By IRIS Mbani Kabory AND fatai Balogun Determination of Potassium levels in water samples from 4 Monitoring wells ON Isle of hope, Wormsloe, GA. By IRIS Mbani Kabory AND fatai Balogun

OUTLINE INTRODUCTION METHODOLOGY RESULTS Possible sources of error CONCLUSIONS

INTRODUCTION Ocean surges onto low-lying coastal areas, caused by tropical storms have been known to have major impacts on ground water in such areas. Salt water intrusion and presence of bacteria are usual indicators for the encroachment of salt water into fresh water aquifers. However, the former will be examined for the purpose of this work. Ca/Mg, Cl/Si, Na/Cl and Br ratios are typical salt water intrusion indicators. However, other elements such as Ca, K and Sr are not necessarily strong indicators of saline water intrusion. For the purpose of this work, concentration levels of Potassium in four monitoring wells on the Wormsloe State Historic Site, Georgia will be investigated using the Atomic Absorption Spectrometry.

INTRODUCTION Cont’d Figure showing network of wells on the Wormsloe Historic Site Figure showing water classification based on the USGS system Diagrams were adapted from a conference presentation by Bush, Farley and Meyer (2016).

Methodology cont’d Ground water samples from 4 monitoring wells were collected in a 5l plastic container and stored in the refrigerator at a temperature of 4⁰C. 100ml aliquot was collected from each bottle, into 4, labelled 250ml Erlenmeyer beakers. 3, 30ml replicate samples was syringed from each beaker and filtered using a 0.22µm PES filter membrane. The filtrate was collected in 12 labelled, 50 ml centrifuge tubes and stored back in the refrigerator for further preparation.

Methodology cont’d AAS Specifications The method adopted for this work was modelled after the u.s.e.p.a. Method 258.1(Methods for Chemical Analysis of Water and Wastes) for detection of Potassium using the Atomic absorption, direct aspiration technique. Using the method, optimum Concentration range of the instrument is : 0.1-2 mg/l at λ of 766.5 nm. However, turning the burner head a complete 90⁰, reduces the sensitivity for Potassium, but the maximum operating range increases from 2 mg/l to 20 mg/l. Another option of increasing the dynamic range is to use λ of 404.4 nm Sensitivity : 0.04mg/l Detection Limit: 0.01 mg/l Hollow Cathode Lamp: Potassium Fuel/ Oxidant : C2H2/ Air

METHODOLOGY cont’d 100 mg/l of KCl stock solution was prepared by weighing 0.1916 grams of KCl crystals into a 1L volumetric flask and filling to the mark with DI Water. 15 ml preliminary calibration standards of concentrations (1mg/l, 10 mg/l and 20 mg/l )respectively were prepared by diluting original stock solution with 18.2ΩM DI water . Calculations for preparation of the standards are given below; Using dilution equation C1V1 = C2V2 Where; C1 and C2 are concentrations of the stock solution and required standards respectively. V1 and V2 are required volumes of the stock and standard solutions respectively. 1 mg/l : 100mg/l x V1(ml) = 1mg/l x 15ml V1= 0.15ml C2 : 0.15ml + 14.85ml DI Water 10 mg/l : 100mg/l x V1(ml) = 10mg/l x 15ml V1 = 1.5ml C2 : 1.5ml + 13.5ml DI Water 20 mg/l : 100mg/l x V1(ml) = 20mg/l x 15ml V1 = 3ml C2 : 3ml + 12ml DI Water Preliminary investigations were also made on the samples. 15ml of undiluted water sample from each Monitoring well was prepared for AAS analysis

Concentration of standard (mg/l) METHODOLOGY cont’d “Getting our feet wet” Standards prepared from 100mg/l KCl Stock solution Concentration of standard (mg/l) Absorbance 1.0 0.141 10 1.827 20 2.700 Reconnaissance analysis of undiluted samples Unknown Samples ID Absorbance MW1 0.041 MW2 0.312 MW3 2.768 MW4 0.956

