CHARLESTON, W.Va. -- Alpha Natural Resources says it has added staff and taken other steps to avoid coal-dust violations of the kind that investigators say caused the Upper Big Branch Mine disaster, according to a letter the company sent last week to federal prosecutors.Alpha did not specify how many staffers were hired, and the company refused to comment on the matter, saying its correspondence with U.S. Attorney Booth Goodwin should have been considered "private correspondence."More information on the matter could become public early next month, when Alpha is to provide a six-month progress report on its efforts to reform former Massey Energy Co. operations under a settlement that avoided corporate criminal prosecution for the April 5, 2010, explosion."We do expect that the company will provide more detail on the specific levels of resources that have been devoted to rock-dusting and cleanup of dust accumulations," Goodwin said Friday.Twenty-nine miners died in the massive methane and coal dust explosion that rocked the Raleigh County mine, making it the worst U.S. coal-mining disaster in nearly 40 years.Federal, state and independent investigations have blamed widespread safety violations, including a systematic failure by Massey management to comply with rules aimed at controlling the buildup underground of explosive coal dust.Goodwin's office is continuing a criminal investigation of individuals thought responsible for the disaster, but agreed in December 2011 not to bring changes against Alpha, which acquired Upper Big Branch and any liabilities associated with it in a June 2011 buyout of Massey.As part of the more than $200 million settlement, Alpha agreed to install significant new safety technology, create a trust to fund health and safety research, and take other steps to improve safety practices, especially at the former Massey operations.Among other things, the Dec. 6 settlement gave Alpha 90 days to implement a plan to ensure that each of its underground mines "has the personnel and resources necessary to meet all legal requirements relating to incombustible material and to prevent accumulations of coal dust and loose coal."The settlement also required Alpha to "conduct mine site training for coal-dust accumulation, cleanup and reporting requirements for all underground workers in an annual training session dedicated to those topics."Under the settlement, the plan to "meet all legal requirements" related to controlling coal dust was to be implemented by Alpha at all of its underground mines by March 6.However, since that date, violations of those requirements have continued at some of Alpha's mines.A cursory review of U.S. Mine Safety and Health Administration records found coal-dust violations at four Alpha mines, including one operation that received five such citations during one quarterly inspection that began in early April.Ted Pile, an Alpha spokesman, said the company is in compliance with the settlement agreement with Goodwin's office, and declined to comment on the coal-dust violations.Goodwin's office, though, released a copy of a May 17 letter from Victor Hou, a New York lawyer representing Alpha, to Steve Ruby, the lead prosecutor on Goodwin's Upper Big Branch team.In the letter, Hou said Alpha began taking steps to improve Massey operations immediately after the June 2011 merger -- long before the settlement with prosecutors."This process included adding safety and technical engineering positions at mining operations to address safety issues," the letter said. "Newly appointed compliance managers conduct safety audits of underground operations and provide oversight and expertise on issues such as mine planning."Alpha has brought in both special teams and outside consultants to assist its subsidiaries in assessing and correcting safety issues," the letter said. "As a result of these efforts, the company has seen an overall decline in the number of coal dust-related citations issued to its subsidiaries since the merger."Alpha said, "a significant number of staff were assigned" to address compliance issues, including "compliance with the legal requirements relating to combustible material and to prevent accumulations of coal dust and loose coal."The letter said some mining sections were shut down to improve compliance, and that staff "worked a significant amount of overtime to meet this directive."After the settlement with Goodwin's office, Alpha required each of its underground mines to submit a plan detailing how they would "address incombustible material and the prevention of accumulations of coal dust and loose coal for each mine at that operation."Alpha's letter said that 80 plans were submitted to corporate safety officers John Gallick and Brian Keaton in February "for review and feedback.""Upon review of the plans and further discussions with the Business Unit Presidents, Mr. Gallick and Mr. Keaton were able to confirm that all underground mine operators have a cleanup plan in place for incombustible material and for preventing accumulations of coal dust and loose coal," the letter stated.The letter said "internal certification" of these plans took place by Feb. 27, in advance of the 90-day deadline in the settlement agreement.Reach Ken Ward Jr. at email@example.com or 304-348-1702.