The Crucial Role of Data Quality Control in Hydrochemical Studies: Reevaluating Groundwater Evolution in the Jiangsu Coastal Plain, China
Abstract
1. Introduction
2. Study Area
3. Methodology
4. Results
4.1. HCA
4.2. PCA
4.3. Environmental Isotopes
4.4. Radioactive Isotopes
5. Discussion: The Processes Affecting Groundwater Evolution in the Jiangsu Coastal Plain
5.1. Evaporation Processes
5.2. Water–Rock Interaction in the DCAS
5.3. Seawater Intrusion in the DCAS
5.4. Residence Times in the DCAS
6. Conclusions
- A QA/QC analysis identified anomalous Fe and Mn concentrations in five samples, which were inconsistent with TDS values. As a result, the Fe and Mn concentrations were discarded for these samples. Consequently, these elements were not included as input data for HCA and PCA, as reliable information was not available for all samples. This underscores the importance of conducting thorough QA/QC procedures to ensure data integrity.
- Charge Balance Error (CBE) is the tool used most usually for laboratory data QA/QC. Even though it is an excellent first approach, it is advisable to use it in combination with additional QA/QC techniques. In the analyzed dataset in this study, CBE validated samples that were later discarded for anomalous Fe and Mn concentrations. In order to take better advantage of CBE it is more helpful to evaluate it using it all ions and not only major ones.
- Three key processes were identified as drivers of hydrochemical variations in the deep groundwater of the Jiangsu Coastal Plain: water–rock interaction, evaporation, and seawater intrusion. Water–rock interaction was found to be the dominant hydrochemical process influencing Na+–HCO3− waters (freshwater). Evaporation was determined to be the primary process responsible for mineralization in Na+–Cl− waters (brackish water).
- The occurrence of seawater intrusion was demonstrated in two wells (20 and 21, classified as saline waters). This conclusion is based on a combination of a statistical assessment (HCA and PCA) of hydrochemical data and environmental isotopes (δ2H and δ18O plots, along with Dex values).
- Seawater intrusion was identified as affecting only Aquifer III of the DCAS. Given the location of the two affected wells, where groundwater flows inland from the shoreline towards drawdown cones induced by groundwater extraction, this process may be considered ongoing. However, this finding remains inconclusive due to contradictory radiogenic isotope data. It is advisable to further study the DCAS, including a more comprehensive analytical suite (including most dissolved anions and cations) plus additional isotopes like 87Sr/86Sr that may help to better refine this process.
- Based on these observations, it is highly advisable to account for seawater intrusion in groundwater management strategies for the area. Step drawdowns are recorded in the Matang area. Hence, a detailed monitoring program for groundwater levels and water quality using telemetry for live data and probably reducing extractions are good first steps.
