The effectiveness of pitcher filters for removing lead and other metals (copper, iron, manganese, and zinc) without removing fluoride in drinking water was evaluated in laboratory and field environments in Denver Water. Effluent from corrosion control pipe racks (control at pH 7.8 adjusted to 8.8 and 1 mg/L as PO4 of orthophosphate) at two water treatment plants was used as challenge water to examine lead removal in five different NSF/ANSI-42 and 53 certified filters. The lead concentration in the challenge water from the control racks ranged between 31 and 97 ppb, and all filters had >94% removal efficiency. Based on the filter challenge study and the manufacturer reported longevity, pitcher Filter B was selected as the most appropriate for Denver's water quality. Field demonstration study samples were collected from at least 50 different sites twice a year. All distributed filters reduced lead levels under the Action Level of 15 ppb, except one sample where the filter concentration was 40.8 ppb and the unfiltered concentration was 1.4 ppb. Overall, filters are generally reliable, but water quality can impact the removal efficacy.

This study directly compared the data obtained from coupon studies and flow-through pipe rack studies from two sources in the Denver Water system. The pipe rack study was completed over multiple years using harvested lead service lines. The coupon studies were completed in about 2 months using pure lead coupons. Orthophosphate at 2 mg/L was found to reduce lead concentrations by about 81% in the pipe racks, whereas 74%-81% was observed in the coupons. At an orthophosphate dose of 1 mg/L lead concentrations were reduced by 62%-65% in the pipe loop and by 55%-75% in the coupons, pH at 8.8 reduced lead by 45%-60% in the pipe racks and by 27%-48% in the coupons. The pipe racks were able to give insights into the transition from one condition to another, which is time-based and dependent on existing pipe scales. Both types of demonstration studies produced similar conclusions about treatment options. The pipe rack was more representative of conditions in the distribution system while the coupon studies were performed in a fraction of the time.

For high levels of TrOC removal by GAC, reducing DOC 0 concentration is more important than the specific DOM removal pretreatment process.

The anticipated hexavalent chromium [Cr(VI)] drinking water standard in California and related national attention has sparked a public policy debate about potential regulatory action, but to date that debate has been lacking in a sound appreciation of the cost implications for Cr(VI) treatment of drinking water. This article imputes national and California‐specific cost implications from low‐level Cr(VI) treatment goals (1, 2, 5, 10, and 20 μg/L) for community water systems based on the best available scientific information regarding occurrence and demonstrated treatment technologies. The annual costs for a national 10‐μg/L Cr(VI) standard would range from $0.55 billion to $5.1 billion/year, substantially higher than those for previous drinking water regulations. The results reported here provide a guide to future cost analyses using the third Unregulated Contaminants Monitoring Rule and other occurrence databases and outline the key information gaps that will need to be addressed in order to arrive at a cost analysis sufficient to support sound regulatory decisions.

Based on the results of over twenty laboratory granular activated carbon (GAC) column runs, models were developed and utilized for the prediction of 2-methylisoborneol (MIB) breakthrough behavior at parts per trillion levels and verified with pilot-scale data. The influent MIB concentration was found not to impact the concentration normalized breakthrough. Increasing influent background dissolved organic matter (DOM) concentration was found to systematically decrease the GAC adsorption capacity for MIB. A series of empirical models were developed that related the throughput in bed volumes for a range of MIB breakthrough targets to the influent DOM concentration. The proportional diffusivity (PD) designed rapid small-scale column test (RSSCT) could be directly used to scale-up MIB breakthrough performance below 15% breakthrough. The empirical model to predict the throughput to 50% breakthrough based on the influent DOM concentration served as input to the pore diffusion model (PDM) and well-predicted the MIB breakthrough performance below a 50% breakthrough. The PDM predictions of throughput to 10% breakthrough well simulated the PD-RSSCT and pilot-scale 10% MIB breakthrough.

Total and hexavalent chromium occurrence in the United States was investigated using three available datasets. The National Chromium and Boron Occurrence Survey, the US Environmental Protection Agency database of chromium from the Second Six‐Year Review, and California Department of Public Health water quality analysis data were obtained and analyzed. The high number of nondetect samples and subsequent nondetect handling had an important effect on the determination of representative chromium concentrations. Chromium was found to occur widely throughout the United States. Total and hexavalent samples were paired, and they indicated that surface water speciation is dominated by trivalent chromium, whereas groundwater speciation is dominated by hexavalent chromium. The potential impact of further chromium regulation ranges more than two orders of magnitude, with as few as 1,000 entry points being affected nationwide at 20 μg/L and as many as 100,000 entry points being affected nationwide at 1 μg/L.

The adsorption of trace organic contaminants by granular activated carbon (GAC) was assessed relative to the control of taste and odor (T&O) compounds and disinfection by‐product (DBP) precursor removal. Adsorbers operated for the control of T&O and DBP precursors were shown to yield good to excellent removal of 17 trace organic contaminant probe compounds. Increasing influent concentration of the trace organic contaminant in the parts‐per‐billion level was shown not to affect compound breakthrough on a normalized basis; however, higher influent concentrations did lead to earlier breakthrough on a mass concentration basis. Increasing background dissolved organic matter concentration increased competition for a fixed number of adsorption sites and led to earlier breakthrough. Optimal empty bed contact time depended on the specific treatment objectives and the contaminant removal level needed to meet those objectives. Series and parallel adsorber operation was calculated to yield a twofold decrease in the GAC use rate.

A granular activated carbon (GAC) adsorption simulation methodology using the observed trace organic contaminant mid-point breakthrough and the pore diffusion model is presented, validated, and used to model adsorption and concentration gradient driven desorption. Trace organic contaminant adsorption was well-simulated by this approach; however, desorption from GAC adsorbers was found to occur at lower concentrations than predicted by either pore or surface diffusion model calculations. The observed concentration profiles during desorption yielded a lower peak concentration and more elongated attenuation of contaminants after intermittent loading conditions than predicted by the models. Hindered back diffusion caused by irreversibly adsorbed dissolved organic matter on the GAC surface is hypothesized to be responsible for slowing the desorption kinetics. In addition, laboratory test results indicate a negligible impact of simulated backwashing the GAC media on trace organic contaminant breakthrough.

The role of particle size on the reduction of granular activated carbon (GAC) adsorption capacity for trace organic contaminants by dissolved organic matter (DOM) is examined and applied to performance scale-up. The adsorption capacity reduction, termed fouling, must be scalable in order to use bench scale tests, such as the rapid small-scale column test (RSSCT) to predict full-scale breakthrough. Equilibrium adsorption capacity tests with GAC preloaded with DOM and RSSCT breakthrough curves at three different GAC particle sizes indicate that GAC adsorption capacity is dependent on GAC particle size when DOM is present. Thus, the RSSCT cannot be expected to match full-scale results regardless of which RSSCT design approach is used (constant or proportional diffusivity), unless a scaling factor is applied to the results. Proportional diffusivity RSSCT breakthrough curves demonstrate that surface concentration of DOM is not a good measure of fouling. It is hypothesized that pore blockage is the mechanism responsible for the dependence on particle size. As GAC particle size increases, the microporous surface area behind a constricted pore also increases. The result is lower adsorption capacity per mass of adsorbent in the larger GAC particles. A scaling methodology for equilibrium and breakthrough data is presented that accounts for the dependence of NOM preloading effects on GAC particle diameter.