Hydrogeologic Factors in the Selection of 

Shallow Land Burial Sites for the Disposal 

of Low-Level Radioactive Waste 

Hydrogeologic Factors in the Selection of 

Shallow Land Burial Sites for the Disposal 

of Low-Level Radioactive Waste 

By John N. Fischer 

U.S. GEOLOGICAL SURVEY CIRCULAR 973 

1986 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication 

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government 

First printing 1986 

Revised 1989 

Library of Congress Cataloging in Publication Data 

Fischer, John N. 

Hydrogeologic factors in the selection of shallow land burial sites for the disposal of 

low-level radioactive waste. 

(U.S. Geological Survey circular; 973) 

Bibliography: 

Supt. of Docs. no.: I 19.4/2:973 

1. Hydrogeology. 2. Water, Underground-United States. 3. Radioactive waste 

disposal in the ground-United States. I. Title. ll. Series. 

GB1005.F57 1989 621.48'38 85-600272 

Free on application to the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 
CONTENTS 

Abstract------------------------------------------------------------------------------

Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - -

Page 

Purpose and Scope - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4 

Acknowledgments----------------------------------------------------------------- 4 

Hydrogeologic Factors - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4 

Precipitation- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 6 

Ground Water - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - 10 

Surface Water - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - 11 

Geology - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - 13 

Hydraulic Conductivity------------------------------------------------------------- 15 

Ion Exchange Capacity - - - - - - - - - - - - - - - - - - - - - - -- - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 17 

Geomorphology - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - -- -- - - - - - - - - - - - - - - - - - - 18 

Sediment and Rock Stability- - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 18 

Buffer Zones ---------- -- -------------------- --- - -------------------- -- ---- ------- 18 

Other Factors - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - 19 

Systems Approach to Site Evaluation - - - - - - - - - - - - - - - - - - -- - -- - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - 19 

Continuing Investigations and Research------------ -- ---- ------------------ -- --------------- 20 

Summary and Conclusions - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - -- - -- - - - - - - - - - - - - - - - - - - - - - - - - - - 21 

Selected References--------------------------------------------------------------------- 21 

ILLUSTRATIONS 

FiouRE 1. Map showing location of commercial and major Department of Energy low-level radioactive waste burial sites in the 

Page 

United States - - ------------------- - -- --- ------ ------------- -- ------ ---- -------------------- ------ ----- 3 

2. Diagram showing volumetric distribution of low-level radioactive waste, by site, through 1986-------------------------- 6 

3. Generalized cross sections showing construction processes for a typical low-level radioactive waste burial site near 

Barnwell, S.C.- - - - - - - - -- - - - - - - - - - - - - -- - - - - - - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 7 

4. Map showing mean annual precipitation in the United States ------------------------------------------------------ 8 

5. Diagram showing a cone of depression and direction of ground-water flow in an unconfined aquifer from which water is 

being pumped from a well - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11 

6. Topographic map of the Radioactive Waste Management Complex and vicinity at the Idaho National Engineering Laborato~. 

Idaho----------------------------------------------------------------------------------------------- 12 

7. Diagram showing subsurface gamma activity near trench 46, Maxey Flats, Ky.--------------------------------------- 14 

8. Maps showing location of drainages, location of cross section, and geologic section A-A' at the low-level radioactive waste 

burial site near Sheffield, Ill. ---------------------------------------------------------------------------- 15 

9. Conceptual view of natural factors related to the suitability of sites for the burial of low-level radioactive waste ------------ 20 

III 
TABLES 

Page 

TABLE 1. Half-lives and predominant sources of typical radionuclides contained in low-level radioactive waste---------------------- 2 

2. Information about commercial low-level radioactive waste burial sites ------------------ -------------------- --------- 4 

3. Historical annual additions and cumulative volume of low-level radioactive waste at commercial sites and at selectei 

U.S. Department of Energy sites-------------------------------------------------------------------------- 5 

4. Hydraulic conductivities of representative unconsolidated aquifer materials ------------------------------------------- 16 

CONVERSION FACTORS AND ABBREVIATIONS 

For readers who wish to convert measurements from the inch-pound system of units to the metric sy:'tem of units, 

the conversion factors are listed below: 

Multiply 

inch (in.) 

foot (ft) 

yard (yd) 

mile (mi) 

cubic yard (yd3

) 

nanocurie (nCi) 

By 

2.540 

.3048 

.914 

1.609 

.7645 

37 

IV 

To obtain 

centimeter (em) 

meter (m) 

meter (m) 

kilometer (km) 

cubic meter (m3 ) 

becquerel (Bq) 
Hydrogeologic Factors in the Selection of 

Shallow Land Burial Sites for the Disposal 

of Low-Level Radioactive Waste 

By John N. Fischer 

Abstract 

In the United States, low-level radioactive waste is disposed 

of by shallow land burial. Commercial low-level radioactive 

waste has been buried at six sites, and low-level radioactive 

waste generated by the Federal Government has been buried at 

nine major and several minor sites. Several existing low-level 

radioactive waste sites have not provided expected protection 

of the environment. These shortcomings are related, at least in 

part, to an inadequate understanding of site hydrogeology at the 

time the sites were selected. 

To better understand the natural systems and the effect of 

hydrogeologic factors on long-term site performance, the U.S. 

Geological Survey has conducted investigations at five of the 

six commercial low-level radioactive waste sites and at three 

Federal sites. These studies, combined with those of other 

Federal and State agencies, have identified and confirmed 

important hydrogeologic factors in the effective disposal of 

low-level radioactive waste by shallow land burial. These 

factors include precipitation, surface drainage, topography, site 

stability, geology, thickness of the host soil-rock horizon, soil 

and sediment permeability. soil and water chemistry, and depth 

to the water table. 

INTRODUCTION 

In the United States, the term "low-level radioactive 

waste" (LL W) means radioactive material that ( 1) is not 

high-level radioactive waste, spent nuclear fuel, or 

byproduct material (as defined by the Atomic Energy 

Act of 1954) and (2) the U.S. Nuclear Regulatory 

Commission (NRC), consistent with existing law and in 

accordance with ( 1) above, classifies as LL W (U.S. 

Congress, 1986). 

Low-level radioactive waste consists of a wide variety 

of material including clothing, animal carcasses, glassware, ion-exchange resins, piping and valves, and paper. 

Although LL W also is generated in liquid form, th~ NRC 

regulation for LLW disposal, Chapter 10 Code of Federal Regulations Part 61 (10 CFR Part 61) (U.S. rruclear 

Regulatory Commission, 1960a) requires that liquid 

LLW be solidified or packaged in material ttat can 

absorb twice the volume of liquid present before the 

LLW is disposed of at a licensed facility. In addit:':ln, 10 

CFR Part 61 also requires that the amount of liquid in 

solid LLW be minimized and, in all cases, be le~s than 

1 percent by volume. Most LLW is generated rt commercial nuclear power plants; the remainder originates 

primarily at research laboratories, hospitals, industrial 

facilities, and universities. 

LL W does not generate significant heat in radhactive 

decay. Table 1 lists the half-lives of typical radionuclides 

in LLW. Radionuclides decay to 1/10,000 cf their 

original activity after 10 half-lives. However, fer some 

radionuclides, 10 half-lives require the passage of substantial periods of time. For this reason, m2ximum 

concentrations are specified for all radionuclides in LL W 

so that, at the end of a 500-year period, radioactivity will 

be at a level that does not pose an unacceptable hazard to 

public health and safety (U.S. Nuclear Regulator:-' Commission, 1960a). 

In the United States, there are six sites where commercially produced low-level wastes have been or are 

being disposed of. The Department of Energy (DOE) 

operates LL W disposal sites for waste that is generated 

through Federal activities. Figure 1 shows the locations 
TABLE 1.-Half-lives and predominant sources of typical 

radionuclides contained in low-level radioactive waste 

[Modified from U.S. Department of Energy, 1983. -.no data] 

Radionuclide Half-life 

Carbon-14 ...... 5770 years 

Cesium-134 ..... 2.2 years 

Cesium-137 ..... 30 years 

Chromium-51 ... 27.8 years 

Cobalt-58 ....... 71 years 

Cobalt-60 ....... 5.3 years 

Iodine-125 ...... 60 days 

Iodine-131 ...... 8.1 days 

Iridium-192 ..... 74 days 

Manganese-54 ... 291 days 

Strontium-90 .... 28 years 

Technetium-99 .. 2.1 X 105 

years 

Tritium ......... 12.3 years 

Uranium-238 .... 4.5X 109 

years 

Zinc-65 ......... 245 days 

Predominant source of 

radionuclides 

Nuclear lnstitupower Industry tional 

reactors 

X 

X 

X X 

X 

X 

X 

X 

X 

X 

X 

X X 

X X 

X X 

X 

X X 

of major LLW disposal sites. Of the six commercial 

sites, those at Barnwell, S.C., Beatty, Nev., and Richland, Wash., remain open at the time of this report (table 

2). 

