United States Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R08-91/050
June 1991
©EPA
Superfund
Record of Decision
Rocky Mountain Arsenal
-------
r2-101
EPORT DOCUMENTATION l' REPORTNO. I ~ 3. Reclpient'a Ac:ceu8on No
PAGE EPA/ROD/R08-91/050
TIle I11III SubIItIe 5 Rapan Date
SUPERFUND RECORD OF DECISION 06/06/91
Rocky Mountain Arsenal (Operable Unit 21), CO
Ninth Remedial Action &.
Aulhar(a) .. PIIrfonning CrglUllzlltlon RepL No
II8rfonnIng OrpInll8lion N8me I11III Add- 10. ProjectlTulclWork Unit No.
11. CoIm8ct(C) 01' GrIllll(G) No
(C)
(G)
~ SpIII-.ing OrgllnlZ8llon N8me I11III ~ 13. Type of R8pIIrt. Penocl CoV8nld
U.S. Environmental Protection Agency 800/000
401 M Street, s.w.
Washington, D.C. 20460 14.
.. Su~NotI8
;. AII8tract (1.IIIId: 2110 _Ida)
The Rocky Mountain Arsenal (RMA) (Operable Unit 21) site comprises part of the
17,000-acre RMA site, which is a former U.S. Army chemical warfare and incendiary
munitions manufacturing and assembly plant in Adams County, Colorado. From the 1950s
until late 1969, the U.S. Army used the RMA facility to produce the nerve agent GB
(isopropylmethyl-phosphonofluoridate). In additl.on, between 1947 and 1982, private
industries leased major portions of the plant's facilities to manufacture various
insecticides and herbl.cides. From 1970 through 1982, U.S. Army facility operatl.ons
have primarily involved the destruction of chemical warfare materials. Because final
remediation of the RMA site will take many years to complete, thirteen l.nterim
response actions (IRAs) were determined necessary prior to implementing the final
On-Post Record of Decision ( ROD). Operable Unit 21 (OU21), the South Tank Farm Plume
(STFP), is one of several areas being addressed as part of the Other Contaminated
Sources IRA. The STFP is located in the southern half of sections 1 and 2 of the RMA
site. From 1947 to 1978, STF tanks 464A, 464B, and others were used intermittently
to store bicyc10heptadiene (BCHPD) and dicyclopentadiene (DCPD) bottoms generated
from pesticide manufacturing. In addition, mixtures of BCHPD, DCPD, and fuel oil
(See Attached Page)
7. Docunwnt An8IY818 L De8criplD18
Record of Decision - Rocky Mountain Arsenal (Operable Unit 21), CO
Ninth Remedial Action
Contaminated Medium: gw
Key Contaminants: VOCs (benzene, toluene, xylenes)
b. 1cIIntifienIOpe&lded T-
Co COSA 11 fiek&tGraup
.. AVIIIl8lllby ~ 11 SecurIty CI- (Th18 Report) 21 No 01 Pages
None 60
20 Secunty CI... (Thl. Pllge) ~ PrIce
Non~
&'''''__on Re- 272 14-'111
. ANSI-Z3I.18)
(Formerty NTlS-35)
-------
EPA/ROD/R08-91/050
Rocky Mountain Arsenal (Operable Unit 21), CO
Ninth Remedial Action
Abstract (Continued)
were pumped onto the ground, or collected or buried onsite during tank cleanings. From
1960 to 1963, leakage of BCHPD/DCPD bottoms occurred from a pipe connected to tank 464A,
and additional spills occurred in 1964 and 1978. The exact spill locations and amounts
are generally not known. Additionally, in 1948, a large spill of benzene containing
toluene and xylene impurities occurred in the STF. A number of U.S. Army investigations
have revealed ground water contamination originating from the areas of light nonaqueous
phase liquid (LNAPL) located near tank 464A. Recent investigations have shown that the
STFP does not pose significant risk to public health or the environment, as originally
suspected, because data indicate that the plume will not migrate into nearby Lake Ladora
or Lake Derby prior to implementation of the final remedy. In addition, biodegration of
the plume may be occurring. This ROD addresses interim management of migration of the
STFP and is consistent with the Final Response Action. The pr1mary contaminants of
concern affecting the ground water are VOCs including benzene, toluene, and xylenes.
The selected interim remedial action for this site includes perform1ng one-time
comprehensive ground water monitor1ng throughout the STFP to verify the extent and
migration rate of STFP constituents and the existence of conditions conducive for
biodegradation within the STFPi and conducting annual ground water monitoring includ1ng
performing quarterly measurement of STFP water levels. No cost informat1on was provided
for this interim remedial action.
PERFORMANCE STANDARDS OR GOALS:
-------
(." ,U 2-1
~/ It::/ q I
FI~AL DECISION DOCUMENT
OTHER CONTAMINATION SOURCES
INTERIM RESPONSE ACTION
SOUTH TANK FARM PLUME
Prepared by
MK-Environmental Services
Denver, Colorado
Prepared for
Shell Oil Company/Holme Roberts & Owen
Denver, Colorado
-------
May 8. 1991
/~ :: -j'
6- G 1"7
,~,~.....",.".....,
i ,
.. c
i ;
\ I
"",,- .. ..,; ~
DEPARTMENT OF THE ARMY
PROGRAM MANAGER FOR ROCKY MOUNTAIN ARSENAL.
COMMERCE CITY COI..ORADO 8C022 2180
UI'L' '0
UYENTIO. Of
Interim Response Branch
Mr. Connally Mears
U.S. Environmental Protection Agency
Region vm
One Denver Place
Suite 801
999-18th Street
Denver, Colorado 80202-2405
. ~
J
-
Dear Mr. Mears:
)
:-...
Enclosed for your information is the Final Decision Document for the South Tank
Farm Plume Interim Response Action (IRA). Pursuant to Section 30.1 of the Federal
Facility Agreement (FF A), dispute of this IRA was informally resolved at the RMA
Committee level on March 13, 1991. Although not required by the FF A, the Army as
Lead Agency issued a letter on April 8, 1991 that fully captured and summarized the
agreements made at the March meeting to resolve the dispute. The agreements and
conditions set forth in our letter of April 8, 1991 will guide the implementation of this
IRA, subsequent phases of this IRA, or the Feasibility Study (FS) data gaps program.
All or some of these commitments and guidance will be reiterated in this, and
subsequent IRA or FS documents when appropriate.
The Draft Implementation Document for this IRA will be issued once the new
piezometers have been installed and monitored. Shell anticipates the issuance date for
this document to be late June 1991.
Also included are responses to EP A comments on the "Draft" Final Decision
Document submitted in their April 26, 1991 letter.
If you have any questions, contact Mr. J.D. Smith at (303) 289-0201.
Sincerely,
~~
RMA Committee Coordinator
-------
Section
1.0
2.0
TABLE OF CONTENTS
INTRODUCTION/EXECUTIVE SUMMARY.
SITE DESCRIPTION. . .
2.1
2.2
2.3
. . . . .
.......
.........
. . . .
. . . .
LOCATION AND SITE HISTORY. . . . . .
. . . .
HYDROGEOLOGY
............
.......
NATURE AND EXTENT OF CONTAMINATION
. . . . .
4.0
3.0 INTERIM RESPONSE ACTION OBJECTIVE AND EVALUATION
. . . .
5.0
6.0
7.0
8.0
9.0
10.0
DESCRIPTION OF THE INTERIM RESPONSE ACTION.
. . . . . .
CHRONOLOGY OF EVENTS. .
. . . . . .
.......
IRA PROCESS
.......
. . . . . .
. . . . .
. . . .
APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS
FOR THE REMEDIATION OF OTHER CONTAMINATION SOURCES
(SOUTH TANK FARM PLUME) INTERIM RESPONSE ACTION. . . .
04/29/91
7.1
7.2
7.3
7.4
7.5
INTRODUCTION
................
AMBIENT AND CHEMICAL-SPECIFIC ARARs .
. . . .
LOCATION-SPECIFIC ARARs
. . . . .
ACTION-SPECIFIC ARARs . .
. . . . . .
. . . .
COMPLIANCE WITH THE OTHER ENVIRONMENTAL LAWS
SCHEDULE. . . .
. . . .
. . . . . .
. . . .
CONSISTENCY WITH FINAL RESPONSE ACTION
. . . .
. . . .
REFERENCES
. . . . . .
. . . .
.......
. . . . .
Appendix A -
RESPONSES TO COMMENTS ON THE DRAFT FINAL DECISION
DOCUMENT OTHER CONTAMINATION SOURCES INTERIM
RESPONSE ACTION SOUTH TANK FARM PLUME
-i-
Paqe
1
4
4
5
6
9
11
13
15
18
18
18
19
21
30
32
33
-------
Fiaure
1-1
1-2
2-1
2-2
2-3
2-4
2-5
2-6
2-7
4-1
4-2
4-3
4-4
LIST OF FIGURES
STFP
Area Location Map...........................
Decision Flow Chart for Interim Remedial
Action versus Monitoring/Maintenance............
Geologic Cross-section A-A'......................
Water Table Contour Map, Fall 1990...............
Benzene in Groundwater, Fall
1990. . . . . . . . . . . . . . . .
