Highway 21 Avalanche Control
Environmental Assessment
Lowman Ranger District
BoiseNational Forest
7359 Highway 21
Lowman, ID83637
October 2006
Figure 1. Snow removal equipment behind avalanche deposit on State Highway 21
1. What is the Purpose of this Environmental Assessment and How is it Organized?
This Environmental Assessment (EA) discloses the effects of a proposal by the Idaho Transportation Department (ITD) to conduct avalanche control activities on National Forest System (NFS) lands. The EA has been prepared pursuant to the requirements of the National Environmental Policy Act (NEPA, 40 CFR 1500-1508), the National Forest Management Act (NFMA implementing regulations of 2005, including transition language at 36 CFR 219.14), and the 2003 Boise National Forest Land and Resource Management Plan (Forest Plan).
The EA first describes the proposed action, and its purpose and location. The EA then discusses the decisions to be made, and the public involvement undertaken. Alternatives to the proposal are then described, followed by a discussion of the effects of the proposal and a “no action” alternative. The EA concludes with a “consultation and coordination” section, which lists those involved in development of this EA, as well as Federal, State, and local agencies, tribes, organizations and citizens consulted during the planning process, and a list of literature citations.
This document is tiered to the FEIS and planning record supporting the 2003 revised Forest Plan, including documentation related to the Continuous Assessment and Planning (CAP) process described in Chapters III and IV of the Forest Plan. This documentation includes monitoring reports. Documented analyses in the Forest Plan FEIS have been referenced rather than repeated in some instances. Analyzes pertaining to the FEIS for the 2003 Forest Plan are contained in the Forest Planning record located at the Forest Supervisor's Office in Boise.
Detailed information that supports the analyses presented in this document, unless specifically noted otherwise, is contained in the project planning record located at the Lowman Ranger District office.
2. What is the Proposed Action?
ITDis proposing to conduct avalanche control in the Canyon Creek drainage, Lowman Ranger District (District), BoiseNational Forest. The 6,350-acreproject area lies within BoiseCounty along Highway 21 (SH-21) from mileposts 94 to 105, approximately 22 miles east of Lowman, Idaho(Figure 1). ITD has applied for a 10-year special-use permit (SUP) to conduct the proposed activities on NFS lands. The proposed action as described herein constitutes the Proposed Action Alternative.
ITD is proposing to implement avalanche control measures recommended by Chris Stethem and Associates Ltd., a company specializing in mitigating avalanche hazards on transportation systems. Stethemand Associates completed an evaluation on potential avalanche mitigation procedures within the project area. The proposed avalanche mitigation methods include utilizing explosives, storing explosives, and constructing a small remote weather station. It is expected that three to six control missions affecting up to17avalanche paths per mission would be required in a typical season. However, 15 missions could be undertaken annually between November and April due to the yearly variability of winter snow packs.
Use of Explosives - Three procedures utilizing explosives would be implemented for avalanche control, targeted primarily at four areas (referenced by mileposts) due to their high rating on the avalanche hazard index. The primarytarget areas include 17avalanche paths, all west of SH-21, at mileposts 97, 99, 100, and 104. These avalanche paths total 231 acres (4 percent) of the project area. In addition, there are 51 avalanche paths, totaling 1155 acres (18 percent) of the project area, that comprise a secondary target area, and that could be treated when these avalanche paths are expected to endanger highway travel. In the remainder of the project area, no active avalanche paths have been detected, and no control procedures would be planned (Table 1).However, in the unlikely event that these areas begin to produce avalanche activity, they too could be treated with explosives.
Figure 1.
