United States        Office of
             Environmental Protection   Emergency and
             Agency           Remedial Response
EPA/ROD/R09-91/067
August 1991
&EPA    Superfund
             Record of Decision:
             Castle Air Force Base,  CA

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50272-101
 REPORT DOCUMENTATION
        PAGE
1. REPORT NO.'
   EPA/ROD/-R09-91/067
                                                                     3. Rociptonrs Accossion No.
 4. Title and Subtitle
    SUPERFUND RECORD OF DECISION
    Castle Air Force Base,  CA
    First Remedial Action
                                           5. Report Date
                                             08/12/91
 7. Author(s)
                                                                     8. Performing Organization Rept No.
 9. Performing Organization Name and Addreaa
                                                                     10. ProjecVTaak/Work Unit No.
                                                                     11. ContractfC) or Grant(G) No.

                                                                     (C)

                                                                     (G)
 12. Sponsoring Organization Name and Addresa    . •
   U.S.. Environmental Protection Agency
   401  M Street,  S.W.
   Washington, D.C.   20460
                                            13. Type of Report ft Period Covered

                                                     800/000
                                                                     14.
 15. Supplementary Notes
 16. Abstract (Limit: 200 words)
   The  2,777-acre  Castle Air Force Base  is  a Strategic  Air Command training  base 6 miles
   northwest of the  City of  Merced in Merced County, California.   Land use  in the area
   is predominantly  agricultural.   Several  irrigation canals and  laterals are located
   within  1  mile of  the base including Canal Creek, which borders  the base on. its
   southwest boundary and receives runoff  from the base and'irrigated land downstream.
   At least  20 agricultural wells  are located within 3  to 4 miles  of the site,  and a
   number  of residential and municipal wells are located within 2  miles of the site.
   Since  1941, the site has been used as a  military air training  base.  Fire training
   activities, as.well as aircraft and jet  engine maintenance activities including metal
   plating and processing, have  occurred onsite.  Both  processes  involve the.use of
   fuels,  solvents,  and chemicals  and have  generated municipal and chemical  wastes..  •
   During  routine  well sampling,  the State  identified elevated TCE concentrations in
   ground  water in the shallow aquifer beneath and south of the site.  In 1984, the base
   was  required not  only to implement remedial measures to correct this identified
   contamination but also to prevent future ground water degradation from waste
   discharges.  The  site has been  divided  into operable units  (OUs)  for remediation.

   (See Attached Page)
 17. Document Analysis, a. Descriptors
    Record of Decision  -  Castle Air  Force Base,  CA
    First Remedial Action
    Contaminated Medium:   gw
    Key Contaminants:   VOCs (benzene^  PCE, TCE)

    b. Identifiers/Open-Ended Terms
   c. COSATI Held/Group
 18. Availability Statement
                                                      19. Security Class (This Report)
                                                              None
                                                      20. Security Class (This Page)
                                                      	None	
                                                       21. No. of Pages
                                                         54
                                                                                 22. Price
 (See ANSI-Z39.18)
                                       See Instructions on Reverse
                                                       OPTIONAL FORM 272 (4-77)
                                                       (Formerly NTIS-35)
                                                       Department of Commerce

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EPA/ROD/R09-91/067        .,    '         .   •      ,
Castle Air Force Base, CA- - ••         .                 •'.•'.
First -Remedial Action       -            .         .            .•  •     ~    •

Abstract  (Continued)   .  .                             .   "             ,       -   •

This Record of Decision  (ROD)  provides an  interim remedy, for the main TCE  plume,  as  OU1.
Future RODs will address remaining soil-and ground water contamination.  The  primary
contaminant's of concern affecting the ground water are VOCs including benzene,  PCE,  and
TCE.   ;               •     -         .  : :•'',.       "            , "    ..        , ' -.

The selected, remedial action for this interim-remedy  includes onsite  .pumping  and
treatment of ground water using air  stripping, followed by natural  biological enhancement
to accelerate the release and  degradation  of hazardous constituents in the saturated
zone; reinjecting the treated  ground water -qnsite to  maintain hydraulic control and  avoid
depletion of the aquifer; treating emissions from the air_stripping process using ^
granular' activated carbon;  and treating the emissions abatement.unit  by onsite steam ,
regeneration, and disposing of the liquid  condensate  offsite.   The  estimated-present'
worth cost for this remedial action  is $28,445,000, which 'includes  an annual  O&M cost  of
$2,744,000.       '     '•••'•   •    ,      -  .        •••••     .         ,  '

PERFORMANCE STANDARDS OR GOALS:  Ground water clean-up goals based  on MCLs' and risk  .
levels will be established  in -a subsequent ROD.              .  *•      .-      .  -    . .   •

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 RECORD OF DECISION
       INTERIM
 OPERABLE UNIT No. 1
CASTLE AIR FORCE BASE
     CALIFORNIA
    August 7,1991

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!                                  TABLE OF CONTENTS
*                                        -                           .

(                                                                         PAGE
         LIST OF TABLES AND FIGURES	'..	    ii
|  .         1.0   DECLARATION FOR THE RECORD OF DECISION	   1-1
           2.0   SITE DESCRIPTION, SITE HISTORY, COMMUNITY RELATIONS	   2-1
[           3.0   SCOPE AND ROLE OF THE OPERABLE UNIT	   3-1
           4.0   SUMMARY OF SITE CHARACTERISTICS . •	   4-1
|           5.0   SUMMARY OF SITE RISKS  	   5-1
           6.0   DESCRIPTION OF ALTERNATIVES	..	   6-1
|           7.0   COMPARATIVE ANALYSIS OF ALTERNATIVES		   7-1
           8.0   THE SELECTED REMEDY	   8-1
           9.0   STATUTORY DETERMINATIONS		....   9-1
         10.0   RESPONSIVENESS SUMMARY	  10-1
  dA:ENG:9327-TOC/061991

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                                         LIST OF TABLES


         TABLE                               TITLE

           .4-1        Summary of TCE Detected in Groundwater for Main TCE Plume

           4-2        Organic Compounds Detected in MTP Groundwater Sampling Rounds 1, 2, 3, 4

           4-3        Metals and Ions Detected in MTP Groundwater Sampling Rounds 1, 2, 3, 4

           7-1        Comparison of Cleanup Alternatives                         .    .

           7-2        Estimated Maximum Annual Waste and Emissions for Remedial Alternatives

           7-3        Potential Federal Applicable, or Relevant and Appropriate Requirements for the
                     Main TCE Plume (Operable Unit No. 1) .

           7-4        Potential State Applicable, or Relevant and Appropriate Requirements for the  ,
                     Main TCE Plume (Operable Unit No. 1)          -

         ,  8-1        Alternative I - Present Worth Analysis

           8-2      -Alternative I-Present Worth Values in 1990 Dollars

                                                  '   *         '      ••.,"•         1 •*


                '..-•'                    LIST OF FIGURES                         ,


         FIGURE    .                   .       TITLE

           1-1        Main TCE Plume, Operable Unit Nq. 1
                ' »>           '      .''''.
           2-1        Major Population Centers Near Castle AFB

           2-2        Regional Drainage Map
.^A:ENG:9327-TOC/061991

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t               '                •                  •         .
\                                    INTERIM OPERABLE UNIT NO. 1
                                      CASTLE AIR FORCE BASE
>                                            CALIFORNIA
                          1.0 DECLARATION FOR THE RECORD OF DECISION

           SITE NAME AND LOCATION
           Castle Air Force Base
           Merced County, California
           STATEMENT OF BASIS AND PURPOSE
           This decision document represents the selected interim remedial action for Operable Unit
           No. 1 at Castle Air Force Base, which was developed in full accordance with the National Oil
           and Hazardous Substances Pollution Contingency Plan (NCR) as well as the Comprehensive
           Environmental Response, Compensation and Liability Act of 1980 (CERCLA), as amended by
           the Superfund Amendments and Reauthorization Act of 1986 (SARA).

           This  decision is based upon the Preliminary Site Characterization Report (PSCR) (IT
           September 1990) and the Feasibility Study (FS) and the Proposed Plan (PP) for Interim
           Operable Unit No. 1 (IT, December 1990). All of these documents are available in the
           Administrative Record for Castle AFB.

          The United States Environmental Protection Agency and the State of California agree on the
          selected remedy.

          ASSESSMENT OF THE SITE
          The Main Trichtoroethytene (TCE) Plume, defined as TCE above the maximum contaminant
          level  (MCL) of 5 ppb in the shallow aquifer beneath the Base, contains TCE which, if not
          addressed by implementing the selected interim remedy in this Record of Decision  (ROD),
          may present an imminent and substantial endangerment to public health and welfare. The
          terms 'Main TCE Plume" and "MTP" are used throughout this document to designate a plume
          that contains a variety of contaminants. TCE has been the most prevalent and mobile of the
          contaminants and can thus be used to determine  the extent of groundwater contamination.
                                                1-1
  vlA:ENG:9327-1/070191

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          DESCRIPTION OF THE REMEDY
          	.   ... .    .   .,	      ,,  ..__      ^
          The remedy described in Interim'Operable Unit No. 1 represents an early effort to extract and
          treat the "contaminated groundwater under the Base.  This operable unit will be succeeded by

          subsequent operable units which will address groundwater contamination on and off Base

          and, ultimately, an overall Base ROD which will assure that all contamination, including any
          contaminated soils, is addressed.  ,                                              '
             *> ' v ' •  '   * *'••*    '                      '•
             •'*'•"    ,,"",        ' 1,                   I'          ' *"i . '-.
             '--1. ..'•='    '     •  '  V  "'  ". • .'"''    ':"          •  '   "             '  •
          The Main TCE Plume (MTP), is one of the sites currently being investigated at the Castle Air
          Force Base. Operable Unit No. 1 (OU-1) addresses the principal MTP groundwater threat
            ..;•••       .••'    '.'''.'•*••'
          posed by TCE concentrations in the shallow aquifer groundwater beneath the central portion
          ".">•      ,  * .       ,".'•.         J
          of Base or  Main Sector of the Base and the contiguous areas to the south and southwest of
          the Base (Figure 1-1). The shallow aquifer in which the plume occurs is also used as a  ''
          drinking/or  irrigation water source for some off-base residents.         •-
               '                           •'"'-,           ' ,-              '   *~\

          The interim remedy addresses the remediation of groundwater contamination by eliminating or

          reducing the risks posed by the site, through treatment and engineering and institutional
          controls. The final remedy will be selected in a subsequent ROD.           •


          The major components of the selected interim remedy are:

              - •  Pumping groundwater from a series of shallow aquifer extraction wells to maintain
                  hydraulic control of the plume  and begin reducing residual TCE concentrations.

               •  Surface treating the extracted  groundwater by air stripping to allow the return of
                  water to beneficial use (resource recovery).          .  .< .'.

               •  Reinjecting the treated groundwater back to the  shallow aquifer to assist in
                  maintaining hydraulic control and to avoid depletion of the aquifer.

               •. Applying natural biological enhancement to accelerate the degradation of hazardous
         -         constituents in the saturated zone.

