48 C.F.R. § 6106.608
No party is required to provide additional evidence. An applicant or grantee may, but need not, supplement materials it previously provided to FEMA regarding the dispute. A party may elect to present additional evidence, i.e., documents, things, or testimony tending to make a factual contention appear more or less likely to be true. If a party so elects, the panel will to the extent practicable allow a response. FEMA shall efile its response to an arbitration request within 30 calendar days after receiving the docketing notice. A panel may not exclude as untimely evidence proffered before arbitration closes under Rule 613. A panel may consider the timing or surprise nature of evidence when assessing the significance, credibility, or probative value of the evidence.
48 C.F.R. §6106.608