between tortoises living in the vicinity of the facility and humans, native predators, and other tortoises.

Because the desert tortoise is protected as a threatened species by the Endangered Species Act, the listing history of this species is relevant to an assessment of impacts of the proposed facility. The desert tortoise occurs in southwestern North America on flats and bajadas with sandy-gravel soils (Luckenback, 1982). At least two distinct desert tortoise populations have been defined on the basis of genetic (Lamb et al, 1989) and morphometric criteria: the Mojave and Sonoran populations, and a possible third population in southern Sonora and Sinaloa, Mexico (USFWS, 1994a).

By the 1980's, desert tortoise populations had disappeared from parts of the western and northern Mojave Desert, and populations had declined in many other areas of the Mojave population's range (Jacobson, 1994; USFWS, 1994a). These declines led to the emergency listing of the entire Mojave desert tortoise population as federally endangered in 1989 (USFWS, 1989), and the final listing of the population as threatened on April 2, 1990 (USFWS, 1990b). The main reasons for this listing included habitat destruction, degradation, and fragmentation; removal or killing of tortoises by humans; increased predation on tortoises by native predators; disease; and failure of existing regulatory mechanisms to protect the desert tortoise and its habitat (USFWS, 1990b; 1994a). The Endangered Species Act mandates the designation of critical habitat and development of a recovery plan for federally listed species (16 U.S.C. § 1533 [1988 and Supp. 1990]). In response to this mandate, the U.S. Fish and Wildlife Service published the final critical habitat designation for the Mojave desert tortoise population on February 8, 1994 (USFWS, 1994b), and approved the final Desert Tortoise (Mojave Population) Recovery Plan (USFWS, 1994a) on June 28, 1994.

Critical habitat for the Mojave population was structured in accord with recommendations made in the Recovery Plan to include 14 Desert Wildlife Management Areas (DWMAs) in 6 Recovery Units. A fundamental goal of the Recovery Plan is to maintain the integrity of the distinct populations within each recovery unit, with DWMAs that contain desert tortoise habitat and viable tortoise populations identified in each unit. DWMAs are viewed as reserves, where human activities that negatively impact desert tortoises are restricted (Figure 8.1) (USFWS, 1994a). Ward Valley occupies parts of the Chemehuevi DWMA of the Northern Colorado Recovery Unit, and Fenner DWMA of the Eastern Recovery Unit, as designated in the Desert Tortoise (Mojave Population) Recovery Plan (USFWS, 1994a). The site for the proposed Ward Valley low-level radioactive waste (LLRW) disposal facility is located in the northern end of the Chemehuevi DWMA less than 2 km south of the Fenner DWMA, the two DWMAs being separated by I-40. The site was selected and characterization activities had begun before designation of the area as a desert tortoise critical habitat or identification of the DWMAs.