Toluene in Groundwater, Fall
1990............... .
Xylene in Groundwater, Fall 1990.................
Bicycloheptadiene in Groundwater, Fall
Dicyclopentadiene in Groundwater, Fall
1990......
1990......
Verification Monitoring Network.................. 11
Proposed Annual Monitoring Network............... 12
Location Map for New Well Points and Piezometers..
Proposed Semi-Annual Water Table
Moni tor ing Network............................. 12
04/29/91
-ii-
After
Paqe
1
3
5
6
7
7
7
7
-------
1.0
INTRODUCTION/EXECUTIVE S~~Y
The South Tank Farm Plume (STFP) is listed under the "Remed~at~on
of Other Contamination Sources" Interim Response Action (IRA)
sites under the Final Technical Program Plan FY88-FY92 and the
Federal Facility Agreement. The process and guidelines used to
assess alternatives, produce this Draft Final Decision Document,
and implement this IRA are specified in and conducted in
accordance with the Federal Facility Agreement.
As listed in Section 22.8 of the Federal Facility Agreement, the
purposes of the Proposed Decision Document for Other Contamina-
tion Sources IRAs are to: (a) state the objective of the IRA;
(b) discuss Interim Response Action alternatives, if any, that
were considered; (c) provide the rationale for the alternative
selected; (d) present the final ARAR decision; (e) summarize the
s~gnificant comments received regarding the IRA and responses to
those comments; and (f) establish an IRA Deadline for completion
of the IRA, if appropriate. Each of the above mentioned issues
is addressed in this document.
The South Tank Farm Plume (STFP) is located in the southern half
of Sections 1 and 2 on the Rocky Mountain Arsenal (RMA) (Figure
1-1). The constituents of the STFP are those present in the
light nonaqueous phase liquid (LNAPL) plume, which is a source of
the dissolved plume.
In 1989, Shell proposed, and the Army and EPA agreed, that the
STFP be added to the list of RMA IRAs. The basis for the
nomination and acceptance of this plume for an IRA was an
apparent increase in concentration and areal distribution of the
STFP compounds, notably benzene which defines the leading edge of
the plume (Shell 1989). The data suggested that benzene was
-1-
-------
Northwe8t Booodary
System
4
Motor Pool --f
Area
9
North Boundary System
-]
'.
19
JO
j_J 11
12~
.
-(-
----
Area of
enarged Map
-----
!&gend
--1111 Railroad
Stream/Drainage
r::::J Study Area
ii
~
cii
211
E!~:!i!iI PI u me
W.a:J lakes
b. NIf\Ih Avenue
29
Elqhth A~~e
J2
north
S..venlh~
~
!)
..,:~
1/2
2
o
l
1
8
MILES
ROCKY MOUNTAIN ARSENAL
South Tank Farm Stud~ Area
Agura 1-1
South Tank Farm Plume
Location Map
--
CORPORATION
(@ MOR~ONJ<~'r1!ROU"
-------
migrating toward Lake Ladora rapidly enough to reach the lake
prior to the implementation of the final remedy.
Based on this interpretation of the rate of contaminant
migration, the original objective of the IRA was to prevent the
STFP from reaching Lake Ladora prior to the implementation of the
final remedy. However, recent investigations have shown that the
STFP is not expected to migrate into either Lake Ladora or Lower
Derby Lake prior to the implementation of the final remedy and ~s
possibly being biodegraded naturally (Shell May 1990, August
1990b, December 1990b).
Since there is no imminent threat of contamination to Lake Ladora
or Upper Derby Lake by the STFP, interim response alternat~ves
cannot be meaningfully developed or evaluated within the context
of the original objective of this IRA. In accordance with
Section 22.1(1) of the Federal Facility Agreement which addresses
the "assessment and, as necessarv, the selection and
implementation of an IRA . . .", an evaluation of monitoring as
the appropriate course for the interim response action has been
conducted. This evaluation shows that: (1) the STFP poses no
risk to human or non-human biotic receptors because it is not
expected to enter the lakes prior to the final remedy, and
(2) there is no significant benefit in terms of cost or
accelerated cleanup by conducting an IRA on the plume because of
the low rate of contaminant migration and field and laboratory
investigations indicate active biodegradation may be occurring in
the plume. Therefore, monitoring with the specific objectives of
verifying the rate of contaminant migration and ensur~ng current
knowledge of the location of the leading edge of the plume over
the time frame of the IRA, is the appropriate course for this
IRA. Determination concerning the implementation of this IRA has
been reached through a consideration of the objectives of
Sections 2.3(a), 22.5, and 22.6 of the Federal Facility
-2-
-------
.
Agre~ment, and by application of the Decision Flow Chart for
Other contamination Sources IRAs adopted by the Organizations and
the State of Colorado at the June 7, 1989 Subcommittee meeting
(F~gure 1-2). The evaluation process is discussed further ~n
Section 3.0.
-3-
-------
SITE CHARACTERIZATION
DOES SITE
POSE A
SIGNIFICANT RISK
TO HUMAN OR
NON-HUMAN BIOTIC
RECEPTORS
?
INTERIM RESPONSE
ACTION SELECTION
From. WOO~E. 1988
NO OR
DATA INADEQUATE
MONITORING/MAINTENANCE
NO
NO
YES
Figure: 1.2
DECISION FLOW CHART FOR
INTERIM REMEDIAL ACTION
VERSUS MONITORING/MAINTENANCE
Prepared by.
-------
2.0
SITE DESCRIPTION
2.1
LOCATION AND SITE HISTORY
The STFP is defined as the composite plume of benzene, toluene,
and xylene (collectively referred to as BTX), bicycloheptadiene
(BCHPD), and dicyclopentadiene (DCPD) dissolved in the uppermost
water-bearing zone (WBZ1) groundwater. Groundwater in WBZ1 flows
radially away from the South Tank Farm to the southeast, south,
and southwest. The dissolved plume originates from the area of a
LNAPL plume located near Tank 464A.
The STFP and u~APL plume constituents include compounds
previously stored in the South Tank Farm (STF) and used in the
manufacture of pesticides and compounds potentially associated
with other production, disposal, and storage activities in the
South Plants. Between 1947 and 1978, Tanks 464A, 464B, and
others were used intermittently to store DCPC and BCHPD bottoms
generated from pesticide manufacturing.
Tanks 464A and 464B were cleaned in 1956, 1966, and 1967. In
1956, BCHPD bottoms were "pumped" onto the ground, and the
affected area was later cleaned up. In 1966, residue from a
mixture of fuel oil and BCHPC bottoms containing DCPD was buried
in the STF. In 1967, a mixture of CCPD bottoms and fuel oil was
collected in a low spot in the STF, and later drummed and shipped
offsite. From 1960-1963, leakage of BCHPD/DCPD bottoms occurred
from a pipe connected to Tank 464A, although the quantity spilled
is unknown. Additional disposal and spill events involving BCHPD
and DCPD occurred at unidentified locations in the STF in 1964
and 1978, respectively.
Although records do not show that either benzene, toluene, or
xylene were stored in the STF, a large spill of benzene
-4-
-------
containing toluene and xylene impurities reportedly occurred at
an unidentified location in the STF in 1948. Toluene may also
have been present in trace amounts in BCHPD.
2.2
HYDROGEOLOGY
Two geologic units occur in the STFP study area: an upper
alluvial unit, underlain by the Denver Formation. The alluvium
consists of brown, unconsolidated, silty sand with increasing
silt and clay content at depth. The alluvium ranges from
approximately 5 feet thick near the STF to 25 feet thick near
Lake Ladora.
The Denver Formation underlying the alluvium is composed of brown
to green, weathered and unweathered claystones, mudstones, and
siltstones. These strata, referred to as the VC (volcaniclast~c
unit) and VCE (volcaniclastic equivalent unit) in the South
Plants study Area Report (Ebasco 1989), are fractured. The
uppermost portion of the Denver Formation is weathered and
averages 4 to 6 feet thick, but may extend to approximately 20
feet at some locations. Lithologic variability near the leading
edge of the STFP is shown by the geologic cross-section in
Figure 2-1.
The STFP affects the WBZ1, as defined in the South Plants Study
Area Report (Ebasco 1989). WBZ1 encompasses saturated alluvium
and the uppermost weathered Denver Formation. The top of WBZ1 is
defined by the water table and the base is defined by a green to
brown Denver Formation claystone exhibiting a lesser degree of
fracturing and weathering (Ebasco 1989, Shell 1989). In the STFP
area, WBZ1 ranges in saturated thickness from approximately 10 to
25 feet.
-5-
-------
A
NORTHWEST
:IUD 1
Sond,
lilt" dr,
Sand. 1.11 r I
cla,I,. elf' 10
.. :1240 IIIOhll, 111011' 5.11, lond" d.,
.
. 50nd,..II" IUOhll,
....
. tnolll
.
III
C Sand, IUI,. dr,
.
. :IUD
:a 50nd, IIIOhll, 111011' Son', clo",. dr, 10 mOil'
! Sandl'o"l, cla",. 8hghll,
.. mOIII, wlDthlnd
... Sand, .,."..." 111011'
.. Cla,lto",. lond,. 50nd,10I11, ."1,. moll'
.
