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Obtaining water quality permits for land application of biomass boiler ash
~9wn1o.r.~ undBiorner~~ Vol.
Pergamon
(’ 1998 Published
PII: SO961-9534(97)10015-O
13. Nos. 415, pp. 279-287. 1997 by Elsevier Science Ltd. All rights reserved Printed in Great Britain 096l-9534,97 $17.00 + 0.00
OBTAINING WATER QUALITY PERMITS FOR LAND APPLICATION OF BIOMASS BOILER ASH THOMAS Baruch
Forest
Science Institute,
Clemson
M.
University,
WILLIAMS
P.O. Box 596 Georgetown,
SC 29442, U.S.A.
Abstract-Land application of biomass fuelled boiler ash can save landfill space and return cations to the forest environment. However. environmental regulations throughout most of the U.S. do not specifically address application of biomass boiler ash to forest land. South Carolina Department of Health and Environmental Control (SCDHEC) treated bark boiler ash from International Paper’s Georgetown, SC. mill as an experimental permit with a requirement of monitoring experimental applications to show it would have “no detrimental impact to the environment or public health”. An initial catchment study showed no evidence of leaching into either the watertable aquifer or outlet streams when ash was applied to moderately well-drained portions of two watersheds at a rate of I I Mg/ha. Concentrations of elements in groundwater samples were well within state drinking water standards, often more than an order of magnitude below the standards. The second study was a replicated block experiment of ash application rates of I I. 22 and 44 Mg/ha. Ash application increased leaching significantly for potassium, calcium and sulfate, although concentration &eases were modest (0.12~0.17 Mg/l for potassium, 0.36.-0.89 mg/l for calcium and 1.92-3.08 mg/l for sulfate). Groundwater heavy metal concentrations were well below drinking water standards, even at the 44 Mgiha rate. $*, 1998 Published by Elsevier Science Ltd. Keywords-Boiler
ash; wood ash; water quality;
groundwater:
1. INTRODUCTION
documented for forest applications of wood ash.’ Recycling biomass boiler ash to forest land would save landfill space and could help replace some of the nutrients removed during harvest of short rotation pine plantations. The International Paper mill, Georgetown, South Carolina demonstrates the problems of landfilling ash. The mill, built in 1939, was reconfigured in 1980-1982 and equipped with a fluidized bed power boiler that burned 85% bark, 10% unusable pulp and 5% coal (to maintain efficient combustion). The boiler has produced 100 Mg of ash per day since conversion. By 1992 the on-site landfill contained about 300 000 m3 of ash. In addition to filling landfill space quickly, landfilling ash also accumulates the small amounts of heavy metals found in bark at a single point. In this case, about 10 Mg lead, 7 Mg nickel, 6 Mg arsenic, 6 Mg chromium, 1 Mg selenium and 300 kg cadmium are present in the ash pile (based on ash analysis conducted from 199 1- 1995). At projected growth rates and present utilization standards, harvests on company land near the Georgetown mill will remove about 10 Mg/ha of major cations. Depending on combustion efficiency, 25-40 Mg of ash will have roughly the same total mass of cations.
Biomass fuels are commonly used for power generation in pulp and paper mills throughout the United States with 2.7 million Mg of ash generated annually by power boilers fired with bark, wood and wood wastes. Over 80% of that ash is landfilled.’ Ash derived from the combustion nutrients to Agronomic amendments increases of cations2.‘.
of biomass enhance soil studies on with wood growth with
heavy metal; chromium
can provide plant and site productivity. the effects of soil ash showed modest moderate ash appli-
Haywood suggests that nutrient removals during short rotations of southern pines require nutrient additions by fertilization in order to be sustainable. Application of ash could be used to maintain forest soil productivity by replacing the cations removed during harvest. Ostrofsky’ demonstrated modest increases in red pine and black spruce growth following application of ash. Foliar content of potassium, phosphorus and calcium is significantly increased by ash application and the beneficial effects are persistent for up to 26 months.” Enhanced forage quality and biomass production for wildlife species were 279
280
T. M. WILLIAMS
By 1990, the company began planning to switch from placing ash in a landfill to land application on company forest lands. However, as an industrial waste, ash is regulated by the U.S. Environmental Protection Agency and by individual state solid waste and water quality programs.’ In South Carolina the South Carolina Department of Control Health and Environmental (SCDHEC) was given the primary responsibility in programs of solid waste and water quality. In 1990, no ash had been land applied in South Carolina and research on ash application to southeastern Coastal Plain soils had been done at much higher rates.’ Ash application could only be done under a Department Research, Development and Demonstration Permit. A requirement of this permit is that the research or demonstration have “no detrimental impact to the environment or public health”. Two projects were done cooperatively between International Paper and Clemson University with active oversight by the SCDHEC, a watershed scale pilot project and a replicated plot rate study. The highest priority was protection of water quality of both groundwater and streams. Specifically, groundwater elemental concentrations were not to exceed primary drinking water standards” as a result of ash application. Conditions of the application permit presented a challenge to design of the these projects. Experimental applications were expected to duplicate the planned operational spreading procedures and none of the experimental applications could result in a detrimental effect to the environment or public health. That is, not even one groundwater sample was to exceed concentrations in the drinking water standards. Rather than simply testing a hypothesis of a treatment effect vs a nil of no effect to be successful, the study needed to test the hypothesis that groundwater concentrations of elements, including any treatment effect, were unlikely (with a high degree of confidence) to exceed a specified value (drinking water standard). The studies also had a number of other objectives. The most important was an economic assessment of transport and spreading procedures. All costs of land application could not exceed the cost of building a new landfill. Movement of metals into small mammals was also studied. ’’ Influence on pine growth was
also measured, although an immediate fertilizer response was not considered vital for success. Two times during a rotation were considered for ash application, either at time of site preparation or after first thinning near age 15. For a valid economic evaluation of the spreading techniques, application areas of 50 ha were considered minimal. High watertables, characteristic of southeastern coastal plain forest lands, created potential for contamination of the watertable aquifer or of streams, by runoff from saturated soils.
2. METHODS
2.1. Catchment study The first study was an operational trial of spreading at a ash catchment scale. Groundwater samplers and piezometers were used to define flow directions and elemental concentrations, while automated stream samplers monitored water leaving the catchments. A portion of International Paper property in eastern Williamsburg County, S.C. (latitude 35”35’N, longitude 79”34’W) had the required combination of forest age and well-defined catchments. A block (roughly 100 ha) of clearcut pine plantation and a similar block of recently thinned (1990) 17-year-old pine plantation were chosen. Two catchments were chosen in each block and an ash application area was chosen to completely enclose one catchment in each block (Fig. 1). Soils on the study site were primarily Eulonia (fine-loamy, siliceous, thermic, Aquic Hapludults), Emporia (fine-loamy, siliceous thermic Typic Hapludults), Yemassee (fineloamy, siliceous, thermic Aeric Ochraqualts) and Ogeechee (fine-loamy, siliceous, thermic Typic Ochraqualts).‘* All of the Ogeechee and portions of the Yemassee soils were poorly drained and were not considered for ash application. An on-site soil survey was conducted in each application area and all soils that were moderately well drained or better were mapped for ash application. Approximately 50 ha received ash in each block at a rate of 11 Mg/ha in December of 1990. Following ash application, the clear-cut areas were bedded and planted to pine. The most likely mechanism for groundwater contamination was macropore flow bypassing the soil matrix.13 Groundwater was collected
Water Well
quality
for biomass
Drained
1 4sh
rd0 ASI
Clear .,
,,
vvells
I hlnned Poorly Drained _, * tlume ond bampler
Cbt \
/
J 7
Fig. I. Schematic diagram of well layout for study 1. Four small (20 ha) watersheds formed a 2 x 2 factorial of ash application (ash vs no ash) and stand age (0, clear cut vs 17, thinned). Ash was applied only to well-drained portions of watersheds. Each watershed had a Parchall flume and ISCO automated sampler at the outlet. Sampling wells were placed in transects from watershed divide to stream. with two wells in the well-drained portion of each transect. Well pairs used in the paired comparison are marked with “t” and “c” for ash applied and control, respectively.
