ENVIRONMENT Engineered barriers are being developed with design lives of more than 300 years. These barriers are being designed to minimise the changes for human and animal intrusion , plant root penetration , seismic stability, and wind and water erosion resistance. D esigns for the arid environment require the specification of mu ltiple layers of en hanced barrier materials. These include variou s asphalt formulations, synthetic liners and grout formu lation s. Wall or subsurface barriers are a physical sys tem that will isolate or contain contaminants in a defin ed zone. This can be an interim action to prevent furth er migration of contam in ation before treatment or can provide longer term containment and confinement. Enhanced barrier materials such as viscous liquids , gels, polymers, silicates and mineral wax dispersions are being developed w hi ch will minimi se the cracking of a barrier and enable the maintenance of the barri er sho uld cracks occur. They are also easier to emplace. These materials so lidify at sub surface temp eratures to produce n early inert imp ermeable barriers. T hese materials are being designed to provide a barrier with lower permeabilities and extend the applica tion to co nta ct with con centrated ch emica l solutions. Drilling technologies and advancements in barrier materials have led to
the development of horizontal barriers. This would enable a floor to be placed undernea th a was te site to preve nt downward migration of contaminants Grout walls are a relatively new technology. The grout wall is created by inj ec ting grout directly into the soil using permeation grouting or by in situ mixing of the soils and grout using technologies such as deep soil mixing. Permeable/ sorbent barriers are being developed for the treatment of gro undwater and to prevent the further migration of contaminants from solid waste sites. These barri ers are located in the vadose zone or aq uifer sediments and minimi se contaminant migration by mixing chemical reagents directly within the barrier materials or placing a layer of reagents next to the barriers. Ice barriers/cryogenics An ice barrier co nsists of a wall of watersa turated soil that has been frozen , producing a temporary barrier. Frozen soil barriers have been used for many years in the construction industry to stabilise soils aro und an excavation site to prevent cave-in of the walls. When the barri er is no longer needed, the refrigeration is stopped and the barrier slowly melts . These barriers are being developed as an interim barrier for use during waste retrieval (tank sluicing) or deploymen t of in situ treatment techn ologies (soil flushing) to prevent the further migration of contaminants.
BOOKS Free-living Freshwater Protozoa: A Colour Guide D J Patterson. Available from UNSW Press, tel. (02) 9398 8900, fax (02) 9398 3408. Cost: $59.95 'Protozoa are found in almost eve1y habitat from cesspit to mountain stream.' They are an extremely di verse group of unicellular 'animals.' Together with unicellular algae and sli me moulds, th ey make up the proti sts. They are an important group as significant consumers of bacteria and used as indica tors of water quality due to their response to changing physical and chemical characteristics. This excellently illustrated book is aimed at students and professionals who need to study protozoa as part of their work . There is an emphasis on tho se animals likely to be encountered in freshwater habitats. The key relies on observing live organisms (with lots of photographs and diagrams provided) so there is no need for specialised training in staining or preservation tec hniqu es. Th e identification is taken to genus level but references are given for th ose wanting to identify to species. 38
WATER JULY/ AUGUST 1997
A classifica tion key starts with key characteristics of the major groups. A dichotomou s key then takes identification to ge nu s using steps and diagram s or photographs together with descriptive notes. If all else fails yo u can search through the numerous and clear pictures to find your 'beast'. Th e text provides a thorough coverage of methods for studying and identifying protozoa including: • how to identify protozoa • techniques for using the micro scope and for finding , collecting, keeping and culturing protozoa . T here are even methods for calming di stressed protozoa from gently blowing on them to drugging them! Finally there is a section on protozoan communi ties including plankton, attached fo rms, benthos and sewage trea tment plant orga ni sm s. The diagram on sewage treatment communities shows the gradation in types. Protozoa are a neglected group of biota. T hi s text provides an easily digestible method of discovering the incredible diversity and beauty of this important freshwater group .
Dr Robyn Tufr
The ice barrier can be easily removed from a site if desired; w hereas other barrier technology would require physical crumbling and excavation to remove.
Site Characterisation Site characterisa tion is a m ajor hurdle that must be overcome in order to effec tively apply remediation technologies. C haracterisa tion data is required to evaluate and assess technology options and to ensure that remediation is accomp li shed. R emediation activities rely on process monitoring and control system s (part of characterisa tion) to ensure that the operating conditio ns are m et. C haracterisation cos ts are enormou s and current technology is ineffective in many cases for locating waste sites and identifying the heterogeneities in the subsurface.
Risk Assessment Ri sk-based planning and decisionmaking is important in the US and its use depends on the stage of developm ent for a particular technology and the scale of the decision. Most large-scale planning decisions follow the NEPA process w hi ch expli citly consid ers environmental, safety and health risk, along with cost and schedule uncertainty. At the technology level, other factors , primarily cos t, becom e the drivers in decision-making. In the US we are making progress in developing and applying ri sk-ba se d decisionmaking processes . However, there is no single widespread process that is being implem ented.
Conclusions T he problem s in the United Sta tes in cleaning up large volumes of contaminated soils and solid waste require us to advance beyond the existing technologies. Permanent solutions , cost-effective approaches and low-risk alternatives that have a minimum of secondary waste generation are needed. T his is especially true as the US D epartment of Energy addresses the issues associated with its radioactive wastes . Through the collective effort s of industry, university research and techn ology development within government agencies , there are a number of very promising emerging technologies. Due to the large potential cost savings , it is anticipated that the emphasis will be placed on in situ cleanup technologies .
Author Mary E. Peterson is a senior program manager at Pa cific Northwest National Laboratory, USA. Sh e has a background in ch emical engineering and has been involved in numerous hazardou s and nuclear waste treatm ent and disposal programs.