PB95-964506
EPA/ROD/R09-95/136
July 1995
EPA Superfund
Record of Decision:
McClellan Air Force Base,
Basewide Groundwater OU,
Sacramento, CA
5/11/95
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Final
Basewide Groundwater Operable Unit
Interim Record of Decision
Prepared for
McClellan Air Force Base
Contract No. F04699-90-D-0035
Delivery Order 5066
Line Item No. 0022
Prepared by
OBHHILL
2485 Natomas Park Drive, Suite 600
Sacramento, California 95833
SWE28722.66.PP May 1995
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I
Contents
Page
Part I: Declaration 1
A Site Name and Location 1
B Statement of Basis and Purpose 1
C Description of the Selected Remedy 1
C.I Role of me Groundwater Operable Unit within the Overall
Site Strategy 1
C.2 Major Components of the Selected Remedy 2
D Statutory Determinations 3
D.I Protectiveness 3
D.2 Applicable or Relevant and Appropriate Requirements 3
D.3 Cost-Effectiveness 4
D.4 Use of Permanent Solutions, Alternative Treatment, or Resource
Recovery Technologies 4
D.5 Preference for Treatment as a Principle Element 4
D.6 Site Review 4
D.7 Environmental Impact Assessment 4
Part II: Decision Summary 7
A Site Name, Location, and Description 7
A.I Site Name and Location 7
A.2 Topography 7
A.3 Climate 7
A.4 Adjacent Land Use 9
A.5 Surrounding Populations 9
A.6 Surface-Water Resources . 9
A.7 Groundwater Resources 10
A.8 Surface 10
A.9 Subsurface Features 10
B Site History and Enforcement Activities 11
B.I History of Site Activities 11
B.2 History of Site Investigations and Interim Actions 11
B.3 History of Enforcement Actions 16
C Highlights of Community Participation . : 18
D Scope and Role of the Groundwater Operable Unit Within the Site Strategy 20
D.I Rationale for Undertaking this Limited Action at McClellan AJFB 20
D.2 Scope of the Groundwater OU Response Action Within the Site
Strategy 21
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Contents (Continued)
Page
D Scope and Role of the Groundwater Operable Unit within the Site Strategy
(continued)
D.3 Role of the Groundwater Operable Unit Response Action Within the
Overall Cleanup Strategy for McClellan AFB 21
D.4 Consistency of this Groundwater Response Action with Future Actions
at McClellan AFB 22
E Summary of Site Characteristics 23
E.I Base Source Areas 23
E.2 Hydrogeologic Conditions 23
E.3 Contaminants of Concern . 37
E.4 Extent of Contamination 38
E.5 Summary of Data Gaps 39
F Summary of Site Risks 39
F.I Risks Addressed by the Groundwater Response Action 47
F.2 Rationale for the Implementation of an Interim Action 47
G Description of Alternatives 48
G.1 Groundwater Containment Options 48
G.2 Groundwater Treatment Options 53
G.3 End-Use Options 57
G.4 Applicable or Relevant and Appropriate Requirements 59 .
G.5 Assembled Alternatives 64
H Summary of the Comparative Analysis of Alternatives . . 67
H.I Overall Protection of Human Health and the Environment 68
H.2 Compliance with ARARs 68
H.3 Long-Term Effectiveness and Permanence 70
H.4 Reduction in'Toxicity, Mobility, and Volume through Treatment 72
H.5 Short-Term Effectiveness 72
H.6 Implementability 74
H.7 Cost 75
H.8 State Acceptance 76
H.9 Community Acceptance 76
I Selected Remedy 77
I.I Basis of Selection 77
1.2 Elements of the Selected Remedy 80
1.3 Priorities for Extent of Contamination Investigation and Containment 83
1.4 Implementation Schedule 85
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Contents (Continued)
Page
J Statutory Determinations 85
J.I Protectiveness 85
J.2 Applicable or Relevant and Appropriate Requirements 86
J.3 Cost-Effectiveness 86
J.4 Use of Permanent Solutions, Alternative Treatment, or Resource
Recovery Technologies 86
J.5 Preference for Treatment as a Principle Element 86
K Documentation of Significant Changes 87
K.1 Changes to the Containment Component of the Selected Remedy 87
K.2 Changes to the End-Use Component of the Selected Remedy 88
Part III: Responsiveness Summary 91
A. Introduction 91
B. Oral Comments from the Public Meeting 91
C. Written Comments 92
Part IV: Works Cited .. . . 93
Figures Page
1 Location of McClellan Air Force Base 8
2 Offbase Remedial Action Area 14
3 Map of OU Boundaries and Source Areas 15
4 Historic Groundwater Contours in the Vicinity of McClellan AFB 27
5 Water Levels and Flow Directions in Zone A, January 1993 29
6 Water Levels and Flow Directions in Zone B, January 1993 30
7 Water Levels and Flow Directions in Zone C, January 1993 31
8 Production, Municipal, and Base Wells in the Vicinity of McClellan
Air Force Base 32
9 Historic Base Activities Influencing Contaminant Migration 34
10 Current Base Activities Influencing Smear Zone 36
11 Extent of TCE Contamination in Monitoring Zone A 40
12 Extent of TCE Contamination in Monitoring Zone B 41
13 Extent of TCE Contamination in Monitoring Zone C 42
14 Extent of VOC Contamination in Monitoring Zone D/E 43
15 Vertical Extent of Contamination in OU A 44
16 Vertical Extent of Contamination in OU B/C 45
17 Vertical Extent of Contamination in OU D47 46
18 Target Areas in Monitoring Zone A 50
19 Target Areas in Monitoring Zone B 51
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Figures (continued)
i
20 Target Areas in Monitoring Zone C 52
21 Standard Groundwater Treatment Technology Screening 54 f
22 Standard Treatment Technologies 55 *
23 Layout For End-Use Options 58
24 Comparison of Long Term Effectiveness of the Three Containment Options 71 f
25 Estimated Times to Cleanup 73 i
26 Schematic of the Selected Remedy 81
27 Extent of Contamination Investigation and Containment of Plume Phasing 84 f
Tables Page
f
1 Summary of Major Investigations at McClellan AFB Under DRP and IAG 12 |
2 Summary of Existing Interim Groundwater Remedial Actions 17
3 Approximate Zone Depths 24 f
4 Summary Statistics of COCs . 37 |
5 Estimated Mass of COCs and Volume of Contaminated Aquifer by Zone 38
6 Area! Extent of Target Volumes 49 »
7 Number of Extraction Wells and Flow Rates Required to Contain |
Different Target Volumes 53
8 Chemical-Specific ARARs for the Groundwater OUIROD 61 .,
9 Location-Specific ARARs for the Groundwater OU IROD 62 |
10 Action-Specific ARARs for the Groundwater OU IROD 63 fe
11 Alternatives for Groundwater at McClellan AFB 65
12 Comparison of Alternatives Against Nine EPA Criteria 67
13 Compliance with ARARs 69 v
14 Implementability 74
15 Cost Summary 75 f
16 Range of Costs for Alternative 4A 79 t
17 GWTP Effluent Limitations and Limits of Quantitation 82
18 Investigation and Containment Priorities 83 f
19 Comparison of Decision Factors for the MCL and Risk Target Volumes 88 1
I
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Glossary of Terms
J
j
1
AFB
AFGE
" aquifer
ARARs
AS
ATSDR
BACT
bgs
BW
Cal-EPA/DTSC
GARB
CatOx
CCR
CERCLA
COCs
CRP
CS
CWA
DCA
DCE
DHS/ODW
DNAPLs
Air Force Base
American Federation of Government Employees
portion of subsurface below the water table
applicable or relevant and appropriate requirements
air stripper
Agency for Toxic Substances and Disease Registry
Best Available Control Technology
below ground surface
Base Well
California Environmental Protection AgencyXDepartment of Toxic
Substances Control
California Air Resources Board
catalytic oxidation
California Code of Regulations
Comprehensive Environmental Response, Compensation, and Liability
Act of 1980
contaminants of concern
Community Relations Plan
confirmed site
Clean Water Act
dichloroethane
dichloroethene
California Department of Health Services/Office of Drinking Water
dense nonaqueous phase liquids
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Vll
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DOD
ECRSC
EE/CA
EPA
FS
gpm
GSAP
GWTP
HC1
hot spot
IAG
IRM
IRP
IWL
IWTP
LGAC
LNAPLs
MAP
MCLs
msl
NAPL
NCP
NOAA
NPL
NO,
Department of Defense
Environmental Community Relations Steering Committee
Engineering Evaluation/Cost Analysis
U.S. Environmental Protection Agency
Feasibility Study
gallons per minute
Groundwater Sampling and Analysis Program
Groundwater Treatment Plant
hydrochloric acid
area with groundwater VOC contamination greater than 500 micrograms
per liter
Interagency Agreement
interim remedial measure
Installation Restoration Program
Industrial Wastewater Line
Industrial Wastewater Treatment Plant
liquid-phase granular activated carbon
light nonaqueous phase liquids
Management Action Plan
maximum contaminant levels as defined by the Safe Drinking Water Act
mean sea level
nonaqueous phase liquids
National Contingency Plan .
National Oceanic and Atmospheric Administration
National Priorities List
nitrogen oxides
I
I
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V1U
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I
1
.1
I
J
O&M
OU
PCBs
PCE
PGOURI
ppb
ppbv
PRL
RAB
RCRA
RD/RA
RI/FS
RME
ROD
ROG
RPM
RWQCB
SARA
SDWA
SMAQMD
SVAB
SVE
T-BACT
TBCs
TCE
RDD10013729.WPS
operations and maintenance
operable unit
polychlorinated biphenyls
tetrachloroethene
Preliminary Groundwater Operable Unit Remedial Investigation
parts per billion
parts per billion by volume
potential release location
Restoration Advisory Board
Resource Conservation and Recovery Act of 1976
remedial design/remedial action
Remedial Investigation/Feasibility Study
reasonable maximum exposure
Record of Decision
reactive organic gases
Remedial Project Manager
Regional Water Quality Control Board
Superfund Amendments and Reauthorization Act of 1986
Safe Drinking Water Act
Sacramento Metropolitan Air Quality Management District
Sacramento Valley Air Basin
soil vapor extraction
Best Available Control Technology - Toxics
to-be-considered criteria
trichloroethene
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TRC Technical Review Committee
USTs underground storage tanks
vadose zone soils above the groundwater
VGAC vapor-phase granular activated carbon
VOCs volatile organic compounds
f
r
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Part I: Declaration
A. Site Name and Location
Department of the Air Force
Sacramento Air Logistics Center
McClellan Air Force Base
Sacramento, California 95652
EPA ID# CA4570024337
1 B. Statement of Basis and Purpose
"3 This Interim Record of Decision (Interim ROD) presents the interim remedial action for the Ground-
:1 water Operable Unit (Groundwater OU) at the McClellan Air Force Base (McClellan AFB) Superfund
site in Sacramento, California. This interim remedial action was selected in accordance with the
) Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) as
j amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), 42 USC § 9601 ei
seq., and with the National Oil and Hazardous Substances Pollution Contingency Plan, 40 CFR
-» Part 300 (National Contingency Plan [NCP]). The Administrative Record identifies the documents
.-j upon which the selection of the remedial action is based. Part n, Section C, discusses the
Administrative Record and where it can be examined.
1 '
i The U.S. Environmental Protection Agency (EPA), Region IX, concurs with the selected remedy.
- The State of California, through the California Environmental Protection Agency's Department of
} Toxic Substances Control (Cal-EPA/DTSC) and the Regional Water Quality Control Board (RWQCB),
concurs with the selected remedy.
:| Releases of volatile organic compounds (VOCs) as a result of historic Base activities have contamina-
^ ted the groundwater at McClellan AFB. Actual or threatened releases of hazardous substances from
this site, if not addressed by implementing the response actions selected in this Interim ROD, may
1 present an imminent and substantial endangennent to public health, welfare, or the environment
] C. Description of the Selected Remedy
, C.1 Role of the Groundwater Operable Unit within the Overall Site Strategy
* The Groundwater OU addresses all of the VOC-contaminated groundwater at McClellan AFB. This
Groundwater OU remedy is designed to prevent the spread of contamination that is already in the
:| groundwater by containing groundwater with concentrations greater than maximum contaminant levels
* (MCLs). The remedy is also designed to remove to the maximum extent practicable the mass of
contamination that lies in mat volume of the groundwater.
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This remedy does not directly address contamination that currently lies in the vadose zone. To more
efficiently achieve overall cleanup, McClellan AFB is developing separate response actions that
address the vadose zone areas of contamination directly.
The overall strategy for McClellan AFB is therefore two-pronged in nature. It is designed to contain *
and remove groundwater contamination at levels above MCLs, preventing exposure to human and
environmental receptors (the focus of the remedy described in (his document). It also focuses on the fj
vadose zone source areas, preventing exposure at the ground surface and eliminating future downward *
contaminant migration to groundwater. A discussion of the specific objectives of the Groundwater OU
interim response action is presented in Part n, Section D.3, Role of the Groundwater Operable Unit ^
Response Action Within the Overall Cleanup Strategy for McClellan AFB. I
C.2 Major Components of the Selected Remedy f
I
The selected remedy has three main components:
Containment of contaminated groundwater by extraction |.
Treatment of the extracted groundwater and offgas
End-use of the treated groundwater e
The selected remedy is Alternative 4A. The rationale for selecting this alternative is presented in the
Decision Summary. The selected remedy consists of the following: *
Containment: Groundwater contaminated at levels greater man Levels MCLs will be
extracted at pumping rates that prevent its further migration. Containment to prevent
offbase plume migration is the highest priority of this remedy, followed by
containment of the hot spots and containment to prevent vertical downward migration.
Eventually, all groundwater will be contained so that no water above MCLs will leave
the Base boundaries. Groundwater extraction wells will also be located in areas with |
the highest contaminant concentrations (hot spots/sources). Aggressive pumping of ^
these wells will rapidly reduce the total amount of groundwater contamination and its
associated risk. [
Treatment: Groundwater extracted on the west side of the Base will be treated at the
existing groundwater treatment plant (GWTP). The GWTP removes the VOCs from |;
the water by air stripping followed by granular activated carbon polishing. The air £
stripper offgas is treated by thermal oxidation. Eventually, the extraction system may
exceed GWTP capacity. Additional treatment capacity, if needed, will be provided at £
an east side GWTP using air stripping and granular activated carbon for water
treatment and vapor-phase carbon filters for treating the air stripper offgas.
End-Use: The Air Force believes it is premature at this time to specify any one or any
combination of end uses for the treated water in this Interim ROD. The final decision
on the end use will be determined in the Final ROD, depending on the actual quantity
of water mat needs an end use and further discussions with potential recipients of the
treated water.
At this time, the Air Force prefers to reuse as much treated groundwater as possible in
the Base's greywater system. The remaining flow will either be discharged into
RDD10013706.WP5 (ROD) 2 5/2/95
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I Magpie Creek or injected into the groundwater. This option is discussed in detail in
( Part II, Section G.3. However, McClellan AFB is continuing to explore with
Cal-EPA, U.S. EPA, and surrounding communities how best to utilize the treated
j water, including providing it to neighboring water districts.
The goal of groundwater containment is to halt the vertical and lateral migration of groundwater that
j exceeds MCLs. Currently, virtually none of the public is exposed to groundwater contamination from
) McClellan AFB; containing the groundwater significantly reduces the potential risk of exposure.
Containment in any area of a plume will be maintained at least until concentrations drop to or below
'} MCLs. The Air Force also plans to isolate the groundwater hot spots, which contain the vast majority
'./ of contaminants. Isolation of the hot spots improves long-term cost effectiveness of the remedy. Final
cleanup values are not established in this Interim ROD but will be established in the Final ROD,
- j currently scheduled for 2003.
D. Statutory Determinations
3 D.I Protectiveness
.1 This interim action is protective of human health and the environment Protection is achieved at the
.} Base and in the aquifers underlying the Base in the following ways:
Initial protection of human health will be achieved by stopping the migration of con-
tamination to private and municipal production wells, and by stopping migration to
and/or treating water from Base production wells.
Containment of groundwater within the MCL target volume, by extraction, will protect
humans from exposure to contamination above the drinking water standards of the Safe
Drinking Water Act
Extraction of contaminated groundwater can reduce the downward migration of con-
taminants and protect the deeper aquifers from degradation.
Decommissioning Base wells that are believed to be vertical migration conduits, such
as BW-18, will protect the deeper aquifers from contaminants migrating from the
shallower aquifers. Pumping of BW-18 and other active Base wells also increases the
migration rate of contaminants in the A and B Zones into the lower zones.
Treatment of VOC-contaminated groundwater to appropriate discharge limits prior to
discharge will protect the environment from degradation. Discharge limits are
presented in Section 1.2.
D.2 Applicable or Relevant and Appropriate Requirements
The selected interim remedy complies with federal and state Applicable or Relevant and Appropriate
Requirements (ARARs) for this limited scope action.
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D.3 Cost-Effectiveness
The remedy is cost-effective because adequate protection is achieved for the estimated cost of f
performance. The selected remedy is to control and treat groundwater within the MCL target volume. T
The analysis contained in the FS and summarized here in Part II, Section I, Selected Remedy, demon-
strates that additional remedial action associated with containing and treating the water within the _
background target volume or the 10"6 cancer risk target volume would not achieve a significantly f-
greater reduction in risk, but would result in higher costs.
D.4 Use of Permanent Solutions, Alternative Treatment, or Resource Recovery f
Technologies *
Although mis interim action is not intended to fully address the statutory mandate for permanence and I
treatment, this interim action of containment of the MCL target volume and treatment of groundwater «
uses treatment and thus is in furtherance of that statutory mandate. The selected remedy represents the
best balance of trade-offs among alternatives with respect to pertinent criteria, given the limited scope f
of the action. Subsequent actions are planned to address fully the threats posed by the conditions at t
this OU. A Basewide Feasibility Study (FS) and ROD, scheduled for completion in the year 2003,
will fully address any Groundwater OU issues beyond this interim remedy. f
D.5 Preference for Treatment as a Principle Element
Because this action does not constitute the final remedy of the Groundwater OU, the statutory prefer- t
ence for remedies that employ treatment and that reduce toxicity, mobility, or volume as a principal
element, although partially addressed in this remedy, will be addressed by the final response action.
D.6 Site Review
f
Because this remedy will result in hazardous substances remaining onsite above health-based levels, a \_
review will be conducted to ensure that the remedy continues to provide adequate protection of human
health and the environment within 5 years after commencement of this interim remedial action. »
Because this is an interim action ROD, review of this site and of this remedy will be continuing as £
McClellan AFB and the regulatory agencies continue to develop final remedial alternatives for the
Groundwater OU. f
I
D.7 Environmental Impact Assessment
The current policy of the United States Air Force is to analyze its response actions conducted under j
CERCLA for potential environmental impacts as described in the National Environmental Policy Act
and as further implemented at 40 Code of Federal Regulation (CFR) Parts 1500 through 1517 and
32 CFR Part 989. 1
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JUMEANDERSON
Diiwor
Federal Facilities Cleanup Office
U.S. Environmental Protection Agency, Region 9
Dafe
ANTHONY
California Environmental Protection Agency
Department of Toxic Substances Control
Chief of Operations
Office of Military Faciljtk
Date
LA WRENCH J. FARRELL, JR.
Lieutenant General, USAF
Vice Commander
Date
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5/5/95
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Part II: Decision Summary
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1
Part II of this Interim ROD summarizes the information, interpretations, and conclusions that led to
McClellan AFB's decision on the remedy, and presents the selected interim groundwater remedy.
A. Site Name, Location, and Description
This section describes McClellan AFB, including its location, topography, climate, land uses adjacent
to the Base, surrounding populations, surface and groundwater resources, and surface and subsurface
features.
A.1 Site Name and Location
Department of the Air Force
Sacramento Air Logistics Center
McClellan Air Force Base
Sacramento, California 95652
EPA ED# CA4570024337
McClellan AFB, an Air Force Logistics Center, is located approximately 7 miles northeast of down-
town Sacramento, California, and covers approximately 2,952 acres. The Base property is approxi-
mately bounded by Elkhom Boulevard on the north, Roseville Road on the south, Watt Avenue on the
east, and Raley Boulevard on the west The Base location is shown in Figure 1.
A.2 Topography
The land surface at the Base slopes gently to the west Elevations range from 75 feet above mean sea
level (msl) on the east side of the Base to approximately 50 feet msl on the west The topographic
relief across the Base is low. Portions of the Base, including parts of Magpie Creek, are within the
100-year flood plain as presented in a flood plain map in the Resource Conservation and Recovery Act
(RCRA) Part B application (CH2M HILL, 1992). The Base is approximately 3.6 miles long in the
north-south, direction and 2.4 miles wide in the east-west direction.
A.3 Climate
McClellan AFB is located in the Sacramento Valley Air Basin (SVAB). Climate in the SVAB is
moderate, with mild winters and hot, dry summers.
In January, the average daily maximum temperature is approximately 53° to 54°F. In July, the aver-
age daily maximum temperature is 95° to 98°F (University of California, Berkeley, undated).
Mean annual precipitation from 1875 to 1975 in the SVAB was approximately 17 inches. Approx-
imately 90 percent of the rainfall occurs between November and April with little or no precipitation
from late spring to early fall. Most of the rainfall is associated with Pacific storms, which are frequent
in winter (NOAA, 1989).
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Elkhom Boulevard
North
Highlands
ASCOT AVElli
|:-i-
McCLELLAN AFB
NORTH
SACRAMENTO
Marconi /We.
Camino Ave. >
SACRAMENTO
FIGURE 1
LOCATION OF
McCLELLAN AIR FORCE BASE
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
CKMHIll
Source: Radian
Corporation
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i In the winter, northeriy and southerly airflow patterns prevail during the day. Calm conditions pre-
dominate during me late evening and early morning. During the spring and summer, the prevailing
-^ airflow pattern is from the delta or sea breezes. Northerly winds and the sea breeze are predominant
| in the fall. Full sea breeze conditions occur 29 percent of the year, northerly winds occur 20 percent
of the year (CARB, 1984).
1 A.4 Adjacent Land Use
Land use in the vicinity of McClellan AFB is a combination of military, industrial, commercial, resi-
i dential, and agricultural uses. Land is not mined for natural resources.
Much of the land around the Base is zoned for residential use. In the Rio Linda area northwest of the
| Base, most of the land is categorized as agricultural-residential. This land category identifies areas
j reserved for large-lot rural residential uses where animals may be kept and crops raised for recreation,
educational use, personal consumption, or supplemental income purposes (Sacramento County, 1985).
::;3 Many of these residences use private well water for nonpotable uses.
Several areas to the north, west and southeast of the Base have been zoned as industrial-intensive.
1 This land category identifies areas reserved for research, manufacturing, processing, and warehousing
j activities.
JMost of the land to the southwest of the Base consists of low-density residential zones. These areas
are reserved for a planned population density range of 5 to 30 persons per acre or a housing density
range of 1 to 12 dwelling units per acre. Some of these residences have private wells, but the majority
have municipal water supplies.
The land to the east of the Base consists of medium-density residential, commercial, and industrial
, zones.