boiler ash
281
tained continuously and pumped whether water was in the stream or not, assuring samples of intermittent flows. Surface samples were collected from January 1992 (the first flow after ash application) until April 1994. Groundwater samples were collected with a battery powered peristaltic pump. Each well was connected to the five-head pump. The pump was run until all samplers produced over three sampler volumes, all pump lines were rinsed with sample, the sample bottles were rinsed with sample, and a 65 ml sample was collected. Pump lines were purged with air between wells. All samples were put in an ice chest and transported to the laboratory. Samples were refrigerated until analysis. Sample aliquots were analyzed for: NOs, P04, SO4 and Cl, by ion chromatography; Ca, Mg, K, Zn by air-acetylene flame atomic absorption, Al by nitrous oxide-acetylene flame atomic absorption; and Cd, Cr, Cu, Ni by graphite furnace absorption. atomic Techniques were as described in Standard Methods for Analysis of Water and Waste Water.”
2.2. Application rate plot study from multi-level samplers designed to measure piezometric potential at four depths and sample groundwater at five depthsI Each sampler installation will be referred to as a well for simplicity (Fig. 1). Wells were placed in transects from the watershed boundary to the stream. It was anticipated that ash application might increase variability, so five transects were placed in the watersheds to receive ash and only three in watersheds receiving no ash. On each transect, two wells were placed on well drained soil, one in poorly drained soil, and one in the creek bottom. Samples were collected in November 1991, prior to treatment in December 1991, after treatment in December 1991, and monthly through May 1994. Piezometer levels were measured weekly throughout the period. Surface water was collected by ISCO brand automatic samplers. Parshall flumes were placed at the outlet of each catchment and a sampler was placed in the stream just upstream of the pond created by the flume installation. The sampler was programmed to pump a sample every 6 h and fill a single sample bottle each day. Samples were removed from samplers weekly. Samplers were main-
Near the catchment experiment, approximately 37 ha of a 27-year-old loblolly pine plantation was harvested in 1992. The site was prepared in spring 1993, by flat shear, burn and spot piling of residual debris. The site was disked and sprayed with Velpar-L (4.5 kg ai/ ha) in June, 1993. Bark boiler ash was applied to designated plots in December 1993, and subsequently re-disked. The stand was planted with loblolly pine in January 1994 at a nominal density of 1360 trees/ha. Ash was applied to four replicates of a randomized block, split plot design. Blocks were rectangular (5660 m2), and split into two, square plots (2830 m2), with one plot receiving no ash and the other either 11.2, 22.4 or 44.8 dry Mg of ash/ha. Blocks were arranged in a single line approximately perpendicular to the land slope. Blocks were separated by 50100 m buffers to avoid cross-contamination. Long axis of each block was aligned with the land slope and the control plot was located on the uphill plot. A groundwater sampling well was located in the center of each plot. Soils on these plots were a closely related Eunola series siliceous, loamy, thermic Aquic (fine Hapludult).
T. M. WILLIAMS
282 Table
Element Aluminum (mg/l) Calcium (mg/l) Cadmium (pg/l) Chromium (pg/l) Copper (pg/l) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mg/l)
1. Mean concentrations
Clear cut ash Mean
(UCL)
1.67 0.74 0.09 0.66 I.14 6.99 0.69 0.66 0.008
(2.17) (0.78) (0.16) (0.75) (1.38) (7.30) (0.77) (0.67) (0.013)
UCL is the upper 99% confidence the main concern.
of daily composited
Clear cut controlMean
(UCL)
0.30 I .08 0.13 0.66 2.87 7.43 1.25 0.83 0.013
limit. Upper
0.54 2.48 0.08 0.73 1.37 8.81 0.69 0.83 0.012
(0.36) (1.14) (0.18) (0.73) (3.47) (10.1) ( I .49) (0.88) (0.016)
confidence
Wells, 2.5 cm diameter polyvinyl chloride, consisted of a 3 m slotted screen lower section with a 1.5 m solid upper section. Wells were installed by hand augering (7.5 cm diameter auger), using a 10 cm casing where aquifer sand was loose. The well pipe was inserted and the hole filled with aquifer sand to a level 15 cm above the slotted pipe. A bentonite seal was placed in the hole and, after waiting 24 h for the clay to swell, the hole was filled with neat cement to form a dome approximately 5 cm over the soil surface. An outer 7 cm casing, with cap, was set into the cement around the well and served to protect the well from outside contamination. All wells were pumped until no evidence of drilling or sealing materials were found in the water. Field sampling began in October 1993, with bi-weekly samples collected until March 1994, and monthly sampling continued until March 1995. Sampling procedures were similar to the catchment study except the peristaltic pump had a single head and the entire well volume was pumped three times prior to sampling. Analysis for cations and heavy metals were also the same as described for the catchment
stream
Thinned ashMean
limits are used because
samples Thinned control Mean
(UCL) (0.62) (2.66) (0.09) (0.8 I) (1.54) (9.19) (0.76) (0.90) (0.017) maximum
0.36 0.80 0.13 0.98 I.13 7.43 0.39 0.54 0.009
(UCL) (0.44) (0.64) (0.23) (1.35) (1.39) (7.84) (0.31) (0.58) (0.014)
likely concentrations
are
study. Instead of using ion chromatography, the anions were determined by automated colorimetric techniques using a Technicon autoanalyzer. I5
3. RESULTS
AND DISCUSSION
Statistical analysis of this study was planned to meet the regulatory demands of the study. Without a long pre-treatment the simple 2 x 2 factorial design has very little power to detect a significant treatment effect. However, the chief concern in this trial was not evaluation of a treatment effect but rather to determine whether concentrations were below water quality standards. An upper confidence (99%) limit below the standard, using operational application procedures, was the criteria used for decision on permitting of land application. The control watersheds were used primarily to estimate natural spatial variability in concentrations. Post-treatment concentrations of both streams (Table 1) and groundwater (Table 2) show means for the all areas where ash was applied were well below drinking water
Table 2. Mean concentrations of elements in groundwater samplers on well drained soils on control watersheds (6) and ash applications (IO). UCL is the upper 99% confidence limit. Compassion of primary concern was between upper confidence limit and drinking water standard (I”)
Element Aluminum (mg/l) Calcium (mg/l) Cadmium (pg/l) Chromium @g/l) Copper @g/l) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mg/l)
Clear cut ash Mean 4.71 3.30 0.16 2.30 1.89 10.5 0.66 0.57 0.063
(UCL) (6.92) (3.79) (0.39) (3.20) (2.68) (11.9) (0.72) (0.65) (0.069)
Clear cut control Mean 0.55 0.44 0.05 25.7 1.37 5.2 0.74 0.45 0.039
(UCL) (0.82) (0.55) (0.06) (64.6) (2.16) (5.5) (0.79) (0.47) (0.045)
Thinned ash Mean 4.13 1.15 0.15 19.0 2.65 7.7 0.83 0.45 0.262
(UCL) (7.52) (1.33) (0.18) (43. I) (5.18) (8.1) (0.90) (0.48) (3.99)
Thinned control Mean 1.37 4.27 0.09 0.80 0.60 7.6 0.65 0.47 0.14
(UCL) (2.27) (4.84) (0.14) (1.00) (0.77) (8.1) (0.70) (0.51) (0.52)
Drinking water standard
IO 50 1000 250
Water
quality
for biomass
