WAL files not being recycled

I have a PostgreSQL server that is not recycling WAL files. Log files are
continually created and no old log files are ever removed.

Running PostgreSQL v 9.4.8 with archive settings:

archive_mode = on
archive_command = /bin/true

Checkpoint logging is enabled and does not record any logs being recycled:

2016-05-16 00:05:37 EDT - LOG: checkpoint starting: xlog
2016-05-16 00:09:51 EDT - LOG: checkpoint complete: wrote 38574
buffers (29.4%); 0 transaction log file(s) added, 0 removed, 0 recycled;
write=252.921 s, sync=1.340 s, total=254.312 s; sync files=48,
longest=1.101 s, average=0.027 s
2016-05-16 00:10:37 EDT - LOG: checkpoint starting: time
2016-05-16 00:14:11 EDT - LOG: checkpoint complete: wrote 43786
buffers (33.4%); 0 transaction log file(s) added, 0 removed, 0 recycled;
write=206.271 s, sync=7.428 s, total=213.765 s; sync files=82,
longest=3.821 s, average=0.090 s
...
2016-05-16 07:32:27 EDT - LOG: checkpoint complete: wrote 7617
buffers (5.8%); 1 transaction log file(s) added, 0 removed, 0 recycled;
write=269.3

Control data records:

pg_control last modified: Mon 16 May 2016 06:23:07 PM EDT
Latest checkpoint location: 1EB/1F008FE8
Prior checkpoint location: 1EB/1E0009E0
Latest checkpoint's REDO location: 1EB/1F008FB0

There is a single replication client:

pid | 23287
usesysid | 10
usename | postgres
application_name | walreceiver
client_addr | 172.16.56.246
client_hostname |
client_port | 58070
backend_start | 2016-05-14 03:27:33.523611+00
backend_xmin |
state | streaming
sent_location | 1EB/1F042760
write_location | 1EB/1F042760
flush_location | 1EB/1F042760
replay_location | 1EB/1F037F40
sync_priority | 0
sync_state | async

Does anyone have suggestions what else to check? What can cause WALs not to
be recycled or removed?

Thanks in advance.

--
Scott Moynes
VM Farms