June 14, 2016

DRAFT
Explanatory Report for Proposed Desired Future Conditions of
the Saline Edwards (Balcones Fault Zone) Aquifer
in Northern Subdivision, Groundwater Management Area 10

Table of Contents
Section ...................................................................................................................................... Page
APPENDICES .............................................................................................................................. iv
FIGURES ........................................................................................................................................v
TABLES ........................................................................................................................................ vi
ABBREVIATIONS ..................................................................................................................... vii
1.

Description of Groundwater Management Area 10 and its Northern Subdivision .....1

2.

Aquifer Description ...........................................................................................................2

3.

Desired Future Conditions ...............................................................................................3

4.

Policy Justification ............................................................................................................4

5.

Technical Justification ......................................................................................................4

6.

Consideration of Designated Factors ...............................................................................6
6.1
Aquifer Uses or Conditions ..................................................................................6
6.1.1
Description of Factors in the Saline Edwards (Balcones Fault Zone)
Aquifer in Northern Subdivision, GMA 10 .............................................6
6.1.2
DFC Considerations.............................................................................7
6.2
Water-Supply Needs .............................................................................................7
6.2.1
Description of Factors in the Saline Edwards (Balcones Fault
Zone) Aquifer in Northern Subdivision, GMA 10 ............................7
6.2.2
DFC Considerations.............................................................................8
6.3
Water- Management Strategies ...........................................................................8
6.3.1
Description of Factors in the Saline Edwards (Balcones Fault
Zone) Aquifer in Northern Subdivision, GMA 10 ............................8
6.3.2
DFC Considerations.............................................................................9
6.4
Hydrological Conditions ......................................................................................9
6.4.1
Description of Factors in the Saline Edwards (Balcones Fault
Zone) Aquifer in Northern Subdivision, GMA 10 ............................96.4.1.1
Total Estimated Recoverable Storage ................................................96.4.1.2
Average Annual Recharge ................................................................10
6.4.1.3
Inflows .................................................................................................10
6.4.1.4
Discharge ............................................................................................11
6.4.1.5
Other Environmental Impacts Including Springflow and
Groundwater/Surface Water Interaction ........................................12
6.4.2
DFC Considerations...........................................................................12

7.

Subsidence Impacts .........................................................................................................12

ii

8.

Socioeconomic Impacts Reasonably Expected to Occur .............................................12
8.1
Description of Factors in the Saline Edwards (Balcones Fault Zone)
Aquifer in Northern Subdivision, GMA 10 .......................................................128.2
DFC Considerations.............................................................................................13

9.

Private Property Impacts ...............................................................................................13
9.1
Description of Factors in the Saline Edwards (Balcones Fault Zone)
Aquifer in Northern Subdivision, GMA 10 .......................................................13
9.2
DFC Considerations.............................................................................................13

10.

Feasibility of Achieving the DFCs .................................................................................14

11.

Discussion of Other DFCs Considered ..........................................................................14

12.

Discussion of Other Recommendations .........................................................................1412.1 Advisory Committees ..........................................................................................1412.2 Public Comments ............................................................................................14

13.

Any Other Information Relevant to the Specific DFCs ..............................................14

14.

Provide a Balance Between the Highest Practicable Level of Groundwater
Production and the Conservation, Preservation, Protection, Recharging, andPrevention of Waste of Groundwater and Control of Subsidence in the Management
Area ...................................................................................................................................15

15.

References .........................................................................................................................15

iii

List of Appendices
Appendix A—Proposed Desired Future Condition Resolution
Appendix B—Water Management Strategies in the 2012 State Water Plan for Caldwell,
Hays and Travis Counties.
Appendix C—Socioeconomic Impacts Analyses for Regions K, L, and M

iv

FIGURES
Figure ....................................................................................................................................... Page
1

Map of the administrative boundaries of GMA10 designated for joint-planning purposes
and the GCDs in the GMA (From Texas Water Development Board website) ..................22

Map showing the extent of the saline portion of the Edwards (Balcones Fault Zone)
Aquifer in Groundwater Management Area 10. Figure from Bradley (2011) ....................3v

TABLES
Table ....................................................................................................................................... Page
1

Estimation of Modeled Available Groundwater (MAG) by using water-budget approach.
Areas and properties are the same as those used in Bradley (2011). ...................................52

Use of the Edwards (Balcones Fault Zone) and Trinity Aquifers in the Barton
Springs/Edwards Aquifer Conservation District for the years 2007–2010 by county andaquifer management zone (the Barton Springs/Edwards Aquifer Conservation District
Management Plan) (in gallons and acre-ft) ..........................................................................7

3

Projected water-supply needs in the counties containing the Saline Edwards (Balcones
Fault Zone) Aquifer in the Northern Subdivision of GMA 10 for the State Water Plan
planning period 2010-2060. All values in acre-feet per year. Negative values indicate aneed whereas a positive value would indicate a surplus. .....................................................84

Projected water management strategies utilizing the Saline Edwards (Balcones Fault
Zone) Aquifer in counties in the northern subdivision of GMA 10 in the 2012 State Water
Plan ......................................................................................................................................9viAbbreviations
DFC

Desired Future Conditions

GCD

Groundwater Conservation District

GMA

Groundwater Management AreaMAG

Modeled Available Groundwater

TWDB

Texas Water Development Board

vii

1.

