地下水流动对砷迁移的影响: 大同盆地试验场的观测与模拟

地下水流动特征对水文地球化学特征具有重要控制作用, 研究分析了大同盆地地下水流动特征对高砷水迁移的影响.以山阴县桑干河南岸地下水试验场(SYFS)的监测数据为基础, 建立了河岸带三维非稳定地下水流模型.结果表明, 灌溉在很大程度上影响着地下水位动态变化.灌溉活动减慢了地下水埋深和水平地下水流速, 加速了不同岩性地层之间的垂向水量交换.粉土(L1、L2、L3和L4)、粘土1(L5)和砂1(L6)之间始终存在由上至下的垂向水量交换, 粘土2(L7)、砂2(L8)、粘土3(L9)和砂3(L10)以水平水量交换为主.灌溉水和大气降水从地表向下垂直入渗至含水层的过程中, 推动了地表和包气带沉积物中的砷逐渐向下迁移; 到达含水层后, 水平交换量占主导, 地下水在水平方向上频繁的水量交换促使As在含水层中发生水平迁移.      

Origin,lithology and weathering characteristics of Upper Tertiary ‐ Quaternary clay aquitard units on the Lower Murrumbidgee alluvial fan

The Lower Murrumbidgee alluvial fan at the eastern edge of the Murray Basin is comprised of high‐yielding coarse‐grained aquifers and interlayered fine‐grained deposits that exert an important control on recharge and vertical leakage of contaminants such as salt. Concerns over increasingly saline shallow groundwater, particularly in irrigation areas, has focused investigations on the depositional origin and spatial distribution of these fine‐grained deposits (aquitard units), which may constitute both a source of leachable salt and a barrier to leakage. Detailed laboratory analysis of a minimally disturbed core to 83m depth, obtained from a drillhole adjacent to an irrigation bore, was augmented with geophysical investigations from this and other boreholes near the apex of the alluvial fan. Previously mapped clay units (aquitards) are redefined as clayey silts based on clay content variation between 10% and 30%. Mineralogical and lithostratigraphic evidence for three clayey silt units is presented: a lower unit (75–83m), a middle unit (45–64m) and an upper unit (0–16m). Electrical image surveys indicate that the upper unit is discontinuous, interrupted by large palaeodrainage features probably containing sands and gravels. These palaeodrainage channels are buried beneath a veneer of clay and significantly increase recharge and leakage. Some evidence suggests an aeolian component near the surface and within the middle clayey silt unit. However, mixing with fluvial deposits and subsequent weathering has also occurred. The clayey silt units are extensively weathered and oxidised, with the degree of oxidation increasing towards the surface and adjacent to aquifers saturated with oxygenated groundwater. Post‐depositional weathering of the middle and lower units may also have been associated with leaching of salts. No salt remains in the middle and lower units, but 10.2kg/m² is stored within 15m of the surface at the Tubbo site. The upper clayey silt unit is a significant source of leachable salt, which is associated with increasing shallow groundwater salinity at some sites.     

Geologically controlled bi-directional exchange of groundwater with a hypersaline lake in the Canadian prairies

Hypersaline lakes occur in hydrologically closed basins due to evaporitic enrichment of dissolved salts transported to the lakes by surface water and groundwater. At the hypersaline Lydden Lake in Saskatchewan, Canada, groundwater/lake-water interaction is strongly influenced by the geological heterogeneity of glacial deposits, whereby a highly permeable glaciofluvial sand/gravel deposit is underlain by glaciolacustrine deposits consisting of dense clay interspersed with silt/sand lenses. Pressure head distribution in a near shore area indicates a bi-directional flow system. It consists of topographically driven flow of fresh groundwater towards the lake in the sand/gravel aquifer and density-driven, landward flow of saline groundwater in the underlying glaciolacustrine deposits. Electrical resistivity tomography, and chemical and isotopic composition of groundwater clearly show the landward intrusion of saline water in the heterogeneous unit. The feasibility of bi-directional flow and transport is supported by numerical simulations of density-coupled groundwater flow and transport. The results suggest that the geologically controlled groundwater exchange processes have substantial influences on both inputs and outputs of dissolved minerals in hypersaline lakes in closed basins.     

