British Columbia Mine Reclamation Symposium

Site remediation of acid damaged soils using sprayed biosolids and lime : a case study of the area near… Mattes, Al; Pommer, Matt; Duncan, William F. A. (William Frederick Alexander) 2006

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SITE REMEDIATION OF ACID DAMAGED SOILS USING SPRAYED BIOSOLIDS AND LIME – A CASE STUDY OF THE AREA NEAR THE TRAIL LEAD ZINC SMELTER IN TRAIL BC  Al Mattes 1 BSc. Matt Pommer 1 WFA Duncan 2 MSc.  1 Nature Works Remediation Corporation   2 Teck Cominco Metals Limited   2196 LeRoi Avenue Unit # 106    Box 1000   Rossland, BC Trail, BC   VOG 1YO V1R 4L8  ABSTRACT  Research was completed on the use of two types of recycled waste products from the pulp and paper industry – composted biosolids and waste lime product – for use as a slurried sprayable soil amendment protocol.  The material is first mixed as a slurry then seeds are added and the material sprayed using a commercial hydro seeder.  Results from four treatments are reported providing details of seed germination, biomass produced and changes in soil pH profile.  A separate study examined the use of this application on steep sandy slopes and initial results from this are reported as well.  INTRODUCTION  Soil reclamation is not an exact science and many successful practitioners rely on practical knowledge gained from many years of trial and error application of basic principles.  If the soil is acidic it must be made basic for plants to survive and propagate, either through germination of seed produced or through rhizomatous or for some species stoloniferous growth.  If the soil is lacking in nutrients it requires fertilizer, and if an available source of carbon is missing then mulch or compost must be added.  In a normal situation these are easily done and off the shelf supplies allow the home gardener to amend soil quickly and easily.  When large-scale remediation efforts are required, then the problem can require heavy machinery and significant amounts of labour to achieve successful wide area remediation. Typically with nutrient rich soil in place and a pH of 5.0 it is recommended that lime be added at a rate of from 0.76 t Ac-1 (Lilly and Baird, 1993).  With mineral soil and low pH buffering capacity material (typical of both the situation in Trail and the type of lime waste product available from the pulp mill) amendments rates can exceed 17.22 T Ac-1 (Spies and Harms, 2004) depending on initial soil pH and the buffering capacity of the lime available for amendment purposes.  Acid soils exist in areas that have been affected by acid rain or acid plume deposition resulting from emissions from heavy industry (e.g., smelting operations).  If this activity has taken place over long periods of time, large areas are often severely affected.  Once the soil acidifies, seeds cannot germinate and plants die off as the low pH destroys root hair growth.  With an absence of plants and roots, soil is quickly eroded and the area reverts to bare rock or colluvium depending on the original substrate and the potential for plants to revegetate an area naturally is impeded. After SO2 deposition no longer occurs then the soil can be amended to support plant growth. Where vast tracts are devoid of biomass sufficient to support plant growth, the reclamation problem becomes one of scale and cost.  Many major reclamation efforts require a thick application of topsoil to support plant growth.  It was recognized that locally available pulp mill biosolids could be applied on the acid damaged soil to support long-term plant growth.  Initially, our treatment was done using a tracked front- end loader and deep layers of biosolid material.  However, this was costly and was difficult to do on steep slopes given equipment limitations. As well, the biosolids are difficult to work with and reduced traction results in problems with equipment maneuverability.  Once applied, wheeled vehicles cannot be used as they quickly get stuck.  A better way to spread the biosolids in a thinner, more consistent manner was required.  Jim Hall of Nature Works designed and constructed a machine that could convert biosolids and/or recycled lime into a sprayable slurry for use by a standard hydroseeder.  With this technology, it is possible to spray biosolids over a large area in an even and consistent manner using less biosolids than application by a tracked loader.  By adding reclamation seed mixtures to the slurry in the hydroseeder, a single pass treatment was possible. The machine was constructed in 2004 and initial research trials were carried out.  During 2005, further research trials substantiated the results of the first summer and provided a better understanding of the amelioration processes taking place.  