PB94-964316
                             EPA/ROD/R07-94/081
                             April 1995
EPA  Superfund
       Record of Decision:
       Cornhusker Army Ammunition Plant
       (O.U. 1), Hall County, NE
       9/29/1994

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                 INTERIM ACTION RECORD OF DECISION DECLARATION

SITE NAME AND LOCATION

Operable Unit  1 - Groundwater
Old Potash Highway
Cornhusker Army Ammunition Plant
Grand Island, Hall County, Nebraska 68803


STATEMENT OF BASIS AND PURPOSE

This decision document presents the selected interim remedial action for the groundwater operable unit
at the Cornhusker Army Ammunition Plant (CAAP).  This action was chosen in accordance with the
Comprehensive Environmental Response,  Compensation and  Liability Act of  1980  (CERCLA),  as
amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA),  and. to the extent
practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This decision
is based on  the administrative record for the site and additional information  supporting the selected
interim remedial action for Operable Unit 1  - Groundwater. is contained in the administrative record for
this site.

The letter from the Nebraska Department of Environmental Quality (NDEQ) regarding concurrence of
the selected remedy as an interim action for this site is attached.

ASSESSMENT OF THE SITE

Actual or threatened releases of hazardous substances from  this site, if not addressed by implementing
the response action selected in  this interim action Record of Decision (ROD), may present a current or
potential threat to public health, welfare, or the environment.


DESCRIPTION OF THE SELECTED INTERIM REMEDY

Operable  Unit One  encompasses the  explosives groundwater piume(s),  both on-post and off-post.
Explosives of concern in  the contaminant plume  include RDX. TNT. HMX. and their decomposition
products.

The objective of this interim action is to contain the plume and prevent further migration of contaminants.
and does not encompass full restoration of the plume of contaminated groundwater.  The recommended
alternatives provide an approach to containing  and removing contaminant mass from the groundwater
plume.   This  approach  will   control further  migration of the plume  and  reduce  the levels  of the
contamination in groundwater.  The overall interim action for OU  1 addresses two areas of groundwater
contamination, the on-post source areas and the off-post or distal end.  The substances detected in the
source area  groundwater are primarily explosives, metals, and nitrates, however the objective of this
action is to focus on the containment of the explosives contaminant plume. The treatment for metals and
nitrates will be applied as necessary to meet the surface water discharge criteria.  The groundwater at the
distal  end of the plume in the off-post area contains primarily RDX at low concentrations.

The interim groundwater remedies were developed to protect public health, welfare and  the environment
by controlling the migration  and reducing the volume  and mass of contaminants  present  in  the

ROM.TXT

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groundwater beneath and downgradient of the facility.  Operable unit interim actions will be consistent
with all planned future remedial activities. The final remedial action for groundwater will augment and
expand upon this interim remedial action to provide an effective overall groundwater remediation project.

The major components of the selected interim remedies include:

       Source Area:  Groundwater will be extracted from multiple extraction wells at a total estimated
       extraction  rate of  1000 gallons per minute  (gpm).   The extraction  of the contaminated
       groundwater will contain the source contamination and prevent further migration.  The extracted
       groundwater will be treated with granular activated carbon for  explosives,  granular media
       filtration for suspended solids, chemical precipitation (as needed to meet NPDES limits), and
       wetlands for nitrates (as needed  to meet  NPDES limits).  Treated water will  be routed via
       pipeline through the easement of the proposed Wood River Diversion Channel to the Platte River.
       The system  will be designed to actively  control  migration  of more highly contaminated
       groundwater in the  source area  and  to rapidly remove contaminant mass  from  the  aquifer.
       Contaminant mass removal will be  monitored by using new  or existing monitoring wells.  A
       schedule of sampling and analysis of the groundwater will be initiated to observe the effectiveness
       and progress of the remediation system.                                                    .

       Distal End:  Groundwater will be extracted at a rate sufficient to prevent further migration of
       the explosives plume at the distal end. Groundwater  will be extracted from multiple wells at an
       estimated total rate of 3000 gpm at the end of the contaminant plume and 1000 gpm at the tongue
       of the 20 ppb isopleth (intermediate location).  The distal end treatment system uses some of the
       same technology  as the Source Area, but due to differences in the groundwater quality does not
       require as  extensive treatment.  This system will prevent further  migration of the end of the
       contaminant plume and the intermediate tongue. The pumped groundwater will be treated with
       granular activated carbon for the explosives.  The  treated water will be routed  via  pipeline
       through the easement of  the proposed  Wood River Diversion Channel to the Platte River.
       Contaminant mass removal will be  monitored by using new  or existing monitoring wells.  A
       schedule of sampling and analysis of the groundwater will be initiated to observe the effectiveness
       and progress of the remediation svstem.
DECLARATION

This interim action is protective of public health, welfare and the environment.  The action complies with
action-specific and chemical-specific federal and state applicable or relevant and appropriate requirements.
are cost effective, and address public concerns.  Although the 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.  This action  does
not constitute a final remedy for the site, therefore the statutory preference for remedies that employ
treatment that reduces toxicity, mobility, or volume as a principal element (although partially addressed
by this remedy),  will be more fully addressed  by the final response action.  Subsequent actions are
planned to fully address the principal threats posed by providing comprehensive remediation of Operable
Unit 1  - Groundwater.
ROD2.TXT
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This interim remedy will result in hazardous substances remaining on site above the health-based levels,
therefore if the final remedy is not underway prior to the five year review, then the requirement of the
five year review is  applicable to the interim action. Review of this interim remedy will be ongoing as
the Army continues to develop the final comprehensive remedial action for CAAP.
Date
                                                   Dennis Grams
                                                   Regional Administrator
                                                   US Environmental Protection Agency
                                                   Region VII
     Date.
                                                   LTC Mtry G. Goodwin
                                                             Army Ammunition Plant
                                                   _. trbD. Walker
                                                   Deputy Assistant Secretary of the Army
                                                   (Environment Safely. *wi Occupational Health)
     Atachnwnttr  Pccisioo Sunniary
                  Rcsponstveneu Soniaiary - Attschracnt A
KO1C.TXT
IN/21W4

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DEC 05  '94 12=15 NEBRASKA DEQ 402*471-2909                     .                 P.I
 STATE OF  NEBRASKA
                                                              DhmXfMliNT OF ENinRflNMFNSU. QUAtlTV
                                                                             Suite 4iKI. Tha AMim
                                                                                  r/OOKTStreot
                                                                                 RO. Eat 98922
                                                                             Phono (403 471-2186
 Governor
      Mr. Dennis Grama
      .Regional Administrator
      BPA Region VII
      726 Minnesota Avenue
      Kansas City/ Kansas 66101

      Dear Mr. drama:

      Upon consideration of the Decision Summary for Cornhusker Army Aonunition Plant
      operable unit one - Grouaduater dated September 20, 1994, the Nebraska
      Department of Environmental Quality (HDBQ) concurs with bhv Interim Action
      Record of Decision remedy selection for the grouodwator at the Cornboeker Army
      Ammunition Plant (CAAP)  aita.

      NOEQ believea this interim remedy will contain and remove grouodwatac
      contaminated wir.h expioeivo compounds posing a threat to human health and tho
      environment.  This interim remedy, when implemented, will prevent the future
      spread of contaminated ground water in the northwest area of Oraad Zalaad.
           appreeia««a ch« njiportunity foe involvement in the'remedy saleetion
      preceea and the Army and EPA'a consideration of NDEQ'a input throughout thin
      investigation.  MflKu conaidere the development of ehxs doetmont and tne
      participation of the citizens of Grand Zaland aad aurroundirtg counties to
      exemplify a high degree of producttva cooperation.
                                             Ranaoipn wooa, P.E.

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                            TABLE OF CONTENTS
                                                                       PAGE
1.0   SITE LOCATION AND DESCRIPTION
2.0   SITE HISTORY, OPERATIONS, PREVIOUS INVESTIGATIONS AND REMEDIAL
      ACTIONS  	:	   i
      2.1   SITE HISTORY  	   1
      2.2   OPERATIONS  	   4
      2.3   PREVIOUS INVESTIGATIONS  	   5
      2.4   REMEDIAL ACTIONS	.  .   6
           2.4.1  ALTERNATE WATER SUPPLY  	   6
           2.4.2  INSTALLATION RESTORATION INCINERATION PROGRAM 	   7

3.0   HIGHLIGHTS OF COMMUNITY PARTICIPATION	.-.	 ....   7

4.0   SCOPE AND ROLE OF OPERABLE UNIT	-	   9

5.0   SITE CHARACTERISTICS	   9
      5.1   GEOLOGY	   9
      5.2   HYDROGEOLOGY	    II
      5.3   RDX GROUNDWATER PLUME	    12
      5.4   CONTAMINATION ASSESSMENT	    12

6.0   SUMMARY OF SITE RISK	    14

7.0   ALTERNATIVES EVALUATION	    17
      7.1   DESCRIPTION OF  REMEDIAL ACTION ALTERNATIVES	   17
      7.2   SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES  	   21
           7.2.1  COMPARISON OF REMEDIAL ACTION ALTERNATIVES FOR THE SOURCE
                 AREA	    24
           7.2.2  COMPARISON OF REMEDIAL ACTION ALTERNATIVES FOR THE DISTAL
                 END  	    27
      7.3   PROPOSED REMEDY	    30

8.0   STATUTORY DETERMINATIONS 	    37
      8.1   DOCUMENTATION OF SIGNIFICANT CHANGES  	   44
      8.2   SUMMARY OF SELECTED REMEDY AFTER MODIFICATION	   45

ATTACHMENT A  RESPONSIVENESS SUMMARY

ATTACHMENT B  GROUNDWATER CONTAINMENT STANDARDS
KOB2.TXT
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                                    LIST OF TABLES
                                                                                    PAGE
Table 6-1      Concentrations of Chemicals of Potential Concern for CAAP	    15
Table 7.1-1    Components of Remedial Action  Alternatives for Source Area  	    22
Table 7.1-2    Components of Remedial Action  Alternatives for Distal End  	    23
Table 7.3-1    Summary Cost Estimate for Source Area, Alternative T-7A	    35
Table 7.3-2    Summary Cost Estimate for Distal End, Alternative T-3A	    36
Table 8-1A    Chemical-Specific ARARs	    38
Table 8-1B    Chemical-Specific ARARs	    39
Table 8-2      Location-Specific ARARs	    40
Table 8-3      Action-Specific ARARs  .  . . . '.	    41
ROD2.TJCT
(W2IAM
-II-

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                                     LIST OF FIGURES
                                                                                      PAGE
                                                                                           ?
Figure 1-1     General Location Map  	
Figure 1-2     Facility Location Map  	    3
Figure 5-1     Geologic Cross Section of the RDX Plume Area	    10
Figure 5-2     Water Table Contour/RDX Plume Map  	    13
Figure 7-2     Groundwater Extraction, Granular Activated Carbon (Spent Carbon Recycled).
              Discharge to Surface Water)  	    32
Figure 7-3     Schematic Diagram of Groundwater Extraction, Chemical Precipitation.
              Granular Media Filtration. Granular Activated Carbon (Spent Carbon
              Recycled), Constructed Wetlands Treatment and Discharge to Surface Water  .  .    33
KOD2.TXT
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                         1.0    SITE LOCATION AND DESCRIPTION

Cornhusker Army Ammunition Plant (CAAP) is located in south-central Nebraska 2 miles west of the
city of Grand Island and lies near the eastern margin of the Great Plains Physiographic Province.  The
site lies approximately 7 miles north of the Platte River, within the flood  plain.  The  terrain is nearly
level to slightly undulatory. The ground surface at CAAP and the surrounding vicinity slopes gently from
southwest to northeast with elevations ranging from 1,950 ft above sea level in the southwest to 1.850
ft in the northeast (Figure  1-1).  The  facility was constructed and fully operational in  1942 as a U.S.
government-owned, contractor-operated (GOCO) facility.  The facility produced artillery shells, mines,
bombs, and rockets for World War II and the Korean and Vietnam Conflicts.  CAAP comprises 11,936
acres consisting of five munitions production facilities (load lines), two munitions storage areas (magazine
areas), a pistol range, sanitary landfill, burning grounds, shop area, ammonium nitrate production area.
administration area, and railroad holding yard (Figure 1-2).

