United Stales
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EPA/ROD/R09-88/021
August 1988
T5EPA
Superfund
Record of Decision
Tucson International Airport Aera, AZ
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------."". ~lOc'~ ;-'----.;"- ---
REPORT DOCUMENTATION 1'1."'""REPORT NO.
PAGE
, ,2.
3. Recipi.nt", Acc.ssion No.
SUPERFUND RECORD OF DECISION
Tucson International Airport
t e t' n
luthor(s)
So R.port Oet.
08/22/88
4. Title and Sub1ltle
Area, AZ
6.
8. Performing Organization Rept. No.
9. Performing O,.anization Name and Address
10. Project/Task/Work Unit No.
----
11. ContracUC) Or Grant(G) No.
(C)
(G)
--. ----.---------.-
12. Sponsoring Organization Nam. and Addr.ss
U.S. Environmental Protection
401 M Street, s.w.
wasnington, D.C. 20460
13. Type of ReDOrt & Period Covered
Agency
800/000
14.
15. Supplem.ntary Notes
16. Abstract (Limit: 200 words)
The Tucson International Airport Area (TAA) site encompasses sections of southwest
Tucson and adjoining lands south of the city in pima County, Arizona. The site is
located in the Tucson Basin and includes industrial, commercial, residential, and
undeveloped areas, as well. as the 'rucson International Airport, the u.s. Air Force Plant
#44 (AFP44), and part of the San Xavier Indian Reservation. The Santa Cruz River
borders the site to the west. The ground water system in the Tucson Basin has been
designated a Sole-Source Aquifer. Before the discovery of ground water contamination in
'he TAA, wells within the site boundaries provided water for over 47,000 people. At
~east 20 facilities have operated in the TAA since 1942. These include aircraft and
electronics facilities, which discharged waste liquids directly to surface soil; fire
drill training areas, where uncombusted residual wastes from training operations were
left in unlined pits; and unlined landfills, which received various wastes from several
sources. The first indications of ground water cont.aminat.ion in TAA appeared in the
early 1950s when elevated levels of chromium were detected in a municipal supply well
adjacent to AFP44 in the southern portion of the site, and residents in another area
complained of foul-smelling water from private supply wells. In 1976, a well was. closed
at AFP44 by the State because of high levels of chromium. By 1981, additional sampling
(See Attached Sheet)
17. Docume",t An.lysis a, D.scriPtors
Recora or DeCLSLon
Tucson International Airport Area, AZ
First Remedial Action
contaminated Media: gw
Key Contaminants: VOCs (benzener TCE, xylens)
b. Identlfiers/Open.Ended Terms
c. COSATI Field/Group
--"vailability Statement
19. Security Class (This Report)
None
21. No. 0' Pages
36
- ------ --.
20. Secur.ity Class (This Page)
None
22. Price
(S.. ANSI-Z39.18)
Se. 'n.tructions on Reyerse
OPTIONAL FORM 272 (4-77>
(Formerly NTI5-3S)
Department 0' Commerce
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EPA/ROD/R09-88/021
~ucson International Airport Area, AZ
lhrst Remedial Action
16.
ABSTRACT (continued)
,
"
by the Air Force and EPA had indicated the presence of VOCs in the ground water.
Consequently, in 1981, the City of Tucson began closing all municipal wells that
exceeded the State Action Level for the principle contaminant TCE, and notified private
well users of potential risks. The site was divided approximately in half along Los
Reales Road, with the Air Force addressing contamination to the south and EPA addressing
contamination to the north. In 1987, the Air Force began operating its ground water
pump and treatment system using ion exchange and packed column aeration followed by
reinjection into the aquifer. This ROD addresses the ground water contamination in the
northern portion of the site, which together with the Air Force remedial ground water
system constitutes the overall ground water remedy for the site. The northern portion
of the site has been divided into two discrete areas, A and B. Area A lies west of the
airport and extends approximately 3.5 miles to t~e northwest in the direction of ground
water flow, and is generally less than a mile wide. Area B consists of two smaller
separate areas north of the airport. If further investigations indicate that there is
soil contamination and that it is a source of continuing ground water contamination, a
ROD will be developed to address soil remediation. The primary contaminants of concern
affecting ground water are VOCs including TCE, benzene, and xylenes.
The selected remedial action for this site includes: ground water pump and treatment
of Areas A and B using packed column aeration, followed by discharge of treated water to
the municipal water distribution system and treatment of emissions from the treatment
'rocess using granular activated carbon, if necessary. The estimated present worth cost
or this remedial action is between $7,328,000 and $7,820,000 with annual O&M between
$393,000 and $450,000 for years 1-20.
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Tucson International Airport Area
R E COR D
.0 P
DEe I S ION
for
G R 0 U N D W ATE R
REM E D I A T ION
North of Los Reales Road
"
United St8tes Environllef'lt8l Protection Agency
.
Region IX .. S." Fr8ncisco, C8lifor"i8
August 1988
~
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SECTION
. 1. 0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11. 0
12.0
13.0
- i -
RECORD OF DECISION
TABLE OF CONTENTS
PAGE
DECLARATION
iii
DECISION SUMMARY
site Location and Description
1
site History
2
Enforcement
4
comm~nity Relations
Decision Scope
4
5
Nature and Extent of Contamination
6
Baseline Site Risks
7
Changes to the Proposed Plan
8
Description of Alternatives
9
ARARS
11
Summary of Alternatives Analysis
12
The Selected Remedy
14
Statutory Determinations
15
-- Attachments --
ADMINISTRATIVE RECORD INDEX
RESPONSIVENESS SUMMARY
. .
...
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- ii -
RECORD OF DECISION
TABLE OF CONTENTS
-- Fiqures --
FIGURE/TABLE
FOLLOWING PAGE
1 -- Regional Location Map
2 -- Tucson International Airport Area Site
(Site Boundaries)
3 -- Subsurface Hydrogeology
4 -- Potential Sources of Groundwater contamination
5 -- Areas of Groundwater Remediation within the Tucson
International Airport Area
6 -- Groundwater Remediation Areas Adressed by the
Feasibility Study
-- Tables --
1 -- Concentration Ranges and Numbers of Detections for
Contaminants Found North of Los Reales Road
2 -- Groundwater Control Alternatives Considered in the
Feasibility study
3 -- Summary of Present Worth Costs of Remedial
Alternatives (Central Facilities)
.
4 -- Summary of Present Worth Costs of Remedial
Alternatives (Wellhead Facilities)
5 -- MCLs, MCLGs & State Action Levels for tontaminants
in the TAA
.
6 -~ Groundwater Controls -- Analysis of'Alternatives
7 -- Treatment Technologies -- Analysis of Alternatives
8 -- Detailed Costs of Selected Remedies for
Contaminated Groundwater North of Los Reales Road
1
1
1
2
3
6
6
10
11
11
11
13
13
15
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- iii -
RECORD OP DECISION
DECLARATION
SITE NAME AND LOCATION
Tucson International Airport Area
Tucson, Arizona
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected groundwater
remedial action for the portion of the Tucson International
Airport Area Site that lies north of Los Reales Road. The
remedial action has been developed in accordance with the
. Comprehensive Environmental Response, Liability, and Com-
pensation Act (CERCLA), as amended by the Superfund Amend-
ments and Reauthorization Act (SARA), and, to the extent
practicable, the National Contingency Plan (NCP). This
decision is based upon the administrative record for this
site. The attached index identifies the items which com-
prise the administrative record upon which the selection of
'the remedial action is based.
The State of Arizona concurs on the selected remedy.
DESCRIPTION OF THE REMEDY
This remedial action is the second to be taken at the site.
As of April 1987, the United States Air Force has been extracting
and treating groundwater in the southern portion of the site.
The remedial action presented herein is the groundwater remedy
for the areas ("Area A" and "Area B") of the site not currently
addressed by the Air Force's action. This action and the Air
Force action together constitute the overall groundwater remedy
for the site. Further investigation of potentially contaminated
s9ils on the site and any resulting decision on remedial
action(s) for soils is anticipated at a later date.
