British Columbia Mine Reclamation Symposium

Effecting change by using innovative techniques in low risk projects Sahlstrom, David 2018

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata

Download

Media
59367-Sahlstrom_D_Effecting_change_low_risk.pdf [ 2.53MB ]
Metadata
JSON: 59367-1.0374936.json
JSON-LD: 59367-1.0374936-ld.json
RDF/XML (Pretty): 59367-1.0374936-rdf.xml
RDF/JSON: 59367-1.0374936-rdf.json
Turtle: 59367-1.0374936-turtle.txt
N-Triples: 59367-1.0374936-rdf-ntriples.txt
Original Record: 59367-1.0374936-source.json
Full Text
59367-1.0374936-fulltext.txt
Citation
59367-1.0374936.ris

Full Text

EFFECTING CHANGE BY USING INNOVATIVE TECHNIQUES IN LOW RISK PROJECTS    David Sahlstrom, B.Sc.(Agr), MBA, P.Ag.   David Sahlstrom Consulting  1990 Everett Rd, Abbotsford, B.C. V2S 7S3   ABSTRACT The ability to maximize the environmental value of reclamation is often constrained by engineering design criteria and protocol as well as specified standards. While standards minimize the chance of project failures, there are situations where strict adherence has stifled innovation. Evaluating the risks associated with projects can identify lower risk opportunities where innovative techniques can be explored. This paper presents a conceptual framework for evaluating risk and applies it to two scenarios; evaluating stream stabilization projects using rip rap and reclamation of acidic tailings. Cases studies are presented where low risk projects have used innovative techniques that have the potential to shift the paradigm with respect to commonly applied approaches in mine reclamation to improve the environmental values of reclamation.  KEY WORDS acidic tailings, ecosystem, environmental values, innovation, revetment, stream stabilization   INTRODUCTION  There has been considerable discussion over the years on designing for closure and much has been said about initiating reclamation planning at the beginning of the project. While it may be part of the planning process, the actuality is that reclamation and closure in practice is often governed by engineering design criteria. In addition, such reclamation is increasingly constrained by published protocols required to meet specified standards which may not apply to the site conditions nor produce a site that maximizes reclamation. This paradigm often subjugates the criteria for reclamation of the natural environment. The goal of such reclamation should be to develop self-sustaining diverse ecosystems and habitats compatible with the site that function similar to pre-mining conditions.   Constraints of Specified Criteria and Standards  Reclamation of B.C. mines was recognized as a priority in the mid-1970s when the B.C. Government established the B.C. Technical Research Committee on Reclamation and the annual B.C. Mine Reclamation Symposium. Ideas, concepts, and project results were shared and the community learned from successes and failures. Out of these meetings Reclamation Guidelines were developed. As time went on they morphed into a Reclamation Code followed by additional standards (both written and assumed). While these have effected a higher level of reclamation, there are situations where it seems that meeting the standards is more important than the actual reclamation results.   We must ask the question of when is it appropriate to not adhere to these so that the quality of reclamation is maximized? One way is to consider the risk associated with the project and if it is low then there is the opportunity to try alternatives.   Assessing Risk  A risked based approach was used to prioritize sites and prescribe appropriate work during the BC Forests Watershed Restoration Program of the 1990s. The concept was relatively basic but it provided a framework. The Risk (R) was evaluated as a function of Hazards (H) and their Threats (T).  Hazards are any features that could impact identified resources. These resources include the obvious such as human life, buildings and structures but also those with more environmental values such as fish habitat, wildlife habitat, visual landscape etc. The hazards included unstable road profiles, gulley crossings, landslides, debris lobes in stream channels, etc. A site could have multiple hazards.  Threats are measurements of the impacts on identified resources. The measurements included a value judgement for the resources, the size of the impact and the probability of it occurring. Thus a hazard that posed a threat to human life was assessed much higher than buildings or environmental values. Assessing the risk requires expertise from a variety of disciplines and so a team approach is necessary. It is important that the respective experts all have an equal contribution to the evaluation. Innovation and adaptation of design criteria can be applied to those projects that have lower risk.  STREAM STABILIZATION PROJECTS  The design and construction criteria of rip rap stream channel and bank protection is detailed with specifications for bank preparation, filter layers, size and composition of the rip-rap, etc. (B.C. Water Management Branch, 2000).  