standards for all regulated elements sampled (arsenic was not determined in these samples due to difficulties with analytic methods). Only for groundwater on the clear-cut control area, did the upper confidence limit exceed drinking water limits for chromium. The stream concentrations were remarkably similar to the groundwater. For many elements, concentration in the stream was lower than in groundwater. Well locations, use of multi-level sampling and piezometery were designed to determine groundwater flow directions and extent of movement of groundwater across the watershed. The watertable aquifer beneath all watersheds was similar. Below the loamy surface and sandy clay loam to clay loam subsoils (at depths of 2.5-3 m) the aquifer was a medium-grained sand of remarkably high chroma (1 OY R 8/6). Piezometer measures confirmed nearly vertical downward movement deep (6 m) into this sandy material, even on the wells in the poorly drained soils. Likewise, piezometers in the streams showed vertical upward movement from the sandy material. Piezometric data clearly showed well samples were derived from moisture moving vertically from the surface near the well, meaning that individual wells were independent measures of the treatment effect at that point. One estimate of the effect of ash application is simply a comparison of the means of wells in areas that received ash and comparable samplers in the and control catchments (Table 3). This simple comparison is the same as the difference of means in Table 2, with the maximum effect estimated as the upper 99% confidence limit of the difference with a pooled variance. Of coarse, this estimate contains all the spatial and temporal variability associated
Table 3. Mean concentration
Element Aluminum (mgil) Calctum (mgil) Cadmium (pgil) Chromium @g/l) Copper @g/t) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mgil)
increases
Clear cut predicted effect 4.16* 2.g1* 0.10 -23.3 0.52 5.33* -O.OY 0.12* 0.016*
of elements
Maximum
boiler ash
283
with sampling from sites separated by several kilometres. For aluminum, chromium, copper and zinc the estimates are plagued with a great deal of variability. Chromium presented a difficult problem with variability. Sediments in the region of this experiment have locally high concentrations of chromium. At the pH of the aquifer (-5.0) the reduced form of chromium (Cr”) adsorbs strongly to soil particles and is immobile.16 However, the oxidized form (Cr6’) is relatively mobile. Well installation introduced oxygen that could mobilize chromium from a local sedimentary accumulation. If this was the case, groundwater samples from some wells might have transient spikes of chromium, with timing dependent on the rate of vertical transport and the length of time required for reducing conditions to be reestablished. There was no significant effect for chromium, with a confidence limit up to 48 pg/l, not a particularly reassuring conclusion. The finding that water moved primarily downward also allowed another comparison to be made. Four wells were installed on each transect to measure lateral transfer towards the stream. However, multi-level samples were actually being taken and piezometery showed movement to be vertical. Therefore, the upper samples in each well were independent estimates of leaching from the soil profile at that point. On each transect, a well in the poorly drained soil was located about 100 m from a well where ash was applied (Fig. 1). There were five pairs of wells in each treated watershed that could be viewed as random split plots with ash applied to the uphill plot. A “paired-t” test was done by comparing the
in groundwater
effect
6.38 3.35 0.33 15.0 1.31 6.71 -0.02 0.18 0.017
attributable
to ash application
Thinned predicted effect 2.76 -3.12* 0.06 18.2 2.00 0.12 0.18* -0.20 0.22
Maximum
effect
6.15 -1.79 0.09 42.0 4.58 0.47 0.35 0.06 3.95
Predicted value is mean of wells in receiving ash - mean of control wells on well drained soil, negative values indicate control concentrations were larger than treatment. Maximum effect is the upper 99% confidence limit on the difference. *Difference is significant at 99% confidence.
284
T. M. WILLIAMS
Table 4. Mean concentration
increases
of elements
Clear cut predicted effect
Element Aluminum (mg/l) Calcium (mg/l) Cadmium @g/l) Chromium @g/l) Copper (ng/t) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mg/l)
in groundwater parisons
Maximum
-0.58 1.17* 0.018* -0.45 0.53 -1.13 -0.064 -0.0098 0.0165*
effect
attributable
to ash application
Thinned predicted effect
1.74 1.96 0.033 2.48 2.24 1.87 0.022 0.09 0.022
based on paired
Maximum
-0.40 -1.30* -0.12 1.64 0.76 -1.13 -0.21* -0.188* -0.217
com-
effect
-0.64 -0.70 0.05 4.31 1.69 0.53 -0.11 -0. I 1 0.53
Predicted value is the mean difference between paired samples in wells in treated areas and nearby untreated areas. negative values indicate concentrations in untreated area were larger than treatment. Maximum effect is the upper 99.9% confidence limit on the difference. *Difference is significant at 99.9% confidence.
concentrations in the upper sampler of each paired well (Table 4). A paired comparison estimate of the effect of ash application is more precise. Physical factors governing groundwater movement display strong spatial correlation.” This spatial correlation increases the power of the “pairedt” comparison. Hinton18 discusses the difficulties of non-detectable samples that are commonly found in environmental monitoring of trace metals. Using only values above the instrument detection limit (as in Tables l-3 and 5) results in a positive bias in both mean and variance, the most conservative position from a regulatory viewpoint. However, a nondetectable sample in a paired comparison is a valid estimate of treatment effect. The instrument detection limit is the smallest of the various estimates of detection limits.t5 Substituting this value for each non-detectable sample in a “paired-t” test eliminates the bias for the mean estimate, although there is still a positive bias in calculation of the variance. Table
5. Mean
groundwater
Element Nitrate N (mg/l) Phosphate P @r/A) Sulfate (mg/l) Chloride (mg/l) Potassium (mg/l) Calcium (mg/l) Magnesium (mg/l) Aluminum (mg/l) Arsenic @g/l) Cadmium (pg/l) Chromium &g/l) Copper @g/t) Nickel @g/l) Zinc @g/t)
Using the “paired-r” analysis, there is only one chance in a thousand cadmium was increased by more than 0.05 pg/l or chromium was increased more than 4.3 pg/l due to ash application. Following this study, a permit was issued for land application of ash using the same rate and spreading techniques. 3.1. Application
rate study
The catchment study was done very cautiously to avoid any violations of the research permit. Confidence that the 11 Mg/ha rate resulted in very little leaching of even calcium and magnesium (the dominant ions in the ash) encouraged tests of higher rates. A rate of 44 Mg/ha was estimated to equal the cation removal during harvest of the fastest growing pine plantations on the company’s land. Applications from 22 to 44 Mg/ha would span the range of removals from the variety of sites now under management. Since groundwater movement was vertical, completely screened wells would collect a representative sample. A
element concentrations with various rates of ash application water standards. Means and upper 99% confidence limit 1 I mg/ha cont. @JCL) 1.21(1.24) KO(6.25) 4.37(5.07) 16.3(18.8) 0.68(0.80) 1.17(1.41) l.lO(1.26) 0.68(0.96) 5.4(6.8) 0.029(0.045) 1.22( I .86) 0.89(1.17) 0.68(2.85) 8.0(10.3)