Parcels designated for commercial and office use, including shopping centers, large office complexes,
and major concentrations of commercial development are also located to the southwest and east of
1 McClellan AFB.
A.5 Surrounding Populations
7
J McClellan AFB is surrounded by four Sacramento County communities that include residential, com-
mercial, and industrial zones. They include Rio Linda and Elverta to the northwest, North Sacramento
] to the west and southwest and North Highlands to the east
The population of the surrounding communities, as determined by the 1980 census, was 107,822. The
1 projected 2005 population is estimated to be approximately 200,000 (Sacramento County, 1985).
1
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A.6 Surface-Water Resources
Surface-water drainage near McClellan AFB occurs predominantly through Magpie, Don Julio, Rio
Linda, and Arcade Creeks. Magpie Creek enters McClellan AFB from the east and is joined by sev-
eral small tributaries before leaving the Base to the west Onbase drainage has been modified by con-
struction of a series of storm drains and channels across the Base. Runoff from streets and runways is
directed into the storm drainage system and exits the Base via Don Julio Creek and Magpie Creek.
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Rio Linda Creek crosses the northern portion of the Base. Magpie Creek crosses the southeast and ;
central portions. Arcade Creek is located just south of Base property. All three of these drainages *'
flow into the Natomas East Drainage Canal west of the Base. The canal flows south and west until it
discharges into the Sacramento River, just northwest of the confluence of the American and |!
Sacramento rivers (Radian, 1989). Stormwater runoff also exits the base via Don Julio Creek. «-
Groundwater is approximately 100 feet below ground surface. The only interconnection between
surface water and groundwater is through infiltration. There are no impacts to surface water quality f^
from adverse groundwater quality. »
A.7 Groundwater Resources f
Groundwater is used regionally for agricultural irrigation, for potable water supply, for fire fighting,
and for industrial uses. Locally, groundwater extracted from the deeper aquifers beneath f!
McClellan AFB is used in the Base water supply for drinking and Base activities. Groundwater |i.
extracted from Base wells is monitored for VOC contaminants. Extracted groundwater from BW-18 is
treated using a wellhead GAC unit There are also several municipal wells located offbase that extract IF
water for potable use (see Figure 8). Groundwater extracted from these wells is monitored and j^
contingency plans are being developed if these wells become threatened by contaminan'oa
A.8 Surface j|
Many buildings located throughout the Base are currently occupied and used for military operations. .-.
Several waste pits, underground and aboveground tanks, and storage facilities also exist Basewide. [
They were installed as part of the historical Base activities. Two hundred fifty-four potential source
areas or sites have been identified thus far within McClellan AFB boundaries (McClellan AFB, 1994).
Many of these sites have the potential to be contributors to the groundwater contamination problem. i
Seventy of the sites are classified as waste pits or landfills, 8 are classified as liquid/sludge holding *"
ponds, and 24 are classified as former underground storage tanks (USTs). The remaining sites are
generally associated with specific buildings, washracks, pipelines, and storage areas where hazardous (v
materials are routinely used. Table 5-1 of the McClellan AFB Management Action Plan (MAP) k
describes each of the 254 sites. All are currently being investigated in accordance with CERCLA.
Surface and subsurface features are most dense in Operable Units A, B, C, and D. These operable t:
units will be discussed further in Section B, Site History and Enforcement Activities, and are discussed
in detail in Chapter 4, Conceptual Model, of McClellan AFB Remedial Investigation/Feasibility Study f?.
(RI/FS) (CH2M HILL, 1994). 1
A.9 Subsurface Features j?
McClellan AFB is centrally located within the Great Valley geomorphic province, a wedge-shaped
accumulation of sediments, bounded to the west by the Coast Range and on the east by the Sierra I..
Nevada foothills. This area consists of sediments and rock units derived from alluvial, fluvial, flood, \;;
and delta deposits of the Sacramento and San Joaquin Rivers, and from alluvial fan accumulations at
the base of the Sierra Nevada foothills. ' r:
The lithology below the Base consists primarily of sand, silt, and clay in various combinations with
localized occurrence of gravel. These deposits were frequently transported and redeposited by local ,
streams. Erosion and redeposition of sediments, and meandering and abandoned channels, make the ,'..;.
distinction between soil units difficult.
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B. Site History and Enforcement Activities
I This section summarizes the history of activities that led to the current contamination, the history of
site investigations and interim remedial actions, and the history of enforcement actions. The site
j investigations and interim remedial actions are summarized chronologically, as follows:
Initial discovery of contaminated groundwater in 1979
] Activities performed under the Department of Defense (DOD) Installation Restoration
Program (IRP)
'.!. Activities performed under the Interagency Agreement GAG), currently governed by
IRP guidelines
| B.1 History of Site Activities
McClellan AFB was established in 1936 as an aircraft repair depot and supply base. Prior to this time,
:] the land on which McClellan AFB was constructed had been devoted to agricultural use, primarily
' raising livestock and growing grain. Base operations expanded significantly during World War II and
in subsequent years. The primary mission of McClellan AFB has been to provide logistics and main-
~\ tenance support for several types of aircraft, as well as maintenance support for several communica-
& tions and electronics systems. Fulfilling this mission has involved the use of a wide range of toxic
and hazardous substances, including industrial solvents and caustic cleaners, electroplating wastes
1 contaminated with heavy metals, oils contaminated with polychlorinated biphenyls (PCBs), low-level
J radioactive wastes, aviation fuels, and a variety of oils and lubricants.
1
1
i
;
4
1
Hazardous wastes from operations at McClellan AFB have historically been discharged to land onbase,
in burial pits, landfills, sludge/oil pits or bum pits, or piped through a subsurface industrial wastewater
line (FWL) to two industrial wastewater treatment plants (rWTPs) formerly located on the east side of
the Base. Sludges from these former IWTPs were then discharged to land onbase. Most of these
former disposal areas were located on the west side of the Base. These land disposal practices were
discontinued in the late 1970s. Currently, wastes are sent offsite to approved disposal sites, or dis-
charged to the existing IWTP constructed on the west side of the Base in the early 1970s. Sludges
from the existing IWTP are disposed of offsite at approved disposal sites.
B.2 History of Site Investigations and Interim Actions
McClellan AFB voluntarily created a committee in August 1979 to determine if groundwater contami-
nation was present at the Base and in the surrounding community. Trichloroethene (TCE) was detec-
ted in onbase water supply wells, resulting in a study to determine the extent of TCE groundwater
contamination, performed in cooperation with state and local agencies. Monitoring of onbase and
offbase water supply wells in November 1979 resulted in closure of several wells. A field survey
program was initiated, including soil sampling and installation of 15 monitoring wells to determine the
sources and extent of onbase TCE contamination. Four areas of TCE contamination were found
onbase, designated then as Areas A, B, C, and D. A summary of the investigations performed at
McClellan AFB is presented in Table 1.
R0D1001370A.WP5 (IROD) 11 5/2/95
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Table 1
Summary of Major Investigations at McClellan AFB Under IRP and IAG
Year
Completed
1981
1983
1984
1985
1986
1988
1989
1989
1991
1993
1994
1994
1994
1994
Contractor
CH2MHILL
Engineering Science
Ludorff & Scalmanini
Radian Corporation
McLaren Environmental
Engineering, Inc.
Radian Corporation
Idaho National Engineering
Laboratory
Radian Corporation
Radian Corporation
Radian Corporation
Agency for Toxic Substances
and Disease Registry
CH2MHILL
CH2MHILL
Radian Corporation
Jacobs Engineering
Scope
IRP Phase I-Inib'al assessment of contamination. Past disposal sites in all areas of the Base
were identified.
IRP Phase II-Definition and quantification of contamination; implementation of a monitoring
program to determine the extent of groundwater contamination
Review of previous investigations
Determination of the nature and extent of contamination in wells offbase. Public health hazards
were identified and remedial alternatives assessed.
Drilling of soil borings to further define the extent of contamination at rites identified during
IRP Phase I
Groundwater Sampling and Analysis Program. The presence and concentration of contaminants
were determined and migration over time was evaluated.
Characterization of the industrial wastewater collection system. Samples were collected and
compared to hazardous waste criteria. Also, the integrity of the collection system piping was
evaluated.
Engineering Evaluation/Cost Analysis-Environmental Assessment
Area B Groundwater Operable Unit Remedial Investigation. Hydrogeologic characteristics of
the southwest portion of the Base were characterized; the horizontal and vertical extent of
groundwater contamination was evaluated.
Preliminary Groundwater Operable Unit Remedial Investigation. A conceptual model of the
hydrogeology was developed and the extent of groundwater contamination at McClellan AFB
was investigated.
Public Health Assessment for McClellan AFB
Operable Unit D Remedial Investigation. A remedial investigation was performed to collect
enough data to reduce the uncertainty in contaminant type and distribution at OU D. In
addition, a risk assessment was conducted. Further action to determine the extent was
recommended.
Groundwater Operable Unit Remedial Investigation/Feasibility Study. The conceptual model of
the site was expanded; a risk assessment was performed; and containment, treatment, and end-
use alternatives were developed and screened.
Operable Unit C Remedial Investigation and the Operable Units E-H Preliminary
Assessment/Site Investigation.
Operable Unit A Remedial Investigation.
B.2.1 Activities Performed Under the Installation Restoration Program
In 1981, the DOD developed the IRP to identify and evaluate suspected contamination problems
resulting from past hazardous waste disposal practices at DOD facilities. The IRP was developed as a
four-phase program. Phase I consisted of record searches to identify problem areas. Phase n corres-
ponded to the RI/FS process for characterizing hazardous waste sites and evaluating remedial action
alternatives described in the NCR Phase HI involved identification and development of remedial
action technologies. Phase IV involved implementation of the recommended remedial action. Until
1990, site investigation activities were performed according to the IRP. After 1990, activities were
performed under the IAG, as described in Section B.2.2.
t
I
I
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RDD1001370A.WP5 (IROD)
12
5/2/95
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i
]
j A Phase I records search, performed in 1981, identified groundwater contaminated by TCE as a main
area of concern and identified 46 potential hazardous waste storage and disposal areas at
McClellan AFB. A Phase n groundwater investigation performed in 1983, involving sampling of Base
:i supply wells, existing monitoring wells, and wells installed during the field program, detected organic
and inorganic compounds in the shallow water-bearing zone under McClellan AFB. Also in 1983,
McClellan AFB began a quarterly offbase sampling program of 240 private wells located to the west
;;', and south of the Base. Results from this sampling program were used to evaluate the extent of
' offbase contamination and as a basis for providing bottled water to residents with contaminated wells.
A second stage of the Phase II groundwater investigation, initiated in 1984, involved installation and
:1 sampling of onbase and offbase monitoring wells and the development of a long-term groundwater
j monitoring program. In 1986, McClellan AFB provided municipal drinking water hookups for drink-
ing water supplies in the area west of the Base. This remedial action area, presented in Figure 2,
'} included all known areas of offbase groundwater contamination.
Site investigations involving sampling of wastes, soils, and groundwater were performed in Areas A,
3 B, C, Di and other areas of concern in 1984. A Phase HI/TV study was performed in Area D in 1985
;| to evaluate remedial action alternatives and to provide conceptual design information for a selected
alternative. An Interim Remedial Measure (TRM) to control further migration of contaminated ground-
water was performed in Area D. This IRM included a cap over Area D and installation of a ground-
water extraction and treatment system. The cap, composed of layers of clay, compacted soil, a plastic
liner, and natural vegetation, was designed to prevent rainwater from percolating through the waste
-, pits. Contaminated sludges and soils were excavated from Area D and sent offsite to an approved
j disposal site prior to construction of the cap, which was completed in 1986. The groundwater extrac-
tion system, also completed in 1986, pumped water from beneath Area D. The groundwater extraction
, system was expanded to Area C in late 1988 to address possible contaminant migration from the
j IWTP and nearby disposal areas. Extracted groundwater from Area C and Area D was then piped to
'-* the Groundwater Treatment Plant (GWTP), which had been completed in 1987. Further migration of
groundwater contaminants in Area B was controlled by pumping BW-18 and by the extraction system
constructed under the OU B Engineering Evaluation/Cost Analysis (EE/CA). Well BW-18 receives
wellhead treatment using activated carbon. A more thorough discussion of the history and role of the
extraction systems, as well as the groundwater treatment methods, is presented in Section D.
B.2.2 Activities Performed Under the Interagency Agreement
In May 1990, the Air Force, U.S. EPA Region K, and the California Department of Health Services
(now known as California Environmental Protection Agency Department of Toxic Substance Control,
or Cal-EPA/DTSQ entered into an IAG requiring restoration activities to comply with applicable state
and federal laws. At the time, the Base was divided into 8 OUs. Currently the Base is divided into
11 OUs. Ten of the 11 OUs have geographic boundaries at the surface and are associated with source
areas at the Base. These OUs are A (formerly Area A), B and Bl (formerly Area B), C and Cl
(formerly Area C), D (formerly Area D), E, F, G, and H (see Figure 3). The eleventh OU is the
Groundwater OU. An OU is a discrete part of an overall site and can be examined separately if the
remedial action for the OU can be done expeditiously, is cost-effective, controls contaminant sources
or migration, and is consistent with the final site remedy. RI/FSs have started at the A, B, Bl, C, Cl,
D, and Groundwater OUs. The RI/FS for OU Bl is complete, and an Interim ROD has been issued.
Results of that study show that the principal pathways of exposure at OU Bl were associated with
PCBs and dioxins/furans in surface soil. Contaminants in soil at OU Bl are not considered to
represent significant sources of groundwater contamination. OUs E through H are deemed to be lower
priority areas, with an RI/FS for these OUs to be initiated in the 1996-1997 timeframe.
j
j
i
RDDI001370A.WP5 (IROD) 13 5/2/95
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\
GST.
EST.
CST.
ASCOT
1ST.
OFFBASE
VINO REMEDIAL
ACTION
AREA
CLAIRE
MAIN
V
^^^^^^^^H^^
BELL
MARTM
_
EST.
McCLELLAN AIR FORCE BASE
3000
6000 FEET
LEGEND
.... INDICATES BOUNDARY OF THE OFFBASE REMEDIAL ACTION AREA
SCALE (Approximate)
NOTE:
ALL RESIDENTS WITHIN THE OFFBASE REMEDIAL ACTION AREA
HAVE BEEN OFFERED MUNICIPAL WATER HOOKUPS.
ROD1631_31
FIGURE 2
OFFBASE REMEDIAL ACTION AREA
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
Cf&iHILL
-------
LEGEND
CONFIRMED SITE/POTENTIAL RELEASE LOCATION
O STUDY AREA
BOUNDARIES OF OPERABLE UNITS
McCLELLAN AIR FORCE BASE BOUNDARY
Source: McCLELLAN AFB Map (December, 1994}
RDD1631_37
FIGURE 3
MAP OFOU BOUNDARIES
AND SOURCE AREAS
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
CHMHIIL'
-------
Removal actions for VOCs in soil, such as TCE, that could migrate to groundwater in the future were
addressed in an EE/CA prepared in 1993. The EE/CA supports the use of Soil Vapor Extraction
(SVE) for a Basewide nontime-critical removal action for VOC contamination in soil at McClellan
AFB. An SVE treatability study was initiated in OU D in 1993 that has become a removal action. f
Additional SVE removal actions were initiated in OUs B and Cl in 1994. «
The Preliminary Groundwater Operable Unit Remedial Investigation (PGOURI) began in 1990. Its f
purpose was to develop a conceptual model of the hydrogeology and groundwater flow patterns under 1
McClellan AFB and to further define the extent of groundwater contamination. Results from the
PGOURI indicated that several contaminants have been consistently detected in groundwater under f
McClellan AFB at levels above federal drinking water standards. The contaminant with the greatest I
spatial extent in groundwater under McClellan AFB is TCE.
Groundwater monitoring is performed by the Groundwater Sampling and Analysis Program (GSAP). f
The GSAP, which has been ongoing since October 1986, has involved quarterly sampling and analysis
of groundwater contaminants and measurement of water levels from onbase and offbase monitoring r
wells. There are currently 300 onbase and offbase monitoring wells. £
The Groundwater OU RI/FS proposed plan, released for public comment in July 1994, included -
PGOURI and GSAP data as they relate to estimating the extent of groundwater remedial action |
required and implementing the remedial actioa The plan included estimated target volumes of
groundwater for remedial action, risk assessment, and modeling of groundwater flow directions under
McClellan AFB. It also evaluated remedial action alternatives, considering the uncertainties in the f
understanding of the nature and extent of groundwater contamination at McClellan AFB.
B.3 History of Enforcement Actions
Since 1979, McClellan AFB has acted voluntarily to respond to groundwater contamination. Since
1981, McClellan AFB has responded to groundwater contamination problems in accordance with the f
IRP. Several investigations and IRMs were performed under the IRP, as described previously. On *~
July 22, 1987, McClellan AFB was listed on the U.S. EPA's National Priorities List (NPL). On
May 2, 1990, the Air Force, U.S. EPA Region IX, and Cal-EPA signed the LAG, which requires com- f
pliance with the NCP, CERCLA guidance and policies, RCRA guidance and policies, and applicable I
state laws. Under the LAG, the Air Force agreed to undertake, seek adequate funding for, fully imple-
ment, and report on RIs, FSs, all response actions, and operation and maintenance of response actions. f
The LAG specifies deadlines and target dates for documents. The LAG fulfills the Federal Facility ti
Agreement under CERCLA Section 120.
f
Several interim groundwater actions have taken place at McClellan, including groundwater extraction [,
systems, surface capping, and construction of the west side treatment plant These actions are
summarized in Table 2. All current extraction systems will be included in the remedy presented in j
this Interim ROD. These extraction systems do not completely contain all groundwater contamination f
in OUs B, C, and D.
A review of grants (leases, permits, licenses, and easements) at McClellan AFB was performed in j
1979 during the LRP Phase I records search to identify other potentially responsible parties. The
records search documented existing grantees (users of McClellan AFB property) or grantors (owners of (
property being used by McClellan AFB), their purposes, and types of agreements. Review of these j
RDD1001370A.WP5 (IROD) 16 5/2/95
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I
I
1
J
1
1
j
TabU 2
Summary of Existing Groundwater Interim Action
Groundwalcr Interim Actions
Faculty
Three OU B Wells
Two 1C 1 Wells
Four OUC Wells
Six OU D Wells
West side GWTP-Air
stripping and gnnular
activated carton-
thermal oxidation
processes
BW-1 8 Wellhead
Treatment
Mechanism
OUBEE/CA
Removal Action
Removal Action
Voluntary
Voluntary/
Commitment to
Groundwater
Hazardous Waste
Task Force
Voluntary/
Commitment to
Groundwater
Hazardous Waste
Task Force
Safe Drinking
Water Act
Date
Online
1993
1990
1988
1987
1987
198S
Well Name
EW-24«
EW-63
EW-24T
EW-233
EW-234
EW-137
EW-140
EW-141
EW-144
EW-73
EW-83
EW-S4
EW-85
EW-86
EW-87
NA
NA
Zone
A
B
C
A
A
B
B
C
B
A/B
MB
A/B
A/B
MB
A/B
NA
NA
Current Flow
Rau(gpm)
10
10
200
52
1.6
7.7
25.4
17.2
19.2
20.3
6.1
6.5
11.7
1Z2
113
NA
NA
Current Treatment
Conveyed to west side groundwater treatment
plant (GWTP)
Wellhead treatment
Conveyed to west side GWTP
Conveyed to west side GWTP
Currently treats groundwater from OUs B, C, and
D. Has capacity to treat higher flows
BW-1 8 is a Base supply well located within
OU B. Its radios of influence is about 200 to 700
feet in the A and B aquifers and is slightly higher
in the C aquifer because of a larger screened
interval. The well was out of service from 1981
to 1985 as a result of detected contaminant
concentration; BW-1 8 currently receives wellhead
treatment that effectively removes any
contamination before releasing the water into the
McClcllan AFB water supply.
Other Interim Actions
Facility
OUBlCap
OU D Cap
Enforcement
M Mian ***
Interim ROD (1993)
Voluntary
Date
Constructed
1994
1985-86
Notes
Constructed to prevent surface-water infiltration,
further vertical migration, and exposure of
contamination to the public
Constructed to prevent surface-water infiltration,
further vertical migration, and exposure of
contamination to the public
"EW-247 is not currently in operation. It is expected to be in operation in mid-1995.
RDD1001370A.WP5 (ROD)
17
5/2/95
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records indicated that none of the existing grants involved activities that could have resulted in releases
of hazardous substances.
This Interim ROD would effectively transfer the current removal actions, i.e., operation of the current V
extraction systems in OUs B, C, and D, into part of the remedy presented in this document *
C. Highlights of Community Participation
McClellan AFB conducts a comprehensive effort to inform the public and involve the community in 1
the environmental decision-making process. Central to McClellan AFB's community relations pro-
gram is the following six-point strategy:
1. Emphasize open communications and free information flow with regulators, media, and the *
public
i
2. Emphasize community involvement in decision processes **
3. Be responsive to real community needs If
4. Press to solve problems quickly
5. Seek to attain fair media coverage t
6. Maintain credibility with the media, regulators, and the public
Following are the highlights of the community relations activities mat have taken place at McClellan
AFB to date: K
Interagency Agreement (IAG). The Air Force, EPA, and Cal-EPA/DTSC have
negotiated an interagency agreement, which includes requirements for community -
relations activities based on provisions in federal (and where applicable, state) statutes, 1
regulations, and guidelines.
Administrative Record/Information Repository. An Administrative Record of infor- tV;
mation that has been used to support Air Force decision making related to the IRP has ^
been established at McClellan AFB. The Administrative Record is staffed full-time by
people who are in the process of converting more than 10 years of documentation to ||
microfilm. In addition, a public information repository for the relevant portion of the ^
Administrative Record and its index has been established at McClellan AFB and Rio
Linda/Elverta Community Center. fc
Community Relations Plan (CRP). The first McClellan AFB CRP was approved in
August 1985 and revised in 1988. A further revision was prepared in January 1991. T
This CRP is currently being implemented under the direction of the McClellan AFB !>
Remedial Project Manager (RPM), and is being updated, based on the continued
monitoring of community concerns and a series of community interviews conducted in p"
August, September, and October 1992. U.
RDD1001370A.WP5 (IROD) 18 5/2/95
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I Technical Review Committee (TRC). The TRC has met quarterly since October
1990. In addition to Air Force, EPA, state, and congressional representatives, the TRC
.^ includes representatives from the County and City of Sacramento and the local
{ American Federation of Government Employees (AFGE) union. TRC meetings pro-
vide updates on all IRP activities for the previous quarter, indicate plans for the
upcoming quarter, and allow representatives a forum for discussion of progress and
j plans. The TRC has transitioned into the Restoration Advisory Board (RAB) as of
' September 1994.
| Mailing List. A mailing list of all interested parties in the community is maintained
I by McClellan AFB and updated regularly. The mailing list has grown from 200
names in 1984 to 2,600 names in 1992. This mailing list has also been used by the
j Agency for Toxic Substances and Disease Registry (ATSDR) to distribute information
/ on public health studies.
3
* Fact Sheets and Newsletters. Newsletters describing the status of the IRP at
McClellan AFB have been distributed to the mailing list since May 1984. Up to four
fact sheets per year have been published and distributed on an as-needed basis.
1
/ Open Houses. Informational meetings on the status of IRP efforts at the Base have
been held with the public at least twice a year since 1983, or more frequently as
required by current events, and these meetings are properly publicized by the media.
The meetings are used to answer the public's concerns and to update citizens on the
progress of the IRP.
