View source for Edwards Aquifer

{{Short description|Source of drinking water in Texas}}
{{Refimprove|date=February 2020}}
{{Infobox landform
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| name              = Edwards Aquifer
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| type              = [[Aquifer]]
| photo             = Edwards-Trinity aquifer system v1.svg
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| photo_caption     = Downstream from the headwaters of the San Marcos River
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| location          = Edwards Plateau, Texas Hill Country, [[Texas]], [[United States]]
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| area              = {{convert|3,237|km2|abbr=on}}
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| geology           = [[Limestone]] [[karst]]<ref>{{cite web|url=http://www.esi.utexas.edu/outreach/caves/edwardsaquifer.php |title=The Edwards Aquifer |work=Environmental Science Institute |publisher=The University of Texas at Austin |access-date=2013-01-24 |archive-url=https://web.archive.org/web/20130128072032/http://www.esi.utexas.edu/outreach/caves/edwardsaquifer.php |archive-date=2013-01-28 }}</ref>
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| website           = [http://www.edwardsaquifer.net/index.html Edwards Aquifer Website]
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[[File:Edwards and Trinity Aquifers Map.png|thumb|300px|Edwards and Trinity Aquifers map]]
The '''Edwards Aquifer''' is one of the most prolific [[artesian aquifer]]s in the world.<ref>{{Cite web |title=Edwards Aquifer Authority › About the Edwards Aquifer - Edwards Aquifer Authority |url=https://www.edwardsaquifer.org/science-maps/about-the-edwards-aquifer/ |access-date=2024-05-14 |website=www.edwardsaquifer.org}}</ref> Located on the eastern edge of the [[Edwards Plateau]] in the [[U.S. state]] of [[Texas]], it is the source of drinking water for two million people, and is the primary water supply for agriculture and industry in the aquifer's region. Additionally, the Edwards Aquifer feeds the [[Comal River|Comal]] and [[San Marcos Springs]], provides springflow for recreational and downstream uses in the [[Nueces River|Nueces]], [[San Antonio River|San Antonio]], [[Guadalupe River (Texas)|Guadalupe]], and [[San Marcos River|San Marcos river]] basins, and is home to several unique and endangered species.

== Basin characteristics ==

=== Geography ===
Located in South Central Texas, the Edwards Aquifer encompasses an area of approximately {{convert|4,350|sqmi}} that extends into parts of 11 counties.<ref name=":6">{{Cite journal|url = https://www.twdb.texas.gov/publications/reports/numbered_reports/doc/R345/R345Complete.pdf|title = Aquifers of Texas|last = Ashworth|first = John|date = 1995|journal = Texas Water Development Board (Report 345)}}</ref> The aquifer's boundaries begin at the groundwater divide in Kinney County, East of Brackettville, and extend Eastward through the San Antonio area and then Northeast where the aquifer boundary ends at the Leon River in Bell County.<ref name=":8">Tremallo, Robin; Hamiton, Mark; Johnson, Steve; Esquilin, Roberto; Chanda, Burgoon (December 2014). "Edwards Aquifer Authority Hydrologic Data Report for 2013". Edwards Aquifer Authority.</ref> The aquifer is hydrologically separated into the Austin and San Antonio regions by a groundwater divide near the town of Kyle in Hays County.<ref name=":6" />

The total area of the aquifer forms roughly the shape of a slight upward curve and approximately measures {{convert|160|mi|km}} east to west at its furthermost boundaries and {{convert|80|mi|km}} north to south at its widest section.<ref>Eeason, Sarah. "EAA Subchapter 713 Regulated Zones". ArcGIS. ESRI. Retrieved 17 October 2015.</ref>  The aquifer is geographically divided into four distinct regions: the total drainage area, recharge zone, artesian zone, and saline zone. These zones run east to west, with the drainage area forming the northernmost portion of the aquifer and the saline zone forming the southernmost portion. The artesian zone intersects the saline zone to the south and west at the fresh water - saline water boundary (FW-SW).<ref>{{Cite journal|last1=Smith|first1=Brian A|last2=Darling|first2=Bruce|date=2017|title=Hydrogeology of the Saline Edwards Zone, Southeast Travis County, Central Texas|url=https://bseacd.org/uploads/Hydrogeology-Saline-Edwards_BSEACD-RI-2017-1015.pdf|journal=Barton Springs Edwards Aquifer Conservation District Report of Investigations}}</ref>

The aquifer's recharge zone,<ref name="Edwards Aquifer Recharge Zone">{{Cite web|title = Edwards Aquifer Recharge Zone|publisher = Texas Commission on Environmental Quality|url = http://www.tceq.state.tx.us/gis/metadata/edw_tsms_met.html|access-date = 12 May 2010|archive-url = https://web.archive.org/web/20100726031033/http://www.tceq.state.tx.us/gis/metadata/edw_tsms_met.html|archive-date = 26 July 2010}} Texas Commission on Environmental Quality</ref> where surface water enters the aquifer, follows the [[Balcones Fault]] line, from [[Brackettville, Texas|Brackettville]] (roughly along [[U.S. Highway 90 (Texas)|U.S. Highway 90]]), through [[San Antonio]], and north to [[Austin, Texas|Austin]] along but a few miles west of [[Interstate 35 in Texas|Interstate 35]].  On certain stretches of highway in Austin and San Antonio, signs indicate that the driver is entering or leaving the recharge zone, as the zone's easternmost edge sits beneath heavy urban and suburban development.

Its drainage area, where water is transported near the surface to the recharge zone, extends about {{convert|40|mi|km|round=10}} north of the recharge zone at the west end, and tapers to end at a point in the east.

The [[Artesian aquifer|artesian zone]],<ref name="The Edwards Aquifer">{{Cite web|title=The Edwards Aquifer |publisher=San Antonio Water System |url=http://www.saws.org/education/h2o_university/virtual_classroom/edwards.shtml |access-date=12 May 2010 |archive-url=https://web.archive.org/web/20100524191508/http://www.saws.org/education/h2o_university/virtual_classroom/edwards.shtml |archive-date=24 May 2010 }} San Antonio Water System</ref> where water springs from wells naturally due to the higher elevation of the recharge zone, extends {{convert|10 to 20|mi|km|round=5}} south on the west end to only a few miles south on the east end.  Across the eastern half of the aquifer, the recharge and artesian zones occupy common area.

=== Geology ===
Approximately 70 million years ago, activity of tectonic plates caused a revival of the [[Rocky Mountains]]. As these tectonic processes were occurring, millions of tons of sediments were deposited by [[Alluvium|alluvial]] and [[fluvial]] processes across Texas. The tremendous weight of these sediments resulted in faulting between the Edwards Plateau and the Gulf. The main geologic unit, known as the Edwards [[Limestone]], is tilted downward toward the south and east and is overlain by younger limestone layers as well as several thousand feet of sediments. The Edwards Aquifer is a group of limestones and is considered a highly heterogenic [[aquifer]].<ref>{{Cite web|title = Hydrogeology of the Edwards Aquifer|url = http://www.edwardsaquifer.net/geology.html|website = www.edwardsaquifer.net|access-date = 2015-11-23}}</ref> Three stratigraphic columns across the San Antonio area represent the Edwards Aquifer. These [[Stratigraphy|stratigraphic]] units are known as the Maverick Basin. the Devils River Trend, and the San Marcos Platform.<ref name=":15">{{Cite journal|url = http://pubs.usgs.gov/wri/1995/4186/report.pdf|title = Geology and Hydrogeology of the Edwards Aquifer in the San Antonio Area, Texas|last = Maclay|first = Robert W.|date = 1995|journal = Water-Resources Investigations Report}}</ref>

The Maverick Basin portion of the Edwards Aquifer consists of the West Nueces, McKnight, and Salmon Peak Formations. The Devils River Trend unit of the Edwards Aquifer is composed mostly of Devils River Limestone with a thickness of approximately {{convert|550|feet|m|round=5}}. The third unit of the Edwards Aquifer, the San Marco Platform, consists of the Kainer, Person, and Georgetown Formations.<ref name=":15" /> [[File:Piedra-horadada.jpg|thumb|Karst formation from Segovia, Spain.]]

