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750357
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A,F OrOr Cr�I.f4ADO —r—_.....
} ss.
COUNTY OF V1iELD
tin. ,. I oF.. Doard ,
of County Com rRssloners
APR23 . i5
1 '
AMLIEDO AND IVEY
424 DENVER HILTON OFFICE BLDG. • 1515 CLEVELAND PLACE • DENVER.CaWaRealfik mtacCLRUGR
gy Deputy
PETROLEUM. MINERAL. ENGINEERING GEOLOGY AND PHOTOGEOLOGY TELEPHONE (303) 5347Th I • LABEL UAILU
CURTIS L. AMUEDO
JOHN B. IVEY
WELD COUNTY COMMISSIONERS
J
is; P Fl j i
March 31 , 1975 P1
it APR 24 1975 16
GREELEY. COLO.
Mr . John Rold
:. Colorado Geological Survey
1845 Sherman
Denver , Colorado 80202
Re : Contract dated April 1 , 1974
Encumbrance 151616
u Dear Mr . Rold :
rat This letter transmits three copies of our report " Coal
Mine Subsidence and Land Use in the Boulder-Weld Coalfield ,
Boulder and Weld Counties , Colorado . "
We anticipate that this work will be of significant bene-
ism
fit to the State , to town and county land planners and to
citizens interested in land development. It has been a pleas-
ure to conduct this research program for you and to prepare
this report. We look forward to being of further service to
the Colorado Geological Survey in the future .
Yours very truly ,
/7„ /, `/
Join B . Ivey '
JBI /cw
La
PLl
11 COAL MINE SUBSIDENCE AND LAND USE IN THE
BOULDER-WELD COALFIELD
BOULDER AND WELD COUNTIES , COLORADO
Prepared for
THE COLORADO GEOLOGICAL SURVEY
L By
AMUEDO AND IVEY
A . R . Myers , J . B . Hansen , R. A. Lindvall ,
J . B . Ivey , and J . L . Hynes
March , 1975
rS
FOREWORD
The problem of subsidence resulting from the undermining
:; of the surface has received a great deal of study over the
past 100 years . Much of this work has been done in Europe
where industry , population density, and coal mining tended to
grow and develop in the same areas . Damage to surface struc-
- tures in highly urbanized areas such as the Ruhr and the English
Midlands led to intensive investigations as to how to predict
where and when subsidence would occur and how to prevent or
minimize such subsidence . Until recently most of the signifi -
cant research on surface subsidence was done abroad and has been
A
published in journals which are not easily obtainable or are in
a language other than English.
Mill
In Europe , most underground coal mining is done by methods
it different than those commonly used in the Boulder-Weld coalfield .
For this reason , one must be cautious in applying European theo-
ries of subsidence prediction to the Boulder- Weld coalfield where
the layout and condition of the mines are quite different .
In the last decade , land development has encroached on the
undermined areas of the Boulder-Weld coalfield , and the impor-
tance of subsidence has been recognized . This study is directed
— primarily toward the problems of land-use in those undermined
areas where subsidence has occurred in the past and may occur in
the future . Absolute predictability of the amount and area of
Ai subsidence in the Boulder-Weld coalfield is not possible with
the records now available .
l
L
In Europe land-use plans have evolved to take subsidence
ai into account, and detailed records have been maintained over
long periods of time . It is unfortunate that the level of record-
, keeping in the Boulder-Weld coalfield has not been geared to land-
use needs , because the present lack of data severely limits the
accuracy of subsidence prediction . Within the limitations imposed
by the adequacy of mine data , this study is intended to bring to -
-
gether a body of information that will be useful to planners and
geologists involved in bringing the land to its optimum use .
w
W
w
5
TABLE OF CONTENTS
'r Page No .
I . SUMMARY I- 1
Ir II . INTRODUCTION AND GENERAL DESCRIPTION OF PROJECT II - 1
Purpose and Scope of Study II-1
Location , Size , and Accessibility of Area II -1
Maps and Photos II -2
Previous Studies II -3
Acknowledgments II -3
III . GENERAL GEOLOGY III-1
Stratigraphy III-1
Fox Hills Sandstone III - 1
Laramie Formation 1I1-2
Quaternary Deposits 1II-4
Structure 1II-5
-Physical Characteristics of the
Geologic Section III -6
IV. REVIEW OF COAL MINE SUBSIDENCE THEORY AND
APPlICATION TO BOULDER-WELD COALFIELD IV-1
W
Basic Framework of Subsidence Problem IV- 1
Subsidence Model IV-2
Subsidence in the Boulder-Weld Coalfield IV-3
V . BASIC DATA MAPS - CONSTRUCTION AND ANALYSIS V-1
-- Ixtent-of-Mining Map V- 1
Depth-of-Cover Map V-3
Mine-Pillars Map V-6
'Probable-Thickness-of-Extracted-Coal Map V-8
Subsidence- Inventory Map V-10
i
VI . FIELD WORK VI- 1
VII . SPECIAL PURPOSE ACTIVITIES V1I-1
'Photogeologic Review VII -1
Comparison of 1949 -and 1969 Aerial
Photography VII-4
Low-sun-angle Photography VII-5
1
4
i
TABLE OF CONTENTS (Cont . )
Page No .
VIII . LAND-USE PLANNING AND MINE SUBSIDENCE VIII- 1
it Background VIII - 1
Subsidence-Hazard Map VIII - 3
Purpose and Procedures VIII - 3
Basic Assumptions Used in Map
Construction VIII -6
Hazard Classification System VIII -7
Safety Factor VIII -l0
Reclassification of Subsidence
-Hazard of Specific Areas VIII -11
fa Planning Review of Subsidence Hazards
of Specific Areas VIII -11
IX . CONCLUSIONS IX-1
X. SELECTED REFERENCES X- 1
A
0.4
APPENDIX A City, County , State , and Federal
Officials ; Miners ; Local Residents and
Others Interviewed During Coal Mine
Subsidence Study
S
r��
t
LIST OF ILLUSTRATIONS
FIGURES
Following Page
figure 1 . Location map Boulder-Weld Coalfield II - 1
figure 2 . Index map of U . S . Geological
Survey 7 1 /2 ' quadrangle -naps II -2
figure 3. Generalized columnar section
Boulder-Weld Coalfield III - 1
figure 4. Subsidence trough before mining
reaches critical width IV-2
figure 5 . Subsidence trough after mining
reaches critical width 1V-2
Figure 6 . Stereo triplet of Marshall area V-1
s
Figure 7 . Collapse over room of Marshall
No . 1 mine V- 10
figure 8. Collapse area over Lewis No . 1
and No . 2 mines V-10
figure 9 . Collapse over room of Lewis
No . 1 mine V- 10
figure 10 . Recent subsidence over Lewis No . 1
and No. 2 mines V- 10
Figure 11 . Large subsidence pit over the
Premier mine V-10
figure 12 . Large , well -developed subsidence pits
over roams of the Shanahan mine V- 10
Figure 13 . Collapse pit over the Allen Bond mine V- 10
Figure 14 . Numerous subsidence pits above an
unreported mine V- 10
figure 15 . Water-fill-ed depression over
Nonpariel mine V-11
i
is LIST OF ILLUSTRATIONS (Cont. )
i
:4 Following Page
Figure 16 . Broad swale over Lincoln mine V- 11
is
Figure 17. Broad sag over Morrison mine V- 11
Figure 18 . Water-filled depression just east
of Russell mine V-11
Figure 19 . Sand dune area one-half mile west
9f Firestone V-11
z Figure 20 . Subsidence over Strathmore mine ,
;W South Longmont Street , Lafayette V-11
Figure 21 . Subsidence over Strathmore mine ,
South Longmont Street , Lafayette V- 11
si
9 Figure 22 . Front stoop of house to the right
in Figure 21 V-11
Ar
Figure 23. Subsidence pit at a trailer court
in Lafayette V-11 ,
d.
Figure 24. Detail of subsidence pit at trailer
court in Lafayette V- 11
" Figure 25 . Garage over Black Diamond mine V-12
Figure 26 . Detail of garage shown in Figure 25 V-12
Figure 27. Damage to VFW hall , Main Street ,
Louisvill-e V- 12
Figure 28 . Abandoned building , Main Street ,
Louisville V-12 il Figure 29 . A .S . C . S . photo of area A , south of
Marshall , high-sun-angle photo VII --5
— Figure 30 . U. S . G . S . photo of area A , south of
Marshall , low-sun-angle photo VII -5
_ Figure 31 . A .S . C. S . photo of area B , north of
Marshall , high-sun-angle photo VII-5
I
u
LIST OF ILLUSTRATIONS (font . )
Following Page
le; Figure 32 . U. S . G. S . Photo of area B, north of
W Marshall , low-sun-angle photo VII-5
DRAWINGS
• ( In Pocket)
73-61 -1 Extent of Mining Map
n
73-61 -2 Depth of Cover Map
7361 -3 Mine Pillars Map
73-61 -4 Probable Thickness of Extracted Coal Map
7361 -5 Subsidence Inventory Map
Yr
7361 -6 Subsidence Hazard Map
•
Ss5
I . SUMMARY
y
This study is intended primarily to _provide basic data
x,
cnnterning mine sutsidence to local and state planners . It is
also intended that other investigators preparing -more detailed
studies of specific areas can use this -data. The project is
not an exhaustive treatment of mine sLbsidence . Rather, it
focuses on basic , subsidence-related problems and on practical
approaches to land development in the project area .
The purpose of this study is to -define the extent of minin-g
as accurately as possible , -commensurate with the scale of the
final maps , and to define the ptysical factors controlling sub-
ma
sidence . Such factors include the extent of pillar removal ,
the thickness of extracted coal , the de-pth of cover above -mine
workings , and the times of mine operations .
V
The scope of this study is confined primarily to a review
of existing data , a limited amount of field work , -and the pre-
y partition of this report. Maps , tables , and photegraThs illus-
trating the findings of the study are presented . Techniques
such as low-sun--angle -photosdraphy and aerial photo interpreta-
tion have been examined as possible tools to be used in subsi—
dence studies .
The most important product of this study is a subsidence
hazard ma-p which shows the sie-gr-ee of subsidence severity which
1 - 1
`r can be expected over the various undermined areas . State and
local planners and land developers will find this map particu-
larly useful in making initial judgements about the feasibility
of projects within the coalfield .
ra Prior to the design stage of many projects , it will be
necessary to gather additional information on the subsidence
hazards of specific properties . This information will he mainly
obtained from core drilling and geophysical surveys , and its
t4
acquisition is likely to be expensive . It is believed that , de-
spite the increased costs and problems brought on by undermining ,
y development in the Boulder-Weld coalfield can be undertaken pro-
Ftt vided that good design and planning practices are followed .
W
I
•
1 -2
II . INTRODUCTION AND GENERAL DESCRIPTION OF PROJECT
w
Purpose and Scope of Study
Yr The purpose of this study is to delineate the extent of
mining in the major portion of the Boulder-Weld coalfield as
accurately as pessible and to define the physical factors eon-
trolliny subsidence in the area . The scope of the study was
confined primarily to a review of existing data and to limited
fi-eld work . It included the preparation of this report end
its accompanying maps, which summarize and illustrate the findings
of the study .
This report is intended to provide basic data to local and
state planners and to other investigators preparing more de-
l . tailed studies of specific areas . A comprehensive discussion
of mine subsidence -and related problems is beyond the scope of
W
this study , which deals with the special problems of a limited
area .
Location , Size , and Accessibility of Area
The Boulder-Weld coalfield lies in north-central Colorado
about twenty miles north and northwest of Denver as shown in
Figure 1 . The study -area extends northeastward from Marshall
(lour miles south of Boulder) to jest north of firestone , two
miles east of Interstate 25 . Approximately 1b0 square miles
were studied . The area inxludes the southeastern corner of
44
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LOCATION MAP
BOULDER --WELD COALFIELD
Boulder County , the southwestern part of Weld County , and the
Li northwestern tip of Adams County .
Accessibility throughout the area is good. Interstate 25
DC
allows ready access to the northeastern -half of the area , while
the Denver-Boulder Turnpike provides access to the southwestern •
r
half. U. S . Highway 287 runs north-south and Colorado Highway
7 runs east-west through the area . In addition to the -paved
major highways , there is a network of un-paved roads throughout
c ';
most of the study area . Asa result, there are few points which
are more than a half mile from either a paved or unpaved road .
Maps and Photos
The study area is completely covered by U . S . Geological
Survey topographic maps ( Figure 2 ) at the scale 1 " =2.000 '
( 1 : 24000) and a contour interval of 1D `e-et . These maps are
sai recent anti vary in date of nublication from 1949 to 1967 . They
were subsequertly photo-revised in 1969 and 1971 , and it is the
revised editions which were used to construct the base maps for
this report .
Aerial photography of the area , taken in 1969 at the scale
1 "=1667 ' ( 1 : 20000) , was obtained from the Agricultural Stabili -
zation and Conservation Service (U . S . Department of Agriculture ) .
During the course of this investigation , specialized low-sun -angle
-aerial photography was made by the U. S . Geological Survey . These
-photos were taken in - the summer of 1974 and covered a few 1-finite-id
AN
I1 -2
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`'' Figure 2
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INDEX MA-P OF _U.S. GEOLOGICAL SURVEY
71/2` QUADRANGLE MAPS
Map published 1965
Map photorevised (1971 )
so
U
areas where there appeared to be subtle subsidence depressions .
