Sustainable Design and Construction of Earthen-Dam Reservoirs for Water Produced in Association with Coalbed Natural Gas in the Powder River Basin, Wyoming

Abstract

Surface impoundment of produced water from coalbed natural gas (CBNG) development is a water management option routinely employed by operators in Wyoming's Powder River Basin (PRB). A substantial increase in CBNG development in recent years has resulted in the need for documented guidance and standards regarding the sustainable design and construction of impoundment structures; specifically earthen-dam reservoirs. Earthen-dam reservoirs are a cost effective, relatively low-impact management alternative for produced water, which also allows for a variety of secondary water management options such as evaporation, infiltration, local aquifer recharge, irrigation, and livestock and wildlife watering. Earthen dams are also high-risk structures with the potential for extensive property damage and possible threat to public safety upon failure. A guidance document is beneficial to all stakeholders, from regulators and local governments to land and resource management agencies, ranchers, and landowners. Design elements and construction procedures presented in the guidance document are based on data collected during the design and construction of nearly 1,000 large reservoirs and more than 4,000 smaller stock reservoirs in the PRB over the past eight years. Soil conditions, subsurface and surface hydrology, topography, and geology specific to the PRB are considered, as are the regulatory requirements of the Wyoming State Engineer's Office and the Wyoming Oil and Gas Conservation Commission. While design considerations vary depending on intended beneficial use, landowner requirements, and pertinent regulations, sustainability and minimal disturbance are the governing objectives in all circumstances. Remediation and mitigation procedures for potential short and long-term concerns such as differential settlement, piping, excess surface erosion, and seepage are derived from field trial observations. Design aspects specific to on- and off-channel impoundments, planned long term use, and reclamation following short term use are provided.