You need to do a risk analysis to validate that every other month is adequate. An environmental monitoring program should be designed to find harborage areas and eliminate them before it becomes a risk in your product, not merely to satisfy SQF requirements. If Listeria and E. Coli are not high risk for your environment and product, then every other month may be sufficient, but you need to justify it.
I'd highly recommend developing a chart of your facility with food contact surfaces, non-food contact surfaces, critical and non-critical.
It would be helpful to know more about the product. Is this ready-to-eat refrigerated produce? Are you processing it into a juice? Are you merely washing and sorting whole produce?
The FDA has some excellent resources available.
Determine if product in question supports the growth of listeria:
Information on frequency for Listeria monitoring:
(critical food-contact surfaces should be tested at least once each month; critical non-food-contact surfaces at least each quarter)
FDA's information for Listeria in refrigerated RTE foods: