The Project
In 2000, the Los Angeles Department of Water and Power (LADWP) was mandated to mitigate the health hazard created by dust storms across the 285 square kilometer dry lake bed know as Owens (Dry) Lake in Southern California, USA. This lake is considered the site of one of the worst PM-10 (10 microns diameter particle matter) airborne dust sites in North America.
The Challenge
At the as Owens (Dry) Lake in Southern California, USA, wind gusts over 30km/hr lifted over 50 tons per second of dust fog off the lakebed. Sometimes reaching over 3km high, these dust storms sent 130 times the United States Environmental Protection Agency's (EPA) limit for particulate matter into the atmosphere, scattering the dust over 400 kilometres away from the lake. Such storms occurred 25 or more times each year, generally in the fall and spring. Composed of microscopic particle matter smaller than ten microns (PM10), this dust contains significant levels of toxic metals like arsenic, lead and selenium along with efflorescent salts. Being the largest single source of PM10 pollution in the United States, these dust storms were an apparent threat to the population of over 45,000 people in Owens Valley and nearby areas.
In order to control the dust mitigation, three solutions were used: Shallow flooding, managed vegetation and the use of a gravel blanket over a nonwoven geotextiles fabric. The solutions of shallow flooding and managed vegetation turned out to be both uneconomical and unfriendly towards the environment due to the constant need for watering that resulted in high water consumption. Thus, in 2012, the construction of phase 8 of the project focused on the use of gravel cover to control windblown dust.
Project Design
Owens Lake represented the largest gravel cover dust mitigation project in the United States. The project encompassed crushing, hauling and placing roughly 535,000 m3 of gravel over 5 km2 to a thickness of 10cm. Under a tight schedule, the Owens Lake construction team placed approximately 5.8 million m2 of geotextile fabric prior to spreading the gravel layer over the soft, unstable lakebed where groundwater is within 50cm of the surface.
Thrace NG geotextiles were chosen for their excellent mechanical properties, tried and tested in leading projects worldwide. The permeable nonwoven staple fibre geotextiles layer used in this project served filtration and separation functions, preventing the gravel from sinking into the sandy soil lake bed with high groundwater and losing its dust control effectiveness.
The Result
The project included various challenges such as a remote location, sensitive (quick) clay soils and dry salt-laden lake bed sediments, tough construction conditions and demanding construction timeline. However, the project was completed one month ahead of scheduled deadline and 2 months ahead of the project completion deadline.
Airborne dust can arise from either anthropogenic (human created) sources or natural sources. Anthropogenic sources include mine and quarries, municipal landfills, and other waste handling facilities. Natural sources include dry river or lake beds. With the increasing need to mitigate environmental dust, creative methods such as this described here can be effectively used in similar situations quickly solve this environmental health and ecological hazard.
