Larry D. Putnam, U.S. Geological Survey 2001 (Version 1.0, January 22, 2001) Digital map Rapid City, SD, USA U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?sd_lcsens_pol Larry D. Putnam 2000 Water-Resources Investigations Report WRIR 00-4103 Rapid City, SD, USA U.S. Geological Survey This data set includes 956 polygons labeled with a sensitivity-unit code that represents the sensitivity of ground water to contamination in Lawrence County, SD. This data set is a result of a larger work (WRIR 00-4103 cited above), which includes a paper plate titled: "Map showing sensitivity of ground-water to contamination in Lawrence County, South Dakota." This data set is part of the digital data that was used to create that map. The sensitivity-unit code is an attribute that consists of a letter followed by three numerical digits, which characterizes sensitivity to contamination. Letter codes that begin with upper case letters (A-Z) and continue with lower case letters (a-s) represent characteristics of the rock and sediments, with 'A' being most sensitive and 's' being least sensitive. The first digit represents recharge rate with 1 being the most sensitive and 4 the least sensitive. Three quantitative categories (1-3) and two qualitative categories (4,5) represent depth to water. Groups 1 through 3 represent areas where data was available to estimate depth-to-water with 1 most sensitive and 3 least sensitive. Qualitative categories 4 and 5 represent areas that only can be compared to each other with 4 being the most sensitive. The third digit represents land-surface slope with 1 being the most sensitive and 5 being the least sensitive. An additional attribute, hydrologic setting, represents areas with common hydrologic characteristics. These 11 hydrologic settings are represented by a letter code symbol. The process step section below describes the attributes in more detail and how the attributes were developed from source data. The source data includes digital maps that characterize the geology, precipitation distribution, and water levels, which have been compiled at 1:100,000 scale and published in 1999 and 2000 as part of the Black Hills Hydrology Study. USGS Digital elevation models were used to describe land-surface altitudes. This data set has been archived at the USGS Water Resources National Spatial Data Information Node. This data set was created to describe the sensitivity of ground water to contamination in Lawrence County, SD. An additional mechanism of transport of potential contaminants is streamflow loss (infiltration). Mechanisms of potential contamination considered were limited to those that can occur near the land surface and did not include deep subsurface injection. Ground water, for the purposes of this data set, refers to the water in the uppermost saturated rocks and sediments that can be yielded in usable quantities to a well or spring. Transport of a potential contaminant was assumed to occur from infiltration of precipitation from the land surface to the uppermost saturated rocks. Runoff from precipitation on drainage basins upstream from streamflow-loss zones affects the sensitivity of map areas containing the losing stream. Therefore, two additional digital data sets delineating and describing streamflow loss zones and drainage basins above them should be conjunctively considered when evaluating sensitivity to contamination (see cross-reference to obtain these digital data sets). These data sets provide some information about the upstream drainage basins that can be compared but no attempt was made to provide a relative ranking of sensitivity based on this information. The intended use of the sensitivity data sets is as a screening tool used in conjunction with other information and analysis. Some relative comparisons can be made between factors that influence sensitivity of ground-water to contamination. The map is not designed to replace the need for site-specific investigations or to be the sole criterion in making land-use decisions. This electronic report was subjected to the same review standard that applies to all U.S. Geological Survey reports. Reviewers were asked to check the topological consistency, tolerances, attribute frequencies and statistics, projection, and geographic extent. The reviewers checked the metadata and a_readme.1st files for completeness and accuracy. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ARC/INFO format, this metadata file may include some ARC/INFO-specific terminology. Other_References_Cited: Aller, L., Bennett, T., Lehr, J.H., Petty, R.J., and Hackett, G., 1987, DRASTIC: A standardized system for evaluating ground water pollution potential using hydrogeologic settings: U.S. Environmental Protection Agency, EPA/600/2-87/035, 455 p. Strobel, M.L., Jarrell, G.J., Sawyer, J.F., Schleicher, J.R., and Fahrenbach, M.D., 1999, Distribution of hydrogeologic units in the Black Hills area, South Dakota: U.S. Geological Survey Hydrologic Investigations Atlas HA-743, 3 sheets, scale 1:100,000. 19990609 The sensitivity polygons are as current as the maps from which the information was derived. The DEM's were compiled from a range of dates specific to each 1:24,000 quadrangle. Precipitation data and the hydrogeologic units map are from 1999 interpretations for the Black Hills Hydrology study. Complete None Planned -104.06234134 -103.43977512 44.60926227 44.13453073 None Contamination Ground water Aquifer sensitivity Black Hills, aquifer vulnerability inlandWaters None Lawrence County Black Hills South Dakota None A limitation that needs to be considered when using the data set is scale. The scale of the map is 1:100,000; therefore, the hydrogeologic information includes numerous generalizations. Modifying or overlaying the map at a scale that is more detailed than the original map may be extremely misleading. Larry D. Putnam U.S. Geological Survey Hydrologist Mailing and physical address