,-~ The selected groundwater remedy for Area A includes control
of groundwater contamination through segregation of the upper and
lower divided aquifers and through extraction from both the upper
,divided a~£er and the regional undivided aquifer (all north of
'Los ~eales Road). The treatment method will be packed column
aeration. The goal is to treat extracted groundwater to an over-
all excess cancer risk level (for all contaminants combined) of
10-6, which will require treatment to a TCE concentration of ap-
proximately 1.5 parts per billion (ppb). Where airborneemis-
'~ipns of volatile organic compounds (VOCs) from new packed column
~cilities have the potential to exceed 2.4 pounds per day,
-------
- iv -
reasonably available control technology (RACT) for the reduction
of air emissions will be proposed. (RACT in this case may con-
sist of vapor phase granular activated carbon.) Treated water
will be fed directly into the municipal water distribution sys-
tem. If any groundwater is treated at the nearby United states
Air Force facility (AFP44), however, this water may be used for
groundwater recharge rather than supplied to the municipal sys-
tem. .
For Area B, groundwater will be extracted from the upper
aqu~fer and treated to an overall excess cancer risk level of
10-. Packed column aeration will be used unless further infor-
mation indicates' that another treatment strategy is more cost-
effective or would be more easily implemented while ~till offer-
ing the same level of protection of human health and the environ-
ment and while still complying with all ARARs. The low levels of
contamination in Area B indicate that no emission controls should
be needed on the packed column(s).
The remedies for Area A and Area B are expected to be in
operation for approximately 20 years. Over this period, at least
two pore volumes of groundwater will be withdrawn from the
aquifer. Groundwater monitoring will also continue.
DECLARATION
The selected remedy is protective of human health and the
environment, attains Federal and state requirements that are ap-
plicable or relevant and appropriate to the remedial action, and
is cost-effective. With respect to contamination in groundwater,
the remedy satisfies the statutory preference for remedies that
employ treatment that reduces toxicity, mobility or volume as a
principal element and utilizes permanent solutions and alterna-
tive treatment technologies to the maximum extent practicable.
The statutory preference is not completely satisfied with respect
to contamination in the air in that the selected treatment method
involves transferral of contamination from water into the air.
However, the remedy still reduces the overall risk to human
health. As part of the remedy, groundwater monitoring at regular
intervals will ensure that the remedy continues to provide a~e-
quate protection of human health and the environment. .
,
/!;, ,: hi -~/il';':' ",- i~".
I J --, , . I~ -- . 1
Daniel W. "McGovern
Regional Administrator
~ ).J 8~~
Date
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- 1 -
RECORD OF DECISION
DECISION SUMMARY
1.0
SITE .LOCATION AND DESCRI.PTION
The Tucson International Airport Area is located in Pima
County, in southeastern Arizona (Figure 1). It encompasses sec-
tions of southwest Tucson, as well as adjoining lands south of
the city. The site includes industrial, commercial, residential
and undeveloped areas. Specifically included are the Tucson In-
ternational Airport, the united States Air Force Plant #44
(AFP44) and part of the San Xavier Indian Reservation. As shown
in Figure 2, the approximate site boundaries are the Santa Cruz
,River on the west, Ajo Way on the north, Alvernon Way on the
east, and the Hughes Access Road south of AFP44 on the south.
The Tucson International Airport Area (TAA)* is located in
the Tucson Basin, an alluvial valley bounded by rugged mountain
ranges. The basin is bounded on the east and north by the Santa
Rita, Empire, Rincon, Tanque Verde, Santa Catalina and Tucson
Mountains and on the west by the Sierrita, Black and Tucson Moun-
tains. The mountains on the east and north generally rise to al-
titudes of. 6,000 to 8,000 feet: the mountains to the west reach
3,000 to 6,000 feet. The area is drained to the northwest by the
Santa Cruz River and its major tributaries. The Santa Cruz
stream system has formed a plain that slopes gently from an ele-
vation of 2,900 feet in the south to approximately 2,000 feet in
the northwest. The 50-mile long basin is 15 to 20 miles wide at
its southern end and thins to about 4 miles wide at its outlet.
The subsurface beneath the TAA primarily consists of basin-
fill deposits (gravels, sandy-gravels, sands, clays, sandy-clays,
and clayey-sands). These deposits form two major aquifer zones
beneath the TAA: the regional divided aquifer and the regional
undivided aquifer. The regional divided aquifer consists of the
unconfined "upper aquifer" and the semi-confined. "lower aquifer",
which are separated by clayey deposits classified as an aquitard.
The aquitard pinches out to the northwest beneath the site, re-
sulting in the regional undivided aquifer. The aquifer system is
shown in a simplified representation in Figure 3. Groundwater
flow beneath the site is generally to the northwest at about 350
to 710 feet per year. (Hydraulic c~nductivity values in the area
range from about 3 to 2,000 gpd/ft .) There are also limited
areas where groundwater is perched upon clay. deposits above the
upper aquifer table.
* In the Feasibility Study, "TAA" refers to a study area whose
southern boundary is Los Reales Road. In this record of deci-
sion, however, "TAA" refers to the entire Superfund site.
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APPROXIMATE SCALE IN MILES
~
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5
10
ARIZONA
.-- ~.. . --- -.-
TUCSON
INTERNA TI NAL
AIRPORT A EA
---.-- .
, .
FIGURE 1
REGIONAL LOCA TION MAP
TUCSON INTERNATIONAL AtaPORT AREA
RECORD OF DECISION
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EXPLANA TION:
APPROXIMATE LIMITS OF
TCE CONT AMINA TION
DURING 1984 (DASHED
WHERE UNKNOWN OR
INFERRED)
FIGURE 2
TUCSON INTERNA TIONAL
AIRPORT A~EA SITE
TUCSON INTERNATIONAL AIRPORT AREA
RECORD OF DECISION
M'LI
I
-------
NORTH
SOUTH
VALENCIA " "', ,"~,,:~:,..,:~::>;J:,::;
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NOTE: GENERALIZED FROM ARIZONA DEPARTMENT
OF WATER RESOURCES (1985)
FIGURE 3
SUBSURFACE HYDROGEOLOGY
TUCSON INTERNA TIONAL ~ 'RT AREA
RECORD OF DECISION
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- 2 -
Flowing surface water occurs only intermittently in the TAA.
Most of the year, in the absence of major rainstorms, the Santa
Cruz River and its major tributaries run dry. Therefore, the
city of Tucson relies solely upon the aquifers of the Tucson
Basin for its drinking water, resulting in the designation of the
basin's groundwater system as a Sole Source Aquifer under the
federal Safe Drinking Water Act. . Before the discovery of con-
taminated groundwater in the TAA, wells within the site bound-
aries provided water for about 47,000 people.
2.0
SITE HISTORY
Waste-related activities in the TAA are believed to have
begun sometime after the start of airplane refitting operatic'.s
in 1942 at the location of what is now the Tucson Aviation
Center. Since then, at least 20 facilities potentially capable
of releasing hazardous materials have operated in the TAA:
-- Aircraft manufacturing, maintenance and reworking
facilities,
-- Electronics components manufacturing and assembly
facilities,
Fire drill training areas, and
-- Landfills.
Waste disposal at several of the aircraft and electronics
facilities consisted of surface discharge of waste liquids to
soils on-site. Liquid waste run-off ponded in drainage areas,
providing the driving force for contaminants to infiltrate into
the underlying groundwater. At fire drill training areas, flam-
mable wastes, including solvents and fuels, were ignited in un-
lined fuel pits and doused with large quantities of water. Water
and uncombusted wastes were then able to migrate to the underly-
ing saturated zone. The on-site unlined landfills received
various wastes from several sources, including facility operators
and tenants. Figure 4 indicates the source areas that have been
identified within the TAA.
First indications of groundwater contamination in the TAA
date back to at least the early 1950's. In 1952, samples from a
municipal supply well adjacent to AFP44 indicated elevated levels
of chromium. At about the same time, residents near what is now
the Tucson Aviation Center complained of foul smelling water from
private supply wells. The residents brought suit against the
city of Tucson and the Grand Central Aircraft Company, the oper-
ator of an aircraft refitting facility at that time. The suit
was dismissea when the city offered the residents access to the
city water system.