It was believed that the long shadows cast while the son was low
in the sky would enhance the recognition of the depressions .
Le; The Geological Survey consented to our review of this photography
and furnished copies of it .
Previous Studies
Three previous major studies of the coal mining industry in
the Boulder-Weld coalfield have been made . The Colorado , School
of Mines Foundation ( Grosvenor , 1-964) compiled and published a
bi study which showed the location and extent of mining in the area .
In addition , the U. S . BureaL of Mines ( Lowrie , 1966 ) published
rr a study of the teal mining industry in the Boulder-Weld coalfield
u•:` which included a map showing previous mining in the area . This asi
map was updated and revised ( Colton a-nd Lowrie , 1973) , and pub -
lished by the 11. S . Geological Survey as a map showing mined areas
of the Boulder-Weld coalfield ,
Acknowledgments
Grateful acknowledgment is made to the Colorado Division of
Mines which made -coal mine data and individual mine maps avail -
able for use in compiling the maps included in this report .
Thanks are also given to Roger B . Colton of the U. S . Geological
Survey for _providing mine maps and information concerning the
coalfield and its -geology . The U. S . Bureau of Mines kindly
3
I1 -3
t .
prepared microfilms of unclassified mine maps for our use . Per-
i w somnel of C. S . Robinson & Associates provided helpful comments
on general subsidence problems in the area and allowed us to re-
view certain maps and core-hole information which they had pre-
; 71 pared for some of their projects in the -area . Mr . D . L . Scro
�s 99s ,
formerly with Amuedo and Ivey , was of great assistance during the
initial stages of this project. Finally , special thanks are ex-
tended to the various city and county officials , residents , and
coal miners of tht aria ( set Appendix A) who gave their time and
supplied useful information for this study.
Y11
1
11 .
II-4
4
III . GENERAL GEOLOGY
Stratigraphy
Two bedrock units, which diT generally eastward into the
1 Denver basin, occur within the area . The Fox Hills SandstonE
H
and the Laramie Formation are bath of Late Cretaceous -age . The
Fox Hills _crops out -extensively in the vicinity of Marshall but
in other areas is covered by younger deposits . It is -conform-
:;
ably overlain by the Laramie Formation, which contains the -coal -
beds mined in the Boulder-Weld coalfield . Outcrops of the
Laramie are rare in the area because of extensive Quaternary
deposits of colluvium, pediment gravels , and wind-blown mate-
rial . The colluvium is ubiquitous ; the pediment gravels are
most widasprea-d in the Marshall area ; and the wind- blown depos- ,
its are common in the Frederick-Firestone area . The general
character of the bedrock and unconsolidated units in this area
is summarized in Figure 3.
Fox Hills Sandstone - This formation is a massive , crossbedded ,
and ripple-marked sandstone, whic-h is in conformable cont-act
with the top of the underlying Pierre Shale . -The lower two-
thirds of the Fox Hills is fine- to coarse- grained and slightly
calcareous , while the upper one—third is fine- to medium-grained
and crossbeddesl . The thickness of the Fox Hills ranges from 60
feet to over 300 feet and appears to have been controlled by
fault movements contemporaneous with deposition .
III -1
Gf'igur-e 3
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PoNM0II0NS AND O1/WHIG Licirm IMICKNtSS
@nnN 50001 VISIONS Lln OL000 DISCFIPII0N
[v n.)pp ] 1NAnMNANr SURE[CIA' �q,
DI POSITS �, o L o
0-50 Io Han deposits and ped n imet gravel,
M
_12a2.&O0
°� O 0
a
H
V 600-Job Claystone, shale, sandy shale and lenticular
hods of sandstone and lignite
an
Loalhed No / 150-190 t /2-S Coal, octurs sporadically: of ismsted
lateral extent
Wneall
I. 95-145 Shale, sandy shale
4
•
("upper seam") 55-120 z 112-8 coal, lenticular, non pe rs I stem
Figleara
{. , 9717-- 10-/S Shale, sandy shale, or sandstone
I ill
Coalbd No. S 3s-NN I ly,-lo coal, ranges over a wide area, but is lenticular
("Middle , m )
r- -"- I-I6 Shale, sandy shale or sandstone
L-3 Sandstone, white to light-gray
•-- 4-5 Sandstone, shaly, white, coarse-grained
"C" Sandstone
tl-lo Sandstone, white, coarse-grained c t re[inna ry;
Lv
Lone hardened ripple marks at too
• --. 0-15 Shale and friable sandstone t
l,oa lbetl No 4 coat, len c;cola r. eiscgn cisoeus. fo one ndiely
- e�tral and soot nw-s to rn part or field 1-35 Shale, may pinch so Coalleds 3 and 4 coalesce
Clol d 80. 3 0 0-14 Coal, very bright, resinous contains
( wits Seam'') small amou
nt unt of pyrite
L. 3-10 Sandstone, white, fine-grained,
lignitic, shaly, quartiose
Coo Iced No Z l-I? Shale, brown to gray, Iignitic, contains
l'-/ coal bed near the base
a.m.
"M" Sandstone H-10 Sandstone. wiitee ,nd fIine-grained,
thin-bedded;n.� 4-8 5andstone, wbi te, brown stained; lenses
laterally to sandy shale
3-6 Sandstone, brown to huff, contains pelecypods
/-11
har
d,rd Sandstone, light gray, mottled with yellow,
bard, fine-grained, guartzoze
Coalbed No. I al thS 1-3 Coal, Coln, nonpersistent, grades laterally
r.--- --- - Into carbonaceous shale
— -- -3 Shale, gray to black, carbonaceous to shaly
..—, f0T HILLS SANNSi0Nt �- Sandstone, greenish huff, fine- to c se-
60-300 grained, icross-bedded; light yellow
Iwr lower
Part wading upward to light yi ll du and
white fine- to medium-grained sandstone
d
81
GENERALIZED COLUMN-AR SECTION
SOUL DE-R -WELD COALFIELD
„'9
a
J
L.
Laramie Formation - This unit conformably overlies the Fox Hills
Sandstone and is divisible into two
parts . The lower part, which
varies in thickness from 80 to 125 feet , is composed of samd-
r 4
stone , claystone , clay , shale , and coal . The upper part , about
600 to 700 feet thick , is made up of claystona and sandy shale
with some lenticular beds of sandstone and coal . The total
thickness of the formation ranges from 600 to more than -800 feet.
Seven coalteds of minable thickness occur in the Laramie ,
and they are numbered , from oldest to youngest, in ascending or-
. der . Coalbed No . 3, known as the "Main ” or " Gorham Seam , " has
been the most extensively mined , and is the most widespread coal -
ita
bed in the field . In certain localities , such as the Imperial
mine , the bed attains a maximal thickness of 14 feet. 8eoause
LA Coalbed No . 3 is the most widely distributed unit in the coal -
field , it is used as a stratigraphic datum to which coalbeds
above and below are referred .
1 . Coalbed No . 1 -and No . 2 are thin and lenticular , and
have no known mine workings within them. Coalbed
No . 1 lies at the base of the L-aramie and is about
65 feat below the No. 3 bed . Coalbed ND . 2 , also
called the "Sump Seam, " lies 10 to 45 feet below
the No . 3 Coalbed .
2 . Coalbed No . 4 is 1 to 15 fe-et above the No . 3 bed .
Iii the Marshall and Lafayette districts , Coalbeds
III-2
'
No . 3 and No . 4 coalesce to form one bed as much
as 12 feet in thickness . This conrbined bed has
been mined Extensively in these two districts and
in the Columbine mine .
r' 3 . Coalted No . 5 , locally called the " Middle Seam , "
is 35 to 80 feet above Coalted No . 3 . It has been
mined in the area west of Firestone and east of
LI Dacono .
r ' 4 . Coalbed No . 6 is known as the " Upper Seam" and is
55 to 120 feet above the Coalbed No . 3 . Tha bed
has been mined east and northeast of Erie by both
r
underground and strip mining methods .
5 . Coalted No . 7 , tha uppermost caalbed , occurs 150
4 to 190 feet above Coalbed No . 3. Because the bed
is thin and very local in occurrence , it has not
been -mined commercially.
The complex geological conditions of the area , namely , un-
even erosion and depositi-on along with intense faulting and
related foldin-g , make corr-elati-on of the coalbeds difficult and
in some places doubt-ful .
In a recent study , Weimer ( 1973) has suggested that the
sandstones -of the Fox Hills are a delta front deposit and that
4
I1I - 3
kl
V
the sandstones , claystones , shales , and coalbeds of the Laramie
Formation are a delta mlaim deposit . Unequal rates of deposi -
yJ
tion caused by shifting channels within this deltaic environment
produced lenticular coalbeds and lithnlogic units of highly
! v-ariable -thi-ckness and composition .
Fault movement -contemporaneous with the deltaic sedimenta -
tion also affected the depositional matter-ns of the two form-a-
tinns . This "growth faulting" allowed imcreased deposition in
the graben areas as these fault -blocks moved downward , whrl-e
deposition over the horst areas was reduced . As a result , vege -
tal matter , which later formed coal , accumulated in greater
ti
thicknesses in the grabens than over the her~sts .
Quaternary Deposits - During Quaternary time , streams des-tending
Sw ,
from the Front Range deposited a series of pediment gravels along
the mountain front. The Rocky Flats , Slocum, and Verdos pedi -
ment gravels cover the Fox Hills Sandstone and Laramie Formation
south and east of Marshall .
Recent aeolian sand dunes exist in the vicinity of Trederick
and Firestone . The sand is derived from the floodplain of
Boulder Creek, which lies to the northwest . The depressions as-
sociated with sand dunes and those created by wind scour (-defla
tiom ) are easily confused with depressions caused by surface
subsidence .
Colluvilim and soil derived by -Recent weathering of the
nonresistant Fox Hills and Laramie Formations are widespread
throu-ghout the project area .
I1I-4
L
Structure
irr
The study area is located on the western flank of the Denver
basin . -Regional dip -on this flank of the basin is gently east-
.' southeastward through nwst of the area , and regional strike is
approximately north-northeast . The north—south trending axis of
the basin passes through the -Frederick-Tireston-e area .
The study area is complexly faulted into a series of narrow
horsts ( upthrown blocks ) and grabens ( dawnthrown blocks ) . These
fault blocks avera-ge about five miles in length and are from 0 . 5
to one mile in width . The trend of these structures is generally
about N10°-20 °E , -and this is superimposed on a re-gional fault
wtrend of N45 °E . Reds in the grabens and horsts are folded into
synclines and anticlines , res-pectivaly . Offset on individual
faults may be as much as 500 feat, but the average offset is only
about 200 feat (Spencer , 1961 ) . Movement along the majority of
the faults was dip slip . Faults with large displacements are
natural barriers to mining and therefore define the limits of
many mine workings throughout the Bauld-er—Weld coalfield .
The faults are not obvious on the surface . Their reco-gni -
tian is based , for the mast _part , on subsurface data obtained
during coal Tine maipping and from core hol-es gilled during coal
exploration prolgrams (Sipencer , 1961 , Lowrie , 19_66 ) . During the
present work , it was not possible to verify , either on the ground
or on the aerial photos , the accuracy of the fault mapping done
by previous workers . The faulting shown on the map by Colton and
lII-5
• ea
Lowrie ( 1971 ) was adopter' for this study with only minor changes .
A few small faults shown on maps of the Baum and Boulder Valley
No. 3 mines were -added to the base map prepared for this report .
(
4 It is believed that there ara probably more faults within
the study araa thar hava bean shown om the present anal pravious
maps . Many of the faults shown on theses maps ara known only
from underground mine workings . It would be expected that an
equal number of faults would occur outside the areas ofrl
mininq
U but , owing to surface cover and lack of subsurface information ,
these faults have remained unrecosdnized.
ti.
Physical ICharacteristics of the Geologic Section
ti In the Boulder-Weld cnalTield all of the mined coalbeds
are within tht Laramie Formation . This formation is composes'
of interbedded shales , claystone-s , sandy stales , coalbeds , and
iti
thin beds of sandstone . Generally, such rock strata are inca m-
patent with respect to stresses imduoesi by underground mine
operations . If left unsupported they are subject to fairly
rapid coll-apse after mining .
Local coal miners who have worked in the Columbine , Washing-
ton , Eagla , Imperial , and -Hiway minas report that while the roof-
, stone of these mines is prone to -collapse , an " ironstone" layer
occurring 12 to 80 feet abava the mine workings tends to stop
further upward staving . This ironstone is one- to five-feet
thick and may be the quartzose , concretionary " C" sandstone
I1I-6
described by Spencer ( 1961 ) . In the past , the ironstone cre-
ii ated problems wherever it occurred immediately above the mine
workings -because of a tendency to bend rather than break . The
Lbending created a " squeeze" on nearby pillars of coal and made
ra it impossible to mine them safely . The floors of the previously
mentioned mines were soft shale or clay, and a "squeese " on the
pillars was sometimes relieved ty a "heave" or rise of the
adjacent mine floor .
