Speciation and Kinetics of Trihalomethane Formation in Drinking Water in Mexico

Water chlorination continues to be one of the most common water disinfection processes, especially in developing countries. When natural organic matter (NOM) is present, the process produces disinfection by-products (DBPs), some of them being trihalomethanes (THMs). This study determined the presence, speciation, and kinetics of THMs formation in the water supply for the northern area of the city of Toluca, Mexico. The results show that the concentrations of THMs are below the maximum allowable limits of 200 μg/L in accordance with NOM-127-SSA1-1994. Regarding THMs speciation, the presence of chloroform was more frequently observed in domestic water; furthermore, in one sample in which bromoform was present, it dominated over the chlorine species. Regarding the kinetics of THMs formation, a maximum concentration of THMs (THMs_Max) of 13.02 μg/L was obtained, and the time required to reach 50% THMs_Max ( t ₅₀) was 39.45 min.     

Generation of Hydrogen Gas as a Result of Drilling Within the Saturated Zone

Hydrogen gas was discovered within the steel casing above standing water in a percussion-drilled borehole on the Hanlord Site in south-central Washington state. In situ measurements of the borehole fluids indicated anoxic, low-Eh (<-400 mV) conditions. Ground water sampled from adjacent wells in the same formation indicated that the ground water was oxygenated. H₂ was generated during percussion drilling, due to the decomposition of borehole waters as a result of aqueous reactions with drilled sediment and steel from the drilling tools or casing. The generation of H₂ within percussion-drilled boreholes that extend below the water table may be more common than previously realized. The ambient concentration of H₂ produced during drilling was limited by microbial activity within the casing-resident fluids. H₂ was generated abiotically in the laboratory, whereby sterilized borehole slurry samples produced 100 times more H₂ than unsterilizcd samples. It appears that H₂ is metabolized by microorganisms and concentrations might be significantly greater if not for microbial metabolism.     

Contamination from Sand-Bentonite Seal in Monitoring Wells Installed in Aquitards

A six year field experiment has shown that a sand-bentonite mixture used to seal monitoring wells in aquitards contributes solutes to the ground water sampled from these wells. Monitoring wells were installed at field sites with hydraulic conductivity (K) ranging from 5 × 10 ^-9 m/s to 3 × 10¹¹ m/s. In most cases the boreholes remained dry during installation which allowed the placement of a dry powdered bentonite/sand mixture tagged with potassium bromide (KBr) to seal and separate sampling points. Over six years, wells were sampled periodically and ground-water samples were analyzed for Br and Cl and other major ions. Typical Br results ranged from 10 mg/1 to 35 mg/1 in the first 700 days, as compared to an estimated initial concentration in the seal material of about 75 mg/1. After six years the bromide concentrations had decreased to between 3 mg/1 and 5 mg/1. The total mass of Br removed in six years is less than 50% of that placed; therefore the contamination effects, although considerably diminished, persist. The trends of Br, Cl, Na, and SO₄ indicate that varying degrees of contamination occur. These data show that the materials used to seal monitoring wells in aquitards can have a significant and long-lasting impact on the chemistry of the water in the wells.     

Vulnerability of a public supply well in a karstic aquifer to contamination

To assess the vulnerability of ground water to contamination in the karstic Upper Floridan aquifer (UFA), age-dating tracers and selected anthropogenic and naturally occurring compounds were analyzed in multiple water samples from a public supply well (PSW) near Tampa, Florida. Samples also were collected from 28 monitoring wells in the UFA and the overlying surficial aquifer system (SAS) and intermediate confining unit located within the contributing recharge area to the PSW. Age tracer and geochemical data from the earlier stage of the study (2003 through 2005) were combined with new data (2006) on concentrations of sulfur hexafluoride (SF₆), tritium (³H), and helium-3, which were consistent with binary mixtures of water for the PSW dominated by young water (less than 7 years). Water samples from the SAS also indicated mostly young water (less than 7 years); however, most water samples from monitoring wells in the UFA had lower SF₆ and ³H concentrations than the PSW and SAS, indicating mixtures containing high proportions of older water (more than 60 years). Vulnerability of the PSW to contamination was indicated by predominantly young water and elevated nitrate-N and volatile organic compound concentrations that were similar to those in the SAS. Elevated arsenic (As) concentrations (3 to 19 μg/L) and higher As(V)/As(III) ratios in the PSW than in water from UFA monitoring wells indicate that oxic water from the SAS likely mobilizes As from pyrite in the UFA matrix. Young water found in the PSW also was present in UFA monitoring wells that tap a highly transmissive zone (43- to 53-m depth) in the UFA.     