- Residence time estimations revealed contradictions in seven samples, representing 33% of the dataset. These samples contained measurable amounts of 3H (with TU values above the detection limit), suggesting a recharge age of less than 60 years. However, the same samples were assigned corrected 14C ages ranging from 17,000 to 23,000 years BP. Due to this inconsistency, paleoclimatic reconstructions based on these data cannot be deemed reliable.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
DCAS | Deep Confined Aquifer System |
QA/QC | Quality Assurance and Quality Control |
HCA | Hierarchical Cluster Analysis |
PCA | Principal Component Analysis |
PAS | Phreatic Aquifer System |
ICAS | Intermediate Confined Aquifer System |
TDS | Total Dissolved Solids |
Dex | Deuterium Excess |
GMWL | Global Meteoric Water Line |
LMWL | Local Meteoric Water Line |
LEL | Local Evaporation Line |
pmc | Percentage of Modern Carbon |
BP | Before Present |
r | Correlation Coefficient |
CBE | Charge Balance Error |
m bgl | Meters Below Ground Level |
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ID | Aquifer | pH | T | TDS | Cl− | HCO3− | SO42− | Ca2+ | Mg2+ | Na+ | K+ | H2SiO3 | Fe | Mn | CBE | TDScalc | TDScalc * |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
(°C) | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | % | mg/L | mg/L | |||
1 | III | 7.9 | 19 | 723.3 | 129.8 | 541 | 3.9 | 83.9 | 37.5 | 112.7 | 2.3 | 35.2 | 1.8 | 0.1 | −0.4 | 673 | 671 |
2 | III | 7.9 | 17.8 | 2479.3 | 1113.3 | 526.3 | 94.4 | 236.3 | 94.7 | 462 | 5.8 | 24.2 | 13.2 | 0.2 | −2.2 | 2303 | 2290 |
3 | III | 7.4 | 24.5 | 462 | 25.2 | 478 | 4 | 64.1 | 26.1 | 82.2 | 1.5 | 33.8 | 1.5 | 0 | 0.3 | 473 | 472 |
4 | III | 7.7 | 23.8 | 464 | 18.9 | 459 | 3.7 | 61 | 26.7 | 78.1 | 1.6 | 31.1 | 0.5 | 0 | 0.5 | 447 | 447 |
5 | III | 7.9 | 25.1 | 534 | 22.1 | 466 | 3.7 | 64 | 26.3 | 78.7 | 1.4 | 33.4 | 0.9 | 0 | 0.5 | 460 | 459 |
6 | IV | 7.7 | 23.8 | 542 | 63 | 490 | 3.8 | 48.1 | 20.6 | 140 | 1.3 | 28 | 0.9 | 0.1 | 0.3 | 547 | 546 |
7 | IV | 7.7 | 24.8 | 2262 | 1236 | 301 | 76.3 | 170 | 61.4 | 587 | 10.1 | 22.1 | 1.4 | 0.2 | −2.1 | 2313 | 2311 |
8 | III | 7.8 | 22.9 | 942 | 357 | 407 | 15.1 | 50 | 23.6 | 278 | 2.6 | 26.5 | 1.8 | 0.1 | −0.5 | 955 | 953 |
9 | III | 8.1 | 20.3 | 852 | 372 | 286 | 19.7 | 31.9 | 20.8 | 286 | 2.4 | 15.2 | 3.6 | 0.1 | 0.2 | 892 | 889 |
10 | III | 7.9 | 23 | 558 | 51.3 | 502 | 7.2 | 50.9 | 24 | 135 | 1.6 | 13.4 | 0.2 | 0.2 | 0.6 | 531 | 530 |
11 | III | 7.8 | 24.5 | 1156 | 375 | 313 | 209 | 115 | 49.3 | 236 | 5 | 11.4 | 2 | 0.1 | 0.1 | 1157 | 1155 |
12 | III | 7.7 | 24.9 | 1106 | 458 | 295 | 7.1 | 72.1 | 35.1 | 263 | 3.4 | 10.6 | 0 | 0.1 | 0.1 | 994 | 994 |
13 | IV | 8.3 | 21.1 | 1066 | 433 | 301 | 11.2 | 69.6 | 33.2 | 255 | 5.2 | 12.1 | 0 | 0 | 0.1 | 967 | 967 |
