NEUTRON PROBE TECHNIQUE FOR MOISTURE MONITORING IN LANDFILLS
S.T.S. Yuen, Q.J. Wang, J.R. Styles and T.A. McMahon
Department of Civil & Environmental Engineering, University of Melbourne, Parkville, Victoria
3052, Australia
SUMMARY :
The paper begins by highlighting the need for indirect/non-destructive
measurements of moisture in MSW landfills. It then presents the findings of a study comprising a
feasibility assessment, a laboratory investigation and a field application to substantiate that a
neutron probe can practically assess moisture content of MSW despite some limitations. A field
application procedure is also recommended.
1.
INTRODUCTION
With the recent shift in the design of municipal solid waste (MSW) landfill moving from a
permanent containment storage (dry cell) concept to a bio-reactor (wet cell) approach, there is a
growing need for in-situ monitoring of MSW moisture. For a successful bio-reactor landfill, it is
essential to maintain the MSW at an optimum moisture state favourable for bio-degradation. The
measurement of MSW moisture is needed in landfill related research such as:
 leachate recirculation studies to assess the performance of the recirculation systems,
 predicating methane formation potential of an existing landfill,
 landfill cell water balance to predict leachate generation, and
 studies of saturated/unsaturated flow in a MSW medium.
While the measurement of moisture content of a landfill can be achieved by gravimetric
determination of samples directly collected from the landfill, the direct method has certain
operational constraints. The sampling of waste, often involving either drilling or excavation in the
landfill, can be destructive to the containment system. It can also be expensive if substantial and
repetitive sampling is required. It also involves the drying of samples which takes time. To avoid
the above limitations, the availability of a rapid, non-destructive, and easily repeatable indirect
method would be desirable, particularly in situations where a large spatial moisture measurement of
a repetitive nature is required.
Although a number of standard techniques of in-situ soil moisture measurement are available
in agricultural and engineering applications, very little information is available in the literature
regarding the measurement of moisture in a MSW medium.
This MSW moisture measurement study was conducted as part of a full-scale leachate
recirculation bio-reactor landfill research project which has been described by Yuen et al. (1995).
The study comprised three components, namely a feasibility assessment of all standard moisture
measurement methods, a laboratory testing program to confirm viability, and a field application in a
real landfill situation.
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
2.
FEASIBILITY ASSESSMENT
A wide range of soil moisture measurement devices commonly employed in agricultural and
engineering applications were assessed. They can be broadly divided into the following categories
based on their principles of operation :
 electromagnetic techniques,
 electrical or thermal conductivity,
 tensiometric techniques, and
 neutron scattering.
The principles of operation, advantages and disadvantages of each of the above methods used
in a soil medium have been discussed in detail by other studies (e.g. Schmugge et al., 1980;
Gardner, 1986; Tyndale-Biscoe and Malano, 1993). However, due to the complexity and highly
heterogeneous nature of MSW, many difficulties and limitations exist when they are used in a
landfill. A detailed discussion regarding their suitability in MSW is given by Yuen et al. (1996).
The selection of a suitable method was based on the following criteria :

reliability,

ease of measurement,

non-destructiveness,

repeatability,

acceptable accuracy, and

large effective sampling volume.
While all of the above criteria are obvious, it is important to emphasise the importance of a
large effective sampling volume to achieve “macroscopic” scale sampling. The heterogeneity of
MSW is much higher than that of soil. Both the composition and size of individual component can
vary in a wide range and each type of material may exhibit a different moisture/suction
characteristic. For example, a pocket of food waste would carry a much higher moisture content
than a piece of plastic even when they are subject to the same hydrological condition. Hence, to
study the moisture state of a landfill, it is only appropriate to look at the moisture regime at a larger
scale and it is important that moisture contents of macroscopic samples are measured.
The high level of salinity and heterogeneity of a MSW medium prevent the use of most of the
above techniques. The feasibility assessment (Yuen et al., 1996) concluded that there is no ideal
indirect/non-invasive method for MSW. Nevertheless, neutron scattering technique combined with
the use of in-situ access tube was identified as having the potential to produce acceptable results
within certain limitations.