Delayed impact of new volcanic ejecta on ground water quality

We observed long-term changes in the concentrations of dissolved ions in ground water caused by leachate from new volcanic ejecta deposited on the ground surface of the volcanic Miyakejima Island, Japan. Water samples were collected from nine wells and two rain collectors over a period of more than 10 years, and samples of runoff water were collected periodically. The samples were analyzed for temperature, pH, alkalinity, Cl⁻, and SO₄²⁻; some of the samples were also analyzed for δ¹³C. Because the leachate from the volcanic ejecta contained sulfate, we recorded an increase in SO₄²⁻ concentrations in the (unconfined) well water. The increase in SO₄²⁻ was initially detected between less than 1.4 and 5.2 years after the eruption, showing peak concentrations from 2.4 to 6.4 years after the eruption. This delayed response reflects the transit time of downward-moving SO₄²⁻ in the vadose zone, corresponding to an apparent movement rate of 0.4 to 7.2 cm/d. The rate relates to the mean recharge, represented as a fraction of local mean rainfall, and is calculated using the Cl⁻ balance method. The magnitude of the recorded increases reflects the volume of volcanic mudflow on the ground surface within the basin. For the management of ground water after an eruption, it is therefore important to know the chemical properties of the volcanic ejecta and the spatial distribution of mudflow to estimate the magnitude of the effect of ejecta on ground water quality.     

Nitrate Source Identification Using δ15N in a Ground Water Plume Near an Intensive Swine Operation

Nitrate-contaminated ground water beneath and adjacent to an intensive swine ( Sus scrofa domesticus ) production facility in the Middle Coastal Plain of North Carolina was analyzed for δ¹⁵N of nitrate (δ¹⁵N-NO₃). Results show that the isotopic signal of animal waste nitrogen is readily identifiable and traceable in nitrate in this ground water. The widespread land application of animal wastes from intensive livestock operations constitutes a potential source of nitrogen contamination to natural water throughout large regions of the United States and other countries. The site of the present study has been suspected as a nitrate contamination source to nearby domestic supply wells and has been monitored for several years by government and private water quality investigators through sampling of observation wells, ditches, and streams. δ¹⁵N of nitrate allowed direct identification of animal waste-produced nitrate in 11 of 14 wells sampled in this study, as well as recognition of nitrate contributions from non-animal waste agricultural sources in remaining wells.     

Hydrogen Peroxide Treatment of Septic Systems and Its Negative Effects on Shallow Ground Water

Soil-solution samplers and shallow ground water monitoring wells were utilized to monitor nitrate movement to ground water following H₂O₂ application to a clogged soil absorption system. Nitrate-nitrogen concentrations in soil water and shallow ground water ranged from 29 to 67 mg/L and 9 to 22 mg/L, respectively, prior to H₂O₂ treatment. Mean nitrate-nitrogen concentrations in soil water and ground water increased and ranged from 67 to 115 mg/L and 23 to 37 mg/L, respectively, one week after H₂O₂ application. Elevated concentrations of nitrate-nitrogen above background persisted for several weeks following H₂O₂ treatment. The H₂O₂ treatment was unsuccessful in restoring the infiltrative capacity of a well-structured soil. Application of H₂O₂ to the soil absorption system poses a threat of nitrate contamination of ground water and its usefulness should be fully evaluated before rehabilitation is attempted.     

