ACQUISITION AND INTEGRATION EXPENSES - 19,

Unaudited Investors Report 2015 2016 2017 2018 ($ in Thousands, Except Per Share Data) Total Total 1st Qtr 2nd Qtr 6 mos 3rd Qtr 9 mos 4th Qtr Total 1st Qtr 2nd Qtr 6 mos 3rd Qtr 9 mos 4th Qtr Total REVENUE 2,299,321 2,583,469 668,851 663,781 1,332,632 685,539 2,018,171 735,188 2,753,360 759,749 700,261 1,460,010 764,795 2,224,805 739,343 2,964,148 REVENUE, NET OF SUBCONTRACTOR COSTS ["Net Revenue" (1)] 1,718,715 1,929,205 489,551 511,954 1,001,505 498,478 1,499,983 534,027 2,034,010 544,847 532,793 1,077,640 570,352 1,647,992 552,742 2,200,734 Government Services Group (GSG) 763,023 951,030 257,159 261,359 518,518 266,114 784,632 282,527 1,067,158 309,966 290,565 600,531 301,019 901,550 310,784 1,212,334 Commercial / International Services Group (CIG) (6) 932,417 960,908 230,597 254,299 484,896 231,462 716,357 250,580 966,938 233,729 241,860 475,589 267,854 743,443 252,885 996,328 ONGOING NET REVENUE (2) 1,695,440 1,911,938 487,756 515,658 1,003,414 497,576 1,500,989 533,107 2,034,096 543,695 532,425 1,076,120 568,873 1,644,993 563,669 2,208,662 Remediation and Construction Management (RCM) / Claim 23,275 17,267 1,795 (3,704) (1,909) 902 (1,006) 919 (86) 1,152 368 1,520 1,479 2,999 (10,927) (7,928) OTHER COSTS OF REVENUE 1,402,925 1,598,994 408,190 430,952 839,141 408,228 1,247,369 433,003 1,680,372 450,702 441,367 892,069 460,758 1,352,827 463,448 1,816,276 SELLING, GENERAL AND ADMINISTRATIVE EXPENSES 170,455 171,985 41,506 45,195 86,702 44,366 131,068 46,152 177,219 45,556 46,792 92,348 50,472 142,820 42,366 185,185 ACQUISITION AND INTEGRATION EXPENSES - 19,548 - - - - - - - - - - - - - - PURCHASE ACCOUNTING AND NON-CORE DIVESTITURES (57,650) (2,823) - 7,149 7,149-7,149 (225) 6,923 - (1,918) (1,918) (3,626) (5,544) (3,643) (9,187) INCOME FROM OPERATIONS, AS REPORTED 87,685 135,855 39,855 42,956 82,811 45,884 128,695 54,647 183,342 48,589 42,716 91,305 55,496 146,801 43,285 190,086 ONGOING INCOME FROM OPERATIONS (1) (2) (3) 153,949 170,060 42,897 44,273 87,170 47,135 134,305 56,825 191,131 49,747 45,123 94,870 59,607 154,477 61,826 216,303 GSG 87,029 101,595 30,168 33,432 63,601 32,047 95,647 42,552 138,199 39,125 34,177 73,302 44,372 117,674 50,537 168,211 CIG (6) 99,472 106,603 21,544 18,459 40,003 24,082 64,085 26,732 90,817 21,294 18,399 39,693 27,892 67,585 19,323 86,908 Corporate (4) (32,552) (38,138) (8,815) (7,618) (16,434) (8,994) (25,427) (12,459) (37,885) (10,672) (7,453) (18,125) (12,657) (30,782) (8,034) (38,816) RCM / Claim (8,614) (11,834) (3,042) (8,466) (11,508) (1,251) (12,759) (1,953) (14,712) (1,158) (489) (1,647) (485) (2,132) (14,898) (17,030) ONGOING OPERATING MARGIN [% of Net Revenue] (1) (2) (3) 9.1% 8.9% 8.8% 8.6% 8.7% 9.5% 8.9% 10.7% 9.4% 9.1% 8.5% 8.8% 10.5% 9.4% 11.0% 9.8% GSG 11.4% 10.7% 11.7% 12.8% 12.3% 12.0% 12.2% 15.1% 13.0% 12.6% 11.8% 12.2% 14.7% 13.1% 16.3% 13.9% CIG (6) 10.7% 11.1% 9.3% 7.3% 8.2% 10.4% 8.9% 10.7% 9.4% 9.1% 7.6% 8.3% 10.4% 9.1% 7.6% 8.7% Interest Expense 7,363 11,389 2,908 3,099 6,007 2,795 8,802 2,779 11,581 3,160 4,092 7,252 4,345 11,597 3,927 15,524 INCOME BEFORE INCOME TAX EXPENSE (BENEFIT) 80,322 124,466 36,947 39,857 76,804 