Office of
Indiana State Chemist and Seed Commissioner
GROUND WATER PROTECTION
STATE OF INDIANA DRAFT GENERIC
PESTICIDE MANAGEMENT PLAN
COMPONENT 5 ASSESSMENT AND PLANNING
A technique for developing ground water vulnerability
to pesticide maps for state-sized areas will be developed that
uses geographic information system (GIS) and other databases commonly
available for such areas. The technique will improve upon existing
techniques that estimate ground water vulnerability as a result
of hydrogeologic factors. The improved map will be compared for
accuracy against results from previous methods. The technique
will be applied to develop a ground water vulnerability to pesticides
map for the state of Indiana. Ground water quality information
will be used to statistically evaluate the resulting vulnerability
maps.
Approach to Vulnerability Assessment
The technique proposed for developing maps of ground
water vulnerability to pesticides will involve several steps.
A description of the proposed technique follows. An initial set
of vulnerability maps will be developed based on hydrogeologic
factors as considered by DRASTIC and SEEPAGE. DRASTIC is an empirical model developed by the National Water Well Association in conjunction with the EPA for evaluating ground water contamination potential on a regional basis. SEEPAGE (System for Early Evaluation of the Pollution Potential of Agricultural Groundwater Environments)
estimates contamination potential of ground water using hydrologic
factors in a manner similar to DRASTIC. DRASTIC and SEEPAGE will
be applied with 1:250,000 scale or more detailed map data.
The factors considered by these programs are:
| DRASTIC
| SEEPAGE
|
| Depth to water
| |
| Recharge
| Soil slope |
| Aquifer media
| Depth to water table |
| Soil Media
| Vadose zone material |
| Topography
| Aquifer material |
| Impact of the vadose zone media
| Soil depth |
| Conductivity (hydraulic) of the aquifer
| Seepage attenuation potential factor uses following factors:
|
| Soil Surface texture
|
| Subsoil texture
|
| Surface layer pH
|
| Organic matter content of surface
|
| Soil drainage class
|
| Soil permeability
|
The results of DRASTIC and SEEPAGE will provide initial
vulnerability maps based on hydrogeologic factors. Pesticide use
maps will be generated using 1:250,000 scale land use/land cover
data from the USGS and county pesticide use data from the Indiana
Agricultural Statistics Service. Crop types as a percentage of
crop land within counties will also be obtained from Indiana Agricultural
Statistics Service.
The maps showing relative vulnerability and pesticide
use will be compared to data from well location and well pesticide
concentration databases. Presently within Indiana, the data compiled
by USGS in cooperation with IDEM Office of Water and data verified
in the Indiana Farm Bureau pesticide databases will be utilized
in this comparison. In areas of the state where predicted vulnerability
are in disagreement with database results, process oriented models
may be utilized to examine the simulated movement of pesticides
into the ground water. GLEAMS (Ground water Loading Effects of
Agricultural Management Systems), RUSTIC (Risk of Unsaturated/Saturated
Transport and Transformation of Chemical Concentration model),
and PRZM (Pesticide Root Zone Model) simulate both hydrology and
chemical transport and are capable of providing more detailed
assessments of contamination potential than DRASTIC or SEEPAGE.
The vulnerability maps that consider pesticide use
data, subsurface materials, ground water, chemical movement simulations
(RUSTIC, GLEAMS and PRZM), and actual pesticide in ground water
data will be developed as described in the attached proposal (Appendix
F). Ground water areas identified as being highly vulnerable to
pesticide contamination will allow Indiana to geographically prioritize
our prevention, monitoring and response activities of the SMP.
Limitations of the Assessment Procedure
This assessment procedure assumes that pesticides
are applied properly as foliage, surface or soil incorporated
applications. Spills, back siphoning of wells, or rapid flow through
the soil zone require consideration as localized sources of contamination.
The published map unit scale is 1:250,000. Map units
and contours represent an interpretation of inherently variable
conditions. The boundaries are transitional by definition, consequently
their positions at the scale of the maps are only a general approximation.
