TETRA TECH, INC.

THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO INCORPORATE A REVISED SOW, INCORPORATE WORK PLAN/COST PLAN (WP/CP), INCREASE HOURS FOR CERTAIN TASKS OF THE SOW, AND ADD FUNDING FOR THE INCREASED HOURS. THE CONTRACTOR SUPPORTS AGENCY OVERSITE OF RSES

THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO INCORPORATE A REVISED SOW TO REFLECT ADJUSTMENTS REGARDING TECHNICAL SUPPORT FOR REMOVAL ACTIONS FOR ENGINEERING REVIEWS FOR THE 60% AND 95% CONSTRUCTION DESIGN DOCUMENTS AND RE-OBLIGATE FUNDING.

THE PURPOSE OF THIS UNILATERAL MODIFICATION IS TO RE-OBLIGATE FUNDS TO SSID 099R. TO FOR UAV SUPPORT ON NAVAJO NATION IN ACCORDANCE UNDER THE RAES2 CONTRACT #68HE0923D0002 FOR EPA FOR REGIONS 6 & 9.

THE PURPOSE OF THIS BILATERAL MOD INCREASE LOE AND FUNDING. THE CONTRACTOR WILL ASSIST EPA IN COMMUNITY INVOLVEMENT OUTREACH SUPPORT INCLUDING CALLS, REMOTE MEETINGS AND FACE TO FACE ASSEMBLIES UNDER THE RAES 2 CONTRACT #68HE00923D0002.

THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO DEOBLIGATE FUNDS FROM SSID A982. TO FOR UAV SUPPORT ON NAVAJO NATION IN ACCORDANCE UNDER THE RAES2 CONTRACT #68HE0923D0002 FOR EPA FOR REGIONS 6 & 9.

THE PURPOSE OF THIS BILATERAL MODIFICATION IS ADD ADDITIONAL UAV/UAS SURVEYS FOR THE IDENTIFIED, POTENTIAL REPOSITORY AND CHARACTERIZATION AND SCOPING PURPOSES AND ANIMATION PRODUCTION . TO FOR UAV SUPPORT ON NAVAJO NATION IN ACCORDANCE UNDER THE RAE

THE PURPOSE OF THIS TASK ORDER IS TO PROVIDE TECHNICAL SUPPORT TO EPA REGION 6 IN FULFILLMENT OF ITS RESPONSIBILITIES FOR OVERSIGHT AND ENFORCEMENT OF ARCO'S ONGOING RI/FS UNDER THE ASAOC AND TO ASSIST EPA IN COORDINATION AND COMMUNICATION WITH

THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO DEOBLIGATE FUNDS FROM SSID09ZDE AND EXTEND THE PERIOD OF PERFORMANCE (POP).

THE PURPOSE OF MODIFICATION P00005 IS TO ADD NEW TASKS AND ADD ADDITIONAL FUNDING FOR THE RSE AT THE SKYLINE AUM UNDER THE RAES II CONTRACT FOR EPA FOR REGIONS 6 & 9.

THE PURPOSE OF THIS BILATERAL MOD IS TO EXTEND THE POP, CHANGE ALTERNATE TOCORS, AND ADD FUNDS. THE CONTRACTOR PROVIDES TA FOR DATA AND RECORDS MANAGEMENT RELATED TO THE NAVAJO AUM PROGRAM. THIS IS MOD P00002, TASK ORDER 6 FOR THE RAES 2 CONTRACT, #6

THE PURPOSE OF THIS BILATERAL MOD IS TO INCORPORATE A REVISED SOW AND KTR WORK PLAN, INCREASE THE LOE FOR A FEW TASKS, AND ADD A NEW ALTERNATE TOCOR. THIS IS MOD P00005 FOR TO 15 THAT PROVIDES SUPPORT FOR NAUM PROGRAM TO DEVELOP PROGRAM STANDARDS UND

THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO ADD TASKS 7 AND 8, WHICH WILL ADD SCOPE AND FUNDING TO COMPLETE THE DATA GAPS INVESTIGATION FIELD WORK AND THE EE/CA. TO IS FOR TIME-CRITICAL REMOVAL ACTION (TCRA) PLANNING AND OVERSIGHT SUPPORT ASSOCI

TO 29 IS TO TO PROVIDE TECHNICAL ASSISTANCE FOR OVERSIGHT OF THE POTENTIALLY RESPONSIBLE PARTY (PRP) BNSF RAILWAY COMPANY (BNSF) AS THEY PERFORM A BACKGROUND STUDY, DATA GAPS ANALYSIS AND ENGINEERING EVALUATIONS/COST ANALYSES (EE/CA).

