Regional Groundwater Quality Research Articles

Assessment of hydrogeochemical characteristics of groundwater in shrimp farming areas in coastal Tamil Nadu, India

Brackishwater aquaculture is basically farming in coastal region, and it utilizes the saline water from either sea or estuary or creek. Assessment of hydrogeochemisty of groundwater resources in shrimp farming areas is very much required not only for monitoring the shrimp farming impacts, but also to suggest better management strategies for the long-term sustainability of shrimp farming and integrated water resources management in coastal regions. Watershed-based assessment is ideal as watershed is a geohydrological unit, and it will give the realistic and cumulative effects more precisely. With this background, the present investigation was carried out to evaluate the geochemical process regulating groundwater quality in shrimp farming areas of coastal miniwatersheds of Vellar and Coleroon river, Cuddalore district, Tamil Nadu, along the east coast of India. Representative groundwater (29) samples from shallow aquifer (hand pump and open well) were collected periodically (June 2008, January 2009, April 2009 and July 2009) using the simple random sampling method and analyzed for various water quality parameters viz. pH, TDS, total hardness, alkalinity, cations (Ca+, Mg+, Na+) and anions (Cl−, SO4 −, NO3 −, HCO3 −). The groundwater data indicated that the HCO3 was the dominant ion in the study area with sodium (Na > Ca > Mg) and bicarbonate (HCO3 > Cl > SO4) as the predominant cation and anion, respectively. The large variations in mean and standard deviation of ionic concentration suggest that the water chemistry in the study region was not homogenous and may be influenced by complex sources for the hydrogeochemical processes. The piper trilinear diagram depicts the status of the groundwater quality and also suggests that the cation exchange and mineral dissolution was responsible for this elevated ionic composition at some locations in the study area. The multivariate statistical analysis viz., principal component analysis and cluster analysis clearly elucidated that the groundwater quality in the area is mainly due to natural process and the shrimp farming is not an influencing factor.

Groundwater quality and management in arid and semi-arid regions: Case study, Central Eastern Desert of Egypt

This study presents a model budget for groundwater in the Central Eastern Desert of Egypt. The stable isotopic composition and hydrochemistry of groundwater samples collected from different aquifers were determined to identify recharge sources and water quality. Stable isotopic values suggest that shallow alluvial and fracture zone aquifers are recharged from seasonal precipitation, while groundwater in deeper sedimentary sub-basins is paleowater that was recharged during periods of less arid regional climate. Hydrochemical analysis indicates elevated salinity in each aquifer type, which is attributed to leaching and dissolution of terrestrial salts and to mixing with marine water. Groundwater from sedimentary sub-basin aquifers can be treated and used for drinking and domestic purposes. Groundwater from shallow alluvial and fracture zone wells is suitable for animal husbandry and mineral ore dressing. A model water budget shows that approximately 4.8×109m3 of recoverable groundwater is stored in sedimentary sub-basin aquifers, or approximately 550years of water at present utilization rates.

Source apportionment of groundwater pollutants in Apulian agricultural sites using multivariate statistical analyses: case study of Foggia province

BackgroundGround waters are an important resource of water supply for human health and activities. Groundwater uses and applications are often related to its composition, which is increasingly influenced by human activities.In fact the water quality of groundwater is affected by many factors including precipitation, surface runoff, groundwater flow, and the characteristics of the catchment area. During the years 2004-2007 the Agricultural and Food Authority of Apulia Region has implemented the project “Expansion of regional agro-meteorological network” in order to assess, monitor and manage of regional groundwater quality. The total wells monitored during this activity amounted to 473, and the water samples analyzed were 1021. This resulted in a huge and complex data matrix comprised of a large number of physical-chemical parameters, which are often difficult to interpret and draw meaningful conclusions. The application of different multivariate statistical techniques such as Cluster Analysis (CA), Principal Component Analysis (PCA), Absolute Principal Component Scores (APCS) for interpretation of the complex databases offers a better understanding of water quality in the study region.ResultsForm results obtained by Principal Component and Cluster Analysis applied to data set of Foggia province it’s evident that some sampling sites investigated show dissimilarities, mostly due to the location of the site, the land use and management techniques and groundwater overuse. By APCS method it’s been possible to identify three pollutant sources: Agricultural pollution 1 due to fertilizer applications, Agricultural pollution 2 due to microelements for agriculture and groundwater overuse and a third source that can be identified as soil run off and rock tracer mining.ConclusionsMultivariate statistical methods represent a valid tool to understand complex nature of groundwater quality issues, determine priorities in the use of ground waters as irrigation water and suggest interactions between land use and irrigation water quality.

