Influence of Small Dams on Downstream Channel Characteristics in Pennsylvania and Maryland: Implications for the Long‐Term Geomorphic Effects of Dam Removal1

Abstract: We evaluate the effects of small dams (11 of 15 sites less than 4 m high) on downstream channels at 15 sites in Maryland and Pennsylvania by using a reach upstream of the reservoir at each site to represent the downstream reach before dam construction. A semi‐quantitative geomorphic characterization demonstrates that upstream reaches occupy similar geomorphic settings as downstream reaches. Survey data indicate that dams have had no measurable influence on the water surface slope, width, and the percentages of exposed bedrock or boulders on the streambed. The median grain diameter (D₅₀) is increased slightly by dam construction, but D₅₀ remains within the pebble size class. The percentage of sand and silt and clay on the bed averages about 35% before dam construction, but typically decreases to around 20% after dam construction. The presence of the dam has therefore only influenced the fraction of finer‐grained sediment on the bed, and has not caused other measurable changes in fluvial morphology. The absence of measurable geomorphic change from dam impacts is explicable given the extent of geologic control at these study sites. We speculate that potential changes that could have been induced by dam construction have been resisted by inerodible bedrock, relatively immobile boulders, well‐vegetated and cohesive banks, and low rates of bed material supply and transport. If the dams of our study are removed, we argue that long‐term changes (those that remain after a period of transient adjustment) will be limited to increases in the percentage of sand and silt and clay on the bed. Thus, dam removal in streams similar to those of our study area should not result in significant long‐term geomorphic changes.     

Transient puffs of trace organic emissions from a batch-fed waste propellant incinerator

Emissions data have been obtained from a waste propellant incinerator. The incinerator is a dual fixed hearth, controlled air incinerator equipped with acid gas and particulate scrubbing. "Puffing" has been evident in this waste propellant incinerator by spikes in the CO concentration. Transient puffs of organics may travel down the combustion chambers and lead to stack emissions. The major conclusions from this study are that (1) transient puffs are formed due to the semi-batch feed nature of the combustion process (causing a local oxygen deficiency) and high water content of the desensitized propellant; (2) in batch-fed combustors, puffs can contribute to most of the organic emissions (which are relatively low) measured with US EPA sampling and analytical methods; (3) it is estimated that batch-fed combustion contributes up to 7-18 times more emissions than steady-state combustion will generate; (4) by applying dispersion analyses to determine the amount of oxygen deficiency in the flame zone, the combustion zone concentration of CO during batch-fed operation could be as high as 160,000 ppm, compared to a measured peak stack concentration of 1200 ppm CO; and (5) an organic sample is collected and averaged over at least a 2-h period that smooths out the transient peaks of organics emissions during batch-fed operation. For emissions that are associated with long-term potential health impacts, this is an appropriate sampling method. However, if a compound has a short-term potential health impact, it may be important to measure the time-resolved emissions of the compound.     

Verification of dioxin formation in a catalytic oxidizer

Emissions and inlet concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) have been measured from a catalytic oxidizer and a thermal oxidizer. The catalyst inlet temperature was 427 degrees C. The thermal oxidizer operating temperature was 791 degrees C. Data of the toxic dioxin and furan congeners are reported. Important results of this field study are: (1) the catalytic oxidizer in this study produced an increase in PCDD/PCDF congener concentration of almost 10-fold from the inlet to the outlet (stack), thus verifying results of a previous study that evaluated only PCDD/PCDF emissions. All congeners increased from inlet to the stack. (2) The thermal oxidizer had little effect on PCDD/PCDF levels. There was a decrease in four of the congeners and an increase in 13 congeners. (3) Ambient air was the main source of PCDD/PCDFs in the stack emissions of the thermal oxidizer in this study. Laboratory investigations are needed to understand how PCDD/PCDFs are formed (and emitted) under conditions of this study.     

Controlling the Flue-Fed Incinerator

This paper examines various health effects of photochemical air pollution in Japan, primarily through the review of epidemiological studies. Health effects discussed include subjective respiratory symptoms, respiratory function testing, ocular effects, and hospital diagnostic tests. The downward trend in oxidant cautions and paralleled health effects, as reported by the Japanese Environmental Agency, are discussed. The methods determined by Japanese ordinance for measurement of oxidants, SO₂, NO _x , and CO are described.     

APCA Financial Statements for FY 1981–82

ABSTRACT

The objective of this study was to determine whether ultraviolet-light-emitting diodes (UV-LEDs) could serve as an efficient photon source for heterogeneous photocatalytic oxidation (PCO). An LED module consisting of 12 high-power UV-A (λ_max?=?365 nm) LEDs was designed to be interchangeable with a UV-A fluorescent black light blue (BLB) lamp for a bench scale annular reactor packed with silica-titania composite (STC) pellets. Lighting and thermal properties of the module were characterized to assess its uniformity and total irradiance. A forward current (I _F) of 100 mA delivered an average irradiance of 4.0 mW cm^?2 at a distance of 8 mm, which is equivalent to the maximum output of the BLB, but the irradiance of the LED module was less uniform than that of the BLB. The LED and BLB reactors were tested for the oxidization of ethanol (50 ppm_v) in a continuous-flow-through mode with 0.94 sec residence time. At the same average irradiance, the UV-A LED reactor resulted in a lower CO₂ production rate (19.8 vs. 28.6 nmol L^?1 s^?1), lower ethanol removal (80% vs. 91%), and lower mineralization efficiency (28% vs. 44%) than the UV-A BLB reactor. Ethanol mineralization was enhanced with the increase of the irradiance at the catalyst surface. This result suggests that reduced ethanol mineralization in the LED reactor relative to the BLB reactor at the same average irradiance could be attributed to the nonuniform irradiance over the photocatalyst, that is, a portion of the catalyst was exposed to less than the average irradiance. The potential of UV-A LEDs may be fully realized by optimizing the light distribution over the catalyst and utilizing their instantaneous “on” and “off” feature for periodic irradiation. Nevertheless, our results also showed that the current UV-A LED module had the same wall plug efficiency (WPE) of 13% as that of the UV-A BLB, demonstrating that UV-A LEDs are a viable photon source both in terms of WPE and PCO efficiency.