43,089 119,893 51,868 171,761 45,429 38,624 84,053 51,150 135,203 39,358 174,562 Income Tax Expense (Benefit) 41,093 40,613 10,358 12,990 23,348 13,114 36,462 17,381 53,844 (623) 9,877 9,254 17,806 27,060 10,545 37,605 NET INCOME ATTRIBUTABLE TO TETRA TECH 39,075 83,783 26,562 26,862 53,424 29,983 83,407 34,467 117,874 46,034 28,725 74,760 33,323 108,082 28,802 136,883 DILUTED AVERAGE SHARES 61,532 58,966 58,145 58,270 58,194 58,161 58,116 57,326 57,913 56,875 56,673 56,825 56,390 56,681 56,349 56,598 DILUTED EPS ATTRIBUTABLE TO TETRA TECH, AS REPORTED $ 0.64 $ 1.42 $ 0.46 $ 0.46 $ 0.92 $ 0.52 $ 1.44 $ 0.60 $ 2.04 $ 0.81 $ 0.51 $ 1.32 $ 0.59 $ 1.91 $ 0.51 $ 2.42 ONGOING DILUTED EPS (1) (2) (3) (5) $ 1.61 $ 1.88 $ 0.49 $ 0.48 $ 0.97 $ 0.53 $ 1.50 $ 0.63 $ 2.13 - $ 0.65 $ 0.54 $ 1.18 $ 0.71 $ 1.89 $ 0.75 $ 2.64 ONGOING EBITDA (1) (2) (3) 195,309 214,088 53,906 55,434 109,340 57,971 167,311 67,708 235,019 59,450 55,190 114,640 69,634 184,274 69,602 253,876 ONGOING EBITDA MARGIN [% of Net Revenue] 11.5% 11.2% 11.1% 10.8% 10.9% 11.7% 11.1% 12.7% 11.6% 10.9% 10.4% 10.7% 12.2% 11.2% 12.3% 11.5% DAYS IN SALES OUTSTANDING 85.3 84.2 86.8 82.3 82.3 80.4 80.4 83.1 83.1 85.4 92.4 92.4 81.3 81.3 85.4 85.4 CASH FLOW FROM OPERATIONS 162,848 142,020 (58,747) 109,111 50,364 21,209 71,573 66,419 137,992 (66,493) 81,267 14,774 52,673 67,447 109,415 176,862 CAPITAL EXPENDITURES 24,296 11,945 2,031 1,865 3,896 3,122 7,018 2,723 9,741 2,143 2,422 4,565 1,781 6,346 3,379 9,726 Y/Y ONGOING NET REVENUE GROWTH % (1) (2) (4.8%) 12.8% 17.9% 8.4% 12.8% 0.3% 8.3% 1.3% 6.4% 11.5% 3.3% 7.2% 14.3% 9.6% 5.7% 8.6% GSG (4.5%) 24.6% 32.4% 22.0% 26.9% 1.7% 17.1% 0.5% 12.2% 20.5% 11.2% 15.8% 13.1% 14.9% 10.0% 13.6% CIG (5.0%) 3.1% 5.0% (2.8%) 0.8% (1.4%) 0.1% 2.2% 0.6% 1.4% (4.9%) (1.9%) 15.7% 3.8% 0.9% 3.0% NET REVENUE % BY CLIENT TYPE International 29% 31% 30% 32% 31% 28% 30% 29% 30% 25% 28% 26% 29% 27% 29% 27% U.S. Commercial 32% 30% 27% 27% 27% 29% 28% 27% 27% 28% 28% 28% 28% 28% 26% 28% U.S. Federal Government 27% 27% 30% 29% 30% 30% 30% 30% 30% 29% 30% 30% 29% 30% 30% 30% U.S. State & Local Government 12% 12% 13% 12% 12% 13% 12% 14% 13% 18% 14% 16% 14% 15% 15% 15% NET REVENUE % BY CONTRACT TYPE Fixed-Price 32% 28% 31% 29% 30% 34% 31% 33% 32% 31% 34% 32% 35% 33% 35% 34% Time-and-Materials 50% 55% 50% 52% 51% 47% 50% 48% 49% 50% 50% 50% 48% 50% 48% 49% Cost-Plus 18% 17% 19% 19% 19% 19% 19% 19% 19% 19% 16% 18% 17% 17% 17% 17% BACKLOG 1,901,712 2,378,894 2,469,511 2,496,857 2,496,857 2,533,672 2,533,672 2,541,105 2,541,105 2,428,698 2,510,037 2,510,037 2,435,461 2,435,461 2,663,814 2,663,814 (1) Non-GAAP financial measure. For a reconciliation of non-gaap financial measures to the most directly comparable GAAP measures, please visit tetratech.com/investor-presentations.html (2) Ongoing excludes Remediation and Construction Management and non-cash claim settlement (3) Excludes purchase accounting and non-core divestitures, and acquisition and integration expenses (4) Corporate costs not allocable to the segments (e.g., acquisition costs, amortization expense, stock option expense, etc.) (5) Excludes one-time tax benefit (6) Excludes non-cash claim settlement

