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Cambridge, MA, United States

Mayer B.K.,Marquette University | Mayer B.K.,Arizona State University | Gerrity D.,Arizona State University | Gerrity D.,University of Nevada, Las Vegas | And 3 more authors.
Critical Reviews in Environmental Science and Technology | Year: 2013

Eutrophication caused by excess phosphorus (P) loading poses a serious environmental risk to freshwater bodies around the world. While conventional P-removal technologies often satisfy maximum effluent levels of 1,000 μg-P/l, the resulting environmental P concentrations can still contribute to eutrophication. The challenge remains to achieve low total P levels of ≤ 10 μg-P/l in very large water flows. This issue is often exacerbated by the presence of unreactive organic phosphorus. The authors critically assess innovative developments in advanced oxidation, adsorption, biological uptake, and ion exchange for their ability to achieve very low total P concentrations in high-flow systems. Adsorption appears to have the greatest potential for near-term implementation. Biological uptake and ion exchange show promise based on laboratory-scale research and may be long-term options. Pretreatment using advanced oxidation may be valuable in converting organic P to the more readily removable orthophosphate form. © 2013 Copyright Taylor and Francis Group, LLC. Source

Hibbard C.S.,Camp Dresser and McKee Inc.
Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA | Year: 2011

A discussion covers EPA's air emissions regulations for combustion sources, including biomass combustion for energy production and biomass conversion for fuels; how small changes in biofuel mix and type trigger differing requirements in EPA's combustion rules; how to obtain exemptions from these rules for bioenergy facilities through determinations that the fuel is not a solid waste, or determinations that the facility is a qualified small power producer or qualified cogeneration facility; and case studies illustrating how the Clean Air Act Section 129 rules for "waste" combustion and the Clean Air Act Section 111 and 112 rules for "traditional fuel" combustion can be applied to bioenergy facilities. This is an abstract of a paper presented at the 104th AWMA Annual Conference and Exhibition 2011 (Orlando, FL 6/21-24/2011). Source

Petersen C.M.,Camp Dresser and McKee Inc. | Rifai H.S.,University of Houston | Villarreal G.C.,RBF Consulting | Stein R.,Texas Commission on Environmental Quality
Journal of Environmental Engineering | Year: 2011

Bacterial levels in Buffalo Bayou in Houston commonly exceed contact recreation standards. Potential sources of bacteria include wastewater treatment plants, sanitary sewer overflows, septic systems, wet and dry nonpoint-source discharges via direct runoff and pipes, direct deposition, and sediment. A water-quality model in the Hydrologic Simulation Program-FORTRAN (HSPF) was calibrated and validated for hydrology, sediment, and Escherichia coli and subsequently used to evaluate the impacts of the bacterial sources in the watershed. In addition, simple estimates of bacterial loads were calculated along with source evaluations from load duration curves. Load reductions based upon the simple estimates indicated that water-quality standards were met by reducing dry-weather indicator bacterial loads by 69% and wet-weather loads by 98%. When these load reductions were implemented in the HSPF model, however, standards were not met under dry-weather conditions. Residual nonpoint-source loading was found to cause the discrepancy between simple load estimate calculations and the developed water-quality model. This paper demonstrates that runoff can play a significant role in maintaining high levels of bacteria under all flow conditions and that understanding the temporal variations in bacterial source loading is critical to ensure that load reductions will achieve water-quality standards. © 2011 American Society of Civil Engineers. Source

Sanderson J.S.,The Nature Conservancy of Colorado | Rowan N.,Camp Dresser and McKee Inc. | Wilding T.,Colorado State University | Bledsoe B.P.,Colorado State University | And 2 more authors.
River Research and Applications | Year: 2012

Growing water demand across the world is increasing the stress on river ecosystems, causing concern for both biodiversity and people. River-specific environmental flow assessments cannot keep pace with the rate and geographic extent of water development. Society needs methods to assess ecological impacts of flow management at broad scales so that appropriate regional management can be implemented. To meet this need in Colorado, USA, we developed a Watershed Flow Evaluation Tool (WFET) to estimate flow-related ecological risk at a regional scale. The WFET entails four steps: (i) modelling natural and developed daily streamflows; (ii) analysing the resulting flow time series; (iii) describing relationships between river attributes and flow metrics (flow-ecology relationships); and (iv) mapping of flow-related risk for trout, native warm-water species and riparian plant communities. We developed this tool in two watersheds with differing geomorphic settings and data availability. In one of the two watersheds, the WFET was successfully implemented to assess ecological risk across the 3400-km 2 watershed, providing consistent watershed-wide information on flow-related risk. In the other watershed, active channel change and limited data precluded a successful application. In Colorado, the WFET will be used to evaluate the risk of impacts on river ecosystems under future climate change and water development scenarios (e.g. for energy development or municipal water supply). As water continues to be developed for people, the WFET and similar methods will provide a cost-effective means to evaluate and balance ecosystem needs at large scales. © 2011 John Wiley & Sons, Ltd. Source

Pekin O.,Camp Dresser and McKee Inc.
Geotechnical Special Publication | Year: 2010

Step-path slope failures in jointed bedrock are analyzed using the PCSTABL slope stability computer program. The model simulates bedrock as anistropic material with variable discontinuity lengths. Discontinuity lengths are varied by adjusting the number of boxes used in the BLOCK search routine. Bedrock discontinuity information is based on visual examination of rock cores and acoustic televiewer data. Anistropic strength parameters are obtained from direct shear testing of rock samples. Results provide an understanding of how slope factor of safety varies with slope direction and discontinuity length. The analysis methods are applied to a proposed 400-foot deep quarry in Central California. Slope stability evaluation is especially important in this case because a steep slope is desired for improved production, but the pit is located close to a highway and a canal. © 2010 ASCE. Source

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