Multi-Level Slug Tests to Measure 3-D Hydraulic Conductivity Distributions

The accurate determination of the transport and fate of pollutants through an aquifer begins with a complete understanding of the complexities of the hydraulic conductivity in that aquifer. Slug tests have been a popular method to define in situ hydraulic conductivity in an aquifer. However, traditional slug tests will provide information about the hydraulic conductivity across the entire screened interval of a well and not provide information about variations that may exist in the vertical direction. Equipment was developed that allowed multi-level slug tests to be conducted at discrete intervals within fully screened 5-cm (2 in) diameter wells. Ten such wells at the Geohydrologic and Experiment Monitoring Site were tested in order to provide a more complete spatial definition of the hydraulic conductivity and to determine the utility of the double-packer apparatus for such studies. Results from multi-level slug tests produced vertical profiles of hydraulic conductivity throughout each well’s screened interval. These vertical profiles provided information about spatial variations in hydraulic conductivity, when they were incorporated into cross-sections and a 3-D fence diagram. This research determined the greatest complexity in hydraulic conductivity in a northeast to southwest trend across the study site. Techniques presented here are valuable tools for greater definition of the hydraulic conductivity distribution in similar hydraulic settings.     

Effect of a Mobile Fine Fraction on Slug Test Results

In recent slug testing at our field site there seemed to be a dependence on flow direction and initial slug height in some of the results for hydraulic conductivity that could not be explained by any known models. At first, we thought the dependence on flow direction and initial height was the result of slug length and friction in the annular space between the slug and casing. Later slug testing with a packer eliminated the effect of the slug in the wellbore, but the initial head and directional dependence observed earlier remained for the packer data. This indicated possible well development problems, so a program of well development was instituted and slug tests were performed at various points in this program. We were not able to eliminate the head and directional dependence of the results for the hydraulic conductivity by well development. However, we have arrived at some conclusions that may be helpful to others interpreting slug test data in aquifers with a mobile fine fraction. It seems that well development and slug testing can cause fine material to be redistributed in an aquifer. Apparently in our slug testing and development program, we have created an artificial distribution of fine material that differs with radius, causing the apparent hydraulic conductivity to differ with volume injected or withdrawn. Directional dependence may be caused by the water moving away from the well carrying fines, resulting in a build up of fine material at some radius and a lower apparent hydraulic conductivity.     

H<Subscript>2</Subscript>-rich and Hydrocarbon Gas Recovered in a Deep Precambrian Well in Northeastern Kansas

In late 2005 and early 2006, the WTW Operating, LLC (W.T.W. Oil Co., Inc.) #1 Wilson well (T.D. = 5772 ft; 1759.3 m) was drilled for 1826 ft (556.6 m) into Precambrian basement underlying the Forest City Basin in northeastern Kansas. Approximately 4500 of the 380,000 wells drilled in Kansas penetrate Precambrian basement. Except for two previous wells drilled into the arkoses and basalts of the 1.1-Ga Midcontinent Rift and another well drilled in 1929 in basement on the Nemaha Uplift east of the Midcontinent Rift, this well represents the deepest penetration into basement rocks in the state to date. Granite is the typical lithology observed in wells that penetrate the Precambrian in the northern Midcontinent. Although no cores were taken to definitively identify lithologies, well cuttings and petrophysical logs indicate that this well encountered basement metamorphic rocks consisting of schist, gneiss, and amphibolitic gneiss, all cut by aplite dikes. The well was cased and perforated in the Precambrian, and then acidized. After several days of swabbing operations, the well produced shows of low-Btu gas, dominated by the non-flammable component gases of nitrogen (20%), carbon dioxide (43%), and helium (1%). Combustible components include methane (26%), hydrogen (10%), and higher molecular-weight hydrocarbons (1%). Although Coveney and others [Am. Assoc. Petroleum Geologists Bull., v. 71, no, 1, p. 39–48, 1987] identified H₂-rich gas in two wells located close to the Midcontinent Rift in eastern Kansas, this study indicates that high levels of H₂ may be a more widespread phenomenon than previously thought. Unlike previous results, the gases in this study have a significant component of hydrocarbon gas, as well as H₂, N₂, and CO₂. Although redox reactions between iron-bearing minerals and groundwater are a possible source of H₂ in the Precambrian basement rocks, the hydrocarbon gas does not exhibit the characteristics typically associated with proposed abiogenic hydrocarbon gases from Precambrian Shield sites in Canada, Finland, and South Africa. Compositional and isotopic signatures for gas from the #1 Wilson well are consistent with a predominantly thermogenic origin, with possible mixing with a component of microbial gas. Given the geologic history of uplift and rifting this region, and the major fracture systems present in the basement, this hydrocarbon gas likely migrated from source rocks and reservoirs in the overlying Paleozoic sediments and is not evidence for abiogenic hydrocarbons generated in situ in the Precambrian basement.     