.. :1220 t"Iht)' 11\0'1' (10'110"1, .ond, .ft po. I.
!i mOIII, ..Olhl..d In par I.
c Cla,.to"l, lill,. biD", .lIuClu..
.!
i dor' ....." 10
. "..n
ki 5210
A'
SOUTHEAST
tl09
251
:12:10
:1240
Sond,I.It, Sond, 1111,. dr,
Sond
Clo,llonl wllh call chi I...ah Sand, 1.11, Sonde .11." cta,.,. :1230
Mild'ion.. hord 105111. land, dr, 1o mO'I'
Cla,I'anl - Mud.lone,
d., Cia,. 1111, 10 Sond, 1111,
UudIIO"I, hord Silt. '10)'8, Sonde la'u,oled
Sonde clo,e, 5220 -
Cla,ltonl ~ Mudslonl. Clo,
wa,.. .nl.r Ing h011
Mu'IIO"1
Cia" 1111, 10 Sondllon~. £10,1,.
Clo,.,one - Mud.lonl, d'r Sand, clar" .,o,herea
Cler.lanl, ..1 ~210
Cla'llanl - Mudl'onl.
1.lIr, no' .,I'r .11
5200
~200
TH04
02584
T
CONE PENETROMETER
TEST HOLE
WELL IDENTIFICATION
WATER
LEVEL
NOV 1989
SCREENED
INTERVAL
CHANGE IN LITHOLOGY
f
N
100
50
o
100
200
Figure 2-1
GROUND SURFACE
HORIZONTAL SCALE IN FEET
I/ERTICAL SCALE 10. EXAGGERATION
Geologic Cross-SectIOn A-AI
P,epo,ed by
TOP OF DENVER
FORMATION
LOCA TlON OF CROSS SECTIONS,
SOUTH TANK FARM PLUME AREA
~ IIIIK-ENI/IRONIIIIENTAL 5ERI/ICES
-------
The water table occurs in the alluvium in the northwestern and
southeastern portions of the study area, and in the weathered
Denver Formation immediately southwest of the STF (Figure 2-2).
Groundwater in WBZ1 flows away from the STF to the southeast,
south, and southwest. The water table gradient is reduced near
the lakes, although near the northwest corner of Lower Derby Lake
groundwater flowpaths are deflected sharply towards the southwest
and in the direction of Lake Ladora.
Water levels in the STF area have been declining (RMA-PMO
database). Since the spring of 1988, water levels near the tank
farm have declined as much as 5 feet, while water levels in wells
near Lake Ladora have declined approximately 1 to 2 feet (Shell
May 1990 and December 1990b).
The hydraulic gradient in the STF area varies from approximately
0.015 ft/ft in the vicinity of the tanks to less than 0.005 ft/ft
near Lake Ladora (Figure 2-2). The water-level data in the RMA
database indicate that the average hydraulic gradient for the STF
area appears to be slightly decreasing with time.
In the Fall of 1989, single-well injection (slug) tests were
conducted within the weathered Denver Formation near Lake Ladora
and Lower Derby Lake. The calculated hydraulic conductivities
from seven slug tests conducted near Lake Ladora ranged from 1.6
x 10-3 to 4.3 X 10-5 em/see, and from 4.0 x 10-4 to 3.4 X 10-4
em/see for the tests performed in the vicinity of Lower Derby
Lake. These estimates appear to be in agreement with the
observed field data.
2.3
NATURE AND EXTENT OF CONTAMINATION
LNAPL near Tank 464A is the primary source for the STF dissolved
phase plume and the highest concentrations in groundwater occur
-6-
-------
~
2180000
I
"
,
~
B
~
leaend
o Well location
. Well location With Data
"*" Cluster Well location
+- Cluster Well location
With Data
. Water Level location
- - DrolOoge
.... - Railroad
-- - - Section Boundary
~ Lakes
CJ BUilding/Structure
o Berm
5241i~
. Water leyel EllIYOtlon
(Ft oboye MSl)
-
# Contour Intervol
14i) Dashed where Inlerred
,--- ApproXimate Contours,
1 foot Interval
north
~
o 250 500
. -
fEET
1000
ROCKY MOlJITAIII ARSENAL
South Tn Fann As..
fIcp. 2-2
WATER TABlE CONTOUt MAP
FBI 1900
~~...~-~I'O\ATDj
-------
primarily near Tank 464A (Figures 2-3 through 2-7). Benzene
exhibits the greatest concentration and areal distribution of tr.e
STFP compounds, and defines the leading edge of the STFP directed
southwest toward Lake Ladora. DCPD is the most widely
distributed contaminant within the south-southeastern component
of the STFP and defines the leading edge of the plume towards
Lower Derby Lake. None of the STFP compounds were detected in
wells located within 500 feet of either Lake Ladora or Lower
Derby Lake.
Based on a comparison between the 1983/84 and Spring 1990 water
quality data, the observed average rate of contaminant migration
at the leading edge of the plume was approximately 33 ft/yr. The
recent Fall 1990 investigations indicate the plume has not
advanced since spring 1990. Using a conservative basis, this
historically observed average migration rate and the current
location of the leading edge of the plume (approximately 1350
feet upgradient of Lake Ladora along the groundwater flowpath and
900 feet from the nearest point of Lake Ladora), the STFP is not
expected to impact Lake Ladora prior to implementation of the
final remedy.
Groundwater quality information obtained during 1990 show an
inverse correlation between dissolved oxygen (DO) concentrations
and the total concentration of BTX, primarily benzene. This
becomes evident along the axis of the STFP; near the suspected
source where BTX concentrations are high, the DO levels are low;
and at the edge of the plume, where BTX concentrations are lower,
DO levels are higher. This inverse correlation is consistent
with data presented by Chiang et ale (1989), and indicates that
these aromatic compounds may be biodegraded in the presence of
appropriate DO concentrations. Biodegradation along the STFP may
contribute to the variability and recently observed decrease in
-7-
-------
Approximate limit of
Saturated Alluvium
~
~
~
--
=.:::=--..:= J -- -
2185000
-- -
Legend
o Well locotlon
. Well location With Data
-?- Cluster Well location
-+- Cluster Well location
With Data
. Water level location
- - Drainage
.......- Rallrood
- - - Section Boundary
~ lakes
o BUilding/Structure
o Berm
10
. Concentration ug/!
-"t::l' Isoconcentratlon Une
CRL Certlflcal Reporting limit
«27)
north
~
o 250 500
1000
L--- - - ----II
FEET
ROCKY MOlHT MI ARSENAL.
South Tn FBlm Alea
FllPe 2-3
BENZEJ£ CONCENTRATIONS
III OROlH>WATER
Fal 1000
~"Cfn9()H IUU>9QI CO'II'CJfIAIION
~~"':-"'nM_IMI'."
-------
I
218OOC1O
21810lIO
21820lIO
--.J
2185000
I
1-
D \
\
\
I
B
~
--
---
--,-=--=-
2185000
1
218OOC1O
1-
2184000
---,---
21820lIO
I
21810lIO
218JOOO
Leaend
o Well Location
. Well Location Wllh Dota
~ Cluster Well Location
+ Clusler Well Location
Wilh Data
. Water Level Location
- - Drainage
-'''t- ROllrood
- - - Section Boundary
~ Lakes
o BUilding/Structure
o Berm
10
. Concentration ug/I
",~ Isocancenlrotlon Une
CRL Certilical Reporting Urnlt
«35)
north
~
1000
.
o 250 500
FEET
ROQ
-------
leaend
0 Well Locotlon
. Well Locotion With Doto
4- Cluster Well Location
2180000 21111000 21112000 21l14OOO + Cluster Well Location
I I With Data
a \ . Water Level Location
\
\ - - Drainage
\ - ...,- Railroad
- - - Section Boundary
\
\ rWJ lake.
\
~ CJ Building/Structure
o Berm
~ 8<24 10 Concentration ug/l
.
",f::/ Isoconcentrotlon LJne
o CRl Certilical Reporting limit
~ «24)
t
j north
~ ~
B
~
0 250 500 1000
. - .
fEET
~ ROCKY MOlHTAJI ARSENAL
- - South Tn Farm AI..
--I , ~. 2-5
2180000 21111000
XYlENE COt«;ENTRAT1ONS
tI GAOlN>WA TEA
Fal 1900
@~..~~..IDW"mAI"'''
-------
.
I ~ ~~~~ (i)
/~ <18 8 c.\~:@ fu@
o <1.8 I 0 <2000 <2000
, <~2~F-!. <18
<1~8 (8<18 <1.8 I 0 <~~~1!~~
, . <'.8 1/ I ~ 1000 J ..?) '*
) 84 I." '\ /.,,/;'(1:-'./. <1 8
" . <2000 \ \. JOO ~:;.' A:
SECTION 2 ~ <18 0 I """'.-q .<18
~ '---=-.....
,,/ .<18 0 0 0 ,,""- .<18. <1.8
,/ <~8 .<18 <18 /.<18 ~.<18~__'
{. 8<1 8 "
I
-------
I
....