               •  Abating the air stripper emissions with granular activated  carbon to avoid degrading
                  ambient air quality. The abatement unit would be steam  regenerated on site and
                  the liquid condensate would be disposed off site at an EPA-RCRA approved  ''
                  recycling facility.
      .    ;     .                ..        .          1-2
MA:ENG:9327-1/070191

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I           DECLARATION
,           This interim action is protective of human health and the environment, complies with Federal
i           and State applicable or relevant and appropriate requirements for this limited-scope action and
.           is cost effective.  Although this interim action is not intended to address fully the statutory
i           mandate for permanence and treatment to the maximum extent practicable, this interim action
            does utilize treatment and thus is in furtherance of that statutory mandate. Because this
i           action does not constitute the final remedy for the operable unit the statutory preference for
            remedies that employ treatment that reduces toxidty, mobility, or. volume as a principal
I           element, although partially addressed in this remedy, will be addressed by the final response
            action. Subsequent actions are planned to address fully the threats posed by the conditions
\           at this operable unit. Because this remedy will result in hazardous substances remaining on
           site above health-based levels, a review will be conducted to ensure that the remedy
           continues to provide adequate protection of human  health and the environment within five
           years after commencement of the remedial action.  Because this is  an interim action ROD,
           review of this site and of this remedy will be ongoing as Castle AFB continues to develop final
           remedial alternatives for the Main TCE Plume operable unit and the overall Castle AFB site.
           Colonel Michaeljy Kehoe
           Chairman, Environmental Protection Committee
           Castle Air Force Base
                 W. McGovem
           Regional Administrator
           United States Environmental Protection
           Agency, Region DC
                                      AUG 2 3 1991
                    •^^^^^^^^^^^^^MV^^MV^^^H^^M
           ValSiebal
           Regional Administrator
           California Department of Health Services
           Toxic Substance Control Program, Region I
                                                   1-3
  MA:ENG:9327-1/070191

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                                                         •


                                                                              I            I     «     1
                                               1314 *
                                                 \
                                                                           CAS
                                                                         BLOC.  1335      \ \ \
                                                                               RQNJECT10N
                                                                                           E    \M
                                                                                  STREET           '(
                PROPOSED OU-1  EXTRACTION  WELL

                PROPOSED OU-1  REINJECTION WELL
  BLOC. 1260
BUILDING  WHERE TCE WAS
HISTORICALLY USED
(ENGINEERING  SCIENCE.  1983)

PROPOSED OU-1  PIPELINES (ARROW
INDICATES DIRECTION OF	
    -175-
 —?-
TOPOGRAPHIC  CONTOUR (FT.  MSL)

APPROXIMATE TCE MCL BOUNDARY; TCE
CONCENTRATION WITHIN BOUNDARY IS 25.0  ppb.
(QUESTION MARKS IMPLY  UNCERTAINTY)

HISTORICAL DIRECTION OF CROUNDWATER
MOVEMENT. AUGUST.  1986
DIRECTION OF GROUNDWATER MOVEMENT.
JULY. 1989
SCALE
           1000
                       2000
                                  3000 FEET
  REFERENCE: UCCS TOPOGRAPHIC QUADRANGLES:
  ATWATER. CAUF. DATED: 1960. REVISED 1967
  AND WINTON. CAUF. DATED: 1961. REVISED 1987.
        FIGURE  1-1

     MAIN TCE  PLUME
OPERABLE UNIT  N0.1 (OU-1)
        PREPARED FOR
  CASTLE AIR FORCE BASE
        CALIFORNIA

        INTERNATIONAL
        TECHNOLOGY
        CORPORATION

CA-UTPU2(CAC71

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                     2.0 SITE DESCRIPTION, SITE HISTORY, COMMUNITY RELATIONS

           SITE NAME. LOCATION. AND DESCRIPTION
           Castle AFB is a Strategic Air Command (SAC) Training Base located in Merced County,
           California approximately six miles northwest of the City of Merced in the State of California.
           Neighboring communities within six miles of the Base include Wirrton (Pop. 7,583), Atwater
           (Pop. 22,585), Livingston (Pop. 7,103), and Merced (Pop. 50,000) (Figure 2-1). The Base
           covers an area of 2,777 acres comprising runway and airfield operations, industrial areas,
           housing, recreational facilities, and several noncontiguous parcels.  In addition, two residential
           off-Base housing annexes that total approximately 206 acres are located southwest of the
           Base for housing of military personnel and their families. The site, the Main TCE Plume
           (Operable Unit No.  1), consists of TCE concentrations above 5 ppb in the shallow aquifer
          groundwater located beneath the central portion or main sector of Castle AFB and the
          contiguous areas to the south and southwest of the Base (Figure 1-1).

          The total relief across the  Base is approximately 35 feet, ranging from 200 feet above mean
          sea lev^l (MSL) at the northwestern comer to 165 feet above MSL at the southern boundary
          comer.  Relief within the Base boundaries is essentially flat

          Land use within a two-mile radius of the Base is primarily agricultural.  Crops grown in the
          area consist primarily of almonds, peaches, and grapes. Several small dairies and a large
          chicken farm are located to the east  Open pasture lands are located to the north and east
          Residential areas are located primarily west of the Base and include Base housing, trailer
          parks, recently constructed residential suburban housing and rural farm residences.

          There are no major  surface water bodies (lakes or rivers) within five miles of the Base.
          Domestic and agricultural water are supplied to the region by both groundwater wells and the
          canals of the California Central Valley irrigation projects.  A number of irrigation canals and
          laterals (Black Rascal Creek) are located within one mile of the Base, the largest and most
          significant is Canal Creek, which is controlled by the Merced Irrigation District Canal Creek
          borders the Base  proper on the southwest boundary (Figure 2-2). .In it's upper reaches
          upstream from the Base, Canal Creek's flow is diverted for irrigation use. Downstream from
          the Base, it receives runoff from the Base and irrigated land.
                                       .                                   >
I                                                  2-1
[*w1A:ENG:9327-2/08p291

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         The Merced Irrigation District operates at least 20 agricultural wells within three to four miles
         of the Base. The City of Atwater, a number of private residences, and the Base operate
         domestic water wells within two miles of the Base proper.  A number of these wells were
         abandoned due to TCE contamination. Under county code the residences were supplied with
         bottled water or connected to new wells installed in the deeper confined aquifers. Other
         residences whose wells were contaminated were furnished with granulated activated carbon
         (GAC) filtration systems. The Base currently monitors approximately 18 off-Base private
         residential wells on a regular basis.
                                    *                    •                    '             \

         Wildlife in the area consists almost exclusively of jack rabbits, rodents, and birds (including
         ducks and pheasants).  The Base Is located in the historical range of three endangered
         species.  The Air force will have a biologist determine the presence or absence of these
         species and also have a qualified agency determine the presence or absence of. wetlands.
         Any surface area disturbance associated with the  selected interim remedy is minimal and
         should not have a significant impact  on endangered species' habitats or wetland areas, should
         they exist. There are no geologic faults identified below the Base.  There are no historic
         places located within three miles  of the Base; nor does the Base  lie within a designated
         floodplain area.  The average annual rainfall is approximately six  inches.

         The natural vegetation of the area consists primarily of salt-tolerant plants. Much of the soils
         in the area contain.soluble salts and alkalis. The  principal grass  is salt grass (Distichlis
         spicata).  Trees such as the white oak, Fremont cottonwood. Oregon ash, box elder, and
         willows are found along surface drainage areas.

         The subsurface geology was Interpreted from over 150 monitoring wells and borings installed
         during the remedial investigation and related to existing geologic  literature. The following
         generalizations about the geology beneath the Base were developed by relating cross-
         sectional  information and established stratigraphic units.

         Sediments from about 0 to 95 feet below grade generally consist of complexly interbedded
         sequences of alluvial deposits consisting of silty sand, silts, sands, and gravels.  These
         sediments are identified regionally as older alluvium. The gravels generally occur from about
         70 to 95 feet below grade, and a high percentage of the gravels are concentrated in the Main

                                                  2-2
/A:ENG:9327-2/080291

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           .                                                                   ..
I          Base Sector.. Hardpan, which is a thin layer of cemented soil, exists intermittently at depths
           generally up to 10 feet below grade.
i       '                 .           •','.,        "  '   •  • .          "-.'   ,'''       .    •-
           The older alluvium unconformably overlies a section composed predominantly of clay. This
I          section was identified as the upper Turtock Lake formation.  The contact between the clay
           section and the overlying alluvial deposits appears to be erosional, and the thickest
I          sequences of gravel in the older alluvium have accumulated in trough-like depressions into the
           clay sequence. The clay sequence itself contains lenses of gravels, sands, and clayey sands
{          which are not correctable throughout the Base.
<              .         ^                         i
{          The Turlock Lake formation is divided into an upper and lower unit.  The upper  unit contains
           mostly finer-grained materials as described above; the lower contains sands. The lower
           Turlock Lake,formation is a fairly continuous unit occurring from about 260 to 320 feet below
           grade.  These sands comprise the confined aquifer at the Base.

           A deep regional aquifer occurs at about 650 feet below grade and is an important source of
           water in the Modesto-Merced Area. The deep water-bearing unit is located in the upper part
           of the Mehrten Formation.  In the region of the Base, this formation consists of claystone,
           siltstone, sandstone, and conglomerate.  The vertical extent of the deep aquifer is unknown.
           However, it would not be usable for beneficial purposes below the level where saline water
           occurs, which is at about 1,200  feet below the ground surface.

           SITE HISTORY AND ENFORCEMENT ACTIONS
           Castle AFB was first used as a  military air base in December 1941. The primary mission of
           the  Base through World War II was the training of Army air crews.  The Strategic Air
           Command assumed responsibility of the Base in 1946 and has occupied the Base with the
,  .        93rd Bombardment Wing since  1947.

           The construction of facilities at the Base has paralleled increases in the size of  its mission and
           the  number of organizations in residence. Originally, the major industrial activities related to
           aircraft maintenance centered in two hangers (Buildings 47 and 51} and the machine shop
           (Building 52, later demolished in 1977), located on the southwestern side of Apron  Avenue
           (Figure 1-1).   In 1955, an additional parking apron, hanger (Building 1550), and other

                                                    2-3
  MA:ENG:9327-2/080291

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I
I
 I
         structures were added to support the newly arrived 456th Fighter Interceptor Squadron (Figure
         1-1). Since 1955, Building 1550 has been used extensively for industrial activities.  Buildings
         1253 and 1260 were built in the late 1970s and assumed the majority of the industrial
         activities previously performed in Building 52. These activities included metal plating and
         processing, and jet engine maintenance.

         Fuels (JP-4), solvents (TCE) and chemicals have been handled at the Base since the 1940s.
         Municipal and chemical wastes have also been generated as a result of maintenance
         operations, fuel management, fire training, and other Base activities.  In the 1950s, expanded
         industrial activities related to the SAC mission resulted in increased waste generation rates.

         Prior to the current remedial investigation, several previous studies and investigations have
         been performed to identify the historical use of chemicals, disposal, and/or leakage of these
         chemicals to the soil, and the extent and impact of these chemicals on groundwater resources
         in and around the Base.                                  .

         During  the routine sampling of several Base and private wells in 1980, trace levels of TCE
         were detected in the four Base water production wells. Seven test wells were then installed  in
         the shallow aquifer by the Base as part of the investigation.  The results of this sampling
         program prompted the Base to  construct a new deep aquifer water supply well (PW-10) and
         provided the impetus for the start of the Air Force's Installation Restoration Program (IRP) at
         CastieAFB.

         In 1981, Phase I of the IRP was conducted by Engineering Science.  A total of 35 separate
         sites were identified and organized into 26 sites or groups of sites having the potential for
         environmental contamination.  Recommendations for further investigative work called for 21 of
         the 26 sites to be evaluated. The 21 sites were grouped into 15 investigation  sites located in
         the central part of the Base, the landfills, and the west and north flight line  areas.

         In March 1984, the California Regional Water Quality Control Board • Central Valley Region
         issued Cleanup and Abatement Order Number 84-027. This order required the Base to
         provide users of the Base water supply and impacted off-Base wells with potable water
                                                - 2-4
MA:ENG:9327-2/080291

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I
           supplies. Also, the Base was required to implement remedial measures to correct identified
           and future groundwater degradation from waste discharges.

           In September 1984. the Phase II, Stage  1 field investigation was conducted by the Roy F.
           Weston Company.  This investigation included the installation of 27 monitoring wells and 11
           unsaturated zone lysimeters into the shallow aquifer to sample for groundwater contamination
           and to test for perched water zones.  Two rounds of water quality sampling were conducted.

           The Phase II, Stage 1 investigation determined that the soils and sediments at the Base had
           not been significantly impacted at the majority of the sites investigated, but that the
           groundwater needed further evaluation. This conclusion Is considered preliminary and will be
           verified in the RI/FS for the overall Base. Significant TCE concentrations were detected in the
           central or Main Base Sector. The Weston Phase II, Stage 1  Final Report recommended
           additional investigations of the landfill, fire training areas, fuel spills, and disposal areas, and
           for further evaluation of the TCE plume in the Main Base Sector.

           Results of  the Phase II, Stage 1 investigation and the  Base's groundwater sampling program
           indicated that TCE contamination may be present not only in the Main Base Sector, but also
           in the South  Base Sector and Disposal Areas Nos. 2 and 4.  As a result of these findings,
           Weston conducted a Phase II, Stage 2 investigation which included further evaluations of the
           landfills; fuel  spills and leaks, and selected disposal areas. The field investigation included
           soil organic vapor (SOV) monitoring at 205 points, the drilling of 48 soil borings, the
           installation of 27 monitoring wells and 5 lysimeters or perched wells, and conducting two
           rounds of groundwater sampling. The Phase II, Stage 2 investigation was completed in April
           1987, and the final report was issued in August 1988.

