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June 27, 2014 Mr. Michael Bower The Boeing Company 5800 Woolsey Canyon Road Canoga Park, CA 91304 Subject: Addendum to Master RFI Data Gap Work Plan – Iteration 2, Boeing RFI Subarea 1A Central, Areas Unaffiliated with RFI Sites, Santa Susana Field Laboratory, Ventura County, California Dear Mr. Bower: MWH is pleased to present the attached Addendum to the Master RCRA Facility Investigation (RFI) Data Gap Work Plan – Iteration 2, Boeing RFI Subarea 1A Central, Areas Unaffiliated with RFI Sites, Santa Susana Field Laboratory, Ventura County, California (2nd Iteration WP). Results from the implementation of the September 2013 Addendum to Master RFI Data Gap Work Plan, Boeing RFI Subarea 1A Central, Areas Unaffiliated with RFI Sites – Iteration 1 (1st Iteration WP), which occurred October 2013, were evaluated. A data usability assessment report has been prepared to assess the data quality of analytical results for soil and soil vapor samples collected during the first iteration field work for Boeing RFI Subarea 1A Central. This is provided as Attachment 1 to Addendum to the Master RFI Data Gap Work Plan – Iteration 2, Boeing RFI Subarea 1A Central, Building 1359 (B359) RFI Site, Santa Susana Field Laboratory, Ventura County, California (B359 2nd Iteration WP, MWH, 2014). Historic and recent data were compared against the data quality objectives (DQOs) presented in Comprehensive Data Quality Objectives, RCRA Facility Investigation, Santa Susana Field Laboratory, Ventura County, California (DQO Report; CH2M Hill, 2013). At this time, based on the most recent historical document review, no new data gaps were identified for the Boeing RFI Subarea 1A Central, Areas Unaffiliated with RFI Sites, in accordance with the DQO process. Subsequently, given the findings associated with the screening level analysis of the most recent information and analytical data, no further soil or soil vapor sampling is warranted. More detailed findings associated with this evaluation are summarized below.

TABLE C-1

BOEING RFI SUBAREA 1A CENTRAL, AREAS UNAFFILIATED WITH RFI SITES – DATA GAP SAMPLING AND ANALYSIS PLAN

Addendum to Master RFI Data Gap Work Plan ‐ Iteration 2

No additional data gaps were identified for the Boeing RFI Subarea 1A Central, Areas Unaffiliated with RFI Sites; therefore, no additional soil or soil vapor

sampling is proposed.

TABLE C-2

BOEING RFI SUBAREA 1A CENTRAL, AREAS UNAFFILIATED WITH RFI SITES – SOIL AND SOIL VAPOR ANALYSES

Addendum to Master RFI Data Gap Work Plan ‐ Iteration 2

No additional data gaps were identified for the Boeing RFI Subarea 1A Central, Areas Unaffiliated with RFI Sites; therefore, no additional soil or soil vapor

sampling is proposed.

TABLE C-3Sample Deviations from Subarea 1A Central Areas Unaffiliated with RFI Sites Data Gap Work Plan Addendum - Iteration 1Addendum to Master RFI Data Gap Work Plan, Boeing RFI Subarea 1A Central - Iteration 2

Una

ffili

ated

Are

as

CU

A C

lust

er (C

C) #

CU

A R

ef #

1

Description Object ID Matrix Tar

gete

d Sa

mpl

ing

Dep

th(s

)2

(Bot

tom

Dep

th, f

t. bg

s)

VO

Cs (

SV)3

VO

Cs (

SM)3

SVO

Cs S

IM (I

ncl.

