[Home]
[Report Table of Contents] [Next Section]
Groundwater Investigation and Associated Source Characterization
Section 2 - Background
CSSA is located in northwestern Bexar County, approximately 19 miles northwest of downtown San Antonio in south-central Texas (Figure 2.1-1). The installation consists of 4,004 acres immediately east of State Highway 3351 (Ralph Fair Road), and is approximately 0.5 mile east of Interstate Highway 10 (Figure 2.1-2).
CSSA is a restricted-access installation with inner cantonment lands to the southwest and outer cantonment areas to the east and north (Figure 2.1-2). Operation buildings and storage magazines are located within the inner cantonment. Outer cantonment land is primarily undeveloped open range.
The eastern boundary of CSSA and part of its northern and southern boundaries are contiguous with the Camp Bullis Military Training Reservation. The surrounding area to the west is primarily rural and zoned for residential use. Some residential development is also present west, northwest, and southwest of the installation.
2.2 - Site Background and History
The land on which CSSA is located was used for ranching and agriculture until the 1900s (Army, 1990). During 1906 and 1907, six tracts of land were purchased by the U.S. Government and designated the Leon Springs Military Reservation. The reservation was used for maneuvers by Army and National Guard units, and the lands included campgrounds and Cavalry shelters.
In October 1917, the installation was redesignated as Camp Stanley. U.S. involvement in World War I spurred extensive construction of temporary buildings and installation support facilities. In 1931, Camp Stanley was selected as an ammunition depot, and construction of standard magazines and igloo magazines began in 1938 (Army, 1990). Camp Stanley was transferred to the jurisdiction of the Red River Army Depot (RRAD) in 1947. In addition to ammunition storage, CSSA lands were used to test, fire, and overhaul ammunition components.
Presently, the primary mission of CSSA is the receipt, storage, issue, and maintenance of ordnance materiel, as well as quality assurance testing and maintenance of military weapons and ammunition (Army, 1971). CSSA also has an agreement with the USDA Agricultural Research Service which permits cattle grazing on CSSA lands. Military personnel or other parties are allowed to hunt wildlife on a restricted basis. Although RRAD is proposed for realignment, no charges to the CSSA mission and military activities are expected in the future.
The investigation of groundwater contamination began in 1992 with a preliminary evaluation to establish the extent of the problem without use of invasive field techniques, followed by preparation and submittal of reports and plans in 1993. Groundwater monitoring continued in 1994, and downhole geophysical logging, discrete interval sampling, and well upgrades and abandonments, were also performed. Work in 1995 focused on source characterization. Upon agreement with EPA and TNRCC at an October 1995 technical meeting, CSSA initiated additional source characterization at two SWMUs in 1996 in preparation for source removal actions. Table 2.3-1 lists work actions and associated dates of the project.
CSSA is located in the south-central part of Texas on the Balcones Escarpment. Northwest of the installation, the terrain slopes upward to the Edwards Plateau; to the southeast, the terrain slopes downward to the Gulf Coastal Plains. This results in a modified subtropical climate, predominantly marine during the summer months and continental during the winter months. The resulting weather is characterized by hot summers with daily temperatures above 90�F over 80 percent of the time and mild winters with below-freezing temperatures occurring on an average of only about 20 days per year. The first occurrence of 32�F is in late November and the average last occurrence is in early March. Average annual temperature is 69�F. The highest average daily maximum temperature is 95�F in July, and the lowest average daily minimum temperature is 39�F in January. Temperature extremes for the period of weather records range from 0�F to 108 �F.
CSSA is situated between a semi-arid region to the west and the coastal area of heavy precipitation to the east. Average annual rainfall is approximately 29 inches. Precipitation is fairly well distributed throughout the year, with the heaviest amounts occurring in May and September. Approximately 61 percent of the rainfall occurs over the period from April through September and is primarily due to thunderstorms. Damaging hail seldom occurs, but light hail is common with springtime thunderstorms. Since CSSA is only 140 miles from the Gulf of Mexico, tropical storms occasionally affect the base with strong winds and heavy rains. Measurable snowfall occurs only once every 3 or 4 years.
The highest relative humidity occurs during the early morning hours (0600 hours) and averages about 84 percent over the year. Monthly averages range from 79 to 88 percent. Between 1200 and 1800 hours, relative humidity averages about 53 percent, with monthly averages ranging from 45 to 59 percent.
