British Columbia Mine Reclamation Symposia

Engineering approach to mine reclamation with biosolids, part II Renken, Karin 1998

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nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  ENGINEERING APPROACH TO MINE RECLAMATION WITH BIOSOLIDS PART II Karin Renken, B.Sc. (Hons. Phys.), M.Sc. (Bio-Resource Eng.) Sperling Hansen Associates Inc., 1401 Crown Street, N. Vancouver, B.C., V7J 1G4, Ph. (604) 986-7723  ABSTRACT This paper outlines the six step engineering approach to mine reclamation with biosolids: 1) site assessment, 2) regulatory constraints identification, 3) reclamation goal definition, 4) biosolids assessment, 5) reclamation plan design, and 6) seed bed preparation and biosolids application, but excludes detailed application rate calculations, best management practices, and monitoring guidelines which were already summarized in "Engineering Approach to Mine Reclamation with Biosolids" (Renken, 1997). This and the abovementioned paper are intended to be a preview of the guidance document for land reclamation for the upcoming British Columbia "Selected Organic Matter Recycling Regulation" (Regulation) which will supersede the 1983 "Guidelines for the Disposal of Domestic Sewage Under the Waste Management Act". '"Land Reclamation' means using Class A or Class B biosolids to rehabilitate the productivity or capability of mining, forest, or agricultural land that has been subjected to processes which have caused impairment of use or productivity, and is managed according to the requirements of the Agricultural Land Commission, Forest Practices Code or a Mine Reclamation Plan." (B.C. MoELP, 1998). INTRODUCTION  The use of biosolids as a soil amendment to reclaim disturbed land can be a win-win biosolids recycling option for the biosolids manager, the land owner, and the environment. Benefits of land reclamation with biosolids include: decreased erosion, accelerated vegetation establishment and soil development, increased biomass production, improved vegetation quality, increased recycling of municipal solid waste, decreased combined costs for disposal and reclamation, and reduced irrigation requirements in arid climates. Land application of biosolids has been shown: 1) to increase the soil's aggregate stability, water holding capacity, cation exchange capacity, and plant nutrient concentrations; 2) to decrease soil bulk density; and 3) to buffer soil pH. Biosolids is municipal sewage sludge or septic tank sludge which has undergone a thorough wastewater treatment process, and which can be safely and effectively recycled on land. Currently, land application of biosolids in British Columbia is regulated by the "Guidelines for Disposal of Domestic Sewage Under the Waste Management Act" (B.C. MoELP 1983).  1  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  STEP 1 - SITE ASSESSMENT To develop a suitable reclamation strategy for a particular disturbed site, key site and biosolids characteristics need to be determined. Typically, site assessment starts with an assessment of overall site characteristics to identify suitable areas for biosolids application. Important overall site characteristics include: site location (legal description and/or latitude & longitude); size; type and extent of the disturbance; land ownership, including surface and mineral rights, and licensed users; climate; general description of surficial geology; proximity to inhabited places; site access; slope steepness; areas currently available for reclamation; and if the site is actively used, the projected lifespan of the operations. Suitable areas for biosolids application include most disturbed areas that are deficient in organic matter. The best sites for biosolids application can accept biosolids in any form and without restrictions on the timing of application, other than those imposed by the vegetation. These sites have soils with moderate hydraulic conductivities and medium texture (silt and silt loams). Poorer sites for biosolids application may restrict the type and quantity of biosolids that can be applied, the method of application, and/or the timing of application. Poorer application sites have soils with one or more of the following characteristics: high coarse fragment content, restrictive layer close to the soil surface, low infiltration rate, very low or very high hydraulic conductivity, very low or very high pH, or phytotoxic concentrations of trace elements or organic compounds. After the overall site characteristics have been assessed, the site needs to be assessed in detail in order to develop a suitable reclamation strategy. Site characteristics that should be identified were summarized by Renken (1997; Table 1). As part of the detailed site assessment, an accurate topographic contour map should be obtained or compiled at a scale consistent