Groundwater Quality in the Red River Basin and Rolling Plains in Texas

Transcription

1 Groundwater Quality in the Red River Basin and Rolling Plains in Texas Srinivasulu Ale Assistant Professor (Geospatial Hydrology) Sriroop Chaudhuri Postdoctoral Research Associate Texas A&M AgriLife Research, Vernon, TX Red River Valley Regional Conference November 21, 2013; Wichita Falls, TX 1

2 Presentation Outline Spatio-temporal variability of groundwater nitrate contamination and salinization in Texas. Groundwater quality in the Red River Basin/Rolling Plains. Nitrate (NO 3 ). Total Dissolved Solids (TDS). Sodium Absorption Ratio (SAR). Residual Sodium Carbonate (RSC). 2

3 Texas Aquifers and Groundwater Use Texas has 9 major and 21 minor aquifers. About 60% of the total water used is supplied from groundwater. More than 95% of rural households rely on groundwater. 3

4 Groundwater Quality Monitoring in Texas Texas Water Development Board (TWDB) maintains a groundwater quality database with data since More than 120,000 groundwater wells and spring locations are monitored. 33 different water quality parameters are assessed. Red River Basin 4

5 Groundwater Quality Thresholds Parameter Threshold Remark Nitrate (NO 3 ) 44.4 mg L -1 (10 mg L -1 as NO 3 -N) Maximum Contaminant Level (MCL) Total Dissolved Solids (TDS) 500 mg L -1 Secondary Maximum Contaminant Level (SMCL) 1000 mg L -1 Brackish >10,000 mg L -1 Saline to Brine Source: USEPA, USDA 5

6 Nitrate Contamination in Texas Data Source: TWDB Nitrates in groundwater exceeded the MCL at several locations since the 1960s. High nitrate concentrations frequently observed in the Texas Rolling Plains and the Southern High Plains. Chaudhuri, Ale, DeLaune, Rajan, 2012 (Journal of Environ. Qual.) 6

7 County-wise Percentage Wells Exceeding Nitrate MCL Number of counties with >30% observations exceeding the MCL increased from 8 in the 1960s to 25 in the 2000s. Data Source: TWDB Chaudhuri, Ale, DeLaune, Rajan, 2012 (Journal of Environ. Qual.) 7

8 Groundwater Nitrate: Texas Rolling Plains and Southern High Plains vs. Texas Texas Rolling Plains (TRP) and the Southern High Plains (SHP) had consistently higher median NO 3 concentrations compared to the entire state. Median NO 3 concentrations in the TRP and SHP increased over time. 8

9 Nitrate In Texas Rolling Plains High NO 3 concentrations mostly from agricultural land use. Other factors that favored faster movement of NO 3 to groundwater: Highly transmissive sandy and gravely geologic formation. Well drained soils and shallow depth of the Seymour aquifer. Chaudhuri and Ale, 2013 (Environmental Earth Sci.) 9

10 Total Dissolved Solids (TDS) in Groundwater TDS is the indicator of amount of dissolved chemical species such as Ca 2+, Mg 2+, Na +, K +, Cl -, SO 4 2- and NO 3-. High TDS increases water s salinity, and reduces clarity and suitability to drinking. High TDS is also undesirable for industrial purposes for potential scaling and encrustation of plumbing fixtures. Factors Affecting TDS: Urban runoff Fertilizer runoff Soil erosion Evapotranspiration Rock weathering (storm water management) (fertilizer recommendations) (reduce surface runoff) Human alteration of ambient conditions 10

11 Groundwater Salinity (TDS) in Texas Groundwater salinity is a wide-spread problem in Texas since the 1960s. A clear spatial pattern according to well depth exists among aquifers. Salinity hotspots. Shallow Wells (< 50 m deep) Deep Wells (> 150 m deep) Chaudhuri and Ale, 2013 (Science of the Total Environment) 11

12 Salinity (TDS) in Texas Rolling Plains Ubiquitous presence of high groundwater TDS (salinity) in the TRP. Frequent occurrence of brackish groundwater, more commonly in Blaine aquifer. Unsuitable for drinking water purposes. Chaudhuri and Ale, 2013 (Environmental Earth Sci.) 12

13 Groundwater Quality in Red River Basin Number of Groundwater Quality Observations 1960s 1970s 1980s 1990s 2000s Diminishing frequency of observations in space and time. Concern over adequate knowledge about current ambient water quality. 13

14 Groundwater Nitrate in Red River Basin High variability from east to west of the basin. TRP stands out from the rest. Increasing trend with time. Percent observations > MCL almost doubled from the 1960s to 2000s. 14

15 Groundwater TDS (Salinity) in Red River Basin High Salinization in the eastern and TRP regions. Lesser salinization in the far west. High abundance of brackish water types, especially in and around the TRP. Increasing trend since the 1970s. 15

16 Sodium Absorption Ratio (SAR) of Groundwater Irrigation water quality indicator. High Na + concentrations in irrigation water raises the SAR, if there is a lack of Ca 2+ and Mg 2+. High SAR destroys soil structure by dispersing the soil grains and forming soil crusts on the surface. Soil dispersion leads to reduced infiltration, and air, water and nutrient movement. SAR range Suitability for irrigation < 10 Acceptable Marginal > 18 Concern

17 Groundwater SAR in Red River Basin High SAR towards the east. High abundance of Na + in groundwater in the east. No apparent concern for soil quality degradation in the TRP. No detectable trend over time.

18 Residual Sodium Carbonate (RSC) in Groundwater Irrigation water quality indicator. Excessive CO 3 2- and HCO 3 - in groundwater combine with Ca 2+ and Mg 2+ and thereby reduce concentrations of Ca 2+ and Mg 2+. This increases the effective concentration of Na + and hence SAR. Increase in SAR causes permeability and infiltration problems. RSC is a less problem in coarse-textured and well-drained soils. RSC range (meq/l) Suitability for irrigation < 1.25 Acceptable Marginal > 2.5 Concern 18

19 Groundwater RSC in Red River Basin RSC closely follows the spatial pattern of SAR. > 9% of observations exceeded the acceptance level. No apparent concern for soil quality degradation in the TRP. 19

20 Summary Groundwater NO 3 contamination and salinization in Texas in general and in the Red River Basin (RRB) in particular have been increasing. High variability in groundwater quality was found across the RRB due to variability in soils, geology, climate, land cover/use, urbanization, groundwater extraction, etc. High NO 3 in groundwater in the TRP region, and high salinity in the eastern and the TRP regions of the RRB are of concern. The excedance of about 9 to 10% of the observations above safety thresholds of SAR and RSC indicate no apparent immediate risk of soil quality degradation in most parts of the RRB. Development and implementation of groundwater quality improvement measures in the RRB should consider high variability in various parameters across the region. 20

21 Thank You Contact details: Srini Ale Assistant Professor (Geospatial Hydrology) Texas A&M AgriLife Research and Extension Center Vernon, TX Phone: x