22 mg/haconc. (UCf-) 0.81(0.97) 9.8(13.7) 3.91(4.64) 12.9(15.6) 0.72(0.84) 1.84(2.15) 1.06(1.15) 3.08(4.25) 16.3(25.2) 0.048(0. I 18) 4.24(6.48) 0.86( I .24) 1.06(2.03) 9.7(18.2)
44 Mg/haconc. (UCL) 0.95(1.11) 3.2(5.0) 3.51(3.77) 12.4(15.5) 0.41(0.46) 1.02(1.16) 0.86(0.93) 0.09(0.33) 3.9(5.5) 0.038(0.073) l.gl(2.61) 0.43(0.83) 1.85(2.84) 8.9(ll.O)
as compared
with drinking
Drinking water standard 10
250
50 10 50 1000
Water
quality
for biomass
split plot approach with the control as the split allowed the greatest control of spatial variability, producing the strongest test between each rate and the control. The primary concern of this test was also groundwater element concentrations that might violate drinking water standards (Table 5). At the higher application rates, groundwater concentrations were still considerably below drinking water standards. Most concentrations were an order of magnitude below the standards. Even for arsenic, the most critical
boiler ash
285
element, the upper confidence limit (99%) of the largest mean was only about half the standard. 3.2. Overall results The application rate study was designed to allow estimation of the effect for each application rate above a control. These results can be combined with the results in Table 4 to examine effects of ash spreading in eastern South Carolina (Fig. 2). The degree of disturbance to the forest floor and competing veg-
3 <
2.5
F
2
: .-
1.5
5
1
$
0.5
:
0
0
O-o.5 -1 -1.5 Nitrate
Potassium
Calcium
Magnesium
Aluminum
3 i2.5
Y
2
g .1
1.5
5
0.5
1
:
0
6 -0.5 -1 M
-l.SF Cadmium 4
-4
Chromium
Copper
Chloride
m
11
Mg/ha
m
11 Mg/ha
Thin
m
CC Rate
Nickel
Arsenic
Sulfate
11 Mg/ha m
22
Phosphate
CC Catch Mg/ha
Rate
0
44
Mg/ha
Fig. 2. Overall changes in groundwater chemistry following ash application as difference Negative numbers indicate decrease from a control. * Indicates statistical significance dence.
Rate
from a control. at 95% confi-
286
T. M.
etation seems to have a large influence on the results when ash is applied at 11 Mg/ha. The results for the 22 Mg/ha rate were elevated above those for the lower rate and more often significant. However, the results of the 44 Mg/ ha application were not higher than at 22 Mg/ ha for most elements. The highest rate did seem to result in a change in soil chemistry that effected concentrations of several elements. Surface soil pH was raised to near neutrality (6.7) for 12 weeks after application at the 44 Mg/ha rate, compared with 4.0 for prior to site preparation and 5.0 for no ash application. I9 Results from these studies were qualitatively similar to other ash experiments on forest land. Potassium, calcium and magnesium were all significantly increased by ash spreading on clear-cut sites. Ohno2’ predicted similar results from studies of soil-ash suspensions. Riekerk and Kohrnak2’ found these same elements elevated in run-off water from small watershed at high (127 Mg/ha) application rates of coal ash. There was no indication of macropore flow resulting in rapid movement of soluble ash elements into the groundwater, a high priority concern prior to the studies. The method International Paper chose to obtain permits for land application of boiler ash involved a high applied research technique. The studies were primarily data collection during production scale ash application. All data collection was focused on a clear objective dictated by the permitting agency. In all cases, the choice of treatments was determined by rates of cation removal in harvest rather than ash application rates that would cause a significant change in groundwater chemistry. Piezometery was used to define flow paths necessary to justify tests that eliminated spatial variability. These tests allow a reliable statement that ash application can replace cations removed in harvest of short rotation pine plantains with only small changes in groundwater quality, which do not violate drinking water standards. After- this study was completed South Carolina implemented new regulations for permitting of land application of solid waste with specific guidelines for wood ash (SCDHEC, 1995)8 Wood ash is now considered a Class I non-hazardous waste, and can be avvlied at rates up to 22 Mg/ha, except within 100 ft (30.5 m) of a property line, surface body of water, drinking water well or 500 ft (152.4 m)
WILLIAMS
of a hospital, school or recreational area. Ash spreading may only take place when the watertable is more than 12 in (30.5 cm) below the soil surface. A table of cumulative loading rates is also included in the regulations, which, for the ash considered in this paper, would allow spreading at 22 Mg/ha for 80 rotations before the arsenic cumulative mass is reached. Acknowledgements-Drs Charles Hollis, Andrew Evans and Bill R. Smith collaborated in design and implementation of the experiments reported here. Charles McCutcheon and James Morris installed field apparatus and collected samples. Louwanda Jolley conducted laboratory analysis of all samples. Funding for these experiments was provided by International Paper Corporation and the State of South Carolina.
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9.
Haywood, J. D., Early growth reduction in short rotation loblolly and slash pine in central Louisiana, Southern J. Applied Forestry,, 1994, 18, 35-39. Ostrofsky, W. D. Ash residue utilization and timber quality improvement. Maine Agric. and Forest Experiment Sta. Misc. Report 383. Universitv of _ Maine CFRU Report, 34, pp. 9-15, 1993. Shepherd, R. K. Sludge and ash. Maine Agriculture and Forest Experiment Station, Misc. Report 383, University of Maine, CFRU Rept., 34, pp. 30-34, 1993. Holhs, C. A. Bark boiler ash recycling in forests: Environmental monitoring results for research test in coastal South Carolina. International Paper Internal Report, 1993. South Carolina Department of Health and Environmental Control. 1995. Proposed Regulation R.61-107. Solid waste management: Land application of solid waste. SCDHEC. Columbia, S.C. Riekerk, H., Coal-ash effects on fuelwood production and runoff water quality, Southern J. Applied Forestry, 1984, 8, 99-102.
Carolina Department of Health and IO. South Environmental Control. 1981. State Primary Drinking Water Standards. SCDHEC, Columbia, S.C. 11. Sweeny, J. R., Jones, P. D. and Cobb, G. P., Small mammal safety of bark boiler ash recycling in southeastern coastal plain forests. In Proc. 8th Biennial Southern Silviculture Research Cm&.. ed. M. B. Edwards, pp. 264-268. Gen. Tech. Rep. SRS-I. USDA Forest Service, Southern Research Station, Asheville, NC., 1995. 12. Ward, B. J., Soil Survey of Williamsburg County. South Carolina. USDA, Soil Conservation Service. Washington D.C., 1989. 13. Jardine, P. M., Wilson, G. V. and Luxmore, R. J., Unsaturated solute transport through a forested soil during rain storm events’Soil Sci., 11990,128, 3440. 14. Williams, T. M. and McCarthy, J. F., Field scale tests of colloid-facilitated transport. In National Research and
Development
Conference
on
the
Control
of
Water
quality
for biomass
Huxrdous Materials. Hazardous Materials Control Institute. Greenbelt. MD. pp. 179-184. 1991. 15. Greenberg, A. E., Clesceri, L. S. and Eaton, A. D. (eds). Standard Methods,for Examination of’Water and Wasrewter. American Public Health Association., Washington DC, 1992. 16. McGrath, S. P. and Smith, S. Chromium and nickel. In Heavy Metals in Soils. ed. B. J. Alloway, pp. 125150. Blackie, London. 1990. 17. de Marsily, G. Quantitative Hvdrogeology. Academic Press, New York, 1986.
