Aquifer Water Quality

1. Aquifer Water Quality Groundwater Hydraulics Daene C. McKinney

2. Introduction • Groundwater Quality • Sampling Plan • Field Measured Parameters • pH • Alkalinity • Conductance • Salinity • Dissolved Oxygen • Turbidity • Chemical Equivalence • Laboratory QA/QC • Diagrams • Piper • Stiff • Water Quality Classification • Irrigation Water • Sodium • Salinity • Arsenic • Iron Bacteria

3. Water Quality Management Process • Identify • Problem • Indicators • Target Values • Assess source(s) • Determine linkages • Sources  Targets • Allocate permissible loads • Monitor and evaluate • Implement

4. Groundwater Quality • Helps us understand the hydrogeologic system • Indicates comingling of groundwater and surface water • Helps us interpret groundwater flow dynamics • Delineates groundwater contamination

5. Basic Water Quality Parameters • pH • Specific conductance (EC) • Salinity • Total dissolved solids (TDS) • Turbidity • Dissolved oxygen (DO) • Biochemical oxygen demand (BOD) • Temperature

6. pH • Measures hydrogen ion concentration • Negative log of hydrogen ion concentration • Ranges from 0 to 14 std. units • pH • 7 neutral • 0 - 7 acidic • 7 - 14 alkaline Thanks to Phil Brown

7. Solubility of Specific IonsBased on Water pH Toxic metals less available in water at pH 6 to 8.

8. Conductivity • Measures electric conductivity (EC) of water • Higher value means water is a better electrical conductor • Increases when more salt (e.g., sodium chloride) is dissolved in water • Indirect measure of salinity • Units are μmhos/cm at 25o C or μsiemens/cm Thanks to Phil Brown

9. Conductivity at Barton Springs • Specific conductance is an indication of the hardness of water. The specific conductance declines in spring water when rainfall enters the aquifer and later discharges in the spring. Below is a graph demonstrating this effect in Barton Springs. Rainfall is indicated in red, and specific conductance in blue.

10. Salinity Salts in Sea Water • Classification of Ground Water • Composition Based on Total Dissolved Solids Content

11. Dissolved Oxygen • Amount of gaseous oxygen (O2) dissolved in water • Oxygen gets into water by diffusion from the surrounding air, by aeration, and through photosynthesis • DO range from 0-18 mg/l • Need 5-6 mg/l to support a diverse population • DO < 2 mg/l - Hypoxia Thanks to Phil Brown

12. Turbidity • Measured in Nephelometric Turbidity Units (NTU) • Estimates light scattering by suspended particles • Photocell set at 90o to the direction of light beam to estimate scattered rather than absorbed light • Good correlation with concentration of particles in water HF Scientific MicroTPI – Turbidity Meter YSI 556 MPS Thanks to Phil Brown

13. Water Uses

15. Abundance of Dissolved Constituents in Surface and Ground Water Major Constituents (> 5 mg/L) Ca Mg Na Cl Si SO42- - sulfate H2CO3 - carbonic acid HCO3-- bicarbonate Minor Constituents (0.01-10 mg/L) B K F Sr Fe CO32- - carbonate NO3- - nitrate

16. Abundance of Dissolved Constituents in Surface and Ground Water Trace Constituents (< 0.1 mg/l) Al As Ba Br Cd Co Cu Pb Mn Ni Se Ag Zn others

17. Water Classification • How? • Compare ions with ions using chemical equivalence • Making sure anions and cations balance • Use of diagrams and models • Why? • Helps define origin of the water • Indicates residence time in the aquifer • Aids in defining the hydrogeology • Defines suitability

18. What is Chemical Equivalence? • Chemical analysis of groundwater samples • Concentrations of ions are reported by • weight (mg/L) • chemical equivalence (meq/L) • Takes into account ionic charge • Equivalent Concentration

20. Formula weight • Formula weight • Multiply atomic weight by # of atoms and add together • E.g., • Formula weight of water H2O = 2*(Atomic Wt of H) + 1*(Atomic Wt of O) 2*(1.008) + 1*(16) = 18.01 Atomic Weight (Relative atomic mass) is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12

21. Ion Balance • If all ions are correctly determined by a lab • sum of cationsshould equal sum of anions (all in meq/L) • Errors in analysis and chemical reactions in samples • 5% difference is considered acceptable • > 5%, question the lab results

22. Calculating Equivalence For instance: The atomic wt. of Sodium (valence of one) = 22.989 And its charge is one Dividing the concentration of sodium in the sample (19 mg/L) by its “combining wt.” = 0.827meq/L or its equivalent concentration.