Press Releases. Press releases have been issued on an as-needed basis for activities,
decisions, updates, and milestones associated with the cleanup effort In addition,
environmental programs are frequently the subject of articles in the Base newspaper,
The Spacemaker, which is available to all workers and visitors to the Base.
Environmental Community Relations Steering Committee (ECRSC). The ECRSC
has met quarterly since October 1987 to monitor issues that affect the public and to
recommend community relations activities. Membership includes congressional,
agency, public, and Air Force representatives.
Videotape and Brochure An Environmental Management videotape and a brochure
have been prepared and distributed to describe IRP goals and progress at
McClellan AFB.
McClellan AFB has had an active community relations program since 1983. The RI/FS and Proposed
Plan for the Groundwater OU were both released to the public in June 1994. These two documents
are made available to the public in the Administrative Record maintained at McClellan AFB. The
notice of availability of these documents was published in the Sacramento Bee and the Spacemaker.
The Proposed Plan was mailed to all parries on the McClellan AFB mailing list, government officials,
representatives of interested community groups, and members of the media.
A 30-day public comment period was held from July 6,1994, through August 5, 1994. A public
meeting was held on the evening of July 20, 1994 from 7:00 p.m to 9:00 p.m. At this meeting, repre-
sentatives from the Air Force, Cal-EPA/DTSC, the RWQCB, and EPA answered questions about con-
1
3
i
:)
RDD1001370A.WP5 (IROD) 19 5/2/95
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lamination at McClellan AFB and the remedial alternatives under consideration. A formal presentation
about the proposed cleanup plan was made by the Air Force. A transcript of this public .meeting is
part of the Administrative Record.
A Responsiveness Summary addressing oral and written comments received during the public com- *
ment period was developed and is attached to this Interim ROD. This decision document presents the
selected remedial action for the Groundwater OU at McClellan AFB, which was chosen in accordance f!
with CERCLA, as amended by SARA, and to the extent practicable, with the NCP. The decision for fc
the Groundwater OU Interim ROD at McClellan AFB is based on documents found in the Administra-
tive Record. «
D. Scope and Role of the Groundwater Operable Unit Within the «
Site Strategy I
This section includes the rationale for undertaking the limited action on die groundwater, the scope of f
the Groundwater OU response action, the role of the Groundwater OU response action within the over- ^
all cleanup strategy for McClellan AFB, and a description of the consistency between the
Groundwater OU response action and future remedial actions at McClellan AFB. e
D.1 Rationale for Undertaking this Limited Action at McClellan AFB
The overriding goal of the McClellan AFB IRP is to reduce risk to public health and the environment |
This goal must be met within the CERCLA process, the Air Force IRP protocols, and resource con-
straints. The immediate risk is reduced by implementing actions such as the operation of the ground-
water extraction systems at OUs B, C, and D. Removal and remedial actions under CERCLA require
decision documents prior to implementation. The appropriate decision documents are action memoran-
dums for removal actions and Records of Decision for remedial actions. _
The CERCLA process recognizes that a site may need actions that are larger in scope than a removal ^
action, even before enough information can be gathered to prepare a final ROD. To fill this nee&
EPA encourages the use of Interim RODs so that as many remedial action decisions as possible can F
occur at the earliest point in the site investigation. k
The decision documents (action memorandums, Interim RODs, and RODs) are supported by the f-:
Administrative Record in general, and by the Proposed Plan, EE/CA, or RJ/FSs, in particular. This £
Interim ROD is supported by the Groundwater OU RI/FS. Information is insufficient to support a
final groundwater ROD. fT
Remedial action cleanup goals for the Groundwater OU are presented in this Interim ROD; remedial
action cleanup standards will be set in the Final ROD. Remedial action cleanup goals have been /
established based on current information but are subject to change prior to the Final ROD. Remedial ];.'
action cleanup standards documented in the Final ROD are fixed and are not subject to change except
through amendment of the ROD. ,'
RDD1001370A.WP5 (IROD) 20 5/2/95
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>/
]
]
!
D.2 Scope of the Groundwater OU Response Action Within the Site Strategy
This interim action is designed to capture and contain all groundwater contamination derived from
McClellan AFB activities that exceeds the MCLs, thereby preventing future lateral and vertical
migration of contaminant plumes. The groundwater interim action will make use of new extraction,
treatment, and end-use systems as described in Section I, as well as maintain existing groundwater
extraction systems in OUs B, C, and D.
McClellan AFB currently has several groundwater removal actions in place (as described in Table 2).
I Groundwater extraction is currently taking place in OUs B, C, and D to limit offbase subsurface
i migration. Built in the mid-1980s, the GWTP is located on the west side of the Base and receives
water from OUs B, C, and D. The plant uses air stripping processes and granular activated carbon-
thermal oxidation processes to remediate groundwater and to treat emissions. The existing actions are
considered part of the baseline conditions in the RI/FS and will become part of the remedy.
The existing west side treatment plant will be expanded to accommodate a higher groundwater influent
flow rate, as well as different influent concentrations from what it presently receives. New extraction
wells will be installed as part of this interim remedy in the west and east parts of the Base. Ground-
water pumped from current and future extraction wells located on the west side of the Base will be
j conveyed to the west side treatment plant Groundwater pumped from new extraction wells located on
| the east part of the Base will be piped to a new east side treatment plant, if required.
-i D.3 Role of the Groundwater Operable Unit Response Action Within the
2} Overall Cleanup Strategy for McClellan AFB
Eleven operable units have been identified at McClellan AFB. Of these, 10 are actually contaminant
j source areas in the vadose zone (soils above groundwater) and are not the direct focus of this ground-
water response action. The eleventh OU, and the focus of this Interim ROD, is the Groundwater OU.
I The Groundwater OU, unlike the other OUs, spans the entire Base because groundwater contamination
does not recognize geographical OU boundaries. The Groundwater OU response action described in
this document is designed to address the Basewide groundwater contamination problem.
The Groundwater OU response action has the following specific remedial response objectives:
Protect public health and the environment from exposure to contaminated groundwater.
Contain the groundwater contamination by stopping lateral migration offbase and verti-
cal migration to deeper aquifers.
Achieve compliance with ARARs.
This Groundwater OU remedy is designed to prevent the spread of contamination that is already in the
groundwater and to remove to the maximum extent practicable the mass of contamination that lies in
the groundwater. This remedy does not directly address contamination that currently lies in the vadose
zone. Only when contamination migrates downward from the vadose zone source areas and enters the
groundwater will it be addressed by this Groundwater OU remedy. The only exception will be the
remediation of the vadose zone in areas where two-phase extraction will take place.
RDD10013775.WP5 (TROD) 21 5/2/95
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To achieve overall cleanup more efficiently, McClellan AFB is developing separate response actions
that address the vadose zone areas of contamination directly. An interim "Plug-in" ROD is being
developed that will function as the primary decision document for the majority of contaminated vadose
zone areas at McClellan AFB. Some areas of vadose zone contamination may not be supported by the . f;
vadose zone Plug-in ROD decision document For such areas, individual ROD or EROD documents *'
will be prepared to support remedial action prior to issuance of the Final Basewide ROD.
In addition, a variety of innovative treatment technologies will be evaluated as part of the ongoing «
Basewide RI. These treatability studies will provide information to allow for possible selection of
innovative technologies as part of the remedy. Individual Interim ROD documents will also be ^
prepared to support the incorporation of innovative technologies into the Basewide remedy. I;
Given the risk reduction goal of the McClellan AFB ERP and the CERCLA process, the following f*
decision documents have been prepared or are planned: t
I
Interim Record of Decision for PCB-, dioxin-, and metals-contaminated soils at
OU Bl. Completed September 3, 1993.
Soil vapor extraction (SVE) EE/CA to support Removal Action for areas highly jg
contaminated by VOCs in the vadose zone. Completed November 1993. fr
Interim/Final ROD for the Basewide Vadose Zone. Scheduled to be completed in the P
fall of 1995. (
fv
Additional Interim RODs for contamination or conditions that do not fit the Interim
ROD for the Basewide Groundwater OU or the Interim/Final ROD for the Basewide
Vadose Zone. Dates not known because need for additional documents is not yet *
determined.
/??
Basewide ROD. Scheduled to be completed March 15, 2003. \~
D.4 Consistency of this Groundwater Response Action with Future Actions at [
McClellan AFB '-
As described in Sections G, H, and I of this document, the response action for the Groundwater OU |::
will use groundwater pump and treat technology. This technology involves installing an array of >&
groundwater extraction wells into the contaminated aquifers, pumping the water and conveying it
through pipelines to a treatment system, and routing the treated water to an appropriate point of end F
use. These extraction, treatment, and end-use systems will generally be consistent with other remedial L
actions that will occur at McClellan AFB to address contamination in the vadose zone.
The groundwater interim remedy will be implemented in phases spanning several years. Ongoing site t.
characterization will be conducted concurrently under the Basewide RI. Data collected from the RI
will be used in the implementation of the selected remedy. j
Future actions that may eventually be implemented at McClellan AFB include SVE systems, construc-
tion of impermeable caps, and excavation of contaminated soils. The groundwater response actions ;
will be adequately designed to be consistent with these other actions and not to interfere with them. [
RDD10013775.WP5 (IROD) 22 5/2/95
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I With proper planning, synergy may be developed between these future actions and the groundwater
1 response action. For example, when groundwater extraction wells are installed, soil or soil gas
samples may be collected to define the depth of contamination in the vadose zone. Such data may be
:| used to better design SVE systems, impermeable caps, or excavations.
In some instances, the groundwater remedy described in this document may need to be slightly modi-
i fied to accommodate the implementation of vadose zone actions that will occur in the future. For
' example, if excavation of contaminated soil is necessary at a site that is traversed by conveyance pipe-
lines, the pipes may need to be rerouted in a manner that will not interfere with the excavation.
3
3
E. Summary of Site Characteristics
This section summarizes the source area information, the hydrogeologic conditions, the contaminants
of concern, the extent of contamination, and the data gaps that still exist The summary of hydrogeo-
logic conditions includes the following:
Sources of groundwater contamination
Explanation of the monitoring zone designations
Historic movement of groundwater
Horizontal groundwater flow
Vertical groundwater flow
Regional pumping
Water table decline
E.1 Base Source Areas
As discussed in Section B, Site History and Enforcement Activities, McClellan AFB developed a
program to investigate and evaluate past operation and waste disposal practices, identify contamination
sources, and determine the extent of contamination in soil and groundwater (Radian, 1990).
At present, 254 sites have been identified as sources of soil and groundwater contamination around the
Base (Radian, 1991). The locations of these source areas are presented in Figure 3. Both confirmed
sites (CSs) and potential release locations (PRLs) are presented in more detail and discussed in
Chapter 4, Conceptual Model, of the Groundwater OU RI/FS (CH2M HILL, 1994). Nearly 90 percent
of the CSs and PRLs are located within the boundaries of OUs A, B, C, and D. Contamination has
been detected at OU G/H, and a detailed investigation is currently being conducted. Because the CSs
and PRLs were used for specific functions and operations, each OU contains its own history of main-
tenance activities, contamination discharges, waste production, and contaminant detection.
E.2 Hydrogeologic Conditions
E.2.1 Monitoring Zone Designations
The groundwater subsurface is divided into five distinct monitoring zones (A, B, C, D, and E) based
primarily on geophysical logs between pilot borings (Radian, 1992). Approximate zone depths and
thicknesses are presented in Table 3.
RDD10013775.WP5 (ROD) 23 5/2/95
-------
As discussed in Chapter 4, Conceptual Model, in the Groundwater OU RI/FS, strong evidence suggests
that the groundwater system functions more as a single unit than as separate hydrostratigraphic units.
The following observations suggest that the units are hydraulically linked:
The lithology is heterogeneous, indicating no laterally continuous aquifers or aquitards.
Water levels and flow directions in the monitoring zones are similar.
The influence of regional pumpage is observed in all monitoring zones without signifi-
cant time lags.
Stiff and Piper diagrams show that the inorganic water quality in all zones is similar.
Table 3
Approximate Zone Depths
Zone
Parameter
Ground Surface (ft msl)
A
B
C
D
E
Zone Thickness (ft)
Elevation (ft msl)
Depth (ft bgs)
Zone Thickness (ft)
Elevation (ft msl)
Depth (ft bgs)
Zone Thickness (ft)
Elevation (ft msl)
Depth (ft bgs)
Zone Thickness (ft)
Elevation (ft msl)
Depth (ft bgs)
Zone Thickness (ft)
Elevation (ft msl)
Depth (ft bgs)
QUA
70
20
-35 to -55
105 to 125
50
-55 to -105
125 to 175
70
-105 to -175
175 to 245
Data not
available
Data not
available
OUB/C
62
35
-45 to -80
107 to 142
65
-80 to -145
142 to 205
75
-145 to -220
205 to 282
88
-220 to -308
282 to 370
52
-308 to -360
370 to 422
OUD
62
35
-37 to -72
99 to 134
60
-72 to -132
134 to 194
80
-132 to -212
194 to 274
Data not
available
Data not
available
OUG
72
20
-30 to -50
102 to 122
40
-50 to -90
122 to 162
55
-90 to -145
162 to 217
Data not
available
Data not
available
Note: Zone thicknesses were estimated from the PGOURI (Radian, 1992).
The monitoring zones serve to provide a basis for discussing the data by depth interval, but do not
represent distinct lithologic or hydrostratigraphic units.
E.2.2 Historic Movement of Groundwater
During this century, groundwater has been pumped from the areas surrounding McClellan AFB for
irrigation and municipal or domestic water supply. As a result of the pumping, more groundwater has
been extracted for use than has been supplied by natural recharge. The water level within the aquifer
system has been dropping continuously for approximately 50 years. At the present time, the only
I
I
I
RDD10013775.WP5 (IROD)
24
5/2/95
-------
I
'I
3
I
discharge of groundwater is by pumping of irrigation and supply wells and by operating the Base's
remedial extraction system.
Historic groundwater flow directions have varied greatly over the past 80 years. They have ranged
from the northwest direction to the south direction. Current groundwater flow in Monitoring Zones A,
B, C, D, and E is generally from the northeast to the southwest in OU A and northwest to southeast in
OU B/C. Average groundwater flow velocities are 10 to 110 ft/yr in OU A, and 25 to 110 ft/yr in
OU B/C. Historic groundwater flow contours are presented in Figure 4. Declines and changes in
groundwater flow can be determined from these contours.
E.2.3 Horizontal Groundwater Flow
Base production wells, offbase production wells, extraction wells, and regional pumping all affect the
local groundwater flow directions at the Base. Some uncertainty exists in the calculation of
groundwater flow velocity because the aquifer's hydraulic conductivity is not well defined.
Groundwater contour maps for the A, B, and C Zones are presented in Figures 5, 6, and 7,
respectively. They are based on water-level measurements collected in January 1993.
In the southern part of the Base (OU B), BW-18 has a high pumping rate; therefore, groundwater
locally moves toward BW-18 from all directions. BW-18 is perforated in the C through E Zones to a
depth of 400 feet and pumps at an average rate of approximately 1,200 gpm with a capacity to pump
1,600 gpm.
There are currently 15 remedial extraction wells onbase: five in OU. B, four in OU C, and six in
OU D. The OU D extraction wells also have a significant local influence on groundwater flow paths.
The six OU D extraction wells appear to have captured the contaminated groundwater in Monitoring
Zones A and B beneath the source areas. Effects of the OU C extraction system in Monitoring Zone B
are also observable. The effects of the OU B extraction system are less apparent because of the super-
imposed influence of the adjacent BW-18 and the low flow rate of these extraction wells.
£.2.4 Vertical Groundwater Flow
The vertical hydraulic gradients that exist at the Base are predominantly downward, except in areas
where shallow extraction is occurring. This downward gradient is mainly the result of regional
pumping withdrawals. Consequently, water moves on a downward gradient from the recharge area
(ground surface) to the discharge area (regional aquifer).
This pervasive downward gradient has implications on the movement of contamination at the Base.
Contaminated groundwater will move horizontally in response to the horizontal gradients, but will also
move vertically in response to the downward gradient The vertical gradients between the A and
B Zones are slightly downward at a gradient of -0.01 to -0.10 in OU A, -0.01 and -0.15 in OU B, and
-0.10 to -0.15 in OU C. Vertical gradient is a measure of the difference in head elevations vertically.
Positive vertical gradients suggest upward groundwater flow; negative vertical gradients suggest
downward groundwater flow.
Because the horizontal hydraulic conductivity of the layered sediments is about 5 to 15 times the
vertical hydraulic conductivity, contaminants will move further in the horizontal plane. However,
RDD10013775.WP5 (IROD) 25 5/2/95
-------
unless groundwater extraction is initiated in the shallow aquifers at the site, contamination will
continue to move downward into deeper units and eventually threaten regional municipal supply wells.
E.2.5 Regional Pumping f
The historical and current pumpage of Base, municipal, and domestic wells have affected the ground-
water flow directions. Except for the hydraulic control of the OU D extraction wells, groundwater T
generally flows to the southern portion of the Base in all zones. This is due primarily to the large &
pumping influences of BW-18 and the municipal wells located to the south of the Base.
Generally, higher pumping occurred in the southwest and northeast regions of the Base. The aquifer I
beneath McClellan AFB receives recharge from the American River to the south, from the Sacramento
River to the west, from various small creeks to the north, and from mountain-front recharge from £
precipitation to the east. I
Locations of all known production wells on and adjacent to the Base are presented in Figure 8. A r*
complete listing of the available information on the regional pumpage and supply wells is included in ^
the Groundwater OU RI/FS report. According to pumpage data compiled in the Groundwater OU
RJ/FS, the estimated groundwater withdrawal from the regional aquifer within 5 miles of McClellan «~
AFB was at least 53,000 acre-feet per year, or 33,000 gpm. The RI/FS further estimates that the total |^
groundwater extraction required for capture of the MCL target volume at McClellan AFB is about
1,100 gpm. This represents approximately 3 percent of the total groundwater withdrawal in the ,
vicinity of McClellan AFB, if it is assumed that the total regional withdrawal is only 33,000 gpm. 1
The percentage of total regional groundwater withdrawal represented by McClellan AFB remedial
pumping is actually significantly smaller for two reasons:
l
Pumpage data were available for only 60 to 70 percent of the production wells within
a 5-mile radius of McClellan AFB, and the total pumpage from this area is likely
significantly larger than the 53,000 acre-feet per year cited in the RI/FS. |
The 20 square miles contained in the 5-mile radius centered on McClellan AFB
represent only a fraction of the groundwater basin beneath the Sacramento urban area j
that contributes groundwater to the regional aquifer beneath McClellan AFB (see I
regional groundwater contour maps presented in the RJ/FS). Therefore, the total
regional groundwater withdrawal from the area is also larger. f::
Ulr-
Remedial pumping planned for McClellan AFB will have no influence on streamflow in the area.
Therefore, the depth to groundwater in the vicinity of the Base is approximately 100 feet, and streams ',"'
in the area are not in direct hydraulic connection with the groundwater system. Small additional i
declines in groundwater levels near extraction wells will have no influence on me rate of infiltration
from local streams. r
E.2.6 Water Table Decline
Agricultural and domestic demands on groundwater have contributed to the regional water table I
decline. Recent declines beneath McClellan AFB are due primarily to a combination of Base and
extraction well pumping superimposed on the regional decline. Within the last 10 years, water levels ;
in Monitoring Zone A have declined at a rate of 1 to 2 feet per year. As a result of this decline, 1
RDD10013775.WP5 (IROD) 26 5/2/95
-------
-no
Spring 1912
SOURCE: CH2M HILL, July 1981
Spring 1953 Spi
SOURCE: County of Sacramento DepL of Pubfc Works. SOURCE: County of Si
Water Resources Division. 1989 Water Resoi
+20
Spring 1971
SOURCE: CH2M HILL July 1981
Spring 1975
SOURCE: County of Sacramento Dept of Public Works,
Water Resources Division. 1989
Sp
SOURCE: County of S.
Water Reso<
LEGEND
GROUNOWATER CONTOURS (ft msl)
0
RO01697_04
5 MILES
-------
+40
J1958
imento Dept of Public Works,
* Division, 1989
Spring 1963
SOURCE: County of Sacramento Dept of Public Works,
Water Resources Division. 1989
Spring 1968
SOURCE: CH2M HILL, July 1981
tcClellan
AFB
-50
91978
amento Dept of Public Works,
es Division, 1989
Spring 1980 I
SOURCE: County of Sacramento Dept of Public Works.
Water Resources Division, 1989
Fall 1989
SOURCE: County of Sacramento DepL of Public Works,
Water Resources Division. 1989
I
FIGURE 4
HISTORIC GROUNDWATER
CONTOURS IN THE VICINITY
OF McCLELLAN AIR FORCE BASE
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
CfGMHILL
-------
1
0 3000 6000 9000
SCALE IN FEET
LEGEND
GROUNDWATER CONTOUR
* GROUNDWATER FLOW DIRECTION
- ADDITIONAL CONTOURS TO SHOW FLOW DIRECTION
Contours based on January 1993 Water Levels.
RDD1697_01
FIGURE 5
WATER LEVELS AND FLOW
DIRECTIONS IN THE A ZONE
JANUARY, 1993
GROUNDWATER OPEFIABLE UNITIROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
O<HIU.-
-------
-36
0 3000
SCALE IN FEET
6000
9000
LEGEND
GROUNDWATER CONTOUR
+ GROUNDWATER FLOW DIRECTION
- ADDITIONAL CONTOURS TO SHOW FLOW DIRECTION
Contours based on January 1993 Water Levels.
ROO1697JK
FIGURE 6
WATER LEVELS AND FLOW
DIRECTIONS IN THE B ZONE
JANUARY, 1993
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
CHMHILL
-------
]
1
1
i
0 3000 6000 9000
SCALE IN FEET
LEGEND
GROUNDWATER CONTOUR
* GROUNDWATER FLOW DIRECTION
- ADDITIONAL CONTOURS TO SHOW FLOW DIRECTION
Contours based on January 1993 Water Levels.
RDD1697_<3
FIGURE 7
WATER LEVELS AND FLOW
DIRECTIONS IN THE C ZONE
JANUARY, 1993
GROUNDWATER OPERABLE UNIT (ROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
CKMHILL
-------
QCU-15
RIO-6
CU-62
,CU-79
DRIO-7
QRIO-2
nRIO-1
URIO-12
CU-21
ARC-S?'
NR-33
QRIO-6
ARC-39
n RIO- 11
DARC-69
nARC-64
ARC-52
ARC-34
,NH-25
NR-24
RIO-4
DCWT54
CW153
QCWM3
LEGEND
CW120
rjAHC-41
ARC-M
QgBASE WELL - ACTI VE
#BASE WELL -TO BE ABANDONED DURING PHASE III
$-BASE WELL - ABANDONED
D Dl STRI CT WELLS
OSEISMIC SURVEY WELLS
BW - BASE WELL
CT - CALTRANS
RIO - RIO LI NDA
CU - CITIZENS UTILITIES
ARC - ARCADE
NR - NOHJHRIDGE
CW - Cl TY WELL
NOTES 1. BW-25 IS LOCATED AT THE LINCOLN COMMUNICATION SITE.