The site at Sheffield, Ill., was closed in 1978 when it 

reached licensed capacity. The commercial disposal site 

at West Valley, N.Y. , ceased disposal operations in 

1975 because of water accumulation in the trenches, but 

the adjacent burial ground formerly licensed by NRC 

continues to store LL W that is generated on site as a 

result of site clean up and water treatment operations. 

The site at Maxey Flats, Ky., ceased disposal operations 

in 1978 when contaminated water from trenches was 

discovered to be moving through fractures and along 

bedding planes in the subsurface (Zehner, 1983). No 

adverse health effects from the migration of low-level 

radioactive waste at any commercial or DOE-operated 

sites have been documented. 

In 1986, about 67,000 yd3 of LL W were buried at 

commercial disposal sites, and about 127,000 yd3 were 

buried at DOE sites (U.S. Department of Energy, 1987) 

(table 3). Figure 2 shows volumetric distribution ofLLW 

by site through 1986. Increased efforts to separate 

radioactive from nonradioactive waste and to compact 

waste resulted in a decrease in commercial disposal 

volumes from 1983 through 1986. Further decreases in 

2 

volume will occur in the near future due to these efforts. 

It is uncertain, however, how long this trend will 

continue. 

In the United States, LLW is disposec of by shallow 

burial in trenches excavated into the natural land surface. 

In some cases, however, fill has been used to create 

terrain for trenches. The dimensions of most trenches 

depend on topography and other local conditions and 

range from 25 to 50ft wide, 20 to 50ft dt'~p. and 125 to 

800 ft long. Soil, sediment, and rock structure and 

stability dictate the slope of trench walls rnd the spacing 

between trenches. Trenches are separated by at least 5 ft 

of undisturbed earth material. Vertical trench walls are 

preferable because void spaces between the waste and 

trench walls can be minimized; however, vertical walls 

frequently are not mechani~ally achievable because of 

the instability of host material. Trend' bottoms are 

sloped. A 6- to 8-in. layer of sand is commonly placed 

on the trench bottom to convey any water that may reach 

the bottom into french drains and sumps at one side of 

the trench for removal through shallow wells. Trenches 

filled with waste are covered with sediment having a 

high clay content. 

Clay-dominated sediments, because of their structure 

and other physical characteristics, generally have low 

permeability; this low permeability can reiuce the infiltration of water into the trench. The surface of the filled 

site is contoured to facilitate runoff and to minimize 

erosion. The trench construction process shown in figure 

3 is typical for trenches at the commercial LL W site near 

Barnwell, S.C. Natural features of the burial environment, such as sediment characteristics and thickness of 

the unsaturated zone, influence the movement of contaminants away from the waste disposal sites. There are 

several mechanisms through which this movement can 

occur. These mechanisms include emission of gases by 

decaying waste, erosion of overlying soil, tectonic activity, the actions of burrowing rodents, anct contaminant 

transport by ground water. The earth-science community 

generally agrees that, in a properly selected and designed 

facility, ground-water transport is the most significant 

mechanism for LLW migration, although other mechanisms may be important under specific circumstances. 

In 1980, the National Low-Level Radioactive Waste 

Policy Act (PL 96-573) established, as Federal policy, 

that "each State is responsible for prov:ding for the 

availability of capacity either within or outside the State 

for the disposal of low-level radioactive wrste generated 

within its borders * * *"except for waste r~nerated as a 

result of Federal activities. To provide the necessary 

disposal capacity, the Act encourages the formation of 

regional compacts among States to develop new LL W 
w 

- j 

~~' 

/lr,~\ 1/ \ ~ ~ /\.\ 

~ 

~ ~~ - . " . \_ .f\ ~ ... Ricl,!a-,-d-~-r------------------- -----------,--~ 1

---',,_,~ 0 -r· / \ ( 

... " ' ' 4 . ' ' . ••ash. f I \ /, -~ · :, I ··. 

• 1', : 1:/ . . ·.: .. 

H 

• ' '• 0 0, ' 'j I '..---

Bnford ' • • • --.. , c- ' 

I 

~!~!'(a_tton. I • • • • · .r ~ \leV • • •. ·' ____ , ;' : __________ .) '; ·· l'• f--c VI est"" \-----\ ~~ f / I .. 

./ : 

'. 

ld a h o 

r. 

National' -\, ., ... ,' ,. ... ·---------------! ' ' 

,•--------- ·• i 

: ' ........... 

• '····-, ' 1 f ~ : 

>-:..(_'!' I 

../ .~. r-7 1 

~ .. ----N.Y ,..... t· -. 

• .. 

\ ~· I E . ' ' , __ .. ' -- - "-· ' 

I 

1 nglnoering I : •, ··.------ J-----~-- \ 

' ' ' ------. .. . • ' I. ' ... ---

·--------~-.... , Laboraro!l< ldah •----------- • .,, ' ' onne, II '• --ch I e ' ; 

0 

: \ j .._ •1\'9 \ }'--1_·· !'''· 

) 

, ---·---- , , ' ' ..- , , na\d, , , ' -----------.. , • • ' ff" \d , 'Fre ,- ,~ f I • I ' .. , -'She le ' • \ OhiO ·< , •• ' i I I • i ..... ---- f 1 I :• . l ' 

: ! ; ··---r-------------·----·; ______ -------- ---\. ~!.'_; ) .:·-'/ ;---- \. _____ J__ --

... I : i : Weldon Mo.'·. v• Fl ts, Ky./ __ .. ,.--- \....._ \ f i : i Spnng, \ ,.,i.laxev ___ a ____ .-..... -· ;q \ , : : : '1 .... -- Nationa\,~ - \ ' Boa .... •• ' ' ' ' • --R.dge - -- ., __ ,, , \ .. ,, ""~· , : ____ , ...... fQ8k I • t _.-- nwiill, • \ , \.,*. \N"1'«1la f·--Tear -----Site · ·----· f 

: 

------------------T 

, --~-~----~--~-- : ----.. ----- \----: · -- :? , .... 

Lobo~~~-'Y! -- , .!~~n-r--- \ --~~c. ···!f-

\ • • • ' • • ' ' • ah- • 

' ' ' • ' ' ' ' ' ' Sovonn \ I \; : : : : .- : \ Plant. \ ..... , •, • los Alamos : o : ; : \ River 

···c. -L -' i National : ·-...... ""•'"····--.,, ) : )s.c. 

' ' ' -' . : ' Laboratory, : ' :-- ' .. ---\, : '. : ,- \ 

~ ' N ••e· : ' r : _, -------" -----· : . '" •. ' ' . ' ----- , __ 

. \ )'r ·-.. ·--------Lr-'"'--:.--:------ ; i j \ 

_____ ~.--- L ... ,~. . ' \!.-

EXPLANATION 

• Department of Energy sites 

* Commercial sites 

\ , ...... -, I" 

'' ..... ,_,' '\ (~ / 

\ ' ' 'l. 

\ 

,_ --.... 

f 0 100 200 300 400 500 MILES I I I I I I I I I I I I I 0 200 400 600 BOO KILOMETERS 

. ,.. 

FIGURE 1.-L~cation of commercial and major Department of Energy low-level radioactive waste burial sites in the United States. 

(Modified from Clancy and others, 1981.) 
TABLE 2. -Information about commerciallo»·-level radioactive 

waste burial sites 

[Modified from Clancy and others, 1981] 

Site 

Beatty, Nev .......... 

Maxey Flats, Ky. . ... 

West Valley, N.Y .... 

Richland, Wash ...... 

Sheffield, Ill ......... 

Barnwell, S.C ........ 

Year 

opened 

1962 

1963 

1963 

1965 

1967 

1971 

Licensed 

land area Current status 

(acres) 

79 Open. 

255 Closed in 1978. 

25 Closed in 1975. 

100 Open. 

20 Closed in 1978. 

259 Open. 

sites and grants to participating States the authority to 

reject waste from other States with which regional 

agreements do not exist. As a result of the Act, State 

compacts have been formed, and efforts are under way 

to establish new LLW sites. 

The U.S. Geological Survey (USGS) has conducted 

hydrogeologic investigations at all the commercial LL W 

disposal sites, except the site at Richland, Wash. The 

USGS also conducted major hydrogeologic investigations at three DOE sites (Argonne, Ill., and Oak Ridge, 

Tenn., National Laboratories, and the Idaho National 

Engineering Laboratory). In addition, the DOE, NRC, 

the Environmental Protection Agency (EPA), and many 

State agencies have conducted research and other site 

investigations related to LL W disposal at most of the 

LLW sites. The objectives of the investigations and 

research, many of which were conducted cooperatively 

between agencies, were to describe the hydrogeology of 

the sites and to gain a better understanding of the 

hydrogeologic factors and processes that influence the 

transport of radionuclides from the sites. Reports resulting from these investigations are included in the selected 

references section of this report. 