           In 1986, the Air Force contracted Oak Ridge National Laboratory (ORNL), operated by Martin
           Marietta Energy System, Inc., and their subcontractor, IT Corporation  (IT), to support the
           Phase IV-A IRP activities.  These activities included conducting an SOV monitoring survey
           and additional record searches.  Approximately 374 SOV points on a 300-foot spacing were
           sampled in the Main Base Sector to identify  potential volatile organic contaminant source
           areas.
                                                  2-5
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           Castle fell under the provisions of the Comprehensive Environmental Response Compensation
           and Liability Act (CERCLA) when amended in 1986. Castle Air Force Base was then placed
           on the National Priorities List (NPL) in 1987.
           Results of all the above field investigations and data collection activities were used to develop
           the current Remedial Investigation/Feasibility Study (RI/FS) program. The first phase of Rl
           field activities was initiated by IT Corporation in August 1988. These activities included the
           installation  of 63 monitoring wells in the upper and lower zone of the shallow aquifer and 9
           monitoring wells in the confined aquifer. In June 1989, the second phase of the Rl was
           initiated and included conducting two rounds of quarterly groundwater sampling in 160 wells.
           These wells included previously installed Base and Phase II wells, new Rl Base wells, and off-
           Base private wells.  In addition, 77 soil borings were drilled and sampled to assist in the future
           characterization of various investigative sites. Two rounds of groundwater level
           measurements were made, and 15 short-term (4-hour) pump tests were also conducted. The
           second phase of the Rl field activities was completed in February 1990. The results of the
•         above field activities are described in the Preliminary Site Characterization Report, which is
           the basjs for the Interim Operable Unit No. 1 Feasibility Study.

™         The third phase of Rl field activities began in March 1990 and continued through May 1991.
           These activities included quarterly groundwater sampling rounds 3, 4, and 5, two 30-day  .
           aquifer pump tests, a preliminary site assessment of Castle Vista landfills, six water level snap
           shots and development of work plan No. 2. Ongoing and near-term future Rl field activities
           include the installation of approximately 50 VOC probes, continued quarterly groundwater
           samplings,  water level snap shots, and a sewer line TV camera survey.

           In addition to Operable Unit No. 1 (OU-1), Operable Unit No. 2 (OU-2) will address remedial
           actions on groundwater contamination in the Wallace Road and DA-4 areas while Operable
           Unit No. 3 (OU-3) will address any remaining groundwater contamination not addressed by
           OU-1 and OU-2. Operable Unit No. 3 will be implemented following additional Rl activities to
           determine the remaining extent of groundwater contamination. A contaminant source
           assessment task will be performed to identify and to characterize any remaining potential
           waste sites at Castle AFB.  Following  this task, an Rl Work Plan for Existing Sites and

                                                    2-6
   M:ENG:9327-2/080291

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        Contaminant Source Assessment Sites will be prepared and implemented to complete the Rl.
        An installation wide RI/FS report and ROD will conclude the RI/FS process at the Base.

        Estimated dates for the completion of these activities are:
              •  Draft Final ROD for Operable Unit No. 2                   October 1992
                 (See Section 3.0)
              •  Draft Final ROD for Operable Unit No. 3                   February 1994
                 (See Section 3.0)
              •  Work Plan for Existing Sites and Contaminant
                 Source Assessment Sites                                July 1992
              •  Implementation of the Work Plan for Existing
                 Sites and Contaminant Source Assessment Sites           April 1993
              •  Installation-wide Remedial Investigation
                 Report (Rl)                                            January 1994
              •  Installation-wide Feasibility Study (FS)                     June 1994
              •  Installation-wide Record of Decision (ROD)                 April 1995

        HIGHLIGHTS OF COMMUNITY PARTICIPATION
        A Community Relations Plan for the Base was finalized in June 1990.  This Plan lists contacts
        and interested parties throughout the Air Force, government, and local community.  It also
        established communication pathways to ensure timely dissemination of pertinent information
        through mailings, public announcements in the local paper, and local information repositories.
        The Interim Operable Unit No. 1 Feasibility Study was released for public comment in
        December 1990.

        A Proposed Plan announcement for Operable Unit No. 1 (OU-1) was mailed to interested
        parties and an announcement of the OU-1  public comment period and community meeting
        was placed in local papers.  The public comment period began on December 20,1990 and a
        community meeting was held on January 8.1991 in the City of Atwater, to discuss the
        proposed TCE greundwater clean up alternatives.  The public comment period was then
        extended to February 21,1991, following a written  request by a concerned member of the
        community. AH comments were received during the public comment period and a
        Responsiveness Summary was prepared by the Air Force addressing these comments
        (Section 10).
                                               2-7
,IA—v  9327-2/080291

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j
                              3.0 SCOPE AND ROLE OF THE OPERABLE UNIT

           Currently three operable units have been identified at the Base.  They include: the Main TCE
           Plume (Operable Unit No. 1), the Wallace Road/DA-4 TCE plumes (Operable Unit No. 2) and
           the remaining groundwater cleanup on/and off-Base (Operable Unit No. 3).  Current
           investigations suggest that the groundwater contamination in the Wallace Road/DA-4 TCE
           plumes stem from sources other than the Main TCE Plume.  Operable Unit No. 3 will address
           groundwater remediation for the remaining portions of groundwater contamination on and off-
           Base not previously covered by Operable Units No. 1 and 2. Operable Unit No. 3 will proceed
           following the completion of site characterization activities and will complete the defintion of
           groundwater contamination at Castle AFB.  the remaining contamination on Base will be
           addressed in the overall RI/FS and ROD for the entire Base.

           The principal risk to public health posed by Operable Unit No. 1  is the TCE plume to the south
           and southwest of the Base which has the potential to impact off-Base residential water wells.
           Delays in remediating the Main  TCE Plume (MTP) could potentially affect additional wells and
           a greater area, making remediation more difficult and costly.

           The lateral area delineated by the MTP, defined as TCE at or above the drinking water MCL
           of 5 parts per billion (ppb), exceeds 212 acres (Figure 1-1).  The full extent of the plume
           delineated at less than 5 ppb in all directions is not completely known at this time. Additional
           off site investigations are planned.  The two other operable units will address the remaining
           problems of  groundwater contamination both  on and off the  Base.

           Since data has shown that Applicable or Relevant and Appropriate Requirements (ARARs)
           have been exceeded in the groundwater under Castle AFB, this  interim operable unit is
           designed to  initiate early action  to mitigate potential threats to public health and  the
           environment Subsequent operable units and the overall Base ROD will define further actions
           to mitigate potential threats. The selected interim remedy in this action is expected to be
           consistent with subsequent remedies and planned future actions at the Base. Pursuant to
           regulatory guidance for Interim remedial actions, the Interim Operable Unit No. 1 Feasibility
           Study does not contain a baseline risk assessment.  Risks to public health and the
           environment will be assessed in a subsequent ROD.

                                                    3-1
  MA:ENG:9327-3/070191

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                              4.0 SUMMARY OF SITE CHARACTERISTICS

          In addition to the original investigative sites identified at the Base, the state has identified
          further areas of potential contamination.  Investigation of these sites is under way.  The sites
          include areas where disposal of wastes or known leaks or spills of significant amounts of fuels
          or chemicals have occurred on the Base.  During the remedial investigations, soil sampling (of
          borings) and groundwater sampling were performed in order to characterize each site. Other
          geophysical and investigative techniques were also used to identify potential buried drums,
          unusual objects, levels of radioactivity, or high levels of significant volatile soil organic vapor.
                                                                                       !
          The site investigation identified three groundwater plumes containing various chemicals but
          primarily TCE (Figure 1-1). The largest plume, the Main TCE Plume (MTP) (Operable Unit
          No. 1), consisted of a number of smaller plumes from different source areas which have
          merged to form one large plume beneath the central portion of the Base. The MTP occurs in
          the shallow aquifer which is used as a drinking/irrigation water source for some off-Base
          residents.  The soils, investigated thus far, were found to contain trace levels of volatile
          organics (Rgure 4-2). A number of sites were found to contain potentially significant levels of
          petroleum-type hydrocarbons as a result of former fuel leaks and spills. Remediation of soils
          will be determined in a later ROD.

          A number of chemicals have been identified in the groundwater within the MTP (Tables 4-1, 4-
         2 and 4-3). Some of the chemicals have established Maximum Contaminant Levels (MCLs)
         under the Federal and State Safe Drinking Water Act (Tables 4-2, 4-3). The remedial action
         MTP chemicals of potential concern which exceed MCL's include:
                  Trichtoroethylene (TCE)                         :
                  Benzene            ~
                  Tetrachtoroethytene (PCE)
                  ds-1,2-Dtehloroethylene (1,2-DCE).
                  Chloroform
                  1,2-Dichtoroethane (1,2-DCA)
                  1,1-Dichtoroethytene
                  Carbon Tetrachtoride
                  Chloromethane
                  1,1-Dichloroethane
                                                 4-1
MA:ENG:9327-4/070191

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         Elevated levels of JP-4 (jet fuel) were also detected, but there are no regulatory cleanup
         standards set for JP-4 since it consists of a diverse mixture of petroleum hydrocarbons.
         However, there are MCLs established for individual components of JP-4 such as benzene,
         toluene, xylene, ethy(benzene, etc., which may pose a health risk (Tables 4*2 and 4-3). Only
         benzene has been detected above MCLs.

         Rgure 1-1 shows the delineation of the TCE plume at the 5 parts per billion (ppb) boundary.
         This level is the drinking water standard for TCE promulgated by the U.S. EPA under National
         Primary Drinking Water Standards. The plume also delineates the extent of contamination of
         the other constituents of concern described above.  The selected interim remedy will remove
         and treat the constituents listed in Tables 4-2 and 4-3 within the delineated area.  Potential
         groundwater users are the Air Force, nearby residents! and farmers.

       '  The highest level of TCE detected during the four rounds of quarterly Rl groundwater
         sampling within the MTP was 1,200 ppb (Table 4-1). A number of TCE hot spots were also
         identified which exceeded 100 ppb.  The vast majority of groundwater within the MTP contains
        TCE at levels less than 50 ppb. Benzene was detected at a maximum concentration of 660
        ppb in a monitoring well located in the immediate vicinity of the petroleum, oils and lubricants
        (POL) storage area (Table 4-2). The POL storage, area is the primary area of the Base where
        fuels (which contain benzene) are handled.             •

        The Main TCE  Plume is in a relatively porous and transmissive formation. It is influenced by
        off-Base pumping of irrigation and municipal wells indicating these wells may be screened
        higher than well log reports indicate.  It is expanding at a rate that is potentially significant to
        water sources.                      .
                                                4-2
,A:ENG:9327-4/070191

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                                     TABLE 4-1

                     SUMMARY OF TCE DETECTED IN GROUNDWATER
                              FOR THE MAIN TCE PLUME
                                       (PPb)
WELL NO/
MW-115
MW-120
MW-125
MW-210
MW-220
MW-245
MW-290
MW-300
MW-310
MW-509
MW-510
MW-511
MW-512
MW-513
MW-514
MW-515
MW-516
MW-517
MW-518
MW-519
MW-520
MW-521
MW-522 — --
MW-523
MW-524
MW-525
MW-527
MW-528
MW-529
MW-530
MW-531
MW-532
MW-534
ROUND 1
20
(Free
product)
0.8
35
16
0.6
ND
8.7
150
0.9
25
2.6
16
ND
3.1
2.3
49
23
4.9
. 530
2.6
240
55
7.3
38
0.5
7.1
24
1,000
1.3
18
0.4
ND
ROUND 2
22
(Free
product)
0.8
39
25
ND
ND
6.4
94
0.8
39
ND
25
0.8
3.0
4.8
76.0
1.8
ND
730
1.3
390
310
14
45
120
8.4
26
1,144
ND
26
0.4
0.4
. ROUND 3
46
Dry
1.4
38
25
ND
ND
6.2
120
22
40
3
32
0.8
3.5
0.7
71
3.4
11
920
1.9
340
160
9.3.
70
140
12
23
1,200
2.1
120
ND
0.3
ROUND 4
Dry
Dry
1.2
43
49
Dry
0.9
0.8
83
2.2
61
5.9
35
0.3
3.5
ND
59
0.7
7.8
1000
1.4
610
330
15
48
170
10
9.5
1.100
1.4
63
0.4
1
MA:ENG:9327T4-1 .BM/061991
4-3

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                                        TABLE 4-1

