Bob Reedy - Nitrate in Texas Groundwater.pdf

Presented at June 6-7 Texas Alliance of Groundwater Districts Business Meeting

1. Assessment of Nitrate in Groundwater and
Public Water Supply Systems in Texas
Robert C. Reedy, P.G., John Malito, and Bridget R. Scanlon, P.G.
Bureau of Economic Geology
Jackson School of Geosciences
The University of Texas at Austin
TAGD Business Meeting
June 7, 2024
Funded byTexas Commission on Environmental Quality
2021-2022
TEXAS COMMISSION ONENVIRONMENTAL QUALITY

2. Objectives
2
The Nature Conservancy
1.Characterize the distribution of
groundwater nitrate in the major
and minor aquifers of Texas
2.Assess linkages to Community
Water Systems (PWSs) and their
associated populations

3. Sources of Nitrogen
•Symbiotic plant/bacterial fixation of atmospheric nitrogen
(legumes, alfalfa, wheat, soybeans, rice, etc)
•Mineralization of decaying soil organic matter
•Animal manures
•Septic tanks, leach fields, and sewage leaks
•Inorganic fertilizers (ammonium nitrate, urea, etc)
Nitrate that is mobilized below the root zone represents a threat to
groundwater quality.

4. State Distribution of Number of Community Water Systems
StateCWS Systems
1Texas4,655
2California2,981
3Washington2,356
4New York2,300
5N. Carolina2,005
6Pennsylvania1,911
7Illinois1,759
8Georgia1,726
9Florida1,626
10Missouri1,431

5. State Distribution of Number of Community Water Systems
StateCWS Systems
1Texas4,655
2California2,981
3Washington2,356
4New York2,300
5N. Carolina2,005
6Pennsylvania1,911
7Illinois1,759
8Georgia1,726
9Florida1,626
10Missouri1,431

6. Rapid growth in populations served by Community Water Systems, and a
shift towards larger systems

7. Rapid growth in populations served by Community Water Systems, and a
shift towards larger systems

8. 0
100
200
300
400
500
600
TXLAPACAOKCONMKSWVAZ
Number of Violating CWS
(2018
-2020)
Texas had the highest number of health-based violations during the study
period

9. Rule /
Rule Group
Texas SystemsTexas PopulationsHighest
Rank
State/Area
No. of
CWS
National
Rank
% of
TX
Systems
AffectedNational
Rank
Affected
(%)
National
Rank
Inorganics3710.8046,65930.168NY
Fluoride3410.7337,68330.135UT
Arsenic7121.53110,36320.3810NN
Nitrates3310.7111,13920.0410ID
Any inorganic11522.47143,37520.5015NY
Radionuclides17013.65195,65730.6818NY
DBPRs24215.20940,42533.2720RI
SWTR3450.73236,45480.828WV
GWR3550.7539,62170.1424LA
RTCR5321.14137,16670.4823NN
Organics330.065,08960.026PA
LCR6811.46100,28380.3511NJ
Any HB Violation545111.712,690,60029.3621RI
Texas ranks highly in the number of Inorganics Rule violations, including
Nitrates

10. 0
20
40
60
80
100
120
1990199520002005201020152020
Number of CWS in violation
Arsenic Nitrate Fluoride
0
50
100
150
200
250
300
1990199520002005201020152020
Affected population (10
3)
Arsenic Nitrate Fluoride
Inorganics Rule Violations in Texas Community Water Systems
Arsenic
FluorideNitrate

11. Nitrate Violations in Community Water Systems
11
The Nature Conservancy
Analyze annual Community Water System
data from 2003 to 2023, EPA nitrate rule
violations
Data Sources:
•Safe Drinking Water Information
System (SDWIS) database
•TCEQ Public Water Supply database

12. •Locations of 50 CWSs with Nitrate
violations during Jan 2022 – Jun 2023
symbolized by reported primary water
source.
•Sources include
•Groundwater (GW)
•Surface water (SW)
•Purchased from another CWS system
•There are many systems that indicate
surface water as their primary source
(purchased or not) that also include one or
more active groundwater wells as a listed
facility.

13. 0
1
2
3
4
5
6
7
8
9
10
1234567891011121314151617181920
Number of Systems
Years with Nitrates Rule violations
Persistence of Violations: Years of Nitrate Rule violations during
2003 – 2023 for CWSs in Texas with current violations.

14. Persistence of Violations: Chronic Non-Compliance
Summary of CWSs with a nitrate-
rule violation between 2018-2020
with persistence of nitrate rule
violations per quarter. No. of
quarters refers to quarters that
CWSs are noncompliant.
Many of these chronically non-
compliant systems are from small-
rural areas.
Infrastructure, funding, and
personnel are key issues.

15. Nitrate Concentrations in Major & Minor Aquifers
15
The Nature Conservancy
Objective:
Quantify the spatial distribution of
groundwater nitrate in major and minor
aquifers
Method:
Spatial analysis of nitrate concentrations
from TWDB groundwater database (33k
samples) using Indicator Kriging

16. Major Aquifers

17. Major Aquifers Nitrate Rule Compliance
Spatial distribution of nitrate-N
concentrations in the major aquifers of
Texas.
33,167 well samples
2,631 samples (7.9%) exceed the MCL.
The highest MCL violation percentages
are located in the Seymour (55%) and
Ogallala (6.5%)
35 community water systems MCL during
at least one quarter period during Jan
2018 – Dec 2020.