2. BW-26 IS LOCATED AT THE DAVIS COMMUNICATIONS SITE.
3. CW-150 HAS BEEN DECOMMISSIONED.
FIGURE I
PRODUCTION, MUNICIPAL. AND
BASE WELLS IN THE VICINITY OF
MCCLELLAN AR FORCE BASE
GROUNOWATER OPERABLE UNIT ROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
CHtHtL-
-------
several Zone A monitoring wells onbase have already been abandoned or converted to soil vapor
monitoring wells.
"1
The groundwater table currently is approximately 100 feet bgs. No interconnection exists between
surface water and groundwater except for infiltration. Groundwater quality does not affect surface
water quality.
E.2.7 Sources of Groundwater Contamination
I Disposal activities and waste management practices at McClellan AFB have substantially improved
' over the years. There may be some continuing sources of contamination to groundwater resulting
from McClellan AFB's operations, but the vast majority of industrial releases have been eliminated.
j The historical sources of groundwater contamination have been discussed in Section B.I, and are
1 shown in Figure 9. The current sources of groundwater contamination are the contaminated vadose
zone, and the non-aqueous phase liquid (NAPL) pools in the vadose zone and groundwater. Current
3 sources are defined as the contaminated areas that must be remediated for the groundwater remedial
I actions to be folly effective.
j NAPLs are immiscible fluids that may be present in the vadose zone and in the groundwater. There
j are two classifications of NAPLs: light and dense. The classification of a NAPL is based on the unit
weight of a NAPL compared to the unit weight of water. Light NAPLs (LNAPLs) are lighter than
> water and will float if they reach the water table. DNAPLs are heavier than water and will sink
g should they encounter the water table. The contaminants of concern (COCs) identified in the ground-
water beneath McClellan AFB are DNAPLs. Although the presence of DNAPLs has not been
^ confirmed at McClellan AFB, TCE has been measured in the groundwater at above 1 percent of its
j solubility. This does not confirm presence of DNAPLs, but is a strong indicator that TCE DNAPLs
are present, especially near the hot spots.
I The areas suspected to contain DNAPLs are two hot spot areas in OU A, two hot spots in OU B, one
hot spot in OU C, and two hot spots in OU D.
I
1
1
i
Contamination in the groundwater is derived from the migration of contamination downward through
the vadose zone. This downward migration occurs through two primary mechanisms: gravity and
hydraulic loading. Hydraulic loading can occur as a result of precipitation percolation, surface-water
discharge to the ground surface, and IWL leaks, broken water lines, and unlined waste pits.
Contaminant migration to the groundwater can occur only in areas where vadose zone VOC
contamination is large. DNAPL presence may be inferred if soil gas concentrations are detected in
excess of 1 x 105 ppbv. Such contaminant levels will generally only be found in vadose zone source
areas, such as abandoned waste pits.
Downward migration of contamination through percolating precipitation can occur anywhere contami-
nation is present, so long as the ground surface is not capped or sealed to prevent water entry.
DNAPLs may also exist in the groundwater, and are especially likely to be found in groundwater hot
spots located in Monitoring Zone A. Such DNAPL also represents a long-term contaminant source to
the groundwater because of the dissolution of contamination from the DNAPL pool into the
groundwater. Thirty-five Base production wells have been identified. Locations of these Base
production wells are presented in Figure 8. These 35 Base wells were used for Base activities.
Almost all of these wells have been scheduled for decommissioning for the following reasons:
RDDI0013775.WP5 (IROD) 33 5/2/95
-------
I
I Base Boundary |
Regional Production Wells
Lower regional water table
Affect regional flow directions
Pull contaminants downward
and away from Base
Waste Pits
Solvents
Sludge
Rainfall
Infiltration
Historic
Water Level
(30 feet bgs)
Industrial
Waste Line
Manufacturing-
Plating Spills
Regional
Groundwater
Row
I
I
I
Waste pit contaminants
dissolve at contact between
waste pit bottom and
water table
Base Wells
Lower water table
Contain plumes on the Base
Affect base flow directions
Pull contaminants downward
Are potential vertical conduits
RODI697JJ2
FIGURE 9
HISTORIC BASE ACTIVITIES
INFLUENCING CONTAMINANT MIGRATION
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
Ct&IHILl.
-------
I
1
I
1
I
The aquifers from which they pump are contaminated
The Base wells may serve as vertical conduits for migration of contaminants
The pumpage from these wells may cause contamination in the shallower zones to be
drawn into the deeper zones
The decommissioning program began in 1991 and is divided into phases. Four wells were
decommissioned in 1991 during Phase I, 9 wells were decommissioned in 1992 during Phase n, and
15 wells are scheduled to be decommissioned during Phase m, which began in April 1994. One well
was abandoned in 1984, one well has not been identified, and two wells are located offbase. Three
wells, BW-10, BW-18, and BW-29, are currently active. BW-18 is scheduled to be decommissioned
and replaced as described in this Interim ROD. Base well decommissioning will continue in Phase IV,
which is scheduled to begin in mid-1995.
£.2.5 Smear Zone
The decline of the water table in areas of significant groundwater contamination results hi contami-
nants remaining adsorbed to soil particles and dissolved in the residual water of the vadose zone. This
process creates what is commonly referred to as the "smear zone." The smear zone is approximately
60 to 70 feet thick. As the water table declines, the thickness of the smear zone increases. The
following processes contributed to the development of the smear zone:
Historically, water levels were close to the bottom of waste pits and source areas.
Contaminants migrated from these source areas to the groundwater at the water table
interface or into rainwater that was infiltrating through the vadose zone to the water
table.
As the water table declined, a portion of the contaminants remained in solution in the
groundwater, partitioned into soil gas, and sorbed onto soil particles, depending on
their relative phase partitioning tendencies. The smear zone is made up of contami-
nants that volatilized into the soil gas and were dissolved hi residual soil water or that
were adsorbed onto soil particles while the water table declined.
Prior to the operation of SVE systems, contaminants in the soil gas have migrated
primarily under diffusive concentration gradients. Compounds sorbed to soil surfaces
are considered immobile, except for the component that is flushed from the soil
particles by infiltration of precipitation.
Contaminants that remained in the groundwater have been migrating primarily with
groundwater flow driven by vertical and horizontal gradients.
Current Base activities influencing the smear zone are shown in Figure 10.
Groundwater levels in the vicinity of McClellan AFB have been declining historically at a rate of 1 to
2 feet per year. These falling water levels have resulted in the creation of a smear zone, in which
contamination originally contained in the groundwater system is retained in unsaturated zone soils.
RDD10013775.WP5 (IROD) 35 5/2/95
-------
Contaminants in
residual porewater
Contaminants
sorbed to
soil organics
Contaminants in the
vapor phase (if volatile)
Contamination in
dissolved water
Some waste pits were
capped to prevent rainfall
infiltration.
[ Base Boundary |
Contaminants sorbed to
soil organics
Containment measures in
place and work procedures
changed to prevent spills.
Historic
(-30'bgs)
Rainfall
Infiltration
Industrial
Waste Line
Regional
Groundwater
Flow
Regional Production and
Base Wells
Continue lowering
water table
Continue affecting
flow directions
Are potential vertical
contaminant conduits
(OnlyBW-18)
NAPLs In the
vadose zone and
groundwater
Smear zone caused by
decline of water table.
Shape caused by historic
water level decline and
groundwater flow.
Extraction Wells
Create drawdown
Lowers Base water
table and affects flow
Contain Base plumes
Some Base Wells were
abandoned and grouted to
prevent contamination
between aquifers.
FIGURE 10
CURRENT BASE ACTIVITIES
INFLUENCING SMEAR ZONE
GROUNOWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
ROD1697_33
Ct&AHILL-
I
1
I
I
c
I
I
-------
.
The long-term water level decline is caused by a regional imbalance in the water budget for the
aquifer in the Sacramento area. Total groundwater production from the basin has exceeded natural
recharge over the long term, and groundwater levels have declined as a result Because McClellan
AFB's remedial pumpage represents such a small proportion of the total groundwater withdrawal from
the basin, it will have little impact on the regional water level trends in the vicinity and, therefore,
little impact in the generation of a smear zone. The only areas where groundwater pumpage at
McClellan AFB may significantly increase the thickness of the smear zone are near individual
extractions wells, where the cone of depression created by pumping may result in a local increase in
smear zone thickness.
E.3 Contaminants of Concern
TCE, cis-l,2-DCE, PCE, and 1,2-DCA were determined to be contaminants of concern (COCs) in the
Groundwater OU RI/FS (CH2M HILL, 1994). The COCs were selected based on the following
criteria:
Frequency of detections
Concentration measurements above MCLs
Health risk posed by contaminant
The four COCs, their MCLs, and summary statistics are presented in Table 4.
Table 4
Summary Statistics of COCs
COCs
TCE
cis-l,2-DCE
PCE
U-DCA
MCL
(M8/1)
5
6
5
0.5
"Mean
(MS/I)
4530
3.54
13.61
1.70
Frequency
of Detects
(%)
51
26
11
9
Maximum
Detect
-------
The water solubility measures the tendency of contaminants to partition between NAPLs and water.
1,2-DCA has high water solubility and would tend to dissolve into groundwater more than cis-1,2-
DCE, TOE, or PCE. Conversely, cis-l,2-DCE, TCE, and PCE would tend to exist as NAPLs more
readily than 1,2-DCA. The partition coefficient measures the tendency of contaminants to partition
between water and soil. PCE has a higher partition coefficient and would tend to sorb to soil more
than 1,2-DCA, TCE, and cis-l,2-DCE. Conversely, the 1,2-DCA, TCE, and cis-l,2-DCE would tend
to remain dissolved in groundwater more than PCE.
The mass of the four COCs in the groundwater is estimated to be approximately 21,000 pounds (9,600
kg). The mass of the COCs and the volume of contaminated aquifer are presented in Table 5. TCE is
the most prevalent COC. The volume of aquifer with TCE concentrations greater than non-detectable
levels occupies approximately 2.2 billion, 1.3 billion, and 1 billion cubic feet in Zone A, Zone B, and
Zone C, respectively, totaling 4.6 billion cubic feet In addition, approximately 17,000 pounds (7,900
kg) of TCE exist in Zone A, 880 pounds (400 kg) of TCE exist in Zone B, and 380 pounds (170 kg)
of TCE exist in Zone C, totaling 19,000 pounds (8,500 kg) of TCE in all three zones.
Table5
Estimated Mass of COCs and Volume of Contaminated Aquifer B; Zone
Gromutwater Operable Unit
Contaminants of Concern
TCE
Mass (Ib)
Volume (million ft3 of aqoif er)
PCE
Mass (Ib)
Volume (million ft3 of aquifer)
cis-U-DCE
Mass (Ib)
Volume (million ft3 of aquifer)
U-DCA
Mass (Ib)
Volume (million ft3 of aquifer)
Total COC
Mass(lb)
Mass (kg)
Zone A
17,000
2000
1,700
ISO
380
1,100
40
130
19.000
8,636
ZoneB
880
1300
73
250
95
510
21
830
1,100
500
Notes:
1. Volume and mass estimates are for portions of the aquifer with concentn
nondetectable levels.
2. Mass estimates include mass of contaminants dissolved in groundwater a
soibed to soil
ZoneC
380
1,000
0
0
75
550
0.13
0.06
460
209
Total
19,000
4,600
1,700
420
550
2,200
60
970
21,000
9,545
itions greater than
nd mass of contaminants
E.4 Extent of Contamination
The nature and extent of VOC contamination were estimated from a representative data set of VOCs
collected primarily during or after 1992. This data set, and the rationale for selecting it, is presented in
Chapter 4, Conceptual Model, of the Groundwater OU RI/FS (CH2M HILL, 1994). Groundwater
contamination at the Base can be divided into three distinct contamination plumes that migrate from
the original source area. These plumes are the OU A, OU B/C, and OU D plumes. The groundwater
system has been divided into four layers: Monitoring Zones A, B, C, and D/E.
f
i
t
I
RDD10013775.WP5 (IROD)
38
5/2/95
-------
I The plumes are presented in plan view in Figures 11, 12, 13, and 14 for the A, B, C, and D/E Zones,
respectively.
-..-.-»
j Contamination in the OU A plume has been measured as deep as 225 feet bgs in a small area; contam-
ination in the OU B/C plume has been measured as deep as 275 feet bgs. Although contamination has
been detected in shallower Zone B OU D wells, contamination has consistently not been detected in
I the deepest OU D wells (screened as deep as 185 feet bgs in the B Zone). As a result of the operation
of the six OU D extraction wells, contamination is not expected to exist below Zone B of OU D. The
estimated vertical extent of contamination for the three plumes is presented in Figures 15, 16, and 17.
J TCE is the most frequently detected and widespread contaminant.
j The residential areas that may be affected by the offbase plume migration are presented in Figure 2.
:.i As discussed previously in Section B.2, History of Site Investigations and Interim Measures, municipal
drinking water connections were offered to all residents in this area to reduce known exposure path-
Si ways between the contaminated groundwater and residents. The only migration pathway between the
fj surface water and groundwater is through infiltration. Because the groundwater table is approximately
100 feet bgs, there is little to no possibility that surface water quality could be impacted by ground-
i water contamination.
J
I
1
\
E.5 Summary of Data Gaps
Principal data gaps as of this writing are as follows:
The extent of the deep plume beneath OUs B and C
The extent of the plume moving offbase from OU B
The extent of the southern OU A plume
The extent of offbase contamination east of OU A
The extent of contamination in OUs G and H
The presence of contamination west of OU A and east of OU C (in the runway area)
The presence of groundwater contamination in OUs E and F
The extent of the low concentration plume west of OU C offbase
The vertical extent and completeness of capture of the OU D plume
The spatial distribution of aquifer parameters and lithology
The need for metals removal and treatment
The compatibility for treated water to be injected into the groundwater .
F. Summary of Site Risks
A risk assessment was prepared during the RI/FS to support development of target volumes, as
discussed in Section G.I, and to fulfill the NCP requirements for a baseline risk assessment. The
baseline risk assessment provides risk managers with an understanding of actual and potential risks to
human health and the environment posed by Groundwater OU site contamination and any uncertainties
associated with the assessment This baseline risk assessment was developed using exposure scenarios
that estimated the reasonable maximum exposure (RME). The RME is defined as the highest exposure
that is reasonably expected to occur at a site. If a population is exposed by way of more than one
pathway, the combination of exposures across pathways must also represent an RME. The elements of
the risk assessment are as follows:
RDD10013T75.WP5 (ROD) 39 5/2/95
-------
LEGEND
BASE WELL OR CITY WELL
EXISTING EXTRACTION WELL
TCE CONCENTRATION CONTOURS (gg/li
NOTE:
CONTOURS WILL BE UPDATED AS NEW DATA ARE MADE
AVAILABLE. THESE CONTOURS REPRESENT DATA THAT
WEHE PRESENTED IN THE CONCEPTUAL MODEL IN THE
OROUNDWATER OU RVFS (CH2M HILL. JUNE IBM)
FIGURE 11
EXTENT OF TCE
CONTAMINATION IN
MONITORING ZONE A
CftOUNOWATOl OPERABLE UNIT TOO
UcCLEUAN AIR FORCE BASE
SACRAMENTO. CALFORNA
CKMMZi
-------
LEGEND
| BASE WELL OR CITY WELL
X EXISTING EXTRACTION WELL
TCS CONCENTRATION CONTOURS (uj/B
More
CONTOURS WLL BE UPDATED AS NEW DATA ARE MADE
AVAILABLE. THESE CONTOURS REPRESENT DATA THAT
WERE PRESENTED IN THE CONCEPTUAL MODEL IN THE
GROUNDWATER OU RI/FS (CH2H HILL. JUNE 1994)
FIGURE 12
EXTENT OP TCE
CONTAMINATION IN
MONITORING ZONE B
CROUNOWATER OPER/8LE LNT ROD
UeCLELLAN AIR FORCE BASE
SACRAMENTO. CACFORN1A
OOliHIU.
-------
LEGEND
BASE WELL OR CITY WELL
EXISTING EXTRACTION WELL
TCE CONCENTRATION CONTOURS (ug/l)
NOTE:
CONTOURS WILL BE UPDATED AS NEW DATA ARE MADE
AVAILABLE. THESE CONTOURS REPRESENT DATA THAT
WERE PRESENTED IN THE CONCEPTUAL MODEL IN THE
GROUNDWATER OU RI/FS (CH2M HILL. JUNE I9M)
FIGURE 13
EXTENT OP TCE
CONTAMINATION IN
MONITORING ZONE C
CROUWWATER OPERABLE UNIT ROD
UCCLEU.AN Am FORCE BASE
SACRAMENTO. CALIFORNIA
'MIL
-------
LEGEND
\ WELL NAME. DATE OF SAMPLING.
CONCENTRATION (ug/l)
BASE WELL OR CITY WELL
EXISTING EXTRACTION WELL
NOTE" MONITORING NETWORK M THE EAST-WEST
DIRECTION IS NOT EXTENSIVE ENOUGH TO DRAW
CONTOURS.
MOTH:
CONTOURS WILL BE UPDATED AS NEW DATA ARE MADE
AVAILABLE. THESE CONTOURS REPRESENT DATA THAT
WERE PRESENTED IN THE CONCEPTUAL MODEL IN THE
GROUNDWATER OU Rt/FS (CH2M KILL. JUNE 1994)
FIGURE 14
EXTENT OF VOC
CONTAMINATION IN
MONITORING ZONE D/E
CROUNOWATER OPERABLE UNT ROD
UcO.El.LAN MR FORCE BASE
SACRAMENTO. CALIFORNIA
T CKf HIIL
-------
North
East
100 r
South
West
(ft ma)
Section A1
L.
Bottom of C Zone
-200 L-
900
iaoO(ft)Approtinale
Southwest
100 r
(ttmsi)
-100
Section A2
200
North East
Januar/ 1393
^ Water Lawns
Bocom of A Zone
Bossm oi 6 Zore
BoSSoni at C Zona
I
2000
4000 (ft) Approximate
LEGEND
Contaminant Contamination ng/1
1,2-DCA 2400
cis-1,2-DCE 2
PCE 3
TCE 5
Risk* 6.4 E-6
Contaminant not analyzed on this date.
Dashed lines represent unbound condition
Solid lines represent bound conditions
TCE Contours
NO: Non Detect
'increased cancer risk based on sample-
specific risk assessment
RDD175B_14
OU A Site Plan
The vertical extent of contamination represents
data that were presented in the Groundwater
OU Rt/FS (CH2M HILL, JUNE 1994).
FIGURE 15
VERTICAL EXTENT OF
CONTAMINATION IN OU A
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
Ct&iHILL
-------
I
North N &
o CS S r>
sssg 1 g§
NO
26000.0
8.1E-3
0
(It nisi)
-100
-200
Section BC1
No
100
100
200
\
:
<.
NO
NO
NO
3601X0
" 1J2E-3
i( 0.1
| /S2.9
1 ,' ND
i 8.4
: ND
giSt*
/ NO
ND
NO
ND __-
8.4E-7
«,<>> South
p> 2> 2?
Sr* CO
^_ to^
ND
15.9
S0.7
467.0
.- "A
NO «,
:NO /?
3W^^^~^^
0.6
IE-7
^^HHHH
0
rth o |
- H ? 3 ft
1 I i i
-
-^
^-
no
2GOOOLO
S.1E-3
Section BC2 u __
o
»*"' :
7
I
1400
^^S $^^ Water Levels
NO NO
ND 23.8
86.2 NO
664.0 299.0
6J£r4_i£rl Bottom ol B Zone
^^^
2800 (ft) Approximate
South
o
i
/
'
-A-A,. \
O6
ND
MU'v
NO i aa
«-4
ii^
S.1
ND
64.6
^^« 4.4E-5
-
- Water Levels
-V
^_| Honomotczone
ND
75.0
L2E-S
400 800 (ft) Approximate
LEGEND
IrJ
\
BC2^
Nfflf ou B/c
\
\BC1
Site
Plan
RDD1753_tS
Conta
1.2-DC
cis-U
PCE
TCE
Risk*
Averai
avera
-Con
unbou
T<
ND N
*lncre
specift
NOTE
The v
datatl
OUR
mlnant Contamination ng/l
:A 2400
!-DCE 2
3
5
6.4 E-
;e: concentrations had fluctuated;
ie was calculated and used in the data set.
aminant not analyzed on this date. Dashed lines represent
nd condition. Solid lines represent bound conditions
3E Contours
on Detect
ised cancer risk based on sample-
c risk assessment
(rtcal extent of contamination represents
fiat were presented in the Ground water
I/FS (CH2M HILL, JUNE 1994).
FIGURE 16
VERTICAL EXTENT OF
CONTAMINATION IN OU B/C
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
aanHiu 1
-------
Nort
100
0
(Itmsi)
-100
-200
North
too
0
(Itmsi)
100
-200
S
LEGEND
h
^ ' o «
in t/j JJ
2 2 2 S
**
t
1
Sed
jjp'
».».. =: =
Si0 ^"-\
^ -
"^-
. NO ft
NO -
J NO 2.1
NO 0 3400
NO
NO
0
tion D1 ^
i |
3 '
i
HI
NC
NO
s i
i i
1
N
g 2 « ? South
fe | i ^ S 1 ?
*,
f 500
NO 1
-^ J!
JjTHJjrV :*?tf3
Water Lweis
, , T
O *fftS NO. -*°
O"^ . Mff
0 -- ' NO
Z«~- o-> < Eens-m c,'
8.6E-4 -^JE-3 ^.iS" AZOn"
^ -- --"lir^'^
»s__
1.9
680.0
i I.TEJ
ND
HO
0
__
J~ ^ i
NO . *
NO
" S
[Jg 6o!iC.-n 4
4JE-7
CZonr.
300 600 (ft) Approximate
in
^
NO NO
NO
HO oJ
0
NO
0
ection D2 i
c
Contaminant Contamination ng/1
1 ,2-DCA 2400
cis-1,2-DCE 2
PCE 3
TCE 5
Risk* 6.4 E-6
Contaminant not analyzed on this date.
Dashed lines represent unbound conditio
Solid lines represent bound conditions
TCE Contours
ND: Non Detect
'Increased cancer risk based on sample-
specific risk assessment
R0017S8_16
M^BI
,0.
c
\
"I ^
1
\
S
T ' " ' I 1
NP QU D Site
Xx "
1.71
^**«^
1
PI,
South
Water Lewis
500 1 000 (ft) Approximate
S
/
^- -
an
NOTE
The vertical extent of contamination represents
data that were presented in the Groundwater
OU RI/FS (CH2M HILL, JUNE 1994).
FIGURE 17
VERTICAL EXTENT OF
CONTAMINATION IN OU D
GROUNDWATER OPERABLE UNIT I ROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
CtGMHIII
i
1
1
1
1
1
1
1
1
1
1
i
i
-------
I
J
3
J
I
I
Identification of contaminants of potential concern
Exposure assessment
Toxicity assessment
Risk characterization
A complete presentation of the risk assessment is presented in the RI/FS, Appendix B, Risk
Assessment Methodology.
This section summarizes the risks addressed by the groundwater response action and the rationale for
implementing an interim action.