Existing LLW sites, studies of which provided the 

basis for much of the information in this report, were 

licensed before promulgation of the NRC regulation for 

LL W disposal (I 0 CFR Part 61). NRC developed this 

regulation on the basis of experience at the existing sites 

to improve performance at future disposal facilities. 

Purpose and Scope 

This report summarizes information gathered in LL W 

site studies and identifies and quantifies hydrogeologic 

factors that influence the transport of radionuclides from 

LLW disposal sites. These hydrogeologic factors are 

important in the selection of sites for any type of disposal 

or storage of LLW (for example, shallow land burial, 

4 

above-ground vaults, or warehouses). If contaminants 

escape into the environment from any system, the natural 

features of the site must provide adeq··ate protection 

from exposure. The information in this report will be 

valuable to regional State compacts, other State and 

Federal agencies, and land and waste ma'lagers who are 

involved in the difficult process of selecting, evaluating, 

designing, and operating LLW disposal sites. 

Acknowledgments 

The information in this report is based primarily on 

hydrogeologic investigations conducted at LL W disposal 

sites by the following scientists, past and present 

employees of the USGS: Jefferson C. Bagby, Jack 

Barraclough, Marcel P. Bergeron, Jarres M. Cahill, 

James B. Foster, George Garklavs, J'1hn R. Gray, 

Richard W. Healy, Roger Jensen, Kenneth L. Kipp, 

Barney D. Lewis, Bryan B. McDonald, David Morgan, 

Peter S. Murdoch, James R. Nicholas, William D. 

Nichols, Julio C. Olimpio, David E. P-udic, John B. 

Robertson, Barbara J. Ryan, David Webs'",~r. and Harold 

H. Zehner. 

HYDROGEOLOGIC FACTORS 

Current regulations require that LLW disposal facilities be sited, designed, and operated in a manner that 

minimizes the contact of water with the disposed waste. 

This requirement exists because analyses have shown 

that the principle potential pathway to the environment 

and the public is by ground-water transpcrt. Such transport can result in potential environment~"' 1 exposure to 

radiation. Geomorphologic processes and container degradation can result in contact between LL W and the 

disposal-site sediment-rock-water system prior to the 

time that the waste ceases to present an unacceptable 

hazard to public health and safety and the environment. 

The assumption that such contact can occur must be 

made, not only for disposal located near surface 

trenches, but also for all other types of LL W disposal 

and storage. When the contact occurs, and later, when 

transport begins, the natural environment at the site must 

protect the biosphere from unacceptable contaminant 

transport and exposure. Therefore, effect1~ve disposal of 

LL W requires a thorough understanding of the hydrogeology of the disposal or storage site. 

The natural site environment is influenced by hydrogeologic factors, several of which are interrelated. Surface runoff and erosion, for example, are dependent 

variables of precipitation, soil characteristks, and topog-
TABLE 3.-Historical annual additions and cumulative volume of low-level radioactive waste at commercial sites and at s~lected 

U.S. Department of Energy sites 

[Volume in thousands of cubic yards; -, no data. Data modified from U.S. Department of Energy, 1987] 

Commercial sites 

Beatty, West Maxey Richland, Sheffield, Barnwell, Annual Cum·.tlative Year Nev. Valley, Flats, Wash. 111. 3 S.C. addition volume N.Y.1 Ky? 

Through 1975 ... 68.7 91.4 155.5 14.7 72.6 77.7 480.6 

1976 .......... 5.1 18.0 3.8 17.6 52.6 97.7 577.7 

1977 .......... 6.2 .6 3.6 23.1 59.7 93.2 f70.9 

1978 .......... 11.6 9.7 2.3 80.5 104.1 i'75.0 

1979 .......... 8.5 15.9 82.5 107.9 f82.9 

1980 .......... 16.6 32.5 71.6 120.7 1,(03.6 

1981 ........... 4.4 53.3 51.6 109.3 1,112.9 

1982 .......... 2.0 51.8 45.5 99.3 1,212.2 

1983 .......... 1.5 52.9 46.0 100.4 1,? 12.6 

1984 .......... 2.7 50.3 45.6 98.6 1.~11.2 

1985 .......... 1.8 52.5 45.0 99.3 1,:10.5 

1986 .......... 3.5 24.6 4

38.7 66.8 1,:77.3 

Total. ........ 132.6 91.4 174.1 365.6 115.6 697.0 

Selected U.S. Department of Energy sites 

Year LANL5 1NEL6 NTS7 ORNL8 HANF9 SRP10 All Annual Cumulative 

other addition vclume 

Through 1975 ... 172.1 111.4 10.9 237.4 457.7 352.0 530.0 1,872 

1976 .......... 11.5 8.1 3.8 5.0 6.1 10.6 23.6 68.7 1,941 

1977 .......... 4.7 8.5 1.2 3.1 14.1 19.2 7.1 57.9 1,999 

1978 .......... 9.8 8.8 17.0 2.6 12.9 20.3 8.5 79.9 2,079 

1979 .......... 6.4 6.9 44.5 2.7 20.7 23.8 5.0 110.0 2,189 

1980 .......... 6.3 6.7 16.2 2.6 13.9 25.6 4.4 75.7 2,265 

1981 .......... 7.2 4.1 19.1 1.8 16.9 26.3 5.5 80.9 2,346 

1982 .......... 6.0 3.9 51.3 1.7 15.3 29.3 9.9 117.4 2,463 

1983 .......... 4.2 6.5 34.8 2.4 23.5 34.9 13.3 119.6 2,583 

1984 .......... 7.1 5.0 15.8 2.9 24.5 34.1 28.9 118.3 2,701 

1985 .......... 8.8 4.1 51.5 2.9 22.2 39.9 29.2 158.6 2,860 

1986 .......... 5.9 4.4 23.4 2.4 27.7 39.4 23.7 126.9 2,987 

Total ........ 250.0 178.4 289.5 267.5 655.5 655.4 689.1 

1

lncludes waste at both the commercial State-licensed site and 5

Los Alamos National Laboratory. 

an adjacent NRC-licensed facility. Ceased disposal operations in 6

Idaho National Engineering Laboratory. 

1975. 7

Nevada Test Site. 2

Closed in 1975. Volumes thereafter resulted from site cleanup. 8

0ak Ridge National Laboratory. 3

Closed in 1978. 9

Hanford Reservation. 4

Preliminary data. 10Savannah River Plant. 

raphy. These and other hydrogeologic factors, such ductivity, and hydraulic gradient, form a hydrog~ologic 

as the depth to the water table, proximity of surface system that governs the transport of radionuclides in the 

water bodies, ambient water quality, hydraulic con- subsurface. 

5 
Richland, Wash. 

365,000 yds3 

8.0% 

West Valley, N.Y. 

91,000 yds3 

2.0% 

Hanford 

Reservation, Wash. 

655,000 yds3 

14.4% 

Idaho National Engineering Laboratory, 

Idaho 179,000 yds3 

3.9% 

Los Alamos 

National Laboratory, 

N. Mex. 250,000 yds3 

5.5% 

Frenald, Ohio 

391,000 yds 3 

8.6% 

Sheffield, Ill. 

115,000 yds3 

2.5% 

Nevada Test Site, 

Nev. 289,000 yds3 

6.3% 

EXPLANATION 

Maxey Flats, Ky. 

177,000 yds3 

3.9% 

Oak Ridge 

National Laboratory, 

Tenn. 518,000 yds3 

11.4% 

Beatty, Ne'f, 

132,000 yds 3 

2.9% 

E arnwell, S.C. 

6""',000 yds3 

1~.2% 

Other sites 

47,000 yds3 

1.0% 

Savannah 

River Plant, S.C. 

655,010 yds 3 

14.4~\ 

r-1 Department of Energy and 

L___j Department of Defense 

~ Commercial 

FIGURE 2.-Volumetric distribution of low-level radioactive waste, by site, through 1986, in cubic yards and percentage. 

(Modified from U.S. Department of Energy, 1987.) 

Precipitation 

Studies have demonstrated that water is the primary 

transporter of contaminants away from LL W burial sites 

(U.S. Nuclear Regulatory Commission, 1982). Because 

precipitation is the source of water, sites in areas of low 

annual precipitation have less potential for waste transport by water than areas that have high amounts of 

6 

precipitation. In the United States, areas of lowest 

annual precipitation are in the West (fig. 4). The LLW 

site at Beatty, Nev., for example, receives an average of 

2.9 in. of precipitation annually (W.D. Nichols, U.S. 

