indicators of seawater intrusion - Seasidebasinwatermaster.org

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FINAL DRAFTNote: It is suggested to collect at least 8 to 10 observations using these statistical methods.a Historical maximum chloride concentrations prior to 1995 are not included in thestatistical analysis and should not be used when determining acceptable maximumchloride concentrations during future monitoring events.b Basin wide screening criteria is based on maximum chloride screening criteria.INDICATOR 2: DECREASING SODIUM/CHLORIDE MOLAR RATIOSA rapid decline in the molar ratio of sodium to chloride may indicate seawaterintrusion. In the early stages of seawater intrusion, sodium often replacescalcium on the aquifer’s clay particles through ion exchange before significantchloride increases are observed. This effectively removes sodium from thewater, and sodium/chloride molar ratios drop. The ratio of sodium to chloride ingroundwater can therefore sometimes be used as an early indicator of seawaterintrusion. Sodium/chloride molar ratios can also be used to differentiatebetween seawater intrusion and other sources of salinity. Jones et al. (1999)suggest that sodium/chloride molar ratios in advance of a seawater intrusionfront will be below 0.86 molar ratio.HISTORICAL SODIUM/CHLORIDE MOLAR RATIOSChemographs showing sodium/chloride molar ratios over time are provided inAppendix D. None of these chemographs show the rapid decline insodium/chloride molar ratios that is indicative of seawater intrusion.SODIUM/CHLORIDE MOLAR RATIO TREND ANALYSISIn addition to evaluating increasing chloride concentrations, decreasingsodium/chloride molar ratios are also evaluated using the Mann‐Kendallstatistical test. Table 2 summarizes the results of the statistical trend analysis.None of the data suggest a downward trend in the sodium/chloride molar ratios.Seawater Intrusion Response PlanNovember 19, 2008 - 10 -
FINAL DRAFTTable 2: Sodium/Chloride Molar Trend AnalysisPrimaryAquiferPaso Robles(shallow)Santa Margarita(deep)Well LocationMSC‐ShallowPCA‐W ShallowPCA‐E (Multiple) ShallowMPWMD #FO‐09‐ShallowMPWMD #FO‐09‐DeepMPWMD #FO‐10‐ShallowMPWMD #FO‐10‐DeepMSC‐DeepPCA‐W DeepPCA‐E (Multiple) DeepOrd Terrace‐ShallowOrd Terrace‐DeepMann‐KendallStatistical TrendNo TrendNo TrendNPIncreasingNo TrendNPNPNo TrendNo TrendNPNPNPNote: It is suggested to collect at least 8 to 10 observations using thesestatistical methods.INDICATOR 3: VISUAL INSPECTION OF CATION/ANION RATIOSSeawater intrusion is often indicated by graphically analyzing shifts ingroundwater quality. Two common graphical techniques for these analyses arePiper diagrams and Stiff diagrams.PIPER DIAGRAMSPiper diagrams plot the relative abundances of individual cations and anions ontwo trilinear plots, and their combined distribution is plotted on a centraldiamond. Waters from similar or related sources will generally plot together.The mixture of two waters will generally plot along a straight line between thetwo end‐member types within the central diamond. The trend towards seawaterintrusion, however, often plots along a curved path.An example Piper Diagram showing changes in molar ratios that are indicativeof seawater intrusion is included in Appendix E. The indicator of seawaterintrusion using Piper diagrams is the water chemistry trending in the direction ofthe curved arrow on the example Piper diagram.Seawater Intrusion Response PlanNovember 19, 2008 - 11 -
Page 3 and 4: FINAL DRAFTTABLE OF CONTENTSSECTION
Page 5 and 6: FINAL DRAFTSECTION 1BACKGROUND AND
Page 7 and 8: FINAL DRAFTSECTION 2CONSISTENCY WIT
Page 9 and 10: FINAL DRAFTThere is no requirement
Page 11 and 12: FINAL DRAFT3.1 INDICATORS OF SEAWAT
Page 13: FINAL DRAFTCHLORIDE CONCENTRATION T
Page 17 and 18: FINAL DRAFTOTHER FACTORSGroundwater
Page 19 and 20: FINAL DRAFTSECTION 4SEAWATER INTRUS
Page 21 and 22: FINAL DRAFT• Identify and/or inst
Page 23 and 24: FINAL DRAFTSECTION 5REFERENCESBachm
Page 25 and 26: FINAL DRAFTAPPENDIX A:OVERVIEW OF S
Page 27 and 28: FINAL DRAFTaquitards, which transmi
Page 29 and 30: FINAL DRAFTCross-hatchingshows seaw
Page 31 and 32: FINAL DRAFTplot along a straight li
Page 33 and 34: FINAL DRAFTFigure 5: Piper Diagram
Page 35 and 36: FINAL DRAFTINCREASING CHLORIDE CONC
Page 37 and 38: FINAL DRAFT2500220001.6Chloride (mg
Page 39 and 40: FINAL DRAFTOTHER INDICATORSHem (198
Page 41 and 42: FINAL DRAFTAPPENDIX B:HISTORICAL CH
Page 43 and 44: FINAL DRAFT450400Chloride Concentra
Page 51 and 52: FINAL DRAFT250Chloride Concentratio
Page 53 and 54: FINAL DRAFT250Chloride Concentratio
Page 55 and 56: FINAL DRAFTAPPENDIX C:STATISTICAL T
Page 57 and 58: FINAL DRAFTWhere n equals the numbe
Page 59 and 60: FINAL DRAFT[ Cl−]average56 + 54 +
Page 61 and 62: FINAL DRAFT4) Because ‐13 is less
Page 63 and 64: FINAL DRAFTTable C‐4: Pearson’s
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FINAL DRAFT90085Chloride Concentrat
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FINAL DRAFT908.585Chloride Concentr
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FINAL DRAFT8007570Chloride Concentr
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FINAL DRAFTAPPENDIX D:HISTORICAL SO
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FINAL DRAFT1.61.41.210.80.60.40.20S
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FINAL DRAFT1.61.41.210.80.60.40.20S
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FINAL DRAFT1.61.41.210.80.60.40.20S
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FINAL DRAFT1.61.41.210.80.60.40.20S
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FINAL DRAFT1.61.41.210.80.60.40.20S
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0Aug-04Aug-05Aug-06Aug-07Aug-08Aug-
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FINAL DRAFTAPPENDIX E:PIPER DIAGRAM
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FINAL DRAFTSulfate (SO4) + Chloride
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FINAL DRAFTAPPENDIX F:STIFF DIAGRAM
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FINAL DRAFTCations meq/l Anions30 2
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FINAL DRAFTSBWM-1Sample taken at1,1
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