with good engineering practice (e.g. 1:2,000 to 1:5,000). The mapping may then be used to: 1) delineate areas with slopes too steep for biosolids application, 2) determine if regrading is necessary or possible in some areas, 3) design surface water control structures (e.g. ditches, terraces, or berms), and 4) plan the reclamation program. Main features of the land surface that should be shown on the topographical map include: areas and types of disturbances, areas and types of previous biosolids applications, buildings and other engineered structures, springs, wells, streams, lakes, creeks, ditches, roads, and property boundaries. STEP 2 - IDENTIFICATION OF REGULATORY CONSTRAINTS When using biosolids, the requirements of the Regulation, and if applicable, the requirements specified by other regulatory agencies have to be met.  2  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  STEP 3 - DEFINITION OF A RECLAMATION GOAL  A reclamation goal should be clearly defined in order to develop the most suitable reclamation strategy and to be able to evaluate the reclamation success at a later date. The definition of the reclamation goal should include the desired end land use, land productivity, and completion date for the reclamation. The final land use must reflect the projected land capability and the level of management that the owner, agent, or manager is willing to provide to maintain this land use. STEP 4 - BIOSOLIDS ASSESSMENT  Similar to the assessment of site characteristics, biosolids assessments typically occurs in two stages: an overall and a detailed assessment. Key questions that need to be answered during the overall biosolids assessment are: • • • •  What type of biosolids are available? Where are available biosolids located? What quantities of biosolids are available? When are biosolids available?  In case that enough biosolids of acceptable quality are available at a reasonable price, the biosolids quality needs to be identified in terms of the parameters listed in Table 1. Biosolids quality should be assessed prior to designing the reclamation plan and as near to the time of biosolids application as possible. STEPS – DESIGN OF A RECLAMATION PLAN The overall goal of reclamation planning is to achieve the best reclamation within technical, economic, and time constraints. The process of designing a reclamation plan can be broken down into 10 parts which are summarized in Table 2 and discussed below. Part 1 - Ranking of Site Characteristics  For site rehabilitation to be successful, the reclamation site's most limiting characteristics with respect to vegetation establishment have to be overcome. Consequently, site characteristics, compiled in the site assessment process, have to be ranked according to their potential of limiting vegetation establishment. Part 2 - What Kind of Site Preparation is Required?  The extent of site preparation required prior to biosolids application to disturbed areas is highly dependent on the physical and chemical site characteristics. Site preparation may necessitate placement  3  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation 1  Table 1. Sampling Parameters to determine Biosolids Quality  4  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  5  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  of additional fine earth (e.g. silt or silt loams) on the soil surface, surface water control and/or other measures to render the site suitable for seed germination and vegetation establishment. Surface water control may be needed: 1) to minimize water erosion before and after vegetation establishment, 2) to prevent biosolids from leaving the application site, and 3) to protect surface water quality. Site preparation may consist of recontouring (e.g. flattening of slopes or eliminating overhangs at the top of slopes). Recontouring may be necessary to affect long-term slope stability, to enable successful vegetation establishment, and to create a final landform that is hydrologically and aesthetically compatible with the surrounding area. Other measures of site preparation may consist of capping a contaminated site with mineral soil or a barrier cover system prior to biosolids application to prevent pollutants contained in contaminated surficial soil from entering the food chain via plants or soil microorganisms. Part 3 - Determination of Regulatory Site Restrictions  When using biosolids, compliance with site restrictions and requirements defined in the Regulation, and if applicable, requirements specified by other regulatory agencies must be achieved. Once the Regulation is in effect, only biosolids that meet the following Class A or Class B pathogen reduction requirements can be applied to without a special authorization under the Waste Management Act (B.C. MoELP, 1998): Class A: The density of fecal coliform in biosolids must be less