Description of Groundwater Management Area 10 and its Northern Subdivision

Groundwater Conservation Districts (GCDs, or districts) were created, typically by legislative
action, to provide for the conservation, preservation, protection, recharging, and prevention ofwaste of the groundwater, and of groundwater reservoirs or their subdivisions, and to control
subsidence caused by withdrawal of water from those groundwater reservoirs or theirsubdivisions. The individual GCDs overlying each of the major aquifers or, for some aquifers,
their geographic subdivisions were aggregated by the Texas Water Development Board (TWDB)
acting under legislative mandate to form Groundwater Management Areas (GMAs). Each GMA
is charged with facilitating joint planning efforts for all aquifers wholly or partially within its
GMA boundaries that are considered relevant to joint regional planning.
Groundwater Management Area 10 was delineated based primarily on the extents of the San
Antonio and Barton Springs segments of the Fresh Edwards (Balcones Fault Zone) Aquifer, but
it also includes the underlying down-dip Trinity Aquifer. Other aquifers in GMA 10 include the
Leona Gravel, Buda Limestone, Austin Chalk, and the Saline Edwards (Balcones Fault Zone)
aquifers. The planning area of Groundwater Management Area 10 includes all or parts of Bexar,
Caldwell, Comal, Guadalupe, Hays, Kinney, Medina, Travis, and Uvalde counties (Figure 1).
GCDs in Groundwater Management Area 10 include Barton Springs/Edwards Aquifer
Conservation District, Comal Trinity GCD, Edwards Aquifer Authority, Kinney County GCD,
Medina County GCD, Plum Creek Conservation District, and Uvalde County Underground
Water Conservation District (UWCD) (Figure 1).
As mandated in Texas Water Code § 36.108, districts in a GMA are required to submit Desired
Future Conditions (DFCs) of the groundwater resources in their GMA to the executive
administrator of the TWDB, unless that aquifer is deemed to be non-relevant for the purposes ofjoint planning. According to Texas Water Code § 36.108 (d-3), the district representatives shallproduce a Desired Future Conditions Explanatory Report for the management area and submit to
the TWDB a copy of the Explanatory Report.
GMA 10 has designated the Saline Edwards (Balcones Fault Zone) Aquifer in the northern
subdivision of the GMA as a minor aquifer for purposes of joint planning. This document is the
Explanatory Report for this aquifer.

1Figure 1. Map of the administrative boundaries of GMA10 designated for joint-planningpurposes and the GCDs in the GMA (From Texas Water Development Board website)
2.

Aquifer Description

The extent of the Saline Edwards (Balcones Fault Zone) Aquifer in the northern subdivision of
GMA 10 is shown in Figure 2. It is the portion of the Edwards (Balcones Fault Zone) Aquiferthat is down-dip (southeast) of the Barton Springs segment of the aquifer. The northern
subdivision of GMA 10 for the Saline Edwards (Balcones Fault Zone) Aquifer is located within
the Regional Water Planning Areas K and L, and is included in portions of Barton
Springs/Edwards Aquifer Conservation District and Plum Creek Conservation District. As
shown in Figure 2, this aquifer includes portions of Hays, Travis and Caldwell counties.

2

Figure 2. Map showing the extent of the saline portion of the Edwards (Balcones Fault Zone)
Aquifer in Groundwater Management Area 10. Figure from Bradley (2011).
3.

Desired Future Conditions

The proposed DFC for the Northern Saline Edwards is as follows: No more than 75 feet of
regional average potentiometric surface drawdown due to pumping when compared to predevelopment conditions. The second round of DFCs was adopted at the GMA10 meeting on____________. Resolution No. 2016-xx is attached in Appendix A. The policy and technicaljustifications for this DFC are described in the remainder of this report.

3

4.

Policy Justification

The DFCs in the northern subdivision of GMA 10 for the Saline Edwards (Balcones Fault Zone)
Aquifer were adopted after considering the following factors specified in Texas Water Code§36.108 (d):1.

Aquifer uses or conditions within the management area, including conditions that differ
substantially from one geographic area to another;a.
for each aquifer, subdivision of an aquifer, or geologic strata; andb.
for each geographic area overlying an aquifer

2.

The water supply needs and water management strategies included in the state water
plan;

3.

Hydrological conditions, including for each aquifer in the management area the total
estimated recoverable storage as provided by the executive administrator, and the averageannual recharge, inflows, and discharge;

4.

Other environmental impacts, including impacts on spring flow and other interactions
between groundwater and surface water;

5.

The impact on subsidence;

6.

Socioeconomic impacts reasonably expected to occur;

7.

The impact on the interests and rights in private property, including ownership and therights of management area landowners and their lessees and assigns in groundwater asrecognized under Section 36.002;

8.

