Browsing by Author "Scardina, Robert P."
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- Applying the RUSLE and SEDD Equations to an Agricultural Watershed in Southwest Virginia - A Case Study in Sediment Yield Estimation Using GISLally, Lindsay Backus (Virginia Tech, 2013-06-12)The goal of this study is to develop a model using GIS to estimate the source and quantity of accumulated sediment in the Emory & Henry College (EHC) duck pond. Located in the Highlands of Southwest Virginia, the 1,194 acre duck pond watershed consists primarily of agricultural, forested, and low density urban land uses. The Revised Universal Soil Loss Equation (RUSLE) and the Sediment Distributed Delivery (SEDD) prediction models were used to determine the quantity of eroded sediment and the sediment yield at the duck pond, respectively. These models require numerous computations, which were performed at the watershed scale with the aid of ArcGIS software. In ArcGIS the watershed was broken into a raster grid of approximately 5,200 discrete 100 foot by 100 foot grid cells. The resulting watershed erosion model identified two main sources of sediment: a cluster of farms relatively close to and east of the duck pond, and a harvested timber site north of the duck pond. The model predicted that 1,076 tons of sediment are delivered into the duck pond annually. The estimated sediment yield was then compared to the estimated amount deposited between October 2011 and September 2012, as measured by a topographic survey. The model prediction was found to be within a factor of 6.3x of the measured value. The predicted and measured sediment yields as well as identified erosion sources can be used to develop a water quality improvement plan and to help alleviate the need for periodic dredging.
- Biological Health Assessment of an Industrial Wastewater Treatment FacilityZivich, Jamie Dionne (Virginia Tech, 2011-06-30)The biological treatment of wastewaters from an industry was studied. Among the more important wastewater constituents of concern were high levels of suspended solids, due to graphite and nitrocellulose, the solvents, ethanol and acetone, and nitroglycerine (NG). The goal of this project was divided into four objectives. The impacts of graphite on a microbial population were evaluated. Sequencing batch reactors (SBRs) were used to monitor the effects of graphite on mixed liquor suspended solids (MLSS), removal of soluble chemical oxygen demand (sCOD), and specific oxygen uptake rates (sOUR). Graphite appeared to have no adverse effect on the microbes. The potential benefits of adding sucrose, nitrogen, and phosphorus to SBRs were evaluated. The MLSS was maintained at 1,250 mg/L, similar to the microbial population in the suspended growth system at the industry. Sucrose addition increased the sCOD removals and sOUR. No direct effect was observed with the addition of nitrogen and phosphorus. The treatability of acetone and ethanol was studied through sOUR and batch testing to determine bacterial response to solvents. Both solvents were utilized by the microbes. The concentrations tested proved to be beneficial, not inhibitory. Ethanol and a 50/50 mixture of acetone and ethanol were more viable substrates than acetone. NG treatability was examined under anoxic and aerobic conditions in SBRs and batch biological reactors. NG degradation occurred under anoxic conditions, but was more favorable in aerobic environments. NG was degraded in all SBR tests to below detection limit (0.5 mg/L); therefore, the optimal treatment could not be determined.
- Chloride Sulfate Mass Ratio (CSMR) and Nitrate Acceleration of Galvanic Lead- Bearing Solder CorrosionStone, Kendall Rose (Virginia Tech, 2010-05-04)Lead corrosion in premise plumbing systems from materials, such as lead pipes, soldered joints, and brass, can cause elevated lead in drinking water. This work examined mechanisms by which galvanic corrosion of lead solder:copper joints is accelerated by high chloride, low sulfate, and high nitrate in the water. Galvanic corrosion studies conducted using simulated copper plumbing joints showed lowered pH and concentrated anions at the lead solder surface. A combination of low pH and high chloride can prevent passivation of the solder surface, indefinitely sustaining high corrosion rates and lead contamination of potable water supplies. The mass of lead leached to water correlated with predictions based on Faraday's law, although a portion of the oxidized lead remained attached to solder in a scale layer. When the level of sulfate in water increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced. The impact of chloride-to-sulfate mass ratio (CSMR) on lead leaching from 50:50 lead:tin solder galvanically coupled to copper was examined at the bench scale.The CSMR can be affected by coagulant changeover, use of desalinated water, anion exchange, brine leaks, and other treatment changes. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from this source. Above this range, while lead leaching was generally very high, there was little correlation between lead release and CSMR. The impact of nitrate was tested at the bench scale using synthesized water. Results consistently showed that increasing nitrate in the range of 0 to 10 mg/L NO??N, could dramatically increase lead leaching from simulated soldered pipe joints. Although higher nitrate slightly increased the galvanic current, the main factor affecting lead release appears to be initiation of non-uniform corrosion, with small pieces of solder detaching into the water. Under some circumstances, the decay of chloramine after it leaves the treatment plant, and formation of nitrate via nitrification, can markedly increase corrosivity of distributed water to lead solder. The bench scale experiments conducted in this work illuminated many issues related to accelerated lead corrosion of solder. However, future research is necessary to further elucidate the mechanisms behind nitrate-accelerated corrosion, as well as methods for inhibition of corrosion due to chloride and nitrate.