-------
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EXPLANA TlON:
APPROXIMATE LIMITS OF
TCE CONT AMINA TION
DURING 1984 (DASHED
WHERE UNKNOWN OR
INFERRED) ,
FIGURE 4
POTENTIAL SOURCES OF
GROUNDWATER CONTAM/NA TION
TUCSON INTERNATIONAL AIRPORT AREA
RECORD OF DECISION
o
0,5
p--"q
W'LII
-------
- 3 -
The next indication of groundwater contamination ocdu~redJ.'
around 1976, when a well at AFP44 was closed by the state because
of high levels of chromium. By 1981, further sampling by the Air
Force and its contractor, Hughes Aircraft Company, verified high
levels of contamination beneath the facility. The sampling at
AFP44 and other sampling .north of the facility conducted under
the direction of the United states Environmental Protection
Agency (EPA) indicated the presence of volatile organic con-
taminants including l,l,l-trichloroethylene (TCE), l-l-di-
chloroethylene (l,l-DCE), l,l,l-trichloroethane (TCA), chloro-
form, benzene and xylene. The presence of chromium, mostly in
hexavalent form, was also confirmed.
The Tucson International Airport Area was listed on the
"Expanded Eligibility List", a preliminary National Priorities
List (NPL) , on July 23, 1982. It was proposed for inclusion on
the original NPL o~ December 30, 1982, attaining final NPL status
on September 8, 1983.
The Air Force continued its investigation of the contamina-
tion at AFP44 under the Department of Defense Installation Res-
toration Program (IRP). Investigations north of AFP44 were
carried out by EPA, with the cooperation of the state of Arizona,"
the city of Tucson and pima County. As the two investigations
continued, there were attempts among the parties to negotiate a
Memorandum of Agreement that would formalize roles and respon-
sibilities. These efforts, however, never resulted in a signed
agreement. Therefore, the parties decided that the site would be
divided -- for purposes of study -- at Los Reales Road, with the
Air Force addressing contamination south of the road and EPA
studying the area north of the road (Figure 5).
The Air Force Remedial Action Plan (RAP) for the area south
of Los Reales Road was released in April 1986. During 1987, the
Air Force began operation of its groundwater reclamation system,
which extracts groundwater, treats it for removal of hexavalent
chromium (ion exchange) and volatile chemicals (packed column
aeration with partial control of emissions using vapor phase
granuLar activated carbon), and injects the t~eated water back
into the aquifer.
In 1985, u~der a Cooperative Agreement with EPA, the Arizona
Department of Health Services (ADHS) completed the Remedial In-
vestigation (RI) for the area north of Los Reales Road. Under a
second Cooperative Agreement, the Arizona Department of Water
Resources (ADWR) conducted the Feasibility Study (FS). Manage-
m~nt and ..technical committees with representatives from EPA,
ADWR, ADHS and Tucson Water, the municipal water purveyor, were
established to coordinate, review and monitor project activities.
On March 3, 1988, the draft "Feasibility Study for Ground Water
Remediation in the Tucson Airport Area" was released for public
review and comment. .
-------
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EXPLANATION:
APPROXIMA TE LIMITS OF
TCE CON T AMINA TION
DURING 1984 (DASHE!)
WHERE UNK NOWN OR
INFERRED)
FIGURE 5
AREAS OF GROUNDW ATE:
REMEDIA TION WITHIN
THE TUCSON INTERNA TlONAL
AIRPORT AREA
TUCSON INTERNATIONAL AIRPORT AREA
RECORD OF DECISION
o
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0.5
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-------
--'-----.--.- ----
- 4 -
Hughes Aircraft has applied for a final RCRA operating per-
mit for its operations at AFP44 pursuant to the Resource Conser-
vation and Recovery Act (RCRA). Hughes has a long RCRA history,
with several inspections by EPA and the state of Arizona that
have identified instances of noncompliance with regulations. Al-
leged violations of environmental 'statutes at the facility are
the subject of continuing investigations.
3.0
ENFORCEMENT
During August and September, 1987, EPA sent Gpnpr~l NQti~p
T~trpr~ to the nine potentially responsible parties (PRPs) listed
below, officially notifying them of their potential liability for
the groundwater remedy north of Los Reales Road.
-- Hughes Aircraft Company
-- u.S. Air Force
-- City of Tucson
-- Tucson Airport Authority
-- McDonnell Douglas Corporation
-- General Dynamics Corporation
Arizona Air National Guard
-- Burr-Brown Research Corporation
-- West-Cap Arizona
EPA held an informational meeting for the PRPs in December
1987. EPA and the state of Arizona also presented a briefing on
the Feasibility Study for technical representatives of the no-
,ticed parties. The PRPs have been meeting among themselves for
the past several months, although initially not all parties were
attending meetings regularly. Attempts by some of the parties to
develop a PRP "steering committee" have not been successful.
Special Notice Letters were mailed
Letter recipients on July 6, 1988. The
moratorium that is triggered by Special
began on July 11th.
to the General Notice
60-day negotiations
Notice Letters officially
4.0
COMMUNITY RELATIONS
.
The public comment period for the FS and the proposed plan
ocened March 3rd and continued through April-1st. The public
meeting was held March 15th at an on-site neighborhood school.
Advance~ notice of the availability of the FS for public
co~ent was "mailed on February 16, 1988. Two other notices about
the'FS, the proposed plan fact sheet and the public meeting were
mailed by March 15th. For such mailings, EPA has a list of over
600 addresses of community members.
-------
- 5 -
EPA and ADWR sent a press release to local newspapers-on
March 1st. A newspaper advertisement was published in two local
newspapers on March 3rd with information regarding the avail-
ability of the FS and the proposed plan and giving the time and
place of the public meetirig. - ,
The proposed plan fact sheet was sent to the people on the
site mailing list on February 25th. In addition, nearly 2000
fact sheets were mailed to community groups for distribution to
their own mailing lists. One thousand fact sheets printed in
Spanish were also made available at a neighborhood center near
the site.
The RI, FS, proposed plan fact sheet and other relevant site
information have been available at seven information repositories
set up at local libraries and at the Tucson ADWR office. The ad-
ministrative record, a compilation of the information upon which
EPA is basing its selection of remedy, has b~~n available sinc~
l~tp- Fphruarv at ADWR's offices in Phoenix and Tucson as well as
at EPA's regional office in San Francsico. The administrative
record index is provided as an attachment to this Record of Deci-
sion.
ADWR and EPA completed the attached responsiveness summary.
The responsiveness summary includes responses to comments sub-
mitted in writing by residents, elected officials, and the PRPs.
It also addresses comments made by attendees at the March 15th
public meeting.
In addition to the release activities described above, the
agencies met regularly with a group of approximately 10 community
members while preparing the FS. This group, called the Community
Advisory Group, had representatives from several concerned com-
munity organizations. Some members were appointed by elected of-
ficials. The ~nmml1l'ity Advi~nry Grnup reviewed and commented
upon ,several ~rafts of the FS. The group also heard presenta-
tions by healt~ and environmental agency officials and were given
the opportunity to discuss their concerns with these officials.
5.0
DECISION SCOPE
As discussed in the Site History (page 2), the Air Force has
begun operation of its remedial groundwater system for the south-
ern area of the' site. The response action that is the subject of
this decision document is the groundwater remedy for the northern
por~ion of the site. Together, these two remedies constitute the
overall remedial strategy for groundwater. This strategy is
necessary to restore the Sole Source Aqui fer of ,the Tucson Basin
to drinking water quality.
-------
- 6 -
Waste disposal practices in the TAA, at AFP44 as well.as
elsewhere within the site boundaries, may have resulted in
residual soil contamination. Some soils may continue to con-
tribute contamination to the underlying groundwater. Investiga-
tions of potential soil contamination throughout the Superfund
site are currently planned under both CERCLA and RCRA. Any
response actions for soils taken pursuant to CERCLA will be the
subject of a future Record of Decision. Actions to be taken pur-
suant to RCRA, particularly potential actions at AFP44, will
likely be incorporated in permit conditions or in administrative
orders.
6.0
NATURE AND EXTENT OF CONTAMINATION
The RI found several areas of groundwater north of Los
Reales Road to be contaminated with the solvent TCE, as shown on
Figure 6. The main area, referred to as "Area A" starts to the
west of the Tucson International Airport and continues to the
northwest. Two smaller areas -- believed to be separate from the
main area and referred to together as "Area B" -- lie north of
the airport.
