United States Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R03-91/125
September 1991
Superfund
Record of Decision
USA Aberdeen - Edgewood,
MD
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50272-101
REPORT DOCUMENTATION
PAGE
1. REPORT NO.
EPA/ROD/R03-91/125
1 Recipient • AccMsion Ho.
4. TNaandSubMa
SUPERFUND RECORD OF DECISION
USA Aberdeen - Edgewood, MD
First Remedial Action
5. Report Date
09/27/91
7. Aidhor(*)
8. Performing OrganizHlon Rapt No.
». Partanrtng Orgalntiatfon Name and Addreaa
10. Pro|ecttTaak/Work IMt No.
11. Contncl(C) or GranqG) No.
(C)
12. Sponsoring Organization Name and Addraaa
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
13. Typo at Report a Parted Covered
800/000
14.
IS. Su
lyNole
18. Aba*aet(Umrt200woRla)
The 17,000-acre USA Aberdeen - Edgewood site is a military ordnance installation in
Edgewood, Maryland. The 4.5-acre Old 0-Field site, which is the focus of this Record
of Decision (ROD), is a fenced hazardous waste and ordnance disposal area located
within the lower half of the Gunpowder Neck in the Edgewood area of the Aberdeen
Proving Ground. Land use in the area consists of military testing ranges, with a
mixture of industrial, military, and civilian residential areas. The site overlies
two aquifers that drain into Watson Creek and the Gunpowder River, which border the
site. From 1941 to 1952, chemical-warfare agents including mustard, lewisite,
adamsite, white phosphorus, munitions, contaminated equipment, and miscellaneous
hazardous waste were disposed of in 35 onsite unlined pits and trenches. Studies
have shown that chemicals buried within the pits have impacted ground water and also
interconnecting surface water in Watson Creek. From 1949 to the mid-1970's, several
decontamination and clean-up operations were conducted as a result of munitions
explosions, which spread mustard into the surrounding soil, air, Watson Creek, and
Gunpowder River. These operations included the application of 1,000 barrels of
decontaminating agent non-corrosive (DANC) containing chlorinated hydrocarbons;
(See Attached Page)
17. Document Analyala a. Deecrtptora
Record of Decision - USA Aberdeen - Edgewood, MD
First Remedial Action
Contaminated Medium: gw
Key Contaminants: VOCs (benzene, PCE, TCE, toluene), metals (arsenic)
c. COSATI FMd/Group
ia AvailabUty Statamant
19. Stcurity CUaa (Thia Report)
None
20. Sacurity CUaa (Thla Paga)
None
21. No.o
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EPA/ROD/R03-91/125
USA Aberdeen - Edgewood, MD
First Remedial Action
Abstract (Continued)
soaking the field with several hundred gallons of fuel oil and setting the field ablaze;
dispersing lime into the surrounding trees to further reduce the amount of mustard
present; and using supertropical bleach, lime, and sodium hydroxide to destroy chemical
agents. Evidence shows that these decontamination efforts have contaminated the ground
water with chlorinated hydrocarbons. Subsequent remediation activities were limited to
removing and securing ordnance items on the surface. The site has been divided into
three operable units (OUs) for remediation. This ROD provides an interim remedy for
contaminated ground water and its effect on surface water, as OU1. Future RODs will
address contaminated onsite soil and surf-ace water. The primary contaminants of concern
affecting the ground water are VOCs including benzene, PCE, TCE, and toluene; and metals
including arsenic.
The selected remedial action for this interim remedy includes installing a downgradient
extraction well network; pumping and onsite treatment of contaminated ground water using
chemical precipitation, followed by ultraviolet-oxidation; monitoring the treated
effluent, then discharging the effluent onsite to the Gunpowder River; and disposing of
the contaminated chemical precipitation filter cake sludge generated during the
treatment process offsite. The estimated present worth cost for this remedial action is
$9,120,000, which includes an estimated annual O&M cost of $466,650 for 30 years.
PERFORMANCE STANDARDS OR GOALS: Chemical-specific ground water clean-up goals are based
on CWA Ambient Water Quality Criteria, and SDWA MCLs and proposed MCLs, and include
benzene 5 ug/1 (MCL), PCE 5 ug/1 (MCL), TCE 5 ug/1 (MCL), toluene 40 ug/1 (PMCLs), and
arsenic 50 ug/1 (MCL).
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INTERIM ACTION
RECORD OF DECISION
OLD O-FIELD SITE
ABERDEEN PROVING GROUND, MARYLAND
/r" J cf -f ^ o o d.
FINAL REPORT
SEPTEMBER 1991
Prepared By:
UNITED STATES DEPARTMENT OF THE ARMY
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DBCXA1UXION FOR TBB XBTBRXJf ACTXC* KBCORD OF DSCTSIOV
old o-rield Site
Edgewood Area, Aberdeen Proving Ground, Maryland
This decision document presents the selected interim remedial action for
operable unit on*/ which concerns the contaminated groundwater located in the
water-table and upper confined aquifers beneath the Old O-Pield Site in the
Edgewood Area of Aberdeen Proving Ground, Maryland, which was chosen in
accordance with the Comprehensive Environmental Response, Compensation, and
Liability Act, a* amended by the superfund Amendments and Reautborization Act,
and, to the extent practicable, the national oil and Hazardous gubstancea
Pollution contingency Plan. This decision is based oa the administrative
record for the Old O-Pield Site.
The State of Maryland concurs with the selected interim action remedy.
Actual or threatened releases of hazardous substances from the Old o~
Field site, if not addressed by implementing the interim response action
•elected in this Record of Decision, may present an imminent and substantial
endangeraent to public welfare, or the environment. This finding of imminent
and substantial endangerment and the remedy selected herein are not baaed on
any presently observed threat to public health at or from the site.
This operable unit, the first of three operable units for the Site,
addresses contaminated groundwater. The second operable unit will address
contamination of the soils and disposed materials in the landfill, and the
third operable unit will address contamination of adjacent surface waters and
sediments in Watson Creek. This interim response action for operable Unit One
addresses contaminated groundwater and its discharge to interconnecting
surface water.
The major components of the selected interim action are as follows t
contaminated groundwater plum containment through downgradient
* extraction using newly installed wellst
on-site treatment of extracted groundwater using chemical
• precipitation for inorganics rraoval followed by ultraviolet-
oxidation for organic* destruction; and
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Discharge of the treated groundwater,
monitoring, to the Gunpowder River.
Statutory Determinations
following compliance
This interim action is protective of human health and the environment,
complies with federal and State applicable or relevant and appropriate
requirements for this limited-scope action, and is cost-effective. Although this
interim action is not intended to fully address the statutory mandate for
permanence and treatment to the maximum extent practicable, this interim action
utilizes treatment and thus is in furtherance of that statutory mandate. Because
this action does not constitute the final remedy for the Site, the statutory
preference for remedies that employ treatment that reduces toxicity, mobility,
or volume as a principal element, although partially addressed in this remedy,
will be addressed by the final response action. Subsequent actions are planned
to address fully the threats posed by the conditions at this Site. Because this
is an interim action Record of Decision, review of this Site and of this remedy
will be continuing as the U.S. Army and the U.S. Environmental Protection Agency
continue to develop final remedial alternatives for the Site. Because the remedy
will result in hazardous waste remaining on-site, a review will be conducted to
ensure that the remedy continues to provide adequate protection of human health
and the environment within five years after commencement of the remedial action.
Ronald V. Hite
Brigadier General, U.S. Army
Commanding
Aberdeen Proving Ground
Date
.ewis D. walker
Deputy Assistant Secretary of the
Army for Environmental Safety,
and Occupational Health
Department of the Army
Date
-9 /
Edwin B.Trickson
Regional Administrator
U.S. Environmental Protection Agency, Region III
Date
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INTERIM ACTION, OLD 0-FIELD SITE
RECORD OF DECISION
DECISION SUMMARY
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TABLE OF CONTENTS
Section Page
1.0 INTRODUCTION 1
1.1 Site Location and Description 1
1.2 Site History and Enforcement Activities 4
1.3 Scope and Role of Operable Unit/Response Action
Within Site Strategy 6
1.4 Community Participation 7
2.0 SITE CHARACTERISTICS 8
2.1 Hydrogeologic Setting 8
2.2 Contamination Assessment Summary 8
2.3 Risk Assessment Summary 11
2.3.1 Human Health Risk Assessment Summary 18
2.3.2 Ecological Assessment Summary 19
2.3.3 Conclusions of the Risk Assessment 20
.3.0 DESCRIPTION OF REMEDIAL ALTERNATIVES 22
3.1 Cleanup Criteria 22
3.2 Groundwater Extraction/Discharge Alternatives 30
3.2.1 Common Elements 33
3.2.2 Alternative E-l - Downgradient Extraction with
Discharge to Surface Water 35
3.2.3 Alternative E-4 - Circumferential Extraction with
Capping and Discharge to Surface Water 35
3.2.4 Alternative E-5 - Circumferential Extraction with
Spray Irrigation/Source Flushing 36
3.2.5 Alternative E-6 - Circumferential Extraction with
Downgradient Re-injection 36
3.3 Groundwater Treatment Alternatives 37
3.3.1 Common Elements 37
3.3.2 Alternative T-l - No Action 38
3.3.3 Alternative T-2 - Minimal Action 38
3.3.4 Alternative T-3 - Chemical Precipitation/
Air Stripping/Carbon Adsorption (liquid phase) 38
3.3.5 Alternative T-4 - Chemical Precipitation/
Ultraviolet-Oxidation 39
3.3.6 Alternative T-5 - Chemical Precipitation/Activated
Sludge Biological Treatment/ Carbon Adsorption 39
3.3.7 Alternative T-6 - Chemical Precipitation/Powdered
Activated Carbon Treatment (PACT) 40
4.0 COMPARATIVE ANALYSIS OF REMEDIAL ALTERNATIVES 41
4.1 Evaluation Criteria 41
4.2 Evaluation of Groundwater Extraction/Discharge Alternatives . . 42
4.2.1 Aquifer Pumping Tests 42
4.2.2 Groundwater Extraction/Discharge
Alternatives Evaluation . 44
4.3 Evaluation of Groundwater Treatment Alternatives 50
4.3.1 Groundwater Treatability Studies ..... 50
4.3.2 Groundwater Treatment Alternatives Evaluation 63
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TABLE OF CONTENTS
(Continued)
Section
5.0 SELECTED REMEDIAL ALTERNATIVE 70
5.1 Alternative Description 70
5.2 Compliance with Statutory Requirements 71
5.2.1 Protection of Human Health and the Environment 71
5.2.2 Compliance with ARARs 71
5.2.3 Cost Effectiveness 71
5.2.4 Utilization of Permanent Solutions and Alternative
Treatment Technologies (or Resource Recovery
Technologies) to the Maximum Extent Practicable 71
5.2.5 Preference for Treatment as a Principal Element 71
5.3 Performance Monitoring Program 72
5.3.1 Groundwater Containment Monitoring 72
5.3.2 Effluent Monitoring Program 72
5.4 Significant Changes from the Proposed Plan 73
APPENDICES
Appendix
Appendix A Responsiveness Summary
Page
A-l
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LIST OF FIGURES
Page
1 Location of Old-0-Field 2
2 Schematic of Old 0-Field Area 3
3 Old 0-Field Hydrogeological Cross-Section A-A' . . 9
4 Locations of Existing Wells and Hydrogeologic Cross-Section 10
5 Old 0-Field Estimated Contaminant Plume 13
6 Optimized Extraction Well Systems 34
LIST OF TABLES
Table Page
1 Comparison of Maximum Groundwater Chemical
Concentrations Detected with Water Quality
Criteria and Maximum Contaminant Levels 12
2 Comparison of Maximum Surface Water Chemical
Concentrations Detected with Water Quality
Criteria and Maximum Contaminant Levels . . 14
3 Comparison of Maximum Bottom Sediment Chemical Concentrations
Detected with Water Quality Criteria and Maximum Contaminant Levels . 16
4 Summary of Technology Identification and Screening 23
5 First-Step Screening of Potentially Applicable
Groundwater Extraction and Discharge Alternatives 25
6 Second-Step Screening of Groundwater
Extraction and Discharge Alternatives 28
7 Site-Specific Applicable or Relevant
and Appropriate Requirements (ARARS) (ng/L) .• 31
8 Detailed Evaluation Summary for Groundwater
Extraction/Discharge Alternatives 45
9 Removal of Contaminants by Activated Sludge, Activated Sludge
Plus Two Granular Carbon Columns, and the PACT Process 51
10 Chemical Precipitation Bench-Scale TreatabllUy Data (yg/L) 53
11 Chemical Precipitation Pilot-Scale TreatabilUy Data (jig/L) 54
12 Air Stripping/Carbon Adsorption
Bench-Scale Treatabllity Data (jig/L) 55
13 Air Stripping/Carbon Adsorption
Pilot-Scale Treatabllity Data (jig/L) 57
14 Ultraviolet-Oxidation Bench-Scale Treatability Data (jig/L) 58
15 Ultraviolet-Oxidation Pilot-Scale Treatability Data (|ig/L) 60
16 Activated Sludge Bench-Scale Treatability Data (ng/L) 61
17 TOC Results for Activated Sludge 62
18 Detailed Evaluation Summary for
Groundwater Treatment Alternatives 64
A-l Public Meeting Panel of Experts • • • • A'2
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1.0 INTRODUCTION
The Old 0-Field Site (the Site), along with the entire Edgewood Area of
Aberdeen Proving Ground (APG), was listed on the National Priorities List (NPL)
pursuant to the Comprehensive Environmental Response, Compensation and Liability
Act, 42 USC §9601 et seq. (CERCLA) on February 21, 1990, due to its history of
on-site hazardous waste and ordnance disposal. Old 0-Field has been the subject
of numerous investigations which identified inorganic and organic contamination
in the soils, groundwater, and interconnected surface water in the vicinity of
the Site. This Interim Action Record of Decision (ROD) addresses only one
operable unit (OU One) for the Site which will address groundwater contamination
at Old 0-Field and the related effects on surface water.
A hydrogeologic assessment (HGA) and preliminary risk assessment were
conducted to define the nature and extent of contamination in all the affected
media, and associated risks to human health and the environment. A focused
feasibility study (FFS) was then conducted to identify potential site-specific
groundwater remediation alternatives. Following the FFS, aquifer pumping tests
and groundwater treatability studies were performed to select a groundwater
remedial alternative which was presented to the public in the Proposed Plan. The
selected groundwater remedial alternative consists of a preferred
extraction/discharge alternative combined with a preferred treatment alternative.
This ROD summarizes the alternative selection process and presents the
selected remedy for groundwater contamination at Old 0-Field. The role of the
public in the remedy selection process is also discussed. The selected remedy
is considered an interim action because the disposed materials (i.e., the
contamination source) remain at Old 0-Field, and a Remedial Investigation (RI),
Feasibility Study (FS), and Risk Assessment are not complete at this time. A
final ROD for the Old 0-Field Site will be issued at the conclusion of the RI/FS.
1.1 SITE LOCATION AND DESCRIPTION
Old 0-Field is a 4.5-acre fenced hazardous waste and ordnance disposal site
located on the lower half of the Gunpowder Neck in the Edgewood area of Aberdeen
Proving Ground, Maryland. As illustrated in Figure 1, the Site is located in
eastern Maryland in close proximity to the Chesapeake Bay. Old 0-Field, as
illustrated in Figure 2, is bordered by surface water on three sides: Watson
Creek to the north and east, and the Gunpowder River to the west. The Gunpowder
River may be considered part of the Chesapeake Bay estuarine system. Watson
Creek, better described as a pond, has a 2,180-acre watershed and discharges into
the Gunpowder River at a man-made culvert. Old 0-Field is situated on a local
topographic high with a 4 to 6 foot relief across the field.
Access to the southern part of the Gunpowder Neck, including Old 0-Field,
is controlled by Watson Creek Road, which runs north-south along the west side
of the field. The field is located within a secure section of the Edgewood Area
where access is restricted and entry is granted only after credentials have been
checked by a security guard. In addition, the area is patrolled routinely by
guards in vehicles and boats. The field is surrounded by a chain-link/barbed-
wire fence with hazardous waste and toxic chemical agent warning signs. The Site
is mostly overgrown with scrub vegetation and small trees, with several partially
open disposal pits visible within the fenced area.
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FIGURE 1
LOCATION OF OLD O-FIELD
PENNSYLVANIA
N
Boundary or Ab»rd««n
Proving Ground
SOURCE U.S.Q.S., I988
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FIGURE 2
SCHEMATIC OF OLD O-FIELD AREA
INCOMING TIDAL CYCLES
OUTGOING TIDAL CYCLES
SOURCE U.S.G.S., 1988
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The majority of the land surrounding Old 0-Field is currently being used
as testing ranges. Test operations south of the field include those of the
Combat Systems Test Activity, (CSTA) which is a major mission of the U.S. Army
Test and Evaluation Command. Within Army property, 3.5 miles north of the field,
is the industrial sector of Edgewood Area, which includes the Chemical Research,
Development and Engineering Center as well as a number of office buildings.
Edgewood Area also includes a number of troop barracks and an on-post family
housing area containing approximately 1700 residents. The town of Edgewood
(population approximately 20,000) is located within 5 miles of the field. The
closest off-post housing development is located in Graces Quarters which is
approximately 2.5 miles due west of the field across the Gunpowder River.
1.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES
During the 1940s and early 1950s, 35 unlined pits and trenches were dug
within Old 0-Field and used for the disposal of chemical-warfare agents (e.g.,
mustard, lewisite, adamsite, white phosphorus), munitions, contaminated
equipment, and miscellaneous hazardous waste. The maximum depth of the trenches
is at least 12 feet, and almost aH of the trenches are covered with soil. The
presence of chemical-agent wastes, munitions, and other hazardous materials
within the landfill has impacted the groundwater at Old 0-Field and the
interconnecting surface water in Watson Creek.
Several decontamination and cleanup operations have been performed at Old
0-Field beginning with surface sweeps and demilitarization efforts in 1949 and
continuing through the early 1970s. The most notable of these was a cleanup
operation carried out in December 1949 which involved application of 1,000
barrels of decontaminating agent non-corrosive (DANC) to the field in an attempt
to detoxify mustard that had been scattered over the area by several spontaneous
detonations. DANC contains 5 percent l,3-dichloro-5,5-dimethylhydantoin (the
active decontaminating agent) in 95 percent 1,1,2,2-tetrachloroethane.
Tetrachloroethane and its degradation products have been identified at elevated
levels in groundwater at Old 0-Field; thus, it appears likely that this effort
directed at chemical-warfare agent decontamination actually resulted in
groundwater contamination with chlorinated hydrocarbon compounds.
Another major cleanup effort was undertaken in 1953 when the field was
soaked with hundreds of gallons of fuel oil, ignited, and allowed to burn for
days. Lime (calcium hydroxide) was dispersed onto surrounding trees through the
use of 2,4,6-trinitrotoluene (TNT) in response to explosions that scattered
mustard throughout the area and into Watson Creek and the Gunpowder River. Other
decontamination efforts involved the use of supertropical bleach (a calcium
hypochlorite/calcium hydroxide mixture), lime, and sodium hydroxide to destroy
chemical agents at the field. Following this operation, further decontamination
and cleanup efforts were limited to removing and securing ordnance items
recovered in surface sweeps of the field; the last surface sweep activity was
reportedly performed in the mid-1970s. No disposal of munitions or hazardous
waste appears to have been performed after 1953.
The Old 0-Field Site, like much of the Gunpowder Neck area, was mixed
farmland and woodland prior to its purchase by the U.S. Army in 1917 for the
formation of Edgewood Arsenal. Historical aerial photographs indicate some
cleared areas at the field in 1929, but show no evidence of disposal activities.
The aerial photographic record supports historical data that suggest that the
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major period of disposal operations at the field was 1941 to 1952 with little
subsequent activity.
The Edgewood Area, including Old 0-Field, was listed on the NPL on February
21, 1990. The U.S. Army conducted several investigations of Old 0-Field
including the HGA, FFSs for groundwater remediation and source control, the
preliminary risk assessment, aquifer pumping tests, and groundwater treatability
studies to identify the types, quantities, and locations of contaminants; and to
develop and evaluate methods for addressing contamination problems at the Site.
These studies have provided the following characterization data regarding
chemical contamination at Old 0-Field:
• On-site soils in the landfill area appear to be contaminated with
unknown amounts of chemical-warfare agents, munitions,
decontaminating agents, and other hazardous substances;
• A plume of contaminated groundwater extends east/northeast from the
landfill to Watson Creek in two aquifers (the water-table aquifer
and the upper confined aquifer);
• The contaminated groundwater plume contains chemical-warfare agent
degradation products, including thiodiglycol and 1,4-dithiane
(degradation products of mustard); various metals including arsenic,
iron, antimony, and zinc; chlorinated aliphatic hydrocarbons
including 1,1, 2 , 2-tetrachloroethane, chloroform,
tetrachloroethylene, trichloroethylene, vinyl chloride, and
methylene chloride; aromatic and nitroaromatic compounds including
benzene, chlorobenzene, and nitrobenzene; organophosphorus
compounds, including diisopropylmethylphosphonate (DIMP), from the
degradation of nerve agent compounds (e.g., GB); and (possibly)
organoarsenic compounds from disposal of arsenicals (e.g., lewisite
and adamsite); and
• Surface water and sediments in Watson Creek contain arsenic,
mercury, transition metals, chlorinated aliphatic hydrocarbons,
aromatic hydrocarbons, and a variety of organic compounds which may
be related to activities at Old 0-Field.
Some of the chlorinated aliphatic hydrocarbons and aromatic hydrocarbons are
likely present due to decontamination efforts at the Site which utilized DANC and
fuel oil, as well as from chemical agent mixtures that utilized these compounds
(e.g., CNC, CNB). In addition, these substances may be present as the result of
chemical and/or biological degradation, and from reactions between waste
compounds and decontaminating agents.