F.1 Risks Addressed by the Groundwater Response Action
The risks to human health and the environment addressed by the groundwater remedy depend on the
magnitude of the initial contaminant concentrations in the groundwater. Initial concentrations vary
spatially, as do the corresponding initial risks. The current maximum potential risk magnitude is
approximately one more cancer case per 100 people (10~2) than would otherwise occur. This risk .
magnitude is calculated on the hypothetical basis of a human ingesting groundwater from one of the
groundwater hot spots at McClellan AFB. As described in Section I of this document, the goal of the
interim groundwater remedy is to contain and extract groundwater to MCLs. This goal corresponds to
risk of 3.1 additional cancer cases per 1 million people (1CT6) than would otherwise occur. This figure
is calculated on the hypothetical basis of a human ingesting the groundwater that remains under
McClellan AFB after the interim remedy has been completed. Cleanup of the hot spots to the
containment goal of MCLs corresponds to a maximum potential risk reduction of 99.97 percent.
F.2 Rationale for the Implementation of an Interim Action
There are three major reasons for implementing an interim groundwater action now, rather than wait-
ing for the full characterization of the extent of contamination and the establishment of mandatory
cleanup levels:
Data are adequate to show that some of the groundwater plumes under McClellan AFB
are beginning to migrate beyond the McClellan AFB boundaries. In particular, plumes
under OUs A, B, and C are moving toward potential water well users and need to be
stopped. Implementation of a Basewide groundwater remedy is needed as soon as
possible to stop the spread of these plumes.
Implementing this groundwater remedy now will allow McClellan AFB more time to
conduct treatability studies and basewide remedial investigations. These studies and
investigations will benefit future Interim RODs and the final groundwater remedy for
the Final ROD. For example, technologies proven successful during treatability studies
will be incorporated into Basewide remedial actions. In addition, a better
understanding of site conditions from remedial investigations will result in remedies
that are designed to target specific areas.
An additional objective of this remedy is to collect and analyze groundwater quality,
groundwater flow, and other data during operation of the remedy to determine final
in situ cleanup standards for the Groundwater OU. Among the critical decisions to be
made are the extent to which, and the timeframe in which, to address lower levels of
RDD1001370B.WP5 (IROD) 47 5/2/95
-------
contamination that may remain in the aquifer after installation and initial operation of
the remedy. The final ROD will include cleanup standards, which may differ for
different portions of the OU, and may call for additional remedial actions. McClellan p
AFB expects that this interim remedy will provide the basis for the final remedy for |
the Groundwater OU.
G. Description of Alternatives I
The FS for the Groundwater OU evaluated six remedial alternatives, as well as the No-Action p
Alternative. The six alternatives are similar in that they all represent some variation to basic £
groundwater pump and treat technology. In addition, each is comprised of three components: a con-
tainment option, a treatment option, and an end-use option. Differences in the six alternatives stem *
from different combinations of these components. I
K'
This section first describes the options considered under each of the three components. Then it
outlines how the components were assembled into six complete alternatives for evaluation in the FS. I
After the public comment period, an additional alternative was assembled from the same components
that were used to assemble the alternatives upon which the public commented. In addition, a feature F
of the end-use options was modified. These changes are considered logical outgrowths of the nine- *-
criteria analysis and the response to comments that occurred during preparation of the Interim ROD.
G.1 Groundwater Containment Options *
During the FS, the extent of VOC contamination was determined using available information. Target
volumes were developed based on this extent of contamination, and containment strategies were
developed to focus on these target volumes. By focusing on these areas, alternatives were generated to
maximize containment, extraction, and treatment effectiveness. F
Hence, three options for containment were developed focusing on the target volumes: containment of
groundwater with contamination in excess of MCLs, containment of groundwater with contamination F
that exceeds a 10"6 cancer risk, and containment of groundwater with contamination above back- \
ground. The containment option selected will determine the volume of aquifer that contains
groundwater targeted for remedial action. These volumes are referred to as target volumes. Target P
volumes are volumes of aquifer, including the soil matrix and the pore space, which contain ^
groundwater with contaminant concentrations greater than particular levels. Area! extents of these
target volumes are based on concentration contours and risk contours of contaminant plumes. These r
target volumes, each of which corresponds to a containment option, are defined below: J
MCL Target Volume: The volume of aquifer with groundwater VOC concentrations ,
greater than MCLs. Under federal drinking water standards, an MCL is the maximum |
permissible level that a contaminant in water can be delivered to any user of a public l
water system. (At McClellan AFB, the MCL target volume is about 1.2 billion cubic
feet of groundwater.)
10"6 Cancer Risk Target Volume: The volume of aquifer with groundwater VOC
concentrations such that if someone were to ingest the water over a lifetime, he or she
would have an additional 1-in-1,000,000 chance of developing cancer. (At McClellan ^
RDD1001370B.WP5 (IROD) 48 5/2/95
-------
]
]
AFB, the 10 risk corresponds to about 2.1 billion cubic feet of groundwater, nearly
double the MCL target volume.)
Background Target Volume: All portions of the aquifer with contaminated
groundwater. (At the Base, the background target volume is almost 4.6 billion cubic
feet of groundwater, roughly double the 10"6 risk target volume.)
Illustrations of these three different target volumes in the A, B, and C Zones in plan view are provided
in Figures 18, 19, and 20. The monitoring netwoik in the D/E Zone is not extensive enough to delin-
eate target volumes. The area each target volume covers is presented in Table 6, in both square feet
and acres.
The MCL target volume is located within the 10"6 risk and the background target volume. The 10"6
risk target volume is located within the background target volume. The MCL target volume encom-
passes all the area within the MCL contour. The 10"6 risk target volume encompasses all the area
within the 10"6 risk contour, including the MCL target volume. The background target volume encom-
passes all the area within the contour of VOCs >0.5 ug/l, including the MCL and 10"6 risk target
volumes. The thicknesses of the target volumes in each of the zones are estimated to be the
thicknesses of the monitoring zone that they are in. These depths are presented in Table 3. The
quantitative volumes of the target volumes were calculated by using the areal extent of the target
volumes and the thickness of the monitoring zones.
Table 6
Areal Extent cf Target Volumes
Zone
A
B
C
Total
Hot Spot
acres
25.84
0.00
0.00
25.84
sqft
1,125488
0
0
1,125488
Target Volume
MCL
acres
663.92
100.87
52.28
817.07
sqft
28,922,385
4394,208
W77387
35493,980
Risk
acres
966.45
187.90
127.84
1,282.19
sqft
42,101,564
8,185,615
5468,954
55,856,133
Background
acres
1470.29
474.40
306.28
2^50.96
sqft
68,406,331
20,666,275
13342,400
102,415,006
The three groundwater containment options include intensified extraction pumping and capture of the
A Zone hot spots shown on Figure 18 (areas with groundwater VOC concentrations greater than or
equal to 500 ug/l) to keep them isolated from the remainder of the plumes.
Approximate well numbers and flow requirements for each of these groundwater containment compo-
nents are summarized in Table 7. These flow requirements are not the target volumes. They are the
amount of extraction flow needed to contain the target volumes and to lower contaminant concentra-
tions to specified cleanup levels. The volume of water extracted is not the target volume; as stated
previously, the target volume is the volume of aquifer containing contaminant concentrations greater
than a specified level. Table 7 was developed on the basis of FS-level analyses, as summarized in the
Groundwater OU RI/FS. The actual number of wells and associated flows will be determined during
remedial design and, in all likelihood, will deviate slightly from the estimates presented in Table 7.
RDD1001370B.WP5 (IROD)
49
5/2/95
-------
NOTE:
CONTOURS WILL BE UPDATED AS NEW DATA ARE MADE
AVAILABLE. THESE CONTOURS REPRESENT DATA THAT
WERE PRESENTED IN THE CONCEPTUAL MODEL IN THE
GROUNDWATER OU RI/FS (CH2M HILL, JUNE 1994)
3000 6000
SCALE IN FEET
9000
LEGEND
HOT SPOTS
MCL
RISK
BACKGROUND
ROD1726_34
FIGURE 18
TARGET AREAS IN MONITORING ZONE A
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA _ _. ,,
CKMHILL
-------
1
J
0
LEGEND
MCL
3000 6000
SCALE IN FEET
9000
RISK
I. . I BACKGROUND
FIGURE 19
TARGET AREAS IN
MONITORING ZONE B
GROUNDWATER OPERABLE UNIT IROO
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
ROD1631.35
CKMHIIL
-------
3000 6000
SCALE IN FEET
9000
LEGEND
MCL
RISK
BACKGROUND
r
i
E
I
ROD 1631.36
FIGURE 20
TARGET AREAS IN
MONITORING ZONE C
GROUNDWATER OPERABLE UNIT IROD
McCUELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
CKUHIIL
-------
J
j
]
Table 7
Number of Extraction Wells and Flow Rates Required to Contain Different Target Volumes
Target Volumes
Background Target
Volume
Risk Target Volume
MCL Target Volume
Monitoring Zone
A
No. Wells
141
106
91
Q (gpm)
1,130
810
650
B
No. Wells
34
31
26
Q (gpm)
470
420
330
C
No. Wells
20
9
5
Q (gpm)
410
180
100
Total
No. Wells
195
146
122
Q (gpm)
2,010
1,410
1,080
As expected, extraction well requirements are largest for the background target volume and smallest
for the MCL target volume. Total flow requirements range from roughly 1,000 to 2,000 gpm, depend-
ing on the selected target volume. Present worth, capital, and operations and maintenance (O&M)
costs for each containment option are addressed in Section H.7.
G.2 Groundwater Treatment Options
The treatment system consists of an existing west side treatment plant and a new treatment plant, if
needed, on the east side of the Base. Groundwater extracted from underneath OUs B, C, and D will
be piped to the GWTP, while groundwater under OU A will be piped to the new east side treatment
plant if required. The existing west side plant will be evaluated to determine if it can handle
increased flow capacity and changes in influent concentrations. If a new east side treatment plant is
needed, it will be designed with standard treatment technologies. This section presents the
groundwater treatment options that were evaluated in detail in the FS; the implementation plans for
these options; uncertainties and 'contingencies incorporated into the plans; and the estimated present
worth, capital, and O&M costs.
G.2.1 Expansion of the West Side Treatment Plant
The west side treatment plant was originally designed in 1986 to treat 1,000 gpm. Several modifi-
cations have taken place, mostly in response to lower-than-planned flows, leaving the plant at a current.
capacity of 750 gpm. The plant can be expanded to match the eventual flow from the extraction wells
on the west side of the Base. The west side treatment plant capacity will be expanded if the flow
from the west plumes exceeds 750 gpm. Hence, if the 10"6 risk or background target volume were
selected, the west side treatment plant would be expanded. The west side treatment plant system is
currently composed of an air stripper (AS) with thermal oxidation to treat offgas and liquid-phase
granular activated carbon (LGAC) for polishing.
G.2.2 Treatment Options for the East Side Treatment Plant
Five groundwater treatment options and three offgas treatment technologies were presented during the
FS for the new east side groundwater treatment plant, if one were required. These eight options were
assembled into eleven treatment trains. These treatment trains were evaluated based on four criteria:
robustness, implementability, effectiveness, and cost. Based on the FS evaluation, three treatment
trains were selected as options for the treatment component of the remedy. This screening process is
presented in Figure 21.
KDD1001370B.WP5 (ROD)
53
5/2/95
-------
DURING THE FEASIBILITY STUDY...
I
EIGHT TREATMENT
TECHNOLOGIES...
GROUNDWATER
TREATMENT
Ultraviolet (UV) ozone
advanced oxidation
process (AOP)
UV/hydrogen
peroxide AOP
Ozone/hydrogen
peroxide AOP
Air stripping (AS)
Liquid-phase granular
activated carbon (LGAC)
OFFGAS
TREATMENT
Catalytic oxidation (CatOx)
Thermal incineration
Vapor-phase granular
activated carbon (VGAC)
RDO1631.42
ASSEMBLY
WEREASSEMBLED
INTO ELEVEN
TREATMENT TRAINS...
UV/hydrogen peroxide AOP
Ozone/hydrogen peroxide AOP
LGAC
AS with CatOx offgas control
AS with VGAC offgas control
AS/CatOx with ozone/hydrogen
peroxide AOP pretreatment
AS/VGAC with ozone/hydrogen
peroxide AOP pretreatment
AS/CatOx with UV/hydrogen
peroxide AOP pretreatment
AS/VGAC with UV/hydrogen
peroxide AOP pretreatment
AS/CatOx with LGAC polishing
AS/VGAC with LGAC polishing
AND THREETREATMENT
OPTIONS WERE SELECTED
FOR DETAILED ANALYSIS.
EVALUATION
AS/CatOx/LGAC
AS/VGAC/LGAC
LGAC
FIGURE 21
STANDARD GROUNDWATER
TREATMENT TECHNOLOGY SCREENING
GROUNOWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
E
The three treatment options presented in Figure 21 have been considered for the new east side ground-
water treatment plant
LGAC to treat influent groundwater
AS to treat influent groundwater and catalytic oxidation (CatOx) to treat offgas
AS to treat influent groundwater and vapor-phase granular activated carbon (VGAC) to
treat offgas
Air stripping technology releases a residual gas stream that must be treated. LGAC does not release a
gas stream.
Each of the three treatment options is summarized below. The typical layout of these technologies is
presented in Figure 22. The costs and uncertainties associated with these technologies will be
presented further in this Interim ROD.
Liquid-Phase Granular Activated Carbon. Carbon is used for groundwater treatment to
remove a wide variety of chemicals, including VOCs. This technology works through adsorption of
the contaminants onto the carbon. For most VOCs, a carbon bed will provide a high (greater than
95 percent) removal of compounds until it is saturated or loaded with contaminants.
f.
RDD1001370B.WP5 (IROD)
54
5/2/95
-------
I
i
i
j
i
j
LIQUID-PHASE GRANULAR ACTIVATED CARBON
Carbon Beds Requiring
Periodic Replacement
(~~/
Pump
Treated Water
AIR STRIPPING
CATALYTIC OXIDATION
Offgas to Treatment
Water Flow
Offgas from Air Stripper^
Heated Air
Natural Gas
for Heating
Ground water
AIR STRIPPING
Offgas to Treatment
Water
VAPOR PHASE GRANULAR ACTIVATED CARBON
Treated Offgas
Carbon Beds
Groundwater
Pump
Fan
Treated Water
Duct Heater
Carbon Vessel
FIGURE 22
STANDARDTREATMENT TECHNOLOGIES
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
RDD1631_38
SACRAMENTO, CALIFORNIA
CtaiHILL
-------
Typically, two carbon beds will be used in series. The first bed will be online until it is fully loaded, .
allowing the second bed to catch the breakthrough contaminants before final discharge. When a bed is
loaded, carbon vendors are employed to remove the spent carbon and refill the bed. The spent carbon «-
is thermally regenerated at a vendor facility offbase. Equipment required consists of aboveground I
skid-mounted tanks that contain the carbon beds and pumps. The only residual generated is the spent
carbon, which is treated by a vendor. If the spent carbon meets hazardous waste criteria, MClellan
will ensure that the waste is treated at a legally permitted facility. If:
Air Stripping with Catalytic Oxidation. Air stripping uses a tower to contact groundwater
flowing downward with air flowing upward. Packing is used to break the groundwater stream into F
small droplets in the tower and enhance air-groundwater contact As a result of this contact, VOCs ^
transfer from the groundwater to the gas and exit the tower in an offgas stream. Air stripping equip-
ment required includes the tower (approximately 40 feet tall), an air blower, and pumps. Residuals £
generated include the offgas, which will be treated using catalytic oxidation before discharging to the I
atmosphere. Treated water may require carbon polishing, depending on end use.
Catalytic oxidation offgas treatment technology oxidizes VOCs in the AS offgas by heating the offgas ti
and passing it through a catalyst bed, which enhances the oxidation of VOCs to nontoxic water vapor,
carbon dioxide, and hydrochloric acid (HC1). HC1 can be removed, if it is present in significant P
amounts, with a separate scrubber. Equipment required includes a packaged oxidizer system and [|
stack. If scrubbing is required, sodium hydroxide storage, delivery, and distribution systems are
required. Residuals include HC1, which is present in the offgas. Air stripper offgas streams usually r
do not contain HC1 concentrations high enough to require treatment before discharge following a [
CatOxuniL
Air Stripping with Vapor-Phase Granular Activated Carbon. This option uses the same [
air stripping technology described previously. The difference is mat carbon is used to treat the AS
gas. The adsorption mechanism for airborne VOCs is similar to that described above for LGAC. In «*
gas-phase adsorption, water vapor in the gas stream adversely affects VOC adsorption. Duct heaters I
are used to raise the temperature of the offgas to lower the relative humidity of the offgas to enhance
VOC adsorption in the fiberglass vessels that house the carbon beds and a stack. Residuals include ...
the carbon, which is regenerated offsite. As with LGAC, if the spent carbon falls within the definition
of hazardous waste, it will be treated at a legally permitted facility.
G.2.3 Uncertainties in Influent Parameters |\:
Several uncertainties regarding groundwater system responses could affect the performance of the
treatment process and should be addressed before a standard technology is selected. The principle
uncertainties identified in the Groundwater OU RI/FS include:
The extent of contamination
The response of the groundwater system to remedial extraction
Influent flows and concentrations. The design of the treatment system should be based
on influent flow rates and concentrations. Therefore, the prospective new east side
treatment plant cannot be designed and the west side treatment plant cannot be eval-
uated until uncertainties regarding the groundwater system are sufficiently reduced.
Uncertainty can be reduced during the remedy by sequencing projects and activities
that address the unknowns. These activities include investigating further the extent of
contamination, performing aquifer tests, and determining metals concentrations in
RDD1001370B.WP5 (IROD) 56 5/2/95
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groundwater and impacts of Base activities on metals contamination. These activities
are discussed further in Section I.
Metals in the groundwater will be investigated as a remedial design activity. Metals concentrations in
groundwater extracted over a long period of time will be evaluated to determine if metals removal is
necessary during treatment; concentrations may be greater than the discharge limits for the end uses
and may need to be treated. If metals removal is needed, the treatment system will either be modified
or a contingency plan will be prepared to treat metals in extracted groundwater.
G.3 End-Use Options
The following four end-use options were carried forward from an initial screening performed during
the Contaminated Groundwater Cleanup Workshop on August 10, 1993:
Discharge to McClellan AFB's existing greywater conveyance system
Discharge to Magpie Creek
Selling to neighboring water districts
Onbase injection to deeper aquifers
These four end-use options have been assembled into two end-use options for treated groundwateT.
They are described below. These end-use options contain similar elements and therefore are not
mutually exclusive. They are also both implementable. The layouts of these two options are
presented in Figure 23.
End-Use Option 1
End-Use Option 1 would convey as much treated groundwater as possible to McClellan AFB's exist-
ing greywater system. The remaining flow would be sold to neighboring water districts. McClellan
AFB currently uses some water from the existing west side treatment unit in a greywater system.
The greywater system consists of a 250,000-gallon storage tank, a pressurizing pump system near the
existing groundwater treatment unit, and a network of piping to cooling towers and Magpie Creek.
The greywater system uses the water in cooling towers. The greywater system is currently being
inspected and tested to determine its water needs. It may be expanded to serve a greater part of the
Base. Current estimates indicate that the greywater system could reuse as much as 700 gpm of the
treated groundwater. Because of greywater connections already located at that site, initially only water
from the west side treatment unit will be used for the greywater system. If an east side treatment plant
needs to be built, treated groundwater from this plant will be sent to a separate east side greywater
system.
Purveyors that have expressed an interest in the treated groundwater and that have facilities nearby
include Northridge Water District and Arcade Water District on the east, and Rio Linda Water District
on the west. Northridge Water District has two existing service connections in the vicinity of the
proposed east treatment unit. Arcade Water District has facilities further north of the proposed east
side treatment unit. Rio Linda Water District has facilities in the vicinity of the west side treatment
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CREYWATER STORAGE TANK
ENtMJSE OPTION 1
LEGEND
*- MAGPIE CREEK
PROPOSED PIPELINE
EXISTING PIPEUNE
3000 6000
SCALE IN FEET
END-USE OPTION t
9000
ROO1631_2T
FIGURE 23
LAYOUT FOR END-USE OPTIONS
GROUNDWATER OPERABLE UNIT IROD
McCLELLANAIR FORCE BASE
SACRAMENTO. CALIFORNIA
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1
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unit. This analysis assumes that up to 650 gpm will be supplied to Northridge Water District and up
to 1,600 gpm to Rio Linda Water District No storage is required because the demand from both
districts is much greater than the discharge flow rates.
Because water from the treatment plant will be treated to standards that are at least as stringent as
those required by the federal Safe Drinking Water Act, McClellan AFB recognizes that any end-use
other than utilization as drinking water could be perceived as a waste of a valuable resource. For this
reason, McClellan AFB is continuing to explore with Cal-EPA, U.S. EPA, and surrounding com-
munities how best to utilize the treated water, including providing it to neighboring water districts.
In the event of maintenance requirements, which may occur only once or twice a year, the backup
system would discharge the treated groundwater to Magpie Creek. Throughout much of
McClellan AFB, Magpie Creek is a concrete-lined canal. Because the canal's existing design capacity
is 700 cfs, or approximately 314,000 gpm, the additional flows from the treatment plant will not
adversely impact the flow capacity of the creek. The existing groundwater treatment plant already
discharges its water into Magpie Creek.
End-Use Option 2
End-Use Option 2 would reuse as much of the treated groundwater in McClellan AFB's existing
greywater system as possible. As stated previously, the greywater system is currently being inspected
to determine its water needs.
The remaining flow either would be discharged into Magpie Creek or injected into the groundwater.
Preference will be to discharge to Magpie Creek, but injection will be re-evaluated if Magpie Creek
cannot handle the flow. For much of the year, Magpie Creek is dry (except for discharge from the
existing GWTP). During winter storms, Magpie Creek occasionally overflows. When the remedy is
in full operation, discharge from the GWTP will represent less than one-half of 1 percent of the
creek's capacity. NPDES substantive requirements regarding discharge limits will have to be met
If the greywater system and Magpie Creek cannot accommodate all the treated groundwater flow,
injection of treated groundwater into wells at the north end of McClellan AFB would be re-evaluated.
Injection was originally evaluated in the FS. The north site was chosen because of its distance from
any known groundwater contamination. Treated groundwater from the east side and west side
treatment units would be injected into the wells.
For this end-use, it has been assumed that water could be injected approximately 600 feet bgs and that
as many as four injection wells would be required. One injection well would be a standby well for
maintenance purposes. Injection pilot tests will determine how much flow potentially could be
injected into the selected aquifers. Injection costs and capacity have been estimated under the
assumption that the inorganic water qualities of the treated water would be similar to those of the
aquifers where injection would take place.