The design of a typical diversion ditch as shown in Photograph 1 is constrained by published design criteria. The flow capacity was designed to handle the flow from the possibility of a 1000-year storm event and the channel stability required to withstand such a flow. Bends in the channel were kept to a minimum with a maximum radius possible to reduce the erosion potential. Changes in gradient are kept constant to reduce the uncertainty in flow velocity and erosion potential. The channel was lined with clean rip rap meeting design criteria necessary to withstand the maximum flow of the 1000-year storm. The rip rap thickness is such that normal flow rates are not visible for most of its length.  Photograph 1. This diversion ditch is designed for a 1000-year flood event and armored with riprap. Normal water flow is concealed in the riprap. (Photograph taken July, 2012)  By engineering standards this is a well designed and constructed channel. However, from a reclamation perspective the channel does not support any productive habitat. The channel is a barrier to wildlife, there is no possibility of vegetation establishment in the riprap and very little chance of the stream supporting aquatic life. Its design and construction pose significant barriers for enhancing habitat/environmental values.  Designs for reclamation (habitat restoration in this case) are limited to additions installed in the channel as long as they do not compromise the generally accepted requirement to ensure integrity. Extra rip rap may be placed in the channel to create small pools and riffles, spawning gravel placed in select areas, channel edges planted with vegetation as long as it does not invade the rip rap. Woody debris may be added as long as it does not reduce the design capacity.  The end result has characteristics far different from those of natural streams which are in a constant state of erosion and accretion, have chaotic sinuosity that abruptly changes direction, have varied channel depth with deep pools and shallow riffles, with varied gradients and plugged with all manner of rocks, woody debris, overhanging creek banks, and vegetation that extends into the channel to the edge of the low water level, and possibly into the actual water.     Risk Assessment  Using the risk assessment described above, the hazard is channel failure and the valued resources are the natural environment. The channel flows into a clarification pond. There are no natural channels that flow into this channel which is an indication that the soils are permeable and the size of the existing channel upstream is small and has not failed since it constructed in the 1980s (Photograph 2). The slopes in this area are neither steep nor prone to erosion or mass failure. The threat from channel failure is uncontrolled overland flow which would flow into the clarification pond. The threat can then be considered low and so there is a low risk associated with this project. It would therefore be an ideal project to modify the design to provide increased wildlife and aquatic habitat.  Photograph 2. The channel in Photograph 1 is an extension of this channel that was built in the 1980s. (Photograph taken July 2012)     INNOVATION TO STREAM STABILIZATION  During the 1980s, a plan to rip rap the Coquitlam River was developed. The river is subject to sudden changes in water discharge from the BC Hydro power dam upstream on Coquitlam Lake. However, the river has very high Salmon habitat value and the Department of Fisheries and Oceans wanted the work to provide fish habitat which required provision for vegetation in the rip rap. As discussed above this is contrary to the established design criteria but the work could not proceed without it. Working with the engineers and DFO, the rip rap design was modified to provide the desired habitat by including vegetation in the rip rap.  Photograph 3. Eco-cells of intact plant communities were excavated from bars in the river channel and installed in excavated pocket in the riprap armoring. Soil was washed into the voids of the riprap followed by installing an erosion control netting to protect the soil from being washed away. Completed eco-cells can be seen in the background. (Photograph taken summer 1985)   A rip rap apron was extended into the riverbed and eco-cell pockets were created in the apron (as shown in Photograph 3). Using an excavator with a large bucket plant islands were excavated from bars in the river channel and installed in the eco-cell pockets. The plant islands were clods of soil with trees, shrubs forbs and grasses intact. They also included the biota of the soil clods. After installation of the plant islands, erosion control netting was staked and secured to the surface. Soil was then spread over the remainder of the apron and lower part of bank and washed into the riprap.     Photograph 4. One year after the installation of the eco-cells on the riprap apron the installed plant islands were established and volunteer plants were colonizing other areas of the riprap. (Photograph taken spring 1986)  Results  The eco-cells survived the erosion of the first winter and as shown in Photograph 4 were well established by the next year. The high flows over the winter deposited additional soil on the apron and volunteer plants were colonizing the riprap. The integrity of the riprap was maintained and over the years the vegetation continued to grow and additional plants grew throughout the riprap providing the desired vegetation for fish habitat with the destabilization of the riprap that was expected.   