|
|
|
Feature
Article November/December 2000
|
|
You
may print one copy of this page for personal use. Please report any
other use to FORESTER COMMUNICATIONS, INC., using the online form at
http://216.55.25.242/crv_report.html
|
|
More than 47,000 ac. in the mountainous terrain around the Los Alamos National Laboratory burned in a few days. Potential flood damage - and the possibility of radiologically and chemically contaminated material washing away from areas that were once used for nuclear testing - could have been more devastating than the fire itself. By Steve Veenis Cerro
Grande Fire Aftermath Late in the evening of May 4, 2000, National Park Service fire personnel at Bandelier National Monument near Los Alamos, NM, ignited a prescribed fire with an approved plan. Firing and line control occurred during the early morning of May 5. Sporadic wind changes caused the spread of some spot fires within the contained area on the upper eastern fire line. Because of these spot fires, the prescribed fire was declared a wildfire during the afternoon of May 5. On May 7, winds increased significantly from the west, resulting in major fire activity and ultimately causing the fire to move out of control to the east in the Santa Fe National Forest. In its most extreme state on May 10, the Cerro Grande prescribed fire was carried by very high winds, with embers blowing a mile or more across the fire lines to the north, south, and east, entering Los Alamos Canyon toward Los Alamos. The towns of Los Alamos and White Rock were in the fire’s path, and more than 18,000 residents were evacuated. By the end of the day on May 10, the fire burned 18,000 ac., destroying 235 homes and damaging many other structures. The fire also spread toward the Los Alamos National Laboratory (LANL), and although fires moved onto the laboratory’s lands, all major structures were secured and no releases of radiation occurred. The fire also burned other private lands and portions of San Ildefonso Pueblo and Santa Clara Pueblo. The total area burned during this catastrophe was 47,650 ac. Many residents of Los Alamos were allowed to return to their homes on May 18, after being displaced for more than a week. The damage was substantial to the western and northern portions of town, and the community was in shock. Most of the residents had never experienced a disaster of this magnitude, and the amount of work to clean up, rehabilitate, and stabilize what remained was staggering. The incredible effort to complete these tasks was performed in concert with several local, state, and federal government agencies. A burned-area emergency rehabilitation (BAER) team was tasked with helping the community address the severe impact to the Santa Fe National Forest directly west of Los Alamos. A Forest Service - led BAER team immediately began assessments of the surrounding Forest Service land and began collaborating with the laboratory to coordinate rehabilitation and flood mitigation. LANL focused on laboratory assessments and protective actions while the BAER team focused on mitigation activities on Forest Service land. An unprecedented local volunteer effort also played a key role in completing rehabilitation work within the Los Alamos town site. At first, only a few people were allowed on-site to begin the assessment of the damage to laboratory property. The buildings, infrastructure, and potentially contaminated sites had to be assessed for health and safety risks, burn severity, and erosion. Soon thereafter, an emergency rehabilitation team was established to address the impacts within the laboratory’s 43-mi.2 boundary. It is important to realize that when a fire destroys a large portion of land within a mountain setting, the flood damage potential is great. The Cerro Grande fire occurred one month before the seasonal monsoons in northern New Mexico; therefore, the urgency of installing appropriate run-on and runoff controls within the National Forest and LANL has been very high. The United States Army Corps of Engineers has played a large role in helping address the potential flood problems by installing several retention structures, weirs, and other flood control devices. Formed after major fires to assess damage and implement a rehabilitation plan, BAER teams consist of highly skilled specialists from across the nation: wildlife biologists, archaeologists, soil scientists, landscape architects, geologists, ecologists, engineers, foresters, botanists, geographic information system and global positioning system (GPS) specialists, and people from other disciplines. The rehabilitation plan’s goal is to prevent loss of life and property and reduce further damage to natural resources.
