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Tracer monitoring techniques forshallow land burial of toxic waste
Item Type Thesis-Reproduction (electronic); text
Authors Betsill, Jeffrey David.
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/191772
TRACER MONITORING TECHNIQUES
FOR SHALLOW LAND BURIAL OF TOXIC WASTES
by
Jeffrey David Betsill
A Thesis Submitted to the Faculty of the
DEPARTMENT OF HYDROLOGY AND WATER RESOURCES
In Partial Fulfillment of the RequirementsFor the Degree of
MASTER OF SCIENCEWITH A MAJOR IN HYDROLOGY
In the Graduate College
THE UNIVERSITY OF ARIZONA
1982
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of re-quirements for an advanced degree at The University of Arizona and isdeposited in the University Library to be made available to borrowersunder rules of the Library.
Brief quotations from this thesis are allowable without specialpermission, provided that accurate acknowledgment of source is made.Requests for permission for extended quotation from or reproduction ofthis manuscript in whole or in part may be granted by the head of themajor department or the Dean of the Graduate College when in his judg-ment the proposed use of the material is in the interests of scholar-ship. In all other instances, however, permission must be obtainedfrom the author.
SIGNED:
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
ateGlenn M. Thompson, As istantProfessor of Hydrology andWater Resources
PREFACE
This study was conducted under NRC contract number NRC-04-81-220.
The purpose of the contract was to examine several different methods of
shallow land burial trench cap construction, perform a cost analysis of
the construction and monitoring methods used, and develop and implement
a hydrologic tracer program with which to monitor water infiltration and
leachate migration. The portion of the contract in which the tracer
monitoring program was developed and implemented is presented in detail
as the thesis which follows. In the thesis the author uses text, tables
and illustrations which also appear in the NRC Annual Report entitled
"Low-Level Nuclear Shallow Land Burial Trench Isolation, Annual Report".
The hydrologic portions of the Annual Report and this thesis were devel-
oped and written concurrently by this author and no further reference
will be given in this thesis for information or statements written by
him which may also appear in the NRC report.
ACKNOWLEDGMENTS
This research was conducted and funded under research contract
number NRC-04-81-220 issued by the Nuclear Regulatory Commission. I
acknowledge their financial support which made this thesis possible.
I give special thanks to my research director Dr. Glenn M.
Thompson who provided guidance and support from the inception of this
project through its completion. I thank Dr. Judith M. Dworkin and
Dr. Lorne G. Wilson for reviewing the manuscript.
I am grateful and thank my friends, fellow graduate students and
co-workers who assisted me in completing the many varied aspects of this
project. These are Paige Bausman, Randy Golding, Joanne Hershenhorn,
Steve Jensen, Mark Kuhn, Mark Malcomson, Rod Stipe and Carmen Parada.
I am especially grateful to Bill Bergmann whose hard work, ingenuity and
high spirits proved invaluable during the field work. I also thank
Dr. Klaus J. Stetzenbach for his assistance in refining the analytical
techniques, Marie Busse for her drafting and Mina Godinez for typing the
manuscript.
I wholeheartly acknowledge Susan Eadens, my mother Demaris Betsill,
Dawn Rita and Janet Durham for their unwavering support in my graduate
career and throughout this project.
iv
TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS vi
LIST OF TABLES vii
ABSTRACT viii
INTRODUCTION 1
Objectives 1
Previous Investigations 4
DESCRIPTION OF EXPERIMENT 6
Site Description and Climate 6
CGHF Site 6
ML Site 10Trenches 12
MATERIALS AND METHODS 14Tracers 14Porous Cup Samplers 18Sample Collection 25Analytical Methods 29
RESULTS 31Sample Collection Program 31Sample Analyses 34
CONCLUSIONS 37Tracer Monitoring Program 37
CGHF Site 40ML Site 40
Tracer Performance 41Recommendations 42
APPENDIX A: Soil Characteristics 45
APPENDIX B: Climatological Records 47
REFERENCES 52
LIST OF ILLUSTRATIONS
Figure Page
1. Schematic Representation of Water Entry Pathways intoa Trench and Tracer Use 3
2. CGHF Site Location Map 7
3. ML Site Location Map 11
4. Schematic of CGHF Site Showing Trench Layout, PorousCup Sampler Locations and Depths, and SprinklerSystem 20
5. Map of ML Site (upper level) Showing Trenches andPorous Cup Sampler Locations and Depths 21
6. Map of ML Site (lower level) Showing Trenches and PorousCup Sampler Locations and Depths 22
7. Cross-Section of Porous Cup Sampler Installation. . • ID 24
8. Schematic of Porous Cup Sampler and Apparatus in Staticand Vacuum Modes 26
9. Schematic of Porous Cup Sampler and Apparatus inSampling Mode 29
10. Tracer Movement in the CGHF Site Trenches 38
11. Tracer Movement in the ML Site Trenches 39
vi
LIST OF TABLES
Table Page
1. Climatological Conditions for Project Duration atthe CGHF and ML Sites 9
2. CGHF Site Tracer Information 16
3. ML Site Tracer Information 17
4. Water Samples Collected at the CGHF Site 32
5. Water Samples Collected at the ML Site 33
6. Tracers Detected, Concentrations and Analytical MethodsUsed for CGHF Site Samples 35
7. Tracers Detected, Concentrations and Analytical MethodsUsed for ML Site Samples 36
A-1 Soil Characteristics for CGHF and ML Sites 46
B-1 Average Monthly Temperatures-CGHF Site 48
B-2 Average Monthly Precipitation-CGHF Site 49
B-3 Average Monthly Temperatures-ML Site 50
B-4 Average Monthly Precipitation-ML Site 51
vii
ABSTRACT
A tracer monitoring program was designed and implemented to
monitor water movement through experimental trench caps, and to examine
fluorinated aliphatic compounds for use as tracers. Trenches were
constructed in Tucson, Arizona and on Mt. Lemon 40 miles northeast of
Tucson. The tracers used were fluorinated aromatic and aliphatic organic
acids, inorganic halide salts and dyes. Soil water samples were collected
using porous cup suction lysimeters placed at various levels inside and
outside the experimental trenches. Samples were analyzed for tracers
using HPLC and GC methods.