The operating principles of a neutron moisture meter are well documented (e.g. Goodspeed,
1981 and Stone, 1990). Neutrons with high energy are emitted by a radioactive source into the soil
and are slowed down (thermalised) by elastic collisions with nuclei of atoms. As hydrogen has a
very low atomic weight, it can slow neutrons more effectively than other elements. The density of
the resultant cloud of slowed neutrons (which can be detected by a counter) is taken to be
proportional to the total number of hydrogen atoms per unit volume of soil. Assuming these
hydrogen atoms have a direct correlation with soil moisture, the volumetric moisture content can
then be determined from an established calibration curve.
There are certain distinctive advantages of using a neutron probe in a MSW medium. It has a
relatively large radius of influence (generally between 150 mm in wet soil to 700 mm in dry soil
(Gardener, 1986) )and can measure a continuous full depth profile through a access tube. Hence it
provides a spatial coverage superior to any point sampling methods. This macroscopic sampling
feature helps to better represent moisture content of a heterogeneous MSW medium. Once the
access tubes are in place, no maintenance is required. To record temporal changes, measurement
can be repeated at the same location as often as required by simply taking readings through the
same tube.
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
However, the neutron scattering method has its limitations particularly when it is applied in a
MSW medium.
3.
POTENTIAL LIMITATIONS WITH NEUTRON SCATTERING
3.1
Bound Hydrogen Effect
n
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Count Ratio
Count Ratio
Hydrogen atoms may exist in a soil as free water or as bound hydrogen (e.g. in the form of organic
matter). Although this bound hydrogen cannot be removed by oven-drying, it affects neutron
response in the same way as free water (Holmes, 1966). This effect in soil has been discussed by
Greacen et al. (1981), Hauser (1984) and Dickey (1990) and can be shown graphically as in Figure
1. Any presence of bound hydrogen would cause a parallel up-shift in the calibration line but
without a change of slope. The magnitude of this vertical shift depends directly on the quantity of
bound hydrogen.
ter
wa
e
tur
u
ne
No
Wit
Soil moisture obtained by oven-drying (mm/m)
Figure 1 - Effect of bound hydrogen on calibration curve
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ap
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Eff
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apt
ct o
utr
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cap
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Soil moisture obtained by oven-drying (mm/m)
Figure 2 - Effect of neutron capture on calibration curve
As MSW by its nature consists of a significant proportion of material containing bound
hydrogen (e.g. plastic and wood), this bound hydrogen bias could be substantial in MSW.
3.2
Neutron Capture Effect
As neutrons are slowed down (thermalised) they are subject to capture by various elements that
have an affinity for neutrons. This absorption capacity varies from element to element. Greacen et
al. (1981), Hauser (1984) and Dickey (1990) suggested that this neutron capture effect can be
reflected graphically as shown in Figure 2. The neutron absorption elements present in the soil
essentially decrease the number of thermalised neutrons and this reduction is proportional to
moisture content. This effectively reduces the gradient of the calibration curve.
Table 1 (Dickey 1990) shows the absorption capacities of some common elements. Boron
although having a relatively high absorption capacity, is considered not important as it is scarce in
soil and MSW. Generally, the elements of concern which are common in MSW are iron, potassium
and chlorine. With their presence, one would expect a certain degree of neutron absorption bias.
Table 1 - Capture Cross-Section for Thermal Neutrons of Common Soil Elements
Element
Oxygen Hydrogen
Capture X-Section 0.0016
0.3
Silicon
0.16.
Carbon Chlorine Boron Aluminium Iron Calcium Sodium Potassium Magnesium
0.0045
33
795
0.23
2.5
0.43
0.5
2.2
0.4
Note : Units are in barns (Source - Dickey 1990)
3.3
Density Effect
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
The effects of soil density on neutron probe calibration have been investigated by many researchers
(e.g. Holmes, 1966; Greacen and Schrale, 1976). Basically, a change in density affects the neutron
count because the density change may result in change in both bound hydrogen and neutron capture
effects. For example, an increase in the density of a soil containing bound hydrogen would increase
the count rate due to more hydrogen per unit volume of soil. On the contrary, increasing the density
of a soil containing neutron absorption elements would decrease the count rate due to more neutron
capture per unit volume.
4.
LABORATORY INVESTIGATION
4.1
Methodology
In order to quantify the above neutron probe limitations associated with its use in MSW, a
laboratory program comprising a series of tests was conducted to determine the calibration curves
for :
 Test (a) - Sand,
 Test (b) - Sand with ferrous metal (2% by dry mass),
 Test (c) - Sand with plastic ( 5% by dry mass),
 Test (d) - Sand with wood (10% by dry mass), and
 Test (e) - Sand wetted with leachate (instead of water).