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287
18. Hinton, S. W., Statistical procedures for addressing nondetect results in environmental data, TAPPI .I., 1994, 77(4), 83-90. 19. Williams. T. M.. Hollis. C. A. and Smith, B. R.. Forest soil and water chemistry following bark boil bottom ash application, J. Environ. Qua/., 1996, 25, 955-961. 20. Ohno, T., Neutralization of soil acidity and release of phosphorus and potassium by wood ash, J. Enivron. Qual., 1992. 21, 433438. 21. Riekerk, H. and Kohrnak, L. V., Use of coal-ash for , Soil and Crop Casurina forest biomass production Sri. Sot. Florida Proc.. 1984, 43, 7680.
Pergamon
(’ 1998 Published
PII: SO961-9534(97)10015-O
13. Nos. 415, pp. 279-287. 1997 by Elsevier Science Ltd. All rights reserved Printed in Great Britain 096l-9534,97 $17.00 + 0.00
OBTAINING WATER QUALITY PERMITS FOR LAND APPLICATION OF BIOMASS BOILER ASH THOMAS Baruch
Forest
Science Institute,
Clemson
M.
University,
WILLIAMS
P.O. Box 596 Georgetown,
SC 29442, U.S.A.
Abstract-Land application of biomass fuelled boiler ash can save landfill space and return cations to the forest environment. However. environmental regulations throughout most of the U.S. do not specifically address application of biomass boiler ash to forest land. South Carolina Department of Health and Environmental Control (SCDHEC) treated bark boiler ash from International Paper’s Georgetown, SC. mill as an experimental permit with a requirement of monitoring experimental applications to show it would have “no detrimental impact to the environment or public health”. An initial catchment study showed no evidence of leaching into either the watertable aquifer or outlet streams when ash was applied to moderately well-drained portions of two watersheds at a rate of I I Mg/ha. Concentrations of elements in groundwater samples were well within state drinking water standards, often more than an order of magnitude below the standards. The second study was a replicated block experiment of ash application rates of I I. 22 and 44 Mg/ha. Ash application increased leaching significantly for potassium, calcium and sulfate, although concentration &eases were modest (0.12~0.17 Mg/l for potassium, 0.36.-0.89 mg/l for calcium and 1.92-3.08 mg/l for sulfate). Groundwater heavy metal concentrations were well below drinking water standards, even at the 44 Mgiha rate. $*, 1998 Published by Elsevier Science Ltd. Keywords-Boiler
ash; wood ash; water quality;
groundwater:
1. INTRODUCTION
documented for forest applications of wood ash.’ Recycling biomass boiler ash to forest land would save landfill space and could help replace some of the nutrients removed during harvest of short rotation pine plantations. The International Paper mill, Georgetown, South Carolina demonstrates the problems of landfilling ash. The mill, built in 1939, was reconfigured in 1980-1982 and equipped with a fluidized bed power boiler that burned 85% bark, 10% unusable pulp and 5% coal (to maintain efficient combustion). The boiler has produced 100 Mg of ash per day since conversion. By 1992 the on-site landfill contained about 300 000 m3 of ash. In addition to filling landfill space quickly, landfilling ash also accumulates the small amounts of heavy metals found in bark at a single point. In this case, about 10 Mg lead, 7 Mg nickel, 6 Mg arsenic, 6 Mg chromium, 1 Mg selenium and 300 kg cadmium are present in the ash pile (based on ash analysis conducted from 199 1- 1995). At projected growth rates and present utilization standards, harvests on company land near the Georgetown mill will remove about 10 Mg/ha of major cations. Depending on combustion efficiency, 25-40 Mg of ash will have roughly the same total mass of cations.
Biomass fuels are commonly used for power generation in pulp and paper mills throughout the United States with 2.7 million Mg of ash generated annually by power boilers fired with bark, wood and wood wastes. Over 80% of that ash is landfilled.’ Ash derived from the combustion nutrients to Agronomic amendments increases of cations2.‘.
of biomass enhance soil studies on with wood growth with
heavy metal; chromium
can provide plant and site productivity. the effects of soil ash showed modest moderate ash appli-
Haywood suggests that nutrient removals during short rotations of southern pines require nutrient additions by fertilization in order to be sustainable. Application of ash could be used to maintain forest soil productivity by replacing the cations removed during harvest. Ostrofsky’ demonstrated modest increases in red pine and black spruce growth following application of ash. Foliar content of potassium, phosphorus and calcium is significantly increased by ash application and the beneficial effects are persistent for up to 26 months.” Enhanced forage quality and biomass production for wildlife species were 279
280
T. M. WILLIAMS
By 1990, the company began planning to switch from placing ash in a landfill to land application on company forest lands. However, as an industrial waste, ash is regulated by the U.S. Environmental Protection Agency and by individual state solid waste and water quality programs.’ In South Carolina the South Carolina Department of Control Health and Environmental (SCDHEC) was given the primary responsibility in programs of solid waste and water quality. In 1990, no ash had been land applied in South Carolina and research on ash application to southeastern Coastal Plain soils had been done at much higher rates.’ Ash application could only be done under a Department Research, Development and Demonstration Permit. A requirement of this permit is that the research or demonstration have “no detrimental impact to the environment or public health”. Two projects were done cooperatively between International Paper and Clemson University with active oversight by the SCDHEC, a watershed scale pilot project and a replicated plot rate study. The highest priority was protection of water quality of both groundwater and streams. Specifically, groundwater elemental concentrations were not to exceed primary drinking water standards” as a result of ash application. Conditions of the application permit presented a challenge to design of the these projects. Experimental applications were expected to duplicate the planned operational spreading procedures and none of the experimental applications could result in a detrimental effect to the environment or public health. That is, not even one groundwater sample was to exceed concentrations in the drinking water standards. Rather than simply testing a hypothesis of a treatment effect vs a nil of no effect to be successful, the study needed to test the hypothesis that groundwater concentrations of elements, including any treatment effect, were unlikely (with a high degree of confidence) to exceed a specified value (drinking water standard). The studies also had a number of other objectives. The most important was an economic assessment of transport and spreading procedures. All costs of land application could not exceed the cost of building a new landfill. Movement of metals into small mammals was also studied. ’’ Influence on pine growth was
also measured, although an immediate fertilizer response was not considered vital for success. Two times during a rotation were considered for ash application, either at time of site preparation or after first thinning near age 15. For a valid economic evaluation of the spreading techniques, application areas of 50 ha were considered minimal. High watertables, characteristic of southeastern coastal plain forest lands, created potential for contamination of the watertable aquifer or of streams, by runoff from saturated soils.