Soil moisture was generally low at both sites. Tracer data
indicated movement in the cap and through the bottom of several trenches.
The fluorinated aliphatic tracers proved useful and reliable to monitor
water movement in the unsaturated zone in and around the trenches.
Trifluoroacetic and chlorodifluoroacetic acids require further quanti-
tative analytical technique development prior to commercial usage.
viii
INTRODUCTION
For years toxic and hazardous wastes have been disposed of in
shallow land burial sites. Many trench caps at these sites collapse with
time as the waste form undergoes decomposition and compaction. Contain-
ment of wastes within a trench has proven difficult since rainwater ponds
on the collapsed cap, infiltrates through tension cracks, and mixes with
the waste material forming a leachate. The leachate often enters the
environment through the trench floor and walls posing potentially serious
water and environmental quality problems. A multidisciplinary study
conducted during the 1981-1982 fiscal year was undertaken by the depart-
ments of Hydrology and Water Resources, Civil Engineering and Nuclear
Engineering at the University of Arizona, Tucson, AZ. for the Nuclear
Regulatory Commission under contract number NRC-04-81-220. The purposes
of the study were to examine the stability of four different trench
backfill and capping methods, and conduct a hydrologic tracer experiment
with which to monitor infiltration into the trench caps. Cost analysis
of the construction and monitoring methods used were also addressed. The
hydrologic monitoring portion of the study is presented here as this
thesis.
Objectives
The hydrologic portion of the study was designed to test several
aspects of monitoring a shallow land burial site. The specific objectives
of this experiment are detailed below.
1
2
The primary objectives were to trace water movement pathways
through a trench, and to examine several new aliphatic fluorinated ions
used as tracers in this study. These new tracers were used in the field
along with conventional tracers, a dye tracer, and other fluorinated
compounds previously used as tracers. The conventional tracers used
were iodide and bromide. The dye tracer was fluorescein. The fluorinated
compounds previously used were the aromatic compounds pentafluorobenzoic
acid and m-trifluoromethylbenzoic acid. The new tracers were the fluo-
rinated aliphatic compounds heptafluorobutyric acid, pentafluoropropionic
acid, chlorodifluoroacetic acid, and trifluoroacetic acid.
Water movement pathways are depicted in Fig. 1. This shows that
water can infiltrate vertically through the trench cap, move laterally
into the trench, or move with both lateral and vertical components
through the trench. Samplers placed outside the trench can also measure
movement of water escaping from the trench.
Water movement out of the trench is an important aspect of this
monitoring experiment. Tracers placed along with wastes within a trench
can provide an "early warning" monitoring function. When used at a
burial site a leaking trench may be detected by tracers before wastes
have the opportunity to leach out. This beneficial function is due to
the nature of the tracer compounds. Since they are in a highly soluble
salt form that show little or no sorption to natural soil materials,
the tracers will be leached first and move out of a leaking trench much
more rapidly than packaged waste materials. Using a variety of tracers
in a burial site can also provide valuable information that can help
pinpoint a specific trench where infiltration and leaching has occurred.
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Previous Investigations
Two previous investigations have been conducted using tracers to
monitor water infiltration of trench caps at the Maxey Flats, KY, low-
level radioactive shallow land waste burial site. A study conducted by
the University of Arizona'a departments of Hydrology and Water Resources,
Civil Engineering and Nuclear Engineering investigated trench capping
designs and water infiltration at the site. Five experimental trenches
were constructed to examine methods of cap construction that would be
stable, facilitate drainage and decrease infiltration. Five non-
radioactive tracers were added to the trenches and backfill to monitor
infiltration. These tracers were benzoic acid, bromide and three
fluorinated aromatic ions, pentafluorobenzoic acid, o-fluorobenzoic acid
and p-fluorobenzoic acid. Water samples from the trenches were collected
and analyzed for tracer content both two months, and six months after
emplacement. No tracers were detected in any of the samples collected
(Nowatzki, Thompson and Wacks, 1981). In retrospect, the aromatic tracers
p-fluorobenzoic acid and o-fluorobenzoic acid were considered unstable.
The monitoring program was of short duration and it was suggested that
little or no water had infiltrated into the trenches through the caps
(Thompson, 1982).
Another experiment involving a non-radioactive tracer was con-
ducted at the Maxey Flats site by the University of California at Berkeley.
A trench in which low-level radioactive waste had been disposed was chosen
for investigation. An array of soil moisture monitoring cells and mini-
porous cups were installed in the trench cap and in the soil profile
in rows between trenches. The fluorinated aromatic tracer
5
pentafluorobenzoic acid was sprayed on the trench cap and on the land-
surface around the cap. The purpose of the experiment was to monitor
soil moisture conditions and collect water samples to determine if
infiltration was taking place through the trench cap or through the soil
profile. The trench was considered aged and proved quite permeable to
water infiltration as shown by the fact that the tracer migrated 8 feet
downward into the trench cap in three months (Schulz, 1981).
To date the author knows of no studies, other than his, which
have used conventional, and fluorinated aromatic and aliphatic tracers
to examine water movement through a trench cap, through the trench bottom
fill contents and escape beyond the trench perimeter through the trench
bottom and walls.
DESCRIPTION OF EXPERIMENT
Site Description and Climate
Two sites, one semi-arid and the other humid, were chosen at
which to construct the experimental trenches. The study sites vary
greatly in climate yet are located only 40 miles apart. The semi-arid
site is located at the University of Arizona's Casa Grande Highway
Experimental Farm in Tucson. This site will henceforth be designated
the CGHF site. The humid site, located 40 miles to the northeast on
Mount Lemmon, is referred to as the ML site. The two sites were chosen
to examine the influence of different climatological factors on the
monitoring program and the construction and stability of the experimental
trench caps. The CGHF site represents hot, arid conditions at which some
disposal sites have been proposed, and the ML site represents a humid
environment experiencing snow and freezing temperatures in the winter
typical of many areas in the United States.