==== Hydrogeology ====
The Edwards Aquifer is a highly productive [[karst]] aquifer made up of [[Edwards Group]] [[limestone]]s.<ref>Rose, P. R. (1972). Edwards Group, surface and subsurface, central Texas. Austin: University of Texas Bureau of Economic Geology Report of Investigations 74.</ref> The Edwards limestone is variable in hydrologic character, but is generally highly porous and permeable, which makes it able to hold and move a lot of water. The limestone is broken by faults and joints. Water flows through these fractures and continues to dissolve the limestone, creating larger and larger pore spaces over time. Some units also store water in eroded fossil burrows that formed through the burrowing action of worms and crustaceans at the seafloor. The [[effective porosity]], or the amount of water that is capable of being recovered, of the Edwards aquifer is estimated to be about 5%.<ref name=":7">Maclay, R. W., and Land. L. F. (1988).  Simulation of Flow in the Edwards Aquifer, San Antonio Region, Texas, and Refinement of Storage and Flow Concepts.  Washington:  US Government Printing Office, US Geological Survey Water-Supply Paper 2336-A.</ref> The aquifer ranges in thickness from about {{convert|300 to 700|ft|m|sigfig=1}}.[[File:BartonSprings_MainSpring.jpg|thumb|Main [[Barton Springs|Barton Spring]] in [[Austin, Texas]], a prominent fracture (visible here) in limestone rock. Through this artesian karst spring water emerges to the surface from the karstic Edwards Aquifer. This spring is situated near the diving board in [[Barton Springs Pool]]. Photo provided by US Geological Survey.]]Unlike sand and gravel aquifers that store water in very small pore spaces, karst aquifers store water in large pockets or caverns, forming underground "rivers" and "lakes".<ref>{{Cite web|title = USGS Kentucky Water Science Center|url = http://ky.water.usgs.gov/projects/cjt_karst/index.htm|website = ky.water.usgs.gov|access-date = 2015-11-03}}</ref> The rate at which groundwater moves through these conduits can vary tremendously. In the Edwards Aquifer some water may barely move, while in other areas water may travel miles (thousands of meters) in a single day. On average, the Edwards aquifer has been modeled with a [[Transmissivity (earth sciences)|transmissivity]] of about {{convert|100|sqft/day|m2/day|0}}.<ref name=":7" />

In the south, the Edwards Aquifer dips beneath the lowland plains of the gulf coast. This area south of the recharge zone is referred to as the Artesian Zone, where the water is held under pressure by low permeability layers, and can flow to the surface without the assistance of pumps through openings like springs and [[artesian wells]].

=== Climate ===
The Edwards aquifer underlies a portion of the Edwards Plateau<ref>{{Cite web|url = http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/texas/placesweprotect/edwards-plateau-fact-sheet-1008-lowres-1.pdf|title = The Edwards Plateau Ecoregion: Extraordinary diversity of life amid hills and canyons in Central Texas|date = 2008|publisher = The Nature Conservancy of Texas}}</ref> thus the climate of the Edwards Plateau can be used to describe the climate in the aquifer's region. The eastern portion of the Aquifer falls in a [[Humid subtropical climate]] ([[Köppen climate classification]] ''Cfa'' or ''Cwa''), while the western has a [[Semi-arid climate|semi-arid steppe climate]] (''BSk'' and ''BSh)'' The average annual temperature on the Edwards Plateau is {{convert|66|F|C|abbr=on}} and the average annual precipitation amounts to {{convert|25.24|in|mm}}.<ref name=":0">{{Cite web |url = http://www.southcentralclimate.org/content/documents/factsheets/Drought_History_TXCD06.pdf |archive-url=https://web.archive.org/web/20151208061247/http://www.southcentralclimate.org/content/documents/factsheets/Drought_History_TXCD06.pdf |archive-date=2015-12-08 |title = Drought History for the Edwards Plateau of Texas |website=South Central Climate Science Center|date = 2013}}</ref> The temperatures vary by season with the lowest average temperature occurring in January, {{convert|50|F|C}}, and the highest temperature occurring in July or August, nearing {{convert|85|F|C}} for both months.<ref name=":0" /> Conversely, January is the month with the lowest precipitation, averaging {{convert|1|in|mm}}, while May and September average the most, {{convert|3|in|mm}}.<ref name=":0" /> The proximity of the Edwards Plateau to the Gulf of Mexico and its location in the middle latitudes creates variation in the weather patterns experienced between different years, seasons, and months.<ref name=":0" />

=== Water quality ===
Approximately 1.5 million people obtain their drinking water from the Edwards Aquifer. At present, the [[water quality]] of the aquifer has satisfied drinking water standards and there have been no significant issues with pollution contamination.<ref>Eberts, S. Hydrogeologic Settings and Groundwater-Flow Simulations for Regional Investigations of the Transport of Anthropogenic and Natural Contaminants to Public-Supply Wells - Investigations Begun in 2004. (2011).</ref><ref name="U.S. Environmental Protection Agency 2009">U.S. Environmental Protection Agency. National Primary Drinking Water Regulations. (2009).</ref> Regular water quality testing through the USGS NAWQA Program occurred between 1996 and 2006. On a yearly basis, ions, metals, nutrients, bacteria, pesticides, [[Volatile organic compound|VOCs]], and synthesized chemicals remained below the EPA's published [[Maximum Contaminant Level|Maximum Contaminant Levels (MCLs)]].<ref>Bush, P. W. et al. Water quality in south-central Texas, Texas, 1996-1998. (2000).</ref><ref name="Fahlquist, L. 1998">Fahlquist, L. & Ardis, A. F. Quality of water in the Trinity and Edwards aquifers, south-central Texas, 1996-1998. (2004).</ref><ref>Moran, M. J., Lapham, W. W., Rowe, B. L. & Zogorski, J. S. Occurrence and status of volatile organic compounds in ground water from rural, untreated, self-supplied domestic wells in the United States, 1986–99.</ref><ref>Long, S., Reece, B. & Eames, D. Water Resources Data Texas Water Year. (2004).</ref>  Dissolved [[Nitrate|nitrates (NO3)]] are detected throughout the entire aquifer at concentrations that exceeded the national background levels, but that are well below the MCL (10&nbsp;mg/L).<ref name="U.S. Environmental Protection Agency 2009"/> These nitrates may be the result of agricultural runoff that enters the aquifer through its recharge zone.<ref name="Fahlquist, L. 1998"/>

Due to the karst hydrogeology of the Edwards Aquifer, chemicals that enter the system have the potential to rapidly travel through the aquifer and contaminate down-gradient water sources in a short period of time (hours to days).<ref>Assessment, U. E. N. C. for E. Karst Hydrology and Chemical Contamination. at <http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=40644></ref> Aquifers can be easily contaminated when pollutants enter the recharge zone. Because of this vulnerability to contamination, organizations have formed to protect the Edward's Aquifer recharge zones.<ref>Edwards Aquifer Protection Program. at <{{cite web |url=http://www.tceq.state.tx.us/field/eapp/program.html |title=Edwards Aquifer Protection Program |access-date=2015-10-24 |archive-url=https://web.archive.org/web/20150906185526/http://www.tceq.state.tx.us/field/eapp/program.html |archive-date=2015-09-06 }}></ref> Anthropogenically sourced pollutants (pesticides, VOCs, and synthetically derived compounds) can be found within the Edwards Aquifer at minuscule levels.<ref name="Fahlquist, L. 1998"/>