Tracing the sources of strontium in karst groundwater in Chongqing, China: a combined hydrogeochemical approach and strontium isotope

Groundwater quality in karst regions is largely controlled by natural processes and anthropogenic activities. Over the past 10 years, dissolved Sr and its radiogenic isotope, 87Sr/86Sr, were widely used to trace the sources of solutes in groundwater. However, there is little research about hydrogeochemistry and Sr isotopic compositions of the karst groundwater in Chongqing karst area. In this paper, thirty-five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types. Hydrochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO3 type or Ca(Mg)-HCO3 type. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the 87Sr/86Sr varied from 0.70751 to 0.71627. The groundwater samples from different aquifers and land use types showed distinctive dissolved Sr concentrations and 87Sr/86Sr. The very positive relationship between Ca/Sr and Mg/Sr in dolomite and limestone aquifers suggests that Ca, Mg and Sr element come mainly from the release of carbonate rock under the groundwater–rock–CO2 gas interaction. According to the 87Sr/86Sr ratio, the Sr element in karst groundwater in Chongqing was controlled by the weathering of limestone, dolomite and silicate rock (allogenic water in a non-karst area). The relationship 87Sr/86Sr versus Sr2+/[K+ + Na+] shows that the anthropogenic inputs also obviously contribute to the Sr contents. The research results show that the karst groundwater in Chongqing is facing serious crisis of water quality, and needs to be protected further.

Deterioration of coastal groundwater quality in Island and mainland regions of Ramanathapuram District, Southern India

A study was carried out in the Island and mainland regions of Ramanathapuram District to characterize the physico-chemical characteristics of 87 groundwater samples in Island and 112 groundwater samples in mainland which include pH, EC, TDS, salinity, total alkalinity, calcium hardness, magnesium hardness, total hardness, chloride and fluoride. Heavy inorganic load in majority of the groundwater samples has been estimated due to the salinity, TDS, TH and chloride beyond the threshold level which substantiates the percolation of sea water into the freshwater confined zones. Although the groundwater sources are available in plenty, the scarcity of potable water is most prevalent in this coastal area. The Water Quality Index (WQI) and Langeleir Saturation Index (LSI) have also been calculated to know the potable and corrosive/incrusting nature of the water samples. The statistical tools such as principal component analysis, box plots and correlation matrix have also been used to explain the influence of different physico-chemical parameters with respect to one another among the groundwater samples. The percentage of groundwater samples in mainland was more than that in Island with respect to the acceptable limit of WHO drinking standard, especially in TDS, CH, TH and chloride but the converse is observed in the case of fluoride. About 8% of the mainland aquifers and 42% of Island aquifers were identified to have fluoride greater than 1.5 mg/l. The signature of salt-water intrusion is observed from the ratio of Cl/CO(3)(2-) + HCO(3) and TA/TH. A proper management plan to cater potable water to the immediate needs of the people is to be envisaged.