Geological Survey, written commun., 1984); the average annual precipitation at the Richlan1, Wash., and 

Idaho National Engineering Laboratory sites is 6.3 in. 

and 8.5 in., respectively (Clancy and ot:'ters, 1981). In 
Remove sand from proposed trench 

perimeter for barrier walls 

~: ."·_ ·: -: .. -:~~~-~~-~:~~~t~~~~~:n :o~."vi~l~v:.· .. ·: --~ Lc1ay 

PHASE I TRENCH PREPARATION 

Replace sand with clay 

and compact barrier walls 

Original grade ~ 

Sand ---"!. ' 

-·-·-·--·-·-·--·-·-·-·-·- ·-·- ...:-;- -·-·- __:_--:-':"' ..:.....--:-_:_--:-:.: -·---~-·-·-·-·-·-·-·-·-·-· .=:-=.. -:-__:_--:-__:_-:----==-_:_-:-__:_---:-_;_ ~=-:--_;_=-:-_:_--:--:..:..=: 

Clay 

PHASE II TRENCH PREPARATION 

PHASE IV ADDITION OF SAND BUFFER 

BARNWELL DISPOSAL TRENCH CONSTRUCTION TECHNIQUE 

FIGURE 3. -Cross sections showing construction processes for a typical low-level radioactive waste burial site near Barnwell, S.C. 

(From Clancy and others, 1981.) 

contrast, at eastern commercial sites near West Valley, 

N.Y. , Maxey Flats, Ky., and Barnwell, S.C., average 

annual precipitation is 39 in. (Prudic , 198.5), 47 in. 

(Zehner, 1985), and 47 in. (Cahill, 1982), respectively. 

Although a high precipitation rate increases the probability of transport in the biosphere, such a rate need not 

eliminate a prospective LL W site because the combination of natural characteristics, more than individual 

factors, controls the transport of radionuclides from a 

burial site. Other factors may provide the necessary 

protection, despite high precipitation. Nevertheless, sites 

at which annual precipitation is high require more 

maintenance and more extensive engineering, such as 

trench cap design and container construction, than those 

sites that have less precipitation. 

In addition to annual precipitation, the intensity, 

frequency, and distribution of individual precipitation 

events in time and space also are important factors in site 

selection. Intense precipitation events can create pulses 

of water that may infiltrate and percolate in vertical 

surges through the soil profile of a waste burial area and 

contribute to contaminant leaching and transport. In 

contrast, a corresponding quantity of precipitation occurring in several events over time will be more subject 

7 

to evapotranspiration and less likely to contribute to 

moisture reaching the buried waste. Intense precipitation 

events also cause increased erosion of trench caps. 

A site at which precipitation falls in relatively evenly 

spaced events during a year is preferable to a site at 

which precipitation occurs in distinct wet and dry seasons. If precipitation falls in evenly spaced events, and 

all other factors are equal, water will be less likely to 

percolate to the buried waste because the surficial soil 

probably will be unsaturated before the precipitation 

event and may, therefore, retain the moisture. When 

antecedent conditions include a saturated soil system, 

water is more likely to percolate to the waste. 

When comparing sites having approximately equal 

annual precipitation, the form in which precipitation 

occurs can be important. For example, precipitation that 

falls as snow is not immediately available for infiltration. 

If the ground surface is frozen when snowmelt occurs, a 

large percentage may run off the disposal site and not 

infiltrate to the subsurface. If the site is located or 

engineered so that runoff from adjacent areas does not 

pass over it, then the water available for contaminant 

transport can be reduced. On the other hand, accumulated snow can melt rapidly, and, if the soils are not 
-460"'" AT lltl WAI.S.lEAt.£ 

,(~ .CO-p; YEAR IIi:: . .. •• /~ 3oo I 

.. "'P I 

Principal Islands~; J' '•-\ 300 I HAWAII ,6 \ ./ 

sc ~u , , P,ooo,ooo 

-' . 

FIGURE 4.- Mean annual precipitation in the 

8 
MEAN ANNUAL PRECIPITATION 

Adapted from a 1; 10,000,000-scale map by 

Environment1l Data Service, Environmental Science Services Administration 

for the period 1931-1960 

Albers Equ.JI Are.1 ProjectiOn 

SCALE 1:17,000,000 

100 zoo 300 .tOO MILES 

zoo •oo 600 Kll0111£TE'ItS 

United States. (U.S. Geological Survey, 1970.) 

TOTAL 

INCHES CENTIMETERS 

128 325.1 

96 243.8 

80 203.2 

64 162.6 

48 121 9 

32 81.3 

24 61.0 

16 40.6 

20 3 

9 
frozen and surface drainage is inadequate, the meltwater 

can provide a significant source of water, which may 

infiltrate into trenches. 

Ground Water 

Under most conditions, the primary offsite hazard to 

public health associated with the burial of LL W is 

ground-water contamination. Ground water underlies all 

disposal sites. When precipitation or surface water infiltrates the ground surface and percolates through LL W 

waste, the water may leach radionuclides from the 

waste. Depending on the thickness of the unsaturated 

zone and other hydrogeologic characteristics, this contaminated water may reside for some time in the unsaturated zone. In most cases, particularly in humid areas, 

the contaminated water eventually will reach the water 

table. There, the water can move laterally and may 

become accessible to wells, or it may appear as surface 

water in springs, streams, ponds, or other bodies of 

water and thus expose the biosphere to radionuclides. 

One of the important ground-water variables is depth 

to the water table. In thick, unsaturated zones, contaminants must travel longer distances before arriving at the 

aquifer. The longer traveltime provides additional time 

for radioactive decay to occur and reduces the hazard of 

the potentially contaminated water. Moreover, if the 

recharge rate is low, the rate of flow in the unsaturated 

zone can be orders of magnitude less than in the 

saturated zone and will cause a significant increase in 

transport time to the accessible environment. 

The depth to the water table at the commercial LL W 

site near Beatty, Nev. , is about 280 ft (Nichols, 1986). 

The depth and the very low recharge rate have been 

important in the successful containment of radionuclides 

at that site. In contrast, at the Oak Ridge National 

Laboratory, Tenn., the water table is less than 20 ft 

below the ground surface in places, and recharge to the 

aquifer is substantial (David Webster, U.S. Geological 

Survey, oral commun., 1983). An investigation by 

Olsen and others (1983) characterized. radionuclide 

migration from a seepage trench at the site. Leachate 

from existing Oak Ridge waste disposal sites has a short 

travel path and traveltime to the water table. Therefore, 

leachate residence time in the unsaturated zone generally 

is short; as a result, containment of radionuclides at Oak 

Ridge is far more difficult than at Beatty. 

The velocity of ground-water flow is an important 

component of site hydrogeologic information because 

this velocity can be used to calculate traveltime of water 

from the disposal trenches to points in the surrounding 

area. The volume of water being transported is as 

10 

important as the velocity, however. Large volumes of 

contaminated water moving at low velocities may 

present a greater radionuclide flux than small volumes 

moving rapidly. Therefore, in evaluating site characteristics, precipitation and infiltration rates, which influence the volume of water available to transport contaminants, must be considered along with soil permeability 

and hydraulic gradient, which are more directly related 

to velocity. 

The quality of natural ground water in the vicinity of 

a proposed site may be a significant factor in determining 

site suitability. If the ground water is naturally high in 

dissolved solids, for example, or has been contaminated 

by previous human activity, the ground water may 

already be undesirable for some uses, and the potential 

risk of additional contaminants from a LL W site may be 

of less consequence. Also, the quality of existing water 

can influence leaching rates of the waste (under saturated 

conditions), solubility of radionuclides, sorption and ion 

exchange reactions, and other chemical aspects of transport (Kirby and Toste, 1983). 

Local and regional water use and the hydrologic 

effects of that use are other' important site selection 

criteria. For example, in an unconfined aquifer, the 

pumping of water from wells will cause a cone of 

depression to form in the water table. Depending on the 

volume of water extracted and the hydraulic characteristics of the aquifer, the cone may extend some distance 

from the pumping center. Within the area of the cone of 

depression, ground-water flow will be in the general 

direction of the well (fig. 5). Therefore, burial of LLW 

in areas where cones of depression from existing or 

future wells might intercept ground water beneath the 

burial area can result in contamination of water supplies. 

In an unconfined aquifer, hydraulic gradient is a 

measure of the slope of the surface of the water table. 

Flow always occurs in the downgradient direction; the 

steeper the gradient, the faster the flow, if the hydraulic 

conductivity and porosity are constant. A slope of zero 

indicates that water in the saturated ground-water system 

is not moving horizontally. The lack of a horizontal 

hydraulic gradient, or the presence of only a very small 

gradient, suggests that contaminants might not be transported rapidly in the horizontal direction away from 

disposal sites when they reach the ground-water table 

(Cherry and others, 1979). The NRC has made provision 

for licensing such sites, including those that will result in 

the burial of waste below the water table (U.S. Nuclear 

Regulatory Commission, 1960a). However, under 10 

CFR Part 61, such a site will be licensed only if it can be 

shown that molecular diffusion will be the dominant 

means of radionuclide transport at the site and that such 
Flreshwatjer recharge! 

I 

Well 

casing . i lde~~ 

J~ 

Unconfined aquifer 

-------------------------------------------------------------------

FIGURE 5.-A cone of depression and direction of ground-water flow in an unconfined aquifer from which water is being pumped 

from a well. 

transport will not violate the performance objective in 

Subpart C of 10 CPR Part 61. 