Helicopter Operations: For 12 avalanche paths west of the highway near mileposts 99 and 100, a helicopter would deliver and drop explosives to avalanche start zones. This control method would also be used as needed on the secondary target areas. The use of a helicopter is necessary due to the remote nature of avalanche starting zones for these avalanche paths. Although helicopter operations are scheduled to last approximately 45 minutes per mission, actual flight time would be less than 45 minutes due to refueling, loading ordnance, and other operational considerations. Implementing an average of five helicopter control missions annually would reduce closure periods by an estimated 50 percent, with more effectiveness realized as the crew improves operational efficiency in subsequent years. Helicopters would not land in the RedMountain or HansonLakes areas identified as recommended wilderness in the Forest Plan.
Avalauncher: An avalauncher cannon, which uses compressed nitrogen to propel explosive charges, would fire pentolite rounds to trigger avalanches in three active slide paths west of the highway. The avalauncher would be located in a pullout at milepost 97; it would be transported to and from the site for each operation for security purposes. These paths are frequently the first to slide in the winter and are some of the few paths in which avalanches will reach the road in a light snow year. Additionally, the threat of avalanches at this site alone is often responsible for a full closure of the highway. The avalauncher would allow ITD personnel to trigger avalanches in this specific area when the remainder of the highway is safe for vehicle travel. It is expected that 3-6 operations would be required annually. The effective useof an avalauncher at milepost 97 would reduce the hazard on this section of road by 86 percent (Stethem, 2004).
Hand Placed Charges: Cut banks directly adjacent to SH-21, specifically near milepost 104, regularly produce slab avalanche activity. Potential avalanches in this area would be mitigated by hand placing pentolite charges. Charges can be hand placedat these locations due to the close proximity of these slide paths to the highway. The threat of avalanches near milepost 104 in November and December is often responsible for a full closure on the highway, even when the remainder of the snow pack is stable. Effective mitigation at this site would reduce the hazard for this section of road by 70 percent (Stethem, 2004).
Target / Avalanche Paths / Acres / % of Project Area / Control MethodPrimary / 17 / 231 / 4 / Helicopter, hand charge, avalauncher
Secondary / 51 / 1155 / 18 / Helicopter
Non Target Areas / 0
(no active paths noted) / 4964 / 78 / None planned
Table 1. Targets for avalanche control.
Storage of Explosives - ITD intends to maintain up to 400 pounds of explosives including ammonium nitrate, pentolite, and blasting caps. Explosives would be stored in a portable 4’x5’x7’ prefabricated ‘magazine’ that meets current Bureau of Alcohol, Tobacco, and Firearms (ATF) security and safety guidelines, thereby allowing for a high level of safety and security for explosive materials. ITD does not intend to store explosives on National Forest System lands. However, ITD has requested a backup storage site for explosives at the Lowman Ranger Station Administrative site in the event that this site is needed in the future. In order for this site to be utilized, the District will apply the first and second level special uses screening criteria which include insuring that National Forest System lands are the only feasible location for storage of explosives when/if requested by ITD.
Install Weather Station – A remote activated weather station would be installed on a ridge top west of milepost 96 on SH-21, outside the HansonLakes and RedMountain recommended wilderness. The station wouldcomplement two existing stations at higher elevations and allow ITD personnel to improve avalanche forecasting for the avalanche paths that frequently run in the lower part of the canyon. The small weather station unit includes a 20-foot tower, 5’x5’x 4’ metal box, solar panels, and requisite instrumentation and electronics. All weather station equipment would be delivered to the site via helicopter.
Design Features, Mitigation Measures, and Monitoring
The proposed action will incorporate the following design features, mitigation measures, and monitoring intended to reduce or minimize the potential effects of the proposal:
Any unexploded charges would be noted with Global Positioning System coordinates for later retrieval and reported immediately to the District permit administrator. All reasonable attempts will be made to retrieve any unexploded charges in coordination with the District permit administrator.
Ammonium nitrate charges (ANFO) will be prepackaged on non-National Forest System lands.
ANFO will not be detonated in Riparian Conservation Areas (RCAs).
All pentolite boosters will be double capped to insure detonation.
Pentolite charges are inoculated with a microbial agent to break down the nitrate compounds in the unlikely event of unexploded and irretrievable ordnance.
