Transition Area

The Transition Zone, a four-mile-long segment of Lone Tree Creek and the adjacent upland areas (including Sections 13-17 and 21-27), connects Area A and Area B. Transition Zone wells are those located approximately between 0.5 and 4 miles downgradient of Area A (i.e., northeast and east of the source area). Most of the 18 wells in this area are monitoring wells, although two production-type stock wells (Kennedy No. 1 and Kerbs No. 2) that formerly supplied water to Site 4 are located along Lone Tree Creek north of Area A. The Cheyenne Board of Public Utilities (BOPU) recently installed a new monitoring well (Kennedy No. 2) adjacent to Kennedy No. 1. Additionally, three domestic wells (Bar 13 Ranch, Fritz Ley #1, and Enlarged Bert McGee No. 8) are located in the northeastern portion of the Transition Zone.

Map of the transition zone connecting area a and area b of the atlas d missile site

Concentrations of Trichloroethylene (TCE) have been detected in samples collected from selected monitoring wells in this area, particularly two wells located ½ mile downgradient of the source area: MW19 (1300 micrograms per liter (µg/L)), located east of the missile site, and MW24 (920 µg/L), located to the northeast. The screened intervals of these wells are 100 to 140 feet deeper than those of the screened zones of the wells in the source area (Area A) located ½ mile upgradient. TCE has not been detected in samples collected from MW35, which is co-located with MW19 but screened through an interval about 120 feet deeper.

TCE concentrations above the EPA drinking-water action level (5 µg/L) have been detected in samples collected from other wells in this area, including MW10, MW15, MW20, MW21, and MW52, which are located about one mile downgradient of the missile site. These concentrations are generally below 100 µg/L. Wells MW10 and MW21, located northeast of the missile site, have screened intervals generally consistent with those of MW24.