Area A extends north from Los Reales Road more than three
and one-half miles to beyond Irvington Road. The area is gen-
erally about three-quarters of a mile wide. Most of the con-
tamination in Area A is in the upper aquifer of the regional
divided aquifer. However, as the main contaminant plume has
migrated to the northwest, its leading edge has also spread into
the regional undivided aquifer. The lower aquifer of the region-
al divided aquifer is not believed to be contaminated except in
the immediate vicinity of wells that form vertical conduits from
the upper to the lower aquifer.
The two parts of Area B are more limited in extent, probably
because of lower hydraulic conductivities north of the airport.
Contamination is believed to be limited to the upper aquifer in
these areas.
The'RI identified many groundwater contaminants in addition
to TCE within the study area. The volatile contaminants of most
concern include l,l-DCE, trans-l,2-dichloroethylene (t-l,2-DCE),
chloroform, benzene and xylene. Some hexavalent chromium was
also found in a limited area north of Los Reales Road. (The
levels of chromium found north of Los Reales Road do not exceed
the Safe Drinking Water Act Maximum Contaminant Level (MCL),
while the MCL is exceeded at and adjacent to AFP44.) Table 1
list~ the contaminants detected in the groundwater north of Los
Reales Road, the range of values detected and the number of
detections. . .
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LEGEND
AREA OF CO NT AMINA TlON
IN UPPER AQUIFER OF
REGIONAL DIVIDED
AQUIFER
AREA OF CONTAMINATION
IN REGIONAL UNDIVIDED
AQUIFER
APPROXIMA TE BOUNDARY
BETWEEN REGIONAL
DIVIDED AND UNDIVIDED
AQUIFER
~PPROXIMATE LIMITS OF
TCE CONTAMINATION
DURING t 984 (DASHED
WHERE UNKNOWN OR
INFERRED)
o
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SCALE IN MIL~S
'~"
. ~ /
FIGURE 6 ,.
GROUNDWA TER REMEDIA nON
AREAS ADDRESSED BY
THE FEASIBILITY STUDY
TUCSON INTERNATIONAL AIRPORT AREA
RECORD OF DECISION
-------
TABLE 1
CONCENTRATION RANGES AND NUMBERS OF DETECTIONS
FOR CONTAMINANTS FOUND NORTH OF LOS REALES ROAD *
Chemical
Concentration
Range .(uq/l)
Number of
Detections
trichloroethylene
0.3 - 1,09
1,35
1,1,1-trichloroethane
0.12 . 5.6
2
1,1-dichloroethylene
0.3 - 31
77
t-1,2-diChloroethylene
L 2 - 13
70
1,1-dichloroethane
0.7
1,2-dichloroethane
2. 1 - 8
3
1,2-dichloropropane
0.1, - 0.9
2
isophrone
9
carbon tetrachloride
0.5 - 0.8
2
chloroform
0.53 - 54
58
chromium (VI)
10 - I, 0
1,8
biS(2-ethrlhexyl)
phtha ate
12 - 265
I,
di-n-butyl phthalate
82
3,3-dichlorobenzidene
5
2-chloroethyl vinyl ether
3 - 6
2
benzene
1.2 - 11,
13
toluene
3
total xylenes
2.7 - 21
5
napthalene
5
2-.ethylnapthalene
5
trichloroflu~ro.ethane
1 - 4
2
tetrac~~~roethylene
0.9
~
chlorobenzene
.
Concentration ranges and numbers of detections represent
data collected from municipal, private and monitoring wells
north of Los Reales Road from May 1981 through February 1986.
-------
\
\
\
- 7 -
I
I
,
Beginning in 1981, the City of Tucson has been closing all
wells that exceed the state Action Level for TCE of 5 parts per
billion (ppb). As a resu~t, no one using the municipal supply
system has been exposed t.o water with TCE concentrations above 5
ppb since 1981. (The water served by the city has also been in
compliance with all other 'federal and state requirements, includ-
ing the MCLs and State Action Levels for chemicals other than
TCE.) However, the RI also identified several private wells that
were contaminated above MCLs and State Action Levels. While all
known private well users hav~ been notified of the potential
risks of using their private wells, there is no reliable mech-
anism for determining the extent of continued private well use.
While the focus of the RI was on groundwater, limited soil
data are available. Although the available data do not suggest
that soil contamination is an immediate public health thr~at,
there is not enough data at this time to conclude that there are
no soil areas that are continuing sources of groundwater con-
tamination. Further investigation will clarify the need for
response actions for soils.
7.0
BASELINE SITE RISKS
The no action risk baseline was calcMlated in the Public
Health Evaluation to be approximately 10-. This number repre-
sents the risk due to exposure to groundwater from the upper
divided aquifer north of Los Reales Road and from the regional
undivided aquifer. While the city of Tucson by law cannot serve
water that exceeds MCLs, the public health evaluation hypotheti-
cally removes this institutional control and assumes ready access
to the contaminated water via municipal supply wells.
While more than 20 chemical contaminants have been detected
at elevated concentrations in the 'TAA, many of these were not
carried through all calculations during the Public Health Evalua-
tion because of (1) low frequency of detection, (2) low concen-
trations when detected or (3) a combination of low frequency and
low concentrations.
In the Public Health Evaluation, TCE, 1,1-DCE, t-l,2-DCE,
chloroform, benzene and hexavalent chromium were selected as in-
dicator chemicals. However, t-1,2-DCE and hexavalent chromium
are not considered potential carcinogens in water; therefore,
they do not contribute to the baseline number stated above. In
addition, because of equivocal evidence of carcinogenicity, 1,1-
DCE wasno~. ~nsidered a carcinogen for the Public Health Evalua-
tio~ for this site. Therefore, TCE, chloroform and benzene are
the chemicals from which the baseline carcinogenic risk was
derived.
-------
,
,
\
\
- 8 -
I
I
I
At sufficiently high exposure levels, the ~oncarcinogens,
along with some ~f the carcinogens, have chronic (noncarcino-
genic) health effects associated with them. aowever, the con-
taminant concentrations in the TAA are all be10w levels believed
to have the pote~tial to result in noncar~i~ogenic health ef-
fects. .
The primary exposure pathway is c~sidered ingestion of
groundwater. For the indicator chemicals, dermal contact is not
a demonstrated pathway of concern. Inhalation of vapors during
activities such as showering would tend to increase the baseline
risk from ingestion, and may, in fact, approach it in magnitude.
However, the risk from this pathway is not currently quantifi-
able.
The risks calculated in the Public Health Evaluation also
reflect the assumption that the ongoing Air Force remedial action
is meeting its goals for groundwater containment and treatment.
Therefore, the higher levels of contamination that have been ob-
served south of Los Reales Road have not been incorporated into
the baseline risk for the current remedial action. Instead, it
is assumed that groundwater "crossing" Los Reales Road has.maxi-
mum levels of contamination that are equivalent to the Air
Force's treatment goals. However, based upon TCE concentrations
that are generally one to two orders of magnitude higher in the
souihern area, the baseline risk would have approached at least
10- if these higher levels had been incorporated.
8.0
CHANGES TO THE PROPOSED PLAN
This decision document presents one substantive change to'
the preferred remedy described in the proposed plan. In addi~
tion, some uncertain aspects that were included in the proposed
plan are clarified herein.
The proposed plan released on February 25, 1988 recommends
extraction of groundwater from both the upper divided aquifer and
the regional undivided aquifer. The remedy includes the sealing
of wells that form conduits between the upper and lower aqu~fers.
Treatment of groundwater -- to an overall risk level of 10- --
would take place at a single packed column aeration facility.
The municipal distribution system would receive the treated water
by gravity flow.
The on~ significant change to the remedy summarized above is
tha~ a reasonably available control technology (RACT) will be
proposed for reduction of emissions from any new packed column
facility having the potential to emit in excess of 2.4 pounds per
day of airborne volatile organic compounds (VOCs). In this case,
RACT may consist of granular activated carbon (GAC). This change
is made in order to comply with Pima County Air Quality co~trol
Regulation 17.12.090 Sub-Paragraph E. (See the ARARs section on
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- 9 -
\
\
\
I
page 11.) Consistency with the Pima County rule is s~pported by
the city, county and state. Control of air emissions was also a
major community concern voiced during the public comm~nt period.