The effects of aquifer heterogeneity on the 3D numerical simulation of soil and groundwater contamination at a chlor-alkali site in China

The simulation of groundwater flow and solute transport at contaminated sites often neglects the important influence that aquifer heterogeneity can have on the sub-surface distribution of contaminants. In this paper, the method of transition probability for geological statistics (T-PROGS) included in the Groundwater Model System (GMS) was applied to a chlor-alkali-contaminated site that was sampled with 68 soil borings and 15 groundwater monitoring wells. A 3-D groundwater numerical model and solute transport model was developed that was constrained by soil and groundwater data from the site. The spatial distribution of chloroethylene concentrations was simulated for a number of times using the levels measured in the field as a baseline. The results of these simulations showed that shapes and distribution of contaminant plumes are irregular both vertically and horizontally. The solute-transport simulations indicated that much of the contamination will preferentially move in groundwater through silt and fine-sands whereas flow is largely blocked in clays. Consequently, fine sand and silts become the most seriously polluted zones at the site, whereas, areas underlain by clays are largely uncontaminated. Heterogeneous lithologies beneath a site increase the complexity of coupling simulations of soil and groundwater.     

基于地中渗透仪的入渗补给方式分析

文章通过在某均衡试验场地中的渗透仪上开展土壤水流穿透试验,分析灌溉水对地下水补给方式。试验结果表明:淹灌条件下,粉细砂扰动土中的穿透曲线为典型的单峰对称型,表明粉细砂中的土壤水通过活塞式入渗补给地下水;而亚粘土中的穿透曲线显示多峰、优先穿透、拖尾等现象,表明亚粘土中的土壤水以优势流方式补给地下水。通过对均衡场降水入渗补给的长观资料分析发现:在自然降雨条件下亚粘土中优势流明显,粉细砂中主要以活塞流为主。     

Soft-sediment deformation during thawing of ice-rich frozen soils: results of scaled centrifuge modelling experiments

The origin of periglacial involutions remains uncertain, largely because of the difficulties of field monitoring in modern permafrost regions. This paper describes an alternative approach, in which process studies are based on scaled centrifuge modelling of thawing ice-rich soils. Centrifuge scaling laws allow similitude in self-weight stresses between the model scale and the prototype (field) scale to be achieved. In these experiments, 120- to 130-mm-thick frozen models comprising a sand unit overlying ice-rich kaolinite clay (three models) or ice-rich silt (one model) were thawed under an acceleration of 20 gravities. The models were therefore equivalent to 2·4–2·6 m of frozen sediments (permafrost) at the prototype scale. Temperature profiles and porewater pressures during the thawing of each model are described. Porewater pressures significantly in excess of hydrostatic were not observed in the sand/silt model. In the sand/clay models, however, excess pressures developed rapidly after thawing, and observed fluctuations in pressure were interpreted as water-escape events. After thawing, careful sectioning of the models revealed small-scale deformation structures at the clay–sand interface, resulting from loading of the upper sand layer into very soft fluid-like clay and injection of clay upwards into the base of the sand. It is concluded that these experiments provide analogues for some Pleistocene involutions. Such involutions therefore mark phases of permafrost degradation when high porewater pressures caused loading and injection along sedimentary boundaries.     

Adsorption studies of 1,2,4-Trichlorobenzene onto shallow aquifer media at the Luhuagang landfill site in Kaifeng,China

The Luhuagang landfill site (LLS) in Kaifeng, China, lacks liner and leachate collection systems. Thus, leachate generated from the waste dump has contaminated the surrounding subsoil and shallow aquifer with various chemicals, including 1,2,4-Trichlorobenzene (1,2,4-TCB). This paper is a part of a series of studies on adsorption, transport and biodegradation and fate of 1,2,4-TCB in the shallow aquifer beneath LLS. Here, adsorption of 1,2,4-TCB onto silt, fine sand and medium sand aquifer deposits collected at LLS was conducted by performing batch experiments involving four common adsorption kinetic models. The results of the analyses showed that the pseudo-second-order adsorption kinetic model provided the best fit for the equilibrium data with a coefficient of determination (R ²) greater than 0.99. Least squares analysis of Henry, Freundlich and Langmuir linearly transformed isotherm models was used to establish the best isotherm for 1,2,4-TCB adsorption onto the three aquifer materials. The Freundlich isotherm provided the best fit for experimental data with R ² > 0.99. The results further suggested that the highest adsorption rate of 1,2,4-TCB (27.55 μg/g) was onto silt deposit, followed by fine sand (21.65 μg/g) and medium sand (14.88 μg/g). This showed that silt layer beneath the LLS was critical for retarding the downward percolation and migration of 1,2,4-TCB into the shallow aquifer systems under the landfill. The findings of the study were adopted as basis for designing the slated transport and biodegradation study of 1,2,4-TCB in aquifer system at LLS.     