=== Ecology ===
[[File:Texas_blind_salamander.jpg|thumb|[[Texas blind salamander]] found in Edwards Aquifer]]
The Edwards Aquifer supports a wide variety of organisms, and several endemic species. The ecosystem is one of the most diverse subterranean aquatic ecosystems in the world.<ref name="Widemouth Blindcat" /> The [[widemouth blindcat]] (''Satan eurystomus''),<ref name="Widemouth Blindcat">{{Handbook of Texas | name=Widemouth Blindcat | id=tfw01|author=Longley, Glenn |  retrieved=12 May 2010}} Texas State Historical Association</ref> a unique species of blind catfish, has been pumped out of wells almost 610 meters deep along the FW-SW boundary.<ref>Glenn Longley and Henry Karnei, Jr. (1978). Status of Satan Eurystomus Hubbs and Bailey, the Widemouth Blindcat 6. S.W. Tex. St. U.</ref> However, all aquatic-dependent plants and wildlife in the Edwards Plateau area rely on the aquifer to support essential components of their habitats. Currently, the terrain is dominated by oak – juniper parks.<ref name=":19">Bexar Metropolitan Water District. (1999). Environmental Assessment ESA Section 10 (a)(1)(B) Incidental Take Permit and Habitat Conservation Plan for Reduction of Withdrawals from the Edwards Aquifer.</ref> The dominant woody plant on the Edwards Plateau is [[Juniperus ashei|Ashe juniper]] (''Juniperus ashei'').<ref>{{cite journal | last1 = Wilcox | first1 = B. P. | last2 = Owens | first2 = M. K. | last3 = Knight | first3 = R. W. | last4 = Lyons | first4 = R. K. | year = 2005 | title = Do woody plants affect streamflow on semiarid karst rangelands? | journal = Ecological Applications | volume = 15 | issue = 1| pages = 127–136 | doi=10.1890/04-0664| bibcode = 2005EcoAp..15..127W }}</ref>

Edwards Aquifer is home to a large number of invertebrate species, 40 of which have been described.<ref name=":19" /> The most diverse groups are the prosobranch gastropods and amphipod crustaceans. The Edwards Aquifer has the highest recorded diversity of [[stygobite]]s in the world.<ref>{{cite journal |author=Culver, D. C. |author2=Master, L. L. |author3=Christman, M. C. |author4=Hobbs, H. H. |year=2000 |title=Obligate cave fauna of the 48 contiguous United States |journal=Conservation Biology |volume=14 |issue=2 |pages=386–401 |doi=10.1046/j.1523-1739.2000.99026.x|bibcode=2000ConBi..14..386C |s2cid=84500413 }}</ref> In the United States, only the fauna of the Edwards Aquifer of Texas has a significant component of marine-derived species. Of the major karst regions in the United States, it is the only one with a significant marine component.<ref>{{cite journal | last1 = Culver | first1 = D.C. | last2 = Christman | first2 = M.C. | last3 = Elliott | first3 = W.R. | last4 = Hobbs | first4 = H.H. III | last5 = Reddell | first5 = J.R. | year = 2003 | title = The North American obligate cave fauna: regional patterns | doi = 10.1023/A:1022425908017 | journal = Biodiversity and Conservation | volume = 12 | issue = 3| pages = 441–468 | s2cid = 7275515 }}</ref> Of the 64 stygobionts known from the Edwards Aquifer, 17 are marine relics.<ref>{{cite journal | last1 = Culver | first1 = D. C. | last2 = Pipan | first2 = T. | last3 = Schneider | first3 = K. | year = 2009 | title = Vicariance, dispersal and scale in the aquatic subterranean fauna of karst regions | journal = Freshwater Biology | volume = 54 | issue = 4| pages = 918–929 | doi=10.1111/j.1365-2427.2007.01856.x| bibcode = 2009FrBio..54..918C | doi-access = free }}</ref>
[[File:Satan eurystomus illustration 2.jpg|left|thumb|The [[Widemouth blindcat]], a species of stygobitic [[catfish]] native to the aquifer ]]
[[United States Fish and Wildlife Service|The U.S. Fish and Wildlife Service]] (USFWS) consider the Comal and San Marcos Springs ecosystems to have one of the greatest known diversities of organisms of any aquatic ecosystem in the Southwestern United States.<ref>San Marcos/Comal Recovery Team, U.S. Fish & Wildlife Service. (1996). San Marcos and Comal Springs and Associated Aquatic Ecosystems (Revised) Recovery Plan 6</ref> This is due in part to the constant nature of the temperature and flow of the aquifer waters that have created unique ecosystems supporting a high degree of [[endemism]].<ref>Wilson, E.O. (1992). The Diversity of Life 397.</ref> The Edwards Aquifer is the sole environment for the rare [[Barton Springs salamander]] (''Eurycea sosorum''), which is a federally listed endangered species.<ref>{{cite journal | last1 = Sharp Jr | first1 = J. M. | last2 = Banner | first2 = J. L. | year = 1997 | title = The Edwards Aquifer: A resource in conflict | journal = GSA Today | volume = 7 | issue = 8| pages = 1–9 }}</ref> At Comal and San Marcos Springs, their openings and in the rivers and lakes originating from the springs, one threatened and seven endangered species have been listed by USFWS under the Endangered Species Act of 1973. The [[San Marcos salamander]] (''Eurycea nana'') is listed as threatened. The [[San Marcos gambusia]] (''Gambusia georgei''), [[Texas Wild Rice|Texas wild rice]] (''Zizania texana''), [[fountain darter]] (''Etheostoma fonticola''), [[Texas blind salamander]] (''Eurycea rathbuni''), [[Heterelmis comalensis|Comal Springs riffle beetle]] (''Heterelmis comalensis''), [[Stygoparnus comalensis|Comal Springs dryopid beetle]] (''Stygoparnus comalensis''), and [[Stygobromus pecki|Peck's cave amphipod]] (''Stygobromus pecki'') are listed as endangered. Another species, the [[Blanco blind salamander]], is unlisted because it is unknown whether the species is extant or extinct.<ref>{{Cite web |last=Jones |first=Benji |date=2022-08-01 |title=Why scientists are desperate to find a salamander that's been missing for 71 years |url=https://www.vox.com/down-to-earth/23205853/lost-species-extinction-salamander |access-date=2022-12-21 |website=Vox |language=en}}</ref>

== Land use ==
Land use through the region atop the Edwards aquifer varies between rangeland, agricultural and residential/urban.
The northern portion is primarily rangelands and contains most of the streams feeding the recharge zone.<ref>{{Cite journal|title = Hydrogeologic Framework of the Edwards-Trinity Aquifer System, West Central Texas|last1 = Barker|first1 = R.A.|date = 1996|journal = U.S. Geological Survey Professional Paper|last2 = Ardis|first2 = A.F.|series = Professional Paper|doi = 10.3133/pp1421B| url=https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=3509&context=kip_articles |doi-access = free}}</ref> Until the late 1990s much of the land area that recharged the aquifer was undeveloped rangeland, but since that time it has undergone a significant increase in development.<ref name=":1">{{Cite web|title = USGS - NAWQA - Water Quality in South-Central Texas - Contents|url = http://pubs.water.usgs.gov/circ1212/|website = pubs.water.usgs.gov|access-date = 2015-10-23}}</ref> From 1996
to 1998 residential land use increased 9 percent in the Edwards aquifer recharge zone; even so, 72 percent remains undeveloped.<ref name=":2">{{Cite journal|url = http://pubs.usgs.gov/wri/wri02-4241/pdf/wri02-4241.pdf|title = Simulation of Runoff and Recharge and Estimation of Constituent Loads in runoff, Edwards Aquifer Recharge Zone (Outcrop)and Catchment Area, Bexar County, Texas, 1997–2000|last = Ockerman|first = D.J.|date = 2002|journal = USGS Water-Resources Investigations Report 02–4241}}</ref> The
region atop the Edwards aquifer continues to increase in population today. In 2012, the US Census Bureau noted four counties located within the Edwards
Region; Kendal, Comal, Hays and Travis were among the fastest growing in the nation, all with growth rates between 25 and 50 percent.<ref name=":16">{{Cite web|title = Texas Dominates List of Fastest-Growing Large Cities Since 2010 Census, Census Bureau Reports - Population - Newsroom - U.S. Census Bureau|url = https://www.census.gov/newsroom/releases/archives/population/cb12-117.html|website = www.census.gov|access-date = 2015-10-24|publisher = US Census Bureau}}</ref> An estimated 4.6 percent of the recharge zone is now covered with impervious surfaces which decrease aquifer recharge and can negatively affect water quality.<ref name=":2" />