THE PURPOSE OF THIS TASK ORDER IS ESTABLISH A TASK ORDER 27 TO PROVIDE TECHNICAL SUPPORT TO REGION 6 FOR OVERSIGHT OF AN ONGOING PRP RI/FS AND GOVERNMENT RI/FS AT THE HOMESTAKE MINING COMPANY UNDER THE RAES 2 CONTRACT.

THE PURPOSE OF THIS BILATERAL MOD IS TO ADD SCOPE AND FUNDING. THE CONTRACTOR SHALL PROVIDE THE SUPPORT NEEDED FOR INTERIM ACTIONS AT TRONOX AUMS UNDER THE RAES II CONTRACT #68HE0923D0002 FOR EPA FOR REGIONS 6 AND 9. MOD P00005.

MODIFICATION REQUEST FOR EQUITABLE ADJUSTMENT 2

THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO ADD SCOPE AND FUNDING TO TO 16 UNDER RAES 2 CONTRACT #68HE0923D0002.

THE PURPOSE OF THIS UNILATERAL MOD IS TO ADD INCREMENTAL FUNDING. CONTRACTOR SHALL PROVIDE TECHNICAL DESIGN SERVICES FOR PLANNING & CONDUCTING CLEANUP VERIFICATION UNDER THE RAES 2 CONTRACT #68HE0923D0002 FOR REGIONS 6 & 9.

ENVIRONMENTAL ASSESSMENT REPLACEMENT OF THE AIR ROUTE SURVEILLANCE RADAR (ARSR) ON MT. KA`ALA, OAHU, HAWAII

THE CONTRACTOR SHALL PERFORM OVERSITE AND TECHNICAL REVIEW FOR REMOVAL SITE EVALUATIONS (RSE) AND RISK ASSESSMENT DOCUMENTS FOR WELLS CARGO ABANDONED URANIUM MINES (AUMS) UNDER THE RAES 2 CONTRACT 68HE0923D0002.

THE PURPOSE OF THIS BILATERAL MOD IS TO ADD SCOPE AND FUNDING TO CONDUCT EE/CAS IN NAVAJO NATION'S NORTHERN AGENCY. THIS IS A MOD 3 FOR TO 07 UNDER RAES 2 CONTRACT #68HE0923D0002.

THE PURPOSE OF THIS UNILATERAL MOD IS TO ADD SCOPE AND DOGE APPROVED FUNDING. THE CONTRACTOR SHALL PROVIDE EVALUATIONS FOR KNOWN 278 UNFUNDED AUMS ON THE NAVAJO NATION UNDER RAES II FOR EPA FOR REGIONS 6 & 9.

THE PURPOSE OF THIS BILATERAL MOD ADDS SCOPE, FUNDING, AND TWO (2) OPTION YEARS. THE CONTRACTOR WILL ASSIST EPA IN COMMUNITY INVOLVEMENT OUTREACH SUPPORT INCLUDING CALLS, REMOTE MEETINGS AND FACE TO FACE ASSEMBLIES UNDER THE RAES 2 CONTRACT #68HE0092

THE PURPOSE OF THIS UNILATERAL MOD IS TO ADD INCREMENTAL FUNDING. THE CONTRACTOR SHALL PROVIDE TECH ASSIST, FOR OVERSIGHT OF PRP AS THEY PERFORM AN EE/CA FOR THE MAC & BLACKJACK MINES FOR CONTRACT 68HE0923D0002, THE (RAES)II FOR EPA FOR RGNS 6 AN

REA MODIFICATION

THE PURPOSE OF THIS UNILATERAL MOD IS TO ADD INCREMENTAL FUNDING. CONTRACTOR SHALL PROVIDE TECHNICAL DESIGN SERVICES FOR PLANNING & CONDUCTING CLEANUP VERIFICATION UNDER THE RAES 2 CONTRACT #68HE0923D0002 FOR REGIONS 6 & 9.