It is possible that the resi-stant ironstone layer has pre—
vented caving from reaching the surface in areas of the Colum-
bine , Washington , Eagle , Imperial , anti Hiway mines . If so ,
ti
voids or untompacted rubble may remain beneath these areas .
Similar conditions may exist over -other mines of the area as
,
�r well .
The material that forms the floor of a mine also plays a
part in subsidence . A hard sandstone floor might support a
standing pillar of ctal, while a floor of soft shale or clay
( underclay) would allow the pillar to sink . The sinking would
continue through the thickness of the soft material and would
cause subsidence of the overlying strata. Soft shale and clay
floors are reported in the Baseli-ne , C-olumbine , Eagle , Eldorado ,
Niway , Imperial , Industri-al , Monarch No . 2 , New Gorham , Para-
mount , Pluto , Standard , Vulcan , Washington , and Withe rtee mines .
Hard sandstone , shale , or " slate" floors exist in the Black
11I -7
Diamond No . 2 , Boulder Valley No . 1 , Evans , Puritan , Shamrock ,
and Star Mines ( L-owriE , 1966 ) . It should be anticipated that
mines with hard floors and standing pillars may have a greater
percentage of remaining void spate than rthose with soft floors .
fi
V
Wtl
III-8
c
1,4
so
L
IV . REVIEW OF COAL MINE SUBSIDENLE THEORY AND
APDLICATIOi1 TO BOULDER-WELD COALFItED
Basic Framework of Subsidenca Problem
Tha basic questions asked with regard to subsidence are
few in numbar a-nd seem dacaptively simple tD ansvrer . Givan an
underground opening of known vertical and horizontal dimensions ,
one wants to know:
1 . How much vertical subsidence will there be at the
surface? ,
2 . What wiT1 ba the lateral extant of surface subsidence?
3. When has ( or will ) subsidence occur?
4 . Has the process of subsidence teen continuous from
beginning to end or has it been episodic?
Generally , the subsidence theories used to answar these
questions are based on the assumption that extraction of coal
has been complete and that a continuous unsupported void has Lean
created . Thesa conditions do result where lontwall mining meth-
ods are utilizad , as in Europe . However , in the Boulder-Weld
coalfield , mining was done ty the room-and-pillar method , and the
underground conditions created cannot easily ba made to fit Euro-
paan subsidence models . It is not within the scope of this report
to go deeply into the many facets o-f subsidence theory , but a re-
view of certain aspects is timely and may to beneficial . For
more det-ailed descriptions of subsidence theory the reader is
IV-1
referred to a recent work by Zwartendyck ( 1973) . This publica-
tion gives a thorough summary of the development of subsidence
the-ory and contains an extensive bibliography .
Subsidence Model
(—' Modern attempts to relate surface subsidence to underground
mining make use of the concept of the subsidence trough . The
concept takes into account one of the most important observed
facts regarding subsidence ; namely , that the surface area af-
fected is larger than the mined-out area . Because the concept
can be dia-grammed , it provides an easy way of looking at, and
describing , subsidence problems .
Figures 4 and 5 illustrate diagrammatically the development
of a typical subsidence trough . The extraction of coal removes '
u
support from the overlyinsg strata causing them to sag into the
void space created . The sag is propagated upward to the surface ,
and , it follows , that the maximum surface subsidence tan to no
.. greater than the thickness of the coal bed mined . However , the
lateral extent of subsidence at the surface is greater than the
extent of underground mining . The surface position of the bound-
ary between areas of subsidence and no subsidence is defined by
the " angle of draw. " This is the angle between a vertical line
and a line drawn from the point of zero surface subsidence to
the edge of the underground opening . The angle of draw varies
IV-2
a a
b <A13
4d
Angle 9f draw
I A_ A— A
a a
2-r < i 0
Direction of Mine Advance
1 Subsidence Trough before Mining Reaches Critical Width
Figure 4 As a mine face ativanxes from point 1 to point 2 the
it
surface subsidence which occurs will t-ake the form of a shallow
trouigh , shown as curve aba. The greatest amount of subsidence
for a -given width of mine opening will be equal to ab and will
be located over the center of -the opening at b . The amount of
Nil surface subsidence will -diminish on either side of b until , at
points a and a', it is nil . Since as >AA it can be seen -that
the area affected by surface subsidence is greater than the
mined out opening . Subsidence at will never be greater than
AB and will in fact be less than AB until a certain " critical
wi-dth" of the mine opening is reached. The line aA tonn-e-cts
the point of nil subsidence and the edge of the mine opening
and forms one side of the "angle of draw . " In British and
American literature this angle (d) is measured from a vertical
line ; in Europe-an references it .is measured from a horizontal
line .
m
L
S
L
a
k^ -- Smax ---
Y rb
ab Smax <A B
d, =Arrgle of draw
Critical Width A. A
' I I
L B _L
e B
rzi
Subsidence Trough after Mining Reaches Critical Width
Fisdure 5 -As the mine face advances , ab and ankle awi11 increase
yy until a "critical width" of the mime _opening is reached . At this
point the amount of vertical subsidence , ab , reaches a maximum
value , Smax . Further enlargement of the mine opening will subject
a larger and larger area at the surface to maximum subsidence
though Smax itself will not increase . In three dimensions the
deepest part of the subsidence trough will change from an axial
line , as would ba the case in Figure 4 , to a flat b-ottom as shown
above .
a
from 25 ° to 35 ° in most instances . The larger the angle of
draw, the wider will be the zone on the surface in which sub-
sidence should occur. By using the largest of several possible
ti
; angles of draw a greater margin of safety is established far
thos-e areas lying outside the boundary of possible subsi-dence .
Subsidence usually _occurs gradually when it is concurrent
with mining . After cessation of mining, subsidence may continue
to _occur in a steady, gradual manner, or it may stop -for a pe-
s
tA
I‘ha riod , to be followed by failure at some later date . In some
European mining -districts , sufficient information has been col -
t lected so that the rate , amount, and direction of subsidence can
be tffectiv-ely controlled . In order to accomplish this , much
basic information had to be gathered , and special mining pro-
grams had to be _designed . Subsidence problems are much mare
difficult to salve in areas where mining has occurred in the
past , and where records da not -include the data needed to devise
means of controlling subsidence . This is true of areas which
have been mined in the past in the Bauldar-Weld coalfield , but
it need not be true of areas mined in the future .
Subsidence in the Boulder—Weld Coalfield
In the Boulder-Weld coalfield , the usefulness DT the subsi -.
— dente trough concept is limited . The model on which the concept
is based is an underground opening which is unsupported and free
IV-3
to collapse as the mine fate is advanced . This is the common
a co-ndition in Europe where the longwall methnd o-f mining is used ;
in the Boulder-Weld coalfielsi the room-and-pillar methnd was
U used almost exclusively . Even though it was common practice to
remove the coal pillars after th-e rooms of -a mining panel were
fully developed , it was not possible to recover all th-e pillars .
Some were left to protect main shafts and haulagew-ays ; others
were left beca_use they could not be mined safely . The pillars
4
which remain in the mines continue to support the roofs of tinder-
ground openings arid prevent subsidence troughs from developing
in an orderly -and predictable pattern . Depending on the number,
dimensions , and distribution of pillars which remain in a mine ,
the width of mine opening could be kept below the critical width
for that mine , and subsidence would he prevented from reaching
its potential maximum. Surface subsidence would remain below
Si
this maximum until the pillars finally gave way sometime in the
future .
$
I1-4
V . BASIC DATA MAPS - CONSTRUCTION AND ANALYSIS
y
Extent—of-Mining Map
In This map delineates areas of coal mining in the Boulder-
Weld coalfielsi ansi thus , partly -defines the limits of mine sub-
_" si-demce hazard . Previous work on the extent of mining in the
caalfield was conducted by the Union Pacific Railroad Company
( 1964) , Grosvenor ( 1969 ) , Lowrie ( 1966 ) , and Colton and Lowrie
u ( 1973) . The extent-ef-mining mam refines the boundaries 'of the
coal mines as shown on earlier, published ma-ps , and shows the
le" differences which exist between this study anti the work of
Colton and Lowrie .
S
This map was compiled by visually reducing the outlines of
individual lard scale 1 "=200 ' ( 1 :2400) mina maps to a scale of
1 "=2000 ' ( 1 : 24600) . 14ost mf these maps are on file with the
rl
Colorado Division of Mines , some are in the microfilm collection
of the U . S . Bureau of Minas , and a few are in the collection of
Roger B . Colton , U. S . Geological Survey . In some are-as , air
photos and field observatimns of subsidence were valuable in re -
—
defining the extent of underground workings and in determining
the existence of several minas which had not been plotted by
previous workers . Such areas included the Marshall #1 , Marshall
?3, fox , Black Diamond , Old Black Diamond , and Allen Bend mines ,
mined areas around the Blue Ribbon adit, and an unknown mine in
SE 1 /4, NE 1 /4 , sec. 18 , T . 1N . , R . 68W . (Figures 6 , 13 and 14) .
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The reliability of the extent-of-mining map is dependent
upon several factors . First, it is limited by the -accuracy
of the original mine surveys . Post-1920 mine maps appear to
be more carefully surveyed than earlier ones , which may be mern
sketches of the mine layouts . The earlier maps may also lack
accurate reference to the land surveys shown on surface maps .
Second , many of the smaller mines and some of the earlier mines
LI have been recorded with the Colorado Division of Mines , but no
maps exist for them. Third , areas of " chiseling" or "poaching "
of coal are not shown on the mine maps . The coal removed in
this unauthorized manner was usually taken from the barrier
w pillars between mines . -Although the problem has diminished in
recent years , miners can point to areas where coal has been
poached as much as 200 feet beyond mine boundaries . Some
v miners -Peel that wherever royalties are being paid on coal ex-
it.
tracted , poaching is common , and thus one might suspect inac-
curacies in even the more recent mine maps . Lastly , it is
evident from an examination of the only available maps of some
mines ( eg . Red Ash-Pittsburg , Marshall No . 1 ) that the maps do
not show the maximum extent of mining . In the case of the Fox
mine , surface collapse features show that the actual limits of
mining extend beyond the boundaries shown on the mine map .
. Given the above factors , it is estimated that mine limits are
within 500 feet of where they are plotted in at least 90% of
the instances .
V-2
Y
'+a
L
Discrepancies which exist between this study , the Colton
and Lowrie study ( 1973 ) , and the Lowrie study ( 1966 ) are gen -
erally differences in the limits of the mine boundaries and may
be accounted for by differences in plotting techniques , or by
Li the utilization of different mine maps . Some of the more impor-
tant areas of discrepancy are :
1 . A small mine north of the Fireside (NE 1 /4 , sec . 7 ,
T . 1S . , R . 69W . )
2 . The area west of the Acme mine (SW 1 /4 , sec . 8 ,
T . 1S . , R .69W . )
3. The area northeast of the Vulcan mine (NE 1 /4 ,
sec. 10 , NW 1 /4 , sec . 11 , T. 1S . , R. 69W . )
"' 4 . The area east -of the Imperial and Eagle min-es ( SW
1 /4 , sec . 11 , NW 1 /4, sec. 14 , T . 1N . , R . 68W . )
5 . The southeast side of the Puritan mine (SW 1 /4 ,
sec . 2 , T . 1N . , R . 68W . )
W 6 . A lobe of the Lincoln mine (SE 1 /A , sec . 24 ,
se T . 1S . , R . 68W . )
7 . A mine south of the Witherbee-Peerless complex
( SW 1 /4 , sec . 4 , T . 1N . , R . 67W . ) .
This study , utilizing the available mine maps , and to some
extent , interviews with residents and miners , could not confirm
the existence of mine workings in these areas .
Depth-of-Cover Map
The purpose of the depth-of-cover map is to show the thick-
-- tress of overburden above mine workings . To simplify the over-
burden thickness determinations , a 50 foot contour interval was
used .
V-3
In obtaining the depth-of-cover values , it was necessary
to determine the elevations of the mine workings . When avail -
kg
able , this data could be taken from individual mine maps , from
a
�r records of shaft depths as reported to the Colorado Division of
Mines , and from drill -hole information of the Rocky Mountain
Fuel Co. With this information , a structure contour map of the
top of the extracted coalbed was made for each mined area . A
surface topographic map was superimposed on this map , and strut-
u ture contour v-alues were subtracted from surface contour values .
The resulting overburden thickness values were plotted to the
extent-of-mining base map and were contoured using the 50 foot
interval . For mined areas with multiple seams , the overburden
above the highest mining level was contoured .
{.+ The main problem involved in determining the overburden
thickness is the lack of elevation data on many mine maps , es-
pecially pre- 1920 mine maps . In such cases , drill -hole data
and shaft-depth records were utilized as an approximation of
the depth to mine workings . If these data were lacking , an es -
- timation of overburden thickness was made by 1 ) extrapolating
structure contours from adjoining mine workings where the same
coalbed was being mined , 2 ) interviewing residents who had
drilled water wells into the mine workings , 3) interviewing
miners who had worked in the mines , and 4) relating the charac-
ter of subsidence in the unknown areas to the character of
V-4
b
subsidence in other areas whEri the overburden thicknesses were
ti known . In all cases in which only one data paint was available ,
the coalbed was assumed to be horizontal , and overburden thick-
r , ness was determine-d accordingly . The data available and the
method used in obtaining overburden thickness determinations for
different mined areas are shown on ,the mad .
