Both physical and biological processes have temporal and Structural pores associated with macropore-type preferential flow spatial patterns of formation and destruction cycles pathways can accelerate chemical transport in unsaturated soils, thereby potentially causing groundwater contamination. To predict chemical (Gupta et al., 2002). Tillage practices and compaction, transport through these pathways, classical deterministic models de-for example, often destroy the continuity of large strucpend on soil hydraulic conductivity, which effectively lumps flow contural pores (Isensee et al., 1990). The coefficient of varitributions from all individual pathways. We contend, however, that quanation of soil hydraulic conductivity, which is often dictifying the pore spectrum of preferential pathways, without lumping the tated by the soil structural pores, ranged from 100 to contributions of individual pores, is the appropriate method for simu-400% (Libardi et al., 1980; Warrick and Nielsen, 1980). lating convective chemical transport through macropore-type prefer-This suggests that the spatial variability of soil structural ential pathways. In this study, we conducted field-scale experiments pores measured by using core-or block-sized samples is by using an improved tile drain monitoring protocol to measure the very large. As a result, the size spectrum of large strucmass flux breakthrough patterns of conservative tracers. The tails of tural pores measured at several random locations by these patterns suggested that the impact of preferential pathways on contaminant transport can be conceptualized as that occurring through small sample sizes in a field may not represent the speccylindrical capillary tubes. We then proposed a distribution function trum of the entire field. Temporal extrapolation of meabracketed by sharp cutoff points to represent the pore spectrum of surements may be similarly invalid. For these reasons, these tubes. Finally, we used the measured tracer breakthrough curves it is difficult to directly measure the field-scale spectrum (BTCs) as data sources to find the parameters of the proposed funcof the large structural pores, yet this property is among tion. Our results, based on the best fitting, showed that the preferential the most important soil properties when dealing with pathways are naturally clustered into domains; preferential pathways issues related to water quality. with a wide range of pore radii could become active simultaneously Soil characteristic curves and hydraulic conductivity when infiltration rate increases. Because the derived pore spectra sicurves were used in past research from the 1950s and multaneously satisfy both water movement and solute transport, pore 1960s [summarized by Hillel (1980, p. 183-185) and Jury spectra can be used to (i) calculate soil hydraulic conductivity of preferential pathways in deterministic approaches, and (ii) construct multi-et al. (1991, p. 89-94)] to quantify the soil pore-size ple probability density functions (PDFs) for the transfer function ap-d...

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Aging wastewater collection and treatment systems have not received as much attention as other forms of infrastructure, even though they are vital to public health, economic growth, and environmental quality. Inflow and infiltration (I&I) are among potentially widespread problems facing central sewage collection and treatment systems, posing risks of sanitary system overflows (SSOs), system degradation, and water quality impairment, but remain poorly quantified. Whole-system analyses of I&I were conducted by regression analyses of system flow responses to rainfall and temperature for 93 wastewater treatment plants in 23 counties in eastern North Carolina, USA, a coastal plain region with high water tables and generally higher rainfalls than the continental interior. Statistically significant flow responses to rainfall were found in 92% of these systems, with 2-year average I&I values exceeding 10% of rainless system flow in over 40% of them. The effects of rainfall, which can be intense in this coastal region, have region-wide implications for sewer system performance and environmental management. The positive association between rainfall and excessive I&I parallels the effects of storm water runoff on water quality, in that excessive I&I can also drive SSOs, thus confounding water quality protection efforts.

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