2. METHODS
2.1. Catchment study The first study was an operational trial of spreading at a ash catchment scale. Groundwater samplers and piezometers were used to define flow directions and elemental concentrations, while automated stream samplers monitored water leaving the catchments. A portion of International Paper property in eastern Williamsburg County, S.C. (latitude 35”35’N, longitude 79”34’W) had the required combination of forest age and well-defined catchments. A block (roughly 100 ha) of clearcut pine plantation and a similar block of recently thinned (1990) 17-year-old pine plantation were chosen. Two catchments were chosen in each block and an ash application area was chosen to completely enclose one catchment in each block (Fig. 1). Soils on the study site were primarily Eulonia (fine-loamy, siliceous, thermic, Aquic Hapludults), Emporia (fine-loamy, siliceous thermic Typic Hapludults), Yemassee (fineloamy, siliceous, thermic Aeric Ochraqualts) and Ogeechee (fine-loamy, siliceous, thermic Typic Ochraqualts).‘* All of the Ogeechee and portions of the Yemassee soils were poorly drained and were not considered for ash application. An on-site soil survey was conducted in each application area and all soils that were moderately well drained or better were mapped for ash application. Approximately 50 ha received ash in each block at a rate of 11 Mg/ha in December of 1990. Following ash application, the clear-cut areas were bedded and planted to pine. The most likely mechanism for groundwater contamination was macropore flow bypassing the soil matrix.13 Groundwater was collected
Water Well
quality
for biomass
Drained
1 4sh
rd0 ASI
Clear .,
,,
vvells
I hlnned Poorly Drained _, * tlume ond bampler
Cbt \
/
J 7
Fig. I. Schematic diagram of well layout for study 1. Four small (20 ha) watersheds formed a 2 x 2 factorial of ash application (ash vs no ash) and stand age (0, clear cut vs 17, thinned). Ash was applied only to well-drained portions of watersheds. Each watershed had a Parchall flume and ISCO automated sampler at the outlet. Sampling wells were placed in transects from watershed divide to stream. with two wells in the well-drained portion of each transect. Well pairs used in the paired comparison are marked with “t” and “c” for ash applied and control, respectively.
boiler ash
281
tained continuously and pumped whether water was in the stream or not, assuring samples of intermittent flows. Surface samples were collected from January 1992 (the first flow after ash application) until April 1994. Groundwater samples were collected with a battery powered peristaltic pump. Each well was connected to the five-head pump. The pump was run until all samplers produced over three sampler volumes, all pump lines were rinsed with sample, the sample bottles were rinsed with sample, and a 65 ml sample was collected. Pump lines were purged with air between wells. All samples were put in an ice chest and transported to the laboratory. Samples were refrigerated until analysis. Sample aliquots were analyzed for: NOs, P04, SO4 and Cl, by ion chromatography; Ca, Mg, K, Zn by air-acetylene flame atomic absorption, Al by nitrous oxide-acetylene flame atomic absorption; and Cd, Cr, Cu, Ni by graphite furnace absorption. atomic Techniques were as described in Standard Methods for Analysis of Water and Waste Water.”
2.2. Application rate plot study from multi-level samplers designed to measure piezometric potential at four depths and sample groundwater at five depthsI Each sampler installation will be referred to as a well for simplicity (Fig. 1). Wells were placed in transects from the watershed boundary to the stream. It was anticipated that ash application might increase variability, so five transects were placed in the watersheds to receive ash and only three in watersheds receiving no ash. On each transect, two wells were placed on well drained soil, one in poorly drained soil, and one in the creek bottom. Samples were collected in November 1991, prior to treatment in December 1991, after treatment in December 1991, and monthly through May 1994. Piezometer levels were measured weekly throughout the period. Surface water was collected by ISCO brand automatic samplers. Parshall flumes were placed at the outlet of each catchment and a sampler was placed in the stream just upstream of the pond created by the flume installation. The sampler was programmed to pump a sample every 6 h and fill a single sample bottle each day. Samples were removed from samplers weekly. Samplers were main-
Near the catchment experiment, approximately 37 ha of a 27-year-old loblolly pine plantation was harvested in 1992. The site was prepared in spring 1993, by flat shear, burn and spot piling of residual debris. The site was disked and sprayed with Velpar-L (4.5 kg ai/ ha) in June, 1993. Bark boiler ash was applied to designated plots in December 1993, and subsequently re-disked. The stand was planted with loblolly pine in January 1994 at a nominal density of 1360 trees/ha. Ash was applied to four replicates of a randomized block, split plot design. Blocks were rectangular (5660 m2), and split into two, square plots (2830 m2), with one plot receiving no ash and the other either 11.2, 22.4 or 44.8 dry Mg of ash/ha. Blocks were arranged in a single line approximately perpendicular to the land slope. Blocks were separated by 50100 m buffers to avoid cross-contamination. Long axis of each block was aligned with the land slope and the control plot was located on the uphill plot. A groundwater sampling well was located in the center of each plot. Soils on these plots were a closely related Eunola series siliceous, loamy, thermic Aquic (fine Hapludult).
T. M. WILLIAMS
282 Table
Element Aluminum (mg/l) Calcium (mg/l) Cadmium (pg/l) Chromium (pg/l) Copper (pg/l) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mg/l)
1. Mean concentrations
Clear cut ash Mean
(UCL)
1.67 0.74 0.09 0.66 I.14 6.99 0.69 0.66 0.008
(2.17) (0.78) (0.16) (0.75) (1.38) (7.30) (0.77) (0.67) (0.013)
UCL is the upper 99% confidence the main concern.
of daily composited
Clear cut controlMean
(UCL)
0.30 I .08 0.13 0.66 2.87 7.43 1.25 0.83 0.013
limit. Upper
0.54 2.48 0.08 0.73 1.37 8.81 0.69 0.83 0.012
(0.36) (1.14) (0.18) (0.73) (3.47) (10.1) ( I .49) (0.88) (0.016)
confidence
Wells, 2.5 cm diameter polyvinyl chloride, consisted of a 3 m slotted screen lower section with a 1.5 m solid upper section. Wells were installed by hand augering (7.5 cm diameter auger), using a 10 cm casing where aquifer sand was loose. The well pipe was inserted and the hole filled with aquifer sand to a level 15 cm above the slotted pipe. A bentonite seal was placed in the hole and, after waiting 24 h for the clay to swell, the hole was filled with neat cement to form a dome approximately 5 cm over the soil surface. An outer 7 cm casing, with cap, was set into the cement around the well and served to protect the well from outside contamination. All wells were pumped until no evidence of drilling or sealing materials were found in the water. Field sampling began in October 1993, with bi-weekly samples collected until March 1994, and monthly sampling continued until March 1995. Sampling procedures were similar to the catchment study except the peristaltic pump had a single head and the entire well volume was pumped three times prior to sampling. Analysis for cations and heavy metals were also the same as described for the catchment