G.4 Applicable or Relevant and Appropriate Requirements
Section 121(d) of CERCLA states that remedial actions on CERCLA sites must attain (or the decision
document justify the waiver of) any federal or more stringent state environmental standards,
requirements, criteria, or limitations that are determined to be legally applicable or relevant and
appropriate (ARAR). Applicable requirements are those cleanup standards, criteria, or limitations
RDD100I370B.WP5 (ROD) 59 5/2/95
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promulgated under federal or state law that specifically address the situation at a CERCLA site. A
requirement is applicable if the jurisdictional prerequisites of the environmental standard show a direct
correspondence when objectively compared with the conditions at the site. ,
If a requirement is not legally applicable, the requirement is evaluated to determine whether it is
relevant and appropriate. Relevant and appropriate requirements are those cleanup standards, standards
of control, and other substantive environmental protection requirements, criteria, or limitations promul- r
gated under federal or state law that, while not applicable, address problems or situations sufficiently *
similar to the circumstances of the proposed response action and are well-suited to the conditions of
the site. The criteria for determining relevance and appropriateness are listed in Title 40, Code of f
Federal Regulations, Section 300.400(g)(2) (40 CFR §300.400(g)(2)). I
ARARs are concerned only with substantive, not administrative, requirements of a statute or f
regulation. The substantive portions of the regulation are those requirements that pertain directly to I.
actions or conditions in the environment Examples of substantive requirements include quantitative
health- or risk-based restrictions upon exposure to types of hazardous substances (e.g., MCLs). F
Administrative requirements are the mechanisms mat facilitate implementation of the substantive |^
requirements. Administrative requirements include issuance of permits, documentation, reporting,
recordkeeping, and enforcement. Thus, in determining the extent to which onsite CERCLA response P
actions must comply with environmental laws, a distinction should be made between substantive |?
requirements, which may be ARARs, and administrative requirements, which are not
Furthermore, the ARARs provision in CERCLA applies to onsite actions. "Onsite" is defined as the |
area! extent of contamination and includes the groundwater plumes to be remediated. According to
CERCLA §121(e), a remedial response action mat takes place entirely onsite may proceed without the
obtaining of permits. This permit exemption applies to all administrative requirements, as well as to
permits. Actions taken offsite will need to comply with the substantive as well as the administrative
requirements of all applicable regulations.
Pursuant to EPA guidance, ARARs generally are classified into three categories: chemical-specific, *-
location-specific, and action-specific requirements. This classification was developed to help identify
ARARs, some of which do not fall precisely into one group or another. These categories of ARARs |
are defined below: *
Chemical-Specific ARARs include those laws and requirements that regulate the |
release to the environment of materials possessing certain chemical or physical t;
characteristics or containing specified chemical compounds. These requirements
generally set health- or risk-based concentration limits or discharge limitations for |~
specific hazardous substances. If, in a specific situation, a chemical is subject to more [;
than one discharge or exposure limit the more stringent of the requirements should
generally be applied. f
Location-Specific ARARs are those requirements that relate to the geographical or
physical position of the site, rather than the nature of the contaminants or the proposed r
site remedial actions. These requirements may limit the placement of remedial action, [
and may impose additional constraints on the cleanup action.
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Action-Specific ARARs are requirements that define acceptable handling, treatment,
and disposal procedures for hazardous substances. These ARARs generally set
performance, design, or other similar action-specific controls or restrictions on
particular kinds of activities related to management of hazardous substances or
pollutants. These requirements are triggered by the particular remedial activities that
are selected to accomplish a remedy. Because a remedial site usually involves several
alternative actions, very different action-specific requirements can apply.
G.4.1 Chemical-Specific ARARs
Table 8 lists the federal and state chemical-specific ARARs for the selected alternative. A brief
description of how the ARAR is applied to the alternative is also provided.
TableS
Chemical-Specific ARARs for the
Groundwater OU DROD
Requirement
Description of Requirement
Federal Chemical-Specific ARARs
Safe Drinking Water Act*
40 CFR §141, Subparts B and G
(See Table 4 for MCLs)
40 CFR §141 Subpart F
National primary drinking water standards are health-based standards fen-
public water systems (maximum contaminant levels [MCLs]). The National
Contingency Plan (NCP) defines MCLs as relevant and appropriate for
groundwater determined to be a current or a potential source of drinking
water in cases where maximum contaminant level goals (MCLGs) are not
ARARs. Groundwater in the vicinity of McClellan AFB has been designated
for drinking water use. Groundwater in the Groundwater OU with
contaminant concentrations above MCLs will be contained.
MCLGs that have non-zero values are relevant and appropriate for
groundwater determined to be a current or a potential source of drinking
water (40 CFR 300.430(eX2Xi)(B) through (D)). Groundwater in the vicinity
of McClellan AFB has been designated for drinking water use. Non-zero
MCLGs exist for some of the chemicals of potential concern; therefore,
groundwater with contaminant concentrations above non-zero MCLGs will be
contained.
Clean Water Act (CWA)a
33 USC §1313 and 40 CFR §13136
Water quality standards are applicable to remedial actions that could impact
surface water, such as Magpie Creek.
State Chemical-Specific ARARs
Cal-EPA Department of Toxic Substances Control (DTSC)"
22 CCR §64435 and 64444.5
Like federal MCLs, state MCLs are tap standards that are relevant and
appropriate for the aquifer at McClellan AFB that is or may be used as a
drinking water source. State MCLs are relevant and appropriate only if they
are more stringent than the federal MCLs.
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Table 8
Chemical-Specific ARARs for the
Groundwater OU IROD
Requirement
Description of Requirement
State and Regional Water Quality Control Board (RWQCB)'
Water Quality Control Plan (Basin Plan)
for the Central Valley Region. Specific
applicable sections include designated
beneficial uses of affected water bodies,
and numerical and narrative water
quality objectives.
Beneficial uses of the groundwater in the vicinity of McClellan AFB, as
identified in the Basin Plan, include agricultural, municipal, industrial, and
domestic water supply. The water quality objectives, including narrative and
numerical standards, are applicable to the groundwater and to affected
surface waters. These objectives and standards need to be met to protect the
beneficial uses.
The specific ARAR citation is listed below the general heading. Only the substantive requirements are considered
ARARs.
G.4.2 Location-Specific ARARs
Federal and state location-specific ARARs for the selected alternative are presented in Table 9. These
ARARs may limit the placement or affect implementation of the remedial action because of the
physical or geographical position of the Base. A brief description of how the ARAR is applied to the
alternative is also provided.
Table 9
Location-Specific ARARs for the
Groundwater OU IROD
Requirement
Description of Requirement
Federal Location-Specific ARARs
Endangered Species Act of 1973*
16 USC §1536(a)
This requirement is applicable because endangered species have been
identified at the Base, the effects that the remedial action may have on
these species will need to be determined. Actions may need to be taken
to conserve endangered species or threatened species, including con-
sultation with the Department of the Interior, Fish and Wildlife Service.
Proposed endangered species that have been identified at the Base
include the California Linderiella and the Vernal Pool Fairy Shrimp.
Clean Water Act*
40 CFR §231.10
The Clean Water Act prohibits discharge of dredged or fill material (i.e.,
bank material that may fall into creeks) into surface water. This
requirement is applicable to construction activities that may affect creeks
at the Base.
State Location-Specific ARARs
California Department of Fish and Game Code
California Endangered Species Act, Fish and
Game Code §2050, et seq.
Because endangered species have been identified at the Base, this
requirement is applicable. The effects that the remedial action may have
on these species will need to be determined. California Species of
Special Concern identified at the Base include the Burrowing Owl and
the Loggerthead Shrike.
The specific ARAR citation is listed below the general heading. Only the substantive requirements are considered
ARARs.
1
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G.4.3 Action-Specific ARARs
]
The federal and state action-specific ARARs for the selected remedy are presented in Table 10. In
some cases, the regulations cited under the federal ARARs are state regulations because, for the
purposes of ARARs analysis, state regulations that are a component of a federally authorized or
delegated state program are generally considered to be federal requirements and potential federal
ARARs (55 Federal Register 8742). Because U.S. EPA has authorized the California RCRA program,
the regulations found in Division 4.5 Title 22 CCR are a source of potential federal ARARs for
CERCLA response actions, including this Groundwater OU.
These ARARs generally set performance, design, or other similar action-specific controls or
restrictions on certain activities related to management of hazardous substances or pollutants.
Table 10
Action-Specific ARARs for the
Groundwater OU ROD
Requirement
Description of Requirement
Federal Action-Specific ARARs
Resource Conservation and Recovery Act (RCRA)9
22 CCR §66262.10(a), §66262.11, and
§6626234
22 CCR §66264.171, 172, 173, 174,'175(a) and
(b), 176, 177, and 178
Substantive requirements of 22 CCR
§66264.601
22 CCR §66264.96, §66264.97(bXD(D), (b)(2),
(b)(4) through (7), §66264.99
Substantive requirements of 22 CCR
§66264.100, with the exception to references
made to groundwater protection standards
Requirements for the identification and accumulation of hazardous
waste are applicable to hazardous wastes (i.e., contaminated soil
cuttings and extracted groundwater) generated during implementation
of the remedial alternative.
Requirements for storage of hazardous waste held for a period greater
than 90 days before treatment, disposal, or storage elsewhere, in a
container, are applicable to hazardous wastes (i.e., contaminated soil
cuttings and extracted groundwater) generated during implementation
of the remedial alternative.
Design and operating standards for miscellaneous units that treat
hazardous waste are relevant and appropriate to aii strippers.
General water quality monitoring and system requirements are
relevant and appropriate because wastes that have been discharged to
land (source areas) are causing groundwater contamination. The
monitoring program will evaluate the effectiveness of the
groundwater corrective action.
Requirements for the implementation of corrective action measures
are relevant and appropriate because wastes that have been discharged
to land (source areas) are causing groundwater contamination.
Corrective action shall include water quality monitoring to
demonstrate the effectiveness of the corrective action.
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Table 10
Action-Specific ARARs for the
Grouodwater OU IROD
Requirement
40 CFR §144.12(a)(e) and §144.13
Description of Requirement
The underground injection control (UIC) program prohibits injection
activities that allow movement of contaminants into underground
sources of drinking water that may result in violations of MCLs or
adversely affect health. The UIC program regulates construction of
Class IV wells. These requirements are applicable to groundwater
injection wells that may be constructed as part of the remedial action.
§144.13 provides that treated groundwater may be injected into the
same formation if such injection is approved under CERCLA cleanup
provisions.
Clean Air Act*
SMAQMD Rule 202
SMAQMD Rule 402 (as promulgated)
SMAQMD Rule 403
Emissions from a new groundwater treatment plant must comply with
new source review regulations. BACT requirements are applicable to
treatment plant emissions.
Emissions from a new groundwater treatment plant may not cause
injury, detriment, nuisance, or annoyance to the public, businesses, or
property.
Fugitive dust control standards must be met within the area! extent of
contamination during any construction activities as a result of
implementing the groundwater remedial action.
State Action-Specific ARARs"
State Water Resources Control Board
Resolution No. 68-16
23 CCR §2510(g)
This resolution requires that quality of waters of the State that is
better than needed to protect beneficial uses be maintained.
Discharges to high quality waters must be treated using best
practicable treatment. Beneficial uses must be protected. These
requirements are applicable to discharges of treatment plant effluent
to Magpie Creek or injection into clean aquifers.
Groundwater monitoring may be required if wastes that were
discharged to waste management units at McQelian AFB prior to
November 27, 1984 threaten groundwater quality. If a known release
has occurred, the corrective action requirements in 22 CCR
§66264.100 will be relevant and appropriate.
The specific ARAR citation is listed below the general heading. Only the substantive requirements are considered
ARARs.
E
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G.5 Assembled Alternatives
The containment, treatment, and end-use systems described in Sections G.I through G.3 were
combined to form seven alternatives. Although various combinations of the three target volumes, the
three treatment technologies, and the two end-use systems do exist, seven likely alternatives were
evaluated. They are summarized in Table 11 and described in the following paragraphs. The alterna-
tives described here, and the priorities for implementing the remedy listed in Section 1.3, are based on
current information. Logistics and priorities for implementing the selected alternative may change as
new data are collected.
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Table 11
Alternatives for Groundwater at McClellan AFB
Alternative
1
2
3
4
4A
5
6
Extraction
Target Volume
Basewide
MCL
Iff6 Cancer Risk
Background
Iff6 Cancer Risk
MCL
Iff6 Cancer Risk
Iff6 Cancer Risk
Extraction
Flow Rate (gpm)
East
460
590
710
590
460
590
590
West
630
820
1,300
820
630
820
820
Treatment System*
East
AS/CatOx/LGAC
AS/CatOx/LGAC
AS/CalOx/LGAC
AS/VGAC/LGAC
AS/VGAC/LGAC
AS/CarOx/LGAC
LGAC
West
GWTP
GWTP (w/expansion)
GWTP (w/expansion)
GWTP (w/expansion)
GWTP
GWTP (w/expansion)
GWTP (w/expansion)
End-Use
System6
Basewide
Option 2
Option 2
Option 2
Option 2
Option 2
Option 1
Option 2
Treatment System Definitions: AS = Air Stripping; CatOx = Catalytic Oxidation Offgas Treatment; LGAC = Liquid-
Phase Granular Activated Carbon; and VGAC = Vapor-Phase Granular Activated Carbon Offgas Treatment.
''End-Use System Definitions: Option 1 = Greywater (primary); Water Districts (secondary); and Magpie Creek (backup).
Option 2 = Greywater (primary); Magpie Creek (secondary); and injection (backup and contingency).
1
Alternative 1
Alternative 1 consists of extracting groundwater from the MCL target volume. Groundwater from OU
B, OU C, and OU D would be piped to the existing west side treatment plant Groundwater from OU
A would be piped to a new east side treatment plant, if needed. This new east side treatment plant
would use AS to treat groundwater, LGAC to polish the treated groundwater, and CatOx to treat the
residual offgas from the air stripper. As much treated water as possible from the west and east side
treatment plants would be used in McClellan AFB's greywater system. The remainder of the treated
water from both plants would be discharged into Magpie Creek and/or injected into the groundwater.
The portion of water to be injected into the groundwater or discharged into Magpie Creek is dependant
on the capacity of the greywater system.
Alternative 2
Alternative 2 consists of extracting groundwater from the 10"6 Cancer Risk target volume. Ground-
water from OU B, OU C, and OU D would be piped to the existing west side treatment plant (which
may need to be expanded to treat higher flow rates). Groundwater from OU A would be piped to a
new east side treatment plant, if needed. This new east side treatment plant would use AS to treat
groundwater, CatOx to treat the residual offgas from the air stripper, and LGAC to polish the treated
groundwater. As much treated water as possible from the west and east side treatment plants would be
used in McClellan AFB's greywater system. The remainder of the treated water from both plants
would be discharged into Magpie Creek and/or injected into the groundwater. The portion of water to
be discharged or injected into Magpie Creek is dependant on the capacity of the greywater system.
Alternative 3
Alternative 3 consists of extracting groundwater from the background target volume. Groundwater
from OU B, OU C, and OU D would be piped to the existing west side treatment plant, which may
need to be expanded to accommodate higher flows. Groundwater from OU A would be piped to a
new east side treatment plant, if needed. This new east side treatment plant would use AS to treat
groundwater, LGAC to polish the treated groundwater, and CatOx to treat the residual offgas from the
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air stripper. As much treated water as possible from the west and east side treatment plants would be
used in McClellan AFB's greywater system. The remainder of the treated water from both plants
would be discharged into Magpie Creek and/or injected into the groundwater. The portion of water to r
be injected or discharged into the groundwater into Magpie Creek is dependant on the capacity of the |
greywater system.
Alternative 4 i
Alternative 4 consists of extracting groundwater from the 10"6 Cancer Risk target volume. Ground-
water from OU B, OU C, and OU D would be piped to the existing west side treatment plant, which E
may need to be expanded to accommodate higher flows. Groundwater from OU A would be piped to fc
a new east side treatment plant, if needed. This new east side treatment plant would use AS to treat
groundwater, LGAC to polish the treated groundwater, and VGAC to treat the residual offgas from the f
air stripper. As much treated water as possible from the west and east side treatment plants would be "
used in McClellan AFB's greywater system. The remainder of the treated water from both plants
would be discharged into Magpie Creek and/or injected into the groundwater. The portion of water to F
be injected into the groundwater or discharged into Magpie Creek is dependant on the capacity of the t<
greywater system.
Alternative 4A L
Alternative 4A consists of extracting groundwater from the MCL target volume. Groundwater from t
OU B, OU C, and OU D would be piped to the existing west side treatment plant Groundwater from |.
OU A would be piped to the existing west side treatment plant or, if necessary, to a new east side
treatment plant, depending on cost-effectiveness. This new east side treatment plant would use AS to
treat groundwater, LGAC to polish the treated groundwater, and VGAC to treat the residual offgas
from the air stripper. As much treated water as possible from the west and east side treatment plants
would be used in McClellan AFB's greywater system. The remainder of the treated water from both *»
plants would be discharged into Magpie Creek and/or injected into the groundwater. The portion of £_
water to be injected into the groundwater or discharged into Magpie Creek is dependant on the
capacity of the greywater system. ' f'
Alternative 5
Alternative 5 consists of extracting groundwater from the 10"6 Cancer Risk target volume. Ground- K
water from OU B, OU C, and OU D would be piped to the existing west side treatment plant, which
may need to be expanded to accommodate higher flows. Groundwater from OU A would be piped to
a new east side treatment plant, if needed. This new east side treatment plant would use AS to treat r
groundwater, LGAC to polish the treated groundwater, and CatOx to treat the residual offgas from the
air stripper. As much treated water as possible from the west and east side treatment plants would be
used in McClellan AFB's greywater system. The remainder of the treated water from both plants will j.
be provided to neighboring water districts. In the event of maintenance requirements, treated water '
would be discharged to Magpie Creek.
Alternative 6
Alternative 6 consists of extracting groundwater from the 10"6 Cancer Risk target volume. Ground-
water from OU B, OU C, and OU D would be piped to the existing west side treatment plant, which £-.
may need to be expanded to accommodate higher flows. Groundwater from OU A would be piped to
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1
a new east side treatment plant, if needed. This new east side treatment plant would use LGAC to
treat and polish the groundwater. There would be no residual .emissions; therefore, offgas treatment
would not be needed. As much treated water as possible from the west and east side treatment plants
would be used in McClellan AFB's greywater system. The remainder of the treated water from both
plants would be discharged into Magpie Creek and/or injected into the groundwater. The portion of
water to be discharged into Magpie Creek or injected is dependant on the capacity of the greywater
system.
H. Summary of the Comparative Analysis of Alternatives
Each of the above-mentioned alternatives was evaluated against nine criteria recommended by the EPA
in guidance documentation for conducting RI/FS work. The evaluation criteria are grouped such that
two are threshold criteria, which any alternative must meet; five are comparison criteria, which allow
the alternatives to be compared against each omen and two are acceptance criteria, which will be
addressed after receiving public comments. These are the minimum criteria recommended by the
EPA. A comparison of the No-Action Alternative and the seven assembled alternatives, using the nine
EPA criteria, is presented in Table 12.
Tiblt 12: Comparison of Altmuttas Against Nine EPA Criteria
Criteria Description
Alternative
No
Action
1
2
3
4
4A
5
«
Threshold Criteria
1. Overall Protection
of Human Health
and Environment
2. Compliance with
ARARs
Comparison Criteria
3. Long-Torn
Effectiveness and
PfMiian*fii *
4. Reduction of
Toxicfty,
Mobility, and
Volume through
Treatment
5. Short-Tom
Effectiveness
6. Implcmentabibty
7. Cost (Present
Worth)*
No
No
No
No
No
Yes
N/A*
Yes
Yes
Yes
Yes
Yes
Yes
S54.900.000
Yes
Yes
Yes
Yes
Yes
Yes
5fi6.100.000
Yes
Yes
Yes
Yes
Yes
Yes
$81,000,000
Yes
Yes
Yes
Yes
Yes
Yes
$66,000,000
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
$57.200,000
Yes
Yes
Yes
Yes
$70,100,000
Yes
Yes
Yes
Yes
$74,000,000
j
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Table 12: Comparison of Alteratives Against Nine EPA Criteria
Criteria Description
Alternative
No
Action
1
Acceptance Criteria
8. State Acceptance
9. Community
Acceptance
No
No
Yes
Yes
2
3
4
4A
S
<
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yese
Yes"
Yes
Yes
Assumptions:
Interest Rate = 5 percent Analysis Period = 20 years.
'The Air Force has spent approximately $10 million on construction and operation of voluntary groondwater remedial actions.
The State of California concurs with all aspects of the alternative, except it has expressed reservations about providing treated gcoundwater to neighboring
water districts.
^ased on acceptance of Jane 1994 Proposed Plan and December 1994 Fact Sheet; if McClellan deviates from the end ose presented to the public.
McClellan will provide public notice.
H.1 Overall Protection of Human Health and the Environment
The No-Action Alternative will not adequately protect human health and the environment While there
are no significant risks to human health or the environment under current conditions, groundwater
contaminants within OUs A, B, and C are not contained and have the potential to migrate offbase and
impact offbase municipal or supply wells.
Alternatives 1 through 6 would protect human health and the environment by containing contaminated
groundwater and preventing future migration offbase. Alternative 3 would offer the greatest level of
protection from potential exposure to contaminated groundwater because it extends containment to
background levels. Containment to background leaves a residual level of increased cancer risk of
3.1 x 10~7. Alternatives 2, 4,5, and 6 would provide equal levels of protection from exposure to
contaminated groundwater because they contain contamination to the level that could cause no more
than a residual level of increased cancer risk of 10"6. Alternatives 1 and 4A would be the least
protective of the alternatives in terms of containing the groundwater contamination, but still meet the
MCL requirements for drinking water. Containment to MCLs leaves a residual level of increased
cancer risk of 3.1 x 10"6.
The National Contingency Plan (NCP), however, expects risks achieved from remedial actions to fall
between 10"6 and 10"4. Hence, the residual risks from all alternatives, including Alternatives 1 and
4A, fall within or below the NCP range.
Water and air treatment systems for all of the alternatives are equally protective. End-use options are
also equally protective because the groundwater will be treated to levels that meet or exceed the
treatment levels required by RWQCB and California Department of Health Services/Office of Drinking
Water (DHS/ODW).
H.2 Compliance with ARARs
The No-Action Alternative is not adequate to meet ARARs or to fully remove the possibility of future
contaminant exposure to public water supplies. Concentrations of groundwater contaminants exceed
allowable levels under state and federal requirements. The OU D capture zone is adequate for the
I
1
I
I
1
1
RDD1001370C.WP5 (ROD)
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i
contamination within the OU D hot spot, but the OU B/C plume and the OU A plume are not fully
contained by the existing systems.
Table 13 summarizes how Alternatives 1 through 6 comply with the ARARs. All of the alternatives
meet MCLs under the Safe Drinking Water Act. Treated water would achieve discharge requirements
under the Clean Water Act and the State Water Resources Control Board ARARs.
Table 13
Compliance with ARARs'
Alternative
No Action
1
2
3
4
4A
5
6
Containment Option
Meets Safe Drinking Water Act Criteria
(MCLs)
Treatment Option
Meets SMAQMD Rule 202, New Source
Review-With Base Action to Offset
NO, or Reactive Organic Gases (ROGs).
BACT will be applied to meet this
requirement
Meets RCRA Requirements for Storage,
Closure, Corrective Action, Groundwater
Monitoring, and Treatment of Hazardous
Waste
Meets the Location-Specific ARARs for
the Protection of Endangered Species
End-Use Option
Meets SWRCB Resolution 68-16
Meets CWA Discharge Requirements
Meets Numerical and Narrative Water
Quality Objectives in the Water Quality
Control Plan for the Central Valley
Region
Meets the Location-Specific ARARs for
the Protection of Endangered Species
Meets the Fish and Game Requirements
for Alteration of Streambeds
Meets the Underground Injection Control
(UIC) Requirements
/
S
s
s
s
s
N/A
/
/
/
s
/
/"
/"
/
/*
/
^
S
/
S
/*
/"
/"
S
s*
/
J
J
J
S
s
/"
/"
/
/*
/
^
J
S
s
s
s
S
J
S
s
S
S
S
S
S
S*
.S*
S
s>
S
S
S
S
S
s
S
S
J
S
N/A
^
. N/A
S
S
S
s
S>
j
s
J
'Specific citations for the ARARs listed above are provided in Section G.4.