Although burial of LL W below the water table may be 

appropriate under special circumstances, burial within 

the zone of water-table fluctuation is not permitted 

because alternating wetting and drying of the waste will 

occur within the zone. These processes can hasten the 

oxidation of metal and the decomposition of containers 

and ultimately can lead to earlier leaching than will occur 

if the waste is not subjected to wetting and drying. 

Surface Water 

Although surface water does not have immediate 

contact with buried contaminants (unless the water 

encounters an open trench), surface water can carry off 

contaminants that may be on the surface of a site through 

waste handling and emplacement accidents. Surface 

water also provides a source of water for infiltration, 

percolation, and subsequent ground-water transport. 

LLW sites, therefore, should be located so that surface 

11 

runoff will not enter the disposal area. This can be 

achieved by avoiding locations in flood plains, d~ainage 

channels, topographic depressions, coastal areas, or 

areas downgradient from dams. Further protecfon can 

be achieved by selecting sites in the upper parts o+ basins 

where potential for flooding is diminished through a 

reduction in upgradient surface area. 

Surface water can create several other prob ~ms at 

LLW disposal sites. Streams subject to flooding may 

cause large volumes of surface water to pass over a 

burial area. As a result, water may find its way irto open 

trenches and into direct contact with waste. Flooding 

also increases infiltration and percolation rates through 

caps and into closed trenches and may cause erosion of 

trench caps, thereby decreasing the capability of those 

caps to inhibit infiltration. During a series of runoff and 

flooding events over the 500-year hazardous lifetime of 

the site, trench caps could be eroded to the poirt where 

waste would be exposed at the land surface. Because one 

of the primary management objectives at shal10w land 

burial sites is to avoid contact between waste ani water, 

such waste exposure is inadvisable. 
43"30' 

Diversion 

Reservoir 

Big Lost River 

113"03' 

EXPLANATION 

--5020 --TOPOGRAPHIC CONTOUR 

Shows altitude of land surface. Hachures 

indicate depression. Contour interval 10 feet. 

Datum is sea level. 

0

1 1 

1 

1000

11 

I 20j>O FEET 

1---r-'--r--..,..._--,-...,...., --r'j 

0 300 600 METERS 

FIGURE 6. -Radioactive Waste Management Complex (RWMC) and vicinity at the Idaho National Engineering Lah1ratory, Idaho. 

(Modified from Bagby and others, 1981.) 

Another problem streams can pose at disposal sites is 

the pathway they provide for rapid contaminant transport. Contaminants may move to streams either by 

overland flow from surface spills, which might occur 

during waste handling at the site, or by discharge from 

the ground-water system. Analyses of stream sediments 

near Maxey Flats, Ky., have shown that cobalt-60, 

strontium-90, cesium-137, and plutonium-238 moved 

2.2 mi from the disposal site during one incident 

(Zehner, 1983). On the basis of the detection of 

niobium-95 (which has only a 35-day half-life) in the 

stream water samples, and a comparison of principal ion 

concentrations in surface and ground waters, Zehner 

concluded that the surface water contamination at Maxey 

Flats resulted from spills within the site boundaries and 

12 

subsequent transport by surface runoff to the offsite 

stream sampling point. 

A third potential problem presented by surface water 

bodies near LL W sites relates to geomorr'tology. Over 

time, the development of stream channels may include 

sloughing of banks and changing_ of channel courses. 

These changes in the land surface may destabilize 

adjacent burial areas and reduce the capabi':ty of a burial 

site to provide long-term protection frmr contaminant 

release to the environment. 

Topography has contributed to surface water problems 

at the Radioactive Waste Management Complex of the 

Idaho National Engineering Laboratory. T·e complex is 

located in a topographic low (fig. 6), and, although mean 

annual precipitation does not exceed 8.5 in. (Clancy and 
others, 1981), the site has been subjected to several 

floods that resulted from rapid snowmelt (Barraclough 

and others, 1976). An extensive system of ditches and 

dikes has been constructed around the site to reduce the 

threat of flooding. Natural surface-water barriers, such 

as a topographic high or a siting near the top of drainage 

basins, offer attractive alternatives to such engineered 

structures, however, because these natural barriers probably will last longer than engineered systems. 

Geology 

The geology of disposal sites plays a major role in 

controlling the rate of ground-water flow and solute 

transport, two important related physical characteristics 

in site selection. Sites that are geologically complex pose 

problems because of the difficulty in understanding and 

characterizing ground-water flow. Complex sites are 

typified by those at Sheffield (glacial deposits) and 

Maxey Flats (fractured shale). Such sites are difficult to 

describe and analyze by using hydrologic models. Models are useful tools for predicting future site performance 

under a variety of conditions. Technical analyses of 

ground-water, surface-water, and other pathways are 

required by 10 CFR Part 61. Although the regulation 

does not require hydrogeologic modeling specifically, in 

most cases, modeling will be necessary to characterize 

the hydrologic framework of the site and for the predictions of performance required to demonstrate compliance 

with regulations. 

An essential component for an effective ground-water 

monitoring system is the ability to accurately describe 

the geohydrologic system of potential sites. One of the 

most troublesome aspects of monitoring the now-closed 

commercial site at Maxey Flats is the difficulty in 

effectively sampling the ground water, which flows 

predominately in fractured shale and intercalated sandstone. Many of the fractures at Maxey Flats are not 

interconnected, and, for those that are, the place and 

mode of connection are difficult to ascertain. At Maxey 

Flats, many wells drilled to monitor the ground water 

have not intercepted fractures and, therefore, yield little 

or no water. Other nearby wells do provide adequate 

water for sampling. Although recent progress has been 

made in characterizing fracture flow (Hsieh, 1983), 

problems in interpretation, such as those associated with 

non-Darcian flow, have yet to be overcome. 

One of the reasons that the Maxey Flats site was 

closed was the seepage of contaminated ground water 

through fractures from an adjacent filled trench into an 

open trench. In the summer of 1977 workers at Maxey 

Flats discovered radioactive soil and water in trench 46 

13 

(fig. 7). An investigation revealed a subsurface a~ea of 

increased gamma activity near trench 46. Soil and water 

having elevated concentrations of cobalt-60 and 

manganese-54 were found in the clay-filled fractures of 

a thin sandstone bed that trench 46 and other trenches at 

Maxey Flats generally intercept. Zehner (1983) concluded that this thin sandstone bed was the tra1sport 

pathway for contaminants and that the effective velocity 

for radionuclide movement along the bedding plan~ was 

50 ft/yr. The velocity greatly exceeds the vdocity 

generally associated with unfractured shale and sandstone and far exceeds that originally expected at tb~ site. 

The incident is illustrative of the difficulty in cha~acterizing fracture flow. 

The LLW site near Sheffield, Ill. (fig. 8), proYides a 

second example of a stratigraphically complex system. 

The site is located in glaciated terrain in an area th::tt was 

once surface mined for coal. Limited data were available 

for use in characterizing the hydrogeology at an1 near 

Sheffield at the time of license application in 1966. 

Permeable stratigraphic units were identified in the 

hydrogeologic characterization, but the units were 

thought to be discontinuous. In one of those u1its, a 

narrow channellike depression filled with coarse, gravelly sand (fig. 8B) was not identified until several years 

later. On the basis of information collected when the site 

opened, ground-water velocities were estimated to be 

0.01 to 0.05 ft/d (E.H. Baltz, U.S. Geological Survey, 

written commun., July 1967). At these velocities, 

ground water will flow from under the site to a small lake 

l, 100 ft downgradient within 60 to 330 years. Ho•vever, 

because of the existence of the gravel-filled channel and 

its downgradient orientation, ground water has moved 

that distance in less than 20 years. Concentrations of 

tritium (a radioactive isotope of hydrogen) of about 400 

nCi/L (nanocuries per liter) have been found in groundwater samples from near the site (Goode, 1986). 

Although significant dilution occurs when the ground 

water reaches the lake, such unexpected transport illustrates the uncertainty inherent in disposing of waste at 

sites that are geologically complex. 

The maximum permissible concentration fer controlled release of tritium to the Sheffield environ'llent is 

3,000 nCi/L, as stipulated in Appendix B to 10 CFR Part 

20, the regulation in effect at the time of licensing of the 

site (U.S. Nuclear Regulatory Commission, 1960'.,). The 

release limits for a LL W disposal facility are now 

defined by the requirement of Subpart C of 10 CFR Part 

61. Currently, releases are required to be as low as 

reasonably achievable but in no case may result in annual 

doses to individuals that are greater than a small fraction 

of the expected annual dose from natural so·•rces-
• Trench 37 (closed December 1972) I • Trench 39 (closed July 1973) 

/ Trench 38 (closed 

'

.,.,.e,CI) *' ~· December 1972) 

e,.8 

>~ i9$o 

"\ \ \ \ "" '\ "\"' " '\ "d}.'\.""' "'"' " " " <'~~700 

0 50 100 FEET 

0 30 ~·~TERS 

"""' """""~~ "'-:::.~ ---- ~'~ :?f.t1 ~ ........... 'Gl? 0">"-o "'-, t'>.] / 

"-..... / 

~~------.,..,.....,..,.... EXPLANATION 

N LINE OF EQUAL GAMMA 

ACTIVITY-Dashed 

~ - where approximated. 