Northerly winds prevail during most of the winter. Strong northerly winds occasionally occur in conjunction with "northers," cold southward flows produced by an area of high pressure that invades the United Stated from Canada. Southeasterly winds from the Gulf of Mexico are predominant in the summer but also occur frequently during the winter. the average annual prevailing wind direction is from the southeast, and the average annual wind speed is 9 miles per hour (mph) with monthly averages ranging from 8 mph to 10 mph. The windiest months are typically March and April; September and October have the least wind.
Skies are clear to partly cloudy on average about 225 days per year, or more than 60 percent of the time, and cloudy conditions occur less than 146 days per year, or less than 40 percent of the time. CSSA has more than 70 percent of the possible sunshine during the summer months and about 50 percent during the winter months.
CSSA is characterized by a rolling terrain of hills and valleys in which nearly flat-lying limestone formations have been eroded and dissected by streams draining to the east and southeast (Figure 2.4-1). Normal faulting has occurred near the central area and the southeastern boundary of the installation. Regionally however, tow major trends of fractures extend northwest-southeast and northeast-southwest. Faulting in the limestone units has juxtaposed strata of different ages, but fault scarps and traces are almost absent because the similar calcareous lithologies weather similarly. The faults are northeast-southwest trending, but most are not as continuous as the fractures. Soil cover is relatively thin, and bedrock is exposed in most areas other than stream valleys.
River and stream dissection of limestone is the major surface feature at CSSA. Most major rivers and streams originating in the Edwards Plateau to the northwest of CSSA tend to follow the northwest-southeast regional fracture patterns. Resistive limestone beds crop out as topographic highs, but none of these beds form buttes or mesas. Rather, the predominant physiography is hills and "saddles" which lead to stream valleys. Topographic relief across the area ranges from about 1,100 feet to 1,500 feet above sea level.
Sinkholes and caverns are present on the surface and in the subsurface, primarily in areas where porous and fractured limestone formations are exposed. the sinkholes and caves result from dissolution of limestone and gypsum by infiltrating surface water. Commonly, fractures are enlarged by moving groundwater which enhances porosity and permeability. Fractures, fault scarps, and karstic low-lying areas can be recognized on aerial photographs.
2.4.3 Drainage and Surface Waters
Drainage from CSSA flows south into Salado and Leon Creeks; a small portion flows northeast into Cibolo Creek (Figure 2.4-2). Approximately 75 percent of CSSA is in the Salado Creek watershed, 15 percent in the Cibolo Creek watershed; and 10 percent in the Leon Creek watershed. Most of the active-use areas of CSSA are in the Leon Creek watershed, including the wastewater treatment plant, which drains into a tributary of Leon Creek at the southern boundary. All of these streams are intermittent at CSSA. The CSSA area can be characterized as hilly with stony soils and high runoff potential. Natural stream channels generally have broad floodplains, and portions of CSSA are in the 100-year floodplain.
The Salado Creek watershed on CSSA extends in a broad swath from northwest to southeast with the Salado Creek headwaters located in adjacent Fair Oaks subdivision. Impervious cover in Fair Oaks is currently estimated at 5 to 10 percent. Drainage from Camp Bullis to the east also flows across CSSA to Salado Creek. Impervious cover for CSSA within the Salado Creek watershed in substantially less than 5 percent, with much of the area undeveloped except for dirt and gravel roads. Four ponds are located within the Salado Creek drainage area of CSSA.
Three tributaries of Cibolo Creek originating on CSSA drain the northeastern part of the outer cantonment. One stock pond is located on the easternmost tributary. The area of the Cibolo Creek watershed within CSSA is undeveloped except for dirt and gravel roads. Impervious cover in the Cibolo Creek watershed is minimal.
A tributary of Leon Creek, originating on CSSA, drains the southwest quarter of the inner cantonment. Reservoir W, in the southwest corner of the inner cantonment, is situated on a subtributary. Overall, impervious cover within the Leon Creek portion of CSSA is estimated at approximately 5 percent or less, much of which is located along Tompkins Road and McElroy Drive.
In the undeveloped areas of CSSA, runoff is conveyed to natural stream channels by ditches and sheet flow. CSSA has sufficient relief to allow the rapid conveyance of runoff from developed areas. In the undeveloped areas, runoff flows overland to natural channels.
Drainage and surface waters are further discussed in the September 1993 Environmental Assessment (Parsons ES, 1993d).