1608 Mt. View Rd

Rapid City South Dakota 57702 USA 1-888-275-8747 (605) 355-4523 (ldputnam@usgs.gov) Compilation of this data set and the associated metadata was funded in cooperation with Lawrence County, SD and the City of Spearfish, SD. SunOS, 5.6, sun4u UNIX ARC/INFO version 8.0.1 Larry D. Putnam 2000 Digital map NA NA Rapid City, South Dakota, USA U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?sd_lcsens_da Larry D. Putnam 2000 Digital map NA NA Rapid City, South Dakota, USA U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?sd_lcsens_lz Multiple visual checks were done to verify that the attribute data was coincident with the original source map. Polygon topology present-polygon have a label and all polygons are closed. The digital map includes all sensitivity polygons and associated sensitivity- unit codes as shown on PLATE 1 in USGS WRIR 00-4103 The physical accuracy of the source maps is unknown. Greg Jarrell, John Schleicher 2000 Digital map Open-File Report USGS OFR 00-471 Rapid City, South Dakota U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?ofr00471_hydrogeo 100000 digital 1999 The ninteen references used to create this map range in date from 1909 to 1998. Some field checking was done in selected areas where less detailed source maps were available. None This map was the primary source for determining the spatial distribution of hydrogeologic units. This source provided the outlines of geologic formation outcrops. U.S. Geological Survey 19790701 Digital map Reston, VA, USA U.S. Geological Survey http://edc.usgs.gov.nsdi/html/dem75/dem75#section7 digital 19790701 Present Range of dates of source material for DEM production DEM The source provided the spatial distribution of land surface elevation for determining depth-to-water and land-surface-slope categories. Joel Galloway, Ghaith Hamade, Gregory Jarrell 2000 Digital map Open-File Report USGS OFR 00-471 Rapid City, South Dakota, USA U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?ofr00471_inkrpcon 100000 digital 19980730 The contours were drawn with information on elevation, geologic outcrops, geologic structure, and water levels from wells drilled as of 1998. None This map was used to calculate the depth to water for the Inyan Kara aquifer. This product is the digital version of the sensitivity polygons on Plate 1 in USGS WRIR 00-4103, which documents the process used in creating the map in detail. The sensitivity polygons were derived by sequential overlaying and intersecting five digital-map coverages that represented hydrologic setting, hydrogeologic unit (aquifer media, unsaturated media, and hydraulic conductivity), recharge rate, depth to water, land-surface slope. The polygons produced from the overlaying layers retained a code from each map layer that was unique to the polygon. The hydrologic setting is represented by a numeric attribute. The letter code, hydrogeologic unit, represents evaluation of (1) aquifer media, (2) unsaturated media (3) hydraulic conductivity for sensitivity comparisons. These factors were grouped because they are all related to the rock and sediments. Forty-five unique hydrogeologic units where characterized and ranked in descending order and sorted on the sensitivity rating for unsaturated media, then aquifer media, and then hydraulic conductivity. The codes begin with an uppercase "A" and continue through lower case "s." When the first 26 uppercase letters were used, the codes were continued with lower case letters. The first digit in the sensitivity-unit code represents the recharge rate with group 1 the most sensitive and group 4 the least sensitive. The second digit in the sensitivity-unit code represents the depth to water. The depth-to-water digit includes two comparison groups, quantitative groups and qualitative groups. The quantitative groups, which include areas where estimates of depth to water were available, were ranked with group 1 the most sensitive and group 3 the least sensitive. The two qualitative groups were areas with highly variable depths to water. The stream valleys in the mountainous areas (group 4) were assumed to have shallower depths to water than adjacent areas (group 5) with highly variable depths to water. Although the depth to water is highly variable, the delineation provides a basis for some relative comparisons of groups 4 and 5 with 5 being the least sensitive. The third digit in the sensitivity-unit code represents the land-surface slope, which consists of five groups, with group 1 the most sensitive and group 5 the least sensitive. Below is a summary of the main process steps used to create the sensitivity polygons shown on USGS WRIR 00-4103 Plate 1. STEP 1: The first step to delineate sensitivity polygons was to subdivide the study area into a geographic framework of hydrologic settings with generally similar hydrogeologic characteristics. Eleven settings were delineated in Lawrence County based on topography, precipitation