Spatial control of groundwater contamination,using principal component analysis

A study on the geochemistry of groundwater was carried out in a river basin of Andhra Pradesh to probe into the spatial controlling processes of groundwater contamination, using principal component analysis (PCA). The PCA transforms the chemical variables, pH, EC, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO \(_3^- \) , Cl^?, SO \(_4^{2-} \) , NO \(_3^-\) and F^?, into two orthogonal principal components (PC1 and PC2), accounting for 75% of the total variance of the data matrix. PC1 has high positive loadings of EC, Na⁺, Cl^?, SO \(_4^{2-} \) , Mg²⁺ and Ca²⁺, representing a salinity controlled process of geogenic (mineral dissolution, ion exchange, and evaporation), anthropogenic (agricultural activities and domestic wastewaters), and marine (marine clay) origin. The PC2 loadings are highly positive for HCO \(_3^- \) , F^?, pH and NO \(_3^- \) , attributing to the alkalinity and pollution controlled processes of geogenic and anthropogenic origins. The PC scores reflect the change of groundwater quality of geogenic origin from upstream to downstream area with an increase in concentration of chemical variables, which is due to anthropogenic and marine origins with varying topography, soil type, depth of water levels, and water usage. Thus, the groundwater quality shows a variation of chemical facies from Na⁺ > Ca²⁺ > Mg²⁺ > K⁺: HCO \(_3^- \) > Cl^? > SO \(_4^{2-}>\) NO \(_3^- \) > F^?at high topography to Na⁺ > Mg²⁺ > Ca²⁺ > K⁺: Cl^? > HCO \(_3^- \) > SO \(_4^{2-}>\) NO \(_3^- \) > F^? at low topography. With PCA, an effective tool for the spatial controlling processes of groundwater contamination, a subset of explored wells is indexed for continuous monitoring to optimize the expensive effort.     

华北隐伏型煤矿地下水水化学演化多元统计分析

为了阐明采动影响下华北隐伏型煤矿地下水化学演化规律,选取淮北煤田任楼煤矿为研究示范,运用系统聚类与主成分分析法对任楼煤矿不同时期的四含、煤系、太灰与奥灰含水层地下水水样的常规水化学指标（K⁺+Na⁺、Mg²⁺、Ca²⁺、Cl^-、SO₄^2-、HCO₃^-与CO₃^2-）开展多元统计分析,从而划分不同水化学类型,进而揭示地下水化学形成条件。研究结果表明：地下水\     

Urban impacts analysis on hydrochemical and hydrogeological evolution of groundwater in shallow aquifer Linares,Mexico

In northeast Mexico is Linares City, which has an extensive agricultural area and many industrial activities. Near this city is the Cerro-Prieto Dam (~12 km NE direction); this drinking water reservoir captures the water of the Pablillo River catchment area and constitutes an important source of potable water for the metropolitan area of Monterrey, the largest urban center of this region. Groundwater sources in this area provide drinking water to Linares inhabitants. A hydrogeological and hydrochemical study was conducted on the shallow aquifers surrounding the urban centers (Linares and Hualahuises) to determine the evolution of the water quality between 1981 and 2009. The hydrochemistry was assessed upgradient and downgradient from the potential contamination sources in Linares city. Groundwater showed a chemical evolution from calcium-bicarbonate type to calcium–sodium-sulfate type. The water qualities in the downstream area after Linares are inferior compared to the upstream area before the city. Nitrate concentrations in groundwater increased significantly after 28 years indicating an important pollutant process in this period of time over the study area. The possible pollution sources could be the agricultural and farm activities, industrial development, landfills leachate, septic tanks and wastewater of municipal and domestic consumption. If the present scenario continues, an aquifer vulnerability assessment would be important for the sustainable water management.     