- Effects of Dissolved Gas Supersaturation and Bubble Formation on Water Treatment Plant PerformanceScardina, Robert P. (Virginia Tech, 2004-01-19)Gas bubbles that form within water treatment plants can disrupt drinking water treatment processes. Bubbles may form whenever the total dissolved gas pressure exceeds the local solution pressure, a condition termed dissolved gas "supersaturation." This project investigated how bubble formation affects conventional drinking water treatment and examined factors that can reduce these problems. Gas bubbles attached to coagulated floc particles can reduce settling efficiency and create "floating floc." In laboratory experiments, bubbles formed on the surface of the mixing paddle, since this was the location of minimum pressure within the system. The formation and stability of floating floc was dependent on many different factors including the amount and type of dissolved gas supersaturation and surface chemistry of the mixing paddle. The intensity and duration of rapid mixing also controlled the amount of floating floc. Bubbles forming in filter media can block pore spaces and create headloss, a process popularly termed "air binding." During benchscale filtration experiments, bubbles were released upwards from the media in a burping phenomenon, and bubbles could also be pushed downwards by fluid flow. Burping is beneficial since it partly alleviates the bubble induced headloss, but the media disruptions might also decrease filter efficiency (particle capture). Bubble formation within filters can be reduced by increasing the pressure inside the filter via greater submergence (water head above the media), lower hydraulic flow rate, or use of a more porous media. The mode of filter operation (declining or constant flow rate) will also affect the local filter pressure profile. Dissolved gas supersaturation and bubble formation are detected in on-line turbidity devices and particle counters causing spurious measurements. The use of bubble traps usually reduced these problems, but one device worsened turbidity spikes. Flow disturbances may also release bubbles upstream of the on-line turbidimeter, which can cause spikes in turbidity readings.
- Evaluating Leachability of Residual Solids Generated from Unconventional Shale Gas Production Operations in Marcellus ShaleSharma, Shekar (Virginia Tech, 2014-09-17)Hydraulic fracturing operations utilized for shale gas production result in the generation of a large volume of flowback and produced water that contain suspended material, salts, hydrocarbons, metals, chemical additives, and naturally-occurring radioactive material. The water is impounded at drilling sites or treated off-site, resulting in significant generation of residual solids. These are either buried on site or are disposed in lined landfills. The objective of this study was to determine the levels of heavy metals and other elements of concern that will leach from these residual solids when placed in typical disposal environments. For this purpose, laboratory leaching experiments were employed wherein representative samples were brought into contact with a liquid to determine the constituents that would be leached by the liquid and potentially released into the environment. The samples used included sludge resulting from the physicochemical treatment of process water (TS), sludge solidified with cement kiln dust (SS), raw solids obtained by gravity separation of process water (RS), and drilling mud (DM). The samples were subjected to both single extraction (i.e. Shake Extraction Test, SET) and multiple extraction (i.e. Immersion Test, IT) leaching tests. For the shake extraction test, samples were mixed with a specific amount of leaching solution without renewal over a short time period. In the immersion test, samples were immersed in a specific amount of leaching solution that was periodically renewed over a longer period of time. For both these tests, analyses were performed on the filtered eluate. The tests were performed as per standards with modifications. Distilled de-ionized water, synthetic acid rain (pH ~ 4.2), weak acetic acid (pH ~ 2.88), and synthetic landfill leachate were used as leaching solutions to mimic specific disposal environments. Alkali metals (Li, K, Na), alkaline earth metals (Ba, Ca, Mg, Sr) and a halide (Br), which are typically associated with Marcellus shale and produced waters, leached at high concentrations from most of the residual solids sample. The SS sample, due to its stabilization with CKD, had a lower extraction efficiency as compared to the unconsolidated TS and RS samples. In EF 2.9 and EF SLL, the leaching took place under acidic conditions, while for EF DDI and EF 4.2, the leaching occurred in alkaline conditions. EF 2.9 and EF SLL were determined to be the most aggressive leaching solutions, causing the maximum solubility of most inorganic elements. Thus, high amounts of most EOCs may leach from these residual solids in MSW landfills disposed under co-disposal conditions. Agitation, pH and composition of the leaching solution were determined to be important variables in evaluating the leaching potential of a sample. The results of this study should help with the design of further research experiments being undertaken to develop environmentally responsible management/disposal strategies for these residual solids and also prove useful for regulatory authorities in their efforts to develop specific guidelines for the disposal of residuals from shale gas production operations.