In general, soils at CSSA are thin, dark-colored, gravelly clays and loams. The soil types are strongly influenced by topography and the underlying limestone. All soil classifications used for this report are taken from the U.S. Department of Agriculture (USDA) Soil Conservation Service (now the Natural Resource Conservation Service [NRCS]) soil survey series for Bexar County, Texas (USDA, 1966) (Figure 2.4-3).
The Brackett (BrE) soils range over a large portion of CSSA. These soils occur on slopes of 12 to 30 percent, such as those found on Steele, McFarland, and Schasse Hills, as well as Taylor Ridge. These loamy and clayey soils are thin (about 4 inches thick), grayish-brown, and strongly calcareous. Gravel and cobblestone lithics occur at the surface and shallow subsurface. The soils can develop over soft limestone and are underlain by hard limestone, which gives the slopes a stairstep appearance. Topographic relief associated with Brackett soils is expressed as steep, cone-shaped hills with "saddles" between them. Brackett soils are nonarable and best-suited to native grasses. They typically have permeabilities of 1.0-1.2 inches per hour (in./hr.) and available water values of 0.14 to 0.16 in./in.
The Tarrant (TaB) soils are thin and form over hard, fractured limestone. The surface layer is usually about 10 inches thick and is a dark grayish-brown, calcareous, clay loam with scattered gravel and cobblestones within, and on the surface layer. Two types of Tarrant soils occur at CSSA: Tarrant association, gently undulating, and Tarrant association, rolling. They typically have permeabilities of 1.0-1.5 in./hr. and available water values of 0.16 to 0.18 in./in.
Tarrant association, gently undulating areas are typical of prairie and plateau topography. They occur primarily in areas not occupied by streams, such as the north-central areas of the inner cantonment, as well as the west sides of Steele and Wells Hills and on the hills north of the inner cantonment. The soils are dark colored, very shallow, calcareous, and clayey and are best suited for native grasses and range use.
Tarrant association, rolling, is found on the eastern sides of Anderson and Schasse Hills in areas not occupied by streambeds. The slopes tend to have a gradient of 5 to 15 percent. The soils are dark colored, very shallow, clayey, weakly calcareous, and typically more stony than Tarrant association, gently undulating.
Except in stream beds and associated floodplains, the Crawford and Bexar (Cb) stony soils occupy the majority of the land not previously mentioned. They occur as broad, nearly level to gently undulating areas with slopes of 0 to 5 percent. The Crawford soils are more prevalent than Bexar soils at CSSA. The soils are stony, very dark gray to dark reddish brown, noncalcareous clay, and are about 8 inches thick. Bexar soils range from a cherty clay loam to gravelly loam. The soils are nonarable and suited for native grass, such as Texas winter grass, little bluestem, sideoats grama, and buffalo grass. Within 17 inches from the surface, these soils typically have permeabilities of 1.0-1.5 in./hr. and available water values of 0.16 to 0/18 in./in.
Two soil units are found in the streambeds and floodplains of Salado Creek and other small tributaries. They are the Krum Complex (Kr) and the Trinity and Frio (Tf) soils. The Trinity and Frio soils, frequently subjected to flooding, are the main channel soils for Salado Creek and a large tributary that joins the creek in southwestern CSSA. Some areas are subject to thin sediment depositions, while other areas are scoured. Channels are poorly defined and are of small capacity. Trinity soils are 3 to 5 feet deep and composed of clayey to gravelly loam. Frio soils are a dark grayish-brown clay loam, 3 to 4 feet deep. Vegetation may consist of elm, hackberry, oak, mesquite, and other thorny shrubs, Texas wintergrass, Johnson grass, buffalo grass, Bermuda grass, and annual weeds. The Trinity soils exhibit permeabilities of 0.2 to 0.4 in./hr. and available water characteristics of 0.18 to 0.21 in./on. The Frio soils exhibit permeabilities of 1.0 to 2.0 in./hr. and available water characteristics of 0.14 to 0.16 in./in.
The Krum Complex soils are dark grayish-brown or very dark grayish-brown, calcareous, and approximately 30 inches thick. The soils developed from slope alluvium of the limestone prairies. They occur on slopes of 2 to 5 percent and occupy "foot" slopes below Tarrant and Brackett soils. The Krum Complex soils receive sediments and runoff from higher elevation soils and are highly prone to hydraulic erosion if unprotected. Tarrant association, gently undulating, and Tarrant association, rolling. Krum Complex soils typically have permeabilities of 0.8 to 1.0 in./hr. and available water values of 0.16 to 0.18 in./in.
