The new deadline is
Nov. 19, 2015.

Information on the proceeding is here, including how to file comments on Docket Nos. PRM-20-28, PRM-20-29, and PRM-20-30, NRC-2015-0057 :
https://www.federalregister.gov/articles/2015/06/23/2015-15441/linear-no-threshold-model-and-standards-for-protection-against-radiation

See the Nuclear Resource and Information Service post about the proceeding, with a sample comment letter here: http://org2.salsalabs.com/o/5502/p/dia/action3/common/public/?action_KEY=21118