The feasibility of achieving the DFC; and,9.

Any other information relevant to the specific DFCs.

These factors and their relevance to establishing the DFCs are discussed in appropriate detail incorresponding subsections within Section 6 of this Explanatory Report.
5.

Technical Justification

The DFC adopted during the first round of joint planning was expressed as: “Well drawdown at
the saline-freshwater interface (the so called Edwards ''bad water line") in the northern
subdivision of GMA 10 that averages no more than 5 feet and does not exceed a maximum of 25
feet at any one point on the interface.”
The TWDB developed a method described in GTA Aquifer Assessment 10-35 MAG (Bradley,2011) that uses analytical solutions to estimate modeled available groundwater. The drawdown
at one point of no more than 25 feet at the interface was determined to be the constraining factor.
4Thus, the resulting MAG is very small. However, the expression of only 5 feet of averagedrawdown throughout the area is also very conservative and would likely result in an evensmaller MAG.
New information from modeling results of a U.S. Geological Survey study (Brakefield andothers, 2015) confirm what Barton Springs/Edwards Aquifer Conservation District staff andothers have concluded from other hydrologic data and studies—that the saline- freshwaterinterface is in fact relatively stable and has little potential for the movement of brackish water
into the freshwater zone. Conversely, the risk of movement of freshwater into the saline zone isalso assumed to be low.
The groundwater conservation districts in GMA 10 regard the saline zone as alternative watersupply that poses little threat to the freshwater Edwards—and in fact can lessen demands placed
upon it. Barton Springs/Edwards Aquifer Conservation District also has rules in place(management zones and buffers) that address potential pumping projects along the interface ofthe saline zone. This being the case, it is prudent to restate the DFC for this area to take into
account the new information and allow for development of this important alternative supply
source.
The newly proposed DFC is an expression of average drawdown of the potentiometric surface.
Table 1 is an estimate of modeled available groundwater using an analytical approach commonlyused by TWDB. The aquifer storage coefficient and surface areas are from Bradley (2011). The
modeled available groundwater is estimated by multiplying the average drawdown (75 feet) by
the dimensionless storage coefficient (7.0 x 10-4) and the area (163,111 acres) to get 8,564 acrefeet per year. As other inflows and outflows are considered to be negligible (described later inthis report), this approach treats the aquifer as a closed system.
Table 1. Estimation of Modeled Available Groundwater (MAG) by using water-budget
approach. Areas and properties are the same as those used in Bradley (2011).
Barton Springs/Edwards
Plum Creek
NonAquifer Conservation
Conservation
District
Total
District
District
Areas
Desired Future
No more than 75 feet of regional average potentiometric surface
Condition (feet ofdrawdown due to pumping when compared to pre-development
drawdown)
conditions
Storage Coefficient
7.0 x 10-4
(dimensionless)Areal extent (acres)
72,363
15,47875,270163,111
Estimated Modeled
Available
3,799
813
3,952
8,564
Groundwater(acre-feet per year)

56.

Consideration of Designated Factors

In accordance with Texas Water Code § 36.108 (d-3), the district representatives shall produce a
Desired Future Condition Explanatory Report. The report must include documentation of hownine factors identified in Texas Water Code §36.108(d) were considered and how the proposed
DFC impacts each factor. The following sections of the Explanatory Report summarize theinformation that the GCDs used in their deliberations and discussions.
6.1

Aquifer Uses or Conditions

6.1.1 Description of Factors in the Saline Edwards (Balcones Fault Zone) Aquifer inNorthern Subdivision, GMA 10
The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013).
Groundwater use within the Barton Springs/Edwards Aquifer Conservation District is comprised
primarily of pumpage from the freshwater Edwards (Balcones Fault Zone) Aquifer with a small
but increasing component of pumpage from the Trinity Aquifer. An incidental amount ofgroundwater is derived from the Taylor and Austin Groups and more geologically recent alluvial
deposits. These withdrawals, however, are largely from exempt wells and are not subject topermitting. Given the current Barton Springs/Edwards Aquifer Conservation District
management scheme of conditional permitting and the drought restrictions and curtailment
requirements associated with mandatory interruptible-supply for new pumpage authorizations forthe freshwater Edwards (Balcones Fault Zone) Aquifer, it is likely that future groundwaterproduction will trend more towards pumpage from the Middle and Lower Trinity Aquifers and,eventually, the Saline Edwards (Balcones Fault Zone) Aquifer.
Data presented in Table 2 are a compilation of the Barton Springs/Edwards Aquifer
Conservation District monthly meter readings reported by the Barton Springs/Edwards Aquifer
Conservation District permittees and are therefore, a more accurate representation of actual
District groundwater use than estimates provided by the TWDB
(http://www.twdb.texas.gov/waterplanning/waterusesurvey/historical-pumpage.asp). The
reported use data are organized by Major Aquifer, County and Management Zone in Table 2.
These data include neither Exempt Use, which is primarily from the Edwards (Balcones Fault
Zone) Aquifer and is estimated to be about 105,000,000 gallons (322.2 acre-ft) annually, nor
Non-exempt Domestic Use under the District’s Non-exempt Domestic Use general permit, whichis also primarily from the Edwards (Balcones Fault Zone) Aquifer and is estimated to be about
20,600,000 gallons (63.2 acre-ft) annually.
Estimates of current use of the saline portion of the aquifer for areas outside Barton
Springs/Edwards Aquifer Conservation District were not available from TWDB, but are believed
to be small as well.

