Water Rock Interaction Experiments Research Articles

Hydrochemistry process and microweathering behaviour of sandstone heritages in the Nankan Grotto, China: Insights from field micro-observations and water–rock interaction experiments

Hydrochemistry process and microweathering behaviour of sandstone heritages in the Nankan Grotto, China: Insights from field micro-observations and water–rock interaction experiments

Elemental dissolution characteristics of granite and gabbro under high-temperature water-rock interactions

In the process of developing hot dry rock (HDR) through enhanced geothermal systems (EGS), it is necessary to inject circulating water to complete thermal energy extraction. However, the injected water will react with the high-temperature rock and produce mineral dissolution, which can destroy the artificial reservoir and affect the development of geothermal energy. To explore the influence of temperature on the solution composition and mineral dissolution after water-rock reaction, this study conducted water-rock interaction experiments on gabbro and granite at different heat treatment temperatures. Subsequently, the changes of solution composition and mineral dissolution with temperature after the reaction were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and XRD. The results demonstrated that Si, Na, Ca, K, Al, and Mg did not enter the aqueous solution at the same dissolution rate. Si was the primary solute in the solution, mainly resulting from the dissolution of quartz, and the dissolution rates of metallic elements were lower. In the granite-water interaction system, metallic elements such as Na, K, Ca, and Al showed a tendency to enter the solution at low temperatures, i.e., 150–180 °C, and the dissolution rate of Si reached its peak when the water was close to the supercritical state. With the increase in temperature, the dissolution rates of Si and metallic elements showed an initial increasing trend followed by a decrease. When water is in the subcritical to the supercritical state, abrupt fluctuations in the physical properties of water can strongly affect the dissolution of minerals or rocks. The results of this study provide insights into rock corrosion fatigue and mineral scaling in EGS water environment.

Impact of Inorganic Solutes’ Release in Groundwater during Oil Shale In Situ Exploitation

Oil shale can produce oil and shale gas by heating the oil shale at 300–500 °C. The high temperature and the release of organic matter can change the physical and mechanical properties of rocks and make the originally tight impervious layer become a permeable layer under in situ exploitation conditions. To realize the potential impact of the in situ exploitation of oil shale on groundwater environments, a series of water–rock interaction experiments under different temperatures was conducted. The results show that, with the increase of the reaction temperature, the anions and cations in the aqueous solution of oil shale, oil shale–ash, and the surrounding rock show different trends, and the release of anions and cations in the oil shale–ash solution is most affected by the ambient temperature. The hydrochemical type of oil shale–ash solution is HCO3-SO4-Na-K at 80 °C and 100 °C, which changes the water quality. The main reasons are that (1) the high temperature (≥80 °C) can promote the dissolution of FeS in oil shale and (2) the porosity of oil shale increases after pyrolysis, making it easier to react with water. This paper is an important supplement to the research on the impact of the in situ exploitation of oil shale on the groundwater environment. Therefore, the impacts of in situ mining on groundwater inorganic minerals should be taken into consideration when evaluating in situ exploitation projects of oil shale.

Geochemical processes during hydraulic fracturing in a tight sandstone reservoir revealed by field and laboratory experiments

The application of hydraulic fracturing has transformed tight sandstone gas into a very important global unconventional resource. The accurate description of geochemical processes during hydraulic fracturing can provide essential information for improving tight gas production. In this study, field fracturing and laboratory water-rock interaction experiments were designed and performed in conjunction with geochemistry, isotope, XRF, XRD and SEM techniques to reveal the prevalent geochemical processes. Sixty-five flowback fluid samples were collected from a hydraulic fracturing well and a tight sandstone sample was drilled from gas reservoir to perform water-rock interaction experiments. The results indicate that hydraulic fracturing flowback fluid is a complex mixture, with high TDS values (0.93–33.04 g/L) and heavy isotopes (e.g., mean δ18O of −5.35‰, mean 87Sr/86Sr of 0.714651). Geochemistry and isotope data reveal that the mixing process between fracturing fluid and formation water exerts an important influence on the flowback fluid chemistry, while water-rock and fluid-fluid interactions are also variably important during the hydraulic fracturing process. Pyrite oxidation process is confirmed during hydraulic fracturing in the tight sandstone reservoir, while the addition of gel breaker makes the process prominent. Due to high clay mineral contents (24%), ion exchange and adsorption/desorption are critical factors affecting the stability of the clay minerals during the entire fracturing and flowback processes. Approximately, 20%-43% of the strontium was removed from the solution by ion exchange between the 8 and 44 h intervals of the flowback process. The fractures derived from fracturing connect different types of high salinity formation water, leading to potential mineral precipitation (e.g., barite and calcite). The analysis of formation water needs to be taken into consideration during hydraulic fracturing operations.