patterns, and the digital hydrogeologic units map for the Black Hills. The hydrologic units map was used as the physiographic base. STEP 2: Because of the significant differences in sensitivity characteristics of the geologic formations, the hydrogeologic-unit coverage, (collectively represents aquifer media, unsaturated media, and hydraulic conductivity) was selected as the next descriptive map layer. This layer was derived from the hydrogeologic units map for the Black Hills, but represents a new coverage. Forty-five hydrogeologic units were delineated based on the intersection of the hydrologic settings layer and outlines of geologic formations with related assessments of aquifer media, unsaturated media, and hydraulic conductivity. Each hydrogeologic unit was identified by an alphabetic character beginning with capital letters and continuing with lowercase letters. The hydrogeologic units were sorted in descending order (A-Z, the a-s) based on the relative sensitivity rating from most sensitive to least sensitive. STEP 3: A map delineating 4 categories of recharge-rate with 1 most sensitive and 4 the least sensitive was overlaid and intersected with the previous map. The recharge rate map was created by developing grided data that estimated recharge rate as a percent of precipitation for each hydrogeologic unit and multiplying this grid by a grid of average precipitation interpolated from precipitation gaging stations. STEP 4: A map delineating 5 depth-to-water categories was overlaid and intersected with the previous map. Smaller depths to water were considered more sensitive. Three quantitative categories (1-3) and two qualitative categories (4,5) were used to describe depth to water. Groups 1 through 3 represented areas where data was available to estimate depth-to-water categories with 1 most sensitive and 3 least sensitive. Areas with steeply dipping strata of fractured rocks were not categorized for depth to water because of the large variations in topography and water levels. In areas where data was insufficient to characterize depth to water, the shallower depth to water generally exists in stream valleys; therefore, areas with land-surface elevations less than 50 ft above streambed elevations were delineated as group 4 to make relative comparisons with areas greater than 50 ft above streambed elevations, which were group 5. STEP 5: A map representing land-surface slope categories was overlaid and intersected with the previous map to create the final map. The land-surface slope categories were calculated from 30-meter resolution digital elevation models (DEM). Flatter slopes were considered more sensitive because a potential contaminant would be more likely to runoff before infiltrating to the water table. Five categories were delineated with 1 most sensitive and 5 least sensitive. The intersecting of these map layers resulted in 956 polygons with associated sensitivity-unit codes. 1999 First draft of metadata created by ldputnam using FGDCMETA.AML ver. 1.33 07/15/99 on ARC/INFO data set /home/project/ldp/projects/lawco.vuln/finalcovs/sens_pol 20010122 Vector Point 956 String 2868 GT-polygon composed of chains 957 Point 4 Transverse Mercator 0.999600 -105.000000 500000.000000 0.000000 coordinate pair 0.985814511776 0.985814511776 Meters North American Datum of 1927 Clarke 1866 6378206.4 294.98 sd_lcsens_pol.aat FID SHAPE FNODE# TNODE# LPOLY# RPOLY# LENGTH SD_LCSENS_POL# SD_LCSENS_POL-ID $ID $FROMNODE $TONODE $LEFTPOLYGON $RIGHTPOLYGON sd_lcsens_pol.pat FID SHAPE AREA PERIMETER SD_LCSENS_POL# SD_LCSENS_POL-ID SETTING HGU-CODE RECH-CODE DW-CODE SLP-CODE COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME 1 AREA 4 12 F 3 5 PERIMETER 4 12 F 3 9 SD_LCSENS_POL# 4 5 B - 13 SD_LCSENS_POL-ID 4 5 B - 17 SETTING 5 5 C - 22 HGU-CODE 2 2 C - 24 RECH-CODE 1 1 I - 25 DW-CODE 1 1 I - 26 SLP-CODE 1 1 I - AREA -Area of polygon in square meters PERIMETER -Perimeter of polygon in meters SD_LCSENS_POL# -Internal feature number SD_LCSENS_POL-ID -Assigned feature number SETTING -Assigned symbol representing hydrogeologic unit HGU-CODE -Assigned number for hydrogeologic unit letter in sensitivity-unit code RECH-CODE -Assigned number for recharge-rate digit in sensitivity-unit code DW-CODE -Assigned number for depth to water digit in sensitivity-unit code SLP-CODE -Assigned number for slope digit in sensitivity-unit code List of hydrologic setting symbols, name, and description for attribute SETTING Ms-e Mountain Slopes-East This setting, located in the southeastern and south-central part of the study area, is characterized by steep slopes, thin soil cover, and fractured bedrock consisting mostly of igneous and metamorphic rocks. Well yields typically are limited, although in local areas the hydraulic conductivity could be high due to fracturing. Thicker weathered zones may develop locally particularly on talus slopes with perched water common. The topographic trend of these slopes is to the east in the rain shadow of the mountains, and limited rainfall is derived from moisture-laden prevailing westerly winds. Because of the orographic effect of the Black Hills, the northern part of this setting receives more rainfall than is typical for this setting. Ground-water levels are extremely variable. Ms-n Mountain Slopes-North This setting, located on the northern slope of the uplift, is similar to Mountain Slopes-East except precipitation generally exceeds that which