Because of the environmental impacts associated with Old 0-Field in
conjunction with other areas of APG, an Interagency Agreement (the Agreement) was
established in March, 1990, under Section 120 of CERCLA between the U.S.
Environmental Protection Agency, Region III, and the U.S. Department of the Army,
Aberdeen Proving Ground. The purpose of the Agreement was to establish a
procedural framework and schedule for developing, implementing, and monitoring
appropriate response actions at APG sites in accordance with CERCLA, the Resource
Conservation and Recovery Act (RCRA), the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP), and other applicable federal and State
regulations. Initial HGA studies of Old 0-Field were conducted as a requirement
of a RCRA Corrective Action Permit issued to the Army. Pursuant to the
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Agreement, the Army agreed to continue the studies in accordance with CERCLA.
All phases of remediation for Old 0-Field are covered under" the Agreement
including investigation, development, selection, and implementation of response
actions.
1.3 SCOPE AND ROLE OF OPERABLE UNIT/RESPONSE ACTION WITHIN SITE STRATEGY
The problems at the Old 0-Field Site are technologically complex. As a
result, the U.S. Army has divided the remediation into three manageable
components called "operable units (OUs)." An operable unit is defined in the
National Oil and Hazardous Substances Pollution Contingency Plan, 40 CFR 300,
(NCP) as a discrete action that comprises an incremental step towards
comprehensively addressing site problems. This discrete portion of a remedial
response manages migration, or eliminates or mitigates a release, threat of
release, or pathway of exposure. The OUs for Old 0-Field are as follows:
Old 0-Field OU One: Contamination of the groundwater aquifers.
Old 0-Field OU Two: Contamination of the soils and the presence
of chemical-warfare agents and munitions in
the landfill (;'.e., the source).
Old 0-Field OU Three: Contamination of Watson Creek.
This ROD addresses the first operable unit (OU One) which deals with the
containment of contaminated groundwater at Old 0-Field. The contaminated
groundwater discharges directly to Watson Creek and indirectly, via Watson Creek,
to the Gunpowder River. Both Watson Creek and the Gunpowder River are part of
the sensitive Upper Chesapeake Bay estuarine system. The contaminated
groundwater poses environmental risks to sensitive aquatic and terrestrial
ecosystems in Watson Creek, the Gunpowder River, and the surrounding wetlands.
The purposes of the OU One response action are to contain the groundwater
contamination to prevent further discharge of contaminants into Watson Creek and
mitigate associated environmental impacts, and to provide treatment of the
extracted groundwater prior to discharge.
Containment of the contaminated groundwater has been identified as an
interim action for the Old 0-Field Site. Extraction of the groundwater for
subsequent treatment will not clean up the aquifers since the source of the
contamination (OU Two) is still present. Accelerated interim action for the
groundwater (OU One) is required to prevent further damage to Watson Creek (OU
Three).
The U.S. Army has not yet made any decisions concerning the types of
actions which may be taken to address OUs Two and Three. The existence of
disposed chemical-warfare agents, munitions, and other hazardous substances in
the landfill is a difficult problem to address at this Site because of the
potential for direct contact with the disposed materials and the continuing
contamination of the soil and groundwater from the source. Active remediation
of the source is likely to be highly hazardous and expensive. Potential
alternatives identified for active remediation of the source area (OU Two) that
can provide source removal, in-place destruction, or permanent isolation create
potentially severe health-and-safety and logistical problems, and are likely to
require extensive research and development efforts as well as very long time
periods for implementation. The Army will continue to evaluate new technologies
for remediating the source of the contamination, including the performance of a
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comprehensive remedialinvestigation/feasibility study (RI/FS) of the entire 0-
Field area.
1.4 COMMUNITY PARTICIPATION
The Proposed Plan for the interim action for OU One at the Old 0-Field Site
was released to the public in July, 1991. The HGA, FFS, Aquifer Testing report,
and the Groundwater Treatability Study report also were made available to the
public on July 3, 1991, in the administrative record file located at the Aberdeen
and Edgewood branches of the Harford County Library. In addition, a public
meeting was held in the Aberdeen Proving Ground Edgewood Area Conference Center
on July 25, 1991. At this meeting, representatives of U.S. Environmental
Protection Agency (EPA), the Maryland Department of the Environment (MDE), and
the U.S. Army Aberdeen Proving Ground (APG) discussed with the public the
preferred remedy, as well as all remedial alternatives under consideration. A
public comment period was held from July 3, 1991 through August 17, 1991.
A transcript of the public meeting is provided in the Responsiveness
Summary (Appendix A) which is part of this Record of Decision, including agency
responses to questions posed by the public attendees. Additional public comments
are also addressed in the Responsiveness Summary. This decision document
presents the selected remedial action for OU One for the Old 0-Field Site, as
discussed in the Proposed Plan, public meeting and Responsiveness Summary.
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2.0 SITE CHARACTERISTICS
This section provides an overview of Old 0-Field characteristics related
to OU One including relevant hydrogeologic descriptions, a summary of the nature
and extent of groundwater and surface water contamination, potential routes of
contaminant migration and exposure, and a summary of human health and ecological
risks. Remedial alternatives, presented in Section 3.0, were developed to
address the conditions at Old 0-Field described below.
2.1 HYDR06EOLOGIC SETTING
The hydrogeologic setting at Old 0-Field of relevance to this interim
action consists of a two-aquifer system (water-table and upper confined
aquifers), each approximately 10 to 15 feet thick, and separated by a thin,
laterally discontinuous clay confining bed. The hydrogeological cross-section
is provided in Figure 3 for Section A-A' identified on Figure 4. The water-table
aquifer lies 9-15 feet below the ground surface; during the rainy winter months,
the groundwater level rises above the bottom of the disposal trenches, which have
been excavated to a depth of 12 feet. The presence of contamination in th'e upper
confined aquifer indicates that the confining bed between the water-table aquifer
and the upper confined aquifer is discontinuous beneath Old 0-Field, or the
trenches may have been excavated through the confining bed. Deeper aquifers that
exist at the Site are believed to be uncontaminated based on current information.
The water-table and upper confined aquifers are recharged by groundwater
flowing from the southern portion of Gunpowder Neck (e.g., H-Field) and by
vertical infiltration of precipitation within the Old 0-Field area. A
groundwater divide in both aquifers is located approximately 300 feet west of Old
0-Field; groundwater along the western side of this divide discharges to the
Gunpowder River, whereas groundwater along the eastern portion of the divide
flows beneath the Old 0-Field landfill and discharges to Watson Creek. Thus,
this divide is very important in controlling the distribution of groundwater
contamination at the Site in that it separates the contaminated, plume area in
both the water-table and upper-confined aquifers from uncontaminated groundwater
flowing northward to discharge into the Gunpowder River. Groundwater flow in the
aquifers beneath Old 0-Field is made additionally complex because of tidal
effects from the Gunpowder River and Watson Creeks, including lagging and missing
tidal cycles in Watson Creek, which are created by the culvert at the creek
mouth.
2.2 CONTAMINATION ASSESSMENT SUMMARY
Chemicals Identified in the groundwater and interconnected surface water
are based on the United States Geological Survey (USGS) hydrologic field
investigation (1988, 1989). Data were collected from existing monitoring wells
located around the field as illustrated in Figure 4.
The groundwater at Old 0-Field contains both inorganic and organic
contaminants. Inorganic contaminants include antimony, arsenic, boron, calcium,
iron, magnesium, manganese, potassium, sodium, and zinc. Dominant organic
contaminants are: 1) chlorinated aliphatic hydrocarbons including 1,1,2,2-
tetrachloroethane, chloroform, tetrachloroethylene, trichloroethylene, vinyl
-------
FIGURE 3
OLD O-FIELD HYDROGEOLOGICAL CROSS-SECTION A-A'
1
CD
O
fc
z
uJ
O
3*
20-
10
0 H
-10
-20H
-30
-40-
-50-
-60-
-70-
-80-
-90
WATSON CREEK
WATER-TABLE AQUIFER
r20
- 10
0
-10
UPPER CONFINED AQUIFER
- -20
- -30
LOWER CONFINED AQUIFER
-40
-50
-60
-70
-80
-90
VERHCAL EXAGGERATION X 4
-------
FIGURE 4
LOCATIONS OF EXISTING WELLS AND
HYDROGEOLOGIC CROSS-SECTION
IM
I2C
IJA
l»
IK
t«A
Wl*
WIA
tlCA'
ICA
«F1*
VIA
UCA
UCA
•n*
•I A
UC*
MA
W1A
UCA
LC*
«n*
uc*
Wl*
•fl*
1C*
>I*
tfl*
IK.A
II
II*
m* - •wn* IMKI
uc* - tint* cuwMtD «ou»i«
ic* - tern* u****a »UU»IH
M
-------
chloride, and methylene chloride; 2) aromatic and nitroaromatic compounds
including benzene, chlorobenzene, and nitrobenzene; and 3) chemical-warfare
agent degradation products which contain sulfur and phosphorus including
thiodiglycol, 1,4-dithiane, and DIMP. A comparison of maximum groundwater
concentrations detected for selected chemicals with Ambient Water Quality
Criteria (AWQC)- and Maximum Contaminant Levels (MCLs) is presented in Table 1.
Major areas of contamination are northeast and east of Old 0-Field. No
significant contamination was found in the well adjacent to the disposal pit west
of Old 0-Field. The estimated overall groundwater contaminant plume is
illustrated in Figure 5. Both the w_ater-table and upper confined aquifer contain
groundwater contamination. In general, the highest concentrations are measured
in the water-table aquifer, although higher concentrations of boron and 1,1,2,2-
tetrachloroethane are present in the upper confined,aquifer than in the water-
table aquifer.
The surface water of Watson Creek contains dissolved constituents including
arsenic, mercury, transition metals, chlorinated aliphatic hydrocarbons, and
aromatic hydrocarbons which may be related to activities at Old 0-Field. A
comparison of maximum concentrations for selected chemicals detected in surface
water with AWQC and MCLs is presented in Table 2. The bottom sediments in Watson
Creek contain arsenic, mercury, transition metals, polynuclear aromatic
hydrocarbons, phthalates, and other organic compounds. A comparison of maximum
concentrations for selected chemicals detected in bottom sediments with AWQC and
MCLs is presented in Table 3.
2.3 RISK ASSESSMENT SUMMARY
There is a limited data set available for use in determining risks posed
by OU One, resulting in considerable uncertainties in computed human health
risks. However, a preliminary risk assessment was performed for Old 0-Field
during 1990 for the purpose of estimating human health and/or environmental
problems that could result if remediation were not performed. This analysis was
conducted in conformance with current EPA guidance regarding risk assessments for
CERCLA sites using existing data on chemical conditions, and groundwater and
surface water hydrology at the Site gathered during the HGA and other studies.
The assessment included a preliminary human health evaluation as well as a
detailed ecological assessment to determine potential impacts to aquatic and
terrestrial species in Watson Creek and nearby wetlands. This summary discusses
only those risks associated with OU One (i.e., contaminated groundwater and
interconnected surface water).
The USGS hydrogeologic field investigation (1988, 1989) was the primary
source of sampling data considered in the preliminary risk assessment. Sampling
data were available for subsurface soil, groundwater, surface water, and sediment
for the Old 0-Field Site. Chemical analyses were limited primarily to volatile,
semivolatile, and inorganic chemical analyses, although selected groundwater
samples were analyzed for agent- and explosive-related compounds, herbicides, and
radionuclides. Based on sampling results,. volatile organic chemicals and
inorganic chemicals (principally metals) are the primary chemicals of concern in
groundwater and surface water; whereas polynuclear aromatic hydrocarbons,
phthalates, and metals are the principal chemicals of concern in sediment. Also,
agent degradation products and explosive-related compounds are of concern in
groundwater which was the only medium sampled for these compounds.
11
-------
TABLE 1
COMPARISON OF MAXIMUM 6ROUNDWATER CHEMICAL CONCENTRATIONS1
DETECTED WITH WATER QUALITY CRITERIA AND MAXIMUM CONTAMINANT LEVELS
PARAMETER
Antimony
Arsenic
Soron
Calcium
Iron
Magnesium
Manganese
Potassium
Sodium
Zinc
Benzene
Carbon Tetrachloride
Chlorobenzene
Chloroform
1,2-Oichloroethane
1,1-Dichloroethylene
Ethyl benzene
Methyl ene Chloride
1 , 1,2,2-Tetrachloroethane
Tet rachl oroethyl ene
Toluene
1,2-Oichloroethylene
1 , 1 ,2-Trichloroethane
Trichloroethylene
Vinyl Chloride
1,4-Oi thiane
Thiodiglyco)
MAXIMUM
CONCENTRATION
DETECTED
(ppb)
100
2.243
11,000
134,000
245,000
108,000
17,400
30,700
859,000
7,890
6,040
750
430
15,000
2.420
14
295
2,430
18,600
6,407
360
2,586
219
3,860
2,200
5,154
1,000.000
CWA AMBIENT WATER QUALITY CRITERIA
FRESHWATER MARINE
ACUTE CHRONIC ACUTE CHRONIC
(pob) (pob) (pob) (ppb)
88P
360"
-
120
5,300
35.200
250
28.900
118,000
11.600
32,000
.5,280
17,500
11,600
18,000
45.000
30"
190d
110
1,240
20,000
2,400
840
9,400
21,000
1,500P
69"
95
5,100
50,000
160
113,000
220,400
430
9,020
10.200
6.300
224,000
2,000
soo"
36d
86
129
450
5,000
ti
SOWA
MAXIMUM
CONTAMINANT
LEVELS
(ppb)
, «P -'
10 :s
50
_.
..
300*
„.
50*
__
...
5,000*
5
5
100°
100°
5
7
700C;30*P
5"
—
Se
,000C;40*P
.SiVl$
5P
5
2
..
--
1 - Source, U.S.G.S., Hydrogeologic and Chemical Data of the 0-Field Area, Aberdeen Proving Ground, Maryland,
April 1989
a - 40 CFR, Part 143 - National Secondary Drinking Water Regulation.
ap - Proposed Secondary Drinking Water Standards.
b - 100 (ig/L is for total trihalomethanes (i.e., the sum of chloroform, bromodichloromethane, and bromoform).
c - Environmental Protection Agency 1991. National Primary Drinking Water Regulations; Final Rule, Federal
Register Vol. 56, No. 20. January 30, 1991.
d - Arsenic III and compounds.
e - Hardness dependent criteria (100 mg/L used).
P - Proposed.
12
-------
FIGURE 5
OLD O-FIELD ESTIMATED CONTAMINANT PLUME
r~I - ~ -"• ~- r t ^ - ~ ~ *~- ^T"
l-^- •-" • _ -* ~*~ ~ - -.
"-T - • *• ~**-~ « - ~ -
- T - - •«» * ^ •• - - - •_
>^:v:^>v*-r^
•~ — .^..?»•» &\»«k«»
- * ? ^--t i- .- ----•
SCALE IN FEET
APPROXIMATE
-------
TABLE 2
COMPARISON OF MAXIMUM SURFACE WATER CHEMICAL CONCENTRATIONS1
DETECTED WITH WATER QUALITY CRITERIA AND MAXIMUM CONTAMINANT LEVELS
PARAMETER
Antimony
Arsenic
Arsenic III
Arsenic V
Soron
Cadmium
Calcium
Copper
Iron
Magnesium
Manganese
Mercury
Nickel
Phosphorus
Potassium
Selenium
Sodi urn
Titanium
Zinc
Benzene
Carbon Tetrachlorlde
Chlorobenzene
Chloroform
1 , 1 -Oi chl oroethyl ene
1,2-Oichloroethane
trans-1 .2-01 chl oroethyl ene
Ethylbenzene
Methylene Chloride
1,1 ,2,2-Tetrachloroethane
MAXIMUM
CONCENTRATION
DETECTED
(ppb)
149
126
95
66
1.020
18
84,100
4
1,060
274,000
874
0.38
11
800
78.600
94
2.180,000
133
332
4
4
0.8
96
260
120
130
5.8
134
90
CWA AMBIENT WATER QUALITY CRITERIA
FRESHWATER MARINE
ACUTE CHRONIC ACUTE CHRONIC
(ppb) (ppb) (ppb) (DDb)
as"
360
3.9"
18'
2.4
1.400*
20
120
5,300
35,200
250
28,900
11,600
118.000
11,600
32,000
30"
190
1.1*
12*
0.012
160*
5
110
1.240
20,000
2,400
1500"
69
43
2.9
2.1
75
300
95
5,100
50.000
160
224,000
113.000
224.000
430-
9,020
500B
36
9.3
0.025
8.3
71
86
129
SDWA MAXIMUM
CONTAMINANT
LEVELS (ppb)
!0P;5P
50
--
--
..
5e
«
1.300"; 1,000"
300*
—
50*
2
100"
--
50e
--
--
5000*
5
5
100e
100"
7
5
100C
700e;30'p
5P
--
14
-------
TABLE 2 (Continued)
PARAMETER
1 , 1 , 1-Trichloroethane
Trichloroethylene
Toluene
Vinyl Chloride
' MAXIMUM
CONCENTRATION
DETECTED
(ppb)
0.2
34
0.4
47.0
CWA AMBIENT WATER QUALITY CRITERIA
FRESHWATER MARINE
ACUTE CHRONIC ACUTE CHRONIC
(ppb) (opb) (ppb) (nob)
18.000
45,000
17,500
31,200
2,000
6,300
5,000
SOWA MAXIMUM
CONTAMINANT
LEVELS (PDD)
200
5
l,000e;40"
^
1 -
a -
ap -
b -
c -
d -
e -
P -
Source, U.S.G.S. Hydrogeologic and Chemical Data of the 0-Field Area, Aberdeen Proving Ground, Maryland,
April, 1989.
40 CFR Part 143 - National Secondary Drinking Water Regulations.
Proposed Secondary Drinking Water Standards.
100 |tg/L is for total trihalomethanes (i.e., the sum of chloroform, brcmodichloromethane, and bromoform).
Environmental Protection Agency 1991. National Primary Drinking Water Regulations; Final Rule, Federal
Register Vol. 56, No. 20, January 30, 1991.
Environmental Protection Agency 1991. National Secondary Drinking Water Regulations; Final Rule, Federal
Register Vol. 56, No. 20, January 30, 1991.
Hardness dependent criteria (100 mg/L used).
Proposed.
15
-------
TABLE 3
COMPARISON OF MAXIMUM BOTTOM SEDIMENT CHEMICAL CONCENTRATIONS1
DETECTED WITH HATER QUALITY CRITERIA AND MAXIMUM CONTAMINANT LEVELS
PARAMETER
Antimony
Arsenic
Arsenic III
Arsenic V
Beryllium
Boron
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Nickel
Phosphorus
Potassium
Selenium
Sodium
Thallium
Zinc
Naphthalene
Phenanthrene
Huoranthene
Butyl Benzyl Phthalate
Oi-n-octyl Phthalate
Bis(2-ethylhexyl (Phthalate
Oi ethyl Phthalate
MAXIMUM
CONCENTRATION
DETECTED
(ppb)
6,000
41,500
13,200
24,200
1,600
19,720
2.200
3,133,000
39,400
66,700
40,370,000
47,900
5,646,000
379,000
2.550
37,500
340,000
2,800,000
480
4,530,000
5,300
394,000
360 .
2,180
2,010
604
6.82
2,460
2,360
CWA AMBIENT WATER QUALITY CRITERIA
FRESHWATER MARINE
ACUTE CHRONIC ACUTE CHRONIC
(ppb) (ppb) (ppb) (oob)
88P
360
130
3.9*
16f
18*
8.3"
2.4
1.400*
20
1,400
120
3,900
30"
190
5.3
1.1*
llf
If
3.2*
0.012
160*
5
40
110
isoo"
69
43
2.9
150
2.1
75
300
2,130
95
300
40
500P
36
9.3
5.6
0.025
8.3
71
86
16
SDVA MAXIMUM
CONTAMINANT
LEVELS (ppb)
10P;5°
50
--
..
lp
..
5e
--
100e
1.300"; 1,000*
300*
50; 5°
--
50*
2
100P
--
50e
--
2P;1P
5000"
4P
16
-------
TABLE 3 (Continued)
PARAMETER
Dimethyl Phthalate
Oi-n-butyl Phthalate
Benzene
Carbon Olsulflde
Chlorobenzene
Chloroform-
c1s/trans-l,2-0ichloroethylene
Ethyl benzene
Hethylene Chloride
1,1,1-Trichl oroethane
Toluene
Trichlorofluoromethane
Xylenes
Sulfur
MAXIMUM
CONCENTRATION
DETECTED
(ppb)
860
1,550
0.8
16
2
0.1
0.2
0.8
19
6.1
2.3
98
0.2
27,000
CWA AMBIENT WATER QUALITY CRITERIA
FRESHWATER MARINE
ACUTE CHRONIC ACUTE CHRONIC
(ppb) (ppb) (ppb) (pob)
9401
5,300
250
28,900
11,600"
32,000
18,000
17.500
3.01
1,240
2.9001
5,100
160
24000s
430
31,200
6,300
3.4'
129
5,000
SOW A MAXIMUM
CONTAMINANT
LEVELS (ppb)
5
100e
100"
100"
700e;30*B
5"
200
l,000e;40*p
10000eh;20"h
1 - Source, U.S.G.S. Hydrogeologic and Chemical Data of the 0-Field Area, Aberdeen Proving Ground, Maryland,
April, 1989.
a - 40 CFR Part 143 - National Secondary Drinking Water Regulations.
ap - Proposed Secondary Drinking Water Standards.
b - 100 pg/l is for total trihalomethanes (i.e., the sum of chloroform, bromodlchloromethane, and bronwform).
c - Environmental Protection Agency 1991. National Primary Drinking Water Regulations; Final Rule, Federal
Register Vol. 56, No. 20, January 30, 1991.
d - Environmental Protection Agency 1991. National Secondary Drinking Water Regulations; Final Rule, Federal
- Register Vol. 56, No. 20, January 30, 1991.
e - Hardness dependent criteria (100 mg/L used).
f - Chromium VI and compounds.
g - Standards are for trans-1,2-Oicnloroethylene.
h - Total Xylenes.
i - Standards are for 01 butyl Phthalate.
