Acceptable results for a DLRO test on a ground connection

I have to connect a #4/0 AWG to an existing ground grid and will be using a C-Tap to perform the connection. After the connection I have to conduct a DLRO test on the connection. I haven't done this type of testing much and am a little unfamiliar with the acceptable results. The existing ground grid pigtail has been installed for over forty years, so what would be an acceptable test result for this connection, less than 100 milliohms or even greater? Thanks
 
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