The paleocurrents and morphology of Pikhåggrottene,Svartisen, North Norway

The Pikhågan caves at Svartisen, North Norway, are described and then analysed using passage morphology and scallop morphometry. The caves consist of a multilevel network of essentially horizontal phreatic tubes with a total length of 2,000 + m. Vadose elements account for only about 4% of the total passage lengths, while paragenetic roof alterations arc more common (?10%). Palcocurrcnt direction and flow rates as deduced from scallops suggest a uniform network flow southwards through the system, which also fits well with hydraulic laws for tube networks. This model requires a hydraulic conductivity between entrances formed by glacial truncation. Evidence of a subsequent sediment fill and paragenetic incision of roof half-tubes is demonstrated. These phases were followed by a lowering of the local watertable from above 610 m to about 575 m, when a phase of high discharge occurred. If this shift of watertable was caused by bedrock erosion, it probably took place more than 220 ka ago. Subsequently the watertable was lowered further to its present level (<560 m). Two alternative origins are suggested: first, a possible pre-glacial genesis of the phreatic network in a paleic valley system, second, a possible sub-glacial genesis. The paragenetic phase is regarded as the most likely to have occurred subglacially, while the coarse sediment infilling and the high discharge regime arc associated with deglaciations. The previously proposed proglacial genesis of this phreatic cave system is rejected because of the present topography and because of the slow paleocurrent regime inferred from scallop measurements.     

Assessment of Nitrate—Nitrogen Distribution in Kansas Groundwater, 1990–1998

Nitrate-nitrogen (nitrate-N) in groundwater is a potential problem in many parts of Kansas.From 1990 to 1998, 747 water samples were collected from domestic, irrigation, monitoring,and public water supply wells primarily from the western two-thirds of the state, and analyzedfor nitrate-N by the Kansas Geological Survey. Nitrate-N concentrations of the 747 samplesanalyzed range from 29% with less than or equal to 3 mg/L, 51% between 3 and 10 mg/L,and 20% greater than or equal to 10 mg/L. Factors that show a statistically significantrelationship with the occurrence of nitrate-N in Kansas groundwater in this assessment includegeographic area of the state, depth of well, and age of well. Nitrate-N levels of wells screenedin the High Plains aquifer in south-central Kansas showed a statistically higher concentrationthan samples collected from the High Plains aquifer in the western portion of the state.Comparison of nitrate-N with depth of well indicated that shallower wells throughout the stategenerally have higher nitrate-N values than deeper wells. Irrigation wells older than 1975showed statistically higher nitrate-N concentration than wells installed during and since 1975,possibly related to changes in well-construction practices and regulations that occurred in 1975.     