~
~
0 0
~
--
~
-r----
2182000
21Il4OOII
- .- --=--==--==-
2185000
I
2180000
--I
2181000
Legend
o Well Locotlon
. Wall Locotlon With Data
-9- Cluster Well Location
-+- Cluster Well Location
With Data
. Woter Level Location
- - Drainage
-H-t..- Railroad
- - - Section Boundary
~ Lakes
D Building/Structure
o Berm
10
. Concentration ug/I
~,r::t' IsoconcentrotJon Une
CRL Certlflcol Reporting Limit
«J 7)
north
~
o 250 500
'--
1000
.
FEET
ROOWA TEn
Fa. 1000
(@~..~~1"
-------
benzene concentrations in wells near the plume margin (Shell May
1990 and December 1990b).
Additionally, laboratory studies conducted using saturated
sediment samples from the RMA verify the existence of bacteria
capable of degrading BTX and demonstrate the increased rate of
biodegradation at higher concentrations of dissolved oxygen
(Shell May 1990 and August 1990b).
Laboratory studies are currently being conducted to study natural
and enhanced microbial degradation of BTX, DCPD, and BCHPD
(Shell, December 1990c). These studies will also determine the
potential for the biodegradation of chloroform and chlorobenzene.
The aquifer cores for this study were obtained adjacent to Wells
01552, 01588, 02506, and 02579. and groundwater was collected
from Well 01581 for the soil-microcosm studies.
Preliminary results of this study indicate that STFP area soils
are similar to those used in the original biodegradation study-
Enumeration of culturable micro-organisms for aerobes and
facultative anaerobes are 103_108 and 103_104, respectively
(Shell, February 1991). The aerobe populations are similar to
those found in the previous study, while the facultative anaerobe
populations are approximately 2 to 3 orders of magnitude greater.
In general available nutrients (N as NH+4 and P as P04-3) are
present in slightly higher concentrations within the STFP aquifer
materials. Comparison of this data with the results from the
original biodegradation study indicate that conditions within the
STFP are favorable for the microbial degradation of BTX and
chloroform.
In summary, the results of the 1990 investigation indicated that:
(1) STFP compounds are not expected to migrate into either lake
before the final remedy can be implemented. Therefore, there is
-8-
-------
no imminent threat of contamination to Lake Ladora or Lower Derby
Lake due to STFP compounds; (2) no STFP compounds were detected
in monitoring wells located within 500 feet of either lake;
(3) cross-contamination probably occurred during the spring 1988
sampling event resulting in the overestimation of the extent and
rate of dissolved benzene migration; and (4) natural
biodegradation causes significant temporal and spatial
variability in the concentrations of benzene, particularly in
wells located near the plume margin.
-9-
-------
3.0 INTERIM RESPONSE ACTION OBJECTIVE AND EVALUATION
The original objective of the STFP IRA was to prevent the STFP
from migrating into Lake Ladora. This objective was based on the
interpretation that the STFP may migrate into Lake Ladora prior
to the implementation of the final remedy (Shell 1989). However,
recent investigations have shown that the STFP will not migrate
into either Lake Ladora or Lower Derby Lake prior to the
implementation of the final remedy, and the plume may be
biodegrading (Shell May 1990, August 1990b, and December 1990b).
Therefore, interim response alternatives cannot be meaningfully
developed or evaluated within the context of the original
objective of this IRA. In accordance with section 22.1(1) of the
Federal Facility Agreement which addresses the "assessment and,
as necessarv, the selection and implementation of an IRA . . .,"
an evaluation of monitoring as the appropriate course for the
STFP IRA has been conducted as specified in the Final Task Plan
for Remediation of Other Sources Interim Response Action
(Woodward-Clyde 1989). The results of this evaluation follow.
Figure 1-2 shows the questions which must be answered to
determine whether monitoring is the appropriate course for
"hotspot" IRAs (Woodward-Clyde 1989). The answers to these
questions for the STFP are as follows:
1. The LNAPL portion of the STFP is an active, primary
source of contaminants; however,
2. Neither the LNAPL nor the leading edge of the dissolved
plume pose significant risk to human or non-human biotic
receptors since neither plume is migrating into the
lakes, nor expected to do so, prior to the final remedy;
moreover,
-10-
-------
3. There is no significant long-term benefit (either cost or
accelerated cleanup) of conducting an interim response
action on the dissolved or LNAPL plumes since migration
is very slow, if moving at all. In addition, natural
biodegradation of the dissolved plume may be occurring.
Therefore, according to the decision logic agreed upon by the
organizations and state, monitoring is the appropriate action for
this IRA. Accordingly, the objective of this IRA is to monitor
the STFP to: (1) verify the data upon which conclusions on the
rate of contaminant migration have been made (Shell May 1990 and
December 1990b), and (2) verify the location of the leading edge
of the dissolved plume over time. The monitoring network
proposed to achieve these objectives is described in Section 4.
-11-
-------
4.0
DESCRIPTION OF THE INTERIM RESPONSE ACTION
The monitoring network proposed to meet the objectives of the
STFP IRA consists of three components:
.
One-time comprehensive verification monitoring program of
groundwater quality throughout the STFP to verify
conclusions regarding the rate of contaminant migratlon and
occurrence of biodegradation presented in Shell May 1990.
The verification monitoring program was completed December
1990 and the results are presented in Shell December 1990b.
.
Routine annual monitoring of
location of the leading edge
South Lakes; and
selected wells to verify the
of the STFP with respect to the
.
Quarterly measurement of water-levels throughout the STFP
area to monitor groundwater flow directions and gradients.
The verification program monitoring network consists of 46 wells
located throughout the STFP area (Figure 4-1). This program was
completed Fall 1990 (Shell December 1990b) in support of this IRA
document. Target analytes included benzene, toluene, xylene,
BCHPD, and DCPD. Target analyte concentrations were determined
using USATHAMA Method UU-8 (volatile compounds). To prevent the
loss of volatile compounds during sample collection, a
submersible pump was used whenever possible. Wells were sampled
sequentially from areas of low concentration to areas of higher
concentration based on analytical data from Spring 1990 sampling.
Field measurements of DO were made at the time of sample
collection. Information from this monitoring program was used to
verify the extent and migration rate of STFP constituents and to
verify the existence of conditions conducive for biodegradation
within the STFP.
-12-
-------
"
,
~0202]
02024
02025+
O~
'~
)
C"
2180000
~
~-
t
t::
-----1- ------.
2180000 2111000
2111000
I
2112000
I
2114000 2185000
01522 J ..L ---
a 001012 0152110 .Do 015~
r~)-';ti,~~~-;'a'011521 u ..
1 ~ OIQlI 801534 01550 '\
01 q;.. 00,..,,) 01531 a
,lflH DU" 3 -bi'5&/)8015~]u015.12 0 01011
00153. 01~90 aOI!>48
001082 OI~00r1D.!lI~I '
001542 Ol~ - r ~Jbl" OIMI ..
1 015418 0153 . Q. ..0, 1m
02583 ..o11lO4015Q1 01552 015.11
. 02L2 1 01558 0'014 <>015l1li
01157 01015 0li71 01021
01MI 801588 801578 01021
1 ..01002 Ol'l
02051
a O~~
02~B5 I 01075 4£:= OT5I1 . - -
0151. ~101' ~ - -j
I ---------
/' - . ..01583
:L SECTION 1
I
2183000
-I
-- ~ --~
a
o
02057
~ 02051
8
02511 8
02512
002573
802514 02L,
~
802510
002511
a 02054
02034
+ 02035
0203.
8025111
02575
8
SEcmON 2
1002515
.02511
0251.
. Dun .
.02501
02581 8 02502
. 02503. ~21W
021W
.
02504
. .
. 02505 0259. 02051
0250. 0 ~2060.........- - - _I
- ~~507 02511 " . 0205210 1
~02508 (.
~:'- f"
2021 ---- if
02027 0102.
02021 + ~ 01025
02021 0 I 02.
---=== ---,--= =- -'---r-=- _I=-. =j -=.-:.
2182000 218J11OO 2184000
.. a02!!11
,
025 ..
o
1002513
02508
8
=--=- r-- -=---=. =
2185000
-I
Lsoend
o Well locolion
. Sampled Well I ocalion
.~ Chisler Well locallon
.+ Cluster Well locallon
Wllh Data
. Water levul location
Drainage
.... Railroad
. - - Secllon Boundary
~ L.akes
r:1 BUilding/Structure
o Berm
01:0 Well Idenlilicollon
...,
..
~
north
~
o
500
1000
,
L--
flIT
ROCKY UOLNT AN ARSENAL
South Yri F8Im Aro.
Fbn 4-1
l/HII.:Al1CH WJNlaHi N.1W01IK
WIllI SAIoIUD
hi IlOO
---------- --
~MIJI'"'''''' I
-------
Routine monitoring will be performed to verify the location of
the leading edge of the STFP (Figure 4-2). Groundwater quality
will be monitored annually in 24 wells to meet this objective.
The design of this monitoring program will be identical to that
of the verification monitoring program with respect to target
analytes, field measurements of dissolved oxygen, sampling and
decontamination procedures, and analytical methods. Monitoring
of the leading edge of the STFP will be performed annually until
the ROD is issued.