Interval 100 picocuries 

per gram 

__,~"""*- FENCE 

D 160 TRENCH-Number indicates 

approximate gamma activity, 

in picocuries per gram 

1 

FIGURE ?.-Subsurface gamma activity near trench 46, Maxey Flats, Ky., low-level radioactive waste disposal site. All values 

indicated are above-background activity levels. (Modified from Zehner, 1983.) 

25 millirem to the whole body or any organ other than 

the thyroid. These release limits apply to all likely 

pathways for exposure, including ground water, surface 

water, air, soil, plants, and animals. 

In general, sites that are hydrogeologically complex, 

not only from a stratigraphic standpoint, but also because 

of variability in other hydrogeologic characteristics such 

as hydraulic conductivity and porosity, are less suited to 

modeling and accurate prediction than sites in unsaturated, thick, relatively homogeneous, unconsolidated 

sediments. More than 49 testholes in a 50-acre area were 

necessary to confirm the existence of the gravel-filled 

channel at the Sheffield site and to identify the channel 

as the pathway for offsite tritium migration (Garklavs 

and others, 1986). There are two reasons for not conducting extensive drilling at LLW sites. First, drilling is 

costly. Second, drilling may create vertical pathways for 

the movement of ground water. 

14 

Unconsolidated sediments, in general, are more easily 

characterized for quantitative ground-,vater analyses 

than are consolidated fractured systems. Moreover, 

ground-water flux is usually less in a fairly homogeneous 

unconsolidated sedimentary system, particularly if that 

system is unsaturated, than flux in rock fractures or on 

interfaces between soil systems and unfractured rocks. 

This difference occurs, in part, because of the longer 

flow paths that exist within the sedime'lts. Migration 

pathways that are long in terms of time and distance, 

such as those in unconsolidated sediment3, also provide 

added opportunity for radioactive decay a"'d for sorption 

of contaminants onto sediment surfaces. 

