Wharf led the pack and achieved its second highest operating cash flow and free cash flow since we acquired the operations 6.5 years ago.
Palmarejo and Kensington were largely on plan and are on track to deliver strong fourth quarters and Rochester's results reflect steady progress despite devoting 38.5 days, or about 45% of the quarter, to crushing and hauling over-liner material to the new Stage VI leach pad before winter.
It's worth pointing out that Rochester's year-to-date results reflect 2.5 months of essentially no stacking on the legacy Stage IV pad as they prioritize activities to support the POA 11 expansion.
We invested $20 million in exploration during the quarter alone.
We anticipate investing $70 million in exploration in 2021, which is nearly 40% higher than the record we set last year and is one of the largest programs in our sector.
Switching over to our expansion projects, I want to walk through some updates starting with the Rochester POA 11 expansion.
Overall progress stood at 42% complete at the end of the third quarter.
We're trying to mitigate some of these impacts by rescoping and rebidding unawarded contracts, but we currently estimate that we're likely to see a 10% to 15% overall increase to the POA 11 construction costs.
To take advantage of such a high-grade and significant resource, a 1,750 ton per day processing facility isn't likely large enough to maximize Silvertip's value.
We're going to take some additional time to evaluate what a larger design and footprint could represent in terms of economics and overall flexibility.
This approach will give us time to continue drilling and hopefully keep growing the resource, allow for the dust to settle on many of these current macroeconomic factors and allow us to focus on delivering POA 11 while not straining the balance sheet.
We now have almost 3.5 kilometer of potential growth defined based on step-out drill holes or more than triple what we knew in 2017, as highlighted on Slide 8.
Impressively, Silvertip accounts for roughly 25% of our $70 million overall budget at Coeur.
The site team led by Ross Easterbrook has done an outstanding job managing the 1,000-meter drill program.
We also expect to continue with three surface rigs testing resource growth to the south in the 1.5-kilometer gap between Southern Silver and Tour Ridge zones.
The team reported last week they've cut the best hole ever with 11 mineralized manto horizons.
The hole is located under Silvertip Mountain about 500 meters or 1,500 feet south of the Southern Silver and Camp Creek zones in an area with no resource shapes at this time.
Quarterly operating costs remain within guidance helping to counterbalance lower realized prices and generate $15 million of free cash flow.
We crushed just under 1.3 million tons of over-liner for the new Stage VI leach pad during the quarter, completing the necessary requirements for POA 11.
The Kensington team did an excellent job balancing multiple priorities and maintaining solid cost controls throughout the quarter, which helped generate nearly $15 million of free cash flow.
Gold production was up 17% and cash flow figures was the second highest since Coeur's acquisition back in 2015.
We wrote off $26 million of Mexican VAT refunds, to which we strongly believe we are entitled, but like many other multinational companies doing business in Mexico, we have experienced significant challenges from SAT in the Mexican courts in obtaining these payments.
Revenue of $208 million was driven by relatively stable metal sales and a lower average realized silver price versus the second quarter.
Operating cash flow totaled $22 million, which was lower than last quarter but also negatively impacted by changes in working capital.
Removing working capital, operating cash flow improved by more than 10% quarter-over-quarter.
Turning over to Slide 12 and looking at the balance sheet, we ended the quarter with approximately $330 million of liquidity, including $85 million of cash and $245 million of availability under our revolving credit facility.
Also, it's worth highlighting that these numbers do not include the $140 million of equity investments on our balance sheet.
We ended the period with a net debt to EBITDA leverage ratio of 1.4 times.
We will continue adhering to our disciplined capital allocation framework and remain focused on our goal of keeping net leverage below 2 times and maintaining liquidity of at least $100 million throughout the entire Rochester construction period.

Summary:
We anticipate investing $70 million in exploration in 2021, which is nearly 40% higher than the record we set last year and is one of the largest programs in our sector.
We're going to take some additional time to evaluate what a larger design and footprint could represent in terms of economics and overall flexibility.
Revenue of $208 million was driven by relatively stable metal sales and a lower average realized silver price versus the second quarter.