falls on eastern slopes. Recharge remains relatively low, however, because of the steep slopes and low primary porosity of the rock. In this particular setting, increased fracturing may occur in areas along the flanks of igneous intrusions. Amv-e Alluvial Mountain Valleys-East This setting, located in east sloping valleys within the mountain slopes-east setting, is characterized by thin alluvium and boulders derived from the surrounding steep slopes. Soil cover generally is gravel sized. Ground water may be obtained from the alluvial deposits and also from the fractures in the underlying bedrock, which are generally in direct hydraulic connection with the alluvium. This type of setting may be expected along most of the streams within the Mountain Slopes-East setting; however, some contiguous mappable areas may be less than 100 acres and consequently may not be shown on the map. Amv-n Alluvial Mountain Valleys-North This setting, located within the Mountain Slopes-North setting, is similar to the Alluvial Mountain Valleys-East setting. Ground-water levels are typically shallower because of higher amounts of precipitation and subsequently greater recharge. This type of setting may be expected along most of the streams within the mountain slopes-north setting; however, some contiguous mappable areas may be less than 100 acres in many areas and consequently may not be shown on the map. Id Igneous Domes This setting, located across the central part of the study area, is characterized by igneous intrusive rocks surrounded by dipping sedimentary rocks. Folding and faulting of the sedimentary rocks along the flanks of the domes may increase the permeability and the recharge rate of these units. Well yields are extremely variable depending on the degree of folding and faulting and the type of rock. Where few fractures exist in the igneous domes, well yields are very low or non-existent; however, well yields typically are greater along the fractured areas on the flanks of the domes. Sedimentary rock outcrops, hydraulically connected to the confined regional aquifers, could have relatively large recharge rates because of increased fracturing and relatively large precipitation amounts. Lp Limestone Plateau This setting, located in the southwestern part of the study area, includes most of the area referred to locally as the "Limestone Plateau." This setting has more relief than the moderate and variable topographic relief described in the "Solution Limestone setting" in DRASTIC (Aller and others, 1984). The limestone is characterized by a network of solution openings where the limestone has been partially dissolved along bedding planes and fractures. Soil usually is thin or absent, but where present commonly is a clayey loam. Recharge usually is high because infiltration of precipitation occurs easily through the fractures and solution openings. Return of recharge into surface water courses can be high. Water levels typically are moderately deep except near surface discharge points. Mf Mountain Flanks This setting, located on the mountain flanks along the western, north-central, and eastern parts of the study area, is characterized by moderately dipping, fractured, consolidated sedimentary rocks. Soil usually is thicker than on mountain slopes. Ground water is obtained from the permeable sedimentary rocks or from fractures in the sedimentary rocks. The recharge rate is higher in the western and north-central parts because of greater precipitation. The mountain flanks serve as recharge areas for aquifers that are confined in adjacent areas. Amv Alluvial Mountain Valleys This setting, located in narrow valleys within the igneous domes and mountain flanks setting, is characterized by thin alluvium and boulders that overlies fractured bedrock of sedimentary or igneous intrusive origin. Surficial deposits have typically weathered to a sandy loam. Ground water is obtained from sand and gravel layers, which commonly are in direct hydraulic connection to underlying bedrock. This type of setting may be expected along most of the streams within the igneous domes and mountain flanks settings; however, some contiguous mappable areas may be less than 100 acres in many areas and consequently may not be shown on the map. Sls Alternating Sandstone, Limestone and Shale-Thin Soil This setting, located in the northern part of the study area, is characterized by low to moderate topographic relief. Relatively thin loamy soils overlie horizontal or slightly dipping alternating layers of fractured, consolidated sedimentary rocks. Ground water primarily is obtained from sandstone layers or fractures along bedding planes or vertical fractures. Recharge generally is moderate to low. Shale or clayey layers often form confining layers and where sufficient relief is present, perched ground-water zones of local importance often are developed. Usd Unconsolidated or Semi-Consolidated Deposits This setting is characterized by moderately low topographic relief and interbedded deposits that consist of layers of clay, silt, and sand. Although soils are typically loamy or sandy, recharge is limited because of moderate precipitation and high evapotranspiration. Ground-water levels typically are less than 50 feet. Ra River Alluvium without Overbank Deposits This setting is characterized by low topographic relief and deposits of alluvium along stream valleys. Ground-water levels typically are shallow. Infiltration