A multiagency team was formed to begin emergency rehabilitation for the Cerro Grande fire. The BAER team arrived on Monday, May 15, and began a preliminary assessment of the fire area. Team members include personnel from the US Forest Service, Bureau of Land Management, National Park Service, US Geological Survey, and LANL. The Multi-Agency Coordination (MAC) team, also formed on May 15, included representatives from all the landowner agencies and acted as the umbrella organization during the assessment and rehabilitation. The goal of the MAC is to provide interagency communications and minimize red tape. After performing an assessment to evaluate the overall severity of the burn, the BAER team initiated short-term rehabilitation measures. The team’s focus is the potential for accelerated erosion and runoff from loss of vegetation and charred soils. "One thing we look at is the hydrophobicity of the burned soils, the way water can be repelled by the soil," explains Judy Hallisey, a forest hydrologist with the Forest Service. "We’re concerned with the potential for flooding from rains and how that will impact infrastructure, roads, and sediment transport, among other things." Hydrophobicity can result from burning litter (organic matter such as leaves and needles), which contains lignin and other waxy compounds that vaporize. After the heat diminishes and the soil cools, the gases from the waxy compounds recondense, forming waxy coatings on soil particles. These coatings create hydrophobic conditions in which water absorption into the soil is greatly diminished. Soil scientists and hydrologists toured the burn area from the air and conducted a digital color infrared study to develop burn-severity maps. Preliminary review of the Los Alamos and White Rock areas indicated that road drainage culverts were inadequate to handle runoff anticipated from the burn area. The BAER team recommended a variety of rehabilitation techniques, including reseeding of ground cover, constructing straw bale dams for small streams, placing fallen trees to catch sediments on steep slopes, and digging below-grade pits to catch runoff and sediment. The team also assessed the need to modify drainage structures by installing debris traps, enlarging culverts, and installing standup inlet pipes to allow drainage to flow if culverts become plugged; adding extra culverts; and constructing emergency spillways to keep roads from washing out during floods.
In a continuation of the BAER effort, hydromulching and hydroseeding were carried out on 1,600 ac. of the burned area to reduce erosion and speed revegetation. The hydromulch - a mixture of water, mulch, fertilizer, seed, and tackifier - was applied to hillsides with a grade of 60% or more. About 300 ac. of LANL land, as well as National Forest and Santa Clara Pueblo lands, were covered. Two companies, Western States Reclamation of Broomfield, CO, and the local Aero Tech Inc., flew about 200 flights each day - approximately 7,000 flights in all through July - from the Los Alamos Airport, applying nearly 2,000 lb./ac. of hydromulch. The single-engine, fixed-wing Air Tractors used were designed for crop dusting but can also be used to drop pesticides, fire retardant, hydromulch, and seed. Each plane carries about 800 gal. of mulch weighing 7,000-8,000 lb. Water and mixing tanks were set up at the airport, where ground crews required one minute to load and fuel an air tanker. With an average of nine minutes’ flying time and a one-minute taxi at both takeoff and landing, each run took about 12 minutes. The pilots traveled at 200 mph to the drop point and released the mixture at about 115 mph from an altitude of 100 ft. Each drop path was about 27 ft. wide. A satellite lock system on each aircraft used GPS to track the flight path and location. The National Park Service administered the contract for this multiagency effort, with funding from the Forest Service, Department of Energy, and Bureau of Indian Affairs.
After the early formation of a rehabilitation steering team and five focus teams, Laboratory Director John Browne announced on June 2 the establishment of a laboratory Emergency Rehabilitation Team (ERT). The ERT directed an aggressive program to address potential impacts of increased runoff resulting from the Cerro Grande fire and to look at potential long-term issues arising from the fire. The three primary goals of the ERT are to protect human life, minimize the movement of contamination off laboratory property, and protect laboratory facilities and infrastructure. To achieve these goals, LANL took actions that will prevent water from rushing down the canyons and (where possible) prevent significant erosion. Advice From Outside Experts In addition to the BAER team, LANL has been closely consulting with outside experts to determine the best way to approach this problem. In particular, the Army Corps of Engineers has studied the watersheds and the land and is recommending engineering solutions to slow down the flow of water to protect facilities and infrastructure and to minimize the potential for the movement of contaminated sediments downstream. Measures recommended by the corps are described below. Division Efforts LANL’s Facility & Waste Operations Division is responsible for overall management of the fire rehabilitation effort within the laboratory. Groups within the Environmental, Safety & Health Division supported the implementation of rehabilitation efforts. Table 1 details the treatments performed to date within LANL. Table 1. Treatment Details (approximate values)
*Note: The acreage listed above is per unit treated. Several of the units required a combination of treatments. Aerial seeding and handseeding were done using the BAER seed mix. This mix includes both annual and perennial seed (30% annual rye grass, 30% mountain brome, 30% slender wheatgrass, and 10% barley). Aerial hydromulching was completed on LANL property along specified canyon walls in Pajarito and Water Canyons and on areas that were steep and inaccessible by road. Land hydromulching was done on ground that was steep but had easy road access. The land treatment done by the rehabilitation crews included removal of hazard trees, contour falling, contour raking, seeding, straw mulching, placing straw wattles on contour (20-ft. biodegradable mesh tubes filled with straw), and building log structures and rock check dams. The mulch (hydromulch or straw mulch) is used to cover the raked and seeded areas to provide a place for seed germination. Land rehabilitation treatment, such as tree felling, raking, wattle placement, and constructing log structures and rock check dams, are all done on the contour to decrease erosion caused by water runoff. As described in the BAER Technical Reference Guide for the Cerro Grand Fire, the treatments were as follows.