Regulation G Information September 30, 2018 Reconciliation of Revenue to Revenue, Net of Subcontractor Costs ("Net Revenue") (in millions) 2017 2018 2015 2016 1st Qtr 2nd Qtr 6 mos 3rd Qtr 9 mos 4th Qtr Total 1st Qtr 2nd Qtr 6 mos 3rd Qtr 9 mos 4th Qtr Total Consolidated (as reported) Revenue 2,299.3 2,583.5 668.9 663.8 1,332.6 685.5 2,018.2 735.2 2,753.4 759.7 700.3 1,460.0 764.8 2,224.8 739.3 2,964.1 Subcontractor Costs (580.6) (654.3) (179.3) (151.8) (331.1) (187.0) (518.2) (201.2) (719.4) (214.9) (167.5) (382.4) (194.4) (576.8) (186.6) (763.4) Net Revenue 1,718.7 1,929.2 489.6 512.0 1,001.5 498.5 1,500.0 534.0 2,034.0 544.8 532.8 1,077.6 570.4 1,648.0 552.7 2,200.7 GSG Segment Revenue 1,011.9 1,289.5 362.9 357.1 720.0 379.3 1,099.3 388.3 1,487.6 442.8 406.0 848.8 423.9 1,272.7 422.2 1,694.9 Subcontractor Costs (248.9) (338.5) (105.7) (95.7) (201.5) (113.2) (314.7) (105.8) (420.4) (132.8) (115.5) (248.3) (122.9) (371.2) (111.4) (482.6) Net Revenue 763.0 951.0 257.2 261.4 518.5 266.1 784.6 282.5 1,067.2 310.0 290.5 600.5 301.0 901.5 310.8 1,212.3 CIG Segment Revenue 1,262.1 1,297.2 318.1 329.1 647.2 318.2 965.4 360.6 1,326.0 331.5 309.7 641.2 352.6 993.8 329.3 1,323.1 Subcontractor Costs (329.7) (336.3) (87.5) (74.8) (162.3) (86.7) (249.0) (110.0) (359.1) (97.8) (67.8) (165.6) (84.8) (250.4) (87.0) (337.4) Non-Cash Claim Settlement - - - - - - - - - - - - - - 10.6 10.6 Net Revenue 932.4 960.9 230.6 254.3 484.9 231.5 716.4 250.6 966.9 233.7 241.9 475.6 267.8 743.4 252.9 996.3 Ongoing Operations Revenue 2,212.7 2,531.3 660.7 663.8 1,324.4 681.3 2,005.8 729.4 2,735.2 752.9 698.8 1,451.7 761.5 2,213.2 747.3 2,960.5 Subcontractor Costs (517.3) (619.4) (172.9) (148.1) (321.0) (183.7) (504.8) (196.3) (701.1) (209.2) (166.5) (375.6) (192.5) (568.2) (183.6) (751.8) Net Revenue 1,695.4 1,911.9 487.8 515.7 1,003.4 497.6 1,501.0 533.1 2,034.1 543.7 532.3 1,076.1 569.0 1,645.0 563.7 2,208.7 RCM / Claim Revenue 86.6 52.2 8.2-8.2 4.2 12.4 5.8 18.2 6.8 1.5 8.3 3.3 11.6 2.6 14.2 Subcontractor Costs (63.3) (34.9) (6.4) (3.7) (10.1) (3.3) (13.4) (4.9) (18.3) (5.7) (1.0) (6.8) (1.9) (8.6) (2.9) (11.6) Non-Cash Claim Settlement - - - - - - - - - - - - - - (10.6) (10.6) Net Revenue 23.3 17.3 1.8 (3.7) (1.9) 0.9 (1.0) 0.9 (0.1) 1.1 0.5 1.5 1.4 3.0 (10.9) (8.0) Reconciliation of Net Income Attributable to Tetra Tech to EBITDA (in thousands) 2017 2018 2015 2016 1st Qtr 2nd Qtr 6 mos 3rd Qtr 9 mos 4th Qtr Total 1st Qtr 2nd Qtr 6 mos 3rd Qtr 9 mos 4th Qtr Total Net Income Attributable to Tetra Tech 39,075 83,783 26,562 26,862 53,424 29,983 83,407 34,467 117,874 46,034 28,725 74,760 33,322 108,082 28,802 136,883 Interest Expense 1 7,363 11,389 2,908 3,099 6,007 2,795 8,802 2,779 11,581 3,160 4,092 7,252 4,345 11,597 3,927 15,524 Depreciation 2 23,110 22,756 5,251 5,764 11,015 5,345 16,360 5,848 22,207 5,169 5,101 10,270 4,864 15,134 4,458 19,592 Amortization 2 20,205 22,078 5,940 5,898 11,838 5,607 17,445 5,342 22,786 4,625 5,038 9,662 5,226 14,888 3,360 18,249 Contingent Consideration (3,113) 2,823 - (7,149) (7,149) - (7,149) 225 (6,923) - 1,918 1,918 192 2,110 2,142 4,252 Goodwill and other IA Impairment 60,763 - - - - - - - - - - - - - - - Income Tax Expense (Benefit) 