Activities  at  the site  have resulted in contamination  of groundwater with  explosives compounds.
Groundwater is die primary drinking water source in Grand  Island and the surrounding areas.  The
explosives contaminant plume has migrated to the east-northeast approximately four miles beyond the
installation boundary, contaminating domestic wells in northwestern Grand Island. Between CAAP and
the Grand Island city limits, a distance of approximately two miles,  the explosives contaminant plume
underlies stockyards and irrigated row crops.  The sources of groundwater contamination were  unlined
cesspools  and leaching pits used to  dispose of explosives contaminated wastewater  from  ordnance
production activities.

 2.0  SITE HISTORY. OPERATIONS. PREVIOUS INVESTIGATIONS AND REMEDIAL ACTIONS

The following sections present a summary of the history of CAAP.  describe the operations that occurred
at the site that resulted  in contamination, and discusses previous investigations and remedial  actions
conducted at CAAP.

2.1          SITE HISTORY

CAAP was operated from  1942 through 1945 by the Quaker Oats Ordnance Corporation, a subsidiary
of the Quaker Oats Company.  CAAP was placed on standby status for munitions production from 1945
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                   Capital Heights
                    Subdivision
                             Grand  Island
                              City Limits
-N-
                                        WATKINS-JOHNSON ENVIRONMENTAL, INC.
                                        Ground-Water Consulting. Environmental Engineering,
                                        Remediation Services
                                       GENERAL LOCATION MAP
                                Date:  June   1994       Figure      1-1

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           Burning
           Grounds
                  f /Railroad
                  'f I Holding
                  '/(  Yard
  North
Magazine
  Area
     Sanitary /
      Landfill
     Pistol Range
Northwest
Sewage   f
Treatment-
Plant
                                         South
                                       Magazine
                                         Area
                                                                  Nitrate
                                                                   Area
                                                                                Southeast
                                                                                Sewage)
                                                                                Treatment
                                                                                   Plant
                                                                                LI
          A
  Administration
       Area
                                                       WATKINS-JOHNSON ENVIRONMENTAL. INC.
                                                       Ground-Water Consulting, Environmental Engineering
                                                       Remediation Services
                                                        FACILITY LOCATION MAP
            0     325    650
                 =5=
                 METERS
                                                                       Figure     1 -2
Date:   June   1994

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through 1950.  From 1945 through 1948, the ammonium nitrate production area was used for the
production of fertilizer.

CAAP was  reactivated in 1950 to produce munitions for the Korean conflict. Operations were directed
by Mason & Hanger-Silas Mason Company (Mason & Hanger) until 1957 when CAAP was again placed
on standby status. In 1963 a total of 809 acres from three parcels of land the northeast, northwest, and
southeast corners of the facility were sold to the State of Nebraska for use as wildlife management areas.
CAAP was  reactivated from 1965 through 1973 to produce munitions for the Vietnam Conflict. Mason
& Hanger was retained as the operator during this period of operation.  CAAP was placed on standby
status when ordnance production operations ceased in 1973. Standby status was terminated on January
30.  1989 when AMCCOM declared CAAP "Excess".  The Excessing process was begun and is currently
in progress.  Activities at CAAP are currently limited to maintenance operations, leasing of property for
agriculture, leasing of buildings for storage, limited manufacturing, and wildlife management.

CAAP was listed as a site on the National  Priorities List (NPL) on July 22. 1987.  As required under
CERCLA of 1980 and amended by the Superfund Amendments and Reauthorization Act (SARA) of 1986.
The U.S. Army initiated  a Remedial Investigation/Feasibility Study (RI/FS).   A Federal Facility
Agreement  (FFA) was signed between the U.S.  Army,  USEPA, and the State of Nebraska (effective
September 4. 1990) to set terms for the RI/FS effort.  The FFA provided the terms, listed documents to
he generated, and established target dates for the delivery of reports.  A number of investigations and
studies to address environmental impacts of activities-at CAAP were conducted during the I980"s and are
continuing today.  These are summarized in Section  2.3.

2.2          OPERATIONS

The principal explosive compounds used during munitions production at CAAP were 2.4.6-trinitrotoluene
(246TNT). cyclotrimethylenetrinitramine(RDX) and. to a lesser extent, cyclotetramethylenetetranitramine
(HMX).  Other chemical materials used to support munitions  production include freon. paints, grease.
oil. and solvents. Solvents reportedly used at CAAP include acetone (ACET). trichloroethylene (TRCLE)
(TCE). and 1 1 1 -trichloroethane ( 1 1 1TCE) (TCA).

Major operations conducted in Load Lines  1 through 4 included screening, melting and mixing, rod and
pellet manufacturing, and remelting and refilling.  These  operations generated explosives dust (246TNT
and RDX).   Ventilation systems with Schneibie wet scrubbers removed explosives dust from the air.
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Process water from the Schneible units was circulated through sealing tanks and recycled through the
scrubbers.  Wastewater from this process was disposed via interior-building open drains into concrete pits
equipped with filter bags called sack sumps. The bags, made of canvas-like material, were designed to
filter out solid explosives particles. The filtered wastewater flowed through open concrete channels into
circular earthen impoundments (cesspools). The walls of these impoundments were masonry lined, with
the bottom open to the sand and gravel strata.  Water that did not infiltrate through the bottom of the
impoundment was routed through an overflow pipe into a leaching pit.

The limited filtering effectiveness of the sack sumps allowed explosive panicles to flow  into the earthen
impoundments.  The residue was periodically scraped from the bottom of the earthen impoundments and
leaching pits and ignited at the Burning Grounds.  Wastewater was also generated from periodic washing
• >f machinery,  interior building surfaces, and carts  used for transporting "the munitions during the
production process. This wash water was also discharged to the sack sumps, cesspools, and leaching pits.

2.3          PREVIOUS INVESTIGATIONS

Several investigations relating to the characterization  and  remediation of contamination at  CAAP have
been completed. As pan of the U.S. Army's Installation Restoration Program. USATHAMA completed
an installation assessment of CAAP.  A follow-on'contamination survey was completed  in  1482.

Results from sampling and analysis or soils and groundwater indicated that some 01 the leaching pits aiul
. jsspoois were  highly contaminated  with explosives (especially  24ATNT .UKI  RDX'i  resulting  in
contamination of the shallow aquifer. The explosives contamination was round to have migrated at least
•••> the installation boundary and potentially migrated off site.   The Army during  ll'X3 through  l°Sft
performed groundwater sampling and analysis  and monitored water table elevations  at CAAP and  in the
 Mwngradiont otfpost area.  The sampling network included up to 472 weils. including monitoring  wells.
irrigation wells, and domestic water supply wells. Sampling and analysis conducted in  1^X4 confirmed
that RDX was migrating northeast, and had moved at least 3 mi offpost. It was confirmed that at least
ZOO domestic water supply wells  in the Capital Heights residential area were contaminated with  RDX.
In  NS4 the Army evaluated remedial  solutions to the groundwater contamination and extension  of the
( "ity of Grand Island water supply system into the affected area was selected. The extension action w;is
carried out during 1984 through 1^86.  In N85 the Army collected samples from eight locations at Load
Lines  I. 2. 3. and 4 including leaching pits, trench drains, cesspools,  and sack sumps. Detections oi
explosives, predominantly 246TNT. 135TNB. and RDX. were found in most samples.
•viic.rxr
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Sampling and analysis of groundwater for explosives contamination was conducted eleven times from
September 1986 through June 1991.  In  1991 an Remedial Investigation/Feasibility Study was initiated
by the Army in accordance with the Interagency Agreement with the U.S. Environmental Protection
Agency (USEPA) and the Nebraska Department of Environmental Quality (NDEQ). The results of this
investigation relating to explosives contamination in groundwater are discussed in Section 5 of this
document.

2.4          REMEDIAL ACTIONS

Confirmation of offpost migration of explosives contaminated groundwater led to response actions to
remove the source(s) of contamination  and provide water to households whose water supplies were
affected.  The following sections summarize these response actions.

2.4. l         ALTERNATE WATER SUPPLY

Bottled water was supplied from January 1984 through June 1986 by the Army to those households
affected by explosives contamination in groundwater. In July 1984 the Army entered into a contract with
the City of Grand Island to extend the city water system to the affected area and provide a permanent
water supply for the impacted area.

Construction  of the Northwest Grand  Island Water Supply Extension commenced  in  August 1984.
Residential water hookups were completed by December 1986.  Approximately 800 residences, both in
the affected area and adjacent areas, were given the opportunity to hook up to the Northwest Grand Island
Water Supply Extension.

As a result of the continued groundwater monitoring, the Army recommended a second extension of the
Grand Island Water Supply. This action was carried out in accordance with the removal action provisions
of CERCLA/SARA. An Engineering Evaluation/Cost Analysis (EE/CA) was issued for public comment.
Following the comment period and public meeting, the decision to extend the water supply system to an
additional 65 residents was selected.  This action started in the fall of 1993 and will be completed in the
fall of 1994.
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2.4.2        INSTALLATION RESTORATION INCINERATION PROGRAM

Fifty-eight impoundments (cesspools and leach pits) were identified  as containing contaminated soil
resulting from  munitions manufacturing at CAAP.   The Installation Restoration Incineration Program
(IRIP)  was an  onsite CERCLA removal action, implemented to remove contamination at these sites.
Incineration of contaminated soil began in August, 1987.  Excavation of contaminated soil was performed
by Mason & Hanger personnel, and incineration of contaminated soil was performed  by  International
Technology (IT).

Incineration, decontamination, and demobilization were completed by August 8, 1988. Ash from the
incineration was placed into trenches northeast of Load Line 2 and south of the North  Magazine Area.
A 2-ft cap of topsoil was applied and the site was fertilized and seeded. Excavated impoundments were
backfilled  with sand taken from a  sand pit located on State Land (Nebraska State Game and Parks
Commission)  along the eastern boundary of the facility.  Excavations were covered with 2 ft of rich
black loam, fertilized, and seeded.