Fate of MTBE Relative to Benzene in a Gasoline-Contaminated Aquifer (1993–98)

Methyl tert -butyl ether (MTBE) and benzene have been measured since 1993 in a shallow, sandy aquifer contaminated by a mid-1980s release of gasoline containing fuel oxygenates. In wells downgradient of the release area, MTBK was detected before benzene, reflecting a chromatographic-like separation of these compounds in the direction of ground water flow. Higher concentrations of MTBE and benzene were measured in the deeper sampling ports of multilevel sampling wells located near the release area, and also up to 10 feet (3 m) below the water table surface in nested wells located farther from the release area. This distribution of higher concentrations at depth is caused by recharge events that deflect originally horizontal ground water flowlines. In the laboratory, microcosms containing aquifer material incubated with uniformly labeled ¹⁴C-MTBE under aerobic and anaerobic. Fe(III)-reducing conditions indicated a low but measurable biodegradation potential (<3%¹⁴C-MTBW as ¹⁴CO₂) after a seven-month incubation period, Tert -butyl alcohol (TBA), a proposed microbial-MTBE transformation intermediate, was detected in MTBE-contaminated wells, but TBA was also measured in unsaturated release area sediments. This suggests that TBA may have been present in the original fuel spilled and does not necessarily reflect microbial degradation of MTBE. Combined, these data suggest that milligram per liter to microgram per liter decreases in MTBE concentrations relative to benzene are caused by the natural attenuation processes of dilution and dispersion with less-contaminated ground water in the direction of flow rather than biodegradation at this point source gasoline release site.     

Field vs. Lab Alkalinity and pH: Effects on Ion Balance and Calcite Saturation Index

Ground water samples for a hydrochemical investigation were collected from 92 observation wells completed in a shallow, unconfined aquifer in southeastern North Dakota. The samples showed predominantly an increase in HCO₃- (positive bias) and both a pH decrease (positive bias) and a pH increase (negative bias) from field to lab. Positive pH bias generally was associated with ground water characterized by dissolved-solids concentrations less than 400 mg/L. Negative pH bias generally was associated with ground water characterized by dissolvedsolids concentrations greater than 400 mg/L.
Observed HCO₃- bias from field to lab slightly distorted ion balance distribution. Excess anions greater than 2 percent generally corresponded to increased HCO₃- from field to lab.
Observed HCO₃- and pH bias significantly distorted the distribution of calcite saturation indices. Samples with dissolved-solids concentrations less than 400 mg/L that generally showed a positive pH bias had a mean change in calcite saturation index of -0.214 (toward undersaturation). Samples with dissolved-solids concentrations greater than 400 mg/L that generally showed a negative pH bias had a mean change in calcite saturation of +0.132 (toward over saturation).
Calcite saturation indices were much more sensitive to observed pH bias than to observed HCO₃- bias. Linear regression analysis indicates % percent of the variability in calcite saturation index change from field to lab is attributed to change in pH from field to lab. Field pH should be used to compute calcite saturation index.     

Long-term trends in chloride concentrations in shallow aquifers near Chicago

The rapid expansion of major cities throughout the world is resulting in the degradation of water quality in local aquifers. Increased use of road deicers since the middle of the 20th century in cities in the northern United States, Canada, and Europe has been linked to degraded ground water quality. In this article, Chicago, Illinois, and its outlying suburban areas are used as an example of the effects of urbanization in a historical context. A statistical study of historical water quality data was undertaken to determine how urbanization activities have affected shallow (<60 m) ground water quality. Chloride (Cl⁻) concentrations have been increasing, particularly in counties west and south of Chicago. In the majority of shallow public supply wells in the western and southern counties, Cl⁻ concentrations have been increasing since the 1960s. About 43% of the wells in these counties have rate increases greater than 1 mg/L/year, and 15% have increases greater than 4 mg/L/year. Approximately 24% of the samples collected from public supply wells in the Chicago area in the 1990s had Cl⁻ concentrations greater than 100 mg/L (35% in the western and southern counties); median values were less than 10 mg/L before 1960. The greater increase in Cl⁻ concentrations in the outer counties is most likely due to both natural and anthropogenic factors, including the presence of more significant and shallower sand and gravel deposits, less curbing of major highways and streets, and less development in some parts of these counties.     