P - Proposed.
17
-------
2.3.1 Human Health Risk Assessment Summary
No human receptors are being exposed directly to groundwater at this OU
under current conditions; rather, the groundwater acts as a transport medium for
contamination from OU One to OU Three. Additionally, the Army believes it is not
practical to estimate human health risks quantitatively for a future-use
scenario, because of the existing institutional controls and no apparent future
uses of the shallow groundwater due to elevated levels of natural constituents
such as iron and chlorides. Therefore, the preliminary risk assessment focused
on determining the human health risks posed by discharge of contaminated
groundwater into Watson Creek.
Access to Old 0-Field is heavily restricted. The only current land use of
Old 0-Field is comprised of environmental sampling and APG workers driving past
Old 0-Field several times a day to get to their work areas. ,Future land_use. is
not.likely._ta.cl»»nge fronucurrejLt_laM-use. The primary pathwaysT>y~which human
populations could be exposed to contaminated groundwater under current land-use
conditions are chronic exposure via inhalation of chemicals that have volatilized
from Watson Creek, and dermal contact and incidental ingestion of chemicals
discharged from OU One into surface water and made available through recreational
uses of the Gunpowder River associated with the groundwater OU. Based on the
preliminary data available, no other potential pathways.are likely to result in
significant exposure under current land-use conditions or for any foreseeable
future uses. J&terLtial human e,xpft
-------
Future Land Use:
• If all institutional controls were relaxed, there is the possibility
that site workers could be more intimately exposed to materials
volatilized from Watson Creek. Potential risks to workers at Old 0-
Field exposed via inhalation to volatile chemicals are likely to be
greater than those associated with current-use exposures. The risks
for this pathway probably could be increased an order of magnitude
above those estimated for current-use .site workers, given that
workers at Old 0-Field would be closer to the emission source and
could be exposed more frequently. Thus, excess lifetime cancer
risks in the range of 10 to 10"6 would be possible. Hazard Indices
likely would remain below one, but potentially significant risks
would be possible for non-carcinogens.
2.3.2 Ecological Assessment Summary
OU One has been shown to affect the surface water quality in Watson Creek
and the Gunpowder River, which are located within the environmentally-sensitive
Upper Chesapeake Bay system. 0-Field has not been declared a critical habitat
for the bald eagle (an endangered species), but most of the shoreline is used by
the large bald eagle population on APG as a potential foraging and feeding area.
Their presence on APG constitutes a valuable resource and the supporting habitat
is important. In addition, endangered species are known to frequent the area.
Therefore, potential ecological impacts were considered to be particularly
important and were evaluated for aquatic and terrestrial wildlife at Old 0-Field.
Aquatic life exposures were evaluated for chemicals in surface water and sediment
in Watson Creek and the Gunpowder River. In addition, exposures were evaluated
for benthic species living in the groundwater discharge zone in Watson Creek.
Terrestrial wildlife exposures were evaluated for heron (a piscivore), sandpipers
(an aquatic insectivore), and muskrat (aquatic herbivore) feeding in Watson Creek
and exposed to chemicals that have accumulated in food. The results of the
ecological assessment are as follows:
Aquatic Life Impacts:
• Surface Water Exposures. Aquatic life in Watson Creek and the
Gunpowder River are probably being impacted by surface water
chemical contaminants associated with Old 0-Field. Impacts in
Watson Creek are likely more severe than those in the Gunpowder
River, given the greater number of chemicals present at higher
concentrations in the creek. Also, the more closed nature of Watson
Creek relative to the Gunpowder River probably makes it more
susceptible to impacts than the river. Impacts associated with
organic contaminants in Watson Creek are probably localized to the
area of groundwater discharge, which likely has the highest
concentrations of volatile organic chemicals being released to
surface water. Predicted impacts on benthic species living within
this area were greater than those predicted for species living
within the water column. Impacts associated with inorganic
contaminants are probably more widespread, given the relatively even
distribution of these chemicals throughout the creek. Further
studies of surface water exposures are planned, and will be
discussed in the final ROD.
19
-------
• Sediment Exposures. Chemical concentrations in Watson Creek and the
Gunpowder River sediments are below those predicted to be harmful to
aquatic life, suggesting that aquatic life impacts from exposure to
chemicals in sediment are not likely. However, the sediment
toxicity values predicted to be harmful were derived from a very
limited toxicity database and, therefore, may not necessarily
reflect conditions which are protective of aquatic life. Further
studies of sediment exposures are planned, and will be discussed in
the final ROD.
Terrestrial Wildlife Impacts:
Wildlife Exposures. Wildlife feeding in Watson Creek could be
impacted by exposure to heavy metals in their food. Sandpipers and
other shore birds feeding on aquatic insects and probably benthic
organisms are potentially at greatest risk of impact as many of the
inorganic chemicals present in Watson Creek can bioaccumulate
significantly in aquatic invertebrates. Piscivorous bird species,
such as heron, eagles, and osprey do not appear to be at risk
because most of the metals present accumulate to a lesser degree in
fish than in invertebrates. Further, heron, eagles, and osprey are
much less susceptible than sandpipers and other small shore birds to
impact from Old 0-Field because their feeding range is so large,
that fish in Watson Creek only constitute a small portion of their
diet. Herbivorous species such as muskrat appear to be at risk from
dietary exposures, even though few chemicals in Watson Creek are
likely to accumulate in aquatic plants, because the chemicals that
could accumulate could be toxic at relatively low dietary
concentrations. Further studies of wildlife exposure are planned,
and will be discussed in the final ROD.
2.3.3 Conclusions of the Risk Assessment
Past activities at Old 0-Field have resulted in significant contamination
of groundwater, surface water, and sediment in the area. Under current land-use
conditions, ecological populations are the principal receptors of concern. Few
human health exposure pathways to contaminated groundwater exist under current
land-use conditions.
It is possible that the aquatic life in Watson Creek and the Gunpowder
River and terrestrial wildlife feeding in Watson Creek are being adversely
affected by chemical contamination associated with Old 0-Field. Acute and
chronic toxicity in Old 0-Field surface waters probably has affected the
composition and structure of the aquatic communities in Watson Creek and possibly
the Gunpowder River near Old 0-Field. Localized reductions in species diversity
and number for resident aquatic life (particularly in Watson Creek) are possible,
as are impacts in nonresident species that use the area as a nursery area (e.g.,
blueback herring, bay anchovy, menhaden). Contamination could also result in
localized reductions in population size and contribute to cumulative impacts
associated with APG as a whole.
Wildlife feeding in Watson Creek appear to be at risk from exposure to
heavy metals in the diet. Dietary exposures to heavy metals can induce a variety
of toxic effects in wildlife including decreased reproductive success, decreased
growth, and abnormal behavior. Such effects could directly affect the health of
wildlife populations in and around Watson Creek. Such localized effects are
20
-------
unlikely to affect the wildlife population of APO as a whole. Nevertheless, the
presence of heavy metals in Watson creek appears to have reduced the value of that
area as wildlife habitat. Further, impacts in species in the Old O-Field area
could contribute to cumulative impacts associated with APG as a whole.
These estimates of risk, however, are not definite at this time. There is a
great deal of uncertainty associated with all risk estimates for the Old O-Field
study area because of limitations associated with the available sampling data and
limitations inherent to the risk assessment process. Additional investigation is
needed to assess more definitively existing or potential impacts associated with
the old o-Field study area.
The conclusions of the preliminary risk assessment are that: (1) there are no
significant human health risks associated with groundwater or interconnected
surface water at Old O-Field if current land-use restrictions remain in place; and
(2) there is a potential for ecological risks, although they cannot be quantified
given existing data. An interim action for the groundwater at old o-Field is
being pursued for several reasons: <1) several contaminants have been detected in
the surface water in watson creek above AWQCS (Table 2); (2) the contaminated
groundwater from old O-Field is known to discharge to Watson Creek) and (3)
containment of the contaminated groundwater whlla investigating alternatives for
addressing the source of the contamination will prevent further degradation of
watson creek and mitigate future impacts.
Since these aquifers are known to discharge into the surface waters of Watson
creek, if the present situation goes unabated, the continued contamination of
surface water and sediments may present an imminent and substantial endangerment
to public welfare, or the environment. This finding of imminent and substantial
endangeraent and the remedy selected herein are not based on any presently
observed threat to public health at or from the site.
21
-------
3.0 DESCRIPTION OF REMEDIAL ALTERNATIVES
Groundwater extraction/discharge and treatment alternatives were developed
for OU One to satisfy the following remediation objectives:
• Provide containment of contaminated zones in the water-table and
upper confined aquifers at Old 0-Field;
• Minimize environmental risks to sensitive aquatic and terrestrial
ecosystems in Watson Creek, the Gunpowder River, and the surrounding
wetlands by reducing or eliminating discharge of contaminated
groundwater to these areas; and
• Control potential human health risks associated with groundwater,
surface water, and food-chain exposures that could result from
continued contaminant migration in groundwater at Old 0-Field.
These objectives are based on the nature and extent of chemically affected
groundwater and its associated risks as discussed in Sections 2.2 and 2.3.
In the FFS, remedial technologies with potential application to Old 0-Field
groundwater initially were identified and screened based on effectiveness,
implementability, and relative cost. Table 4 presents those technologies
considered along with the results of the initial screening process. Individual
technologies retained were then combined to form a series of extraction/discharge
alternatives, and a separate series of treatment alternatives. Because 14
groundwater extraction/discharge alternatives initially were identified from the
remaining technologies, an initial screening of these alternatives was performed
again based on effectiveness, costs, and implementability. A second screening
of those alternatives remaining after the initial screening was then performed
using groundwater modelling to estimate performance. Four extraction/discharge
alternatives remained following the two-step screening process which is
summarized in Tables 5 and 6. Treatment alternatives were not screened as only
six alternatives were identified from remedial technologies.
This section presents the four groundwater extraction/discharge and six
groundwater treatment alternatives remaining following initial screening
performed in the FFS. Note that all cost and implementation times presented are
estimated. The alternatives described herein are compared against detailed
evaluation criteria in Section 4.0 in order to select a preferred remedy for Old
0-Field groundwater. A discussion of cleanup criteria is presented as a
necessary prelude to the remedial alternative discussion.
3.1 CLEANUP CRITERIA
As previously noted, existing data for groundwater (Table 1), surface
water (Table 2), and sediment (Table 3) at Old 0-Field are sufficient to indicate
aquatic life in Watson Creek may be impacted by chemical contamination migrating
in groundwater from the landfill area. However, these data do not provide a
comprehensive basis for establishing chemical-specific target cleanup goals
because of: (1) the complex, multimedia exposure pathways for the Site; (2)
insufficient ecotoxicological data on many of the chemicals of potential concern
(e.g., thiodiglycol); and (3) the need for additional surface water, sediment,
and biological data for Watson Creek.
22
-------
TABLE 4
SUMMARY OF TECHNOLOGY IDENTIFICATION AND SCREENING
General
Response Action
No Action
Minimal Action
Hydrologic
Control
Collection
On-site
Treatment
Technology
Types
None
Long-Term
Monitoring
Administrative
Actions
Passive
Controls
Active
Controls
Extraction
Systems
Physical
Treatment
Process Options
—
Groundwater Monitoring
Public Education
Emergency Provisions
Institutional Restrictions
Slurry Wall
Grout Curtain
Sheet Piling Cut-Offs
Single-Layer Cap
Multi-Layer Cap
Extraction Well
Subsurface Drain
Extraction Well
Subsurface Drain
Carbon Adsorption
Air Stripping
Steam Stripping
Granular Media Filtration
Reverse Osmosis
Ion Exchange
Process Process
Option Option
Eliminated Retained
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
-------
TABLE 4
SUMMARY OF TECHNOLOGY IDENTIFICATION AND SCREENING (Continued)
General Technology
Response Action Types
Process Options
Process
Option
Eliminated
Process
Option
Retained
On-site Treatment
(Continued)
Chemical
Treatment
Biological
Treatment
Discharge/
Disposal
Thermal
Treatment
Off-site
Disposal
On-site
Discharge
Precipitation
Neutralization
Ultraviolet/Oxidation
Activated Sludge
Trickling Filters X
Rotary Biological
Contactors X
PACT
Anaerobic Biodegradation
In-situ Biological
Treatment X
Wet Air Oxidation X
Deep Well Injection X
APG Sewage/Industrial
Treatment Plant X
Local POTW X
Commercial Treatment
Facility X
Groundwater Re-injection
Discharge to
Watson Creek X
Discharge to
Gunpowder River
Spray Irrigation/Source Flushing
X
X
X
X
X
X
X
-------
Allemalive
•.me/Description
Groundwafer
Extract ion
technology
Nvdroloaic Control technologies
Hydraulic
Control
Rarrlers
Active
lister-level
Infiltr»tion
farriers
Discharge/
artificial
Recharge
Qptlona
Advantages
Disadvantages
Screening Decision and Rationale
I. Oowngradient pumping
Mells (with optional
hydraulic barrier)
?. Doungradient puaping
wells Mtth source
area capping and
upgradient water-
level aNMkage«ent
(will) oplion.il
hydraulic barrier)
}. Downgradient puaping
wells with
upgradient water-
level Management
r\> (wi Ih opl ion.il
V hydraulic barrier)
<.. ftowngt adtenl pumping
welI* with soulce
area capping (with
optional hydraulic
barrler)
S. Downgradienl pumping
wells with
upgradient re-
injection ol treated
water (with optional
hydraulic barrier)
6. Downgradient puaping
wells with spray
irrigation/source
flushing with
treated water (with
optional hydraulic
barrier)
Downgradient
pulping welli
Downgradient
puaping wells
Downgradienl
puaping wells
Downgradient
puaping wells
Oowngradient
pulping wells
Dovngradienl
pusping wells
Downgradient
(optional)1
Oowngradient
(optional)1
Downgradient
(optional)1
Nora
Upgradient
puaping
Upgradient
puaping
Nora
Capping
Oowngradient Nona
(optional)'
Oowngradient Nora
(optional)1
Downgradient None
(optional)'
Capping
None
Discharge to Staple, straightforward approach
surface water with Halted subsurface work and
relatively low capital costs.
Discharge to Ulll provide aoplfer resMdiation
surface water while aiinlaililng direct contact
between waste and groundwater and
infiltration leaching.
Discharge to NinlsiKea direct contact between
surface Mater groundwater and waale by lowering
water table. In addition to
removing conta»lnat ton froa
aquifer.
Discharge to Nlnusiiei leeching of waste
surface water aaterlale by Infiltrating
precipitation; operationally
staple.
Upgradient Provides recharge to upgradient
re-Inject Ion are* of the aquifer that a»y be
required to maintain aggressive,
continuous downgradlant puaping
and aquifer flushing.
Spray Provides aojulfer recharge end
Irrigation/ also actively flushes
source contamination from; source
flushing aaterlels; aay represent the only
safe, active source reaediatlon
alternative.
long operation period likely; saiy
have significant OM costs;
source Is not isolated or
actively flushed.
Operationally coaplex;
aubstantial on-site engineering
and construction reojulred; source
is untreated and a*jy reswin
haxardous indefinitely.
Does not prevent leaching of
waste eiaterials by Infiltrating
precipitation; not as
coaprehensive as Alternative 2.
Does not signif icently lower the
Hater table (USGS. 1MB) due to
Mail ted areal extent of cap
coepared to aquifer recharge
tone.
Coaplex to dealgn and operate;
re-Injection probleeB likely;
source reealna active and thus
dnwngradlent water quality a»y be
hlgkly variable.
Infiltration will cause
groundwater Bounding, which will
cause contamination to •Igrate
Into previously uncontealnsted
area* (e.g., upgradieni, cross
gradient) not included in
downgradient capture tone.
•etein for further screening;
aosl staple, straightforward
approach'; likely to be cost-
effective.
Retain for further screening;
eosl coaprehenslve waste
isolation/Migration i
alternative.
Not retained; likely to be less
effective for waste isolation
than Alternative 2, without
cosparablc cost savings.
Not retained; based on USCS
study, this approach is likely lu
be significantly less effective
than Alternative 2.
Retain for further screening; e»y
provide needed recharge to
a»intaln aufflcient pumping rates
for aoulfer Hushing.
Not retained; groundwater
aaunding probleai eay cause
inefficient or Ineffective pluae
capture by downgradient puaping
wells.
-------
IE S
MISI SIEP SOKENIK Of FOIEsHIAUl MVtICAME CMMBWIEI EIIRACIIOD MB 01 SOURCE AllERMHVES
(Cart inued)
Mydroloaic Control technologies
Discharge/
Groundwater lydraullc Active' Artificial
Alternative Extraction Control Water-level Infiltration Recharge
Mane/Description technology terriers Mansgta«nt farriers Options
Advantages
Disadvantages
Screening Decision
and Rationale
O>
Ungradieni puling
wlls (lor hydraulic
gradient reversal
and plume capture).
8. Upgrodient pumping
wells with source
area capping.
9. Upgradienl pumping
wells with spray
irrigat ion/source
Mushing with
treated water.
10. Circumfcrenlially
placed puling
wells.
II. Cirruafrrenlially
placed pumping
wells with source
area capping.
12. Circumferentially
placed piping
wells with
encircling
hydraulic terrier
and source area
capping.
Upgradient
puiping uellt
Upgradienl Mont
pusping wells
upgradienl Hone
pumping wells
Circuaferen-
tially placed
puling Mill
Circumferen-
Iially placed
pusping wells
Circuaferen- Circunteren-
tially placed tial (outside
putting well* well network)
Capping
Capping
Capping
Oischarjte to
surface water
Discharge to
surface water
Spray
Irrigation/
source
flushing
Discharge to
surface Mater
Discharge to
surface water
Discharge to
surface water
Kill allow puiping at sufficient
rates to provide aiajifer flushing
while •ininiiing potential
infiltration probleas with Uatson
Creek.
Reduces infiltration in source
area, which aay help to reverse
hydraulic gradient; isolates
waste Materials.
Active source remediation.
Will contain conieaination in
close proalsiity to source in all
potentially contaaiinaied areas.
Plume can be contained in close
proxisiity to source; cap
•InlMlie* Infiltration and
leachate generation, and svjy
penal t Inward gradient toward
source area to be a»intained.
Providea effective source
isolation, while Maintaining
Inward hydraulIc gradient and
caplure/treatsMnt of near-source
groundwater; lisiited puvplng
required.
Will result in canton.natIon of Hot retained; Mill result in
previously uvanttwintled aquifer conta-tinelion of previously
lone; -My not provide Affective uncantM.neted areas of th«
capture/flushing (n previously water-table and upper conli.tei
far doMntfradient areas. acyjlfert.
As above; also, requires on-slle
engineering and construction.
Ulll cause grounduater anundlng
and contamination aiigratlan Into
previously uncantasiinated a<>iifer
tones that Bay not be Included In
capture lone.
Does not provide significant
advantages over oWigradlent
pusping unless combined with
certain ancillary technologies.
Requires on-site engineering and
construction; aquifer reaadiatlon
In downgradlent areas will be
vary slow without additional
doMngrsdient puaplng well*.
Requires eatenslve e»cavatlon
and construction activities in
patent Ul UU)/cheBic*l agent
areas; water Is likely to be
highly contaminated.
lot retained; s
Alternstive T.
rationale as
lot retained; same rationale as
Alternative 6.
Not retained; no apparent
advantages over downgredienl
pusping wells as a slend'alone
technology.
Retain for further screening; My
provide very effective waste
Isolation/ migration control with
limited pimping.
Mot retained; engineering and
eflcevatfon requirements in
hl(h-hnard IMO/agenl aiaas
are considered too entenslve.
-------
IAW.E S
HISI-SIEP SCKEHIHC Of POIEHIIMir APPtlCAME OKUOVAIE*. EIIUCIIOI MB 01
(Continued)
SCHAMX ALIEUUIIVES
Mydroloaic Control technologies
Al (prnat ive
NaMe/Oescr ipt ion
Croundwater
Extraction
technology
Hydraulic
Central
terriers
Active
Water-level
Management
Infil tret ion
Barriers
Discharge/
Art if iciel
Recharge
Options Advantages
Screening Decision
Disadvantages and Rationale
13. Circumferentially
placed pwpino,
uells with «pr«y
irrigation/source
flushing with
treated water.
CircumlerentUtly
placed and
domgredtent
puaping wells.with-
dDungredienl
re- injection.
Circumteren-
lialty placed
pumping veils
Circuit eren-
Itally placed
None
Hone
Hone
gradient
puaping Metis
Spray Provides active source
irrigation/ mediation/flushing, while
source Maintaining capture in all areas
flushing surrounding landfill; Mill
•inlailie previously outlined
groundMter mounding/ineffective
capture problem associated Hith
otlMT source flushing
alternatives.
Doungradient Will create a *freshHater ridge*
re-inject Ion near UMson Creak to minimi le
brackish Hater infiltration and
act as a barrier to additional
plum* ailgrstlan; Hill also
provide needed recharge for
active aquifer flushing.
Captured groundweter likely to be letaln (or further screening.
highly contmmtnited and of highly a»sl entensive alternative tor
variable cheailcal quality; combined source reamliatiun I«K|
despite leaching, source Bay aquifer flushing.
resailn haiardous Indefinitely.
Very coaple> to design and
operate; tidal Influence and
seasonal fluctuation* •at*
performance difficult to predict.
•eteln for further screening;
Innovative alternative that auy
provide active reaedlailon of
currently contaminated ere*.
While islniaiiiing surface water
infiltration and excavation
difficulties.
