Eric Mead, P.E., PMP, Solid Waste Engineer, HDR Engineering

Klickitat County (County), Washington, owns the Horsethief Landfill, a former municipal solid waste (MSW) landfill which has been in post-closure care under the requirements of Chapter 173-304, Washington Administrative Code (WAC) for 20 years. The landfill has been monitored and maintained by the Klickitat County Solid Waste Department (KCSWD) who is currently seeking to terminate post closure care of the landfill and release the property to the Washington State Parks for incorporation into a regional park. KCSWD effort to exit post-closure care requires a demonstration to the State of Washington Department of Ecology (Ecology) that the site has been stabilized. Ecology's standards for a stabilized landfill include minimal settlement, cover integrity, little leachate and gas generation, and clean groundwater monitoring results. To address the stability standards, KCSWD has performed periodic site surveys, groundwater quality monitoring, and landfill gas source testing. The purpose of these activities is to be able to effectively evaluate whether or not the landfill's long-term stability is at risk by being left untended.

This presentation provides the following info regarding the Horsethief Landfill:

• Site's background, history, and unique characteristics,
• Discussion of applicable regulations,
• Description of stabilized state elements,
• Approach used for exiting post-closure care,
• Field work completed to date and results,
• Remaining steps to seek approval to exit post-closure care,
• Proposed use after exiting post-closure care, and
• Lessons learned on the project.

This presentation is provides useful guidance to landfill owners and consultants interested in assisting clients to exit post-closure care in a responsible and sustainable manner.