Almost all of agricultural lands and a large portion of San Antonio overlie the confined portion of the aquifer (Barker 1996). In an effort to preserve undeveloped land the city of San Antonio passed the Edwards Aquifer Protection Plan in 2000 (renewed in 2005, 2010 and 2015). The plan allows the city to purchase conservation easements for land in Bexar, Medina and Uvalde
counties. The landowners retain and upon agreement the landowners cannot divide or develop the land and are paid 40-45% of market value for the easement.  The
plan has over {{convert|130000|acre|km2|round=5}} enrolled.<ref>{{Cite web|title = Prop 1: Edwards Aquifer Protection Plan up for renewal|url = http://www.ksat.com/news/prop-1-edwards-aquifer-protection-plan-up-for-renewal|website = KSAT|access-date = 2015-10-24|date = 2015-05-04}}</ref>

== Demographics ==
[[File:Edwards Aquifer Population Projections, 1990 - 2050.JPG|thumb|388x388px]]
More than 1.7 million people rely on water from the Edwards Aquifer for municipal, industrial and daily use.<ref name=":10">GEAA. (2014). Edwards Aquifer Background Information. Retrieved October 13, 2015, fromhttp://www.aquiferalliance.net/unique-resource/</ref>  One of the major cities on the aquifer is San Antonio, America's 7th largest city, with a population of over 1 million. San Antonio is heavily dependent on the Edwards Aquifer for their municipal, industrial and daily use.<ref name=":16" /> Another major city on the aquifer is Austin. More than 50,000 people in the city of Austin (6% of Austin's population) rely on the [[Barton Springs]] segment of the Edwards Aquifer.<ref name=":10" />

Between 1990 and 2015, the population increased by two thirds, at this rate, the population of the basin will be doubled in 2050. The population across the counties have approximately the same growth rate of 10% per year. However, Comal and Guadalupe have a greater growth rate of more than 25% per year. This will increase the number of people relying on the aquifer for daily water use.

== Economy ==
The Edwards Aquifer underlies 38 counties in South and Western Texas.<ref>Ashworth, J. B. (1995). Aquifers of Texas. Texas Water Development Board. Report 345. Pdf: http://www.cctexas.com/Assets/Departments/Water/Files/TWDB%20Aquifer%20Report.pdf</ref> [[West Texas]] is regionally defined by jobs in the oil and gas industries, but is also home to mining support, agriculture, and transportation support, among other sectors.<ref>Regional Snapshot: West Region. (2015) Texas Comptroller of Accounts. Pdf available at: http://www.texasahead.org/regionalrpts/</ref> [[South Texas]] is regionally defined by recent economic growth in shipping industries, irrigation based farming, and manufacturing.<ref name=":9">Regional Snapshot: South Region. (2015) Texas Comptroller of Accounts. Pdf available at: http://www.texasahead.org/regionalrpts/</ref> According to the Texas Comptroller and Texas Water Development Board, the Southern region's economic growth and irrigation practices have put pressure on water demands that exceed supply, and this is expected to increase with economic and demographic trends between 2010 and 2060.<ref name=":9" />

All of these economic practices in the region put pressure on both the quantity and quality of water in the Edwards Aquifer.  A recent study showed that salinity in groundwater wells in the aquifer is high, potentially affected by adjacent, natural salt deposits as well as brine seepage from nearby oil fields.<ref>{{cite journal | last1 = Chaudhuri | first1 = Sriroop | last2 = Ale | first2 = Srinivasulu | year = 2014 | title = Temporal evolution of depth-stratified groundwater salinity in municipal wells in the major aquifers in Texas, USA | journal = Science of the Total Environment | volume = 472 | pages = 370–380 | doi=10.1016/j.scitotenv.2013.10.120| pmid = 24295753 | bibcode = 2014ScTEn.472..370C }}</ref>  Additionally, irrigated agriculture is a significant user of the Edwards Aquifer groundwater, with a variety of crops cultivated, including: " vegetables, hay sesame, soybeans, peanuts, cotton, corn, sorghum, wheat, and oats".<ref>{{cite journal | last1 = Chowdhury | first1 = Manzoor E. | last2 = Lacewell | first2 = Ronald D. | last3 = McCarl | first3 = Bruce A. | year = 2011 | title = Effect of USDA Commodity Programs on Annual Pumpage from the Edwards Aquifer | journal = Journal of Contemporary Water Research and Education | volume = 106 | issue = 1| page = 11 }}</ref>  Also, the city of [[San Antonio]] is located along the eastern edge of the aquifer and was listed as the 7th largest city in the United States by population in 2014.<ref>{{Cite web|url = https://www.census.gov/content/dam/Census/newsroom/releases/2015/cb15-89_graphic.jpg|title = 1 Million Milestone|access-date = November 3, 2015|publisher = U.S. Census Bureau}}</ref>

== Stakeholders ==
Historically, the Edwards Aquifer has served as the sole source of water for the city of San Antonio.<ref name=":11">{{cite journal | last1 = FitzHugh Thomas | first1 = W. | last2 = Richter | first2 = Brian D. | year = 2004 | title = Quenching Urban Thirst: Growing Cities and Their Impacts on Freshwater Ecosystems | journal = BioScience | volume = 54 | issue = 8| pages = 741–754 | doi=10.1641/0006-3568(2004)054[0741:qutgca]2.0.co;2| doi-access = free }}</ref> This eight-county metropolitan area is the second fastest-growing area in the state of Texas and depends on the aquifer for both recreational use and clean drinking water.<ref name=":12">{{Cite web|title = San Antonio (city) QuickFacts from the US Census Bureau|url = http://quickfacts.census.gov/qfd/states/48/4865000.html|website = quickfacts.census.gov|access-date = 2015-11-05|archive-date = 2009-03-28|archive-url = https://web.archive.org/web/20090328041312/http://quickfacts.census.gov/qfd/states/48/4865000.html|url-status = dead}}</ref><ref name=":13">{{Cite web|title = San Antonio Water System|url = http://www.saws.org/|website = www.saws.org|access-date = 2015-11-05}}</ref> San Antonio Water System (SAWS) is the largest public water utility system that serves the eight counties of the San Antonio metropolitan area. A total of 92 water wells with a daily pumpage rate of {{convert|203.7|e6U.S.gal|ML|abbr=off}} supply water to SAWS' customers.<ref name=":14">{{Cite web|title=Edwards Aquifer Authority |url=http://www.edwardsaquifer.org/eaa |website=www.edwardsaquifer.org |access-date=2015-11-05 |archive-url=https://web.archive.org/web/20150907212603/http://www.edwardsaquifer.org/eaa |archive-date=2015-09-07 }}</ref>

In addition to the 2.3 million San Antonio residents are the communities of New Braunfels and San Marcos that depend on the aquifer for clean drinking water.  Farming and ranching communities are other significant dependents of the aquifer.<ref name=":14" /> From the 1930s to the 1980s, withdrawals have quadrupled with over half of the current withdrawals serving municipal water purposes while the remaining goes to agricultural needs.<ref>Hamilton JM. 2003. Edwards Aquifer Authority Hydrogeologic Data Report for 2002. San Antonio (TX): Edwards Aquifer Authority.</ref><ref>US Fish and Wildlife Service. 1995. San Marcos and Comal Springs and Associated Aquatic Ecosystems (Revised) Recovery Plan. Albuquerque (NM): USFWS.</ref> More than 50,000 people in the city of Austin (6% of Austin's population) rely on the [[Barton Springs]] segment of the Edwards Aquifer.<ref name=":10" />

Five groups of stakeholders have played significant roles in shaping the use and conservation of the aquifer, including the Edwards Aquifer Authority (EAA), New Braunfels, San Marcos, San Antonio, and Texas State University.<ref>"Water for All. Diverse stakeholders are lauded for work to conserve Edwards Aquifer."  Texas Parks and Wildlife Magazine July 2014.</ref><ref>{{cite journal | last1 = Ernst | first1 = C. | last2 = Gullick | first2 = R. | last3 = Nixon | first3 = K. | year = 2004 | title = Conserving forests to protect water | journal = Opflow | volume = 30 | issue = 5| pages = 1–7 | doi = 10.1002/j.1551-8701.2004.tb01752.x | bibcode = 2004Opflo..30e...1E }}</ref>  Additionally, federal entities including US Geological Survey, US Fish and Wildlife Service, and US Environmental Protection Agency have been involved in water steward activities and recovery management plans of the Edwards aquifer system.<ref name=":11" /><ref name=":12" /><ref name=":13" />