Seeding. Rehabilitation crews applied BAER seed mix using handseeders set to apply seed at a rate of 35 lb./ac. Contour Raking. Contour raking was performed to increase precipitation infiltration rates on hydrophobic soils. Straw Mulching. Straw mulch was applied where the fire consumed the preburn ground cover and the expected overland runoff would threaten areas at risk. First-year effectiveness includes stabilizing ashes on-site, preventing loss of topsoil, improving infiltration rate, and replacing organic litter consumed by the fire. Burn areas are usually flood source areas, and therefore mulching has a secondary benefit of controlling flood peaks to an acceptable level. Straw Wattles. Straw wattles were placed on slopes to act as terraces to prevent slope erosion and facilitate revegetation. Straw wattles act as grade control structures in stream channels with flatter gradients and finer streambed materials or in streams with uneven bottoms. Log Structures and Rock Check Dams. These structures were used as stream-channel control structures. Their purpose is to reduce water velocity, thereby reducing the in-channel erosive force to prevent downcutting and capture sediment of the streamflow. Contour Tree Felling. Contour tree felling was done on two types of slope conditions. The first was moderately sloping to steep slopes that have hydrophobic soil conditions (moderate- to high-burn severity) and where there are few downed trees or surface rock to protect soil surface. Theses sites must also have adequate standing tree size (6-14 in. diameter at breast height) and an adequate number of trees (30-40) per acre. The second condition was steep to very steep slopes where erodible soils occur, few downed trees are present, an adequate number and size of standing trees are present, and safety concerns make minimizing the number of personnel on the slope a priority. Environmental Restoration Project Activities to Reduce Potential Movement of Contamination Established in 1989 as part of a Department of Energy nationwide program, the LANL Environmental Restoration Project is designed to find out if hazardous chemical and/or radioactive wastes are present as a result of past LANL operations. Sites where such materials are still found and that require remediation are being cleaned up to protect public health and the environment, in accordance with the requirements of LANL’s Hazardous Waste Facility Permit. In general, the contaminants found in potential release sites were deposited during the 1940s and ’50s. Over the course of the last 50 years, soil and other materials have been deposited on top of the contaminants, putting them at least 12-18 in. below the surface at most of the sites. Initial reports indicate that the fire burned only the top 3 in. of the ground in most places. Thus, it may be unlikely that contaminants would have been released from most sites that were burned.
The majority of the sites have been evaluated, and a large percentage was found to contain no contamination or insignificant quantities of chemical or radioactive contamination. The sites are called potential release sites, or PRSs, because they might or might not contain contamination. After the fire, New Mexico Environment Department and LANL crews evaluated all PRSs located in the burned area and determined that 315 PRSs had been touched by flame. The joint crews then evaluated the 315 sites to determine which ones needed erosion control best management practices (BMPs). Previously completed surface-water site assessments were reviewed to assess the pre-fire erosion potential of each of these PRSs (see "Ranking Sites’ Erosion Potential at Los Alamos National Laboratory" in the April 2000 issue of Erosion Control for details of the assessments). Of the 315 PRSs affected by the fire, 91 were recommended for BMPs. LANL field teams have completed the placement of BMPs at the 91 PRSs. BMPs include the protective jute matting, hand reseeding, rock check dams, log silt barriers, and straw wattles, as well as other actions to control runoff and erosion. The issue with these sites is not the fire but the aftermath of the fire. Soil and sediment will be displaced when rains begin to wash down the canyons. Soil erosion experts predict much heavier runoff in the canyons than before the fire because of the inability of soil and vegetation on the hillsides to absorb rainwater runoff and to slow its course into and through the canyons as they normally would. Rainwater runoff can displace these contaminated soils and sediments and transport them down the canyons and, potentially, off LANL property. LANL scientists are working together with the Forest Service to evaluate this situation and are now planning work to minimize the impacts of the expected floods before the beginning of the summer monsoons.
