POST CLOSURE INSPECTION AND MONITORING REPORT FOR CORRECTIVE ACTION UNIT 417: CENTRAL NEVADA TEST AREA - SURFACE, HOT CREEK VALLEY, NEVADA; FOR CALENDAR YEAR 2005
Corrective Action Unit (CAU) 417, Central Nevada Test Area - Surface, is located in Hot Creek Valley in northern Nye County, Nevada, and consists of three areas commonly referred to as UC-1, UC-3, and UC-4. CAU 417 consists of 34 Corrective Action Sites (CASs) which were closed in 2000 (U. S. Department of Energy, National Nuclear Security Administration Nevada Operations Office, 2001). Three CASs at UC-1 were closed in place with administrative controls. At CAS 58-09-01, Central Mud Pit (CMP), a vegetated soil cover was constructed over the mud pit. At the remaining two sites CAS 58-09-02, Mud Pit and 58-09-05, Mud Pits (3), aboveground monuments and warning signs were installed to mark the CAS boundaries. Three CASs at UC-3 were closed in place with administrative controls. Aboveground monuments and warning signs were installed to mark the site boundaries at CAS 58-09-06, Mud Pits (5), CAS 58-25-01, Spill and CAS 58-10-01, Shaker Pad Area. Two CASs that consist of five sites at UC-4 were closed in place with administrative controls. At CAS 58-09-03, Mud Pits 9, an engineered soil cover was constructed over Mud Pit C. At the remaining three sites in CAS 58-09-03 and at CAS 58-10-05, Shaker Pad Area, aboveground monuments and warning signs were installed to mark the site boundaries. The remaining 26 CASs at CAU 417 were either clean-closed or closed by taking no further action. Quarterly post-closure inspections are performed at the CASs that were closed in place at UC-I, UC-3, and UC-4. During calendar year 2005, site inspections were performed on March 15, June 16, September 22, and December 7. The inspections conducted at the UC-1 CMP documented that the site was in good condition and continued to show integrity of the cover unit. No new cracks or fractures were observed until the December inspection. A crack on the west portion of the cover showed evidence of lateral expansion; however, it is not at an actionable level. The crack will be sealed by filling with bentonite during the first quarter of 2006 and monitored during subsequent inspections. The cover vegetation was healthy and well established. No issues were identified with the CMP fence, gate, or subsidence monuments. No issues were identified with the warning signs and monuments at the other two UC-1 locations. The inspections at UC-3 indicated that the sites are in excellent condition. All monuments and signs showed no displacement, damage, or removal. A small erosion gully from spring rain runoff was observed during the June inspection, but it did not grow to an actionable level during 2005. No other issues or concerns were identified. Inspections performed at UC-4 Mud Pit C cover revealed that erosion rills were formed during March and September exposing the geosynthetic clay liner. Both erosion rills were repaired within 90 days of reporting. Sparse vegetation is present on the cover. The overall condition of the monuments, fence, and gate are in good condition. No issues were identified with the warning signs and monuments at the other four UC-4 locations. Subsidence surveys were conducted at UC-1 CMP and UC-4 Mud Pit C in March and September of 2005. The results of the subsidence surveys indicate that the covers are performing as expected, and no unusual subsidence was observed. The June vegetation survey of the UC-1 CMP cover and adjacent areas indicated that the revegetation has been very successful. The vegetation should continue to be monitored to document any changes in the plant community and identify conditions that could potentially require remedial action in order to maintain a viable vegetative cover on the site. Vegetation surveys should be conducted only as required. Precipitation during 2005 was above average, with an annual rainfall total of 21.79 centimeters (8.58 inches). Soil moisture content data show that the UC-1 CMP cover is performing as designed, with evapotranspiration effectively removing water from the cover. It is recommended to continue quarterly site inspections and the collection of soil moisture data for the UC-1 CMP cover.
- Research Organization:
- DOE/NNSA NEVADA SITE OFFICE
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 901908
- Report Number(s):
- DOE/NV-1122; TRN: US200717%%105
- Country of Publication:
- United States
- Language:
- English
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Post-Closure Inspection and Monitoring Report for Corrective Action Unit 417: Central Nevada Test Area Surface, Hot Creek Valley, Nevada, for Calendar Year 2007
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