than 1,000 MPN per gram of total solids (dry weight basis). If the density of fecal coliform is more than 1,000 MPN per gram for any one sample then the density of Salmonella sp. bacteria in the biosolids must be less than 3 MPN per 4 grams of total solids (dry weight basis). Class B: The density of fecal coliform must be less than 2,000,000 MPN per gram of total solids (dry weight basis). In the Regulation, site restrictions have been defined based on the class of pathogen reduction, the level of vector attraction, and the total solids content of biosolids. Table 3 summarizes these restrictions for Class A and Class B biosolids. Part 4 - Compilation of Target Levels  To facilitate successful site rehabilitation, a site-specific target list of achievable nutrient, organic matter, total trace element, and water quality levels needs to be compiled for the reclamation site. Target levels should comply with limits specified in applicable regulations, site permits and/or regulatory approvals and should be a reflection of the ranked site characteristics.  6  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  7  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  The definition of target levels for a particular site may be based on: 1) results of test trials or past reclamation projects completed in the immediate vicinity, 2) characteristics of a reference area that are comparable to characteristics of the reclamation site, and/or 3) other technical standards. Table 4 lists total trace element limits given in the draft Regulation (June 1998) as well as suggested maximum soil concentrations for the reclaimed land. Part 5 - Scale of Biosolids Application; Operational or Test Trial? Biosolids are usually applied on an operational scale if sufficient, relevant reclamation experience exists. Biosolids are typically applied on a test trial basis to sites for which no or little comparable reclamation experience exists. Test trials may be conducted at any time, but are generally limited to the initial startup phase of a large reclamation project: to quantify design application rates, to determine the best reclamation technology, or to determine if biosolids as a soil amendment is suitable for reclaiming a problematic site. Compared to operational scale biosolids applications, test trials have higher monitoring requirements, and require more planning and tighter quality control. Part 6 - Biosolids Application Rate Calculations In mine reclamation, biosolids application rate calculations are primarily based on the organic matter and nitrogen contents and to a lesser degree on the trace element concentrations in the biosolids to be applied and the soil to be amended. Biosolids are typically applied at either a fertilizer or a reclamation application rate. Biosolids is usually applied at a fertilizer application rate to vegetated, but nutrient deficient, areas and at a reclamation application rate to unvegetated and nutrient and organic matter deficient areas. Fertilizer application rates are typically lower than reclamation application rates. The calculation of appropriate application rates for biosolids is somewhat convoluted as several, interdependent design criteria have to be met. Algorithms for application rate calculations were already given by Renken (1997). Please note that in those algorithms, all references to "Sequence 4" should be ignored. Part 7 - Design of a Monitoring Plan An effective monitoring plan is crucial to assess the revegetation success and associated costs. The type and extent of a monitoring program depends on: 1) the site characteristics, 2) the type of biosolids to be applied, 3) the method of biosolids application, and 4) regulatory requirements. Monitoring programs for biosolids application should be based on the collection and analysis of composite samples with  8  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  Table 4. Guideline Values for Total Trace Element Concentrations  Notes: 1 2 3  4 5 6  7  All concentrations are on a dry weight basis. Class A Biosolids mixed with mineral soil which may also be blended with stabilizing material such as woodchips, peat or compost. "Selected organic matter means food waste, treated municipal sewage sludge, septage, brewery waste, untreated wood waste, plant matter derived from processing plants, manure, animal bedding, hatchery waste, poultry carcasses, fish wastes and other organic materials which may be approved by the Director from time to time" (B.C. MoELP, 1998). Biosolids that meet requirements of the Regulation and the Federal Fertilizer Act. If soil to be amended has trace element concentration higher than suggested, conduct a test trial or document relevant, conclusive research before commencing operational scale biosolids application. The maximum tolerable soil concentration in mine reclamation is largely controlled by the requirements of the current and projected animal population using on-site vegetation for shelter and food. Thus, it depends on the vegetation grown as well as on other soil properties (e.g.max Mo depends on the Cu:Mo ratio in plants). In "Final Rules for Use and Disposal of Sewage Sludge" (U.S. EPA, 1996), the upper limit for lead is 300 mg/kg.  one important exception: the determination of pathogens in biosolids which should be based on discrete samples. A monitoring program for operational scale biosolids applications was suggested by Renken (1997; Table 10). The suggested program may have to be modified based on site characteristics.  