The sources from which mine data were obtained generally
gave elevations to the nearest -foot and in same cases to the
! 'I nearest 0 . 1 foot. Considering the 50-foot contour interval
used , the depth-of-cover ma-p is believed to be fairly reliable .
Because of the scarcity o-f mine elevation data , all available
s1 information sources sometimes had to be utilized to make a rea-
rs
sonable estimation of depth of cover . Where information was
sufficient and where different methods of determining overburden '
were available , an effort was made to cross-check the overburden
determination by testing one method against another . For ex-
ample , elevations taken from mine maps were checked against data
from nearby drill holes .
Incongruities between overburden determinations of differ-
ent mined areas on this map are attributable to four variables .
First , topography above different mined areas varies over the
coalfield . Because overburden thickness in areas of nearly hori -
zontal beds is largely a function of topography , it can be ex-
pected that the depth of cover will vary with the topography
u
— V-5
i*
•
throughout the area . Second , there is a considerable variation
in the stratigraphic interval betweenthe various coal seams
throughout the coalfield . Third , faults disrupt the continuity
r'
of strata in the coalfielsl, ansi the resulting offset of coal
a seam-s has produced differences in overburden thickness in adja-
C1
cent mined areas . Finally, there is a slight amount of dip to
the south and east throughout the study -area . Coalbeds become
progressively deeper, and overburden increases in thickness , in
-- these directions .
Mine-Pillars Map
* The purpose of the mine-pillars map is to delineate within
each mine , -and mine level , the areas where pillars of coal have
been removed ( "pulled" or "mined--out" ) and the areas where pil -
lars were left standing . It is important to realize that pillars
which are shown in place en the most recent mine maps may have
deteriorated , and possibly collapsed , since the maps were made .
The reliability of the map showing areas where pillars have
been pulled is commensurate with the accuracy and completeness
of the original mine maps .
Individual coal mine maps with a scale of 1 " =200 ' ( 1 :2400)
were reviewed to determine the areas of -pillar extraction and
the areas of remaining pillars . The areas of pillar extraction
and pillar non-extraction shown on the individual mine maps
were visually reduced to a scale of 1 " =2000 ' ( 1 : 24000) and were
s
compiled to a copy of the extent-of-mining map.
V-6
1
It became apTarent during the compilation of the mine—pit -
Lars map that many of the individual mine miaps were of dubious
accuracy -and are considered unreliable as far as delineating
Is; areas where pillars were pulled . Often , the individual mine
maps merely inditatexl that large areas are "worked-out;' but did
t. a
not show the outlines of pillars which were left standing and
pillars which were pulled . On such maps, it is impe ssible to
tell how many -pillars , if any , remain in these "worked-out"
i
areas .
In fact, miners report that an average of 30 of the onig -
4 inally available 'coal must be left in a mine , even under the
. best of conditions . Usually , the {percenage 9f coal remaining
is mu'ch higher , and commonly 40% to 50% of the coal originally
sa in place is left behind . This residual coal is left in the
backs of mines as a means of roof support , in mine floors , and
6.0
in pillars . Some pillars are purposely left to protect main
haula-geways and shaft areas ; others are left in order to maintain
a margin of safety while nearby areas are worked . If it is as -
sumed that 3D% of the coal originally in place was left behind
when a given area was " mined-out,' it is probable that some pil -
lars still exist in that area even though active mining ceased
years ago .
The presence or absence of standing pillars underground is
_ critical to the question of mine subsidence potential . If near-
1 ly all pillar support has been removed beneath an area , it is
V-7
PI
likely that subsidence over that area occurred shortly after
the cessation of mining and is mow -essentially complete . How-
ever , in those areas where 'pillars are still standing it is
likely that subsidence is not complete . Eventually the pillars
in these latter areas will collapse -due to the separate or com-
bined effects of air slaking , ground water, stress build-up from
other parts of -the mine , and increased surface loading -from newly
constructed buildings . Therefore , areas shown on the mine-pillars
map as having remaining pillars should be regarde-d as potentially
more hazardous than those areas which are shown as having most
L of the pillars removed .
Probable-Thickness-of-Extracted-Coal Map
The purpose of the probable-thickness-of-extracted-coal map ,
is to determine the maximum possible heigght of the void spate
which could exist as a result of mining activities . The height
of the void space is assumed to be equal to the thickness o-f the
coal extracted in a given area . This thickness would then be
equivalent to the maximum amount of surface subsidence which
could occur over that area .
It should be -mentioned that , in many cases , mining practice
was to leave a certain thickness of coal in the mine roof to
provide support for the mine opening . Where this practice was
followed , the full height of the coal was not removed. Since
no records were kept of the amount and distribution uf roof coal
WAt
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„i
u
left in the various mimes , it was decided to isdnore this possible
discrepancy and to assume that in all cases the thickness of the
coal extracted equalled the total thickness of the coal in place .
In compiling the probable-thickness-of-extracted-coal map ,
the following procedure was adopted . First , coalbed thickness
Li
data were accumulated from 1 ) mine maps and mine history reports
of the Colorado Division of Mines ; 2) drill -hole records of the
Rorky Mountain Fuel Co . ; 3) coalbed isapechous (equal thickness )
L maps made by F. D. Spencer and included in Lowrie ' s report ( 19-66 ) ;
and 4 ) information obtained in interviews with local coal miners .
Spencer ' s isopacheus maps cover the area north of Baseline Road
u (40° N . latitude ) and supplied most of the information used in
making the probable-thickness-of-extracted-coal map in that area .
The other three sources provided the -data which was used for the
area south -of Baseline Road . The thickness information was plot-
ted on the extent-of-mining map and was contoured using a five -
foot imterval . The values used in contouring areas underlain by
multiple- level mining were obtained by summing the void spaces
heights of the individual levels .
It sheuld be noted that the estimated void space in certain
mined areas , such as the Nonpariel -Centennial (Old) mine complex
and the Black Diamond No . 2 , is based on widely spaced data
points . As a result of this scarcity of data , the map may not
represent the actual variations in coalbed thickness within
J these mined areas .
',i-9
iY
LI
In spite of the above problems , the map is considered re-
liable within certain probable minimum and maximum void-space
heights . The heights of mine openings were seldom less than
five feet because of Economics and the limitations of machine
Gj mining (after 194-6 ) . Since there are few areas where coalbeds
attain a thickness of more than 15 feet , it can be assumed that
_ mine openings are usually less than that figure . The map shows
that most of the maximum -possible subsidence falls within the
5 to 10 foot range , and that the are-as of maximum possible sub-
sidence greater than 15 feet occur mainly over those localities
itoo
where there was multiple-level mining .
Subsidence-Inventory Map
The subsidence-inventory map is the result of a program
composed of field observations and interviews with local resi -
r
ila dents . The purpose of this program was to locate the known
subsidence areas in the Boulder-Weld coalfield . Areas of pre-
sently ( 1974 ) observable subsidence and areas of reported , but
no longer observable , subsidence were noted . Also , observations
were made in areas where there is some question as to whether
el114.
the -area was even undermined .
A number of criteria were used to determine where subsi -
dence had occurred . In the field , pits and collapse features
over areas of known shallow mining were considered positive
identification features of subsidence ( Figures 7- 14) . Closed
V 10
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Figure 7. Collapse over room of Marshall No . 1 mine . The
collapse area is -approximately 15 feat by 30 feet and is
about three feet deep . From five -to tan fact of co-al ware
74 extractedfrom this area at a depth of about 50 feet . Lower
slopes of hill in background are also shown in Figures 6
(Area -A) , 8, 31 , and 32 . Locality 4, subsidence-inventory
map .
y -
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144
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Figure 8 . Collapse area over _Lewis No . 1 and No. 2 mines .
Rooms of these mines are expressed by depressions and pillars
by ridges . Mining was at a depth of less than 100 feet , a-nd
five to ten feet of coal was extracted , _Compare joints in
exposed sandstone in foreground with same area shown on Fig-
ures 31 and 32 . Locality 7 , subsidence- inventory map .
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Figure 9 . Collapse over room of Lewis No , 1 mine . Pit is
about ten feet by 15 feet and is three feet deep . From five
to ten feet of coal was extracted a-t a depth of approxi -
mately 50 feet. flume carrying irrigation water in middle
background must be periodically re-set because underground
mine fires in this area are causing continued subsidence .
Locality 7 , subsidence- inventory map .
t 4 rn t p
Figure 10 . Recent subsidence over Lewis No . 1 and to . 2 mines
brought on by underground fire . Note three puffs of grayish-
"_ white smoke . Mine is less than 50 feet deep and is -above
water table . Collapse and fracturing of overlying beds permits
circulation of air for continued combustion . Between localities
7 and 8 , subsidence- inventory map .
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Figure 11 . Large su-bsid-ence pit over the Premier mine . The
pit is approximately 30 feet in diameter and eight feetzieeo .
Five to ten feet of coal was mined at a depth of about 100
feet. Near locality 1 , subsidence- inventory map .
'{kfe a 7/r.s 9
F4 � ryi agiVi�..�, 'M�lM1 7h 4.1C , e. �.. '4• •
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Figure 12 . Large , well -developed subsidence pits over rooms
of the Shanahan mine . Pits are eight to ten feet deep and
are 15 to 25 feet across . The coal seam at this mine was un-
usually thick ( 10 to 15 feet) , which accounts for the large
amount of verti cal subsidence . The mining depth was less than
50 feet. Locality 21 , subsidence-inventory map .
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yJn I �'� 1C � 1 ' tyti t ✓',� xlil
• R 1 Y'' t �nit, rt i,�
r � � ' � HJ.y��I, x,�
1r y9 'A Y • Fl... xtit T j55pp,,
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Figure 13. Collapse pit over tire Allen Bond mine . Features
such as thi-s aided in locating the true position of the Allen
his Bond mine . The previously reported position of the mine
showed no evidence of surface subsidence . A thick ( 10 to 15
feet) coal seam was mined here at a depth of approximately
• 50 feet. Locality 19 , subsidence-inventory map .
•
n, .v, ...- sue.."�,r r' e+�'yf ..a^�✓�� +:^
Figure 14. Numerous subsistence pits above an unreported mine
just east of Erie . No maps were found of this mine in the
files of either the Colorado Division of Mines or the U . S .
Bureau of Mines . Examples such as this illustrate the neces -
sity for field reconnaissance of all prospective development
areas . Based on conditions in nearby mines , it is estimated
that five to ten feet of coal was extracted at depths of 50
to 100 feet. Locality 67 , subsidence-inventory map .
depressions ( Figure 15 ) , features of less positive subsidence
evidence (swales and broad ground "sags , " Figures 16- 17) and
areas of reported but unverified subsidence were also noted .
Yi Recent (1969 ) aerial photographs were of some use in delineating
areas of subsidence over areas of shallow mining such as the
Li
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Fox, Allen Bond , Pluto, Northwestern , and an unknown mine in NE
1 /4, sec . 18, T. 1N . , R. 68W . In Weld County , older ( 1949 ) aerial
photographs were used to determine an area of subsidence over
1u the Shamrock mine (depth of cover about 100 feet) . This area
was leveled and reclaimed for farming in 1956 and all surface
evidence of subsidence was obliterated at that time .
Interviews with local residents were valuable in pinpointing
areas where subsidence and related structural damage had occurred
in the past. Interviews with miners were especially useful in
determining where subsidence had occurred because these men were
aware at the time that a given area was being undermined , and
were watchful for surface effects . Field observations of struc-
tural damage to buildings , streets and sidewalks ( Figures 20-24)
were also used to determine subsidence occurrence .
Numerous complicating factors were encountered in the iden-
tification of subsidence features . In addition to the land-
leveling program conducted by the U. S . Department of Agriculture
over the Shamrock and other mines , individual farmers sometimes
restored land damaged by subsidence . Shafts and pits were filled
,01 with debris and were then covered with topsoil . Subsidence evidence
also is masked by crops and tillage . This is probably the case
V 11
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Figure 15 . Water-filled depression over Nonpariel mine . De-
pression is partially closed by base of section line road .
This is a typical example of a questionable subsidence feature .
Near Near locality 40 , subsidence-inventory map .
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is -f,. -'°tom' ffcgr -' t,.t�-•-fr.--�'.:.
., ,,.�> f ,.�e t •y,Sr Wi.,.jY .e�j� •a.J wyyf
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Figure 16 . Broad swale over Lincoln mina . The swale in mid-
- dle foreground is fortuitously outlined by shadows Last by
setting sun . Normally , this feature would be har-de to discern
by the unaided eye since it is quite broad ( 100 feet) and is
only two or thre-e feet deep . The mining depth at this locality
is 150 to 200 feet and five to ten feet of coal has been ex-
tracted . Tipple of the Lincoln mine is in background .
Locality 77 , subsidence- inventory map .
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tgjter
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M1fJ'�L,+w 1' ♦ < ,L y b F .-+ , 3 C'tR° t `] ,�`
xN PS,yht,p i 1 rja'� V'�i'�f} y,�tyh ,� "`ti8"Ysa.