A minor soil type found at CSSA is the Lewisville silty clay found on slopes of 1 to 3 percent. It typically occupies long, narrow, sloping areas separating nearly level terraces from upland soils. It can be found in small areas south of Dietz Elkhorn Road and north of the inner cantonment boundary around Moyer Road. Surface soils are dark grayish-brown and about 20 inches thick. This is a highly productive soil but is also susceptible to hydraulic erosion if unprotected. Tarrant association, gently undulating, and Tarrant association, rolling. Lewisville soils typically have permeabilities of 1.0 to 2.0 in./hr. and available water values of 0.16 to 0.18 in./in.
Information on the stratigraphy of CSSA was taken from the TDWR report 273 (Ashworth, 1983). The oldest and deepest known rocks in the study area are of Paleozoic age (225 to 570 million years ago [mya]). The lithologies consist of slate, schist, and hard massive limestone and dolomite. They underlie the predominant carbonate lithology of the Edwards Plateau. The Cretaceous-age (65 to 135 mya) sediments were deposited unconformably over the Paleozoic strata as onlapping sequences on a submerged marine plain during the early to middle Mesozoic (135 to 225 mya). According to well logs and outcrop observations, these Cretaceous sediments thicken to the southeast. Table 2.4-1 summarizes the stratigraphy about the Cretaceous system in central Texas.
The Travis Peak Formation attains a maximum thickness of about 940 feet, and in the area of Bexar County, a thickness of 510 feet. It is divided into five members, in ascending order: the Hosston Sand, the Sligo Limestone, the Hammett Shale, the Cow Creek Limestone, and the Hensell Sand. The Hosston Sand is generally composed of conglomerate, sandstone, and claystone, becoming increasingly more dolomitic and shaley downdip to the southeast. The Sligo Limestone exists downdip where the Hosston grades into a sandy limestone. Overlaying the Sligo is the Hammett Shale, which has an average thickness of 60 feet. It is composed of dark blue to gray fossiliferous, calcareous, and dolomitic shale. It pinches out north of the study area and attains a maximum thickness of 50 feet to the south.
Above the Hammett Shale is the Cow Creek Limestone. It is a massive fossiliferous, white to gray, shaley to dolomitic limestone that attains a maximum thickness of 90 feet downdip in the area.
The youngest member of the Travis Peak Formation is the Hensell Sand, locally known as the Bexar Shale. The shale thickness averages from 80 to 150 feet. It is composed of silty dolomite, marl, calcareous shale, and shaley limestone, and thins by interfingering into the Glen Rose Formation.
The Glen Rose Formation of the Trinity Group was deposited over the Bexar Shale and represents a thick sequence of shallow water marine shelf deposits. This formation is divided arbitrarily into upper and lower members. At CSSA, the Glen Rose is exposed at the surface and in stream valleys (Figure 2.4-4). In particular, the lower Glen Rose is exposed in the central and southwest portions of the installation (see Section 8.6.1 for discussion of site-specific geology).
In Bexar County, the lower Glen Rose member is approximately 300 feet thick and consists primarily of massive bedded limestone with few layers of marl and marly limestone. The upper member is approximately 500 feet thick and consists primarily of alternating resistive and nonresistive beds of limestone and marly limestone. At CSSA, the upper bed thickness is estimated at 0 to 30 feet as it thickens to the south. A distinct stratigraphic marker bed known as the Corbula bed (a bed of small clamshells 3 to 5 millimeters in diameter) is the dividing boundary between the upper and lower Glen Rose members. In addition, two distinct evaporite beds (primarily gypsum) are present in the upper member. The depth of the second (deeper) evaporite bed is close to that of the Corbula bed, allowing the contact between the upper and lower members to be found on subsurface geophysical logs.
Fredricksburg Group sediments, including the Edwards Formation, overlie the Glen Rose Formation in many areas as erosional remnants outcropping as topographic highs (Figure 2.4-4). For this report, the Fredricksburg Group limestones will not be discussed because of the lack of outcrop in the immediate vicinity of CSSA.
The predominant structural features are regional vertical fractures, the regional dip, and the Balcones fault zone (escarpment). The regional fractures are the result of faulting in the Cretaceous sediments and in the deeper Paleozoic rocks. The two sets of fracture patterns trend northwest-southeast and northeast-southwest across the region (Figure 2.4-4). The regional dip is to the east and southeast at a grade of about 100 feet per mile near the fault zone in Bexar and Comal Counties, decreasing to 10 to 15 feet per mile northwest of CSSA.