Test (a) would provide a basic calibration curve to be used as the standard for comparison.
The material used was a very fine laboratory grade silica sand which contained no bound hydrogen.
The constitutional elements of the sand, i.e. silicon and oxygen, should exhibit negligible neutron
capture (refer to Table 1). Hence the resultant calibration curve could be considered to have no bias
due to either bound hydrogen or neutron capture effects.
The materials in Tests (b), (c) and (d) were chosen to represent some of the most common
MSW components that may exhibit bias in neutron counts. The percentages used were based on
their average proportions commonly found in landfills. The mixtures were used to test sensitivity on
neutron count rather than to represent their true proportion in a landfill.
Test (b) was conducted with a mixture of sand and ferrous metal filings. The result would
reflect any neutron capture effect due to the presence of the strong neutron absorption iron element
(refer to Table 1). Ferrous metal is a common component in landfills although it is only present in a
very small proportion.
Test (c) used a mixture of plastic granules and sand. Polyethylene (PE) was used in the test. It
is the most common form of plastic (generally used for sheetings and carrier bags) in the plastic
component of MSW. The result would provide some indication of the bound hydrogen effect
coming from the hydrogen atoms attached to the polyethylene polymers. The use of polyvinyl
chloride (PVC) was avoided as the attached chlorine atoms would produce a secondary effect of
neutron capture which may complicate the interpretation of the results.
Test (d) was conducted with wood chips which would reflect the bound hydrogen effect due
to the presence of natural organic matter such as cellulose which is also common in paper, garden
waste, timber and kitchen waste that occupy a substantial portion of MSW.
Test (e) with the presence of leachate was expected to show both bound hydrogen and
neutron capture bias in the calibration curve, as leachate commonly contains a considerable amount
of organic matter (bound hydrogen effect) as well as a high level of chloride (neutron capture
effect). The leachate used in the test was collected from a young landfill cell and was tested to
exhibit both contents in typical concentrations.
All six tests were conducted in a 120 litre, 700mm diameter drum with a vertical aluminium
access tube (40mm internal diameter 2mm thick) installed in the centre. In selecting the size of the
tube, it is desirable to minimise the air gap between the probe (of 38mm diameter) and the tube as
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
the gap constitutes a discontinuity in the system being measured. This is also important from the
point of view of reproducibility of probe location and avoidance of possible asymmetry effects.
Aluminium tubing was used as it is virtually transparent to neutrons. Steel and PVC tubings were
avoided because of their high absorption of slow neutrons. The neutron counts were measured by
using a CPN Corporation model 503 DR neutron depth moisture probe. Seven neutron counts were
taken for each moisture measurement, averaged and then converted to count ratio (i.e. average
count to standard count).
In order to minimise the effect due to density change, every attempt was made to maintain a
consistent density for each batch during compaction. Large samples were taken from various
locations of the drum for gravimetric moisture determination. For the conversion of gravimetric
moisture to volumetric measurement, the bulk density of each batch was required. In this case an
average bulk density was used and obtained by weighing all the material placed in the test drum of a
known volume.
4.2
Results and Discussions
Results of each test on dry densities suggest that the compaction of the mix was maintained
reasonably consistent through out. However, to minimise any density effect, count ratios were
corrected to account for density variation as proposed by Greacen and Schrale (1976) which uses an
empirical relationship that assumes count rate at constant total volumetric water content is
proportional to the square root of density.
The calibration curves (with corrected count ratios) as fitted by the least squares method are
plotted in Figure 3. The slopes, m and intercepts, c of the six lines are listed in Table 2.
1.60
Count Ratio
1.20
Sand
0.80
Sand + 2%Fe
Sand + 5% Plastic
0.40
0.00
0.00
Sand + 10% Wood
Sand with Leachate
0.05
0.10
0.15
0.20
0.25
0.30
Volumetric Moisture Content
Figure 3 - Calibration Curves of Laboratory Tests (a) to (e)
Table 2 - Results of Calibration Curves
Test
Mix
Equation y = mx +c
Slope (m)
Intercept (c)
(a)
Sand
6.24
-0.21
(b)
Sand with 2% Fe
5.67
-0.22
(c)
Sand with 5% plastic
6.34
0.22
(d)
Sand with 10% wood
5.64
0.17
(e)
Sand wetted with leachate
5.94
-0.14
To assess bound hydrogen effect, we can take the intercept of Test (a) (c= -0.21) as the datum
for comparison since the sand mix contained no bound hydrogen. Referring to Table 2, the variation
in intercepts c agrees very well with the bound hydrogen theory and follows the trend as discussed
in Section 3.1. While the increase in the leachate mix (c = +0.07) was relatively mild, the
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
increases in the 5% plastic mix (c = +0.43) and in the 10% wood mix (c = +0.38) were very
obvious. The 2% Fe mix gave an intercept value very close to the sand line (c = -0.01) which
reflected the absence of bound hydrogen.