- Evaluation of Constructed Wetlands and Pretreatment Options For the Treatment of Flow-through Trout Farm EffluentDoheny, Ryan Matthew (Virginia Tech, 2011-07-01)Horizontal subsurface flow (HSSF) constructed wetlands were evaluated for the treatment of flow-through trout farm effluent, phosphorus sorption affinity of gravel-bed media, and influence on Rhodamine WT (RWT) transport. HSSF wetlands coupled with mechanical pretreatment demonstrated significant (p <0.05) removal of total ammonia-nitrogen (TAN), total phosphorus (TP), total organic carbon (TOC), total suspended solids (TSS), five-day biochemical oxygen demand (BOD5), and turbidity. Treatment occurred predominantly within the wetland cells, with minimal removal of studied water quality parameters by means of sedimentation or microscreen filtration (80 ?m mesh). HSSF wetlands removed 69% of influent TSS, 24% of influent TP, and reduced turbidity by 66%. The removal of organic matter within the wetlands, as measured by BOD5, COD, and TOC was 62%, 50%, and 55%, respectively. After receiving effluent from a flow-through trout farm for about one year, the gravel media exhibited moderate removals of soluble phosphorus in batch and column sorption experiments. Partition coefficients (Kd) from batch sorption tests ranged from 45-90 mL/g. Low (60 mL/min) and high (165 mL/min) flow column experiments removed about 50 and 40% of influent PO4-P, respectively. The conservative nature of RWT in subsurface media has been called into question by many authors. Tracer response curves from tests conducted in pilot-scale HSSF wetlands exhibited elongated tails and dual peaks, in addition to mean tracer retention times far exceeding the theoretical value. Laboratory column testing of RWT and the more conservative NaCl tracer supported field data, indicating that RWT was more reactive within the wetland media.
- Evaluation of In-Service Residential Water Meters: Analysis of Registration Error and Metering Infrastructure UpgradesMantilla Pena, Carlos Fernando (Virginia Tech, 2020-01-22)The American Water Works Association (AWWA) and the International Water Association (IWA) have designated the volume of water not registered by water meters as a form of "apparent loss" in a distribution system. The term apparent is given because this volume is not technically a water loss, as is the case of wasted water from real leaks in the distribution system. Large volumes of apparent losses hurt the revenue of utilities that rely on water metering to bill their customers. This is critical to utilities given that billed consumption is often the main source of income to provide adequate service. This form of apparent losses is a challenge to water management, particularly, in the case of significant drought because of the uncertainty about the real volume of water consumed. Although the impact of apparent losses from a single residential service connection is not as significant compared to an industrial meter with low accuracy, the cumulative effect of apparent losses across residential users can be very significant. Until the early 2000's water utilities in the U.S. relied on mechanical water meters to measure residential water use. Since then, electronic meters with higher accuracy at low flow rates have been developed. Data collection from meters has also evolved as well, from the manual reading by an operator, to drive-by systems and most recently to remote readings using a network of transmitters/receivers (i.e., advanced metering infrastructure or AMI). An expectation of this dissertation is that it will help water utilities to have a better idea of the volume of apparent losses due to metering inaccuracy (i.e., registration error) and provide insights into the effects of installing AMI systems to residential metered water (MW). To achieve this goal, two main objectives are fulfilled 1) to expand on the knowledge of registration error (RE) in mechanical nutating-disc (ND) meters used to monitor residential consumption, and 2) to evaluate the impact of metering infrastructure upgrades on the volume of metered water (MW) from residential service connections. This dissertation follows the manuscript format with three journal articles constituting the main chapters after a general introduction characterizing the issues in Chapter 1. Chapter 2 is an experimental study that evaluates the influence of service time (ST) and volumetric throughput (TP) on the accuracy of ND meters within the recommended flow rates set by the U.S. water industry for meters with an internal diameter of ⅝-in. (15-mm). Over 300 meters removed from service were tested for accuracy. Key findings of this study are 1) ND meters that have been in service over 25 years have a greater likelihood of poor accuracy at the minimum recommended flow rate (Q^min) of 0.25 gallons per minute (gpm) (57 liters per