Development and Implementation of a Bayesian-based Aquifer Vulnerability Assessment in Florida

The Florida Aquifer Vulnerability Assessment (FAVA) was designed to provide a tool for environmental, regulatory, resource management, and planning professionals to facilitate protection of groundwater resources from surface sources of contamination. The FAVA project implements weights-of-evidence (WofE), a data-driven, Bayesian-probabilistic model to generate a series of maps reflecting relative aquifer vulnerability of Florida’s principal aquifer systems. The vulnerability assessment process, from project design to map implementation is described herein in reference to the Floridan aquifer system (FAS). The WofE model calculates weighted relationships between hydrogeologic data layers that influence aquifer vulnerability and ambient groundwater parameters in wells that reflect relative degrees of vulnerability. Statewide model input data layers (evidential themes) include soil hydraulic conductivity, density of karst features, thickness of aquifer confinement, and hydraulic head difference between the FAS and the watertable. Wells with median dissolved nitrogen concentrations exceeding statistically established thresholds serve as training points in the WofE model. The resulting vulnerability map (response theme) reflects classified posterior probabilities based on spatial relationships between the evidential themes and training points. The response theme is subjected to extensive sensitivity and validation testing. Among the model validation techniques is calculation of a response theme based on a different water-quality indicator of relative recharge or vulnerability: dissolved oxygen. Successful implementation of the FAVA maps was facilitated by the overall project design, which included a needs assessment and iterative technical advisory committee input and review. Ongoing programs to protect Florida’s springsheds have led to development of larger-scale WofE-based vulnerability assessments. Additional applications of the maps include land-use planning amendments and prioritization of land purchases to protect groundwater resources.     

Kansas Energy Sources: A Geological Review

Kansas produces both conventional energy (oil, gas, and coal) and nonconventional (coalbed gas, wind, hydropower, nuclear, geothermal, solar, and biofuels) and ranks the 22nd in state energy production in the U.S. Nonrenewable conventional petroleum is the most important energy source with nonrenewable, nonconventional coalbed methane gas becoming increasingly important. Many stratigraphic units produce oil and/or gas somewhere in the state with the exception of the Salina Basin in north-central Kansas. Coalbed methane is produced from shallow wells drilled into the thin coal units in southeastern Kansas. At present, only two surface coal mines are active in southeastern Kansas. Although Kansas has been a major exporter of energy in the past (it ranked first in oil production in 1916), now, it is an energy importer.     

A Petroleum System for the Salina Basin in Kansas Based on Organic Geochemistry and Geologic Analog

The Salina Basin historically has been an exploration desert—a home of dryholes. Although this basin, which underlies much of north-central Kansas, may never be a prolific source of hydrocarbons, recent research into the maturation and geochemistry of organic matter and oils in Kansas can provide guidelines for a new exploration strategy. The Salina Basin is similar to the oil-productive Forest City Basin in northeastern Kansas in many ways. Both basins originated as a single large basin (i.e., the North Kansas Basin) prior to the rise of the Nemaha Uplift in Late Mississippian-Early Pennsylvanian time. Their Paleozoic stratigraphy thus is similar and the axes of both basins are presently at approximately the same depth. Thermal maturation modeling and available organic-matter maturation data indicate that the lower Paleozoic rocks in the axes of both basins are in the early stages of oil generation. In the Forest City Basin the Ordovician Simpson Group is the deepest known hydrocarbon source-rock—oil-reservoir interval, and by analogy, exploration tests in the Salina Basin, at a minimum, should penetrate through this stratigraphic interval. Ordovician Simpson Group shales in the Forest City Basin are the source rocks for a geochemically distinct oil, which also occurs in Ordovician reservoirs in the extreme southern end of the Salina Basin. To increase the odds of success in an exploration program in the Salina Basin, wildcat wells should be drilled where thermal maturation is greatest. The broad NW–SE-trending basin axis is the most logical area. Exploration tests along this axis in the northern end of the basin may have an extra advantage as organic matter in the Simpson Group may be more thermally mature because of greater burial depth during the Cretaceous. Along the eastern margin of the nearby Central Kansas Uplift and Pratt Anticline, several Paleozoic geologic structures, some of which contain major oil fields, are attributable to tectonic reactivation along the western margin of the Precambrian Central North American Rift System (CNARS). Prospective structural trends in the Paleozoic section of the Salina Basin are anticipated to be associated with this underlying tectonic boundary. The western margin of the CNARS trends NNE–SSW where it passes under the axis of the Salina Basin in northeastern Lincoln and southeastern Mitchell counties. This area is sparsely drilled, with less than two tests per township. If an exploration program can define lower Paleozoic structural closures in this region, these structures may represent the best chance for future petroleum discoveries.     

