EVALUATION
OF THE MC-300A SOIL MOISTURE METER
TO DETERMINE IN-PLACE MOISTURE CONTENT
OF REFUSE AT LAND DISPOSAL SITES
Progress Report
A Division of Research and Development
Open-File Report
written by
Richard J. Wigh, Engineer
U.S. ENVIRONMENTAL PROTECTION AGENCY
Solid Waste Management Office

-------
EVALUATION
OF THE MC-300A SOIL MOISTURE METER
TO DETERMINE IN-PLACE MOISTURE CONTENT
OF REFUSE AT LAND DISPOSAL SITES
Progress Report
A Division of Research and Development
Open-File Report
written by
Richard J. Wigh, Engineer
U.S. ENVIRONMENTAL PROTECTION AGENCY
Solid Waste Management Office
1971

-------
TABLE OF CONTENTS
Page
Abstract 		v
Introduction 		1
Instrument Selection		2
Experimental Program 		4
Test Results and Discussions 		7
Conclusions 		9
Recommendations 		9
References	11
List of Figures
Figure 1 - Refuse Calibration Curves
Figure 2 - Compost Calibration Curves
List of Tables
Table 1 - Evaluation Data
Appendix
Outline of Calibration Procedure
Hi

-------
ABSTRACT
This report presents the results of a laboratory investigation
of a portable soil moisture meter (MC-300A)*for the determina-
tion of in-place moisture of refuse.
The laboratory investigation consisted of preparing several sam-
ples of fresh and composted refuse at varying moisture contents.
Moisture meter probes were inserted into the refuse samples and
meter readings obtained. Calibration curves relating moisture
content to'meter readings were then drawn.
The preliminary results of this investigative effort indicate
that the usefulness of the instrument is probably limited only
to noting changes in moisture rather than specific changes in
moisture content. Also, the decomposition of the refuse with
time could further limit the usefulness of the equipment.
*Mention of commercial products does not imply endorsement
by the U.S. Government.
v

-------
EVALUATION OF EQUIPMENT FOR
DETERMINATION OF IN-PLACE MOISTURE
CONTENT OF REFUSE AT LAND DISPOSAL SITES
INTRODUCTION
The moisture content of solid waste materials at land disposal
sites influences the rate of decomposition of the solid waste and
¦j	»
the subsequent gas and heat production. There are also indica-
tions that the moisture content of the materials can influence
the dry density that can be achieved by compaction in a manner
similar to the moisture-density relationship of soils. The
changing moisture content can also be used to determine the
effectiveness of a soil cover to prevent moisture movement into
2 3
the waste and to evaluate moisture routing theories 5 for pre-
dicting the amount and timing of water movement out of a fill.
Additional interest in the moisture content of landfills could
develop if refuse materials should be used for the disposal of
liquids and sludges as a storage and treatment media.
A method for determining the moisture content of solid waste
4
materials is available, however, this oven drying procedure

-------
requires the use of a sample of the material. This makes field
measurement somewhat difficult and would involve the retrieval
of actual samples from the location desired. This is especially
critical in research efforts where boring or other efforts to
obtain a sample could possibly disturb other study efforts.
In planning the Division of Research and Development's field
land disposal research facility, the need for a moisture measure-
ment method was envisioned and a study was initiated to select
an appropriate method. This report presents the results of some
preliminary work in the evaluation of the selected instrument.
INSTRUMENT SELECTION
Planned experiments at the field land disposal research facility
required a method of moisture measurement or an instrument that
would hopefully meet the following basic requirements:
1.	Capability of monitoring from depths of as much as 50
feet
2.	Simple construction and operation
3.	Durable
4.	Portable
5.	Relatively inexpensive
- 2 -

-------
6.	Simple calibration
7.	Continuous monitoring capability
Accuracy was also considered, but due to the field usage and the
heterogeneous nature of the refuse materials, within + 20% of
the actual moisture content was considered sufficient.
Three pieces of equipment were considered for use. These were
the agricultural gypsum block, the electrically operated fiber-
glas moisture cells and meter, and a nuclear moisture meter.
The nuclear moisture-depth meters (neutron scattering technique)
fail to meet many of the requirements established for the experi-
ments. They also require either access tubes into the fill so
the neutron source can be lowered to various depths, or estab-
lishment of multiple nuclear sources throughout the fill. Given
the expense of purchasing this equipment and the possible loss
of radioactive sources in the fill, this alternative was not
seriously considered.
The gypsum block and the fiberglas cell operate very similarly,
both providing a readout of electrical resistance as relates to
the moisture content of the probe. Of the two probes, the fiber-
glas cell was considered to be more accurate and also gave a
- 3 -