Raman shifts ofc-BN as an idealP-Tsensor for studying water-rock interactions in a diamond-anvil cell

AbstractCubic boron nitride (c-BN) has the same structure as diamond, and it shows very inert reaction activity in different chemical environments, even under high-pressure (P) and high-temperature (T) conditions. Furthermore, the P- and T-dependent Raman shift of c-BN (e.g., TO mode) can be distinguished from that of the diamond anvil (c-BN at ~1054 cm–1 vs. diamond at ~1331 cm–1 at ambient conditions), making c-BN a potential P-T sensor for diamond-anvil cell (DAC) experiments. However, the Raman shift of c-BN has not been well studied at high P-T conditions, especially at temperatures above 700 K. In this study, we systematically calibrated the Raman shift of the TO mode (νTO) for synthetic c-BN grains at high-P and high-T conditions up to 15 GPa and 1300 K. Both ruby (Mao et al. 1986) and Sm2+:SrB4O7 (Datchi et al. 2007) were used as internally consistent standards for calibration of c-BN P-T sensor. Our results show that the Raman shift of c-BN is negatively correlated with temperature [∂νTO/∂T = –0.02206(71)] but positively correlated with pressure [∂νTO/∂P = –3.35(2)]. More importantly, we found that the P-T cross derivative for the Raman shift of c-BN [∂2νTO/∂P∂T = 0.00105(7)] cannot be ignored, as it was assumed in previous studies. Finally, we calibrated a Raman shift P-T sensor of c-BN up to 15 GPa and 1300 K as follows:P = A ( T ) − A ( T ) 2 + 0.2194 B ( T , Δ v ) 0.1097where A(T) = 3.47(6) + 0.00105(7)T, B(T, ΔνTO) = 2.81(51) – 0.0053(16)T – 1.78(11) × 10–5T2 – ΔνTO. The c-BN Raman shift P-T sensor in this study fills the P-T gap ranging from previously performed externally resistance-heated to laser-heated DAC experiments. The effect of c-BN grain size and Raman system laser power on the calibration were also tested for the P-T sensor. In addition, we conducted three sets of high-P-T experiments to test the practicability of c-BN P-T sensor for water-rock interaction experiments in DAC. Testing experiments showed c-BN has very stable chemical activity in water and clear Raman signal at high-P-T conditions in comparison with other P-T sensors (e.g., ruby, Sm2+:SrB4O7, and quartz). Hence, the Raman shifts of c-BN may serve as an ideal P-T sensor for studying water-rock interactions in a DAC, especially at high-P and high-T conditions relevant to subduction zones.

The Effect of Formation Water Salinity on the Minimum Miscibility Pressure of CO2-Crude Oil for Y Oilfield

CO2 miscible flooding is an important technology for enhancing oil recovery and greenhouse gas storage in the world. As a tertiary recovery technology, it is usually applied after water flooding. Therefore, the actual reservoirs usually contain a lot of injected water in addition to connate water. The salinity of these formation waters varies from place to place. CO2 is an acid gas. After it is injected into the reservoir, it easily reacts with formation water and rock and affects the physical properties of the reservoir. However, no research results have been reported whether this reaction affects the minimum miscibility pressure (MMP) of CO2-crude oil, a key parameter determining miscible flooding in formation water. Based on CO2-formation water–rock interaction experiments, this paper uses the core flooding method to measure the CO2-crude oil MMP under different salinity in formation water. Results show that CO2 causes a formation water pH decrease from 7.4 to 6.5 due to its dissolution in formation water. At the same time, CO2 reacts with formation water, albite, potassium feldspar, and carbonate minerals in the cores to generate silicate and carbonate precipitates, which could migrate to the pore throat together with the released clay particles. Overall, CO2 increased core porosity by 5.63% and reduced core permeability by 7.43%. In addition, when the salinity of formation water in cores was 0, 4,767, and 6,778 mg/L, the MMP of CO2-crude oil was 20.58, 19.85, and 19.32 MPa, respectively. In other words, the MMP of CO2-crude oil decreased with the increase of salinity of formation water.