The proposed plan discusses several aspects of the remedy
that may require adjustments during design. For ins~ance, con-
tinuing discussions with the Air Force may reveal greater via-
bility of the AFP44 reclamation system for some portion of the
water from north of Los Reales Road. Any water treated at AFP44
would likely be injected back into the aquifer rather than put.
directly into the distribution system. In addition, partial use
of AFP44 might make one or more wellhead treatment facilities a
reasonable alternative. Depending upon the final configuration
of the extraction system and treatment facility(ies), therefore,
it may be necessary to reinject some water while putting other
treated water to direct use through the municipal distribution
system. Finally, as mentioned in the proposed plan, some refine-
ment of extraction well locations and capacities is expected
during design.
The r~medy for Area a, as proposed, is basically a smaller
scale copy of the remedy for Area A. As stated in the proposed
plan, however, the Area a recommendation is considered prelimi-
nary, based upon a mor-e limited data base. Therefore, there may
be some changes in the remedial strategy for Area a as more in-
formation becomes available, providing that the changes maintain
the same level of protection of human health and the environment
and the same level of compliance with ARARs as does the selected
remedy. .
9.0
DESCRIPTION OF ALTERNATIVES
The project management committee for the TAA Feasibility
Study developed objectives for response actions in the TAA:
-- To manage migration of contaminants,
-- To achieve public acceptance of the remedy,
--To protect public health and the environment,
-- To attain consistency with ARARs,
-- To determine the most environmental~ sound, technically
feasible, and cost-effective remedy, which can be imple-
mented in a timely manner, and
-- To ensure consistency with AFP44 remedial actions.
The natural conditions at the TAA, including the desert en-
vironment .and the depth to the water table, limit the range of
ava~lable response actions for contaminated groundwater. For in-
stance, no surface water control options were developed in detail
because of the lack of flowing surface waters. containment op-
tions such as slurry walls and sheet piling were inappropriate
because of the areal extent of contamination and the depth to
groundwater (generally >120 feet).
-------
- 10 -
\
\
\
The remedial alternatives (except the no ':action alternative)
that were developed in detail for the Tucson tnternational Air-
port Area consist of three main components: groundwater control
measures, treatment of contaminated groundwater and an end use
for treated water. I
As shown in Table 2, the groundwater control options con-
sist of variations of the areas from which water would be
pumped. Extraction from the upper aquifer only, from the un-
divided aquifer only and from both the upper and undivided
aquifers were considered. Options entailed extraction rates
from 650 gpm to 4,200 gpm for Area A and a rate of 300 gpm for
Area B. Extraction options were developed with and without
reinj ection. .
Several treatment methods underwent detailed analysis:
-- Packed column aeration,
-- Packed column aeration with vapor phase granular ac-
tivated carbon,
-- Liquid phase granular activated carbon, and
-- Tr~atment at AFP44.
UV/ozone oxidation was considered but was eliminated due to
questionable performance in treating to the low levels required
and due to a' lack of cost-effectiveness when compared to other
remaining treatment options. In-situ aerobic biodegradation was
also dropped from consideration because of questionable im-
plementability and because of cost estimates of up to an order
of magnitude higher when compared to the technologies listed
above. .
Treatment at a central facility (one each for Area A and
Area B) and at each wellhead were analyzed. The FS assumed that
each treatment method would be sized according to the selected
pumping option. Based upon TCE's chemical characteristics and
upon regulatory requirements for TCE, treatment alternatives
were analyzed over a range of treatment levels from attainment
of MCLs down to EPA laboratory method detection limits.
.
In many instances, several end uses for. treated water are
theoretically available in the development of response actions.
In this case, however, the aquifer of concern has been desig-
nated a 501e Source Aquifer under the Safe Drinking Water Act,
and according to the Groundwater Management Plans for the Tucson
Active Management Area, any water withdrawn from the aquifer
must be put to its highest beneficial use. Therefore, the end
use options were limited to direct drinking water use or rein-
jection for drinking water use at a later time.
-------
TABLE 2
GROUNDWATER CONTROL ALTERNATIVES CONSIDERED
IN THE FEASIBILITY STUDY
.
ALTERNATIVE
EXT R ACT ION"
REINJECTION
ESTIMATED
PROJECT TIME
Area A
A-3
3 wells in the upper
divided aquifer
NONE
20 yrs
A-I.
NONE
20 yrs
3 wells in the upper
divided aquifer & 2
wells in the undivided
aquifer
A-5
NONE
20 yrs
2 wells in the
undivided aquifer
A-6
15 yrs
3 wells in the upper
divided aquifer
SOX reinjected
I. wells in the
upper divided
aQuifer
A - 7
15 yrs
3 wells in the upper
divided aquifer & 2
wells in the undivided
aquifer
50% reinjected
I.. we I I sea chi n
the upper divided
and undivided
aQuifers
Area 8
s-z
Z wells in the upper
divided aquifer
NONE
20 yrs
B-3
15 yrs
2 wells in the upper
'divided aquifer
. '
at least 50%
reinjected --
2 we II s
.
Letter/number
'The number of
more wells --
designations for alternatives are thos~ used in the FS.
wells actually indicates the number of locations for one or
the exact number and locati'on w(ll be determined in design.
-------
\
.
- 11 -
Estimated costs ~or alternatives that were developed in
detail for Area A ranged from about 1.5 to 14.2 million dollars.
The range for Area B/is from about 0.9 to 2.3 million dollars.
Tables 3 and 4 give a summary of capital and operations and
maintenance costs for the alternatives.
I -
10.0
APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS
( ARARs )
The Groundwater Management Plans mentioned above are an im-
portant ARAR, limiting the potential uses of any groundwater
withdrawn during remediation. The requirements of Title 45 of
the Arizona Code and Environmental Quality Act are also ap-
plicable for actions in the TAA. In addition, all of the Safe
Drinking Water Act MCLs are applicable at the site. Arizona has
its own State Action Levels, a few of which are more stringent
than the MCLs. While the state Action Levels are not promul-
gated and are not, therefore, ARARs, they have been taken into
consideration during the development of remedial alternatives.
Table 5 lists the MCLs and State Action Levels for indicator
chemicals from the Public Health Evaluation.
Table 5 also lists the Maximum contaminant Level Goals
(MCLGs) for the indicator chemicals. MCLGs, which are based
only upon health criteria, are not directly applicable as
chemical-specific requirements because they are not enforceable
standards. The MCLs are considered the chemical-specific ARARs
because they are (1) the enforceable drinking water standards,
(2) required to be set as close to the MCLGs as is feasible,
taking intq consideration the best technology, treatment tech-
niques and other factors (including cost), and (3) protective of -
pu~~ic health to within EPA's acceptable risk range of 10- to
10 .
Pima County Air Quality Control Regulation 17.12.090 Sub-
Paragraph E is also an important ARAR in the TAA. The ordinance
requires a proposal of reasonably available control technology
(RACT) in the event that any stationary source has the potential
to emit a total of 2.4 pounds per day of volptile organic com-
pounds (VOCs).
with certain exclusions, the Arizona Environmental Quality
Act (EQA) delegates air pollution control authority to the
counties. Therefore, having been duly promulgated by the Pima
County Board of Supervisors in accordance with the EQA, Pima
Couhty Air Quality Control Regulation 17.12.090 Sub-Paragraph E
constitutes a promulgated state requirement under a state en-
vironmental law -- as set forth in ~121(d) of CERCLA -- and is
generally applicable.
-------
TABLE 3
SUMMARY OF PRESENT WORTH COSTS OF REMEDIAL ALTERNATIVES
(CENTRAL FACILITIES)
A-3 A-I. A - 5 A-6 A - 7 8 - 2 B -:3
Packed Column
Aeration
............------
Cap it III 1 .68 2.83 1 .56 :3 . , 5 6.97 0.66 1 .09
o & M Q..,Ll L.ll l..:...il. L..1.Q. LJ..! 0.36 0 .62
Total S2.39 U.69 S2.98 U .65 S11.15 S 1 .02 S 1. 71
Packed Column
wit h GAC
........-e.._..__.