23. Use of Diagrams • There numerous types of diagrams on which anions and cations (in Meq/L) can be plotted. These include: • Piper • Stiff • Pie • Schooler • Depth Profile

24. Stiff Diagrams • Concentrations of cations are plotted to the left of the vertical axis and anions are plotted to the right (meq/L) • The points are connected to form a polygon. • Waters of similar quality have distinctive shapes.

25. Stiff Diagrams in Cyprus

26. Average Composition of Sea Water and Mississippi River water

27. Ground Water Quality in Different Aquifers

28. Aquatic Freshwater Protection Criteria (USA EPA Guidelines)

29. Drinking Water Criteria(USA EPA Guidelines)

30. Hardness of Water T07_04_02

31. WELL SAMPLING • Calculate Well Volume: • Determine static water level • Calculate volume of water in the well casing • Purge the well: • A minimum of three casing volumes is recommended.

32. ANALYSIS OF WATER SAMPLES • Field: • pH, specific conductance, temperature, dissolved oxygen, and alkalinity • Laboratory: • Cations: sodium, calcium magnesium, potassium, and iron • Anions: bicarbonate, carbonate, sulfate, and chloride • Trace Metals, Radioactivity

33. Sodium and Irrigation • Sodium reacts with soil to reduce permeability. • Alkali soils - High sodium with carbonate • Saline soils – High sodium with chloride or sulphate • Neither support plant growth • Sodium Adsorption Ratio (SAR)

34. Salinity and irrigation • Low salinity water • used for most crops • Medium salinity water • used with moderate amount of leaching (potatoes, corn, wheat, oats, and alfalfa) • High salinity water • Cannot be used on soils having restricted drainage. • Very high salinity water • Can be used only on certain crops and then only if special practices are followed

35. Arsenic in Groundwater • Long-term exposure to arsenic from drinking water is directly linked to: • Cancer of the skin, lungs, urinary bladder and kidneys. • Acute gastrointestinal and cardiac damage as well as vascular disorders such as blackfoot disease. • Sub-lethal effects include diabetes, keratosis, heart disease and high blood pressure. • Toxicity is dependent on diet and health, but is cumulative. Arsenic is excreted very slowly by the body through deposition in the hair and nails.

36. BACKGROUND • Arsenic (As) • toxic metal widespread in groundwater • Occurs widely in aquifers • deltaic sediments near mountain uplift zones • deep sandy aquifer layers originating as riverine, lake or coastal deposits. • Ganges, Mekong and Red River deltas, sandy alluvial deposits in South Asia, South East Asia, South America, and in many parts of North America and Europe.

37. Arsenic Contamination • Associated with fluctuating water tables and flooding cycles particularly in • Acidic sulfate soils or • Iron and/or manganese-enriched layers, • saline-layered aquifers • Levels in water supplies can vary through a year adding to the difficulties of identification and monitoring.

38. Drinking Water Standards • Worldwide 50 ppb limit (1942) • US EPA • Acceptable mortality = 1 death per 1,000 people for carcinogens • Lifetime risk from exposure to 50 ppb As • 13 cancer-related deaths per year per 1000 people (1992) • Current standard = 10 ppb standard

39. Arsenic in the United States

40. Summary • Sampling Plan • Field Measured Parameters • pH • Alkalinity • Conductance • Salinity • Dissolved Oxygen • Turbidity • Chemical Equivalence • Laboratory QA/QC • Diagrams • Piper • Stiff • Water Quality Classification • Irrigation Water • Sodium • Salinity • Arsenic