For neutron capture effect, as indicated in Table 2, the changes in gradient followed very
closely the pattern as predicted by the theory described in Section 3.2. The gradient of Test (a)
(m=6.24) was taken as the datum since the sand exhibited no neutron capture. For the 5% plastic
mix with no neutron capture, the gradient remained almost the same (m= +0.1 or +1.6%). For the
leachate mix, the gradient dropped only slightly (m = -0.3 or -4.8%). For the 2% Fe mix, the drop
was higher (m= -0.6 or -9.6%) but the change was still small. The above reflects that neutron
capture effect caused by the presence of chloride in the leachate and the presence of the iron filings
in the Fe mix was relatively mild. However, for the 10% wood mix line, there was no logical
explanation for the gradient drop (m = -0.6 or -9.6%). As this drop in gradient was small, it might
simply be due to experimental error.
The above results thus indicate that the intercept of calibration curve can change substantially
in a MSW medium from sample to sample due to the presence of material containing a high amount
of bound hydrogen. This means a successful application to measure absolute moisture content
would require an individual calibration curve appropriate to each in-situ sample and that would be
practically very difficult to achieve.
Nevertheless, the results also suggest that the gradient of calibration curve may drop only
slightly from sample to sample even with the presence of neutron capture elements provided their
presence is not excessive. Based on this assumption, one can use the gradient of the standard sand
curve to interpret moisture change from the change in neutron count and the error involved would
be small.
An example can be taken to quantify this error. Considering a change in count ratio of 0.5 is
detected by the neutron probe, using the gradient of the standard curve would interpret a
corresponding change of moisture of 0.080. If the sample actually contains a neutron capture
element as in the case of the 5% Fe mix, using the gradient of the correct curve, the actual moisture
change should then be 0.088. In this case the moisture change is under-estimated by 9 %. Of course
this error grows as the presence of neutron capture element increases. In general the use of the
standard curve would tend to slightly under-estimate moisture change.
Working with MSW of high heterogeneity, it would be very difficult to quantity this error
associated with each sample. Using the standard curve to measure all samples would inevitably
produce results of unacceptable errors in occasional cases of extreme composition. However, the
macroscopic sampling feature as discussed previously would help to smooth out any of these
extreme measurements and to maintain a reasonable “average” moisture change profile.
If a knowledge of the composition of the MSW sample is available, the error can be
minimised by selecting a closer and more representative calibration curve. However, this is difficult
to achieve in practice. For practicality, the standard curve can be used in most applications provided
the above limitations are observed.
In practice, when a hole is being drilled to install the access tube, in-situ samples along the
depth profile can be collected to determine the gravimetric moisture content and to estimate dry
density. Once the initial volumetric moisture profile is established, any subsequent moisture change
detected by change in neutron count can then be used to calculate the new volumetric moisture
content.
5.
FIELD APPLICATION
5.1
Description of Full-Scale Trial
The above neutron probe technique was applied in a real landfill situation to measure MSW
moisture. In-situ vertical aluminium access tubes each 12 m long were installed in the Lyndhurst
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
bio-reactor landfill test cell (located 35 km south-east of Melbourne, Australia) to monitor seasonal
moisture change as well as to monitor moisture change due to leachate recirculation (Yuen et al.
1997).
The same neutron probe used in the laboratory tests was employed except in this case a longer
connection cable was used to allow the probe to reach the full depth of the access tubes. The
material and size of the access tubes were identical to that used in the laboratory.