6

Table 2. Use of the Edwards (Balcones Fault Zone) and Trinity Aquifers in the Barton
Springs/Edwards Aquifer Conservation District for the years 2007–2010 by county and aquifer
management zone (the Barton Springs/Edwards Aquifer Conservation District ManagementPlan) (in gallons and acre-ft)
Trinity Aquifers
Edwards (Balcones Fault Zone)
Aquifer
TotalsFreshwater
SalineMiddle
Lower
Zones
Zone
Trinity
Trinity
Hays County
862,705,785
00
2007
862,705,785
2,648
0
0
2,648
1,130,608,005
00
2008
1,130,608,005
3,470
0
0
3,470
892,759,134
00
2009
892,759,134
2,740
0
0
2,740
1,079,339,042
0
0
2010
1,079,339,042
3,312
0
0
3,312
1,171,615,241
0
8,937,000
2011
1,180,552,241
3,596
0
27
3,623
Travis County
619,854,938
0
129,680
3,508,300
2007
623,492,918
1,902
0
0.4
11
1,913
831,133,678
0
111,640
9,107,100
2008
840,352,418
2,551
0
0.3
28
2,579
704,741,741
0
139,5105,801,300
2009
710,682,551
2,163
0
0.4
18
2,181
659,006,656
0
81,5206,449,900
2010
665,538,076
2,022
0
0.3
20
2,042
850,458,404
0
1,502,910
5,694,600
2011
857,655,914
2,610
0
5
17
2,632
6.1.2 DFC Considerations
The Saline portion of the Edwards (Balcones Fault Zone) Aquifer in the Northern Subdivision of
GMA 10 is not currently a significant water source in the area. However, pressure on the primarysource of groundwater in the area – the freshwater Edwards (Balcones Fault Zone) Aquifer – has
led to the need for viable alternative supplies. The proposed DFC allows for a modeled available
groundwater that is far above the current use of the aquifer and is designed to make room fordevelopment of the aquifer as an alternative supply.
6.2.

Water-Supply Needs

6.2.1 Description of Factors in the Saline Edwards (Balcones Fault Zone) Aquifer inNorthern Subdivision, GMA 10
The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013) and7

the Plum Creek Conservation District Management Plan (Plum Creek Conservation District,2012). For estimating projected water supply needs (i.e., water demand vs. supply) the districts
used data extracted from the State Water Plan and provided by the TWDB. The TWDB provides
water-supply needs estimates by decade as well as by county. A summary of the projected watersupply needs is provided in Table 3 by decade in acre-ft/yr.
Table 3. Projected water-supply needs in the counties containing the Saline Edwards (Balcones
Fault Zone) Aquifer in the Northern Subdivision of GMA 10 for the State Water Plan planning
period 2010-2060. All values in acre-feet per year. Negative values indicate a need whereas apositive value would indicate a surplus.
2010
2020
2030
2040
2050
2060
Travis-3,538-11,053-14,067-18,134-55,470-92,045
Hays-1,674-5,738-11,146-18,871-28,549-36,273
Caldwell-210-892-1,910-3,054-4,300-5,694
Totals-5,422-17,683-27,123-40,059-88,319-134,012
The projections in Table 3 show that for the State Water Plan planning period (2010-2060), there
is a progressively increasing water-supply deficit, increasing from 5,422 acre-ft in 2020 up to134,012 acre-ft in 2060. These water-supply needs in the area arise primarily from and aredominated by the burgeoning growth on the southern fringe of the Austin metropolitan area, andalso in the gradual diminution of the surface-water supplies, as reservoir capacity decreases withtime. As in prior plans, some of the water-demand deficits in the area in the out-years (the later
years in the planning period) include numerous contractual shortages. These contractual
shortages will be addressed on an ad-hoc basis, through the renewal and expansion of contracts
with wholesale water suppliers and the contractual reallocation of existing supplies in order toaddress the projected water demands for these and other area water-user groups. But even so, it isprojected that there will be unmet needs under drought-of-record conditions and in the out-years.
6.2.2 DFC Considerations
The population growth of the Austin-San Marcos metropolitan area is creating demand for
additional water supplies from all sources, both within and outside of the northern subdivision.
The DFC allows for considerable drawdown of the Saline Edwards (Balcones Fault Zone)
Aquifer to encourage its use in the future as an alternative water supply that, based on our current
understanding of the aquifer, poses little thread to conditions in the freshwater Edwards Aquifer.
6.3

Water-Management Strategies

6.3.1 Description of Factors in the Saline Edwards (Balcones Fault Zone) Aquifer inNorthern Subdivision, GMA 10
The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013), thePlum Creek Conservation District Management Plan (Plum Creek Conservation District, 2012),
and the 2012 State Water Plan, which relies on the Water Planning Group Plans.