Storage of fuels and other toxicants or refueling within RCAs will not be authorized unless there are no other alternatives. Storage of fuels and other toxicants or refueling sites within RCAs shall be approved by the responsible official and have an approved spill containment plan commensurate with the amount of fuel.
To protect fish from swimbladder effects and egg disturbances, the maximum charge weight of any hand-placed charges near Canyon Creek will conform to the following table (from Wright and Hopky 1998):
Explosive Charge Weight (pounds)Distance from stream (feet)
0.5 30
1.0 50
2.0 80
5.0120
10.0170
25.0270
100.0530
A reconnaissance flight will be made prior to helicopter operations to determine whether forest carnivores (wolverine, fisher, lynx, and wolves) or mountain goats are present in the vicinity of control actions. Avalanches will not be triggered in areas where these species are observed and would be caught in snow and debris flows. Potential sightings of wolverine, fisher, lynx, or mountain goats should be reported to the Forest Service the same day of observation, so that a biologist has the option of verifying the sighting and monitoring.
The Lowman Ranger District will monitor all activities during the duration of the permit, and insure project activities meet the aforementioned mitigations as well as Forest Service standards for using, storing, and transporting explosives and helicopter operations.
3. Why Has the Project Been Proposed? (Purpose and Need)
The project area lies in Canyon Creek along SH-21 between the Grandjean turnoff and Banner Summit. The area is generally characterized by steep terrain, closely spaced avalanche paths, and a deep winter snow pack. These characteristics are the primary contributors for the ‘very high’ rating on the Avalanche Hazard Index for SH-21 in the project area. Although the threat of avalanches is not always imminent, SH-21 is frequently closed when avalanche danger increases due to snowfall, rain-on-snow events, or rapid warming during the spring. These closures can last from several days to over a month while the avalanche danger subsides and snow and avalanche debris are cleared from the roadway. During these closures the primary transportation route between the Stanley, Challis, and Salmon region and the Boise metropolitan area is no longer available and motorists must use lengthy alternate routes or postpone traveling.
Over the past twenty years, ITD has utilized severalstrategies for managing the 68 avalanche paths that affect the eleven-mile section of SH-21 in the project area. The original management for this section of highway, which opened in 1964, began as a full winter closure period. However, in 1986, ITD developed a policy mandating SH-21 remain open throughout the winter season. Since that time, ITD has instituted a passive avalanche mitigation program through weather observations, avalanche forecasting, and road closures to insure the safety of the traveling public and ITD maintenance personnel. Although this approach is successful from a passive management standpoint, it still leads to frequent and lengthy closure periods. Additionally, it does not sufficiently meet the intent of the ITD policy to keep SH-21 open through the winter months.
ITD began evaluating proactive avalanche mitigation measures in 2004 due to increasing public demand and the recognition that the economic stability of rural communities depends on reliable access via SH-21. In the fall of 2004, ITD contracted Chris Stethem and Associates Ltd., acompany noted for its expertise in highway avalanche mitigation, to review ITD’s current program and propose feasible active avalanche mitigation measures.
The purpose of this project is to safely maintain access on SH-21 in the Canyon Creek drainage throughout the winter season. ITD has identified several reasons to transition their avalanche program from a passive to an active model. The current passive model lacks a consistent means to safely sustain access on the highway. The following elements support the need for an active approach to avalanche mitigation:
Safety – The current passive method of avalanche mitigation does not provide a consistent means to safely maintain access on SH-21. Implementing an active mitigation program would increase safety to the traveling public and ITD maintenance personnel by remotely triggering avalanches. Thiswould reduce the avalanche danger by removing unstable snow in avalanche zones above the highway and, subsequently, decrease the threat of large destructive avalanches.