ND

MA

)

TPH

Met

als

pH Soil

Moi

stur

e

DT

SC G

SU C

omm

ent

No(

s) C

ross

Ref

eren

ce

DQ

O C

ross

Ref

eren

ce

Rationale/Comments Deviations from Work PlanUABS1006 Soil 0.5 X X X X X

Soil 1.5 X X XSoil 3 VH XSoil 6 X X X X XSoil 10 H H H H H

UABS1007 Soil 0.5 X X XSoil 1.5 X X XSoil 3 VH HSoil 6 X X X X XSoil 10 H H H H H

UASV1000 Soil Vapor 5 XSoil Vapor 10 X

UABS1009 Soil 0.5 X X XSoil 1.5 X X XSoil 3 VH HSoil 6 X X X X XSoil 10 H H H H H

UASV1002 Soil Vapor 5 XSoil Vapor 10 X

UABS1010 Soil 0.5 X X XSoil 1.5 X X XSoil BA X X X X X

UABS1011 Soil 0.5 X X X X XSoil 1.5 X X XSoil BA X X X X X

Met refusal at 0.5 ft. bgs; therefore, proposed 1.5, 6, 10 foot and soil matrix VOC soil samples were not collected. Sample added at 0.5 ft bgs for SVOCs and TPH due to refusal depth.

N/A

N/A

Table 2

N/A Table 2

N/A

Met refusal at 3.75 ft. bgs; therefore, the proposed 6 and 10 foot soil samples were not collected. In addition, soil vapor probes were not installed and soil matrix VOC samples were collected instead at 3.75 ft. bgs.

N/A

Met refusal at 0.5 ft. bgs; therefore, the proposed 1.5 foot and deeper samples were not collected. Sample added at 0.5 ft bgs for SVOCs and TPH due to refusal depth.

Table 2 Sample location moved 38 feet north to avoid oak tree canopy. Met refusal at 4 ft. bgs; therefore, the proposed 6 and 10 foot soil samples were not collected. In addition. soil vapor probes not installed and soil matrix VOC samples were collected instead at 4 ft. bgs.

Table 2

Collect soil samples from one location within former vegetation clearance area (observed in aerial photos) measuring approximately 16,000-square-feet. Adjust proposed sample location in the field if needed to target any topographiclow points, suspected burn areas, or other feature of interest. Shallow bedrock anticipated therefore soil matrix VOC samples proposed for soils less than 5 feet bgs; if 5 ft. depth achieved, add soil vapor probe and samples.

Table 2

Sample location moved 46 feet north to target downslope surface water pathway feature.

N/A A Moderately flat area along a low ridge separating the HVS RFI Site to the south and the B359 RFI Site to the north. Located approximately 500 feet southeast of the main B359 RFI Site area

Collect soil and soil vapor samples from one location within former vegetation clearance area. Adjust proposed sample location in the field if needed to target any topographic low points or suspected burn areas. Also, shallow bedrock anticipated therefore soil matrix VOC samples proposed for soils less than 5 feet bgs; collect VOC soil matrix samples at a minimum depth of 3 feet bgs andjust above bedrock for soils less than 5 feet. If soils greater than 5 feet are encountered, a soil vapor probe will be installed to collect soil vapor VOC (sample co-located with UASV1000).

Collect soil and soil vapor samples from one location within former vegetation clearance area. Adjust proposed sample location in the field if needed to target any topographic low points or suspected burn areas. Also, shallow bedrock anticipated therefore soil matrix VOC samples proposed for soils less than 5 feet bgs; collect VOC soil matrix samples at a minimum depth of 3 feet bgs andjust above bedrock for soils less than 5 feet. If soils greater than 5 feet are encountered, a soil vapor probe will be installed to collect soil vapor VOC (sample co-located with UASV1002).

Collect soil samples from one location along the downstream surface water pathway from former vegetation clearance area. Adjust proposed sample location in the field if needed to target the surface water drainage pathway. Collect and analyze deepest sample just above bedrock.

Collect soil samples from one location along the downstream surface water pathway from former vegetation clearance area. Adjust proposed sample location in the field if needed to target the surface water drainage pathway. Collect and analyze deepest sample just above bedrock.