Urban Ground Water Pollution: A Case Study in Cuttack City, India

A large number of ground water samples (360) was collected from 60 stations over six consecutive seasons to study the influence of the main sewerage drain on shallow ground water table beneath the municipal area of Cuttack, India. A majority of the samples collected from stations close to the drain exceeded the maximum permissible limits set by the World Health Organization (WHO). Almost all the samples near the drain exceeded the WHO limit for NO₃^- and Na⁺. However, the concentrations decreased as the distance from the drain increased. The winter season registered the maximum concentrations of NH₄⁺, NO₃^-, and SO₄^2- ions whereas the minimum values always coincided with the rainy season. R-mode factor analysis was conducted to find relationships amongst the 16 chemical parameters studied. Fluoride showed a negative correlation with Cl^-, Na⁺, NO₃^-, SO₄^2-, and PO₄^3-. The concentration of F^- may be lower in raw waste water than naturally occurs in the ground water. Therefore, a decrease in the concentration of F^- near the drain may be attributed to dilution by contributions of waste water to the ground water. The rest of the parameters were found to be directly related to the distance of collection points to the sewerage. The distribution of nutrients is strongly affected by leaching of waste water into the ground water.     

Tracing coalbed natural gas-coproduced water using stable isotopes of carbon

Recovery of hydrocarbons commonly is associated with coproduction of water. This water may be put to beneficial use or may be reinjected into subsurface aquifers. In either case, it would be helpful to establish a fingerprint for that coproduced water so that it may be tracked following discharge on the surface or reintroduction to geologic reservoirs. This study explores the potential of using δ¹³C of dissolved inorganic carbon (DIC) of coalbed natural gas (CBNG)–coproduced water as a fingerprint of its origin and to trace its fate once it is disposed on the surface. Our initial results for water samples coproduced with CBNG from the Powder River Basin show that this water has strongly positive δ¹³C_DIC (12‰ to 22‰) that is readily distinguished from the negative δ¹³C of most surface and ground water (−8‰ to −11‰). Furthermore, the DIC concentrations in coproduced water samples are also high (more than 100 mg C/L) compared to the 20 to 50 mg C/L in ambient surface and ground water of the region. The distinctively high δ¹³C and DIC concentrations allow us to identify surface and ground water that have incorporated CBNG-coproduced water. Accordingly, we suggest that the δ¹³C_DIC and DIC concentrations of water can be used for long-term monitoring of infiltration of CBNG-coproduced water into ground water and streams. Our results also show that the δ¹³C_DIC of CBNG-coproduced water from two different coal zones are distinct leading to the possibility of using δ¹³C_DIC to distinguish water produced from different coal zones.     

Sources of Ground Water Salinization in Parts of West Texas

Abstract
Determination of chemical constituent ratios allows distinction between two salinization mechanisms responsible for shallow saline ground water and vegetative-kill areas in parts of west Texas. Mixing of deep-basin (high Cl) salt water and shallow (low Cl) ground water results in saline waters with relatively low Ca/Cl, Mg/Cl, SO₄4/ Cl, Br/Cl, and NO₃/Cl ratios. In scattergrams of major chemical constituents vs. chloride, plots of these waters indicate trends with deep-basin brines as high Cl end members. Evaporation of ground water from a shallow water table, in contrast, results in saline water that has relatively high Ca/Cl, Mg/Cl, SO₄/Cl, and Br/CL ratios. Trends indicated by plots of this water type do not coincide with trends indicated by plots of sampled brines. Leaching of soil nitrate in areas with a shallow water table accounts for high NO₃ concentrations in shallow ground water.     

Assessment of Water Quality After 10 Years of Reclaimed Water Injection: The Nardò Fractured Aquifer (Southern Italy)

Experimental studies have been carried out in a fractured coastal aquifer of the Salento region (Nardò, Italy), which has been subjected to 12,000 m³/day of treated municipal waste water injected into a natural sinkhole since 1991. The analytical parameters of ground water sampled in 30 monitoring wells in the area down gradient from the sinkhole, taking into account the direction of ground water flow, have been compared before and after injection. The water table mound (1.5 m), the reduction of sea water extent (2 km), and the spreading of injected pollutants were evaluated by means of a mathematical model. The predicted values in the monitoring wells were adjusted to inorganic nitrogen biodegradation using transformation rates developed in laboratory tests. After 10 years, the injection has increased the volume of the available resource for agricultural and drinking water use, without any notable decrease in the preexisting ground water quality. Moreover, to preserve water resources from pollution, the mathematical model allowed the maximum constituent concentrations (standards) in waste water reclamation for recharge to be identified. A precautionary area around the sinkhole was also defined so that withdrawal prohibition could be implemented to avoid risks to human health.     

