; (4) development of metrics to gauge the effectiveness of the implementation and enforcement of such integrity management regulations; (5) an assessment of how integrity management informs operator activities, including planning and completion of repairs, and whether the implementation of integrity management regulations by operators of pipeline facilities has had a demonstrable effect on improving gas and hazardous liquid pipeline safety; and (6) identification of areas where pipeline safety has improved and where it has not improved due to integrity management. (d) Report to Congress The Secretary shall— (1) require the National Academies to submit to the Secretary a report on the results of the study under subsection (a); and (2) not later than 2 years after the date of enactment of this Act, submit to the Committee on Transportation and Infrastructure and the Committee on Energy and Commerce of the House of Representatives and the Committee on Commerce, Science, and Transportation of the Senate such report. 20. Hydrogen study (a) In general The Comptroller General of the United States shall conduct a study on existing natural gas pipeline systems that, as a result of hydrogen-natural gas blending, contain a percentage of hydrogen that is greater than 5 percent by volume to identify the changes that operators have implemented, including— (1) modifications or alternatives to— (A) odorants and leak-detection methods; (B) pipeline materials; and (C) operational standards; and (2) modifications to pipeline infrastructure. (b) Additional contents The study under subsection (a) shall include— (1) an identification of any technical challenges with repurposing existing natural gas infrastructure to allow such infrastructure to be used for hydrogen-natural gas blended service