Nitrate Leaching Classes of Illinois Soils

This data set was designed for statewide evaluation of
agrichemical leaching characteristics and associated
aquifer sensitivity to contamination. It was created to
classify soils and aquifer settings according to predictions
of leaching potential. The classifications have not been
validated by the results of water quality sampling. In
addition, the use of these aquifer sensitivity ratings as
predictors of water quality has not been evaluated.

This is a statewide Arc/Info data set of soil characteristics
relating to nitrate leaching. It was generated to aid in
determining aquifer sensitivity to nitrate leaching in Illinois.
The source map was digitized at 1:250,000, but was developed from
source data mapped at 1:15,000. The publication of this map was at
1:500,000. Nominal scale is 1:250,000.

Two statewide data sets were identified as containing
information that would be useful for producing aquifer
sensitivity maps: a soil association map (and database)
and a map of geologic materials to a depth of 50 feet
(Stack-unit map). The soil association map and database
were used in an interpretive mapping model that generated
a map of nitrate leaching classes by evaluating factors that

relate to water movement characteristics of the soil.

The result is six nitrate leaching classes that group soil
associations based on the relative probability of nitrate movement
through the associated soil profiles. The ranking is qualitative,
and is based on the median leaching value of the soil map units
that comprise each soil association. Nitrate leaching classes
include: Excessive, High, Moderate, Somewhat Limited, Limited,
and Very Limited. See ISGS EG 148 for the derivation of these
classes.

To provide a measure of leaching class variability within each
association, leaching class range values were calculated. To
reduce the impact of extreme leaching class values on this
estimate, the the range values were trimmed so that the upper
and lower 10% of values were not included in the calculation.
These trimmed range values were used as an overprint on the
published map of nitrate leaching classes (see cross reference
entries).

Disturbed land and surface water areas are also shown.

These data are to be used in conjunction with ISGS Environmental
Geology report 148. This data set is one of a suite of six
related data sets (listed below). Full citation details are
available in the Cross References section.

Aquifer Sensitivity to Contamination by Nitrate Leaching in Illinois
Nitrate Leaching Classes of Illinois Soils (this data set)
Nitrate Leaching Class Ranges

Aquifer Sensitivity to Contamination by Pesticide Leaching in Illinois
Pesticide Leaching Classes of Illinois Soils
Pesticide Leaching Class Ranges

This coverage includes county lines. These lines are not directly
relevant to the data, but are necessary for technical reasons.
Without the additional county lines, some of the polygons exceed
the maximum allowable vertex limit in ARCPLOT. This problem is
solved by the additional county lines, which serve to divide polygons
with too many vertices into smaller units. Accordingly, to remove
the county lines from maps created with ARCPLOT, the DROPLINE
command must be used on conjunction with the COUNT-FED-FIPS
polygon item.