The South Dakota Geological Survey collects a large amount of natural resources data across the state of South Dakota. Databases have been built to manage this data and provide an efficient means for retrieval and analysis. A GIS system is being implemented to enhance the analysis and management of this data. Improved access for the user is one of the benefits of standardizing databases for a GIS system.
A GIS system is also being used to assist in the production of digital aquifer boundary maps for the state. Maps are initially being generated at a small scale to provide general information about where the aquifer systems exist in the state. Larger scale maps will be produced to provide the user with detail that can be used for more specific determination of where the aquifer systems exist in the state.
The South Dakota Geological Survey (SDGS) is a program within the South Dakota Department of Environment and Natural Resources (DENR). SDGS is responsible for collecting and assembling information about the geologic and hydrologic resources of the state. Emphasis is placed on ground water quality and quantity and other resources of economic value to the state. This data is gathered through a structured program of county geology studies and various other studies focusing on regional resource assessment. The data collected and analyzed, along with the resulting reports and maps produced by SDGS enhance the understanding and use of the state's geologic and hydrologic resources.
The basic data collected by the SDGS consists of testhole and well lithologic data, water quality data, and water level data. The SDGS maintains a high level of field activity with various drilling and sampling operations. Drilling programs generate new testhole and well data each year. Data from testholes and wells are logged, coded, and entered into a lithologic logs database. This database currently consists of over 32,000 testhole and well entries, spreading across the entire state. Baseline water sampling for various projects generates inorganic and organic water analyses. Results from these analyses are stored in a water quality database, which currently contains about 3,000 analyses. Water level measurements from a network of about 2000 observation wells are taken on a frequent basis by the DENR-Water Rights Program. SDGS accesses the water levels database maintained by this program and relates the data into the previously mentioned databases.
SDGS plays an integral role in implementing GIS throughout its parent organization, DENR. A GIS Advisory Group has been formed in DENR. It is responsible for implementing GIS, and coordinating GIS related activities between DENR and other entities. The general goals of the advisory group are:
The Advisory Group is migrating primary DENR databases to Visual FoxPro under a Windows NT network. The purpose of this is to
The SDGS lithologic logs database is an example of this effort. The database has an easy to use query screen so those users unfamiliar with database management software can still retrieve information from the database on their own. Currently, users can retrieve lithology and water level data from this interface. Access to the water quality database is being integrated into this system. Although the databases are currently only accessible online by departmental employees, methods are being developed to make online database access available to the general public. An example of the query screen and the results from the query are shown in figures 1 through 3.
Figure 1. Lithologic logs query screen. [58 K GIF]
Figure 2. Query output screen -- part 1. [60 K GIF]
Figure 3. Query output screen -- part 2. [56 K GIF]
The lithologic logs database is one of many databases being incorporated into GIS. The usefulness of GIS becomes apparent when users are able to perform queries and other analytical functions on a database such as the lithologic logs database. Figure 4 shows a representation of the database in ArcView. All of the 32,000 plus records are plotted in figure 4. This gives a visual indication of where the work has been done in South Dakota and where data is available. It is also a tool for pointing out areas where there are gaps in the data coverage.
Figure 4. Plot of testhole and well locations. [34 K GIF]
SDGS has been producing maps of the geology of the state for many years. In 1953, a generalized geologic map of the state was published at a scale of 1:500,000. Much more accurate data has been collected since that time as a result of the Survey's county study program and other projects. A newly revised and more detailed geologic map of the state is currently being published at a scale of 1:500,000.
It is also necessary, however, to produce maps which clearly delineate aquifer boundaries in the state. SDGS is in the process of producing a 1:500,000-scale map which shows a general view of the aquifer boundaries in the state (figure 5). Currently, the eastern half of the state has been completed and is being digitized into a GIS layer. This map is based on the recently revised 1:500,000-scale geology map of the state. Boundaries of surficial aquifer materials were outlined and categorized to generate this map. The scale of the map limits its application. It will be used to depict the general location of surficial aquifers in the state. It should not be used for site specific aquifer boundaries. The availability of geologic data at this scale and the time frame required to produce the map made it a desirable product. It took approximately 160 man-hours to generate the boundaries and digitize the map into ArcView. It will serve as a precursor to larger scale aquifer maps.
Figure 5. Aquifer boundaries at 1:500,000 scale. [46 K GIF]
SDGS is also beginning to incorporate 1:100,000 scale aquifer boundary maps on a county basis into digital form. The maps are based on the 1:100,000 scale geologic maps that are produced from the county study program. The level of detail that this scale of map provides allows the user to begin to define aquifer boundaries within the square mile. This makes the map useable on a project level. Siting of landfills, contaminant spills, and other environmentally sensitive subjects can be improved with these maps. It is estimated that each county map can be produced with about 120 man-hours of work. This includes generating surficial aquifer material boundaries and digitizing these boundaries into ArcView. Figure 6 is an example of 1:100,000 scale aquifer boundaries from the central portion of Codington County in northeastern South Dakota.
Figure 6. Aquifer boundaries at 1:100,000 scale. [36 K GIF]
Figure 7. Aquifer boundaries at 1:24,000 scale. [42 K GIF]
Aquifer boundary maps at a 1:24,000 scale are needed by many public and private entities. Generating a map of this scale for the entire state will be a major undertaking. The following list describes the basic data that will be used for generating accurate 1:24,000 scale aquifer boundary maps.
Accurate 1:24,000 aquifer boundary maps will be used for site specific analysis of many environmental issues. The detail that will be available will allow users to make site-specific judgments with regard to aquifer locations. The time and effort involved to produce statewide coverage will be on the order of man-years. It is likely that some parts of the state will be designated high priority for 1:24,000 mapping and will be done long before other remote parts of the state. Complete statewide coverage of 1:24,000 aquifer maps, however, remains a goal of the state.
The efforts of data collection, storage, and analysis by the DENR, including SDGS, warrant the development of a GIS system to assist in the management and analysis of data. Migrating primary databases into a common database management system and development of user friendly access system is an important part of developing the GIS system.
One of the products of the GIS system will be digital aquifer mapping. Digital aquifer maps are being generated at 1:500,000, 1:100,000, and 1:24,000. The detail and usefulness of each scale is inversely related to the time and human resources required to produce the map. Digital aquifer boundary maps at 1:500,000 scale are readily produced, but of limited value for anything but a general overview of where the state's surficial aquifers are. Digital aquifer boundary maps compiled at a 1:100,000 scale begin to provide enough detail for site specific use, and the time and cost of preparation is reasonable. It is a good investment of time and resources to produce this scale of map for the state. Large-scale maps, such as 1:24,000, are the ultimate product for this type of mapping. However, the time it will take to prepare them will be considerably longer.