of precipitation is rapid but limited by the amount of precipitation. Interaction between the stream and the ground-water system is significant. List of hydrogeologic unit code, hydrologic setting, geologic unit, and comments for attribute HGU_CODE A Igneous Domes Madison Limestone-Englewood Formation This part of the Madison Limestone outcrop is located across the central part of the study area near intrusive rocks. Inventoried well yields in the regional Madison aquifer are highly variable with the largest group ranging from 10 to 200 gal/min and a significant number of wells between 400 and 1,750 gal/min. Permeability is mainly from enhanced solution openings, which occur predominantly in the upper 200 ft of the formation, and fractures. Additional fracturing is possible due to igneous intrusive activity. Hydraulic conductivity determined from aquifer tests of wells with larger yields are in the range of 200 ft/d. Rapid movement of potential contaminants with little attenuation through solution openings or fractures in the aquifer media and unsaturated media is likely. Little well information is available for the Englewood Formation, and hydrogeologic characteristics were assumed to be similar to the overlying lower Madison Limestone. B Limestone Plateau Madison Limestone-Englewood Formation This part of the Madison Limestone outcrop, located within the Spearfish Creek drainage basin, includes a large part of Limestone Plateau setting. Inventoried well yields within the unconfined outcrop area are less than 20 gal/min. Permeability is from enhanced solution openings, which occur predominantly in the upper 200 ft of the formation and fractures. Ground-water flow is towards springs discharging to Spearfish Creek and Rapid Creek, and to the regional Madison aquifer. Rapid movement of potential contaminants with little attenuation through solution openings or fractures in the aquifer media and unsaturated media is likely. C Mountain Flanks Madison Limestone-Englewood Formation This part of the Madison Limestone outcrop is located in the southeastern and southwestern part of the study area, near Spearfish Creek, and a small area in the east-central part of the study area. Ground-water flow generally is radially outward from the central part of the Black Hills. Sensitivity characteristics are similar to unit A without the additional fracturing due to igneous intrusive activity. D Limestone Plateau Madison Limestone-Englewood Formation This part of the Madison Limestone outcrop is located east of Spearfish Creek. The yields of the few inventoried wells located within the hydrogeologic unit range from 2 to 200 gal/min. Ground-water flow directions are related to topography and surface drainage patterns. The area is not directly connected to the regional Madison aquifer but does contribute base flow to headwaters of Spearfish, Whitewood, Elk, and Rapid Creeks. Hydraulic conductivity probably is less than determined for higher producing wells in the regional aquifer due to limited saturation and erosion of the more permeable upper parts of the formation. Movement of potential contaminants with little attenuation through solution openings or fractures in the aquifer media and unsaturated media is possible. E Mountain Flanks Minnekahta Limestone This part of the Minnekahta Limestone outcrop is located in an east-west direction across the north-central part of the study area. Most inventoried well yields range from 2 to 200 gal/min with some well yields as much as 500 gal/min. Permeability primarily is from fractures with some solution openings. Estimates of hydraulic conductivity from production well data range from less than 10 to 60 ft/d. Vertical movement in the unsaturated zone is rapid with little attenuation of potential contaminants. F Alternating Sandstone, Limestone, and Shale Minnekahta Limestone This part of the Minnekahta Limestone outcrop is exposed in a narrow band around Elkhorn Peak. G Alluvial Mountain Valleys-East Alluvium This alluvium is located in the southern part of the study area within mountain slopes-east. Particle size probably is larger than most alluvium because of high stream velocities. Similar alluvium is likely along all streams in this setting although the area may not be shown due to size and map-scale limitations. Saturation is variable depending on streamflow conditions. H Alluvial Mountain Valleys-North Alluvium This alluvium is located in the central part of the study area within Mountain Slopes-North. Sensitivity characteristics are similar to unit G. I Alluvial Mountain Valleys Alluvium This alluvium is located around the perimeter of the Black Hills uplift in the southern and central part of the study area within the Igneous Domes and Mountain Flanks settings. Similar alluvium is likely along streams in this setting although the area may not be shown due to size and map-scale limitations. Saturation is variable depending on streamflow conditions. J River Alluvium without Overbank Deposits Alluvium This alluvium is located along streams in the northern part of the study area with gentler topographic relief than in the mountain settings. Inventoried well yields range from 10 to 60 gal/min. Saturation is more consistent along the perennial streams. K Unconsolidated and Semi-Consolidated Deposits Gravel deposits These deposits are local aquifers where saturated and generally consist of terraces and former flood plains located