The foregoing discussion does not constitute an 

endorsement of a specific type of hydrologic system for 

the disposal of LLW. It is important to evaluate a 

potential disposal environment as a total system. In so 

doing, a wide variety of factors are con~idered, and a 
W47'30" 

~~~A II 

::H 

/ttl ~ _/ rlii . ... Lliil 

II Iii I 

:,':,' 1,,1,111 Low-level radioactive 

~~ waste disposal site Iii I 

ii Iii I . 

"'-.. ... 

\\ "'·· '"'-·. 1!1 ... / 

\\ -~ .·· ,: I EXPLANATION \\ ···~ .. '----" ·-1 I i! I A Line of section A' 

II ------

!! I !ill ==~~;== . 11 (._JilL -·surface.drain"age ___ _L--=---==-~--- 41020'00" ~::.:--<::::.~==:.:=~=~.=:=-:..::-=~== -..:..=~=--=--_=:=:=-===-=-::::t::::.-======'-====-=---.JJ.I:'-==-::.-=-=-=============-=-=-=====--=--=====-~--=====-=-=-_=_=_=_=_=_=_-_-_-....J...__-:_-:_:_-:_ _ ___J 

0 

I 

0 

200 

I 400 

I 

I 

100 

800 

I 1000 FEET I 

I 

300 METERS 

FIGURE 8A.-Location of drainages and line of secti_on A-A' at the low-level radioactive waste burial site near Sheffi~ld, Ill. 

(Modified from Foster, Erickson, and Healy, 1984.) 

system that appears to be satisfactory geologically may 

not satisfy other criteria. 

Hydraulic Conductivity 

The shallow land burial method of waste isolation 

includes the concept of naturally constrained release of 

contaminants over long periods of time. This approach is 

particularly appropriate for LL W disposal because, over 

time, radioactive isotopes decay into stable isotopes that 

do not present health hazards. Thus, known decay rates 

can be combined with calculations of transport velocities 

to help determine the area within which a radioactive 

hazard will exist. Hydraulic conductivity is a fundamentally important component in these calculations. Table 4 

lists the hydraulic conductivity of representative unconsolidated aquifer materials. 

15 

In selecting LL W burial sites in the easterr., more 

humid regions of the United States, host material of low 

hydraulic conductivity has been sought on the premise 

that these earth materials retard the movement of ground 

water and dissolved contaminants away from disposal 

trenches. The sites at Maxey Flats, Ky., and West 

Valley, N.Y., were selected, in part, because h~·draulic 

conductivity at those sites was thought to be low. Zehner 

(1983) calculated that the hydraulic conductivit~' of the 

upper members of the unfractured shale at Maxey Flats 

ranges from 0.3 to 3.7 ft/yr. At West Valley, Prudic 

(1986) estimated that the hydraulic conductivity of the 

unweathered glacial till and associated lenses o+' sorted 

material, in both the horizontal and vertical dir,~ctions, 

ranges from 0. 02 to 0. 06 ft/yr. 

Although the shale at Maxey Flats and the glacial till 

at West Valley meet the general criteria of low hydraulic 
EXPLANATION 

A Ca, Cahokia Alluvium Pe, Peoria Loess A' 

740- Gt, Glasford Formation, Toulon Member 

Gh, Glasford Formation, Hulick Till Member 

730 Pc, Carbondale Formation 

tw 

w Ms, mine spoils LL 

~ 

J 

w 720 Pe Gt 

> w 

....J 

<( 

w 

rJ) 710 w 

> 0 

m 

<( Gt 

w 700 

c 

::::> 

ti= 

....J 

<( '690 Gh 

Pc 

Pc 

680 VERTICAL EXAGGERATION X 12.5 

0 500 FEET 

0 150 METERS 

FIGURE 8B. -Geologic section A-A' showing location of buried gravel-filled channel at the low-level radioactive waste disposal 

site near Sheffield, Ill. (Modified from Foster, Garklavs, and Mackey, 1984. Stratigraphy follows the usaf!'! of the Illinois 

State Geological Survey.) 

conductivity, problems occurred at both sites when 

subsidence in the buried waste caused the trench caps to 

slump and crack. The cracks created pathways through 

which large quantities of precipitation and surface-water 

runoff entered the trenches. There is evidence that lateral 

migration of water through the upper weathered and 

fractured till layer may have contributed to the presence 

of water in trenches at West Valley. Because the earth 

materials at both sites have low hydraulic conductivity, 

water passing through the breeched cap could not drain 

rapidly enough from the trenches. Over time, the 

trenches were filled with water, and a "bathtub effect" 

was created. 

Left unattended, water-filled trenches present several 

problems. When sediments surrounding the waste 

become saturated, large volumes of leachate may be 

generated. Also, as water levels in the trenches rise, the 

contaminated water may encounter shallow, permeable 

sediment layers. These layers may not offer a pathway 

for contaminant transport if they remain in the unsaturated zone, but, under saturated conditions of a water16 

filled trench, the layers can provide pathways for rapid 

lateral migration. 

A contaminant plume at the burial ground formerly 

licensed by NRC at West Valley exists at about 9 ft 

below ground surface in a weathered, relatively permeable layer of glacial till. Current data iniicate that the 

plume extends about 70 ft downgradient from its probable source and moved that distance in rbout 12 years 

TABLE 4.-Hydraulic conductivities of representative 

unconsolidated aquifer materials 

[Modified from Freeze and Cherry, 1079] 

Aquifer materials 

Clean gravel ....................... . 

Clean sand, sand and gravel. ........ . 

Silty sand ......................... . 

Silt, loess .......................... . 

Till. ............................... . 

Unweathered marine clay ........... . 

Hydraulic conductivity 

(feet per day) 

104-105 

102-104 

10-2-102 

10- 3-10 

10-6-10-1 

10-6-10-3 
(M. Bergeron, U.S. Geological Survey, oral commun., 

May 1984). These figures suggest a ground-water velocity of about 5 ft/yr, a much larger figure than might be 

expected on the basis of hydraulic conductivity of the 

unweathered host sediments reported by Prudic ( 1986). 

One explanation for this rapid movement is that water 

entered the source trench either through the cap or from 

a transient perched water table that was intercepted by 

the trench. Due to the low permeability of the unweathered host sediments, water levels in the source trench 

increased until the water encountered the weathered till. 

Once in this layer, lateral transport of the water as 

saturated flow and at elevated velocity was possible 

(Herbes and Clapp, 1984; U.S. Nuclear Regulatory 

Commission, 1985). Similar circumstances are believed 

to have existed along the thin sandstone beds within the 

fractured shale at Maxey Flats and to have led to the 

transport of cobalt-60 and manganese-54 (Zehner, 

1983). 

Water overflow from disposal trenches can result in 

seepage of contaminants at the land surface. Trenches at 

the West Valley site did overflow (Prudic and Randall, 

1979), and, as a result, the site was closed. At Maxey 

Flats, trenches had to be pumped because of accumulating water; eventually the Maxey Flats site also was 

closed. These events led to a reevaluation of siting 

disposal areas in soils of low hydraulic conductivity. 

Generally, trenches in sediments of high hydraulic 

conductivity material will not fill with water even if 

trench caps are breeched because water will pass through 

the trench bottom. However, contaminant transport will 

be rapid in these materials if water is available, and the 

process of radioactive decay will have less time to take 

place before the contaminant travels beyond the control 

(buffer) area. 

Host sediments of an intermediate hydraulic conductivity may be preferable. Such sediments will permit 

water that percolates through the trench cap to drain 

through the trench bottom without accumulating. If the 

flow rate is relatively slow, an unreasonably large buffer 

zone will not be required to protect public health and 

safety and the environment. The host soil at the Barnwell, S.C., site, for example, has an intermediate 

hydraulic conductivity, and the data available at this 

time, although limited, indicate that waste is effectively 

contained. Cahill (1982) reported that horizontal hydraulic conductivity of sandy clay, in which the trenches are 

excavated at Barnwell, ranges from 10-7 to 10- 1 ft/d; 

vertical values average about 10-3 ft/d, a value of 

sufficient magnitude to conclude that water entering the 

trenches will not be retained within the trenches. In fact, 

because trenches at Barnwell commonly do not accumulate water, either the trench caps are completely er~ctive 

in preventing infiltration of surface water or th~ host 

sediments are permeable enough to permit the wat~r that 

does enter to pass through the trench bottom. Thr. latter 

explanation is more probable. 

In more arid zones, hydraulic conductivity, alt-hough 

still important, may be less critical than in the humid 

parts of the country. The site near Beatty, Nev., for 

example, is located in valley-fill deposits of the 

Amargosa Desert where sand and gravel fractio'ls are 

high. In his investigation of site hydrogeology, Nichols 

found the saturated hydraulic conductivity of the 

Amargosa Desert soils to be about 200 ft/yr (W.D. 

Nichols, U.S. Geological Survey, written corrmun., 

May 1984). Percolation to the ground-water table at 

Beatty is retarded, however, by an unsaturated zone, 

approximately 280 ft thick, which lies between the waste 

and the ground-water table. Nichols estimates the unsaturated hydraulic conductivity of the sediments at Beatty 

to range from 4X 10-4 to 4X 10-9 in./d (Nichols, 1986). 

The steady-state unsaturated flow rate is estimated. to be 

about 0.1 ft/1 ,000 yr. These figures and the combined 

effects of low annual precipitation (less than 3 in . ) and 

high annual potential evaporation (about 100 in.) indicate that transport of contaminants to the water tab ~ will 

be very slow and will be strongly influenced by the 

magnitude and frequency of extreme precip~tation 

events. USGS unsaturated zone studies underv1 ay at 

Beatty will help to quantify unsaturated flux at the site 

(Schneider and Trask, 1984). 

17 

lon Exchange Capacity 

The ground-water transport of radionuclides tl'"'ough 

porous media is influenced by the characteristics of the 

radionuclide itself and by soil and water chemistr:'. The 

complexity of this relation hinders the quantifiable, 

predictable, and reproducible interpretation of radionuclide transport in ground water. However, studies at the 

Idaho National Engineering Laboratory have shown that 

mineral and water chemistry can be effective in ret:>rding 

the movement of certain radionuclides (Robr.rtson, 

1974). 

Attenuation can occur through a variety of pl':rsical 

and chemical processes, but the two most prominent 

processes appear to be sorption and ion excl ~nge. 

Sorption involves the adhesion of molecules to the 

surface of aquifer material; the ion exchange p"'ocess 

displaces ions on the surface of minerals by ions in 

solution. Both processes can result in the removal of 

contaminants from ground water moving from LL W 

disposal areas (Brown, 1967). The sorption ard ion 
exchange processes are caused primarily by the electrical 

surface charge in mineral particles, generally clay-rich 

materials that carry an excess of negative charges. 

Studies by Olsen and others (1983) at disposal sites at the 

Oak Ridge National Laboratory reaffirmed that illite clay 

retards the migration of cesium-137. In his investigation 

of the hydrogeology at the West Valley, N.Y., commercial LLW site, Prudic (1986) found that the transport of 

cesium and strontium was retarded because of ion 

exchange between the contaminants in solution in 

ground water and the clay component of the glacial till. 

In contrast, investigators at a cold-scrap recovery plant 

in Rhode Island found that the clay-free sands did not 

retard significantly the transport of strontium-90 (B.J. 

Ryan, U.S. Geological Survey, oral commun., 1984). 

Thus, the clay fraction and clay type play key roles in 

sorption and ion exchange processes, and their determination is an important element of the site-selection 

process. 

Geomorphology 

Certain low-level wastes require stabilization for at 

least 300 years because of their half-life or concentrations of radionuclides. Others need to be isolated from 

accidental direct contact by humans for at least 

500 years. To ensure that waste in the facility is 

adequately contained, stability of the site for 300 to 500 

years must be ensured. Because of the long times 

involved, the projected geomorphic change at potential 

sites is an important component of site evaluation. Of 

particular interest are the processes of erosion and 

slumping, which may occur naturally or may be stimulated by the burial activity. 

Important factors influencing erosion rates are rainfall 

and rainfall intensity, vegetative cover, slope, water 

velocity (a function of slope), wind velocity and direction, and soil characteristics. The potential for the flow 

of water over the land surface can be reduced through 

proper site selection; however, some surface-water flow 

at LLW disposal sites is inevitable, particularly because 

trench caps are constructed of low-permeability material 

and are mounded to inhibit infiltration and percolation of 

surface water into the filled trenches. The rejected 

infiltration becomes surface-water flow. 

The selection of sites that have minimum slope and no 

nearby surface-water courses can minimize erosion and 

reduce other site stability problems. Minimizing slope 

reduces the velocity and thereby minimizes the erosiveness of surface runoff; eliminating surface-water courses 

diminishes the likelihood of surface flow from outside 

