According to the episode SG1:S2-E14-Touchstone, the two gates were not "simultaneously active". One gate was utilized "a split-second" according to Captain Samantha Carter after, after the first gate was closed in order to hide the signature of the second gate.
The second gate, however, caused a spike in the power readings of the first gate as it was shut down. The closure of the first gate masked the existence of the second one. (11:05)
A tertiary backup log tracked the use of the second gate after the first one was closed. The gates are not active simultaneously, instead the wormhole is hijacked as the gate is closing allowing the connection to the location to remain open. (11:52)
At 28:07 the SG1 team dial from Madrona and their wormhole signal is intercepted by the second stargate. The first stargate is NOT ACTIVE at the same time. The signal is traced to southern Utah.
At 40:21, the General in charge of the SGC reports the gate will have an iris welded across the second gate and it will remain in the custody, under guard at the SGC. At 40:27 the scene shows the iris being welded into place over the second stargate.