WAL size many times data size?

Our streaming replication and WAL archiving keep having trouble because of
the sheer size of the WAL files. The number of bytes in the WAL files seems
to be a large multiplier, like 5x or 10x, the amount of data that we load.
It's hard to know exactly, because in addition to the size of the actual
data files, there are indexes and auxiliary tables of crunched data. But
these shouldn't even double the total data.

The other day we loaded about 5-8 GB of data, and the WAL directory ended
up with 75GB in it. Streaming replication to our standby server broke
because the network couldn't keep up, so it had to fall back to the
secondary stream of WAL files.

Is this expected?

Thanks,
Craig