hour (L/h)) and 0.5 gpm (114 L/h) independent of TP, and 2) comparison with data from accelerated laboratory testing showed that simulated use may not necessarily reflect the actual performance of ND meters in service, particularly, at 0.25 and 0.5 gpm. Chapter 3 is an experimental study that investigates REs of ND meters below the minimum recommended flow rate (Q^min = 0.25 gpm), particularly, at ½, ¼ and ⅛ of Q^min. Over 100 meters removed from service were tested in this study. Key findings of this study are 1) confirmed how performance decreases with reducing flow rate below Q^min, 2) of the variables considered, TP was found to be a better indicator of RE at Q_(1/8)^min up to an approximate meter reading of 0.66 MG (2.5 ML) compared to ST for 10 ≤ ST ≤ 24 years, with minimal influence at Q_(1/4)^min and none at Q_(1/2)^min, and 3) a strong linear relationship was found between RE at Q_(1/2)^min and RE at Q^min independent of TP or ST. Chapter 4 is a study that evaluates the extent to which the implementation of a new AMI system combined with a system-wide installation of new ND meters impacted the volume of MW from residential service connections of a 22,000-person municipality in southwest Virginia. Time-series analysis techniques were employed to evaluate changes in the trend of bimonthly MW and median daily MW over a six-year period. Key findings of this study are 1) the AMI system improved the accountability of MW for the utility, 2) despite an ongoing downward annual trend in MW, average bimonthly MW mildly increased after the AMI system was fully operational, and 3) annual MW increased by 2.2% in the 12-month period immediately following the metering infrastructure upgrade.
- Flow Induced Failures of Copper Drinking Water TubeCoyne, Jeffrey Michael (Virginia Tech, 2009-05-05)Excessive water flow velocities can contribute to rapid failures of copper premise plumbing systems. This is the first fundamental study to scientifically isolate mechanistic impacts from distinct flow induced failure mechanisms that include concentration cell corrosion, cavitation, particle/bubble impingement and high velocity impingement. Concentration cell effects resulting from exposing different copper surfaces to different flow regimes created a strong electrochemical cell that caused rapid corrosion that persisted for periods lasting from hours to days in certain waters. Free chlorine appeared to inhibit this effect in a range of waters. Under typical water chemistries the resulting non-uniform attack diminished, presumably due to formation of a protective scale or rust layer. Consequently, concentration cell corrosion would not be a major contributor to damage from high flow rates in the range of fresh waters investigated. In experiments using an ultrasonic processor, implosion of vaporous cavitation bubbles against a copper surface caused dramatic pitting, considerable copper weight loss, and, in some cases, the development of pinhole leaks. Changes in water chemistry and the existence of a pre-existing protective scale layer had nearly no mitigating effects on copper cavitation damage. An exponential relationship was found between the initial copper pipe wall thickness and the time necessary to cause a leak via vaporous cavitation. On the basis of this relationship, a Type M tube would be expected to last 23 and 3000 times less than a Type K and L tube, respectively, when facing continual cavitation attack. However, it was not possible to re-create cavitation damage in any practical circumstance that was tested in copper pipes, even though it is strongly believed that cavitation can play a practical role in service failures. On the basis of the above results, it was hypothesized that brief intervals of cavitation could remove protective scale from portions of the copper pipe surface exposed to high turbulence. In this case, even if minimal damage from cavitation occurred directly, it could allow concentration cell corrosion to become a significant contributor to non-uniform corrosion damage. On the basis of preliminary testing, it appears that this idea has considerable merit. A combination of brief cavitation and waters that create strong concentration cell effects is expected to cause serious damage to copper pipe. These potential synergies are deserving of additional research. In experiments testing the effect of high velocity jets (17.5 ft/sec) impinging against submerged copper plates perpendicularly and longitudinally, plates in heated sea water were aggressively gouged and penetrated. It is believed that the copper plate damage resulted from a combination of mechanisms including concentration cell corrosion, cavitation implosion, and high velocity impingement. Impingement of sand on the surface of copper tube created very little damage. This was surprising given prior reports in the literature.
