Abstract

The occurrence of organic wastewater compounds (components of “personal care products” and other common household chemicals), pharmaceuticals (human prescription and nonprescription medical drugs), and coliphage (viruses that infect coliform bacteria, and found in high concentrations in municipal wastewater) in onsite wastewater (septic tank effluent) and in a shallow, unconfined, sandy aquifer that serves as the primary source of drinking water for most residents near La Pine, Oregon, was documented. Samples from two types of observation networks provided basic occurrence data for onsite wastewater and downgradient ground water. One observation network was a group of 28 traditional and innovative (advanced treatment) onsite wastewater treatment systems and associated downgradient drainfield monitoring wells, referred to as the “innovative systems network.” The drainfield monitoring wells were located adjacent to or under onsite wastewater treatment system drainfield lines. Another observation network, termed the “transect network,” consisted of 31 wells distributed among three transects of temporary, stainless-steel-screened, direct-push monitoring wells installed along three plumes of onsite wastewater. The transect network, by virtue of its design, also provided a basis for increased understanding of the transport of analytes in natural systems.

Coliphage were frequently detected in onsite wastewater. Coliphage concentrations in onsite wastewater were highly variable, and ranged from less than 1 to 3,000,000 plaque forming units per 100 milliliters. Coliphage were occasionally detected (eight occurrences) at low concentrations in samples from wells located downgradient from onsite wastewater treatment system drainfield lines. However, coliphage concentrations were below method detection limits in replicate or repeat samples collected from the eight sites. The consistent absence of coliphage detections in the replicate or repeat samples is interpreted to indicate that the detections reported for ground-water samples represented low-level field or laboratory contamination, and it would appear that coliphage were effectively attenuated to less than 1 PFU/100 mL over distances of several feet of transport in the La Pine aquifer and (or) overlying unsaturated zone.

Organic wastewater compounds were frequently detected in onsite wastewater. Of the 63 organic wastewater compounds in the analytical schedule, 45 were detected in the 21 samples of onsite wastewater. Concentrations of organic wastewater compounds reached a maximum of 1,300 μg/L (p-cresol). Caffeine was detected at concentrations as high as 320 μg/L. Fourteen of the 45 compounds were detected in more than 90 percent of onsite wastewater samples. Fewer (nine) organic wastewater compounds were detected in ground water, despite the presence of nitrate and chloride likely from onsite wastewater sources. The nine organic wastewater compounds that were detected in ground-water samples were acetyl-hexamethyl-tetrahydro-naphthalene (AHTN), caffeine, cholesterol, hexahydrohexamethyl-cyclopentabenzopyran, N,N-diethyl-meta-toluamide (DEET), tetrachloroethene, tris (2-chloroethyl) phosphate, tris (dichloroisopropyl) phosphate, and tributyl phosphate. Frequent detection of household-chemical type organic wastewater compounds in onsite wastewater provides evidence that some of these organic wastewater compounds may be useful indicators of human waste effluent dispersal in some hydrologic environments. The occurrence of organic wastewater compounds in ground water downgradient from onsite wastewater treatment systems demonstrates that a subgroup of organic wastewater compounds is transported in the La Pine aquifer. The consistently low concentrations (generally less than 1 μg/L) of organic wastewater compounds in water samples collected from wells located no more than 19 feet from drainfield lines indicates that the reactivity (sorption, degradation) of this suite of organic wastewater compounds may limit their usefulness as tracers of onsite wastewater discharged into aquifers.

Ground-water samples from 1 of the 3 ground-water transects, along with 1 sample from the onsite wastewater treatment system associated with that transect, were analyzed for a suite of 18 pharmaceuticals. Eight pharmaceuticals were detected in the onsite wastewater, at concentrations up to about 120 μg/L (acetaminophen). In downgradient ground-water samples, sulfamethoxazole (an antibacterial), acetaminophen (an analgesic), and caffeine (a stimulant, and not a medical drug) each were detected once, at concentrations between 0.10 μg/L and 0.18 μg/L—typical of the range of concentrations observed in other studies of wastewater-impacted ground water. In addition to the readily identified pharmaceuticals, two pharmaceuticals—the anticonvulsant drugs primidone and phenobarbitol—were tentatively identified in three ground-water samples from one nest of wells at another transect. Tentative identification of primidone and phenobarbitol occurred during analysis of ground-water samples for organic wastewater compounds; chromatogram peaks not associated with the target organic wastewater compounds were observed and the mass spectra of the unidentified compounds were matched to known mass spectra in a mass spectral reference library. Estimated concentrations reached as high as 12 μg/L (primidone). As was the case with organic wastewater compounds, the pharmaceutical occurrence data indicate that some pharmaceuticals may be useful indicators of the presence of human waste in the environment, and a subset of pharmaceuticals is transported to ground water from onsite wastewater treatment systems.
Introduction

Revised July, 2009

First posted December 16, 2005