A doungradient hydraulic barrier (e.g., slurry twill say be required for alternatives that include doungradlent pusplng veils In order to •IntBiiV- Induced Infiltration from Watson Creek and sllou for
efficient plusn capture. Model results are used to delensine whether a downgradienl hydraulic barrier Is required. It should be noted that: (I) significant excavation/construction problems related to
potentiel UXO/chesMcal agent haiards, limited uork area, and potential wetlands dmmage "ay greatly Impact the cost and feasibility of • downiradienl terrier at Old 0-fleld; and (2) some induced Infiltration
is probably acceptmble as it will help to maintain constant, predictable pumping rates end will provide torn* dilution of highly contaminated groundwater. Potential problems with Induced infiltration are: (I)
possible disruption of plume capture tones (i.e., wells mmy capture * large percentage of their total pumped volume from Induced infiltration, while contaminated orounoVater remains nearly stagnant); and (?)
different chemical characteristics of Watson Creek water, including high total dissolved solids and dissolved oxygen content, mmy affect local I ted aquifer characteristics and treatment system efficiency.
-------
TABLE 6
SECOND-STEP SCREENING Of GROUNDUATER EXTRACTION AND DISCHARGE ALTERNATIVES
Alternative
Nuifcer/Name
Alternative Description/
Major Components
Advantages
Disadvantages
Screening Decision and
Rationale
Alternative E-1: .
Doungradient Extraction
with Discharge to Surface
Uater
Alternative E-2:
Doungradient Extraction
with Capping, Upgradient
Water-Level Management,
and Discharge to Surface
Water
Alternative E-3:
Downgradient Extraction
with Upgradient Re-
Injection
ro
00
Alternative E-4:
Circunferential Extraction
uith Capping and Discharge
to Surface Uater
Downgradient extraction system
(14 wells); discharge of
treated water to Gunpowder
River.
Downgradient extraction system
(U wells); low-permeability
nuiti-layer cap over source
area; upgradient subsurface
drain (1,150 feet) for water-
level management; discharge of
treated water to Gunpowder
River.
Downgradient extraction system
(U wells); upgradient
reinjection of 100X of treated
water into water-table aquifer
via two injection wells.
Circunferential extraction
system (26 wells); low-
permeability multi-layer cap
over source area; discharge of
treated water to Gunpowder
River.
Simple, straightforward
approach; easy to design and
operate; low capital costs.
Provides effective water-level
management over a large area
of the aquifer; waste
Isolation is also achieved by
restricting infiltration by
capping source area.
None
Provides effective waste
isolation by minimizing
infiltration and lowering
water levels in the water-
table aquifer beneath the
landfill, preventing direct
contact of groundwater with
buried wastes.
Long operation period likely;
source is not isolated or
actively flushed.
Constructability of subsurface
drain is highly questionable
(similar effect cannot be
achieved by pimping wells);
water captured by drain may be
contaminated with chemicals from
New 0-Field greatly increasing
cost and complexity of
treatment.
Upgradient re-inject ion'does not
appear to provide additional
recharge to contaminated aquifer
zone (flows mostly toward
Gunpowder River); groundwater
divide between Old 0-Field and
Gunpowder River is shifted
toward disposal site, possibly
introducing contamination into
previously uncontaminated
aquifer areas.
Although source may be isolated,
it will remain potentially
active for an indefinite (but
likely very long) time period;
thus, extended OtM costs for cap
and extraction system are
likely.
Retain for detailed analysis;
simple straightforward, cost-
effective approach that serves
as a baseline for comparison
with other alternatives.
Not retained; construetabiIity
and potential treatment
problems severely impact
implementability; similar
effectiveness can apparently be*
achieved by Alternative E-4
with less potential
implementation/cost problems.
Not retained; major
effectiveness problems
predicted by groundwater
modeling; does not appear
suitable for complex
hydrogeologic conditions found
at Old 0-field.
Retain for detailed analysis;
provides similar effectiveness
to Alternative E-2, uith
greater implementability.
-------
TABLE 6
SECOND-STEP SCREENING OF GROUNDUATER EXTRACTION AND DISCHARGE ALTERNATIVES
(Continued)
Alternative
Nunfcer/Name
Alternative Description/
Major Components
Advantages
Disadvantages
Screening Decision and
Rationale
AlternativtnE-5:
Circumferential Extraction
uith Spray Irrigation/
Source Flushing
Alternative E-6:
Circumferential Extraction
with Downgradient Re-
Injection
ro
to
Alternative E-7:
Downgradient Extraction
with Downgradieat Slurry
Wall Barrier • .
Circumferential extraction
system (26 wells); SOX of
treated water re-applied to
landfill by spray irrigation;
regaining water discharged to
Gunpowder River.
Modified circumferential
extraction system (21 wells);
100X of treated water re-
injected at 11 injection wells
located downgradient from Old
0-Field near Uatson Creek
(water re-injected into upper
confined aquifer).
Downgradient extraction system
(U wells); downgradient
subsurface barrier (slurry
wall) located along Uatson
Creek and extending downward
through water-table and upper
confined aquifers.
Provides aquifer recharge and
also actively flushes
contamination from source
materials; may represent the
only safe, active source
remediation alternative;
captures highly contaminated
groundwater near landfill.
before migration/dispersion
has occurred.
Provides additional aquifer
recharge and flushing; causes
gradient reversals that
prevent additional contaminant
migration into the upper
confined aquifer and prevent
off-site migration of
contamination in the upper
confined aquifer; minimizes
induced infiltration from
Uatson Creek.
None
Captured grounduater may be
highly contaminated and highly
variable in chemical quality,
making treatment difficult;
despite leaching, source may
remain hazardous indefinitely,
and no safe method exists for
verifying the effectiveness of
source flushing.
Very complex to design and
operate; performance monitoring
is also very difficult.
Major constructability problems
due to potential UXO and
chemical agent problems, wetland
considerations, limited working
area; slurry wall restricts
discharge from water-table and
upper confined aquifers into
Uatson Creek, resulting in
increased heads over large
portions of both aquifers; some
induced infiltration from Uatson
Creek into the upper confined
aquifer occurs in response to
punping, despite placement of
the slurry wall.
Retain for detailed analysis;
most aggressive alternative for
combined source/aquifer
remediation; may be
implementable despite
difficulties noted here.
Retain for detailed analysis;
innovative alternative that
offers several advantages not
achievable by other
alternatives.
Not retained; no apparent
advantages and many potential
effectiveness,
implementability. and cost
problems.
-------
Maximum Contaminant Levels (MCLs) promulgated by the Safe Drinking Water
Act and AWQCs for the protection of aquatic life promulgated pursuant to the
Clean Water Act could be considered relevant and appropriate requirements for
Watson Creek and the Gunpowder River. These are presented for the contaminants
of concern at the Site in Table 7. MCLs are based on health effects associated
with the chemical and the technical capabilities available to detect and treat
that chemical. AWQCs are risk-based standards established for the protection of
aquatic organisms as well as human health. AWQCs are based on exposures related
to direct contact, ingestion of contaminated water, and ingestion of contaminated
organisms (i.e., food-chain exposures). MCLs may not be as appropriate as AWQCs
for the Old 0-Field Site because neither the groundwater, Watson Creek, nor the
Gunpowder River are used for drinking water and the preliminary risk assessment
has shown that human health risks are not significant while ecological risks,
although not quantifiable, may potentially exist. The containment of groundwater
as an interim action for OU One would reduce the discharge of contamination into
surface water bodies, and AWQCs are considered relevant and appropriate
requirements even though the source of contamination remains.
An evaluation of the surface water data from the HGA indicates the
contaminant levels in Watson Creek periodically have exceeded AWQCs for arsenic
(trivalent), arsenic (pentavalent), mercury, and the fish consumption Lowest
Observed Effect Level for 1,1,2,2-tetrachloroethane. The arsenic (pentavalent)
and mercury levels also are above the Water Quality Standards promulgated by the
State of Maryland, also presented in Table 7. These Ambient Water Quality
Criteria and Water Quality Standards, together with effluent limitations
established under the National Pollutant Discharge Elimination System (NPOES),
may be considered relevant and appropriate requirements for this action, because
contaminated groundwater discharge to the surface water body may contribute to
the observed concentrations. In addition to the above-mentioned contaminants,
several chlorinated VOCs have been detected periodically in Watson Creek; as
noted in the preliminary risk assessment, it is possible that some of these
compounds may be present at levels exceeding AWQCs or other standards during
transient conditions of "pulse" discharge of contaminated groundwater. MCLs and
AWQCs have not been established for thiodiglycol, 1,4-dithiane, and other
chemical-agent degradation products found in groundwater at Old 0-Field.
3.2 GROUNDWATER EXTRACTION/DISCHARGE ALTERNATIVES
Four groundwater extraction/discharge alternatives were retained for OU One
following the two-step screening process in the FFS. These alternatives,
numbered to correspond with the numbers in the FFS report, are as follows:
Alternative E-l: Downgradient Extraction with Discharge to
Surface Water
Alternative E-4: Circumferential Extraction with Capping and
Discharge to Surface Water
Alternative E-5: Circumferential Extraction with Spray
Irrigation/Source Flushing
Alternative E-6: Circumferential Extraction with Downgradient Re-
Injection
30
-------
TABLE 7
SITE-SPECIFIC APPLICABLE OR RELEVANT AND
APPROPRIATE REQUIREMENTS (ARARS) (jig/L)
PARAMETER
TCL METALS
Aluminum
Antimony
Arsenic
Barium
Beryl! ium
Cadmium
Cnromi urn '
Copper
Cyanide
Iron
Lead
Manganese
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
CHLORINATED VOCS
Bromof onn
Carbon Tetrachloride
Chlorobenzene
Chloroform
1,2-Oichloroethane
l,l-0ichloroethylen«
trans-l,2-Dichlorottnylene
1 ,2-Dichloroproparw
cis-1 ,3-Oichloropropylene
trans- 1,3-01 chl oropropylene
Methyl ene Chloride
1,1,2 , 2-Tetrachl oroethane
Tetrachloroethylene
1 , 1 , 1 -Tri chl oroethane
1 , 1 ,2-Tri chl oroethane
SDWA
MAXIMUM
CONTAMINANT
LEVEL
50-2001
10P;5P
50
1000:2000"
1"
5"
100"
1300P;1000*
200"
300*
50; 5"
SO*
2
100"
50h
50;1001
2P;1P
5000*
100*
5
100"
100"
5
7
100h
5"
5"
5h
200
5P
CWA AMBIENT WATER QUALITY
CRITERIA FOR PROTECTION OF
AQUATIC LIFE
FRESHWATER
ACUTE
CHRONIC
MARINE
ACUTE
CHRONIC
PROPOSED MARYLAND TOXIC
SUBSTANCES CRITERIA FOR
AMBIENT SURFACE WATER1
FRESHWATER
ACUTE
CHRONIC
750
88P
360*
130
3.9J
16*
18J
22
8.3J
2.4
140QJ
20
0.92P
1400
120
35200
250
28900
118000
11600
11600
23000
6060*
6060*
5280
18000
18000
87
30P
190b
5.3
1.1J
lle
12J
5.2
3.2J
0.012
160J
5
0.12P
40
110
1240
20000
5700
244'
244*
2400
840
9400
1500"
69"
43
2.9
1
150
2.1
75
300
7.2P
2130
95
50000
160
113000
224000
224000
10300
790*
790'
9020
10200
31200
500P
36"
9.3
5.6
0.025
8.3
71
0.92P
86
129
3040
450
750
360"
3.9
18
22
82
2.4
1400
20
4.1
120
37
190"
1.1
12
5.2
3.2
0.012
160
5
0.12
110
31
-------
TABLE 7 (Continued)
PARAMETER
Tri chl oroethy 1 ene
Vinyl Chloride
AROMATIC VOCS
Benzene
Toluene
Ethyl benzene
Chlorobenzene
Ortho- Xylene
Met a- and'Para-Xylene
1,2-Di Chlorobenzene
1 , 3-Di chl orobenzene
1,4-Oi Chlorobenzene
SOWA
MAX I HUH
CONTAMINANT
LEVEL
5
2
5
1000h;40*p
700h;30tp
100"
10000h;20*pf
10000h;20*pf
600";10*p
75;5*p
CVA AMBIENT WATER QUALITY
CRITERIA FOR PROTECTION OF
AQUATIC LIFE
FRESHWATER
ACUTE
45000
S300
17500
32000
250
11209
1120'
11201
PESTICIDES
Aldrin
DOT
Dieldrin
Endrin
Lindane
PCP
PCB
Toxaphene
Tributyltin (TBT)
0.2:2P
0.5h
3"
EXPLOSIVES
Nitrobenzene
3.0
0.080
2.0
0.73
CHRONIC
763«
7639
763«
MARINE
ACUTE
2000
5100
6300
430
160
19709
19709
1970"
CHRONIC
5000
129
PROPOSED MARYLAND TOXIC
SUBSTANCES CRITERIA FOR
AMBIENT SURFACE WATER1
FRESHWATER
ACUTE
1
2.0
0.014
0.0002
27000
1.3
0.16
10
0.21
6680
0.16
0.03
0.0002
3
1.1
2.5
o.ia
2
20
2
0.73
CHRONIC
0.001
0.0019
0.0023
0.08
13
0.014
0.0002
0.026
1 - These values are measured In the mixing zone.
a - 40 CFR, Part 143 - National Secondary Drinking Water Regulations.
ap - Proposed Secondary Drinking Water Standard
b - Arsenic III and compounds
c - Chromium VI and compounds
d - 100 |ig/L Is for total trihalomethanes (I.e., the sun of chloroform, bromochloromethane, and bromoform)
e - AWQC does not distinguish between cis- and trans-l,3-d1chloropropy1ene
f - Total xylenw
g - AWQC does not distinguish between 1,2-. 1.3-, and 1,4-dichlorobenzene
h - Environmental Protection Agency 1991. National Primary Drinking Water Regulations; Final Rule,
Federal Register Vol. 56, No. 20, January 30, 1991.
i - Environmental Protection Agency 1991. National Secondary Drinking Water Regulations; Final Rule,
Federal Register Vol. 56, No. 20, January 30, 1991.
j. - Hardness dependent criteria (100 mg/L used).
P - Proposed.
32
-------
Proposed downgradient and circumferential extraction well networks for Old 0-
Field are shown in Figure 6.
3.2.1 Coimon Elements
A11 of the. groundwater extraction/di scharge alternatives considered for the
Site include a number of common components. All of the extraction systems have
been developed to provide complete capture of the contaminated groundwater plume
that is discharging to Watson Creek through the water-table and upper confined
aquifers. All extraction wells will be constructed of 6-inch diameter Type 304
stainless-steel wire-wrapped screen and riser, and submersible pumps will be
required for all wells. Due to chemical agent and explosive hazards that exist
at Old 0-Field, all drilling associated with new well installation must be
performed remotely and cannot be performed safely during downrange ordnance
testing operations or during weather conditions that could allow for a
contaminated plume to disperse into populated areas. Extracted water will be
piped to an on-site treatment system for treatment prior to discharge.
Aboveground piping will be used for transferring groundwater from the wellheads
to the' on-site treatment system to avoid dangerous and expensive excavation
required for burial of piping.
Each alternative includes long-term groundwater and surface water
monitoring in compliance with requirements of RCRA Subpart F, 40 CFR §264.91 -
264.100. These monitoring activities will be conducted to gauge the
effectiveness of the selected remedy. This effectiveness/performance monitoring
program will include an off-site monitoring plan for groundwater, surface water,
sediment, and biota in proximity to Old 0-Field; installation of additional
monitoring wells; and closure of existing wells that are screened in the lower
confined aquifer to prevent possible cross-contamination of this unit. Any wells
that are damaged, unusable, or no longer necessary for the monitoring program
will be closed in accordance with federal and State requirements.
It should also be noted that all extraction/discharge alternatives and
associated cost estimates were developed under two major assumptions: (1) that
the extraction well network would incorporate existing 4-inch PVC monitoring
wells to the extent practicable; and (2) that extraction would be achieved from
both aquifers (water-table and upper confined) through the use of extraction well
pairs, with one well in the pair screened in each aquifer. The first assumption
was made because of the high cost and logistical difficulties (e.g., the
previously-mentioned remote drilling requirements) involved in extraction well
installation, while the second assumption was based on hydrogeologic data and
groundwater modeling results from the HGA that suggested the two aquifers were
hydro!ogically separate systems.
However, data generated during subsequent aquifer testing activities at the
Site (refer to Section 4.2.1) showed existing wells were unsuitable for use in
an extraction system because of short screened intervals and poor efficiency.
In addition, data on vertical leakage between the water-table and upper confined
aquifers indicate the two systems are hydraulically interconnected to some
extent, and there could be cost and operational advantages to constructing single
extraction wells screened through both aquifers. Thus, these assumptions, which
served as a partial basis for cost estimates generated during the FFS, may not
be applicable to actual site conditions as encountered during the aquifer testing
program. However, considerable uncertainty still exists regarding the optimal
33
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FIGURE 6
OPTIMIZED EXTRACTION WELL SYSTEMS
APPROXIMATE
CAPTURE ZONE
OOMWOUOOfT CnWACTlCN SYSTEM
APPROXIMATE
CAPTURE ZONE
LEGEND:
NEW WELL CLUSTER
LOCATION
EXISTING *€LL
CLUSTER LOCATION
CAPTURE
ZONE
CIRCUMFERENTIAL EXTRACTION SYSTEM
34
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number and detailed design of extraction wells for the selected remedy, and
installation of large-diameter test wells and additional aquifer testing will be
required before the remedy can be designed. Therefore, the FFS cost estimates
have been maintained, because they provide a consistent basis for direct
comparison of the extraction/discharge alternatives.
3.2.2 Alternative E-l - Downqradient Extraction with Discharge to Surface Water
Alternative E-l consists of the installation of a downgradient extraction
well network with discharge to surface water following appropriate treatment.
The downgradient extraction well network will consist of seven extraction well
pairs (one in the water-table aquifer and one in the upper confined aquifer) for
a total of 14 wells. Existing wells which are not closed will not be used as
part of the extraction system due to their inefficiency. They may, however, be
used for monitoring purposes. The total extraction rate for this system under
high recharge/high flow conditions has been estimated at 21.9 gallons per minute
(gpm).
The treated groundwater will be discharged to the Gunpowder River or Watson
Creek. The substantive aspects of an NPDES permit as required by the Clean Water
Act including weekly monitoring for selected parameters, biomonitoring, and
periodic priority pollutant scans will be required to be met for discharge of the
treated groundwater.
Alternative E-l has an estimated capital cost of $504,000 and operation and
maintenance costs of $81,650. Its present worth is estimated at $1,763,000 for
a 30-year period at a 5 percent discount rate. The installation of the
downgradient extraction system will require approximately 12 months to implement.
3.2.3 Alternative E-4 - Circumferential Extraction with Capping and Discharge to
Surface Water
Alternative E-4 consists of the construction and installation of a
circumferential extraction well network, the construction and installation of a
low-permeability multi-layer cap, treatment of groundwater in accordance with the
selected treatment alternative, and discharge to surface water. This alternative
will meet two objectives for groundwater contaminant control: waste isolation
and migration control. Installation of the cap will restrict precipitation
infiltration through the waste materials, and circumferential extraction of
groundwater will lower the water table sufficiently to prevent contact with the
waste materials in the disposal area. Although capping is primarily considered
a source control remedy, it offers additional benefits for groundwater
remediation at the Old 0-Field Site (as noted above) and, therefore, is being
considered as a component technology for groundwater extraction/discharge
alternatives for the field.
The circumferential extraction well network will consist of 13 extraction
wells or well pairs for a total of 26 wells. Existing wells which are not closed
will not be used as part of the extraction system due to their inefficiency.
They may, however, be used for monitoring purposes. The estimated total
extraction rate for the circumferential extraction system with capping is 20.6
gpm. A low-permeability, multi-layer cap will be installed over the
contamination source area and will conform to RCRA landfill closure requirements
in 40 CFR §264.310, which, among other things, includes an impermeable high
density polyethylene (HOPE) liner. The cap will be installed by first advancing
a thick clay layer across the Site, using a bulldozer, to prevent direct contact
35
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between the Site surface and heavy equipment, thereby minimizing potential
explosive and direct contact hazards during cap construction.
The extracted groundwater will be treated in accordance with the selected
treatment alternati-ve. The treated groundwater will be discharged to the
Gunpowder River or Watson Creek. Discharge of treated groundwater will require
that substantive requirements of an NPDES permit be met, including weekly
monitoring of the effluent for selected parameters and periodic priority
pollutant scans.
Alternative E-4 has an estimated capital cost of $2,598,000 and operation
and maintenance costs of $97,000. Its present worth is estimated at $4,078,000
for a 30-year period at a 5 percent discount rate. Alternative E-4 will require
approximately 24 to 36 months to implement.
3.2.4 Alternative E-5 - Circumferential Extraction with Spray Irrigation/Source
Flushing
Alternative E-5 consists of circumferential extraction with spray
irrigation/source flushing. The same circumferential extraction system described
in Alternative E-4 will be used; however, the total extraction rate is estimated
at 46.1 gpm to ensure effective capture of the additional water infiltrating the
landfill from the spray irrigation system. Approximately half of the treated
water will be re-applied to the landfill using a spray irrigation system; the
remainder of the treated water will be discharged to the Gunpowder River or
Watson Creek. This alternative is a highly aggressive approach in which water
is re-applied to waste materials to effect more rapid source degradation, as well
as to provide additional recharge for enhanced aquifer flushing. Re-application
of water to the source area will result in additional leaching and mobilization
of soil-bound or solid-phase contaminants to groundwater for subsequent
extraction and treatment. It may also enhance the degradation of buried
munitions and metal containers, resulting in more rapid extraction and treatment
of their contents. While there may be disadvantages to enhancing source
degradation in this manner, this alternative represents the most aggressive
approach without removing the source.
Discharge to Gunpowder River or Watson Creek will require meeting the
substantive aspects of an NPDES permit, with required effluent monitoring
conducted weekly.