                       SUMMARY OF TCE DETECTED IN GROUND WATER
                                 FOR THE MAIN TCE PLUME
                                          (ppb)
MW-536
MW-543 ;
MW-544
MW-551
MW-552
MW-554
MW-556
MW-557
MW-602
MW-603
MW-606
MW-608
MW-711
MW-712
MW-752
MW-TW-13
MW-TW-14>
MW-TW-15 ,
MW-TW-16
MW-TW-17
MW-TW^18 ,
MW-PW-2
MW-PW-3 ..
MW-PW-4 ••••—-
MW-PW-9
MW-PW-10
MW-BOYLE2 -
MW-BOYLE4
MW-MI0228
MW-4781
MW-2679
0.3 "
46
23
16
0.4
29
30
9.9
ND
NO
ND
ND
ND
0.3
1.3
2.3
58
4.7
470
7.3
(Not
. functioning)
2.6
2.9
3.1
0.3
0.5
ND
ND
12
1-3
ND
0.3 ....
73
24
31
ND
47
36
6.6
12
ND
10
0.8
0.3
1.6
1.8
2.1
, 69
5.5
350
7.4
20
2.3
2.3
— ..
0.3
ND
ND
0.7
, 13
0.9
0.3
" ...ND
. 130
22
13
ND
61
150
16
ND :
30
15
0.5
ND
4.8
2.4
3.3
120
5.5
480
10
34
—
—
'. ~
~
"~-
0.3
^2
— .:
~.
•. —
0.8
130
45
- 46
ND
.66
100
9.6
ND
51
5.6
ND
ND
2
•3-' "...
1.1
~
6.1
— • •
—
.34
• '„ —
— .
_-
— 	
—
ND
1.5
—
•' ':.'--
	
        * Well locations are shown on Figure 1-4 in the Interim Operable Unit No. 1
          Feasibility Study for Castle AFB, December 1990
        ND = None detected                                .   -
MA:ENG:9327T4-1 .BM/061991
4-4

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                                     TABLE 4-2
                  ORGANIC COMPOUNDS DETECTED IN MTP GROUNDWATER
                            SAMPLING ROUNDS 1, 2, 3, AND 4
f *•
COMPOUND ,
Trichloroethylene*
Benzene*
fetrachloroethylene*
Cis-1 ,2-Dichloroethylene*
Methylene Chloride
Xylenes
Ethyjbenzene
Acetone
Toluene
1,1-Dichloroethylene*
1 ,2-Dichloroethane*
Carbon tetrachloride*
Chloroform*'
Dichlorbdifluoromethane
JP4
1,1-Dichloroethane*
Chloromethane*
Trichlorofluoromethane
Trans-1 ,2-Dichloroethylene
1,2-Dichloropropane
Chloroethane
Chlorobenzene
1 ,2-Dichlorobenzene
Bromoform
.HIGHEST
CONCENTRATION
DETECTED WITHIN
MAIN TCE PLUME
(Ppb)
1,200
660
180
140
44
43
38
26
17
17
16
15
12
7.5
7.4
5.5
5.0
2.3
2
1.2
1.1
0.4
0.4
0.4
MCL
(Ppb)
5
1
5
6
•—
1750
680
~
•
6
0.5
0.5^
100
~
— •
5
~
150
1°
5
—
30
~
.
SAMPLE LOCATION
MW-529
MW-531
MW-521
MW-531
MW-519
MW-531 - ' • '.
MW-531
MW-608
MW-531
MW-529
MW-531
MW-525
MW-523
MW-Boyle-2
MW-609
MW-533
MW-521
MW-352
MW-522 .
MW-609
MW-709
MW-531/523/524/607
MW-608
MW-Boyle-4
     * Contaminants of Concern
MA:ENG:9327T4^2.BM/061291
                                    4-5

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                                    TABLE 4-3
                   METALS AND IONS DETECTED IN MTP GROUNDWATER
                           SAMPLING ROUNDS 1, 2, 3 AND 4
•• ' •'-
Arsenic
Barium
Bromide
Cadmium
Calcium
Chloride
Chromium
Copper
Cyanide
Fluoride
Hardness
Iron
Lead
Magnesium
Manganese
Nitrate
Phosphate
Potassium
Selenium
Silver
Sodium
Specific Conductance
Sodium Sutfate •
Total Dissolved Solids
Zinc
pH (low)
pH (high)
HIGHEST
CONCENTRATION
DETECTED WITHIN
MAIN TCE PLUME
(ppm)
ND
0.32
1
0.005
71
59
0.01
0.025
0.02
0.4
280
0.9
0.005
29
2.4
14
2.2
50
0.005
0.01
.68
790 umhos/cm
69
500
0.06
6.3 std units
9.7 std units
MCL
(ppm)
0.05
1
—
0.01
~
- '•• i.
0.05
' -
•-
~
-
•—
0.05
—
. —
45
-
— . .
0.01
0.05
- .
-
-
—
— '
, • -
—
SAMPLE LOCATION
~ . , - •
MW-536/TW-17
MW-525
MW-533/557
MW-TW-13
MW-559
MW-557
MW-557
MW-557
MW-608
MW-531/532
MW-115
MW-125
MW-115
MW-533
MW-TW-15
MW-513
MW-605
MW-557
MW-557
. MW-559
MW-115
MW-245
MW-536
MW-525
MW-Boyte-3
MW^05/607/TW-16
MA:ENG:9327T4-3.BM
                                          4-6

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                                      5.0  SUMMARY OF SITE RISKS

          Site risks have not been fully characterized, however, ft is clear that MCLs have been
          exceeded for several contaminants as discussed in Section 4 (Tables 4-2 and 4-3).
          Therefore, ft is appropriate to initiate early cleanup action via an interim remedy. Ten organic
          chemicals of potential concern were previously identified for the MTP area. The general goals
          of this interim action are to prevent the further spread of contamination and initiate mass
          removal of contamination from the aquifer. This action is designed to stabilize the spread of
          contamination, prevent further degradation, and to achieve risk reduction quickly.  Risks are
          partially addressed by this interim remedy in that treatment actions will be expedited. More
          specific findings on risk and ultimate target cleanup levels for the groundwater will be
          established in a  subsequent final action ROD.      •:
                                                -  5-1
MA:ENG:9327-5/070191

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                                 6.0 DESCRIPTION OF ALTERNATIVES

         As discussed in Section 5.0, the goals of this interim action are to prevent the spread of
         further contamination and to initiate removal of contamination from the aquifer. The cleanup
         target for the aquifer will be established in a subsequent ROD. Any residual contaminants
         resulting from the cleanup alternatives will be treated or disposed of in accordance with the
         Resource Conservation and Recovery Act (RCRA).  A description of the nine alternatives
         developed and screened is provided below. For purposes of comparing the net present worth
         of each alternative, a discount rate of seven percent and an annual inflation rate of six percent
         were, assumed (Table 7-1). These rates were considered to be representative of the
         economic conditions at the time the Operable Unit No. 1 Feasibility Study was prepared.
         Alternatives 6 through I are based on pumping groundwater through extraction wells located in
         the Main  Base Sector. The pumping rate and optimum configuration of the wells will be
         determined during the remedial design phase. Based on conceptual modeling, a total
         pumping rate of 1250 gallons per  minute from five extraction wells was used for the
         preliminary design basis.

         The air stripping towers, identified in Alternatives B, C, D, and I, were conceptually sized for
         estimating purposes at 84 inches  diameter, 25 foot packing depth, and a required air flow rate
         of 3345 SCFM. The preliminary tower sizing is based on (worst case) high levels of detected
         organic compounds in the Base groundwater sampling data from rounds one, two, three, and
         found, and on achieving a removal concentration level to meet established MCLs for the
       .  chemicals of concern.

         As noted  in Section 5.0, this action does not set specific cleanup levels.  All pump and treat
         Alternatives (B through I) would initiate the remediation of groundwater to meet the objectives
         of this action. As a part of this action, cleanup levels will be established for the treated
         effluent and any possible air emissions from the air stripper.  The treated groundwater will be
         cleaned to the MCLs and/or ARAR listed on Tables 4-2 and 4-3.

         ALTERNATIVE A                   .
         Alternative A is the no-action alternative. This alternative was evaluated for baseline
         comparison purposes. The alternative considers taking no active remedial measures such as

                                                  6-1
MA:ENG:9327-6/070191

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         groundwater pumping or removal of contamination. There is no reduction of toxicity, mobility,
         and volume through treatment. A site monitoring period of 30 years is used as the basis for
         estimating a reasonable cost and present worth.  A net present worth of $9,368,000 is
         estimated for this alternative resulting from an estimated annual operating cost of $360,000
         over a 30-year period.

         ALTERNATIVE B              .
         Alternative  B considers groundwater removal by pumping and surface treatment of the
        " groundwater using air stripping.  The emissions from the air stripper would be abated using a
         gas fired thermal combustor. Burning the emissions would destroy contaminants and
         eliminate the  need to dispose of waste off-site. Treated groundwater would be reinjected into
         the same aquifer, increasing the flushing rate of contaminants and avoiding aquifer depletion
         caused by groundwater pumping.

         This alternative is estimated to have  a net present worth of $34,020,000, an initial capital cost
         of $2,277,000, and an annual operational cost of $1,438,000. A remedial duration of 25 years
         is estimated for this alternative.

         ALTERNATIVE C
         Alternative C  considers groundwater removal by pumping and the same treatment and control
         measures as  Alternative B.  In addition, in situ biological enhancement is included which
         stimulates naturally occurring soil bacteria to accelerate the degradation of contaminants in
         the groundwater and those adsorbed onto soil particles. Upon completion of the remediation,
         the bacteria die off leaving no residuals. Treated groundwater would be reinjected, preventing
         regional aquifer depletion.  In some applications, the process reduces the clean  up time by as
         much as 90 percent         .                            ......

         This alternative  is estimated to have  a net present worth of $26,308,000, an initial capital cost
         of $2,437,000, and annual operational costs of $2,530,000.  A remedial duration of 10 years is
         estimated .for this alternative.                                                     .
                                                  6-2
MA:ENG:9327-6/070191

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         ALTERNATIVE D                                        :                   .
         Alternative D evaluates groundwater pumping and surface treatment using the same
         equipment configuration and emission controls as Alternative B. Treated groundwater is
         disposed through a surface outfall into an irrigation or drainage canal instead of reinjection
         back into the aquifer.  In situ biological enhancement is not considered as part of this
         alternative. This alternative wouTd be expected to deplete the aquifer at a rate of up to  10 feet
         per year if implemented.    •    ....           ,

         This alternative is estimated to have a net present worth of $39,302.000, an initial capital cost
         of $2,027,000, and annual operational costs of $1,438,000.  A remedial duration of 30 years is
         estimated for this alternative.
          •                         •                           '          '                '

  ;       ALTERNATIVE E
         •••^^^•••^^^•••^^^•MHM^V^B •       .                 -V               •
         Alternative E evaluates groundwater pumping and reinjection of treated groundwater. The
         surface treatment technology for the pumped groundwater is liquid phase granular activated
         carbon adsorption. The carbon would be regenerated on-site using medium pressure steam.
         The regeneration process generates a condensate  from the units which contains contaminants
         removed from th'e groundwater. Regenerant condensate  containing recovered contaminants
         would be collected and taken off-site to an approved recycling facility.  Treated groundwater
         will  be reinjected into the same aquifer.  In situ biological  enhancement is not considered as
         part of this alternative.                                               , •       "        -

         This alternative is estimated to have a net present worth of $39,330,000, an initial capital cost
         of $3,484,000, and annual operational costs of $1,623,000.  A remedial duration of 25 years is
      __ estimated for this alternative.    ._                     V  ,            —-:-	

         ALTERNATIVE F                  .                    .,     .
         Alternative F considers the same removal, .surface treatment, and groundwater disposal
         (reinjection) technologies as Alternative E. Similar to Alternative C, in situ biological
         enhancement is also included. The alternative is unique in that on-site treatment of the
         condensate generated from the granular  activated carbon regeneration process  is included.
         The technology evaluated for on-site treatment of the regenerant is ultra-violet (UV) photolysis
         which is considered an innovative technology.                           .