Containment landfills: the myth of sustainability

A number of major problems associated with the containment approach to landfill management are highlighted. The fundamental flaw in the strategy is that dry entombment of waste inhibits its degradation, so prolonging the activity of the waste and delaying, possibly for several decades, its stabilisation to an inert state. This, coupled with uncertainties as to the long-term durability of synthetic lining systems, increases the potential, for liner failure at some stage in the future whilst the waste is still active, leading to groundwater pollution by landfill leachate. Clay liners also pose problems as the smectite components of bentonite liners are subject to chemical interaction with landfill leachate, leading to a reduction in their swelling capacity and increase in hydraulic conductivity. Thus, their ability to perform a containment role diminishes with time. More critically, if diffusion rather than advection is the dominant contaminant migration mechanism, then no liner will be completely impermeable to pollutants and the containment strategy becomes untenable.

There are other less obvious problems with the containment strategy. One is the tendency to place total reliance on artificial lining systems and pay little attention to local geological/hydrogeological conditions during selection of landfill sites. Based on the attitude that any site can be engineered for landfilling and that complete protection of groundwater can be effected by lining systems, negative geological characteristics of sites are being ignored. Furthermore, excessive costs in construction and operation of containment landfills necessitate that they are large scale operations (superdumps), with associated transfer facilities and transport costs, all of which add to overall waste management costs. Taken together with unpredictable post-closure maintenance and monitoring costs, possibly over several decades, the economics of the containment strategy becomes unsustainable. Such a high-cost, high-technology approach to landfill leachate management is generally beyond the financial and technological resources of the less wealthy nations, and places severe burdens on their economies. For instance, in third world countries with limited water resources, the need to preserve groundwater quality is paramount, so expensive containment strategies are adopted in the belief that they offer greatest protection to groundwater. A final indictment of the containment strategy is that in delaying degradation of waste, the present generations waste problems will be left for future generations to deal with.

More cost-effective landfill management strategies take advantage of the natural hydrogeological characteristics and attenuation properties of the subsurface. The ‘dilute and disperse’ strategy employs the natural sorption and ion exchange properties of clay minerals, and it has been shown that in appropriate situations it is effective in attenuating landfill leachate and preventing pollution of water resources. Operated at sites with thick clay overburden sequences, using a permeable cap to maximise rainfall infiltration and a leachate collection system to control leachate migration, ‘dilute and disperse’ is a viable leachate management strategy. Hydraulic traps are relatively common hydrogeological situations where groundwater flow is towards the landfill, so effectively suppressing outwards advective flow of leachate. This approach is also best employed with a clay liner, taking advantage of the attenuation properties of clays to combat diffusive flow of contaminants. These strategies are likely to guarantee greater protection of groundwater in the long term.     

Weichselian palaeoenvironments at Kobbelgård, Møn, Denmark

Lithostratigraphical and palynological investigations of a coastal cliff section at Kobbelgård, Møn (Denmark) reveal a sedimentary sequence of Weichselian age. Bedded clayey sediments are overlain by stratified silt, sand and occasional beds of clay and gravel. The clay was deposited in water, and most of the silt and sand is aeolian, forming fairly thick units of loess and sand-loess. The lower part of the sequence forms an anticlinal structure, probably of glacio-tectonic orìgìn. The upper part of the sequence appears to represent a depression filling. In the lower part of this, clayey layers alternating with loess deposits suggest wet conditions periodically. In the upper part, loess and fine sand were deposited, interfingering with slope sediments in a periglacial environment from around 24,000 BP almost until the Weichselian glacial maximum. Pollen investigations at the site point to three periods of vegetation. The lowest pollen sequence contains much Ericales, Empetrum and occasionally also Pinus , and is thought to be of Early Glacial or Lower Pleniglacial age. Overlying pollen-bearing strata with high proportions of herbs, including Artemisia , antedate a TL dating of c. 27,000 BP. An upper pollen sequence, derived from slightly organic layers in the depression fill, points to a palaeovegetation almost exclusively of herbs, with Artemisia as an important component. This vegetation is thought to represent a relatively moist site, and is TL dated to c. 24,000 P.     