Considerable difficulties were encountered in the installation of the access tube. Each tube
had to penetrate 12m down into the landfill and the longest available tubing length was 6m,
therefore at least one joint was required. As the internal diameter of the tube (40mm) is only
marginally larger than the diameter of the neutron probe (38mm), welding the tubes inevitably
reduces the effective internal diameter at the joint and would not allow the probe through. After
some trials, a “pin and socket” joint was successfully employed and glued with Araldite (a twopack epoxy glue). The joint was pre-made in the workshop by machine turning to remove half of
the thickness of the tubes, one end externally and the other end internally.
Another installation constraint was the requirement to keep the air gap between access tube
and MSW to a minimum. During installation, it was important to minimise any MSW disturbance
around the hole. Subsequent to some earlier unsuccessful trials, installation was finally achieved by
first pre-drilling to the required depth with a slightly oversized continuous flight auger. A steel
casing marginally larger than the external diameter of the aluminium tube, was then pushed through
the pre-drilled holes. The tube was then inserted inside the casing prior to withdrawal of the casing.
While it is impossible to install any tube without causing any disturbance to the surrounding MSW,
the above method managed to minimise it. The finished tubes were bottom sealed and top capped to
prevent ingress of moisture.
During pre-drilling of the holes, samples were collected at each metre interval to allow
subsequent gravimetric moisture determination and to provide information on waste composition.
As soon as each tube was installed, neutron counts were taken at 250mm vertical intervals to record
the initial base profile measurement.
5.2
Results and Discussions
For illustration purposes, data obtained from one of the access tubes (Hole AC2) is presented.
Figure 4 shows the composition of each of the 1m interval samples collected from the hole. Figure
5 plots the neutron counts (standardised to count ratios) against depth.
The gravimetric moisture contents of the samples were determined by oven-drying at 60 oC.
They were then converted to volumetric moisture. In-situ densities of the samples were required in
the conversion but they were proved to be extremely difficult to measure. In this case the
conversion was done based on a bulk average density value of 0.83 tonne/m3 which was determined
by volume survey and weighbridge records (Yuen et al., 1997).
The volumetric moisture contents of the samples are plotted against depth in Figure 6. The
neutron count ratios were averaged for each 1m interval to represent the average count
corresponding to each sample. They are also plotted against depth in Figure 6.
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
0%
10%
20%
30%
40%
50%
Inert (covers/buildings)
Paper
Plastic
60%
70%
80%
90%
100%
1 to 2 m
Depth (m)
3 to 4 m
5 to 6 m
7 to 8 m
9 to 10 m
11 to 12 m
Garden/food
Textlle/fabic
Metal(incl.fe)
Glass
Neutron Count Ratio
Figure 4 - Composition By Dry Mass of Samples Collected From AC2
2.5
2
1.5
12.00
11.50
11.00
10.50
10.00
9.50
9.00
8.50
8.00
7.50
7.00
6.50
6.00
5.50
5.00
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
1
Depth (m)
Figure 5 - Neutron Counts Ratio vs. Depth (AC2)
2.50
Volumetric Moisture
Neutron count ratio
0.30
2.00
0.25
0.20
1.50
0.15
0.10
11.50
10.50
9.50
8.50
7.50
6.50
5.50
4.50
3.50
2.50
1.00
1.50
0.05
Neutron Count
Ratio
Volumetric
Moisture
0.35
Depth (m)
Figure 6 - Volumetric Moisture and Averaged Neutron Count vs. Depth (AC2)
This “smoothed” neutron count curve exhibits a trend remarkably close to the volumetric
moisture trend. The minor inconsistencies as observed were contributed by both the bound
hydrogen effect and errors incurred by the use of a single bulk density value in the moisture
conversion.
These two effects are best illustrated in Figure 7 where neutron count ratio against volumetric
moisture is plotted along with the previous laboratory calibration curves. Any existence of bound
hydrogen in the sample would shift the point up. Under-estimating the in-situ dry density would
under-estimate the volumetric moisture in the conversion and the point would be shifted to the left
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
from its correct position. The opposite would be true for over-estimating in-situ dry density. This
explains the considerable scatter of points above the standard curve.
2.50
Count Ratio
AC2
2.00
Sand
1.50
Sand + 2% Fe
1.00
Sand + 5% Plastic
0.50
Sand + 10% Wood
0.00
0.00
Sand with Leachate
0.05
0.10
0.15
0.20
0.25
0.30
Volumetric Moisture Content
Figure 7 - Neutron Count Ratio against Volumetric Moisture for AC2
Both two effects are difficult to quantify and because of these effects, a calibration curve produced
from these sample points would be subject to bias (both gradient and intercept). Hence the use of
such a curve is not recommended as it may result in substantial errors in measuring both absolute
moisture and moisture change. However, using the gradient of the standard curve to calculate
moisture change can avoid such problems.