adjacent to recent alluvial deposits. Inventoried well yields range from 10 to 100 gal/min. Saturation of the unit varies with the altitude of the unit in relation to adjacent alluvium and hydrologic conditions. L Mountain Flanks Minnelusa Formation This part of the Minnelusa Formation outcrop is located east to west across the central part of the study area and north to south along the southwestern part of the study area. Inventoried well yields are highly variable with the largest group ranging from 10 to 200 gal/min, a considerable number between 200 and 700 gal/min, and a few wells as much as 1,700 gal/min. Permeability is from the primary porosity of sandstone layers. Secondary porosity is from fractures and dissolved anhydrite collapse features. The lower part of the formation, with interbedded shales, generally is considered a confining layer with highly variable leakage to and from the Madison Limestone due to fractures and brecciation. Hydraulic conductivity is variable with values of about 50 ft/d determined from aquifer tests at public supply wells. Some attenuation of potential contaminants is possible with movement through sandstone; however, considerable variability is probable due to fractures and collapse features. M Alternating Sandstone, Limestone, and Shale Minnelusa Formation This part of the Minnelusa Formation outcrop is located in the northeastern part of the study area. Erosion of the more permeable upper parts of the formation probably decreases the hydraulic conductivity and vertical movement of a potential contaminant in the unsaturated zone compared to unit L. N Igneous Domes Deadwood Formation This part of the Deadwood Formation outcrop is located east to west across the central part of the study area. Inventoried well yields are highly variable with the largest group less than 50 gal/min, several between 50 and 300 gal/min, and a few wells as much as 1,100 gal/min. Wells generally are located near to or on the outcrop. Permeability is from the primary porosity of sandstone layers and secondary porosity from fractures. This part of the outcrop is near intrusive igneous bodies and often includes sills, which increase the fracturing. The ground-water flow patterns are very complex because of the intrusive bodies and include a mixture of local and regional ground-water flow systems. Movements of potential contaminants could be highly variable because of the complex fracturing patterns. O Limestone Plateau Deadwood Formation This part of the Deadwood Formation outcrop is located along Spearfish Creek and the headwaters of Elk, Boxelder, and Rapid Creeks. Ground water could be close to the surface in parts of this area because of the interaction between the streams and the Deadwood aquifer. Many of the smaller tributaries flowing across this area have perennial flow because of springs discharging from the Madison or Deadwood aquifers. P Igneous Domes Minnelusa Formation These small areas of Minnelusa Formation outcrop, located on the eastern and western edges of the central part of the study area, are isolated from the regional Minnelusa aquifer. Erosion of the more permeable upper part of the formation probably decreases hydraulic conductivity and the movement of potential contaminants in the unsaturated zone. No inventoried well information is available for the unit and saturation could be limited because of discharge to the surrounding Madison aquifer, which has a lower altitude. Q Limestone Plateau Minnelusa Formation This small area of Minnelusa Formation outcrop, located within the Limestone Plateau, is isolated from the regional Minnelusa aquifer. Erosion of the more permeable upper part of the formation probably decreases hydraulic conductivity and the sensitivity characteristics of the unsaturated zone. No inventoried well information is available for the unit and saturation could be limited because of discharge to the surrounding Madison aquifer, which has a lower altitude. R Mountain Flanks Deadwood Formation This part of the Deadwood Formation outcrop is located in the southeastern part of the study area, and a small area is located near Spearfish Creek. Permeability is from the primary porosity of sandstone layers and secondary porosity from fractures. The general direction of ground-water flow in the southeastern area is to the east, and average precipitation is less than on the other Deadwood Formation outcrops. S Mountain Slopes-East Deadwood Formation This part of the Deadwood Formation outcrop is located within the Precambrian rocks in the southern part of the study area. Permeability is from the primary porosity of sandstone layers and secondary porosity from fractures. Some of the areas may be isolated from the regional Deadwood aquifer with ground-water flow patterns determined by local topography and hydraulic connection to underlying rocks. T Mountain Slopes-East Igneous and metamorphic rocks This hydrogeologic unit, located in the southeastern and south central part of the study area is a local aquifer where saturated. Wells are located on or very close to the outcrop. Most inventoried well yields range from 5 to 20 gal/min with some well yields up to 60 gal/min. The depth of wells generally are less than 200 ft. Permeability is from fracturing that decreases with depth. Ground-water flow patterns are complex and variable. U Mountain Slopes-North Igneous and metamorphic rocks This hydrogeologic unit, located in the