Analysis of the distribution of inorganic constituents in a landfill leachate-contaminated aquifer: Astrolabe Park,Sydney, Australia

An investigation was conducted at Astrolabe Park landfill, a decommissioned municipal landfill in Sydney, Australia, to assess the physical and chemical processes affecting the distribution of inorganic constituents in the leachate plume. The plume is migrating from the landfill towards a groundwater-fed pond into which leachate-impacted groundwater discharges. Borehole geophysical logging and depth-discrete groundwater sampling were used to delineate the distribution of the leachate plume along two groundwater flow paths between the landfill and the shore of the pond. Borehole geophysical logs indicate a strong correlation between bulk and fluid electrical conductivity (EC) values, and help to identify small-scale heterogeneities that comprise a major constraint on contaminant transport within the aquifer. Variations in the distribution of several indicator parameters (EC, HCO₃^–, pH, Eh, NH₄⁺/NO₃^–, S^2–/SO₄^2–) are used to assess the dominant processes affecting contaminant distribution along the flow path, including mixing of fresh and contaminated groundwater, oxidation/reduction reactions and ion exchange.     

Developing conceptual hydrogeological model for Potsdam sandstones in southwestern Quebec,Canada

A hydrogeological study was conducted in Potsdam sandstones on the international border between Canada (Quebec) and the USA (New York). Two sandstone formations, arkose and conglomerate (base) and well-cemented quartz arenite (upper), underlie the study area and form the major regional aquifer unit. Glacial till, littoral sand and gravel, and marine silt and clay discontinuously overlie the aquifer. In both sandstone formations, sub-horizontal bedding planes are ubiquitous and display significant hydraulic conductivities that are orders of magnitude more permeable than the intact rock matrix. Aquifer tests demonstrate that the two formations have similar bulk hydrologic properties, with average hydraulic conductivities ranging from 2?×?10^?5 to 4?×?10^?5 m/s. However, due to their different lithologic and structural characteristics, these two sandstones impose rather different controls on groundwater flow patterns in the study area. Flow is sustained through two types of fracture networks: sub-horizontal, laterally extensive fractures in the basal sandstone, where hydraulic connectivity is very good horizontally but very poor vertically and each of the water-bearing bedding planes can be considered as a separate planar two-dimensional aquifer unit; and the more fractured and vertically jointed system found in the upper sandstone that promotes a more dispersed, three-dimensional movement of groundwater.     

硝基苯在傍河地下水源地迁移转化的数值模拟研究

通过开展室内模拟实验研究,探讨硝基苯在傍河水源地的迁移规律、转化机理及其影响因素。在实验的基础上,构建描述硝基苯在傍河地下水源地迁移转化的数学模型。数值模拟结果表明：淤泥介质对硝基苯的吸附能力相对较高,硝基苯在淤泥中的线性吸附系数为0.526 cm³/g,在砂砾中的线性吸附系数为0.123 cm³/g;硝基苯在淤泥介质中的生物降解作用也明显大于在砂砾介质中,其在淤泥介质中的生物降解速率常数可达0.043 h^-1,而在砂砾介质中仅为0.002 h^-1。本次对室内硝基苯迁移转化实验的数值模拟效果较为理想,模拟结果对硝基苯在含水层中的迁移过程和转化规律进行了科学合理的量化描述,可将该模型进一步用于野外硝基苯迁移转化的模拟预测中。     

Estimation of groundwater flow from temperature monitoring in a borehole heat exchanger during a thermal response test

To estimate the groundwater flow around a borehole heat exchanger (BHE), thermal properties of geological core samples were measured and a thermal response test (TRT) was performed in the Tsukuba upland, Japan. The thermal properties were measured at 57 points along a 50-m-long geological core, consisting predominantly of sand, silt, and clay, drilled near the BHE. In this TRT, the vertical temperature in the BHE was also monitored during and after the test. Results for the thermal properties of the core samples and from the monitoring indicated that groundwater flow enhanced thermal transfers, especially at shallow depths. The groundwater velocities around the BHE were estimated using a two-dimensional numerical model with monitoring data on temperature changes. According to the results, the estimated groundwater velocity was generally consistent with hydrogeological data from previous studies, except for the data collected at shallow depths consisting of a clay layer. The reasons for this discrepancy at shallow depths were predicted to be preferential flow and the occurrence of vertical flow through the BHE grout, induced by the hydrogeological conditions.     