- Galvanic Lead Corrosion in Potable Water: Mechanisms, Water Quality Impacts, and Practical ImplicationsNguyen, Caroline Kimmy (Virginia Tech, 2010-08-27)As stagnant water contacts copper pipe and lead solder (simulated soldered joints), a corrosion cell is formed between the metals in solder (Pb, Sn) and copper. If the resulting galvanic current exceeds about 2 µA/cm², a highly corrosive microenvironment can form at the solder surface, with pH <2.5 and chloride concentrations 11 times higher than bulk water levels. Waters with relatively high chloride tend to sustain high galvanic currents, preventing passivation of the solder surface and contributing to lead contamination of potable water. If the concentration of sulfate increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced, and solder surfaces were readily passivated. Mechanistically, at the relatively high concentrations of lead and low pH values that might be present at lead surfaces, sulfate forms precipitates while chloride forms soluble complexes with lead. Considering net transport of anions in water, a chloride-to-sulfate mass ratio (CSMR) above 0.77 results in more chloride than sulfate transported to the lead anode surface, whereas the converse occurs below this CSMR. Bicarbonate can compete with chloride transport and buffer the pH, providing benefits to lead corrosion. Although orthophosphate is often an effective corrosion inhibitor, tests revealed cases in which orthophosphate increased lead and tin release from simulated soldered joints in potable water. Phosphate tended to increase the current between lead-tin and copper when the water contained less than 10 mg/L SO₄²⁻ or the percentage of the anodic current carried by SO₄²- ions was less than 30%. Additionally, nitrate in the potable water range of 0-10 mg/L N dramatically increased lead leaching from simulated soldered pipe joints. Chloramine decay and the associated conversion of ammonia to nitrate during nitrification could create much higher lead contamination of potable water from solder in some cases. In practical bench-scale studies with water utilities, the CSMR was affected by the coagulant chemical, blending of desalinated seawater, anion exchange, and sodium chloride brine leaks from on-site hypochlorite generators. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from lead-tin solder connected to copper.
- Influences of Water Chemistry and Flow Conditions on Non-Uniform Corrosion in Copper TubeCustalow, Benjamin David (Virginia Tech, 2009-07-24)Water chemistry and fluid velocity are factors that can perpetuate certain types of non-uniform pitting corrosion in copper tube, specifically in waters with high chlorine and a high pH. These two parameters can further act synergistically to alter pitting propensities in copper pipes subjected to this type of water. A preliminary short-term experiment considered pitting propensity in copper pipe as a function of water chemistry. This study used a water chemistry that had been documented to promote and sustain pitting in copper tube that further developed into fully penetrating pinhole leaks. Modifications to this base water chemistry found that dosing a chloramine disinfect (rather than free chlorine) or the addition of silica greatly reduced corrosion activity and pitting propensity on copper pipes. In another short-term experiment, copper pitting propensity was considered as a function of fluid velocity. A number of different fluid velocities were tested in several different pipe diameters using the same documented pitting water. Velocity was observed to significantly increase pitting propensity in all pipe diameters considered. At the highest fluid velocity tested (11.2 fps) a pinhole leak formed in ¼â tubing after only 2 months of testing. Larger pipe diameters were also found to increase the likelihood of forming deeper pits on the pipe surface at the same fluid velocity. Chlorine was a driving factor in corrosion for preliminary tests conducted using this pitting water. The reduction of chlorine to chloride is believed to be the primary cathodic reaction limiting the overall rate of corrosion in this type of water. As such, a subsequent study considered the relationship between the rate of chlorine reduction and corresponding corrosion activity. Chlorine reduction or demand rates were found to be good indicators for pitting propensity and corrosion activity for this particular type of water. All preceding work led to the development and design of a large scale, long-term, copper pitting study. A matrix of 21 unique conditions tested various water chemistries, flow conditions, corrosion inhibitors, and galvanic connections of copper pipes to other metallic plumbing materials. The severity of pitting corrosion was observed to be dramatically decreased by lower free chlorine residual concentrations, high alkalinity, and sufficient doses of copper corrosion inhibitors such as natural organic matter, silica, and orthophosphate. Pitting severity was consequently observed to increase at a low alkalinity, indicating that this parameter has a significant effect on corrosion reactions. Furthermore, the addition of aluminum solids to the base pitting water chemistry dramatically increased the formation of tubercle mounds on the inside of the copper pipes in contact with the waster. Aluminum solids have been observed to be a vital constituent for sustaining pit growth in this specific water at lower pHs, however, the role of this constituent at the high pH levels tested in this study was previously unknown. From simple visual observation, aluminum solids appear to increase the aggressiveness of this water even at higher pHs.