                                                  6-3
MA:ENG:9327-6/070191                          '

-------
1
1                            '    •                               '••'"'
J                              .
*           This alternative is estimated to have a net .present worth of $26,752,000, an Initial capital cost
            of $4,010,000, and annual operational costs of $2,411,000. A remedial duration of 10 years is
I           estimated for this alternative.                ,

I           ALTERNATIVE G
.           Alternative Q evaluates the potential advantages of smaller decentralized treatment units.
i           This alternative considers the advantages of using individual granular activated carbon
            treatment units at each groundwater extraction well location. After treatment, groundwater
|            would be reinjected. The carbon units would be regenerated using a mobile skid mounted
            boiler system.  Regenerant condensate containing recovered contaminants would be collected
            and taken off-site to an approved recycling facility.  The primary disadvantage of decentralized
            operation is the cost of system maintenance and monitoring.
                                                                                  '\  -      .   '

            This alternative is estimated to have a net present worth of $65,240,000, an initial capital cost
            of $4,333,000, and annual operational costs of $2,753,000. A remedial duration of 25 years is
            estimated for this alternative.

            ALTERNATIVE H'       '
            Alternative H evaluates'utilizing UV photolysis treatment for treating the entire groundwater
            volume.  Groundwater  would be pumped to the surface and the contaminants broken down by
            passing the groundwater past strong ultra-violet lights.  In addition, hydrogen peroxide would
            be added to accelerate decomposition.  The technology is innovative and avoids some of the
            problems associated with other alternatives such as waste generation and disposal.  Following
            treatment, the groundwater would be reinjected,  minimizing aquifer depletion.  In situ biological
            enhancement is also included as a technology option with this alternative.

            This alternative is estimated to have a net present worth of $44,013,000, an Initial capital cost
            of $7,735,000. and annual operational costs, of $3,836,000. A remedial duration of 10 years is
            estimated for this alternative.
                                           ..-  -   .              "                             *>

            ALTERNATIVE I                                       '
            Alternative I is identical to Alternative C except that the thermal combustor used for air
            emission abatement under Alternative C is replaced with a vapor phase granular activated

                          "•,  '.       ,               6-4'          .    '            '   .
  MA:ENG:9327-6/070191                ,          •    . , •

-------
         carbon (GAC) abatement unit  Groundwater extraction, centralized air stripping treatment,
         treated groundwater reinjection and in situ biological enhancement are technology options
         included as part of Alternative I. The carbon would be regenerated on-site using medium
         pressure steam. The regeneration process generates a condensate from the units which
         contain contaminants removed from the groundwater. This condensate would be collected
         and taken off-site to an EPA-RCRA approved recycling facility.

         This alternative is estimated to have a net present worth of $28,445,000, an initial capital cost
         of $2,541,000, and annual operational costs of $2,744,000.  A remedial duration of 10 years is
         estimated for this alternative.
                                                   6-5
MA:ENG:9327-6/070191

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                          7.0 COMPARATIVE ANALYSIS OF ALTERNATIVES

         The nine alternatives were evaluated according to the nine National Contingency Plan (NCP)
         evaluation criteria to determine the most appropriate or preferred alternative.

         NCP EVALUATION CRITERIA                                   .
         The nine-point evaluation criteria includes the following:
                •   Overall Protection of Human Health and the Environment
                •   Compliance with ARARs
                •   Long-Term Effectiveness and Permanence
                •   Reduction of Toxicity, Mobility, or Volume
                •   Short-Term Effectiveness
                •   Implementability
                •   Cost
                    State and/or Support Agency Acceptance
                •   Community Acceptance.

         EPA policy states that in the case of interim remedial actions, ARARs for aquifer restoration
         do not apply. It is understood that the interim remedy will be followed up by a final remedy
         which will establish cleanup levels  based  on ARARs and a risk assessment.

         A summary comparison of cleanup Alternatives A through I is shown on Table 7-1. A
         discussion of each of the evaluation criteria follows.

         OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
         Alternative A is least protective of human  health and the  environment due to the long
         anticipated duration to achieve protective  levels in the groundwater and the likelihood that
         more wells would become contaminated.  Under Alternatives B, C, D, F, and H destruction will
         ideally reduce contaminants to simpler less toxic compounds. However, an assessment of
         thermal abatement equipment for Alternatives B, C, and D will be performed to insure

                                                7-1
MA:ENG:9327-7/070191

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4           incomplete combustion by-products are not formed. Risk due to media transfer of chemicals
            to the air must be managed to insignificant levels under air stripper Alternatives B, C, D, and I.
i           Monitoring of air emissions will be performed upon implementation of these alternatives in
•           order to assure adequate human health protection is being achieved. Waste transferred off
I           site to a state approved recycling facility under Alternatives E, Q, and I (and to a lesser extent
T           B, C, D, and F) have a residual risk associated with the proper control of the off site facility.
1           In-situ biological enhanced recovery under Alternatives C.  F, H, and I is expected to achieve
            better risk reduction and protection of human health and the  environment than the remaining
•           treatment alternatives since it is expected to result in earlier cleanup. Alternative G is the
            most responsive alternative for addressing hew areas of contamination in a short period of
\     .      time, simply by installing additional units to add treatment capacity. .Under Alternative D,
            discharging to surface  water contributes to aquifer depletion. Alternatives C, F, H, and  I are
            the  most effective alternatives in terms of overall protection of human health and the
            environment, with Alternative H being the most protective.

            COMPLIANCE WITH ARARs/TO BE  CONSIDERED (TBCS1 MATERIALS
            The Superfund Amendments and Reauthorization Act (SARA) requires that remedial actions
            meet legally applicable or relevant and appropriate requirements (ARARs) of other
            environmental laws. These laws may include:  the Toxic Substances Control Act, the Safe
            Drinking Water Act, the Clean Air Act, the Clean Water Act the Resource Conservation and
            Recovery Act, and any state law which has stricter requirements than the corresponding
            federal law. A list of potential Federal and State ARARs for the MTP are shown on Tables 7-
          .  3 and 7-4, respectively.

            A legally applicable" requirement is one which would legally apply to the response action if
            that action were not taken pursuant to Sections 104,106 or 122 or CERCLA.  A 'relevant and
            appropriate* requirement is one that,  while not "applicable" is designed to apply to problems
            sufficiently similar that  their application is appropriate.

            Since this is an interim remedial action, it is not necessary to establish cleanup levels for the
            groundwater.  MCLs are  therefore not ARARs for the groundwater.  Grpundwater cleanup
            levels based on MCLs  and risks will .be established in a subsequent ROD.  ARARs do apply
            for treated water prior to  disposal or reinjection.  All alternatives, with the exception of  -.

                                                     7-2
   MA:ENG:9327-7/070191

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4
I
•           Alternative A, will comply with ARARs specific to this action to cleanup the treated water to
            appropriate levels (as defined by discharge permit requirements) prior to reinjection and to
g                                             i                    •
i           properly address air emissions (as defined with emission permit requirements).
\                                                                  -•'•••;•
I           Air emission limitations (ARARs) will be established by the more stringent of either (1) the
            Merced County Air Pollution Control District permit to operate requirements (Rules 210.1
\           and/or 210.2) or (2) EPA's OSWER Directive 9355.O28 (Guidance to Control Air Emissions
            From Air Strippers at Superfund Sites).  Discharge/re-injection limitations (ARARs) will be
I           established by the more stringent of either (1) the State's Porter-Cologne Water Quality Act
            (Water Code, Division 7, Section 13000 et seq., CCR Title 23) or (2) the State's RWQCB
•            permit requirements. Additional ARARs may apply pending review of permit requirements,
            remedial design documents and the  outcome of the wetlands and endangered species
            assessments.

            Long-Term Effectiveness and Permanence
            Alternative A, the no action alternative, has a high residual risk and poor control due to the
            fact that residuals are left in place and natural attenuation may not occur for a significant
            period of time. During this time the plume would be expected to continue expanding into
            unaffected areas.  This alternative is not considered to be long-term effective and permanent.
            Alternatives C, F, H, arid I are expected to have the least residual risk due to the flushing
            effect, of reinjection combined with the enhanced desorption of chemicals from the vadose
            zone soils as a result of in-sltu biological enhancements.  Carbon adsorption Alternatives E, F,
          •  G, and I retain some risk due to possible mismanagement at an off-site location.

            Alternatives C and H provide the most long-term effective and permanent solution due to the
            utilization of on site destruction of chemical contaminants removed from the aquifer.
            Alternatives with thermal abatement will destroy the contaminants on site, however extensive
            testing would be required to ensure that incomplete combustion is not creating more
            hazardous substances.

            Reduction of Tbxicitv. Mobility and Volume bv Treatment
            Under the Alternative A (no action), mobility and expansion of the plume would occur resulting
            in an increase in the volume of affected groundwater.  Under the active treatment Alternatives

                                                     7-3
  MA:ENG:9327-7/070191                         -

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i               '         •                                     •
*           B through G, treatment reduces the toxicity, mobility, and volume of chemicals in affected
            groundwater. Under Alternatives B, C, D, and H (and to a lesser extent F), the chemicals of
•           concern are destroyed through thermal treatment, while Alternatives E, G, and I result in
(           moving chemicals to an approved off site or recycling facility.  Alternatives F and H destroy
•           contaminants on site through photolytic oxidation. Table 7-2 lists quantities of hazardous
j           wastes and emissions that would be generated by Alternatives A through I and assumes no
'           products of incomplete combustion will occur. Toxicity and exposure will be managed through
            abatement and compliance with risk assessment-derived health protective limits on air
.           emissions set by permit requirements.

            Short-Term Effectiveness
            Alternatives C, F, H, and I using  in situ biological enhancement are expected to achieve
            protection in the shortest time period.  Under Alternative G, the ability to move and deploy
            additional treatment systems rapidly upon discovering a new hot spot will be a short term
            advantage over other treatment alternatives. Alternative D is expected to take the longest
            period of time of all the active alternatives to achieve protection. Alternative A will not meet
            NCP criteria for short-term effectiveness. Alternative B which utilizes incineration, has the
                                                                   .            '      '  •  i  "-
            potential for Incomplete combustion which may result in the production of highly toxic
            compounds which  could pose a threat to public health and the  environment.

            Wells known to be contaminated were either previously removed from service or had filtration
            units placed on them to protect the community during remedial actions.  Should additional
            wells become contaminated, the Base will take prompt action to properly remove these wells
            from service or install filtration units to provide a safe water supply. Any well taken out of
            service will be abandoned through proper procedures or converted to a monitoring well in
            order to monitor contamination levels.

            Air exposure pathways generated from media transfer operations and a small level of
            incomplete abatement will occur under the air stripper Alternatives B, C, D, and I.  Alternatives
            which use thermal  abatement will take longer to implement due to the need to conduct
            extensive testing to assure there  are no highly toxic substances being produced via
            incomplete combustion.
                                                  .  7-4
   M:ENG:9327-7/080291

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*           Compliance with standard operating procedures, the Occupational Safety and Health
 :           Administration (OSHA) requirements, and health and safety plans, if required, are expected to
»                                                         ...
i           protect workers during remedial activities.           ,

»                                     • .          .
i           Under Alternative A, relying on natural attenuation/dilution could environmentally impact the
                                  :       ^'
            deeper aquifers and contaminate larger volumes of water.  Under Alternative D, the discharge
j           of treated groundwater to surface waters will result in groundwater depletion, possible
            subsidence, wells drying out, and disturbance of an existing surface water regime could occur.
            Implementabilitv
            All alternatives are constructable and implementable. The use of ultraviolet (UV) photolytic
            treatment under Alternatives F and H are innovative, however difficulties with technical
            implementation  are not expected. Reliance on material attenuation only renders Alternative A
            technically ineffective. The decentralized GAC Alternative G Is the most flexible alternative in
            terms of remediating new areas, but would also require the largest number of effluent
            discharge monitoring stations. As a  result, labor and maintenance costs would be higher.  Air
            emission monitoring will be required  under Alternatives B, C, D, and 1.  Test bum and air
            dispersion modeling will be required  for all alternatives that require thermal abatement. A
            contract with an off site facility and/or disposal facility will be  required for alternatives utilizing
            GAC.                                                                         .
            Under Alternatives B, C, D, and I the substantive requirements of any necessary air permits
            and air monitoring would have to  be met by the Air Force upon implementation.  Manifesting
            of off site waste shipments is required under Alternatives B, C, D, E, F, G, and I.  The
            substantive requirements of the National Pollutant Discharge Elimination System (NPDES)
            permitting and monitoring will have to be met for treated groundwater for Alternative D.
           On a net present worth basis, Alternative A was the most economical alternative while
           Alternative G costs the most A comparison of present worth cost for all nine alternatives is
           shown on Table 7-1.
                                                     7-5
  MA:ENG:9327-7/070191