Thirty years later the vegetation has colonized most of the riprap and the river has buried most of the lower banks and aprons (Photographs 5 and 6).  This work challenged two misconceptions of the engineering community; one, riprap must have voids, and filling them with finer soils reduces the riprap stability and, two, vegetation in riprap negatively impacts its stability. On the first, a correctly designed and installed riprap revetment creates a matrix of interlocking angular rock. The addition of fines to this matrix does not affect its integrity as the integrity is based on the stability of the matrix. If the integrity were affected, every project on a river that transported silt would be in danger of failure.     Photograph 5. Thirty years later the riprap is barely visible in the stream bank. The cluster of rocks in the river is the same one that is in the middle of Photograph 4. This photograph is taken looking downstream. (Photograph taken July 2017)  Photograph 6. Thirty-five years later the riverbank (shown on the left of the photograph) is lined with vegetation. The area is now a park with a walking trail along the apron. Photograph was taken from the pedestrian bridge in the back of Photograph 3 and from a spot close to where Photograph 4 was taken. (Photograph taken July, 2017)  As for the second, the unique characteristics of root systems strengthen the soil creating soil columns or blocks which have a very high strength and behave as a unit. Slope failures associated with vegetation result not from the failure of the roots and trees but from undercutting of the root system by a stream or instability downslope. Poorly selected plant species may have improper root system or upper growth that can increase forces acting against slope stability (Gray, 1982).  The success of this project in providing vegetation cover for improved fish habitat, while maintaining the erosion control of the riprap revetment, has effectively changed the accepted design criteria and protocols. Existing riprap revetments on most rivers in the lower mainland have been retrofitted with vegetation and today most of them are greenways used as parks. Current river riprap projects often have vegetation and other environmental features incorporated into the design.  RECLAMATION OF ACIDIC TAILINGS  It is generally accepted that the appropriate reclamation of acidic tailings involves significant engineered construction projects. The preferred reclamation methods include covering with a thick impervious layer of till or flooding with water to keep them from being exposed to oxygen and water which accelerates the acidity. The purpose of these actions is to control the potential for acidic drainage containing unacceptable levels of heavy metals that can negatively affect the surrounding environment, in particular the aquatic environment.  From an engineering perspective, these techniques are effective but they also have shortcomings. First, the associated costs are high; exceeding an estimated $165k per ha in 2015 for just the construction phase (Norwest, 2015). Second, they create hazards including creating oxygen deficient atmospheres or requiring a dam in perpetuity. Third, they do not account for the capabilities of the living biological component of the environment which can impair the integrity of the cap through a variety of mechanisms. And fourth, there is additional responsibility and cost for long-term care and maintenance in perpetuity.  The end result is an unnatural system that requires continued maintenance and is an impediment to achieving reclamation goals, in particular those related to end land use and quality. The end result does not function as a self-sustaining natural ecosystem. In contrast, naturally occurring instances of acidic soils that have similar impacts rely much more on the living biological component for control and mitigation.  Risk Assessment  Using the risk assessment as described earlier the hazards of acid tailings include the release of acidic water with dissolved metals, release of sediment, accumulation of elevated levels of metals in vegetation, and more. The impoundment has the additional hazards of the tailings dam and stored water. Further, capping unsaturated tailings creates the hazard of oxygen deficient atmosphere. The team examining the hazards may identify additional hazards.  The threat of acidic discharge water is to negatively affect the receiving environment. It is generally accepted that acidic water and mobilized heavy metals negatively affect fish and other aquatic organisms and there are standards for acceptable concentrations in discharge waters. The threat of tailings dams and stored water is the potential for catastrophic failure impacting the receiving environment. The potential for oxygen deficient atmosphere poses an extremely serious threat including death to humans.  