Design and Construction of an Earthen Impoundment for Water Management

Tetra Tech, Inc. (Tetra Tech) provided engineering support to Anadarko Petroleum Company (Anadarko) for water storage alternatives proposed for use in hydraulic fracturing operations. Tetra Tech conducted a geotechnical investigation to determine the suitability of an Anadarko site located south of Greeley, Colorado. The property, which is located near the geologic floodplain of the South Platte River, is underlain by clayey sand and low plasticity clay, gravelly sand, and claystone bedrock. An earthen impoundment was designed to maximize storage capacity and balance earthwork quantities. The footprint of the facility was 6.3 hectares (15.5 acres) with impoundment dimensions of 107 m by 235 m (350 ft by 770 ft). The embankment crest ranged from 1.5 m to 2.9 m (5 ft to 9.5 ft) above existing grade, and the capacity was approximately 79,500 m³ (500,000 barrels or 21,000,000 gal). During construction, coarse gravel that would not be a suitable liner subgrade was encountered. The material was removed and stockpiled; clay material from other Anadarko sites was trucked in and used as liner subgrade. The gravel was screened on site and used by Anadarko as road base at various other sites. Construction of the impoundment was completed in summer 2013 and has performed well; it was not damaged during the flooding of September 2013.