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Figure 17. Broad sag over Morrison mine . Depression has a
relief of only a few feet and does not really provide defini -
tive evidence of subsidence . Careful survey measurements
i„ might show that the depression is closed , and this would
strengthen the case for a subsidence origin . Fiv-e to ten feet
of coal were extracted at depths ranging from 100 to 150 feet.
Near locality 69 , subsidence- inventory map .
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Figure 18 . Water—filled depression just east of Russell mine .
This depression lies a few hundred feet beyond the reported eastern limit of the Russell mine . This may be a case of sub-
sidence over an are-a which was poached and the mining was not
reported . The shallow ( one to two feet) depression may also
be the result of wind erosion . Locality 94 , subsidence-
inventory map .
4
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v x�i il,�w4�-^�B�"T�} '.�''r 4,4v, 44%.0 !,,•.4”,,r3'�'�.}� ,Nµµµ���r��3� �a �
Y / S IW 9 9
�'. . � eAgs. "Tn„t Y ',ea ` r��"hd,ICY�+"4 " ��
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Figure 19 . Sand dune area -one-half mile west of Firestone .
Undulations -of fence line indicate the irregular nature of the
topography . This area overlies the Frederick mina where a
five to ten foot coal seam was mined at a depth of 100 to 150
feet. The poor , sandy soil of the area and the close proximity
of an undoubted dune fiel-d indicate that the irregular topog-
raphy` is due to wind deposition rather than subsidence .
S
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Figure 20 . Subsidence over Strathmore mine , South Longmont
Street, la-Fayette . The low sag in the front lawn and the
— trout walk are subsidence related . This "subsidence " is ac-
tually the result of compaction of trash and rubble used to
fill a true subsidence -pit which formed in 1956 ( Denver Post ,
— May 27 , 1956 ) . There was rapid collapse and overnight develop-
ment of a hole 40 feet deep and 15 to 20 feet square . Locality
55 , subsidence— inventory maip .
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vigai ama-Li .
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Figure 21 . Subsidence over Strathmore mine , South Longmont Street ,
is
Lafayette . The most recent damage to -the street has not yet been
fully rep-aired . Note unpaved section of street and sagging side -
74 walk . The to-al seam in this area of the Strathmore mine was quite
— thick , and the probable thickness of coal extracted was 20 to 25
feet. Depth of mining was 100
to 125 feet. Locality 5 , sub•-
u sidence - inv-entory map .
1%; cat .,;., ;„4 y r ;
al
. �
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.', r .
T Figure 22 . Front stoop of house
— � r to the right in figure 21 . This
cl•' �
' r ' ' house is immediately south of
y � �i` �1 home shown in figurn 20 . The
i iIi ; walk has pulled away from the
J ' stoop and it in turn has pulled
away from the house . Bricks
have been jammed beneath the
. ,• ' I 1 house and beneath the stoop for
'114: k
4; temporary support . Locality 55 ,
subsidence- inventory map .
-.terra T,j '.. <• t1.,
y .-.r .1 v' _... ._.. - - .7y iy2
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Figure 23 . Subsidence pit at a trailer court in
y Lafayette . Ground began caving in the early morning
of August 29 , 1974, and continued to enlarge until
noon . Final dimensions of the subsidence pit were
24 X 18 X 15 feet . The subsidence occurred in a
vacant area and only minor damage to utility lines
was sustained . Had one of the large " mobile" homes
shown in the background of this figure been parked
on top of the subsidence area it is doubtful that it
could have been moved quickly enough to save it .
This recent avent is a dramatic example of continuing
21
subsidence problems in an area where mining ceased
over half a -century ago .
Ih`.
.n la ♦ .R4 �'T 5 .1 4 g: rid. T 144, ,Arw ` '0:Hy
r :4,i ..,141Ans
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figure 24 . Detail of subsidence pit at trailer court
in Lafayette . The upper 12 feet of -the subsidence
pit walls are composed of sand and silt size material ;
the lower three feet of the pit -consists of bedded ,
angular gravel . The subsidence occurred over the
Strathmore mine which lies at a -depth of 100 to 130
feet and was last worked in 1919 . Normally only one
level was worked in this mine but in the area of the
trailer court two levels were mined and it is esti -
- mated that -a total void space -of 20 to 25 feet was
created .
a
4
in a great many areas of the coalfield , notably over the New
r7 Crown , Matchless , Helca , Rex #1 , Mitchell , Morrison , Frederick ,
Puritan , Grant, and Witherbee-Peerless mines .
lr Another complicating factor in subsidence identification
is that surface effects above deeper mines (greater than 20D
r4
feet) are likely to be faint. Unless observed immediately after
mining , they may soon be totally obscured . Subsidence over
deeper mines is not represented by well -defined pits and swales ,
1
but is typified by broad depressions several hundred yards in
diameter . Even broad depressions over known mined areas may be
suspect because " blowouts" (wind-eroded depressions ) occur in
+ the area , especially around Frederick and Firestone ( Figures
18-19) .
Damage to structures built over mined areas cannot always
be attributed to surface effects of caving in the mines . Other
factors which must be considered before ascribing damage to
subsidence are 1 ) instability of the slope on which the struc-
ture is built, 2 ) compaction of fill , 3) swelling clays around
foundations ( Figures 25-26 ) , 4) thermal effects , 5 ) faulty de-
sign or construction ( Figure 27 ) , and 6 ) gradual structural
deterioration with time (Figure 28) . Furthermore , minor struc-
tural damage to highways , railroads , and irrigation systems , as
a result of subsidence , is usually repaired on a routine basis .
Lastly , subsidence damage to residences may be repaired or dis-
guised so that property values will not be lowered .
V- 12
u
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ri uln'�J� f tirrLb
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Figure 25 . Garage over Black Diamond mine . At this locality ,
r,,; five to ten feet of coal were extracted at a depth of 150 to
200 feet . The garage and house are fairly isolated , so that
the surrounding terrain is relatively undisturbed by man . No
pits , swales , or other indications of subsidence were found in
the -fields -around the house . For this reason , the damage to
the garage is thought to be due to swelling soils . Note bow
in roof line along gutter. Locality 15 , subsidence- inventory
�- map .
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.- !'0rrrlrr ^s+rrrr }�� .■ nR
fi�
,rsx��ilFT�csiTrri
i ' >, .„,12 a Fain ��m
1".Min INILI Mill Iblesa=liiiiallts
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Figure 2b . Detail o-f gar-age -shown in Figure 24. Stairstep cracks
in brickwork are one—half inch wide . Window has rhomboid shape ,
and glass is cracked . this damage is similar to what one might
expect if ground ben-eath founiiation had subsided . Locality 15-,
subsidence-inventory map .
a
V I
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Figure 27 . Damage to VFW hall ,
la j Main Street , Louisville . This
ra Vi part of Louisville was under-
mined\ many years ago . A s-eam
Li. 1 113 to 15 feet was extracted at
''` � '' a depth of about 100 feet . Be-
/ illa� cause the mining occurred so
• long acrd , it is thought that
l the damage to this relatively
recant building is related to
g( ti l faulty design or construction ,
rather than to subsidence .
1 Locality 43 , subsidence-
inventory map .
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ry Figura 28. Abandoned building , Main Street, Louisville . The un-
dulatory line -of the siding and the rhomboid shape of the windows
suggest torsional effects which might be associated with subsi -
dence . However , the obvious age of the building suggests that the
structural warping is simply -due to gen-eral deterioration over a
long span of time . Locality 4 subsid-ence-inventory map .
1
Reports by residents and miners are useful in locating
rl past evidence of subsidence , but are often difficult to verify .
In one such instance , a miner pointed out that he had assisted
L. in surveyinig a -grid of points over the Eagle mine SW 1 /4 , sec .
14, T. liN . , R .b8W. , where the depth to mine workings is approxi -
mately 300 feet. A subsidence of 23 inches was measured three
to six months after pillar removal . The area is presently being
farmeti , appears to be a smooth slope , and no distinct subsidence
evidence is discernible .
-+ After taking the above complications into consideration , it
is estimated that 90% of the subsidence which can be presently
observed has been identified . The subsidence inventory has
shown that no well -defined , presently observable subbsidence
si occurs in areas where overburden is greater than 150 feet . Sub - '
sidence in areas with a greater depth of overburden is difficult
to verify by routine field oibservation .
V - 13
VI . FIELD WORK
si
Field work consisted of personal interviews , foot traverses
over mined areas , and examination of local historical records .
((°� Approximately 15 man-days were spent in -interviews with persons
y'
having knowledge of past mining and subsidence in the area . Such
people included active and retired miners , local librarians , his—
torians , newspaper editors , city and county iplanners , and -land-
u owners with property overlying mines . Initial contacts were made
through letters of introduction -provided by the Colorado Geolo-gi -
-L
cal Survey and through advertisements placed in local newspapers .
As the interview irosdram progressed , word- of-mouth suggestions
led to meetings with additional knowledgeable people . A list of
the individlals contacted is included as Appendix A of this
rr report .
Retired miners were most helpful in providing information
on mining practices and subsidence over the more recent mines
in Weld County . In Boulder County , many local residents gave
descri-tions of past subsidence events and pointed out present-
day subsidence features . All subsidence reports stemming from
these interviews were then field checked . ,
Approximately 25 man-days were spent in field checking the
above reports and investigating other areas of possible subsi -
dence . The land above the coal mines was traversed to observe
evidence 9f subsidence and unrec-orded mining activities . Every
d
Vi -- 1
`' mined area in the coalfiel-d was walked am-d ( or ) driven over , or
was , at last , observed from the nearest section line road .
Aeri-al photographs were carried im the field , and the lo-
t4
(„ cations of possible subsidence features were plotted on them .
.1 Observations were summarized in field notes written at each lo-
b cation visited . The results of the field survey were utilized
in the construction -of the subsidence- inventory map . In a few
cases , field observations indicated that mine boundaries on the
L,; extent-of-mining map had to be enlarged or reduced .
Historical records dealing with coal mining and mine sub-
�" sidence were examined in the town libraries of Louisville and
Lafayette and in the homes of long-time residents of the area .
The State Historical Society library , the Denver Public Library ,
6a and the Denver Post library provided access to back issues of
local and regional newspapers now long defunct. With few ex-
ceptions , the newspapers and records -examined dealt with mine
collapse only as it affected the miners or the mine workings .
.+ Instamces of surf-ace subsidence during the time of greatest
mining activity ( 1905- 1945 ) usually occurred in sparsely in -
-
y habited areas where land values were low and were either not
newsworthy events or went unnoticed .
Fl
Vi -2
VII . SPECIAL-PURPOSE ACTIVITIES
r
+ In addition to the main programs of basic—data map com-
L% pilation , field work , and interviews , certain other activities
relating to mine -subsidence detection were carried out . These
F
activities consisted of a photogeologic review of recent (1969)
aerial photography , a comparative study of this photography with
aerial photos taken 20 years earlier, and a study of special , low-
u sun-angle , low-altitude aerial photos taken over selected mine
areas . Acquisition and study of multi -band photography was ini -
V
tially considered , but it was later decided that the low-sun-angle
y4 photography offered a more fruitful line of research .
Photogeologic Review
A photogeologic review of the coalfield was made using Agri -
* cultural Stabilization and Conservation Service (A . S . C . S . ) photos
taken in 1969 at a scale of approximately 1 "= 1667 ' ( 1 : 200-00 ) .
Stereo-scopic examination of the photos showed that soil and vege-
tation cover obscured nearly all the bedrock geology . Only two
rock units occur within the area , and neither have any distinc-
tive Thotogeologic characteristics . More disappointing is the
fact that few of the many northeastward-trending faults which
have been reported in the area can be detected on the photos .
It has been equally difficult to find field evidence for these
VII - 1
Lfaults . As noted above , most of the faults are based on sub-
surface data , and their lack of recognition in the field and on
ra
the photos is probably due to a combination of low dip , soil
►� and vegetative cover , and similarities in lithology between the
two surface rock units .
11
The air photos were useful in making a rapid appraisal of
the surface overlying mineil areas . The surface could be clas -
sified as showing 1 ) well -defined subsidence features , 2) pos-
I sible indications of subsidence , and 3 ) no evidence of subsidence .
Well -defined subsiidence features usually take the form of small
pits 10 to 30 feet across and 3 to 10 feet deep ( Figures 7-14) .
Rarely , there are larger areas of collapse forming depressions
50 to 100 feet across and 5 to 10 feet deep . At a scale of 1 "=
1667' ( 1 : 2-0000) , the pits appear quite small on the photos and
IV single , isolated pits are easily overlooked (Figure 6 ) . For-
tunately , they commonly occur in easily recognizable clusters of
a half dozen to a hundred or more pits . In untilled pastureland ,
the pits have remained undisturbed since their formation and are
easily recognized on the photos . Where the land has been tilled ,
the pits have lost their definition , either because the ground
has been worked over many times during the normal course of farm-
ing , or because an active program of pit-filling and land- leveling
has been tarried out by the landowner .