Clean-up action levels for incinerated soils were set jointly by U.S.  Army and the Nebraska Department
of Environmental Quality (NDEQ).  These levels were as follows: 246TNT.  5 ppm; RDX, 10 ppm;
135TNB,  15 ppm; 24DNT. 0.5 ppm: and 26DNT, 0.4 ppm.  Excavation and incineration  were carried
out until these action levels were met or until soil had been removed to a depth of 5 ft  below the water
table.   Verification  sampling and  analysis  was accomplished using composite samples comprised  of
subsamples from the bottoms and sides of the excavations.  Since vertical excavation was limited by high
water table and the discharge requirement action levels were almost always achieved laterally, inclusion
of subsamples from the excavation sidewails in the composite sample tended to underestimate contaminant
content of the soils.  In order to determine whether any of the 58 excavated impoundments are continuing
sources of explosives contamination in groundwater, groundwater samples were collected upgradient and
downgradient of the locations of these impoundments.  Results from this sampling are forthcoming.
                   3.0   HIGHLIGHTS OF COMMUNITY PARTICIPATION

CERCLA Section 113(K)(2)(B)(i-v) requirements for public participation were met through the following
activities. Community relations activities for the CAAP site were initiated by the Army in 1984.  Early
community relations activities included meeting with City and state officials to discuss the extension of
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the water line to homes with contaminated domestic wells. A Public Meeting was held on July 25. 1985
to explain the dewatering process and health risks of RDX.   As part of the remedial  action plan for
CAAP. the Army conducted thermal treatment of the explosive-contaminated soils and debris.  In order
to keep the community informed of Army actions, the Army established information repositories at CAAP
and at the Grand Island Public Library.

In 1985. the Army provided funding for a waterline extension to affected residences.  The Army offered
access to city water for those residents whose wells were in the approximate  area of the contaminated
plume.  In an ongoing effort to assure protection of human health, the Army is currently extending the
waterline to 65 additional residences.  Estimated completion of this project is in the fall  of  1994.

In January  1991 the Army and EPA conducted interviews with the community and in March of 1991 a
community meeting was held to announce the interagency Agreement between the Army, EPA. and the
State.  A Technical  Review Committee (TRC) was formed  in  November.  1991  with local  citizens
participating in  these meetings.   The TRC has met periodically throughout the RI/FS process.  The
Community Relations Plan for CAAP was prepared in November 1991 and approved in January 1992.
The public  notice for this interim action for OU1 - Groundwater was issued on April 19.  1994.  This
notice announced the availability of the Administrative Record  for public review and the location of the
public repositories at CAAP and at the Grand Island Public Library, the public comment period and set
dates for the public meetings.

The Army held a public comment period from April 26.  1994 to May 26. 1994 following the release or
the Proposed  Plan  for this Interim  Action for OU1- Groundwater.  The Proposed Plan identified the
preferred alternative for the Interim Action for GUI - Groundwater.  On May 4. 1994 the Army held
a public  availability  session, a  less formal open  house to allow visitors to speak one-on-one with
representatives of the Army.  NDEQ. and EPA.  The public meeting was conducted on May 5.  1994. to
discuss the preferred alternative and to receive citizens' comments and questions. Agency responses to
these comments received at the meetings and otherwise during the public comment period are  included
in the Responsiveness Summary.
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                       4.0    SCOPE AND ROLE OF OPERABLE UNIT

The purpose of the Interim Action for this Operable Unit 1 -Groundwater is to contain the plume and
prevent further migration of contaminants.  It is the first  of two operable units planned for the site.
According to the NCP, the EPA regulation which establishes procedures for the selection of response
actions, an interim  action  is appropriate where  a contamination problem  will become worse  if left
unaddressed and where the interim action will be consistent with a final remedial action. Consistent with
the principles of the NCP, this Interim Action is designed to promptly initiate an interim remedial  action
response which will prevent further degradation of the aquifer, and contain the plume, thereby preventing
further migration of contaninants.

The implementation of the interim Action for OU1  is key to the stabilization of groundwater leading to
the final remedy.  Remedial activities planned for OU2 will consist of actions necessary to remediate the
soils and groundwater to final clean-up  goals,  for explosives  and any other contaminants determined to
be present as a result of past activities at CAAP.

                               5.0   SITE CHARACTERISTICS

The following sections describe the geology and hydrogeology of the site, the nature and extent  of the
RDX groundwater plume, and the results  of the contamination assessment conducted as part of the Site
Characterization Study.

5.1          GEOLOGY

The RDX plume area is underlain by Quaternary deposits of unconsolidated eolian.  fluvial, and  lacustrine
silt and clay and fluvial sand  and gravel (Figure 5-1). These units rest on an erosional surface carved
into the Tertiary Ogallala Formation, a heterogeneous deposit of poorly lithified to unconsolidated fluvial
sand. silt, and clay.  In most of the offpost explosives plume area, the Ogallala was completely removed
by erosion prior to deposition of Quaternary deposits, exposing the underlying Cretaceous Pierre Shale
and Niobrara Chalk.

The Quaternary deposits are comprised, in descending order, of the Peorian Loess and the Grand Island.
Fullerton. and Holdrege Formations.  The Peorian Loess consists of silt and silty clay which covers most
of the onpost area.  It ranges from 5 to 25 ft in thickness and thins to the east.  The Grand Island
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             A
       SOUTHWEST
     A'
NORTHEAST
                  UNDtfTERENTIATED
                    SURFACE SILT
                     AND CUT
FULLERTON
FORMATION
(BLUE CUT
AQUnARO)
                                                      (SAND &
                                                      CRAVa)
                                                     (PALEOVALLET
                                                     FU.AQUFER)
                                                                            JJOLDREGE
                                                                            FORUATKIN'
                                                                           (SOT & CLAY)
             APPROXIUATE VERTICAL SCALE:  f = 75'
             APPROXBUTE HORIZONTAL SCALE:  T = t.l Uik
                                                             WATKINS-JOHNSON ENVIRONMENTAU INC.
                                                             Craundwoter Consulting. Environmental Engineering.
                                                             Remediation Services
                                                             GEOLOGIC  CROSS SECTION
                                                             OF THE RDX  PLUME AREA
                                                     CH4I002XOV1
                                                     Date:  June  1994
Figure   5-1

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Formation is a laterally persistent, fluvial sand and gravel and ranges from 40 to 65 ft thick in the RDX
plume area.  The Grand Island Formation is underlain by the Fullerton Formation, locally referred to as
the Blue Clay. The Fullerton consists predominantly of bluish green, silty clay of eolian, fluvial, and/or
lacustrine origin and ranges from 5 to 25 ft in thickness. East of the plume area,  the Fullerton has been
locally removed by erosion which occurred prior to  deposition of the Grand  Island Formation.  The
Fullerton Formation is underlain by the Holdrege Formation, a heterogeneous unit consisting of fluvial
sand and gravel  and silt and clay of fluvial, lacustrine, and eolian origin. The Holdrege was deposited
on an erosional surface developed on the Tertiary and Cretaceous bedrock units.  The Holdrege is thicker
and contains proportionately more sand and  gravel where the erosional surface is most deeply incised into
the underlying bedrock.  These erosional  lows are paleovalleys.  In the  explosives  plume area the
Holdrege ranges from 30 ft in thickness, over the erosional high, to greater than 220 ft in the paleovalley.

5.2          HYDROGEOLOGY

The Quaternary  sand and gravel deposits are the primary source for groundwater in the Grand Island
area.  In the explosives plume area. Quaternary deposits consist of three hydrostratigraphic units: the
Alluvial aquifer, the Blue  Clay aquitard. and the  Paleovalley Fill aquifer (Figure 5-1).  The Alluvial
aquifer is comprised of the saturated sand and gravel of the Grand Island Formation. The silty clay of
the Fullerton Formation is the Blue Clay aquitard.  The sand and  gravel deposits  of the Holdrege
Formation constitute the Paleovalley Fill aquifer.   East of the explosives plume, and other areas where
the Fullerton Formation is  not present, the  Alluvial and  Paleovalley Fill  aquifers  comprise one aquifer.

The Alluvial aquifer is an uncontlned aquifer and has a saturated thickness ranging from approximately
28 to 65 ft  in the study area.   Analysis of data obtained  during a constant rate pumping test of the
Alluvial aquifer at CAAP yielded hydraulic conductivities ranging from 263 to 337 ft/day. The Blue C'lay
aquitard separates the Alluvial and Paleovalley Fill aquifers and is laterally continuous throughout CAAP
and the explosives plume area.  Detailed analysis of all available  lithologic  logs  from subsurface
penetrations in the RDX plume area and surrounding vicinity indicate  that the  Blue  Clay aquitard is
continuous in this area. Groundwater sampling results indicate that the Blue Clay is an effective barrier
to the vertical migration of contamination in the RDX plume area. Analysis of potentiometric surface
data,  aquifer testing in the plume area, and  laboratory permeability testing of the Blue Clay support this
conclusion.  The Paleovalley Fill aquifer consists of laterally discontinuous deposits of sand, gravel, silt.
and clay.  Analysis of data obtained during slug tests of the Paleovalley Fill  aquifer both on and offpost
yielded hydraulic conductivities ranging from 10 to  147 ft/day.  The thickness and relative proportion of
                                              -11-

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coarser sediments, and therefore transmissivity, of the Paleovailey Fill aquifer are greatest over the
paleovalley axis.

The water table slopes uniformly with an average gradient of 0.001 from southwest to northeast in the
explosives plume area (Figure 5-2).  Depth to groundwater ranges from 5 to 20  ft.  Since groundwater
pumpage and recharge occur over broad areas, consequent changes in groundwater flow direction and
lateral  hydraulic  gradients are minimal.   Recharge of the Alluvial  aquifer  occurs  by seepage of
streamflow, infiltration of precipitation and irrigation water, and lateral movement of groundwater from
areas west of CAAP. Except for water-supply and irrigation wells, there are no groundwater discharge
areas at CAAP. '

5.3      "    RDX GROUNDWATER PLUME

The ROX groundwater plume is approximately six miles long and one half mile wide. The main plume
originates in the ordnance production facilities at CAAP and trends east-northeast to a point about 4 miles
beyond the eastern boundary of CAAP (Figure 5-2).  Past investigations have noted that the depth to the
maximum contamination increases with distance from CAAP.  This apparent downward migration of
RDX with distance from the source is not a density phenomenon,  but a function of aquifer recharge at
the surface from infiltration of precipitation and irrigation water.

5.4          CONTAMINATION ASSESSMENT

During the RI process, several areas were identified  in the load lines which were potentially associated
with explosives contamination of groundwater.  These include wastewater impoundments:  areas where
explosives  were produced, handled,  or stored: interior floor drain outlets: surface depressions and
drainage  ditches  associated  with   munitions  productions  areas:  and   nonexpiosive  wastewater
impoundments.

During the RI process 96 groundwater monitoring wells, including 25 well clusters were sampled in the
explosives plume area.  Forty-six of the wells were installed  during the  RI process.  Well clusters were
designed to provide groundwater samples from the upper, middle, and lower portions  of the Alluvial
aquifer.  Four clusters located  along the axis  of the plume in the offpost area included a well screened
in the upper portion of the Paleovalley Fill aquifer.  One onpost well (G0070), located along the plume
axis, is also screened in this aquifer.  Each well was sampled two times and analyzed for a variety of

-------
                                                   -CAAP
                                              I   \ BOUNDARY
                                                              Grand  Island
                                                               Cliy  Limits
1900-
 Water Table Elevation
(ft above mean sealevel)
                                                           -N-
                                                       0     6000   18000
                                                           = '
                                                           METERS
WATKINS-JOHNSON ENVIRONMENTAL. INC.
Groundwoler Consulting, Environmental Engineering.
Remediation Services
                                                                                 WATER TABLE CONTOUR/RDX
                                                                                       PLUME  AREA MAP
                                                              CH41001\DV1
                                                                           Dote; June 1994      | Figure   5-2

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contaminants, including explosives compounds.   Evaluation of these analytical results  and previous
groundwater investigations at the site yields the following conclusions.