8

Water management strategies for the northern subdivision included in the regional and statewater plans are diverse, arising from the increasing deficit in supply relative to the burgeoning
demand in the northern subdivision. Strategies include increased public/municipal water
conservation, drought management, use/transfer of available or re-allocated surface watersupplies, purchase of water from wholesale water providers, purchase of Carrizo-Wilcox water,development of the Trinity Aquifer, Edwards/Middle Trinity aquifer storage and recovery, anddevelopment of the saline zone of the Edwards (Balcones Fault Zone) water. Details of the water
management strategies in Caldwell, Hays and Travis counties is included in Appendix B. Table 4
below includes the water management strategies that target development of the saline zone of the
Edwards (Balcones Fault Zone) Aquifer.
Table 4. Projected water management strategies utilizing the Saline Edwards (Balcones Fault
Zone) Aquifer in counties in the northern subdivision of GMA 10 in the 2012 State Water Plan.
County
Hays

Hays

Hays

Water Management
Strategy
Development of Saline
Zone of Edwards-BFZ
AquiferDevelopment of Saline
Zone of Edwards-BFZ
AquiferDevelopment of Saline
Zone of Edwards-BFZ
Aquifer
TotalsVolume (acre-feet per year)
2010 2020 2030 2040 2050 2060
0
0
0
0
0
500

EntityBuda

Cimarron Park
Water
CompanyCounty-Other

0

0

250

350

500

600

0

250

2,500 2,500 5,000 6,000

0250

2,750 2,850 5,500 7,100

6.3.2 DFC Considerations
The proposed DFCs allow for development of the saline portion of the Edwards (Balcones Fault
Zone) Aquifer in the northern subdivision of GMA 10 as contemplated in the water management
strategies in the 2012 State Water Plan. The estimated modeled available groundwater of 8,564
acre-feet per year is greater than the peak use in the water management strategies of 7,100 acrefeet per year.
6.4

Hydrological Conditions

6.4.1 Description of Factors in the Saline Edwards (Balcones Fault Zone) Aquifer inNorthern Subdivision, GMA 10
6.4.1.1 Total Estimated Recoverable Storage
Texas statute requires that the total estimated recoverable storage of relevant aquifers be
determined (Texas Water Code § 36.108) by the TWDB. Texas Administrative Code Rule§356.10 (Texas Administrative Code, 2011) defines the total estimated recoverable storage as the9estimated amount of groundwater within an aquifer that accounts for recovery scenarios that
range between 25 percent and 75 percent of the porosity-adjusted aquifer volume.
Total estimated recoverable storage values may include a mixture of water-quality types,
including fresh, brackish, and saline groundwater, because the available data and the existing
Groundwater Availability Models do not permit the differentiation between different waterquality types. The total estimated recoverable storage values do not take into account the effectsof land surface subsidence, degradation of water quality, or any changes to surfacewater/groundwater interaction that may occur due to pumping.
Though the total estimated recoverable storage may include saline groundwater, the estimates arelimited to the official aquifer boundaries as defined by TWDB as opposed to the geologic
formation boundaries. For instance, in Figure 2, the saline portion of the Edwards (Balcones
Fault Zone) Aquifer is defined as the portion of the aquifer that is east and south of the official
Edwards (Balcones Fault Zone) Aquifer boundary defined by TWDB. Though the Edwards
geologic formation is present and contains recoverable saline groundwater, it is outside theofficial boundary of the aquifer. For this reason, TWDB has not developed estimates of the total
estimated recoverable storage for the saline portion of the Edwards (Balcones Fault Zone)
Aquifer (Jones and others, 2013).
6.4.1.2 Average Annual Recharge
As the Saline portion of the Edwards (Balcones Fault Zone) Aquifer in the Northern Subdivisionof GMA 10 is outside the official boundary of the Edwards (Balcones Fault Zone) Aquifer, theTexas Water Development Board does not develop estimates of average annual recharge, inflows
and outflows. This portion of the aquifer is also not included in a groundwater availability modelfor the Edwards (Balcones Fault Zone) Aquifer. However, some information is still known about
the dynamics of potential inflows and outflows from other sources.
The Saline portion of the Edwards (Balcones Fault Zone) Aquifer in the Northern Subdivision of
GMA 10 is confined above by younger Cretaceous-age formations of the Taylor Group that are
generally not significant sources of groundwater (USGS and TWDB, 2006). The saline portionof the aquifer, therefore, does not receive direct recharge from precipitation.
6.4.1.3 Inflows
As the Saline Edwards (Balcones Fault Zone) Aquifer in the Northern Subdivision of GMA 10 is
not in direct communication with the land surface, any flows into and out of the aquifer mustoccur as lateral flows from the fresh portion of the aquifer to the east or as vertical flows fromoverlying or underlying formations. Based on information from a recent USGS study andobservations of Barton Springs/Edwards Aquifer Conservation District staff, the salinefreshwater interface is relatively stable (Brakefield and others, 2015). That is, the movement ofgroundwater into the saline portion of the aquifer from the freshwater portion of the aquifer issmall.
The amount of cross-formational inflow (subsurface recharge) occurring through adjacentaquifers into the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer is10