Investigation of hydrochemical characteristics of groundwater from the Cretaceous-Eocene limestone aquifer in southern Ghana and southern Togo using hierarchical cluster analysis

The most relevant controls on the water quality within the Cretaceous-Eocene limestone aquifer of the Keta Basin, Ghana, and the coastal sedimentary basin of Togo were assessed using Q-mode hierarchical cluster analysis (HCA) and mass-balance modelling. The pattern recognition technique of HCA was employed for partitioning hydrochemical data from a total of 65 surface and borehole samples from the study area into water groups. A spatial plot of the water groups consisting of samples from the limestone aquifer shows that the vast majority of samples belonging to the same group are located in close proximity to one another, suggesting the same processes and/or flow paths in the limestone aquifer system. Geochemical reaction models of selected water groups were constructed using PHREEQC-2. The hydrochemical compositions of the water groups and the mass-balance calculations indicate that the dominant processes and reactions responsible for the hydrochemical evolution in the system are: (1) carbonate equilibria, (2) silicate weathering reactions, (3) limited mixing with saline water, and (4) ion exchange. The combined use of HCA and mass-balance modelling has shown to be a useful approach in interpreting groundwater hydrochemistry in an area where large uncertainties exist in the understanding of the groundwater flow system.     

滦河三角洲地区深层地下水化学演化规律及成因分析

以滦河三角洲地区第Ⅲ含水层组为例,选取两条水文地质剖面分析深层地下水化学组分特征。文章利用Piper图分析了上下游水化学的分带性,从上游到下游演化顺序为HCO3—Ca·Na型、HCO3·SO4—Na·Ca型和HCO3·Cl—Na型。上游地下水沿流动方向主要发生了溶滤作用,引起HCO-3和Ca2++Mg2+等比例增加,Cl-+SO2-4和Na+也等比例增加。下游地下水沿流动方向不仅发生了溶滤作用,还发生了阳离子交换和脱硫酸作用,引起下游地区Ca2+、Mg2+和SO2-4逐渐减小,Cl-和Na+显著增加,且Na+增加幅度明显大于Cl-。本研究加深了承压含水层地下水从山前到滨海地区整个循环路径上的水化学演化规律及成因的认识。     

泾惠渠灌区地下水硫酸盐水文地球化学演化过程研究

泾惠区具2200多年的灌溉历史,灌区人口密度大,地下水不仅是工业和农业的主要水源,也是当地主要饮用水源.为了查明灌区地下水硫酸盐的水文地球化学特征、成因及其演化过程,在分析灌区1982年、1990年和2009年地下水水化学特征、SO4 2-时空分布特征的基础上,通过灌溉试验和Hydrus-1D模拟灌溉对地下水SO4 2-的影响.结果表明,灌区地下水水化学类型由HCO3(1982年)向SO4 2-(2009年)型演化.2009年SO4 2-是地下水中主要阴离子组分,具有西部低,北部、东部和南部高的区域分布特征.虽然地下水中最初的SO42-主要来源于地层中Na2SO4和CaSO4等硫酸盐的溶解,但灌溉试验和模拟计算表明,近年来地下潜水中高硫酸盐主要是由于灌溉水源引起的.     

Multiple group principal component analysis

Common Principal Component Analysis is a generalization of standard principal components to several groups under the rigid mathematical assumption of equality of all latent vectors across groups (i.e., principal component directions), whereas the latent roots are allowed to vary between groups (differing inflations of dispersion ellipsoids). In practice, data that fulfill these strict requirements are relatively rare. Examples from palaeontology are used to illustrate the principles. Compositional data can be made to fit the Common Principal Component (CPC) model by the appropriate logratio covariance matrix.     

Modeling freshening time and hydrochemical evolution of groundwater in coastal aquifers of Shenzhen,China

This work investigated the freshening time and hydrochemical evolution of coastal groundwater in two brackish aquifers in Shenzhen, China. One was the brackish aquifer that resulted from heavy pumping, and the other was the aquifer reclaimed from the coastal sea. Freshening time and hydrochemical evolution of brackish aquifers were quantitatively evaluated using PHREEQC 2.0, a one-dimensional reactive-transport model. Freshening time was shown to mainly depend on pore water velocity, while the chemical composition of groundwater was determined by the cation exchange capacity of the aquifer. It was shown that after heavy pumping ceased, the freshening time for the original coastal aquifer ranged from 20 to over 80 years. While for the coastal reclaimed aquifer, the freshening time was from 85 to 140 years, which depended on the hydraulic conductivity of the fill materials in the reclaimed site. During aquifer freshening, groundwater evolved from Na–Cl type to Ca–Mg–HCO₃ or Na–HCO₃ type. A sensitivity analysis showed that the freshening time was most sensitive to the pore water velocity in the aquifer, while the groundwater chemical composition was most sensitive to the values of cation exchange capacity of the aquifer. As for the dispersivity, it had almost no effect on the freshening time and the chemical composition of groundwater.     

