No sorting possible

Do you mean that all recycling is co-mingled but is still kept separate from the trash, or that all recycling and trash are co-mingled?

I'm making the assumption that this is not a US city....so taking that as the starting point I hope that I can at least point you in some directions. First wherever the total co-mingled ends up (usually at the transfer station), investigate if they have a separation plant that will divide up the recycle form the trash. If so gather details of how they do it (include pictures) and then gather results from the company showing the %'s of the different streams. If there is no such operation then I'm afraid that it is down to you. While you may feel that it makes no sense this is what market-leadership is all about (in any case you'll need to do an on-site dumpster dive to create the baseline "what's in the trash/recycle stream")....and you're going to have to sort on site, find recyclers to take the various items (every different stream will need weighing and recording). Yes, I know that sounds a lot, but what we're trying to do is move the marketplace and, I hope, that your work will be reported on and start the local process of separate stream recycling. (It's not easy being the market leader)

I work for a municipality where all trash and recycled materials are gathered at each of the 300+ facilities owned and operated by the city and then sorted and weighed to arrive at numbers for the city facilities as a whole. We are currently attempting to design a protocol for LEED EB volume but if each buildings waste has to be accounted for at the building level we will not be able to participate in certification of any of our buildings using the LEED EB rating system on an individual or volume basis. Is it acceptable to submit a protocol for the entire organization and apply the percentage we arrive at for each building?

Dionne, Ok, great question and I'm going to answer it not in the way that you think.
The difficulty of trash/recycling is that the generation of the same is dependent on each of the buildings. In a volume process we have, to quote both ends of the spectrum, one end where the recycling is 100% and there is no trash to speak of (a net-zero waste facility) to the other end where no-one in the building gives a tinkers cuss and the recycling is 1%. If we the combined these two buildings recycling and trash output then we would have a 50% recycling rate. But unless you were actually in the building recording the output from them you would have no idea which building was 100% and which building was 1%...(and of course we want to take all the great ideas and processes from the 100% building and instruct the 1% to create improvements)
So...sounds like to me you will need to perform 300 dumpster dives to gain a clear understanding of where each of the building stands...between 100% recycling and 1%.
This MIGHT be possible by getting the hauler to help you, but previous experience shows that they tend to 'round the numbers' and the accuracy leaves a lot to be desired.