THE PURPOSE OF THIS BILATERAL MOD IS TO INCREASE LOE AND ADD FUNDING. CONTRACTOR SHALL PROVIDE TECHNICAL DESIGN SERVICES FOR PLANNING & CONDUCTING CLEANUP VERIFICATION UNDER THE RAES 2 CONTRACT #68HE0923D0002 FOR REGIONS 6 & 9.

THE PURPOSE OF BILATERAL MODIFICATION P00004 IS TO ADD LOE AND FUNDING. THE CONTRACTOR SHALL PROVIDE SUPPORT NEEDED FOR NTCRA PLANNING AND OVERSIGHT ON BABBITT RANCHES UNDER RAES 2 CONTRACT #68HE0923D0002.

THE PURPOSE OF MODIFICATION P00002 EXERCISE OPTION 0003, ADD FUNDING, AND CHANGE THE TOCOR FOR THE RSE AT THE SKYLINE AUM UNDER THE RAES II CONTRACT FOR EPA FOR REGIONS 6 & 9.

THE PURPOSE OF THIS UNLITERAL MOD IS TO INCORPORATE A REVISED SOW AND KTR WORK PLAN. THIS IS MOD P00004 FOR TO 15 THAT PROVIDES SPT FOR NAUM PROGRAM TO DEVELOP PROGRAM STANDARDS UNDER THE RAES 2 CONTRACT #68HE0923D0002.

THE PURPOSE OF THIS BILATERAL MOD IS TO INCORPORATE REVISED SOW, EXTEND THE POP, AND CHANGE THE TOCORS. THE CONTRACTOR SUPPORTS AGENCY OVERSITE OF RSES,, INTERIM RAS, WATER STUDIES, EE/CAS, AND RAS AUMS IN THE PHASE 2 EXPANDED TRUST AGREEMENT UNDER T

THE PURPOSE OF THIS MODIFICATION IS TO INCORPORATE CHANGES PER THE REVISED SOW AND TETRA TECH WP/CE. THE CONTRACTOR SHALL PROVIDE THE SUPPORT NEEDED FOR INTERIM ACTIONS AT TRONOX AUMS UNDER THE RAES II CONTRACT #68HE0923D0002 FOR EPA FOR REGIONS 6 AN

THE PURPOSE OF THIS BILATERAL MOD IS TO EXTEND THE POP, CHANGE TOCORS, AND ADD FUNDS, AND SCOPE. THE CONTRACTOR PROVIDES TA FOR DATA AND RECORDS MANAGEMENT RELATED TO THE NAVAJO AUM PROGRAM. THIS IS MOD P00001, TASK ORDER 6 FOR THE RAES 2 CONTRACT, #

THE CONTRACTOR SHALL PROVIDE SUPPORT REQUIRED FOR AGENCY OVERSIGHT OF THE UNITED NUCLEAR CORPORATION/GENERAL ELECTRIC (UNC/GE) WORK AT THE NORTHEAST CHURCH ROCK (NECR) MINE SITE UNDER RAES 2 CONTRACT.

THE PURPOSE OF THIS BILATERAL MOD IS TO INCORPORATE CHANGES INTO THE SOW AND ADD FUNDING. THE CONTRACTOR SHALL PROVIDE SUPPORT NEEDED FOR NTCRA PLANNING AND OVERSIGHT ON BABBITT RANCHES UNDER RAES 2 CONTRACT #68HE0923D0002.

THE CONTRACTOR SHALL PROVIDE TECHNICAL ASSISTANCE TO USEPA FOR TECHNICAL ASSISTANCE TO THE CONTAMINATED STRUCTURES PROGRAM UNDER THE RAES 2 CONTRACT.

