Semivolatiles US EPA Method 625 is an analytical method for the monitoring of acid and base neutral extractable fractions in municipal and industrial wastewater by GC/MS. US EPA Method 8270 is a general analytical method for the monitoring of semivolatiles in environmental and waste samples by GC/MS. CLP Series Methods: The US EPA retains analytical services through the Contract Laboratory Program (CLP). The CLP follows detailed SOPs derived from EPA methods and SW-846. The CLP Volatile Organic Analysis Method is an analytical method for the analysis of aqueous or solid samples for VOCs by GC/MS.