"This ARAR applies only to discharges to Magpie Creek as a contingency.
This ARAR applies to discharges to Magpie Creek and/or injection to the groundwater as a contingency.
Alternatives 1, 2, 3, and 5 would use air stripping with CatOx for offgas control from air stripping
towers. These alternatives are subject to ARARs limiting acceptable NOX discharges and requiring
BACT for offgas control on new emission sources. Currently, McClellan AFB is not permitted to
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BACT for offgas control on new emission sources. Currently, McClellan AFB is not permitted to
discharge additional amounts of NOr These alternatives potentially would meet SMAQMD rules for |_
new source review if McClellan AFB would offset NOX emissions from other sources within the Base
or would purchase NOX credits. r;
Alternatives 4 and 4A would use vapor-phase carbon for offgas control in the new east side treatment
plant, if the new plant is needed. This option is expected to allow slight VOC emissions into the air, m*
but will not create NOX or SOX. This technology has been considered BACT. Removal efficiencies ||
are expected to be in the range of 95 to 99 percent for most compounds in stripper offgas. Methylene-
chloride and vinyl chloride, which have relatively limited extent in groundwater, would not be f?
efficiently controlled by vapor-phase carbon. Generally, offgas concentrations would be low or £
nondetect, with occasional transient peaks. Of all the alternatives that release air emissions.
Alternatives 4 and 4A would most easily comply with ARARs for air emissions because they do not
emit NOX.
f
Alternative 6 does not have air emissions. Hence SMAQMD rules are not applicable.
The existing GWTP is currently operating under substantive requirements for water and air discharge. *~
These discharge limitations were initially given based on water flow rates of 1,000 gpm. Alternatives
2, 3, 4, 5, and 6 require expansion of the existing GWTP to greater than 1,000 gpm. Compliance with P
ARARs would be readily achievable for Alternatives 2, 3, 4, 5, and 6. L.
H.3 Long-Term Effectiveness and Permanence I
This criterion applies to all alternatives. It is applied to each alternative in terms of the risk remaining
at the site after the response objectives have been met; that is, after concentrations of contaminants in f
the target volumes have been reduced to the target concentrations (MCL, 10* cancer risk, or back- |
ground). The primary focus of this evaluation is the extent and effectiveness of controls that may be
required at the conclusion of remedial activities. The effectiveness can be measured by remaining p
residual risk, risk reduction, mass removal, and volume of contaminated groundwater that exist These [
measurements are depicted on Figure 24.
The No-Action Alternative is not effective in the long-term because containment of hot spots in
OUs A, B, and C is not achieved, and contamination may migrate offsite from these areas.
Alternatives 1 and 4A contain and treat contaminants in the MCL target volume. These alternatives K
provide 99.97 percent risk reduction and leave a residual risk of S.lxlO"6. About 20,500 pounds
(9,300 kg) of VOCs would be extracted within the approximately 1.25 billion cubic feet of
contaminated groundwater.
Alternatives 2, 4, 5, and 6 contain and treat contaminants in the 10"6 risk target volume. These .
alternatives provide 99.98 percent risk reduction and leave a residual risk of 1x10"*. About 20,700 !
pounds (9,400 kg) of VOCs would be extracted within the approximately 2.1 billion cubic feet of '
contaminated groundwater.
Alternative 3 contains and treats contaminants in the background target volume. Alternative 3 pro- I
vides 99.99 percent risk reduction and leaves a residual risk of 3.1xlO"7. About 21,000 pounds
(9,545 kg) of VOCs would be extracted within the approximately 4 billion cubic feet of contaminated
groundwater.
RDD1001370C.WP5 OROD) 70 5/2/95
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RESIDUAL RISKS OF TARGET VOLUMES
REDUCTION IN RISK ACROSS TARGET VOLUMES
ROD1631_t8
RD0163I_17
0.00001
0.000001
0.0000001
I
o
BE
100
99.7S
9955.
MCL Risk Background
Target Target Target Volume
Volume Volume AIL 3
AIL 1 Alt. 2, 4,
and 4A 5, and 6
.Target Volume
MASS REMOVAL OF
ALL VOCs ACROSS TARGET VOLUMES
Background Alt 3
1O-6 Cancer Alt 2,4,5, and 6
ICL Alt. 1 and 4A
to zero
-4-
-f-
90 1 2 3 4 5 6 78 9
Target Volume (Billions of Cubic Feet)
CONTAMINATED VOLUME ACROSS TARGET VOLUMES
10000
MCL
Alt. 1
and4A
10^ Cancer
AIL 2, 4. 5.
and 6
Target Volume
Background
Alt 3
MCL
Alt.1
and4A
10< Risk
Alt 2,4,5,
and 6
Target Volume
Background
AILS
RD0175a_39
FIGURE 24
COMPARISON OF
LONG-TERM EFFECTIVENESS OF
THE THREE CONTAINMENT OPTIONS
GROUNDWATER OPERABLE UNIT I ROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
-------
Hence, all the alternatives achieve essentially 100 percent toxicity reduction. Alternatives 1 through 6
are comparable with respect to risk reduction and mass removal, and they leave a residual risk within
EPA's acceptable risk range. The only significant difference between the alternatives is in the volume f:
of contaminated groundwater to be contained and extracted. Mass removal and risk reduction can be I
achieved as well though Alternatives 1 and 4A as through Alternatives 2, 3, 4, 5, and 6, while
containing less volume and requiring less cost. Thus, although all the alternatives provide equal long-
term effectiveness and permanence. Alternatives 1 and 4A provide the best cost-effectiveness. Cost f
will be discussed in Section H.7.
H.4 Reduction in Toxicity, Mobility, and Volume through Treatment |
This comparison criterion applies to all alternatives. It focuses mainly on reduction of contaminant
mass through treatment Alternatives 1 through 6 would equally reduce the toxicity, mobility, and f
volume of contaminants through their treatment methods. I
All the treatment processes are similar since spent carbon is commonly regenerated by desorbing the f
contaminants and oxidizing the resulting airborne gaseous compounds (possibly by thermal or catalytic L
oxidation processes). Hence, there is not a significant difference hi the ultimate destruction of the
contaminants; the difference is where it occurs. F
In the cases of Alternatives 1, 2, 3, and 5, destruction of the contaminants from OU A takes place in
the catalytic oxidation unit of the east side treatment plant In the cases of Alternatives 4, 4A, and 6, f
destruction of the contaminants from OU A takes place at the carbon regeneration facility, which [
potentially could be outside California. For all alternatives, including the No-Action Alternative,
destruction of contaminants from OUs B, C, and D take place in the thermal oxidation unit of the
existing west side treatment plant Given that the ultimate destruction of the contaminants is similar t
for the three treatment options., the alternatives are considered equivalent with respect to reduction of
toxicity, mobility, and volume by treatment -,
H.5 Short-Term Effectiveness
This comparison criterion applies to all alternatives. Alternatives will be evaluated with respect to |
effects on human health and the environment during the installation and operation phases of the
remedial action, until the remedial response objectives are met
The No-Action Alternative is acceptable in that the operation of the existing groundwater treatment k.
plant does not pose a threat to workers, the community, or the environment As a Basewide Ground-
water OU remedial action, it is unacceptable because it does not address various source or uncontained f
contaminated areas and effectively would require an infinite time to clean up these areas. <-
Workers involved with construction of facilities for Alternatives 1 through 6 would not be exposed to {
any greater risks than normally encountered during installation activities. Installation activities would I
not be expected to expose the public to increased risks.
Short-term health risks during implementation could be associated with emissions of acid and oxidant )...
gases from CatOx offgas treatment in Alternatives 1, 2, 3, and 5. Mitigation of these impacts could
involve selection of a remedial action alternative that does not involve the use of CatOx, such as in
Alternatives 4, 4A, and 6, installing emission controls for acid and oxidant gases, or siting the facility
so that air quality impacts fall on uninhabited locations.
RDD10013B11.WP5(IROD) 72 5/2/95
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;
1
i
1
J
I
J
1
The time needed to reach the protection varies with each target volume and is primarily a function of
water flow rate, and initial and final contaminant concentration. Initial concentration and final concen-
tration vary with the target volumes and the specific location of contaminants within a target volume.
Figure 25 estimates the time required to reach the target concentration, and the effect of initial con-
centration and final concentrations by target volume for TCE.
Figure 25 has been developed assuming that the NAPLs are isolated within the target volumes. Times
to cleanup increase as initial concentrations increase, indicating that hot spot areas will take longer
than containment areas. On the other dimension, Figure 25 shows that cleanup times will be longer if
the final concentration is lower, as is the case with the background target volume versus the 1CT6
cancer risk, versus the MCL. It would take approximately 35 to 100 years to extract groundwater to
MCLs in Alternatives 1 and 4A, 65 to 120 years to extract groundwater to 10"6 risk levels in Alterna-
tives 2, 4, 5, and 6, and 100 to 160 years to extract groundwater to background level in Alternative 3.
Hence, Alternatives 1 and 4A would achieve protectiveness first If the DNAPLs were not isolated,
the remediation time could be hundreds of years.
HD01631_4O
0.5 |ig/l (Background)
(AIL 3)
1.7ng/l (10 Risk)
(Alt 2,4,5, and 6)
5^g/l(MCL)(AIUand4A)
FIGURE 25
ESTIMATED TIMES TO CLEANUP
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO, CALIFORNIA
RDDI0013BI 1.WP5 (IROD)
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H.6 Implementability
This comparison criterion applies to all alternatives. It compares alternatives on the basis of technical
and administrative feasibility, as well as availability of materials and services required for
implementation.
Alternatives 1 through 6 are similar in their technical feasibility. All standard treatment technologies
identified for the alternatives are proven in applications at similar hazardous waste sites. Engineering
principles and calculations can be applied to design and specify the types of equipment in the options
chosen with relatively high accuracy. In addition, numerous vendors are available for each compo-
nent, providing excellent availability of most services and materials.
The treatment option in Alternative 6 would be easiest to implement. LGAC does not emit offgas and
therefore does not require permits. Alternatives 4 and 4A would be next easiest to implement because,
although they would be subject to substantive requirements of air discharge permits, VGAC does not
emit NOX and would not require offsets or credit purchases. The treatment options in Alternatives 1,
2, 3, and 5 would be subject to substantive requirements of air discharge permits and, possibly, would
require NOX offsets or NOX credit purchases.
Injection, the end-use option in Alternatives 1, 2, 3, 4, 4A, and 6, would be easier to implement from
an administrative standpoint than providing water to the water districts, the end-use option in
Alternative 5.
Table 14 summarizes the implementability of each alternative, including the No- Action Alternative.
I
Table 14
Implementability
Factor
Alternatives
No Action
1
2
3
4
4A
5
6
Containment Option
Technically Feasible
N/A
S
^
S
^
^
/
S
Treatment Option
Technically Feasible
Vendors, Installation Contractors, and
Operation Resources Locally Available
Does Not Require Air Discharge Permit
Does Not Require NOX Offsets or Credit
Purchases
N/A
N/A
N/A
N/A
^
/
J
J
S
s
/
/
/
J
J
S
/
V
S
S
S
S
End-Use Option
Technically Feasible
N/A
S
S
S
/
S
S
S
I
I
II
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H.7 Cost
3
This comparison criterion applies to all alternatives. It compares alternatives on the basis of
capital costs, both direct and indirect, as well as O&M costs. In addition, the time value of
money is considered in analyzing and comparing alternatives.
The cost of the alternatives is directly related to the size of the target volume to be contained.
Target volume size affects the number of extraction wells, the number of wellhead treatment
units, the length of conveyance pipelines, the size of the treatment units, annual operations
and maintenance costs, and ultimately the length of operation.
Table 15 presents capital costs, O&M costs, net present value, total cash outlay, and cash
outlay after 11 years for each of the alternatives. These costs were performed for an analysis
period of 20 years, using an interest rate of 5 percent
1
Tablets
Cost Summary ($)
McClellan AFB Groundwater Operable Unit
Cost Indicator
Capital Cost
O&MCost-
fiist 5 yean
O&M Cost-
yean 6 through
19
Net Present
Value*
Total Cash
Outlay*
Cash Outlay
after 11 years*
Alternative
1
23,293.518
2.208.000
2,845,000
54.900,000
74,200,000
22.800,000
2
27,221,668
2,610,000
3,558.000
66,100.000
90,100,000
28400,000
3
35,620.337
3335.000
3,993.000
81.000.000
108.200,000
31.900.000
4
26,638,666
2,553,000
3,656.000
66,000,000
90.600.000
29,200,000
4A
23,257.873
2,208,000
3.144,000
57,200.000
78,300,000
25.200.000
S
26,696,499
2,912.000
3.977,000
70,100,000
96,900,000
31.800,000
6
26,536,860
2,553,000
4,699,000
74,000.000
105,100,000
37,600,000
'Assumptions:
Interest Rate = 5 percent
Analysis Period = 20 years
1
Alternatives 1 and 4A are the least costly alternatives because they contain the MO- target volume.
Alternatives 2, 4, 5, and 6 are more costly because they contain the 10"6 risk target volume.
Alternative 3 is the most costly because it contains the background target volume.
Because the time to achieve cleanup is considerably shorter for containing the MCL target volume
than the risk or the background target volumes, as discussed in Section H.5, the total costs of
Alternatives 1 and 4A would be much lower than the other alternatives.
The difference between Alternatives 1 and 4A is the treatment system in the prospective new east side
treatment plant For conditions at McClellan AFB, operating a catalytic oxidation system is less
expensive than operating a granular activated carbon system. Hence, of these two alternatives,
Alternative 1 is the least costly.
RDD10013B11.WP5 (ROD)
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H.8 State Acceptance ,
The FS and the Proposed Plan were reviewed by the U.S. EPA, Cal-EPA/DTSC, and the RWQCB. p
The proposed remedy in those documents recommended Alternative 4: containment of the 10"6 risk I
target volume, treatment with AS/VGAC/LGAC, and an end-use option that included discharge to
McClellan AFB's greywater system, discharge to Magpie Creek, and injection.
Since then, however, McClellan AFB has selected containment of the MCL target volume as the *
containment option, rather than containment of 10"6 risk target volume. In a letter dated September
27, 1994, the RWQCB acknowledged that in light of the fact that mis is an Interim ROD and that ^
cleanup criteria are not being established at this time, the interim remedial action does not need to *
comply with ARARs regarding final cleanup values. Also, the RWQCB does not object to reducing
the volume of water captured to that which contains contaminants exceeding MCLs, but only because §'
this is an Interim ROD. The RWQCB cautioned that, when the Final ROD establishes final cleanup I.
standards for McClellan AFB, the final cleanup level may be more restrictive than MCLs.
ARARs affecting final cleanup standards will be evaluated in 2003, the proposed date of the Final L
ROD. The Final ROD will establish final cleanup standards for McClellan AFB.
Hence, Alternative 4A was added to the list of alternatives in this Interim ROD. Alternative 4A £
includes the same treatment and end-use options as Alternative 4, but selects containment of the MCL
target volume instead of containment of the 10"^ risk target volume. A more thorough discussion of *
this significant change is presented in Section K.1. I
In letters to McClellan AFB and the Department of Toxic Substances Control, dated December 6,
1993, April 18, 1994, October 28, 1994, and February 28, 1995, DHS/ODW stated its concerns l{
regarding use of treated groundwater from McClellan AFB as a source for a domestic water supply.
The State understands that McClellan AFB is continuing to evaluate use of the treated groundwater as _
a possible domestic water supply, and that a final end-use decision will be presented in the Final ROD. |
H.9 Community Acceptance
The Proposed Plan was presented to the community in June 1994. A public comment period was held *
from July 6 to August 15, 1994. During the public comment period, two comment letters were
received. A public meeting was held on July 20, 1994, during which approximately 30 comments |;
were made and questions asked. &
Of the two letters received, one inquired about compensation to the community that experienced f
property value declines as a result of offbase groundwater contamination. The second letter stated «-'-
preference for containment to background levels.
During the public meeting, individuals from the local community made formal comments stating I
preference for containment of the background target volume as the containment option, over
containment of the MCL and 10"6 risk target volumes. The community prefers containment to (
background levels because this option would leave the minimal amount of residual risk and would I
restore the aquifer to its conditions before Base activities began.
Also during the public meeting, one formal comment stated objection to sale of treated water to water [.,
districts for domestic uses. The public is concerned about treatment plant malfunctions and the
RDDI0013B1I.WP5 (IROD) 76 5/2/95
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I
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I
possibility that the local community could ingest contaminated groundwater that was not properly
treated. The public stated preference for water being used in McClellan's greywater system,
discharged into Magpie Creek, or injected into deeper aquifers, as in Alternatives 1, 2, 3, 4, and 6.
No formal comments were made regarding the treatment system.
Several individual questions were asked during the public meeting regarding topics such as surface
runoff in Magpie Creek, sampling and decommissioning of municipal wells, and the future funding for
McClellan AFB.
None of the comments received provided McClellan AFB with the technical justification to select an
option that contained groundwater to 10"6 risk or background levels, over Alternative 4A, which
contains groundwater to MCLs. McClellan AFB remains convinced that Alternative 4A is essentially
as protective of human health and the environment as any of the options that would contain ground-
water to 10"6 risk or background levels. McClellan AFB believes that the actual percent of risk
reduction, remaining risk, and mass removal through containment of the three target volumes are
identical. The only difference is the volume of contaminated groundwater to be contained and, hence,
the substantial cost differences between containing the groundwater in the three different target
volumes.
All community concerns and comments received during the public comment period are addressed in
the Responsiveness Summary (Part fiT) in this Interim ROD.
I. Selected Remedy
1.1 Basis of Selection
The remedy was selected after performing the comparative analysis in Section H. The selected remedy
includes Alternative 4A and a component of End-use Option 1. The selected remedy consists of the
following actions:
Containment: Alternative 4A calls for groundwater contaminated at levels greater than
Maximum Contaminant Levels (MCLs) to be extracted at pumping rates that prevent
its further migration. Containment to prevent offbase plume migration is the highest
priority of this remedy, followed by containment of the hot spots and containment to
prevent vertical downward migration. Eventually, all groundwater will be contained so
that no water above MCLs will leave the Base boundaries. Groundwater extraction
wells will also be located in areas with the highest contaminant concentrations (hot
spots/sources). Aggressive pumping of these wells will rapidly reduce the total
amount of groundwater contamination and its associated risk.
Treatment: Alternative 4A calls for groundwater extracted on the west side of the
Base to be treated at the existing groundwater treatment plant (GWTP). The GWTP
removes the VOCs from the water by air stripping followed by granular activated
carbon polishing. The air stripper offgas is treated by thermal oxidation. The
extraction system may exceed GWTP capacity. An east side treatment plant will be
constructed if necessary; it will use air stripping and granular activated carbon for
water treatment and vapor-phase carbon filters for treating the air stripper offgas.
RDD10013B11.WP5 (IROD) 77 5/2/95
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f
End-Use: Alternative 4A calls for using as much treated water as possible in the
Base's greywater system. Surplus water not used in the greywater conveyance system
would be discharged into Magpie Creek and/or injected into the groundwater. The
selected remedy may also include providing the treated water to neighboring water I
districts, which is a component of End-Use Option 1.
The Air Force believes it is premature at this time to specify any one or any §:
combination of end-uses for the treated water in this Interim ROD. The final decision *
on the end-use will be determined in the Final ROD, depending on the actual quantity
of water that needs an end-use and further discussions with potential recipients of the f*
treated water. fc
All of the end-uses presented above were evaluated in the Feasibility Study. Each f
end-use option included using the existing greywater system to the fullest extent I
possible, which at the time the FS was performed was 200 gpm. McClellan AFB has
proceeded to evaluate and repair the greywater system to increase its capacity and also f"
has worked with industrial users onbase to identify other nonpotable uses for the [
treated groundwater. Several industrial uses are available, and it appears that
continuous use of the treated groundwater at nearly 600 to 800 gpm is possible. At K
McClellan AFB, the greywater system is the nonpotable use system and could be used |
to provide treated groundwater to industrial users. The total flow that may require an
end-use is estimated to be greater than 1,000 gpm, but the actual quantity could be .
substantially higher once the full extent of contamination of the D Zone is identified. I
It is the Air Force's preference at this time to provide all the water to the greywater
system for onbase industrial and nonpotable use. If the greywater system cannot be
upgraded to receive the total quantity of water that will be extracted, then the Air
Force will evaluate providing the water to neighboring water districts, discharging the
water into Magpie Creek, injecting the treated water, and combinations of these F
options. Each of these options complies with ARARs. The Air Force will be seeking *-
the end-use with the least cost and the fewest institutional obstacles. The cost and
feasibility of each option are dependent on the flow rate, which will be determined f
during the course of the interim remedy. These options are discussed in detail in '
Section G.3.
A more detailed discussion of the elements of the Selected Remedy is presented in Section 1.2. The £;
remedy was selected for the following reasons:
f
Although the least stringent of all the containment options, the level of protection to L
human health and the environment provided by the containment option in Alternative
4A meets MCL requirements for drinking water. The treatment and end-use r
components of Alternative 4A offer the same level of protection as the other f
alternatives.
Alternative 4A meets all ARARs without the need to acquire NOX offsets or purchase j
NOX credits.
Alternative 4A provides the same level of long-term effectiveness and permanence as |
the other alternatives, but requires the containment of less volume of groundwater.
RDD10013B11.WP5(IROD) 78 5/2/95
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j
Therefore, groundwater extraction, treatment, and end-use costs are reduced
significantly. Long-term effectiveness and permanence are measured by risk reduction,
residual risk, and mass removal.
The treatment option in Alternative 4A reduces toxicity, mobility, and volume to the
same level as the treatment options in the other alternatives.
Short-term risks as a result of the construction of Alternative 4A are the same as for
the other alternatives. Alternative 4A will not cause short-term health.risks due to
emissions of acid and oxidant gases, as alternatives that use catalytic oxidation to treat
air stripper emissions would.
Alternative 4A is technically and administratively implementable. Some of the other
alternatives are not
Of the seven alternatives, Alternative 4A is the second least costly. Costs presented in
Table 16 for Alternative 4A assume that the end-use option would require four
injection wells. If the greywater system and Magpie Creek have the capacity to
receive all treatment plant discharge, injection will not occur and capital and O&M
costs will be reduced. Likewise, if the treated water is provided to the water districts,
capital and O&M costs are likely to be reduced.
Alternative 4A received state and federal acceptance.
The treatment and end-use options of Alternative 4A have met with community accep-
tance. A Fact .Sheet documenting the selection of the containment option, containment
of the MCL target volume, has been distributed to the community (see Section K. 1 for
a further discussion).
i
Table 16: Range of Costs for Alternative 4A
Cost Indicator
Capital Cost
O&M Cost-first 5 years
O&M Cost-years 6
through 19
Net Present Value*
Cash Outlay after 11 years*
Alternative 4A Without Injection (S)
21,050,431
2JQ8.000
3,091,000
54,600.000
75.400,000
Alternative 4A With Injection (S)
23.257.873
2^08.000
3,144,000
57,200,000
78300.000
'Assumptions:
Interest Rate = 5 percent
Analysis Period = 20 years
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1.2 Elements of the Selected Remedy [
The preferred remedy for the Groundwater OU is Alternative 4A. Providing treated water to p
neighboring water districts, as described in End-Use Option 1, is also being explored as an end-use *
for the treated water. The layout of the main components of the remedy is presented in Figure 26.
