The Surficial Aquifer Potential Map of Connecticut is a 1:125,000 scale analysis, identifying areas considered to have the greatest potential for ground water yield. This map has been prepared for statewide ground water resource protection, water management, non-point source pollution prevention, and land use planning. The map was compiled from a geospatial analysis of the surficial materials and thickness of glacial sediments digital data layers of the Surficial Materials Map of Connecticut, Stone and others (1992) and Quaternary Geologic Map of Connecticut and The Long Island Sound Basin, Stone and others (1998, 2005).  The map identifies areas with greater potential for ground water development based upon the texture and thickness of surficial aquifer deposits. The resulting hydrostratigraphic units define areas of coarse grained deposits, coarse overlying fine grained deposits, fine grained deposits, and areas where fine grained deposits overly coarse grained deposits.  Aquifer deposit thickness intervals are 1-50 feet, 50-100 feet, 100-200 feet, 200-300 feet, and 300-400 feet. 

The Surficial Aquifer Potential Map was prepared by the Connecticut Geological Survey at the request of the Water Protection and Land Reuse Bureau of the Department of Environmental Protection. A statewide view of surficial aquifer resources is necessary to facilitate proactive aquifer protection and water supply planning. Previous statewide groundwater availability (Meade 1978) and ground water yields mapping (Mazzaferro 1986) provided excellent planning documents at the time of publication. The compilation presented here incorporates geologic mapping and interpretations of Stone et al (1992; 1998; 2005) unavailable in the earlier treatments. Notably, the Surficial Materials Map of Connecticut (Stone et al 1992), used in this compilation, provides detailed 1:24,000 scale mapping which delineates larger and more numerous areas of coarse-grained deposits than previously known. 

Connecticut citizens rely on a readily available water supply, derived from both surface and ground water sources. Ground water occurs in the pore spaces of unconsolidated materials overlying the bedrock, and within bedrock fracture systems. Any geologic formations (sediment or rock) capable of yielding a sufficient quantity of ground water to wells are called aquifers. 

The amount of ground water available from an aquifer depends on many factors, including: the physical properties of the aquifer (how permeable and well-connected the pore spaces or fractures are), the size and composition of the watershed, climate, connection to surface water bodies, the amount of runoff due to impervious surfaces, and other water uses in the basin. In general, coarse-grained surficial aquifers (unconsolidated sediments overlying bedrock) have more, better connected pore spaces and are more productive than bedrock aquifers.

Surface water reservoirs and surficial aquifers serve most of Connecticut's urban areas.   Bedrock aquifers have smaller to more moderate yields, but are also an important source of ground water, particularly in the upland areas of Eastern and Western Connecticut, away from urban population centers. 

The Surficial Aquifer Potential Map delineates areas considered to have the greatest potential for ground water yield. The thicker and coarser-grained deposits have higher potential for water supply development. The most productive surficial aquifers in Connecticut are sand and gravel deposits originating from glacial meltwaters. These deposits are mapped where they occur at the surface and where they occur beneath fine- grained deposits.  The map shows total estimated surficial deposit thickness. This includes the combined thickness of fine and coarse-grained portions of the surficial aquifer for units designated as such. Other glacial meltwater deposits are shown on the map to display the full extent of the surficial aquifers, but these fine-grained deposits have significantly lower potential yields. The white areas of the map are areas of till and shallow rock. Till is generally a thin, very poorly sorted glacial deposit with low potential yields. Potential bedrock yields were not included in this compilation.

The surficial aquifer potential areas are mapped based upon their geologic features, without regard to possible natural or man-made water quality issues that may exist. For example, coastal and estuarine aquifers may have naturally impaired water quality due to unacceptable levels of salinity. In some urbanized or industrialized areas, chemical contamination may impair ground water quality. Water quality was not considered in constructing this map, but would be critical in determining if the potential aquifer is viable as a water supply.