METHODS  Initial Research Trials – Summer 2004  During the initial research trials the following treatments were investigated:  1. Controls; 2. Treatment with lime alone at 3.09 T Ha-1; 3. Treatment with biosolids alone at rate of 12.36 T Ha-1; and 4. Treatment with a mixture of lime and biosolids (15.45 T Ha-1).  For each of the large, replicated plots (625 m 2), sub-plots (30 cm x 30 cm) were randomly located for detailed monitoring.  A total of five replicate plots for each treatment allowed for statistical analysis. Plots were laid out along roadways for easy accessibility and marked with flagged stakes. Plots were laid out in a random block design with no two adjacent treatments being the same.  Using specialized equipment, recycled lime and/or pulp mill biosolids were converted to a slurried mixture.  The mixture contained lime at a rate of 3.09 T Ha-1 and biosolids at a rate of 12.36 T Ha-1. This mixture was pumped into a hydro seeder where the reclamation seed mixture could be added prior to spray application. The plots were then sprayed with a thin coating (< 1cm) of the slurried mixture according to the research design.  Control plots were sprayed with a seed mixture alone. The seed mixture that was a standard reclamation mixture used in the area and contained:  Rangelander Alfalfa 4% Surrey Annual Ryegrass 15% Barley  20% Single Cut Red Clover  3% Creeping Red Fescue 10% Perennial Ryegrass   10% Dahurian Wildrye 10% Smooth Bromegrass   5% Red Top 3% Quatro Sheep’s Fescue  10% Climax Timothy  5%  A detailed examination of the Celgar pulp mill biosolids was completed (McKay and Duncan, 1999).  They reported a bulk carbon content of 35% and bulk nitrogen content of 1.12% with a resultant C:N ratio of 30 to 32 which is ideal for plant growth maintenance and long-term soil amendments. Following the 2004 spraying treatment, sampling of the sub-plots was conducted as follows:  a) Measurement of germination and growth Over the summer months, measurements of productivity in the sub-plots were recorded (germination rate, % coverage, grass height, biomass produced, flower and seed production). These plots were observed daily starting 7 days after application for germination success. This continued for approximately one week until germination was well established. At weeks 2 and 3 each blade of grass in each sub-plot was counted and recorded. Other data, including survival rates, visible plant health observations and photographs of each plot and sub-plot were collected throughout the summer.  b) Determination of biomass production At the end of September, each sub-plot was destructively harvested. Root penetration into the original soil was recorded.  Plants were separated into roots and shoots, the roots were washed free of soil particles, and both were dried and weighed to determine total plant biomass production. Treatment differences were analyzed using a One-Way ANOVA.  Follow-up Research Trials – Summer 2005  Given the positive findings of 2004, the project was extended for a second year to examine if a self- sustaining remediation system had been developed. The follow-up monitoring included the following:  a) Monitoring for sustaining growth in plots in their second year An important consideration was to determine if the growth observed during the first summer after application would continue in subsequent years. To monitor the second year’s growth in the sites a three separate set of new sub-plots were staked out in two replicates of the different treatment blocks (no controls were included) and the above-ground only biomass produced in each of these was removed, bagged, dried and weighed.  b) Soil pH profiles The pH differences through the soil depth profile were measured during a period of active growth (end of August) and a period of plant senescence (October).  Due site access issues only 4 of 5 replicates were completed. Using a tree-planting spade, an intact soil sample approximately 12 cm x 12 cm and 20 cm deep was collected. Sub-samples were then taken from the below root zone (representing background soil conditions), in the middle of the root zone and near the surface (in the treatment zone) and placed in labeled bags. Soil pH measured as follows: 1. Samples were air dried; 2. 10 grams of material was placed in a small cup; 3. 20 ml of 0.01 M CaCl2 solution was added to replace the ions in pore water when the soil sample is in-situ; 4. samples were stirred and allowed to rest for 20 minutes; 5. samples were stirred again and allowed to rest for a further 30 minutes; and 6. the solution pH recorded.  The mean soil pH for the two sampling periods showed no significant differences so they were combined and mean data (n=2) used for between treatment comparisons.  