The EAA was created as a result of Edwards Aquifer Authority Act enacted by Texas State Legislature in 1993. The main purpose of EAA is to oversee the permitting system for water withdrawals from the aquifer system. A subdivision of state government, EAA is more of a liaison between federal agencies (e.g. USFWS, USEPA, USGS), state agencies (e.g. Texas Water Development Board, Texas Commission on Environmental Quality, etc.) and non-governmental organizations (e.g. Texas Water Conservation Association, Texas Association of Groundwater Districts).<ref name=":11" />
{| class="wikitable"
|+Main stakeholders involved in water resources management in the Edwards aquifer system
!Stakeholders
!Involvement in aquifer resources management
|-
|Farmers and ranchers
|Depend on water for crops and animal husbandry
|-
|Edwards Aquifer Authority
|Responsible for permitting process for water withdrawal from the Edwards aquifer system
|-
|Metropolitan areas: Uvalde, San Antonio, New Braunfels, and San Marcos
|Depend on water for drinking, recreational uses, utilities, and for irrigation
|-
|San Antonio Water System (SAWS)
|Largest public utility system that relies on Edwards aquifer system.
|}

==History==

=== European colonization ===
Spanish missionaries who arrived in Texas in the 1700s looked to the Edwards Aquifer as their primary source of water. Springs fed by the aquifer played a key role in deciding the location of the Alamo mission and other settlements in the Texas Hill Country.<ref>1. ''Gulley, Robert L. (2015). Heads Above Water: the Inside Story of the Edwards Aquifer Recovery Implementation Program. Texas A&M University Press. {{ISBN|978-1-62349-268-7}}.''</ref> As Europeans continued to settle the region, and as Texas was acquired by the United States, the Edwards Aquifer continued to supply water for farming, ranching, and rural domestic use.<ref>1. ''Rivard, Robert. "An Oral History: War and Peace Over the Edwards Aquifer". The Revard Report.''</ref>

=== Regulation and management ===
In the 1950s Texas experienced the [[1950s Texas drought|worst drought on record]].<ref>''Smith, Brian; Hunt, Brian (2010). "A Comparison of the 1950s Drought of Record and the 2009 Drought, Barton Springs Segment of the Edwards Aquifer, Central Texas". Central Texas: Gulf Coast Association of Geological Societies Transactions.''</ref> Legislature for protection of the Edwards aquifer began in 1959 with the creation of the Edwards Underground Water District, which created and supplied maps and worked with licensing departments for development interests. Starting in the 1970s, the Texas Water Quality Board (TWQB) first recognized the aquifer and issued regulations regarding surface recharge zones. Following these first steps, regulations began to include the need for geologic assessments prior to development, design standards for underground storage tanks and pipes, and fees for development.<ref>{{Cite web|title = Regulatory History of the Edwards Aquifer|url = http://www.tceq.state.tx.us/field/eapp/history.html|website = www.tceq.state.tx.us|access-date = 2015-11-03|archive-url = https://web.archive.org/web/20150918073311/http://www.tceq.state.tx.us/field/eapp/history.html|archive-date = 2015-09-18}}</ref>

In 1992, the TWQB declared the Edwards aquifer an underground river due to the presence of endangered species, but this was overturned later the same year. In 1993, Texas Senate Bill 1477 established the Edwards Aquifer Authority to manage the aquifer and to limit pumping to protect the spring flow levels.<ref>{{cite journal | last1 = McCarl | first1 = Bruce A. | display-authors = etal   | year = 1999 | title = Limiting pumping from the Edwards Aquifer: An economic investigation of proposals, water markets, and spring flow guarantees | journal = Water Resources Research | volume = 35 | issue = 4| pages = 1257–1268 | doi=10.1029/1998wr900116 | bibcode=1999WRR....35.1257M| hdl = 10211.3/200435 | s2cid = 130985737 | hdl-access = free }}</ref>

In 1997, Chapter 36 of the Texas Water Code was amended by Senate Bill 1 of the 75th Texas Legislature to require all underground [[water conservation]] districts in Texas to develop a groundwater management plan and submit it for approval by the Texas Water Development Board every five years on the anniversary of initial approval (September 17, 1998 for the Edwards Aquifer Authority). The initial requirements of the groundwater management plans were that they address the efficient use of groundwater, methods of controlling and preventing waste of groundwater, conjunctive surface water issues, natural resource issues that affect the use and availability, of groundwater, and methods of controlling and preventing subsidence.

The requirements of groundwater management plans have since undergone expansion to require the inclusion of planning requirements for addressing drought conditions and conservation (2001, the 77th Texas Legislature Senate Bill 2), estimates of the managed available groundwater, the amount of groundwater used within each district, the amount of recharge from precipitation, projected surface water supply, total water demand within the district, and consideration of water management strategies that were included in the adopted state water plan (2005, 79th Texas Legislature HB 1763). Senate Bill 2 of the 77th Texas Legislature also required the groundwater conservation districts to submit groundwater management plans to the Chair of any Regional Water Planning Group in which any part of the district is located so that they may specify any area(s) that conflict with the approved Regional Water Plan[1].

In addition to the groundwater management plan, the Edwards Aquifer Authority board of directors maintains a three-year rolling strategic plan that is updated annually. The 2015-2017 strategic plan adopted on October 14, 2014 identifies six major goals:
* Goal A: Sustain Federally Protected Aquifer-Dependent Species
* Goal B: Ensure Effective Management of the Edwards Aquifer
* Goal C: Enhance Recharge Program for Improved Aquifer Management and Springflow Maintenance,
* Goal D: Prevent the Pollution of the Aquifer
* Goal E: Conduct Research that Enhances Understanding and Effective Management of the Aquifer
* Goal F: Develop a Diverse, Service-Oriented Organization
* Goal G: Build Shared Value in the EAA Mission
* Goal H:  Sustain Fiscal Stability [3]
With the growth of regional
cities such as San Antonio, municipal demand for water increased.<ref>''Rattan Lal, B.A. Stewart, ed. (June 19, 2012). Soil Water and Agronomic Productivity. Boca Raton, FL: CRC Press. pp. 126–128.{{ISBN|978-1-4398-5080-0}}.''</ref> The second half of the twentieth century saw a high volume of legal activity regarding rights to the aquifer.

== Water balance ==
Although between {{convert|25 and 55|e6acre ft|TL|abbr=off|sp=us|round=5}} of water may be present in the Edwards aquifer, only a small portion of this water is practically or legally available for use.<ref name=":7" /> Storage is the difference between recharge (inputs) and discharge (outputs) from the Edwards Aquifer.

Annual storage can be negative during dry years with high water use and positive during wet years with relatively low water use. A long-term negative imbalance between recharge and discharge in an aquifer may lead to the depletion of the available water in the aquifer.

