After you refresh database from Production to UAT environments make sure to run below scripts to drop production users first then grant data read access to UAT users.
use [Database_Name]
go
go
select 'DROP USER' , '['+ name+']'
from dbo.sysusers
where name LIKE '%PRD-%'
GO
use [Database_Name]
go
select 'EXEC sys.sp_addrolemember ' , ''' db_datareader ''' , '['+ name+']'
from master.dbo.syslogins
go
select 'EXEC sys.sp_addrolemember ' , ''' db_datareader ''' , '['+ name+']'
from master.dbo.syslogins
GO