Conditions at a specific site may differ from those shown on the
maps. These maps are intended to assist with regional scale modeling
activities and are not sufficient as the sole source of information
for site specific investigations.
Spatially referenced information concerning sources
of drinking water has been identified as our most problematic
data. The spatially referenced data that exists is biased to area
where small scale studies have been conducted. Efforts have begun
to assign a unique identifier number to each new water well record
recorded in the IDNR Division of Water. The location of each well
log is then digitized allowing water quality information collected
by other agencies to be related to a geographic location, soil
profile characteristics, water well construction, depth of aquifer,
and depth of screening information if the well record numbers
are matched.
Data Availability
The development of the data described in this component
is expected to enhance the capability of other environmental regulatory
programs whose focus is other than pesticides.
- Annual Pesticide Use - lists the approximate acres
of corn, soybeans and wheat planted for each county, types of
pesticides applied, average rate of each herbicide applied, percentage
of acres treated by each product. Status: maps competed for 1991,
1992 and 1993 crop years. Source: USDA Agricultural Statistics
Service.
- Land Use - spatial map which categorizes different
types of land use activities occurring in the state. For example
agricultural, residential, recreational. Status: map completed.
Source: USGS.
- Elevation - spatial maps which identify the elevation
of the land. Can be developed into other products including slope,
watershed or aspect maps. Status: map completed. Source USGS.
- Wetlands - spatial map identifying the location and
classification of wetlands in Indiana. Uses the U.S. Fish and
Wildlife classification system. Status: map completed. Source:
Indiana Department of Natural Resources.
- Hydrography - spatial location of streams and rivers
in Indiana. Status: map completed. Source USGS.
- Soils - Modern soil surveys have been completed
and published for each county in Indiana at a 1:24,000 or more
detailed scale. Efforts have begun to digitize these county maps
in accordance with SSURGO standards. In addition, digital 1:250,000
scale soil association maps have been published which meet STATSGO
standards. The STATSGO data will be utilized in developing aquifer
vulnerability to pesticide map products. Source: NRCS.
- Indiana Water Well Records - sites files resulting
from the collection of water well drilling information during
the installation/abandonment of water wells. Examples of information
include: static water level, aquifer materials, age of well, well
construction. Status: Data collected 30 years, electronic retrieval
system began development March 1994. Source: Indiana Department
of Natural Resources, Division of Water.
- Hydrogeologic Framework - spatial map identifying
the distributions of major hydrogeologic regions, settings, and
sub setting in Indiana. Status:
- Northern 1/2 Indiana under development,
expected completion date: December 1994.
- Southern 1/2 Indiana, expected completion date: December
1995. Source: Indiana Geological Survey and Indiana Department
of Natural Resources, Division of Water.
Supplementary spatial data includes:
- thickness of fine-grained confining units where present between
soil surface and confined aquifers at depth;
- thickness of unconfined sand and gravel aquifers for unconfined
hydrogeologic settings;
- depth to water table for unconfined hydrogeologic settings;
- depth to permeable bedrock where less than 50 feet.
- Pesticides in Ground Water Data - government agency data on the occurrence of pesticides and pesticide metabolites
in Indiana ground water. Results of analyses of 725 samples were
summarized for the period December 1985 through April 1991. The
data had been collected during 6 statewide surveys and 15 localized
studies by the IDEM Office of Water, IDNR Division of Water, US
EPA and USGS. Source: USGS.
Roles of State Agencies and Universities - For Assessment
The Office of Indiana State Chemist and the other
agencies identified as having roles and responsibilities for the
assessment and planning component of the SMP organized a technical
advisory committee to provide input during the hydrogeologic settings
(Appendix B) and ground water vulnerability to pesticide (Appendix
F) map development. The representatives to the technical advisory
committee will meet periodically to review the hydrogeologic settings
and the aquifer vulnerability mapping process.
