[en] Ground water compliance for the Uranium Mill Tailings Remedial Action (UMTRA) Project sites, including the Riverton, Wyoming, site, is governed by the Uranium Mill Tailings Radiation Control Act and the US Environmental Protection Agency's Health and Environmental Protection Standards for Uranium and Thorium Mill Tailings. The compliance strategy proposed for this site is natural flushing in conjunction with institutional controls. The essential premise of natural flushing is that ground water movement and natural attenuation processes will reduce the detected contamination to background levels or alternate concentration limits that do not pose a risk to human health or the environment within 100 years. This document contains the following sections. Section 2.0 of this SOWP describes the requirements for meeting standards at UMTRA Project sites. Section 3.0 provides site-specific data and the related conceptual model. Section 4.0 provides the justification for the recommended ground water compliance strategy for the Riverton site. Section 5.0 provides the justification and process for collection and assessment of additional required data. Section 6.0 provides a list of the references cited. The appendixes include data on monitor wells and lithography, ground water, surface water, and sediment quality