CGHF Site
The CGHF site in Tucson, AZ. is located in the semi-arid Basin
and Range province of the southwestern United States. The terrain here
is flat or gently rolling with many dry washes. The elevation is approxi-
mately 2,400 feet above sea level. Rugged mountain ranges jut from the
valley floor and encircle the city.
Figure 2 shows the CGHF site lying between the Santa Cruz River
and I-10 on Tucson's west side. The site lies well within the 100 year
6
N Wetmore Road
Prince Road
Miracle Mile
1 Mile
SCALE
7
Ironwood Hill Drive
Fig. 2 CGHF Site Location Map
8
flood plain of the Santa Cruz River only 300 feet to the west. The soil
cover of the area is silty-sand. See Appendix A for the results of a
series of standard soil tests conducted according to American Society
for Testing and Materials (ASTM) specifications. Native vegetation here
is mostly brush, cacti, grass and small desert trees such as mesquite
and palo verde trees.
The climate of Tucson is characterized by a long hot season
beginning in April and ending in October. Temperatures above 90 °F occur
from May through September with temperatures reaching above 100 °F not
uncommon in June, July and August. At night, temperatures drop thirty
to forty degrees. The average annual temperature is approximately 68 °F.
See Appendix B for the average monthly temperatures at the CGHF site.
The average precipitation is about 11 inches. Precipitation in
Tucson is divided into two rainy seasons. More than 50% of the annual
total falls between July 1 and September 15 as scattered, convective,
thunderstorm-type events. December through March is the second rainy
season with over"20% of the annual total falling in this period, mainly
as winter, frontal-type storm events. See Appendix B for the average
monthly precipitation and annual totals at the CGHF site.
The project contract period for this experiment was from October
1, 1981, through September 30, 1982. The climatological conditions for
this period are shown on Table 1. The CGHF site experienced an average
high temperature of 84.2 °F, an average low temperature of 53.2 °F, an over-
all average temperature of 68.7 °F, a total precipitation of 14.80 inches,
and total evaporation measured at 66.81 inches. The evaporation is many
times the precipitation total, as would be expected in desert conditions.
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ML Site
Mount Lemmon lies approximately 40 miles northeast of the CGHF
site in the Santa Catalina Mountain Range and with its highest peak at
approximately 9,100 feet above sea level rises to over 6,000 feet above
Tucson. The ML site, at 7,800 feet above sea level, is sharply con-
trasted to the desert floor below. Figure 3 shows the site, leased from
the U.S. Forest Service, located about 300 feet southeast of the Mt.
Lemmon sawmill.
The conditions on Mt. Lemmon are cooler and wetter than those
found at the CGHF site. For this reason the plant life is comprised of
Canadian Zone type vegetation consisting of large conifers such as
Ponderosa Pine, Douglas Fir and Canadian Spruce. Underbrush can be quite
dense. The soil cover is generally a thin layer of silty-sand derived
from decomposed granitic rocks lying just below the soil cover. See
Appendix A for soil test results.
The summers here are quite mild or even cool with the highs in
the low 70's. Occasional scattered shows occur during the summer months.
Average winter temperatures have lows in the 20's and highs in the 40's.
This presents a freeze-thaw condition which is an effective weathering
process. See Appendix B for average monthly temperatures at the ML site.
Precipitation falls as both rain and snow. The average annual precipita-
tion on ML is 30.5 inches. The majority of the precipitation falls as
rain during the months of July through late September. Precipitation as
snow falls during the months of November through March. See Appendix B
for average monthly precipitation and annual totals at the ML site.
11
lf X 7883 0M LEMMON
AWMIL
Fig. 3 ML Site Location Map
12
Climatological conditions for the ML site during the contract
period are shown in Table 1. During the period the site experienced
an average high temperature of 60.8 °F, an average low temperature of
35.5 °F, an overall average temperature of 47.0 °F, and a total precipitation
(snowfall has been converted to inches of water) of 35.00 inches. Evapo-
ration data were not recorded at this site. However, based on recording
stations at similar elevations experiencing similar climatological
conditions, an estimated value of 24.0 inches of evaporation is given.
Note that evaporation for winter months are not recorded due to freezing
conditions.
Trenches
A set consisting of four different experimental trenches was
constructed at the CGHF site. The trench construction set was duplicated
at the ML site. The trenches measured approximately 10 feet by 20 feet
and were 10 feet deep. A 5 foot layer of baled hay was placed in the
bottom of each trench (except Trench No. 3) to simulate a waste form
which would decompose and compacted slowly with time. Trench No. 3 at
each site had a collapsible platform constructed 5 feet above the trench
bottom. After backfilling, the platform supports were removed rapidly in
order to create an immediate void space beneath the trench cap. At the
CGHF site this was accomplished with explosive charges set in the supports.
The supports at the ML site were pulled out with a cable and winch.
Experimental trench caps were constructed immediately above the
hay and platforms and extended to, or just slightly above, land surface.
A different capping technique employing combinations of compacted native soil,
13
geofabrics, and soil beams was used for each trench in the set. Settle-
ment plates placed on the simulated waste and in the cap backfill allowed
the rate of settlement of the waste and backfill to be measured (McCray,
Nowatzki and Thompson, 1982). Further discussion of trench construction,
capping methods, and settlement plate monitoring results are beyond the
scope of this presentation. Interested readers are referred to the NRC
Annual Report for more detailed information on the engineering aspects
of the study.
During trench construction tracer compounds were added to the
trench bottom and backfill. A complete description of tracers and moni-
toring techniques is discussed in detail in the following chapter,
Materials and Methods.