             1. The most extensive explosive compound detected in all zones of the Alluvial aquifer is
               RDX.  RDX has migrated at least 4.2 mi beyond the  CAAP  boundary.  HMX has
               migrated at least 2.2 mi beyond the CAAP boundary. Although 246TNT and several
               of its breakdown products were detected  at the installation boundary, they were not
               detected in the next tier of monitoring wells approximately 1 mi downgradient.

             2. The primary sources of explosives contamination in groundwater are  located in Load
               Lines 1 and 2.

             3. Explosives have not contaminated the Paleovalley Fill aquifer.  The wells screened in
               this aquifer,  all located along the RDX plume axis, did not yield  any  detections of
               explosives compounds during the Remedial Investigations.

             4. The depth to the maximum concentration of RDX in the plume increases with distance
               from CAAP.  At and near CAAP, groundwater contamination  is detected only in the
               upper and middle part of the Alluvial aquifer. At the far end  of the plume. RDX is
               detected only in the lower part of this aquifer.
                              6.0    SUMMARY OF SITE RISK

The  chemicals  detected in the groundwater are presented in Table  6-1.   A  statistically designed
background study will be performed to refine the final list of site-specific chemicals of concern (COCs).
Any additional  COCs identified will  be addressed by the final remedial action.  The volume of the
affected groundwater is estimated to be approximately 7.2 billion gallons.
ROOS.TXT
09/5IW4

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Table 6-1    Concentrations of Chemicals of Potential Concern for CAAP
Groundwater Concentration (ue/D
Chemical
12DCLE
135TNB
13DNB
246TNT
24DNT
2A46DT
B2EHP
CH2CL2
HMX
NB
RDX
TCLTFE
TFDCLE
AS
AL
SB
BA
BE
CD
CL
F
FE
PB
MN
HG
Nl
NIT
SE
SO4
V
ZN
Minimum
31.000
0.839
2.310
0.898
0.106
0.203
0.920
30.000
1.590
1.230
2.060
70.000
7.000
2.100
270.000
26.000
61.700
2.190
11.800
1690.000
1070.000
116.000
6.980
21.400
1.340
29.200
14.300
2.930
7190.000
8.360
21.400
Maximum
31.000
180.000
2.310
820.000
24.000
87.000
23.000
30.000
79.200
1.230
96.400
1000.000
10.000
17.900
8050.000
60.100
1 130.000
2.190
24.300
190000.000
1310.000
14000.000
14.200
1640.000
1.340
59.500
270000.000
17.800
970000.000
57.600
107.000
Average
31.000
54.963
2.310
101.028
6.750
11.366
2.938
30.000
11.746
1.230
14.664
423.333
8.500
4.734
1948.920
37.680
348.694
2.190
19.022
32842.581
1 190.000
1545.871
11.160
246.816
1.340
45.850
14719.143
6.139
1 10503.978
17.110
38.914
No. of Detections
1
7
1
11
7
16
20
1
19
1
28
3
2
72
25
40
99
1
9
93
2
62
3
55
1
4
82
35
93
56
14
 ROIH.TXT
 CW2I/W
-15-

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The results of the site characterization indicate that the levels of RDX in groundwater at the distal end
are continuing to migrate to east-northeast at levels above the drinking water health advisory. In addition.
high levels of 246TNT, RDX, and HMX have been located on the CAAP facility. The health advisories
for these compounds are 2 ppb for 246 TNT, 2 ppb for RDX,  and 400 ppb for HMX.  The results of
the sampling conducted during the  1986  through 1992 time-frame,  indicate that the compounds will
continue to migrate and affect additional drinking water sources.  Refer to the Focused Feasibility Study
(1994) (FFS) and the Site Characterization Report (1993) for sampling data. Concentrations of explosive
compounds in groundwater samples range from 2 ppb to 95 ppb RDX, 0.8 ppb to 820 ppb 246-TNT. and
1.6 ppb to 79.2 ppb HMX.  The high stability and high mobility RDX compound warrants  the need to
contain and prevent further degradation of the aquifer.   If  left unchecked,  further  spread  of the
contaminants in  groundwater would  increase human exposure to explosives and further degrade the
drinking water aquifer. Increased exposure could result from additional residential drinking water wells.
additional irrigation wells, and a City of Grand Island supply well becoming affected by the contaminant
plume.

A  baseline risk assessment will be included  in the site-wide RI/FS and in the subsequent final action
ROD.  The risk assessment will determine the final remedial action criteria for the aquifer. The proposed
interim remedy  is consistent with the expected final remedy in that this interim action contains the
contaminant plume and prevents its spread into unaffected areas.

Information on the human health  effects resulting from over-exposure to explosive compounds comes
primarily  from workers exposed  during munitions production.   At sufficient concentrations, explosive
compounds can affect the Central Nervous System (CNS) and may cause headaches,  irritability, anorexia.
insomnia, seizures and in extreme cases unconsciousness.  The primary contaminants which are TNT and
RDX are listed as EPA Group C. possible human carcinogens.  Lifetime feeding studies in rats and mice
showed increased mortality, weight loss, anemia, liver and kidney toxicity. testicular degeneration, and
prostate inflammation.
ROK.TXT
W2IN4                                         -ID-

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                           7.0    ALTERNATIVES EVALUATION

A total of fourteen remedial action alternatives were developed for groundwater containment at the on-
post source area (load line).  A total of five remedial action alternatives were developed for the distal end.
These alternatives were developed in the FFS and summarized in the Proposed Plan, prior to public
comment.  Modification of these alternatives, based on public review and comment is addressed in
Section 8.0.  Except for the No Action and  Limited Action alternatives, all remedial action alternatives
involve pumping and treatment of groundwater. The remedial action alternatives were developed to meet
the  interim discharge requirements for groundwater remediation.   The pump  and treat options for
groundwater consists of the following steps:

           •  pumping of the contaminated groundwater from the source area, and the distal end of the
              plume.
           •  groundwater containment to  meet interim action standards
           •  discharge of treated water to meet NPDES requirements

Discharge limits would be established during the NPDES permit process by NDEQ and the Army. This
process is applicable due to the necessity of discharging of treated water.

A groundwater monitoring system would be established to evaluate the extraction system's effectiveness
in containing the plume.

7.1         DESCRIPTION OF REMEDIAL ACTION ALTERNATIVES

Based on the FFS, this section presents a description of the remedial  action alternatives analyzed for
OU1.  The explosives contaminated groundwater extends from the load lines at  the CAAP through the
Capital Height subdivision to approximately 2 miles into the Grand Island city limit in the off-post areas.
Two separate treatment facilities have been proposed for the pump and treat options.  A treatment facility
is proposed to  be installed near the load lines  which  are the sources of contamination for groundwater.
Another treatment facility would be installed to treat contaminated groundwater from the distal end of
the  plume.

Response of the groundwater system was evaluated with the  aid of a three-dimensional  flow  model
(MODFLOW) and  a corresponding flowpath model (PATH3DX  Model development and  use is
ROO2.TXT                                        _
04/21/94                                        -17-

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documented in Appendix A of the FFS (WJE, 1994).  The groundwater flow model was calibrated to the
measured distribution of hydraulic heads during 1993.  Water-level variations as large as 5 ft occurred
in response to seasonal variations in recharge and discharge.  The difference between measured and model
estimated hydraulic head was generally less than 1 ft. Recharge and discharge was simulated using the
Nebraska soil-water program (NEB_SWP).  Results of flowpath simulations corresponding to long-term
average recharge and discharge conditions were compared to the present-day plume configuration.  This
comparison demonstrated  that  the  model is a reliable means of  estimating advective contaminant
migration. . The developed models  were used  to estimate  the capture zones and cones  of depression
associated with various groundwater extraction  rates  and well-field locations.

Source Area:  The substances detected in the groundwater at the source area are primarily explosives,
other organics. metals and nitrates.  Treatment for explosives are required at the CAAP.  Metals and
nitrates in the groundwater may  have to be treated if  during the implementation phase, the levels exceed
discharge  requirements.  Except for the No Action and Limited Action alternatives,  all alternatives
represent  pump and treat option and involve extraction and  treatment of the groundwater.  The
components for the pump and treat options are described as follows:

Ground water  Extraction:
• Extraction  Wells:  Based on  preliminary modeling, the groundwater extraction rate from the source
area is approximately 1.000 gpm.  The actual extraction  rate  would be determined during remedial
design.

Metals Removal:
• Chemical Precipitation: The extracted groundwater would be fed to a chemical precipitation unit, if
required.   This technology would  be  employed to remove metals  and other inorganics  from the
groundwater.    The  process includes addition  of  a precipitating agent  followed by  coagulation.
flocculation. and sedimentation.  The metals and other inorganics would precipitate as sludge and would
be removed from groundwater.  The sludge would be tested and disposed of in accordance with RCRA
standards as applicable.

The effluent from the chemical precipitation unit would be pumped through sand filters where any floes
which were not settled in the sedimentation process would be  removed.  The filter media would be
periodically backwashed to remove trapped suspended panicles.   Filtration would be employed following
precipitation and before carbon adsorption or Enhanced Oxidation.
KOK.TXT                                        . „
OW2I/44                                         - I O~

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Organics Removal:
The explosives and  other  organics from the  groundwater would be  removed  using either Granular
Activated Carbon or Enhanced Oxidation.

• Granular Activated Carbon:  This is one of the two technologies selected for removal of explosives
and other organics. This technology can remove dissolved organics, including explosives, to levels below
1 pg/L.  The groundwater  leaving the granular media filters would flow through GAC columns which
would adsorb the explosives from the groundwater.  The  GAC columns would be designed based on
average flowrate of 1,000 gpm.  Regarding disposal of spent carbon, the first protocol would be to look
at fuel amendment recycling.  The spent carbon would be tested in accordance with TCLP protocols, if
TCLP is not triggered subtitle C standards would be applied for disposal of the spent carbon. Treatability
studies would be performed to determine the performance efficiency of the GAC system, carbon usage
rates, breakthrough time and other operating parameters prior to remedial design.

• Enhanced Oxidation:   Enhanced Oxidation would be  employed to  destroy organic contaminants
dissolved in water by chemical oxidation with or without the presence of ultraviolet radiation.  Chemicals
such as ozone and hydrogen peroxide may be used alone or  in combination to generate hydroxyl radical.
The hydroxyl radicals  destroy organic contaminants by initiating a series of oxidative reactions  that
eventually  lead  to destruction of organics including explosives.  If complete oxidation  is achieved.
explosives and other organic contaminants would be oxidized to  simpler non-toxic forms.  It" oxidation
is not complete, small chain aliphatics compounds, organonitrogen intermediates and other undesirable
by-products may form.  Treated  effluent from the Enhanced Oxidation  will be subject to neutralization
prior entering the ion-exchange unit or constructed wetland.

Nitrates Removal
After the groundwater has been treated for metals and explosives, the nitrates in the groundwater would
be treated if required. The following treatment technologies were considered:

• Ion Exchange:  Following removal of explosives and other organics  either using GAC or Enhanced
Oxidation,  the treated effluent would enter ion exchange units or  flow through constructed wetlands.
Multiple ion-exchange units consisting of 3 to 5 feet of anionic resin  beds would be used to  remove
nitrate from the groundwater.  Once resin has been exhausted, one of the two actions may be taken.
Some vendors offer regeneration services.  This service replaces the entire ion exchange unit with a new
ROW.TXT
OM2I/M                                         -19-

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one. thereby avoiding downtime caused by regeneration cycles.  Another option is to set up a number
of permanent units which would be occasionally rinsed with brine to remove nitrate. This process would
prolong the life of the resin and reduce the frequency of resin change-out.  The second option has been
considered in the costing of alternatives.  Brine used for regeneration of the resin beds is not expected
to be hazardous because all contaminants  in the groundwater except nitrate  is essentially treated  prior
entering the ion-exchange units.  Brine would be disposed to an appropriate facility or reclaimed.  The
treated effluent from ion-exchange units would be discharged either to an infiltration basin or to surface
water.

