Data Series 190
U.S. GEOLOGICAL SURVEY
Data Series 190
The USGS collects and maintains water-level data for sites at the Nevada Test Site. As part of this data-collection program, current and historic water-level data are compiled, reviewed, and stored in the USGS NWIS database (http://waterdata.usgs.gov/nv/nwis/nwis). For the Rainier Mesa area, the database contains about 1,000 water-level measurements from 50 discrete intervals within 18 boreholes. Additionally, about 200 water-level measurements of impounded tunnel water at four tunnel sites in Rainier Mesa (Charles Russell and others, Desert Research Institute, written commun., 2003) were compiled for this report but are not in the NWIS database. Water-level data for the 54 measurement sites (fig. 1, table 1) were collected periodically from 1957 to 2005.
Water-level data contained in the database and in this report were collected from multi-screen completion wells, from wells or boreholes with packers temporarily installed during or after drilling, and from open boreholes that may later have been deepened or completed into a well. In these situations, a unique site identification number and site name were established in the database for each discrete open interval where data were collected. In other situations, multiple piezometers, open at different intervals, were placed in a single borehole. In these cases, each piezometer is considered a site in the database. Site names from the same borehole are distinguished from each other by a parenthetical expression following the borehole name—for example: UE-12t 6 (1378 ft). A single number in the parenthetical expression refers to the depth of the well or borehole; two numbers separated by a dash refer to the depth of the top and bottom of the open interval in the well or borehole. For the purposes of this report, a discrete open interval where water levels were monitored may be referred to as a well or a site.
Periodic water-level measurements were made by the USGS or private contractors working at the NTS using calibrated electric-cable units (also known as iron-horse and wire-line devices), calibrated electric tapes, and less commonly, a fluid-density geophysical log, float recorder, pressure gauge, or pressure transducer. Most water-level measurements prior to 1996 were made with an electric-cable unit (Garber and Koopman, 1968); whereas, more recent measurements typically were made using electric tapes. The tapes and cable units are calibrated annually at different water-level depths with a USGS 2,000-ft steel reference tape. At the time of measurement, a correction factor is applied to the depth-to-water reading based on the annual calibration. Recent (post-1995) measurements using electric tapes generally are more accurate (±0.1 ft) than older measurements using electric-cable units or other methods (±0.5–1 ft).
A systematic quality-assurance review of data contained in the NWIS database from 1957 to 2005 for sites in the Rainier Mesa area was completed for this study. This included removing or correcting duplicate sites or erroneous water-level data, and adding missing water-level measurements and construction information. A summary of water-level measurements from the 54 sites is shown in table 2. The earliest measurement was made in 1957 and 11 sites were measured in 2005. The deepest measured depth to water was 3,116 ft in well ER-12-3 main (fig. 1).
An interpretive database using Microsoft® Access format was constructed that provides information on the external conditions influencing each water level measured in the Rainier Mesa area. The database contains site information for each well, well-construction records, borehole lithology, aquifer data, and water-level data (appendix 1). Information in this database was derived from data sets created for this study and data sets available from NWIS. All tables are linked by the USGS local site name and site identification number, a unique 15-digit number used to identify the site (table 1). Several of the tables also are linked by water-level date. The structure of the water-level database is shown in figure 2. An effort was made to maintain a database structure that is consistent with the structure of the NWIS database (U.S. Geological Survey, 2004). For example, the four well-construction tables from NWIS are preserved in the water-level database.
Hydrographs and site locations in Rainier Mesa are interactively presented with a Microsoft® Excel workbook. The workbook is designed to be an easy-to-use tool to understand the water-level history for any site in the Rainier Mesa area. It also can be used to filter water-level data by restricting the data to certain sites, dates, or hydrologic conditions.
An example page from the workbook (fig. 3) shows well UE-12t 6 (1378 ft), which was selected using the Excel built-in AutoFilter. Selected water-level information from the water-level database is shown for this well. Additionally, a short narrative is displayed that describes the well and hydrograph.
Site, well-construction, and lithology information for the 54 Rainier Mesa water-level sites are stored in the water-level database (appendix 1). This information, which can be used to support interpretations of the water levels and water-level trends, is contained within nine tables in the water-level database (table 3). Five additional tables in the database provide water-level information, including water-level data, hydrologic conditions of each water-level measurement, and a water-level history for each site (table 3).
Water-level measurement source, method, accuracy, and hydrologic conditions at the time of the water-level measurement are attributed in the water-level database. Interpretations for individual water-level measurements and for the period of record for a site have been incorporated into the attributes. Abrupt water-level changes and long-term water-level declines are examples of typical hydrologic conditions that were interpreted. These interpretations are noted in the water-level remark, detailed hydrologic condition, or hydrograph narrative.
Hydrologic-condition attributes were used to describe the state of each water level that was measured at sites in the Rainier Mesa area. They also describe the external factors that may have affected the measured depths-to-water at each site. Hydrologic-condition attributes were categorized as either general or detailed (table 4). General-condition attributes describe the state of a water level. Examples are steady state, transient, and nonstatic level. Detailed-condition attributes can denote a factor affecting a water level, describe the effect that a factor may have on a water level, or denote the uncertainty of a water-level interpretation. Factors affecting water levels include perched water, pumping, and recent well construction. Water-level effects include abrupt change, equilibration, and rising trend. One general-condition attribute and 0–6 detailed-condition attributes were assigned to each water-level measurement in the Rainier Mesa area.
The water-level history of each site is documented as a narrative. The narrative consists of comments or explanations about the site or about water-level data at the site. An interpretation of the hydrograph and its hydrologic significance is provided for most sites as part of the narrative. The narrative may include information about the open interval, testing done in the well, the well productivity, specific influences near the site that may have affected water levels, and other details that may provide additional information about the conditions affecting water-level data at the site. Basic information included in the narrative was derived from published reports or from USGS data files stored in Henderson, Nev.
U.S.
Department of the Interior | U.S. Geological
Survey
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