unknown, although it is thought to be relatively small on the basis of water-budget analyses forsurface recharge and discharge (Barton Springs/Edwards Aquifer Conservation District, 2013;
Slade et al., 1985). Recent studies by the Barton Springs/Edwards Aquifer Conservation District
and others have shown some potential for cross-formational flow both to and from the Barton
Springs segment of the Edwards (Balcones Fault Zone) Aquifer. Sources of cross-formational
flow are discussed below and include the San Antonio segment of the Edwards (Balcones Fault
Zone) Aquifer and the Trinity Aquifer.
Subsurface flow into the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer
from the adjacent San Antonio segment located to the southwest is limited when compared withsurface recharge (Slade et al., 1985). Hauwert et al. (2004) indicated that flow across thesouthern boundary of the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer
is probably insignificant under normal conditions. Though these studies were primarily focusedon the freshwater portion of the Edwards (Balcones Fault Zone) Aquifer, it is believed that thefinding of limited interaction with the San Antonio segment hold for the saline portion of theaquifer as well.
In addition, Brakefield and others (2015) estimated that vertical flow into the Saline Edwards(Balcones Fault Zone) Aquifer was very limited. This is consistent with findings in the Barton
Springs/Edwards Aquifer Conservation District management plan that inflow from the Trinity
Aquifer to the Edwards (Balcones Fault Zone) Aquifer - as a whole, not just the saline portion is not significant (Barton Springs/Edwards Aquifer Conservation District, 2013).
For the purposes of developing desired future conditions and estimated modeled available
groundwater, we have considered inflows to the Saline Edwards (Balcones Fault Zone) Aquifer
to be negligible.
6.4.1.4 Discharge
Leakage from the saline-water zone into the freshwater zone is probably minimal, althoughleakage appears to influence water chemistry at Barton Springs during low-flow conditions(Senger and Kreitler, 1984; Slade et al., 1986). On the basis of a geochemical evaluation,
Hauwert and others (2004) state that the saline-water zone contribution could be as high as 3
percent for Old Mill Spring and 0.5 percent for Main and Eliza Springs under low-flow
conditions of 17 cubic feet per second (combined) Barton Springs flow. These estimates wereindependently recalculated and corroborated by Johns (2006) and are similar to the results ofGarner and Mahler (2007). Under normal flow conditions outflow from the saline-water zone
would be smaller. Massei et al. (2007) noted that specific conductance of Barton Springs
increased 20 percent under the 2000 drought condition, probably from saline-water zone
contribution.
For the purposes of developing desired future conditions and estimated modeled available
groundwater, we have considered outflows from the Saline Edwards (Balcones Fault Zone)
Aquifer to be negligible.

116.4.1.5 Other Environmental Impacts Including Springflow and Groundwater/Surface Water
Interaction
As described in previous sections relating to inflows and discharges, our current understandingof the Saline portion of the Edwards (Balcones Fault Zone) Aquifer in the Northern Subdivisionof GMA 10 is that it is largely isolated from springs and surface process such as interaction withsurface water. We do not expect that the proposed DFCs will have detrimental environmental
impacts.
6.4.2 DFC Considerations
Analysis of the hydrological conditions of the Saline portion of the Edwards (Balcones Fault
Zone) Aquifer in the Northern Subdivision of GMA 10 indicates that the aquifer can serve as analternative water supply that poses little threat to the freshwater Edwards (Balcones Fault Zone)
Aquifer. However, since it has not seen large development historically, the amount of
information available for how the saline portion of the aquifer will respond to significant
pumping is limited. The proposed DFC allows for considerable drawdown and a significantly
higher modeled available groundwater than the DFC proposed in 2010. If this development of
the aquifer is realized, aquifer monitoring and future studies will allow for updates to theunderstanding and consideration of the hydrological conditions presented here.
7.

Subsidence Impacts

Subsidence has historically not been an issue with the Edwards (Balcones Fault Zone) Aquifer in
GMA 10. The aquifer matrix in the northern subdivision is well-indurated and the amount ofpumping does not create compaction of the host rock and/or subsidence of the land surface.
Hence, the proposed DFCs are not affected by and do not affect land-surface subsidence orcompaction of the aquifer.
8.

Socioeconomic Impacts Reasonably Expected to Occur

8.1
Description of Factors in the Saline Edwards (Balcones Fault Zone) Aquifer inNorthern Subdivision, GMA 10
Administrative rules require that regional water planning groups evaluate the impacts of not
meeting water needs as part of the regional water planning process. The executive administrator
shall provide available technical assistance to the regional water planning groups, upon request,
on water supply and demand analysis, including methods to evaluate the social and economic
impacts of not meeting needs [§357.7 (4)]. Staff of the TWDB’s Water Resources Planning
Division designed and conducted a report in support of the South Central Texas Regional Water
Planning Group (Region L) and also the Lower Colorado Regional Water Planning Group(Region K). The report “Socioeconomic Impacts of Projected Water Shortages for the South
Central Texas Regional Water Planning Area (Region L)” was prepared by the TWDB in supportof the 2011 South Central Texas Regional Water Plan and is illustrative of these types ofanalyses.

