The custom method is suitable for analysis of complex water samples such as wastewater effluents. One-liter samples, collected in amber glass bottles and stored at 4 °C, are necessary to achieve the low level of detection. Because many of the target compounds are common food additives (caffeine, butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT)), or found in detergents and plasticizers (nonylphenol-NP, NPEO), care must be taken to avoid sample contamination. Field processing blanks and method blanks are used to monitor low-level contamination of samples. To meet the needs of USGS projects, the NWQL has included several sewage indicators such as pesticides, caffeine, and alkylphenols to select USEPA targeted compounds and developed a custom wastewater method. Other semi-volatile organic compounds that have been detected frequently in samples at the NWQL since 1995 were also added to the method even though many are currently unregulated. Samples are extracted by continuous liquidliquid extraction (CLLE) using methylene chloride as the extraction solvent. The unique design of the extractor (fig. 1) uses a porous glass frit that disperses methylene chloride solvent in micro-droplets, improving extraction efficiency compared to conventional designs. Extraction of whole-waters samples by this technique has been in use at the NWQL since 1994, and CLLE has become the extraction method of choice for a wide range of polar and non-polar organic compounds. Once extracted, the CLLE sample volumes are reduced to 500 microliters prior to analysis by gas chromatography/mass spectrometry (GC/MS). Operation of the mass spectrometer in the selected-ion-monitoring (SIM) mode is necessary to achieve detection levels ranging from 0.05 to 0.20 micrograms per liter, which are required for most environmental samples.