41,093 40,613 10,358 12,990 23,348 13,114 36,462 17,381 53,844 (623) 9,877 9,254 17,806 27,060 10,545 37,605 Acquisition Expenses - 7,925 - - - - - - - - - - - - - - Integration Expenses - 11,623 - - - - - - - - - - - - - - EBITDA 188,496 202,990 51,019 47,464 98,483 56,844 155,327 66,042 221,369 58,365 54,751 113,116 65,755 178,871 53,234 232,105 Non-core divestitures - - - - - - - - - - - - 3,434 3,434-3,434 Non-cash claim adjustment - - - - - - - - - - - - - - 12,457 12,457 Contingent Consideration - Compensation - - - - - - - - - - - - - - 1,501 1,501 RCM 6,813 11,098 2,887 7,970 10,857 1,127 11,984 1,666 13,650 1,085 439 1,524 445 1,969 2,410 4,379 Ongoing EBITDA 195,309 214,088 53,906 55,434 109,340 57,971 167,311 67,708 235,019 59,450 55,190 114,640 69,634 184,274 69,602 253,876 1 Includes amortization of deferred financing fee 2 Varies slightly from the Statements of Cash Flows, which includes amortization of deferred financing fee

Consolidated Balance Sheets (unaudited - in thousands, except par value) September 30, 2018 October 1, 2017 Assets Current assets: Cash and cash equivalents $ 146,185 $ 189,975 Accounts receivable - net 837,103 788,767 Prepaid expenses and other current assets 56,003 49,969 Income taxes receivable 3,282 13,312 Total current assets 1,042,573 1,042,023 Property and equipment - net 43,278 56,835 Investments in unconsolidated joint ventures 3,370 2,700 Goodwill 798,820 740,886 Intangible assets - net 16,123 26,688 Deferred tax assets 6,440 1,763 Other long-term assets 38,843 31,850 Total assets $ 1,949,447 $ 1,902,745 Liabilities and Equity Current liabilities: Accounts payable $ 160,222 $ 177,638 Accrued compensation 180,153 143,408 Billings in excess of costs on uncompleted contracts 143,270 117,499 Current portion of long-term debt 12,599 15,588 Current contingent earn-out liabilities 13,633 2,024 Other current liabilities 100,409 81,511 Total current liabilities 610,286 537,668 Deferred tax liabilities 27,999 43,781 Long-term debt 264,712 341,283 Long-term contingent earn-out liabilities 21,657 414 Other long-term liabilities 57,693 50,975 Commitments and contingencies Equity: Preferred stock - authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at September 30, 2018 and October 1, 2017 - - Common stock - authorized, 150,000 shares of $0.01 par value; issued and outstanding, 55,349 and 55,873 shares at September 30, 2018 and October 1, 2017, respectively 553 559 Additional paid-in capital 148,803 193,835 Accumulated other comprehensive loss (127,350) (98,500) Retained earnings 944,965 832,559 Tetra Tech stockholders' equity 966,971 928,453 Noncontrolling interests 129 171 Total stockholders' equity 967,100 928,624 Total liabilities and stockholders' equity $ 1,949,447 $ 1,902,745