12

The report on socioeconomic impacts summarizes the results of the TWDB analysis anddiscusses the methodology used to generate the results for Region L. The socioeconomic impact
report for Water Planning Group L is included in Appendix C as an example. These reports aresupportive of a cost-benefit assessment of the water management strategies and thesocioeconomic impact of not promulgating those strategies.
8.2

DFC Considerations

The proposed DFC allows for development of the Saline Portion of the Edwards (Balcones Fault
Zone) Aquifer above what is called for in the water management strategies in the 2012 State
Water Plan. For this reason, the proposed DFC will not have a socioeconomic impact associatedwith an unmet water need.
9.

Private Property Impacts

9.1
Description of Factors in the Saline Edwards (Balcones Fault Zone) Aquifer inNorthern Subdivision, GMA 10
The interests and rights in private property, including ownership and the rights of GMA10
landowners and their lessees and assigns in groundwater, are recognized under Texas Water
Code Section 36.002. The legislature recognized that a landowner owns the groundwater below
the surface of the landowner's land as real property. Joint planning must take into account the
impacts on those rights in the process of establishing DFCs, including the property rights of both
existing and future groundwater users. Nothing should be construed as granting the authority todeprive or divest a landowner, including a landowner's lessees, heirs, or assigns, of thegroundwater ownership and rights described by this section. At the same time, the law holds thatno landowner is guaranteed a certain amount of such groundwater below the surface of his/herland.
Texas Water Code Section 36.002 does not: (1) prohibit a district from limiting or prohibiting thedrilling of a well by a landowner for failure or inability to comply with minimum well spacing or
tract size requirements adopted by the district; (2) affect the ability of a district to regulate
groundwater production as authorized under Section 36.113, 36.116, or 36.122 or otherwise
under this chapter or a special law governing a district; or (3) require that a rule adopted by a
district allocate to each landowner a proportionate share of available groundwater for production
from the aquifer based on the number of acres owned by the landowner.
9.2

DFC Considerations

The DFC is designed to allow for development of the aquifer as an alternative water supply. The
DFC does not prevent use of the groundwater by landowners either now or in the future,
although ultimately total use of the groundwater in the aquifer is restricted by the aquifer
condition, and that may affect the amount of water that any one landowner could use, either atparticular times or all of the time.

13

10.

Feasibility of Achieving the DFCs

The feasibility of achieving a DFC directly relates to the ability of the Groundwater
Conservation Districts to manage the Saline portion of the Edwards (Balcones Fault Zone)
Aquifer to achieve the DFC, including promulgating and enforcing rules and other board actions
that support the DFC. The feasibility of achieving this goal is limited by (1) the finite nature of
the resource and how it responds to drought; and (2) the pressures placed on this resource by thehigh level of economic and population growth within the area served by this resource. Texas
State law provides Groundwater Conservation Districts with the responsibility and authority toconserve, preserve, and protect these resources and to ensure for the recharge and prevention ofwaste of groundwater and control of subsidence in the management area. State law also provides
that GMAs assist in that endeavor by joint regional planning that balances aquifer protection andhighest practicable production of groundwater. The feasibility of achieving these goals could bealtered if state law is revised or interpreted differently than is currently the case.
The caveats above notwithstanding, there are no current hydrological or regulatory conditions
that call into question the feasibility of achieving the DFC.
11.

Discussion of Other DFCs ConsideredNo other DFC of the Saline portion of the Edwards (Balcones Fault Zone) Aquifer in the GMA’s
northern subdivision was considered.
12.

Discussion of Other Recommendations

12.1

Advisory Committees

An Advisory Committee for GMA10 has not been established.
12.2

Public Comments

Each GCD must hold a public meeting within 90 days after the GMA approves its DFCs. During
this meeting, the GCD needs to document stakeholder input. This input is to be submitted by areport from the GCD to the GMA within 90 days after the GMA approves its DFC.
GCDs in GMA 10 have not yet approved its second round of DFCs. The GCDs have not yet held
public meetings to gather public comment on the DFCs. No public comments have yet beenoffered regarding the northern fresh Edwards (Balcones Fault Zone) Aquifer.
13.

Any Other Information Relevant to the Specific DFCs

No additional information relevant to the specific desired future conditions has been identified.

