Saturday, 15 July 2006

Soil Reclamation and Surface Stabilization at Owens Dry Lake Using Irrigated Saltgrass.

John B. Dickey1, Mica H. Heilmann1, Jason K. Smesrud1, Jim L. Jordahl1, Richard Coles1, and Richard Harasick2. (1) CH2M HILL, INC, 2485 Natomas Park Drive, Suite 600, Sacramento, CA 95833, (2) LADWP, P.O. Box 111, Los Angeles, CA 90051

In 1997, the Los Angeles Department of Water and Power (LADWP) entered into a historic agreement with Great Basin Unified Air Pollution Control District (GBUAPCD) committing LADWP to control dust emissions from the surface of Owens Dry Lake playa (Playa), the leading source of dust (PM10) emissions in the United States. The State Implementation Plan (SIP) for mitigation of this major PM10 source specified three acceptable dust control measures, one of which was irrigated, native Owens Lake saltgrass (Distichlis spicata). This dust control measure is termed “managed vegetation” and currently requires that saltgrass cover 50 percent of the land surface in a given acre. Widely diverse saline-sodic soils present specific challenges to vegetating the Playa. Diverse soils include surface horizons dominated by soluble salt; extremely saline (ECe > 100 dS/m), sodic and alkaline (pH > 10) root-zone conditions; and textures ranging from sand to expansive, cracking clay that is prone to dispersion and sealing. Other major impediments to vegetation of the Playa include (1) arid climate; (2) saline (about four times the salinity of seawater), anoxic shallow groundwater seasonally or perennially near to the soil surface; (3) abrasive conditions occasioned by plentiful, loose, sand-sized particles and frequent high winds; (4) no established method for large-scale propagation of Owens Lake native saltgrass; (5) native, potentially plant-and-animal-toxic concentrations of specific elements; and (6) challenges to construction and operation occasioned by high winds, drifting sand and blowing dust, low bearing capacity soils (bulk densities < 0.9 g/cm3), and the presence of special-status bird species. After several years of collaborative research with GBUAPCD, the LADWP, working with CH2M HILL and other contractors, designed, permitted, constructed, and is now operating over 900 hectares of managed vegetation. The facility's features include a 137-centimeter pipeline from the Los Angeles Aqueduct, water treatment, blending, fertigation and filtration, subsurface drip irrigation, saltwater drainage, storage, and recycling. Numerous design and operational innovations were required to construct this facility, the only one of its kind. Saltgrass has been successfully established on about 96 percent of the project area, with the target 50 percent cover on about 75 percent of the site at the end of 2004. Performance monitoring of sand motion and air quality indicate that the existing saltgrass cover is effective in suppressing dust emissions.

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