Disinfection byproducts (DBPs), including total trihalomethanes (TTHM) and the sum of five haloacetic acids (HAA5) are regulated by the US Environmental Protection Agency Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR). This study compiled DBP and related water quality parameter data for 395 public drinking water systems serving populations greater than 100,000 across 44 US states from 1980 to early 2015. Assessing DBP occurrence data from two years before (2010–2012) and after (2012–2014) Stage 2 DBPR implementation shows improved capture of higher DBP exposure locations within water distribution systems due to the initial distribution system evaluation. After Stage 2 DBPR implementation, TTHM and HAA5 concentrations have mean values of 30.5 µg/L and 19.6 µg/L and 95th percentile values of 71.2 µg/L and 46.5 µg/L, respectively. Comparing this data set with the 1997–1998 Information Collection Rule data set suggests a 20 µg/L reduction in average TTHM occurrence for the highest 5% of systems nationally from 1997–1998 to 2010–2014.
A combined reflection/refraction (wide-angle) seismic survey was conducted on the continental shelf north-west of Britain, using a conventional streamer with an airgun source, and static ocean-bottom seismometers (OBS) to record wide-angle energy. The shallow structure down to a basaltic layer was reasonably well imaged on the stacked reflection section. The basalts, however, proved to be opaque to the conventional reflection method and prevented the imaging of deeper horizons, where an important velocity inversion was anticipated. This paper reports on the processing, modelling and interpretation of the densely sampled wide-angle OBS data that were coincident with the reflection profile. Eleven OBS instruments were deployed along a 75 km line and recorded signal from a powerful 149 litre (9100 in.3) airgun array fired every 50 m. Data processing was performed using a standard industrial reflection seismic software package prior to first-arrival picking. Processing steps included geometry definition, trace summation and display of the data using various scaling algorithms. An initial model was constructed from 1D velocity-time profiles digitized every 4 km along the stacked section. First arrival traveltime modelling rapidly converged to a detailed model of the structure of the top 5 km of the crust. Modelling revealed the existence of a buried low-velocity Mesozoic sedimentary basin, of a prominent basement horst and of a normal fault penetrating to the basement. lntroduction Many regions of the world are difficult to explore using conventional reflection profiling because a strongly reflective horizon high in the stratigraphic column effectively masks the underlying structure (Jarchow, Catchings and Lutter 1994). I
Both chlorinated and brominated trihalomethanes (THMs) and haloacetic acids (HAAs) are regulated under the US Environmental Protection Agency's Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR). All four chlorinated and brominated THMs are regulated as total THMs (TTHM) and of the nine HAAs, the sum of five HAAs (HAA5) are regulated; the four unregulated HAAs are all brominated species. The objective of this study was to assess national occurrence of all nine HAAs (HAA9) and disinfection byproduct (DBP) speciation. Modeling techniques are applied and validated to estimate HAA9 concentrations using TTHM and HAA5 species, as HAA9 data are limited. DBP speciation is assessed using bromine incorporation factors (BIFs). While national HAA9 occurrence, assessed using modeled HAA9 concentrations, decreased from 2005 through 2014, it increased in the two years after the Stage 2 DBPR implementation (when different sampling locations were used) compared with the two years prior. BIF values increased from 2005 through 2014, and spatial analysis showed higher BIF values in Southern California and Texas.
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