In addition to groundwater quality monitoring, water-levels will
be measured regularly throughout the STFP area to monitor
hydraulic gradients and groundwater flow directions. A component
of this program will be to better understand the hydrology in the
vic1nity of Lake Ladora. To meet this objective, piezometers and
well points will be installed along the northeastern edge of Lake
Ladora (Figure 4-3). This additional water-level information
w1ll be used to evaluate the interaction between Lake Ladora and
local groundwater. As part of th1S effort, the Army has agreed
to monitor the elevation of Lake Ladora and, if practicable,
maintain the lake at an elevation which allows the lake to
recharge the aquifer.
Water-levels will be measured quarterly, as a minimum, for the
network shown on Figure 4-4, and including the new piezometers
and well points. This data will be used to identify significant
changes in gradient or flow direction which may affect the
historically observed STFP migration pattern or rate.
-13-
-------
~
218JOOO 2114000 2115000
.---.---~--'!I~~,b!?1:'" _JTOI~-1----
~ 00151J 6 1152. a \
02~7 I (c;j 0IMIij!J[;J 10 (V '.
02~ ~ 0- oD15.Jt 0155D \
..... :2511 0 'Ifot 0'.1"3 ~515~I~f~015J2 01i3:I018
'-I 02572 0015.18 OIMto 001548
01125110 002573 001012 0II,~91~"O!l'~~7 '.
002574 000 I <>G15t! OliM 0 iJ!t1 OIMI \
015410 015.18 . . ~~), 015.17
02513 ..011104 011iQ1 01552 0 5Ja
o 02ta I OIW 0'014 1101589
82575 0 0lL7 01015 0li78 01027
o 01558 801581 801571 01028
I 001002 OI~8
82584 02051
. 0 801510 801587 0~5IO
02~85 I 4{:1075 4(:::: OT581 - - '
01581 1018 ~
I .--
/" - - <>0158]
SECTION 1
I
218OODO
I
""
'~
)
("
082517
082064
021\34
~ 020»
021\31
002571
SECTION 2
002515
o 025}8
~
0257.
802577 8
802501
02588 802502
. 0250.)8 ~21\32
0211.U
.
. 02:'104 .
8 02505 8259. 0~8
02501 8 ~20~......-- . . .
- ~~2507 025" ,.- 020520 ~
'-........... .02501 ( .
-~:':- -- r'"
o~g~~ - L f 01024
02028 + + 01025
02021 0 I 021
- ------,- -=-- -,=- -=l==-_,_=--=
2182000 211JODO 2114000
==--=-- r-- = =
2111:1000
02514
o
002511
02501
8
I.
t:
---r------'
2180000 2181000
-j
Leoend
o Well Locution
8 Sumpled Well Locution
4 Cluster Well Locubon
+- Cluster Well Locution
With Ootu
. Woter LeVIII t occftion
Orolnoge
"" Ruilrood
- - - Section Boundury
~ Lukes
C) Building/Structure
o Benn
01:0 Wall Idenbrlcullon
j
norlh
I
~
1000
----,
o 500
L-- ---
FrET
ROCKY UOltUAH ARSfNAL
South Tn Farm AI..
F1gw8 4-2
PROPOSED AtNJAt
MONTOONJ tElWOllK
--
--
~"'JI":M"I""I"'N aU'UIAIlU"
~~ ~"."'IIIII ..tIo'I.. .....
. . ""loUn I II "
-------
Approximate l .
Saturated All 1~lt of
uVlum
2181IlOO
2182IlOO
L
~
c
0
o
o 0
o
o 0
2184000
218!1OOO
L-
o r- --
D .
o .
..J4
@b!o. 0
o
0 i2J ~o~
o 0 0
o [Q]tJ
o
0
o~ 0
0
o
o
o
o
r= ---=-
2185000
,
,
o
0\
o
o
,
,
,
i
legend
u EXlsllng Well L
V E ocollon
Xlsllng CI t
locallon us er Well
II Water level
locotion
Droinoge
.......- Roilrood
- - - Section Bound
~ LOry
okcs
C"J BUild /
(0) 1n9 Siructure
I Berm
. New W
11 W ell Locotlon
ell POint l
+ PICZ ocotlon
-+- ometcr l t
POlred P oeo Ion
loco lion Iczomel.r
north
~
o 250 500
~--
fEET
ROCKY MO
South Ta:T~'N ARSI:NAL
FIQI.a 4-3 arm Area
1000
LOCATION MA
WI:lL POI~T~O:N~W
PEZOMI- TERS
@unruu
uv,.."..'.()N ktl.),*N -
.,'111. l'tll~I" .,~.::,u."AIArluN
,".10
-------
Legend
o Wen Locotlon
. Sampled Wen Location
<> Cluster Well Location
2180000 2,.,000 21.2000 218:RJOO 21.4000 21.5000 + Cluster Well Location
01522 With Data
o 001012 015210 015288 . Water Level Locab~n
e015ti 1528 D ,
02057 I ~ 01ga1 r.t 0 (D \ --- Droinoge
02058 01 801534 01~ ~
:2L, 8 1'ra. 0\,013 -6t5es2'5~01532 OIi3~,OI. -+tt+- Railroad
C 02572 801531 015488 .01548 --- Section Boundary
802510 """" 0"'" .~ .. mziI Lakes
I. .02517 .02574 . 1801542 01i55 ~ 18 01551 '
802054 02582 015418 0153 () 1531 I a Building/Structure
~ 02W oDIC 015Q8 01552 0 Berm
02034 802571 8 0::82 I 01 0~014 8015118
.02035 01 7. 01:'0 Well Identilication
02038 02175 ~ 01157 010111 a 01027
8EC'I1ON I 02181 0 W 8015118 801578 01028
I 001002 01"
025114 02051
802515 .02578 8 0 801510 801587 °L5IIO
~- 02585 I .c'075 ~::: oT5II1 ~/
02514 8 ~ 1~8 ~ i
. 0 5118
I --- 801583 - -
802513 02501 ~
.
t I LO::m ~ ~
~ I
~ 1
- -- --- --- -- ---- --- - -
2180000 21.,000 2182000 218JOD11 2184000 218:10l1li
north
~
0 500 1000
L.-- - - ...
fEET
ROCKY MOUNTAN ARSENAl
Soulh 1enk Ferm Aree
Agure 4-4
PROPOSED WATrR - LEVEL
MO/IITORNG t.ETWORK
~aMJIl'S()N KNJ'- ('.(IfI'01A11ON
~ tMW"....NI.<\I N,IVI.:lI.....
"iii. 'I .,11,l1li
-------
5.0
CHRONOLOGY OF EVENTS
The significant events that led to the decision to implement a
monitoring program for the STFP IRA are as follows:
Date
Event
June 1987
The State of Colorado, Shell oil
Company, U.S. EPA, and U.S. Army
agreed to 13 Interim Response
Actions, including Remediation of
Other Contamination Sources (also
known as the "Hotspot Sources").
February 1988
Proposed Consent Decree lodged in
the case of U.S. v. Shell Oil
ComDany with the U.S. District
Court in Denver, Colorado. The
Consent Decree specified 13 Interim
Response Actions, including the
Hotspot Sources.
February 1989
The Federal Facility Aqreement
incorporated the 13 Interim
Response Actions specified in the
Proposed Consent Decree including
the Hotspot Sources.
July 1989
Shell Oil Company completes the
ReDort of HYdroqeoloqic and Water
Ouality Investiqations in the South
Tank Farm Plume. Section 2. RMA
report. In the cover letter to the
report, Shell proposes the STFP be
included as a "Hotspot" IRA.
August 1989
Shell oil Company submitted ReDort
of the Investiqation of the LNAPL
Plume Near Tank 464A. section 1.
RMA to the U.S. Army- The U.S Army
and U.S. EPA agree to include the
South Tank Farm Plume as a
"Hotspot" IRA.
-14-
-------
May 1990
Shell oil Company submitted
Hvdroaeoloaic and Water Oualitv
Conditions. South Tank Farm Plume.
RMA to the U.S. Army. The Army
issued this report to the
Organizations and State for review
and comment.
June 1990
Shell Oil Company submitted Draft
Final Alternatives Assessment for
Other Contamination Sources.
Interim ReSDonse Action. South Tank
Farm Plume to the U.S. Army. The
Army issued this report to the
organizations and State for review
and comment.
July 1990
Shell oil Company received comments
from the U.S. EPA, U.S. Department
of Interior (DOI), and the State on
the Draft Final Alternatives
Assessment for Other Contamination
Sources. Interim ReSDonse Action.
South Tank Farm Plume and
Hvdroaeoloaic and Water Oualitv
Conditions. South Tank Farm Plume.
RMA on July 24, 1990.
August 1990
Shell Oil Company submitted Final
Alternatives Assessment for Other
Contamination Sources. Interim
ReSDonse Action. South Tank Farm
Plume and ProDosed Decision
Document. Other Contamination
Sources. Interim ReSDonse Action.
South Tank Farm Plume to the U.S.
Army. The Army issued this report
to the Organizations and State for
review and comment.
September 1990
Shell oil Company received comments
from the U.S. EPA and the State on
the ProDosed Decision Document.
Other Contamination Sources.
Interim ReSDonse Action. South Tank
Farm Plume on September 24. 1990.
