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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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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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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36

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

0

0

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39

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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