Using electronic conductivity and hardness data for rapid assessment of stream water quality

A graphical screening method was previously developed by Kney and Brandes (2007) for assessing stream water quality data using electronic conductivity (EC) and alkalinity data. The method was aimed at providing citizen scientists involved in stream monitoring programs with a relatively simple way to interpret EC data. The method utilizes a plot of EC against concurrent alkalinity data, and is used to distinguish EC values for impacted or degraded streams from those that can be considered background values in a particular geologic setting. The method performs well in areas underlain by carbonate bedrock, as streams in those areas characteristically have EC values that are strongly correlated with alkalinity. However, in areas of low stream alkalinity (less than approximately 50 mg/L as CaCO(3)), the Kney and Brandes (2007) method was found to be much less effective in identifying impacted streams. This paper extends the graphical screening approach to streams with low alkalinity, specifically regions underlain by clastic sedimentary or crystalline bedrock, by using the strong correlation between EC and total hardness (TH). A baseline relationship of EC vs. TH is developed using surface water chemistry data from Hydrologic Benchmark Network streams (deemed as having minimal anthropogenic impacts) and regional groundwater quality data. The usefulness of the method is demonstrated by application to publicly available stream chemistry data and to field data collected from streams of eastern Pennsylvania under baseflow conditions. Results demonstrate that for streams with alkalinity <75 mg/L as CaCO(3), the TH-based graphical screening method should be used rather than the alkalinity-based method of Kney and Brandes (2007).

Assessing regional groundwater quality and its health implications in the Lokpaukwu, Lekwesi and Ishiagu mining areas of southeastern Nigeria using factor analysis

Unusual occurrence of mental-related illnesses has been reported in the Ishiagu mining area of South Eastern Nigeria and this may be related to the long-term consumption of heavy metal-contaminated groundwater. Groundwater from 27 domestic water sources (mainly open hand dug wells and springs) was therefore sampled within two seasons and analyzed for both physical and chemical parameters. Results were compared with international standards for drinking water and also subjected to factor analysis. The analysis showed that iron has the highest concentration of heavy metals exceeding the WHO-permitted desirable limit of 0.3 mg/l in about 73% of cases. Manganese was ubiquitous in groundwater samples exceeding the EU-permitted limits in about 41% of cases. Zinc, although within acceptable international limits was also common in samples from the Ishiagu central area, the Ayaragu, and the Amaubiri-Lokpauku axis. Lead and cadmium occurred in 3 and 13% of cases, respectively, and was outside international regulatory standards for drinking water. Long-term exposure to manganese and cadmium may therefore be a significant cause of the prevalence of mental related illness in the study area. There is also the possibility of impacts from other elements previously undetected in the groundwater system of the study area (but revealed through factor analysis) including arsenic, vanadium, bromine and fluorite (ide) and this needs urgent investigation. Major factors affecting groundwater quality included mineral dissolution and polluted discharge/recharge from mining operations.

Characterisation of groundwater chemistry in an eastern coastal area of Cuddalore district, Tamil Nadu

The groundwater quality detoriation due to various geochemical processes like saline water intrusion, evaporation and interaction of groundwater with brines is a serious problem in coastal environments. Understanding the geochemical evolution is important for sustainable development of water resources. A detailed investigation was carried out to evaluate the geochemical processes regulating groundwater quality in Cuddalore district of Tamilnadu, India. The area is entirely underlined by sedimentary formations, which include sandstone, clay, alluvium, and small patches of laterite soils of tertiary and quaternary age. Groundwater samples were collected from the study area and analyzed for major ions. The electrical conductivity (EC) value ranged from 962 to 11,824 μS/cm, with a mean of 2802 μS/cm. The hydrogeochemical evolution of groundwater in the study area starts from Mg-HCO 3 type to Na-Cl type indicating the cation exchange reaction along with seawater intrusion. The Br/Cl ratio indicates the evaporation source for the ion. The Na/Cl ratios indicate groundwater is probably controlled by water-rock interaction, most likely by derived from the weathering of calcium-magnesium silicates. The plot of (Ca+Mg) versus HCO 3 suggests ions derived from sediment weathering. The plot of Na+K over Cl reflects silicate weathering along with precipitation. Gibbs plot indicates the dominant control of rock weathering. Factor analysis indicates dominance of salt water intrusion, cation-exchange and anthropogenic phenomenon in the study.