One of the missions of the Army Corps of Engineers is to provide assistance when natural disasters or other emergencies occur. Although emergency preparedness and response is primarily a state and local responsibility, when a disaster or emergency exceeds local capabilities, the Army Corps of Engineers may provide help to save human life, prevent immediate human suffering, or mitigate property damage. The following flood control projects are being completed by the Army Corps of Engineers within Los Alamos County. Low-Head Filter Weir. Construction of a low-head weir in Los Alamos Canyon will retain sediment during high water flows. Retention Dam. A roller constructed concrete flood-retention structure is being installed in Pajarito Canyon. One 42-in. culvert will extend through the base of the structure at the streambed, and outflow will be restricted to less than 400 cfs. Emergency Road Hardening. Hardening embankments with shotcrete will protect the Highway 501 crossing of Water, Two-Mile, and Pajarito Canyons. Los Alamos Reservoir Drainage. The existing Los Alamos Canyon Reservoir was drained to accommodate the expected large volumes of runoff, ash, and debris from the upper watershed. The dam embankment has been hard armored. Diamond Drive Crossing. A 432-ft.-long, 86-in.-wide steel-pipe culvert was installed through the existing embankment to protect the Diamond Drive crossing of Pueblo Canyon. When Will the Forest Come Back? With over 47,000 ac. destroyed by the Cerro Grande fire, many wonder if or when the forest will come back. Earlier fires in the area provide some clues to how the burned area will recover, although the heat of the fires and the actions taken afterward determine the current state of the sites. Fire is a natural process that can benefit an ecosystem by clearing out undergrowth and thinning saplings. In the dry Southwest, where plant material decomposes slowly, fire can also speed up the return to the soil of nutrients trapped in wood and other organic matter. Fire-suppression efforts and other human activity during the last century, however, have resulted in very dense areas of forest. For example, grazing removes the grass that periodically would have burned and cleared out areas of forest. Grass also competes with young seedlings, so removing the grass through grazing allows more seedlings to mature and denser stands of trees to grow. With such concentrated fuel sources available, portions of the Cerro Grande fire burned with devastating heat and will require seeding to spur regrowth. In other places the fire was less intense, more like a naturally occurring fire or a controlled burn. The sites of three fires in the Jemez Mountains - the La Mesa fire in 1977, the Dome fire in 1996, and the Oso fire in 1998 - are in various stages of recovery. Like the Cerro Grande fire, all occurred in areas dominated by ponderosa pine. Large ponderosas, with their platelike bark, can sometimes survive small fires if the fire does not burn hot enough to destroy the root system. The roots of the Gambel oak often survive a fire as well, and the oak can sprout back within a few weeks with or without rain. Grasses often spring up with the first rain. New ponderosas grow only a few inches in their first few years, developing more taproot than aboveground growth. By 10-15 years, however, the trees can grow as much as 2 ft./yr. The La Mesa fire, which burned more than 15,000 ac. of ponderosa pine forest, today has stands of ponderosa pine as high as 15 ft., with grassland in between. Two years after the Oso fire, that 5,000-ac. site now contains a mixture of herbaceous grasses and small shrubs. Reseeding took place over much of the 16,000 ac. hit by the hotter-burning Dome fire, and today the area contains grassland with brushy oaks and aspen groves. Seeds can take years to germinate in hydrophobic soils, although after the Dome fire, germination took place in about six months. The Cerro Grande fire was the largest and most destructive in New Mexico history. The devastation to the community, forest, and laboratory will not soon be forgotten. But there is a cause for optimism: the massive rehabilitation effort by volunteers; local, state, and federal government agencies; and LANL took place before any substantial flooding occurred. There might be additional setbacks along the way to recovery, but the community is beginning a long healing process. Although it is impossible to mention everyone who contributed to the Cerro Grande fire rehabilitation, the individuals, contractors, and supporting agencies involved deserve special thanks for their efforts. Web Sites With More Information on the Cerro Grande Fire http://www.baerteam.org/cerrogrande/ Steve Veenis, CPESC, is a technical staff member with the Water Quality and Hydrology Group at Los Alamos National Laboratory in Los Alamos, NM.
MSW Management Magazine | Stormwater Magazine Forester Communications | E-mail Us
|
|
|
|