• Constructed wetlands: Wetlands (80 to 160 acres) would be designed and constructed specifically to
remove nitrate from the groundwater.  The bed of the constructed wetland would be compacted in-situ
to prevent infiltration of nitrates into the groundwater. Plant uptake and microbial activities would remove
nitrates from the groundwater. The plants used most frequently in constructed wetland include cattails.
reeds, rushes, bulrushes, and sedges.  The plants would be periodically harvested and disposed  of at a
landfill, by composting, or burning.  Cold weather slows the nitrates removal process but does not stop
it all together. To compensate for the slowing of the removal process, the cells are designed with extra
capacity for operations during the winter months.  Constructed wetlands have been used to treat nitrates
in municipal wastewater treatment facilities and are becoming increasingly popular. Constructed wetlands
are a proven technology with low maintenance requirements.  Infiltration of nitrates, if any. from the
constructed  wetlands  into the  groundwater  would be  monitored using  one upgradient  and two
downgradient wells which would be sampled twice a-year.

Discharge Options The treated effluent from the treatment facility at the source area would be discharged
either to an infiltration basin or to surface water.

•Surface Water Discharge
The Proposed Plan recommended that the  treated groundwater would be discharged to surface water.

• Infiltration Basin
The treated effluent would be applied through an infiltration area.  Soil with  permeabilities of 1.0  in/hr
or more are necessary for successful rapid infiltration. It is estimated that approximately 80 acres of land
would be required for infiltration.
ROM.TXT
0*11/»                                          -20-

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The  combination of the above treatment components for each alternative is shown in Table 7.1-1.
Alternatives T-3 to T-6  are similar to Alternatives T-7 to T-10 except for the variation in the discharge
option.

Distal  End:  The groundwater  at  the distal end  of the plume contains  primarily  RDX  at low
concentrations.  Should metals or other inorganics be detected  in the influent groundwater above the
interim discharge standards, appropriate treatment units would be incorporated at the distal end treatment
system.  This system uses some of the technologies as described above for the source area.  Based on
preliminary modeling, the groundwater would be extracted at an approximate rate of 3,000 gpm in order
to prevent further migration of the contaminants.  The actual extraction rate would be determined during
remedial design.  The pumped groundwater at the distal end would be treated using either GAC or
Enhanced Oxidation System.  The treated water would be discharged to surface water.

The  combination of the treatment components for each of the five alternatives for the distal end are
presented  in Table 7.1-2.

7.2         SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES

The  NCR sets forth nine evaluation criteria which serve as a basis  for comparing the remedial action
alternatives for final  actions.   Interim actions,  such as proposed here, may not achieve  final discharge
requirement levels for groundwater although they are effective in the short-term in preventing further
degradation of the groundwater and initiating reduction in toxicity. mobility or volume.  The following
is a discussion on the comparison  of the remedial action alternatives with respect to the nine evaluation
criteria.
ROD2.TXT                                         _
OW2I/94                                         -2.1-

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                                              TABLE 7.1-1    COMPONENTS OF REMEDIAL ACTION ALTERNATIVES FOR SOURCE AREA
Rcmedhil
Action
Alternatives
T-l
T-2
T_3<.>
T-4W
T-5
T-6
7.70
T-8W
T-9
T-IO
Groundwuior
Monitoring
X
X
X
X
X
X
X
X
X
X
Administrative
Control

X








Groundwater
Extraction


X
X
X
X
X
X
X
X
Chemical
Precipitation


X
X
X
X
X
X
X
X
(iramikir
Media
Filtration


X
X
, X
X
X
X
X
X
Granular
Activated
Carbon


X
X


X
X


Enhanced
Oxidation




X
X


X
X
Wetland


X

X

X

X

Ion
Exchange



X

X

X

X
Discharge
To
Infiltration
'Basin


X
X
X
X




Discharge
To
Surface
Water






X
X
X
X
Cost
($)
1,016,000
1,068,400
17,244,000'"-
17,714,000«>
I7,057,000<"-
17,528,000"'
28,129,000
27,941,000
I6,398,000fl"-
16,870,000W
\6,2\0,m«*-
16,681,000"
27,282,000
27,094,000
(a)     For GAC units, both regeneration/reuse and disposal of spent carbon have been studied. Carbon regeneration/reuse considered for Alternatives: T-3A, T-4A, T-7A, and T-8A.
       Carbon disposal considered for Alternatives: T-3B, T-4B, T-7B, and T-8B.  (b) Cost for alternative based on regeneration/reuse of spent carbon,  (c) Cost for alternative based on disposal of spent
       carbon.

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                        TABLE 7.1-2    COMPONENTS OF REMEDIAL ACTION ALTERNATIVES FOR DISTAL END
Remedial
Action
Alternatives
T-l
T-2
T-3
T-4
Groundwater
Monitoring
X
X


Administrative
Control

X


Groundwater
Extraction


X
X
Granular
Activated
Carbon


X

Enhanced
Oxidation



X
Discharge ;
to
Surface
Water


X
X
Present
Worth
S $ 217,000
'•'; $ 270,000
$ 9,320,000(b)-10,747,000w
$38,406,000
(a)    For GAC units, both regeneration/reuse and disposal of spent carbon have been studied.  Carbon regeneration/reuse considered
      for Alternatives: T-3 A.
(b)    Cost for alternative based on regeneration/reuse of spent carbon,   (c)  Cost for alternative based on disposal of spent carbon.

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7.2.1       COMPARISON OF REMEDIAL ACTION ALTERNATIVES FOR THE SOURCE AREA
A. Threshold Criteria
I.         Protection of Human Health and the Environment

Alternative T-l, No Action would not meet this criterion since no actions are taken to eliminate, reduce
or control exposure pathways.  Alternative T-2, Limited Action, does provide some protection in that it
limits access to, and use of the contaminated groundwater through institutional controls. However, these
controls do not prevent further migration of COCs present in the groundwater.

The remaining alternatives would provide adequate protection of human health and the environment as
defined by the interim action objectives. The objective is to contain and prevent migration which would
result in  further  degradation  of the aquifer.   When implemented  with an extraction system,  the
contaminated groundwater would be contained and migration of  COCs would be  prevented.  These
alternatives would be able to meet the interim action objectives focused to protect human health and the
environment.

2.         Compliance with ARARs

Alternatives T-l and T-2 would not comply with chemical-specific ARARs.  Over a long period of time.
the concentrations of explosives and other organics may decrease due to natural degradation and dilution.
In this case, eventual compliance with the ARARs may be achieved. However, the length of time before
this occurs may be extensive.   Alternatives T-3 to T-6 would be designed to  meet chemical specific
ARARs (Nebraska Groundwater Standards. Federal MCLs. TBCs). Alternatives T-4 to T-10 would be
designed to meet NPDES permit limits to be specified by the regulatory agencies.  Alternatives T-3B.
T-4B. T-7B and T-8A would comply with RCRA requirements for pre-transportation and transportation
of  hazardous wastes.   A detailed analysis of the ARARs  is  presented in chapter 3 of the Focused
Feasibility Study and chapter 8 of this Record  of Decision.

B.  Primary balancing Criteria:
 1.         Long-Term Effectiveness and Permanence
 ROMDCT                                        0/,
 (M/2I/W                                        -ifr-

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Alternatives T-l and T-2 would not provide long-term effectiveness and permanence.  The remaining
alternatives T-3 to T-10 would provide long-term effectiveness and permanence to  varying degrees.

Alternatives T-3 and T-7 incorporating GAC and constructed wetland as treatment units for removal of
organics and nitrate respectively, would offer moderate long-term effectiveness and permanence.  Under
this alternative, explosives and other organics would not be permanently destroyed, but transferred from
the groundwater to GAC.   Nitrate would be effectively removed in the constructed wetland system
through plant uptake and biological denitrification.  These reactions are irreversible and would result in
permanent removal of nitrate from the groundwater.

Alternatives T-4 and T-8 which include GAC and ion exchange as treatment units would offer lesser long-
term effectiveness and permanence  than  Alternative  T-3 and T-7 respectively.  This is  because  both
organics and nitrate would not be destroyed, but transferred from the groundwater to GAC and ion-
exchange  resin respectively.  Both the GAC and ion exchange units combined would generate larger
quantity of spent residuals which may be  regenerated, recycled  or disposed.
                                          i
Alternatives T-5 and T-9 incorporating Enhanced Oxidation and constructed wetlands would offer  very
high long-term effectiveness and permanence. The reactions involving organics and nitrate are irreversible
and result in permanent transformation of the COCs: The treatment residual generated by this alternative
is  minimum compared to Alternatives T-3, T-4, T-6.  T-7,  T-8 and T-IO.

Alternatives T-6 and T-IO are similar to Alternatives T-5 and T-9 respectively, except that ion exchange
would  be used to  remove nitrate instead of constructed wetlands.   These alternatives  would offer
moderately long-term effectiveness and permanence. Explosives and other organics would be completely
mineralized.  Nitrate would be  transferred to  resins and  eventually to brine solution  through the
regeneration process.

2.           Reduction of Toxicitv. Mobility and Volume Through Treatment

Alternatives T-l  and T-2 do not result in any reduction  of toxicity.  mobility  and volume  of the
contaminants, because removal and treatment are not components for this alternative. With effective
extraction process  as implemented  in all the pump and  treat options,  there would be  considerable
reduction of toxicity, mobility and volume of COCs present in the groundwater.
ROO2TXT
(M/2I/M

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Alternatives T-3 and  T-7 would offer moderate reduction  of toxicity, mobility and volume through
treatment.  The concentration, mobility or the volume of the  explosives and other organics would not be
reduced by GAC treatment.  This constructed wetland treatment would result in  reduction of toxicity,
mobility and volume of nitrate present in the treated groundwater.

Alternatives T-4 and T-8 would result in lower  reduction  of  toxicity, mobility and volume than
Alternative T-3 and T-7, respectively  .   Explosives  and other  organics, and  nitrate would  not be
transformed;  these  contaminants would  be transferred from  the groundwater to either GAC or  ion
exchange resin.

Alternatives T-5 and T-9 would result in very  high reduction of toxicity, mobility and volume.
Explosives and other organics would be completely mineralized to carbon dioxide, nitrogen oxides and
water.   Nitrate would be converted to organic nitrogen (plant assimilation) and molecular nitrogen.

Alternatives T-6 and T-10 would be less effective than Alternatives T-5  and T-9. respectively, in  the
reduction  of toxicity, mobility and volume.  Although  explosives and  organics would be destroyed
through Enhanced Oxidation, nitrate will be  not  be destroyed  or transformed.   Nitrate would be
eventually transferred to brine which will be disposed.

3.         Short-Term Effectiveness

This criterion is not applicable for Alternatives  T-l or T-2.