THE CONTRACTOR SHALL PERFORM REQUIRED TO CONDUCT EE/CAS IN NAVAJO NATION'S NORTHERN AGENCY. THIS IS A MOD P00001 FOR TO 07 UNDER RAES 2 CONTRACT #68HE0923D0002.

THE PURPOSE OF THIS UNILATERAL MODIFICATION IS TO DE-OBLIGATE UNLIQUIDATED FUNDS. THIS WILL BE MODIFICATION P00006 FOR TO# 28 (68HE0920F105) UNDER CONTRACT #EPS91703 (RAES).

THE PURPOSE OF THIS UNILATERAL MOD IS TO DEOBLIGATE UNLIQUIDATED FUNDS. THIS WILL BE MOD P00007 FOR TO #00027(68HE0920F0071) UNDER CONTRACT #EPS91703-RAES.

THE PURPOSE OF THIS UNILATERAL MODIFICATION IS TO DE-OBLIGATE UNLIQUIDATED FUNDS. THIS IS MOD P00007 FOR RAES CONTRACT EPS91703, TASK ORDER 34.

THE PURPOSE OF THIS UNILATERAL MOD IS TO DE-OBLIGATE UNLIQUIDATED FUNDS. THIS IS MOD P00003 FOR TASK ORDER 68HE0922F0051 (TO 35). TO IS FOR RA AT THE OLD CHURCH ROCK MINE SITE IN THE NAVAJO NATION, NEW MEXICO.

THE PURPOSE OF THIS UNILATERAL MOD IS TO DE-OBLIGATE UNLIQUIDATED FUNDS. THIS TO IS FOR THE REMOVAL SITE EVALUATIONS (RSE) AT THE SKYLINE MINE, UT.

THE PURPOSE OF THIS UNILATERAL MOD IS TO DEOBLIGATE UNLIQUIDATED FUNDS. THIS WILL BE MOD P00005 FOR TO #00027(68HE0920F0071) UNDER CONTRACT #EPS91703-RAES.

THE PURPOSE OF THIS BILATERAL MOD CHANGES THE PRIMARY TOCOR AND ADDS A NEW ALTERNATE TOCOR. IT ALSO ADDS FUNDS. THE CONTRACTOR WILL ASSIST EPA IN COMMUNITY INVOLVEMENT OUTREACH SUPPORT INCLUDING CALLS, REMOTE MEETINGS AND FACE TO FACE ASSEMBLIES UNDE

THE PURPOSE OF THIS UNILATERAL MODIFICATION IS TO DE-OBLIGATE UNLIQUIDATED FUNDS.CONTRACTOR SHALL PROVIDE TECHNICAL SUPPORT FOR THE NAVAJO CONTAMINATED STRUCTURES PROGRAM (CSP). THIS IS MOD P00010 OF THIS TASK ORDER UNDER CONTRACT EP-S9-17-03.

THE PURPOSE OF THIS UNLITERAL MODIFICATION IS TO CHANGE THE COR. THIS WILL BE MODIFICATION P00009 FOR TASK ORDER 0003 UNDER CONTRACT #EP-S9-17-03 (RAES).

THE PURPOSE OF THIS UNILATERAL MOD IS TO DEOBLIGATE UNLIQUIDATED FUNDS. TO PROVIDED TECHNICAL SERVICES FOR NAUM DATA SUPPORT. RAES TO #26 (DO #68HE0920F0027) - MOD P00011.

THE PURPOSE OF THIS UNILATERAL MOD IS TO DE-OBLIGATE UNLIQUIDATED FUNDS. THIS WILL BE MOD P00004 FOR TASK ORDER 00029(68HE0920F0106) UNDER CONTRACT #EPS91703 (RAES).

THE PURPOSE OF THIS UNILATERAL MOD IS TO DE-OBLIGATE UNLIQUIDATED FUNDS. THIS IS MODIFICATION #P00022 TO TASK ORDER #16(68HE0919F0017) UNDER THE RAES CONTRACT #EPS91703.

THE PURPOSE OF THIS UNILATERAL MOD IS TO DEOBLIGATE UNLIQUIDATED FUNDS. THIS WILL BE MOD P00005 FOR TO #00027(68HE0920F0071) UNDER CONTRACT #EPS91703-RAES.