18. Major Aquifer Ambient Nitrate-N Levels
Probability of Nitrate exceeding 4 mg/L (background) and 10 mg/L [Nitrate-N MCL]

19. Major Aquifer Ambient Nitrate Levels
33,167 groundwater well
samples (TWDB), 1930 to 2021

20. Major Aquifer Ambient Nitrate Levels
AquiferAquifer
Group
Total
Number of
Samples
DetectsNon-
Detects
Nitrate-N >4 mg/LNitrate-N >10 mg/L
Samples% of
TotalSamples% of
Total
Carrizo-WilcoxMajor3,8681,6192,2491564.03711.8
EdwardsBFZMajor1,4651,2352301389.42241.6
Edwards-Trinity
PlateauMajor5,1624,4826801,01319.621763.4
Gulf CoastMajor6,9164,6412,2751,03014.893154.6
Hueco-Mesilla BolsonMajor54747968458.2371.3
OgallalaMajor6,4396,2242151,32620.594196.5
Pecos ValleyMajor6615926913720.73598.9
SeymourMajor2,1992,149501,84083.671,20254.7
TrinityMajor5,7633,8601,90377913.522945.1
LipanMinor14714169061.226443.5
Total33,16725,4227,7456,55419.762,6317.9

21. Major Aquifers Nitrate Rule Compliance (2018 – 2020)
Aquifer
TCEQ DatabaseEPA Non-compliant
CWS SystemsCWS Systems
N >4 mg/LN >10 mg/L
Number ofCWSCWS At-riskCWSPopulationNCWSPopulation
Carrizo-Wilcox2542,506--
Edwards BFZ1520,867111,007
Edwards-Trinity Plateau21109,0891195
Gulf Coast141154,6821460
Hueco-Mesilla Bolson36,109--
Ogallala718164,670187,017
Pecos Valley1----
Seymour17123,33092,237
Trinity82270,10746,631
Lipan (Minor)4416,15814,569
Total 153287,5183532,116
Percent of 2020 pop.0.990.09

22. Minor Aquifers

23. Minor Aquifers Ambient Nitrate Levels
Spatial distribution of nitrate-N
concentrations in the minor aquifers of
Texas.
8,220 well samples
747 samples (9.1%) exceed the MCL.
The highest MCL violation percentages for
N are located primarily in the Lipan, Bone
Spring-Victorio Peak, Cross-Timbers,
Blaine, Rustler, and Dockum aquifers.

24. Minor Aquifers Ambient Nitrate Levels
Probability of Nitrate Levels exceeding 4 mg/L and 10 mg/L [Nitrate-N MCL]

25. Minor Aquifers Ambient Nitrate Levels
Aquifer
Total
Number of
Samples
Number
of
Detects
Number
of Non-
Detects
Nitrate-N > 4 mg/LNitrate-N > 10 mg/L
Samples% of TotalSamples% of Total
Blaine282 208 74 100 35.5 37 13.1
Blossom76 49 27 6 7.9 2 2.6
Bone Spring-Victorio Peak161 145 16 74 46.0 30 18.6
Brazos River Alluvium216 167 49 27 12.5 12 5.6
Capitan Reef Complex64 46 18 5 7.8 1 1.6
Cross Timbers2,252 1,588 664 530 23.5 336 14.9
Dockum889 680 209 198 22.3 90 10.1
Edwards-Trinity (High Plains)71 60 11 25 35.2 6 8.5
Ellenburger-San Saba376 317 59 64 17.0 24 6.4
Hickory476 390 86 110 23.1 42 8.8
Igneous206 182 24 13 6.3 5 2.4
Lipan*1476439061.26443.5
Marathon44 40 4 4 9.1 2 4.5
Marble Falls47 36 11 7 14.9 3 6.4
Nacatoch204 113 91 9 4.4 7 3.4
Queen City651 456 195 80 12.3 27 4.1
Rita Blanca34 30 4 1 2.9 - -
Rustler53 39 14 18 34.0 6 11.3
Sparta362 254 108 21 5.8 6 1.7
West Texas Bolson260 246 14 26 10.0 9 3.5
Woodbine685 410 275 15 2.2 4 0.6
Yegua-Jackson664 409 255 51 7.7 34 5.1
Total8,220 5,929 2,2111,47417.97479.1
•Summary of nitrate-N analyses
in the minor aquifers of Texas.
Values represent the latest
samples from the TWDB
groundwater database for wells
sampled between 1930 and
2023.
•The remaining minor aquifers
(those NOT highlighted) had
from 0.6% to 8.8% of samples
above the MCL and the average
for all minor aquifer samples
was 9.1%. This is similar to but
slightly larger than the
exceedance rate of major
aquifer samples (7.9%).
•*The Lipan aquifer was included
in the major aquifers study.

26. Summary
26
The Nature Conservancy
•Texas has the largest number of active
Community Water Systems in the country
•Majority of the population has access to
Community Water Systems

•35 PWSs exceeded the nitrate-N MCL during
2018 - 2020
•32,116 people affected
•Violations tend to be persistent
•Three of the major aquifers account for the
majority of violations:
•Seymour, Ogallala, Gulf Coast and Trinity

27. Summary
27
The Nature Conservancy
Ambient Nitrate Concentrations
Major Aquifers
2,631 groundwater samples from the TWDB well
database exceeded the nitrate-N MCL of 10
mg/L, representing 7.9% of the most recent
nitrate analyses from wells
Minor Aquifers
747 samples exceeded 10 mg/L, representing
9.1% of nitrate analyses from wells

28. Thanks!