Does road salt affect groundwater in Denmark?

Chloride (Cl) from dissolved salt is a major threat to groundwater quality in many regions of the world. In arid regions near present-day coastlines, where old seawater occurs in deeper sediments and where road salt is frequently used, Cl can be a significant pollutant (European Environmental Agency 2009). European Union member states have recently reported that next to nitrogen, Cl is the most commonly found pollutant and is often responsible for groundwater bodies being at risk or having a poor ecological status (European Commission 2010).

Modeling the effects of agricultural management practices on groundwater in Shelton, USA

An integrated methodology was developed to assess the impact of recharge rates, nitrate leaching from crop root zones, and irrigation pumping rates on groundwater quality and quantity. Monthly values for deep percolation of water, irrigation pumping and leaching of nitrate-nitrogen were calculated with a soilwater-plant model. An Intermediate Vadose Zone Model (IVZM) was developed and used together with models for groundwater flow (MODFLOW) and solute transport (MT3D) to simulate the movement of water and nitrate-nitrogen. The IVZM generates recharge files used by MODFLOW and MT3D. The methodology was applied to an area near the town of Shelton, Nebraska, where a shallow sand-gravel aquifer is highly contaminated by nitrate-nitrogen. MODFLOW was calibrated using historic groundwater level data from 1981 to 1996. Simulation results suggest that concentration reductions of 10% in the upper third of the saturated zone are possible after 10 years of improved irrigation and nitrogen fertilizer management. Groundwater quality changes slowly propagate down-gradient from the field and towards the lower part of the aquifer. A particle tracking technique showed that water from a well does not provide a good indication of the influence of improved management in the adjacent field. The quality of water pumped from a well represents the effect of management over 15 years and from more than 1.5 km up-gradient from the well. Regional groundwater quality depends on local management practices over a long period. Regulatory programs to improve water quality require therefore, widespread adoption and substantial time to provide significant water quality improvements.

Geochemical Processes Regulating Groundwater Quality in Coastal Aquifer in Odawara Region, Kanagawa Prefecture, Japan

Groundwater in the coastal aquifer in the Odawara region, the southern region of the Ashigara plain, is considerably used for industrial, agricultural and municipal water supplies. Since 1980s, many studies focused on the problems of water level decline and groundwater salinization in this region. However, for considering a better management of this groundwater resource, more precise understanding of the geochemical processes occurring in this aquifer and changes in the underground environment due to salinization is necessary. For this purpose, field surveys were carried out in winter (January and February, 2009) and in summer (July and August, 2009). More than 100 groundwater samples were collected from the unconfined and confined aquifers in the region and analyzed for their chemical and stable isotopic compositions. A series of comprehensive interpretations on water quality data using Piper diagram and Stiff diagram together with stable isotopic data have been carried out to gain insight into the spatial and temporal variations of the quality and the geochemical evolution of the groundwater. Several geochemical processes were identified as principal factors controlling the groundwater quality in this region. Silicate weathering which is the result of water rock interaction is an important process dominating unconfined and confined aquifers, over a wide area. The other geochemical processes such as ion exchange reactions and salinization are also occurring in this region. The latter process, salinization, is limited in area but an important phenomenon and seems to be caused by salt water up-coning in the confined aquifer due to the over-extraction of groundwater since 1970s. This phenomenon was detected typically at particularly deep wells in the industrial area near the coast where the pumping rate is high. These phenomena, which occurred in the study region, were summarized in a schematic conceptual model as a helpful tool for the management of the groundwater resources.