MATERIALS AND METHODS
Tracers
A varied battery of chemical tracers was used to follow the
pathways of water as it infiltrated into the trenches. These tracers
consisted of aromatic and aliphatic fluorinated organic acids as well as
inorganic halide salts and dyes. To make the acids highly soluble in
soil water they were neutralized with sodium bicarbonate (NaHCO 3 ) to form
the sodium salt of the acid. The organic compounds, iodide and bromide,
were purchased in a salt form and required no preparation.
The variety of tracers used in these trench studies were chosen
for several reasons: (1) a large number of tracers were needed to sepa-
rate different water infiltration pathways; (2) the tracers selected are
highly soluble in water; (3) they are not sorbed to soil particles
(except fluorescein); (4) they are nonvolatile at room temperature; (5)
they are easily detected in the low part per million (ppm) range using
conventional high performance liquid chromatography (HPLC) or gas chroma-
tography (GC) methods; (6) several fluorinated compounds previously unused
as tracers were chosen for use in order to test their performance as
tracer substances, and to compare their results with the other previously
used or conventional tracers also used in this experiment; (7) the fluori-
nated compounds are completely foreign in the environment, and the other
ions are applied at such high concentrations as to ensure their anomalous
detection above background in soil water samples.
14
15
The quantity, depth of application, name and chemical formula
of each tracer used at the CGHF site is shown on Table 2. The same
information for the ML site is given on Table 3.
Tracers were applied to the bottom of the trenches and in the
backfill. The bottom tracers were applied in one uniform layer along the
bottom of the trench. The backfill tracers were applied in one or more
uniform layer(s) in the trench backfill.
To achieve a uniform layer a tracer was applied using a stainless-
steel garden sprayer. The tracer was added to the sprayer and mixed with
one gallon of water. The water was necessary to have a sufficient volume
of solution to ensure uniform coverage. Between each tracer application
the sprayer was thoroughly washed to prevent cross-contamination.
The tracers in the backfill of Trench ML-2a, bromide and fluores-
cein, were applied in a dry form by hand. This was done because of the
difficulty experienced in sprayer application of the fluorescein at the
CGHF site. The sprayer was also extremely difficult to clean thoroughly
after using fluorescein in it.
Although the acids were previously neutralized, and all tracers
considered safe to handle in the concentrations used, it was judged
prudent to use safety equipment. Therefore, the person applying the
tracers wore a respirator, goggles and gloves to prevent excess contact
with aerosols while spraying. This proved to be a sound decision since
breezy conditions were often encountered at the CGHF site.
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18
Porous Cup Samplers
Porous cup samplers are also known as soil water samplers,
suction lysimeters, or simply as lysimeters. They are used to obtain
water in both the saturated and unsaturated zones. Porous cups were
chosen for use in this experiment because of their excellent ability to
obtain soil water samples from the unsaturated zone. Unsaturated con-
ditions exist in and around the experimental trenches.
The samplers were obtained from the Soilmoisture Equipment Corp.,
Santa Barbara, CA. They consist of a two inch porous ceramic cup (air
entry value 1 bar) attached to a short length of PVC pipe. Additional
lengths of PVC pipe were glued to the samplers to extend the whole assem-
bly from a few feet above land surface to any desired depth below land
surface. When a vacuum is drawn on the sampler a pressure differential
is created across the ceramic cup. This pressure differential induces
soil water to migrate into the cup where it can be collected and later
analyzed.
Porous cup samplers are often prepared using a dilute hydrochloric
acid both followed by a distilled water rinse prior to emplacement
(Wilson, 1979). This leaches out Ca, Mg, Na, HCO3'
and SiO2 which are
often present in new porous cups. However, these compounds were not used
as tracers, analyzed for, or expected to cause any chromatographic inter-
ference in sample analysis and therefore rinsing was not performed. Con-
tact of a water sample with PVC and PVC glue can often contaminate a
sample with solvents and other organic compounds. This was not a problem
in this experiment since only a few milliliters of water were drawn into
the porous cup and the sample never came into contact with the PVC or glue.
19
The location and depth of each sampler varied due to the geometry
of the site, trench depth, excavation method employed, and water pathways
intended to be intercepted. The location of each sampler and its depth
below land surface is given in Fig. 4 for the CGHF site and in Figs. 5
and 6 for the ML site.
The installation methods of the porous cup samplers varied from
place to place at both CGHF and ML sites. The general methodology of
installation is described below. A hole was dug to the desired depth,
and the soil removed was sieved through a 1/4 inch mesh screen. Some of
the sieved soil was mixed with water to form a mud slurry and a portion
of the slurry was poured back down the hole. The slurry insures a good
soil-to-cup surface contact (Soilmoisture Equipment Corp.). Next, the
porous cup sampler, with the proper amount of extension attached was
pushed into the slurry at the bottom of the hole. More slurry was poured
in to ensure complete coverage of the cup. Finally, the rest of the dry
sieved material was poured into the hole and the annular space around the
PVC pipe tamped with a rod. The tamping was necessary to develop a good
seal between the PVC pipe and the adjacent soil.
The method of backfilling around the PVC pipe varied depending
on sampler location. Those samplers placed below the bottom of the
trench at the CGHF site were backfilled as described above to within a
few inches of the trench bottom. Then, a layer of cement was used to cap
the annular space. The cement was applied to reduce the possibility of
seepage along the interface between the PVC pipe and the soil in the event
of ponding on the trench bottom.
CGHF-1
CGHF-2
CGHF-3
OVERLAPPINGSPRAY PATTERN
CGHF-4
Pl-I (15')Pl-D (25') • • • P-1S (5.4')
1-D(15.5'). 01-I (10')
1:S (3')
P2-D P2-S
(1;1)(1.5') (
2-D (13') 2-1 (10')• •2-S (3')
P3-D P3-I P3-S• • •
(22'X15)(5 )
COLLAPSED
P4-D P4-I P4-S_:1.
