Our Environmental Services segment outperformed our expectations, driven by a combination of factors, including the level of high-value waste in our disposal network, greater-than-expected COVID decontamination work and ongoing cost controls.
Adjusted EBITDA in Q4 increased to $136.1 million, which included $5.6 million in benefits from government programs, primarily from Canada.
For the full year, adjusted EBITDA grew by 3% to $555.3 million, with annual margins growing to 17.7%.
We generated record adjusted free cash flow of $265 million, a noteworthy accomplishment considering the economic disruption caused by the pandemic.
Typically, Q4 is a seasonally weaker quarter for us, but the $18 million increase from Q3 is evidence that many of our markets are on the road to recovery.
Adjusted EBITDA grew by 13% from a year ago, with margins up nearly 400 basis points.
This was driven by a combination of business mix, cost savings and $3.9 million in benefits from government assistance programs in Q4.
Revenue from our COVID-19 decon work totaled $31 million in Q4.
For the full year, our team completed nearly 14,000 responses and was an essential resourcing and protecting our customers' people and facilities.
This resulted in an average price per pound increase of 16% from the year earlier period when we saw more bulk streams.
Incineration utilization in the quarter was 84% due to a higher-than-expected number of maintenance days.
Landfill volumes were down 37% in the quarter as the lack of remediation and waste projects opportunities intensified with the resurgence of the pandemic.
However, our strong base landfill business largely offset that decline with a 42% increase in our average price per ton.
Safety-Kleen revenue was down 15% from a year ago, but was flat sequentially as the ongoing recovery offset normal year-end seasonality.
Safety-Kleen's adjusted EBITDA declined 21%, mostly due to the lower revenue and business mix.
This decline was partly offset by our cost reductions initiatives as well as the government assistance programs that provided $1.4 million of benefits in Q4.
Waste oil collections were 49 -- no, excuse me, were 49 million gallons in Q4 with a healthy average charge for oil, given the lack of available outlets for generators.
We expect Field Services to generate $25 million to $35 million of COVID-related revenues in 2021.
The document highlights the integral role that sustainability plays in our business decisions as well as our environmental, social and government goals and benchmarks for 2030.
Revenue declined 9% year-over-year, but was up in the third quarter despite Q4 typically being a sequentially lower quarter due to seasonality.
Our efforts to control costs and grow our highest margin businesses, combined with some further government program assistance, resulted in 180 basis point improvement in gross margin.
Adjusted EBITDA grew 3% to $136.1 million.
Our Q4 adjusted EBITDA margin rising 190 basis points from last year speaks to the effectiveness of the actions we have taken this year.
We have improved our adjusted EBITDA margins on a year-over-year basis for 12 consecutive quarters.
For the full year, our adjusted EBITDA margins grew 17.7% -- grew to 17.7%.
If you excluded the $42.3 million of government assistance, those margins would have been 16.3% or a 50 basis point improvement from 2019.
For the full year, SG&A as a percentage of revenue was 14.3%, which beat our target of 14.5%.
Depreciation and amortization in Q4 was down to $71.4 million.
For the full year, our depreciation and amortization was $292.9 million, which was within our expected range.
For 2021, we expect depreciation and amortization in the range of $280 million to $290 million.
Income from operations in Q4 increased by 18%, reflecting a higher gross profit, cost controls and mix of revenue.
For the full year, our income from operations rose 10% to $251.3 million.
Cash and short-term marketable securities at December 31 were $571 million, up nearly $40 million from the end of Q3.
Our debt was at $1.56 billion at year-end, with leverage on a net debt basis at 1.8 times, our lowest level in a decade.
Our weighted average cost of debt is 4.2%, with a healthy mix -- healthy blend of fixed and variable debt.
Cash from operations in Q4 was $113.2 million.
capex, net of disposals, was up slightly to $43.6 million.
That combination resulted in adjusted free cash flow in Q4 of $69.6 million.
For the year, we hit our net capex target, excluding the purchase of our headquarters, with $165.6 million of spend.
That helped us deliver record annual adjusted free cash flow of $265 million, which is toward the high end of our guidance range.
For 2021, we expect net capex in the range of $185 million to $205 million, which is higher than prior year.
During the quarter, we increased the level of our share repurchases as we bought back 500,000 shares at an average price just under $71 for a total buyback of $35 million.
In 2020, we repurchased slightly over 1.2 million shares of our authorized $600 million share repurchase program, we have just under $210 million remaining.
Based on our 2020 results and current market conditions, we expect 2021 adjusted EBITDA in the range of $545 million to $585 million.
That amount in 2021 should be about $16 million to $18 million compared with $18.5 million in 2020.
Looking at our guidance from a quarterly perspective, we expect Q1 adjusted EBITDA using our revised definition to be 5% to 10% below prior year levels given the record Q1 results we posted in 2020 prior to the pandemic taking hold and the deep freeze we are experiencing in the Midwest and the Gulf here in February.
We expect to benefit from growth and profitability within incineration, a rebound in the majority of our service businesses, along with our comprehensive cost measures, but not enough to fully offset the decline in high-margin decontamination work as well as the large contribution from government assistance programs in 2020 that totaled $27.1 million in this segment.
Despite the fact this segment received $12.2 million in government assistance last year.
In our Corporate segment, we expect negative adjusted EBITDA to be flat with 2020, which includes $3 million of governance assistance.
For 2021, our EBITDA guidance assumes receiving $2 million to $3 million of Canadian government assistance.
Based on our EBITDA guidance and working capital assumptions, we now expect 2021 adjusted free cash flow in the range of $215 million to $255 million.
The Chemical Activity Barometer, published by the American Chemistry Council, show that industry levels have been climbing sequentially from May to January, and January was the first time in 10 months that the activity levels were above the prior year, which is a great sign for us.

Summary:
Our Environmental Services segment outperformed our expectations, driven by a combination of factors, including the level of high-value waste in our disposal network, greater-than-expected COVID decontamination work and ongoing cost controls.
Based on our 2020 results and current market conditions, we expect 2021 adjusted EBITDA in the range of $545 million to $585 million.