华北平原地下水动态及其对不同开采量响应的计算——以河北省栾城县为例

自从20世纪60年代大规模开采地下水以来,栾城县的地下水位以每年大约0.65 m的速度下降.降雨量的减少、农业产量的大幅度提高、种植结构的变化以及上游水利工程的修建,都与地下水位的下降有着密切联系.利用Visual Modflow软件,在分析该县水文地质条件与水资源利用的前提下,运用三维地下水流模型,通过有限差分方法对栾城县的地下水系统进行了模拟,结果表明:5个观测孔的地下水位计算值与实测值拟合程度很好,模拟出的地下水流场与实际情况基本一致.利用掌握的水文地质资料,进行参数分区,通过实测资料的校正、调参,模拟出各分区参数值.利用校正后的数学模型,对栾城县地下水对不同开采量的响应进行了计算,结果如下:在现状农业开采量1.01×108m3基础上分别减少14%(0.14×108m3)、29%(0.29×108m3)和增加29%(0.29×108m3)的情况下,到12月份5个观测孔的平均地下水位分别比现状地下水位上升了0.33 m,0.64 m和下降了0.45 m.     

A Model-Based Evaluation of Horizontal Wells for Improving the Functionality of an Urban Reservoir System

A method is proposed for utilizing the storage capacity of unconfined aquifers to increase the efficiency of existing water-supply reservoirs presently losing water to seasonal spillages. The approach proposed uses horizontal wells to control the watertable elevation in the reservoir catchments, permitting a degree of control over the discharge of the streams flowing to the reservoirs. This may provide an alternative to reservoir construction, thus avoiding loss of ecosystems or productive land. The use of horizontal wells provides a range of control options, including increasing stream discharge during summer and reducing and delaying peak discharge from rainfall events during winter. A numerical groundwater model is utilized to simulate the operation of hypothetical horizontal wells within a water supply catchment of Auckland City, New Zealand. Results suggest potential for a significant increase in summer stream flow, coupled with a reduction in winter peak discharges associated with present reservoir spillage.     

Groundwater regime and calculation of yield response in North China Plain: a case study of Luancheng County in Hebei Province

The groundwater table has been declining at a rate of 0.65 m/yr in Luancheng County since large scale groundwater extraction carried out in the 1960s. The drop of precipitation, substantial increase in agricultural output, variations of crop planting structure and construction of water conservancy projects in the headwater area all tie up with the decline of the groundwater table. On the basis of analyzing the hydrogeological conditions and the water resources utilization of Luancheng County, a three-dimensional groundwater flow model was developed to simulate the county’s groundwater flow through finite-difference method using Visual Modflow software. We divide the research field into four parts after analyzing the hydrogeological condition. Based on parameter calibration and adjustment using measured data, the hydraulic conductivity and specific yield were simulated. Using the calibrated model, we analyze the agricultural water saving potentiality and its influence on the groundwater. The results are as follows: (1) if we decrease the amount of water extracted by 0.14×108 m3, the average groundwater table of the five observation wells in December will rise by 0.33 m; (2) if we decrease the water by 0.29× 108 m3, the average groundwater table of the five observation wells in December will rise by 0.64 m; and (3) if we increase the water by 0.29×108 m3, the average groundwater table of the five observation wells in December will decline by 0.45 m. So we can draw a conclusion that controlling the agricultural water use is an important way to prevent the decline of groundwater table.     