DISCUSSION
Coarse-grained glacial deposits have the greatest potential to both store and transmit water. The locations and thickness of these aquifers are of utmost importance for water management. Coarse-grained deposits of thicknesses greater than 50' are considered to have the greatest long term potential ground water yields, particularly where they occur near large rivers and streams. Where coarse-grained deposits have a water saturated thickness of 10' or greater, moderate to very large ground water yields of 50-2000 gallons per minute have been documented. The saturated thickness of these deposits has not been mapped statewide. Therefore, the overall thickness of these deposits may be used as a proxy for saturated thickness in that, given equal recharge, a greater coarse grained deposit thickness would have a higher potential of containing a greater volume of saturated material. 

Detailed mapping of the surficial materials thickness at 1:24,000 scale is available for only 15% of the State. A wealth of historic hydrogeologic data is available for major watersheds of the State from the USGS Water Resources Bulletins (1968-1975). Generalized thickness estimates for coarse-grained deposits were assigned by geologic region for volume calculations conducted at 1:250,000 scale by DiGiacomo-Cohen and Quarrier (1992). Nevertheless, the most useful statewide compilation of surficial materials thickness became available recently as an element of the Quaternary Geologic Map of Connecticut and Long Island Sound Basin (Stone et al, 1998; 2005). 

The compilation of surficial aquifer potential presented here is suitable for statewide and regional environmental planning, however there are several mapping enhancements that may be explored. These include evaluation of additional sources of information relative to potential yields and saturated thickness of surficial aquifers. Additional work regarding the nature and impact of bedrock fractures relative to regional ground water flow may reveal a systematic effect on the quantity of available ground water to surficial aquifers. Additional work toward detailed surficial thickness estimates would refine current surficial aquifer potential mapping units. Also, consideration of known water quality threats of both natural and man-made origins would further support assessments of potential surficial aquifer use for water supply.

Margaret Thomas of the Connecticut Geological and Natural History Survey, Department of Environmental Protection in consultation with Janet Stone, U.S. Geological Survey for Surficial Aquifer Textures and Textural Groups used in the development of this map. Corinne Fitting, of CT DEP Aquifer Protection Program, provided comments on the map. This project was supported by the DEP Nonpoint Source Management Program, through the Federal Clean Water Act Section 319 administered by the U.S. Environmental Protection Agency. 

Publication date of 1:125,000 scale Surficial Materials Map of Connecticut, Stone and others, 1992

All information compiled for this map is available as digital data from the Connecticut Department of Environmental Protection. http://ct.gov/deep

The Surficial Aquifer Potential Map of Connecticut is suitable for regional and statewide water resource planning at 1:125,000 scale, and may be a useful tool for water resource classification relative to potential ground water availability. A surficial aquifer texture map was prepared as an intermediate product of the surficial aquifer potential map compilation. As a reclassification of the original mapping of Stone and others (1992), the aquifer texture map is suitable for use at the original data compilation scale of 1:24,000.

Connecticut Surficial Aquifer Texture is a derivative data product of the 1:24,000-scale Connecticut Surficial Materials data. Connecticut Surficial Materials was digitized from 1:24,000-scale compilation sheets used to prepare and publish a 1:125,000-scale statewide map, Surficial Materials Map of Connecticut, Stone and Others, 1992.
Development of the Surficial Aquifer Texture Map was supported by the Connecticut Department of Environmental Protection  Nonpoint Source Management Program, through Section 319 of the Federal Clean Water Act, administered by the US Environmental Protection Agency.

The Surficial Aquifer Potential Map of Connecticut is a 1:125,000 scale analysis, identifying areas considered to have the greatest potential for ground water yield. This map has been prepared for statewide ground water resource protection, water management, non-point source pollution prevention, and land use planning. The map identifies areas with greater potential for ground water development based upon the texture and thickness of surficial aquifer deposits.

Dataset shows the distribution and thickness of coarse-grained glacial sediment deposits in Connecticut. Mapping units include areas of glacial meltwater deposits, with particular value to ground water resources. Coarse-grained deposits are delineated in intervals of 0-50 ft thick; 50-100 ft thick; 100-200 ft thick; 200-300 ft thick; 300-400 ft thick. Fine-grained deposits overlying coarse-grained deposits include areas 0-50 ft thick; 50-100 ft thick; 100-200 ft thick; 200-300 ft thick. Other glacial meltwater deposits with lower potential ground water yield are also delineated.