-------
reading of temperature on the same meter so that the moisture
content resistance reading could be corrected. The readout
meter was a small battery-operated model easily carried by hand.
Cost of the meter was approximately $210 and the individual cells
cost approximately $10 each, the price depending upon the length
of the lead wires.
EXPERIMENTAL PROGRAM
Some efforts have been made in the past to utilize the fiberglas
15 6	7
cells ' ' and the nuclear moisture meter, however, very
little information is available on the method of calibration or
the success during field usage. Personal communication with
Mr. Ralph Stone indicated a general lack of success with the
fiberglas cells and Dr. A. A. Fungaroli of Drexel reports very
erratic results with the nuclear meter. Additional work with
fiberglas and asbestos cells has been conducted at the Univer-
sity of Wisconsin, however, difficulties were encountered in
measuring the high moisture contents. A description of the
calibration procedure used at the University of Wisconsin is
5
available.
The largest drawback to the use of fiberglas cells is the exten-
sive calibration required before field usage. The instrument is
- 4 -

-------
normally used for agricultural and soils work, and even in these
applications, calibration is required for each specific soil
Q
type and for each probe. This makes the heterogeneous nature
of the refuse especially important in transfer of the equipment
and placement from the lab to the field.
In considering this application on comparison to its usage in
soils, one additional question arose. This consideration was
that of the effect of the changing characteristics of the refuse
with time. Although there is little data available on the time
c
variance of moisture properties of refuse, it was suspected
that the field capacity of the refuse would change with decompo-
sition. Thus, fiberglas cells calibrated in fresh refuse and
placed in similar material in the field might not be reliable
but for a short period of time. This would have to be compen-
sated for by burying new probes. The new probes would have to
be calibrated in refuse at various stages of decomposition which
is no simple task.
One possible alternative that might avoid this problem would be
calibration in a uniform and nondecomposing material. This
could be soil surrounded by refuse through which the water is
allowed to move to compensate for the varying conductivity of
- 5 -

-------
the water. Calibration in this manner, however, creates a
different problem when one considers the different moisture
storage properties of soil and refuse. The measurement of a
moisture content in the soil might not be at all indicative of
that in the refuse due to these capillary and hydroscopic prop-
erties. Hopefully, this could be compensated for in the cali-
bration.
Use of an alternative such as the soil-refuse combination might
not entirely remove the problem of the decomposing refuse and
changing moisture properties, and since it does introduce the
additional consideration due to different moisture properties,
it was felt that initial tests should be conducted with refuse
only. Refuse that was fresh, some that had been buried three
months, and composted refuse from Johnson City, Tennessee, was
used to determine the effect of decomposition.
Laboratory tests were conducted during the summer of 1969. A
detailed outline of the calibration procedure appears in the
appendices. No attempt was made to quantitatively measure the
stage of decomposition of the materials.
- 6 -

-------
TEST RESULTS AND DISCUSSIONS
The data obtained from the limited number of tests is shown in
Table I.
Figure I shows the calibration curves obtained using fresh refuse
and 3-month old refuse. Considering the curve for the fresh
refuse with the 10' lead, the high range of moisture content
over the relatively narrow range of resistance is quite alarming.
3
A corrected reading of 4 x 10 ohms would indicate a dry weight
3
moisture content of 158%, and a corrected reading of 3 x 10
ohms would give 225%. A slight error in reading or temperature
correction could lead to a rather large error in moisture con-
tent. Equally alarming is the comparison of the two calibration
curves for the fresh refuse. Although there is some difference
in lead and probe resistance, the vertical and horizontal separa-
tion of the curves is quite large. This seems to indicate a
large effect due to heterogenity of the refuse (both probes were
buried in the same sample) in some moisture ranges and that
field usage might not be at all representative of lab condi-
tions. For example, a corrected probe reading of 10^ ohms would
mean a dry moisture content of either 40% or 140% for the fresh
refuse. No comparisons can be made in the high moisture portions
- 7 -

