In Reply Refer To:                                                December 21, 2004 
Mail Stop 415

In Reply Refer To:
Mail Stop 415


SUBJECT: Interim Plan for Accessing Confined-Space Stilling Wells

Stilling wells remain critical to the streamgaging operations of the U.S. Geological Survey. However, many stilling wells meet the definition of confined space under Title 29 of the Code of Federal Regulations (CFR) sections 1910.146. The Occupational Safety and Health Administration (OSHA) requires employees to be protected from hazards associated with entry into confined spaces.

WRD Memorandum No. 97.32 provided guidance governing entry into stilling wells based on a confined-space standard proposed by the National Institute for Occupational Safety and Health (NIOSH). The Occupational Safety and Health Administration (OSHA) has since promulgated 29 CFR 1910.146 with some requirements that make WRD 97.32 obsolete. In general, the new OSHA standard does not impose significant procedural changes beyond those of WRD 97.32, but it does require enhanced monitoring of the quality of air in confined spaces prior to and during entry unless an alternative process can be justified.

As explained in WRD 97.32, atmospheric tests conducted during the summer and early fall of 1995 in 1,998 of the 2,876 stilling wells then in operation, and follow-up tests in 879 wells, demonstrated that the air-quality in stilling wells is generally acceptable, and that open ventilation of the wells prior to entry almost always results in acceptable air-quality within a few minutes. However, because of accumulation of organic debris, oils, and exhaust vapors, acceptable air-quality can not be guaranteed in every well during every entry. At the same time, monitoring of air-quality in stilling wells can be cumbersome. Hence, the USGS proposes requiring forced-air ventilation prior to and during entry of stilling wells using mobile electric air ventilators. Typical commercial ventilation units should provide complete replacement of the air within a stilling well with air from the external ambient atmosphere within 3 minutes or less. This approach will provide acceptable air-quality and safe working conditions. We are working with NIOSH to demonstrate the efficacy of this approach in an effort to obtain an OSHA waiver under the alternate procedures section of 29 CFR 1910.146 so that the USGS does not have to meet the standard requirement for air-quality monitoring each time a stilling well is entered.

While the USGS is working to obtain an OSHA waiver to use this alternative procedure, the Bureau Safety and Environmental Management Branch, the Regional Water Safety Officers, and the Office of Surface Water have collaborated to produce new interim guidance governing entry of USGS stilling wells. The most important element of the new guidance is the use of forced-air ventilation every time a confined-space stilling well is entered. OSHA defines a confined space in 29 CFR 1910.146. Most stilling wells are considered confined spaces unless access is not limited or restricted. For example, a stilling well is not considered a confined space when exit doors are large relative to the volume of the well and can be used by an employee without the assistance of mechanical aides such as a ladder. The interim guidance has been prepared as Appendix 40-1 of the USGS SM 445-2-H. and is available at

Districts should implement the requirements of Appendix 40-1 as soon as is practical. The Regional Hydrologists, working with the Regional Safety Officers (RSOs) will establish deadlines for this work, but OSW suggests a target date no later than June 30, 2005. Questions regarding the new policy or about entry of confined spaces should be directed to the RSOs (currently Clyde Scholar (NR), Roger Rumenik (SR), or
Ron Kuznair (CR); the western RSO position is currently vacant), or to the Bureau Industrial Hygienist (Cynthia Duffield). Once the USGS receives a response from OSHA, a final confined space stilling well policy will be issued.

Stephen F. Blanchard /signed/
Chief, Office of Surface Water