Alternative E-5 has an estimated capital cost of $1,324,000 and operation
and maintenance costs of $110,000. Its present worth is estimated at $3,027,000
for a 30-year period at a 5 percent discount rate. Alternative E-5 will require
approximately 36 to 60 months to implement.
3.2.5 Alternative E-6 - Circumferential Extraction with Downgradient Re-
Injectlon
Alternative E-6 consists of circumferential extraction with downgradient
re-injection. The proposed extraction system is a modified circumferential
network that includes 21 rather than 26 wells (circumferential wells are not
included on the western boundary of the landfill in the upper confined aquifer).
Thus, the system is actually a circumferential system in the water-table aquifer
and a downgradient system in the upper confined aquifer. The total extraction
rate for this system is estimated at 34.3 gpm. All of the extracted groundwater
will be re-injected, following treatment, into the upper confined aquifer at 11
36
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injection wells located downgradient of the landfill near the shoreline of Watson
Creek; however, a contingency for surface discharge of some water has been
included in this alternative. Therefore, monitoring and other requirements of
both re-injection permits pursuant to federal and State underground injection
control regulations .-and an NPDES permit will be required for this alternative.
This is a highly complex system with regard to design, operation, and
performance monitoring; however, this alternative may provide necessary recharge
for additional aquifer flushing and control of induced infiltration from Watson
Creek and associated wetlands by creating a hydrologic barrier (or "freshwater
ridge") between these water bodies and the contaminated portions of the water-
table and upper confined aquifers.
Alternative £-6 has an estimated capital cost of $1,420,000 and operation
and maintenance costs of $104,000. Its present worth is estimated at $3,004,000
for a 30-year period at a 5 percent discount rate. Alternative E-6 will require
approximately 36 to 60 months to implement.
3.3 GROUNDHATEft TREATMENT ALTERNATIVES
Six groundwater treatment alternatives were identified for OU One in the
FFS. These alternatives, numbered to correspond with the numbers in the FFS
report, are as follows:
Alternative T-l: No Action
Alternative T-2: Minimal Action
Alternative T-3: Chemical Precipitation/Air Stripping/Carbon
Adsorption (liquid phase)
Alternative T-4: Chemical Precipitation/Ultraviolet-Oxidation
Alternative T-5: Chemical Precipitation/Activated Sludge
Biological Treatment/Carbon Adsorption
Alternative T-6: Chemical Precipitation/Powdered Activated Carbon
Treatment (PACT)
3.3.1 Common El^aents
All of the active groundwater treatment alternatives (Alternatives T-3
through T-6) considered for the Site include a number of common components.
Implementation of each treatment alternative will require site clearing and
preparation; construction of a treatment building, installation of a concrete pad
and containment system; extension of water and electrical lines; long-term system
operation; long-term influent and effluent monitoring including chemical analysis
and biotoxicity testing; long-term groundwater monitoring in compliance with
requirements of RCRA Subpart F, 40 CFR §§264.90-264.101 and a NPOES permit; and
periodic reviews of site conditions as long as chemically affected media remain
at the Site (i.e., the. source), in accordance with CERCLA §121(c), 42 USC
§9621(c), the NCR, and applicable EPA guidance.
37
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water is discharged to the Gunpowder River to ensure that chemical-specific
federal and State applicable or relevant and appropriate requirements (ARARs) and
the substantive requirements of an NPOES permit are satisfied. Monitoring will
involve chemical sampling as well as acute and chronic biotoxicity testing. In
the event that monitoring indicates ARARs or NPDES substantive requirements are
not achieved, treatment system operating parameters will be modified to improve
performance such that the requirements are satisfied.
If the contaminant source (;.e., the buried munitions and chemical agents)
remains, chemicals will continue to leach into the groundwater far into the
future, even if a cap is constructed over the field to isolate the wastes. Given
the need for groundwater treatment to continue for a long period of time, it may
become necessary to replace the entire treatment system one or more times during
the remedial action lifetime. Replacement times will be approximately the same
for any of the groundwater treatment alternatives; therefore, for comparative
purposes, we have assumed that the treatment equipment will be maintained at
least 30 years.
3.3.2 Alternative T-l - No Action
The Superfund program requires that the "no action" alternative be
evaluated at every site to establish a baseline for comparison. Under this
alternative, the Army would take no further action at the Site to prevent
exposure to the groundwater contamination.
Alternative T-l does not have associated capital and operation and
maintenance costs, and will not require any time for implementation.
3.3.3 Alternative T-2 - Minimal Action
Alternative T-2 consists of implementation of institutional restrictions
such as access restrictions, deed restrictions, and land use restrictions; public
education programs to inform workers and local residents of the potential site
dangers; emergency provisions; long-term environmental monitoring including
quarterly groundwater monitoring; and five-year reviews as required by CERCLA
§121(c), 42 USC §9621(c), the NCP, and applicable EPA guidance when hazardous
chemicals remain untreated. Aspects of Alternative T-2 are also included in each
of the active groundwater treatment alternatives (Alternatives T-3 through T-6).
Alternative T-2 has an estimated capital cost of $50,000 and operation and
maintenance costs of $104,000. Its present worth is estimated at $1,692,000 for
a 30-year period at a 5 percent discount rate. Alternative T-2 will require
approximately six or less months to implement.
3.3.4 Alternative T-3 - Chemical Precipitation/Air Strloolno/Carbon Adsorption
(liquid phase)
Alternative T-3 consists of the three most common groundwater treatment
technologies: chemical precipitation, air stripping, and liquid-phase carbon
adsorption. Chemical precipitation will provide the necessary treatment for
reduction of inorganic contaminant concentrations, and the combination of air
stripping followed by carbon adsorption will provide the necessary treatment for
reduction of organic contaminant concentrations. Chemical precipitation involves
modifying the chemical structure of metallic compounds such that they precipitate
out of solution as solids, flocculate together, and settle out of the water by
gravity. This process .will produce sludge containing the metal contaminants
38
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which will be dewatered in a filter press. The resultant filter cake will be
properly disposed at a facility permitted to accept such waste.
Air stripping is a mass transfer process in which volatile organic
compounds (VOCs) dissolved in the groundwater are transferred to the vapor phase
by countercurrent contact with a stream of air. Air pollution controls such as
a vapor-phase carbon adsorption unit or a catalytic converter will be required
to reduce VOC emissions and comply with air regulations. Carbon adsorption
involves physically adsorbing organic compounds from the groundwater onto porous
carbon media containing sites prepared to accept the contaminants. Because many
VOCs will be removed through air stripping, organic loading on the carbon will
be reduced. Carbon adsorption will, therefore, be used primarily for removal of
less volatile organic compounds. Spent vapor- and liquid-phase carbon will
require proper off-site disposal or regeneration.
Alternative T-3 has an estimated capital cost of $1,263,000 and operation
and maintenance costs of $525,000. Its present worth is estimated at $9,392,000
for a 30-year period at a 5 percent discount rate. Alternative T-3 will require
approximately 18 to 24 months to implement.
3.3.5 Alternative T-4 - Chemical Precipitation/Ultraviolet-Oxidation
Alternative T-4 consists of chemical precipitation for reduction of
inorganic contaminant concentrations and ultraviolet (UV)-oxidation for reduction
of organic contaminant concentrations. UV-oxidation is an emerging technology
which uses ultraviolet light in conjunction with a strong oxidizing agent, such
as hydrogen peroxide or ozone, to destroy organic compounds in groundwater. The
ultraviolet light reacts with the hydrogen peroxide or ozone forming hydroxyl
radicals which oxidize organic compounds. In addition, many compounds absorb
ultraviolet light causing them to be more reactive to chemical oxidants. UV-
oxidation will not produce treatment residuals. This alternative will only
require disposal of chemical precipitation filter cake, in accordance with RCRA
Subtitle C.
Alternative T-4 has an estimated capital cost of $1,377,000 and operation
and maintenance costs of $385,000. Its present worth is estimated at $7,357,000
for a 30-year period at a 5 percent discount rate. Alternative T-4 will require
approximately 18 to 24 months to implement.
3.3.6 Alternative T-5 - Chemical Precipitation/Activated Sludge Biological
Treatment/Carbon Adsorption
Alternative T-5 consists of chemical precipitation for reduction of
inorganic contaminant concentrations and activated sludge followed by carbon
adsorption for reduction of organic contaminant concentrations. Activated sludge
is a biological treatment process in which microorganisms destroy organic
compounds in groundwater by consuming them as food. Residual sludge will be
dewatered in a filter press and the resultant filter cake will be properly
disposed in accordance with RCRA Subtitle C. Carbon adsorption will then be used
as a final polish to treat organic compounds which are not readily biodegradable.
This alternative will require disposal (or regeneration) of chemical
precipitation filter cake, activated sludge filter cake, and spent carbon.
Alternative T-5 has an estimated capital cost of $1,623,000 and operation
and maintenance costs of $311,000. Its present worth is estimated at $6,449,000
39
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for a 30-year period at a 5 percent discount rate. Alternative T-5 will require
approximately 18 to 24 months to implement.
3.3.7 Alternative T-6 - Chemical Precipitation/Powdered Activated Carbon
Treatment fPAC.Tl
Alternative T-6 consists of chemical precipitation for reduction of
inorganic contaminant concentrations and PACT for reduction of organic
contaminant concentrations. PACT is a biological treatment process in which
powdered activated carbon (PAC) is added directly to the activated sludge reactor
so that biodegradation and adsorption occur simultaneously in one vessel. The
PAC is removed in the clarifier and recycled along with the activated sludge,
thus providing an increased retention time for those compounds adsorbed to the
carbon, allowing further biodegradation. Spent carbon will be expelled along
with the activated sludge. This alternative will require disposal of chemical
precipitation filter cake and activated sludge filter cake containing powdered
activated carbon, in accordance with RCRA Subtitle C.
Alternative T-6 has an estimated capital cost of $1,551,000 and operation
and maintenance costs of 5259,000. Its present worth is estimated at $5,582,000
for a 30-year period at a 5 percent discount rate. Alternative T-6 will require
approximately 18 to 24 months to implement.
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4.0 COMPARATIVE ANALYSIS OF REMEDIAL ALTERNATIVES
The groundwater extraction/discharge and treatment alternatives described
in Sections 3.2 and 3.3 were evaluated against nine specified criteria in
accordance with CERCLA §121(b), 42 USC §9621(b), and the NCR, 40 CFR 300.430(e),
to select an overall preferred remedial alternative for interim action at Old 0-
Field. The extraction/discharge alternatives were evaluated separately from the
treatment alternatives so that a preferred approach from each of the two
categories could be identified. The overall preferred remedial alternative was
then developed by combining the preferred extraction/discharge alternative with
the preferred treatment alternative.
This section discusses the evaluation of the extraction/discharge and
treatment alternatives against the specified criteria. Aquifer pumping tests and
groundwater treatability studies were conducted to obtain important information
required to make an informed evaluation.
4.1 EVALUATION CRITERIA
The following evaluation criteria were used in the comparative analysis of
alternatives and are based on Section 121(b) of CERCLA, 42 USC §9621(b), and the
NCR, 40 CFR 300.430(e):
1. Overall Protection of Human Health and the Environment addresses
whether or not a remedy provides adequate protection and describes
how risks posed through each pathway are eliminated, reduced, or
controlled through treatment, engineering controls, or institutional
controls.
2. Compliance with ARARs addresses whether or not a remedy will meet
all of the applicable or relevant and appropriate requirements of
federal and State environmental statutes and/or provide grounds for
invoking a waiver.
3. Long-term effectiveness and permanence refers to the magnitude of
residual risk and the ability of a remedy to maintain reliable
protection of human health and the environment over time once
cleanup goals have been met.
4. Reduction of toxicity, mobility, or volume through treatment is the
anticipated performance of treatment technologies that may be
employed in a remedy.
5. Short-tern effectiveness refers to the speed with which the remedy
achieves protection, as well as the remedy's potential to create
adverse impacts on human health and the environment that may result
during the construction and implementation period.
6. Implementabllity is the technical and administrative feasibility of
a remedy, including the availability of materials and services
needed to implement the chosen solution.
7. Cost includes capital and operation and maintenance costs, and
present worth. All of the remedial alternatives will operate until
the final remedy for all operable units for Old 0-Field is
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determined. An operating period of 30 years was selected to allow
for comparison of alternatives. Although not included in the cost
estimates, equipment such as wells, multi-layer caps, and treatment
units will likely require replacement after 20 to 30 years of
operation or less.
8. State Acceptance indicates whether, based on its review of the FFS
and Proposed Plan, the State concurs with, opposes, or has no
comment on the preferred alternative; and
9. Community Acceptance indicates the public support of a given remedy
and is discussed in the Responsiveness Summary provided in Appendix
A.
The first two criteria relate to statutory requirements and are, therefore,
categorized as threshold criteria that must be satisfied by the alternative. The
next five criteria are grouped together as primary balancing criteria upon which
the analysis was based. The final two criteria were addressed following comment
on the-Proposed Plan and are considered modifying criteria.
4.2 EVALUATION OF GROUNDWATER EXTRACTION/DISCHARGE ALTERNATIVES
4.2.1 Aouifer Pumping Tests
Groundwater extraction/discharge alternatives were developed and evaluated
in the FFS for groundwater remediation at Old 0-Field based on hydrogeologic and
contaminant data generated by the HGA. A USGS groundwater flow model (MODFLOW)
was used to develop and optimize extraction well networks under several scenarios
for the Site, and to compare the effectiveness, implementability, and cost of
each alternative. However, significant uncertainty was found to exist in
predicting extraction system performance based on groundwater modeling results.
Specifically, the response of the Old 0-Field aquifer systems to pumping (i.e.,
stressed conditions) was not known, and data were lacking with regard to: 1)
capture zone sizes for individual wells and the overall extraction network; 2)
interactions between Watson Creek and the aquifer system (i.e., the extent of
induced infiltration); and 3) the effects of pumping on vertical gradients and
leakage rates between the water-table and upper confined aquifers. Also, the
assumption that existing monitoring wells could be incorporated into the
extraction system (a significant cost factor) required verification through
actual testing.
Based on these considerations, an aquifer testing program was implemented,
consisting of step-drawdown tests and constant-discharge tests on three existing
monitoring wells in the contaminated plume area. Existing monitoring wells were
used in this program to determine whether these wells could be incorporated into
a full-scale extraction well network; and because logistical difficulties (;'.e.,
remote drilling) associated with installation of extraction test wells would
cause schedule delays of at least one year before any type of aquifer testing
program could be implemented.
However, step-drawdown testing indicated that several of the wells selected
for testing would not sustain long-term pumping at extraction rates sufficient
to adequately stress the aquifer system. Because the low-yield wells are located
in what would appear to be high-permeability areas (based on HGA data), it
appears that the observed yields are almost certainly a function of well
42
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inefficiencies. Well inefficiencies are most likely the result of short screen
lengths, small screen slot sizes, and the use of fine-grained filter pack
materials. Therefore, long-term constant-discharge tests for low-yield wells
were canceled based on the limited additional data that they would provide.
Additional information on aquifer properties and boundary conditions in the
affected areas of Old 0-Field will be gathered by testing extraction wells
installed during an early period of the design/construction phase of the
remediation effort. Suitably designed extraction wells, made available by
implementation of the proposed interim remedy, will provide data needed for
evaluating the performance of long-term or permanent remedies. Analysis of
groundwater from these wells also will provide data for design of the treatment
system, and the performance parameters that will need to be monitored.
Despite the fact that aquifer tests at Old 0-Field were unable to proceed
as initially planned, the modified program provided important information to
support the selection of the preferred extraction/discharge alternative, and
provided essential data for refinement of groundwater modeling efforts and
preliminary design of groundwater extraction alternatives. More detailed
discussion of relevant data can be found in the Aquifer Testing Report.
Important findings concerning the aquifer properties and character are summarized
as follows:
• Leakage through the clay layer between the water-table aquifer (WTA)
and the upper confined aquifer (UCA) occurs almost instantaneously
as evidenced by early-time drawdown in the WTA (with pumping in the
UCA). This verifies the assumed hydraulic connection between the
two shallow aquifers, and suggests that single extraction wells
screened in both aquifers may be preferable to extraction well
pairs.
• The semi-confining unit is laterally extensive in the contaminated
plume area northeast of the Old 0-Field landfill, as evidenced by
early-time drawdown in wells screened in the UCA at these locations.
Early drawdown observed in monitoring wells several feet away from
the pumping well indicate that the aquifer is under confining
pressures.
• Tidal changes observed in Watson Creek are responsible for water-
level changes in monitoring wells in the water-table, upper
confined, and lower confined aquifers. Water-level changes in wells
due to tidal influences are roughly half the amplitude of the tides
observed in Watson Creek.
• Existing monitoring wells are not appropriate for groundwater
extraction as maximum attainable yields in these wells are not
representative of aquifer materials. This factor, as previously
noted, appears to be related to well inefficiency rather than
misinterpretation of aquifer hydraulic properties.
The above findings provide additional data for analysis of the
extraction/discharge alternatives developed in the focused FS, and support the
selection of the preferred alternative. The shallow aquifer system present at
the Site, including the water-table aquifer and the upper confined aquifer,
responds to pumping stresses as a single, semi-confined, or leaky aquifer. The
interconnected nature of these aquifers permits the design of a groundwater
43
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extraction system that retrieves water from both horizons, thereby minimizing
drawdown and maximizing the area of influence for each extraction well. This
allows for the installation of the fewest number of wells necessary to capture
contaminants emanating from the 'fenced area at Old 0-Field. However, as
previously noted, additional testing (during the early stages of extraction
system design/construction) will be required to determine the exact number and
location of extraction wells required for the preferred alternative, and to
provide detailed information needed to complete the extraction system design such
that all contaminant plumes emanating from the waste are captured to the maximum
extent possible. Because of the uncertainties, stringent performance monitoring
will be required during the interim remedy to ensure plume containment. If
monitoring indicates plume containment is not achieved, the extraction system
will be modified to accomplish this.
4.2.2 Groundwater Extraction/Discharge Alternatives Evaluation
Groundwater extraction/discharge alternatives are evaluated below with
respect to the nine criteria specified in Section 4.1. A summary of the
evaluation results is presented in Table 8.
Overall Protection of Human Health and the Environment. All of the
alternatives would provide adequate protection of human health and the
environment by protecting nearby ecosystems, minimizing the potential for human
exposure to contaminants., and preventing off-site migration of hazardous
substances via groundwater pathways. Each extraction/discharge alternative
considered would minimize environmental risks to sensitive aquatic and
terrestrial ecosystems in Watson Creek, Gunpowder River, and the surrounding
wetlands by preventing discharge of contaminated groundwater to these areas. The
extraction/discharge alternatives would also control potential human health risks
associated with direct contact, food-chain, surface water, and groundwater
exposures that could result from groundwater contamination at the Site.
The capping of the landfill area and the groundwater level control included
in Alternative E-4 offers additional human health and environmental benefits:
1) it effectively controls air emissions from the disposal site, including direct
volatile emissions and airborne transport of contaminated dust particles; and 2)
it isolates wastes beneath the cap and minimizes direct contact between the
wastes and the groundwater. However, the extreme potential safety problems
associated with any direct-intrusion remedies such as capping will need to be
addressed before this alternative could be implemented.
Alternative E-5 may be more protective than some of the other alternatives
because additional contamination is trapped by the extraction system within the
immediate vicinity of the landfill, rather than as it migrates downgradient
toward potential discharge points. However, uncertainty regarding the chemical
quality and treatability of extracted groundwater following source flushing is
a significant potential disadvantage for this alternative in protection of human
health and the environment. System failure could result in extensive flushing
of contaminants into previously uncontaminated zones of the aquifers, and greatly
increased mass loading to Watson Creek, possibly with toxic effects. This
alternative has too many areas of uncertainty to be rated as fully protective of
human health and the environment.
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TABLE 8
DETAILED EVALUATION SUMMARY
FOR CROUHDUATER EXTRACTION/DISCHARGE ALTERNATIVES
Alternative
Effectiveness
Iroplementability
Cost.
Conclusions
E-1: Downgradient
Extraction with Discharge
to Surface Water
E-A: Circumferential
Extraction with Capping
and Discharge to Surface
Water
E-5: Circumferential
Extraction with Spray
Irrigation/Source Flushing
Effective in capturing
contaminated groundwater and
minimizing human health/
ecological risk. Does not
provide waste isolation or
active source remediation.
Long operating period likely to
be required.
Effective in capturing
contaminated groundwater, and
in providing waste
isolation/migration control by
restricting infiltration
through waste materials and
direct contact between
grounduater and wastes. Source
will be isolated but will
remain potentially active.
Long operating period likely to
be required.
Spray irrigation/source
flushing will provide active
source remediation in addition
to aquifer flushing, and
circumferential system will
extract contaminated
groundwater near source area,
minimizing additional
downgradient contamination.
Source flushing may result in
very highly contaminated
groundwater that may be
difficult to treat. System
failure could result in severe
contaminant loading to aquifers
and Watson Creek.
Simple, straightforward alternative C
to design, operate, and monitor. O&N
Technical and administrative PV
feasibility appear to be very good,
based on use of well-proven
technologies and straightforward
approach.
Utilizes well-proven existing C
technologies; design and operation OCM
appear straightforward. Regulatory PV
agency and public acceptance are
predicted to be good. Cap
installation over source area may be
difficult because of potential UXO
hazards.
Treatment of groundwater may be C
difficult, due to highly variable and O&H
potentially very poor chemical PV
quality caused by source flushing.
Risks associated with system failure,
include contaminant loading to Watson
Creek and contamination migration
into "clean" aquifer zones, also
limit implementability.
$ 504,000
$ 81,650/year
$ 1.763.000
$2,598,000
S 97,000/year
$4,078.000
$1.324,000
$ 110,000/year
$3,027,000
Most cost-effective remedy
available for grounduater
extraction. Operationally
versatile, and can be combined
with additional technologies or
remedial actions in the future.
