Cdm Smith

Cambridge, MA, United States

Cdm Smith

Cambridge, MA, United States

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Described are methods of removing one or more heavy metals from water. A source of calcium carbonate is added to the water, which is treated to cause coprecipitation of calcium carbonate and the one or more heavy metals. Then, the coprecipitated calcium carbonate and one or more heavy metals are separated from the water.

Apell J.N.,University of Florida | Apell J.N.,Cdm Smith | Boyer T.H.,University of Florida
Water Research | Year: 2010

Dissolved organic matter (DOM) and hardness cations are two common constituents of natural waters that substantially impact water treatment processes. Anion exchange treatment, and in particular magnetic ion exchange (MIEX), has been shown to effectively remove DOM from natural waters. An important advantage of the MIEX process is that it is used as a slurry in a completely mixed flow reactor at the beginning of the treatment train. Hardness ions can be removed with cation exchange resins, although typically using a fixed bed reactor at the end of a treatment train. In this research, the feasibility of combining anion and cation exchange treatment in a single completely mixed reactor for treatment of raw water was investigated. The sequence of anion and cation exchange treatment, the number of regeneration cycles, and the chemistry of the regeneration solution were systematically explored. Simultaneous removal of DOM (70% as dissolved organic carbon) and hardness (>55% as total hardness) was achieved by combined ion exchange treatment. Combined ion exchange is expected to be useful as a pre-treatment for membrane systems because both DOM and divalent cations are major foulants of membranes. © 2010 Elsevier Ltd.

Olsen R.L.,Cdm Smith | Chappell R.W.,Environmental Science Solutions LLC | Loftis J.C.,Colorado State University
Water Research | Year: 2012

Comprehensive water quality investigations to characterize large watersheds include collection of surface water samples over time at various locations within the watershed and analyses of the samples for multiple chemical and biological constituents. The size and complexity of the resulting dataset make overall evaluations difficult, and as a result, multivariate statistical methods can be useful to evaluate environmental patterns and sources of contamination. The most commonly applied multivariate method in watershed studies is principal components analysis (PCA), which uses correlation among multiple water quality constituents to effectively reduce the number of variables. The reduced set of variables may assist in the identification and description of spatial patterns in water quality that result from hydrologic and geochemical processes and from sources of contamination.The utility of PCA for identifying important environmental factors in a given study is obviously affected by sampling design, constituents analyzed, data quality, data treatment prior to PCA, methods of interpreting PCA results, and other factors. Unfortunately no comprehensive evaluations have been performed and no standard procedures exist for dealing with these issues. This paper examines and evaluates the current state-of-the-science by review of 49 published papers dealing with multivariate (typically PCA) techniques to evaluate watershed water quality.Additionally an example PCA for a surface water quality study in the Illinois River Watershed (IRW) is provided to illustrate methods to address the above issues and to evaluate the sensitivity of results to alternative methods. The example PCA evaluations were consistent with two dominant sources of surface water contamination in the IRW: 1) discharge to the streams from municipal wastewater treatment plants and 2) runoff and infiltration from fields with land applied poultry waste. © 2012 Elsevier Ltd.

Bell K.Y.,Cdm Smith | LeBoeuf E.J.,Vanderbilt University
Chemosphere | Year: 2013

This study demonstrates differences in sorptive capacity of volatile organic compound (VOC) trichloroethylene (TCE) onto natural organic matter (NOM) coated and uncoated mineral surfaces above and below the NOM glass transition temperature. TCE sorption isotherms for dry NOM-mineral systems below the NOM glass transition temperature (Tg) demonstrated sorption behavior characteristic of micropore filling, with sorption capacities reduced relative to uncoated mineral matrices. Such differences were not entirely associated with differences in surface areas of the coated and uncoated mineral matrices, but were likely associated with either a blockage of pore space available to the VOC or a kinetic limitation that does not allow the VOC access to the internal porosity of the model soil within the time periods of the experiment. TCE sorption in dry NOM-mineral matrices above the Tg, however, was described in terms of sorption within a more fluid, macromolecular dissolution medium that does not hinder access to mineral surfaces. Such observations have potential important implications for modeling the fate and transport of VOCs in soils and sediment systems. © 2012 Elsevier Ltd.

