Hydraulic barriers

Principal Option for Containment/ Recovery Excavation Vacuum extraction Temporary cap/cover Hydraulic modification No action Groundwater pumping Subsurface drains Hydraulic barriers Low permeability barriers No action Overflow/underflow containment (i.e. oil booms) Run off/run on control Diversion/collection No action Capping/ nsulation Operations modifications Gas collection/removal No action... 

The landfill liner, cover, and hydraulic barrier all belong to the subsurface pollutant engineered containment system. The liner is designed at the bottom of a landfill to contain downward leachate. The cover is designed at the top of a landfill to prevent precipitation from infiltrating into the landfill. The hydraulic barrier, or cutoff walls, is a vertical compacted earthen system to contain horizontal flow of plume. The ultimate purpose of these barriers is to isolate contaminants from the environment and, therefore, to protect the soil and groundwater from pollution originating in the landfill or polluted site. 

Most spent foundry sand discarded is green sand. The primary components of green sand are silica and bentonite. Thus, green sands are essentially a sand-bentonite mixture, which makes them potentially useful as a liner and cover materials, that is, for hydraulic barrier layers. 

Some end-use applications may prefer the characteristics of foundry solid waste. For instance, spent foundry sand is a uniformly graded fine aggregate containing chemically active iron and organics. Spent foundry sand can be superior to other types of granular materials, such as compacted soils or clays, for hydraulic barriers. In this case, spent foundry sand provides better performance at lower cost. 

A composite hydraulic barrier, consisting of (a) a 0.5-mm-thick GM upper component and (b) a 0.6-m-thick CCL lower component, with the CCL having a minimum hydraulic conductivity of 1 x 10 7 cm/s. 

Reinjection of coproduced groundwater through the use of wells is commonly used to return the water to the same aquifer and to set up hydraulic barriers in an effort to contain the plume. Injection wells are commonly used in conjunction with withdrawal systems to enhance the recovery of hydrocarbons. Injecting water at appropriate locations will create a pressure ridge to increase the hydraulic gradient effectively toward the withdrawal point. Normally, the water pumped from the recovery wells is used as the injection water and is injected, without treatment. This method provides an economical way of handling the produced water, as well as being beneficial to the recovery effort. 

Figure 15 13 Hydraulic barrier along the coastline in the Bagnoli brownfield site.

Effect of Hydraulic Barriers in the Through-Flow and Stagnation Zones... 

The through-flow zone has so far been described in a simplified mode, assuming all the hosting rocks are homogeneously permeable. Deviations from the simplified L-shape of the flow path are caused by the presence of hydraulic barriers, such as clay and shale, that may in certain places block the downflow and create local perched water systems and springs (Fig. 2.16) or cause steps in the path of the lateral flow zone. But the overall L-shape is generally preserved, as the water of perched systems finds pathways to resume the vertical downflow direction. 

Fault zones may be open and highly conductive, or they may be sealed by mineral precipitation, forming hydraulic barriers. 

The surface waters incised the landscape, forming deep channels that were filled with new terrestrial and marine sediments as the seawater rose again. These deep paleochannels serve, according to the nature of the filling sediments, either as potentially preferred flow paths and preferred underground drainage systems or as hydraulic barriers. 

The accumulation of pollutants around one of the electrodes may cause the pore fluid flow rate to fall, and hence, a partial hydraulic barrier can be formed. 

The potential materials for each layer are summarized in Table VI. Some layers, such as the hydraulic barrier layer, may consist of more than one material, such as a composite barrier comprising a geomembrane overlying a compacted clay. 

Bath, A. H. 1993. Clays as chemical and hydraulic barriers in waste disposal Evidence from pore waters. In Manning, D. A. C., Hughes, P. L. Hughes, C. R. (eds.) Geochemistry of Clay Pore Fluid Interactions. Chapman Hall, London, 316-330. 

Peterson, S. R. Gee, G. W. 1986. Interactions between acidic solutions and clay liners permeability and neutralisation. In Johnson, A. I., Frobel, R. K., Cavalli, N. J. Pettersson, C. B. (eds) Hydraulic Barriers in Soil and Rock. ASTM STP 874, American Society for Testing and Materials, Philadelphia, 229-245. 

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