Effect of high salinity and temperature on water–volcanic rock interaction

In order to understand the processes occurring in natural hydrothermal systems, it was carried out a series of water–volcanic rock interaction studies in the laboratory and an intermediate volcanic rock samples from geothermal production wells in Tuzla geothermal field (TGF) in western Turkey. A high-pressure autoclave was used to conduct water–rock interaction experiments under similar conditions of the field. Rainwater and seawater were treated with volcanic rocks at 140 °C (reservoir temperature) and 4.5 bar pressure. The change in the ionic content of the resulting fluids was examined in terms of the type of volcanic rocks and mineral saturation index. The results indicate that talc and diopside minerals in geothermal systems may cause scaling at high temperatures depending on the geothermal fluid and pH.

Sources of metasilicate in mineral water of Jingyu County, northeastern China

The source of metasilicate in mineral water of Jingyu County. located in Changbai Mountains of northeastern China, was analysed through two groups of water-rock interaction experiments. One is a hydrolysis immersion experiment using basalt and the other is an immersion experiment utilizing a mixture of soil, scoria, and clastic basalt under the same conditions. Results indicate that the metasilicate in mineral water is mainly derived from the hydrolysis of silicates and silica in the basalt, scoria, and soil. In the first immersion experiment, the release of metasilicate is linear, with dissolved metasilicate increasing continuously through time at a stable release rate of about 0.01 mg/(kg·day). The second experiment indicates that the contribution of soil and scoria to metasilicate in mineral water is higher than that of clastic basalt under the same conditions.

Understanding the evolution of thermal fluids along the western continental margin of India using geochemical and boron isotope signatures

Thermal springs lined up for about 350 km along the Western coast of Maharashtra, India, have been studied for major, minor, trace and rare earth elements, along with the boron isotope ratios for selected samples, to understand their evolution pattern. These alkaline springs have discharge temperatures varying from 40 to 72 °C. Based on the major ion composition, it is established that most of the thermal springs are of Na(Ca)-Cl or Ca(Na)-Cl type, with a few of Na-Cl(SO4) type. Only one thermal spring at Rajapur is Na-HCO3 type behavior. Trace elements concentration vary significantly e.g., Li (19–386 ppb), B (104–1362 ppb), Sr (16–13560 ppb), Rb (13–220 ppb), Cs (0.75–44 ppb) and Ba (3–2077 ppb). Chondrite-normalized REE patterns indicate a pronounced ‘Eu’ anomaly probably due to the involvement of plagioclase, but the effect of temperature reaching more than 250 °C cannot be ruled out in case of some springs. First-time study of δ11B isotope (range between 2.5‰ to 27.0‰) of the West Coast thermal fluid suggests role of leaking marine sediments in their evolution. Water-rock interaction experiments with granite, basalt and diluted seawater at elevated temperatures and pressures have given an insight into the evolution of the thermal springs. Based on all the findings, a conceptual model has been prepared, which gives an overview of the evolution of the thermal springs.

An ideal geothermometer in slate formation: A case from the Chingshui geothermal field, Taiwan

The use of geothermometers derived from fluid solution compositions is a well-established practice for estimating geothermal reservoir temperatures. The most commonly used geothermometers in hot-spring environments are based on the solubility of SiO2, mineral equilibria involving the exchange of Na-K and K-Mg, and the empirically-derived Na-K-Ca geothermometer. The preferred geothermometer for a reservoir is determined based on the rock type of each specific reservoir. Geothermal reservoirs in the Chingshui Region of northeastern Taiwan are predominantly composed of slate. Therefore, this study examines water-rock interaction in a slate environment to determine the ideal geothermometer for estimating reservoir temperature in the Chingshui Region. Water-rock interaction experiments between 100°C to 300°C were conducted at various durations with the longest being 60days. The traditional experiment of a closed system was modified into a two-step system by separating solid and reacted liquid during cooling. Comparison with the major elemental geothermometers and agreement with downhole temperature measurements indicate that the silica geothermometer is the most useful in assessing subsurface temperatures in the Chingshui hot-springs region and in the slate environment.