Provides very effective waste
isolation, but costs are high and
source will remain potentially
active for a long time period
despite isolation. Host
protective option available
without extensive RSO, major
excavation, etc.
Despite major uncertainties and
potentially serious consequences
associated with system failure,
this alternative may be the only
possible permanent remedy for
combined source/groundwater
remediation. Will require some
RCD and field testing, with
extensive monitoring to ensure
adequate performance.
Aggressive, high-risk alternative
that may provide additional
benefits.
-------
TABLE B
DETAILED EVALUATION SUWIARY
FOR GROUNDUATER EXTRACTION/DISCHARGE ALTERNATIVES (Continued)
Alternative
Effectiveness
Implementability
Cost1
Conclusion
E-6: Circumferential
Extraction with
Downgradient Re-Inject ion
Very effective in preventing
off-site migration in upper
confined aquifer, reversing
hydraulic gradients to provide
•ore effective capture, and
minimizing indirect
infiltration fro* Watson Creek.
Vertical gradient reversal also
prevents migration of
contaminants into the upper
confined aquifer. Long-term
effectiveness is questionable
due to potential performance
problems with injection wells
and possible aquifer clogging.
Highly complex to design, operate,
and monitor. Problems with
demonstrating performance through
actual field measurements (rather
than modeling predictions) restrict
implementability.
C = $1,420,000
DIM = S 104.000/year
PV = S3.004.000
Offers several advantages with
regard to plune capture and
migration control coopered to all
other alternatives, but will be
difficult to implement because of
complexity and difficulty in
design, operation, and
performance monitoring. Long-
term effectiveness could be
affected by re-inject ion
problems. Costs are high, and
administrative feasibility may be
poor due to highly complex nature
of alternative.
Capital costs (C), annual operating and maintenance costs (OtM), and present worth (PV) for 30 years at a 5X discount rate are presented.
continue for an indefinitely long time period.
O&M costs may
O»
-------
The effectiveness of Alternative E-6 is difficult to demonstrate in the
field due to the highly complex nature of the alternative. However, even if some
system failure does occur, it will not have the potentially severe consequences
that are associated with Alternative E-5.
Compliance with ARARs. Groundwater extraction/discharge alternatives will
comply with chemical-specific ARARs if accompanied by treatment of extracted
water. Attainment of groundwater discharge limitations for discharge to
Gunpowder River, Watson Creek, and/or re-injection is addressed under groundwater
treatment alternatives. Extraction and treatment of groundwater may eventually
result in attainment of groundwater remediation in the water-table and upper
confined aquifers at the Site; however, a very considerable time period may be
required to reach these conditions because of the continued existence of an
active contamination source. Alternative E-4 may achieve groundwater standards
more rapidly because the waste is isolated; however, such attainment may be
temporary or intermittent as additional contaminants are leached from the source.
Alternative E-5 initially will result in increased levels of contaminant
concentrations; however, this more highly contaminated water will be captured by
the extraction system and treated to meet discharge standards before release to
surface water or re-application to the field. The flushing action provided by
the re-injection of treated water back into the aquifer under Alternative E-6
will aid in the attainment of groundwater remediation, but will not improve
performance of the containment objective.
Location-specific and action-specific ARARs that apply to groundwater
extraction are: 1) obtaining the necessary permits and/or complying with their
substantive requirements; and 2) avoiding resource damage that could potentially
be caused by groundwater pumping, such as wetlands dewatering. The multi-layer
cap included in Alternative E-4 will comply with RCRA closure requirements for
landfills. All alternatives are expected to meet location and action-specific
ARARs, including protection of nearby wetlands and satisfying treated water
standards established for surface water discharge and re-injection.
Long-term Effectiveness and Permanence. Assuming that the extraction
systems are optimized and adequate flow rates can be maintained to provide the
necessary capture of the contaminated groundwater plume that is currently
discharging to Watson Creek through the water-table and upper confined aquifers,
it is highly likely all the alternatives will be effective in meeting remedial
action objectives. Aquifer remediation may never be accomplished, however, if
an active contamination source remains in place at Old 0-Field. Therefore, any
groundwater extraction alternative that is implemented at the field must operate
for an indefinite (but probably very long) time period and, to some extent, must
be considered a maintenance action.
The waste isolation afforded by the cap included in Alternative E-4 will
restrict groundwater contamination by providing long-term reductions in the
amount of water that otherwise would pass through the contaminated soils, thus
reducing the generation of contaminated leachate that could migrate to
groundwater. However, the cap will not prevent liquid wastes from migrating to
the groundwater by gravity although it will slow the migration process. The
longevity and maintenance requirements of the multi-layer cap will affect the
long-term effectiveness of Alternative E-4. After approximately 30 years,
replacement of the cap may be necessary due to weathering and erosion. The long-
term effectiveness of Alternative E-4 may be no better than the more simple and
less costly Alternative E-l; however, short-term benefits with regard to
groundwater quality may be significant and Alternative E-4 may be valuable as an
47
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interim action that will address major site problems (/.e., potential for direct
contact with disposed materials) until an active source (OU Two) remediation
strategy can be implemented.
A potential advantage for Alternative E-5 is that the extraction/source
flushing sequence results in a hydraulic gradient pattern that causes radial
groundwater flow outward from the center of the landfill which results in capture
very near the Site and, therefore, very short migration pathways; thereby
minimizing additional contamination of downgradient zones of the aquifers.
However, the disadvantages associated with Alternative E-5 are likely to outweigh
any potential advantages. These disadvantages are: 1) extracted water quality
is difficult to predict and may be quite poor and variable making treatment more
difficult than for other alternatives; 2) effectiveness of source flushing in
achieving source remediation is impossible to predict and very difficult to
monitor because of the unknown characteristics of the source; and 3) problems
with re-infiltration through the surface of the field are possible over the long
term, and may be difficult to solve due to unexploded ordnance and chemical agent
hazards associated with on-site activities; and 4) groundwater mounding beneath
the disposal site caused by increased recharge may result in contaminant
migration into previously uncontaminated zones of the aquifer. Despite these
disadvantages, Alternative E-5 is the only alternative that provides any
potential for active source remediation and, therefore, holds a major advantage
over all other remedies in providing a permanent solution to site problems.
Potential long-term effectiveness concerns- specific to Alternative E-6
include: 1) performance monitoring and effectiveness demonstration of this
complex system may not be possible; 2) operational problems that may occur with
re-injection wells, including screen clogging, airlocks, and metal precipitation;
and 3) possible changes in the physical and chemical characteristics of the
aquifers (e.g., iron/manganese precipitation) that may result from re-injection
of treated water could affect the overall performance of the extraction system.
Based on these factors, long-term effectiveness of Alternative E-6 is considered
questionable.
Reduction of Toxicity, Mobility, or Volume Through Treatment. Groundwater
extraction at Old 0-Field does not directly affect toxicity or volume of
contaminants contained in the groundwater, but rather removes contamination from
the aquifers so that treatment can be performed. Alternative E-4 will reduce the
mobility of wastes within the source area by limiting the development of leachate
and the dissolution of wastes by direct contact with groundwater. Alternative
E-5 will initially increase the mobility of wastes contained within the landfill;
however, these contaminants will be captured by the extraction system in close
proximity to the landfill.
Alternative E-6 limits the mobility of wastes migrating toward Watson Creek
by creating a hydrologic barrier and containing contamination to a small portion
of the aquifer near the source area. Alternative E-6 also is very effective in
preventing off-site migration in the upper confined aquifer, reversing hydraulic
gradients to provide more effective capture, and minimizing indirect infiltration
from Watson Creek. Vertical gradient reversal caused by the re-injection of
treated groundwater into the upper confined aquifer prevents migration of
contaminants from the water-table aquifer into the upper confined aquifer.
t
Short-term Effectiveness. Alternative E-l involves installation of the
fewest number of new extraction wells. Remote-drilling will be required for well
installation and extensive health and safety precautions will be necessary, and
48
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SOPs for these activities will need to be developed. Health and safety concerns
and logistical problems associated with start-up of the extraction systems are
not negligible, but major delays or greatly increased costs do not appear to be
likely. Uncertainties also exist because the treatability of the groundwater
withdrawn in an improved well design is not known precisely.
Discharge of treated groundwater to the Gunpowder River or the Old 0-Field
aquifer system will require meeting the substantive requirements of NPDES and/or
re-injection permits for all of the extraction/discharge alternatives. Discharge
requirements may be very stringent and may be difficult to establish because of
the concern regarding potential impacts to the sensitive upper Chesapeake Bay
area.
Several major logistical and health and safety problems will need to be
addressed prior to implementation of Alternative E-4, which may cause delays and
limit short-term effectiveness of this alternative, including: 1) detailed
development of an approach for installation of the cap over the landfill; and 2)
installation of circumferential wells in very close proximity to suspected
disposal areas. Capping Old 0-Field has the potential to be an extremely
hazardous activity due to the presence of unexploded ordnance and chemical
warfare agents in the disposal area.
Implementation of Alternative E-5 may involve several short-term problems
as some research and development (e.g., pilot-scale field tests on a small
portion of the Site) may be required due to considerable uncertainty that exists
regarding its performance. More information on the expected chemical quality of
the extracted groundwater is necessary to ensure that discharge limits from the
treatment system are not exceeded.
Implementation of Alternative E-6 may be restricted by the inability to
develop a performance monitoring system and program to be utilized in the field.
Implementability. Alternative E-l is the most simple, straightforward
alternative under consideration.
The implementability of Alternative E-4 is limited by health and safety
hazards associated with installation of the cap which involves working within the
boundaries of Old 0-Field. Extensive safety review will be required prior to
construction. In addition, some of the locations for installation of
circumferential wells, utilized by Alternatives E-4, E-5, and E-6, are in very
close proximity to the disposal site boundaries, and will, require special caution
during drilling and installation activities, and possibly more extensive
geophysical characterizations prior to drilling.
For Alternative E-5, a spray irrigation network would be required to be
installed within the source area boundaries, where work is greatly restricted by
ordnance and chemical agent hazards; however, installation and maintenance can
probably be achieved by use of remote equipment and surface sweeps by explosive
ordnance disposal experts to clear "work pathways". Implementation, however,
will be difficult because of the safety hazards associated with Old 0-Field.
The greatest difficulty with Alternative E-6 is developing a workable
approach to demonstrating the system's effectiveness in the field and monitoring
its performance.
49
-------
Cost. The present worth of Alternative E-l is 51,763,000 for a 30-year
period at a 5 percent discount rate. Alternative E-6 has a present worth of
53.004,000. Alternative E-5 and E-4 have present worth of 53,027,000 and
54,078,000, respectively.
State Acceptance. The State of Maryland concurs with the selected
extraction/discharge alternative indicated in the Declaration and in Section 5.0.
Community Acceptance. As mentioned in Section 1.4, the public was invited
to review the administrative record, attend a public meeting, and submit comments
on all extraction/discharge alternatives under consideration. The Responsiveness
Summary provided in Appendix A gives a.thorough review of public comments as well
as Army and EPA responses. Community Acceptance is assessed in detail in the
Responsiveness Summary.
4.3 EVALUATION OF GROUNDWATER TREATMENT ALTERNATIVES
4.3.1 Gt'oundwater Treatabilitv Studies
The feasibility study analysis indicated a lack of performance data for the
treatment alternatives with respect to chemical agent degradation products such
as thiodiglycol, 1,4-dithiane, and explosives. Therefore, a series of
treatability studies were conducted to evaluate the ability of each treatment
alternative to treat Old 0-Field groundwater, and to compare the effectiveness
of each treatment alternative in satisfying treatment ARARs. Bench-scale
treatability studies were conducted for treatment Alternatives T-3 through T-5.
Treatment Alternative T-6 was not tested because literature studies indicated
that activated sludge followed by carbon adsorption (Alternative T-5) and PACT
(Alternative T-6) provide comparable treatment results (refer to Table 9).
Pilot-scale tests, for those alternatives determined to be effective in treating
Old 0-Field groundwater based on bench-scale testing, were then conducted at Old
0-Field using groundwater extracted during the aquifer pumping tests to evaluate
and compare the effectiveness and implementability of the alternatives under
actual field conditions.
As noted, water quality standards or criteria (as well as toxicity data for
some compounds) are lacking for several key chemicals of concern at Old 0-Field,
especially degradation products of chemical agents and other military-specific
compounds. In addition, toxicity information for complex mixtures of organic
contaminants and metals, such as those present at Old 0-Field, is generally
incomplete; therefore, possible synergistic effects or other interactions can be
very difficult to predict. Based on these factors, it was considered important
to develop direct methods for measuring treatment system performance as a
function of overall reduction of toxicity, rather than evaluating system
performance solely on the basis of chemical removal efficiency. To meet this
goal, samples of untreated groundwater and unit process effluents from the
various operations (e.g., chemical precipitation, UV-oxidation, air stripping,
carbon adsorption, activated sludge) were collected and used in a series of acute
biotoxicity studies involving several aquatic organisms that would typically be
found in environments similar to Watson Creek (mysid shrimp, daphnids, fathead
50
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TABLE 9
REMOVAL OF CONTAMINANTS BY ACTIVATED SLUDGE,
ACTIVATED SLUDGE PLUS TWO GRANULAR CARBON COLUMNS,
AND THE PACT PROCESS
Compound
Toluene
Ethyl benzene
Chlorobenzene
Benzene
Carbon . Tetrachl oride
Trichloroethylene
1,1, 1-Tri chl oroethane
1,2-Dichloroethane
Chloroform
Methyl ene Chloride
Tetrachl oroethyl ene
Activated
Sludge (AS)
% Removal
99.7
99.8
99.3
99.5
99.5
99.5
98.0
99.8
97.0
94.0
97.0
AS Plus One
Carbon Column
% Removal
99.8
99.7
99.7
99.7
99.5
99.1
97.0
98.0
97.0
92.0
96.0
AS Plus Two
Carbon Columns
% Removal
99.9
99.8
99.7
99.7
99.9
99.8
94.0
97.0
98.0
96.0
98.0
PACT
% Removal
99.9
99.9
99.8
99.6
99.0
98.8
98.0
98.0
97.0
95.0
93.0
Source: Hutton, David 6. February 1981. "Priority Pollutant Removal -
Comparison of the DuPont PACT Process with Activated Sludge Followed
by Granular Carbon Columns." E.I. DuPont de Nemours & Company, Inc.
Paper presented at the Symposium on Application of Adsorption to
Wastewater Treatment, Vanderbilt University, Nashville, Tennessee.
51
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and sheepshead minnows). Acute biotoxicity studies were performed as part of
both the bench-scale and pilot-scale treatability testing programs. The results
of these tests are summarized in the paragraphs below along with treatment system
performance data. Chronic biotoxicity studies were not performed during
treatability testing because treated effluent was not generated over the time
frame required for the studies. Chronic biotoxicity studies will be performed
during start-up of the full-scale treatment system, and as part of a monitoring
program during operation. Results of chronic studies will be presented in the
final ROD for Old 0-Field.
Chemical Precipitation. Chemical precipitation using lime to raise the pH
of the groundwater to 11.0 was determined to provide the best metals removal
based on bench-scale testing results. Table 10 presents metals removal data from
this chemical precipitation bench-scale test. The data demonstrate that chemical
precipitation is effective in reducing metals concentrations and meeting MCLs and
AWQCs with the exception of iron which had a concentration of 701 ug/L after
precipitation compared to its secondary MCL of 300 jig/L. Secondary MCLs are
established for contaminants that primarily affect the aesthetic quality relating
to the public acceptance of drinking water and are not health-based or Federally
enforceable. Calcium content increased substantially due to the addition of
lime. The chemical precipitation" process was found to eliminate the acute
toxicity to fathead minnows and daphnids exhibited by the untreated groundwater.
A continuous flow, pilot-scale chemical precipitation study was performed
over a four-day period. The pilot-scale study was operated under the same pH
conditions as the bench-scale study. Table 11 presents metals removal data for
chemical precipitation from Day 3 of the pilot-scale test. The data demonstrate
that chemical precipitation is effective in reducing metals concentrations and
satisfying MCL/AWQC criteria with the exception of iron and lead. Iron was
present at 442 ug/L following precipitation compared to its secondary MCL of 300
ug/L. Lead was present at 5.80 ug/L compared to a freshwater chronic AWQC of 3.20
(ig/L and marine chronic AWQC of 5.6 ug/L. Lead was, however, reduced below its
MCL and acute AWQCs. Pilot-scale chemical precipitation was conducted without
the benefit of field data necessary to optimize operating parameters such as pH.
It is possible that system performance could have been improved if field data
were available to make field adjustments. Calcium was also found to increase due
to lime addition. The calcium came from calcium sulfate solids produced during
neutralization of the groundwater with sulfuric acid. The calcium level in the
final effluent can be reduced by filtering the groundwater following
neutralization with a multi-media filter. The chemical precipitation process was
found to eliminate the acute toxicity to fathead minnows, daphnids, sheepshead
minnows, and mysid shrimp exhibited by the untreated groundwater.
Air Stripping/Carbon Adsorption. The bench-scale air stripping process
consisted of aerating metals-pretreated groundwater in sealed 55-gallon drums
using compressed air at 3 cfm. Aeration continued for 18 hours after which
volatile emissions measured less than 1 ppm with an HNu meter. The aerated
groundwater was then sent through three continuous flow carbon adsorption columns
arranged in series over a period of 10 days. Table 12 presents organic* removal
data from the air stripping/carbon adsorption bench-scale test following carbon
column 3 on the first day of operation. The data demonstrate that air stripping
followed by carbon adsorption is effective in reducing volatile organic
contaminant concentrations and satisfying MCL/AWQC criteria for these compounds
with the exception of carbon tetrachloride and tetrachloroethylene. Carbon
tetrachloride had a concentration after carbon adsorption of 10 ^g/L compared to
52
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TABLE 10
CHEMICAL PRECIPITATION
BENCH-SCALE TREATABILITY DATA (j»g/L)
FOLLOWING
a
b
c
U
B
PARAMETER8
Aluminum
Arsenic
Barium
Calcium
Cobalt
Iron
Magnesium
Manganese
Nickel
Potassium
Selenium
Sodium
Vanadium
Zinc
UNTREATED
WATER5
254.00
100.00
137.00 B
26,400.00
15.90 B
48,500.00
21,400.00
1,290.00
29.10 B
3,180.00 B
15.00 U
20,100.00
9.50 B
538.00
CHEMICAL
PRECIPITATION0
46.00 U
33.20
21.50 B
56,900.00
6.00 U
701.00
9,050.00
10.10 B
20.00 U
1,930.00 B
3.90 B
14,800.00
5.00 U
15.80 B
- Only includes compounds detected in groundwater samples. Does not
include compounds analyzed for and not detected.
- Based on treatability trailer samples.
- Based on lime jar test samples.
- Undetected at the listed detection limit.
- Reported value is less than the Contract Required Detection Limit
(CRDL) and greater than the Instrument Detection Limit (IDL).
53
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TABLE 11
CHEMICAL PRECIPITATION
PILOT-SCALE TREATABILITY DATA (jig/L)
PARAMETER"
UNTREATED
WATER6
FOLLOWING
CHEMICAL
PRECIPITATION6
Arsenic
Barium
Calcium
Copper
Iron.
Lead
Magnesium
Manganese
Potassium
Sodium
Vanadium
Zinc
4.
226.
35,100.
24.
83,500.
136.
16,500.
1,690.
1,100.
15,600.
13.
125.
5 B
00
00
90 B
00
00
00
00
00 U
00
60 B
00
4.00
223.00
151,000.00
9.00
442.00
5.80
4,950.00
12.20
1,360.00
17,900.00
8.00
27.70
U
U
B
B
B
U
a - Only includes compounds detected in groundwater samples. Does not
include compounds analyzed for and not detected.
b - Based on Day 3 samples.
U - Undetected at the listed detection limit.
B - Reported value is less than the Contract Required Detection Limit
(CRDL) and greater than the Instrument Detection Limit (IDL).
54
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TABLE 12
AIR STRIPPING/CARBON ADSORPTION
BENCH-SCALE TREATABILITY DATA (jig/L)
FOLLOWING
CHEMICAL FOLLOWING
PARAMETER' PRECIPITATION" AIR STRIPPING
Chlorinated VOCs:
Bromoform 400.0 U
Carbon Tetrachloride 24.0 U
Chloroform 1500.0
Dibromochloromethane 23 J
1,1-Dichloroethane 22.0 U
1,2-Dichloroethane 280.0
trans-l,2-0ichloroethylene 210
1,2-Dichloropropane 23.0 J
trans-l,3-Dichloropropylene 23 J
Methylene Chloride 210.0
1,1,2,2-Tetrachloroethane 760.0
Tetrachloroethylene 760.0
1,1,2-Trichloroethane 23 J
Trichloroethylene 510*0
Aromatic VOCs;
Benzene 790
Toluene 22 J
Ethyl benzene 88
Chlorobenzene 32 J
Ortho-Xylene 9.7 J
Meta- and Para-Xylene 24 J
1,2-Dichlorobenzene 49 J
1,3-Di Chlorobenzene 3.6 J
1,4-Di chlorobenzene 11 J
Orqanosulfur Compounds;
Thiodiglycol 25,000
1,4-Dithiane 1,000
1,4-Oxathiane 120
Orqanoohosohorus Compounds:
Dimethyl Methyl phosphonate 3.90
Explosives:
HMX 16. 2C
400.0 U
24.0 U
100.0
78.0 U
22.0 U
32.0 U
23.0 J
15.0 J
78.0 U
28.0 U
340.0
340.0
78.0 U
20.0 J
0.60 J
0.44 J
0.28 J
0.23 J
1.6 J
0.47 J
5.0 U
2.9 J
3.5 J
38,000
570
92
3.32
NA
a - Only includes compounds detected in groundwater samples
include compounds analyzed for
b - Based on bulk chemical precipi
c - Based on lime jar test sample.
and not detected.
tation samples.