Kingsbury R.S.,Cdm Smith | Singer P.C.,University of North Carolina at Chapel Hill
Water Research | Year: 2013

The purpose of this research was to investigate the performance of treatment with magnetic ion exchange (MIEX) resin followed by ozonation in achieving disinfection goals while controlling bromate and chlorinated disinfection by-product (DBP) formation. Three water samples were collected from raw water supplies impacted by the San Francisco Bay Delta to represent the varying levels of bromide and total organic carbon (TOC) that occur throughout the year. A fourth water was prepared by spiking bromide into a portion of one of the samples. Samples of each water were pre-treated with alum or virgin MIEX resin, and the raw and treated waters were subsequently ozonated under semi-batch conditions to assess the impact of treatment on ozone demand, ozone exposure for disinfection (" CT" ), and bromate formation. Finally, aliquots of raw, coagulated, resin-treated, and ozonated waters were chlorinated in order to measure trihalomethane formation potential (THMFP). In the waters studied, MIEX resin removed 41-68% of raw water TOC, compared to 12-44% for alum. MIEX resin also reduced the bromide concentration by 20-50%. The removal of TOC by alum and MIEX resin significantly reduced the ozone demand of all waters studied, resulting in higher dissolved ozone concentrations and CT values for a given amount of ozone transferred into solution. For a given level of disinfection (CT), the amount of bromate produced by ozonation of MIEX-treated waters was similar to or slightly less than that of raw water and significantly less than that of alum-treated water. MIEX resin removed 39-85% of THMFP compared to 16-56% removal by alum. Ozonation reduced THMFP by 35-45% in all cases. This work indicates that in bromide-rich waters in which ozone disinfection is used, MIEX resin is a more appropriate treatment than alum for the removal of organic carbon, as it achieves superior TOC and THM precursor removal and decreases the production of bromate from ozone. © 2012 Elsevier Ltd.

Parthasarathi P.,Cdm Smith
PloS one | Year: 2013

The purpose of this research is to test the systematic variation in the perception of travel time among travelers and relate the variation to the underlying street network structure. Travel survey data from the Twin Cities metropolitan area (which includes the cities of Minneapolis and St. Paul) is used for the analysis. Travelers are classified into two groups based on the ratio of perceived and estimated commute travel time. The measures of network structure are estimated using the street network along the identified commute route. T-test comparisons are conducted to identify statistically significant differences in estimated network measures between the two traveler groups. The combined effect of these estimated network measures on travel time is then analyzed using regression models. The results from the t-test and regression analyses confirm the influence of the underlying network structure on the perception of travel time.

Watts J.L.,Cdm Smith
World Environmental and Water Resources Congress 2014: Water Without Borders - Proceedings of the 2014 World Environmental and Water Resources Congress | Year: 2014

The Greater New Orleans (GNO) area is often referred to as "a bowl of water surrounded by water," an indication of the area's continuous struggle with stormwater management, including the more recent problems of subsidence and sea level rise. To address some of these challenges, the City of New Orleans commissioned the development of an H&H computer model. As envisioned, this evaluation would serve as a baseline and assess possible levels to either exceed service levels or reduce costs. The model has fulfilled its vision and blossomed into more than just a tool for traditional drainage design. The model has been essential in developing plans and proving benefits for several projects in the GNO area, including many green infrastructure projects, and has been used to help prove the benefits of changing the stormwater management paradigm of the GNO area. © 2014 American Society of Civil Engineers.