Consolidated Statements of Income (unaudited - in thousands, except per share data) Three Months Ended Fiscal Year Ended September 30, October 1, September 30, October 1, 2018 2017 2018 2017 Revenue $ 739,343 $ 735,188 $ 2,964,148 $ 2,753,360 Subcontractor costs (186,601) (201,161) (763,414) (719,350) Other costs of revenue (463,448) (433,003) (1,816,276) (1,680,372) Gross profit 89,294 101,024 384,458 353,638 Selling, general and administrative expenses (43,867) (46,152) (190,120) (177,219) Contingent consideration - fair value adjustments (2,142) (225) (4,252) 6,923 Income from operations 43,285 54,647 190,086 183,342 Interest expense (3,927) (2,779) (15,524) (11,581) Income before income tax expense 39,358 51,868 174,562 171,761 Income tax expense (10,545) (17,381) (37,605) (53,844) Net income 28,813 34,487 136,957 117,917 Net income attributable to noncontrolling interests (11) (20) (74) (43) Net income attributable to Tetra Tech $ 28,802 $ 34,467 $ 136,883 $ 117,874 Earnings per share attributable to Tetra Tech: Basic $ 0.52 $ 0.61 $ 2.46 $ 2.07 Diluted $ 0.51 $ 0.60 $ 2.42 $ 2.04 Weighted-average common shares outstanding: Basic 55,341 56,338 55,670 56,911 Diluted 56,349 57,326 56,598 57,913 Cash dividends paid per share $ 0.12 $ 0.10 $ 0.44 $ 0.38

Consolidated Statements of Cash Flows (unaudited - in thousands) Fiscal Year Ended September 30, October 1, 2018 2017 Cash flows from operating activities: Net Income $ 136,957 $ 117,917 Adjustments to reconcile net income to net cash provided by operating activities: Depreciation and amortization 38,636 45,756 Equity in income of unconsolidated joint ventures, net of distributions (568) (647) Non-cash stock compensation 19,582 13,450 Deferred income taxes (16,425) (9,957) Provision for doubtful accounts 7,167 2,847 Fair value adjustments to contingent consideration 4,252 (6,923) Loss (gain) on sale of assets and divested business 1,045 (103) Changes in operating assets and liabilities, net of effects of business acquisitions and divestitures: Accounts receivable (46,273) (64,781) Prepaid expenses and other assets (12,638) (8,317) Accounts payable (16,032) 18,597 Accrued compensation 27,492 13,413 Billings in excess of costs on uncompleted contracts 15,228 28,298 Other liabilities 16,127 2,167 Income taxes receivable/payable 4,661 (13,725) Cash settled contingent earn-out liability (2,349) - Net cash provided by operating activities 176,862 137,992 Cash flows from investing activities: Capital expenditures (9,726) (9,741) Payments for business acquisitions, net of cash acquired (68,256) (8,039) Investments in unconsolidated joint ventures - (85) Proceeds from sale of assets and divested business, net 35,348 905 Net cash used in investing activities (42,634) (16,960) Cash flows from financing activities: Payments on long-term debt (485,946) (233,889) Proceeds from borrowings 401,965 243,553 Payments of contingent earn-out liabilities (1,412) (1,319) Debt pre-payment costs (1,737) - Repurchases of common stock (75,000) (100,000) Net proceeds from issuance of common stock 13,520 18,555 Dividends paid (24,477) (21,672) Net cash used in financing activities (173,087) (94,772) Effect of exchange rate changes on cash (4,931) 3,256 Net increase (decrease) in cash and cash equivalents (43,790) 29,516 Cash and cash equivalents at beginning of period 189,975 160,459 Cash and cash equivalents at end of period $ 146,185 $ 189,975 Supplemental information: Cash paid during the period for: Interest $ 15,570 $ 11,504 Income taxes, net of refunds received of $2.5 million and $2.1 million $ 49,842 $ 72,578