Effect of Various Materials in Multilevel Samplers on Monitoring Commonly Occurring Agrichemicals in Ground Water

Studies have shown that materials, such us polytetra-fluoroethylene (PTFE), rigid polyvinyl chloride (rigid PVC). flexible polyvinyl chloride (flexible PVC), stainless steel (SS). low-density polyethylene (LDPE), and high-density polyethylene (HDPE), have the potential to influence certain analyte concentrations in ground water samples. The effects of HDPE, LDPE, PTFE, rigid PVC, and SS on aqueous concentrations of nitrate-N, atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) were evaluated in a field study A laboratory study was conducted to evaluate sorption of atrazine DEA, DIA, cyanazine, alachlor, metolachlor, and butachlor to PTFE, HDPE, and SS materials. Butachlor is rarely use in the United States, but was included because of its expected high sorptivity. No significant differences between HDPE, LDPE, PTFE, rigid PVC, and SS were determined for any of the analytes tested in the field study. In the laboratory study, sorption of DIA to PTFE and SS was significant at 2.6 × 10⁻⁵ and 4.1 × 10⁻⁵μg/m² respectively. Sorption of DIAA to HDPE was not significantly > 0 sorption of all other compounds to HDPE, PTFE, and SS were also not significantly >0. Results of the two studies indicate that for these analytes (relatively polar or ionized compounds), representative ground water samples are not dependent on the materials used for multilevel sampler construction. When considering these compounds, it appears that the least expensive materials (HDPE, rigid PVC, and LDPE) are good choices for the construction of ground water monitoring wells.     

Monitoring the Removal of Phosphate from Ground Water Discharging through a Pond-Bottom Permeable Reactive Barrier

Installation of a permeable reactive barrier to intercept a phosphate (PO₄) plume where it discharges to a pond provided an opportunity to develop and test methods for monitoring the barrier's performance in the shallow pond-bottom sediments. The barrier is composed of zero-valent-iron mixed with the native sediments to a 0.6-m depth over a 1100-m² area. Permanent suction, diffusion, and seepage samplers were installed to monitor PO₄ and other chemical species along vertical transects through the barrier and horizontal transects below and near the top of the barrier. Analysis of pore water sampled at about 3-cm vertical intervals by using multilevel diffusion and suction samplers indicated steep decreases in PO₄ concentrations in ground water flowing upward through the barrier. Samples from vertically aligned pairs of horizontal multiport suction samplers also indicated substantial decreases in PO₄ concentrations and lateral shifts in the plume's discharge area as a result of varying pond stage. Measurements from Lee-style seepage meters indicated substantially decreased PO₄ concentrations in discharging ground water in the treated area; temporal trends in water flux were related to pond stage. The advantages and limitations of each sampling device are described. Preliminary analysis of the first 2 years of data indicates that the barrier reduced PO₄ flux by as much as 95%.     

A Field Test of Electromigration as a Method for Remediating Sulfate from Shallow Ground Water

Eloctromigraiion offers a potential tool for remediating ground water contaminated with highly soluble components, such as Na⁺, Cl, NO₃ and SO₄⁻. A field experiment was designed to lest the efficacy of electromigration for preconcontrating dissolved SO₄² in ground water associated with a fossil-fuel power plant. Two shallow wells, 25 feel apart (one 25 feel deep, the other 47 feet deep), were constructed in the upper portion of an unconfined alluvial aquifer. The wells were constructed with a double-wall design, with an outer casing of 4-inch PVC and an inner lube of 2-inch FVC; both were fully slotted (0.01 inch). Electrodes were constructed by wrapping the inner lulling with a 100-foot length of rare-earth metal oxide/copper wire. An electrical potential of 10.65 volts DC Was applied, and tests were run for periods of 12, 44, and 216 hours. Results showed large changes in the pH from the initial pH of ground water of about 7.5 to values of approximately 2 and 12 at the anode and cathode, respectively. Despite the fact that the test conditions were far from ideal, dissolved SO₄^2-; was significantly concentrated at the anode. Over a period of approximately nine days, the concentration of SO₄^2- at the anode reached what appeared to he a steady-state value of 2200 mg/L. compared lo the initial value in ground water of approximately 1150 mg/L. The results of this field lest should encourage further investigation of electromigration as a tool in the remediation of contaminated ground water.     

