Coalbed Methane Produced Water In The Western Us

values are higher than those studied by Bauder and Brock (2000), were generally not suitable for direct land application.

Numerous research efforts have focused on producing definitive characterization of the impact of waters of various SAR on soil quality. The principal soil characteristic which has been investigated has been either infiltration or soil hydraulic conductivity. Suarez et al. (2006) reported that for some soils (loam, a soil having relatively uniform proportions of sand, silt, and clay), adverse impacts of sodium on infiltration when applied water had a SAR greater than 2, while for a dispersive clay soil adverse impacts occurred above SAR of 4. In both soils the SAR behavior was similar for water having a TDS concentration of approximately 640 or 1280 mg/L, indicating that in this range TDS did not affect infiltration. Reductions in infiltration were evident during irrigation and rain events, with lower infiltration during the rain simulations. In an earlier and similar study, Mace and Amrhein (2001) reported that irrigation with water having SAR 5 and 8 resulted in irreversible plugging of soil pores by dispersed clay, as well as internal swelling.

Plant Growth and Survival

Vance et al. (2008) examined the effects of irrigation with CBM produced water on soils and plants of the Powder River Basin by comparing soil and plant conditions following various irrigation practices with those from nonirrigated sites. Irrigation with CBM produced water significantly increased the production and cover of native perennial grasses, but overall plant community diversity and uniformity of species across the landscape decreased. The researchers concluded that adverse changes in soil quality with CBM irrigation can restrict plant growth and cause plant water stress. Salinity has the potential to have significant impact on plant communities, plant community sustainability, and livestock and wildlife forage compatibility (Soil Improvement Committee, 1995). High salt content of soil pore water can also reduce the availability of water for plants and cause agricultural crops to expend more energy extracting water from the root zone than would be required in the absence of elevated salinity in the soil water (Arthur et al., 2008).

Prospects for Produced Water Irrigation

Many studies on the effects of using CBM produced water for irrigation demonstrate the challenges associated with directly putting CBM produced water to beneficial use in agricultural fields via surface irrigation or land application. Although the response of clay-rich soils to CBM produced water is not universal, the use of most CBM produced waters for irrigation, especially in smectite10 clay-rich soils, could reduce infiltration and may require intensive management, including selection of crops to be irrigated, timing and amount of produced water applied, and the use of soil amendments. Use of CBM produced water for irrigation appears practical and sustainable, with various combinations of selective application to nondispersive soils, treatment, dilution or blending of CBM produced water with other water sources, amendment of produced water and soils to be irrigated, and appropriate timing of irrigation practices to take advantage of ameliorating effects of rainfall and snowmelt. After use of CBM produced water ceases, additional soil management, including soil amendments,11 may be required to restore soil agricultural resources to pre-CBM water application conditions.

Much of the actual practice of applying CBM produced water to landscapes is limited to industry's efforts—largely on industry-owned land or land for which the industry has paid a rental or lease fee—and application of CBM produced water to landscapes or for irrigation is not a widespread practice at present. Nonetheless, challenges to WYDEQ-issued permits to manage CBM produced water through direct applications to land have been raised by several landowners, environmental groups, scientists, and the EPA. These issues are still being scientifically documented and analyzed (see also section later in this chapter on "Registered Citizen Complaints") and speak toward the infancy of the CBM industry (see Chapter 1) and of the rules, regulations, and policies being applied to CBM produced water management, particularly in Wyoming, as they related to surface discharges.

ECOLOGICAL EFFECTS

In this section, potential and observed ecological effects of CBM produced water on aquatic life and riparian habitats are discussed. Few on-site, in situ, or real-time studies have been completed and published on this topic, specific to the study area of this report. Many of the studies involve laboratory experiments that have neither employed water with chemistry in concert with average CBM produced water chemistry nor been verified against field studies. The committee provides an overview of this topic and suggests areas for further examination.

10Smectite is a group of clay minerals composed of layers of aluminum ions which lie between silicon-oxygen sheets. These kinds of clays have the ability to absorb water molecules between the sheets, allowing the mineral structure to expand.

"Soil "amendments" such as gypsum, organic matter, and elemental sulfur may be added to agricultural soils to liberate sodium. This release of sodium, accompanied by a supply of calcium, enhances improvement in soil structure, and sodium-affected soils can be restored to agricultural productivity. Soil amendments are sometimes called "soil conditioners."

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