Surficial Aquifer Potential Map of Connecticut, 2008, State of Connecticut, Geological and Natural History Survey, Department of Environmental Protection and U.S. Geological Survey, Department of the Interior, Hartford, CT, vector digital data, compilation scale 1:125,000. http://www.ct.gov/deep

State of Connecticut, Geological and Natural History Survey, Department of Environmental Protection and U.S. Geological Survey, Department of the Interior

Polygon features conform to the following topological rules. Polygons are single part. There are no duplicate polygons. Polygons do not self overlap. Polygons do not overlap other polygons. Lines are single part. Line features conform to the following topological rules. There are no duplicate lines. Lines do not self overlap. Lines do not overlap other lines. Lines intersect only at nodes, and nodes anchor the ends of all lines. Lines do not overshoot or undershoot other lines they are supposed to meet and intersect. In general, there are no duplicate features, unresolved intersections, overshooting lines, open polygons, sliver polygons, or unlabeled (unattributed) polygons. 

The tests of logical consistency were performed by the State of Connecticut using ESRI ArcInfo software to maintain feature topology in ArcInfo coverage format. The data is topologically clean. The ArcInfo Clean function was repeatedly used following edits to verify topology and enforce a minimum distance between vertices of 4 feet (fuzzy tolerance) and a minimum allowed overshoot length of 0 feet (dangle length).

The data reflects the content of the data sources: the Surficial Aquifer Texture data layer, a derivitive product of the Surficial Materials datalayer, and the thickness of glacial sediments datalayer of the Quaternary Geologic Map of Connecticut and The Long Island Sound Basin. The Surficial Materials datalayer was digitized 1:24,000-scale mylar compilation sheets.The materials texture was taken from a set of 1:24,000 scale mylar sheets used to compile and publish the Surficial Material Map of Connecticut, Stone and others, 1992 (U.S. Geological Survey in cooperation with the Connecticut Geological and Natural History Survey, DEP, 2 sheets, 1:125,000 publication scale).  The thickness of glacial sediments..............................

The Connecticut Surficial Aquifer Texture data retains the underlying surficial material polygon feature and attribute information of the 1:24,000-scale Connecticut Surficial Materials layer, which retains the feature types and information identified on the 1:24,000-scale compilation sheets for the Surficial Materials Map of Connecticut, Stone and others, 1992. All attributes have valid values. Values are within defined domains. The accuracy test for the SMPOLY_COD attribute values was conducted by comparing the geologic map unit information presented on the source mylar overlays with 1:24,000-scale check plots or interactive displays of the digital data on a computer graphic system. These check plot maps and computer displays depicted and labeled the surficial material polygon features in different colors and line-fill patterns based on SMPOLY_COD attribute values for comparison with the original data source. SURFM_POLY and DESCRIP represent both brief and full text English language equivalents of (decodes) the SMPOLY_COD attribute, respectively. The TEXTURE, TEXTURE_GRP and STRAT_DRIFT that classify the SMPOLY_COD values into various texture categories and were populated by joining the Surficial_Aquifer_Texture_Data lookup data table to the polygon features using SMPOLY_COD as the relate key field instead of manually entering these values for each polygon feature. The Surficial_Aquifer_Texture_Data lookup table accounts for all 50 values of SMPOLY_COD, assigning each value a corresponding TEXTURE, TEXTURE_GRP and STRAT_DRIFT value.

The horizontal positional accuracy of this data complies with the United States National Map Accuracy Standards for 1:24,000 scale maps. According to this standard, not more than 10 percent of the locations tested are to be in error by more than 1/50 inch (40 feet) measured on the publication scale of a USGS 7.5 minute topographic quadrangle map. Feature locations were interpolated from the transporation features, surface water features, elevation contours, buildings,  built-up areas, and other natural features and landforms depicted on USGS 7.5 minute topographic quadrangle maps.

Connecticut Surficial Aquifer Potential