site boundaries over or around the site during floods. 

18 

Sediment and Rock Stability 

Stability problems have occurred at the commercial 

LLW sites at West Valley and Maxey Flats. The sediment in which waste is buried at West Valley is fine, 

unconsolidated glacial till (Prudic, 1986), which is 

susceptible to slumping along the walls of incised 

streams and gullies. This slumping has, in fact, occurred 

near the West Valley site (U.S. Nucl~ar Regulatory 

Commission, 1985). Through erosion and slumping 

sequences, gullies have cut into the till near the West 

Valley site, and, if allowed to continue, some buried 

waste may become exposed while still hazardous. Ensuring site stability probably will be a neces"qry element of 

site maintenance at West Valley for an e:xtended period 

to ensure that natural geomorphic prC'~esses do not 

expose the waste. 

The Maxey Flats, Ky., facility is situated on a 

flat-topped hill located 300 ft above the surrounding 

valley floor. In his description of the hydrogeology of 

the site, Zehner (1983) estimated the. slope of the 

hillsides extending from the burial area to the valley 

floor to be between 30° and 40°. In closing the site, an 

impermeable cover on the land surface was emplaced to 

decrease leachate formation within th~ waste-filled 

trenches (Kentucky Department of Envi-:-onmental Protection, 1983). As a temporary measure, membranes of 

polyvinylchloride, 0.08 in. thick, have been placed over 

the area in which trenches have been C1

'1mpleted. This 

cover has been effective in reducing infiltration, but the 

cover has also caused a substantial increase in surface 

runoff. The runoff is directed to retention areas constructed at the south and east sides of the site, which 

serve to diminish peak flows from runoff events. However, very large volumes of runoff frqm the 

polyvinylchloride-covered surface of the site can exceed 

the capacity of the retention areas and can flow rapidly 

down the steep slopes (A.L. Knight, U.S. Geological 

Survey, oral commun., May 1984). Rapid flow of large 

volumes of water on steep slopes can result in rapid 

erosion and gully formation. Therefore, maintenance of 

ponds and hillside channels is likely to be a long-term 

component of site monitoring and maintenance at Maxey 

Flats. 

Buffer Zones 

It is unlikely that any shallow land bu':'ial system can 

provide absolute containment of LL W within its trenches 

for the entire hazardous lifetime of rad:0active waste, 

particularly in those areas where annual precipitation is 

high. Therefore, near-surface disposal fa~ilities must be 
designed with the possibility in mind that there will be 

some release of LLW from trenches. Because radionuclide decay to nonhazardous waste occurs in predictable 

time frames, the risks from such releases can be managed. Siting, design, construction, operation (including 

waste form and packaging), and closure requirements are 

provided by 10 CFR Part 61 to ensure that releases that 

may occur are minimized and comply with strict limits to 

protect public health and safety. 

The potential release of contaminants from disposal 

areas has resulted in an NRC requirement to establish a 

three-dimensional buffer zone surrounding a disposal 

area. The buffer zone is a controlled, restricted area that 

allows for environmental monitoring and facilitates the 

implementation of mitigative action. It is the zone into 

which contaminants from trenches might migrate during 

the contaminants' hazardous lifetime. Buffer zones 

allow time for radioactive decay to occur and allow 

dispersion and geochemical processes between the waste 

and host sediment and rocks to take place. Through these 

processes, radioactivity of contaminated ground water 

may be attenuated to within regulatory limits before the 

ground water migrates to the site boundary. 

The natural characteristics of some environments may 

be less favorable for shallow land burial than others. 

Nevertheless, a less favorable environment may provide 

an acceptable shallow land burial site for LL W if the 

buffer zone surrounding the site is large enough to 

contain migrating contaminants long enough for decay to 

reduce radioactivity to safe levels. _.~ 

The dimensions of the buffer zone depend upon 

complex, site-specific interrelations of factors, many of 

which are hydrogeologic. The dimensions can be estimated, in part, through the use of numerical transport 

models, if the waste can be adequately characterized and 

if the hydrologic system can be accurately described. 

Dimensions of the buffer zone may range from tens to 

hundreds of yards laterally and from tens to hundreds of 

feet vertically. 

OTHER FACTORS 

At Sheffield, Ill., and Beatty, Nev., disposal sites for 

both LL W and nonradioactive hazardous waste are 

collocated under separate operating licenses. Although 

problems caused by the proximity of the two types of 

facilities have not been documented at this time, evidence exists that the mobility of some radionuclides may 

be increased by interaction with organic compounds 

present either naturally or in chemical waste. This 

organic-radionuclide interaction was investigated by 

Cleveland and Rees ( 1981) at Maxey Flats. Their work 

19 

suggests that, when plutonium occurs in trench leachates 

as a dissolved species, the plutonium can cherr.ically 

chelate with some types of waste organic moleculr.s and 

then become more mobile. Pietrzak, Columbo, Weiss, 

and others have conducted water-chemistry investigations at LLW burial sites since 1976. Their findin.~s are 

published in a series of quarterly NRC reports, only one 

of which is cited here (Pietrzak and others, 1982). 

Among their many findings, the authors conclude1 that 

low concentrations of organic chelating agents m~.y be 

responsible for keeping radionuclides, partic·.tlarly 

cobalt -60, in solution. Investigations conducted at 

Maxey Flats by Kirby and Toste (1983) support these 

conclusions. These latter studies were of organic waste 

buried directly with radioactive waste. 

At the Sheffield, Ill., and Beatty, Nev., sites, the two 

waste types are not buried in direct contact wit'l one 

another but are collocated at adjacent facilities. This 

separation precludes mixing of the wastes in the unsaturated zone where vertical water flow dominates but 

cannot be assumed to do so in the saturate zone where 

horizontal components of flow can predominate. 

Because of the possible increase in radionuclide mobility 

when organic and radioactive leachates mix, the collocation of organic and radioactive waste-disposal sites can 

result in an increased risk to the environment. 

The possible development of l).n area's n<~tural 

resources should be considered in the selection of a LL W 

site. In addition to ground water, such resources irclude 

oil, coal, and other mineral resources beneath, and 

immediately downgradient from, the disposal site. The 

primary concerns with respect to the presence of exploitable natural resources are (1) the likelihood of inadvertent intrusion by a resource exploiter and (2) the effe:cts of 

resource development on site performance afte:r the 

period of institutional control. The relative value of the 

natural resources should be considered in evaluating the 

likelihood of exploitation. 

Geologic hazards can decrease site integrity ard are 

important factors in site selection. These hazards include 

volcanic eruption, active faulting, land subsidence, and 

mass soil and rock movements. Any of these hrzards 

may alter the hydrogeologic system or the ph~'sical 

integrity of a site, can cause releases of radioactive 

contaminants to the environment, and can comrlicate 

predictions of future site performance. 

SYSTEMS APPROACH TO SITE EVALUATI0N 

In the site evaluation process.- the hydrologic system 

as a whole should be considered, and a particular site 
. ·.· ·.· ... . . . . . . . 

. . · ... · .·: . ·.· · ... 

EXPLANATION 

NATURAL FACTORS 

1 Low rainfall 

7 Topography and soils that 

minimize erosion 

2 Deep water table 

3 Modest soil permeability 

8 Absence of exploitable resources 

9 Absence of surface-water bodies 

4 Slow moving ground water 

5 High adsorption and ion 

10 Low probability for geologic faulting 

or volcanic activities 

exchange rates 11 Adequate buffer zone 

6 Homogeneous geology +-- Direction of water flow 

FIGURE 9. -Conceptual view of natural factors related to the suitability of sites for the burial of low-level radioactive waste. 

should not be disqualified automatically on the basis of 

deficiencies in only one or two of the critical parameters. 

This "systems" approach to site selection is related to the 

multiple-barrier concept, which utilizes the complementary effects of natural features that inhibit contaminant 

mobilization and transport. Figure 9 is a conceptual 

diagram illustrating how the factors discussed in this 

report combine to form such a natural barrier system. 

Each factor provides a part of the overall protection 

system, and the protection provided by a particular factor 

may vary from site to site. Therefore, assigning acceptable, minimum, or maximum numerical values to particular factors is usually inappropriate. Each factor 

should be considered as part of the overall barrier 

system, and the overall system should be evaluated. In 

its approach to a total system evaluation of potential 

disposal sites, described in 10 CFR Part 61, NRC 

includes factors such as waste form and engineering 

criteria, in addition to the hydrogeologic factors discussed in this report. 

In the development of plans for the next generation of 

LL W disposal facilities, consideration is being given to 

alternatives to shallow land burial, such as above- and 

below-ground vaults. If and when such engineered 

20 

structures are incorporated into disposal systems, the 

protection they provide will be considered as another 

element in the system of barriers to the transport of LL W 

contaminants. Engineered barriers alone are unlikely to 

qualify a LL W disposal site that has teen previously 

designated as unsuitable on the basis of hydrogeologic 

factors. Instead, the total system of prC'tection will be 

evaluated with the objective of establishing multiple 

barriers to human exposure. 

CONTINUING INVESTIGATICI\JS AND 

RESEARCH 

The hazards associated with existing LL W sites will 

persist for at least 300 to 500 years. Most investigations 

of existing sites have been in progress for less than a 

decade. This is an inadequate period to assess either all 

of the environmental factors surroundin_g such a longterm hazard or the performance of current sites. The 

information in this report represents tl·~ state of our 

knowledge to date. Although the underst1nding of LL W 

fate and transport is not complete at this time, there is 

considerable knowledge available to form a technical 
basis for practical disposal decisions and to incorporate 

conservatism to counter the uncertainties associated with 

long-term site performance. 

To improve our understanding, the USGS is continuing to conduct research and investigations related to the 

earth-science aspects of burial of LL W (Dinwiddie and 

Trask, 1986). The major thrusts of the field investigations and the complementing research program are to ( 1) 

develop improved solute transport models, (2) achieve a 

better understanding of unsaturated flow phenomena, (3) 

clarify radionuclide geochemistry, and (4) develop techniques to detect the subsurface transport of radionuclides 

in the gaseous phase. 

The USGS LL W investigations are complemented by 

those of other Federal and State agencies. The NRC, 

DOE, and EPA are active in supporting investigations of 

many aspects of the disposal process. The DOE plays a 

particularly important role in support of the research of 

investigations of the National Laboratories and as lead 

agency in assisting State governments in the implementation of provisions of the Low-Level Waste Policy Act 

(PL 96-573). 

SUMMARY AND CONCLUSIONS 

Due to weathering and other geomorphologic processes, 

burial of LL W can be expected to result in the transport 

of contaminants into the immediate subsurface environment of the burial site. Moreover, because engineered 

structures, such as above- and below-ground vaults, 

probably will not maintain their integrity throughout the 

hazardous life of the waste, the contaminants most likely 

will be transported from these engineered structures as 

well. For this reason, it is important that the natural 

factors at disposal sites provide barriers to transport to 

achieve the necessary protection of the environment. On 

the basis of hydrogeologic field investigations at commercial and DOE LLW disposal sites, pertinent natural 

factors have been identified and confirmed, and insights 

have been gained into their relation to effective disposal. 

The most important natural factors are precipitation, site 

stability, sediment and rock permeability, hydraulic 

gradient, proximity of surface water, site location in the 

drainage basin, topography, thickness of the unsaturated 

zone, native ground-water quality. homogeneity of site 

hydrogeology, and proximity of geohazards. Careful 

evaluation and incorporation of these factors into a 

multiple-barrier concept of environmental protection will 

increase the probability of identifying effective shallow 

land burial sites for low-level radioactive waste. 

21 

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u US GOVERNMENT PRINTING OFFICE 1989 - 242-338 - 226/80065