Annual storage between 1955 and 2012 estimated from data provided by a continuing program between the U.S. Geologic Survey and the Edwards Aquifer Authority ranged from {{convert|-633,000 to 1,653,000|acre ft/year|GL/year|abbr=off|sp=us|sigfig=2}}. The average storage during this period was {{convert|37000|acre ft/yr|GL/yr}}.<ref name=":8" />

[[File:Edwards Aquifer Water Balance 1955-2012.png|thumb|526x526px|Water inputs, outputs, and storage to the Edwards Aquifer based on data collected by the Edwards Aquifer Authority between 1955 and 2012]]

=== Inputs (recharge) ===
Water mainly enters the Edwards Aquifer in two ways: it either falls as [[precipitation]] and percolates directly into the aquifer, or it enters as streamflow flowing through the Recharge Zone.  The Recharge Zone occurs along the Balcones Fault Zone where the Edwards Plateau drops steeply and meets the Gulf Coastal Plain. Here, highly fractured limestones are exposed at the Earth's surface, which allow rain and streamflow to infiltrate directly into the aquifer.<ref>Ogden, A. E., Quick, R. A., Rothermel (1986). Hydrochemistry of the Comal, Hueco, and San Marcos Springs, Edwards Aquifer, Texas.  In The Balcones Escarpment, Abbott, Patrick L, and Woodruff, C.M., eds.  San Antonio:  Geological Society of America,  pp. 51-54.</ref>

The Contributing Zone, which occurs on {{convert|5400|sqmi|km2|sigfig=2}} of the Edwards Plateau (Texas Hill Country), collects precipitation and streamflow that drain to the Recharge Zone. Major streams draining the Contributing Zone include [[Cibolo Creek]], [[Helotes Creek]], [[Barton Creek]], and [[Onion Creek (Texas)|Onion Creek]].<ref>Blome, Charles D., Jason R. Faith, Diana E. Pedraza, et al. (2005). USGS, US Department of Interior, and US Geological Survey. <http://pubs.usgs.gov/sim/2005/2873/pdf/2873_Print.pdf></ref> Water is unable to percolate into the aquifer in the Contributing Zone because much of the underlying geology is impermeable.<ref>{{Cite web|title = Introduction to the Edwards Aquifer|url = http://www.edwardsaquifer.net/intro.html|website = www.edwardsaquifer.net|access-date = 2015-11-05}}</ref>

Average precipitation in the region is around {{convert|30|in|mm|round=10}} per year.<ref name=":20">Official Aquifer Level and Statistics (2015). San Antonio Water System. Retrieved 13 October 2015. <http://www.saws.org/Your_Water/aquifer/></ref> Only precipitation that falls on the contributing area is available for infiltration. With a contributing and recharge area of over 2{{convert|6650|sqmi|km2|sigfig=2}}, the mean annual volume of precipitation that is available for recharge is {{convert|10660000|acre ft|TL|1}}, or the equivalent of 5.3 million Olympic sized swimming pools. The average annual recharge rate between 1934 and 2013 is estimated to be {{convert|699000|acre ft|GL}}. The median annual recharge is {{convert|556,950|acre ft|GL|sigfig=3}},<ref>Edwards Aquifer Authority (2013). Scientific Research & Reports: Hydrologic Data Reports. Retrieved 15 October 2015. <{{cite web |url=http://www.edwardsaquifer.org/scientific-research-and-reports/hydrologic-data-reports |title=Edwards Aquifer Authority |access-date=2015-11-03 |archive-url=https://web.archive.org/web/20150909103102/http://www.edwardsaquifer.org/scientific-research-and-reports/hydrologic-data-reports |archive-date=2015-09-09 }}></ref><ref name=":21">Charts and Graphs (2015). The Edwards Aquifer Website. Retrieved 13 October 2015. <http://www.edwardsaquifer.net/charts.html#Estimated_Annual_Recharge_to_the_Edwards_Aquifer></ref> or only 6% of the total inputs to the system.

=== Outputs (discharge) ===
Water from the Edwards Aquifer is discharged in two ways: it is either pumped from wells (well discharge) or it leaves as stream outflow (spring discharge). The Edwards Aquifer Authority (EAA) and the United States Geological Survey (USGS) have monitored annual well and spring discharges since 1934.

Annual well discharge—the sum of all well discharges in a year— ranged from {{convert|219,300 to 542,500|acre ft|GL|sigfig=3}} between 1955 and 2012. The average well discharge for this period was approximately {{convert|371,667|acre ft|GL|0|sigfig=2|round=5}}, equivalent to 183,000 Olympic-sized swimming pools.<ref name=":8" />

Annual spring discharge ranged from {{convert|69,800 to 802,800|acre ft|GL|0}} between 1955 and 2012. The average spring discharge for this period was approximately {{convert|392,991|acre ft|GL|0}}.<ref name=":8" />

During dry years, more water is discharged from wells while during wet years, more water is discharged from springs. Annual total groundwater discharge from pumping and springs ranged from {{convert|388,800 to 1,130,000|acre ft|GL|0}}, and the average total groundwater discharge for 1955 to 2012 period was approximately {{convert|764,431|acre ft|GL|0}}.<ref name=":8" />
{| class="wikitable"
|+
Edwards Aquifer discharge summary for 2013 in acre-feet, by county and use<ref name=":8" />
!
! colspan="3" |Reported Use (Permitted Wells)
! colspan="2" |Unreported Use
! colspan="2" |Subtotals
! rowspan="2" |Total Discharge
|-
!County
!Irrigation
!Municipal
!Industrial
!Domestic/Livestock
!Non-reporting facilities
!Well
!Spring
|-
|Atascosa
|1,208
|0
|0
|0
|0
|1,208
|0
|'''1,208'''
|-
|Bexar
|4,179
|216,051
|15,648
|8,893
|5,046
|249,817
|51
|'''249,868'''
|-
|Comal
|63
|5,781
|7,061
|390
|0
|13,295
|141,412
|'''154,707'''
|-
|Guadalupe
|0
|69
|167
|0
|0
|236
|0
|'''236'''
|-
|Hays
|177
|2,341
|1,292
|858
|195
|4,863
|91,210
|'''96,073'''
|-
|Medina
|33,755
|5,911
|2,007
|1,089
|0
|42,762
|0
|'''42,762'''
|-
|Uvalde
|36,959
|3,870
|95
|2,510
|209
|43,643
|133
|'''43,766'''
|-
|'''Totals''':
|'''76,341'''
|'''234,023'''
|'''26,270'''
|'''13,740'''
|'''5,450'''
|'''355,824'''
|'''232,806'''
|'''588,630'''
|}

=== Hydrologic modeling ===
Scientists with the United States Geologic Survey have developed numerical groundwater flow models for the San Antonio and Barton Springs aquifer segments to determine the amount of water in the aquifer, the direction it is flowing, and its velocity. These are used to estimate the sustainable levels of groundwater withdrawal throughout the aquifer.<ref>[[John D. Bredehoeft|Bredehoeft, J.]] 2002. The Water Budget Myth Revisited: Why Hydrogeologist Model. Groundwater, 40 (4), 340-345.</ref> Given ample data is needed for numerical simulations, yet often lacking,<ref>Zhou, Y., Li, W. 2011. A review of regional groundwater flow modeling. Geoscience Frontiers, 2 (2), 205-214.</ref> regional modeling of large aquifers is difficult, but modeling segments within an aquifer is common and provides useful information for water users throughout the aquifer.

Aquifer storage is correlated with water levels recorded in the J-17 Bexar [[Monitoring wells|index well]] which serves as the sole official monitoring well in the Edwards Aquifer.<ref name=":20" /><ref name=":21" /> The J-17 well, is located in the artisanal confined Edwards Aquifer at a location AY-68-37-203 based on the latitude and longitude.<ref name=":21" /> Water levels have been recorded in the J-17 well since the 1910s, and is used to generalize the entire aquifer system.  Changes in aquifer storage are used to estimate recharge rates.