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           .                                   ..
            STATE AND COMMUNITY ACCEPTANCE
 i           U.S. Environmental Protection Agency (EPA) Region IX and the California Department of
 I           Health Services (DHS) and Regional Water Quality Control Board (RWQCB) have been
•            involved in the technical review of the Interim Operable Unit No. 1 Feasibility Study (OUFS)
 t .          and the development of the Proposed Plan and Record of Decision (ROD). The EPA and the
            State agree with the preferred alternative as presented in this Record of Decision.
 i
 i                                -                                 • *            .
            Community acceptance of the interim remedial action has been positive.  During the public
 •    ,       comment period, only three written comments were received. The comments, along with
            questions  raised during the public meeting, were intelligent and pertinent.  The community
 '           seemed most concerned about; the depletion in the groundwater supply caused by
            remediation, the length of clean-up actions, and the possible production of additional
            hazardous wastes during the clean-up.  The Responsiveness Summary (Section 10.0)
            provides a thorough review of the public comments received on the OUFS and Proposed
            Plan, and  the Air Force's responses to the comments received.
                                                   7-6
   MA:ENG:9327-7/070191

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                                                                                        POOR QUALITY
                                                                                           ORIGINAL
                                                  TABLE 7-1
                                        COMPARISON OF CLEANUP ALTERNATIVES

A
B
C
0
E
r
0
H
1
MM****
Mo Action
Contrasted thermally
abated air flrifpor.
CW rminjoclion
Controlled thermally
obotod air stripper. .
CW reinjection with «l-
situ biotreatment
Centrolnod thermally
abated air stirpper
surface water discharge
Centralized 6AC.
adsorption, steam
regeneration, OH
romjoction
Centralized GAC
adsorption, steam
rooenot udon. condonooto
photolysis and recycle.
CW reinfection with in-
situ biotreatment
Oecentrafied CDC
adsorption, steam
regeneration. CW
rejection
Centralized W
photolysis treatment.
CW nm/*caca mill in
situ biotreatment
Cfntrafiod air
ttrtppar with (MC
ODatomont, CW
nmjfCllon mttt in trtu
blotrtttmmt
OMDMU.
monn»M
Nat Protfctnm .
' (.«* protoctiv*
duo to lonoor
duration
Hail pral«cM«
Un pratoeUM
out to longor
duration
Lot* protoctiro
duo to .longar
auntlon
Uott prottctk*
Lon prottctiv*
duo to tonoor
duration
MM! fWQtfCtlM
Mod pntKUro
COMPLMMCC
Mm100 years
Potential air exposure
poth*ay Remedial
duration: 25 years
Potential air exposure
pothfoy Remedial
duration: 10 yoorm
Potential air exposure
pathway Remedial
duration: JO years
Limited interim
exposure Remedial
duration: 2S years
Very limited interim
exposure Remedial
duration: 10 yean
Limited interim
exposure Remedial
duration: 25 rears
Very limited interim
exposure Remedial
duration: 10 years
Potential air exposure
pathway Remedial
duration: 10 years
MUMCMMUnr
Eoiieit
to implement
knptemmlaM*
bnplomentablo
Impletnentable
tmplemontoHo
rniJamentoblo

Implementatle
Implomontoblo
rnphmentablo
*eosr
(pnoo* ***)
$ ».3t».000
$ J4.020.000
- $ 25.JO&000
1 M.XIOOO
$ J9.JJO.OOO
$ 2S.7i2.000
t 6S.240.000
$ 44.0IJ.OOO
1 28.445.000
svnt
.: ACctrtAMce
Not expected
to approve
May have
concern over
thermal abatement
Hay have
concern over
thermal abatement
Hoy hove concern
over aquifer depletion
and thermal abatement
fxpected to
approve
expected to
approve
expected to
approve
Hay have a
concern over
unwanted by-products
expected to
approve
COHUUHTT
Mxtrwete
Hot expected
to approve
concern over
thermal abatement
Hay have
concern over
thermal abatement
May have concern
aver oqui/or depletion
and thermal abatement
expected to
approve
fxpected to
approve
£>pected to
approve
Hoy have a
concern over
unwanted by-products
expected to
approve
co-ccl2(ca-97) 6/91
^ASSUMES A IX WfUIMN AMD 7X DISCOUNT RATE.


                       7-7

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                                                                      TABLE 7-2

                                    ESTIMATED MAXIMUM ANNUAL WASTE AMD EMISSONS FOR REMEDIAL ALTERNATIVES
                                                                       (Pounds)
ALTERNATIVES
Hazardous Waste Solid'
Spent Carbon
Hazardous Waste.UaukT
Steam Regenerant w/organlcs
Chlorinated Organlcs
(free liquid) .
Spent Add
(from air stripper washing)
Priority Air Pollutants*
•Parflculates
•Sulfur Dioxide
•Nitrogen Oxides
'Carbon Monoxide .
•Organlcs (as Hydrocarbons)
•Organlcs (as chlorinated
hydrocsftXMis)
Hydrochloric Add (gas)
A

None

None
None

None


None
None
None
None
None
None

None
8

>» — i
wone

None
None

48.800


00.3
23.8
5.560
1.300
240
62

17,100
C

None

None
None

48,800


00.3
23.8
5.560
1.390
240
82

17,100
D

None

None
None

48.800


99.3
23.8
5.560
1.390
240
82

17,100
E

32.200

1,145.000
25,100

None


3.5
0.84
198
49
8.5
"•

Trace
F

32.200

None
25.100

None


3.5
0.84
198
49
8.5
•*•

Trace
0

32,200

1.250.000
24,880

None

..
3.0
0.03
217
54
0:3
*"

Trace
H

None

None
None

None


None
None
None
None
"Trace
"5.5

"17.100
1

32.200

1,250.000
24,880

48,800


3.0
0.03
217
54
274
822

Trace
 *      A net reduction In overall base emissions would result since Ihese emissions would be offset by a 110 percent equta
        required for meeting regulatkms to permit new sources.

 "      Not emitted as air pollutants, returned dissolved In treated groundwater. emission offsets do not apply.  ,

 *"     Storage tank breathing and working losses only.

 1 Residuals to be sent to EPA-RCRA Permitted Facility
 1 Air pollutants win meet established ARAR's
nt reduction In emissions from existing sources as
                                  1VN19WO
MA: ENG:9352-T/061991/3

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                                             TABLE 7-3
                                PAGE 1 OF 5
                        POTENTIAL FEDERAL APPLICABLE, OR RELEVANT AND
            APPROPRIATE REQUIREMENTS FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)

                                     CHEMICAL SPECIFIC ARARS
                    REQUIREMENT
   APPLICATION TO THE MAIN TCE PLUME
              Resource Conservation and
              Recovery Act (RCRA) as amended
              by Hazardous and Solid Waste
              Amendments (HSWA) (42 USCA
              7401-7642)
              (40 CFR 260-280)
    RCRA-related regulations are generally action
    specific.  However, RCRA provides Maximum
    Concentration Limits (RCRA MCLs) as part of
    groundwater protection standards (40 CFR
    264.94).
      (RELEVANT AND APPROPRIATE)
          II.   Safe Drinking Water Act (SDWA)
              [42 USCA 300(f)]
              (40 CFR Parts 141-149)
              (54FR22Q64, Federal Register,
              May 22,1989)
II.   Established MCLs which are enforceable
    standards for chemicals in public drinking
    water supplies. They not only consider health
    factors, but also economic and technical
    feasibility of removing a chemical from a
    water supply system.
      (RELEVANT AND APPROPRIATE)
              Clean Water Act, amended (CWA)
              (33 USCA 1251-1376)
              (40 CFR 100-149)
III.  Ambient Water Quality Criteria (AWQC);
    established under Section 304 of CWA (51
    FR 43665), are based on effects on human
    health and aquatic life that do not reflect
    technological or economic considerations.
    CWA AWOC's would be applicable to water,
    to a sewer, or site runoff directed to a water
    body (including a storm drain or flood
    channel) with or without treatment.
    (MUST MEET RELEVANT AND
    APPROPRIATE DEFINITION)
MA:ENG:9327T7-3/061291
                                               7-9

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                                               TABLE 7-3
                                  PAGE 2 OF 5
                          POTENTIAL FEDERAL APPLICABLE, OR RELEVANT AND
             APPROPRIATE REQUIREMENTS FOR THE MAIN TCE PLUME (OPERABLE UNIT NO; 1)
           IV.  Clean Air Act (CAA)
               (42 USCA 7401-7642)
               (40 CFR 50-69)
IV.  a.  National Ambient Air Quality Standards
        (CAA Sec. 109)
  .  National primary and secondary ambient air
    quality standards (NAAQS) are required to be
    met under Section 109 of the CAA and are
    Bsted In 40 CFR 50.  No air pollutants have
    been measured at Castle Air Force Base.
    (MAY BE RELEVANT AND APPROPRIATE-
    AMBIENT AIR)

    b.  National Emission Standard for
        Hazardous Air Pollutants
  .  National Emission Standards for Hazardous
    Air Pollutants (NESHAPs) are process and
    industry specific and must be industry
    specific.  They must be converted from point
    source standards to area source standards in
    order to be applied at CAFB.  NESHAPs are
    currently limited to very few chemicals (40
    CFR 61).
    (MAY BE RELEVANT AND APPROPRIATE-
    AMBIENT AIR)
                                  LOCATION SPECIFIC ARARS - FEDERAL

         There are no location-specific ARARs associated with CAFB.  The Base is located in the historical
         range of three endangered species. The Air Force will have a biologist determine the presence or
         absence of these species. Any surface area disturbance associated with the selected interim remedy
         is minimal and should not have a significant impact on these species habitats, should they exist The.
         Air Force will also have a qualified agency assess the Base to determine the presence or absence of
         wetlands.  Any surface area disturbance associated with the selected interim remedy will be minimal
         and should not significantly impact any wetlands should they exist.  The Base is not In a floodplain,
         nor are there any known surface water bodies that are being affected.  There are no geologic faults
         below or near the base.  No historic places are located within  3 miles.  Consequently, the following
         federal statutes are not "appropriate and relevant" to the Castle Air Force Base Operable Unit No. 1
         (Main TCE Plume):   .                                              ;

                National Historic Preservation Act (NHPA) 16 CFR Part 470, el seq. Endangered Species
                Act (ESA) 50 CFR Sections 402.01 and 402.04. Protection of Wetlands Executive Order
                11990 (40 CFR 6.302 (a).  Wild and  Scenic Rivers Act (WSRA) 36  CFR Section 297.4
                Coastal Zone Management Act (CZMA)  15 CFR Section 930.30 and 930.34.  Wilderness
                Act (WA) 50 CFR Section 35.5.
                                          7-10
MA:ENG:9327T7-3/080291

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                                             TABLE 7-3
                             PAGE 3 OF 5
                         POTENTIAL FEDERAL APPLICABLE, OR RELEVANT AND
            APPROPRIATE REQUIREMENTS FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)


                               TO BE CONSIDERED MATERIAL - FEDERAL
                       REQUIREMENT
              National Contingency Plan (NCP)
              (55 FR 8666, Federal Register,
              March 8,1990)
              (40 CFR 300)
          II.   Toxic Substances Control Act
              (TSCA) PCB Spill Cleanup Policy
              (52 FR 10688, April 2, 1987)
              (40 CFR Part 61, 'Suppart G)
          III.  Groundwater Protection Strategy of U.S.
              EPA
          IV. ^40 CFR 264.94
  APPLICATION TO THE MAIN TCE PLUME
Baseline Risk Assessment will determine safe
levels for those chemicals w/o MCLs, and will
Judge whether MCLs are sufficiently health-
protective for the.chemical mixture found in the
plume.
While not potential ARARs, the requirements of
the PCB spill cleanup policy may by
"appropriate relevant" for CERCLA actions.
While not potential ARARs, the groundwater
classification guidelines are considered in the
Baseline Risk Assessment and Feasibility
Study.
Establishes three categories of groundwater
protection standards: background, RCRA
MCLs and Alternate Concentration Limits
(ACLs). CERCLA Sec. 121(d)(2)(B)(ii) list
three additional conditions limiting use of ACLs
at Superfund sites.
                                 ACTION-SPECIFIC ARARS-FEDERAL