Assessment of groundwater water quality in central and southern Gulf Coast aquifer,TX using principal component analysis

Principal component analysis has been applied for source identification and to assess factors affecting concentration variations. In particular, this study utilizes principal component analysis (PCA) to understand groundwater geochemical characteristics in the central and southern portions of the Gulf Coast aquifer in Texas. PCA, along with exploratory data analysis and correlation analysis is applied to a spatially extensive multivariate dataset in an exploratory mode to conceptualize the geochemical evolution of groundwater. A general trend was observed in all formations of the target aquifers with over 75 % of the observed variance explained by the first four factors identified by the PCA. The first factor consisted of older water subjected to weathering reactions and was named the ionic strength index. The second factor, named the alkalinity index explained greater variance in the younger formations rather than in the older formations. The third group represented younger waters entering the aquifers from the land surface and was labeled the recharge index. The fourth group which varied between aquifers was either the hardness index or the acidity index depending on whether it represented the influences of carbonate minerals or parameters affecting the dissolution of fluoride minerals, respectively. The PCA approach was also extended to the well scale to determine and identify the geographic influences on geochemical evolution. It was found that wells located in outcrop areas and near rivers and streams had a larger influence on the factors suggesting the importance of surface water–groundwater interactions.     

典型黄土塬区地下水水化学成因机制及碳循环意义

水岩相互作用包括了溶解、沉淀和离子交换等作用, 其参与了各种地质作用和生态-环境过程; 而目前对离子交换作用在水中离子来源解析和同位素示踪等方面考虑不足, 这限制了对水化学演化规律和碳循环刻画等方面的认识。本研究选择水文地质条件较为简单的甘肃陇东地区董志塬, 在对降水入渗补给评估、地下水定年(³H和¹⁴C)等水循环规律刻画的基础上, 通过对降水元素输入和阳离子交换容量分析, 以及应用硝酸盐同位素(δ¹⁵N-NO₃和δ¹⁸O-NO₃)、硫酸盐同位素(δ³⁴S-SO₄和δ¹⁸O-SO₄)、⁸⁷Sr/⁸⁶Sr (包括地下水及黄土各分量)、阳离子关系等手段, 解析了董志塬地下水中主要离子来源。研究结果显示, 降水入渗补给量为39±8mm/a, 土壤水运移速度为0.13±0.03m/a; 研究区包气带较厚(主要在40~75m), 这说明年降水需要250~750年才能补给到地下水, 但持续的补给使得自然条件下每年约有(3167±650)×10⁴m³地下水通过泉水补给两侧河流。地下水年龄较老, 不含³H, ¹⁴C校正年龄在417年至19420年之间, 因此水化学组成受现代人类活动影响可忽略; 地下水中Cl^-和SO₄^2-主要来自于古降水, 并反演出古降水SO₄^2-平均含量为1.2mg/L, 显著低于受化石燃料等影响的现代含量(平均为6.6mg/L); 而地下水NO₃^-则主要来自于土壤氮的硝化。地下水⁸⁷Sr/⁸⁶Sr比值(0.7107至0.7114)与黄土中碳酸盐的比值(0.7103至0.7111)基本一致, 表明Ca²⁺和Mg²⁺主要来自于碳酸盐矿物的溶解, 部分被吸附至粘土矿物。研究区黄土具有较高的阳离子交换容量(149±33meq/kg), 地下水总Na⁺中, 降水贡献平均占29%, 其余Na⁺主要来源于水中Ca²⁺和Mg²⁺和粘土矿物中Na的交换(平均为71%), 硅酸盐溶解对水中Na⁺贡献可忽略(硅酸盐溶解会导致⁸⁷Sr/⁸⁶Sr增加), 而以往研究大多认为除了降水输入、蒸发岩溶解外, 水中Na⁺主要来自于硅酸盐矿物的溶解, 并贡献了碳汇。本研究认为在研究区地下水中, 硅酸盐风化的碳汇效应可忽略; 同时强调了在含有粘土矿物的流域或水岩体系, 阳离子交换作用在示踪水中离子来源及碳循环中的重要性。

     

Thoughts on use of principal component analysis in petrogenetic problems

The use of principal component analysis in studying chemical trends in volcanic rock suites is described. It is suggested that eigenvectors generated from a correlation matrix, rather than a covariance matrix, could be used in this context. In the latter situation many elements are swamped by silicon's numerical size and range. In the former situation the alkalies and titanium begin to show their true importance.     

