Evaluation of the Migration of Palliative Chemicals Used for Dust Abatement, Clark County, Nevada Completed

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To minimize dust generated during the construction and operation of a solar power facilities in southern Nevada, the Bureau of Land Management (BLM) has approved the use of selected dust palliatives. Each palliative acts as an adhesive, binding soil particles together forming a layer of crust which reduces the susceptibility of surficial soils to erosion caused by wind and rain. The palliative formulation being evaluated as part of this study contains the polymer, butyl acrylate vinyl acetate. These palliative chemicals may pool in water down gradient from areas of palliative application after rain events which could expose the desert tortoise and other wildlife to these chemicals.

BLM is concerned with any potentially harmful effect that the use of dust palliatives may have on surface water chemistry, wildlife, and plant communities. The lands approved for solar energy development are habitat for the threatened desert tortoise. The desert tortoise, Gopherus agassizii, consumes water opportunistically from pools and saturated soils through their beak and nares. The migration of palliative from the solar energy facilities to areas where the desert tortoise can be exposed to palliative constituents in water and forage is of concern. Migration of palliatives can occur as a result of run-off, leaching, deposition of palliative laden dust, and release from tires after traffic has traversed areas treated with palliative. BLM is primarily concerned with the transport of palliatives during storm events from areas of approved use into depressions and washes that may be sources of water for tortoises in the area.

Study areas

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Two solar energy facilities located within Clark County are being studied. The primary area for evaluation, Silver State Solar South (SSSS), is located in Ivanpah Valley. SSSS is being developed on approximately 2,427 acres about 40 miles southwest of Las Vegas near Primm, Nevada. Retention basins have been installed along the periphery of the facility in the alluvial fan to capture storm water and are designed to capture the projected runoff associated with a 100-year storm event. The design of the SSSS facility will make use of retention basins and natural drainages where runoff from storm events will be directed away from the site. Suspended soil loads, when transported, are expected to eventually end up in Roach and Ivanpah Lakes.

The Playa Solar Project (PSP) will be developed on a 1,700 acre area in the Dry Lake Solar Energy Zone located about 14 miles northeast of Las Vegas and 8 miles southwest of the Moapa River Indian Reservation. The PSP is located in the topographically closed Dry Lake Valley and perennial surface waters and ephemeral channels are absent within the development area. Generally, offsite flow enters the project area from the south through culverts under US93. To maintain existing terrain, storm runoff entering the site will be captured by retention basins, directed toward existing natural drainages using rip-rapped grouted channels, or will be conveyed as sheet flow across the site.

Sampling and Analysis

To determine if dust palliatives are transported during storm events, storm water samples will be collected from retention basins and from surficial depressions in areas within and down gradient from point(s) of application and evaluated for concentrations of polymers contained in palliative formulations (polyvinyl alcohol; butyl acrylate vinyl acetate polymer; and(or) acrylic vinyl acetate polymer). One rain gage each, equipped with real-time capability, will be installed near SSSS and PSP.  The rain-gages will be used in association with more general weather information to alert sampling personnel to storm events within the vicinity of each study area. Environmental samples will be collected, as possible, over 3 years in association with storm events that occur on the areal extent of the areas under development and areas down gradient of those approved for palliative application.

One of the main challenges for the project has been the development of an analytical method to determine polymer concentrations in soil and water matrices. The USGS has been successfully working with a laboratory in Canada to develop this analytical method. Preliminary samples have been collected from one of the two solar energy facilities.  These samples have been used to finalize the analytical method and determine the amount of matrix required for laboratory analysis.  Now that soil and water matrices can be evaluated for polymer concentrations, the USGS will be collecting samples to evaluate the potential environmental degradation of butyl acrylate vinyl acetate over time and the presence of the polymer and any degradation products in soil and storm water matrices.