If, after conducting the risk assessment the acidic tailings risk is low, there is the opportunity to modify the generally acceptable reclamation procedures. It may not be necessary to cover or flood the tailings. Rather, in these instances, it may be acceptable to harness natural processes to mitigate the risks associated with acid rock drainage.  Photograph 8. There were large areas of the tailings that were exposed sand and had no vegetation. Adjacent areas had a layer of blackened duff and no vegetation. Other areas had dead or dying shrubs and trees. The pH of discrete samples taken from these areas in 2003 ranged from 2.7 pH to 4.4 pH. (Photograph taken June, 2003)  INNOVATION OF ACIDIC TAILINGS RECLAMATION  Tailings of the closed Boss Mountain Mine in central Cariboo that had been revegetated in the early 1990s were found to have become acidic by 2002. The established vegetation was dying off (Photograph 8) and soil testing for pH showed that the affected areas had pH as low as 2.7. Characterization of the tailings during reclamation planning in the 1980s had determined that there was a potential for the tailings to become acidic but it was predicted that weathering of the tailings would neutralize the acidity over the long.     Innovation  The importance of vegetation in ameliorating tailings acidification has long been recognized (Brooks, 1989). Recently, topics such as phytoremediation, phytostabilization and microbial treatment have focused on specific components of biological amelioration (Mendez, 2008, Haakensen, 2016). However, these are only parts of a well-functioning ecosystem which includes the complete range of living organisms. An ecosystem develops over time as the biotic factors interact with, effect changes to, and respond to the abiotic factors. The re-reclamation of these tailings was based on the thesis that by addressing specific constraints of a site, the natural development of an ecosystem can be encouraged and will eventually become self-sustaining which will, at the same time, function to ameliorate the acidification.  Photograph 9. By 2008, the barren areas supported a diverse plant community. Bare areas provided opportunity for native species to colonize. The seeded grasses and legumes in many areas that had no plants in the beginning were being replaced by native forbs, shrubs and trees. (Photograph taken July, 2008)  The tailings were increasingly acidic, devoid of nutrients (including organic matter) and characterized as having a very low capacity to retain nutrients as they were primarily sand. These characteristics were limiting the development of a biological complex. To resolve these limitations, the re-reclamation program focused on providing the lacking nutrients, increasing the pH through application of agricultural dolomite lime and establishing a plant community. Because the tailings had no nutrient holding capacity, only incremental amounts required for plant growth were applied annually in order to minimize the leaching of excess nutrients from the soil. The annual application would continue until sufficient organic matter was built up to provide sufficient nutrient retention and recycling.   Recognizing that the plant community would change over time as the site conditions changed, the site was seeded with a grass and legume mixture selected for their abilities to establish quickly and initiate the nutrient cycling. The site was then managed to encourage native plant colonization that would eventually replace the agronomics.  Photograph 10. By 2015, the native shrubs and trees had become the dominant form in some areas. The plant community was continuing to change as the biota changed the site characteristics. Soil organic matter was increasing. (Photograph taken July, 2015)  A trial program, initiated in the fall of 2003 on small areas of the tailings proved to be very successful in establishing a vegetation cover. The acidity of the untreated areas increased dramatically over the next year with pH decreasing by up to 1.0 pH units. In 2005 the program was expanded to eventually treat the entire tailing area.   Since then, an annual program of assessments and treatments prescribed through an adaptive management process has continued. Over time the vegetation has changed in most areas as the biota have modified site characteristics. In some areas the plant community changed as the seeded agronomic grasses and legumes were replaced with native plants. The stunted and dying shrubs and trees reversed this trend and began to flourish becoming the predominant vegetation in some areas. In recent years, legumes and willows have begun to show up in areas where a heavy grass cover had become established (Photographs 9 and 10).  Figure 1. From 2003 to 2015, the average pH of samples from the treatment areas increased from 3.7 pH to 5.3 pH.   The average pH of soil samples taken from treatment areas increased from 3.7 pH in 2003 to 5.3 pH in 2015. In 2003, 3 samples had less than 3.4 pH and none were greater than 4.5 pH. In 2015 no samples were less than 3.4 pH and 6 samples were greater than 5.5 pH  (Figure 1).   