The hydrochemical characteristics and evolution of groundwater and surface water in the Heihe River Basin, northwest China

A combination of isotopic and chemical indicators has been used to characterize rainfall, surface water and groundwater in the Heihe River Basin, China. Surface- vs. groundwater chemistry data enabled geographical zones and chemical types to be differentiated. The dissolution of halite, Glauber’s salt, gypsum, dolomite and calcite determine Na⁺, Cl^?, Mg²⁺, Ca²⁺, $ {\text{SO}}^{{2 - }}_{4} A combination of isotopic and chemical indicators has been used to characterize rainfall, surface water and groundwater in the Heihe River Basin, China. Surface- vs. groundwater chemistry data enabled geographical zones and chemical types to be differentiated. The dissolution of halite, Glauber’s salt, gypsum, dolomite and calcite determine Na⁺, Cl⁻, Mg²⁺, Ca²⁺, and chemistry, but other processes such as evaporation, ion exchange, and deposition also influence the water composition. The majority of deep confined groundwaters are tritium-free and less mineralized than in the shallow aquifer. Radiocarbon values in the deeper groundwaters range from 18.8 to 38.9 pmc, and 80 pmc probably represents the upper limit of initial ¹⁴C activity; this yields ages of approximately 5,960–11,971 years BP, which is about 3,000 years older than those calculated by models in previous work. The shallow aquifer exhibits fairly high and variable tritium activities (4–75 TU), evidence of recent recharge and low residence time (<60 years), which is in line with estimates from previous work. Isotopic signatures indicate formation of deeper groundwaters in a colder and wetter climate during the late Pleistocene and Holocene. The results suggested that significant changes are urgently needed in water-use strategy to achieve sustainable development.

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Résumé Une combinaison de plusieurs indicateurs isotopiques et chimiques a été utilisée dans le but de caractériser les précipitations, les eaux de surface et les eaux souterraines dans le Bassin de la Rivière Heihe, en Chine. La confrontation des chimies des eaux souterraines et de surface a permis de différentier plusieurs secteurs géographiques et faciès chimiques. Les compositions chimiques en Na⁺, Cl⁻, Mg²⁺, Ca²⁺, et sont déterminées par la dissolution de la halite, du sel de Glauber, du gypse, de la dolomite et de la calcite, mais d’autres processus peuvent également avoir une influence, comme l’évaporation, les échanges de bases et la sédimentation. La majorité des eaux souterraines captives profondes ne contiennent pas de tritium, et sont moins minéralisées que dans l’aquifère superficiel. Les valeurs de carbone 14 dans l’aquifère le plus profond sont comprises entre 18.8 et 38.9 pcm, pour une valeur maximum probable d’activité initiale de 80 pcm; les ages estimés correspondants sont compris entre 5,960 et 11,971 ans, soit environ 3,000 ans de plus que ceux calculés auparavant par les modèles. L’aquifère superficiel présente des activités tritium plut?t élevées et variables (4 à 75 UT), démontrant l’existence d’une alimentation récente et d’un temps de résidence faible (<60 ans), ce qui concorde avec les études antérieures. Les signatures isotopiques indiquent une alimentation des eaux souterraines les plus profondes au cours d’épisodes climatiques plus froids et plus humides qu’actuellement, à la fin du Pléistocène et à l’Holocène. Les résultats suggèrent que des changements significatifs dans la planification des usages de l’eau sont nécessaires et urgents dans des perspectives d’exploitation durable.