The Balcones system is the main system of faults across Bexar County and is a series of normal (gravity) faults with downthrow usually to the east or southeast. Total displacement in northwest Bexar County is approximately 1,200 feet. The faulting is a result of structural weakness in the underlying Paleozoic rocks and susbsidence in the Gulf of Mexico basin to the southeast. Small grabens are produced by faulting with throws to the west or northwest. For the most part, faults of the Balcones system trend slightly oblique to the trend of the fault zones and approximately parallel to the strike of the strata. The trends are reported as east-northeast (Arnow, 1959; Hefner, 1993; Watterus, 1992). Strikes of faults in the Camp Bullis area ranged from N40-90E, with the majority trending N45-55E (Watterus, 1992). Fault trends by Hefner in CSSA measured N12-85E, with the majority between N43-55E (Hefner, 1993).
Many lines on Bexar County structural maps do not represent faults with a single sharp break, but mark the trace of shatter zones. These shatter zones are a series of smaller step faults within a narrow zone. No single fault or shatter zone has been traced across the whole county, although some faults and shatter zones have been traced as much as 25 miles. The largest amount of displacement along the fault zones is typically in the center of the faults rather than the ends (Arnow, 1959).
Major faults trend east-northeastward in the area, but some are intersected by cross or branch faults. The faults generally have straight traces, suggesting nearly vertical fault planes (Arnow, 1959). Additional sources report near vertical to high angle faults (Hammond, 1984; Guyton and assoc., 1993; Watterus, 1992). Fault dips measured by Hefner in the area around CSSA ranged from S37-S98E with estimated fault displacements of 1.5 to 50 feet (Hefner, 1993). Because formations on both sides of faults are of similar lithology and are equally resistant to erosion, many faults are not reflected by the topography (Arnow, 1959).
The results of a preliminary evaluation of groundwater contamination in 1992 were submitted to AL/OEB and CSSA as a report entitled "Hydrogeologic Report for Evaluation of Groundwater Contamination at Camp Stanley Storage Activity, Texas" (ES, 1993a). This section summarizes information generated during that project, and from the TDWR report 273 (Ashworth, 1983), and a water resources study in north Bexar County (Simpson Company and Guyton Associates, 1993).
Three aquifers are present in the area of CSSA: the upper, middle, and lower Trinity aquifers. These divisions are based upon hydraulic continuity. The Travis Peak Formation and the Glen Rose Formation are the principal water bearing units. Beneath these are metamorphosed Paleozoic rocks, which act as a lower hydrologic barrier. Generally, the depths to water at CSSA range from approximately 150 to 260 feet bgl.
Upper Trinity Aquifer
The upper Trinity aquifer is located in the upper Glen Rose Limestone. Recharge to the upper Trinity aquifer is from direct precipitation to upper Glen Rose Limestone outcrop and from stream flow infiltration. Additional recharge in the Camp Bullis area occurs from reservoirs built by the NRCS on Salado and Lewis Creeks, approximately 1 mile south of CSSA (USGS 7.5 minute topographic map, Camp Bullis quadrangle photorevised, 1973).
No transmissivity values have been determined for the upper Trinity aquifer. Movement of groundwater in the upper Trinity is restricted to lateral flow along bedding planes between marl and limestone, where solution has enhanced permeability. Static water levels in adjacent wells completed in different beds within the upper Glen Rose are not concordant, demonstrating the possibility that beds are not hydraulically connected by avenues of vertical permeability. The only place where extreme development of solution channels has been reported is in evaporite layers in or near the outcrop of the upper Glen Rose Limestone. Discharge from the upper Trinity aquifer is predominantly from natural rejection through seeps and springs and from pumping.
The upper Trinity aquifer is, in general, unconfined. Fluctuations in water levels in the upper Trinity are predominantly a result of seasonal rainfalls and pumping from domestic and public wells.
Middle Trinity Aquifer
The middle Trinity aquifer consists of the Cow Creek Limestone, the Bexar Shale (Hensell Sand), and the lower Glen Rose Limestone. The average combined thickness of the aquifer members is approximately 520 feet. The only member found in outcrop at CSSA is the lower Glen Rose, which has been mapped north of CSSA along Cibolo Creek and within the central and southwest portions of CSSA.