Sprinkler(24'1)0 ;i')(180°
1pray
20
\:#\S ' )
a'• K114.5D
-
P5-D P5-I P5-S• • •
( 22. 5') ( 1 5.59 ( 5. 5 0
VALVE AND TIMER
SPRINKLER WATERDELIVERY PIPE
Fig. 4 Schematic of CGHF Site Showing Trench Layout, Porous CupSampler Locations and Depths, and Sprinkler System
• SETTLEMENT PLATESO POROUS CUP SAMPLER (CAP)ID POROUS CUP SAMPLER
(TRENCH BOTTOM)e POROUS CUP SAMPLER
(OUTSIDE TRENCH)
44
A,
21
APPROXIMATE MATCH LINEWITH FIG. 6
TRICO ELECTRICSTORAGE SHED
.--CONCRETE SLAB
ML-4-1\1 (10 1 ) .t0
1 N
(3')'.."'Ir4;11-4-I-4-S1 --TRENCH 4
6DML (-iA2) Iii3' 7'
IMPROVED ACCESSROAD TO PIMA COUNTY
WASTEWATER MANAGEMENTDIVISION'S SEWAGE
DISPOSAL FACILITY
Fig. 5 Map of ML Site (upper level) Showing Trenches and PorousCup Sampler Locations and Depths
• SETTLEMENT PLATEO POROUS CUP SAMPLER (CAP)
POROUS CUP SAMPLER(TRENCH BOTTOM)
e POROUS CUP SAMPLER(OUTSIDE TRENCH)
OL AND ROCK BERM
TRENCH 2a
,ML-2a-I (9'):/®-ML-2a-P (8.5')
ML-2a-S (3')
ML-3-I1 (9')
e-ML-3-P (10')
eML-1-P (10')
• TRENCH 1(8')
ML-1-S (3')
22
Scale
Fig. 6 Map of ML Site (lower level) Showing Trenches andPorous Cup Sampler Locations and Depths
23
Samplers installed on the trench floor were not placed in a
borehole. Therefore, to ensure operability under unsaturated conditions,
the porous cups on the trench bottom were packed in a one foot high mound
of sieved soil (Fig. 7). Guy wires were attached at the top of the sampler
pipe and were staked outside the trench at land surface to keep the sampler
upright until the bottom fill contents of the trench could be emplaced.
The methods to dig a hole in which to install the samplers also
varied depending on location. At the CGHF site a heavy gravel and cobble
layer existed just below the trench bottom. Because the bottom of the
trenches were not easily accessible to a truck mounted auger rig, bore-
holes in the bottom of the trenches were dug by hand using a post hole
digger and hand auger. These boreholes reached no more than 5.5 feet
below the bottom of the trench. The boreholes in the trench backfill
were excavated using a post hole digger. They presented no particular
problems in excavation.
The boreholes around the trench perimeter were drilled using a
CME-55 rig with 6 inch hollow-stem auger. The drilling was performed by
Desert Earth Engineering Co. of Tucson, AZ. Due to gravel and cobbles
the greatest depth drilled was to 25 feet below land surface. This is
15 feet below the bottom of the adjacent trench. The samplers were
installed through the hollow-stem auger flights. The auger flights were
then removed allowing the soil to cave in around the PVC pipe remaining
in the hole. The annular space around the pipe collapsed immediately
to within a foot or two of land surface. This was then filled in by
hand and tamped.
PerimeterSampler
Land Surface
Dry Sieved MaterialSlurryBackfill
Trench
Bottom Fil/ Contents
Dry Sieved Material
SlurryCement PlugDry Sieved MaterialBoreholeSlurry
Porous Cup
Dry Material
Slurry
Porous Cup
ShallowSampler
Deep IntermediateSampler Sampler
24
Fig. 7 Cross-section of Porous Cup Sampler Installations
25
At the ML site hard granitic rock occurred at the bottom of each
trench. It was decided that it would be too difficult and expensive to
place samplers below the bottom of the trenches. Therefore, the only
boreholes necessary were those located in the trench backfill and just
outside the perimeter.
The boreholes in the trench backfill were dug by hand using a
post hole digger. The boreholes for the trench perimeter proved much
more difficult to excavate. They were dug using a series of tools.
First, a hole was dug as deep as possible using a post hole digger.
Next, a 2 inch hand bucket auger was used until hard granite rock was
encountered. To complete the borehole, a compressed-air, rotary jack-leg
rock hammer was used. The deepest borehole dug in this manner was to
10 feet below land surface. After the borehole excavation, samplers
were installed and backfilled following the general method described
above.
Sample Collection
Water samples were collected in the porous cup samplers and then
analyzed for tracer content in order to monitor the water movement
through the trenches. Soil water was induced into a cup by pulling a
vacuum on the sampler with a vacuum pump. See Fig. 8 for schematic of
the sampling apparatus. The clamp was then closed on the rubber tube
leading out of the stopper and the vacuum pump was moved on to another
sampler. A vacuum was thus applied to all samplers. The samplers were
kept under a vacuum for several hours (2 to 48 hours) to allow soil water
to be drawn into the cup.
PINCH CLAMP ----RUBBER HOSE—
GLASS TUBE-_
STOPPER--A"
II
--- VACUUM HOSE
LAND SURFACE'.....
— —SAMPLING TUBE
---PVC PIPE
1:
NOTE: Apparatus depictedin drawings are not toscale.
CENTERING STOPPER
---POROUS CUP
Fig. 8 Schematic of Porous Cup Sampler and Apparatusin Static and Vacuum Modes
26
VACUUM PUMP
27
To prevent cross-contamination each sampler had its own sample
tube, stopper assembly, and trap assembly. The sample tube consists of
a 3/8 inch nylon tube running from the bottom of the cup to the sampler
top. The bottom of the sample tube was weighted with a tapering nest
of onehole rubber stoppers. The stoppers were needed to keep the sample
tube centered at the bottom of the cup. During the static and vacuum
modes, the excess length of sampler tubing was curled just beneath the
stopper assembly. See Fig. 8.
The stopper assembly sits atop of the PVC sampler pipe. It con-
sists of a one-hole rubber stopper with a glass tube running through it.