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Resumen Se ha utilizado una combinación de indicadores isotópicos y químicos para caracterizar la precipitación, el agua superficial y el agua subterránea en la Cuenca del Río Heihe, China. Los datos químicos de aguas superficiales frente a las subterráneas no permiten diferenciar zonas geográficas y tipos químicos. La disolución de halita, sal de Glauber, yeso, dolomita y calcita determina la química de Na⁺, Cl⁻, Mg²⁺, Ca²⁺, y , pero otros procesos, como evaporación, intercambio de iones y precipitación influyen también en la composición del agua. La mayoría de las aguas subterráneas profundas confinadas no tienen Tritio y están menos mineralizados que el acuífero superficial. Los valores de radiocarbono en las aguas subterráneas más profundas oscilan entre 18.8 y 38.9 pmc, y el valor de 80 pmc representa probablemente el límite superior de la actividad inicial de ¹⁴C; proporcionando edades de aproximadamente 5,960–11,971 a?os BP, que son unos 3,000 a?os más antiguas de las calculadas mediante modelización en trabajos previos. El acuífero superficial tiene actividades de tritio bastante más altas y variables (4–75 UT), evidenciando una recarga reciente y unos tiempos de residencia bajos (<60 a?os), lo cual está en la línea de lo estimado en trabajos previos. Los datos isotópicos apuntan a la formación de aguas subterráneas más profundas en un clima más frío y húmedo durante el Pleistoceno superior y el Holoceno. Los resultados sugieren que se necesita hacer cambios significativos en la estrategia de uso del agua para alcanzar un desarrollo sostenible.

     

主成分分析法在页岩气有利区优选中的应用

在多因素叠合法优选页岩气发育有利区的基础上,构建了涵盖地质背景、页岩生烃、储集、保存、资源和开采条件6个方面17项指标的页岩气发育有利区综合评价原始指标体系,并运用主成分分析法对湘鄂西地区下寒武统牛蹄塘组页岩气发育有利区进行了实例分析。结果表明,主要影响湘鄂西地区牛蹄塘组页岩气发育有利区分布的因子为页岩品质的优劣、资源规模的大小和保存条件的好坏,通过定量评价,综合得分排在前3位的有利区分别为中央复背斜有利区、桑植—石门复向斜南有利区和宜都—鹤峰复背斜有利区。     

贺兰山以北乌兰布和沙漠地下水水化学特征演化规律研究

乌兰布和沙漠对中国西北部干旱地区气候变化和水文循环过程研究具有指示意义, 以水文地球化学运移为导向, 通过分析33个地下水样, 探讨了该区地下水的补给与演化过程. 结果表明: 巴彦乌拉山浅层地下水水化学类型为Cl^--HCO₃^--SO₄^2--Na⁺; 从吉兰泰盐湖至乌兰布和沙漠, 主要水化学类型变化浅层地下水为Cl^--HCO₃^--Na⁺到Cl^--HCO₃^--SO₄^2--Na⁺, 深层地下水为HCO₃^--Cl^--Na⁺再到HCO₃^--Cl^--Na⁺或HCO₃^--Cl^--Ca²⁺. Gibbs图表明, 研究区地下水的水化学特征主要受蒸发浓缩作用影响和岩石风化作用控制, 大气降雨机制影响甚微. 主要离子相关关系图及饱和指数表明, 岩盐、芒硝、钠长石、方解石、白云石、石膏等矿物的风化溶解是该区地下水主要离子来源. 此外, 氯碱指数和Ca/Na的指示, 说明阳离子交换作用也是形成该地区地下水水化学组分的重要机制.     

The hydrochemical facies and anomalous fluoride content in the Serra Geral aquifer system,southern Brazil: a GIS approach with tectonic and principal component analysis

Groundwater with high fluoride content and water mixture patterns were studied in Serra Geral aquifer system (SGAS) using three aspects, principal component analysis (PCA), tectonic scenery and hydrochemical interpretation from 309 groundwater chemical data information from deep wells. A four-component model is suggested and explains 81% of total variance in the PCA. Six hydrochemical facies were identified. These facies suggest two different fluoride sources. Tectonic approach shows the relationship between defined hydrochemical facies and regional fracture control. The applied methodology reveals a minimum level to understand hydrochemical mixtures. The fluoride enrichment mechanisms into the groundwater are comprised in advance to guide the future uses of SGAS to the public supply.     

Application of principal component analysis to understand variability of rainfall

The usefulness of principal component analysis for understanding the temporal variability of monsoon rainfall is studied. Monthly rainfall data of Karnataka, spread on 50 stations for a period of 82 years have been analysed for interseasonal and interannual variabilities. A subset of the above data comprising 10 stations from the coherent west zone of Karnataka has also been investigated to bring out statistically significant interannual signals in the southwest monsoon rainfall. Conditional probabilities are proposed for a few above normal/below normal transitions. A sample prediction exercise for June–July using such a transition probability has been found to be successful.     

