26 3.9 RECREATION ............................................................................................. 28 3.10 VISUAL RESOURCES ................................................................................ 30 3.11 TRAFFIC ..................................................................................................... 32 3.12 PUBLIC HEALTH AND SAFETY ................................................................. 34 3.13 HAZARDOUS AND TOXIC WASTES .......................................................... 36 4.0 CUMULATIVE IMPACTS ................................................................. 38 4.1 PAST, PRESENT, AND FORESEEABLE FUTURE ACTIONS .................................... 38 4.2 CUMULATIVE IMPACTS ANALYSIS ..................................................................... 42 5.0 COMPLIANCE WITH APPLICABLE ENVIRONMENTAL LAWS AND REGULATIONS ......................................................................................... 45 6.0 PUBLIC NOTICE AND RESPONSE TO COMMENTS ........................... 46 7.0 LIST OF PREPARERS ...................................................................... 49 2 1.0 INTRODUCTION This Environmental Assessment (EA) has been prepared by the U.S. Army Corps of Engineers (Corps) for the construction of the Rainbow Canyon Debris Flow Diversion Structure Project in compliance with the National Environmental Policy Act (NEPA) (42 USC 4321 et seq.), the Council on Environmental Quality (CEQ) regulations published at 40 CFR Part 1500 et seq., and the Corps’ NEPA regulations published at 33 CFR Part 230. This EA is anticipated to be incorporated by reference into the U.S. Forest Service’s Decision Memo for the Corps’ proposal and the Forest Service’s issuance of a Special Use Permit to the State of Nevada. 1.1 Location The project area is located within Rainbow Canyon, near the town of Mt. Charleston, Clark County, Nevada. The town of Mt. Charleston is comprised of private inholdings within the Spring Mountains National Recreation Area which is administered by the U.S. Forest Service. 1.2 Background The July 2013 Carpenter 1 Fire burned approximately 27,881 acres. Approximately 26,939 acres was located in the Springs Mountains National Recreation Area, including portions of Rainbow Canyon. Fire damage to vegetation weakens soil stability, making it susceptible to debris flows during rain events. Monsoon rains in 2013 and 2014 caused substantial debris flows and erosion that damaged dozens of residences and public infrastructure including Rainbow Canyon Road. The potential for a debris flow during the 2014 winter storm season affecting Rainbow Subdivision is high. As a result, the State of Nevada requested assistance from the Corps to protect life and property from debris flows from fire-damaged areas during the period of fire recovery. 1.3 Federal Actions The State of Nevada requested direct and technical Advance Measures from the Corps on February 27, 2014, pursuant to Public Law 84-99 (PL 84-99), as amended, and codified in 33 United States Code 701n. Pursuant to PL 84-99, Advance Measures consists of those activities performed prior to flooding or flood fighting to protect against loss of life and damages to urban areas and/or public facilities. Advance Measures are considered when requested by the Governor of a state confronted with an immediate threat of unusual flooding. Projects are designed for a specific threat and, unless specifically exempted, are temporary in nature. U.S. Army Corps of Engineers The Corps would provide Advance Measures to the State of Nevada pursuant to PL 84-99. Advance Measures include technical services as well as construction. The Corps would enter into a cooperation agreement (CA) with the Forest Service and the State of Nevada under P.L. 84-99, and would enter into a Support Agreement with the Forest Service pursuant to the Economy Act. Under the agreement the Corps would fund the Forest Service to construct a debris flow diversion structure on Forest Service lands using Forest Service construction crews. The Corps would prescribe interim maintenance requirements for the life of the temporary structure. 2 U.S. Forest Service The Forest Service would enter into an agreement with the Corps pursuant to the Economy Act to construct a debris flow diversion structure as part of Corps Advance Measures authority under PL 84-99. The construction would occur on Forest Service lands using Forest Service construction crews. The Forest Service would also issue a Special Use Permit (SUP) to the State of Nevada for operations, maintenance, and removal of the structure pursuant to Forest Service regulations at 36 CFR 251. The Forest Service is anticipated to prepare a separate Decision Memo, incorporating this EA by reference, in support of its issuance of the SUP. Lead and Cooperating Agency As the agency responsible for planning, engineering, and funding construction of the project, the Corps is the lead NEPA agency pursuant to criteria at 40 CFR 1501.5(c). The Forest Service, the primary permitting federal agency for the project, is the cooperating NEPA agency providing technical assistance in evaluating impacts to cultural, tribal, visual, and biological resources. 1.4 Public Sponsor PL 84-99 provides authorization for federal assistance to the construction of temporary flood fighting measures. Furthermore, all flood fight efforts require a Cooperation Agreement (CA) signed by the Public Sponsor, typically a state or local jurisdiction. The terms and conditions of the CA require the Public Sponsor to operate and maintain the flood fighting structure at no cost to the Corps during its operational life and remove all flood fight material after threats from floods have subsided, or upgrade the work to standards acceptable to the Corps. The state of Nevada is the Public Sponsor assuming all terms and conditions of the CA for the Rainbow Canyon Debris Flow Diversion Project through the following state agencies: Nevada Division of Emergency Management, Nevada Department of Transportation, and Nevada Department of Conservation and Natural Resources. 1.5 Purpose and Need Statement of Need The July, 2013 Carpenter 1 Fire burned approximately 27,881 acres. Approximately 26,939 acres was located in the Springs Mountains National Recreation Area (SMNRA) including portions of Rainbow Canyon. During the 2013 and 2014 monsoon seasons, debris flows damaged dozens of residences and public infrastructure. Storm flows washed out roads, leaving rocks and sediment on the roadways. Roadways including Rainbow Canyon Road, the primary access road into Rainbow Canyon, were rendered unusable. Water, mud, and debris entered a number of residential structures. The potential for additional debris flow during the winter storm season affecting Rainbow Subdivision remains high. During the period of recovery from fire damage, debris flows from weather events will continue to pose an imminent threat to homes and critical infrastructure with unusual flooding unless action is taken. 3 Statement of Purpose The purpose of the project is to protect the residential subdivision within Rainbow Canyon downstream of Forest Service land prior to the onset of winter storm season, from debris flows during the period of recovery from the Carpenter Fire. 2.0 ALTERNATIVES Alternatives Considered But Not Carried Forward Debris Basin A debris basin would be excavated within Rainbow Canyon up gradient of all residences. However, there is not sufficient available land to construct a debris basin large enough to