c) 2005 Steep Slope Application and Stabilization Trials These trials were designed to investigate the potential to use a spray application technology on steep slopes, to assess grass establishment and survival and ultimately, to determine the stability of spray-applied materials over time.  Several sites were identified that were sufficiently close to a road to allow for access by the hydroseeder.  The selected slopes were steep (>1:1 slope) and sandy.  These slopes, typical in the Trail region, are prone to erosion with rocky debris at their base and poor vegetation coverage. These trials were to determine if spray technology (using recycled lime, biosolids and seed) is a cost-effective reclamation treatment for steep slopes. Two applications were tested – 1) spraying the mixture on steep sandy slopes without any site preparation and 2) preparing the site by installing erosion control blanket on the slopes prior to spraying.  At a very steep (>2:1) site, additional trials employing single, double and triple layers of erosion control blanket were conducted. Sub-plots (30 cm x 30 cm) were established in each of the different treatment areas and weekly counts of germinated sprouts were recorded.  RESULTS OF 2004 TRIALS  Biomass  The highest mean total biomass of any treatment was when lime and biosolids were applied together (Table 1, Figure 1).  All three treatments fared better than the controls by over ten-fold in biomass production and 3 to 6 times higher plant counts (Table 1, Figure 1).  Table 1. Mean and range of total (shoots and roots) biomass (g), mean number of plants counted in each sub-plot and rated growth success in 2004.  Test Plots Germination 3rd Week Mean Total Weight (g) Range of total biomass (g) Rated Growth Success* Control A4 26 1.58 .01-6.1 Poor B3 79 2.91 .01-7.55 Poor C2 67 28.87 8.85-61.3 Poor D1 25 1.86 .01-5.5 Poor E3 88 4.98 .01-15.6 Poor Mean 57 8.0 Lime Only A3 111 130.22 97.9-182.45 Excellent B2 146 113.24 39.2-255.3 Very Good C3 131 141.82 102.7-188.95 Excellent D4 162 121.27 42.35-169.75 Very Good E2 133 144.96 49.55-253.3 Excellent Mean 136.6 130.3 Biosolids Only A1 282 99.17 72.6-109.65 Good B1 228 100.03 28.00-157.7 Very Good C4 171 91.77 30.6-144.3 Good D3 176 118.17 52.75-178.65 Very Good E1 290 139.18 106.05-166.45 Excellent Mean 229.4 109.7 Biosolids & Lime A2 275 140.07 78.6-203.6 Excellent B4 310 123.51 39.65-178.35 Very Good C1 245 128.44 95.2-193.7 Excellent D2 280 100.44 34.5-179.95 Very Good E4 356 234.61 136.95-356.35 Excellent Mean 293.2 145.4 Growth Success Rate Legend (ranked by total biomass (g)) 0-50 Poor; 51-75 Average; 75-100 Good; 101-125 Very Good; 126+ Excellent  The differences in biomass between each treatment and controls (Figure 1) are statistically significant at the 95% confidence level using a One-Way ANOVA, while between lime only and biosolids only treatments is significant at the 90% confidence level (Table 2). All other treatment differences are not statistically significant (Table 2). The higher biomass in the treatments using lime shows pH adjustment is essential for successful revegetation in acidified soils.  Germination  Differences in germination between each treatment and controls (Table 1) mirror the biomass differences that were reported and differences between controls and all treatments were highly significant (>99%; One-Way ANOVA; Table 3). Mixtures containing the biosolids had the best germination rates, likely due the increased water-holding capacity the biosolids.  While germination in the lime only treatment was lower, the biomass in the lime only (130.3 g) was similar to the lime and biosolids treatment (145.4 g).  While some seeds did germinate in the controls, the total biomass produced was low (8.0 g) for the controls.  Figure 1: Mean total biomass produced in 2004 from four replicate treatments. 0 20 40 60 80 100 120 140 160 1 Treatments M ea n B io m as s in  g ra m s Control Mean Biomass Lime Only Mean biomass Celgar Only Mean Biomass Celgar and Lime Mean Biomass   Table 2.: One-Way ANOVA analysis of the mean above ground biomass produced for the four treatments trials tested in 2004.  Treatments Compared P-value F Control and Lime 3.23E-07 235.46 Control and Biosolids 7.75E-06 102.45 Control; Lime & Biosolids 0.0004 33.33 Lime and Biosolids 0.08 3.89 Biosolids; Lime & Biosolids 0.18 2.09 Lime; Lime & Biosolids 0.54 0.39   Table 3. One-Way ANOVA analysis of the mean germination success rate determined after 3 weeks following initial spraying in 2004.  Treatments Compared P-value F Control and Lime 0.0009 25.53 Control and Biosolids 0.0003 36.62 Control; Lime & Biosolids 6.97 E-06 105.42 Lime and Biosolids 0.008 12.18 Biosolids; Lime & Biosolids 6.3 E-05 57.78 Lime; Lime & Biosolids 0.07 4.12   RESULTS OF 2005 TRIALS  Second year’s growth between treatments  The general 2004 trend for the mean plant biomass accumulation remains same for 2005 with biosolids only (3.52 g) < lime only (4.56 g) < biosolids and lime together (7.10 g) (Figure 2).  