14

14.
Provide a Balance Between the Highest Practicable Level of Groundwater
Production and the Conservation, Preservation, Protection, Recharging, and Prevention ofWaste of Groundwater and Control of Subsidence in the Management Area
Texas Water Development Board has not developed guidance on how to approach this factor. It
is up to the wishes of the Groundwater Conservation Districts on how to approach it, whether ina qualitative, quantitative, or combination manner. But, the Groundwater Conservation Districts
need to include stakeholder input so that this factor can be satisfactory addressed. Participationby the project team at town hall meetings or with individual Groundwater Conservation Districts
is not included in the scope of this work. Groundwater Conservation District management plans
will be used to complete this requirement.
Each Groundwater Conservation District must hold a public meeting within 90 days after the
Groundwater Management Area approves its Desired Future Conditions. During this meeting,
the Groundwater Conservation District needs to document stakeholder input regarding whether
the Desired Future Conditions provide a balance between the highest practicable level ofgroundwater production and the conservation, preservation, protection, recharging, andprevention of waste of groundwater and control of subsidence in the management area. This
input is to be submitted by a report from the Groundwater Conservation District to the
Groundwater Management Area within 90 days after the Groundwater Management Area
approves its Desired Future Conditions.
15.

References

Barton Springs/Edwards Aquifer Conservation District, 2013. Barton Springs/Edwards Aquifer
Conservation District Management Plan, 94 p. + appendices.
Bradley, R.G., 2011. GTA Aquifer Assessment 10-35 MAG, Texas Water Development Board
Aquifer Assessment Report, 13 p.
Brakefield, L.K., White, J.T., Houston, N.A., and Thomas, J.V., 2015, Updated numerical modelwith uncertainty assessment of 1950–56 drought conditions on brackish-water movement within
the Edwards aquifer, San Antonio, Texas: U.S. Geological Survey Scientific Investigations
Report 2015–5081, 54 p., http://dx.doi.org/10.3133/ sir20155081.
Garner, B.D., and B.J. Mahler. 2007. Relation of specific conductance in ground water tointersection of flow paths by wells, and associated major ion and nitrate geochemistry, Barton
Springs segment of the Edwards aquifer, Austin, Texas, 1978–2003: U.S. Geological Survey
Scientific Investigations Report 2007–5002, 39 p., 5 appendixes.
Hauwert, N. 2009. Groundwater flow and recharge within the Barton Springs segment of the
Edwards Aquifer, Southern Travis and Northern Hays Counties, Texas: Ph.D. Dissertation,
University of Texas at Austin, 328 p.
Hauwert, N. 2011. Water budget of stream recharge sources to Barton Springs segment of
Edwards Aquifer: Abstracts, 14th World Lake Conference, Austin, Texas, Oct. 31-Nov. 4, 2001,
p. 46.
15

Hauwert, N. M., D.A. Johns, J.W. Sansom, and T.J. Aley. 2004. Groundwater Tracing of theBarton Springs Edwards Aquifer, southern Travis and northern Hays Counties, Texas: Barton
Springs/Edwards Aquifer Conservation District and the City of Austin Watershed Protection andDevelopment Review Department, 100 p. and appendices.
Johns, D. 2006. Effects of low spring discharge on water quality at Barton, Eliza, and Old Mill
Springs, Austin, Texas: City of Austin, SR-06-05, November 2006.
Jones, I.C., J Shi, and R Bradley. 2013. GAM Task 13-033: Total estimated recoverable storage
for aquifers in Groundwater Management Area 10.
Lambert, R.B., A.G. Hunt, G.P. Stanton, and M.B. Nyman. 2010. Lithologic and physiochemical
properties and hydraulics of flow in and near the freshwater/saline-water transition zone, San
Antonio segment of the Edwards aquifer, south-central Texas, based on water-level and borehole
geophysical log data, 1999-2007: U.S. Geological Survey Scientific Investigations Report 20105122, 69 p. + Appendices.
Massei, N., B.J. Mahler, M. Bakalowicz, M. Fournier, and J.P. Dupont. 2007. Quantitative
Interpretation of Specific Conductance Frequency Distributions in Karst: Ground Water, MayJune 2007, Vol. 45, No. 3, p. 288-293.
Plum Creek Conservation District, 2012. Plum Creek Conservation District Management Plan,
55 p.
Senger, R. K. and C.W. Kreitler. 1984. Hydrogeology of the Edwards Aquifer, Austin Area,
Central Texas: The University of Texas at Austin, Bureau of Economic Geology Report ofInvestigations No. 141, 35 p.
Slade, R. Jr., M. Dorsey, and S. Stewart. 1986. Hydrology and Water Quality of the Edwards
Aquifer Associated with Barton Springs in the Austin Area, Texas: U.S. Geological Survey
Water-Resources Investigations, Report 86-4036, 117 p.
Smith, Brian A., Brian B. Hunt, and Steve B. Johnson, 2012, Revisiting the Hydrologic Divide
Between the San Antonio and Barton Springs Segments of the Edwards Aquifer: Insights from
Recent Studies: Gulf Coast Association of Geological Societies Journal Vol. 1, 62nd Annual
Convention, October 21-24, 2012, Austin, TX.
U.S. Geological Survey and Texas Water Development Board, 2006, Digital Geologic Atlas of
Texas: U.S. Geological Survey and Texas Water Development Board, available through the
Texas Natural Resources Information System.

16