Possible subsidence indicators include slight depressions ,
areas of mottled crop cover , and areas of poor drainage . The
V ! I -2
mottled vegetation patterns are produced by areas of darker-
toned lush vegetation whose vigor is due to a more abundant
supply of water collecting in subsidence-formed depressions
L ( Figure 15 ) . If too much water collects , however , the vegeta-
1 tion is killed and the depression is marked by a small pond or
by a mud flat ( Figure 18) . The latter sometimes have alkali
crusts whose white color is distinctive on the -photos . Mottled
vegetation , shallow depressions , and poor drainage are not de-
W finitive subsidence features . All can be produced by natural
processes other than subsidence , such as wind (deflation ) , or
u
by the activities of man , such as the construction of stock ponds
and the apening of borrow pits .
The ptotogeologic review showed that in the coalfield well -
, defined sutsidence features are usually present in those areas
rr
where depth of mining is less than 100 feet . Where mining depths
are 100 to 200 feat , good subsidence indicators are s-parse , and
one must work with less definitive features such as swales , shal -
low depressions , and areas of poor drainage . In those areas
where mining has been at depths greater than 200 feet , the sur-
face usually has no sutsidence features which can be observed on
the photos .
As a rule , the correlation between mining depth and photo rec-
ognition of subsidence features was also found to apply to field
- observations . Even though subsidence has undoubtedly occurred
in -areas where mines lie more than 200 feet below the surface ,
VII-3
Lis
the affects of such subsidence are probably spreat1 aver a wide
rl area . It is possible that these subtle subsidence affects
might be detected in the field by comparing precise surveying
measurement's made before and after mining .
r
P '. Comparison of 1949 and 1969 Aeri-al Photography - -A set of aerial
photos taken in 1949 by the U . S . Geological Survey at a scale
of 1 "=13185 ' (1 : 16620 ) was examined anzl compared with the A . S . C . S .
photography taken in 1969 . As to be expected , the larger scale
of the earlier photos made reco-gnition of subsidence features
somewhat e-asier . Moreover , the older photography in one case
(Shamrock mine ) showed subsidence pits which were not visible an
the more recent photo coverage . Further investigation showed
that between the two dates of photography an extensive program
of pit- filling and land- leveling was carried out by local ranch-
ers in cooperation with the Soil Conservation Service ( U . S .D .A . ) .
The older _photos prove that, in at least one area, subsidence did
~ occur even though present—day surface evidence of subsidence is
lacking .
A photo comparison was also made of areas where new coal
mining had taken place during the time spanned by the two dates
of photography . The later photography did not show any subsi -
- dence features over the newly undermined areas . The lack of
subsidence evidence in these areas leads to two very different
VTI -4
p
La
conclusions . The first, arid most obvious , is that nn subsistence
.i occurred over the areas mined between 1949 and 1969 . The second
conclusion is that subsidence h-as occurred , but that its effects
1Yr
on the surface are subtle and diffuse . The fact that the areas
mined during the period 1949- 1969 generally had an overburden
thickness of more than 200 feet lends support to the second
ptssibi1ity .
Low-Sun-Angle Photography - Through the cooperation of the U . S .
Geological Survey , a number of large scale , low-sun-angle aerial
fr photographs of selected areas in the coalfield were attained .
The photos were taken on July 23 , 1974 during the early morning
( 7 : 00-8: 30 AM) , while the sun was still low on the horizon . The
low angle of the sun caused ground features of low relief to
cast long shadows , and it was hoped that these shadows would en-
hancn th-e outlines -of the shallow depressions , pits , and swales
which so frequently indicate subsidence .
The areas selected for low-sun-angle photogra-phy included
a control area of well -known and well -defined subsidence and a
half dozen areas where there was doubtful evidence of surface
subsidence . The photos used for study have a scale of approxi -
mately 1 "= 45D ' ( 1 :5450 ) and were made by enlarging 2 . 25 " X 2 . 25 "
negatives . Enhancement is most apparent in the control area at
Marshall and can be seen by comparing Figures 29 and 31 with
.Figures 3-0 and 32 . The former were made from a photo taken
VII -5
W
"'i �+• � a `l1C i t i'%l k, ,r t 1`
yee
+ -N' a C `l\ �i4 y 4e^CF 4s-44 ,✓° \a 3rr i 7 'H.'
.,itl6 34 s 'z''''.''''.‘
, P ,e C 1 .: e Z 4 q F
`4 ils k''' a L� 4eJ ( �\ Cur`s: .',. ..el,
„ `,a ` �A. 7. "�e1'a
' 1 • 51r M1t 1,,, 1,,,. 1l( I 4.1 +�W.! TAT. . �iItS
y laJ �. J), '�'p'3%+ I14' % '. r, 'is
ti 'T icS �
', lit
,1- *+n f § w : a'k ,k. ,. ./
1,.+ L.: ire , sr li ,hy'yy,,.�,,yt,� '4",::4.
,. t tye i
, lt, • ACT` + i M` s'� '�•1‘-,..,wan....,.".., ,-, rM.
t
'*'�4 4 4 p g .•N ;1 eO •''s
k1
\‘'4., v?;,,,,..
' •y�'y'4714 !X. r e r1 es .,� `'z r xt -1;4f.`t .�
a?t ay A 7 + %y. + _ t1 M a+� .
2
�� ' e � �� � elf7,011k,••*.;!. a}! �,.4'ti.;:
na r n f I a pe•. , ''' w L.. i'
1,c;4. �.. - r-1....
•9 1,111,;;;,....., y+• :\,',..•,„'
+.b , •
'; r 'O'1 ' l
Ise
d
Figure 29 . -A. S . C . S . photo of Figure 30 . U. S . G . S . photo of
area A , south of Marshall area A , south of Marshall
— Hi gh-sun-angle Photo Low-sun-angle Photo
a
The shadows on the low- sun-angle photo enhance the outline of col -
lapsed rooms at a and b . The same features ( a ' , h ' ) are nearly
indiscernible on the nigh- sun-angle -photo . The subsidence pits at
c ( c ' ) are also more strongly enhanced on the low-sun-angle {photo .
The two figures are both enlargements end have an approximate
scale of 1 " =-450 ' (1 : 5450) . The enhancement of -detail brought
— about by enlargement is seen by comparing Figures 6 and 29 , both
o-f whi-ch ware made tram the same negative .
..V Y
[.. t ,
f o e °jB 1 At r i l•, r F-'to ' 'rl y 1 .�
9 ..,4 • h .•6 Y,c- ri 'fk: 1 �. H A ' ' , -44. 'u'kl+,,i, ��y, -
Ini
..3 ' .fig ,, I. • + AI f ,i,�, �; k . ,F N, .11 P�: t.
e .: i rl r t y.. �'1 ' ii A ,t
v ., /f 1 "d�`�\r, . '�a '�'r.'•lA A+ '"� ,'" /.yt • a f.'� �•fN� .•4, v �?...
p y, a , i;g \ „•iAki `T' t r s Yf �. Yjw, +0 1# /� 1y'a.
Y ;hx; 44S V •Ar l; t .e 1 ^ _ >>�„• d +,ter• 9 SZY
1 's • -,4q2,{ (( T("�• � N. Y s vv "- Aa t tsp;
ts It '4
t 111,,t ”1/4/t, Al4
▪4\ 1 1� t
si• t
t t , r=\''',•;5' d ' Ar of , `tr 4 +,�,• ,
t 'iF n R x ,f . �" '+:5< yt.� tf. .v' I ` ri. Y�O .. * „* ' .
W li L ," -F' J Rk W �.
��$j�,yY.
Figure 31 . A. S . C. S . photo of Figure 32 . U. S . G. S . photo of
area B , north of Marshall area B , north of Marshall
High—sun-angle Photo Low- sun— angle Photo
Collapse features a (a ' ) outlining the rooms and pillars of the
Lewis No . 1 and 2 -mines are enhanced by the shadows of the low-sun-
angle photo . The same features become blurred on the high-sun-
- angle photo because of the large amount of light reflected from the
bare rock near mid-day . for the salve reason, subsidence induced
joints at b ( b ' ) are also bEtter displayed on the low-sun-angle
photo . Joints at t (b ' ) are also shown in foreground of Figure 8
and flume r ( c ' ) of irrigation ditch is in middle ground of Figure
9 . The figures above are enlargements and have an approximate
stale of 1 "=450 ' ( 1 : 5450 ) . Figures 6 and 31 were Trade from the
satire negative . A comparison of the two shows -the enhancement of
detail brought about by enlargement.
r
when the sun was high above the horizon ; the latter were made
from a low-sun-angle photo . Subsidence pits , room and pillar
outlines , and subsidence induced fractures are all better ex-
pressed on the low-sun-angle photos than on the more conventional
photos . The use of low-sun-angle photography to relieve the
doubt surrounding "subsidence" features in other parts of the
coalfield was less successful . Features which appe-ared doubtful
when visited in the field ( Figure 17 ) still seemed doubtful when
i
observed on the photos .
This study has shown that aerial photographs have a number
of applications , as well as some limitations , in mine subsidence
investigations . Repetitive photo coverage can provide a histori -
cal record of where subsidence has occurred in the past and , to
some extent, when it occurred . It can also show where the ef-
fects of subsidence have been masked by the later work of time
and man . A major constraint on the use of aerial photographs as
a means of determining past subsidence history is that the dates
at which the various photo coverages were flown are not neces-
sarily the dates of greatest mining activity .
In areas of shallow (less than 100 feet) mining , subsidence
features are strongly developed and can easily be recognized on
air photos . Recognition is made easier by using low-sun-angle
photography and by enlargement of the photos . The effect of
enlargement is strikingly shown by comparing Figure 6 with
VII-6
L
Figures 29 and 31 . The latter are merely enlargements of the
former , but the subsidence features which they show have been
greatly enhanced by an increase in perceived depth and detail .
It should he noted that there is a trade-off involved when one
is choosing between large and small scale photos . Large scal-e
photos show subsidence features very well , bit require a large
number of photos to cover a given area . Fewer small scale
y photos are needed to cover the same area , but there is a greater
r
likelihood of overlooking subsidence features .
r " In areas of deep (more than 200 feet ) mining , well -defined
V
depressions and subsidence pits are lacking and subsidence as
expressed at the surface is probably too subtle to detect by
normal photo interpretation methosis . It is possible that such
subtle subsidence might be identified by using sophisticated
photogrammetric plotters in conjunction with large scale photo-
graphs taken before and after an area was undermined . Good
plotters can measure very small differences in el_evation , and
changes of only a foot or two over newly mined areas could prob-
- ably be detected . The use of photos as a future historical
record is limited by the costs of obtaining ground control , the
costs of repetitive flying , and the costs of plotting machine
time .
V1I -7
VIII . _LAND- USE PLANNING AND MINE SUBSIDENCE
-a
Background
;: Mining activity in the Boulder-Weld coalfield started in
3 the early 1860 ' s in the Marshall area and presently continues
rl
only in the Eagle mine . Although instances of subsidence had
been recognized for many years , little thought was given to the
relationship between underground mining , subsidence , and man-
made structures on the surface . Towns in the coalfield viere
small , and rural housing was widely scattered . Subsidence could
y take place and go unnoticed , and damage to existing , relatively
small structures could easily be repaired. Fields and roads
SPE
could be regraded and kept in usable condition . These inconven-
iences apparently were not of sufficient magnitude or intensity
to cause widespread concern , and subsidence-related problems
Et
were accepted as a part of life and were dealt with as they oc-
curred . The subsidence-hazard issue remained one of limited
interest until recently , when accelerated population growth
throughout the region produced significant increases in the
density of residential development in-and adjacent-to undermined
areas .
Due to increased emphasis on land-use planning , and to ex-
panding development pressures , it has become apparent that a
close look must be taken at areas of potential subsidence . The
41
VIII- 1
II
increasing -concernfor the wise and safe development of land
is reflected in the passage of House Bill 1-041 by the 1974
Colorado General Assembly . This law has brought -subsidence
problems ( classified as a natural hazard) within the purview
of the State , as well as the county and municipality .
When considering land use in areas which have been under-
mined , the following questions must be addressed .
1 . Is or was there coal under the tract to be developed?
4
■r 2. Has the full amount of subsidence occurred over
worked-out areas , or can more subsidence be expected?
3. If more subsidence can be expected , when will it
occur, and what will be its magnitude?
4 . In an area in which subsidence is likely to occur ,
L.
can remedial measures be taken so that the land
can be developed safely?
W
:.� 5 . What are the legal problems likely to be associated
with land development in— and adjacent— to areas of
potential subsidence?
6 . Will advancing technology make it feasible to re
enter old mines?
This list of questions is not complete , but it illustrates the
complexity of the problem .
Since the Boulder-Weld coalfield is in the path of Front
Range urbanization , it is timely that answers to the above ques-
tions be found . Some of the questions are quite complex , and it
VIII -2
L
will not be economically practical to obtain answers for them .
saj
In such cases , the land in question may best be left as open
space or -greenbelt. When answers to land subsidence problems
are not clear cut and definitive , the pttential land developer
, , should follow a program of investigation which , hopefully , will
L
provide the data needed . The first step in such a program would
be to study the mays which accompany this report , particularly
the subsidence-hazard map .
Certain areas , because of land ownership or because of
proximity to previously developed areas , will be subject to con -
siderable pressure for development . In these areas it will be
necessary to undertake detailed, and relatively expensive studies
to determine the extent to which viable and safe development is
feasible .