Injection experiments and thermal recovery in corehole OH-1, Lake City,California

Two injection tests, shallow and deep, followed by repeated temperature logging were performed in the Lake City, California OH-1 corehole, to delineate permeable zones, investigate the permeability of rocks adjacent to the wellbore, and to test the validity of maximum-reading thermometer (MRT) measurements collected during the drilling process that show lower than static temperatures above a depth of 2100 ft and significantly higher than static temperatures below a depth of about 2500 ft. The tests confirmed several permeable zones in OH-1. At about 300 ft, there is a strong zone of lateral flow, and at 947 ft there is a major outflow zone for injected fluid. Two other possible permeable flow zones were detected from the thermal recovery logs: one at about 1500 ft and another at about 2300 ft. The 2300 ft permeable zone seems to be an inflow zone, and the source of a probable downflow responsible for cooling the wellbore below about 2500 ft. The hotter MRT data obtained during drilling may be reconciled with the significantly lower static temperature logs if downflow from about 2300 ft is present.     

Quantitative assessment of mineral resources with an application to petroleum geology

The probability of occurrence of natural resources, such as petroleum deposits, can be assessed by a combination of multivariate statistical and geostatistical techniques. The area of study is partitioned into regions that are as homogeneous as possible internally while simultaneously as distinct as possible. Fisher's discriminant criterion is used to select geological variables that best distinguish productive from nonproductive localities, based on a sample of previously drilled exploratory wells. On the basis of these geological variables, each wildcat well is assigned to the production class (dry or producer in the two-class case) for which the Mahalanobis' distance from the observation to the class centroid is a minimum. Universal kriging is used to interpolate values of the Mahalanobis' distances to all locations not yet drilled. The probability that an undrilled locality belongs to the productive class can be found, using the kriging estimation variances to assess the probability of misclassification. Finally, Bayes' relationship can be used to determine the probability that an undrilled location will be a discovery, regardless of the production class in which it is placed. The method is illustrated with a study of oil prospects in the Lansing/Kansas City interval of western Kansas, using geological variables derived from well logs.     

Regional groundwater flow modelling of Upper Chaj Doab of Indus Basin, Pakistan using finite element model (Feflow) and geoinformatics

A 3-D finite element model (Feflow) has been used for regional groundwater flow modelling of Upper Chaj Doab in Indus Basin, Pakistan. The thematic layers of soils, landuse, hydrology, infrastructure and climate were developed using Geographic Information System (GIS). The numerical groundwater flow model is developed to configure the groundwater equipotential surface, hydraulic head gradient and estimation of the groundwater budget of the aquifer. Integration of GIS with groundwater modelling and satellite remote sensing capabilities has provided an efficient way of analysing and monitoring groundwater status and its associated land conditions. The Arcview GIS software is used as additive tool to develop supportive data for numerical groundwater modelling, integration and presentation of image processing and modelling results.
The groundwater behaviour of the regional model shows a gradual decline in watertable from year 1999 onward. The persistent dry condition and high withdrawal rates play an influential role in lowering down the groundwater levels. Different scenarios were developed to study the impact of extreme climatic conditions (drought/flood) and variable groundwater abstraction on the regional groundwater system. The results of the study provide useful information regarding the behaviour of aquifer in order to organize management schemes on local and regional basis to monitor future groundwater development in the area.     