9  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  Part 8 - Design of a Recordkeeping System An ideal recordkeeping system for biosolids projects is flexible, expandable, simple, easy to use, and easy to follow. It is recommended to organize and prioritize project information by: 1) regulatory designation or project number or project name; 2) reclamation site location; 3) reclamation unit; and 4) sampling unit. Part 9 - Transportation and Storage of Biosolids The choice of which transportation method should be selected to convey biosolids from the wastewater treatment plant to an application site depends on several factors including: 1) the total solids content of biosolids, 2) the quantity of biosolids, 3) the hauling distance, and 4) the accessibility of the site. The conveyance system has to be able to contain the biosolids completely, i.e. biosolids should not leak out of the system. The use of trucks for transporting biosolids is usually the most flexible and cost-effective method of transport. At the reclamation site, short-term biosolids storage is almost always required, medium-term storage may be required, and long-term storage is only rarely required. Short-term biosolids storage at the reclamation site is almost always required to accumulate enough biosolids in close proximity to the site so that the application crew and equipment can work efficiently. Suggested minimum requirements for storage areas are given in Table 5. Part 10 - Revegetation Species Mix & Seeding Methods After a suitable seed bed has been prepared with biosolids, the site is ready for revegetation with plant species appropriate for the site conditions such as elevation, aspect, biogeoclimatic region, soil fertility, and available water storage capacity. In mine reclamation projects using biosolids, usually a mixture of grasses and legumes is seeded to provide a quick cover and shrubs and trees may be seeded or planted to provide long-term erosion control and a diverse cover. Seeds of herbaceous legumes and some of the shrubby legumes should be inoculated with the appropriate Rhizobium bacteria prior to seeding. STEP 6 - SEED BED PREPARATION & BIOSOLIDS APPLICATION A "good" seed bed containing biosolids is usually prepared by incorporating biosolids into a surface soil containing sufficient fines or by applying a premixed soil product containing biosolids. The optimum mixing ratio of biosolids to fine earth to create a friable seed bed and to achieve in good vegetation establishment depends on: 1) the type of vegetation to be grown, 2) the biogeoclimatic zone, 3) the amount of fines available in the vicinity of the application site, and 4) the financial resources available for reclamation. For most sites, 300 mm thick layer of fines such as silt or silt loam to blend biosolids  10  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  11  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  4) 5) 6) 7) 8)  where needed, lime or gypsum are applied, biosolids is applied to the surface, where needed, additional fertilizers are applied to the surface, all soil amendments are incorporated, and the soil is harrowed or chained.  For slopes with an adequate factor of safety that assures long-term stability, the maximum slope angle for biosolids application depends on: 1) the total solids content of the biosolids, 2) the environmental sensitivity of the site, and 3) the limitations of the application equipment. It is not recommended to apply biosolids to slopes steeper than 2H:1V (26.5°). Steeper slopes should be flattened prior to revegetation. If a reduction of the slope angle is not possible (e.g. in a narrow valley) or prohibitively expensive, the next best approach to slope reclamation is to create benches (e.g. one slope break for every 15 to 20 vertical m) to reduce the velocity of surface water run-off. If the slope angle cannot be reduced at reasonable costs, and if slope breaks are difficult to incorporate, the top of the slope should at least be rounded off to prevent overhangs from forming. The choice of which biosolids application method is most suitable for a site depends on the site's topography and the total solids content of the biosolids. Typically, the