Trichloroethene (TCE) in groundwater is one of the most prevalent contamination problems at hazardous waste sites; a problem that is substantially greater if the TCE is present as a dense non-aqueous phase liquid (DNAPL). Shallow, low permeability aquifer systems compound the problem at many sites in the eastern and central US due to the ease with which the contamination enters the shallow groundwater and the difficulty in extracting sufficient pore volumes from the tight formations for effective and timely remediation. This article describes a remediation project that demonstrates the effectiveness of dual-phase extraction technology, pneumatic fracturing and air injection for remediation of aqueous, sorbed and free-phase TCE from a shallow, low permeability aquifer. The clean up is being performed under the Illinois Environmental Protection Agency's voluntary remediation program, which allows flexibility within a less rigid regulatory framework than enforcement driven programs.
Microorganisms such as algae, bacteria, fungi and protozoa in water come in a variety of shapes and sizes some exhibiting their own means of locomotion, others clinging to other solid matter, but most behave like other organic or inorganic particles in the water column. As microbes associate with other particles, their behavior may take on that of the host particle Armed with an understanding of particles and their properties in water, one can make at least some qualitative statements about the behavior of microbes in a clarification system. In this summary we present some relevant aspects of particle theory, including the nature of microorganisms and some summary comments.
subject to complex flow patterns and varying tides, urban development in coastal areas can be difficult to design. Two-dimensional finite-element computer models are often the best choice for analysis of a coastal environment. However, practicing engineers must overcome many obstacles when using such inherently unstable models. Running numerous trials to obtain good results can be frustrating. This paper presents a case study of scour analysis for a barrier island bridge near Charleston, South Carolina, where the applicability and limitations of two-dimensional modeling were closely examined.
A methodology for finding the optimal layout of a detection system in a municipal water network is formulated and demonstrated. The detection system considered consists of a set of monitoring stations aimed at detecting a random external input of water pollution. The level of service provided to the consumers is defined by the maximum volume of consumed polluted water prior to detection. The methodology involves the establishment of an auxiliary network that represents all possible flow directions for a typical demand cycle, an “all shortest paths” algorithm to identify domains of pollution, and a “set covering” algorithm to optimally allocate the monitoring stations. The algorithm outcome is a minimal set of monitoring stations that satisfies a given level of service. The methodology is demonstrated on a small illustrative case and on a midsize water network.
Over the last few years stormwater retrofitting has become widely accepted terminology and a specialty in engineering design. While the rush to address retrofitting needs has led to the development of new BMP's. After the engineers, contractors and permitting agencies have left, it is usually the responsibility of a municipality's Public Works or Stormwater Utility to properly maintain the BMP's to ensure that stormwater treatment will not decline with the age of the project. While intentions are often noble, the long term costs for maintenance are often underestimated and/or misunderstood.
Biodegradation of chlorinated ethenes was studied both in laboratory cultures and in the field. Optimal tetrachloroethene (PCE) degradation was accomplished by sequential activity of anaerobic PCE-dechlorinating bacteria and aerobic cometaboic mineralization of dechlorination products (trichloroethene, TCE; cis-1,2-dichloroethene, cDCE; and vinylchloride, VC) by phenol-utilizing microbes. A novel PCE-dechlorinating anaerobic bacterium, Desulfitobacterium sp. strain TCE1, was isolated. Its PCE-dehalogenating activity was controlled by the availability of PCE and alternative electron acceptors sulfite, nitrate and fumarate. Metabolic interactions observed in co-cultures of strain TCE1 and a sulfate reducing Desulfovibrio species included competition for shared electron donors and H{sub 2}-transfer from the sulfate reducer to the dechlorinating anaerobe.
The water distribution system problem consists of finding a minimum cost system design subject to hydraulic and operational constraints. In this paper a paddy irrigation system and a municipal (Hanoi) water distribution system are considered. Because the problems are nonconvex, a global search scheme called Stochastic Probing method is employed to search among the various local minima. The paddy irrigation system is solved for multiple loadings. The optimal solution for the Hanoi network has significantly smaller cost than the ones previously reported.
As part of an on-going groundwater modeling research program, a numerical model based on discrete networks was developed to simulate fluid flow and contaminant transport through porous media. A fundamental problem in applying the discrete model is relationship between discrete quantities and their conceptualization in a continuum setting. This paper describes pre- and postprocessing procedures for interaction between the continuum idealization of the Groundwater Modeling System and the discrete network model.
Conemaugh River Lake was authorized by the 1936 Flood Control Act for the sole purpose of reducing flood stages on the Kiskiminetas, lower Allegheny, and upper Ohio Rivers and placed in full operation in December 1952. However, over the years sedimentation problems, seriously aggravated by erosion from extensive surface mining operations in its tributary drainage basin, has forced the Pittsburgh District to gradually increase the project's minimum pool elevation. Much of the accumulated sediment in the lake is located immediately upstream of the dam. The sediment, deposited since construction of the dam, exceeds 30 feet in thickness in the lower three miles of the reservoir and is adversely impacting the operation of the dam.
This paper discusses the participation of the Seattle District of the Army Corps of Engineers in trans-boundary water management with its Canadian counterparts. The District Commander plays a pivotal role as a representative of the U.S. Section of the International Joint Commission. In addition, the District is involved in other water resources operations with trans-boundary implications, such as operations at Ross Dam on the Skagit River under flood conditions.
The research described in this paper investigates the utility of Artificial Neural Networks (ANNs) for short term forecasting of streamflow. The work explores the capabilities of ANNs and compares the performance of this tool to a conventional approach used to forecast streamflow. A number of issues associated with the configuration of the ANN are examined. Some of these issues include the type of input data, the number and size of hidden layer(s), and the composition of the data set. The application of the ANN approach is to a portion of the Winnipeg River system in northwestern Ontario, Canada.
Geographic Information Systems (GIS) are now being used by many agencies to do their work. There are GIS computer tools on the market that can and should be used by Engineers to do mapping analysis. One of these tools is ArcView(R) (ESRI, 1992). This paper presents and overview of GIS concepts and definitions. Examples of possible uses of these tools in the water resources field are presented.
In a contracting reach at a bridge crossing over a wide, flat floodplain, the stored water at the limits of the floodplain is considered an area of ineffective now. One-dimensional, standard step, open channel models are widely used and provide reasonable predictions of water surface elevations. Cross sections upstream of a contracting reach are recommended to be placed where the flow lines are parallel and the full cross section is effective within these models. Hydraulic properties near the bridge may be desired, requiring cross sections that are not fully effective. For example, to estimate scour using WSPRO, a cross section one bridge length upstream of the bridge opening is recommended. To accurately predict hydraulic properties within a contracting stream reach using one-dimensional standard step models, determination of areas of ineffective now is required.This study compares one-dimensional modeling methods in use to define ineffective now areas at a cross section one bridge length upstream of a bridge crossing a wide, flat floodplain. In addition, a method is suggested to eliminate ineffective flow areas based upon the premise that a cross section is to be perpendicular to flow at all locations. Flow distribution and energy losses through the bridge (i.e. backwater) are compared with and without consideration of ineffective flow areas in the one-dimensional models. For validation, all results are compared to a two-dimensional model.