        A.  GROUNDWATER PUMP AND TREAT REMEDIATION ALTERNATIVE:

            1. TREATMENT OF GROUNDWATER (DISCHARGES TO GROUNDWATER &
               DISPOSAL OF RESIDUALS):
                      REQUIREMENTS
              Resource Conservation and Recovery Act
              (RCRA) as amended by Hazardous and
              Solid Waste Amendments (HSWA)
              (40 USCA 7401-7462)
              (40 CFR 264-265)
  APPLICATION TO THE MAIN TCE PLUME
Although RCRA was not In effect during active
waste disposal and is not strictly applicable, the
similarity between the historical disposal at
CAFB and RCRA regulated practices makes it
reasonable to judge RCRA requirements
generally relevant and appropriate. SARA
relieves the requirement of obtaining a permit,
but all RCRA requirements must be met
MA:ENG:9327T7-3/061291
                                              7-11

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                                               TABLE 7-3
                                   PAGE 4 OF 5
                          POTENTIAL FEDERAL APPLICABLE, OR RELEVANT AND
             APPROPRIATE REQUIREMENTS FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)
           II.   Resource Conservation and Recovery Act
               (RCRA) as amended by Hazardous and
               Solid Waste Amendments (HSWA)
               (40 CFR 264.90)
               (40 CFR 264.94) Monitoring
           III.   Underground injection Control Regulations
               (40 CFR Parts 144 through 147)
          IV.  Clean Water Act (CWA)
               33 USCA 1251-1376
               40 CFR 100-149
          (1).  National Pollutant Discharge
               Elimination System (NPDES)
               40 CFR 122-125
          (2). Water Quality Standards
              CWA402(a)(1j
     Hazardous constituents entering groundwater
     must not exceed concentration limits In the
     aquifer underlying the waste management unit
     (WMU). The groundwater monitoring program
     must provide a reliable indication of
     groundwater quality below the WMU.
     Potentially applicable for alternatives utilizing a
     groundwater injection option.
     The Clean Water Act requires permitting if
     effluent discharges under the NPDES permit
     program and seeks to protect the existing and
     attainable uses of waters of the U.S.  Permit
     may not be required, but all requirements must
     be met.
     NPDES permits contain applicable standards,
     monitoring requirements, and standard and
     special conditions for water discharges. Both
     pn-site and off-site discharges from CERCLA
     sites to surface waters are required to meet the
     substantive CWA requirements, and best
     management practices. Only off-site CERCLA
     discharges must be permitted. The base
     wastewater treatment facility has a NPDES
     discharge permit.
     Effluent limitations are required to achieve all
     appropriate State water quality standards. EPA
     Policy for the Development of Water Quality
     Based Permit Limitations for Toxic Pollutants.
     (49 FR 9016, March 9,1984) states that toxic
     pollutants contained in direct discharges will be
     controlled beyond Best Control
     Technology/Best Available Technology
     (BCT/BAT) equivalents in order to meet
     applicable state water quality standards.
             2.  TREATMENT OF GROUNDWATER (DISCHARGE TO POTW)
REQUIREMENT
(1). Discharge to Publicly Owned Treatment
Works (POTWs)
(CWA 307)
APPLICATION TO THE MAIN TCE PLUME
Pretreatment regulations (40 CFR 403) control
the introduction of pollutants to POTWs.
,dA:ENG:9327T7-3/061291
7-12'

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                                               TABLE 7-3
                              PAGE 5 OF 5
                          POTENTIAL FEDERAL APPLICABLE, OR RELEVANT AND
             APPROPRIATE REQUIREMENTS FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)

             3.  TREATMENT OF GROUNDWATER (DISCHARGE TO AMBIENT AIR):
                       REQUIREMENTS
  APPLICATION TO THE MAIN TCE PLUME
           (1).  National Ambient Air Quality Standards
               (CAASec. 109)
No air pollutants have been measured at
Castle Air Force Base.
(MAY BE RELEVANT AND APPROPRIATE-
AMBIENT AIR
           (2).  National Emission Standard for
               Hazardous Air Pollutants
National Emission Standards for Hazardous Air
Pollutants (NESHAPs) are process and industry
specific and must be industry specific. They
must be converted from point source standards
to area source standards in order to be applied
at CAFB. NESHAPs are currently limited to
very few chemicals (40 CFR 61).
           (3).  EPA - OSWER Directive 9355.0-28,
               "Guidance on the Control of Air Emissions
               from Air Strippers at Superfund Sites."
               Guidance seeks to incorporate air quality
               concerns into the Superfund remedy
               selection.  Policy may set target levels
               (TBCs) where ARARs do not exist. The
               directive applies to future remedial
               decisions at Superfund sites located in
               ozone non-attainment areas.  Such sites
               are required by the directive to control
             ,  total volatile organic compound emissions
               from air stippers and soil vapor extraction
               operators to fifteen pounds per day.
1) Requires FS to evaluate the impact of VOC
emissions in attainment and nonattainment
areas for ozone.
2) Requires consideration in the FS of health
risks from the execution of the remedy as well
as form the uncontrolled site.
3) Requires alternatives and their costs In FS
evaluation of control measures.
4) Requires FS to evaluate compliance wtth
Air ARARs with implementation of alternative.
5) Requires a determination in the FS of
estimated cumulative uncontrolled air emission
rate from all air strippers at the site.
                                          7-13
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                                   TABLE 7-4
                              PAGE 1 OF 5
 POTENTIAL STATE APPLICABLE, OR RELEVANT AND APPROPRIATE REQUIREMENTS
                FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)

                       CHEMICAL SPECIFIC ARARS - STATE
            REQUIREMENT
   I.  State Drinking Water Act (SDWA)
     Health and Safety Code, Division 7,
     Part I, Chapter 7, Section 4010 et
     seq.
     Mulford-Carrell Air Resources Act
     (Health and Safety Code Sections
     39000-44563) as regulated by the Air
     Resources-Board and enforced by
     local Air Quality Management
     Districts under CAC, Title 17, Part III.
 APPLICATION TO THE MAIN TCE PLUME
SDWA establishes drinking water standards
for sources of public drinking water. Federal
MCLs are incorporated into State regulations,
and in some cases the State may promulgate
more stringent State MCLs. The DHS has
set MCLs for 10 of the constituents found in
the TCE plume at CAFB. Several of the
MCLs are at the same levels or more
stringent levels than PDWS-MCLs.
(RELEVANT AND APPROPRIATE)
Ambient Air Quality Standards are listed
under Section 70200/70200.5 of CAC Title
17. Benzene is identified as a toxic air
contaminant. However, no threshold value
has been determined. (MAY BE RELEVANT
& APPROPRIATE-AMBIENT AIR)
                       LOCATION SPECIFIC ARARS-STATE

  There are no location-specific ARARs associated with CAFB. The Base is located in the
  historical range of three endangered species. The Air Force will have a biologist
  determine the presence or absence of these species.  Any surface area disturbance
  associated with the selected interim remedy is minimal and should not have a significant
  impact on these species habitats, should they exist The Air Force will also have a
  qualified agency assess the Base to determine the presence or absence of wetlands.
  Any surface area disturbance associated with the selected interim remedy will be minimal
  and should not significantly impact any wetlands should they exist. The Base is not in a
  floodplaln, nor are there any known surface water bodies that are being affected. There
  are no geologic faults below or near the base. No historic places are located within 3
  miles.  Consequently, the following  state statutes are not 'appropriate and relevant" to
  the Castle Air Force Base Operable Unit No. 1 (Main TCE Plume):
NOTE: California DHS will provide a Ust of pertinent statutes for location-specific
       ARARs.
                                      7-14
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                                           TABLE 7-4
                             PAGE 2 OF 5
         POTENTIAL STATE APPLICABLE, OR RELEVANT AND APPROPRIATE REQUIREMENTS
                        FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)

                             TO BE CONSIDERED MATERIAL - STATE
                    REQUIREMENT
  APPLICATION TO THE MAIN TCE PLUME
          1. DHS Applied Action Levels (AALs)
Applied action levels are exposure limits that
are pollutant-and receptor-specific and are used
as a point of departure for establishing cleanup
levels. They are similar to the levels
established by the Baseline Risk Assessment
to assure that MCLs are  adequately health-
protective.
(MUST BE APPROPRIATE AND RELEVANT)
          2.  Central Valley RWQCB. A
             compilation of Water Quality Goals.
             (10/88)
This guidance document contains a compilation
of Water Quality Goals developed by CVWQCB
for various beneficial uses of groundwater.
          3.  Safe Drinking Water & Toxics
             Enforcement Act (Proposition 65)
Reporting of hazardous materials
(developmental toxicants) releases will be
required if fisted substances are being
discharged to the environment at significant risk
levels given in the statute.
(MUST BE APPROPRIATE AND RELEVANT)
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                                              7-1S

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                                           TABLE 7-4
                           PAGE 3 OF 5
         POTENTIAL STATE APPLICABLE, OR RELEVANT AND APPROPRIATE REQUIREMENTS
                        FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)

                                ACTION-SPECIFIC ARARS - STATE
         A.  GROUNDWATER PUMP AND TREAT REMEDIATION ALTERNATIVE:

            1.  TREATMENT OF GROUND WATER (DISCHARGES TO GROUND WATER &
               DISPOSAL OF RESIDUALS):
                      REQUIREMENT
APPLICATION TO THE MAIN TCE PLUME
              Hazardous Waste Control Act (Health
              & Safety Code Section 25100-25395)
              as administered by the Department of
              Health Services (DHS) under the
              California Administrative Code Title 22,
              Chapter 30; Minimum Standards for
              Management of Hazardous and
              Extremely Hazardous Wastes.
1:  HWCA has many elements that are
   intended to control hazardous wastes
   from their point of generation through
   accumulation, transportation, treatment,
   storage, and ultimate disposal,  ft is
   implemented largely through regulations
   under the CAC, Title 22, Division 4,
   Chapter 30. Section 66300 of
   Chapter 30 provides no RCRA-type
   exemption for CERCLA sites; therefore
   most regulations will be directly
   applicable to CAFB alternatives.
          (1)  Criteria for identifying Hazardous
             , Wastes (Title 22, 66693-66746)
              Disposal of Residuals from
              groundwater treatment
(1) Tests for identifying hazardous
   characteristics are described in Title 22,
   Article 11, Sections 66693-66746. If a
   chemical is either listed or tested and
   found hazardous, ft must comply with
   the hazardous waste requirements
   under TOe 22. While these standards
   are not treatment or disposal limits, the
   resulting classification as hazardous
   waste results in efforts to meet the
   standard, thereby making hazardous
   designation methods a form of
   treatment standard.
          (2)  Persistent and Biocumulative Toxic
              Substances (66699) Disposal of
              Residuals from groundwater treatment.
(1) Total Threshold Limit Concentrations
   (TTLCs) and Soluble Threshold Limit
   Concentrations (STLCs) have been
   established for selected toxics.
MA:ENG:9327T7-4/061291/3
                                               7-1&

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                                   TABLE 7-4
                           PAGE 4 OF 5
 POTENTIAL STATE APPLICABLE, OR RELEVANT AND APPROPRIATE REQUIREMENTS
                FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)
              REQUIREMENT
  (3)  Porter-Cologne Water Quality Act
      Water Code, Division 7, Section 13000
      et seq., CCR Title 23, Chapter 3,
      Subchapter 9 and Subchapter 15,
      1050-2836
 APPLICATION TO THE MAIN TCE PLUME
Similar to the Federal CWA, the Act and its
associated regulations apply to protection of
waters of the state.  An NPDES permit is
required for off-site discharges, whereas,
only substantive requirements are required
for on-site discharges. Porter-Cologne
delegates standard
2. TREATMENT OF GROUNDWATER (DISCHARGE TO POTW)
REQUIREMENT
(1) Discharge to Publicly Owned
Treatment Works (POTWs) County
Sanitation District of Merced County
APPLICATION TO THE MAIN TCE PLUME
Pretreatment regulations (40 CFR 403)
control the introduction of pollutants to
POTWs
3. TREATMENT OF GROUNDWATER (DISCHARGES TO AMBIENT AIR)
             REQUIREMENT
APPLICATION TO THE MAIN TCE PLUME
  (4)  Mulford-Carrell Air Resources Act,
      Hearth and Safety Code, Division 26,
      Section 39000 et seq. 17 CAS Part III
      Chapter .1, Section 60000 et seq.
The State counterpart of the Federal CAA,
Murford-Carrell, establishes the California
Air Resources Board (CARB) and the local
Air Quality Management Districts (AQMDs).
Permitting authority is delegated in this act
While the treatment unit may not need a
federal permit, It is not relieved from the
requirements of this act. Allocation of
allowable air emissions are on an air basin
specific basis.
  (5)  Merced County Air Pollution Control
      District Rule 210.1 Standards for
      Authority to Construct and Rule 210.2
      Standards for Permits to Operate.
There may be specific sections of the local
Air Pollution Control Board regulations that
must be met by the design and operation of
an air stripping unit. These may include:
Nuisances (including odors).
                                      7-17
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                                        TABLE 7-4
                         PAGE 5 OF 5
        POTENTIAL STATE APPLICABLE, OR RELEVANT AND APPROPRIATE REQUIREMENTS
                       FOR THE MAIN TCE PLUME (OPERABLE UNIT NO. 1)
                    REQUIREMENT
APPLICATION TO THE MAIN TCE PLUME
          (6) Rute.1167-Air Stripping Operations
             (Reg. Xl-Source Specific Stds)
This rule is designed to reduce volatile
organic compound (VOC) emissions from
new and existing air stripping equipment
used in the treatment of affected
groundwater.
MA:ENG:9327T7-4/061291/5
                                           7-18

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                                      8.0  THE SELECTED REMEDY

          The selected interim remedy for this ROD is Alternative I, which consists of:
                •  Pumping groundwater from a series of shallow aquifer extraction wells to maintain
 •                  hydraulic control of the TCE  plume and begin removing residual TCE
                   concentrations.
                •  Surface treating the extracted groundwater by air stripping to allow the return of
                   water to beneficial use (resource  recovery).
           •-.   •  Reinjecting the treated groundwater back to the shallow aquifer to assist in
                   maintaining hydraulic control and  avoid depletion of the aquifer.
                •  Applying natural biological enhancement to accelerate the release/ degradation of
                   hazardous constituents in the saturated zone.
                •  Abating the air stripper emissions with granular activated carbon (GAC) to avoid
                   degrading ambient air quality. The abatement unit would be steam regenerated on
                   site and the liquid condensate would be disposed off site at a permitted recycling
                   facility.