IMPLICATIONS Mercury (Hg)-vapor lamps are common UV sources for photocatalysis but create safety and environmental concerns because they contain Hg; furthermore, they have a relatively short life span. This paper demonstrated that the UV-A LED is a viable alternative to the Hg-vapor lamps without sacrificing PCO efficiency if the design of the LED arrays is improved to increase the lighting uniformity. The use of LEDs could eliminate hazardous Hg wastes and extend the application of photocatalysis in places requiring more compact and robust air purification solutions.     

Environmental release of dioxins from reservoir sources during beach nourishment programs

In late 1990s, USEPA/FDA made an important connection regarding the presence of elevated levels of dioxins (e.g., 1500 ng kg⁻¹ TEQ) in ball clays mined in Mississippi (USA) from a geological deposit dated to ∼40 million years (Mississippi Embayment) that stretches over several states (northern part of Mississippi to Kentucky) and levels of dioxins in selected animal food sources. Following a recent beach nourishment program along the mid-Atlantic coast of the US, a number of dark gray, blue tinted nuggets of varying sizes were found on beach strands and near the shoreline. Using the presence of these balls of clay (shape, color, and knowledge regarding their use in pottery) on the beach, together with our direct experience analyzing ball clays for dioxins, we made a possible association between these clays and elevated dioxins. Concerns regarding the potential of nourishment programs to cause severe damage to our beaches drove us to test the dioxin content of nourishment exposed clays. A number of the nuggets, along with freshly dredged and deposited sand (collected the morning after nourishment) with the same coloration, and others (sun-bleached), collected approximately 2 weeks after the completion of the nourishment efforts, were analyzed for the presence of PCDD/Fs, PCBs, and selected semi-volatile chlorinated organics. The clay PCDD/F WHO2005-TEQs (dry weight; ND = DL; EMPC = EMPC) ranged from 0.41 to 5.78 ng kg⁻¹ with an average of 2.64 ng kg⁻¹, whereas the sand sample’s TEQs ranged from 0.18 to 0.31 ng kg⁻¹ PCDD/F WHO-2005, with an average of 0.22 ng kg⁻¹. The average total tetra- through octachlorinated dibenzo-p-dioxin concentration was 2700 ng kg⁻¹ (with a maximum of 5800 ng kg⁻¹) for the clays and 8.5 ng kg⁻¹ (with a maximum of 16.8 ng kg⁻¹) for the sand samples. The congener 2,3,7,8-TCDD (TEF = 1) was detected in half of the clay samples (0.11-0.77 ng kg⁻¹). All of the clay and sand samples displayed an unambiguous and dominating 1,4,6,9-chlorination pattern across homolog groups. No other chlorinated aromatics were detected above background levels. The observations, along with the absence or an extremely low level of polychlorinated dibenzofurans, together with the mineralogical analysis, supports the conclusion that off-shore dredging activities are reaching reservoir sources containing dioxin-tainted, smectic/kaolinite clay minerals. Subsequent beach erosion provides additional environmental releases over time, as buried balls of clay from previous nourishment efforts become exposed.     

Mapping Patterns of Human Use and Potential Resource Conflicts on Public Lands

Focusing on a 2.2 million hectare area surrounding the Lolo National Forest in western Montana, USA, we illustrate a GIS method for predicting patterns of human use on public lands and highlighting potential for impacts on fish and wildlife species. Data inputs include human population count (derived from the 1990 Census), roads and trails, and the predicted distributions of bull trout (Salvelinus confluentus) and 41 terrestrial vertebrates of special concern. Because results highlight areas where conflicts between humans and resources may occur, they are of potential use to land managers. This approach can be applied wherever data are available, and inputs can be varied according to the topics of interest.     

Overview of particulate exposures in the US trucking industry

As part of a large epidemiologic study of lung cancer, 55,000 subjects, we have conducted a nation-wide survey of particulate exposures in the US trucking industry. The goal is to differentiate the risks from various types of particulate exposures, such as traffic emissions and general air pollution. We hypothesize that exposures defined by job and work site characteristics can be linked with subjects using their personal job histories. This report covers exposures at 36 randomly chosen large truck freight terminals in the US. Measurements were made of PM2.5, elemental carbon (EC), and organic carbon (OC) upwind of the terminal (background) and in work areas, and by personal samples. Significant differences in exposure intensity, microg m(-3), were found for work locations and jobs relative to background levels (GM[GSD]) at terminal sites: PM2.5 9.8[2.34], EC 0.5[3.24], and OC 5.0[1.76]. Using EC as a marker for diesel particles, work locations varied significantly: office 0.3[3.7], dock area 0.7[2.89] and shop area 1.5[3.52]), as did job titles (non-smokers): clerk 0.1[9.98], dock worker 0.8[2.13], and mechanic 2.0[3.82]. Cigarette smoking contributed substantially to personal exposures, approximately doubling PM2.5 and OC, but having less of an effect on EC. Large differences were seen across the terminal sites due to differences in local regional air pollution levels from traffic and other sources. We conclude that it will be possible to estimate current exposures of the cohort using an exposure assignment matrix based on job title, work location, and terminal site. This distribution overlaps substantially with the general public's exposure to these sources.