Someone

from prspro in _context.Db.UpaPrsWellProcessData
                          where (prspro.Timestamp > startDate || prspro.Timestamp < endDate)
                          join prsconfig in _context.Db.UpaPrsWellConfigurationData
                          on prspro.EntityId equals prsconfig.EntityId
                          group prspro by new {prspro.EntityId, prsconfig.Timestamp}
                          into ut
                          select new
                                {
                                
                                    Variance = ut.Sum(c => c.GrossVariance),
                                    Production = ut.Sum(c=>c.MeteredOil),
                                    EPF = ut.Sum(c=>c.EPF)
                                 };