In the Edwards aquifer, groundwater flow models have been developed for the San Antonio and Barton Springs aquifer segments in the San Antonio region of Texas. Two model simulations were conducted: steady state and transient. A steady-state groundwater flow model requires magnitude and direction of flow remain constant, whereas a transient model simulation allows for a change in water storage over time. Steady-state results suggest water leaving the aquifer occurs through springs (73.3 percent), water well pumping (25.7 percent), and to the Colorado River (0.6 percent). Inflow of water to the aquifer mostly occurs through natural recharge (93.5 percent) and water delivered through the aquifer's regional boundaries (6.5 percent). The transient simulation model also suggests discharge primarily occurs through springs, followed by water well pumping; however, changes in water storage is heavily dependent upon the amount of monthly precipitation and water well pumping volumes.<ref>Lindgren, R., Dutton, A., Hovorka, S., Worthington, S. Painter, S. 2004. Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region Texas. United States Geological Survey Scientific Investigations Report 2004-5277, 154 p.</ref>

== Policy ==
Edwards Aquifer
Authority regulates withdrawal permits, transfers, and groundwater conservation
plans under authority granted by the Texas legislature. Groundwater law in the
state of Texas is governed by the Rule of Capture, which gives landowners the
right to pump groundwater beneath their land, with the exception of drilling a
lateral well extending under a neighbor's property, wasting water, or pumping
with the intention of causing harm to a neighbor's well.<ref>{{Cite web|title = Texas water law|url = http://texaswater.tamu.edu/water-law|website = texaswater.tamu.edu }}</ref> In order to construct a well to withdraw water from the Edwards Aquifer, however,
a user requires a permit that is granted by the Edwards Aquifer Authority. Permits
for existing users are determined by maximum historical use, taking into
consideration the overall availability of water in the aquifer.<ref>{{Cite web|title=Edwards Aquifer Authority |url=http://www.edwardsaquifer.org/legislation-and-rules |website=www.edwardsaquifer.org |archive-url=https://web.archive.org/web/20160403133604/http://www.edwardsaquifer.org/legislation-and-rules |archive-date=2016-04-03 }}</ref>

Wells that produce less than 25,000 gallons per day, wells that are solely for the purpose of watering livestock, and a few other exceptions are considered exempt wells that do not require a permit. Permits for withdrawal can be transferred to another user, provided that the new use is beneficial and occurs within the boundaries of the Authority, with a few geographical exceptions.

Groundwater conservation plans are required for permit holders who withdraw more than {{convert|3|acre ft/yr|U.S.gal/day kL/day}}, unless irrigators can prove more than 60 percent efficiency in their water use. Conservation plans require the use of Best Management Practices, as determined by the Edwards Aquifer Authority.<ref>"Rules and
Statutes." ''Edwards Aquifer Authority''. N.p., n.d. Web. 9 Oct. 2015.</ref>

In recharge zones of the aquifer permits are required to store regulated substances that could damage water quality. Additionally, The Texas Commission of Environmental Quality requires special permits for construction in the recharge zones of the aquifer.<ref>{{Cite web|url = https://www.tceq.texas.gov/field/eapp/apps.html|title = Texas Commission on Environmental Quality}}</ref>

=== Conservation efforts ===
Encompassing an area of 8 counties across south-central Texas including the City of San Antonio and its surrounding communities,<ref name=":17" /> the Edwards Aquifer is the main water supply source for the region, providing water for agricultural and industrial purposes and necessary water flow for endangered species habitat, as well as recreational purposes. As a result of a lawsuit filed by the [[Sierra Club]] under the Federal Endangered Species Act in 1991, the Edwards Aquifer Authority (EAA) was created to oversee the aquifer in its conservation efforts.<ref name=":14" />

The Texas Legislature directed the EAA to regulate pumping from the aquifer, implement critical period management restrictions, and pursue measures to ensure minimum continuous spring flows of the [[Comal Springs (Texas)|Comal]] and [[San Marcos Springs]] are maintained to protect endangered and threatened species to the extent required by federal law.<ref name=":17" /> In 2013, the [[United States Fish and Wildlife Service|U.S. Fish and Wildlife Service]] approved Edwards Aquifer Authority's [[Habitat Conservation Plan]] (HCP), which is a regional 15-year plan designed to protect the water flow and species in the Edwards Aquifer region.

The HCP supports three major project groups of habitat protection measures, flow protection measures, and supporting measures such as applied research, ecological and biological, and water-quality monitoring. HCP project examples include minimization and mitigation of the impacts of low flow, by restoring native riparian zones in order to benefit the Comal Springs riffle beetle by increasing the amount functional habitat and food sources (i.e., root structures and associated biofilms).<ref name=":18">"Habitat Protection Measures." EAHCP — Restoration of Riparian Zones and Riffle BeetleRiparian Improvement. N.p., n.d. Web. 23 Oct. 2015 http://www.eahcp.org/index.php/habitat_protection/comal_springs/restoration_of_riparian_zones_and_riffle_beetle_riparian_improvement {{Webarchive|url=https://web.archive.org/web/20151208114201/http://www.eahcp.org/index.php/habitat_protection/comal_springs/restoration_of_riparian_zones_and_riffle_beetle_riparian_improvement |date=2015-12-08 }}</ref> The method of riparian zone establishment will include the removal of non-native, followed by the replanting of native vegetation that may be considered representative of a healthy, functioning riparian zone.<ref name=":18" />

Although implementation of the HCP exists primarily within the EAA, a broad group of stakeholders plays a role in the management of the Edwards Aquifer. The [[National Research Council (United States)|National Research Council]] (NRC) committee, formed by the [[National Academy of Sciences]] (NAS), released the first of three scientific reports in 2015 that evaluate and make recommendations for Habitat Conservation Plan programming of the Edwards Aquifer.<ref name=":17" />

== Legal activity ==
In the past conflict existed between the [[Sierra Club]] and US Federal and State agencies, cities, and industrial water users.<ref name="SierraClub1">{{cite court | litigants = Sierra Club v. Babbitt | vol = MO-91-CA-069 | court = W.D. Texas | date = 1993 | url= http://www.lrl.state.tx.us/scanned/archive/1993/3492.pdf }}</ref><ref name="SierraClub2">{{cite court | litigants = Sierra Club v. Babbitt | vol = 995 F.2d 571 | court = Court of Appeals, 5th Circuit | date = 1993 | url= https://scholar.google.com/scholar_case?case=9179294810440528251&q=995+F.+2d+571+-+Sierra+Club+v.+Babbitt&hl=en&as_sdt=6,38&as_vis=1 }}</ref><ref name="SierraClub3">{{cite court | litigants = Sierra Club v. City of San Antonio | vol = 112 F. 3d 789 | court = Court of Appeals, 5th Circuit | date = 1997 | url= https://scholar.google.com/scholar_case?case=5604672849277069443&hl=en&as_sdt=6&as_vis=1&oi=scholarr }}</ref>  The conflict is between groups that want to pump more water from the aquifer for human use and those that want to keep water in the aquifer, to feed springs which provide habitat from [[endangered species]].<ref name="SierraClub1" />   This conflict tends to emerge after periods of drought in 1988<ref>{{cite journal | last = Changnon | first = Stanley A. | title = The 1988 Drought, Barges and Diversions | journal = Bulletin of the American Meteorological Society | volume = 70 | issue = 9 | pages = 1092–1104 | date = September 1989 | doi=10.1175/1520-0477(1989)070<1092:tdbad>2.0.co;2| bibcode = 1989BAMS...70.1092C | doi-access = free }}</ref> and in 1995-1996<ref>{{cite web | url =http://www.cpc.ncep.noaa.gov/products/assessments/assess_96/toc.html | title = Climate Assessment for 1996 | last1 = Halpert | first1 = Michael S. | last2 = Bell | first2 = Gerald D. | date = 1996 | website = NOAA.gov | publisher = Climate Prediction Center, NCEP/NWS/NOAA | access-date = 16 October 2015 }}</ref>

In the initial lawsuit was ''Sierra Club v. Babbitt'' in 1991.<ref name="SierraClub1" />  The plaintiffs included environmental groups ([[Sierra Club]]), water districts ([[Guadalupe-Blanco River Authority]] and Bexar Metropolitan Water District), municipalities (City of [[San Marcos, Texas|San Marcos]] and City of [[New Braunfels]]), and utilities (Green Valley and Atascosa Rural Water Supply corporations).  The defendants included, government agencies (US [[Fish and Wildlife Service]], State of [[Texas]], [[Texas Parks and Wildlife Department]]), City of [[San Antonio]], and multiple industrial water users.

