Deprecated
The SCT and GWT time file formats are deprecated. It is now recommended to use the APDV or AIDV formats with dates as analyte names to handle time domain data. See Creating Analyte Files Representing Measurements Over Time for details.
Overview
The SCT and GWT analyte time formats are legacy formats and are no longer recommended for new work. Use APDV or AIDV with dates as analyte names instead — see Creating Analyte Files Representing Measurements Over Time. This page documents the legacy formats for reading and maintaining existing files.
Legacy analyte time files store 3-D sample locations together with values for one or more analytes or properties measured over a series of dates. They are ASCII text files and use one of two suffixes:
- .sct — Soil Chemistry Time (point samples)
- .gwt — Ground Water Time (well-screen intervals)
Each data line holds the coordinates for one sampling location (or well screen) plus any number of chemistry or property values. There is no limit on the number of borings or samples, though kriging run times increase with more samples.
Unlike the APDV and AIDV formats, time files require analyte names and units on the first line and do not specify the number of samples, analytes, or times.
Coordinate Systems and Geology
Time data can be visualized on its own or within a domain bounded by a geologic system. When using a geologic domain, the chemistry and geology must share a consistent coordinate system (same projection and overlapping spatial extents). Boring and sample locations need not match those in the geology files; only samples within or near the geologic domain are used for kriging.
To honor site topography when posting borings and samples, include the top surface elevation of each boring.
File Format
Entries on a line may be delimited by commas, spaces, or tabs. Comment lines may appear anywhere and must begin with #. The line numbers below refer to non-comment lines only.
Line 1 — Analyte Names and Units
Lists the name of each analyte, followed by the units for each analyte. Units are required for time chemistry files.
Line 2 — Analyte-Date Mapping
Maps each data column to an analyte and a date, written as analyte name | date. Provide one mapping per data column.
- Enclose the entry in quotes to allow spaces in the name — e.g.
"Vinyl Chloride|6/1/2004". - The analyte name may be omitted (date only); the first analyte from Line 1 is then assumed.
- Columns must be ordered oldest to newest for each analyte.
Dates follow your computer’s regional settings (Control Panel). C Tech uses the SHORT DATE and SHORT TIME formats — if a date/time works in Excel, it generally works in EVS. In the U.S. (12-hour clock) the form is "m/d/yyyy hh:mm:ss AM" or "m/d/yyyy hh:mm:ss PM". Any date/time containing spaces must be quoted.
Line 3 — Elevation/Depth and Coordinate Units
Begins with either Elevation or Depth:
- Elevation — true elevations (right-handed coordinate system)
- Depth — depth below the top surface elevation
GWT files only: the next value is a real number (not an integer) giving the Max-Gap in the same units as the coordinates. Max-gap is the maximum spacing between kriging samples. If a screen interval is shorter than max-gap, one sample is placed at its center; if longer, two or more equally spaced samples are distributed across it (interval ÷ max-gap, rounded up).
The last value is the coordinate units (e.g. feet or meters), or the flag word reproject.
Lines 4+ — Sample Data
One sample per line. SCT files give a single elevation for a point sample; GWT files add a second elevation column for the top and bottom of each screen interval.
Column order:
- X, Y
- Z (SCT) — or Well Screen Top, Well Screen Bottom (GWT)
- One or more analyte values
- Boring name
- Top of boring elevation (optional)
Boring names cannot contain spaces (use an underscore, e.g. B_1) unless quoted ("B 1"). The boring name and top-of-boring elevation are needed only by the post_samples module, which posts tubes along borehole traces from the ground surface. When top-of-boring elevations are supplied, they must appear on every line. Blank entries (cells) are not allowed.
Flag Words
For missing values, use any of: unmeasured, not-measured, nm, missing, unknown, unk, na.
For non-detect values:
- Prepend
<to the detection limit for that sample (e.g.<5). This lets you set the “Less Than Multiplier” (0.1–0.5, i.e. 10–50%) in modules that read the data. Preferred and most rigorous method. - Or use one of:
nondetect,non-detect,nd.
Examples
Soil Chemistry Time (SCT)
Ground Water Time (GWT)
GWT lines carry an extra elevation column (well screen top and bottom) and a Max-Gap value on the Elevation line.