FOLLOWING
CARBON
ADSORPTION
3.0 J
10.0 J
65.0
78.0 U
27.0
32.0 U
16.0 J
34.0 U
78.0 U
28.0 U
48.0 J
48.0 J
78.0 U
28.0 U
0.51 J
0.21 J
0.17 J
3.0 U
0.15 J
0.23 J
0.34 J
5.0 U
0,25 J
<9.97
<2.22
<2.14
<2.48
<0.869
. Does not
U - Undetected at the listed detection limit.
J - Compound is present below the
NA - Not Analyzed.
Practical Quantitation Limit (PQL).
55
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its MCL of 5 \ig/l. The total concentration of 1,1,2,2-tetrachloroethane and
tetrachloroethylene was 48 ug/L after carbon adsorption compared to the MCL for
tetrachloroethylene of 5 jig/L. Organosulfur, organophosphorus, and explosive
compounds were all reduced to below detection limits after carbon adsorption.
Final effluent water exhibited no acute toxicity to fathead minnows and daphnids.
The pilot-scale air stripping/carbon adsorption treatment system was a
continuous-flow process which operated over a two-day period. Metals-pretreated
groundwater initially was pumped to a 16-inch diameter air stripper containing
20 feet of packing. The air-to-water ratio in the stripper was maintained at
120:1. Emissions from the air stripper were directed to a vapor-phase carbon
adsorption unit. Following air stripping, the groundwater was pumped to five
carbon adsorption units installed in series. This arrangement allowed collection
of contaminant breakthrough data while maintaining final effluent quality.
Table 13 presents organics removal data for the air stripping/carbon adsorption
pilot-scale test. Concentrations listed for groundwater following chemical
precipitation are from an air stripping influent sample collected following
treatment of 12,600 gallons of groundwater. This was the final influent sample
collected. Concentrations listed for groundwater following air stripping and
each of the five carbon units are from samples collected during the final
sampling event after treatment of 18,500 gallons of groundwater. The data
demonstrate that air stripping followed by carbon adsorption is effective in
reducing VOC concentrations and satisfying MCL/AWQC criteria for these compounds.
The carbon adsorption data indicates that, even after treatment of 18,500
gallons, VOC concentrations were reduced to levels below the practical
quantitation limits. Carbon adsorption also treated organosulfur and explosive
compounds to below detection limits. Contaminant breakthrough was observed in
the first two units for thiodiglycol and in the first unit for 1,4-oxathiane.
Data on compounds exhibiting breakthrough are necessary to properly size a full-
scale carbon adsorption system. With this data, a full scale system can be
designed such that residual VOCs as well as thiodiglycol and 1,4-oxathiane will
be treated to near or below detection limits along with the remaining organic
contaminants. The effluent from the final carbon adsorption unit was not acutely
toxic to fathead minnows, daphnids, sheepshead minnows, and mysid shrimp.
Ultraviolet-Oxidation. The bench-scale UV-oxidation study was conducted
on metals-pretreated groundwater in an enclosed reactor operating in a recycle
batch mode. A high intensity UV-lamp was used in the reactor along with hydrogen
peroxide as an oxidant. A hydrogen peroxide concentration of 25 mg/L with 8
minutes of exposure time, determined to be necessary for complete contaminant
destruction based on preliminary testing, was utilized. In addition, a control
test, using an external heat source rather than UV light, was conducted to
determine whether VOC reduction could be attributed to vaporization from
temperature increases caused by the UV light rather than destruction. Table 14
presents organics removal data from the UV-oxidation bench-scale study. The data
demonstrate that UV-oxidation is effective in reducing volatile organic compound
concentrations and satisfying MCL/AWQC criteria for these compounds. 1,4-
Dithiane, 1,4-oxathiane, and RDX were all reduced to below detection limits
following UV-oxidation. Thiodiglycol was reduced to 13.2 ug/L and 1,3,5-
trinitrobenzene was reduced to 1.12 yg/L. There are no MCL or AWQC criteria for
these compounds. The UV-oxidation control sample shows some reduction of VOCs
due to volatilization; however, the majority of VOC removal can be attributed to
destruction in the UV-oxidation process rather than through volatilization.
Final effluent water was not acutely toxic to fathead minnows and daphnids.
56
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TABLE 13
AIR STRIPPING/CARBON ADSORPTION
PILOT-SCALE TREATABILITY DATA
FOLLOWING
. CHEMICAL
PARAMETER* PRECIPITATION6
Chlorinated VOCs:
Carbon Tetrachloride
Chlorobenzene
Chloroform
D i bromoch loromethane
1,2-Dichloroethane
1,1-Dichloroethylene
trans-1 ,2-Dichloroethylene
trans-1,3-Dichloropropylene
Hethylene Chloride
1 , 1 ,2,2-Tetrachloroethane
Tetrachloroethylene
1,1,2-Trichloroethane
Trichloroethylene
Trichlorofluoromethane
Vinyl Chloride
Aromatic VOCs;
Benzene
Toluene
Ethylbenzene
Chlorobenzene
Ortho-Xylene
Heta- and Para-Xylene
Oroanosulfur Compounds;
Thiodiglycol
1,4-Oithiane
1,4-Oxathiane
Benzathiazole
Explosives;
1, 3, 5 -Tri nitrobenzene
1 , 3-D i nitrobenzene
Tetryl
0.32
1.5
28
1.0
11
0.32
77
1.0
3.7
5.6
5.6
1.0
8.6
1.4
2.9
30
1.9
1.1
1.8
4.2
3.4
769.0
<2.22
<2.14
<3.47
19.4
<0.27
0.37
J
J
J
J
J
J
U
J
J
J
J
J
FOLLOWING
AIR
STRIPPING5
1.2
3.7
0.12
3.9
1.6
1.8
0.34
3.9
0.40
5.0
5.0
3.9
1.4
0.53
20
2.0
3.0
3.0
3.0
6.0"
6.0d
640.0
120.00
60.00
10.60
22.3
<0.27
0.302
U
U
J
U
U
U
J
U
J
U
U
U
U
J
u
u
u
u
u
u
u
FOLLOWING CARBON
UNIT 1
0.20
3.7
1.0
3.9
1.6
1.8
1.6
3.9
.40
5.0
5.0
3.9
1.4
0.31
20
2.0
1.0
3.0
3.0
6.0d
6.0d
295.0
<2.22
15.00
<3.47
<0.388*
<0.27*
<0.191*
J
U
U
U
U
u
u
u
J
u
u
u
u
J
u
u
J
u
u
u
u
UNIT
1.2
3.7
1.0
3.9
1.6
1.8
1.6
3.9
0.52
5.0
5.0
3.9
1.4
0.23
20
2.0
3.0
3.0
3.0
6.0"
6.0"
109.0
<2.22
<2.14
<3.47
<0.388*
-------
TABLE 14
ULTRAVIOLET-OXIDATION
BENCH-SCALE TREATABILITY DATA (pg/L)
FOLLOWING
CHEMICAL
PARAMETER* PRECIPITATION6
Chlorinated VOCs:
Carbon Tetrachloride 33
Chlorobenzene 81
Chloroform 2600
1,2-Dichloroethane 400
trans-l,2-Dichloroethylene 640
Methyl ene Chloride 260
1,1,2,2-Tetrachloroethane 170
Tetrachloroethylene 170
Trichloroethylene 1800
Aromatic VOCs:
Benzene 1200
Toluene 80
Ethyl benzene 39
Chlorobenzene 49
Total Xylenes 4.3 J
1,2-Dichlorobenzene 5.0 U
1,4-Dichlorobenzene 5.0 U
Orqanosulfur Compounds:
Thiodiglycol 35,000.00
1,4-Dithiane 1300.00
1,4-Oxathiane 300.00
Explosives:
1, 3, 5-Tri nitrobenzene 980.000°
RDX 10.100C
a - Only includes compounds detected in
include compounds analyzed for and
b - Based on different raw groundwater
technologies.
FOLLOWING
ULTRAVIOLET-
OXIDATION
1.2 U
3.7 U
1.0 U
1.6 U
1.6 U
1.4 U
5.0 U
5.0 U
1.4 U
0.74 J
1.1 J
0.44 J
3.0 U
2.8 J
4.0 J
3.8 J
13.2
<2.22
<2.14
f
1.120
<0.617
groundwater samples.
not detected.
FOLLOWING
ULTRAVIOLET-
OXIDATION
CONTROL
18
54
2400
350
580
220
46
46
1300
1000
43
28
38
5.88
5.0
5.0
NA
NA
NA
NA
NA
Does not
J
U
U
than used for other treatment
c - Based on field raw groundwater sample.
U - Undetected at the listed detection
limit.
J - Compound is present below the Practical Quantitation Limit
NA - Not Analyzed.
(PQL).
58
-------
Metals-pretreated groundwater was treated in a semi-continuous mode in a
pilot-scale ultraviolet-oxidation unit which housed four high intensity 15-kW
lamps mounted in series. Hydrogen peroxide was used as the oxidant. After
exiting the reactor, treated water passed through a manganese-greensand filter
to reduce residual hydrogen peroxide to less than 1 ppm. Table 15 presents
organics removal data for the ultraviolet-oxidation pilot-scale test.
Concentrations listed for groundwater following chemical precipitation are from
Day 2 of operation which represent the feed water to the UV-oxidation tests. The
UV-oxidation results are for the test run which yielded the best oxidation rates
(/.e., an initial hydrogen peroxide dosage of 60 mg/L). The data demonstrate
that UV-oxidation is effective in reducing VOC concentrations and satisfying
MCL/AWQC criteria. Organosulfur and explosive compounds were also reduced to
levels below detection limits, except for 1,3,5-trinitrobenzene which was
detected at 0.528 jig/L. There are no MCLs or AWQCs for these compounds. The
final UV-oxidation effluent exhibited no acute toxicity to fathead minnows,
daphnids, sheepshead minnows, and mysid shrimp.
Activated Sludge/Carbon Adsorption. Bench-scale activated sludge testing
consisted of an aeration reactor and a settling column. Effluent from the
reactor entered the settling column where the sludge was recycled back to the
aeration basin. The system was designed to operate as a continuous-flow process
allowing a 12-hour retention time. The sludge was acclimated over a 4-day period
with a mixture of groundwater and sewage. After acclimation, the system operated
24 hours per day for 22 consecutive days. In addition, a control test, whereby
metal s-pretreated groundwater was sent through the process without sludge under
otherwise normal operating conditions for 12 hours, was conducted to determine
whether VOC reduction in the groundwater could be attributed to inadvertent air
stripping during aeration in the reactor rather than biodegradation.
Table 16 presents organics removal data for activated sludge collected
after 22 days of operation. The data demonstrate that activated sludge is
effective in reducing VOC contaminant concentrations and satisfying MCL/AWQC
criteria with the exception of 1,2-dichloroethane, tetrachloroethylene,
trichloroethylene, and benzene, which were present at 8.3, 19, 7.3, and 7.6 ng/L,
respectively (the MCL for each of these compounds is 5 ng/L). Thiodiglycol, 1,4-
oxathiane, and HMX were all reduced below detection limits following activated
sludge treatment. 1,4-Dithiane was reduced to 36 jig/L, and dimethyl
methylphosphonate (DMMP) was reduced to 10.2 jig/L. There are no MCL or AWQC
criteria for these compounds. Although the data are not presented, carbon
adsorption following activated sludge was effective in reducing the remaining
organic contaminants. The final effluent following carbon adsorption was not
acutely toxic to fathead minnows and daphnids. Although the activated sludge
results presented in Table 16 seem somewhat promising, the control test results
demonstrate that much of the VOC reduction can be attributed to volatilization
rather than biodegradation. In addition, total organic carbon (TOC) data
collected during the activated sludge bench-scale test (Table 17) indicate that
the system did not reach steady state within the 22 days of operation (i.e., the
effluent TOC content is highly variable). This inability to reach steady state
has been attributed to the level of organic contamination in the groundwater
which is too low to maintain a healthy biomass as demonstrated by the sludge
culture which was slowly dying off. Since the activated sludge system proved to
be unstable given the organic contaminant levels in the Old 0-Field groundwater
and much of the VOC reduction was due to volatilization rather than
biodegradation, activated sludge treatment was determined to be inappropriate for
59
-------
TABLE 15
ULTRAVIOLET-OXIDATION
PILOT-SCALE TREATABILITY DATA (ng/L)
PARAMETER*
FOLLOWING
CHEMICAL
PRECIPITATION" LAMP 1
FOLLOWING ULTRAVIOLET-OXIDATION'
LAMP 2 LAMP 3
LAMP 4
Chlorinated VOCs:
Bromodichloromethane 1.4 U
Carbon Tetrachtoride 1.2 U
Chlorobenzene 4.5
Chloroform 40
Oibrofflochloromethane 2.6 J
1,1-Dichloroethan« 0.35 J
1,2-Oichloroethane 19
1,1-Dichloroethylene 0.74 J
trans-1,2-0ichloro«thylen« 218
trans-1,3-Oichloropropylene 2.6 J
Methylene Chloride 8.5
1,1,2,2-Tetrachloroethane 5.0 J
Tetrachloroethylene 5.0 J
1,1,1-Trichloroethane 1.3 U
1,1,2-Trichloroethane 2.6 J
Trichloroethylene 25
Vinyl Chloride 15 J
Aromatic VOCs;
Benzene 53
Toluene 0.96 J
Ethylbenzene 1.0 J
Chlorobenzene 8.2
Ortho-Xylene 5.9
Meta- and Para-Xylene 1.5 J
1,2-Dichlorobenzene 5.0 U
1,3-0iChlorobenzene 5.0 U
1,4-OiChlorobenzene 1.9 J
Organcsulfur Compounds;
Thiodiglycol 495.0
1,4-Oithiane 210.00
1,4-Oxathiane 86.00
Benzathiazole 17.80
Explosives;
1,3,5-Trinitrobenzene 15.8
Tetryl 0.306
0.19
0.14
3.7
12
0.46
0.99
1.6
1.8
0.55
0.46
1.5
1.3
1.3
0.47
0.46
0.40
20
J
J
U
J
J
U
U
J
J
J
J
J
J
J
U
2.0
0.38
3.0
3.0
0.46
1.4
2.7
5.0
5.0
<10.0
<2.22
<2.14
<3.47
NA
NA
1.4
0.30
3.7
5.7
3.9
1.1
1.6
1.8
1.6
3.9
0.56
5.0
5.0
1.3
3.9
1.4
20
2.0
3.0
3.0
3.0
3.0
6.0
5.0
5.0
5.0
<10.0
<2.22
<2.14
<3.47
NA
NA
1.4
0.17
3.7
1.7
3.9
1.1
1.6
1.8
1.6
3.9
0.39
1.0
1.0
1.3
3.9
1.4
20
2.0
3.0
3.0
3.0
3.0
6.0
5.0
5.0
0.87
<10.0
<2.22
<2.U
<3.47
NA
NA
1.4
0.36
3.7
1.2
3.9
1.1
1.6
1.8
1.6
3.9
1.1
5.0
5.0
1.3
3.9
1.4
20
2.0
3.0
3.0
3.0
3.0
6.0
5.0
5.0
0.83
<10.0
<2.22
<2.14
<3.47
0.528
b
c
U
J
NA
Only includes compound* detected in groundmter sanples. Does not include compounds analyzed for
and not detected.
Based on Day 2 sanples.
Based on total H20, concentration of 180 mg/L.
Undetected et the listed detection limit.
Compound is present below the Practical Quantitat ion Limit (POL).
Not Analyzed.
60
-------
TABLE 16
ACTIVATED SLUDGE
BENCH-SCALE TREATABILITY DATA
PARAMETER8
FOLLOWING
CHEMICAL
PRECIPITATION6
FOLLOWING
ACTIVATED
SLUDGE6
FOLLOWING
ACTIVATED SLUDGE
CONTROL6
28 U
24 U
20 U
22 U
9.1 J
32 U
8.4 J
26 J
26 J
26 U
13 J
Chlorinated VOCs:
Bromodichloromethane 3.2 J 1.4 U
Carbon Tetrachloride 7.9 J 1.2 U
Chloroform 780 23
1,1-Dichloroethane 21 J 1.1 U
1,2-Oichloroethane 160 8.3
trans-l,2-Dich1oroethylene 92 1.6 J
Methylene Chloride 120 3.9
1,1,2,2-Tetrachloroethane 83 J 19
Tetrachloroethylene 83 J 19
1,1,1-Trichloroethane 7.5 J 1.3 U
Trichloroethylene 210 • 7.3
Aromatic VOCs:
Benzene 230 7.6
Toluene 5.0 0.33 J
Ethyl benzene 15 3.0 U
Chlorobenzene 11 0.46 J
Ortho-Xylene 2.4 J 0.96 J
Meta- and Para-Xylene 1.4.J 6.0 U
1,2-Dichlorobenzene 3.9 J 5.0 U
1,3-Dichlorobenzene 3.5 J 5.0 U
1,4-Dichlorobenzene 2.8 J 5.0 U
Organosulfur Compounds:
Thiodiglycol 13,000 <9.97
1,4-Dithiane 67 36
1,4-Oxathiane 2.77 <2.14
Orqanophosphorus Compounds;
Dimethyl Methylphosphonate 11 10.2
Explosives:
HMX 16.2d <0.869*
.0
,2
3.5
0.96
3.0
3,
1,
6.0
5.0
5.0
5.0
NA
NA
NA
NA
NA
J
U
U
J
U
U
U
U
a - Includes only compounds detected in groundwater samples. Does not
include compounds analyzed for and not detected.
b - Based on bulk chemical precipitation samples.
c - Based on week 3 activated sludge samples.
d - Based on lime jar test sample.
e - Based on week 1 activated sludge sample.
U - Undetected at the listed detection limit.
J - Compound is present below the Practical Quantitation Limit (PQL).
NA - Not Analyzed.
61
-------
TABLE 17
TOC RESULTS FOR ACTIVATED SLUDGE
Day of Operation TOC. TOC
in out
Loom)
Al
A2
A3
A4 .. 9.5
2 II II
3 23.5 17.3
J 23.3 17.5
f 22.2 18.0
f 20.4 17.7
I 22 19.5
J 21.2 19.9
?n 20.9 18.1
0 18.1 12.5
J 17-2 6.2
f 17.6 6.1
3 18.1 5.6
}* 20.0 16.5
f 20.0 n.s
}f 20.0 11.5
17 18.8 7.6
18 20.4 13.1
19 20.9 10
20 9.8 6.2
21 ? ?
22 ? 4
62
-------
application at Old 0-Field and no pilot-scale testing was performed. Activated
sludge followed by carbon adsorption offers no benefits over the other treatment
alternatives.
4.3.2 Groundwater Treatment Alternatives Evaluation
Groundwater treatment alternatives are evaluated below with respect to the
nine criteria specified in Section 4.1. A summary of the evaluation results is
presented in Table 18.
Overall Protection of Human Health and the Environment. All of the active
groundwater treatment alternatives (T-3 through T-6) would be designed to reduce
the chemical concentrations in the groundwater to below MCL/AWQC criteria, thus
adequately protecting human health and the environment. Groundwater treatment
alternatives, when coupled with a complementary groundwater extraction/discharge
alternative, will provide active remediation of the contaminated groundwater,
thus reducing future risk associated with the Site.
Because the "no action" and "minimal action" alternatives are not
protective of human health and the environment, they are not considered further
in this analysis as options for this Site.
Compliance with ARARs. All of the active treatment alternatives shall meet
their respective applicable or relevant and appropriate requirements of federal
and State environmental laws and would be operated in accordance with all federal
and Maryland treatment facility requirements. Treatment systems shall be
designed to reduce chemical concentrations in the groundwater to below MCL/AWQC
criteria for each chemical present for which such standards exist. Target levels
specified for groundwater treatment, whether they are statutory or risk-based,
are expected to be sufficiently low such that re-injection and/or surface water
discharge requirements are also satisfied. All active groundwater treatment
alternatives are expected to comply with all ARARs related to the groundwater
media by treating extracted groundwater to acceptable levels for discharge to the
Gunpowder River.
Air stripping is a cross-media treatment technique; that is, it solves the
groundwater problem by transferring contamination to the atmosphere. Air
emissions regulations established by the State of Maryland and the EPA will
require control of volatile organic emissions from the air stripper. Addition
of either a vapor-phase carbon adsorption unit or a catalytic converter should
be adequate to meet action-specific ARARs.
As demonstrated during bench-scale treatability testing, biological
treatment techniques (Alternatives T-5 and T-6) are likely to remove volatile
organic contaminants through air*stripping rather than biodegradation. Control
of air emissions to comply with air emissions regulations established by the
State of Maryland and the EPA would be more difficult to implement than for an
air stripper.
All of the active groundwater treatment alternatives generate a precipitant
sludge. The precipitant sludge will require Toxicity Characteristic Leaching
Procedure (TCLP) analysis prior to disposal at a RCRA permitted facility.
Failure to pass the TCLP test may result in the need for sludge stabilization or
solidification in order to meet RCRA ARARs. Initial analyses of the precipitant
sludges from bench-scale and pilot-scale treatability testing
63
-------
TABLE 18
DETAILED EVALUATION SUMMARY FOR GftOUNMMTER TREATMENT ALTERNATIVES
Alternative
Effectiveness
Implementability
Cost*
Conclusion
II: No Action
T-2: Minimal Action
1-3: Precipitation/
Air Stripping/
Carbon Adsorption
en
T-4: Precipitation/
UV-Oxidation
Hot effective in reducing human health
risks. Not effective in reducing
environmental impact of migrating
contaminants.
Effective in reducing human health
risks as long as institutional controls
are properly enforced. Not effective
in reducing environMntal impact of
•igrating contaminants.
Precipitation proven effective in
removing inorganics. Combination of
air stripping and carbon adsorption
proven effective in removing most
organics. Treatability studies
confirmed effectiveness of treatment
processes in removing netals, VOCs, and
chemical agent degradation products
such as thiodiglycol and 1,4-dithiane.
