Nevada Division of Environmental Protection, Central Nevada Test Site (CNTA)

Corrective Action Unit (CAU) 417 addresses the remediation and closure of only the surface lands associated with testing activities. Initial environmental investigations at the CNTA in the 1980s detected the presence of chromium and organic compounds in surficial materials found in uncovered drilling mud pits, however, no radionuclides above background levels were detected at the surface.

Detailed characterization of CAU 417 occurred between September 1996 and June 1998. The results of these characterization activities showed that the only constituent of concern detected was total petroleum hydrocarbons (TPH) in the diesel/motor oil range whose concentration exceed the Nevada Administrative Code (NAC) action level of 100 milligrams per kilogram (mg/kg).

A decision on the appropriate corrective measure for each of the 34 identified Corrective Action Sites (CASs) was made in 1999. The proposed corrective action alternatives included: 1) clean closure with removal of materials or consolidation at the UC-1 Central Mud Pit; 2) administrative controls (such as soil covers, fencing, and signs) to prevent human exposure to petroleum contaminated materials; and 3) the "no action" alternative for those sites where contaminants were measured below State of Nevada regulatory levels and long-term impacts to the groundwater resource were judged to be extremely unlikely.

Preliminary field work to implement the corrective measures at the CNTA was begun in 1999 and full-scale operations continued through 2000.

Table 1 shows a summary of the closure activities.

cnta uc-1 central mud pit looking to the southeast

The largest corrective action site addressed was the UC-1 Central Mud Pit (CMP). The UC-1 CMP was closed with a vegetated monolayer cover - (Diagram) designed to isolate hydrocarbon-impacted drilling muds from casual contact by humans and animals. In addition to the vegetated cover on the UC-1 CMP, an engineered cover - (Diagram) was designed for the UC-4 Mud Pit C.

All corrective actions for the CNTA surface (CAU 417) were completed in 2001. Post-closure monitoring is conducted quarterly and includes the inspection of the UC-1 Central Mud Pit cover, the UC-4 Mud Pit C cover, and all fences, diversion channels, vegetation, above-ground monuments, and attached warning signs at sites UC-1, UC-3, and UC-4.