Capital 1 .90 3. 10 1 .90 3. 70 7.1.8 0.88 1 .108
o & M L..1L 3.31. L.1.1. L:.1.L L.L.1. 0.50 0.77
Total S3.27 S6.I.I. S5.02 S5.97 S1I..19 S 1 .38 S 2.25
l i qu i d Phase
GAC
-..--------...-
Capita~ 2.00 3. 70 2.29 3.92 8.83 0 .81 1 .2l.
o & M L..li l.:J.i 2.06 3. 06 7.08 0.'3 0.69
Tot a I S3.81 S7.25 U.35 S6.98 S15.91 S1.2I. S 1 .93
Treatment at
AFPI.4
--.-.-..-----
Capital 1.51 2.1.1. 1 .30 3.1.7 . 6.43
0 & M W2. L..1.!. 3. 03 L.ll L...1i
Total $2.96 $6.58 U.33 S5.78 S1l..58
#
Costs are in .illions. Operations and maintenance costs assume a discount
rate of 101 over 20 years for A-3. A-I.. A-5 and 8-2. A 101 discount rate
over 15 years is assumed for A-6. A-7 and 8-3.
-------
TABLE 4
SUMMARY OF PRESENT WORTH COSTS OF REMEDIAL ALTERNATIVES
(WELLHEAD- FACILITIES)
A-3 A-I. A-5 B-2 B . 3
Packed Column
Aeration
...._e"'."''''''''''''''''''
Capital 1 . 6 5 2.'9 1 . 2 9 0.66 1 . , 5
o & '" 0.82 L.Q1. L..il. ~ ~
Total 2. 47 4.52 2.76 1 .09 , .75
Packed Column
w i-t h GAC
-.......-.........---......
Capital 2.48 3. 61 1 . 76 1 .1 2 , .58
o & '" L..i.1. L2.l. 2.27 0.60 Q...J!.
Tot a l 3.99 7. 13 '.03 1 .72 2.36
LiQuid Phase
GAC
... ... ... ... ... ... ... ... ... ... ......
Capital 1 .12 3. 95 1 .95 1 . 1 1 , .57
o & '" Lll L.ll. ~ 0.6-' 0.79
Total 3.67 7.61 3. 94 1 . 72 2.36
Costs are in .illions. Operations and maintenance costs assume a discount
rate of 10% over 20 years for A-3, A-I., A-5 and 8-2. A 10% discount rate
over 15 years is assumed for 8-3.
~
-------
TABLE 5
MCLS, MCLGs , STATE
FOR CONTAMINANTS
(~g/l )
ACTION LEVELS
IN THE TM
CHEMICAL
MCl OR
PROPOSED
MCl
MClG 011
PROPOSED
MClG
STATE
ACTION
.
LEVEL
trichloroethylene
5
zero
5
'.'-dich~oroethylene
7
7
-7
chloroform
100
3
chromium (VI)
50
120
t-'.2-dichloroethylene
70
70
benzene
5
zero
s
*
State Action leve{s are set by the Arizona Department of Health Services.
~
-------
- 12 -
However, the EQA reserves for the state exclusive air pol-
lution control authority with respect to facilities operated by
the state or a subdivision of the state. Therefore, because the
extent of state involvement in the operation of the proposed
treatment system(s) has not been determined, the pima County
rule may not pe applicable to "all remedial actions in the TAA.
But regardless of who operates any treatment facility(ies), the
county rule remains relevant with respect to conditions in the
TAA. In addition, because the county's rule would be applicable
in the case of privately-operated facilities, it is appropriate
that state-operated facilities should comply with the same re-
quirements. In all cases, therefore, Pima County Air Quality
Control Regulation 17.12.090 Sub-Paragraph E is a requirement
that is applicable or relevant and appropriate~
While the city of Tucson is in an area that exceeds the
level of ambient carbon monoxide allowed by the Clean Air Act
(CAA),' none of the contemplated remedial actions are e~pected to
affect carbon monoxide levels. But the area is also ~ithin 4%
of exceeding its CAA limit for ozone; several of the VOCs
that have been found in the the groundwater (and that would be-
come airborne during water treatment) act as ozone precurso,rs.
, '. t
, I
None of the remedial alternatives presents any t~reat ~o
natural resources or any impact upon the 100-year flo~dplai~.
No other site-specific siting requirements have been identified.
11.0
SUMMARY OF ALTERNATIVES ANALYSIS
Several alternatives that were originally developed in the
FS were eliminated before detailed development and analysis.
Examples are alternatives that include no aquifer cleanup but
call for continued groundwater monitoring and alternate water
supplies as a means of protecting public health. In general,
these options were eliminated because they are less protective
.of the environment and because they tend to be costly in com-
parison to alternatives that offer greater protection.
In addition to the information provided in this section,
Tables 6 and 7 provide summaries of the ana~yses of groundwater
controls and of treatment technologies, respectivley.
Groundwater Control. Alternatives
The groundwater control alternatives involving'extraction
from only .the upper divided aquifer are not considered protec-
ti~ of human health and the environment because they would al-
low the leading edge of the contaminant plume to continue to
migrate and potentially contaminate more wells. Extraction from
only the regional undivided aquifer also is not considered fully
protective of human health and the environment. This option as-
sumes that all contamination from the upper divided aquifer can
-------
- 13 -
be removed when it migrates to the undivided zone, but subsur-
face conditions are such that they introduce uncertainty as to
the fate of contaminants. This situation supports the more ag-
gressive strategy of pumping from both the upper and the un-
divided aquifers. Alternatives that include reinjection of
treated water are generally 'eliminated because of cost increases
of about 50% and because of concerns about the potential for ex-
tensive operations and maintenance requirements for reinjection
wells. However, in the event that any water is treated at
AFP44, reinjection or some other form of groundwater recharge
may be necessary to maintain consistency with current operations
at the facility.
Groundwater Treatment Alternatives
All of the treatment technologies that went~through de-
tailed analysis are capable of treating the water to desired
levels. In addition, all technologies are virtually equal in
proteption of human health.
Packed column aeration without vapor phase GAC is somewhat
less able to decrease the toxicity and mobility of contaminants
than are packed column aeration with vapor phase:GAC ~nd liquid
phase GAC (AFP44 utilizes packed column aeration,: wi th: some vapor
phase controls). However, aeration without emission ~ontrols
was considered slightly more reliable, with fewer operations and
maintenance requirements. Aeration with emission controls is
preferred by the community over aeration alone because of a per-
ceived health risk difference between the two. But when calcu-
lated in the Public Health Evaluation, this risk difference was
not significant. In addition, packed column aeration is at
least 25% less in overall project cost than the other three
treatment options. However, depending upon well configuration
and pump rates, packed column aeration may exceed the 2.4 pounds
per day level for VOCs that is referred to in the Pima County
air quality regulations.
End Use of Treated Groundwater
As discussed previously, the options for ~se of groundwater
extracted from the Tucson Basin are limited by the Groundwater
Management Plans. As a result, after elimination of reinjection
alternatives because of high costs (with the possible exception
for water treated at AFP44, as stated previously under Ground-
water Control Alternatives), there is only on~ available option:
use treated water for drinking water.
~
-------
TABLE 7
, TREATMENT TECHNOLOGIES
Analvsis of Alternatives
PROTECTION OF PERFORMANCE I I ACCEPTANCE COST
HEALTH AND ENYIRONMENT COMPLIANCE FEASIBILITY OF OF ALTERNATIVE C.pital
AlTERNATIYE Short Term, I Long Tera '"TH ARARS OF TECHNOLOGY I IMPLEMENTATION I State I Community + 0 & M
Total
Packed I Can treat t'o 10.6. May exceed I Adequate I Feasible I Yes I No I 560,000
Column I level in I I I I
Aeration TCE and other,YOCs Pima Co. I I Supported 1060,000
I lIay act as ozone . i r emis. I ,I I by most -----..............
precursor after being lion rule PRPs. S 1,020,000
I stripped from the under some I 'I I
..ater. extraction
scenarios. I
10- 6. I I
UP,': I Can treat to I Not yet I May require I Already in I Yes
Aeration certain. addi t lonal operation; cO-
wi t h some I Secondary packed I I reinjection I ordination & I
Vapor Phase columns em it airborne I we II s. cooperation
GAC I VOCs. I I I are major can- I
cerns.
I I I I
Packed
Column
Aeration
with Vapor
Phase GAC
l i qu i d
I Phase GAC
I . 6
I Can treat to 10 ;.
I very small risk reduc'
tion compared to aera'
I tion alone over the 20
years of operation.
I Ozone precursor emis-
sions also reduced.
I
I
I Can treat to 10'6.