-15-
-------
October 1990
An RMA Committee Meeting was held
October 12, 1990. The parties
agreed to postpone issuing the
Draft Final Decision Document,
Other Contam~nation Sources.
Interim Response Action, South Tank
Farm Plume until mid-January 1991.
In the interim Shell and the Army
were to provide support documents.
December 1990
Shell Oil Company submitted Results
of the Verification Monitorina
Proaram, South Tank Farm Plume,
RMA, Technical Work Plan, LNAPL
Plume Soil Vapor Extraction Process
Field Demonstration Treatability
StudY, Laboratory Screenina Studies
on the Biodearadation of Oraan~cs
in RMA Groundwater, and proiect
Status Report. Laboratory Studies
on Biodearadation or Oraanics in
South Tank Farm Plume Aauifer
Samples, to the u.S. Army- The
Army issued these reports and the
Army report Potential Miaration of
Contaminated Groundwater to Lakes
Ladora and Lower Derby to the
Organizations and State for review
and comment.
-16-
-------
6.0
IRA PROCESS
The IRA process for the STFP IRA is as follows:
04/29/91
1.
As Lead Party, Shell prepared a "Draft Final
Alternatives Assessment for Other Contamination
Sources, Interim Response Action, South Tank Farm
Plume, RMA." The report was submitted to the u.S. Army
for issuance to the DOI and the other organizations and
the State for review and comment. Comments were
submitted by the DOI, u.S. EPA, and the State.
2.
Shell, DOI, and the other Organizations and State will
be afforded the opportunity to participate, at the RMA
Committee level, in the identification and selection of
ARARs pertinent to this IRA.
3.
As Lead Party, Shell submits this Proposed Decision
Document for the South Tank Farm Plume IRA to the u.S.
Army for issuance to the DOI and other Organizations
and State. It includes the Army's final ARARs
decision. Upon issuance, the Proposed Decision
Document is subject to a 30-day public comment period
during which the other organizations and State, the
DOI, or any other person may comment on it. Time
permitting, the Army shall hold at least one public
meeting during the comment period to inform the
community in the vicinity of the RMA about this IRA.
4.
Promptly after the close of the comment period, Shell
will submit the Draft Final Decision Document for the
South Tank Farm Plume IRA to the u.S. Army for
transmittal to the DOI and other organizations and
State.
-------
04/29/91
5.
Within 20 days after issuance of the Draft Final
Decision Document for the South Tank Farm Plume IRA, an
organization (including the State if it has agreed to
be bound by the Dispute Resolution process, as required
by the Federal Facility Agreement, or DOI under
circumstances set forth in the Federal Facility
Agreement) may invoke Dispute Resolution. Dispute
Resolution may concern either the proposed IRA or the
Army's ARAR decision.
6.
After the close of the period invoking Dispute
Resolution (if Dispute Resolution is not invoked) or
after the completion of Dispute Resolution (if
invoked), Shell shall submit a Final Decision Document
for the South Tank Farm Plume IRA to the Army. The
Final Decision Document will include comments received
on the Proposed Decision Document and responses to
those comments. The Army shall then issue a Final
Decision Document to the other Organizations, the
State, and DOI. If Dispute Resolution has been
invoked, the decision may be subject to judicial review
in accordance with Section 39.2 of the Federal Facility
Agreement.
7.
Following issuance of the Final IRA Decision Document,
Shell shall be the Lead Party responsible for designing
and implementing the IRA in conformance with the
Decision Document. Shell shall issue a Draft
Implementation Document to the DOI and the other
Organizations for review and comment. This Draft
Implementation Document shall include final drawings
and specifications, final design analyses, a cost
estimate, and a schedule for implementation of the IRA.
-------
04/29/91
8.
As Lead Party for design and implementation of this
IRA, Shell will issue the Final Implementation
Document, as described above, and will be responsible
for implementing the IRA in accordance with the IRA
Implementation Document.
-------
7.0 APPLICABLE OR RELEVANT AND APPROPRIATE
REOUIREMENTS FOR THE REMEDIATION OF
OTHER CONTAMINATION SOURCES (SOUTH TANK FARM PLUME)
INTERIM RESPONSE ACTION
7.1
INTRODUCTION
These Applicable or Relevant and Appropriate Requirements (ARARs)
address a specific area identified for evaluation for remed~ation
prior to the issuance of a Record of Decision (ROD) for the
Onpost Operable Unit of the Rocky Mountain Arsenal. The actions
selected involve monitoring the plume which emanates from the
area of the South Tank Farm. Some standards are discussed in
general terms, to be further defined as more specific remedial
actions are identified.
7.2
AMBIENT AND CHEMICAL-SPECIFIC ARARs
Ambient or chemical-specific requirements set concentration
limits or ranges in various environmental media for specific
hazardous substances, pollutants, or contaminants. Such ARARs
either set protective cleanup levels for the chemicals of concern
in the designated media or indicate an appropriate level of
discharge based on health and risk-based analyses and
technological considerations.
The objectives of this IRA are discussed in the Assessment
Documents. This IRA will be implemented prior to the final
remediation to be undertaken in the context of the Onpost
Operable Unit ROD. The lists of specific contaminants included
in the Assessment Documents have been completed based upon the
field data concerning these specific sources. Since the selected
approaches for this IRA do not involve the treatment of
groundwater from the area of the South Tank Farm Plume, no
-20-
-------
chemical-specific ARARs concerning water were selected for this
IRA.
Air Emissions
The approaches selected by this IRA do not involve the operation
of any treatment system which will result in air emissions. The
monitoring to take place in the area of the South Tank Farm Plume
will not affect any emissions that may originate in that area,
but air monitoring will identify any potential concerns regarding
emissions from this area.
The standards contained at 40 CFR Part 50 were reviewed and
determined to be neither applicable nor relevant and appropriate
to this IRA. These standards apply to Air Quality Control
Regions (AQCR), which are markedly dissimilar from the area
within which activity is being conducted pursuant to this IRA.
An AQCR is generally a very large area, covering many square
miles. The South Tank Farm Plume covers an extremely small area,
far smaller than an AQCR. These standards are not generally
applied to specific emissions sources, such as automobile
tailpipes and smokestacks. These considerations lead to the
determination that these ambient air standards are neither
relevant nor appropriate to apply within the context of this IRA.
other air standards, such as those contained at 40 CFR Parts 60
and 61 and similar state standards such as those contained at 5
CCR 1001-10, Regulation 8 were not considered as potential ARARs
since the IRA will not include a treatment system which causes
air emissions.
-21-
-------
7.3
LOCATION-SPECIFIC ARARs
Location-specific requirements set restrictions on activities,
depending on the characteristics of the site or the immediate
environment, and function like action-specific requirements.
Alternative remedial actions may be restricted or precluded,
depending on the location or characteristic of the site and the
requirements that apply to it.
Paragraph 44.2 of the Federal Facility Agreement provides that
"wildlife habitat(s) shall be preserved and managed as necessary
to protect endangered species of wildlife to the extent required
by the Endangered Species Act (16 U.S.C. 1531 et sea.), migratory
birds to the extent required by the Migratory Bird Treaty Act (16
U.S.C. 703 et sea.), and bald eagles to the extent required by
the Bald Eagle Protection Act, 16 U.S.C. 688 et sea."
While this provision is not an ARAR, the statutory requirements
are ARARs and will be complied with for purposes of this IRA.
Based on where facilities related to this IRA are likely to be
located the Army believes that this IRA will have no adverse
impact on any endangered species or migratory birds or on the
protection of wildlife habitats. Coordination will be maintained
with the U.S. Fish and Wildlife Service to ensure that no such
adverse impact arises from implementation of this IRA.
The provisions of 40 CFR 6.302(a) and (b) regarding construction
that would have an adverse impact on wetlands or be within a
floodplain are considered relevant and appropriate to apply in
the context of this IRA. The Army will comply with these
regulations to the maximum extent practicable to avoid
construction conducted pursuant to this IRA in a manner
have an adverse impact on wetlands or be within a flood
the would
plain.
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The regulations at 40 CFR 230 were reviewed and determined not to
be applicable within the context of this IRA because no discharge
of dredged or fill material into waters of the United States is
contemplated. Because these regulations address only the
disposal of such materials into the waters of the United states,
which is not contemplated, they are not considered to be relevant
and appropriate to apply in the context of this IRA.
The regulations at 33 CFR 320-330 were reviewed and determ~ned to
be neither applicable nor relevant and appropriate because they
address actions affecting the waters of the United states. No
such actions are contemplated within the context of this IRA.
7.4
ACTION-SPECIFIC ARARs
DescriDtion
Performance, design, or other action-specific requirements set
controls or restrictions on activities related to the management
of hazardous substances, pollutants, or contaminants. These
action-specific requirements may specify particular performance
levels, actions, or technologies as well as specific levels (or a
methodology for setting specific levels) for discharged or
residual chemicals.
Construction Occurrina Incident to the IRA
Air Emissions
On the remote possibility that there may be air emissions during
the course of the construction associated with this IRA, the Army
has reviewed all potential ambient or chemical-specific air
emission requirements. As a result of this review, the Army
found that there are, at present, no National or State ambient
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air quality standards currently applicable or relevant and
appropriate to any of the volatile or semivolatiles chemicals in
the ground water found in the area in which construction is
contemplated.