Groundwater regime and calculation of yield response in North China Plain: a case study of Luancheng County in Hebei Province

The groundwater table has been declining at a rate of 0.65 m/yr in Luancheng County since large scale groundwater extraction carried out in the 1960s. The drop of precipitation, substantial increase in agricultural output, variations of crop planting structure and construction of water conservancy projects in the headwater area all tie up with the decline of the groundwater table. On the basis of analyzing the hydrogeological conditions and the water resources utilization of Luancheng County, a three-dimensional groundwater flow model was developed to simulate the county’s groundwater flow through finite-difference method using Visual Modflow software. We divide the research field into four parts after analyzing the hydrogeological condition. Based on parameter calibration and adjustment using measured data, the hydraulic conductivity and specific yield were simulated. Using the calibrated model, we analyze the agricultural water saving potentiality and its influence on the groundwater. The results are as follows: (1) if we decrease the amount of water extracted by 0.14xl0⁸ m³, the average groundwater table of the five observation wells in December will rise by 0.33 m; (2) if we decrease the water by 0.29x 10⁸m³, the average groundwater table of the five observation wells in December will rise by 0.64 m; and (3) if we increase the water by 0.29 x 10⁸m³, the average groundwater table of the five observation wells in December will decline by 0.45 m. So we can draw a conclusion that controlling the agricultural water use is an important way to prevent the decline of groundwater table.     

江苏省里下河沼泽地地下水位对Ⅰ-69杨生长的影响

长江中下游地区丰富的江河滩地和水网沼泽地是重要的土地资源,也是血吸虫(Schistosoma japonicum)病的主要发生区域。营造人工林有利于控制血吸虫的中间寄主钉螺(Oncomelania hupensis)的孳生,也有利于提高土地的生态效益和经济效益。耐湿树种的选择是滩地和沼泽地造林的重要环节。通过对江苏省里下河沼泽地主要造林树种I-69杨(Populus deltoides)的生长状况进行调查可知,在高水位(年平均地下水位-29cm,每年淹水1～2个月)、中水位(年平均地下水位-59cm,每年淹水0～10d)、低水位(年平均地下水位-87cm,常年不淹水)立地上,10a生的I-69杨平均树高分别为16.4m、19.8m、22.9m;平均胸径分别为12.8cm、18.2cm、21.2cm;平均蓄积量分别为67.9m3/hm2、193.1m3/hm2、313.6m3/hm2;地上部分生物量分别为51.8t/hm2、130.0t/hm2、201.4t/hm2;总生物量分别为67.1t/hm2、161.7t/hm2、241.2t/hm2。因此,I-69杨虽然具有较强的耐水能力,在地下水位较高的情况下,其生长也会受到明显抑制,这一结果将为今后湿地造林中的立地选择和树种选择提供参考。     

Implementation of Rock Typing on Waterflooding Process During Secondary Recovery in Oil Reservoirs: A Case Study,El Morgan Oil Field,Gulf of Suez,Egypt

Waterflooding is one of the most common secondary recovery methods in the oil and gas industry. Globally, this process sometimes suffers a technical failure and inefficiency. Therefore, a better understanding of geology, reservoir characteristics, rock typing and discrimination, hydraulic flow units, and production data is essential to analyze reasons and mechanisms of water injection failure in the injection wells. Water injection failure was reported in the Middle Miocene Hammam Faraun reservoir at El Morgan oil field in the Gulf of Suez, where two wells have been selected as injector’s wells. In the first well (A1), the efficiency of injection was not good, whereas in the other analog A2 well good efficiency was assigned. Therefore, it is required to assess the injection loss in the low efficiency well, where all aspects of the geological, reservoir and production data of the studied wells were integrated to get a complete vision for the reasons of injection failure. The available data include core analysis data (vertical and horizontal permeabilities, helium porosity, bulk density, and water and oil saturations), petrographical studies injection and reservoir water chemistry, reservoir geology, production, and injection history. The quality of the data was examined and a set of reliable X–Y plots between the available data were introduced and the reservoir quality in both wells was estimated using reservoir quality index, normalized porosity index, and flow zone indicator. Integration and processing of the core and reservoir engineering data indicate that heterogeneity of the studied sequence was the main reason for the waterflooding inefficiency at the El Morgan A1 well. The best reservoir quality was assigned to the topmost part of the reservoir, which caused disturbance of the flow regime of reservoir fluids. Therefore, it is clearly indicated that rock typing and inadequate injection perforation strategy that has not been aligned with accurate hydraulic flow units are the key control parameters in the waterflooding efficiency.