- Interplay of Water Chemistry and Entrained Particulates in Erosion Corrosion of Copper and Nonleaded Alloys in Potable Water SystemsRoy, Siddhartha (Virginia Tech, 2018-03-26)Erosion corrosion of plumbing materials in domestic water systems is a complex phenomenon driven by water quality, hydrodynamic and electrochemical factors. Erosion corrosion accounts for over a third of copper hot water system failures in the U.S., hundreds of millions in damage, and may be expected to increase with newer Legionella control strategies including increased use of water recirculation and high temperatures. Additionally, some nonleaded alloys introduced after the passage of a new federal law restricting lead content in plumbing, have been anecdotally implicated as failing prematurely from erosion corrosion compared to traditional alloys. This dissertation includes 1) a critical review of the literature, 2) investigation of a recent rapid erosion corrosion failure in a large building plumbing system, 3) replication of this phenomena in copper and nonleaded brass in laboratory studies, and 4) evaluation of 12 nonleaded alloys against conventional leaded brass. Current plumbing codes and guidelines to prevent erosion corrosion were found to be widely inconsistent and lacking scientific evidence. Large-scale recirculating hot water pipe-loop experiments demonstrated that an aggressive hard water with entrained aragonite (CaCO3) particles could cause fully penetrative failures (i.e., leaks) in brand new copper pipe and nonleaded brass fittings in just 3-49 days. This represents the first time rapid erosion corrosion failures have ever been replicated in the laboratory under conditions similar to those encountered in practice. The entrained particulates dramatically accelerated attack on metals, especially at pipe bends. In general, lowering pH, increasing flow velocity, increasing temperatures, entrainment of particles (of bigger sizes), and addition of chlorine disinfectant increased erosion corrosion rates. These results scientifically proved that hard waters are not inherently less aggressive than soft water, and in fact if CaCO3 solids form they can be much more aggressive. Finally, cavitation and erosion corrosion resistance of 12 nonleaded alloys was evaluated against leaded brass; stainless steels demonstrated superior performance, silicon brass had the greatest susceptibility and remaining alloys were in the middle. This performance data can aid decision making regarding choice of alloys for various water applications. Our work over the years, including involvement in the Flint Water Crisis, demonstrated that practicing trustworthy science as a public good requires commitment to scientific rigor, truth-seeking, managing conflicts of interest, and comprehensible evidence-based science communication. Critical problems in 21st century public science were highlighted including perverse incentives, misconduct, postmodernist "science anarchist" thought, and ineffectiveness of U.S. water utilities in communicating tap water safety to the American public.
- Lead and Copper Corrosion Control in New Construction: Shock Chlorination, Flushing to Remove Debris & In-line Device Product TestingRaetz, Meredith Ann (Virginia Tech, 2010-07-30)Several aesthetic, health, and plumbing quality issues can arise during new construction or renovation of premise plumbing. There has been little research done on many of these concerns and therefore few guidelines or regulations are in place to protect the health of the consumer or the integrity of the plumbing infrastructure. This work examines common construction practices including: 1) effect of residual construction debris, 2) shock chlorination of new plumbing lines, and 3) lead leaching propensity of new brass ball valves. During installation of plumbing systems, residual chemicals and debris including copper brass particles and flux, can be left in plumbing lines following construction and installation. This debris is considered undesirable from health, aesthetic, and corrosion perspectives. Soldering flux is of particular concern due to its corrosive nature. Experiments were conducted to determine the effects of residual solder flux, PVC glue, and metallic debris and to quantify flushing velocities and durations to effectively remove them from a new plumbing system. A flushing velocity of 3 fps for 30 minutes is needed to remove water soluble flux, while petroleum based flux still persists after extensive flushing at 7 fps. Currently a practice known as shock chlorination, whereby super chlorinated water is used for disinfection, is used in water mains after installation or repair as specified in the ANSI/AWWA C651 Standard. This practice is now starting to be required by some building codes in premise plumbing for new construction. Water mains are typically made of concrete where as premise plumbing using copper or PVC piping. Copper pipe is susceptible to attack by high chlorine, and this reaction will also remove the chlorine residual. There is concern about potential damage to copper from free chlorine and that in some systems targeted residuals of chlorine might not be obtained. Experiments did not detect serious damage to copper pipe, but in some waters it was not possible to meet targeted residual levels of chlorine. The addition of orthophosphate corrosion inhibitor or adjustment of pH can sometimes reduce the chlorine decay rate. Extremely high and persistent lead leaching in a brand new building at the University of North Carolina (UNC) traced to leaded bronze ball valves, prompted an extensive forensic evaluation how existing standards (National Sanitation Foundation Section 8) could allow for installation of products that could create a human health hazard due to high lead. Diffusion of lead from within the device to water in the pipe, high velocity, microbial activity and other factors caused more leaching in practice than would be expected based on NSF testing and normalization factors applied to certify a valve as safe. Moreover, use of flux during soldering of joints, increased lead leaching by orders of magnitude relative to results of NSF testing without flux.