Groundwater Sampling at ISCO Sites: Binary Mixtures of Volatile Organic Compounds and Persulfate

In situ chemical oxidation involves the introduction of a chemical oxidant into the subsurface for the purpose of transforming groundwater contaminants into harmless by‐products. Owing to oxidant persistence, groundwater samples collected at hazardous waste sites may contain both the contaminant(s) and the oxidant in a “binary mixture.” Binary mixtures composed of sodium persulfate (2.5 g/L; 10.5 mM) and volatile organic compounds (VOCs) (benzene, toluene, m‐xylene, perchloroethylene, trichloroethylene) were analyzed to assess the impact on the quality of the sample. A significant decline (49 to 100%) in VOC concentrations was measured in binary mixtures using gas chromatography (GC) purge and trap, and GC mass spectroscopy headspace methods. Preservation of the binary mixture samples was achieved through the addition of ascorbic acid (99 to 100% VOC average recovery). High concentrations of ascorbic acid (42 to 420 mM) did not interfere in the measurement of the VOCs and did not negatively impact the analytical instruments. High concentrations of ascorbic acid favored the reaction between persulfate and ascorbic acid while limiting the reaction between persulfate and VOCs. If an oxidant is detected and the binary sample is not appropriately preserved, the quality of the sample is likely to be compromised.     

Comparison of Two Integrated Methods for the Collection and Analysis of Volatile Organic Compounds in Ground Water

The principal difficulties with determinations of volatile organic compounds (VOCs) in ground water are the reliability of sampling procedures and analytical methods. Two integrated methods have been developed for routine sampling, processing, and analysis of VOCs in ground water. These methods involve in situ collection of ground water using a modified syringe sampler from PVC piezometers or using dedicated glass syringes from stainless steel multilevel bores. The samples are processed in the syringe using purge and trap or microsolvent extraction and analyzed by GC/MSD.
The modified purge-and-trap method is time-consuming and limited to volatile organic compounds. However, it is extremely sensitive and flexible: the volume of sample used can be varied by the use of different-size glass syringes (sample volumes from 1 to 100 mL).
In cases where extremely low sensitivity (<10 mg 1⁻¹) is not critical, the microextraction technique is a more cost-effective method, allowing twice as many samples to be analyzed in the same time as the purge-and-trap method. It enables less volatile compounds such as polynuclear aromatic hydrocarbons, phenol, and cresols to be analyzed in the same GC run. Also, the microextraction method can be used in the field to avoid delays associated with transportation of ground water samples to the laboratory.     

Analysis of Nitrate-Nitrogen Movement Near High-Capacity Irrigation Wells

AGalerkin finite-element model coupled with a particle tracking routine was developed to analyze the flow and transport dynamics near a high-capacity irrigation well. The model was used to compute the head distribution around the pumping well, to determine the area of influence, and to define ground water flowlines during short-term pumping periods typical of those used to collect water quality samples from high-capacity wells. In addition to hypothetical example results, the model was used to qualitatively analyze data obtained from pump-and-sample experiments conducted in an unconfined alluvial aquifer within the Platte River valley of south-central Nebraska where nitrate-nitrogen (NO₃-N) contamination is prevalent.
Simulation results of both the hypothetical and field cases suggest that short-term pumping events, impact a limited volume of aquifer. The area of influence and flowlines are affected by aquifer anisotropy, pumping rate, and well construction characteristics). Ground water above or below the screened intervals does not enter a partially penetrating well in anisotropic aquifers. In aquifers where NO₃-N concentration varies vertically and horizontally, waler quality samples from an irrigation, or other high-capacity, well provide only limited information about ground water contamination. A numerical model is thus recommended for calculating the area of influence and determining flowlines around high-capacity wells so that information derived from water quality samples collected at the wellhead can be better interpreted.