A rubber hose with a pinch clamp is attached to the glass tube. The
stopper assembly is left on the sampler at all times except during the
sampling mode to keep dirt and leaves out of the pipe.
After several hours the vacuum was released and the rubber
stopper removed. The sampling tube leading to the bottom of the cup was
then attached to a trap. The trap also served as a sample bottle with
each sampler having its own trap/sample bottle. Next, the trap was
connected to the vacuum pump. A vacuum was then drawn on the trap
causing water to rise in the sampling tube. The sample flowed out of the
sampling tube and was collected in the trap. See Fig. 9.
Once the sample was collected in the trap, the sample bottle was
immediately capped and a label noting the sampler number, date, location
and time was attached. All samples collected were then stored in a
refrigerator until they were analyzed for tracer content.
,r.-_--SAMPLING_... --SAMPLING TUBE
SURGICAL TUBING CONNECTOR
CONNECTING TUBEVACUUM
--CONNECTING TUBE // PUMP
I m1.1/-- 110
28
TRAP/SAMPLEBOTTLE'
WATER 2SAMPLE
NOTE: Apparatus depictedin drawings are not to scale.
---WATER SAMPLE
Fig. 9 Schematic of Porous Cup Sampler and Apparatusin Sampling Mode
29
Analytical Methods
Four techniques were used to analyze for tracer content in the
water samples collected. Bromide, iodide and pentafluorobenzoic acid
were measured by ion exchange HPLC methods with UV absorption detection
following methods described by Stetzenbach and Thompson, 1982. A reverse
phase HPLC with UV absorption detection was used to measure m-trifluoro-
methylbenzoic acid.
The fluorinated aliphatic compounds, chlorodifluoroacetic acid,
heptafluorobutyric acid, pentafluoropropionic acid, and trifluoroacetic
acid, were measured in the gas phase following a derivatization procedure
that converted the aliphatic anions into a methyl ester. The derivati-
zation step was necessary to make these compounds volatile and therefore
amendable to gas phase measurement.
The apparatus and conditions for sample analyses are given below.
An Altex model 332 gradient liquid chromatograph (Berkeley, CA) with a
Schoeffel model 770 variable wavelength UV detector (Klane Scientific,
Tustin, CA) and a Spectra-Physics model 4100 computing integrator (Santa
Clara, CA) were used for HPLC sample analyses. The column used for
detection of iodide, bromide and pentafluorobenzoic acid was a Whatman
Partisil lOpm SAX/25 cm (Clifton, NJ) ion exchange column. The mobile
phase consisted of 25% H20, 55% methanol and 20% 0.1 M KH
2PO
4 at a flow
rate of 2.0 ml/min. Sample injection loop size was 50p1. The UV
detector was set at 200 rim.
A Merck Lichrosorb RP-18 lOpm/25 cm (Darmstadt, GFR) reverse
phase column was used for detecting m-trifluoromethylbenzoic acid in the
samples. The mobile phase consisted of 40% acetonitrile and 60% 0.005 M
30
tetrabutylammonium phosphate at a flow rate of 1.0 ml/min. The sample
injection loop size was 20p1. The UV detector was set at 195 rim.
The samples potentially containing the fluorinated aliphatic
compounds, were derivatized by adding 1 ml of the sample to 5 ml of
sulfuric acid and 1 ml of dimethyl sulfate in a 40 ml bottle sealed with
a teflon-lined septum cap. The tightly capped sample bottles were then
immersed in a water bath at 60 °C for 30 minutes. The aliphatic anions,
now in a methyl ester form, were analyzed in the gas phase using a
Hewlett-Packard model 5992-A GC/MS system (Palo Alto, CA) with a Porapak-
Q, 100-120 mesh, 2.1 mm ID stainless steel column, operated isothermally
at 190 °C. A helium carrier gas was used at a flow rate of 20 ml/min.
The analyses were performed on 3 ml gas samples removed from the head
space of the sample bottles and injected into the GC/MS.
Samples potentially containing trifluoroacetic acid were also
run on a Tracor model 565 gas chromatograph system employing a Hall
electrolytic conductivity detector (Austin, TX) with a Porapak-Q, 100-
120 mesh, 2.1 mm ID stainless steel column, operated isothermally at
140 °C. The carrier gas consisted of helium at a flow rate of 20 ml/min.
The sample injection size was 3 ml of gas removed from the head space of
the sample bottles.
RESULTS
Sample Collection Program
Sampling runs were made on two week to one month intervals at
the CGHF and ML sites. Although all samplers were excavated not all
produced water samples. Table 4 shows a list of location, sampling dates,
and whether a sampler was dry or wet at the CGHF site. Table 5 gives the
same information at the ML site.
There are two probable causes for samplers to remain dry. In
most cases the soil conditions were too dry, and thus the soil moisture
tension was too high to extract water. The high percentage of dry
samplers at the arid CGHF site compared with the much lower percentage
at the humid ML site bears this out. In addition, mechanical failure
of a sampler would prevent a vacuum from holding long enough to draw
a sample, even in wet conditions.
Mechanical failure may be due to cracks in the ceramic cup or
imperfect seals at the glued PVC pipe extension connections. Many of
the dry samplers were noted to lose a vacuum over a period of several
minutes or hours. This wasmost likely due to dry soil conditions.
Other samplers, however, were observed to lose a vacuum in a few short
minutes. This indicates mechanical failure of the samplers.