In ''Sierra Club v. Babbitt'' the plaintiffs claimed that the defendants were not fulfilling their duties under the [[Endangered Species Act]], to protect endangered species and their ecosystems.  The endangered species included the [[Fountain Darter]], [[San Marcos Salamander]], [[San Marcos Gambusia]], [[Texas Blind Salamander]], and [[Zizania texana|Texas Wild-rice]].  The ecosystems for these species depends on water from [[Comal Springs]] and [[San Marcos Springs]] which have the potential to run dry if too much water is withdrawn from Edwards Aquifer.<ref name="SierraClub1" />

The final decision sided with the Sierra Club and other plaintiffs and in 1993 restrictions were placed on pumping from Edwards Aquifer.<ref name="SierraClub1" /><ref name="SierraClub2" />  As an outcome of ''Sierra Club v. Babbitt'' as a result of this lawsuit, legislation was passed which created the Edwards Aquifer Authority.<ref name=":17">{{cite book | title = Review of the Edwards Aquifer Habitat Conservation Plan | year = 2015 | publisher = National Academies Press | location = Washington D.C. | isbn = 978-0-309-36887-2}}</ref>  This was also not the end of litigation, there was an attempt to appeal the initial ''Sierra Club v. Babbitt'' in 1993 ''Sierra Club v. Babbitt'' the appeal was denied because the US [[Fish and Wildlife Service]] agreed with the original ruling, and the City of [[San Antonio]] and industrial water users were unable to prove that they were injured by the original Sierra Club v. Babbitt ruling.

Due to ''Sierra Club v. Babbitt'' the Edwards Aquifer Act 1993 was passed which created the Edwards Aquifer Authority to oversee pumping regulations.<ref>Tex. Gen. Laws § 2350, ch. 626, 73rd. Leg. (1993).
http://www.edwardsaquifer.org/files/download/5a48e1d88ffe061 {{Webarchive|url=https://web.archive.org/web/20150903232550/http://www.edwardsaquifer.org/files/download/5a48e1d88ffe061 |date=2015-09-03 }}</ref>  In the case ''Barshop v. Medina Under. Wat. Cons. Dist.'' 1996, Medina County Under Water Conservation District challenged the Edwards Aquifer Authority over the constitutionality of the Edwards Aquifer Act.<ref name="Barshop">{{cite court | litigants = Barshop v. Medina Under. Wat. Cons. Dist. | vol = 925 S.W.2d 618 | court = Supreme Court of Texas | date = 1996 | url = http://www.leagle.com/decision/19961543925SW2d618_11482/BARSHOP%20v.%20MEDINA%20UNDER.%20WAT.%20CONS.%20DIST }}</ref>  The challenge was over whether property owners have the constitutional right to pump water from their land, or whether concerns for water conservation and endangered species take precedence. ''Barshop v. Medina Under. Wat. Cons. Dist.'' went to the Texas Supreme Court where the Edwards Aquifer Act was upheld.<ref name="SierraClub3" /><ref name="Barshop" />

In an effort to reduce San Antonio's dependency on the solitary supply of the Edward's Aquifer, the San Antonio Water System (SAWS) has proposed a water supply pipeline, the Vista Ridge, extending 82,000&nbsp;ft from Burleson County to San Antonio.  SAWS reports that the Vista Ridge pipeline, running 54" in diameter, will supply as much as 50,000 ac-ft of water per year for 30 years, upon the project's estimated completion in 2019.<ref name=":3">{{Cite web|url = http://www.saws.org/your_water/waterresources/projects/vistaridge/docs/20140922_SAWSBoardBriefing_VistaRidgeContract.pdf|title = SAWS Board of Trustees Briefing; Vista Ridge Water Supply Contract|last = Puente|first = Robert|archive-url = https://web.archive.org/web/20150317181555/http://www.saws.org/your_water/waterresources/projects/vistaridge/docs/20140922_SAWSBoardBriefing_VistaRidgeContract.pdf|archive-date = 2015-03-17}}</ref>  This will increase the city's current water supply by 20%.<ref name=":4">{{Cite web|title = Vista Ridge exec discusses failed pipeline bill|url = http://www.expressnews.com/news/local/article/Vista-Ridge-exec-discusses-failed-pipeline-bill-6302809.php|website = San Antonio Express-News|date = 3 June 2015|access-date = 2015-10-24}}</ref>

By 2020, SAWS estimates the average San Antonio residential water bill to be $88/mnth; this would place San Antonio at the lowest rate for water in any major Texan city. The water is provided through over 3,400 leases with private landowners drawing from the Caririzo and Simsboro aquifers. In an effort to protect the ratepayer (i.e. San Antonio citizens), the project proposes an undetermined lifeline rate. Any water that fails to be delivered (i.e. shortages, contamination) will be compensated by Blue Water Systems, L.P and not at the expense of the ratepayer.<ref name=":5">{{Cite web|url = http://www.saws.org/your_water/waterresources/projects/vistaridge/docs/SAWS_VistaRidge_PipelineFactSheet.pdf|title = Vista Ridge Fact Sheet|access-date = 2015-10-24|archive-date = 2016-02-25|archive-url = https://web.archive.org/web/20160225134121/http://www.saws.org/your_water/waterresources/projects/vistaridge/docs/SAWS_VistaRidge_PipelineFactSheet.pdf|url-status = dead}}</ref>

This project is projected to promote job growth and prosperity surrounding the city, as the supply will withstand San Antonio's projected growth rate of 20,000 people/year.<ref name=":5" /> Companies invested in the project lobbied for a state drought-planning bill to enable regional approval for the sale of private activity bonds. Despite strong support from the house, the bill failed at the end of May 2015, due to lack of support in the senate. Consequently, the project requires approval from each of the seven counties along the route.<ref name=":4" />

Those in favor of the Vista Ridge pipeline believe the project will help protect and sustain the Edwards Aquifer, as well as enable the conservation of diversified water.<ref name=":3" /> Those who oppose the pipeline are concerned that installment will damage the natural system's ability to recharge the Edwards Aquifer and retain soil moisture. Further, whether or not the city needs additional supply is in question, as projected increase in water demand is speculated to present commercial expansion, not San Antonio's municipal population demand. Environmental groups, such as the Sierra Club, suggest the project is allocating funds to an unsustainable solution, and that San Antonio should instead be "investing in alternative and innovative resources that are less expensive, less energy-intensive, and locally accessible."<ref>{{Cite web|title = Sierra Club: San Antonio Doesn't Need Vista Ridge Pipeline|url = http://therivardreport.com/sierra-club-why-san-antonians-dont-need-the-vista-ridge-pipeline/|website = The Rivard Report|date = July 2015|access-date = 2015-10-24}}</ref>

==See also==
{{Portal|Texas}}
{|
|- valign="top"
|
*[[Balcones Canyonlands National Wildlife Refuge|Balcones Canyonlands NWR]]
*[[Balcones Fault]]
*[[Barton Springs]]
*[[Barton Springs Salamander]]
|
*[[Central Texas]]
*[[Comal River]]
*[[Comal Springs]]
*[[Edwards Aquifer Authority v. Day and McDaniel]]
*[[Edwards Plateau]]
*[[Guadalupe River (Texas)|Guadalupe River]]
|
*[[San Antonio Water System]]
*[[San Marcos River]]
*[[Texas Blind Salamander]]
*[[Texas Hill Country]]
|}

==Notes==
{{Reflist|2}}

==External links==
*[http://edwardsaquifer.org/ Edwards Aquifer Authority]
*[http://www.tshaonline.org/handbook/online/articles/mwe01 Handbook of Texas Online, s.v. "EDWARDS UNDERGROUND WATER DISTRICT,"]
*[http://www.edwardsaquifer.net/ Edwards Aquifer Home Page, Gregg Eckhardt]
*[http://www.edwardsaquifer.net/species.html Endangered Species of the Edwards Aquifer]
*[https://web.archive.org/web/20060221014632/http://www.sosalliance.org/eaproplan.shtml Save Our Springs Alliance - Edwards Aquifer Protection Plan]
*[http://www.aquiferalliance.org/ Greater Edwards Aquifer Alliance]
*[http://lib.utexas.edu/geo/fieldguides/edwardsaquifer.html Edwards Aquifer Guide University of Texas Library]

{{Clear}}
{{Aquifers}}
{{Greater Austin}}
{{Texas}}

[[Category:Aquifers in the United States]]
[[Category:Bodies of water of Texas]]
[[Category:Geology of Texas]]
[[Category:Greater Austin]]
[[Category:Texas Hill Country]]