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The matrix of each OWS effluent, groundwater, and surface water sample collected has been char- acterized by general water and wastewater parameters. A wide range in concentrations has been measured for on- site system wastewater effluents, as would be expected from the diver- sity of wastewater sources sampled (e.g. ranging from single - family homes to large commercial and institutional establish- Table 1. Eight compounds of interest, their uses and sources Compound Use Source 4- Methylphenol Disinfectant Cleaners 3- p- Coprostanol Animal fecal steroid Animal Cholesterol Animal steroid Animal Caffeine Stimulant Beverages, drugs EDTA Metal- complexing Shampoos, cleaners agent Triclosan Antimicrobial Soaps, disinfectants, toothpaste 4- Nonylphenol Surfactant metabolite Industrial and domestic cleaners NPEC Surfactant metabolite Industrial and domestic cleaners ments). The median values, though, are comparable to typical values reported for constituents in OWS effluents. For example, a typical effluent from an onsite system serving a residential source would be charac- terized by a carbonaceous biochemical oxygen demand (cBODS) around 450 mg /L, total nitro- gen of 100 mg /L, ammonia of 65 mg /L, and total phosphorus of 47 mg /L. Each OWS effluent, groundwater, and surface water sample collected has also been analyzed for a suite of 25 organic wastewater contami- nants. OWCs were identified frequently and at high concentrations in the wastewater effluents. Twenty three of the 25 compounds were identi- fied in one or more of the wastewater effluents in concentrations ranging from less than the report- ing level to greater than 1 mg /L. The number of compounds in each wastewater effluent sample ranged from 8 to 19, with the veterinary hospitals and convenience stores having the highest aver- age number of compounds and the residential sources having the lowest average number of compounds. Eight of the most frequently de- tected compounds are listed in Table 1 with their uses and some common sources. The occurrence and concentrations of OWCs in OWS effluents can be related to the water use distribution at the wastewater source. For ex- ample, significantly higher concentrations of cho- lesterol, 3- p- coprostanol, caffeine, and triclosan were found in both convenience stores as com- pared to any other wastewater source included in the study. At convenience stores, approxi- mately 90% of the water discharged to the onsite system originates from the public restrooms, i.e. from toilet and urinal flushing and sink faucets, therefore, higher concentrations of human-de- rived compounds (e.g. cholesterol, 3-(3- coprosta- nol, and caffeine) and ingredients found in hand soaps such as triclosan are be expected in the wastewater effluent. Restaurants and veterinary hospitals that have a higher percentage of waste- water originating from clothes and dish washing reported elevated concentrations of EDTA, 4- methylphenol, and the surfactant metabolite and endocrine disruptor NPEC. The occurrence of endocrine disruptors such as surfactant metabolites in wastewater raises con- cerns about their adverse impacts on the envi- ronment following recharge of groundwater and potential recharge of surface waters. Concen- trations of nonylphenol as low as 10 ug /L have been reported to induce production of the egg yolk precursor vitellogenin, an indicator of endo- crine disruption, and significantly decrease the rate of growth of the testes in rainbow trout. In 2003 the U.S. Environmental Protection Agency proposed that the 4 -day average concentration of nonylphenol in freshwater should not exceed 5.9 ug /L to ensure aquatic life water quality. Twen- ty five of the 30 sites included in the study had detectable concentrations of nonylphenol and -` -- 11