Regional Transportation – SH- 21 is an important regional link between the Boise metropolitan area and small communities north and west of the project area. When the highway is closed, sometimes for several consecutive weeks, there are negative impacts to regional commerce as well as access to medical services and recreation areas. Motorists must use lengthy alternative routes or postpone their travel. Regional transportation and commerce along this route would be sustained by increasing safety along this route and by decreasing the frequency and duration of road closures from the current average of 60 total days to 30 total days in a typical winter season. Therewould still be periods when closures are the best method to safely protect the public until storms move beyond the project area and crews can mitigate the current hazards.
Protection of Highway Infrastructure – Currently, avalanche debris creates damage to the highway, highway apparatus, equipment, vegetation, and the surrounding terrain. An active approach to avalanche mitigation would reduce the volumes of snow that accumulate and subsequently descend in the form of avalanches, and would minimize much of this damage.
The 2003 Land and Resource Management Plan for the BoiseNational Forest (Forest Plan) contains direction for Management Area 10 – UpperSouthForkPayetteRiver, which encompasses the project area (Forest Plan, pp. III-202 through III-215). This proposed project is tiered to the Forest Plan and is consistent with standards and guidelines provided in the plan. Specific direction for Management Area 10 includes guideline 1073 which states that the Forest Service will:
“Cooperate with Idaho Transportation Department to keep Highway 21 open year-round north of Lowman, and to maintain Highway 21 corridor (e.g. waste sites, road maintenance, hazard tree removal, etc.). Continue to cooperate with the Transportation Department for avalanche detection and control within recommended wilderness areas.” (Forest Plan, p.III-215)
The Upper Lowman Landscape Assessment, completed in May 2004 and included in the project record,identified the winter management of Highway 21 as an issue that should be collaboratively resolved by the Forest Service and ITD. Some respondents to the public survey portion of the assessment wanted more intensive winter management to reduce road closure periods.
4. Where Would the Proposed Project Be Located?
The project area lies within BoiseCounty along Highway 21 (SH-21) from mileposts 94 to 105, approximately 22 miles east of Lowman, Idaho. The project is located in two 6th HUCs (hydrologic unit codes), Upper Canyon Creek and Lower Canyon Creek, which together make up the Canyon Creek 5th HUC. The legal location of the project area includes: T10N, R10E, Sections 1, 2, 10, 11, 14, 15, 16, 21, 22, and 23; T11N, R10E, Sections 11, 12, 13, 14, 22, 23, 24, 25, 26, 35 and 36; and T11N, R11E, Section 33; Boise Meridian.
5. What Decisions Are to Be Made?
Based on the analysis documented in this EA, the Forest Supervisor will make decisions on this project, documented in a Decision Notice/Finding of No Significant Impact (FONSI). The decisions to be made include:
- Should a 10-year special use permit to implement avalanche control measures on National Forest System land be granted to ITD, and if so,
- Should the Boise National Forest consider a backup storage site for explosives as part of the special use permit on National Forest System land if no other alternative sites are available, and
- What design features, mitigation measures, and/or monitoring should be applied to the project?
6. What Public Involvement was Undertaken and What Major Issues were Identified?
Public involvement was undertaken throughout the analysis process. Scoping was initiated for this project on September 7, 2005. Approximately 140 letters were sent out to individuals, organizations, agencies, and local governments. Individual scoping packages were also forwarded to the Shoshone-Paiute, Shoshone-Bannock and Nez Perce tribes in September 2005.
Additionally, a press release was issued on September 13, 2005, and articles describing the project were published in the Idaho Statesman and Idaho World newspapers. The project has also been included in the quarterly Schedule of Proposed Actions (SOPA) sinceApril2005. Thirteen responses were received from the scoping process. Nearly all respondents expressed support for the proposal; other respondents noted concerns for safety, as well as for potential effects on recommended wilderness and wildlife.
Based on comments received during scoping, as well as input from Forest Service resource specialists, and review of the Forest Plan, comments were evaluated against the following criteria to determine whether or not the concern would be a major factor in the analysis process: