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Track: Environmental Management
James Bollinger
Westinghouse Savannah River Company
Building 786-6A
Aiken, SC 29808
Telephone: 803-72508253
Fax: 803-725-2956
E-mail: jameso2.bollinger@srs.gov
Robert Hiergesell
Locating Monitoring Well Screen Zones within the Vertical Hydrostratigraphy at the Savannah River Site
Defining Issue: Groundwater samples taken from wells that breach confining units produce unreliable data and represent potential conduits for the migration of contaminants to deeper aquifer units. Examining well geophysical logs and related well data to locate wells with screen and annular-materials zones that may breach a confining unit is a time intensive process. GIS, therefore, was utilized as an inexpensive screening tool to determine which wells at the Savannah River Site's administrative and technical area potentially penetrate aquifer-confining units. GIS Solution: Three-dimensional gridded surfaces representing the interfaces of aquifer and confining units were used in conjunction with well construction data from a relational database in a GIS application written to locate well screen and annular-materials zone top and bottom elevations within the vertical hydrostratigraphy. The application then was used to identify wells with screen and annular-materials zones that potentially breach a
confining unit. Methodology: Three-dimensional hydrostratigraphic surfaces were imported into ArcInfo as ARCGRID coverages, and the surfaces were used in ArcInfo to determine the vertical elevation of each well projected onto each surface. These projected well elevations were written to an ArcInfo point attribute table containing the geographic coordinates of each well, screen, and annular-materials zone top and bottom elevations, and other descriptive attributes. AMLs then were written and used to determine the locations of the tops and bottoms of well screen and annular-materials zones within the vertical hydrostratigraphy and to identify wells that might breach aquifer-confining units. As a result of this study, sixty-six wells were found that might breach such units. Software: EarthVision software was used to develop the 3D gridded surfaces representing the hydrostratigraphic contacts. ArcView Avenue scripts with embedded SQL strings were used to access well construction data in an Oracle
database, and ARC GRID and AML were used to process the 3D gridded surfaces and well construction data. The purpose of this paper is to demonstrate the use of GIS as an effective screening tool to rapidly process and use 3D hydrogeologic data to locate groundwater wells that should be evaluated for removal from service.
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