Alternatives T-3 to T-10 would  require approximately equal amount of time, similar construction
equipment and  effort, and none  would entail any additional  risk beyond those inherent in construction
projects. The short-term effectiveness for  Alternatives T-3  to T-10 is the same  because no additional
risks are incurred in the implementation of one  alternative as compared to another.

4.         Impiementabilitv

All alternatives are implementable. However, some alternatives are easier  to implement then others.  In
some instances, requirement of  administrative  approval may  make an alternative less implementable.
Administrative requirements can encompass property easements, permits for off site discharge, and/or
ROO2.TXT
OW21/44                                          -26-

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waivers.   From the administrative standpoint. Alternative T-l is the least implementabie. since a waiver
would very likely not be granted.

5.         Cost

Among the alternatives implementing surface water discharge, Alternative T-8A has the lowest cost. The
cost of Alternative T-7A exceeds that of Alternative T-8A by one percent.

Of those alternatives developed for discharge to infiltration basins (T-3 to T-6), Alternative T-3A has the
lowest present worth value.  The overall costs of Alternative T-5 and T-6 are significantly higher than
Alternatives T-3 and T-4.  This is primarily due to the considerably  high capital Cost of Enhanced
Oxidation compared  to  GAC units.  The cost of pump and treat options incorporating  discharge to
infiltration basin range between $17,056,400 and $28,128,900; those incorporating  discharge to Silver
Creek range between $16,209,800 and $27,094,200.
7.2.2      COMPARISON OF REMEDIAL ACTION ALTERNATIVES FOR THE DISTAL END

A. Threshold Criteria
I.         Overall Protection of Human Health and the Environment

Alternative T-l. No Action would not meet this criterion since no actions are taken to eliminate, reduce
or control exposure pathways.  Alternative T-2, Limited Action, does provide some protection in that it
limits access  to, and  use of the contaminated ground water through institutional controls.  However.
institutional controls would be difficult to  implement at the distal end of the plume which is located at
the off-post areas of CAAP.

The remaining alternatives are capable of providing adequate protection of the human health and the
environment.  The explosives contaminated groundwater would be contained and prevented from further
migration. These alternatives would be able to meet the interim discharge requirements which would be
focused to protect human health and the environment.

2.         Compliance with ARARs
KOB2.TXT
0*31(94                                         -27-

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Alternatives T-l and T-2 would not comply with chemical-specific ARARs.

Alternatives 3 and 4 would be designed to meet the NPDES permit limits. Both these alternatives would
comply with all Federal and State air quality standards.

Primary Balancing Criteria:
1.         Long-Term Effectiveness and Permanence

Over  a  period of time. Alternatives T-l  and T-2  may  be able to  meet the criterion of long-term
effectiveness and permanence due to natural or biological degradation and dilution.

Alternative T-3  incorporating GAC  for  removal  of explosives would  offer moderate long-term
effectiveness and permanence.  Explosives would not be permanently destroyed, but transferred from the
groundwater to the GAC media.

Alternative T-4  incorporating Enhanced  Oxidation would offer high long-term  effectiveness  and
permanence.  The organics would be transformed into simpler non-toxic by-products.
2.         Reduction of Toxicitv. Mobility and Volume through Treatment

The  Alternatives T-l and T-2 would not result in any reduction of toxicity. mobility and  volume of
organics. except through natural degradation or dilution over a period of time.

The GAC treatment by itself in Alternative T-3 would not reduce the toxicity. mobility and volume of
explosives. If spent carbon is utilized for fuel amendment, there would be a significant reduction in the
toxicity. mobility and volume of contaminants adsorbed by the GAC units. If spent carbon is disposed
to a permitted facility, there would no such reduction in the toxicity. mobility or volume of contaminants.

Alternative T-4 would result in very high reduction of toxicity. mobility and volume of explosives which
will be mineralized to simpler non-toxic by-products.

3.         Short-Term Effectiveness
ROIH.TXT
                                             -28-

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This criterion is not applicable for Alternatives T-l and T-2.

Alternatives T-3  and T-4 would require approximately  equal  period  of time,  similar  construction
equipment and  effort, and would not entail  any additional risk beyond  those inherent in  construction
projects. The short-term  risks for both these alternatives are the same because no additional risks are
incurred in implementation of one alternative as compared to another.

4.          Implementabilitv

From the  administrative standpoint. Alternative T-l is  the least implementable.   All  alternatives are
technically implementable.

5.          Cost

Alternative T-4 incorporating Enhanced Oxidation has the highest present worth.  The cost of remedial
action alternatives ranges  between $217,400 and $38,405,900.
Modifying Criteria
i. State Acceptance
The letter from the Nebraska Department of Environmental Quality (NDEQ) regarding concurrence of
the selected remedy as an interim action for this site is attached.

2. Community Acceptance
The Army held a public meeting and public comment period to allow the community to comment on the
preferred alternative as set forth in the Proposed Plan and the alternatives considered.  Many community
members were opposed  to the discharge of treated effluent to Moores Creek.   The residents were
concerned  that continuous discharge of 3.000 gpm of water would  potentially flood their basement and
property, and would result in significant  loss of property,  crops and livestock.  The residents and City
of Grand Island representatives were also concerned that extraction of groundwater at the distal end would
induce contaminant migration from  intermediary locations  of the plume to the distal end.
ROK.TXT
                                              -29-

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In response, the Army has decided to extract an additional 1,000 gpm of groundwater from intermediary
location under the Capital Heights area.  The total discharge of treated  water will be transferred through
a pipeline constructed to and through the easement of the Wood River Diversion Channel to the Plane
River.  The rationale supporting this amendment is documented in Section 8.1.

7.3         PROPOSED REMEDY

The Army has selected the following interim actions (Alternative T-7A for the source area and T-3A for
the distal end of the plume) to address groundwater contamination (OU 1):

A. Source Area
            •  Extraction of contaminated groundwater.
            •  Treatment of contaminated  groundwater using chemical  precipitation,  granular  media
              filtration, granular activated  carbon, and constructed wetlands.
            •  Discharge of treated  effluent to surface water

The flow diagram for this alternative is presented in Figure 7-2.

B. Distal End
            •  Extraction of contaminated groundwater
            •  Treatment of contaminated groundwater using granular activated carbon.
            •  Discharge of treated  effluent to surface water

Should nitrate and metal concentrations in the groundwater at the point of discharge exceed the discharge
limits, then contingencies for nitrate and metal treatment will be implemented.

The flow diagram for this alternative is presented in Figure 7-3.

The groundwater plume would be monitored to determine effectiveness of the Alternative T-7A (source
area) and Alternative T-3A (distal end) as selected interim  action remedies.

The Army has identified these interim actions as its selected alternatives  because they provide  the best
balance among other alternatives with respect to the evaluation criteria based on the information available.
The  Army believes that these  interim actions  are protective  of human health and the environment.
ROO2.TXT
(N/21/94                                          -30-

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implementable, and effective in reducing the toxicity, mobility and voiume of contamination present in
the groundwater plume.  This approach will contain and prevent further migration of the contaminant
plume.  This approach has been modified based on public comment.  Discussion of the modifications is
found in Section 8.1.

For treatment of explosives, the Army considers the GAC a better option than Enhanced Oxidation since
it  is a proven technology, which is  half the cost of  Enhanced Oxidation for this site.  The GAC
technology has been used by the Army since the mid 70's to treat explosive contaminated discharge water
from production facilities.

Chemical precipitation was the proposed metals treatment process,  should it be needed. The Army has
proposed to carry a metals process as a contingency should the metals levels in the extracted groundwater
be determined to be above discharge levels.  A statistically designed background study is being conducted
and should be finalized prior to the design of the selected remedy.  The background study will be used
to determine if chemical precipitation of metals is necessary as a pan of the final action.
ROU2.TXT
M/7I/M                                          -31-

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                                                  FILTER
                                                BACKWASH
                                              TO FILTER PRESS
                                                                                                 pH ADJUSTMENT
              CHEMICALS
GROUNDWATER
                                                                       TREATED
                                                                       WATER
                                                                       DISCHARGE
                                                                       TO SURFACE
                                                                       WATER
           ;   CHEMICAL     CLARIFICATION
            PRECIPITATION         j
GRANULAR
  MEDIA
FILTRATION
GRANULAR
ACTIVATED
 CARBON

                                                                                                         WETLANDS
                                                                                                        SPENT CARBON TO
                                                                                                       REGENERATION FOR
                                                                                                            RECYCLE
                     FILTRATE
                                                                               SLUDGE TO DISPOSAL
                                                     FILTER PRESS
                                                                   LEGEND
                                                            	  SLUDGE
Ml 193064
                                                                         GROUNDWATER

                                                                         SPENT CARBON
                                                                                                     WATKINS-40HNSON ENVIRONMENTAL. INC.
                                                                                                     Ground-Water Consulting. Environmental Engineering
                                                                                                     Remediation Services
                                                           ALTERNATIVE T-7A
                                                   SCHEMATIC DIAGRAM OF GROUNDWATER
                                               EXTRACTION, CHEMICAL PRECIPITATION, GRANULAR
                                               MEDIA FILTRATION, GRANULAR ACTIVATED CARBON
                                               (SPENT CARBON RECYCLED), WETLANDS TREATMENT
                                                    AND DISCHARGE TO SURFACE WATER
                                                                                               Date:  June  1994
                                                                                                                         Figure 7-2

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                 GROUNDWATER
CO
                                                                     TREATED WATER DISCHARGE TO SURFACE WATER
                                        GRANULAI.
                                        ACTIVATED
                                         CARBON
                                                               SPENT CARBON TO REGENERATION FOR RECYCLE
                                                                 LEGEND
  M1193069a
                                                                       GROUNDWATER

                                                                       SPENT CARBON
                                                                                                 WATKWSOOtMSOM EMVMONUCWTAL, INC.
                                                                                                   OAOUKOWATmCCTBACTTOH
                                                                                                  QflANUtAD ACTIVATED CMtBOK
OSCMMWeiO SUKFACCWATEfl
                                                                                           Date:  June  1984
                                                                                                                    Figure 7-3

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Constructed wetlands were compared to ion exchange, which  removes the nitrates through the use of
synthetic resins.  The ion exchange technology is  effective but is prone to clogging which increases
maintenance requirements over that of constructed wetlands approach.  Constructed wetlands have been
used to treat nitrates in municipal wastewater treatment facilities and are becoming increasingly popular.
The Army viewed constructed wetlands as a better option for on-post remediation.

Surface water discharge is the selected discharge option.  The  alternative to surface water discharge is
reinjection through infiltration basins which is a proven technology, but prone to clogging and requires
higher maintenance than surface water discharge.