Heineman M.,Cdm Smith
World Environmental and Water Resources Congress 2012: Crossing Boundaries, Proceedings of the 2012 Congress | Year: 2012

Many recent studies predict changes in annual precipitation patterns and impacts on water supplies based on global climate modeling. This research is less valuable for forecasting changes in severe storms, which is of primary interest for urban infrastructure studies, such as flood control and water quality planning. Examination of extreme rainfall trends over the last century can be an indicator of likely future patterns, and can illuminate deficiencies in available frequency statistics that are usually based on assumed stationarity in the historic data. This study analyzes daily data from 1893 to 2010 for the 1,100-station U.S. Historical Climatology Network (USHCN). Stations were grouped according to nine climate regions for the contiguous US. Each USHCN station dataset was analyzed to identify 1-year and 5-year rainfall at 1-day and 7-day durations. The methodology follows the analysis presented by Kunkel et al. (1998) in an analysis of 1931-1996 data. Each station dataset was considered stationary for establishment of comparative precipitation thresholds. Each partial duration series of maxima was fitted to the generalized extreme value function using CDM Smith's NetSTORM rainfall analysis software to identify station-specific rainfall maxima. In the five eastern-US climatic regions (Northeast, Southeast, East North Central, Central, and South), the annual incidence of 5-year 1-day rainfall in the 40 years since 1970 averages 26 percent higher than in the preceding 77 years. The annual incidence of 5-year 1-day rainfall in the 20 years since 1990 is 38 percent higher than in the preceding 97 years. In the Northwest, Southwest, and West, the annual incidence of 5-year 1-day rainfall is nearly identical for the pre- and post-1970 periods. Comparable trends are apparent even for 1-year 1-day rainfall: the four decades since 1970 have 19 percent more events per year than the preceding eight decades across the Northeast, South, Central, and East North Central regions. Since 1990, there have been 23 percent more 1-year 1-day rainfall events per year than during the previous century in those same regions. Analysis of 7-day rainfall yielded results similar to the 1-day findings in most climate regions. The increases correlate with shifts in annual precipitation - the eastern stations recorded seven percent more precipitation in the four decades since 1970 compared with the prior eight decades, while western stations recorded four percent more precipitation than previously over those same periods. The changes in large storm frequency are greatest in the northeastern quarter of the country; the incidence of 5-year, 1-day events since 1990 compared with the preceding nine decades increased by 51, 39, and 44 percent for the Northeast, Central, and East North Central climatic regions. While these changes may in part be driven by random variation, interdecadal patterns, and artifacts of the monitoring methodologies, they also indicate larger climatic trends, and demonstrate that the assumption of stationarity in existing extreme rainfall atlases is inappropriate in many places. © 1012 ASCE.

Cdm Smith | Date: 2013-12-23

Transportation services may provide nationwide tolling interoperability. Multi-agency electronic tolling transponders each compatible with multiple tolling agencies are provided to clients. The multi-agency transponders are linked to respective accounts associated with the clients. Transponder tolling data for respective clients is obtained from the multiple tolling agencies. Payments may be sent to each agency corresponding to the clients respective transponder tolling data and the clients may be billed based upon the transponder tolling data.

Schaefer C.E.,Cdm Smith
Environmental Technology and Innovation | Year: 2016

Chlorinated solvents in rock matrices can serve as a long-term contaminant source in fractured rock aquifers, sustaining groundwater plumes for extended periods of time. The intensity and longevity of the groundwater plume will be impacted by the diffusional flux between the rock matrix and adjacent conductive fractures, as well as the fate of contaminants residing within the rock matrix itself. In this study, 1-dimensional numerical simulations are performed to assess the impacts of slow naturally occurring abiotic dechlorination reactions on TCE fate and transport in rock matrices. Simulation parameters for the rock matrix, including effective diffusion coefficients and trichloroethene (TCE) first order dechlorination rate constants, are derived from experimental data from intact rock cores. Simulations show that a TCE dechlorination rate constant of 1×10−8  s−1 can have a substantial impact on TCE uptake and release from the rock matrix. In addition, varying the simulated matrix porosity indicates that the impacts of matrix reactions are exacerbated in low porosity matrices. Overall, simulation results show that contaminant removal from rock matrices can be dominated by abiotic reaction, and that the back-diffusion timeframes for sustaining bedrock plumes above regulatory levels may be limited to a few decades if these abiotic reactions are occurring within the rock matrix. © 2016 Elsevier B.V.

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