Long‐Term Reaction Characteristics of CO2–Water–Rock Interaction: Insight into the Potential Groundwater Contamination Risk from Underground CO2 Storage

AbstractCO2 sequestration into saline aquifers is considered to be one of the most promising options for reducing industrial CO2 emissions to the atmosphere. However, there are still many uncertainties regarding the storage of CO2 in the subsurface because of a lack of knowledge about CO2–water–rock interaction within CO2 reservoirs and the potential risk of CO2 leakage. In this study, we construct a semi‐open type experimental system that can reproduce the interactions under conditions close to those of actual CO2 reservoirs. Using the system, we conduct CO2–water–rock interaction experiments for 8 months to monitor the long‐term reaction and the mobilization of harmful metal elements. Altered tuffaceous rock is used in the experiment because these tuffaceous rock formations (called “Green Tuff”) are a potential candidate for CO2 storage in Japan. The results show that the major‐element water composition will converge to the point where host rock dissolution and secondary mineral precipitation are balanced; then, the interaction will proceed under a certain groundwater composition. In addition, we found that groundwater contamination by some metal elements (Ni, Ba, and Mn) may reach unsafe levels for drinking water as a result of CO2‐water–rock interaction.

Europium anomaly variation under low-temperature water-rock interaction: A new thermometer

The positive europium (Eu) anomaly, enrichment of Eu abundance relative to the neighboring elements, is often observed for water interacted with the rocks. Not only high temperature (~400°C) water-rock interaction such as seafloor hydrothermal fluids, but also relatively lower temperature interaction, less than 100°C, cause positive Eu anomaly. However, relationship between the degree of Eu anomaly and interaction temperature has not been investigated. Water-rock interaction experiments at three different reaction temperatures were performed in this study to reveal the cause of positive Eu anomaly. Comparison of the results under different solution chemistry and temperature conditions showed that the basalt containing plagioclase released larger abundances of REEs than the basaltic glass. The degree of Eu anomaly assessed by Eu/Eu* value was smaller when 0.7 M NaCl solution was used for liquid phase for both solid phases. On the other hand, the Eu/Eu* became larger with increasing reaction temperature for basalts interacted with ultra-pure water. Therefore, it is suggested that the Eu anomaly is potentially used as a fluid-rock interaction thermometer under low salinity condition.

Geochemical impact of injection of Eagle Ford brine on Hosston sandstone formation—Observations of autoclave water–rock interaction experiments

This study investigates water–rock interactions induced by brine injection into the Cretaceous clastic Hosston Formation in South Central Texas, a potential host formation for disposal of produced water from the Eagle Ford Shale during oil and gas extraction. The primary objectives of this experimental study were to (1) predict the geochemical reactions between the injected brine and the host formation during disposal operation, and (2) assess potential impact on flow properties of the host rock. The results provide important information of potential impact to injectivity and available methods to alleviate the problems if they occur during brine disposal. Five batch autoclave experiments were conducted to react an argillaceous sandstone of the Hosston Formation with a series of synthetic brines and the Eagle Ford brine for 3 weeks at 193 bar and 80 °C. To better identify mineral dissolution and precipitation, rock samples were ion-milled and examined using scanning electron microscopy (SEM) before and after the experiments. For each experiment, approximately 15 aqueous samples were taken with increasing time intervals from hours to days. Dissolution of anhydrite, which results in a rapid increase of SO4 and Ca concentrations in the solution of ∼500 ppm and ∼200 ppm respectively, is the most significant reaction. Small amounts of dolomite and K-feldspar were also dissolved to release Mg, Ca, K, and Si. Small amounts of iron hydroxides and kaolinite precipitated. Geochemical modeling is able to reproduce the behavior of the major aqueous components and of the observed mineral dissolution and precipitation. Overall, change in flow properties from the water–rock interaction is insignificant: mercury intrusion capillary pressure (MICP) data show little difference in porosity, permeability, and pore-throat-size distribution between the pre- and post-experiment samples. This study suggests that injection of Eagle Ford brine into the Hosston Formation will pose minimum risks for the brine disposal operation.