stream
Thinned ashMean
limits are used because
samples Thinned control Mean
(UCL) (0.62) (2.66) (0.09) (0.8 I) (1.54) (9.19) (0.76) (0.90) (0.017) maximum
0.36 0.80 0.13 0.98 I.13 7.43 0.39 0.54 0.009
(UCL) (0.44) (0.64) (0.23) (1.35) (1.39) (7.84) (0.31) (0.58) (0.014)
likely concentrations
are
study. Instead of using ion chromatography, the anions were determined by automated colorimetric techniques using a Technicon autoanalyzer. I5
3. RESULTS
AND DISCUSSION
Statistical analysis of this study was planned to meet the regulatory demands of the study. Without a long pre-treatment the simple 2 x 2 factorial design has very little power to detect a significant treatment effect. However, the chief concern in this trial was not evaluation of a treatment effect but rather to determine whether concentrations were below water quality standards. An upper confidence (99%) limit below the standard, using operational application procedures, was the criteria used for decision on permitting of land application. The control watersheds were used primarily to estimate natural spatial variability in concentrations. Post-treatment concentrations of both streams (Table 1) and groundwater (Table 2) show means for the all areas where ash was applied were well below drinking water
Table 2. Mean concentrations of elements in groundwater samplers on well drained soils on control watersheds (6) and ash applications (IO). UCL is the upper 99% confidence limit. Compassion of primary concern was between upper confidence limit and drinking water standard (I”)
Element Aluminum (mg/l) Calcium (mg/l) Cadmium (pg/l) Chromium @g/l) Copper @g/l) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mg/l)
Clear cut ash Mean 4.71 3.30 0.16 2.30 1.89 10.5 0.66 0.57 0.063
(UCL) (6.92) (3.79) (0.39) (3.20) (2.68) (11.9) (0.72) (0.65) (0.069)
Clear cut control Mean 0.55 0.44 0.05 25.7 1.37 5.2 0.74 0.45 0.039
(UCL) (0.82) (0.55) (0.06) (64.6) (2.16) (5.5) (0.79) (0.47) (0.045)
Thinned ash Mean 4.13 1.15 0.15 19.0 2.65 7.7 0.83 0.45 0.262
(UCL) (7.52) (1.33) (0.18) (43. I) (5.18) (8.1) (0.90) (0.48) (3.99)
Thinned control Mean 1.37 4.27 0.09 0.80 0.60 7.6 0.65 0.47 0.14
(UCL) (2.27) (4.84) (0.14) (1.00) (0.77) (8.1) (0.70) (0.51) (0.52)
Drinking water standard
IO 50 1000 250
Water
quality
for biomass
standards for all regulated elements sampled (arsenic was not determined in these samples due to difficulties with analytic methods). Only for groundwater on the clear-cut control area, did the upper confidence limit exceed drinking water limits for chromium. The stream concentrations were remarkably similar to the groundwater. For many elements, concentration in the stream was lower than in groundwater. Well locations, use of multi-level sampling and piezometery were designed to determine groundwater flow directions and extent of movement of groundwater across the watershed. The watertable aquifer beneath all watersheds was similar. Below the loamy surface and sandy clay loam to clay loam subsoils (at depths of 2.5-3 m) the aquifer was a medium-grained sand of remarkably high chroma (1 OY R 8/6). Piezometer measures confirmed nearly vertical downward movement deep (6 m) into this sandy material, even on the wells in the poorly drained soils. Likewise, piezometers in the streams showed vertical upward movement from the sandy material. Piezometric data clearly showed well samples were derived from moisture moving vertically from the surface near the well, meaning that individual wells were independent measures of the treatment effect at that point. One estimate of the effect of ash application is simply a comparison of the means of wells in areas that received ash and comparable samplers in the and control catchments (Table 3). This simple comparison is the same as the difference of means in Table 2, with the maximum effect estimated as the upper 99% confidence limit of the difference with a pooled variance. Of coarse, this estimate contains all the spatial and temporal variability associated
Table 3. Mean concentration
Element Aluminum (mgil) Calctum (mgil) Cadmium (pgil) Chromium @g/l) Copper @g/t) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mgil)
increases
Clear cut predicted effect 4.16* 2.g1* 0.10 -23.3 0.52 5.33* -O.OY 0.12* 0.016*
of elements
Maximum
boiler ash
283
with sampling from sites separated by several kilometres. For aluminum, chromium, copper and zinc the estimates are plagued with a great deal of variability. Chromium presented a difficult problem with variability. Sediments in the region of this experiment have locally high concentrations of chromium. At the pH of the aquifer (-5.0) the reduced form of chromium (Cr”) adsorbs strongly to soil particles and is immobile.16 However, the oxidized form (Cr6’) is relatively mobile. Well installation introduced oxygen that could mobilize chromium from a local sedimentary accumulation. If this was the case, groundwater samples from some wells might have transient spikes of chromium, with timing dependent on the rate of vertical transport and the length of time required for reducing conditions to be reestablished. There was no significant effect for chromium, with a confidence limit up to 48 pg/l, not a particularly reassuring conclusion. The finding that water moved primarily downward also allowed another comparison to be made. Four wells were installed on each transect to measure lateral transfer towards the stream. However, multi-level samples were actually being taken and piezometery showed movement to be vertical. Therefore, the upper samples in each well were independent estimates of leaching from the soil profile at that point. On each transect, a well in the poorly drained soil was located about 100 m from a well where ash was applied (Fig. 1). There were five pairs of wells in each treated watershed that could be viewed as random split plots with ash applied to the uphill plot. A “paired-t” test was done by comparing the
in groundwater
effect
6.38 3.35 0.33 15.0 1.31 6.71 -0.02 0.18 0.017
attributable
to ash application
Thinned predicted effect 2.76 -3.12* 0.06 18.2 2.00 0.12 0.18* -0.20 0.22
Maximum
effect
6.15 -1.79 0.09 42.0 4.58 0.47 0.35 0.06 3.95
Predicted value is mean of wells in receiving ash - mean of control wells on well drained soil, negative values indicate control concentrations were larger than treatment. Maximum effect is the upper 99% confidence limit on the difference. *Difference is significant at 99% confidence.
284
T. M. WILLIAMS
Table 4. Mean concentration
increases
of elements
Clear cut predicted effect
Element Aluminum (mg/l) Calcium (mg/l) Cadmium @g/l) Chromium @g/l) Copper (ng/t) Chloride (mg/l) Potassium (mg/l) Magnesium (mg/l) Zinc (mg/l)
in groundwater parisons
Maximum
-0.58 1.17* 0.018* -0.45 0.53 -1.13 -0.064 -0.0098 0.0165*
effect
attributable
to ash application
Thinned predicted effect
1.74 1.96 0.033 2.48 2.24 1.87 0.022 0.09 0.022
based on paired
Maximum
-0.40 -1.30* -0.12 1.64 0.76 -1.13 -0.21* -0.188* -0.217
com-
effect
-0.64 -0.70 0.05 4.31 1.69 0.53 -0.11 -0. I 1 0.53
Predicted value is the mean difference between paired samples in wells in treated areas and nearby untreated areas. negative values indicate concentrations in untreated area were larger than treatment. Maximum effect is the upper 99.9% confidence limit on the difference. *Difference is significant at 99.9% confidence.