Subsidence-Hazard Map
Purpose and Procedures - The purpose of the subsidence-hazard
map is to designate , insofar as possible , those areas where
development of the land surface may be affected by subsidence
related to undermining . The most direct approach to the prepa-
ration of a subsidence-hazard map would be to compare and con-
trast information on the various mining factor maps with data
on the subsidence-inventory map . Comparisons were made with
this objective in mind to determine if any positive correlations
VIII - 3
existed. It was hoped that such correlations would identify
those factors which are most critical to the development of
subsidence .
Instances of known subsidence were evaluated with respect
Fv to the following factors and combinations of factors :
LI
1 . Presence or absence of pillars
2. Depth of cover
ti 3. Probable thickness of extracted coal
4 . Dates of mine operation
5 . Proximity to mapped faults
A 6 . Presence or absence of pillars plus probable
thickness of extracted coal
4 , 7 . Presence or absence of pillars plus proximity to
{r mapped faults
8. Depth of cover plus probable thickness of
extracted coal
r'
9 . Depth of cover plus proximity to mapped faults
10 . Depth of cover plus presence or absence of pillars .
A positive relationship was observed only between depth of
cover and the presence or absence of pillars (No . 10 ) .
1 . In the depth-of-cover range 0-100 feet , instances
of surface subsidence evidence occur just as often
over areas where pillars are absent as over areas
where pillars are present .
VLII -4
5:4
2 . In the depth-of-cover range 100-200 feet , instances
li of surface subsidence evidence occur twice as often
over areas where pillars are absent as, over areas
4
L where pillars are present .
3 . In the depth—of-cover range 200- 300 feet , instances
of surface subsidence evidence occur three times
as often over areas where pillars are absent as over
areas where pillars are present .
4 . In cases where the depth of Lover is greater than
300 feet , instances of surface subsidence evidence
it
occur twice as often over areas where pillars are
A.
j absent as over areas where pillars are present.
These observations indicate that , as depth of cover increases
w
to 300 feet , the occurrences of subsidence evidence over areas
Yr where pillars are absent become increasingly more frequent rela-
tive to those areas where pillars are present . Below 300 feet
this trend is reversed , possibly due to the increased "bridging"
effect provided by a thicker overlying rock section .
It should be str-essed that comparisons can be made only
where evidence of subsidence exists . In areas where there is no
surface evidence of subsidence , any conclusions drawn from the
above observations should be used with great caution . This is
particularly true with any attempts to relate the possibility of
future subsidence to depth of cover and the presence or absence
of mine pillars .
VIII-5
'S
Si
The almost total lack of correlation in the above compari -
a
est sons (Nos . 1 -9 ) is probably due to the complexity of the rela-
tionship which exists between room-and-pillar mines and surface
subsidence . In addition , the records kept throughout the years
of mining activity in tare area are not sufficient for a thorough
1.r
analysis of the relationship between subsid-ente and other mining
factors . Another major problem is that the subsidence-inventory
map shows only observed subsidence , and does not record subsi -
`� dence which may have gone unnoticed . It is possible that had a
full and accurate record of subsidence teen available , some
correlations might have been established .
Ns
w
Basic Assumptions Used in Map Construction - The problems des-
cribed above indicate that no consistent rule can be adopted
for predicting subsidence . The best approach appears to be one
w
6.4 which is based upon the probable relative severity of potential
subsidence in any given area . Since any undermined area may be
affected by subsidence or post-subsidence settlement , all such
areas have been assigned a degree-of-hazard classification based
on the following simple assumptions :
1 . Large undermined areas with no support ( ie . pillars
removed ) subside shortly (within months ) after
support is removed .
2 . Caving proceeds upward from the mine roof , and by
the time subsidence effects have been transmitted
4r
VIII-6
U
to the surface it can be expected that no large
voids remain beneath that particular area .
YE
3. Occurrences of partial collapse ( that is , cases
where subsurface caving has occurred , but where
°"• the caving has not reached the surface ) were not
1
L,1
detected during this study. Therefore , it is
assumed that , where surface subsidence has oc-
curred , the subsidence is essentially complete .
;
This does not include post- subsidence compaction
and attendant surface settling .
ti
4 . The inability to confidently predict the relative
•
stability of a given undermined area requires a
conservative approach to hazard classification .
Accordingly , it has been assumed that pillars left
S standing after mining ceased will undergo deterior-
ation with time , and will eventually fail . The
amount of time required for a pillar to completely
deteriorate will depend on many factors , which vary
in importance in different areas of the coalfield .
Eventually , all pillars will probably fail , and
subsidence will probably occur over all voids in
the study area .
Hazard Clas-sification System - Using the above assumptions , a
classification system has been established to define the degree
VIII -7
of subsidence hazard in relative terms . This appears to be
the most useful approach to the problem of the relationship be --
tween land subsidence and land use . The categories of subsidence
r hazard are severe , moderate , and low.
1 . Severe Areas labelled " severe" are those in which
rapid and violent subsidence effects may endanger
occupants of the area by causing the failure of
building foundations , roadways , gas mains , and s;imi -
lar man-ma-de features . These areas are characterized
by either 1 ) the presence of pillars (which are as-
sumed to be undergoing decomposition ) plus physical
evidence of void space , or by 2 ) the absence of evi -
dence of surface subsidence . The collapse of decom-
posed pillars could alter the complex stress and
r strain patterns in the overlying rock . This could
initiate almost instantaneous local surface subsi -
dence or displacement, thereby causing equally rapid
destruction of structures in the area . The only ac-
ceptable land use for these areas , without undertaking
relatively expensive remedial measures , are agriculture
or open space .
- 2 . Moderate - Areas subject to "moderate " subsidence are
those in which the effect of subsidence might be suf-
fi-cient to render man-made structures unsafe or
VIil -8
unusable . The rate of subsidence would probably be
.� slow enough to allow time for recognition of the
problem, and if necessary , for the safe and orderly
L abandonment of the area . Possibly , there would be
sufficient time for remedial action which could
r
offset the effects of the subsidence . "Moderate"
areas are characterized by the presence of subsi -
dence features over undermined areas where pillars
are reported to be present . This condition produces
the potential for further subsidence and differential
its settlement . Appropriate land uses would include ag-
riculturo , open space , open storage areas , unoccupied
warehouses , and similar uses which would require only
a low population density .
3. Low - Areas of " low" hazard are those in which the
w
rate and magnitude of any anticipated surface dis-
placement would be small enough to warrant repair
of affected existing structures . By using adequate
engineering design , future structures in these areas
could be built to withstand the anticipated stresses
on their foundations . Below these areas , all or
essentially all , pillars have been removed , and re-
latively uniform and complete subsidence has already
occurred. Problems in such areas would be reduced
mainly to post-subsidence compaction and related
VIII -9
1
surface settling . The only restrictions placed on
land use would be the requirement that structures
planned for these areas would be designed to with-
stand any small movements which might be induced
by post-subsidence compaction .
Li
Safety Factor - Factors such as angle of draw, attitude of bed-
-- ding , and presence of zones of weakness due to faulting can
'. extend the surface influence of a particular void well beyond
th-e limits of the undermined area . Determination of the extent
of subsidence at the surface is further complicated by the possi -
1..•
bility of significant inaccuracies in the original mine maps .
The effect of the inter-relationship of the above factors
is not amenable to quantification . It is therefore prudent to
incorporate a "safety factor" into the determination of the ex-
6 tent of surface area which might be affected by mining . This
has been done by assuming a nominal angle of draw ( 35° ) . This
angle was used in conjunction with the maximum mining depth
(580 feet) recorded in the coalfield to calculate the width
(400 feet) of a safety zone which extends beyond the mine bound -
aries . This 400 foot wide safety zone is used throughout the
entire coalfield even though nearly all mines are less than 580
feet deep . The hazard classifications used for the zones of
safety are the same as those used for the adjacent areas which
are directly over the mine .
VITT -10
414
Where faults , or intersections of faults , lie only a short
distance beyond the 400 foot boundary , the zone of safety has
been extended to those faults and intersections . Small modifi -
cations in the width of the zone have also been made based on
t , surface topographic control .
Reclassification of Subsidence Hazard of Specific Areas - The
hazard classification of all areas within the coalfield was
based on the data available for this study . Reclassification of
any part of these areas could be justified by the accumulation
L. of more or better information . Such information might be de-
rived from 1 ) more detailed maps than those available for this
study , 2) field observations and measurements of additional sub-
sidence not observed during this study , and 3) subsurface tech-
V
niques such as core drilling and geophysical surveys . It is
certain that the economic attractiveness of land development in
the coalfield area will prompt investigations to re-define the
`- subsidence hazard in- and adjacent- to specific properties .
Planning Review of Subsidence Hazards of Specific Areas
During the early stages of this study , it was hoped that a
set of guidelines could be developed for use by those persons
investigating the subsidence hazards of specific areas . It
later became apparent that the complexity of the problems associ -
ate-d with subsidence was such that the most reasonable approach
VIII-11
4
to further investigations would te to acquire additional data
i similar to , but much more detailed than , that used in the prep-
aration of this report. The preferred ma-p scale on which to
display the detailed data would be 1 "=200 ' ( 1 : 2400 ) .
0 For most areas , the development of large-scale maps showing
basic data such as extent of minin-g , depth of cover , pillars ,
probable thickness of extracted coal , and subsidence occurrences
will be only the first step in a land-use compatibility investi -
i
tai gation . In some instances , the basic data will indicate ' that
further investigations will be needed to demonstrate the via-
" bility of development . As in the case of hazard re-classification ,
such additional investigations will probably consist of subsur-
face testing through core drilling and geophysical surveys .
j„ Subsurface investigations are expensive , and it should be
expected that land development projects in the coalfield will be
111
subject to some financial burdens not associated with projects
of similar size in other areas . However , the area still appears
to be attractive for development , and the more astute engineers ,
designers and planners will find ways to overcome the problems
which exist.
I
VIII - 12
1
IX . CONCLUSIONS
r
1 . Much of the land between the towns of Marshall (Boulder
County) and Firestone (Weld County) is now undermined
with abandoned coal workings .
kl
2. The workings lie at depths which range from 30 to 580
feet. Most are within the 100 to 300 foot depth range .
3 . The coal mines were worked by the room-and-pillar
method rather than by the longwall method . In most
cases , the miners attempted to " pull " as many of the
ri pillars as they could during the later stages of
development in any given mine .
4 . Most of the theories of coal mine subsidence and most
of the methods of predicting the time , duration , and
extent of subsidence are derived from European experi -
ments and observations in longwall mines . These theo-
ries and predictive methods are not entirely applicable
to the room-and-pillar mines of the Boulder-Weld coal -
field . This is because the presence of unpulled pillars
(even in so-called "worked out" mines ) disrupts the or-
- derly development of subsidence and introduces a great
deal of uncertainty as to the time of subsidence rela-
tive to the time of mining .
1X-1
K,X
5 . The extent of subsidence in the coalfield can be fairly
well defined by field observations . Strong evidence of
surface subsidence consists of well -defined pits and
I' depressions ; less definitive evidence consists of broad
swales and shallow, poorly drained depressions .
6 . Unequivocal evidence of subsidence is often observed on
the surface in those areas where the mining depths do
"1 not exceed 200 feet . In areas where mining depths are
greater , surface subsidence is not readily observable
by the unaided eye , even though its presence could log-
ically be expected . Precise surveying in such areas
might detect shallow, closed depressions and might show
that previously established benchmarks have subsided .
Ir
7 . Observed damage to homes , streets , buildings , highways ,
NM
and irrigation ditches should not automatically be as -
cribed to subsidence because , in many cases , the damage
could be induced in other ways .
8. Interviews with local residents and miners are often
helpful in locating surface subsidence features and in
determining the time and duration of subsidence occur-
rences . However, it should be noted that memories of
events which occurred 30 to 40 years ago are sometimes
IX--2
L
uncertain , and that reports of subsidence must be
rr cross-checked through field observations or through
other interviews .
V
9 . In some cases Federal government aerial photography
is helpful in studying subsidence in the coalfield .
Because the scale ( 1 "=1667 ' , 1 : 20000 ) of these photos
is quite small , relative to the size and depth of the
subsidence features being investigated , interpretation
of subsidence is often uncertain . Nevertheless , a
study of various sets of aerial photo coverage taken
over the years ( 1937-1969 ) by different government
r
agencies could provide a rough historical record of
subsidence development in the coalfield since the late
INS
1930 ' s .
w
ba
10 . Low-sun-angle aerial photos , taken early in the morn-
ing , are a decided improvement on the normal government
photography because the long shadows cast at that time
of day enhance the outlines of low-relief subsidence
features . In the detection of subsidence , the low-sun-
angle photos are not a significant improvement over
on-the-ground field observations .
11 . There appears to be little correlation between instances
of surface subsidence and other mining factors such as
IX-3
O.
Iss
depth of cover , presence or absence of pillars , and
Si probable thickness of extracted coal . There does
seem to be a relationship between cases of surface
ii subsidence and depth of cover coupled with the presence
or absence of pillars .
12 . A classification of "severe , " "moderate , " and " low"
"' hazard has been adopted for all undermined areas in
the coalfield . These areas and their ratings are
V
-shown on a subsidence hazard map . The three categories
-of hazard are based on estimations of the relative
-amount of danger to which persons and structures in a
_given area might be subjected should subsidence occur
in the future .