central part of the study area, is a local aquifer where saturated. Wells are located on or very close to the outcrop. Most inventoried well yields are less than 20 gal/min with one reported yield of 60 gal/min. This well was in an area where numerous sills have penetrated the Precambrian rocks. Permeability is from fracturing that decreases with depth. Ground-water flow patterns are complex and variable. V Mountain Flanks Igneous and metamorphic rocks This hydrogeologic unit, located in the southeastern part of the study area and surrounded by the Deadwood Formation, is a local aquifer where saturated. An inventoried well yield was 5 gal/min. Permeability is from fracturing that decreases with depth. Ground-water flow patterns are complex and variable. W Mountain Slopes-East Colluvium This hydrogeologic unit, located within the Precambrian rocks in the southern part of the study area, could supply limited quantities of water where saturated. No information is available to describe well yields or hydraulic conductivity. Considerable variation in sensitivity characteristics is likely depending on the particle size and sorting of the deposits. X Igneous Domes Colluvium This hydrogeologic unit, located on the slopes of igneous domes in the western part of the study area, probably would have limited saturation because of the land-surface slope. Y Mountain Flanks Colluvium This hydrogeologic unit, located in the east-central part of the study area, could supply limited quantities of water where saturated. No information is available to describe well yields or hydraulic conductivity. Considerable variation in sensitivity characteristics is likely depending on the particle size and sorting of the deposits. Z Alternating Sandstone, Limestone, and Shale Inyan Kara Group: Fall River Formation and Lakota Formation The Inyan Kara Group outcrop is located in the northeastern part of the study area. Inventoried well yields in the Inyan Kara aquifer mostly are less than 50 gal/min, with a few wells between 50 and 200 gal/min. The majority of permeability is from the primary porosity of the sandstone. a Igneous Domes Tertiary intrusive igneous rocks This hydrogeologic unit, located in the central part of the study area, includes most of the centers of igneous activity in the northern Black Hills in South Dakota. Inventoried well yields completed in intrusive rocks generally are less than 20 gal/min. Well yields and hydraulic conductivity in the massive domes probably would be low. Larger well yields could be expected where the outcrop is exposed as shallow sills intruding the Deadwood Formation. The lithology for several of the wells in this area that are identified as Deadwood aquifer wells include layers of intrusive rocks. Ground-water flow patterns are complex and variable. b Mountain Slopes-East Tertiary intrusive igneous rocks These two hydrogeologic units are located within the Precambrian rocks in the south-central part of the study area. No well inventory information is available. c Mountain Slopes-North Tertiary intrusive igneous rocks This hydrogeologic unit is located within the Precambrian rocks in the central part of the study area. Larger well yields generally are found adjacent to Precambrian rocks intruded with shallowly placed sills, laccoliths, dikes, and plugs. Ground-water flow patterns are complex and variable. d Igneous Domes Whitewood Formation-Winnipeg Formation This hydrogeologic unit is located in narrow bands adjacent to Deadwood Formation outcrops and intrusive rocks in the east- to west-central part of the study area. The combined Whitewood Formation and Winnipeg Formation is considered a semiconfining unit in the study area. No well inventory information is available for the unit. The overlying Madison aquifer or the underlying Deadwood aquifer would be more likely sources of water. The Whitewood Formation extends as far south as the intersection of Spearfish Creek and Highway 85 with only few places where the Winnipeg Formation extends farther south. Permeability from fractured limestone, dolomite, and siltstone could produce small quantities of water. e Mountain Flanks Whitewood Formation-Winnipeg Formation This hydrogeologic unit is located in the part of the Spearfish Creek drainage basin just above the City of Spearfish. The unit is exposed along Spearfish Creek and its tributaries. f Limestone Plateau Whitewood Formation-Winnipeg Formation This hydrogeologic unit is located in the upper part of the Spearfish Creek drainage basin and the headwaters of Elk, Boxelder, and Rapid Creek in the southern and central parts of the study area. The part of the unit exposed along Spearfish Creek and its tributaries is a narrow band located part way up the canyon wall above the Deadwood Formation outcrop, which is exposed at the bottom of the canyon. Most of these areas have very steep slopes causing most precipitation that falls on the outcrop to run off. g Mountain Flanks Whitewood Formation-Winnipeg Formation This hydrogeologic unit, located in the southeastern corner of the study area, dips to the east, and the general direction of ground-water flow is to the east. h Alternating Sandstone, Limestone, and Shale Morrison Formation, Unkpapa Sandstone, Sundance Formation, Gypsum Spring Formation This hydrogeologic unit, located in the northeastern part of the study area, is a semiconfining unit with parts of the unit used as an aquifer locally. Reported well