Unaff Table C-3_20140626 Page 1 of 2

TABLE C-3Sample Deviations from Subarea 1A Central Areas Unaffiliated with RFI Sites Data Gap Work Plan Addendum - Iteration 1Addendum to Master RFI Data Gap Work Plan, Boeing RFI Subarea 1A Central - Iteration 2

Una

ffili

ated

Are

as

CU

A C

lust

er (C

C) #

CU

A R

ef #

1

Description Object ID Matrix Tar

gete

d Sa

mpl

ing

Dep

th(s

)2

(Bot

tom

Dep

th, f

t. bg

s)

VO

Cs (

SV)3

VO

Cs (

SM)3

SVO

Cs S

IM (I

ncl.

ND

MA

)

TPH

Met

als

pH Soil

Moi

stur

e

DT

SC G

SU C

omm

ent

No(

s) C

ross

Ref

eren

ce

DQ

O C

ross

Ref

eren

ce

Rationale/Comments Deviations from Work PlanColor designations represent:Red text indicates that the sample could not or was not collected due to deviations from the work plan.Blue text indicates a location, sample, or analysis was added.

Notes:1 The CUA Reference number refers to the CUA the proposed sample either is within or associated with due to operational history and/or geographic proximity.2 Actual sampling depths may change as field conditions warrant; however, a sample will be collected from the bottom of each boring except where noted in rationale/comments.

If burnt materials are observed during sampling activities, add dioxins and PAHs to analytical suite.

Acronyms:BA = base of alluvium ID = identificationBaP = benzo(a)pyrene NDMA = n-nitrosodimethylamineCC = CUA Cluster PAH = polynuclear aromatic hydrocarbonCUA = Chemical Use Area RFI = RCRA Facility InvestigationDQO = data quality objective SIM = selected ion monitoringDTSC GSU = California Department of Toxic Substances Control Geological Services Unit TPH = total petroleum hydrocarbonsft. bgs = feet below ground surface VH = Vapor intrusion hold sample. Vapor intrusion will be evaluated using a soil matrix sample at this location if a soil vapor sample cannot be collected.H = Sample to be held until needed VOC = volatile organic compound

3 For proposed VOC analysis, soil vapor will be the preferred method of analysis. In areas where soils are not deep enough for soil vapor analysis and/or if moist or saturated soils are encountered in the boring, soil matrix samples will be collected for VOC analysis, as appropriate.

Unaff Table C-3_20140626 Page 2 of 2

Base Map LegendAdministrative BoundariesRFI Site Boundary RFI Group BoundaryRFI Subarea 1A CentralPipes

( ( FencesRock OutcropContours(10 foot interval)

!( NPDES Outfall

DrainageOperational ChannelsSurface Water DividePondSumps

! ! ! ! !

! ! ! ! !

! ! ! ! ! Structures

Aboveground Storage TankTank Type Not Yet Determined

Underground Storage TankWellsDirt Road

Paved RoadLeachfieldA/C Paving

Figure LegendSoil Vapor CMS AreaSoil CMS Area Cluster CUAsBoeing Subarea 1A NorthBoundary of Unaffiliated Areas

U U U UU U U UU U U U Undefined Feature

Chemical Use Area (CUA)

!! Transformer Pole

Transformer Pad'­ Debris Point

Debris AreaStorage YardExcavated and Backfill Excavated AreasDisturbed Soil AreaVegetation Clearing

Path: T:\projects\rock3\RFI\Figures\Group1A\Central_2ndIteration\Unaffiliated Central\Unaffil_CUAs_FigC-1.mxd Date: 6/23/2014

I1 inch = 140 feet

0 70 140Feet

Boeing RFI Subarea 1A Central,Areas Unaffiliated with RFI Sites

S A N T A S U S A N A F I E L D L A B O R A T O R Y

FigureC-1

Note:No additional data gaps were identified for the Boeing RFI Subarea 1A Central, AreasUnaffiliated with RFI Sites; therefore, no additional soil or soil vapor sampling is proposed.

CUA Reference Number1a