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+# Groundwater ubiquity score based on Gustafson (1989)
+
+The groundwater ubiquity score GUS is calculated according to the
+following equation \$\$GUS = \log\_{10} DT50\_{soil} (4 - \log\_{10}
+K\_{oc})\$\$
+
+## Usage
+
+``` r
+GUS(...)
+
+# S3 method for class 'numeric'
+GUS(DT50, Koc, ...)
+
+# S3 method for class 'chent'
+GUS(
+  chent,
+  degradation_value = "DT50ref",
+  lab_field = "laboratory",
+  redox = "aerobic",
+  sorption_value = "Kfoc",
+  degradation_aggregator = geomean,
+  sorption_aggregator = geomean,
+  ...
+)
+
+# S3 method for class 'GUS_result'
+print(x, ..., digits = 1)
+```
+
+## Arguments
+
+- ...:
+
+  Included in the generic to allow for further arguments later.
+  Therefore this also had to be added to the specific methods.
+
+- DT50:
+
+  Half-life of the chemical in soil. Should be a field half-life
+  according to Gustafson (1989). However, leaching to the sub-soil can
+  not completely be excluded in field dissipation experiments and
+  Gustafson did not refer to any normalisation procedure, but says the
+  field study should be conducted under use conditions.
+
+- Koc:
+
+  The sorption constant normalised to organic carbon. Gustafson does not
+  mention the nonlinearity of the sorption constant commonly found and
+  usually described by Freundlich sorption, therefore it is unclear at
+  which reference concentration the Koc should be observed (and if the
+  reference concentration would be in soil or in porewater).
+
+- chent:
+
+  If a chent is given with appropriate information present in its chyaml
+  field, this information is used, with defaults specified below.
+
+- degradation_value:
+
+  Which of the available degradation values should be used?
+
+- lab_field:
+
+  Should laboratory or field half-lives be used? This defaults to lab in
+  this implementation, in order to avoid double-accounting for mobility.
+  If comparability with the original GUS values given by
+  Gustafson (1989) is desired, non-normalised first-order field
+  half-lives obtained under actual use conditions should be used.
+
+- redox:
+
+  Aerobic or anaerobic degradation data
+
+- sorption_value:
+
+  Which of the available sorption values should be used? Defaults to
+  Kfoc as this is what is generally available from the European
+  pesticide peer review process. These values generally use a reference
+  concentration of 1 mg/L in porewater, that means they would be
+  expected to be Koc values at a concentration of 1 mg/L in the water
+  phase.
+
+- degradation_aggregator:
+
+  Function for aggregating half-lives
+
+- sorption_aggregator:
+
+  Function for aggregation Koc values
+
+- x:
+
+  An object of class GUS_result to be printed
+
+- digits:
+
+  The number of digits used in the print method
+
+## Value
+
+A list with the DT50 and Koc used as well as the resulting score of
+class GUS_result
+
+## References
+
+Gustafson, David I. (1989) Groundwater ubiquity score: a simple method
+for assessing pesticide leachability. *Environmental toxicology and
+chemistry* **8**(4) 339–57.
+
+## Author
+
+Johannes Ranke