In the context of this IRA, there is only a very remote chance of
any release of volatiles or semivolatiles and, even if such a
release did occur, it would only be intermittent and of very
brief duration (because the activity that produced the release
would be stopped and modified appropriately if a significant air
emission, based upon specific standards contained in the Health
and Safety Plan, was detected by the contractor's air monitoring
specialist). Both the Army and Shell have significant experience
with the construction of monitoring, extraction and reinjection
wells and have not experienced any problems from air emissions
during construction of such facilities. Since minimal excavation
of saturated material is anticipated, it is not believed that air
emissions are likely to occur, as they might if large amounts of
saturated material were excavated and necessitated drying. The
site-specific Health and Safety Plan will adequately address
these concerns. This plan to be developed for use in the IRA
will detail operational modifications to be implemented in the
event monitoring detects specific levels of such emissions.
The National Emissions Standards for Hazardous Air Pollutants
(NESHAPS) were evaluated to determined whether they were
applicable or relevant and appropriate to apply in the context of
construction of this IRA. These standards were not considered
applicable because they apply to stationary sources of these
pollutants, not to construction activity. These standards were
not considered relevant and appropriate because they were
developed for manufacturing processes, which are significantly
dissimilar to the short-term construction activity contemplated
by this IRA.
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The provisions of 40 CFR 50.6, and any more stringent standards
found at 5 CCR 1001-14, will be considered relevant and
appropriate. These standards are not applicable because they
address Air Quality Control Regions, which are areas
significantly larger than and different from the area of concern
in this IRA. Pursuant to these regulations, there will be no
particulate matter transported by air from the site that is in
excess of 50 micrograms per cubic meter (annual geometric mean)
and the standard of 150 micrograms per cubic meter as a maximum
24-hour concentration will not be exceeded more than once per
year.
Worker Protection
The provisions of 29 CFR 1901.120 are applicable to workers at
the site because these provisions specifically address hazardous
substance response operations under CERCLA. The final rule found
at 54 FR 9294 (March 6, 1989) will be operative. (The final rule
became effective on March 6, 1990.)
General Construction Activities
The following performance, design, or other action-specific state
ARARs have been identified by the Army as relevant and
appropriate to this portion of the IRA and more stringent than
any applicable or relevant and appropriate federal standard,
requirement, criterion, or limitation. These standards are not
applicable because they specifically do not address a remedial
action or circumstance under CERCLA:
Colorado Air Pollution Control Commission Regulation No.1, 5 CCR
1001-3, Part III (D) (2) (b), Construction Activities:
a.
Applicability - Attainment and Nonattainment Areas
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b.
General Requirement
Any owner or operator engaged in clearing or leveling
of land or owner or operator of land that has been
cleared of greater than one (1) acre in nonattainment
areas for which fugitive particulate emissions will be
emitted shall be required to use all available and
practical methods which are technologically feasible
and economically reasonable in order to minimize such
emissions, in accordance with the requirements of
section III.D. of this regulation.
c.
Applicable Emission Limitation Guideline
Both the 20% opacity and the no off-property transport
emission limitation guidelines shall apply to
construction activities; except that with respect to
sources or activities associated with construction for
which there are separate requirements set forth in this
regulation, the emission limitation guidelines there
specified as applicable to such sources and activities
shall be evaluated for compliance with the requirements
of Section III.D. of this regulation. (Cross
Reference: Subsections e. and f. of Section III.D.2 of
this regulation).
d.
Control Measures and Operating Procedures
Control Measures or operational procedures to be
employed may include but are not necessarily limited to
planting vegetation cover, providing synthetic cover,
watering, chemical stabilization, furrows, compacting,
minimizing disturbed area in the winter, wind breaks,
and other methods or techniques.
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Colorado Ambient Air Quality Standards, 5 CCR 1001-14, Air
Quality Regulation A, Diesel-Powered Vehicle Emission Standards
for Visible Pollutants:
a.
No person shall emit or cause to be emitted into the
atmosphere from any diesel-powered vehicle any air
contaminant, for a period greater than 10 consecutive
seconds, which is of such a shade or density as to
obscure an observer's vision to a degree in excess of
40% opacity, with the exception of Subpart B below.
b.
No person shall emit or cause to be emitted into the
atmosphere from any naturally aspirated diesel-powered
vehicle of over 8,500 lbs gross vehicle weight rating
operated above 7,000 feet (mean sea level), any air
contaminant for a period of 10 consecutive seconds,
which is of a shade or density as to obscure an
observer's vision to a degree in excess of 50% opacity.
c.
Diesel-powered vehicles exceeding these requirements
shall be exempt for a period of 10 minutes, if the
emissions are a direct result of a cold engine start-up
and provided the vehicle is in a stationary position.
d.
This standard shall apply to motor vehicles intended,
designed, and manufactured primarily for use in
carrying passengers or cargo on roads, streets, and
highways.
The following performance, design, or action-specific state ARAR
is applicable to this portion of the IRA and is more stringent
than any applicable or relevant and appropriate Federal standard,
requirement, criterion or limitation:
04/29/91
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.
Colorado Noise Abatement statute, C.R.S. Section 25-12-103:
Zone
a.
Each activity to which this article is applicable shall
be conducted in a manner so that any noise produced is
not objectionable due to intermittence, beat frequency,
or shrillness. Sound levels of noise radiating from a
property line at a distance of twenty-five feet or more
there from in excess of the db(A) established for the
following time periods and zones shall constitute prima
facie evidence that such noise is a public nuisance:
7:00 a.m. to
next 7:00 'C.m.
7:00 p.m. to
next 7:00 a.m.
Residential
Commercial
Light Industrial
Industrial
04/29/91
55 db(A)
60 db (A)
70 db (A)
80 db (A)
50 db(A)
55 db(A)
65 db(A)
75 db(A)
b.
In the hours between 7:00 a.m. and the next 7:00 p.m.,
the noise levels permitted in subsection (1) of this
section may be increased by ten db(A) for a period of
not to exceed fifteen minutes in anyone-hour period.
c.
Periodic, impulsive, or shrill noises shall be
considered a public nuisance when such noises are at a
sound level of five db(A) less than those listed in
Subpart (a) of this section.
d.
Construction projects shall be subject to the maximum
permissible noise levels specified for industrial zones
for the period within which construction is to be
completed pursuant to any applicable construction
permit issued by proper authority or, if no time
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limitation is imposed, for a reasonable period of time
for completion of the project.
e.
For the purpose of this article, measurements with
sound level meters shall be made when the wind velocity
at the time and place of such measurement is not more
than five miles per hour.
f.
In all sound level measurements, consideration shall be
given to the effect of the ambient noise level created
by the encompassing noise of the environment from all
sources at the time and place of such sound level
measurements.
In substantive fulfillment of Colorado Air Pollution Control
Commission Regulation No.1, this IRA will employ the specified
methods for minimizing emission from fuel burning equipment and
construction activities. In substantive fulfillment of
Colorado's Diesel-Powered Vehicle Emission Standards, no diesel
motor vehicles associated with the construction shall be operated
in manner that will produce emissions in excess of those
specified in these standards.
The noise levels pertinent for construction activity provided in
C.R.S. Section 25-12-103 will be attained in accordance with this
applicable Colorado statute.
Wetlands ImDlications
Through estimation of the general area where any construction
would occur or facilities be located and the nature of the
facilities to be constructed, the Army does not believe that any
wetlands could be adversely affected. However, until a final
design is selected, it cannot be definitively determined that no
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adverse impact on wetlands will occur. If the final site
selection and/or design results in an adverse impact on wetlands,
the Army will review the regulatory provisions concerning
wetlands impact, generally identified as relevant and appropriate
in the discussion of location-specific ARARs above, and other
appropriate guidance, and will proceed in a manner consistent
with those provisions. Actions taken will be consistent with any
requirements of Section 404 of the Clean Water Act. Coordination
will be maintained with the U.S. Fish and Wildlife Service
concerning any potential impacts on wetlands.
Groundwater Monitorinq
The Army has determined that the substantive provisions of the
regulations contained in 40 CFR S 264.97, and any provisions of 6
CCR 1007-3, S 264.97 which are more stringent than the federal
regulations, are relevant and appropriate to apply to the
groundwater monitoring which is to occur pursuant to this IRA.
Pursuant to CERCLA Section 121(e), 42 U.S.C. S 9621(e), no
federal, state or local permit is required for the groundwater
monitoring to be conducted. The specific monitoring program will
be developed later in the IRA process and may utilize some number
of the existing monitoring wells on the Arsenal, sampling
conducted under the Comprehensive Monitoring Program, the
addition of new wells and/or sampling requirements or any
combination of these approaches in order to fulfill the
substantive requirements of these regulations.
Land Disposal Restrictions and Removal of Soil
There are no action-specific ARARs that pertain to the excavation
of soil during the construction associated with this IRA.
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EPA ~s currently developing guidance concerning the Land Disposal
Restrictions (LOR) and their application during CERCLA response
actions. while guidance is limited, the Army has not, at this
time, made a determination that any listed waste subject to LDR
will be present in the soil removed by this IRA. Further EPA
guidance concerning the applicability of LDRs to CERCLA actions
is likely to be issued prior to the implementation of this IRA
and the Army will review such guidance as it is released. If it
is determined that a listed waste is present, the Army will act
in a manner consistent with EPA guidance for the management of
such w~thin the context of CERCLA actions.