31
32
Table 4 Water Samples Collected at the CGHF Site
Sampler 7/28/82 8/14/82
CGHF-Pl-S dry wet
CGRF-Pl-I wet dry
CGHF-Pl-D dry dry
CGHF -1-S wet dry
CGHF -1 -I dry dry
CGRF-1-D dry dry
CGHF-P2-S dry dry
CGHF-P2 -I dry dry
CGHF-P2-D dry dry
CGRF-2-S wet wet
CGHF-2-I dry dry
CGHF-2-D dry dry
CGRF-P3-S dry dry
CGHF-P3 -I dry dry
CG1F-P3-D wet wet
CGHF-P4-S dry dry
CGEF -P4 -I dry dry
CGHF -P4-D wet wet
CGHF-4-S wet wet
CGHF-4 -I dry wet
eGHF-4-D wet wet
CGHF-P5-S dry dry
CGHF-P5-I dry dry
CGHF -P5-D wet wet
S = shallowI = intermediateD = deepP = perimeter
Table 5 Water Samples Collected at the ML Sites
Sampler 7/30/82 8/14/82 9/11/82 10/26/82
ML-1-s wet wet wet wet
ML-1I wet wet wet dry
ML-1-P dry dry wet dry
ML-2A-S wet wet wet wet
ML-2A-I wet wet wet dry
ML-2A-P wet wet wet dry
ML-3-S1 dry dry dry dry
ML-3-S2 wet wet wet dry
ML-3-I1 wet wet wet dry
ML-3-I2 wet wet wet dry
ML-3-P dry dry dry dry
ML-4-S1 wet wet wet dry
ML-4-S2 dry dry dry dry
ML-4-I wet wet wet dry
ML-4-P wet wet wet wet
S = shallowI = intermediateD = deepP = perimeter
33
34
Sample Analyses
The results of sample analyses are shown in Table 6 for samples
collected at the CGHF site and in Table 7 for ML samples. These tables
list compounds found in each sample analyzed, their concentrations and
methods used for detection.
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CONCLUSIONS
Tracer Monitoring Program
Results of the hydrologic monitoring of the experimental trenches
indicate that water content in the trenches is generally low. This is
especially true at the CGHF site. Water collected from porous cups in
which no tracer was detected could have originated from the water used
in making the slurry which was packed around the porous cups at the time
of their installation (see Material and Methods), or from infiltration
through the soil profile between trenches. The high percentage of dry
samplers at the CGHF site is probably due to the antecedent conditions
there. The soil at the site is extremely dry and the slurry water may
have moved out of the borehole and into the dry surrounding formation.
At the ML site antecedent soil conditions were near field capacity.
Therefore, slurry water probably was not lost to the formation. Soil
water collected at the ML site which contained no tracers may also have
originated from dewatering of the formation as well as from the slurry.
The presence of tracer in some samples clearly indicates movement
of soil water and the resultant mobilization and transportation of the
tracers along with it. The monitoring results are effectively summarized
in Tables 6 and 7. Samples which contained tracers and the implications
thereof are discussed below. The pathways of tracer movement, wherever
indicated from the tracer data, are shown in Fig. 10 for the CGHF site
and Fig. 11 for the ML site.
37
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40
CGHF Site
Many porous cup samplers remained dry at the CGHF site. This is
probably due to the low soil moisture conditions there. A few of the
samplers may have failed if their ceramic cups were inadvertently frac-
tured or pipe connections improperly glued during installation. Either
incident would result in a vacuum leak and thus a dry sampler.
The water sample from the shallow porous cup CGHF-2-S (Trench
No. 2) showed the tracer bromide. This indicates water movement in the
trench cap (Fig. 10).
Trench No. 4 showed water in its shallow, intermediate and deep
samplers. These unusually wet conditions are probably the result of the
sprinklers being inadvertently left on (on this trench only) overnight
following a test of the sprinkler system in July. The water sample from
CGHF-4-S showed the tracer m-trifluoromethylbenzoic acid indicating
water movement in the trench cap. The water samples from CGHF-4-I and
CGHF-4-D showed the tracer pentafluorobenzoic acid. This indicates
water movement along the trench floor and escaping from the trench bottom.
Water samples from CGHF-P4-D, along the north perimeter of Trench No. 4,
shows the tracer trifluoroacetic acid. This tracer originated from the
bottom of Trench No. 3 and indicates water escaping from the bottom of
the trench and moving laterally beyond the perimeter of the trench
(Fig. 10).
ML Site
Porous cup samplers at the ML site yielded water more frequently
compared to those at the CGHF site. This is most likely due to the wetter
climatic conditions and lower evaporation rates which exist at the site.
41
The water sample from the ML-1-I sampler (Trench No. 1) showed
the tracer heptafluorobutyric acid. Water movement along the trench
bottom is indicated by the presence of this tracer in the intermediate
sampler (Fig. 11).
Analyses of the water collected from sampler ML-2A-I (Trench
No. 2a) showed the tracer pentafluoropropionic acid indicating movement
along the trench bottom (Fig. 11).
Trench No. 4 had movement of water along the trench floor and
escaping laterally from the trench bottom. This is evident from the
bottom tracer, pentafluorobenzoic acid, being detected in samplers
ML-4-I and ML-4-P (Fig. 11).
Tracer Performance
Generally, the tracers used in this experiment have proven to be
useful and reliable indicators of soil water movement based on previous
tracer experiments. A tracer in this experiment had to be mobilized by
infiltrating soil water, collected in a sampler, and detected in the
laboratory in order to be considered successful. Those tracers fitting
the above criteria are bromide, pentafluorobenzoic acid, m-trifluoro-
methylbenzoic acid, pentafluoropropionic acid, heptafluorobenzoic acid,
and trifluoroacetic acid. Iodide is considered a good tracer although
it was not detected in this experiment probably due to lack of soil water
infiltration through the cap. Fluorescein has been used in the past as
a tracer but is highly sorbed by soil particles. This is probably why
although both fluorescein and bromide were emplaced in the cap backfill
of CGHF Trench No. 2 only bromide was detected in sampler CGHF-2-S.
42
Chlorodifluoroacetic acid suffered from analytical difficulties as
described below.