most cost-effective method of biosolids application is the application of dewatered, dried, or composted biosolids with a typical total solids content ranging from 15 to 30%. The application of liquid biosolids with a typical total solids content of less than 12% used to be popular in the Pacific Northwest in the 1980s, but has fallen out of favour primarily due to relatively high capital and operational costs, especially if the application site is not close to the wastewater treatment plant. To relatively flat sites, dried, dewatered, or composted biosolids may be applied with conventional machinery such as commercial box spreaders or farm manure spreaders pulled behind tractors. Although practiced, the use of bulldozers, graders, or front-end loaders to spread biosolids is not recommended due to their tendency to compact soil and to distribute biosolids unevenly. To steep sites, dried, dewatered, or composted biosolids may be applied aerially either as a top dressing or in the form of a premixed soil product. Aerial application may be accomplished by using an aerospreader or similar equipment. If a slope is too steep for equipment to work on it safely and if that slope has a high coarse fragment content, soil or overburden mixed with biosolids, or other soil material may be end-dumped from the top of the slope to prepare a seed bed. The problem with this method is that soil is usually applied thicker in the upper reaches of a slope than on the lower reaches. This problem of uneven soil distribution may be corrected by the following three step procedure: 1) end-dumping soil from the top of slope, 2) pushing soil upslope from the toe of the slope, and 3) dragging a heavy chain with a cylindrical heavy weight at  12  nd  Proceedings of the 22 Annual British Columbia Mine Reclamation Symposium in Penticton, BC, 1998. The Technical and Research Committee on Reclamation  its end across the slope after the soil has been placed (with swivel at the top of slope). For a detailed description of the latter soil placement process, refer to Lacarte (1997). Liquid biosolids with a typical total solids content of less than 12% may be applied with several methods. To relatively flat sites, liquid biosolids are usually either injected into the soil with injection equipment or surface-applied with spray application vehicles (e.g. farm tank wagons, liquid manure spreaders) or irrigation equipment. To steep sites, liquid biosolids are usually applied with a hydroseeder. When applying liquid biosolids with a spray application vehicle, a storage or mixing tank is usually required on the reclamation site to facilitate efficient application. Before liquid biosolids are surface-applied, the maximum hydraulic loading rate for the reclamation site has to be determined. The hydraulic loading rate depends on the total solids content of the biosolids and the infiltration characteristics of the soil. Typically, the actual infiltration rate after biosolids application is lower than before application, because the solids in liquid biosolids settle in surface pores. This effect has to be taken into account when determining the maximum hydraulic loading rate for application. If the surface soil is clogged, it may be necessary to temporarily halt biosolids application and loosen the surface soil. SUMMARY  This paper presents a systematic six step engineering approach to design a mine reclamation plan for biosolids applications to disturbed areas characterized by a unique combination of soil disturbances, soil conditions, and climate. Properly followed, the systematic approach ensures that a disturbed site is successfully reclaimed within technical, environmental, and economic constraints. ACKNOWLEDGEMENT  I would like to gratefully acknowledge the GVRD's Residuals Management Group for giving me the opportunity and support to develop technical documentation for biosolids use. REFERENCES B.C. MoELP (B.C. Ministry of Environment, Lands and Parks). 1983. Draft Guidelines for Disposal of Domestic Sludge under the Waste Management Act. 19p. B.C. MoELP. 1998. Draft Selected Organic Matter Recycling Regulation (June 1998). 18p. Lacarte, M. W. 1997. The Reclamation Process at Bullmoose Operating Corporation. In Proc. of the Twenty-first Annual British Columbia Mine Reclamation Symposium and Twenty-second Annual Land Reclamation Association Meeting. Cranbrook, B.C. Sept. 22-25, 1997. pp. 46-53. Renken, K. 1997. Engineering Approach to Mine Reclamation with Biosolids. In Proc. of the Twenty-first Annual British Columbia Mine Reclamation Symposium and Twenty-second Annual Land Reclamation Association Meeting. Cranbrook, B.C. Sept. 22-25, 1997. pp. 108-121. U.S. EPA. 1993. Final Rules for Use and Disposal of Sewage Sludge. Federal Register. Vol. 58. No.32. 40 CFR Part 503.  13  

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