Comparing the profiles of neuron count ratio in Figure 5 (taken at 250mm intervals) and in
Figure 6 (average of 5 counts in the 1m interval), the significance of interpreting MSW moisture at
a microscopic scale cannot be more obvious. In most applications, the “smoothed” profile as shown
in Figure 6 would be much preferred.
Due to possible errors incurred in the moisture conversion, gravimetric moisture should be
quoted whenever an absolute moisture value is important. However, this is not important if the
emphasis is on moisture change.
The results of another access tube (AT4) employed to detect moisture change next to a
leachate recirculation infiltration trench are plotted in Figure 8. The curve of 19.2.1996 represents
the initial volumetric moisture profile soon after the tube was installed. No significant change in
neutron counts was observed up to 23.7.1996. Leachate was then fed into the recirculation trench.
The curve of 24.7.1996 was obtained by taking neutron counts after 1 day leachate injection. The
curve of 31.7.1996 represents the moisture after 7 days of recovery from the 1 day wetting. In both
cases, the standard curve was used to interpret change of moisture from the change in neutron
count.
Volumetric Moisture
0.50
19.2.1996
0.40
23.7.1996
0.30
24.7.1996
31.7.1997
0.20
12.00
11.00
Depth (m)
10.00
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
0.10
Figure 8 - Volumetric Moisture Profile of Access Tube AT4
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
6.
CONCLUSIONS
This study demonstrates that neutron probe can be a practical tool for monitoring moisture in MSW
landfills. However, the following limitations associated its use should be observed:
 It cannot be used to measure absolute moisture due to the heterogeneous nature of MSW.
 It can be used to measure moisture change. The error is expected to be small unless the
presence of neutron capture elements is excessive.
 The use of the standard sand calibration curve tends to slightly under-estimate moisture
change.
 If in-situ density is not known, errors may result in the conversion of gravimetric moisture
to initial volumetric moisture.
In practice, there are other limitations. As MSW is bio-degraded, some bound hydrogen will
be lost during the conversion of solid organic matter into gas and liquid phases. On the contrary,
densification of MSW due to settlement would increase the bound hydrogen count per unit volume.
Both may be significant if the rate of decomposition or settlement is high and the time elapsed
between counts is relatively long. However, as the two produce opposite effects, they would tend to
cancel each other out.
It is believed that neutron probe is the best available indirect/non-destructive method and will
produce acceptable results in most applications. It also offers the advantages of reliability, ease of
measurement, non-destructiveness, repeatability, and most importantly a large effective sampling
volume to achieve macroscopic moisture measurement.
The following field application procedure is recommended :
 Install access tube.
 Collect MSW samples during above drilling to determine gravimetric moisture and waste
composition.
 Convert gravimetric moisture to volumetric moisture.
 Plot initial volumetric moisture against depth.
 Plot subsequent moisture change (use standard sand curve to calculate moisture change
from change in neutron count).
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Dickey, G. L. (1990). Relationship of Soil Type and Chemicals to the calibration of Neutron
Meters. Paper presented at the Irrigation and Drainage: Proceedings of the 1990 National
Conference.
Gardner, W. H. (1986). Water Content. In A. K. Klute (Ed.), Method of Soil Analysis: Madison,
Wisconsin USA.
Goodspeed, M. J. (1981). Neutron Moisture Meter Theory. In E. L. Greacen (Ed.), Soil Water
Assessment by the Neutron Method: CSIRO Australia.
Greacen, E. L., Correll, R. L., Cunningham, R. B., Johns, G. G., & Nicolls, K. D. (1981).
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Australia.
Greacen, E. L., & Schrale, G. (1976). The Effect of Bulk Density on Neutron Meter Calibration.
Australian Journal of Soil Research, 14, 159-169.
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy
Hauser, V. L. (1984). Neutron Meter Calibration and Error Control. Transaction of the American
Society of Agricultural Engineering, 722.
Holmes, J. W. (1966). Influence of bulk density on neutron moisture meter calibration. Soil Science,
102, 355-60.
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Sardinia 97 Sixth International Landfill Symposium, October 1997, Cagliari, Sardinia, Italy