This alternative consists of the following actions: -*
L
Groundwater contaminated at levels above MCLs will be extracted at pumping rates
that prevent its further migration. _
Groundwater extraction wells will also be located in areas with the highest contami-
nant concentrations (hot spots/sources).
Operation of existing extraction systems in OU B, OU C, and OU D and the existing *
west side treatment plant will be continued.
If necessary, extracted groundwater will be treated at a new east side treatment plant t
by air stripping followed by further polishing using liquid-phase granular activated
carbon filters until discharge limits are met. Air stripper offgas will also be treated p?
with vapor-phase granular activated carbon filters. I
As much treated water as possible will be reused in the McClellan AFB greywater
system. The remaining water will be discharged to Magpie Creek or injected into the
groundwater beneath the Base. Preference will be to discharge the remaining water to
Magpie Creek. McClellan AFB is continuing to explore with Cal-EPA, U.S. EPA, r
and surrounding communities how best to utilize the treated groundwater, including j
providing it to neighboring water districts.
r
Effluent discharge limits and limits of quantitation for any new units that treat i
groundwater and discharge effluent to surface and/or groundwater are presented in
Table 17. Inorganic discharge limits for injection of treated groundwater will be
established after inorganic background concentrations are determined.
Further characterization and evaluation will be conducted during design of the
remedy: (1) determining appropriate locations for extraction wells and injections
wells, (2) field testing of groundwater injection, (3) determining the need for removal
of metals from extracted groundwater, (4) searching for existing wells that are at risk
of spreading contaminated groundwater, (5) determining aquifer parameters through |
aquifer tests on new extraction wells, and (6) continuing to monitor water levels and '
water quality in monitoring wells.
Treatment of the BW-18 wellhead will continue so long as BW-18 is in operation as a
water supply well.
i
Existing wells at risk of spreading contaminated groundwater will be sealed or
destroyed. Contingency plans will be designed for the appropriate offbase wells
(currently CW-132 and CW-155, but there could be additional wells threatened by OU [
A contamination). BW-18 will be properly decommissioned, and the water supply [
will
RDD10013B11.WP5(IROD) 80 5/5/95
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NOTE:
CONTOURS WILL BE UPDATED AS NEW DATA ARE MADE
AVAILABLE. THESE CONTOURS REPRESENT DATA THAT
WERE PRESENTED IN THE CONCEPTUAL MODEL N THE
GROUNDWATER OU RI/FS (CH2U HILL, JUNE 1994).
THE OPTION OF PROVIDING TREATED WATER TO
NEIGHBORING WATER DISTRICTS WILL ALSO BE
CONSIDERED.
GROUNDWATER INJECTION WELLS
DISCHARGE INTO
MAGPIE CREEK
WEST SIDE TREATMENT PLANT
DISCHARGE INTO
MAGPIE CREEK
GREYWATER STORAGE TANK
EAST SIDE
TREATMENT
PLANT
LEGEND
HOT SPOTS
3000 6000
SCALE IN FEET
9000
MCL TARGET VOLUME
INJECTION PIPELINE
« EXTRACTION RELD PIPELINE
»-- MAGPIE CREEK
ROD 1726.41
FIGURE 26
SCHEMATIC OF THE SELECTED REMEDY
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA f^jOUtUlll _____
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be replaced. Other Base wells that may serve as conduits to contamination will also
be properly decommissioned. This is an ongoing program.
The long-term data acquisition system, a telemetry system for gathering continuous
data remotely, will be designed, if required.
The effectiveness of the Basewide and plume-specific extraction well fields will be
evaluated. Operations and maintenance plans will be prepared.
Phased design and construction efforts will be staged hi a sequence that allows the
worst contamination problems to be addressed first and promotes efficient integration
with existing groundwater extraction and treatment system.
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Table 17
GWTP Effluent Limitations and Limits of Quantitation
McClellan AFB- Groundwater OU
Contaminant
Benzene
Carbon Tetrachloride
Chlorobenzene
Chloroethane
Chloroform
1 ,2-Dichlorobenzene
1 ,3-Dichlorobenzene
1 ,4-Dichlorobenzene
1,1-Dichloroethane
1,2-Dichloroethane
1 , 1 -Dichloroethy lene
t- 1 ,2-Dichloroethy lene
Dichloromethane
Ethylbenzene
1 , 1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
1,1,1 -Trichloroethane
Trichloroethylene
Trichlorofluoromethane
Vinyl Chloride
Xylenes
Total Petroleum Hydrocarbons
pH (pH Units)
Limit of Quantitation*
(ten)
0.12
0.20
0.22
0.50
0.13
0.09
0.19
0.19
0.12
0.08
0.18
0.01
0.10
0.18
0.09
0.25
0.26
0.17
0.37
0.46
0.25
0.11
-
-
Limit of Quantitationb
(«!/«)
0.063
-
0.046
-
0.053
0.252
0.179
0.372
0.067
0.080
0.050
0.043
-
0.035
-
0.076
0.045
-
0.103
'
-
0.061
-
Effluent Limit*
(Mg/1)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
P-5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
50.0
6.5 to 8.5
Note: Receiving waters limitations and effluent limts for SVOCs as specified in the discharge requirements for the
existing GWTP will be met.
"Quantitation limits currently achieved by McClellan AFB using EPA Methods 502.1 and 503.1 for GWTP.
"Reporting limits currently achieved by McClellan AFB using Methods 8010 and 8020, GSAP results.
"Daily maximum value.
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1
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1.3 Priorities for Extent of Contamination Investigation and Containment
All the elements described in Section 1.2 are of high priority because they are either predecessors to
achieving containment, or predecessors to major design decisions or activities that could alleviate
imminent threats.
At this time, the extent of contamination is not completely defined. Because data gaps exist, as
presented in Section E.5, the extent of contamination will be investigated further. In addition,
containment of the ground water plume will occur concurrently with further investigative efforts.
The remedy will be implemented in a phased approach because of the need to resolve uncertainties,
the magnitude of the potential remedy, and resource constraints. Hence, areas requiring more
investigation and areas where containment would be implemented have been prioritized. These
priorities are summarized in Table 18.
Table 18
Investigation and Containment Priorities
Portion of Contaminant Plume
OUs B and C deep plume
OU 8 offbase plume moving
south
OU A southern plume
OU A eastern offbase plume
OUs A, B, and C hot spots
OU G and H plume
OU A onbase western plume
(along runway)
OU C onbase eastern plume
(along runway)
OUs E and F contamination
Low concentration offbase plume
west of OU C
Further remedial action at OU D
plume
Investigation Priority
Highest
X
X
X
X
X
Other
X
X
X
X
X
X
Containment Priority
Highest
X
X
X
X
X
Other
X
X
X
X
X
X
The phasing planned for the investigation of extent of contamination and the containment of ground-
water is discussed in Section 1.4, Implementation Schedule, and shown in Rgure 27.
The OU A and B offbase plumes are high priorities because they are potential threats to offbase water
users. The deep plume beneath OUs B and C is a high priority because the contamination is in the
more permeable materials subject to pumpage by water users. The hot spots are a high priority
because the isolation of the vast majority of contaminant mass can be achieved by containment of the
hot spots.
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NOTE
THE REMEDY MUST BE IMPLEMENTED IN A
PHASED APPROACH. THE PLUMES SHOWN ARE
MCL TARGET AREAS.THIS FIGURE PRESENTS
THE PHASING OF THE EXTENT OF CONTAMINATION
INVESTIGATIONS AND THE PHASING OF CONTAINMENT.
WITH THE EXCEPTION OF THE OU B/C DEEP PLUME. THE
PLUMES PRESENTED HERE ARE IN THE A-ZONE.
GENERALLY, THE EXTENT OF A ZONE CONTAMINATION
IS MORE WIDESPREAD THAN IN THE OTHER ZONES.
PLUMES IN THE B. C. AND D/E ZONES WILL ALSO BE
DELINEATED AND CONTAINED IN A PHASED APPROACH.
OU D EXPANSION
(IF NECESSARY)
OU B/C ONBASE
CONTAMINATION
OUE, F. G.ANDH
ONBASE CONTAMINATION
I
OU A ONBASE
CONTAMINATION*
OUC
HOT SPOTS
OUB
HOT SPOT:
OUB/C
DEEP PLUME
OU B OFFBASE PLUME
0 3000 6000
SCALE IN FEET
LEGEND
HOT SPOTS/HIGH PRIORITY PROJECTS
HIGH PRIORITY PROJECTS .
LOWER PRIORITY PROJECTS
RODJ631.28
SPOTS
PLUME TO THE EAST
OU A SOUTHERN PLUME
HEADING OFFBASE
9000
FIGURE 27
EXTENT OF CONTAMINATION
INVESTIGATION AND CONTAINMENT
OF PLUME PHASING
GROUNDWATER OPERABLE UNIT IROD
McCLELLAN AIR FORCE BASE
SACRAMENTO. CALIFORNIA
CfOf H/U
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,1 Onbase contamination is a lower priority because threat to the public or onbase workers does not exist.
The offbase contamination west of OU C is a lower priority because the Air Fofce has replaced
-? individual water wells with potable supply, thereby removing the threat to the public. In addition, the
| concentrations are low and much farther from water supply wells than the OU B plume.
i 1.4 Implementation Schedule
The preferred alternative will be implemented in three phases:
I Phase 1 will reduce data gaps and begin containment of the high-priority areas.
Phase 2 will further define the plume boundaries, complete containment of the high-
J priority areas, and begin containment of lower-priority areas.
Phase 3, if necessary, will complete the containment of the contaminated groundwater.
1
3 When groundwater extraction rates and concentrations are sufficiently defined, con-
struction will begin on the major water pipelines and, if needed, the east side treatment
| plant Each phase is estimated to take up to 2 years to complete.
J. Statutory Determinations
» The applicability and compliance of the following statuatory determinations are discussed in this
section: . .
J Protectiveness
| Applicable or Relevant and Appropriate Requirements
Cost-Effectiveness
j
Use of Permanent Solutions, Alternative Treatment, or Resource Recovery
Technologies
j Preference for Treatment as a Principle Element
> J.1 Protectiveness
This interim action is protective of human health and the environment in the short term and is
i intended to provide adequate protection until the Final Basewide ROD is signed. Protection is
| achieved at the Base and in the aquifers underlying the Base in the following ways:
, Initial protection to human health will be achieved by preventing offbase contaminant
{ migration to private and municipal production wells.
Containment of groundwater within the MCL target volume by extraction will protect
humans from exposure to contamination above acceptable risk levels.
RDD10013B11.WP5 (IROD) 85 5/2/95
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I
Extraction of contaminated groundwater from Monitoring Zones A, B, and C will halt
the downward migration of contaminants and protect the deeper aquifers from
degradation. _
Decommissioning Base wells that are believed to be vertical migration conduits, such *;
as BW-18, will protect the deeper aquifers from contamination migration from the
shallower aquifers. BW-18 also increases the migration rate of contaminants from the 1
A and B Zones into the lower zones. *
Treatment of VOC-contaminated groundwater to discharge limits prior to discharge f-
protects the environment from degradation. Discharge limits are discussed in Section E
1.2.
r
As much treated water as possible will be reused in the Base greywater system. Treat- ti
ment of VOC-contaminated groundwater to discharge limits protects humans from
inhalation exposure. «!
Granular activated carbon used in the standard treatment technology will be
regenerated at an offbase facility, removing any local health risks from the extracted £
VOCs. [f
J.2 Applicable or Relevant and Appropriate Requirements f
The selected remedy complies with federal and state ARARs for this limited scope action.
J.3 Cost-Effectiveness L
The remedy is cost-effective because adequate protection is achieved for the estimated cost of perfor-
mance. The selected remedy is to control and treat groundwater within the MCL target volume. The j|
analysis contained in the FS and summarized in Section I, Selected Remedy, of this Interim ROD
demonstrates that additional remedial action and cost associated with containing and treating the water
within the 10"6 risk volume or the background target volume will not achieve a significantly greater f
reduction in risk. It would result, however, in a dramatically higher cost because greater groundwater *
volumes would be extracted and treated.
J.4 Use of Permanent Solutions, Alternative Treatment, or Resource Recovery *
Technologies
Although this interim action is not intended to fully address the statutory mandate for permanence and *~
treatment, this interim action of containment of the MCL target volume and treatment of groundwater
to less than discharge limits uses treatment and thus is in furtherance of that statutory mandate. The f
selected remedy represents the best balance of tradeoffs among alternatives with respect.to pertinent £
criteria, given the limited scope of the action. Subsequent actions are planned to address fully the
threats posed by the conditions in this OU. f
J.5 Preference for Treatment as a Principle Element
)
Because this action does not constitute the final remedy of the Groundwater OU, the statutory i,
preference for remedies that employ treatment and that reduce toxicity, mobility, or volume as a
RDD10013B11.WP50ROD) 86 5/2/95
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1
principal element, although partially addressed in this remedy, will be addressed by the final response
action. Because this remedy will result in hazardous substances remaining onsite above health-based
levels, a review will be conducted to provide adequate protection of human health and the environment
within 5 years after commencement of the remedial action. Because this is an interim action ROD,
review of this site and this remedy will be ongoing as remedial alternatives for the final remedy are
developed.
K. Documentation of Significant Changes
The Proposed Plan for the Groundwater OU was released for public comment from July 6 to
August 15, 1994. The Proposed Plan identified Alternative 4, which consists of the following
components:
Groundwater contaminated at levels greater than 10"6 cancer risk would be extracted at
pumping rates to prevent its further migran'oa Aggressive pumping would also occur
at areas with highest contaminant concentrations.
. Extracted groundwater would be treated by air stripping followed by further cleaning
j using granular activated carbon filters until discharge limits are met
Up to 200 gpm of treated water would be reused in the McClellan AFB greywater
J system. The remaining water would be discharged to Magpie Creek and/or injected
« into the groundwater beneath McClellan AFB.
The containment and end-use components of the selected remedy presented in this Interim ROD differ
J from those of the selected alternative presented in the Proposed Plan. The differences and the reasons
for these significant changes are discussed in the following paragraphs.
l K.1 Changes to the Containment Component of the Selected Remedy
The preferred containment component of the selected remedy, as presented in the Proposed Plan, has
changed from containment of groundwater at contaminant levels greater than 10"6 cancer risk. During
the public comment period for the Proposed Plan, however, McClellan AFB, in consultation with the
agencies, decided to choose containment of the MCL target volume as the containment component of
the selected remedy. Containment of the MCL target volume was selected over containment of the 10"
6 cancer risk target volume for the following reasons:
Risks remaining to the public are virtually the same after containing the groundwater
contamination either to the MCL target volume or to the 10"6 risk target volume.
Use of the MCL target volume instead of the risk target volume reduces the amount of
groundwater to be pumped. The number of wells and pipelines and the treatment
system capacity are therefore also reduced, resulting in lower capital costs of as much
as $3.3 million for the interim remedy.
Time to achieve containment is reduced. Because the volume of aquifer to be con-
tained is reduced, the number of extraction wells is reduced, and the implementation
schedule could be shortened by as many as 3 years.
RDD10013B11.WP5 (ROD) 87 5/2/95
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Alternative 4A was included in this Interim ROD to evaluate containment and extraction of the MCL
target volume as the containment option, keeping the same treatment and end-use as Alternative 4.
The decision to contain the MCL target volume was made in conjunction with the U.S. Environmental
Protection Agency and Cal-EPA (DTSC and RWQCB).
Table 19 is a comparison of the decision factors-volume, cost, time, and risk-for containment of the
MCL and the risk target volumes. This change in remedy was summarized in a Fact Sheet that was
distributed to the public in December 1994. A new public comment period was not held because the
MCL containment option was thoroughly examined in the FS and presented in the Proposed Plan. The
combination of the MCL containment option with the other two preferred options to form the new
alternative is a logical outgrowth of the final review of the previously released documents, response to
comments, and preparation of this Interim ROD.
Table 19
Comparison of Decision Factors for the MCL and Risk Target Volumes
Decision Factors
Volume of Aquifer
(including soil matrix
and pore space)
Cost of the Remedy
Time to Implement
Containment
Remaining Risk after
Containment
Containment of the
MCL Target Volume
(Alternative 4A)
1.24 billion ft3
.Capital: $23.3 million
Net Present Value3:
$57.2 million
4 years
3.1 x lO^XaS-in-
1,000,000 additional
risk)
Containment of the
Risk Target Volume
(Alternative 4)
2.06 billion ft3
Capital: $26.6 million
Net Present Value":
$66.0 million
7 years
1 x IV6 (a 1-in-
1,000,000 additional
risk)
Result of Changing to
MCL Target Volume
Reduces volume of
aquifer to be contained
by 0.82 billion ft3 (2.91
billion gallons)
Saves $3.3 million
Saves $8.8 million
Saves up to 3 years
Remaining risk will
increase slightly but still
falls within the accept-
able National Contin-
gency Plan rangeb
"Net Present Value assumes an interest rate of 5 percent and an analysis period of 20 years.
bThe National Contingency Plan acceptable risk range that remedial actions are expected to achieve is 10"4 to
1CT6, or 1 in 10,000 to 1 in 1,000,000.
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K.2 Changes to the End-Use Component of the Selected Remedy
The two end-use options presented in the Proposed Plan have been modified. In the Proposed Plan,
both end-use options include reusing the first 200 gpm of treated groundwater in McClellan AFB's
greywater system. In this Interim ROD, a limit has not been placed on the quantity of treated water to
be reused in the greywater system.
During the FS, it was determined that McClellan AFB's greywater system had a need for only 200
gpm. Since the Proposed Plan, investigations and testing of the greywater system have suggested that
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i it may be able to reuse significantly more than 200 gpm of treated water. Hence, under both end-use
options, it has been stated in this Interim ROD that as much treated groundwater as possible would be
-n reused in the greywater system. The remaining treated water would be provided to the water districts,
as in End-use Option 1, or discharged to Magpie Pie Creek and/or injected, as in End-Use Option 2.
J)
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Part III: Responsiveness Summary
A. Introduction
This section presents information about community preferences and public concerns regarding the
remedial alternatives and the preferred alternative for the groundwater beneath McClellan AFB,
referred to as the Groundwater OU site. Opportunities for community involvement in the groundwater
remedial action at the Groundwater OU site consisted of a public comment period on the site-related
documents held from July 6 to August 15, 1994. On July 20, 1994, a public meeting was held at Bell
Avenue School in Rio Linda to present the McClellan AFB proposed cleanup plan for the site contam-
ination. The meeting format consisted of a formal presentation by McClellan AFB and a formal ques-
tion and answer period. The proceedings of the meeting were recorded by a court reporter and the
transcript became part of the Administrative Record for the Groundwater OU site. Two formal
comments were also received in writing during the public comment period. Approximately 30 oral
comments were made or questions asked during the public meeting. Responses to oral comments that
were not answered during the public meeting and responses to the two written comments are presented
below. The transcript from the public meeting is part of the Administrative Record.
After the public comment period, McClellan AFB in December 1994 distributed to the public a Fact
Sheet that explained the change in the containment goal (from 10"6 risk to MCLs). As explained in
greater detail in Section K.I, Changes to the Containment Component of the Selected Remedy, a new
public comment period was not held because the MCL containment option was thoroughly examined
in the FS and presented in the Proposed Plan.
Historic and current concerns of the public primarily have focused on the potential effects of
contaminated groundwater on long-term health and residential property values. The community has
also been concerned with aesthetic effects on and contamination of Magpie Creek.
B. Oral Comments from the Public Meeting
Comment: "...I'm concerned that the stuff off-base that's originating from McClellan Air Force
Base...that it would be cleaned up. And so in fact I'd like it to be cleaned up to the
background levels instead of 10 to the minus 6 because I'd like to see the water clean
like it was before all this began."
"...I would like to state for the record that I prefer the background levels rather than 10
to the minus 6."
"...Why not have natural background levels as the preferred cleanup alternative and
aim for a higher and achievable standard, which I favor?"
Response: It has been shown in this Interim ROD that containing and extracting the groundwater
to background levels would result in only incremental risk reductions in comparison to
containing and extracting groundwater MCLs, yet would require the pumpage of signi-
ficantly higher quantities of water. This would result in significantly higher costs. In
RDD10013B11.WP5 (ROD) 91 5/2/95
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additioa the mass of VOCs that would be removed is almost equal in the background,
risk, and MCL target volumes. The background target volume is more than three
times larger than the MCL target volume and nearly two times larger than the risk
target volume.
Comment: "...what's the cost per gallon for some of these processes?"
Response: At this time it is not possible to predict the gallons that would need to be extracted
for each of the alternatives or the absolute costs for the duration of operations. .
Comment: "...And then the emissions from the air stripper is [sic] just vented into the air, or do
you collect that?"
Response: The offgas emissions from the air stripper are passed though a vapor phase granular
activated carbon unit to collect the VOCs that were removed from the groundwater
during the air stripping process. Offgas emissions from the air stripper are not vented
into the air.
Comment: "...I don't think it's a good idea to use water [for domestic uses] that's contaminated
and being drawn up and cleaned just in case there is a slight remote possibility... that
for some reason the equipment will go... awry... and., people could be possibly drink-
ing contaminated water. I don't think that this would ever happen, but just the same, I
feel safer with it going to industrial uses such as cooling towers, or getting re-circu-
lated through the shops or being injected into the underground aquifer or discharged to
Magpie Creek. These are alternatives that I think are viable, and we don't have to
worry about somebody drinking contaminated water. Even if the chance is slight and
minute, it's still slight and minute...."
Response: As mentioned in Part II of this document, DHS/ODW also has concerns about sale of
treated water to the water districts. That was the primary reason End-Use Option 1,
providing to the water districts, was not selected for the preferred alternative.
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C. Written Comments
Comment: "... has. there been any consideration given to compensation or the purchase of affected
properties by the Air Force?"
Response: Compensation to property owners is not part of the groundwater remedial action.
Comment: "We believe the cleanup and containment of contamination in the groundwater on and
around McClellan AFB should be to background levels not to risk levels."
Response: As stated previously, it has been shown in this Interim ROD that containing and
extracting the groundwater to background levels would result in only incremental risk
reductions in comparison to containing and extracting groundwater to MCLs, yet
would require the pumpage of significantly higher quantities of water. This would
result in higher costs. In addition, the mass of VOCs that would be removed is almost
equal in the background, risk, and MCL target volumes. The background target
volume is more than three times larger than the MCL target volume and nearly two
times larger than the risk target volume.
L
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Part IV: Works Cited
1
California Air Resources Board. 1984. California Surface Wind Climatology.
i
j CH2MHILL. 1992. RCRA Part B Application.
CH2M HILL. 1994. Ground-water Operable Unit Remedial Investigation/Feasibility Study. June.
McClellan Air Force Base. 1994. Management Action Plan. December.
| National Oceanic and Atmospheric Administration. 1989. Climatological Data Summary for
'*' California Vol. 93, No. 13.
Jj Radian Corporation. 1989. Engineering Evaluation/Cost Analysis-Environmental Assessment.
:-' Prepared for McClellan AFB, Sacramento, California.
j Radian Corporation. 1990. Preliminary Groundwater Operable Unit Remedial Investigation
* (Hyarogeologic Assessment) Sampling and Analysis Plan. February.
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