14 | IV | 7.7 | 22 | 992 | 338 | 419 | 12.7 | 63.1 | 24 | 250 | 2.5 | 18.1 | 775 | 16.4 | −0.6 | 1706 | 914 |
15 | IV | 8 | 19.6 | 622 | 68.1 | 475 | 38.8 | 20.9 | 11.7 | 190 | 2.6 | 19.5 | 725 | 15.6 | −0.2 | 1326 | 585 |
16 | IV | 7.8 | 29 | 1432 | 606 | 304 | 18.3 | 102 | 49.8 | 287 | 4.2 | 23.8 | 2010 | 61.3 | −0.7 | 3312 | 1241 |
17 | IV | 8.1 | 34.3 | 1238 | 418 | 413 | 58.5 | 55.6 | 33.7 | 316 | 4.1 | 21.3 | 2120 | 66.5 | −0.4 | 3297 | 1110 |
18 | III | 7.8 | 23.7 | 688 | 114 | 493 | 8.4 | 53.5 | 26.3 | 155 | 1.6 | 21.1 | 3120 | 89.5 | 0.1 | 3832 | 622 |
19 | III | 7.8 | 24.3 | 608 | 29.8 | 621 | 8.8 | 45.7 | 21.6 | 166 | 1.5 | 22.2 | 730 | 55.7 | 0.1 | 1387 | 601 |
20 | III | 8 | 18.2 | 19,962 | 9608 | 401 | 1190 | 887 | 687 | 4438 | 37.4 | 23.3 | 49 | 0.5 | −7.6 | 17,117 | 17,068 |
21 | III | 7.9 | 18.8 | 19,718 | 9740 | 382 | 1203 | 533 | 534 | 5454 | 44.7 | 23.7 | 130 | 0.3 | 2.9 | 17,851 | 17,720 |
ID | Aquifer System | Membership | δ2H | δ18O | Dex | 3H | 14C Based Age | 14C Activity |
---|---|---|---|---|---|---|---|---|
(‰) | (‰) | (‰) | TU | Years BP | pmc | |||
1 | DCAS | Aquifer III | −42.94 | −5.25 | −0.94 | <2 | 17,940 ± 140 | 9.70 |
2 | DCAS | Aquifer III | −36.58 | −3.97 | −4.82 | <2 | 11,270 ± 110 | 21.75 |
3 | DCAS | Aquifer III | −41.84 | −5.25 | 0.16 | 15.8 | 18,490 ± 340 | 9.08 |
4 | DCAS | Aquifer III | −43.8 | −5.52 | 0.36 | <2 | 16,100 ± 100 | 12.12 |
5 | DCAS | Aquifer III | −39.92 | −5.17 | 1.44 | <2 | 17,260 ± 100 | 10.54 |
6 | DCAS | Aquifer IV | −45.13 | −5.72 | 0.63 | <2 | 18,200 ± 130 | 9.40 |
7 | DCAS | Aquifer IV | −39.92 | −5.13 | 1.12 | <2 | 16,140 ± 130 | 12.07 |
8 | DCAS | Aquifer III | −44.9 | −5.97 | 2.86 | <2 | 26,140 ± 300 | 3.60 |
9 | DCAS | Aquifer III | −46.25 | −6.61 | 6.63 | 2.47 | 22,950 ± 510 | 5.29 |
10 | DCAS | Aquifer III | −40.79 | −4.86 | −1.91 | <2 | 20,380 ± 280 | 7.22 |
11 | DCAS | Aquifer III | −46.66 | −6.48 | 5.18 | <2 | 24,880 ± 260 | 4.19 |
12 | DCAS | Aquifer III | −49.12 | −6.38 | 1.92 | <2 | 22,150 ± 250 | 5.83 |
13 | DCAS | Aquifer IV | −50.33 | −6.34 | 0.39 | <2 | 18,870 ± 230 | 8.67 |
14 | DCAS | Aquifer IV | −48.8 | −6.37 | 2.16 | 6.94 | 22,310 ± 280 | 5.72 |
15 | DCAS | Aquifer IV | −55.31 | −7.22 | 2.45 | 5.31 | 16,900 ± 230 | 11.01 |
16 | DCAS | Aquifer IV | −48.05 | −6.4 | 3.15 | 8.7 | 19,540 ± 180 | 8.00 |
17 | DCAS | Aquifer IV | −52.76 | −6.97 | 3 | <2 | 25,890 ± 300 | 3.71 |
18 | DCAS | Aquifer III | −41.64 | −4.54 | −5.32 | 13.3 | 22,490 ± 170 | 5.60 |
19 | DCAS | Aquifer III | −51.42 | −5.96 | −3.74 | 12 | 18,600 ± 170 | 8.96 |
20 | DCAS | Aquifer III | −28.2 | −3.67 | 1.16 | <2 | 7410 ± 800 | 34.69 |
21 | DCAS | Aquifer III | −28.15 | −3.25 | −2.15 | <2 | 9370 ± 80 | 27.36 |
22 | None | River | −50.45 | −7.18 | 6.99 | - | - | |
23 | None | River | −50.43 | −6.98 | 5.41 | - | - | |
24 | None | River | −28.35 | −2.96 | −4.67 | - | - | |
25 | None | Sea | −6.32 | −0.56 | −1.84 | - | - | |
26 | None | Sea | −14.52 | −1.73 | −0.68 | - | - | |
27 | PAS | Phreatic Aquifer | −38.67 | −5.71 | 7.01 | - | - | |