Assessment of groundwater quality for irrigation use and evolution of hydrochemical facies in the Markanda river basin,northwestern India

The Markanda river basin occupying an area of about 1547 km² is a part of the alluvial deposits of the Indo- Gangetic plain near the Himalayan foothills in the northwest India. The region is associated with active agricultural activities and makes significant contribution to the country’s agricultural products. Assessment of groundwater quality for irrigation use and hydrochemical evolution of groundwater has been studied. Hydrochemical analysis has been carried out based on concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, SO₄ ²⁻, CO₃ ²⁻ and HCO₃ ⁻. Sodium adsorption ratio (SAR), percent sodium (%Na), permeability index (PI) and Trilinear diagram have been studied to evaluate suitability of irrigation use. Hydrochemical evolution has been analyzed based on the Chebotarev sequence and expanded Durov diagram. SAR, %Na and PI results indicate that the groundwater in the basin is suitable for irrigation use. Analysis on Trilinear diagram reveals that hydrochemical facies are dominated by HCO₃ ⁻- Ca²⁺- Mg²⁺ facies indicating that the groundwater is associated with recharge waters percolating through sandstone and limestone rocks which are exposed in the northern part of the basin. Studies based on Chebotarev anion sequence and expanded Durov diagram indicate that the evolution of groundwater belongs to initial to intermediate stage indicating fresh water quality. Thus, the present work reveals that groundwater in the Markanda basin is of good quality and is suitable for all uses including interbasin water transfer in the region.     

基于灰色关联度分析法和主成分分析法对泥页岩储层评价方法的探讨

泥页岩储层的影响因素众多,明确各因素间的内部联系才能更好地评价储层。为对比灰色关联法和主成分分析法在储层评价中的适用性,本文选取鄂尔多斯盆地东缘上古生界Y88井丰富的储层数据进行分析。通过对比两种多元统计方法的原理、算法和结果,认为主成分分析法把各项因子视为离散变量,通过降维后用三个综合评价指标来反映储层的优劣,是对各项指标的概括性分析;灰色关联法将参数分为参考数据列和比较数据列,参考数据列的有机碳含量高低与储层的优劣成正相关,参考数据列对评价对象具有可测性。因此,若是对评价对象的概括性分析,用主成分分析法比较合适;若是对评价对象的可测性分析,如有机碳含量的高低决定能不能形成泥页岩储层,则用灰色关联法评价更合理。     

Assessing spatial variability in soil characteristics with geographically weighted principal components analysis

Dimensionality reduction methods such as principal components analysis (PCA) provide a means of identifying trends in soil characteristics which may be represented by a wide range of variables. However, these characteristics may be highly spatially variable and so the results from PCA represent, in some sense, an “average” of locally distinct characteristics. One approach to account for these local differences is to introduce a geographical weighting scheme into the PCA process. In this paper, such an approach is assessed in the exploration of soil characteristics in the state of Pennsylvania, USA. Data from 878 georeferenced soil profiles which include different soil parameters (n = 12) were extracted from the National Soil Survey Center database. Where data are parts of compositions (e.g., percentages of sand, silt, and clay), analysis using raw data is not appropriate and such data were transformed using log ratios (specifically, balances). Single variables (i.e., those which are not parts of compositions) were logged. The first two principal components explain over 50% of the variance. The mapped values suggest marked spatial variation in soil characteristics, but it is not possible to assess which of these variables explain most variation in particular regions from the simple maps of raw variables. Geographically weighted PCA (GWPCA) provides additional information which is obscured by PCA, and it also provides a set of component scores and loadings at all data locations. The soil variable with the largest loading at most locations of Pennsylvania is the logged base saturation (BSln), and this supports the findings of the conventional PCA analysis. While BSln loads most highly in most of the eastern third, the middle and the south west of the state, the northwest is less spatially consistent in terms of the variables which explain most variation. For GWPC 1, the variable with the second largest loading at most locations (i.e., primarily the south and west) is CEC.B1 (the log ratio of Ca, Mg, and Na to K and EXACID), while CEC.B2 (the log ratio of Ca and Mg to Na), pHln (logged pH) and BSln dominate in other areas. The GWPCA results suggest that there is marked spatial variation in multivariate soil characteristics across Pennsylvania state and that results from standard PCA obscure this considerable variation.