I
I
Completetlyelimlnates
Olone precursor emis.
sions and exposure to
air toxies.
I full
I Compliance
I
I full
Compliance
I
All analyses assume the same groundwater control
I Adequate
I
I
I
I
I
I Adequate
I
I
alternative (A.4)
I Feasible
I Disposal of
I spent carbon
is a potential
I problem.
I
I
I
I Feasible
I
I
I Yes
I
I
I
I
I
I No
I
I
I I
I Yes . - most 825,000
I public'com' I .
Cost share ments de' 1,01,000
issues have I manded I ..........................
not been I vapor GAC. I S 2,Z96,OOO
f u I I Y d is' I I
cussed.
I I
I I
I No pub I i c I 1,416,000
comment but
I would be I 2,lS6,OOO
supported. .. .. .. .. .. .. .. .. ... .. .. ..
I I S 3,572,000
I
I Pub lie not I 157,000
confident
I in Hughes. I 2,71,6,000
I .. .. ... .. .. .. .. .. .. .. .. .
I I S 2,901,000
I I
Disposal of
spent carbon
is a potential
problem.
for each
treatment
option.
UV/ozone oxidation and in'situ aerobic biodegradation were also considered but did not
evaluation. Major negative factors were questionable performance and high costs.
.
Annual 0&" cost for Packed Column
The high-side estimate for carbon
pass through
screening
t O' de t a i led
Aeration with Vapor
replacement results
Phase GAC includes the minimum estimate for carbon replacement cost.
in 20-year O&M of S1,939,OOO.
-------
I Feasible I No I City's pre. I
I I I ference. I
I I I No public I............
comment. S 2,255,000
I I I I
Does not Somewhat bet- I Reinjection I No I No public I
completely ter control wells likely comment.
satisfy of plume mi. I to introduce I I I
AZ EQA. gration with complications ............
I I reinjection. I during O&M. I I I S 3,996,000
I Full I Somewhat bet. I Reinjection I May support I No public I
I Compliance Iter control I wells likely I in lieu of II comment. I
of plume mi' to introduce A'~.
I I gration with 1 complications I I I ...-.-......
reinjection. d~rin9 O&M. S 9,368,000
I I I I I I I
11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
I I I I I I. I
B.2: Pump protective.of health: I Full. I Adequate I Feasible I Yes I No public ~95,OOO
from upper controls migration. ComplIance comment. .
. aquifer I I I I I I I ....~~~:~~~.
I I I I I I I S 758,000
I I I I I I I
I Otlf'(~ !>omf'whel more lull Somewhal hel- Reinjection I No I No public I
I I' f ,. I r, I I 11" I hen B - l ,n I (u m p I I a n (e I I e r (0 n I . " I I w c I I s I i k e I y I I com men I . I'
, I"" I '.. ... f' (I I II I I 0" I' III f' I I 0 f P I u PI I I o. i n t rod u eel I
\ t\ \) u I ,1 t.l ~ (J r (. , r a ~ to d . I I (J I _t ( I 0 11 ' h I (0 m p' i c a [ ion s I I a . ~ . . . - . . - . -
I I I C' I f\ ) e ( I . II f\ - I d u r , n 9 08. M I I , 1.." ~S , 0.fJ 0
.I ..J. I. - -~~ I ---".~~~......J__~___n_- ----'____00'1. ~~____m~_____-
.-
At TERMAT I VE
A-3: Pump
from upper
aquifer
A'4: Pump
from upper
& undivided
aquifers
A.5: Pump
from un.
divided
aquifer
A . 6: Pump &
reinject in
undivided
aquifer
A-7: Pump &
reinject in
upper & un-
divided
aquifers
II \: P ulllp
, 'r I " , r I ,
,r. .,~, II ,. I
of f'" t.. I
I PR~TECTION OF
HEALTH AND ENVIRONMENT
Short Term I Long Term
I Protecti„e of heatth
I o~ty in ~onjunctlon
with Instltutlonat
controls; does not
stop migration.
Protective of heatth
white atso controtting
contaminant migration.
I Adequately protective
I of health: some uncer-
tainty about aquifer
I protection as plume
approaches wells.
I
I
I
I
I
I
Offers somewhat more
protection than A-5 in
that remediation time
should be decre.sed.
Offers somewhat more
protection than A-4 in
that remediation time
should be decreased.
TABLE 6
GROUND~ATER CONTROLS
Analysis of Alternatives
COMPLIANCE I
WITH ARARS
PERFORMANCE I FEASIBILITY OF I ACCEPTANCE OF ALTERNATIVE I
OF TECHNOLOGY IMPLEMENTATION State Community
+
COST
Capital
o & M
Tot a I
.Does not I Adequate I Feasible I No I No public
satisfy I I 1 I comment.
Al EQA.
1 1 I I
I . I
F u II I Adequate I F.e a sib I e I. Yes I Yes
Comptiance
I I I I Most PRPs
support.
1,409,000
561,000
-------.......
S 1,970,000
2,276,000
1,399,000
.......--.....
S 3,675,000
I Does not
I completely
satisfy
I AZ EQA.
I
I.
I Adequate
I
I
I
I
1,1105,000
1,110,000
3,050,000
946,000
6,012,000
:$,356,000
922,000
503,000
-------
- 14 -
12.0
THE SELECTED REMEDY
The selected remedy for Area A includes ,control of ground-
water contamination through extraction from both the upper
divided aquifer and the regional undivided aquifer. Wells that
fo~m vertical conduits between the upper and lower aquifers will
be sealed to limit the spread of contamination to the lower
aquifer. The treatment technology will be packed column aera-
tion. Where emissions of airborne VOCs from new packed column
facilities have the potential to exceed 2.4 pounds per day,
reasonably available control technology, potentially consisting
of granular activated carbon, will be proposed for the reduction
of emissions. Treated water will be gravity-fed directly into
the municipal water di~tribution system. If any groundwater is
treated at AFP44, this~water will likely be reinjected or other-
wise returned to the aquifer rather than supplied directly to
the municipal system. ~
Extraction from bo:th the upper and undivided aquifers is
chosen because this strategy will contain the migration of con-
tamination and will remove high levels of contamination from
areas where they are currently believed to be. Packed column
aeration is chosen for ~reatment because this method provides
virtually the same pub~ic health protection as the other tech-
nologies with substant1ally less cost. Air emission controls
will be used to comply with local air quality regulations if VOC
emissions are likely to exceed 2.4 pounds per day. Direct
drinking water use is chosen as the end use because of the re-
strictions of the Groundwater Management Plans for the Tucson
Active Management Area and because of concerns about the reli-
ability of reinjection wells. However, the option to reinject
water treated at AFP44 'is preserved in order to maintain consis-
tency with current operations of the facility.
The target TCE concentration for treated water is 1.5 ~g/l
(1.5 ppb), well below TCE's MCL of 5 ppb and below its 10-6 ex-
cess cancer risk level of 3.0 ppb. Taking into account the
presence of other contaminants, this treatment goal for TCE will
result in an overall excess cancer risk of 1~-6. With a design
for a level ~f TCE that is less than its 10-. excess cancer risk
concentration, treatment will bring the levels of other contami-
nan~s well below their respective MCLs, State Action Levels, and
10- ex~ess cancer risk concentrations. The choice of an over-
a11610- level versu~ treatment to MCLs or to, for instance,. the
10- level for TCE was made because a measurable difference
(reduction.bY 1/2 or more) in risk could be made for less than a
5% cost increase.
For Area a, the remedy will include extraction from the up-
per aq~ifer and treatment to an overall excess cancer risk level
of 10-. Packed column aeration will be used unless further in-
formation indicates that another treatment method is more cost-
-------
- 14 -
12.0
THE SELECTED REMEDY
- -
The selected remedy for Area A includes -control of ground-
water contamination through extraction from both the upper
divided aquif~r and the regional undivided aquifer. Wells that
form vertical conduits between the upper and lower ~quifers will
be sealed to limit the spread of contamination to the lower
aquifer. The treatment technology will be packed column aera-
tion. Where emissions of airborne VOCs from new packed column
facilities have the potential to exceed 2.4 pounds per day,
reasonably available control technology, potentially consisting
of granular activated carbon, will be proposed for the reduction
of emissions. Treated water will be gravity-fed d~rectly into
the municipal water distribution system. If any groundwater is
treated at AFP44, this water will likely be reinjected or other-
wise returned to the aquifer rather than supplied directly to
the municipal system.