yields, primarily from wells completed in the Sundance Formation, range from 5 to 70 gal/min. Permeability mostly is from sandstone layers within the unit. i Mountain Slopes-East White River Group This part of the White River Group outcrop, located in the east-central part of the study area, is a small area within Precambrian rocks that has not been removed by erosion. No well inventory information is available. Permeability mostly is from sand and gravel lenses and fractured limestone. Bentonite within volcanic ash deposits could limit vertical movement of contaminants. j Mountain Slopes-North White River Group This part of the White River Group outcrop, located in the central part of the study area is a small area in a valley of Precambrian rocks. k Igneous Domes White River Group This part of the White River Group outcrop is located in the central part of the study area near igneous intrusive rocks. No well inventory information is available. l Limestone Plateau White River Group This part of the White River Group outcrop, located in the east-central part of the study area east of Spearfish Creek, is a small area overlying Madison Limestone and Deadwood Formation outcrops. m Mountain Flanks White River Group This part of the White River Group outcrop is located near Madison Limestone and Minnelusa Formation outcrops along the northern mountain flanks in the central part of the study area. n Alternating Sandstone, Limestone, and Shale White River Group This part of the White River Group outcrop is located near the Inyan Kara Group outcrop in the northeastern part of the study area. o Alternating Sandstone, Limestone, and Shale Spearfish Formation This hydrogeologic unit, located in an east-west direction across the northern part of the study area, is a confining unit that supplies water to several wells. Most reported well yields are less than 20 gal/min with a few between 20 and 100 gal/min and one well yielding 300 gal/min. Thickness ranges from 375-450 ft along the eastern side of the Black Hills uplift to 700-800 ft on the northwestern flank of the uplift.12 Permeability is from porous lenses and secondary porosity associated with gypsum solution openings. Attenuation of potential contaminants by silts and shale is probable. p Mountain Flanks Spearfish Formation This hydrogeologic unit is isolated areas of the Spearfish Formation that have not eroded away. The part of the unit located on the western side of the study area slopes to the northwest. The part of the unit located on the east side of the study area slopes to the northeast. Limited saturation in these two areas is likely. No inventoried well information is available. q Alternating Sandstone, Limestone, and Shale Belle Fourche Shale, Mowry Shale, Newcastle Sandstone, Skull Creek Shale This hydrogeologic unit, located in the northeastern corner of the study area, is a confining unit. The Newcastle Sandstone may yield water to wells locally where saturated. A single well in the Belle Fourche Shale produced 20 gal/min. Vertical movement of potential contaminants is limited by shale and bentonite layers. r Mountain Flanks Opeche Shale This hydrogeologic unit is located in narrow bands between the Minnelusa Formation and Minnekahta Limestone across the north-central part of the study area. The Opeche Formation is a confining unit that produces water to wells in isolated areas. Most reported well yields range from 2 to 20 gal/min with a few wells as much as 75 gal/min. Permeability is from porous lenses, solution features, and/or fractures. Attenuation of potential contaminants by silt and shale is probable. Drainage from the area could recharge the Minnekahta aquifer. s Alternating Sandstone, Limestone, and Shale Opeche Shale This hydrogeologic unit is located in a narrow ring between the Minnelusa Formation and Minnekahta Limestone around a peak in the northeastern part of the study area near Polo Creek. Drainage from the area could recharge the Minnekahta aquifer. List of Recharge-rate group, Recharge rate (inches/year) and Sensitivity rank for attribute RECH-CODE 1 7 to <10 Highest 2 4 to <7 3 2 to <4 4 0 to <2 Lowest List of depth-to water group, depth to water (feet), and relative sensitivity rank for attribute DWA-CODE 1 0 to <20 feet Highest 2 20 to <50 feet Compare group 1, 2, 3 3 50 or >50 Lowest (not to groups 4 and 5) 4 Highly variable (areas of fractured rock in stream valleys) Compare group 4 and 5 5 Highly variable (other areas) (not groups 1, 2, and 3) List of land-surface-slope group, land-surface slope (percent) and sensitivity rank for attribute SLP-CODE 1 0 to <2 Highest 2 2 to <6 3 6 to <12 4 12 to <18 5 18 or >18 Lowest none U.S. Geological Survey Ask USGS - Water Webserver Team mailing

445 National Center

Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+sd_lcsens_pol Although this data set has been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Export Full coverage zipped 1 http://water.usgs.gov/GIS/dsdl/sd_lcsens_pol.e00.gz SDTS Full coverage zipped 1 http://water.usgs.gov/GIS/dsdl/sd_lcsens_pol_sdts.tar.gz Other Full coverage zipped 1 http://water.usgs.gov/GIS/dsdl/sd_lcsens_pol_shape.tar.gz None. This dataset is provided by USGS as a public service. 20041108 U.S. Geological Survey Ask USGS -- Water Webserver Team mailing

445 National Center

Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+sd_lcsens_pol FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998