Estimation of aquifer scale proportion using equal area grids: Assessment of regional scale groundwater quality

The proportion of an aquifer with constituent concentrations above a specified threshold (high concentrations) is taken as a nondimensional measure of regional scale water quality. If computed on the basis of area, it can be referred to as the aquifer scale proportion. A spatially unbiased estimate of aquifer scale proportion and a confidence interval for that estimate are obtained through the use of equal area grids and the binomial distribution. Traditionally, the confidence interval for a binomial proportion is computed using either the standard interval or the exact interval. Research from the statistics literature has shown that the standard interval should not be used and that the exact interval is overly conservative. On the basis of coverage probability and interval width, the Jeffreys interval is preferred. If more than one sample per cell is available, cell declustering is used to estimate the aquifer scale proportion, and Kish's design effect may be useful for estimating an effective number of samples. The binomial distribution is also used to quantify the adequacy of a grid with a given number of cells for identifying a small target, defined as a constituent that is present at high concentrations in a small proportion of the aquifer. Case studies illustrate a consistency between approaches that use one well per grid cell and many wells per cell. The methods presented in this paper provide a quantitative basis for designing a sampling program and for utilizing existing data.

Application of Solute Transport Modeling to Study Tsunami Induced Aquifer Salinity in India

Natural processes such as flooding, earthquakes, tsunami, sea water intrusion and rock-water interaction processes will all result in deterioration of groundwater quality. One such natural catastrophic event, in the form of a massive tsunami occurred on December 26, 2004, triggered by a 9.2 magnitude earthquake off the west coast of Sumatra, killed more than 2,50,000 people and displaced thousands in countries around the Indian Ocean. Extensive damage is not only to the life and property but also for deterioration of groundwater quality in coastal regions. Study of processes of salinization of groundwater by tsunami and the time that it might take for the natural recharge processes to flush this salinity is of great importance. The study area includes a portion of Kalpakkam region situated in the Kancheepuram District of Tamil Nadu state in southern India. A groundwater model was developed to simulate the groundwater flow and solute concentration in the study area. Finite element code FEFLOW 5.2 was used for this purpose. The model was used to simulate groundwater flow and solute transport for a period of two years from January 2005 to January 2007. The results indicate that tsunami-induced salinity in this aquifer system would be flushed out with normal annual rainfall by the year 2008-09. The post audit results also confirms that the model have been calibrated and simulated with high accuracy. The present work has demonstrated the application of groundwater modeling to understand the process of salinisation of groundwater resources by tsunami. It has also helped to determine the time that it would take for remediation of the aquifer system by rainfall recharge.

Evaluation of regional groundwater quality using PCA and geostatistics in the urban coastal aquifer, East Coast of India

A systematic groundwater quality-monitoring program was conducted, and a total of 201 groundwater samples were collected. Multivariate and geostatistical techniques were employed to investigate major contamination types and its spatial characteristics in the study area. Principal Component Analysis (PCA) reveals that salinity (Factor 1) and nutrient (Factor 2) are very predominant contaminants in the shallow coastal aquifer. The factor (F1 and F2) scores of each well during three seasons were indicated a spatial correlation of salinity factor (F1) up to 10 km and no spatial correlation were found for nutrient factor (F2).

Assigning land use to supply wells for the statistical characterization of regional groundwater quality: Correlating urban land use and VOC occurrence

summary Many national and regional groundwater studies have correlated land use ‘‘near” a well, often using a 500 m radius circle, with water quality. However, the use of a 500 m circle may seem counterintuitive given that contributing areas are expected to extend up-gradient from wells, and not be circular in shape. The objective of this study was to evaluate if a 500 m circle is adequate for assigning land use to a well for the statistical correlation between urban land use and the occurrence of volatile organic compounds (VOCs). Land use and VOC data came from 277 supply wells in four study areas in California. Land use was computed using ten different-sized circles and wedges (250 m to 10 km in radius), and three different-sized ‘‘searchlights” (1–2 km in length). We define these shapes as contributing area surrogates (CASs), recognizing that a simple shape is at best a surrogate for the actual contributing area. The presence or absence of correlation between land use and the occurrence of VOCs was evaluated using Kendall’s tau ( s). Values of s were within 10% of one another for wedges and circles ranging in size from 500 m to 2 km, with correlations remaining statistically significant (p < 0.05) for all CAS sizes and shapes, suggesting that a 500 m circular CAS is adequate for assigning land use to a well. Additional evaluation indicated that urban land use is autocorrelated at distances ranging from 8 to 36 km. Thus, urban land use in a 500 m CAS is likely to be predictive of urban land use in the actual contributing area. Published by Elsevier B.V.