Dissolution of altered tuffaceous rocks under conditions relevant for CO2 storage

We conducted CO2–water–rock interaction experiments to elucidate the dissolution characteristics and geochemical trapping potential of three different altered andesitic to rhyolitic tuffaceous rocks (Tsugawa, Ushikiri and Daijima tuffaceous rock) relative to fresh mid-ocean ridge basalt. The experiments were performed under 1MPa CO2 pressure to reproduce the water–rock–CO2 interactions in CO2 storage situations. Basalt showed high acid neutralization potential and rapid dissolution of silicate minerals. Two of the tuffaceous rocks (Ushikiri and Daijima) showed relatively high solubility trapping potential, mainly due to the dissolution of carbonate minerals in the andesitic Ushikiri tuffaceous rock and the ion-exchange reaction with zeolite minerals in the rhyolitic Daijima tuffaceous rock. The mineral trapping potential of the Ushikiri tuffaceous rock was found to be relatively high, due to the rapid dissolution of Mg- and Ca-bearing silicate minerals. Our experimental results suggest that regions of porous and andesitic tuffaceous rock hold global promise as CO2 storage sites.

Characteristics and genesis of mineral water from Changbai Mountain, Northeast China

Mineral water from Changbai Mountain is the main source of drinking water, and a major component of the economy, in Jingyu County, Jilin Province, Northeast China. In this study, the hydrochemical characteristics of 18 mineral springs are examined. Mineral water samples from each of these springs were collected and analysed for major anions and cations, electrical conductivity and pH. Results showed that the ion concentrations were low, suggesting that there is minimal influence from anthropogenic activities. Silica and strontium were the dominant components of the water. The mineral water is classified as a silicate type. The type of mineral water is Ca2++Mg2+–HCO3 −. Mineral water ages ranged from 11 to 61 years, which indicate that the mineral water circulation is local. Rocks in the area mainly consist of olivine, albite, anorthite, pyroxene and potassium feldspar. Geochemical modelling showed that they are undersaturated with respect to olivine, albite, anorthite, pyroxene, fluorite and strontianite. Olivine, albite, anorthite, pyroxene and potassium feldspar dissolved in the water–rock interaction experiments. Hydrochemical elements are produced by water–rock interactions: silica is produced from olivine, albite, anorthite and pyroxene, and strontium is produced by strontianite. CO2 is beneficial for silicate and strontium formation.

Geochemometric modeling and geothermal experiments of Water/Rock Interaction for the study of alkali-feldspars dissolution

Water/Rock Interaction (WRI) experiments, Na–K geothermometry and geochemometrics modeling have been used for the study of the kinetic behavior of the volcanic rock dissolution under geothermal conditions. Ionic exchange reactions between Na–K and alkaline-feldspar minerals were monitored at 90 °C and 150 °C for a period of nearly 24 and 3 months, respectively. Na/K ratios (inferred from WRI experiments and Na–K geothermometers) and reaction times were used for estimating the most probable quasi-steady state conditions.A geochemometrics modeling was also performed to predict the reaction times required to achieve quasi-steady state conditions in the WRI experiments. This modeling was validated with WRI experimental data reported in the literature for which quasi-steady state conditions were known with accuracy. New WRI experiments were additionally carried out using batch reactors under controlled pressure and temperature conditions. Volcanic rock (basalt and dacites) crushed samples (500–1000 μm grain size) were reacted with distilled water at 90 °C and 150 °C using a W/R mass ratio of 5. Rock and fluid samples were collected and analyzed for major composition, before and after each experiment. The experimental results were subsequently used to calculate log(Na/K) values for describing the kinetic behavior of the alkaline-feldspar mineral dissolution. Values of log(Na/K) and reaction time at quasi-steady state conditions were reproduced with good accuracy by using the rational polynomial and logarithmic transformation regression models. These results were compared with those values inferred from the Na–K geothermometry, which theoretically assume deep geothermal equilibrium conditions.

Experimental investigation of CO 2-rich fluids production in a geothermal area: The Mt Amiata (Tuscany, Italy) case study

Water–rock interaction experiments have been performed to investigate the production of CO 2-rich gas in the deep reservoir of the geothermal system of Mt Amiata (Italy) through the interaction between a natural phyllite sample (coming from 1115 m below ground level and considered representative of the deep reservoir) and a coexisting fluid phase. Experiments were conducted with an externally heated pressure vessel, a chamber furnace and a stirred micro-reactor at 300 °C and at P up to 35 MPa, using different solid/liquid ratios, and also under nominally anhydrous conditions. Experimental results show that CO 2-rich gases containing variable amount of CO, CH 4 and other aliphatic and aromatic hydrocarbons were produced by fluid–rock interaction. Compositional data of the gas, coupled with solid residua characterization, show that thermal decomposition of magnesian siderite in phyllite is the process responsible for the gas genesis. This process is particularly effective when aqueous solutions interact with phyllite and it may represent the thermometamorphic reaction mainly responsible of the production of CO 2-rich gas under hydrothermal conditions similar to those of the main reservoir in the Mt Amiata geothermal area.

