San Simon Sub-Basin - Arizona Department of Environmental Quality

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Figure 15. Sodium - TDS and Fluoride - Calcium Concentration Covariation Sodium (mg/L) 1000 900 800 700 600 500 400 300 200 100 0 0 1000 2000 3000 4000 5000 TDS (mg/L) Among SS sample sites, TDS concentrations are best predicted among major ions and cations by sodium concentrations (multiple regression analysis, p≤ 0.01, y = 3.84x + 128, n = 77, r = 0.92). Although recharge areas usually contain low concentrations of sodium, it’s frequently the dominant cation in downgradient areas. 20 TDS concentrations are greatest in the northern portions of the sub-basin. The elevated TDS concentrations are related to increasing sodium concentrations from silicate weathering and halite dissolution along with ion exchange. 28 Fluoride (mg/L) 20 15 10 5 0 0 100 200 300 400 500 Calcium (mg/L) This graph illustrates the negative exponential relationship between fluoride and calcium at sites in the San Simon sub-basin (Pearson correlation coefficient test, p≤ 0.01, y = -1.3x + 7.4, n = 77, r = 0.46). These findings support previous assertions that there are multiple controls on fluoride concentrations. 28 Calcium appears to be an important control on the highest fluoride concentrations (>5 mg/L) though precipitation of the mineral fluorite. High concentrations of fluoride had corresponding depleted concentrations of calcium. Previous studies have cited hydroxyl ion exchange or sorption-desorption reactions at providing controls on lower (< 5 mg/L) fluoride concentrations. 28
Aquifer Constituent Co-variation Alluvial Aquifer - Sample sites in the alluvial aquifer reflected the relative uniformity of this waterbearing unit with strong positive correlations among TDS, SC, hardness, major ions (calcium, magnesium, sodium, chloride, and sulfate), and nitrate (Pearson Correlation Coefficient test, p ≤ 0.05). Other patterns of interest include positive correlations among pHlab, pH-field, bicarbonate, and fluoride as well as among temperature, potassium, and bicarbonate. TDS concentrations are best predicted among cations equally by calcium, sodium and magnesium concentrations while among anions, sulfate is the best predictor (multiple regression analysis, p≤ 0.01). Bedrock - Sample sites in bedrock areas exhibited the highest degree of significant correlations and the most interesting patterns. TDS and SC were positively correlated with major ions (calcium, magnesium, sodium, bicarbonate, chloride, and sulfate) as well as with temperature, pH-lab, hardness, boron, and fluoride (Pearson Correlation Coefficient test, p ≤ 0.05). However, this pattern bifurcated depending on whether the dominant cation was calcium or sodium. Calcium was intercorrelated with hardness, magnesium, bicarbonate, and sulfate. In contrast sodium was inter-correlated with potassium, bicarbonate, chloride, nitrate, arsenic, boron, and fluoride. Perhaps the most interesting bedrock correlation was between nitrate and both oxygen-18 and deuterium; this indicates that higher nitrate concentrations are more likely to be from recently recharged water. Lower Aquifer - Sample sites in the lower aquifer had relatively few significant correlations. Positive correlations occurred among TDS, SC, temperature, sodium, and sulfate (Pearson Correlation Coefficient test, p ≤ 0.05). Fluoride concentrations from samples collected from the lower aquifer are often elevated over water quality standards. This constituent has important correlations with both pH-field (positive) and calcium (negative). TDS concentrations are best predicted among cations by sodium concentrations while among anions, sulfate and chloride are almost equally the best predictor (multiple regression analysis, p≤ 0.01). Upper Aquifer - Sample sites in the upper aquifer had the common significant positive correlations among TDS, SC, hardness, major ions (calcium, magnesium, sodium, potassium, chloride, and sulfate) and nitrate (Pearson Correlation Coefficient test, p ≤ 0.05). Of particular interest is the TDS-nitrate relationship which may indicate that the poor quality, salt-laden irrigation water that recharges the upper aquifer also frequently carries with it nitrate. TDS levels are best predicted among cations by sodium concentrations while among anions, sulfate is the best predictor (multiple regression analysis, p≤ 0.01). TDS concentrations are best predicted among cations by calcium concentrations while among anions, sulfate is the best predictor (multiple regression analysis, p≤ 0.01). GROUNDWATER QUALITY PATTERNS Spatial Variation 29
Page 2 and 3: Ambient Groundwater Quality of the
Page 5 and 6: Table of Contents Abstract ........
Page 7 and 8: Tables Table 1. Well log of BLM Hot
Page 9: “One August night in the early 18
Page 12: INTRODUCTION Purpose and Scope The
Page 15 and 16: Figure 2. The San Simon sub-basin e
Page 17 and 18: thought. 44 An excellent example of
Page 20 and 21: Figure 5. Jason Mahalic samples an
Page 22 and 23: Groundwater Movement, Storage and L
Page 24: Figure 11. A 1957 Buick is permanen
Page 29: Table 3. SS Sites Exceeding Aesthet
Page 32 and 33: Table 5. Summary Statistics for SS
Page 34: GROUNDWATER COMPOSITION Groundwater
Page 37: Table 6. Correlations Among Groundw
Page 41 and 42: Figure 16. TDS and Gross Alpha Conc
Page 43 and 44: Table 8. Summary Statistics (95% Co
Page 45 and 46: Table 10. Summary Statistics (95% C
Page 47 and 48: Table 12. Summary Statistics (95% C
Page 49 and 50: CONCLUSIONS Groundwater Suitability
Page 51 and 52: levels may be elevated to the exten
Page 53 and 54: REFERENCES 1 Arizona Department of
Page 55 and 56: Appendix A. Basic Data on Sample Si
Page 57 and 58: Appendix A. Basic Data on Sample Si
Page 59 and 60: Appendix B. Groundwater Quality Dat
Page 77 and 78: APPENDIX C. INVESTIGATION METHODS V
Page 79 and 80: Table 13. ADHS/Del Mar Laboratory M
Page 81 and 82: APPENDIX D. DATA EVALUATION Quality
Page 83 and 84: The maximum difference between dupl
Page 85 and 86: Table 16. Summary Results of 1997/2
Page 87: Constituent Concentration Correlati

San Simon Sub-Basin - Arizona Department of Environmental Quality

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