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The PSUs awarded cliff-vest after a 3-year performance period.  The Performance Period was the Company's fiscal years 2015, 2016 and 2017.  The number of PSUs earned by the Awardee for the Performance Period was determined at the end of the Performance Period by measuring relative total shareholder return (\"TSR\"), with equal weight given to the selected industry peer group and to the S&P 1000.  The TSR peer group performance percentile was 89%, and the TSR S&P 1000 performance percentile was 82%.  Straight line interpolation determined the vesting credit percentage.  Therefore, 189% of the 2,649 PSUs awarded on November 21, 2014 were earned and vested on November 21, 2017."}],"balance_after":41509,"source":{"system":"sec-edgar","filing":"0000831641-17-000095","document":"wf-form4_151138576464162.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/831641/000083164117000095/wf-form4_151138576464162.xml","form_type":"4"}},{"id":4153406,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP, CIO"}}],"security":"COMMON STOCK","published_at":"2017-11-22T21:22:58.000Z","date":"2017-11-21","kind":"grant","acquired":true,"shares":5298,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"Each performance share unit (\"PSU\") represents the right to receive one share of Common Stock.  The PSUs awarded cliff-vest after a 3-year performance period.  The Performance Period was the Company's fiscal years 2015, 2016 and 2017.  The number of PSUs earned by the Awardee was determined at the end of the Performance Period by measuring earnings per share (\"EPS\") growth, which was  35% year-over-year growth.  Therefore, 200% of the 2,649 PSUs awarded on November 21, 2014 were earned and vested on November 21, 2017."}],"balance_after":36503,"source":{"system":"sec-edgar","filing":"0000831641-17-000095","document":"wf-form4_151138576464162.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/831641/000083164117000095/wf-form4_151138576464162.xml","form_type":"4"}},{"id":4155400,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP, CIO"}}],"security":"STOCK OPTION (RIGHT TO BUY)","published_at":"2017-11-21T22:13:23.000Z","date":"2017-11-17","kind":"grant","acquired":true,"shares":5580,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F4","text":"The option becomes exercisable as to 25% of the Shares on each anniversary of the grant date."}],"balance_after":5580,"derivative":{"exercise_price":47.95,"exercise_date":"2018-11-17","expiration_date":"2027-11-17","underlying":"COMMON STOCK","underlying_shares":5580},"source":{"system":"sec-edgar","filing":"0000831641-17-000052","document":"wf-form4_151130238920729.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":4,"url":"https://www.sec.gov/Archives/edgar/data/831641/000083164117000052/wf-form4_151130238920729.xml","form_type":"4"}},{"id":4155399,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP, CIO"}}],"security":"COMMON STOCK","published_at":"2017-11-21T22:13:23.000Z","date":"2017-11-20","kind":"tax_withholding","acquired":false,"shares":268,"price":48.55,"value":13011.4,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F3","text":"268 of the shares underlying restricted stock which vested on 11/20/2017 were withheld to pay the related tax liability."}],"balance_after":31205,"source":{"system":"sec-edgar","filing":"0000831641-17-000052","document":"wf-form4_151130238920729.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":3,"url":"https://www.sec.gov/Archives/edgar/data/831641/000083164117000052/wf-form4_151130238920729.xml","form_type":"4"}},{"id":4155398,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP, CIO"}}],"security":"COMMON STOCK","published_at":"2017-11-21T22:13:23.000Z","date":"2017-11-18","kind":"tax_withholding","acquired":false,"shares":184,"price":47.95,"value":8822.8,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F2","text":"184 of the shares underlying restricted stock which vested on 11/18/2017 were withheld to pay the related tax liability."}],"balance_after":31473,"source":{"system":"sec-edgar","filing":"0000831641-17-000052","document":"wf-form4_151130238920729.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/831641/000083164117000052/wf-form4_151130238920729.xml","form_type":"4"}},{"id":4155397,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP, CIO"}}],"security":"COMMON STOCK","published_at":"2017-11-21T22:13:23.000Z","date":"2017-11-17","kind":"grant","acquired":true,"shares":1720,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"1,720 restricted stock units (RSUs) were awarded to the reporting person on November 17, 2017.  The RSUs become vested as to 25% of the shares on November 18, 2018, and the anniversary of that date going forward until fully vested."}],"balance_after":31657,"source":{"system":"sec-edgar","filing":"0000831641-17-000052","document":"wf-form4_151130238920729.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/831641/000083164117000052/wf-form4_151130238920729.xml","form_type":"4"}},{"id":4329196,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP & CIO"}}],"security":"EMPLOYEE STOCK OPTION (RIGHT TO BUY)","published_at":"2017-05-09T23:12:23.000Z","date":"2017-05-08","kind":"exercise","acquired":false,"shares":16750,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"The option became fully vested on November 12, 2014."}],"balance_after":0,"derivative":{"exercise_price":23.48,"exercise_date":"2014-11-12","expiration_date":"2018-11-12","underlying":"COMMON STOCK","underlying_shares":16750},"source":{"system":"sec-edgar","filing":"0001206709-17-000002","document":"edgar.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":3,"url":"https://www.sec.gov/Archives/edgar/data/831641/000120670917000002/edgar.xml","form_type":"4"}},{"id":4329195,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP & CIO"}}],"security":"COMMON STOCK","published_at":"2017-05-09T23:12:23.000Z","date":"2017-05-08","kind":"sale","acquired":false,"shares":16750,"price":46.5463,"value":779650.525,"ownership":{"direct":true},"footnotes":[{"field":"price","element":"transactionPricePerShare","label":"F3","text":"$46.5463 is a weighted average price.  These shares were sold in multiple transactions at prices ranging from $46.40 to $46.575"}],"balance_after":29937,"source":{"system":"sec-edgar","filing":"0001206709-17-000002","document":"edgar.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/831641/000120670917000002/edgar.xml","form_type":"4"}},{"id":4329194,"issuer":{"id":3570,"kind":"organization","name":"TETRA TECH INC"},"owners":[{"id":122590,"kind":"person","name":"CHRISTENSEN CRAIG L","position":1,"cik":"0001206709","reported_name":"CHRISTENSEN CRAIG L","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"SVP & CIO"}}],"security":"COMMON 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