Lithology, Biostratigraphy, and Magneto stratigraphy of Gas Hydrate-Bearing Sediments in the Eastern Nankai Trough

Abstract: Stratigraphic controls on the formation and distribution of gas hydrates were examined for sediments from a BH-1 well drilled in the landward slope of the Nankai Trough, approximately 60 km off Omaezaki, Japan. Three lithologic units were recognized in the 250 m-thick sequence of sediments: Unit 1 (0–70 mbsf) consists of calcareous silt and clay with thin volcanic ash layers, Unit 2 (70–150 mbsf) consists of calcareous silt and clay with volcanic ash and thin sand layers, and Unit 3 (150–250 mbsf) consists of weakly consolidated calcareous silt and clay with thick and frequent sand layers. Soupy structures and gas bubbles in the sediments indicate the presence of two hydrate zones between 40 and 130 mbsf and below 195 mbsf. Nannofossil biostratigraphy and magnetostratigraphy indicate that the sequence recovered at the BH-1 well is mostly continuous and represents sediments deposited from 0 to 1.5 Ma. Calculation of the sedimentation rate reveals a condensed section between 65 and 90 mbsf. The inferred distribution of gas hydrates in the BH-1 well appears to be strongly controlled by the stratigraphy and lithology of the sediments. Thick, gently inclined sand layers in Unit 3 provide a conduit for the migration of gases from deeper regions, and are considered responsible for the formation of the hydrate zone below 195 mbsf. At shallower levels, thin, gently inclined sand layers are also considered to allow for the migration of gases, leading to the formation of the upper hydrate zone between 40 and 130 mbsf. The overlying sub-horizontal silt and clay of the condensed section, truncating the underlying gently inclined sand and silt/clay layers, may provide an effective trap for gases supplied through the sand layers, further contributing to hydrate formation in the upper hydrate zone.     

Effect of sand lenses on groundwater flow and contaminant migration

The effect of homogeneous sand lenses on the groundwater flow in an otherwise homogeneous clayey deposit is examined by performing Monte Carlo simulations using a finite element flow model. In the simulations, the locations of the sand lenses are assumed to be mutually independent. The paper examines the effect on the flow field in a clayey deposit of (a) different percentages of sand lenses, (b) different hydraulic conductivities of the sand lenses, (c) different average sand lens sizes, (d) non-uniformity of the sizes of the sand lenses, and (e) localization of the sand lenses. The effect of these non-uniform flow fields on contaminant migration is then examined using a finite element contaminant transport model. For the range of cases considered it is shown that: the volume of sand lenses present has a greater influence than the shape, size, location and hydraulic conductivity of the sand lenses; simplified calculations performed using the geometric and harmonic means of hydraulic conductivity bracket the behaviour evident from more complex analyses; and the maximum impact on an aquifer separated from a waste disposal facility by a deposit containing sand lenses can be modelled to sufficient accuracy, using quite simple flow and contaminant transport models.     

Numerical modeling of contaminant transport resulting from dissolution of a coal-tar pool in an experimental aquifer

A previously developed two-dimensional numerical model is further developed for simulating the transport of dissolved contaminants originating from dissolution of a coal tar pool in a stratified, saturated porous medium. The model is used to simulate contaminant transport resulting from a rectangular-shaped coal-tar-pool dissolution experiment conducted in a large-scale experimental aquifer. The experimental porous medium consists of two sand strata, a high-hydraulic-conductivity upper stratum and a low-hydraulic-conductivity bottom stratum. The experiment was conducted to a time of 354 days and the groundwater velocity was changed several times within this duration. Model simulations show good agreement against observed contaminant concentrations, and simulations show that dissolved solute below the pool migrated deeper into the bottom stratum as compared to the upper stratum. Furthermore, simulations also suggest that contaminant concentrations in the lower stratum never reached quasi steady-state during the experimental time frame.     