28 | PAS | Phreatic Aquifer | −31.13 | −4.4 | 4.07 | - | - | |
29 | PAS | Phreatic Aquifer | −30.69 | −3.91 | 0.59 | - | - | |
30 | ICAS | Aquifer I | −33.37 | −4.04 | −1.05 | - | - | |
31 | PAS | Phreatic Aquifer | −42.83 | −6.39 | 8.29 | - | - | |
32 | PAS | Phreatic Aquifer | −37.9 | −5.28 | 4.34 | - | - | |
33 | PAS | Phreatic Aquifer | −38.63 | −5.46 | 5.05 | - | - |
Methodology Steps and Results | This Study | Xu et al. [10] |
---|---|---|
Data QA/QC before statistical analysis | Yes | No |
Dataset log-transformation and/or normality test | Yes | No |
Used anomalous Fe and Mn data in statistical process | No | Yes |
HCA linkage method | Ward | |
HCA measure of similarity | Euclidean distance | |
Number of identified clusters | 3 | 4 |
Number of significant components identified (Eigenvalue > 1) | 2 | 3 |
Cluster | pH | TDS | Cl− | HCO3− | SO42− | Ca2+ | Mg2+ | Na+ | K+ | H2SiO3 | Water Type |
---|---|---|---|---|---|---|---|---|---|---|---|
mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | |||
C1 | 7.81 | 698 | 136.3 | 480.3 | 14.1 | 55.1 | 25.2 | 165.1 | 2.1 | 25.3 | Na-HCO3 |
sC1a | 7.72 | 545 | 51.8 | 486.8 | 3.8 | 64.2 | 27.4 | 98.3 | 1.6 | 32.3 | Na-HCO3 |
sC1b | 7.88 | 784 | 169.9 | 487.2 | 22.4 | 48.3 | 23.6 | 202.0 | 2.3 | 19.3 | Na-HCO3 |
C2 | 7.9 | 1479 | 656.2 | 332.3 | 62.3 | 113.8 | 49.2 | 339.4 | 5.2 | 17.1 | Na-Cl |
C3 | 7.95 | 19840 | 9674 | 391.5 | 1196.5 | 710 | 610.5 | 4946 | 41.1 | 23.5 | Na-Cl |
Variable | PCA1 | PCA2 |
---|---|---|
pH | 0.12 | −0.41 |
Log TDS | 0.38 | 0.10 |
Log Cl− | 0.37 | −0.11 |
Log HCO3− | −0.16 | 0.52 |
Log SO42− | 0.36 | −0.02 |
Log Ca2+ | 0.35 | 0.26 |
Log Mg2+ | 0.36 | 0.21 |
Log Na+ | 0.38 | 0.02 |
Log K+ | 0.38 | 0.01 |
Log H2SiO3 | −0.06 | 0.65 |
Eigenvalue | 6.58 | 1.76 |
Percentage of explained variance | 65.8 | 17.6 |
Cumulative percentage of variance | 65.8 | 83.4 |
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Moya, C.E.; Scheihing, K.W.; Taulis, M. The Crucial Role of Data Quality Control in Hydrochemical Studies: Reevaluating Groundwater Evolution in the Jiangsu Coastal Plain, China. Earth 2025, 6, 62. https://doi.org/10.3390/earth6030062
Moya CE, Scheihing KW, Taulis M. The Crucial Role of Data Quality Control in Hydrochemical Studies: Reevaluating Groundwater Evolution in the Jiangsu Coastal Plain, China. Earth. 2025; 6(3):62. https://doi.org/10.3390/earth6030062
Chicago/Turabian StyleMoya, Claudio E., Konstantin W. Scheihing, and Mauricio Taulis. 2025. "The Crucial Role of Data Quality Control in Hydrochemical Studies: Reevaluating Groundwater Evolution in the Jiangsu Coastal Plain, China" Earth 6, no. 3: 62. https://doi.org/10.3390/earth6030062
APA StyleMoya, C. E., Scheihing, K. W., & Taulis, M. (2025). The Crucial Role of Data Quality Control in Hydrochemical Studies: Reevaluating Groundwater Evolution in the Jiangsu Coastal Plain, China. Earth, 6(3), 62. https://doi.org/10.3390/earth6030062