- New Insights into Lead and Copper Corrosion: Impacts of Galvanic Corrosion, Flow Pattern, Potential Reversal, and Natural Organic MatterArnold, Jr, Roger Brooke (Virginia Tech, 2011-04-29)The EPA Lead and Copper Rule set Action Limits for lead and copper concentrations in potable water, but accelerated corrosion of lead in potable water systems due to a galvanic connection to copper remains a significant health risk to consumers. In addition to elevated lead release due to galvanic corrosion of lead-tin solder and leaded brass fixtures, partial lead service line replacements with copper pipe present long-term health concerns. Prior research has demonstrated that the effects of galvanic corrosion can be controlled by water chemistry, and the interplay between alkalinity, natural organic matter (NOM), and orthophosphate (added as corrosion inhibitor) may have a significant influence on corrosion of common lead plumbing materials. Results of bench-scale experiments demonstrate that in some waters galvanic corrosion can multiply lead release from lead pipe by up to 60 times, but other waters curtail the galvanic current and alleviate the effects of galvanic corrosion. Measurements of pH at the lead surface demonstrate that a corrosive micro-environment forms during stagnation in which the local pH drops to 3.0 or lower, demonstrating that the worst-case scenario for galvanic corrosion of lead occurs during long stagnation periods. In addition to water chemistry, flow pattern also has an impact on galvanic corrosion of lead. Conventional wisdom regarding lead release indicates that continuous flow results in the greatest mass of lead release, but reports of anomalously high lead concentrations after long periods of stagnation point to the contrary. In this experiment, continuous flow of chlorinated water through a Pb-Cu galvanic couple promoted Pb(IV) formation and resulted in potential reversal that caused lead pipe to become cathodic to copper and minimized lead release to water. In contrast, intermittent flow resulted in sustained galvanic attack, and a mass balance of Pb release indicated that a greater total mass of lead was released with intermittent flow. These results have important implications for assessing lead risk at the tap, especially considering long stagnation periods at facilities such as schools and increasing efforts for water conservation. Elevated copper release in potable water can cause aesthetic problems and mild health concerns and often occurs in new plumbing systems prior to the formation of a protective scale layer on the pipe surface. While solubility in new copper pipes tends to be controlled by an amorphous solid of high solubility, over time, the natural copper aging process results in the formation of a protective scale of much lower solubility, but the transition can be inhibited in waters with high levels of NOM. Experiments demonstrated that GAC treatment to remove NOM accelerates the aging process to a protective scale that provides a long-term reduction in copper release even after GAC treatment is terminated. Therefore, compared to pH adjustment and orthophosphate addition, which must be continued perpetually, GAC treatment may be a more holistically pleasing method of copper corrosion control. This approach could be useful in the commissioning of new buildings to facilitate rapid aging and avoid potential long-term copper corrosion problems.
- Sorption and desorption of the industrial chemical MCHM into polymer pipes, liners and activated carbonAhart, Megan Leanne (Virginia Tech, 2015-05-21)Polyethylene pipes and epoxy or polyurethane linings are increasingly used in drinking water infrastructure. As a recent introduction to the water industry, there are still many unknowns about how polymers will behave in the distribution system specifically relating to sorption and desorption of chemical contaminants. This study is in response to a spill of 4-methylcyclohexane methanol (MCHM) that occurred in January 2014 contaminating the drinking water of nine counties in West Virginia. This study investigated sorption and desorption of the odorous chemical MCHM into polymer drinking water infrastructure and granular activated carbon (GAC). Experiments for sorption of non-polar toluene and polar 1-butanol were conducted as a comparison for MCHM sorption. Additionally, a brief odor analysis was done on the ability of activated carbon to remove odor from contaminated water and on leaching of MCHM from pipe material into clean water. The results show that MCHM diffusion and solubility in polyethylene pipe materials is low. Solubility in polyethylene ranged from 0.003-0.008 g/cm3 and was more similar to the polar contaminant n-butanol than the non-polar contaminant toluene. Desorption experiments indicated that MCHM sorbed to polyethylene diffused back into water at levels that produced odor. MCHM diffused very quickly into epoxy; its solubility was similar to polyethylene pipe. MCHM caused the polyurethane lining to swell and deform. Granular activated carbon effectively sorbed MCHM to below its odor threshold. The sorption properties of MCHM indicate the potential for contamination of infrastructure and the desorption indicates subsequent recontamination of drinking water.
