If anyone is wondering why their log messages are appearing in multiple log files, here is one answer applying to *nix systems:
If your syslog.conf looks like this (assuming you use LOG_LOCAL0 for web app logging) :
This will collect *all* messages of LOG_INFO level and higher, i.e everything except debug messages
Try this instead to ensure that only messages of the named log level go into the relevant log file:
Additionally, you may like to add this to ensure your messages don't end up in generic log files like "messages" "all" "syslog" and "debug":
saves disk space among other things - more at "man syslog.conf"