Flow dynamics at the origin of thin clayey sand lacustrine turbidites: Examples from Lake Hazar,Turkey

Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focused on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced thin beds. Depositional processes and sources for three of those eleven clusters are studied at three coring sites. Bathymetrical data and seismic reflection profiles are used to understand the specific geomorphology of each site. X‐ray, thin sections and CT scan imagery combined with grain‐size, geochemical and mineralogical measurements on the cores allow characterization of the turbidites. Turbidites included in each cluster were produced by remobilization of surficial slope sediment, a process identified in very few studies worldwide. Three types of turbidites are distinguished and compared with deposits obtained in flume studies published in the literature. Type 1 is made of an ungraded clayey silt layer issued from a cohesive flow. Type 2 is composed of a partially graded clayey sand layer overlain by a mud cap, attributed to a transitional flow. Type 3 corresponds to a graded clayey sand layer overlain by a mud cap issued from a turbulence‐dominated flow. While the published experimental studies show that turbulence is damped by cohesion for low clay content, type 3 deposits of this study show evidence for a turbulence‐dominated mechanism despite their high clay content. This divergence may in part relate to input variables, such as water chemistry and clay mineralogy, that are not routinely considered in experimental studies. Furthermore, the large sedimentological variety observed in the turbidites from one coring site to another is related to the evolution of a sediment flow within a field‐scale basin made of a complex physiography that cannot be tackled by flume experiments.     

Vertical electrical sounding (VES) and multi-electrode resistivity in environmental impact assessment studies over some selected lakes: a case study

A combined geophysical investigation consisting of vertical electrical sounding (VES) and multielectrode system was carried out to map the subsurface resistivity in all major lakes which are highly polluted by the discharge of sewage and other chemical effluents in greater Hyderabad, India. The structural features identified in the study area play a major role in groundwater flow and storage. The interpretation of geophysical data and lithologs indicates that a silt/clay zone (predominantly silt) has a thickness of 5–10 m all along the drainage from Patelcheruvu to the Musi River. The silt/clay zone inferred close to the lakes is a mixture of clay, silt and sand with more silt content as indicated from the lithologs during drilling. The low resistivity values obtained can be attributed to the pollutant accumulated in the silt which can reduce the resistivity values. Further, the TDS of the water samples in these wells are more than 1,000 mg/l which further confirms the above scenario. The pollution spread is less in the upstream areas whereas it is more in the downstream which can be attributed to the shallow water table conditions and also due to the interaction of surface water and groundwater.     

Emplacement of massive deposits by sheet flow

Turbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross-laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms for emplacement of these massive basal units are still under debate. It is well accepted that the sequence considered here can be deposited by waning-energy flows, and that the parallel-laminated units are deposited under transport conditions corresponding to upper plane bed at the dune–antidune transition. Thus, transport conditions that are more intense than those at the dune–antidune transition should deposit massive units. This study presents experimental, open-channel flow results showing that sandy massive units can be the result of gradual deposition from a thick bedload layer of colliding grains called sheet flow layer. When this layer forms with relatively coarse sand, the non-dimensional bed shear stress associated with skin friction, the Shields number, is larger than a threshold value approximately equal to 0·4. For values of the Shields number smaller than 0·4 the sheet flow layer disappeared, sediment was transported by a standard bedload layer one or two grain diameters thick, and the bed configuration was characterized by downstream migrating antidunes and washed out dunes. Parallel laminae were found in deposits emplaced with standard bedload transport demonstrating that the same dilute flow can gradually deposit the basal and the parallel-laminated unit in presence of traction at the depositional boundary. Further, the experiments suggested that two different types of upper plane bed conditions can be defined, one associated with standard bedload transport at the dune–antidune transition, and the other associated with bedload transport in sheet flow mode at the transition between upstream and downstream migrating antidunes.     

Hydrogeology and historical assessment of a classic sequential-land use landfill site,Illinois, U.S.A.

The Blackwell site in northeastern Illinois was a classic sequential-use project combining land reclamation, a sanitary landfill, and a recreational park. This paper adds a recent assessment of leachate generation and groundwater contamination to the site's unfinished record. Hydrogeological studies show that (1) the landfill sits astride an outwash aquifer and a till mound, which are separated from an underlying dolomite aquifer by a thin, silty till; (2) leachate leaks from the landfill at an estimated average rate between 48 and 78 m³/d; (3) the resultant contaminant plume is virtually stagnant in the till but rapidly diluted in the outwash aquifer, so that no off-site contamination is detected; (4) trace VOC levels in the dolomite probably indicate that contaminants have migrated there from the landfill-derived plume in the outwash. Deviations from the original landfill concepts included elimination of a leachate collection system, increased landfill size, local absence of a clay liner, and partial use of nonclay cover. The hydrogeological setting was unsuitable for the landfill as constructed, indicating the importance of detailed geological consideration in landfill and land-use planning.