Changes to other biota present on site have also occurred. Mosses and lichens have established. An increasing variety of mushrooms have sprouted from the soil fungi that are changing soil characteristics. Insects, amphibians, animals and birds have been observed using or residing onsite. The tailings pond which was barren of vegetation in the beginning now resembles a marshland (Photograph 10).  Results  The re-reclamation program has resulted in reversing the acidification trend using incremental inputs. The plant community is complex and evolving with the changing site conditions and the biota necessary for a self-sustaining ecosystem are developing. This has been accomplished on the exposed tailings without the addition of capping material or topsoil. All of this has been accomplished by spending less than the interest on the estimated $3M cost of capping the site. Challenging the paradigm reclamation strategy for on tailings reclamation acidic tailings has created a site that resembles a mountain meadow in less than 15 years. Photograph 10. There were no plants growing in the tailings pond or the beach area when the program began. With time, the beaches and marsh areas have been colonized with willows, sedges and rushes. The area is used by moose, deer, bear, and waterfowl. Each year there is a population of tadpoles in the pond. (Photograph taken August, 2017)   CONCLUSION  The established engineering protocols and regulatory standards have addressed many failings identified in the mining industry for achieving reclamation objectives. However, their adherence and implementation may produce results that may not maximize the project’s value with respect to sustainable development. In particular these engineering design standards can pose impediments to maximizing specific environmental features and general ecological values. Challenging these presents a risk to both the project’s success as negative response from regulatory agencies the risk should be evaluated before doing so.  This paper presents a framework for assessing such a risk that requires evaluation using a team with expertise in the disciplines affected. Projects that pose a low risk are ideal candidates for challenging the established system.  The case of innovation in streambank stabilization showed the benefits to incorporating vegetation in riprap and has led to gradual acceptance of this novel approach. However, the approach is still not incorporated into the engineering design criteria, rather it is tagged on as and when necessary. The stream channel shown in Photograph 1 and Photograph 11 is a typical example of many projects that do not include vegetation as design elements nor does it provide conditions that enable vegetation (or almost any other biota) to colonize it. This resistance to vegetation can be seen in other types of engineered projects such as steep slope stabilization.  Photograph 11. This diversion ditch was constructed in 2005. Photograph 1 shows it in 2012 and this photograph was taken in 2017. There has been no vegetation encroachment into the channel and it remains a barrier to animal movement. (photograph taken August, 2017) Photograph 12. The diverse vegetation cover of the tailings includes seeded grasses and legumes, and native forbs, shrubs and trees. Figure 7 shows the same area at the beginning of the project in 2003. The revegetation was accomplished through a multi-year program of treatments directly on the acidic tailings. Note: some of the grass areas are in summer dormancy and are a dry brown colour. (photograph taken August, 2017)   The case of innovation of acidic tailings reclamation showed the benefits of implementing a multi-year program to reclaim ultra-acidic tailings that targeted the development of a self-sustaining ecosystem. It demonstrated that select inputs to address the constraints of the site conditions could reverse the acidification and encourage the natural processes of reclamation at a cost much less than the generally accepted engineered mitigation.  This approach to assessing the risks associated with projects and then applying innovative reclamation approaches for low risk scenarios has the potential to shift the paradigm with respect to commonly applied approaches in mine reclamation.  REFERENCES B.C. Water Management Branch. 2000. Riprap Design and Construction Guide. Province of British Columbia, Ministry of Environment, Lands and Parks, 87pp. Brooks, B.W., T.H. Peters and J.E. Winch. 1989. Manual of Methods Used in Revegetation of Reactive Sulphide Tailings Basins. MEND Report 2.24.1. Gray, Donald and Andrew Leiser. 1982. Biotechnical Slope Protection and Erosion Control. Van Nostrand Reinhold Company Inc. New York. 271pp. Haakensen, Monique, Vanessa Friesen, Rachel Martz, Marke Wong, Jenny Liang, and Elain Qualtiere. 2016. Assessment of the Huckleberry Mine Site for potential passive or semi-passive acid rock drainage treatment options. In Proceedings of the Fortieth Annual British Columbia Mine Reclamation Symposium. BCTRCR, Victoria, B.C. (117-130). Mendes, Monica O. and Raina M. Maier. 2008. Phytostabilization of mine tailings in arid and semiarid environments. In Environmental Health Perspectives, 116(3), (278-283).  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.59367.1-0374936/manifest

Comment

Related Items