Although removal of soil from the area where any treatment system
will be located is a TBC, not an ARAR, it will be performed in
accordance with the procedures set forth in the Task No. 32
Technical Plan, Sampling Waste Handling (November 1987), and
EPA's July 12, 1985, memorandum'regarding "EPA Region VIII
Procedure for Handling of Materials from Drilling, Trench
Excavation and Decontamination during CERCLA RI/FS Operations at
the Rocky Mountain Arsenal." Soils, not included for further
treatment, generated by excavation during the course of this IRA,
either at surface or subsurface, may be returned to the location
from which they originated (i.e., last out, first in). Any
materials remaining after completion of backfilling that are
suspected of being contaminated (based on field screening
techniques) will be properly stored, sampled, analyzed, and
ultimately disposed as CERCLA hazardous substances, as
appropriate.
For material determined to be hazardous waste resulting from
construction activities, substantive RCRA provisions are
applicable to their management. These substantive provisions
include but are not limited to: 40 CFR Part 262 (Subpart C, Pre-
Transport Requirements), 40 CFR part 263 (Transporter Standards),
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and 40 CFR Part 264 (subpart I, container Storage and subpart L,
Waste Piles). The specific substantive standards applied will be
determined by the factual circumstances of the accumulation,
storage or disposal techniques actually applied to any such
material.
soil Treatment and DisDosal
These proposed remedial actions do not include any significant
possibility of on-site or off-site disposal of soils or
contaminated material excavated pursuant to this IRA. The
selected alternative of monitoring for the South Tank Farm Plume
only involves minimal excavation and should result in only small
amounts of excavated soil remaining to be handled as discussed
above. In the event that some material is later considered for
disposal, ARARs for such activities have been generally
identified, with more specific analysis to follow after any
specific disposal determination is made. On-site disposal of
material is not contemplated. For off-site disposal of hazardous
material the administrative and substantive provisions of 40 CFR
Part 262, Subparts A, B, C, and D, and any provisions of 6 CCR
1007-3, Part 262, Subparts A, B, C, and D which are more
stringent than the corresponding federal regulations, are
considered relevant and appropriate.
7.5
COMPLIANCE WITH THE OTHER ENVIRONMENTAL LAWS
As is evident from the various portions of
IRA was prepared in substantive compliance
(the regulations implementing the National
Act of 1969).
this document, this
with 40 CFR 1502.16
Environmental Policy
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8.0
SCHEDULE
Consistent with the Federal Facility Agreement and the Final
Technical Program Plan FY88-FY92, the milestone for completing
the Draft Implementation Document for the South Tank Farm Plume
IRA is June 28, 1991. The Deadline for completing the IRA will
be established in the Implementation Document.
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9.0
CONSISTENCY WITH FINAL RESPONSE ACTION
Although the Final Response Action has not yet been selected, it
is believed that this IRA will be consistent with and contribute
to the efficient performance of the Final Response Action by:
(1) monitoring the migration of dissolved contaminants in
groundwater emanating from the South Tank Farm site; and
(2) verifying that the STFP does not impact either Lake Ladora or
Lower Derby Lake prior to the Final Response Action. In
addition, the natural biodegradation which is occurring ~s
beneficial for any possible response action selected for the
plume under the ROD.
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10.0
REFERENCES
Chiang, C. Y., J. p. Salanitro, E. Y. Chai, J. D. Colthart, and
C. L. Klein. 1989. Aerobic Biodegradation of Benzene,
Toluene, and Xylene in a Sandy Aqu~fer - Data Analysis and
Computer Modeling. Groundwater vol. 27, no. 6, pp. 823-834.
Ebasco, Services Inc. (Ebasco) 1989a. Final Remedial
Investigation, South Plants Study Area Report.
Shell oil Company, 1989. Report of Hydrogeologic and Water
Quality Investigations in the South Tank Farm Plume,
Section 2, RMA.
Shell oil Company, May 1990. Hydrogeologic and Water Quality
Conditions, South Tank Farm Plume, RMA.
Shell oil Company, June 1990. Draft Final Alternatives
Assessment, Other Contamination Sources, Interim Response
Action, South Tank Farm Plume.
Shell oil Company, August 1990a. Final Alternatives Assessment,
Other Contamination Sources, Interim Response Action, South
Tank Farm Plume.
Shell Oil Company, August 1990b. Laboratory screening Studies on
the Biodegradation of Organics in RMA Ground Water.
Shell Oil Company, December 1990a. Technical Work Plan, LNAPL
Plume Soil Vapor Extraction Process Field Demonstration
Treatability Study.
Shell oil Company, December 1990b. Results of the Verification
Monitoring Program, South Tank Farm Plume, RMA.
Shell Oil Company, December 1990c. Project Status Report.
Laboratory Studies on Biodegradation of Organics in South
Tank Farm Plume Aquifer Samples.
Shell oil Company, February 1991. Laboratory Studies on
Biodegradation of Organics in South Tank Farm Plume (STFP)
Aquifer, Soil and Microbiological Analyses of STFP Aquifer
Core Samples.
U.S. Army Waterways Experiment station, January 1991. Potential
Migration of Contaminated Groundwater to Lakes Ladora and
Lower Derby.
Woodward-Clyde, 1989. Final Task Plan for Remediation of Other
Sources Interim Response Action.
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APPENDIX A
Responses to Comments on the
Draft Final Decision Document
Other Contamination Sources
Interim Response Action
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Copies Furnished:
Major John M. Fomous, U.S. Army Environmental Law Division, 901 N. Stuart
Street, Suite 400, Arlington, Virginia 22203-1837 (w/encl)
Mr. Bradley Bridgewater, U.S. Department of Justice, 999-18th Street,
Suite SOl, North Tower, Denver, Colorado 80202 (w/encl)
Mr. John Barth, Assistant Regional Counsel, U.S. Environmental
Protection Agency, One Denver Place, Suite SOD, 999-18th Street,
Denver, Colorado 80202-2405 (w/encl)
Mr. Gene Czyzewski, CDM Federal Programs Corporation, 1626 Cole Boulevard,
Suite 100, Golden, Colorado 80401 (w/encl)
Document Tracking Center, AMXRM-IDT, Room 132, Building 111, Rocky
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RESPONSES TO EPA COMMENTS
ON TIlE "DRAFr' FINAL DECISION DOCUMENT
Comment 1. Page 6, Section 2.3, the text fails to mention the commitment to find other
sources of LNAPL during the Feasibility Study. We take the Army's April 8, 1991, letter
to reaffirm that commitment. '
Response 1. The Army disagrees with the EP A's assertion that the agreement was to in
fact find other sources of LNAPL during the FS. The commitment made in the April 8,
1991 letter was that "... the issue of source identification is important and will be
addressed by the Feasibility Study". This element is an FS issue and does not need to be
reiterated in this IRA document.
Comment 2. Page 12, Section 4.0. The Army has agreed to maintain the level of Lake
Ladora at an elevation to maintain a higher head in the lake than in the ground water, if
possible, thus, hopefully, inducing a losing condition in the lake. This should be stated in
the Decision Document as it is key to the collection of meaningful water level data as
well as, potentially, to the relationship of the lakes to the ground water.
Response 2. Page 13 of the Final Decision Document states"... the Army has agreed to
monitor the elevation of Lake Ladora and, if practicable, maintain the lake at an
elevation which allows the lake to recharge the aquifer".
Comment 3. Page 13, first paragraph, the text needs to add the commitment made in
the Army's April 8, 1991, letter to collect groundwater samples near the lakes and
analyze for contjlminants of concern. It should be stated the results of lake/groundwater
interaction study may lead to additional water quality sampling if it is shown that ground
water is interacting with the lakes. In that event, the document also needs to include a
list of the analytes to be analyzed, particularly in regard to any additional monitoring
that occurs as a result of the water level monitoring program. This analytes list should
include all contaminants previously detected as requested in EP A's letter of April 11,
1991.
Response 3. The Army is committed to this agreement concerning groundwater sampling
and analysis as stated in the April 8, 1991 letter. However, the Army believes this
element is more appropriate for inclusion in the Implementation Document and does not
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Comment 4. Page 13, last paragraph, the text should be amended to add that quarterly
reports of the water level data and groundwater sampling results will be prepared for
evaluation by the RMA Committee to determine the need for further remedial action as
part of this IRA. The Decision Document should state that the first round of water level
monitoring data will be presented in the Draft Implementation Document, again as
stated in the Army's letter of April 8, 1991. The text needs to further clarify which wells
on Figure 4-4 will be measured quarterly for water level data.
Response 4. Quarterly reports will be prepared as part of the implementation of thts
IRA, for the water level measurements as stated in the April 8, 1991 letter. This is
implied in the Decision Document with the performance of the field data collection
program. The results of the first water level sampling will be included in the
Implementation Document as specified in the April 8, 1991 letter. The specific process
by which the RMA Committee will evaluate these reports and determine any need for
further remedial action is more appropriate for inclusion in the Implementation
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