METHODOLOGY cont’d “The real deal” 200 mg/l of KCl stock solution was prepared by weighing 0.328 grams of KCl crystals into a 1L volumetric flask and filling to the mark. 30 ml preliminary calibration standards of concentrations (0.25mg/l, 0.5 mg/l , 1.0 mg/l, 1.5mg/l , 2.0mg/l and 3.0mg/l). Calculations for preparation of the standards are given below; Using dilution equation C1V1 = C2V2 Where; C1 and C2 are concentrations of the stock solution and required standards respectively. V1 and V2 are required volumes of the stock and standard solutions respectively. 0.25 mg/l : 200mg/l x V1(ml) = 0.25mg/l x 30ml V1= 37.5µl C2 : 37.5µl + 29.96ml DI Water 0.5 mg/l : 200mg/l x V1(ml) = 0.5mg/l x 30ml V1 = 75µl C2 : 75µl + 29.93ml DI Water 1.0 mg/l : 200mg/l x V1(ml) = 1.0mg/l x 30ml V1 = 150µl C2 : 150µl + 29.85ml DI Water 1.5 mg/l : 200mg/l x V1(ml) = 1.5mg/l x 30ml V1= 225µl C2 : 225µl + 29.77ml DI Water 2.0 mg/l : 200mg/l x V1(ml) = 2.0mg/l x 30ml V1 = 300µl C2 : 300µl + 29.70ml DI Water 3.0 mg/l : 200mg/l x V1(ml) = 3.0mg/l x 30ml V1 = 450µl C2 : 450µl + 29.55ml DI Water

METHODOLOGY cont’d “The real deal” Due to the low absorbance values obtained from analysis of water samples from wells 1 and 2, no dilution was carried out on them. However, absorbance values of 2.768 and 0.956 0btained for Wells 3 and 4 respectively, gave an indication that dilutions are required for these water samples. The six (6) water samples were diluted by 10 fold. Using dilution equation : Dilution Factor = Solution Volume/ Concentrate Volume . Where; DF = 10 & Final solution vol. =30ml 10 fold = 30ml/Concentrate volume. Therefore, Volume of Concentrate needed is 3ml. To achieve a final solution of 30ml, 3 ml of concentrate was diluted with 27ml of DI water.

METHODOLOGY cont’d “The real deal” Absorbance values for the standards Concentration (mg/l) Absorbance Standard Deviation 0.000 0.25 0.032 0.0007 0.5 0.056 0.0011 1.0 0.125 0.0082 1.5 0.173 0.0025 2.0 0.236 0.0063 3.0 0.359 0.0066

RESULTS Sample ID Absorbance Standard Deviation MW1-1 0.060 0.0013 0.0009 MW1-3 0.058 0.0011 MW2-1 0.302 0.0083 MW2-2 0.0023 MW2-3 0.298 0.0039 MW3-1 0.125   MW3-2 0.126 0.0028 MW3-3 0.123 0.0015 MW4-1 0.075 0.0014 MW4-2 0.076 0.0010 MW4-3 0.074 12

“Bracketing the samples”   Sample ID Absorbance Standard Deviation 0 mg/l 0.000 0.0000 0.25 mg/l 0.031 0.0064 MW1-1 0.063 0.0009 MW1-2 0.065 0.0088 MW1-3 0.060 0.0011 0.001 0.5mg/l 0.055 0.0008 MW4-1 0.077 MW4-2 0.076 0.0020 MW4-3 0.074 1.0 mg/l 0.126 0.0024 MW3-1 0.127 0.0021 MW3-2 0.0082 MW3-3 0.123 0.0017 0mg/l 1.5 mg/l 0.170 0.0018 MW2-1 0.302 0.0040 MW2-2 0.305 0.0037 MW2-3 0.306 3.0 mg/l 0.352 0.0043

RESULTS cont’d Sample ID Absorbance (average) Standard Deviation Concentration (mg/l)   MW1 0.062 0.0025 0.51 MW2 0.304 0.0020 2.56 MW3 0.125 0.0021 10.51 MW4 0.076 0.0013 6.39

SOURCES OF ERROR Loss of KCl crystals while preparing stock solution. CsCl wasn’t added, therefore, ionization interference from Sodium could have affected the results. Concentrated HNO3 wasn’t added to the filtered samples at the time of preparation. Since the flame works on C2H2/air combination; the burner head’s slot is probably about 10cm in length. This could result in higher percentage of aerosol reaching the flame. Hence, larger sizes of droplets are formed

CONCLUSIONS Investigation of concentration levels of metals using the AAS requires a good understanding of the instruments mode of operation. Without this, Preparation of calibration standards, and sample dilutions could be a laborious task. Samples from wells 1 and 2 showed low levels of Potassium concentration as opposed to 10.51ppm and 6.39ppm observed for wells 3 and 4. Observation the placement of Well 3 in the LIDAR map, it appears to lying in an area of lower elevation in comparison to Well 4. Therefore, there is a possibility of inundation of this area by rainwater. However, the absence of addition of CsCl in the standards and Samples could be responsible for the “low” concentration values observed in Wells 3 and 4, when compared to 19ppm and 51ppm (ICP results) obtained for these two wells, pre-Mathew.

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