If you set aside the $38 million of operating EBITDA contribution from ADS and the $60 million fuel tax credit benefit in the fourth quarter of '19 versus 2020, our legacy WM operating EBITDA grew 4% versus Q4 of 2019.
This was our seventh consecutive quarter to generate operating EBITDA of more than $1 billion, showcasing the strength and consistency of our business.
As with the third quarter, our fourth-quarter operating EBITDA margin was impressively strong at 28.1% when you consider that it included 50 basis points of dilution from ADS.
For the full year, 2020 matched our highest annual operating EBITDA margin of 28.4%.
And excluding ADS, we set a new record with 2020 operating EBITDA margin of more than 28.5%.
As a result, we anticipate overall operating EBITDA growth between 10 and 13 and a half percent in 2021.
As expected, legacy Waste Management collection and disposal volumes improved sequentially in the fourth quarter from a decline of 5.5% in the third quarter to a decline of 2.7% in the fourth.
Fourth-quarter MSW volume grew 1.2% and C&D volume, excluding hurricane cleanup, grew 1.8%, both strong indicators of continued economic recovery.
Collection and disposal yield was 2.3% in the fourth quarter, and core price was 3.2%.
Adjusted for the impact of lower volume, core price would have been 3.8%.
Our residential yield improved 60 basis points to 3.7% in the fourth quarter compared to the same period in 2019 and was up again sequentially from 3.5% in the third quarter.
Residential volumes declined 1.4% as we shed business that does not meet our return requirements.
Overall, our actions to improve the residential line of business in 2020 resulted in $40 million of operating EBITDA benefit, and we expect this to carry forward into 2021.
In the post-collection business, fourth quarter landfill core price was 3.3% and transfer station core price was 3.1%, demonstrating our continued pricing discipline in these key lines of business.
Operating costs were 61.5% of revenue in the fourth quarter compared to 60.2% in the fourth quarter of 2019.
In the quarter, as expected, the ADS acquisition increased operating expense as a percentage of revenue by 40 basis points.
Aside from these impacts, operating costs as a percentage of revenue improved 60 basis points, demonstrating that we are laser-focused on cost control and continue to benefit from a lower cost structure.
As an example, commercial yards and industrial halls declined between 5% and 6% during the fourth quarter, yet overtime decreased in the range of 15% to 18%, and we see additional opportunities.
We expect organic revenue growth from yield and volume in the collection and disposal business of between four and four and a half percent and overall revenue growth between 10.75% and 11.25% during 2021.
We expect to achieve between $50 million and $60 million in synergies during 2021.
Combined with the $10 million to $15 million of annualized synergies already achieved in the fourth quarter, our run rate synergies exiting 2021 is expected to be between $60 million and $75 million.
We estimate that our onetime cost to achieve these synergies will be $50 million in 2021.
We expect continued improvement in recycling from our fee-for-service model, improved operating cost structure at new MRFs and stable demand for recycled materials, which, together, provide a tailwind of between $40 million and $50 million to 2021 operating EBITDA.
We also expect an incremental $10 million of year-over-year contribution from our renewable energy business from the sale of RINs as pricing for those credits has increased over the last several months.
Excluding $25 million of SG&A for the ADS business, SG&A improved by $56 million in 2020 to 10.2% of revenue, a 10-basis-point improvement over 2019.
Fourth quarter capital spending was $394 million, and that included $29 million of capital to support [Inaudible] ADS and about $30 million of capital that we intentionally pulled forward given the strong recovery in our operations during the third and fourth quarters.
2020 capital spending was $1.632 billion.
Waste Management generated free cash flow of $2.656 billion in 2020.
After-tax proceeds from the divestitures of ADS and Waste Management businesses to GFL were $691 million.
These proceeds were partially offset by after-tax transaction and advisory costs to support the acquisition of $117 million.
Normalizing for these two items, 2020 free cash flow was $2.082 billion.
This result demonstrates the resilient nature of our business and the strength of capital discipline as we nearly achieved our original 2020 free cash flow guidance of $2.15 billion despite the impact of COVID-19.
Given the strong result, at the end of 2020, we were positioned to forgo relief provided by the CARES Act, and we elected to pay approximately $120 million of payroll taxes that we had planned to defer.
As we repay that amount in 2021 and 2022, as anticipated, 2020 free cash flow, excluding the ADS impact I mentioned, would have been about $2.2 billion for the year, which is better than we expected at the end of the third quarter.
In the fourth quarter, we used our free cash flow to pay $231 million in dividend.
For the full year, we returned $1.33 billion to shareholders, comprised of $927 million in dividends and $402 million in share repurchases.
In November, we issued $2.5 billion of senior notes at an extremely attractive pre-tax weighted average cost of less than one and a half percent.
2021 cash interest savings are expected to be more than $90 million.
Fourth quarter total debt-to-EBITDA of 3.19 times and forecasted leverage ratios are both well within the financial covenants of our revolving credit facilities.
As John mentioned, we anticipate 10.75% to 11.25% revenue growth in the year ahead with solid organic growth in the collection and disposal business of between four and four and a half percent.
This underpins our 2021 operating EBITDA guidance of $4.75 million and $4.9 million.
We expect this strong earnings growth to drive free cash flow of between $2.25 billion and $2.35 billion.
Capital expenditures are expected to be between $1.78 billion and $1.88 billion in 2021.
Excluding about $90 million of capital planned to support the ADS integration, this expectation is in line with our long-term capital spend as a percentage of revenue target of nine and a half to 10 and a half percent even while we step up our investments in CSD.
We expect our dividend payments to be about $975 million in 2021.
Given our focus on the ADS integration, we expect tuck-in acquisitions to be on the lower end of our typical range of $100 million to $200 million.
With more than $1 billion remaining from our free cash flow guidance, we plan to allocate that to a combination of debt repayment, share repurchases and the high-return, sustainability-focused, capital investment opportunities I described earlier.

Summary:
We expect organic revenue growth from yield and volume in the collection and disposal business of between four and four and a half percent and overall revenue growth between 10.75% and 11.25% during 2021.
As John mentioned, we anticipate 10.75% to 11.25% revenue growth in the year ahead with solid organic growth in the collection and disposal business of between four and four and a half percent.
This underpins our 2021 operating EBITDA guidance of $4.75 million and $4.9 million.
Capital expenditures are expected to be between $1.78 billion and $1.88 billion in 2021.