-------
of the fresh refuse curves because of the failure to obtain the
data with both leads and probes.
The two curves for 3-month old refuse do not show as large a
variance between each other, but what is notable is the differ-
ence between these curves and those for the fresh refuse. A
3
corrected reading of 10 ohms shows a moisture content of 47% or
11% for the 3-month old refuse, yet a moisture content of 335%
was obtained for the fresh refuse. Much of this could be due to
material heterogenity since maximum moisture in the fresh refuse
was 342% and in the older material only 77%. Some of the dif-
ference, though, is probably related to the varying moisture
holding properties with decomposition. This moisture holding
difference is substantiated further by tests with compost where
upper moisture contents (field capacity) varied from 113% to
192% which is far less than the 342% for the fresh material.
Figure II shows the curves obtained using the same probe on
three different samples of composted refuse. It is not felt
that the first curve (—-•—•—) is too meaningful because
of errors in sample preparation. The other two curves are on
compost of different ages and are somewhat similar. Disturbing,
though, is the fact that for different moisture contents the
same corrected resistance was obtained.
- 8 -

-------
CONCLUSIONS
Although the investigation is incomplete at this time, the
discrepancies noted so far indicate that the instrument being
used is far less accurate than first thought. Its usefulness is
probably limited only to noting changes in moisture rather than
specific changes in moisture contents. This could still be use-
ful in studying movement of moisture fronts, but not necessarily
in correlating moisture content and gas production or temperature
The problem of changing moisture properties with time due to
decomposition is probably serious enough to further limit the
usefulness of the equipment. If the probes are to be placed
directly in refuse in the field, the data should be considered
qualitative and little confidence should be placed in the quan-
titative measurements.
RECOMMENDATIONS
Further tests should be conducted to investigate the effects of
heterogenity and moisture changes due to decomposition and to
more clearly define the limitations. Tests should include the
development of curves over two or more drying cycles. All
- 9 -

-------
glass, metals, rocks, plastics, rubber, and ceramics should be
removed to lessen the effects of heterogeneous materials.
Tests should also be expanded to include soil surrounded by ref-
use to try to improve reliability and quantitative capability.
Future investigations in relation to this equipment should con-
sider the phenomena of changing field capacity in order to define
limits of moisture retention.
- 10 -

-------
REFERENCES
1. Merz, R. C., and Stone, R. Factors Controlling Utilization
of Sanitary landfill Sites, Final Report to the Depart-
ment of Health, Education, and Welfare, Project No.
EF-00160-03, 126 p., July 1963.
2. Remson, I., et al. Water Movement in an Unsaturated Sani-
tary Landfill, JSED, ASCE, Volume 94, No. SA2, April
1968, pp. 307-317.
3. California State Water Pollution Control Board, Effects of
Refuse Dumps on Ground Water Quality, Publication No. 24,
Sacramento, 1961, 107 p.
4. American Public Works Association, Municipal Refuse Disposal,
1st ed., Chicago, Public Administration Service.
5. City of Madison, Wisconsin and the University of Wisconsin,
Third Progress Report, City of Madison Demonstration
Grant 1-DPI-UI-0004, March 1969, unpublished.
6. California State Water Quality Control Board, In-Situ
Investigation of Movements of Gases Produced from Decom-
posing Refuse, Publication No. 31, 1964.
7. Drexel Institute of Technology, Research Grant Reports.
8. Colman, E. A. Instruction Manual, MC-300A Soil Moisture
Meter and Cells, Soiltest, Inc..Bulletin C172-64, 1964.
- 11 -

-------
KWBfflttBai
100	150	200
MOISTURE CONTENT - I DRV WEIGHT
350
FIGURE I

-------
MOISTURE CONTENT - % DRY WEIGHT	FIGURE II

-------
TABLE I
EVALUATION DATA
Sample
Probe
% Moisture
Meter Reading
Range
Corrected

(length &
(dry weight)
(average)
Resi stance

constant)


(ohms @ 60°F)
F
20'
76.7
184.5
Low
3.4x10?
(3-month old
1.07
48.2
159.3
Low
8.8x10";
refuse)

36.8
120.0
High
4.4x10?


31.2
91.8
High
6.9x10?