     

Effects of Microtopographically Concentrated Recharge on Nitrate Variability in a Confined Aquifer: Model Simulations

Simulated recharge to a shallow confined aquifer indicates that locally concentrated recharge through microtopographically determined recharge areas (having elevation differences of less than 2 cm) can have a substantial effect on the spatial variability of nitrate-N concentrations [N-NO₃] in the upper meter of an aquifer. For an aquifer that is confined and near pressure equilibrium with the watertable, hydraulic mounds formed under recharge areas can cause temporary large local increases in hydraulic gradient and subsequent flux from the aquitard to the upper aquifer. These hydraulic surges carry nitrates from the aquitard to the upper aquifer, where they move as local plumes and disperse according to the properties of the prevailing aquifer flow system, until discharged, reduced to ammonia, or denitrified. Under conditions of maximum local recharge the ratio of aquifer nitrate concentration to till nitrate concentration ([N-NO₃]_a/[N-NO₃]_t) may approach an upper limit of 1. Understanding these processes is important for interpretation of nitrate and other solute measurements near the aquifer-aquitard boundary.     

Application of Weights of Evidence Method for Assessment of Flowing Wells in the Greater Toronto Area,Canada

Flowing wells extracted from the Ministry of Ontario Environment and Energy (MOEE) water well data set from the Oak Ridges Moraine (ORM) area, Ontario, Canada, were treated as training point set to evaluate the potential distribution of artesian aquifers and their spatial associations with other geological and topological features in the study area. Evidential layers of geological and topographical features were constructed on the basis of the digital elevation model (DEM) and a geological map using GIS buffering functions in conjunction with weights of evidence method. It has been demonstrated that the locations of the flowing wells in the Oak Ridges Moraine area are associated spatially with the distances, (a) 500–5000 m from the oak ridges moraine deposits, (b) 500–4000 m from thick drift layer delineated on the drift thickness map created from water well data, and (c) 1500–2500 m from steep slope zones with slope above 8 degree calculated from a DEM. Applying a combination of these conditions can reduce the predicting target areas of having flowing wells by two thirds. Outcomes of this research are important both because the impact of the results on understanding of characteristics of aquifers and their relationships with other geological and topographical features and because it generates a probability map showing the potential location of artesian aquifers in the ORM area. In addition, the methodologies used in the paper will be applicable for modeling the distributions of other types of objects such as surface water bodies and low flow of streams in a watershed context in the study area.     

Hydrogeomorphic control on tree growth responses in the Elton area of the Cheshire Saltfield, UK

Increment cores were sampled from oak (Quercus robur) and ash (Fraxinus excelsior) growing at Elton, an area of the Cheshire Saltfield that has experienced significant subsidence and damage to the natural and built environments in the latter part of the twentieth century. Ring-width measurements for Elton trees permitted the construction of one main site chronology (Elton) and four sub chronologies (Elton A, Elton B, Elton C, Elton ASH). Ring-width difference between these and a control chronology identified periods of sustained growth reduction in oak trees commencing in AD 1859/1861, 1886 and 1934. Growth reductions after 1934 are related to watertable draw down caused by brine pumping from a concentration of nine boreholes at Elton, up to 2 km from tree sampling locations. Growth reductions in 1859/1861 and 1886 are likely to be the result of earlier phases of brine pumping in the Wheelock Valley, up to 5 km to the east of Elton, and these reductions correlate well with historic records of subsidence and pumping activity. Cessation of pumping in 1977 led to a lagged growth recovery in oak trees between 1981 and 1986, indicating that an artificial drought had been imposed on the Elton area for a period in excess off 100-y. This research demonstrates a hydrological separation of surface water and groundwater in an area where salt beds are overlain by till and that ring-width records of Q. robur can be used to reconstruct watertable variability and also the spatial impact of solution mining.