Yr 13 . When specific properties in the coalfield are con-
sce
sidered for development , an examination of the subsi -
- H dence hazard map will give a first approximation as
to the feasibility of the project. In most cases ,
more detailed information than is given in this re-
v port will have to be acquired . Much of this data will
have to be derived from test drilling and geophysical
surveys and its acquisition will undoubtedly be
expensive .
I')-4
ikU
X . SELECTED REFERENCES
Averitt , P . , and Lopez , L. , 1972 , Bibliography and index of
U . S . Geological Survey publications relating to coal ,
1882-1970 : U . S . Geol . Survey Bull . 1377 , 173 p .
1 Babcock , S . D . , 1973 , Undermining as an element in land use
L planning [M . S . thesis ] : Edwardsville , Southern Illinois
Univ . , 84 p .
Brauner , G. , 1973, Subsidence due to underground mining ( In
two parts ) 1 . Theory and practices in predicting surface
deformation : U . S . Bur . Mines Inf. Circ . 8751 , 56 p .
1973 , Subsidenc-e due to underground mining ( In two 'parts )
2 . -Ground movements and mining damage : U. S . Bur . Mines
Inf . Circ. 8572 , 53 p .
Candeub, Fleissig and Associates , 1971 , Demonstration of a
technique for limiting the subsidence of land over
abandoned mines , N . T.I . S . , Tech . Rept . , P . B . 212708 , 57 p .
1973 , Demonstration of a technique for limiting the
subsidence of land over abandoned mines , final report :
-City of -Rock Springs , Wyo . , 28 p .
Colorado Division of Mines , 1973, Coal 1973: Colo . Div . Mines
Inspection Div . , 28 p .
Colorado Springs Planning Department , 1967 , Mining report ,
Colorado Springs coalfield , a _guide for future land use :
W Colorado Springs Planning Dept . , Geol . Sec . , 10 p .
Colorado State , 1963 , Coal mining laws : -State of Colorado ,
revised statutes , chap . 92 , pt . 1 , arts . 1 - 12 , sec . 1 ,
124 p .
Colton , R . B . , and Lowrie , R. L. , 1973, Map showing mined areas
of the Boulder-Weld coalfield , Colorado : U. S . Geol .
Survey Misc. Field Studies Map MF-513.
Dunrud , C . R . , and Barnes , B . K. , 1972 , Engineering geologic
map of the Geneva Mine area , Carbon and Emery Counties ,
Utah : U. S . Geol . Survey Misc . Geol . Inv . Map I - 704.
Flaschentrager , H . , 1958, Considerations on ground movement
phenomena : Colliery Eng . , v. 35 , no . 8 , p . 342- 350 and
no . 9 , p . 391 - 398 .
X- 1
Gillen , G . , 1974 , When coal was king : Focus Magazine in
Boulder Daily Camera , March 24, 1974 , p . 3-6 .
-Grosvenor , N . E . , 1964 , Coal mines of Colorado , Adams County
(map ) : Colorado Sch . of Mines Found . , Golden , Colo .
1964 , Coal mines of Colorado , Boulder County ( map) :
Colorado Sch . of Mines Found . , Golden , Colo .
1964 , Coal mines of Colorado , Weld County ( 2 maps ) :
Colorado Sch. of Mines Found . , Golden , Colo.
• Herbert , C . A. , and Rutledge , J . J . , 1927 , Subsidence due to
coal mining in Illinois : U. S . Bur . Mines Bull . 238 , -59 p .
y Holt, R . D . , 1972 , Bibliography , coal resources in Color-ado :
yq Colorado Geol . Survey Bull . 34-A , 32 p .
-Hornbaker, A. L. , and Holt , R . D . , 1973 , Coal resources of
Colorado , 1972 summary of: Colorado Geol . Survey Spec .
isl Pub . no. 3, 15 p .
1 Hutton , T . , 1956 , Deep hole closes Lafayette street as old
mine caves in : Denver Post, May 27 , 1956 .
King , H . J . , and Whetton , J . T. , 1958 , Mechanics of mining
subsidence : Colliery Eng . , v . 35 , no . 6 , p . 247 -252 and
no . 7 , p . 285- 388.
Landis , E . R. , 1959 , Coal resources of Colorado : U. S . Geol .
-Survey Bull . 1072-C , T . 131 -232 .
Litwiniszyn , J . , 1958 , The theories and model research of
-- movements of ground masses : Colliery Eng . , v . 35 ,
no . 10 , p . 438-444.
Lowrie , R . L . , 1966 , Analysis of the coal industry in Boulder-
-
Weld coalfield , Colorado : U . S . Bur . Mines Rept . Inv .
6726 , 79 p .
Malde , -H . E. , 1955 , Surficial geology of the Louisville
quadrangle , Colorado : U . S . Geol . Survey Bull . 996-E ,
T . 217-257 .
Martin , S . C. , 1910 , Coal of the Denver basin , Colorado :
U. S . Geol . Survey Bull . 381 -C , p . 297- 306 .
Mohr , H . F . , 1956 , Influence of mining on strata : Mine and
� Quarry Eng . , v . 22 , no. 4 , p . 140-152 .
X-2
National Coal Board , 19-66 , Subsidence engineer ' s handbook :
National Co-al Board - Production Department, London , 118 p .
Panek , L . A . , 1973 , 'Pro-gram for control of surface subsidence :
U. S . Bur. Mines Prog . Rept . , no . 10011 , 23 p .
Perez , W . , 1958 , Subsidence observations in Austria : Colliery
Eng . , v . 35 , no . 11 , p . 479-482 and no . 12 , p . 333-535 .
ij Scott , G . R . , 1962 , Geology of the Littleton quadrangl-e ,
Jefferson , Douglas , and Arapahoe Counties , Colorado :
U. S . Geol . Survey Bull . 1121 -L , 53 p .
Smith , R . 0 . , Schneider, F . A. , Jr . , and Petri , L. R. , 1954 ,
Ground water resources of the South Platte River basin in
western Adams and southwestern Weld Counties , Colorado:
ii U . S . Geol . Survey Water-Supply Paper 1638, 132 p .
Soister , P . E . , 1965 , Geologic map of the Fort Lupton quad-
r ; rangl-e , Weld and Adams Counties , Colorado : U . S . Geol .
4" Survey Geol . Quad . Map GQ- 397 .
1965 , Geologic map of the Hudson quadrangle , Weld and
Adams Counties , Colorado : U . S . Geol . Survey Geol . Quad .
Map GQ-3-98.
1965 , Geologic map of the Platteville quadrangle , Weld
County , Colorado : U . S . Geol . Survey Geol . Quad . Map GQ- 399 .
Spencer , T. D. , 1961 , Geologic map of the bedrock geology of
the Louisville quadrangle , Colorado : U .S . Geol . Survey
Geol . Quad . Map GQ- 151 .
Stefanko , R . , 1973 , Subsidence and ground movement , in S . M . E .
handbook : Soc. Mining Eng . , Am. Inst . Mining , Met . and
Petr. Eng . , Inc . , New York , p . 13-2 to 13- 9 .
Turnbull , D . , -and Potts , E . L . J . , 1938 , Surface and underground
subsidence correlation : Colliery Jng . , v . 35 , no . 2 ,
-p . 65- 72 .
Van Horn , R. , 1957 , Geologic map of the bedrock geology of the
Golden quadrangle , Colorado : U . S . Geol . Survey Geol .
Quad . Map GQ-103.
Weimer , R . J . , 1973, A guide to uppermost Cretaceous -stratig-
raphy , central Front Range , Colorado : Mountain Geologist ,
v . 10 , no . 3 , p . 53-'97 .
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4
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L
Wells , J . D . , 1967 , Geology of Eldorado Springs quadrangle ,
Boulder and Jefferson Counties , -Colorado : U . S . Geol .
Ai Survey Bull . 1221 -D , 85 p .
Woodhuff , S . D . , 1966 , Methods of working coal and metal mines ,
Vol . 2 , Ground support methods : New York , Pergamon Press ,
�+ 429 p .
Yinst , P . O . , 1960 , Coal resources of Colorado : Colo. Sch .
Mines Min . Ind . Bull . , v . 3, no. 5 , 8 p .
Young , C . M . , 1917 , Percentage of extraction of bituminous
coal with special reference to Illinois conditions : Univ .
Illinois -Engineering Experiment Station Bull . 100 , 175 p .
ti
L. Young , L . E . , 1916 , Surface subsidence in Illinois : Illinois
Geol . Survey Bull . 17 , 112 p .
and Stoek , H . H . , 1916 , Subsidence resulting from mining :
Ss Univ . Illinois Engineering Experiment Station Bull . 91 , 205 p .
Zwartendyk , J . , 1971 , Economic aspects of surface subsidence
r resulting from underground mineral -exploitation [Ph . D .
thesis] : University Park , Pennsylvania State Univ . ,
University Microfilms , Ann Arbor , 411 p .
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{Ar ARPINDIX A
rr CITY , COUNTY , STATE AND REDERAL
OFFICIALS ; NIINIRS ; LOCAL RESIDENTS AftD OTHERS
INTERVIEWED DURING COAL MINE SUBSIDENCE STUDY
City an-d County Governments
Brouillette , Jason , Boulder Co . Plannin-g Dept. , H-ead
of Op-erations
Heffington , William, Boulder Co . Eng . Dept .
Pendleton , James , City of Boulder , -Geologist
Bedford , James , City of Lafayette , former Mayor
Deppa , Daniel , City of Lafayette , Asst . City Manager
White , Daniel , City of Louisville , City Engineer
Wurl , Leon , City of Louisville , City -Administrator
Lorenson , Burman , Weld Lo . Planning Dept . , Planning
Director
Olsen , Gill , Weld Co . Engineer ' s Offica
y
Colorado State Government
�- Debnrski , Andrew E . , Colo . Div . of Minas , Chief Coal
Mine Inspector
Platt, Thomas , Water Commissioner , Dist . b
Gilmore , John , State Highway D-ept. , Geologist , -Denver
Region
Bower , Dwight, St-ate -Highway Dept. , Ingineer , Dist . 4
SRringer , John , State Highway Dept. , Maintenance Ass ' t . ,
Dist. 4
U . S . Government
Dunrud , -C . Richard , U. S . Geological Survay
Colton , Roger B . , B. S . Geological Survey
Appendix A - Continued
A
as
U. S . Government (Cont. )
�i Panek , Louis A . , U . S . Bureau Df Mines
Morgan , Thomas A . , U. S . Bureau Df Mines
Darnell , Richard , U . S . Bureau of Mines
Donner , Donald , U. S . Bureau of Mines
Moreland , Donald , Soil Conservation Service , U. S . D. A.
Active and Retired Miners
Astle , John , Lincoln Mine , General Manager
Amicarella , Lawrence
Clyncke , Marian
Clyncke , Oliver
De Novellis , Anthony
De Vischer , Andy
Dhieux, August
Ferguson , William, Lincoln Mine , former Mine Superintendent
Gunther , Wilbur , Imperial Coal Co . , General Manager
Hawkins , -Henry
Kolar , Frank , Eagle Mine , former Mine Superintendent
Miller , Manford
Reese , Charles , Eagle Mine , Mine Superintendent
Sidle , Samuel
Stolns , Edward , Lincoln Mine , Mine Superintendent
Vaughn , Ambrose
Appendix A - Continued
w
Local Residents
( Mrs . ) Amicarella , Librarian , Lafayette
Barlow, Niles , resident , Lafayette
,+
Bateman , Albert, owner of -property above El-ectric Mine
Coonts , Phyllis , resident, Marshall
Dhieux, Vivian , City Councilwoman , Louisville
”.i
Di Giacomo , Susie , owner of property above Paramount Mine
._" Lewis , K. D . , homeowner near Shanahan Mine
Ostdiek , Walter, Paclamar Farms , Louisville
Reichert , A . I . , owner of property above Black Diamond Mine
Rodelli , James , resident , Superior
Sampson , Johana , re-silent , Marshall
Waremburo , Clubert, owner of property above Acme Mine
Zabler , ( Mrs . ) R. A . , resi-dent, Lafayette
Miscellaneous
Boyle , Clyde , Charles Robinson and Associates
Cochran , Dale , Charles Robinson and Associates
Darnell , Clinton , Adolph Coors Co . , Engineer on Coors
Pipeline
(Mr . ) Ferryman , Burlington Northern and Colorado and
Southern RR , Chief Engineer
Gillen , Gary, Boulder Daily Camera
McPhail , Donald , Univ . of Colorado , Professor
kl
Appendix A - Continued
Miscallaneous (Cont_)_
Miller , Dean , Public Service Co . of Colo . , Supervisor ,
Transmission Engineering
Rahmiamian , Victor , Colo . School of Mines , graduate
student
Russell , William, Rocky Mtn . Energy Co . , -Senior Engineier
Sarchet, M. C . , Former Reservoir and Irrig . Co . ,
E` President
Schreiner , Robert , Centaurus High School , Principal
.. Waneke , George , Waneka -and Sons Drilling Co .
Weimer , R-obert , Colo . School of Mines , Professor
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