Precipitation proven effective in
removing inorganics. UV-oxidation
process has been demonstrated to
successfully destroy a variety of
organic compounds. Treatability
studies confirmed effectiveness of
treatment processes in removing metals,
VOCs, and chemical agent degradation
products such as thiodiglycol and 1,4-
dithiane.
No implementability concerns.
Requires coordinated efforts with APG,
the State of Maryland, and the USEPA to
ensure continuity of long-term
management and monitoring of the site.
Treatment process equipment is
commercially available. Treatment
system operation requires a part-time
operator. Treatment system can
accommodate the variable waste streams
and flow rates fairly easily due to
modular nature of system components.
Extensive management and administrative
oversight is required to ensure the
operation, maintenance, and monitoring
of the treatment system.
Treatment process equipment is
commercially available; however, UV-
oxidation units are available only
through a small number of companies.
Treatment system operation requires a
part-time operator. Can accommodate
variable waste streams and flowrates
fairly easily due to modular nature of
system components. Extensive management
and administrative oversight is required
to ensure the proper operation,
maintenance, and monitoring of the
treatment system.
No Cost
C
DIM
PV
C
OM
PV
S 50,000
$ 104.000/yr
$1.692.000
il, 263,000
* 525,000/yr
$9,392,000
C = » 1,377.000
OIM «* 385,000/yr
PV - »7,357.000
Not acceptable to USEPA or
State of Maryland.
Minimally effective in overall
protection of human health and
the environment. Does not
comply with chemical- and
location-specific ARARs.
Provides active remediation ot
contaminated groundwater, thus
providing some degree of
overall protection of human
health and the environment. Is
expected to comply with ARARS,
including action-specific air
emission control requirements
for the air stripper.
Treatment processes for this
alternative are more proven arid
reliable in removing
contaminants than any other
alternative.
Provides active remediation of
contaminated groundnutcr, thus
providing some degree of
overall protection of human
health and the environment, is
expected to comply with ARARs.
Overall, more desirable than
Alternative 1-3 because of
lower cost and no generation of
treatment residuals by uv-
oxidation.
-------
Alternative
TABLE 18
DETAILED EVALUATION SUMMARY FOR GROUNDUATER TREATMENT ALTERNATIVES (Continued)
Effectiveness
Implementability
Cost'
Conclusion
T-5: Precipitation/
Biological
Treatment/Carbon
Adsorption .
1-6: Precipitation/
PACT
Precipitation proven effective in
removing inorganics. Biological
treatment proven effective on many
organic contaminant*. Treatabllity
studies showed less effectiveness of
biological treatment in removing VOCs
and che«iical agent degradation products
such as thiodigtycol and 1,4-dithiane.
Carbon adsorption effective in removing
residual organics.
Precipitation proven effective in
removing inorganics. Although
ttestability studies were not
performed. PACT is expected to perform
like biological treatment followed by
carbon adsorption.
Treatment processes are commercially
available. Biological treatment may
present operational difficulties since
the system can be affected by highly
variable waste streams and/or variable
flow rates, both of which are
anticipated at Old O-field. Treatment
system operation requires an experienced
system operator because careful operator
control and influent monitoring are
required. Extensive management and
administrative oversight is required to
ensure the proper operation, maintenance
and monitoring of the treatment system.
Treatment process equipment is
commercially available; however, PACT
system currently available only through
one company. PACT system not as
susceptible to being upset by highly
variable waste streams as is biological
treatment alone, due to the buffering
effect of the activated carbon.
Treatment system operation would require
a part-time operator. Extensive
management and administrative oversight
is required to ensure the proper
operation, maintenance, and monitoring
of the treatment system.
C = $1.623,000
OCM ° S 311,000/yr
PV = S6.449.000
C = $1,551,000
O&N = $ 259,000/yr
PV = $5,582.000
Provides active remediation of
contaminated groundnuter, thus
providing some degree of
overall protection of human
health and the environment.
Careful operation of system
required to ensure continuous
compliance with ARARs. In
general, biological treatment
technology is the least
reliable alternative-under
variable waste stream
conditions. Also, biological
treatment not as effective as
other alternatives for organic
contaminant removal
demonstrated by treatability
studies.
Provides active remediation of
contaminated grounduater, thus
providing some degree of
overall protection of human
health and the environment. Is
expected to comply with ARARs.
Alternative 1-6 is expected to
be as ineffective as
Alternative 1-5, but not as
susceptible to upset by highly
variable flowrates or
contaminant concentrations.
Capital costs (C), annual operating and maintenance costs (04*1), and present worth (PV) for 30 years at a 5X discount rate are presented.
an indefinitely long time period.
O&H costs may continue fur
-------
indicate that the sludge is non-hazardous. However, changes in the contaminant
make-up of the groundwater could impact the composition of the precipitant sludge
so that it is hazardous.
Alternatives T-3 and T-5 also generate spent carbon. Typically, activated
carbon vendors supply the carbon as well as handle removal and regeneration of
spent carbon. Initial analyses of the spent carbon from bench-scale and pilot-
scale treatability testing indicate that the spent carbon is non-hazardous.
The UV-oxidation process used in Alternative T-4 generates no sludge or air
emissions.
Alternatives T-5 and T-6 also generate biological treatment sludge. The
biological sludge will require TCLP analysis prior to disposal at a RCRA
permitted facility. Failure to pass the TCLP test may result in the need for
stabilization or solidification in order.to meet ARARs. Initial analyses of the
spent activated sludge from bench-scale treatability testing indicate that the
sludge is non-hazardous, except possibly for the characteristic of reactivity.
Long-term Effectiveness and Permanence. All of the active groundwater
treatment alternatives utilize precipitation for metals removal. Precipitation
is controlled by the solubility of the inorganic species, which is in turn
controlled by the pH of the groundwater. At the optimum pH range for the metals
present in the groundwater, it is expected that metals and inorganic contaminants
present in the groundwater at Old 0-Field will be effectively precipitated based
on the groundwater treatability testing results described above.
Alternative T-3 utilizes air stripping in combination with carbon
adsorption to remove organic contaminants from the groundwater. Air stripping
is controlled by the volatility of each individual chemical as measured by the
Henry's Law constant, which accounts for the compound's solubility and vapor
pressure, among other parameters. Air stripping works best for contaminants with
high volatility and low solubility; the higher the Henry's Law constant, the
easier the chemical is removed via air stripping. Air stripping can achieve 90+
percent removal efficiency for many organic contaminants based on the groundwater
treatability testing results described above. Generally, a compound's solubility
and absorbability are inverse (i.e., the more soluble a compound is, the less it
adsorbs to activated carbon). Theoretically, carbon adsorption is capable of
reducing organic contaminants to non-detectable levels as long as adequate carbon
depth, and therefore contact time, is available. Air strippers and activated
carbon adsorption are often used in conjunction and complement each other's
effectiveness. Many of the chemicals in Old 0-Field groundwater having
relatively short activated carbon breakthrough times are volatile and may be
readily removed via air stripping. Contaminants such as 1,1,2,2-
tetrachlorethane, thiodiglycol, and 1,4-dithiane are not effectively removed via
air stripping; however, these contaminants are effectively captured by the
activated carbon unit as demonstrated by groundwater treatability testing.
Alternative T-4 utilizes UV-oxidation to destroy organic contaminants.
Treatability data indicate that UV-oxidation will destroy most, if not all, of
the organic groundwater contaminants present at Old 0-Field including
thiodiglycol and 1,4-dithiane. Oxidation may take longer or require greater
dosages for low molecular weight polar compounds (e.g., chloroform) and complex
66
-------
organic compounds built around a benzene ring structure (e.g., polynuclear
aromatic hydrocarbons). These compounds, therefore, are the rate limiting
compounds.
Alternative T-5 utilizes biological treatment (e.g., activated sludge) and
carbon adsorption for destruction/removal of organic contaminants from the-
groundwater. Activated sludge has been applied to numerous industrial
wastewaters containing a wide variety of organic compounds. Addition of
activated carbon polishing units generally improves the overall organic removal
efficiency of the biological treatment system. Treatability data indicate that
biological treatment is not appropriate for Old 0-Field groundwater for two
reasons: 1) the organic contaminant concentrations in the groundwater are too
low to maintain a healthy biomass, creating an unstable system as demonstrated
in the groundwater treatability tests; and 2) volatile organic compounds are air
stripped from the aeration basin before the microorganisms have an opportunity
to biodegrade them. In addition, biological treatment may present operational
difficulties since the system is susceptible to upset by highly variable waste
streams and/or variable water flowrates, both of which are anticipated at Old 0-
Field. '
The effectiveness of the PACT system used in Alternative T-6 to destroy
organic contaminants is comparable to that of the activated sludge system with
activated carbon polishing units used in Alternative T-5; however, PACT is less
susceptible to upset from variable flowrates and influent contaminant
concentrations because the activated carbon in the PACT unit acts as a buffer to
the varying concentrations. - :
Stringent performance monitoring of the treated effluent will be required
of all alternatives throughout the life of the operation prior to discharge to
ensure groundwater treatment goals are consistently met. Monitoring will include
chemical analysis and biotoxicity testing.
Reduction of Toxldty, Nobility, or Volume Through Treatment. All of the
active groundwater treatment alternatives reduce both the toxicity and the volume
of contaminants in the groundwater by removing the contaminants. The mobility
of the chemicals in the groundwater is a function of the groundwater extraction/
discharge alternative selected.
Chemical precipitation, utilized for metals removal in all of the active
groundwater treatment alternatives, removes the metal and other inorganic
contaminants from the groundwater reducing its toxicity. This is accomplished
by concentrating the contaminants into a metal sludge.
Alternative T-3 incorporates air stripping and carbon adsorption for
organics removal. Air stripping, a cross-media treatment technique, solves the
groundwater problem by transferring contamination to the atmosphere. Air
emissions from the air stripper likely will require control in the form of: 1)
a catalytic converter that destroys the organic contaminants but requires
scrubbing of acid gases thereby generating a wastewater; or 2) a vapor-phase
carbon adsorption unit that captures the organic contaminants which are later
destroyed through off-site regeneration. Liquid-phase carbon adsorption also
captures organic contaminants; these contaminants are later destroyed through
off-site regeneration or are disposed as waste materials. Therefore, Alternative
T-3 reduces the toxicity of the groundwater by transferring the contaminants to
other media that require off-site destruction or disposal.
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Alternative T-4 incorporates UV-oxidation for organics removal. UV-
oxidation completely destroys organic contaminants in the groundwater on site
thereby reducing the toxicity of the groundwater while generating no treatment
residuals.
Alternative T-5 incorporates activated sludge treatment and carbon
adsorption for organics removal. When operating effectively, as shown by
treatability testing to not be the case for Old 0-Field groundwater, activated
sludge treatment completely destroys organic contaminants on site. However,
activated sludge systems typically transfer organic contaminants to the air
through inadvertent air stripping in the aeration basin as demonstrated by
groundwater treatability testing. Spent activated sludge, which should not
contain organic compounds if the treatment is effective, is generated. The
liquid-phase carbon adsorption unit captures any remaining organic contaminants;
these contaminants are later destroyed through off-site regeneration or are
disposed as waste materials. Therefore, Alternative T-5 reduces the toxicity of
the groundwater by contaminant destruction and by transferring the contaminants
to the air or other media that require off-site destruction or disposal.
Alternative T-6 is similar to Alternative T-5.
Short-term Effectiveness. The short-term effectiveness is similar for all
the active groundwater treatment alternatives. Construction of the treatment
facility and support structures will be completed with standard construction
equipment, but will entail additional risks to workers beyond that risk inherent
with construction projects because of the potential for encountering unexploded
ordnance (UXO).
Stringent performance monitoring of the treated effluent will be required
during treatment plant start-up operations to ensure that groundwater treatment
goals are met.
Implementability. Component technologies of Alternatives T-3 and T-5 are
well-proven, commercially available, and commonly used in water and wastewater
treatment processes.
Although UV-oxidation (Alternative T-4) has been used at several CERCLA and
industrial sites, it is still considered an innovative technology. The equipment
is available through only a few companies; the units may be available 6 to 12
weeks after receipt of a purchase order.
The PACT system used in Alternative T-6 is patented and only available
through one vendor. It has been utilized at a number of industrial and hazardous
waste sites..
Cost. The rate of groundwater extraction, and therefore the flow to the
treatment system, varies with the selection of an extraction/discharge
alternative. Extraction rates for the groundwater extraction/discharge
alternatives considered range from 20.6 gpm (Alternative E-4) to 46.1 gpm
(Alternative E-5). For costing purposes, a flowrate of 25 to 30 gpm was used for
treatment alternatives.
Alternative T-3 has a present worth of $9,392,000 and Alternative T-4 has
a present worth of $7,357,000 for a 30-year period at a 5 percent discount rate.
These estimates are based on equipment characteristics determined following
treatability testing. Alternatives T-5 and T-6 have present worth of $6,449,000
and $5,582,000, respectively, based on initial estimates prior to performance of
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the treatability studies. The costs associated with Alternatives T-5 and T-6
were not updated since bench-scale treatability testing showed biological
treatment to be inappropriate for Old 0-Field groundwater.
State Acceptance. The State of Maryland concurs with the selected
treatment alternative indicated in the Declaration and Section 5.0.
Community Acceptance. As mentioned in Section 1.4, the public was invited
to review the administrative record, attend a public meeting, and submit comments
on all treatment alternatives under consideration. The Responsiveness Summary
provided in Appendix A gives a thorough review of public comments as well as Army
and EPA responses. Community Acceptance is assessed in detail in the
Responsiveness Summary.
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5.0 SELECTED REMEDIAL ALTERNATIVE
This section identifies and summarizes the selected interim action in
response to OU One for Old 0-Field. Extraction/discharge and treatment
components of the remedy are described along with an overview of the rationale
for selection. .A discussion of how the selected remedy satisfies the statutory
requirements of Section 121 of CERCLA is also included.
5.1 ALTERNATIVE DESCRIPTION
The preferred alternative for containing the contaminated groundwater at
Old 0-Field is downgradient extraction of the contaminated groundwater plume, as
described in Alternative E-l, followed by on-site treatment utilizing chemical
precipitation followed by ultraviolet-oxidation to remove the full range of
inorganic and organic contaminants, and discharge to the Gunpowder River, as
described in Alternative T-4. This remedial approach is believed to provide the
best balance of trade-offs with respect to the evaluation criteria. The total
estimated capital cost of the remedy is $1,881,000, and the total estimated
operation and maintenance costs are $466,650 per year. The total estimated
present worth is $9,120,000 based on a 30-year period and a 5 percent discount
rate. The remedy is expected to require 18 to 36 months to implement.
New groundwater extraction wells will be located in areas of highest
groundwater contamination downgradient of the source. The extraction system will
be designed to capture contamination emanating from the landfill to the maximum
possible extent. The number and specific design of the extraction wells, will
be specified by testing newly installed wells during an early period of the
design/construction phase of the remediation effort. These tests also will be
used to determine the capture zone, aquifer yield, and optimal pumping rate for
each well and the combined system. At least three piezometers shall be utilized
in the vicinity of each extraction well to monitor horizontal and vertical
hydraulic gradients and contaminant distributions in groundwater. The useability
of existing wells as monitoring points will be determined during the design
phase.
Collected groundwater will be treated by chemical precipitation followed
by ultraviolet-oxidation prior to discharge to the Gunpowder River. The
processes likely will be continuous-flow operated at the groundwater extraction
flowrate. Chemical precipitation will generate a sludge which will be evaluated
for hazardous waste characteristics and transported and disposed in accordance
with applicable federal and State regulations. Based on treatability test
results and 24 hour/day operation, approximately 43,000 gallons/year of sludge
will be generated. The ultraviolet-oxidation process will not generate any
treatment residuals. The extracted groundwater will be treated to attain
chemical-specific ARARs which shall include Ambient Water Quality Criteria
promulgated under the Clean Water Act and Maximum Contaminant Levels promulgated
under the Safe Drinking Water Act. Treatability test results confirm these ARARs
are attainable with this treatment sequence. Treatability testing also
demonstrated that compounds not regulated by these ARARs, such as chemical-
warfare agent degradation products, can be treated to less than instrument
detection levels using the selected treatment approach. Stringent performance
monitoring of the treated effluent, including chemical sampling and biotoxicity
testing throughout the life of the operation, will be performed prior to
discharge to ensure ARARs are satisfied consistently.
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5.2 COMPLIANCE WITH STATUTORY REQUIREMENTS
5.2.1 Protection of Human Health and the Environment
The selected interim action alternative protects human health and the
environment from the risks associated with groundwater contamination from Old 0-
Field and its migration into interconnecting surface waters. This is
accomplished by containing the contaminated groundwater near the source so that
it does not discharge to Watson Creek. Furthermore, the extracted groundwater
will be treated to acceptable levels prior to discharge to the Gunpowder River.
Human populations will be protected from direct contact and food-chain exposures
associated with contaminant migration from the groundwater into Watson Creek and,
ultimately, the Gunpowder River. Aquatic life in Watson Creek and the Gunpowder
River, and terrestrial wildlife feeding on aquatic life, will also be protected
from risks associated with groundwater contaminant migration from Old 0-Field.
5.2.2 Compliance with ARARs
•The selected interim action alternative will comply with chemical-specific
ARARs applicable to groundwater remediation as demonstrated by treatability
testing. ARARs considered for Old 0*F1eld groundwater treatment include Ambient
Water Quality Criteria promulgated under the Clean Water Act and Maximum
Contaminant Levels promulgated under the Safe Drinking Water Act. In addition,
chemical precipitation sludge will be analyzed for RCRA hazardous waste
characteristics to ensure that RCRA land disposal restrictions are satisfied.
5.2.3 Cost Effectiveness
The selected interim action has been determined to provide the best overall
effectiveness proportional to its costs of all the alternatives considered.
Downgradient extraction with discharge to surface water is the lowest cost
extraction/discharge alternative identified; however, it is effective in
capturing the contaminated groundwater plume from Old 0-Field. As demonstrated
through treatability testing, Alternatives T-3 and T-4 are the only groundwater
treatment alternatives effective in removing inorganic and organic contaminants
below target cleanup and acute toxicity levels while maintaining a stable mode
of operation. Of these, chemical precipitation followed by ultraviolet-oxidation
(Alternative T-4) is the lower cost alternative. Alternative T-4 has the added
benefit over Alternative T-3 of destroying organic contaminants in the
groundwater on site without generating treatment residuals.
5.2.4 Utilization of Permanent Solutions and Alternative Treatment
Technologies (or Resource Recovery Technologies) to the Maximum
Extent Practicable
This interim action is not designed or expected to be final, but the
selected remedy represents the best balance of trade-offs among alternatives with
respect to pertinent criteria, given the limited scope of the action.
5.2.5 Preference for Treatment as a Principal Element
By treating the contaminated groundwater by chemical precipitation followed
by ultraviolet-oxidation, the selected remedial action addresses one of the
principal threats posed by the Site through the us« of treatment. Therefore,
although this action is not a final remedy, the statutory preference of treatment
as a principal element is satisfied.
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5.3 PSRTORMaVCZ MOBUTUaiMO PROGRAM
A monitoring program shall be developed to evaluate the extent to which the
groundwater extraction and treatment components of the interim response action
perform in compliance with applicable chemical criteria for chemicals present in
the extracted groundwater. These chemical specific criteria shall be developed in
accordance with the results of the performance monitoring program, the Ambient
water Quality criteria, and substantive requirements of the National Pollutant
Discharge Elimination System.
5.3.1 Cro""
A groundvater monitoring plan shall be developed and implemented during the
interim response action to ensure that hydraulic control of the plume of
contamination emanating from Old O-rield towards Watson creek is maintained.
specifically, an inward and upward gradient, within the plume most exist to
mitigate the discharge of contaminated groundvater to Watson creek. Information
necessary for this determination includes:
horizontal and vertical gradients in the groundvater between Old 0-Field
and Watson creek;
horizontal and vertical contaminant concentration gradients in groundwater
between old O-Pield and Watson creek;
changes in contaminant concentration or distribution over time;
effects of tidal influence on the plume capture cone; and
effects of any modifications to the original interim response action.
TO provide this information, the groundwater containment performance monitoring
plan shall include, at a minimum, the following: locations of new or existing
monitoring wells for water quality sampling; frequency of water quality sampling;
analytical parameters (focusing on chemicals of concern) and analytical procedures
to be employed; field sampling methods; specification of water level monitoring
locations, methods and frequencies using new or existing wells; and methods for
capture zone analysis.
5.3.2 Effluent Moaitorlna Program
A monitoring plan for the effluent from the treatment plant shall be developed
and implemented during the interim response action to ensure that control of the
effluent is maintained prior to discharge. A monitoring program shall be
developed during the design phase that provides periodic and/or continuous
information on the following parameters:
chemical constituency of the treatment plant effluent; and
acute and chronic toxic ity of the effluent.
TO provide this information, the effluent monitoring program shall include, at a
minimum, the following: analysis of 2 4 -hour composite samples at a frequency of
twice a month for total suspended solids, total trsenic, other metals of
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concern, volatile organic compounds, and other chemicals of concern; continuous
monitoring of pH and control within the limits of 6 and 9; acute to.xicity testing
performed on a quarterly basis for a period of two years, according to
established EPA protocols; and short-term chronic testing performed during the
third and fourth quarters of each year for a period of two years, according to
established EPA protocols.
5.4 SIGNIFICANT CHANGES FROM THE PROPOSED PLAN
The Proposed Plan for OU One at Old 0-Field was released for public comment
in July 1991. The Proposed Plan identified Alternative E-l, downgradient
extraction with discharge to the Gunpowder River, combined with Alternative T-4,
chemical precipitation followed by ultraviolet-oxidation treatment of
contaminated groundwater, as the preferred interim response action. The Army and
the EPA reviewed all written and verbal comments submitted during the public
comment period. Upon review of these comments, it was determined that no
significant changes to the interim action, as it was originally identified in the
Proposed Plan, were necessary.
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