The Army estimates that the interim actions for the source area and the distal end are $16.398,100 and
S9.320.000 respectively. The cost breakdown for these alternatives is presented in Tables 7.3-1 and 7.3-
2.  Based upon the cost of the alternatives  and the degree of protect!veness that one alternative affords
as compared  to the other alternative,  the Army has selected the most cost  effective alternatives which
meet the evaluation criteria.
KOD:.TXT
                                               34

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Table 7.3-1    Summary Cost Estimate (or Source Area, Alternative T-7A.
ITEM
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
A.
B.
C.
Site Preparation/Support
Extraction Wells
Chemical Precipitation
Granular Media Filtration
Sludge Disposal
Granular Activated Carbon
Wetlands Treatment
Surface Water Discharge
Piping, Connections, and Pumping
Treatment Systems Operator
Groundwater Sampling
Subtotal
Contingency 35% of total Capital Costs
Contingency . 5% of total Annual Costs
TOTAL CAPITAL COSTS
TOTAL ANNUAL COSTS
TOTAL PRESENT WORTH OF ANNUAL COSTS
CAPITAL
COST
$103,300
$31,200
$510,400
$387,000
$180,000
$929.800
$552,000
$569.900
$3,263,600
$1,142,300
$4,405,900
ANNUAL
O&M
COST
$17,600
$409,900
$115,600
$28,900
$151,100
$37.100
$26.600
$58,400
$576,200
$1,421,400
$71,100
$1,492,500
PRESENT WORTH OF
ANNUAL COSTS
30YEARS,5% 30YEARS,7%
$270,600
$6,301,200
$1,777,000
$444,300
$2,322,700
$570,300
$408,900
$897,800
$1,045,900
$14,038,700
$701,900
$14,740,600
$218,400
$5,086,400
$1,434.500
$358,600
$1,875,000
$460,300
$330,100
$724,700
$933,100
$11,421,100
$571,100
$11,992,200
TOTAL PRESENT WORTH OF CAPITAL AND ANNUAL COSTS (A + C)
$19,146,500    $16,398,100

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Table 7.3-2   Summary Cost Estimate for Distal End, Alternative T-3A.
ITEM
1.
2.
3.
4.
5.
6.
7.
8.
g.
A.
B.
C.
Site Preparation/Support
Extraction Wells
Granular Activated Carbon
Surface Water Discharge
Piping, Connections, and Pumping
Treatment Systems Operator
Groundwater Sampling
Subtotal
Contingency 35% of total Capital Costs
Contingency 5% of total Annual Costs
TOTAL CAPITAL COSTS
TOTAL ANNUAL COSTS
TOTAL PRESENT WORTH OF ANNUAL COSTS
CAPITAL
COST
$117,700
$33,800
$540,000
$283,000
$188,500
$1,163,000
$407,100
$1,570,100
ANNUAL
O&M
COST
$49.700
$496,300
$26,600
$8,300
$13,900
$594,800
$29,700
$624,500
PRESENT WORTH OF
ANNUAL COSTS
30YEARS,5% 30YEARS,7%
$764,000
$7,629,300
$408,900
$127,600
$213,700
$9,143,500
$457,200
$9.600,700
$616,700
$6,158,600
$330,100
$103,000
$172,500
$7,380,900
. $369,000
$7,749,900
TOTAL PRESENT WORTH OF CAPITAL AND ANNUAL COSTS (A -f C)
$11,170,600     $9,320,000

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                           8.0    STATUTORY DETERMINATIONS

The selected interim remedy will contain and prevent further migration of the contaminant plume, which
left uncontained would  result  in further degradation  of the aquifer.  This will be  accomplished by
pumping and treating the groundwater.

All ARARs potentially considered  for this action are listed in  section 3.0 of the Focused Feasibility
Study.  The requirements determined to  be Applicable or Relevent and Appropriate are listed in tables
8-1 A, 8-1B. 8-2 and 8-3 which respectively are the chemical-specific, location-specific and action-specific
ARARs. The numeric standards for the containment criteria for explosives are presented in Appendix
B.  In the absence of chemical-specific ARARs for explosives: health  advisories and risk concentrations
are utilized for determining the containment goals.

The selected remedy consists of extraction of contaminated groundwater from three areas of the plume:
source area, intermediary and distal end.  The objective is to capture the groundwater at the source area
containing relatively high concentrations of contaminants, primarily RDX and prevent migration of these
contaminants. The extraction rate will be ascertained during the preliminary implementation stages based
on the ability of the well  network to capture the contaminants.  Groundwater exposure is likely through
the usage of private wells in  the  Capital Heights area, therefore, groundwater will be  extracted an ^
intermediary location  before the plume  enters Webb  Road and Capital Avenue.  In this area.  RDX
concentrations range  between  4.2 and  21.0 (ig/L.   Continuous extraction of groundwater at an
approximate rate of 1.000 gpm  is expected to result in significant decrease in both the concentrations and
volume of  contaminants.   The distal  end contains RDX  at concentrations slightly  above the health
advisory of 2 ng/L. The extraction of groundwater at the distal end will prevent migration of" the plume
to a municipal supply  well  located  approximately 1.5 miles down gradient.  Extraction of groundwater
at the distal end will also prevent impact to additional  downgradient residential and irrigation wells.
ROIH.TXT
04/21/M                         .                -371'

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                                        Table 8-1A     Chemical-Specific ARARs for Groundwater Containment
  Standard Requirement,
  Criteria, or Limitation
          Citation
            Description
 Applicable/
Relevant and
 Appropriate
            Comments
National Primary Drinking
Water Standards
40 CFR Part  141
Maximum Contaminant
Levels
Establishes maximum contaminant
levels (MCLs) which are health-
based standards for public water
systems.
  No/Yes
The MCLs for organic and
inorganic contaminants are relevant
and appropriate for deriving the
NPDES discharge levels.
National Secondary
Drinking Water Standards
40 CFR Part  143
Establishes secondary maximum
contaminant levels (SMCLs) which
are non-enforceable guidelines for
public water systems to protect the
iicslhclic quality of the water.
Relevant and appropriate for
establishing discharge limits.
                                                                          No/Yes
                    SMCLs may be relevant and
                    appropriate for deriving the
                    NPDES discharge levels.
Maximum Contaminant
Level Goals (MCLGs)
Stat. 642(1986)
Establishes drinking water quality
goals set at levels of no known or
anticipated adverse  health with an
adequate margin of safety.
                                                                                                     No/Yes
                    MCLGs for organics and inorganic
                    contaminants may be relevant and
                    appropriate for deriving the
                    NPDES discharge levels.  SB,
                    BA,CD,BE,CD,F,HG have non-
                    zero MCLGS.
Groundwater Quality
Standards and Use
Classification
NDEQ, Title  118,
Chapter 5,
Appendix A
Establishes standards and use
classifications for groundwater
sources of drinking water.
   Yes/-
Is applicable because groundwater
is a drinking water source.
     
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                                      Table 8-IH    Chemical-Specific ARARs for Surface Water Discharge
 Standard Requirement,
 Criteria, or Limitation
         Citation
          Description
 Applicable/
Relevant and
 Appropriate
          Comments
Water Quality Standards
for Surface Water of the
State
NDEQ, Title 117
Chapter 4
Establishes standards for the
surface waters of the state.
   Yes/-
Applicable because treated
water will be discharged to
surface water.  More relevant
than Federal ambient water
quality criteria.  Contains
antidegradation clause and
numeric waste quality
standards for water bodies in
the state.  Does not contain
standards for explosives.
Antidegradation policy apply
to discharge to Platte River.
Discharge standards  will be
established in accordance with
(IAW) NPDES permit.

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                                                  Table 8-2    Location-Specific ARARs
Standard Requirement.
Criteria, or Limitation
Federal

Floodplain Management






pish and Wildlife
Coordination Act 6





Farmland Protection
Policy Act








Protection of Wetlands





Citation



40 CFR 6.302(D)
Executive Order
1 1988 and 40 CFR, Part 6,
Appendix A



16 USC 66! el seq.






7 USC 420 et seq.









40 CFR Part 6.
Appendix A. Part (j)
Executive Order 11990 Part
7(c)


Description

Establishes requirements
for federal agencies to
reduce risk of flood loss,
minimize the impacts of
floods on human safely,
health and welfare, and
restore and preserve the
natural and beneficial
values of floodplains.
Establishes requirements
for actions taken to
prevent, mitigate, or
compensate for project-
related damages or losses
to fish and wildlife
resources.
Establishes requirement
for federal agencies for
acquiring, managing and
disposing of lands and
facilities; or provide
criteria that identify and
take into account the
adverse effects of actions
on the preservation of
farmland.
Establishes requirements
for federal agencies to
avoid or minimize adverse
impacts on wetlands.


Applicable/
Relevant and Appropriate


Yes/-








No/Yes





No/Yes








Yes/-





Comments

.

Applicable, the treatment
facility will be is located
within a floodplain.
Executive Order 11988 is
TBC guidance.


Relevant and appropriate
if project related activities
affect fish and wildlife
resources.



Relevant and appropriate
if treatment facility
location and project
related activities affect
farmland.





Wetlands are likely to be
present in the vicinity of
(he piping route to the
Platte River. Executive
Order 11990 Part 7(c) is
TBC guidance.
KIIII:. r\i
in :i •n
-41)-

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                                               Table 8-3    Action-Specific ARARs (page I of 3)
 Standard Requirement,
 Criteria, or Limitation
          Citation
       Description
 Applicable/
Relevant and
 Appropriate
            Comments
        Federal

(Hazardous Waste
Classification
40 CFR Part 261
 Provides determination
 of hazardous waste;
 procedures for delisting
 of wastes.
  No/Yes
Relevant and appropriate if
treatment residuals such as
sludge/spent carbons are determined
to be hazardous.
Hazardous Waste
Determination
40CFR262.il
 Requires hazardous
 waste generator to
 determine if a waste is
 hazardous pursuant to
 40CFR Part 261.
   Yes/~
Potentially applicable to sludge
from dewatering and backwash
residue.
Hazardous Waste
Management
40 CFR Part 264
.Establishes requirement
 that affects generation,
 transportation,
 treatment, storage and
 disposal of hazardous
 waste.
  No/Yes
Relevant and appropriate if
treatment residuals are determined
to be hazardous.
Land Disposal
40 CFR Part 268
 Establishes regulations
 on land disposal
 restrictions and
 treatment standards for
 land disposal of RCRA
 hazardous waste.
                                                                                          Yes/No
                    Relevant and appropriate if
                    treatment residuals such as sludge
                    are determined to be hazardous.
     IMP.' IX I
     IN'.'I-'M
                         41-

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                                                     Table 8-3   Action-Specific ARARs (page 2 of 3)
CO
ro
• •
CO
CD
Standard Requirement,
Criteria, or Limitation
Standards Applicable to
Transporters of
Hazardous Waste
Wetlands Protection
State
Tr&StC nf cUlfl&CVflCllt
Rules
Hazardous Waste
Management
Citation
40 CFR Part 263
dean Water Act 404,
40 CFR 230.3(1)
33CFR328(b)
«
NDEQ, Title 126, Chapter
18
NDEQ, Title 128, Chapter 3
Description
Establishes standards
which apply to
tttutspurlets of
hazardous wastes.
Establishes requirement
to avoid degradation of
wetlands due to
construction activities.

Establishes regulations
on releases of oil or
hazardous substances
into water or land.
Establishes requirement
for notification of
hazardous waste
activity.
Applicable/
Relevant and
Appropriate
No/Yes
Yes/No

Yes/No
No/Yes
Comments
Relevant and appropriate if
treatment residuals such as
sludge/spent carbon are determined
to be hazardous.
Applicable to construction activities
near the wetlands which may be
present near the Platte River.