Most of the new aliphatic tracers performed equally well when
compared to the conventional and aromatic tracers used. The only excep-
tions were trifluoroacetic acid and chlorodifluoroacetic acid. These
tracers had detection limits in the 1-10 ppm range and were more prone
to chromatographic interferences. Development is in progress to improve
and refine analytical techniques that will increase the detectability of
these two tracers. Overall, the aliphatic tracers were considered
successful as tracer compounds in that they were easily mobilized by soil
water and were detectable in the low ppm range using conventional
analytical methods and instrumentation. In addition, aliphatic compounds,
as well as the aromatic tracers used should have no background concentra-
tions in the environment or in toxic and hazardous waste materials. When
used at a commercial shallow land burial site these tracers can be a good
monitoring tool.
Recommendations
From the experience gained in performing this experiment several
recommendations for future hydrologic tracer monitoring programs can be
made. First, all porous cup samplers should be checked by evacuation in
the laboratory and again in the field during emplacement. This would
identify cracked porous cups and improperly glued pipe connections before
backfilling takes place. Also, porous cup samplers with an air entry
value greater than the 1 bar cups used in this experiment should be chosen
for use in soils with low moisture content, such as the CGHF site.
43
Porous cup samplers should be evacuated for 24-48 hours in order
to collect a sample with sufficient volume for several analyses. Also,
a sampling analysis program should be implemented immediately after the
completion of trench construction in order to establish a background
pattern for samples collected. This is especially important if bromide
and iodide are used since they occur naturally in the environment.
A tracer should be placed around the perimeter of the trench
to show water infiltration pathways from areas other than infiltration
through the trench cap. Sampling points for an experimental trench should
be located in the trench cap, on the trench bottom, below the bottom of
the trench, and most importantly at one or more levels a few feet down-
gradient of the trench perimeter. In a commercial burial site samplers
placed at several levels around the trench perimeter should be sufficient.
Most of the tracers, including the aliphatics performed well and
are recommended for use in tracer monitoring studies. However, trifluoro-
acetic acid and chlorodifluoroacetic acid are not recommended for use in
commercial shallow land burial sites until further testing is completed
and more sensitive analytical techniques developed. The tracers m-
trifluoromethylbenzoic acid and pentafluorobenzoic acid are not recom-
mended for use in the same trench since a sample from such a trench must
be analyzed using two different techniques to separate the compounds.
Finally, it is recommended that the tracer monitoring program
be continued for one to two more years at the CGHF and ML sites. During
this time the sprinklers at the CGHF site should be used to simulate
more humid conditions in order to mobilize all tracers and facilitate the
further testing of tracer monitoring techniques at the site. Continued
44
monitoring of the ML site through several winter seasons should provide
important information about tracer monitoring in areas experiencing
repeated freeze-thaw conditions. Also, an alternate monitoring technique
to provide a back-up in the event of porous cup sampler failure should
be used. Neutron probes and gypsum blocks could monitor the soil moisture
conditions in a trench and indicate if infiltration takes place. Tensio-
meters placed near the porous cup samplers could also indicate soil
moisture conditions. These tensiometers could also indicate whether the
samplers are dewatering the surrounding soil and influencing flow condi-
tions near the the samplers.
APPENDIX A
SOIL CHARACTERISTICS
45
46
Table A-1 Soil Characteristics for CGHF and ML Sites(McCray, Nowatzki and Thompson, 1982)
Soil Property CGHF Site ML Site
Unified Soil Classification Designation SM SMSpecific Gravity of Solids 2.55 2.55Shrinkage Limit (%) 21 20Plastic Limit (%) 23 NP*Liquid Limit (%) 24 27Plasticity Index 1 0Maximum Dry Density-ASTM D698 (pcf) 102 101Optimum Moisture Content-ASTM D698 (pcf) 14.0 15.8Maximum Dry Density-ASTM D1557 (pcf) 113 108Optimum Moisture Content-ASTM D1557 (%) 13.5 13.4Unconfined Compressive Strength (psf) 354 1683Peak Effective Friction Angle (degrees) 33 35Peak Effective Cohesion Intercept (psf) 1200 240Residual Effective Friction Angle (degrees) 30 35Residual Effective Cohesion Intercept (psf) 750 240Permeability (cm/sec) 8.6 x 10
-72.9 x 10
-6
Organic Content (%) 1.38 1.45Compression Index (strain) 2.32 4.12Coeffective of Consolidation (in
2/sec) 5.0 x 10-7 6.0 x 10
-7
Sovell (5) +0.24 -0.32
Non Plastic
APPENDIX B
CLIMATOLOGICAL RECORDS
47
48
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REFERENCES
McCray, J. G., E. A. Nowatzki and G. M. Thompson, 1982, "Low-LevelNuclear Shallow Land Burial Trench Isolation", AnnualTechnical Report, NRC-04-81-220.
National Oceanic and Atmospheric Administration, 1970-1982, ClimatologicalData.
Nowatzki, E. A., G. M. Thompson and M. E. Wacks, 1981, "Trench Cap andTracer Studies," Research Program at Maxey Flats and Consider-ations Other Shallow Land Burial Sites, NUREG/CR-1832, p. IX-1/IX-7.
Schulz, R. K., 1981, "Study of Unsaturated Zone Hydrology", ResearchProgram at Maxey Flats and Considerations of Other ShallowLand Burial Sites, NUREG/CR-1832, p. VII-1/VII-10.
Soilmoisture Equipment Corp., "Operating Instructions for the Model1900 Soil Water Sampler", Santa Barbara, CA.
Stetzenbach, K. J. and G. M. Thompson, Sept. 1982, "A New Method forSimulataneous Measurement of Cl- , Br- , NO3- , SCN- , and I - atSub - ppm Levels in Groundwater", submitted for publication.
Thompson, G. M., 1982, Asst. Professor, Dept. of Hydrology and WaterResources, University of Arizona, personal communication.
Water Resources Research Center Field Lab, 1970-1982, unpublished data,University of Arizona, Tucson, AZ.
Wilson, L. G., 1979, "Monitoring in the Vadose Zone: A Review of TechnicalElements and Methods", Report Number GE79TMP-55, General ElectricCompany-TEMPO, Center for Advanced Studies, Santa Barbara, CA.
52