concentrations in the upper sampler of each paired well (Table 4). A paired comparison estimate of the effect of ash application is more precise. Physical factors governing groundwater movement display strong spatial correlation.” This spatial correlation increases the power of the “pairedt” comparison. Hinton18 discusses the difficulties of non-detectable samples that are commonly found in environmental monitoring of trace metals. Using only values above the instrument detection limit (as in Tables l-3 and 5) results in a positive bias in both mean and variance, the most conservative position from a regulatory viewpoint. However, a nondetectable sample in a paired comparison is a valid estimate of treatment effect. The instrument detection limit is the smallest of the various estimates of detection limits.t5 Substituting this value for each non-detectable sample in a “paired-t” test eliminates the bias for the mean estimate, although there is still a positive bias in calculation of the variance. Table
5. Mean
groundwater
Element Nitrate N (mg/l) Phosphate P @r/A) Sulfate (mg/l) Chloride (mg/l) Potassium (mg/l) Calcium (mg/l) Magnesium (mg/l) Aluminum (mg/l) Arsenic @g/l) Cadmium (pg/l) Chromium &g/l) Copper @g/t) Nickel @g/l) Zinc @g/t)
Using the “paired-r” analysis, there is only one chance in a thousand cadmium was increased by more than 0.05 pg/l or chromium was increased more than 4.3 pg/l due to ash application. Following this study, a permit was issued for land application of ash using the same rate and spreading techniques. 3.1. Application
rate study
The catchment study was done very cautiously to avoid any violations of the research permit. Confidence that the 11 Mg/ha rate resulted in very little leaching of even calcium and magnesium (the dominant ions in the ash) encouraged tests of higher rates. A rate of 44 Mg/ha was estimated to equal the cation removal during harvest of the fastest growing pine plantations on the company’s land. Applications from 22 to 44 Mg/ha would span the range of removals from the variety of sites now under management. Since groundwater movement was vertical, completely screened wells would collect a representative sample. A
element concentrations with various rates of ash application water standards. Means and upper 99% confidence limit 1 I mg/ha cont. @JCL) 1.21(1.24) KO(6.25) 4.37(5.07) 16.3(18.8) 0.68(0.80) 1.17(1.41) l.lO(1.26) 0.68(0.96) 5.4(6.8) 0.029(0.045) 1.22( I .86) 0.89(1.17) 0.68(2.85) 8.0(10.3)
22 mg/haconc. (UCf-) 0.81(0.97) 9.8(13.7) 3.91(4.64) 12.9(15.6) 0.72(0.84) 1.84(2.15) 1.06(1.15) 3.08(4.25) 16.3(25.2) 0.048(0. I 18) 4.24(6.48) 0.86( I .24) 1.06(2.03) 9.7(18.2)
44 Mg/haconc. (UCL) 0.95(1.11) 3.2(5.0) 3.51(3.77) 12.4(15.5) 0.41(0.46) 1.02(1.16) 0.86(0.93) 0.09(0.33) 3.9(5.5) 0.038(0.073) l.gl(2.61) 0.43(0.83) 1.85(2.84) 8.9(ll.O)
as compared
with drinking
Drinking water standard 10
250
50 10 50 1000
Water
quality
for biomass
split plot approach with the control as the split allowed the greatest control of spatial variability, producing the strongest test between each rate and the control. The primary concern of this test was also groundwater element concentrations that might violate drinking water standards (Table 5). At the higher application rates, groundwater concentrations were still considerably below drinking water standards. Most concentrations were an order of magnitude below the standards. Even for arsenic, the most critical
boiler ash
285
element, the upper confidence limit (99%) of the largest mean was only about half the standard. 3.2. Overall results The application rate study was designed to allow estimation of the effect for each application rate above a control. These results can be combined with the results in Table 4 to examine effects of ash spreading in eastern South Carolina (Fig. 2). The degree of disturbance to the forest floor and competing veg-
3 <
2.5
F
2
: .-
1.5
5
1
$
0.5
:
0
0
O-o.5 -1 -1.5 Nitrate
Potassium
Calcium
Magnesium
Aluminum
3 i2.5
Y
2
g .1
1.5
5
0.5
1
:
0
6 -0.5 -1 M
-l.SF Cadmium 4
-4
Chromium
Copper
Chloride
m
11
Mg/ha
m
11 Mg/ha
Thin
m
CC Rate
Nickel
Arsenic
Sulfate
11 Mg/ha m
22
Phosphate
CC Catch Mg/ha
Rate
0
44
Mg/ha
Fig. 2. Overall changes in groundwater chemistry following ash application as difference Negative numbers indicate decrease from a control. * Indicates statistical significance dence.
Rate
from a control. at 95% confi-
286
T. M.
etation seems to have a large influence on the results when ash is applied at 11 Mg/ha. The results for the 22 Mg/ha rate were elevated above those for the lower rate and more often significant. However, the results of the 44 Mg/ ha application were not higher than at 22 Mg/ ha for most elements. The highest rate did seem to result in a change in soil chemistry that effected concentrations of several elements. Surface soil pH was raised to near neutrality (6.7) for 12 weeks after application at the 44 Mg/ha rate, compared with 4.0 for prior to site preparation and 5.0 for no ash application. I9 Results from these studies were qualitatively similar to other ash experiments on forest land. Potassium, calcium and magnesium were all significantly increased by ash spreading on clear-cut sites. Ohno2’ predicted similar results from studies of soil-ash suspensions. Riekerk and Kohrnak2’ found these same elements elevated in run-off water from small watershed at high (127 Mg/ha) application rates of coal ash. There was no indication of macropore flow resulting in rapid movement of soluble ash elements into the groundwater, a high priority concern prior to the studies. The method International Paper chose to obtain permits for land application of boiler ash involved a high applied research technique. The studies were primarily data collection during production scale ash application. All data collection was focused on a clear objective dictated by the permitting agency. In all cases, the choice of treatments was determined by rates of cation removal in harvest rather than ash application rates that would cause a significant change in groundwater chemistry. Piezometery was used to define flow paths necessary to justify tests that eliminated spatial variability. These tests allow a reliable statement that ash application can replace cations removed in harvest of short rotation pine plantains with only small changes in groundwater quality, which do not violate drinking water standards. After- this study was completed South Carolina implemented new regulations for permitting of land application of solid waste with specific guidelines for wood ash (SCDHEC, 1995)8 Wood ash is now considered a Class I non-hazardous waste, and can be avvlied at rates up to 22 Mg/ha, except within 100 ft (30.5 m) of a property line, surface body of water, drinking water well or 500 ft (152.4 m)
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of a hospital, school or recreational area. Ash spreading may only take place when the watertable is more than 12 in (30.5 cm) below the soil surface. A table of cumulative loading rates is also included in the regulations, which, for the ash considered in this paper, would allow spreading at 22 Mg/ha for 80 rotations before the arsenic cumulative mass is reached. Acknowledgements-Drs Charles Hollis, Andrew Evans and Bill R. Smith collaborated in design and implementation of the experiments reported here. Charles McCutcheon and James Morris installed field apparatus and collected samples. Louwanda Jolley conducted laboratory analysis of all samples. Funding for these experiments was provided by International Paper Corporation and the State of South Carolina.
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Carolina Department of Health and IO. South Environmental Control. 1981. State Primary Drinking Water Standards. SCDHEC, Columbia, S.C. 11. Sweeny, J. R., Jones, P. D. and Cobb, G. P., Small mammal safety of bark boiler ash recycling in southeastern coastal plain forests. In Proc. 8th Biennial Southern Silviculture Research Cm&.. ed. M. B. Edwards, pp. 264-268. Gen. Tech. Rep. SRS-I. USDA Forest Service, Southern Research Station, Asheville, NC., 1995. 12. Ward, B. J., Soil Survey of Williamsburg County. South Carolina. USDA, Soil Conservation Service. Washington D.C., 1989. 13. Jardine, P. M., Wilson, G. V. and Luxmore, R. J., Unsaturated solute transport through a forested soil during rain storm events’Soil Sci., 11990,128, 3440. 14. Williams, T. M. and McCarthy, J. F., Field scale tests of colloid-facilitated transport. In National Research and
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18. Hinton, S. W., Statistical procedures for addressing nondetect results in environmental data, TAPPI .I., 1994, 77(4), 83-90. 19. Williams. T. M.. Hollis. C. A. and Smith, B. R.. Forest soil and water chemistry following bark boil bottom ash application, J. Environ. Qua/., 1996, 25, 955-961. 20. Ohno, T., Neutralization of soil acidity and release of phosphorus and potassium by wood ash, J. Enivron. Qual., 1992. 21, 433438. 21. Riekerk, H. and Kohrnak, L. V., Use of coal-ash for , Soil and Crop Casurina forest biomass production Sri. Sot. Florida Proc.. 1984, 43, 7680.