         CONCEPTUAL DESIGN OF SELECTED REMEDY
         The selected interim remedy under Alternative I will conceptually consist of groundwater
         extraction from an intercepting well field consisting of five wells, one well located at or near
         each of the TCE hot spots or identified  source locations within the Main TCE Plume.  The
         wells will tentatively be pumped at a rate of  approximately 250 gallons per minute each.
     •    Pumping tests, scheduled to be performed later in the Rl field program, will provide design
         data on the number of extraction wells required, their location, and discharge rates.

         The surface treatment facility will conceptually consist of a new centralized treatment plant in
         an undeveloped area northeast of the POL/storage tank farm (Rgure 1-1). The remedial
         treatment technology option will conceptually consist of twin air stripping towers operating in
         series, equipped with three double bed  vapor phase GAC abatement units with the double
         beds operating in series flow. Two of the double bed units will be on-line continuously (one
         pair for each of the two strippers), while the  third pair of beds remain on standby.  An on-site
         oil or gas fired boiler will  provide steam for the regeneration cycle. Regenerant steam will be
         condensed using a Hastelloy alloy heat exchanger and collected in a holding tank pending off-
         site disposal to an approved EPA-RCRA recycling facility. The third GAC unit is necessary for

                                             . - . 8-1
MA:ENG:9327-8/061991

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            continuous operation of the stripper, since the regeneration cycle will require approximately
•            eight hours. Each adsorber vessel will be sized to contain 6,000 pounds of GAC.  A life of 20
I            regeneration cycles for the GAC is assumed for estimating purposes. The steam requirement
. •           is estimated at 10,350 pounds for each single carbon bed.
1                        •              '  .
            The air stripping towers were conceptually sized for estimating purposes at 84 inches
(            diameter, 25 foot packing depth, and a required air flow rate of 3345 SCFM. The preliminary
            tower sizing was based on (worst case) high levels of detected organic compounds in Base
)            groundwater sampling data from rounds one, two, three, and four, and on achieving a removal
            concentration level to meet re-injection ARARs pursuant to the discharge permit
I
            The treated groundwater effluent  will be piped to a reinjection well field upgradient from the
•            extraction well field, with the exact locations to be specified after pumping tests are
            conducted. Reinjection wells will  be spaced to maximize plume capture and to minimize time
            of cleanup.

            In addition, nutrients and hydrogen peroxide will be reinjected with treated groundwater to
            increase available oxygen in the contaminated aquifer. This action serves to stimulate growth
            of natural indigenous bacteria, increase the release rate of contaminants from soil particles,
           and degrade some of the contaminants In-sltu.  A partial stream of 250 gallons per minute of
           the treated groundwater will.be used as the carrier for the nutrients and  returned to the  aquifer
           by a combination of reinjection wells and separate biotreatment injection wells.

           Details of the selected interim remedy will be finalized during the remedial design phase.

;           SUMMARY OF PRELIMINARY COST ESTIMATES
                                                                        • *
:           The selected Interim remedy provides overall effectiveness proportionate to its  costs, such that
1           ft represents a reasonable value.  Tables 8-1 and 8-2 show the preliminary estimates of
i           capital costs, operation and  maintenance costs, and total net present value of the selected
           remedy (Alternative I).  Final cost  estimates may vary from the estimates presented due to
           changes that may occur as a result of hydraulic modeling, and difference in environmental
           setting at the time of remedial design and construction.  Such changes, in general, will reflect
           modifications resulting from the engineering design process.  The hydraulic gradient control

                                                    8-2
  dA:ENG:9327-8/061991

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          system and system performance evaluation and schedule will be developed during the
          remedial action design process.            .   '        •
                                                 8-3
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                                             TABLE 8-1
                            ALTERNATIVE I - PRESENT WORTH ANALYSIS
         Installed cost of 5 extraction welt-pumps
         Installed cost of 5 hotspot extraction wells      .
         Installed cost of double contained groundwater transfer piping
         Installed cost of air stripper treatment system with
         GAC emission abatement system
         Annual operating cost of air stripper treatment plant
         Installed cost of treated water reinjection transfer piping
         Installed cost of 8 reinjection wells
         Installed cost of biotreatment nutrient feed system
         Installed cost of biotreatment injection wells
         Annual operating cost of biotreatment nutrient feed system
         (assumes 250 GPM of 1250 GPM total groundwater extracted
         treated for bio-reinjection)
         Cost tQ abandon MID No. 228
         Replacement cost of 8 reinjection wells (assume 5 year well
         lifetime for present worth analysis)
         "Annual maintenance cost
$   COST
   96,000
  110,000
  214,000
 1,548,000

 1,567,000
  149,000
  176,000
  100,000
   60,000
 1,092,000

   88,000
  176,000

   50,000
        Total estimated capital expenditure (1990 basis)
        Total estimated annual operating and maintenance cost (1990 basis)
        * Costs shown on 1990 dollar value basis
        ** Includes disposal costs for periodic stripper cleaning
4A:ENG:9352-T/061991/4
2,541,000
2,744,200
                                                     8-4

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                                       TABLE 8-2
                  ALTERNATIVE I • PRESENT WORTH VALUES N 1990 DOLLARS*
                                 ANNUAL INFLATION RATE
DISCOUNT RATE
5%
7%
9%
11%
13%
4%
28,420
25,939
23,795
21,934
20,310
6%
31,263
28,445
26,004
23,890
22,049
8%
34,478
31,247
28,469
26,067
23,981
10%
38,065
34,382
32,220
28,492
26,128
12%
42,085
37,898
34,292
31,194
28,515
        •Values In thousands of dollars.
MA:ENG:9352-T/06199i/5
                                              8-5

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                                   9.0  STATUTORY DETERMINATIONS

'           The Comprehensive Environmental Response Compensation and Liability Act (CERCLA) as
I           amended has designated Federal Facilities as responsible for undertaking remedial actions.
I           EPA has the responsibility to ensure that the selected response actions protect human health
/     .      and the environment. In addition, Section  121 of CERCLA establishes several other statutory
I  . .        requirements and preferences. These specify that when complete, the selected remedy for
           the site must comply with local, state and federal ARARs unless a waiver is justifiable (tables
I                        •                   •                                          •
           7-3 and 7-4).  ARARs will have to be established for ten contaminants of potential concern
           (Section 4.0) for both the treated groundwater and any potential air emissions.  ARARs apply
           whether the groundwater is to be disposed of via re-injection or by another means. Similarly,
           ARARs apply whether the air emissions from the air stripper are controlled or not controlled.
           Potential ARARs may be identified by EPA, the California DHS, Water Board, Air Board or by
           Merced County Health Department or any other agency with an applicable enforceable
           standard.

           The selected remedy also must be cost effective and utilize  permanent solutions and
           alternative treatment technologies to the maximum extent practicable.  Remedies that employ
           treatment that permanently and significantly reduce the volume, toxicity, or mobility of
           hazardous wastes as a major part of the remedy are preferable. How the selected interim
           remedy meets these requirements is discussed below.

           The selected interim remedy represents the best balance of trade-offs among alternatives with
           respect to pertinent criteria, given the limited scope of this action.  An in-situ biotreatment
           treatability study willbe performed prior to the final design. This study will not cause a delay
           to the implementation of the remedy. Re-injection may begin without bio-enhancement should
           the treatability study results not be available.  Further, bio-enhancement can begin when ail
           parameters controlling bio-enhancement are determined.

           PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
           The selected remedy protects human health and the environment through extraction of TCE
           contaminated groundwater and removal/treatment of volatile organic contaminants by air
           stripping.  The volatile contaminants will be transferred to the gas phase, removed by granular

                                                   9-1
  MA:ENG:9327-9/070191

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          activated carton (QAC) adsorption; then recovered by steam regeneration.  The condensed
          steam containing contaminants adsorbed on the carbon will be collected for treatment or
          disposal at an approved facility, as would any spent carbon generated by the treatment
          process.
                    •••..-         .             '
          Extraction of the groundwater will eventually eliminate the threat of exposure to the
          contaminants from direct contact, from inhalation, and from ingestion.  Once pumping begins
          and hydraulic control is achieved, there are no short term threats associated with the selected
          remedy. Wells (exposure routes) known to have been contaminated will have previously been
                                                  f                 ,•'"-,'
          removed from service or had filtration units placed on them prior to the start of remediation.
          Any new wells which become contaminated will also be taken out of service (Section 7.0).

          No adverse affects as a result of cross media transfer are expected.  Control of emissions
          using GAC will adequately control any potential exposure risk.

          ATTAINMENT OF ARARs
          The selected interim remedy will achieve ARARs (Tables 7-3 and 7-4) for the treated
          groundwater and any potential air emissions (including TBCs such as EPA's OSWER Directive
          9355.0-28 regarding the control of emissions from air strippers). ARARs for the groundwater
          will be documented tn a subsequent ROD.                    .

          ARARs for the treated groundwater will be determined by the California Regional Water
          Quality Control Board in the permit requirements for the discharge water.  ARARs for the air
          emissions will be set by the Merced County Air Pollution Control District in the permit
          requirement for the air emissions.
            '  '       -                   '     ' '       '  ' •           '•."'"'-
         COST EFFECTIVENESS
         The selected remedy  (Alternative I) was evaluated for cost effectiveness against the other
         eight alternatives (A-H). The selected remedy was one of the least costly alternatives and
         provides the same benefits and  level of protection in the shortest period of time compared to
         the other alternatives  (Table 7-1).  The interim remedy will provide effectiveness proportional
         to the cost of the remedy given the operation and maintenance and present worth cost for the
         protection of human hearth and the environment.

                            '                     9-2
MA:ENG:3327-9/070191

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           UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE TREATMENT
           TECHNOLOGIES OR RESOURCE RECOVERY TECHNOLOGIES TO THE MAXIMUM
|          EXTENT POSSIBLE
           The selected interim remedy is not designed nor expected to be final but it represents the best
|          tradeoffs among alternatives with respect to the pertinent criteria, especially the balancing
           criteria of implementability, short-term effectiveness and cost.  The permanent solution will be
|          established in a subsequent ROD. Contaminants will be permanently removed and eliminated
           by groundwater extraction and surface treatment Contaminants will be reclaimed in the
/          steam condensate and disposed off-site at an  EPA-RCRA state approved recycling facility.

|          Resources will be conserved to the maximum extent possible using the selected remedy.
           Treated water will be reinjected back into the shallow aquifer.  The fife of the carbon used for
           abatement will be maximized by on site steam regeneration. Contaminant recovery will be
'          implemented to the maximum extent possible without losing the removal efficiency of the
           abatement unit.     .

           PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT
'          The requirement that treatment be a principal element of the remedy will be satisfied in the
           final decision document for the site or final operable unit This operable unit action is
           consistent with planned future actions, to the extent possible.
                                                 9-3
  MA:ENG:9327-9/070191

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