Extraction from both the upper and undivided aquifers is
chosen because this strategy will contain the migration of con-
tamination and will remove h~gh levels of contamination from
areas where they are currently believed to be. Packed column
aeration is chosen for treatment because this method provides
virtually the same public health protection as the other tech- .
nologies with substantially less cost. Air emission controls
will be used to comply with local air quality regulations if VOC
emissions are likely to exceed 2.4 pounds per day. Direct
drinking water use is chosen as the end use because of the re-
strictions of the Groundwater Management Plans for the Tucson
Active Management Area and because of concerns about the reli-
ability of reinjection wells. However, the option to reinject
water treated at AFP44 is preserved in order to maintain consis-
tency with current operations of the facility.
The target TCE concentration for treated water is 1.5 ~g/l
(1.5 ppb) , well below TCE's MCt of 5 ppb and below its 10-6 ex-
cess cancer risk level of 3.0 ppb. Taking into account the
presence of other contaminants, this treatment goal for TCE will
result in an overall excess cancer risk of 19-6. With a design
for a level of TCE that is less than its 10-. excess cancer risk
concentration, treatment will bring the levels of other contami-
nan~s well below their respective MCLs, State Action Levels, and
10- ex~ess cancer risk concentrations. The choice of an over-
al1610- level versus treatment to MCLs or to, for instance, the
10- level for TCE was made because a measurable difference
(reduction-bY 1/2 or more) in risk could be made for less than a
5% cost increase.
For Area B, the remedy will include extraction from the up-
per aq~ifer and treatment to an overall excess cancer risk level
of 10-. Packed column aeration will be used unless further in-
formation indicates that another treatment method is more cost-
-------
TABLE 8
DETAILED COSTS OP SELECTED REMEDIES POR CONTAMINATED GROUNDWATER
NORTH OF LOS REALES ROAD
CONSTRUCTION
-.................
Piping
Wells
Aquifer Segregation
Land"
Concrete Foundation & Clearwell
Engineering Overhead & Profit
1. SUBTOTAL
PUMPING .. CAPITAL
."'."'''''-----..--..--...
',jell Pumps
Booster Pumps
Pump Facilities
Installation Cost
Contingencies & Shipping
2. SUBTOTAL
PUMPING .. ANNUAL 0 & M
...-----------..-..- -----.....
Power
Ms"terials
Maintenance"
Monitoring
SUBTOTAL
3. PRESENT ',jORTH (20 yrs ; 10X)
4. TOTAL CONSTRUCTION & PUMPING
COSTS (LINES 1,2 & 3)
PACKE~ COLUMN AERATION .. CAPITAL
.......... --- ---.. --- -................. --.. --.... --..
Excavation
Equipment
Electrical & Instrumentation
Piping & Valves
Contingencies
Contractor Overhead & Profit
Engineering
5. SUBTOTAL
AREA A
AREA B
8"1 9 , 00 0
385,000
1,0,000
37,000
35,000
235.000
65,000
85,000
o
6,000
35,000
3' .000
S222,OOO
S1,551,OOO
172,000
15 000
475:000
8,000
52.000
S722,OOO
102,000
15,000
190,000
10,000
21.000
S272,OOO
112,3107 13,797
10,000 ',000
15,600 7,800
26.360 9.010
1610,307 310 ,607
11,399,000 S295,OOO
-"'---....-- .. ... .. ... .. .. ..
S3,672,OOO 1789,000
36 000
2St.:000
86,000
50,000
" 1,8,000
38,000
48.000
S560,OOO
9,600
88,000
23,000
13,000
13,000
10,000
13.000
S170,OOO
PACKED COLUMN AERATION .. ANNUAL 0 & M
....... ----... --........ ......- -... --- --....... ...-...
Power
Labor
Maintenance Materials
Monitoring
SUBTOTAL
" .
6. PRESENT WORTH
(20 YRS a 10X)
7. TOTAL PACKED COLUMN AERATION
COSTS (LINES 5 & 6)
8. ~OTAL CONSTRUCTION! PUMPING
& PACKED COLUMN AE~ATION
COSTS (LINES 4 & 7)
19, I, 00
9 700
18:300
6.600
St.,OOO
2,300
1 , 100
2,1.00
800
6,600
"60,000
S56,OOO
.. ... ... .. .. .. ..
.. .. ... .. .. ..
S1,020,OOO
S226,OOO
"",692,000
S1,015,000
-------
TABLE 8
(CONTINUED)
UEA A
AREA B
VAPOR PHASE GAC -- CAPITAL
-..------..... --.. -- -..-.-..... --.....
Contactor
Initial GAC
Blowers
Ductwork
Heaters
Pip i ng .
Contingencies
Contractor Overhead
Engineering
& Profit
100,000
40,000
18,000
10,000
12,000
6,000
28,000
22,000
28.000
S264,OOO
100,000
40,000
6,000
3,000
4,000
2,000
23,000
18,000
23.000
9. SU8TOTAl
S219,OOO
VAPOR PHASE GAC .. ANNUAL 0 & M
.. ..--...... --.. ------ ---.....- -- ..-- -...-
Heating
Power
Maintenance Materials
Carbon Replacement
38,000
107,500
9,500
23.580 . 78.800
800 -
6,000
7,500
1,500
2.600
SUBTOTAL
118,580 .
173,800
15,000 .
17,600
10. PRESENT WORTH
(20 YEARS i 10%)
S1,010,OOO . 1,480,000
S128,OOO .
150,000
.-..-..--------..-...--.....
------....----.............
11. TOTAL VAPOR PHASE GAC COSTS,
HIGH ESTIMATE (LINES 9 & 10)
S1,744,OOO
S369,OOO
=========================================================================
12. TOTAL CONSTRUCTIONt PUMPING,
PACKED COLUMN AERA ION &
VAPOR PHASE GAC COSTS
(I.lNES 8 & 11)
=========================================================================
S6,'36,000
S1,384,OOO
Costs reflect extraction well configurations A-4 and 8-2, as described in
detail in the FS and as summarized in Table 2 of this Record of Decision.
- .
~
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- 16 -
Packed column aeration will still be more cost-effective
than the other treatment options even if it is necessary to add
air emission controls to comply with ARARs. However, from the
viewpoint of risk reduction, the incremental costs-to-benefits
ratio that accompanies the additi~n of emission controls (e.g.
GAC) is considerably higher than the costs~to-benefits ratio for
the use of packed column aeration alone. This is because the
risk from air emissions that will be reduced by emission con-
trols is already so small that the effective change in risk is
virtually zero.
The selected remedy permanently and significantly reduces
the mobility and volume of hazardous substances wit~ respect to
their presence in groundwater. The migration of contamination
is controlled and contaminants are removed from the groundwater.
Packed column aeration will result in at least a short term
increase in the toxicity, mobility and volume of hazardous sub-
stances with respect to their presence in the air. TCE, the
principal contaminant of concern, is more toxic when inhaled
than when ingested. In addition, VOCs are generally more mobile
when they become airborne. Finally, packed column aeration in-
creases the volume of contamination in the air by transferring
the volume of contamination that was once in the water into the
air. Despite these factors, however, the proposed packed column
aeration facility is estimated to add virtually no risk to the
project via airborne contaminants. The absence of added risk is
due largely to (1) dilution of contamination as it exits the
packed column, and (2) the remoteness of the proposed facility
with respect to populated areas. Furthermore, a point not taken
into account in the Public Health Evaluation is that chemicals
such as TCE are broken down rather rapidly by natural ultra-
violet radiation, thereby reducing their volume in the air, fur-
ther reducing the opportunity for human exposure. It is
notable, however, that the reactivity that gives TCE a short
half-life when it is exposed to ultraviolet radiation also makes
it a precursor in the formation of ozone in the lower atmos-
phere.
Packed column aeration will increase the toxicity, mobility
and volume of hazardous substances in the air. to some degree
even if, for compliance with ARARs, air emission controls are
added. Controls such as GAC will reduce air emissions by 70 to
90 percent, but .will not completely eliminate VOC releases into
the air. Em~ssions c~ntrols will, however, simultaneously
redu~e the .risk from air toxics and limit the release of ozone
precursors.
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