WOCA hosts four S&ME presenters
May 30, 2013
CCP Landfill Leachate Management and Leachate Generation
Immanuel K. Baucom, P.E. and Cedric H. Ruhl, P.E.
Traditional disposal of coal combustion products / byproducts (CCPs) consists of mixing CCPs with water and sluicing the ash and water slurry to an ash basin, known as wet ash handling. The ash basin functions essentially as a CCP storage device with settling time such that suspended CCP particles are deposited within the basin.
Pending legislation may restrict or prohibit the use of ash basins. Many utilities are transitioning to dry ash handling methods and placing CCPs into landfills. The transition from wet ash handling to dry ash handling marks a very different approach to water management. With the wet ash handling approach, water is added to CCPs at the plant and the water is eventually discharged to the environment. With dry ash handling, water that contacts the ash or infiltrates through the waste mass at the landfill must be collected and treated.
The leachate collection system must be included as part of the landfill design based on leachate generation rates. Hydrologic Evaluation of Landfill Performance (HELP) software is typically used to develop theoretical leachate generation rates.
This paper presents methods utilized during operations to aid in leachate management at two CCP landfills. A comparison of the theoretical leachate generation from HELP modeling to actual leachate generation rates measured at the two landfills over a period of 1 to 3 years is provided. The effects of waste height, rainfall, and operational practices on theoretical and measured leachate generation are discussed, as well as calibration of the HELP model parameters to measured results.
Characterization and Estimation of Settlement of In-Place Sluiced CCP Materials Under Monotonic Loading
Jason S. Reeves, PE and Michael G. Rowland, PE
Geotechnical characterization of coal combustion products/residuals (CCP) placed by wet placement methods and construction of permanent caps or landfills over former impoundments present unique geotechnical design challenges. Of particular concern is the need to estimate the expected settlement of the wet-placed CCP in former impoundments under the load of the planned cap system or landfill mass such that positive drainage is maintained. Lined dry-placed CCP landfills require that minimum slopes be maintained for leachate collection systems. Cap systems also require positive drainage to convey surface water fl0ws.
Historically, settlement parameters for wet-placed CCPs have been developed through a combination of in-situ testing such as Standard Penetration Testing (SPT), Cone Penetration Testing (CPT), Marchetti Dilatometer Testing (DMT), and laboratory testing such as one-dimensional consolidation testing. In support of the design of a new CCP landfill overlying a former sluiced-ash impoundment, an extensive field and laboratory testing program was carried out, and expected settlements were estimated using several methods. Subsequently, an instrumented test fill was completed at the site that allowed the field performance of the wet-placed CCP material to be observed, and also allowed for review and calibration of the settlement prediction methodologies used.
The in-situ and laboratory test data, test fill construction process, and instrumentation data are discussed. Comparisons are made between various methods of estimating settlement of the sluiced CCP materials from this project, along with comparisons from similar projects based on published data. Recommendations are provided for settlement prediction methods for use on other similar future projects.