The lower Glen Rose portion of the middle Trinity aquifer derives its recharge from direct precipitation on the outcrop and stream flow infiltration. Stream flow loss has been observed in Cibolo Creek between the towns of Boerne and Bulverde, where stream flow is diverted underground via sinkholes except during flood stages. This is the only area of lower Glen Rose that is considered to be part of the recharge zone for the Edwards aquifer (EUWD, 1987).
In the area of CSSWA, the Bexar Shale acts as a hydrologic barrier to certical leakage except where faulted; therefore, most recharge to the Cow Creek Limestone comes from overlying updip formations. It is inferred that the Cow Creek is in natural hydraulic communication with the lower Glen Rose. The middle Trinity aquifer appears to be unconfined in the CSSA area.
The average coefficient of transmissivity in the middle Trinity aquifer is 1,700 gallons per day per foot (gpd/ft). Groundwater flow is towards the south and southeast. Flow velocities calculated by carbon 14 analysis indicate a regional flow that ranges from 13.6 to 15.9 feet per year (Hammond, 1984). Middle Trinity discharge occurs both artificially through well use and naturally by springs and seeps. Groundwater geochemistry is typical for calcium magnesium bicarbonate type, with total dissolved solids (TDS) content usually less than 500 milligrams per liter (mg/L) (Ashworth, 1983).
The primary groundwater source at CSSA is the middle Trinity aquifer, the most prolific producer with the best quality of water of the three Trinity aquifers. These wells are typically completed as open holes without well screens. To maximize yield, water wells in the area that are completed in the middle Trinity are also open to the upper Trinity aquifer.
There were nineteen water wells at CSSA (Figure 2.4-5). These wells have been used for drinking water supply and livestock. Wells 1, 9, 10, 11, G, H, and I are active wells. Wells 2, 3, 4, D, and 16 are currently used for groundwater monitoring. Well 1 is used by CSSA, though located on Camp Bullis property. Five wells were plugged in September 1994 and reported to TNRCC. The well plugging activities are further discussed in Section 3.6.
Groundwater movement at CSSA in the middle Trinity aquifer was defined using October 1992 through April 1996 water well data. Groundwater elevations were calculated from measured depths to static water levels in the wells. Groundwater flow direction generally has been to the south-southeast with gradients of 0.003 to 0.1 foot per foot. However, during a period of little or no precipitation in August and December 1995, a significant decline in aquifer water levels corresponded with a change in flow direction to the south-southwest. Section 8.2.1 summarizes results of groundwater monitoring to date.
Lower Trinity Aquifer
The lower Trinity aquifer is made up of Hosston Sand and the Sligo Limestone of the Travis Peak Formation. These strata do not outcrop in CSSA. The Hosston and the Sligo thicken in a downdip direction (south and southeast) to as much as a combined thickness of 370 feet near the Balcones fault zone. The lower boundary of the lower Trinity aquifer is composed of Paleozoic basement rocks.
The lower Trinity aquifer receives infiltration recharge from the overlying Hensell Sand (Bexar Shale) in the updip direction, where the overlying Hammett Shale and Cow Creek Limestone is thin or absent. Some recharge may come from leakage of overlying strata in areas where the Hammett Shale is disrupted by faulting. The lower Trinity aquifer is artesian, the Hammett Shale acting as a hydraulic confining unit. The average coefficient of transmissivity in the lower Trinity aquifer is approximately 10,000 gpd/ft in the Kerrville area (Ashworth, 1983). The groundwater gradient is generally to the south and southeast except in areas of continuous pumping, where flow is directed towards the active wells. Discharge from the lower Trinity aquifer occurs primarily by pumping from wells.
2.4.6.2 Edwards Aquifer Recharge and Transition Zones
The Edwards aquifer is not found in the CSSA area. However, the Edwards Underground Water District (EUWD) has defined recharge and transition zones of concern for the Edwards aquifer. Two such zones are located north and south of CSSA and are shown on Figure 2.4-6. One recharge area is along Cibolo Creek where the lower Glen Rose outcrops. This is the only area of the lower Glen Rose that is defined as a recharge zone to the Edwards aquifer. The closest area of this recharge zone is 0.5 mile north from the northeast corner of CSSA. A second recharge zone located on Edwards limestone is about 4 miles to the south-southeast. A transition zone is 5 miles southeast of CSSA.