In 2005, only the above-ground biomass was measured so the mean biomass reported is much lower than 2004.  Additionally, the summer was drier in 2005 and likely biomass production was reduced due to this as well.  The 2005 trials further support the lime and biosolids treatment when applied as a thin single amendment layer.  Figure 2. Mean above-ground biomass produced in 2005 for two replicates of each of three treatments.   0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 1 M ea n Pl an t M as s G ra m  Celgar Only Lime Only Celgar and Lime   The higher above ground biomass of the biosolids with lime treatment was significantly better than biosolids alone (Table 4). These findings support those observed in 2004 where lime appears to be the most important contributing factor but that when combined with Celgar biosolids an increased plant biomass production is observed. While the lime conditions the soil, the biosolids increase the supply of available nutrients as biosolids have an ideal ratio of carbon and nitrogen, contain important trace minerals required for plant growth and increase the water-holding capacity of the soil which all contribute to increased biomass.  Table 4. One-Way ANOVA comparisons of mean above-ground biomass produced by the three treatments in 2005.        a=:significant at better than 0. 05 level o f confidence  Soil pH profiles  Mean soil pH in the control plots was approximately 4 and very consistent over the soil depth profile (Figure 3).  For three soil amendment treatments soil pH is higher than controls at all soil depths but most pronounced at the near surface (Figure 3). Using a One-Way ANOVA, almost all mean pH values were statistically significant between the treatments, especially when compared with controls (Table 5).  The increases through the soil pH profile from biosolids alone were not as large compared to areas where lime or a mixture of biosolids and lime were added.  Figure 3. Soil pH versus depth from surface in 2005 (mean of August and October samples).    Treatment P-value F Summer and Fall Combined Biosolids and Lime 0.431 0.64 Biosolids with Lime and Lime 0.066 3.61 Biosolids with Lime and Biosolids 0.042a 4.52  0.00 1.00 2.00 3.00 4.00 5.00 6.00 1 2 3 Sample Depth (1 = 1 - 4 cm, 2 = 5 - 10 cm, 3 = 15 - 19 cm) M ea n so il pH  Celgar Only Lime Only Celgar and Lime Mixed Control The effect of lime remains as important in the second year as it was in the first year. Once established and growing with sufficient nutrients the soil chemistry appears to change as the effects of the lime move downwards through the soil profile.  If revegetation involves using plants with deep penetrating roots, it is important to assess the soil pH profile to determine how much lime should be added, as root growth may be disrupted if the roots encounter low pH soil at depth which mobilizes phyto-toxicants such as aluminum.  Where deep-rooting plants are desired, applying lime prior to topsoil application may be beneficial even in cases where thick layers of topsoil or biosolids are to be applied.  The lime would condition the sub-soil and reduce potential toxicity of metals to plant roots.  Table 5. One-Way ANOVA comparisons of soil pH between treatments and soil depth in 2005.  Treatment P-value F Top Biosolids and Biosolids with Lime 0.036748 b 4.52 Lime  and Biosolids with Lime 0.012135 b 6.60 Biosolids and Lime 2.59E-06 a 25.73 Biosolids and Control 1.5E-06 a 27.97 Biosolids, Lime and Control 1.05E-08 a 42.79 Lime and Control 1.18E-14 a 97.79 Middle Biosolids and Biosolids with Lime 0.005667 a 8.10 Lime  and Biosolids with Lime 0.490444 0.48 Biosolids and Lime 0.000185 a 15.43 Biosolids and Control 0.035491 b 4.61 Biosolids with Lime and Control 0.000261 a 14.90 Lime and Control 1.04E-05 a 22.81 Bottom Biosolids and Biosolids with Lime 0.004518 a 8.55 Lime  and Biosolids with Lime 0.172617 1.89 Biosolids and Lime 0.171373 1.91 Biosolids and Control 0.014224 b 6.35 Biosolids with Lime and Control 5.54E-06 a 24.44 Lime and Control 0.000941 a 12.00   a = significant at better than 0.01 level of confidence  b = significant at better than 0.05 level of confidence  Steep Slope Application and Stabilization Trials  Work was completed in late July.  Poor germination occurred during the summer as grass mixtures require cool wet weather to germinate.  However, past experience has shown that germination will occur with the fall rains. In September, following a rain event, the grass seeds immediately began to germinate. With continuing rain, the slope continued to germinate over the latter weeks of the 8-week project. The sprayed mixture formed a mat-like surface that inhibited erosion.  