How to conduct a review of an environmental monitoring plan for orange juice production?

Can you clarify what it is that you need to do?
"No evidence of an annual review of the site's environmental monitoring plan" seems to imply that there is a plan, but it isn't being reviewed?

Do you have Environment Monitoring program describing areas to monitor, tests, testing procedures & methods, sampling frequencies, tolerances, corrective actions in case of negative results, verification procedures, trend analyses, etc? Your program/plan should be reviewed at the established frequency to ensure effectiveness, feasibility, compliance to current regulations, etc.

Your environmental monitoring program should include testing of not only the line area but also the surrounding environment. There are a number of posts on hygienic zoning (zone 1 to 4) and how to build a solid environmental monitoring program. 

Environmental monitoring is a hot topic right now and is honestly very much under utilised in so many food industries. You can gather a fair amount of data on your plant hygiene and cleanliness. 

To begin, I would gather your ATP readings per sampling site and start trending this data. You can set up some basic excel tables to follow your data per sampling site, per zone, per month, etc. Once you begin having data trends, you can use this to review your environmental monitoring program (are your limits too high, too low? do you always have higher results in specific areas? etc.) 

I would also suggest using more than only ATP for your environmental monitoring. ATP is a great tool to be used as a rapid indicator of surface cleanliness, but it can easily be misused and give misleading results. I would add in some indicator organism testing - TPC, and Coliforms as well as some basic pathogen environmental monitoring - E. coli and Listeria spp.