Applicable to sludge from
dewatering, backwash, and residues
that are hazardous substances and
could be spilled or leaked to land or
water during treatment operations.
Relevant and appropriate if
treatment residuals are determined
to be hazardous.
             ROD2.1XT
             OMMM

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                                        Table 8-3  Action-Specific ARARs (page 2 of 3)
Standard Requirement,
Criteria, or Limitation
hazardous Waste
Management
Air Pollution Controls
Rules & Regulations
Air Pollution Control
Rules and Regulations
i
Groundwater
Monitoring Wells
Requirements
Groundwater
Management or Control
Citation
NDEQ, Title 128, Chapter
17
NDEQ, Title 129. Chapter
32
NDEQ, Title 129, Chapter
20
Neb. Rev. Stat 46-602, 46-
1201, 46-651 to 46-655
Neb. Rev. Stat 46-656 et.
seq.
Description
Establishes requirement
that affects generation,
transportation,
treatment, storage and
disposal of hazardous
waste.
Pertains to generation
of dust and air-borne
paniculate matter.
Establishes standards on
paniculate matter
emissions.
Provides
requirements/restriction
s for groundwater
monitoring wells.
Restricts access to
groundwater from
certain surface areas.
Applicable/
Relevant and
Appropriate
No/Yes
Yes/No
No/Yes
Yes/No
Yes/No
Comments
Relevant and appropriate if
treatment residuals are determined
to be hazardous.
Dust/air borne paniculate matter
may generate during construction,
transportation or handling.
Relevant and appropriate if
treatment residuals are determined
to be hazardous.
Potentially applicable for all
groundwater wells to be used for
extraction.
Potentially applicable.
mn>:.m
                                           43-

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The selected treatment processes consisting of extraction, chemical precipitation, GAC and constructed
wetlands which are capable of meeting discharge criteria and containing the contaminant plume to the
levels as prescribed in attachment B.  However, the actual design and configuration of these treatment
units will be based on the required discharge limits to be specified by the regulatory agencies during the
NPDES  permitting process for off site surface water discharge.  The treatment process will  utilize
permanent solutions and alternative treatment technologies or resource recovery technologies  to the
maximum extent practicable.  The treatment processes will result in reduction of toxicity, mobility and
volume of contaminants present in the groundwater extracted from the different locations of the plume.
This action will stabilize the risk and prevent further degradation of the environment, therefore protecting
human health  and the environment.  This selected alternative based on capital and operational costs
balanced with  community acceptance and compliance with ARARs provides for an implementable and
cost effective alternative.

It is expected that the final remedy  would be implemented prior to the five-year review period.  If the
final remedy is not underway within five years  after the commencement  of this interim action, a review
would  be conducted to ensure that the remedies continue to contain the  plume  and reduce the risk
associated with the contaminated groundwater.

8.1         DOCUMENTATION OF SIGNIFICANT CHANGES

The FFS and Proposed  Plan recommended that groundwater would be  extracted from the  source area
(1000 gpm) and the distal end (3000 gpm). treated, and discharged to surface water  in the areas of Silver
Creek and Moores Creek respectively.  During the public meeting held on May 5,1994, the residents of
Merrick  County were concerned that continuous discharge of 4000  gpm of water  would exceed the
creeks' capacity and potentially flood their basements and property. The discharge of treated groundwater
to the  creeks was found to  be unacceptable by the local residents.   In addition, the residents were
concerned that extraction of groundwater at the distal end would induce contaminant migration from
intermediary locations of the plume to the distal end.

In response, the Army evaluated potential flooding problems that may result due to discharge  of treated
water to the creeks.  It was estimated that flooding would most likely occur during winter months (culvert
icing is expected) and also during temperate months when high flow events occur.  During high  flows.
the additional 7000 gpm discharged from the treatment facility would  make the natural problem worse.
A gross estimate based on a visual site inspection and discussions with the local community,  estimated
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that approximately 1900 acres of land and about 90 residences could be potentially affected by flooding
due to discharge of treated water to the Silver and Moores creeks.  The loss of crops that could result
due to flooding  of property is estimated to be $  1,000.000 each year.    Based on new information
obtained during  the  public meeting,  the Army re-evaluated the  surface  water  discharge point and
determined discharge to Silver or Moores Creek may not comply with 40 CFR Part 6, which has been
determined to be an ARAR.

In response to the concerns raised by the citizens, the Army evaluated the option  of discharging the
treated water directly to the Plane River by means of pipeline. A piping system was evaluated based on
a total discharge rate of 7000 gpm including an additional 1000 gpm of groundwater extracted from the
groundwater plume before it enters the intermediary area under the Capital Heights area.  This additional
1000  gpm of extracted groundwater would  prevent migration of contaminants, particularly RDX from
the central portion of the plume where  RDX  concentration  exceeds 20 jig/L.   Note that  additional
discharge capacity will be designed into the pipe line as a contingency for the final remedial action
selection. The pipeline traverses a total distance of 25 miles  and the present worth (7% ,30 years) ranged
between $10,392,000 and $14,041,300.   The surface water discharge of treated water to Platte River
will eliminate potential flooding impacts  and will become cost comparative over the system life-cycle
should the metals and nitrate treatment not be needed to meet the discharge levels at the Platte River.

The treated  effluent discharged to the Silver and Moores creek would have had to meet MCLs. where
applicable, due to the fact that both Silver Creek and .Moores are hydraulically connected to the aquifer.
If discharged directly to Platte River, the treated  effluent would be required to meet  NPDES permit
limits.  It is expected that effluent limits for the NPDES at the Platte may not warrant the  treatment tor
metals and nitrates. This reduced treatment requirement would offset the cost associated with  piping the
treated effluent to the Platte River.

If for any unforseen reasons the Wood River  Diversion Channel is not implemented, the Army will
undertake the responsibility of completing the piping route  (not the diversion channel) and provide the
piping system for discharge of treated water to the Platte River.  This may require  additional time for
construction of the selected treatment system.

8.2         SUMMARY OF SELECTED REMEDY AFTER MODIFICATION
A.         Source Area
            •  Extraction of contaminated groundwater.
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             • Treatment of contaminated groundwater using granular activated carbon  and granular
               media filtration; and chemical precipitation and constructed wetlands, if necessary.
             • Discharge of treated effluent to the Platte River through Wood River Diversion Channel
               easement.

 B.          Distal End/Intermediary Area
             • Extraction of contaminated groundwater at the distal end and the intermediate area.
             • Treatment of  contaminated  groundwater using granular activated carbon and  granular
               media filtration.
             • Discharge of treated  effluent to Platte River through Wood River  Diversion  Channel
               easement.
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                         GROUNDWATER - OPERABLE UNIT ONE
                       CORNHUSKER ARMY AMMUNITION PLANT
                               RESPONSIVENESS SUMMARY

SUMMARY OF COMMENTS  RECEIVED  DURING THE PUBLIC  COMMENT PERIOD AND
AGENCY RESPONSES

The public comment period on  the preferred interim remedial action alternative for Groundwater -
Operable Unit One, Cornhusker Army Ammunition Plant extended from April 26 to May 26, 1994. A
public availability session took place on May 4,  1994 from 4pm to 8pm at the Grand Island City Hall.
Grand Island, Nebraska.  The Public Meeting took place on May 5, 1994 from 7pm to 9pm, also at the
Grand Island City Hall.  Approximately 16 people attended the public availability session with 7 people
making oral statements or asking questions. 19 people attended the Public meeting on May 5, 1994, with
7 people making oral statements or asking questions.  Seven written statements were received during the
comment period.  The transcript of the  Public Availability  Session and the Public  Meeting for the
Proposed Plan  is attached.  During the question  and  answer session, the Army,  EPA. and the State of
Nebraska representatives responded to questions  from the audience.  These responses are contained the
transcript of the proceeding, which is included in the Administrative Record for the site.  A summary of
the written comments and the Army's response is provided herein.

Overview
Four of the seven written comments reflect the opinion that the groundwater should be cleaned up, but
the discharge of treated water should not be to the local drainage due to chronic flooding problems along
these drainages. One comment received voiced a concern about the lack of extraction wells in die central
portion of the plume and one comment concerned the effect infiltration basins would have on the water
table in Capitol Heights.

Comments on the Discharge Options

           1.    Several citizens of Merrick County commented that any water discharged to  Moores
                or Silver  Creek would adversely impact them by causing flooding.  The area where
                these individuals reside along Moores Creek is prone to flooding.  The citizens also
                opposed the discharge because  they believed that the added water to the creeks would
                raise the water table sufficiently to  prevent farming of adjacent land.

              Army's Response:  Prior  to the Public Meeting and Public Availability Session the
              Army's estimates of stream capacity  and ability to  bear the additional  water  did not
              indicate flooding problems would occur if the treated water would be discharged into these
              drainage.  Due to the concern of Merrick County residents voiced during the 2 day public
              information  gatherings, the Army has reassessed the discharge options for the treated
              groundwater. Information about the planned diversion channel for Wood River has been
              collected to develop other viable discharge options which were assessed according to the
              same criteria used in the Focused Feasibility Study.   Through this evaluation the Army
              has determined that discharge of treated water via pipeline through the  easement for the
              diversion channel to the Platte River is a viable alternative and the Army has changed the
              discharge option for the selected remedy as documented in this ROD.
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Other Comments
            1.   One citizen asked what effect the infiltration basins would have on the groundwater
                table in the Capital Heights area.

              Army's Response:  Computer modeling indicates that the areas beneath and immediately
              adjacent to the basins would  see a  1 to 2 foot rise in the water table,  causing what is
              referred to as a groundwater mound. This mounding effect would dissipate by the time
              the  groundwater reached the  site boundary.  Therefore,  no impact on the water table
              would occur in the Capital Heights area.

            2.   The City of Grand Island  voiced a concern over the lack  of extraction wells in  the
                central  portion of the plume.  They were concerned that pumping at  the distal end
                would  cause  groundwater with  higher  concentrations of RDX  to  migrate  at  an
                accelerated rate, causing an  increase in RDX  levels in areas which currently have
                detections at or around the detection limit. The City  expressed that the accelerated
                migration of the plume would cause a reduction in property values and would cause
                problems if any dewatering had to be done for  construction projects due to discharge
                of more highly contaminated groundwater into ditches.  They expressed a concern that
                potential for growth and development would be hindered due to the complications of
                providing construction dewatering due to the anticipated increases in contaminant levels
                in this area of the plume.

              Army's Response:  The Army has reconsidered the option to control migration of the 20
              ppb RDX zone in the central portion of the plume.  Currently it is anticipated that 3 wells
              would  be utilized to contain the explosive contaminants in this  area.   Actual well
              placement and extraction rates will be ascertained  during the final design phase.

            3.   The NDEQ raised the issue of the applicability of the State's Title  118 to the proposed
                action and requested the Army to clarify its position on Title 118.

              Army's Response:  The Army has since requested the  State's  action specific ARAR
              determinations and their  interpretation.  The Army has since included  Title  118 as an
              applicable ARAR for this selected action.
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                                       ATTACHMENT B

                       GROUNDWATER CONTAINMENT STANDARDS


                 COMPOUND                                    STANDARD (ppb)

                 2,4,6,-trinitrotoluene                                      2.0 (b)

                 HMX                                                 400.0 (b)

                 RDX   .                                                  2.0 (b)

                 nitrobenzene                                             3.5 (c)

                 1,3-dinitrobenzene                                        1.0 (b)

                 1,3.5-trinitrobenzene                                      3.5 (c)

                 2-amino-4,6-dinitroluene                                  0.4 (d)

                 2,4-Dinitrotoluene                                        0.05  (a)
Note:
a. USATHAMA. Assessment of ARARs. January 1992 (Based on Carcinogenic Slope Factor)
h. USEPA. Office of Drinking Water Lifetime Health Advisory (72-year Lifetime advisory)
c. WJE. Modified USATHAMA's Assessment of ARAR's. December 1991 (Based on Estimated RfD)
d. Based on provisional RfD of 6E-05 mg/kg-day. USEPA/ECAO 1993
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