Groundwater geochemistry and identification of hydrogeochemical processes in a hard rock region, Southern India

Hydrogeochemical investigations were carried out in Chithar River basin, Tamil Nadu, India to identify the major geochemical processes that regulate groundwater chemistry. For this study, long-term (1991-1997) and recent water quality data (2001-2002) for 30 groundwater wells spread over the study area were used to understand the groundwater geochemistry and hydrogeochemical process regulating groundwater quality. Groundwater quality data obtained from more than 400 water samples were employed. Results of electrical conductivity and chloride express large variation between minimum and maximum values and high standard deviation, which suggests that the water chemistry in the study region is not homogeneous and influenced by complex contamination sources and geochemical process. Nitrate and depth to water table expose the influences of surface contamination sources, whereas dissolved silica, fluoride and alkalinity strongly suggest the effect of rock-water interaction. In the study region, weathering of carbonate and silicate minerals and ion exchange reactions predominantly regulate major ion chemistry. Besides, the concentrations of sulphate, chloride and nitrate firmly suggest the impact of agricultural activities such as irrigation return flow, fertiliser application, etc on water chemistry in the study region.

Geochemical process regulating groundwater quality in a coastal region with complex contamination sources: Barka, Sultanate of Oman

An investigation was carried out to evaluate the geochemical processes regulating groundwater quality in a coastal region, Barka, Sultanate of Oman. The rapid urban developments in Barka cause depletion of groundwater quantity and deterioration of quality through excessive consumption and influx of pollutants from natural and anthropogenic activities. In this study, 111 groundwater samples were collected from 79 wells and analysed for pH, EC, DO, temperature, major ions, silica and nutrients. In Barka, water chemistry shows large variation in major ion concentrations and in electrical conductivity, and implies the influence of distinguished contamination sources and hydrogeochemical processes. The groundwater chemistry in Barka is principally regulated by saline sources, reverse ion exchange, anthropogenic pollutants and mineral dissolution/precipitation reactions. Due to ubiquitous pollutants and processes, groundwater samples were classified into two groups based on electrical conductivity. In group1, water chemistry is greatly influenced by mineral dissolution/precipitation process and lateral recharge from upstream region (Jabal Al-Akdar and Nakhal mountains). In group 2, the water chemistry is affected by saline water intrusion, sea spray, reverse ion exchange and anthropogenic pollutants. Besides, high nitrate concentrations, especially in group 2 samples, firm evidence for impact of anthropogenic activities on groundwater quality, and nitrate can be originated by the effluents recharge from surface contamination sources. Ionic ratios such as SO4/Cl, alkalinity/Cl and total cation/Cl indicate that effluents recharged from septic tank, waste dumping sites and irrigation return flow induce dissolution of carbonate minerals, and enhances solute load in groundwater. The chemical constituents originating from saline water sources, reverse ion exchange and mineral dissolution are successfully differentiated using ionic delta, the difference between the actual concentration of each constituent and its theoretical concentration for a freshwater–seawater mix calculated from the chloride concentration of the sample, and proved that this approach is a promising tool to identify and differentiate the geochemical processes in coastal region. Hence, both regular geochemical methods and ionic delta ensured that groundwater quality in Barka is impaired by natural and human activities.