- Two Issues in Premise Plumbing: Contamination Intrusion at Service Line and Choosing Alternative Plumbing MaterialLee, Juneseok (Virginia Tech, 2008-04-18)Worldwide water distribution infrastructure system is old and deteriorating. A water system with its myriad appurtenances (including pumps and valves and tanks) is susceptible to hydraulic transients resulting in high and low pressure waves alternatively passing through the network. While both low and high pressure events structurally tax the already weak system, there is copious evidence indicating intrusion of contaminants into the drinking water pipes from the pipe's exterior environment due to low pressure events associated with water hammer phenomenon. These contaminants enter into the drinking water as the home plumbing system is a passive recipient from the water main. While the major (municipal) system is readily recognized as a vast infrastructure system of nearly 1,409,800 km of piping within the United States, the minor (plumbing) system that is at least 5 to 10 times larger is generally not well analyzed. In this study, an experimental plumbing rig was designed and implemented that replicates the range of pressures encountered in actual minor water distribution systems. This research addresses how a pressure transient triggered within a house and from municipal systems can impact the service line with a possible suction effect. Experimental results on low pressure events and the accompanying numerical modeling showed good agreement. The experiment also enabled visualization of the various pressure transient phenomena. It is demonstrated that hydraulic transients triggered from water mains result in low pressures events (up to -10 psig) in service lines which can allow possible intrusion of microbial and chemical contaminants at the service line. Structural integrity of service line and hydraulic integrity at water mains should be maintained to minimize any public health risks. In the USA, about 90% of residential drinking water plumbing systems use copper pipes. Pinhole leaks in copper plumbing pipes have become a nationwide concern because these leaks cause property damage, lower property values, and result in possibility of adversely affecting homeowners' insurance coverage. In addition, resulting mold damage may cause health concerns. This research also addresses the concerns of the affected homeowners by enabling them to decide on whether to continue to repair or replace their plumbing system, the factors to be considered in a replacement decision, and the type of material to use for replacement. Plastic pipes such as PEX (cross-linked polyethylene), CPVC (Chlorinated Polyvinyl Chloride), and copper are considered in present analysis. Other alternatives include an epoxy coating technique on the existing piping systems, without the need to tear into walls. Multiple attributes of a plumbing system including cost (material plus labor charges), taste and odor impacts, potential for corrosion, longevity of the pipe system, fire retardance, convenience of installation or replacement, plumber or general contractor's opinions or expertise, and proven record in the market are considered. Attributes and material rankings are formalized within the framework of the preference elicitation tools namely AHP (Analytical Hierarchical Process). Surveys are conducted with selected homeowners in pinhole leak prone area in Southeastern US Community to observe their revealed and stated preferences. Participants' overall preference tradeoffs are reported in addition to comparing their revealed and stated preferences. Health effects, taste and odor of water turned out to be the most important factors from the survey. In real life, however, homeowners were not well aware of these safety issues related with plumbing materials. It is recommended that water professionals should work on bridging the gap between public perception and research results related to major and minor systems.
- Water Treatment: Fundamentals and Practical Implications of Bubble FormationScardina, Robert P. (Virginia Tech, 2000-02-11)Water utilities can experience problems from bubble formation during conventional treatment, including impaired particle settling, filter air binding, and measurement as false turbidity in filter effluent. Coagulation processes can cause supersaturation and bubble formation by converting bicarbonate alkalinity to carbon dioxide by acidification. A model was developed to predict the extent of bubble formation during coagulation which proved accurate, using an apparatus designed to physically measure the actual volume of bubble formation. Alum acted similar to hydrochloric acid for initializing bubble formation, and higher initial alkalinity, lower final solution pH, and increased mixing rate tended to increase bubble formation. Lastly, the protocol outlined in Standard Methods for predicting the degree of supersaturation was examined, and when compared to this work, the Standard Methods approach produces an error up to 16% for conditions found in water treatment. Air entrainment and ozonation are the key causes of dissolved gas supersaturation and eventual bubble formation in water treatment plants. Total dissolved gas probes (TDGP) are now available to directly measure supersaturation and have many advantages compared to conventional techniques. Bubble formation during coagulation-flocculation hindered particle sedimentation, producing settled turbidities double that of solutions without dissolved gases. In a filtration study, run time to one half of initial flow was decreased by 54% when the source water was increased from 0.1 to 0.2 atm supersaturation. Indeed, even at 0.05 atm supersaturation, run length was only 21 hours in solutions without added particulate matter. A case study confirmed that bubble formation can interfere with coagulation and filtration processes at conventional treatment plants.