23.0
94.7
High
7.0x10
F
10'
76.7
155.7
Low
1.0x10,
(3-month old
1.04
48.2
92.7
Low
5.6x10^
refuse)

36.8
83.0
Low
6.1x10-


31 .2
54.8
Low
1.4x10?


30.0
152.8
High
2.6x10
E
10'
342.7
194.8
Low
1.2x10?
(fresh
1.01
326.4
142.0
Low
1.6.10,
refuse)

197.8
116.5
Low
3.4x1Oo


114.6
93.5
Low
4.7x10,


63.6
83.0
Low
6.4x10*


36.9
60.0
Low
1.1x10
E
20'
197.8
103.7
Low
4.0x10?
(fresh
1.02
114.6
187.8
High
1.4x10?
refuse)

63.6
159.7
High
2.4x10?


36.9
153.5
High
2.7x10
B
10'
154.6
158
Low
1.05xlQ3
(8-week old
1.01
153.6
190
Low
2.4x10?
compost)

148.7
180
Low
4.5x10?


139.9
193
Low
1.8x10?


134,6
191
Low
2.2x10?


120.7
193
Low
1.9x10~


97.4
137
Low
2.0x10?


86.0
179
Low
4.6x10
C
10'
192.4
187
Low
2.7x10?
(8-week old
1.01
180.1
189
Low
2.6x10?
compost)

164.2
194
Low
1.6x10?


151.8
194
Low
1.6x10?


137.9
194
Low
1.6x10?

'
109.6
191
Low
2.IxlOo


103.8
131
Low
2.3x10
D
10'
112.7
189
Low
2.5x10?
(42-day old
1.01
106.3
190
Low
2.5x10?
compost)

96.9
193
Low
1.8x10?


1)3.0
VJ'o
Low
1.4x10?


87.2
187
Low
2.9x10^


82.7
124
Low
2.6x10o


76.0.
107
Low
3.8x10
- 14 -

-------
APPENDIX

-------
OUTLINE OF CALIBRATION PROCEDURE
Preparation of Sample
1.	Dry out sample of approximately 500 grams of refuse at 70°C
until workable enough to cut into approximately 1" square chunks.
Remove all metal and break up glass chunks.
2.	Replace sample in oven at 70°C» dry for 12 hours, let cool
in dessicator. Transfer to plastic perforated sheet (24" x 30"),
tie with wire to form a bag, and weigh. Subtract weight of sheet
and wire to obtain dry weight of sample.
Saturation of Sample
1.	Suspend bag over 1-gallon jug containing 2000 ml distilled
water, open bag, and pour additional 600 ml directly over and
around bag. Force bag into water as much as possible (will tend
to float). Spread edges of bag over lip of jug, screw on top,
and label jug. Allow water to soak in over night.
2.	After soak, water should be standing in bag. Pour out most
of water in jug and suspend bag over the water in the jug.
Water should drip out of holes in bag, but if drainage is slow»
the bag can be squeezed lightly to force water out. Allow
drainage untiI there is no more standing water and the bag no
longer drips water.
- 17 -

-------
Permeation
1. After bag is drained, open it up, place bag on a No. 4 sieve
so that any excessive water can drip through. Place probes in
sample, fold the bag around the probes, and pile the remainder
of the leads onto the bag. Then put the sieve, bag, and leads
into a glass dessicator with 1-2" of water in bottom. Allow the
sample to permeate within the dessicator over night. If possible,
extend the leads out of the dessicator so that readings can be
taken without removing the lid.
After preparation, readings with the meter were taken according
to the following procedure:
Readings
1.	After night permeation, take readings the following morning.
Monitor each lead for at least 60 minutes to assure a constant
reading. Then hook up a particular lead and take six readings
at 2-minute intervals. This many readings should make up for
any mistaken readings or other errors involved. Record readings
(and range) on data sheet (temperature always low range).
2.	After all leads are completed for a particular sample, take
the bag from the dessicator, remove the probes, tie the bag up
with the wire, and weigh. Record weights, determine amount of
water present in sample, and divide this number by the dry
weight of sample. This gives the % moisture.
- 18 -

-------
3. This procedure was repeated at varying time intervals to allow
drying of the sample to obtain different moisture contents.
- 19 -

-------