Great gardeners and landscape architects have always planned and planted for the benefit of future generations, seldom living to see the full fruits of their visions. Miners are in similar positions; they are obliged to restore the landscapes they labor in, for the ultimate benefit of flora, fauna, and their children's children.
Land reclamation and revegetation at Boron
At the U.S. Borax mine in Boron, California, the problems of reclamation are both practical and creative. How do you deal with tons and tons of overburden each working day, and how do you emulate mother nature convincingly in such apparently arid surroundings as the Mojave Desert?
Add to this a commitment to minimizing the impact of present-day operations and implementation of the environmental policies of our parent company, Rio Tinto—a code which in most respects is more stringent than either state or federal law requires—and it all amounts to a formidable ongoing challenge. Environmental reclamation is one of the costs of a continuing supply of high quality industrial minerals. And the solutions to this challenge are of vital interest to borate users all over the world.
In the 1990s, charge of the land reclamation project at Boron was given to U.S. Borax senior geologist Joe Siefke. The assignment also made him the mine's head gardener in the high desert. The soil he worked with most was Boron's overburden—the sands, silt, and clay that have to be removed before the borate ores can be extracted. That overburden results in millions of tons of garden potential per year.
The Mojave Desert is by no means a barren, lifeless wilderness; it is a complex ecosystem to which dozens of plant species have adapted. These are species that can thrive in intense heat, recurrent drought, sub-zero winters, and an evaporation/precipitation ratio of 25 to one. The creosote bush and desert saltbush scrub groups are among the most numerous perennial plant species growing today in the western Mojave Desert. There is archaeological evidence that some of the creosote bush shrubs growing in rings at Boron are the direct descendants of shrubs which were growing there 10,000 years ago.
In 1991, Siefke began the reclamation project by taking baseline measurements of undisturbed land at the site. On 200 plots of 100 square meters each, he and his team of consultants measured the number of plants and the number of species per plot. This data provides the yardstick for transforming huge banks of overburden into natural terrain.
The next step was to plant a number of gardens to act as laboratories for discovering optimum seed mixtures, planting techniques, and slopes. When the overburden is dumped outside the ultimate perimeter of the mine, it comes to rest at an angle of about 36 degrees. This was found to be much too steep and therefore vulnerable to erosion. Angles of up to 18 degrees, achieved by using bulldozers, proved viable.
Plowing furrows along the contour of the slope (a form of terracing) also helps to prevent erosion and 'harvest' the meager supply of water. Rain accumulates in the furrows so that it lasts longer and brings maximum benefit to the plants. Siefke's horticultural labs also revealed that, unlike in normal gardening, a rough, rocky surface makes a better nursery in this environment than a smooth seedbed or fine tilth. This is because rocky lumps offer very young plants both shade from the sun and protection from the desert winds.
Ongoing experimentation and partnerships in reclamation
Seed experiments began with several varieties of saltbush. Assisted by Jim Gude (Boron's training officer who also lectured in biology at a nearby community college), Siefke harvested local species by whacking the saltbushes with a tennis racquet and catching the seeds in a burlap bag. These local seeds germinated and grew significantly better than seeds purchased from professional seed suppliers. Some of Gude's students became skilled and enthusiastic seed gatherers. Comstock Seed of Reno collected seed from locations on and around the 22,000-acre U.S. Borax property, and from nearby native plant locales. Comstock then made the seed available to U.S. Borax on a share-the-harvest basis or at nominal cost.
In 1994, another major experiment was conducted, involving 32 test plots and twelve different indigenous species. Half the plots were predominantly loam, the other half were predominantly sand and silt. Soils originated from different levels of the open pit and their fertility was compared with that of the natural desert floor. It was discovered that overburden taken from more than 200 feet below surface level supports plant life better than desert topsoil. Research on growth-medium characteristics continues, with the object of establishing the best possible final surfaces for the future wildlife habitat.
Subsequent experiments involving different seed recipes suggested that the standard seed mix of twelve pounds per acre might be wasteful and perhaps counter-productive. All planting is now done by a machine that prepares the soil surface, plants a mixture of native seeds, then covers the seeds all in a single operation—one-pass farming. Sowing is normally carried out at the beginning of November, the onset of the rainy season.
Irrigation is taboo in the Mojave since the plants obviously have to be able to survive in ordinary desert conditions without help from man. Sometimes, however, very young plants have been given a little 'drought assistance' to get them off to a healthy start. Siefke reckoned that the ideal natural start for most species is two wetter-than-average winters in succession. Statistically there is nearly a 15% chance of this happening—in fact it has occurred seven times over the last half century.
The irrigation ban also applies to fertilizers and micronutrients, and for much the same reason. Every plant must be self-sustaining, as in the wild. One thing is reasonably certain: There is no real likelihood of boron deficiency in the local soil.
One of the most interesting experiments at Boron is the macro imprint test area. Here overburden loads of about 190 tons each are clumped back to back to give a level but broken surface at the top of the dumps. With recesses up to five feet deep, the broken surface is perfect for erosion control, water harvesting, and natural germination by seeds such as saltbush and pepper grass, blown in on the desert winds.
After years of leveling, planting, experimentation and research, parts of the Boron habitat already take us back to the future and forward to the past. But with the mine's estimated life of more than 40 years, Joe Siefke and his team will only be able to enjoy the full fruits of their current endeavors if they break several world records for longevity.