Evolution of fluid chemistry in quartz compaction systems: Experimental investigations and numerical modeling

The evolution of fluid chemistry in compacting rock is controlled by coupled chemical processes and rock deformation. In order to characterize this evolution, we conducted water–rock interaction experiments using quartz aggregates at 150 °C and effective pressure of 34.5 MPa. A coupled fluid flow, chemical reaction, and creep compaction model is developed, in which both free-surface reaction and grain-contact dissolution are considered as system volume and porosity evolve. The direct experimental measurement and numerical modeling indicate that effective pressure has significant effects on pore-fluid chemistry. At the early stages of compaction, pore fluids are supersaturated with respect to bulk quartz. With increasing compaction and time, solute concentrations gradually decrease to saturated conditions. Supersaturation is caused mainly by dissolution of ultrafines and high-energy, unstable surfaces which are produced by stress concentrations at grain contacts during the very early stages of compaction. Grain-contact dissolution also contributes to the solute increase in pore fluid in the early stage of compaction, but the effect is small compared to that of ultrafines and unstable surfaces and only slight supersaturation can be produced by it. The gradual decrease in pore-fluid concentration is related to the mechanical removal of ultrafines by pore-fluid flow and the dissolution of ultrafines and unstable surfaces. It also results from the lessening of grain-contact dissolution. Pore fluids in compacting sedimentary basins of quartz sandstone are nearly saturated throughout most of diagenetic processes. Ultrafines and unstable surfaces produced by stress appear not to be the major sources of quartz cement.

Diurnal hydrological – physicochemical controls and sampling methods for minor and trace elements in an Alpine glacial hydrological system

Summary We present diurnal (i) 0.45 and 0.1 μm pore-size filtered and (ii) operationally defined labile particulate-associated major, minor and trace element concentrations and fluxes in glacial outflow waters draining Haut Glacier d’Arolla, Switzerland. We use speciation modelling (PHREEQCi) and water-suspended sediment interaction experiments are utilised under conditions analogous to the subglacial channellised hydrological system, in order to assess controls on, and the most suitable sampling methods to investigate short-term variations in the mode of major, minor and trace element species export from a glacierised headwater catchment. 0.45 μm pore-size filtered major ions, Sr and U are exported in glacial outflow waters predominately as mobile monovalent or divalent ions or as carbonate complexes, and are controlled by hydrological variations over diurnal cycles, exhibiting an inverse concentration with increasing meltwater discharge. Conversely, 0.45 μm pore-size filtered concentrations of most minor and trace elements (e.g. Fe, Mn, Co, Ba and Pb) exhibit variations that are not strongly inter-correlated with meltwater discharge or suspended sediment concentrations (SSC) over diurnal periods. The use of 0.45 and 0.1 μm pore-size filter membranes indicates that significant colloidal material is not passing through the 0.45 μm pore-size filters, and these unsystematic variations are not a result of colloid measurement. Speciation modelling applied to meltwaters and observations during water–rock interaction experiments suggest that these unsystematic temporal variations reflect physicochemical controls. This includes sorption, and the oversaturation and precipitation of Fe and Al (oxi)hydroxides, and the co-precipitation of other species. Diurnal pH variations appear important in controlling such short-term physicochemical controls, which limits such species use for hydrological investigations. The percentage of total elemental fluxes exported as the labile particulate-associated flux (%PAF) for each minor and trace element changes dramatically between and during the diurnal cycles, reflecting species-specific sensitivity to hydrological and physicochemical controls. Hydrological interpretations of hydrochemical data must be made carefully when using chemical determinations by ICP-MS, since we demonstrate that measurements will comprise of any material that passes through the filter. This can lead to higher concentration measurements than if determined by ion chromatography, which measures truly ionic dissolved species.