Analisis Implementasi Lean Sigma DMAIC dengan Pertimbangan Lingkungan pada Proses Pengolahan Minyak Bumi di Lapangan Tua (Studi Kasus: Lapangan Onshore Santan Terminal - PT Pertamina Hulu Kalimantan Timur) = Analysis of Lean Sigma - DMAIC implementation with enviromental considerations in oil processing at mature field (Case Study: Onshore Santan terminal field - PT Pertamina Hulu Kalimantan Timur)