Not only was the sandy sub-soil kept in place but it also slowed down the rock falls that had previously impacted the road below.  Mean sprout counts for the three treatments at the 7th week (Figure 4) were not significantly different (all p values >0.5 by One-Way ANOVA).  The highest above-ground biomass was produced with a single layer of erosion blanket but differences were not statistically significant using One-Way ANOVA test (Figure 5).  Good germination rate is evident on the single coverage of erosion blanket (Figure 4) together with the highest total of above-ground biomass produced.  Therefore, while the erosion blanket may help to hold the slurried mixture, the increased in germination and biomass production was not significant in these trials. The possible long-term benefits of the use of erosion blanket on the final stability of the hillside needs to be assessed and their cost-effectiveness evaluated in a longer-term project.  Figure 4. Mean sprout count (week 7) versus the number of layers of erosion control blanket.     0 200 400 600 800 1000 1200 1400 Treatments Ei gh t W ee k Sp ro ut  M ea n C ou nt No Erosion Blanket 1 Layer Erosion Blanket 2 Layers Erosion Blanket 3 Layers Erosion Blanket Figure 5. Mean above-ground biomass versus number of layers of erosion control blanket.    DISCUSSION  Sprayed Treatments  The application rates were estimated on the lime required to elevate the pH and sufficient biosolids to supply essential nutrients to support long-term growth.  With little organic material present in the acidified (pH <5) sandy substrate, seeds had poor germination and very little biomass production on the control plots.  All treatments had successful germination and produced considerable biomass indicating that the relatively low application rates of lime and biosolids applied as a slurried mixture allowed successful revegetation. The highest overall success was the mixture of lime and biosolids with visibly better greening, more re-growth during the second year, the highest pH increase at depth and the significantly higher biomass produced  than other treatments.  We have monitored the sites for two years and intend to continue with monitoring over the next two seasons to determine long-term sustainability as well as examine the cost- effectiveness of spraying slurried mixtures compared to more traditional treatment options.  Soil pH Profiles  Changes seen in the soil pH profile also support the use of lime and biosolids applied together as a slurried mixture.  While the addition of lime alone has a very beneficial effect, the greatest biomass production was observed in the lime with biosolids treatments. The addition of acid   0.0000 0.2000 0.4000 0.6000 0.8000 1.0000 1.2000 1.4000 1.6000 1.8000 Treatment B io m as s No Erosion Blanket 1 Layer Erosion Blanket  2 Layers Erosion Blankets 3 Layers Erosion Blankets neutralizing lime combined with the excellent plant growth supporting characteristics of the biosolids promotes the best biomass production.  Steep Slope Stabilization  It has been clearly demonstrated that steep sandy slopes can be stabilized and revegetated by spraying on a slurried mixture of lime and biosolids (with or without layers of erosion control blanket).  The highest biomass rate was observed when a single layer of erosion blanket was applied but there was higher germination success observed when a double layer of cloth was utilized.  The need for erosion control blankets requires a longer-term assessment at this and other sites.  In many cases, spraying lime and/or biosolids may be all that is required.  CONCLUSION  We have successfully developed a new technique for soil reclamation using readily available waste by-products of a local pulp mill.  In order to use these by-products, specially designed equipment was used to produce a slurried mixture of lime and/or biosolids.  The best results to date are the use of a mixture of the two materials although either material alone will result in successful re-vegetation.  In the second year the grasses continue to grow vigorously although the plant mixture has changed somewhat from that initially seeded.  Long-term results look promising as there are substantive changes in soil pH that should mean that native species will also be able to recolonize the area in future.  REFERENCES  Lilly, P and J. Baird, 1993. Soil Factors, Soil Acidity and Proper Lime Use. North Carolina Co- operative Extension Services web page (  Spies, D.D. and C.L. Harms, 2004. Soil Acidity and Liming of Indiana Soils. Department of Agronomy, Purdue University web page (  Mackay, F. and W. F. A.  Duncan, 1999. Beneficial Reuse of Biosolids Generated by Celgar Pulp Company. PAC West Conference, Jasper, AB, May 1-4, 1999. 


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