Temporal Trends in Nitrate and Selected Pesticides in Mid‐Atlantic Ground Water

Evaluating long-term temporal trends in regional ground-water quality is complicated by variable hydrogeologic conditions and typically slow flow, and such trends have rarely been directly measured. Ground-water samples were collected over near-decadal and annual intervals from unconfined aquifers in agricultural areas of the Mid-Atlantic region, including fractured carbonate rocks in the Great Valley, Potomac River Basin, and unconsolidated sediments on the Delmarva Peninsula. Concentrations of nitrate and selected pesticides and degradates were compared among sampling events and to apparent recharge dates. Observed temporal trends are related to changes in land use and chemical applications, and to hydrogeology and climate. Insignificant differences in nitrate concentrations in the Great Valley between 1993 and 2002 are consistent with relatively steady fertilizer application during respective recharge periods and are likely related to drought conditions in the later sampling period. Detecting trends in Great Valley ground water is complicated by long open boreholes characteristic of wells sampled in this setting which facilitate significant ground-water mixing. Decreasing atrazine and prometon concentrations, however, reflect reported changes in usage. On the Delmarva Peninsula between 1988 and 2001, median nitrate concentrations increased 2 mg per liter in aerobic ground water, reflecting increasing fertilizer applications. Correlations between selected pesticide compounds and apparent recharge date are similarly related to changing land use and chemical application. Observed trends in the two settings demonstrate the importance of considering hydrogeology and recharge date along with changing land and chemical uses when interpreting trends in regional ground-water quality.

O.096 Hemimandibular elongation: evaluation of a therapy protocol

Hydraulic fracturing operations have been viewed as the cause of certain environmental issues including groundwater contamination. The potential for hydraulic fracturing to induce contaminant pathways in groundwater is not well understood since gas wells are completed while isolating the water table and the gas-bearing reservoirs lay thousands of feet below the water table. Recent studies have attributed ground water contamination to poor well construction and leaks in the wellbore annulus due to ruptured wellbore casings. In this paper, a geospatial model of the Barnett Shale region was created using ArcGIS. The model was used for spatial analysis of groundwater quality data in order to determine if regional variations in groundwater quality, as indicated by various groundwater constituent concentrations, may be associated with the presence of hydraulically fractured gas wells in the region. The Barnett Shale reservoir pressure, completions data, and fracture treatment data were evaluated as predictors of groundwater quality change. Results indicated that elevated concentrations of certain groundwater constituents are likely related to natural gas production in the study area and that beryllium, in this formation, could be used as an indicator variable for evaluating fracturing impacts on regional groundwater quality. Results also indicated that gas well density and formation pressures correlate to change in regional water quality whereas proximity to gas wells, by itself, does not. The results also provided indirect evidence supporting the possibility that micro annular fissures serve as a pathway transporting fluids and chemicals from the fractured wellbore to the overlying groundwater aquifers.

Regional Nitrate and Pesticide Trends in Ground Water in the Eastern San Joaquin Valley, California

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this study, spatial and temporal trends in concentrations of nitrate and pesticides in ground water in the eastern San Joaquin Valley, California, were evaluated to determine the long-term effects of agricultural and urban development on regional ground-water quality. Trends in concentrations of nitrate, the nematocide 1,2-dibromo-3-chloropropane, and the herbicide simazine during the last two decades are generally consistent with known nitrogen fertilizer and pesticide use and with the position of the well networks in the regional ground-water flow system. Concentrations of nitrate and pesticides are higher in the shallow part of the aquifer system where domestic wells are typically screened, whereas concentrations are lower in the deep part of the aquifer system where public-supply wells are typically screened. Attenuation processes do not seem to significantly affect concentrations. Historical data indicate that concentrations of nitrate have increased since the 1950s in the shallow and deep parts of the aquifer system. Concentrations of nitrate and detection of pesticides in the deep part of the aquifer system will likely increase as the proportion of highly affected water contributed to these wells increases with time. Because of the time of travel between the water table and the deep part of the aquifer system, current concentrations in public-supply wells likely reflect the effects of 40- to 50-yr-old management practices.