National Academies Press: OpenBook

Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas (2014)

Chapter: Chapter 2 - Characterization of Highway Runoff

« Previous: Chapter 1 - Introduction
Page 4
Suggested Citation:"Chapter 2 - Characterization of Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 4
Page 5
Suggested Citation:"Chapter 2 - Characterization of Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 5
Page 6
Suggested Citation:"Chapter 2 - Characterization of Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 6
Page 7
Suggested Citation:"Chapter 2 - Characterization of Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 7
Page 8
Suggested Citation:"Chapter 2 - Characterization of Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 8
Page 9
Suggested Citation:"Chapter 2 - Characterization of Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 9
Page 10
Suggested Citation:"Chapter 2 - Characterization of Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 10

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

42.1 Stormwater Composition Highway runoff is comprised of a number of soluble and insoluble constituents that vary with respect to their behav- ior in the environment. Metals such as cadmium (Cd), chro- mium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) originate from sources as varied as brake pads, wheel weights, and galvanized structures (signs, guardrails, etc.). These metals are known to exist in a variety of different physical and chemical forms that dictate their mobil- ity, bioavailability, and toxicity to aquatic organisms. A sum- mary of observed metals concentrations in highway runoff from the FHWA database is presented in Table 2-1. Review of these data suggests that the concentrations of heavy metals in highway runoff can be significantly higher than observed in natural waters. As a result, there is concern regarding the impacts of these discharges on ecosystems and water quality. Highway runoff has been shown to have acute and chronic effects on ecosystem biotic diversity and mortality rates downstream from discharge outfalls (Ellis et al. 1997). Metals constitute a common class of pollutants identified in numerous 303(d) lists for stormwater. In California, the most commonly listed metals are mercury, copper, lead, selenium, zinc, and nickel. Less frequently listed metals are cadmium, arsenic, silver, chromium, molybdenum, and thallium (California Stormwater Quality Association 2002). However, cadmium is one of the more frequent causes of impairment in New York, New Jersey, Maryland, and several other states (U.S. EPA 2010). Since both receiving water standards and the concentrations of dissolved metals in highway runoff are often near method detection limits, it is important to have appropriate protocols in place for sample collection and analysis. Guidance on these issues is provided in Appendices A and B. An important consideration is that the distinction between dissolved and particulate associated metals is operational rather than chemically based. Laboratory methods for determining the fraction of a metal in the “dissolved” phase are based on the mass passing through a 0.45 mm filter. Clearly this is a rather arbitrary division, since many particles can be smaller than this threshold. In addition, metal ions can be associated with organic and inorganic ligands rather than existing as free ions. Consequently, dissolved is not synonymous with ionic. A good example of this is a study conducted by the USGS on metals transport in the Sacramento River (U.S. Geological Survey 2001). This study analyzed for dissolved metals using ultrafiltration (equivalent to 0.005 mm pore size), in addi- tion to the standard capsule filters (0.45 mm) to determine the amount of metal that is actually associated with colloi- dal size particles rather than actually being dissolved. They found that metal concentrations in the ultrafiltrates were about 40 to 70% lower than conventional filtrates, with the percentage for copper being higher than for zinc or cadmium. In the water column, colloids appeared to be the dominant form of aluminum, iron, lead, and mercury. This distinction is significant because the relative amounts of colloidal and dis- solved metals influence the rates and mechanisms of metal bioaccumulation. Organic constituents in highway runoff also have an impor- tant role in determining the bioavailability of dissolved metals and the effectiveness of various treatment processes. These constituents include oil, grease, humic acids, plastics, tire rub- ber, fecal material, PAH’s, phthalates, pesticides, and herbicides, which are derived from a variety of natural and anthropogenic sources. A detailed study of the composition of stormwater runoff from Los Angeles, CA reveals the complex nature of the organic matter as shown in Table 2-2. Dissolved metal complexes are often categorized as electro- chemically available, chelex removable, and strongly bound. The chelex removable species are readily taken up by aquatic biota and include ionic species of metals as well as weakly bound organic species (Morrison et al. 1989). Strongly bound metals are less toxic, forming complexes with hydroxides, car- bonates, and dissolved organic matter (DOM), which acts as a biogenic chelator (Ammann 2001). C H A P T E R 2 Characterization of Highway Runoff

5 Constituent Mean (µg/L) Median (µg/L) Range (µg/L) Dissolved Cu 15.9 9.2 < 1 - 620 Total Cu 50.1 26 < 1 – 9650 Dissolved Zn 94.8 41.0 3.6 – 14,786 Total Zn 273 150 1 – 21,060 Dissolved Pba 5.6 < 1 < 1 – 480 Total Pb 246 32 < 0.5 – 13,100 Dissolved Cda 0.36 < 0.2 < 0.1 – 9 Total Cd 5.0 0.7 < 0.1 – 400 Dissolved Ni 5.3 3 < 1 – 82 Total Ni 11.4 7.7 < 1 – 208 Dissolved Cr 3.4 2.1 < 1 – 54 Total Cr 13.8 7.2 < 0.5 – 190 Dissolved Fe 315 114 6 – 8,970 Total Fe 6,543 3,170 < 25 – 162,000 Dissolved Cab 10.2 (mg/L) 10.6 (mg/L) 3.4 – 19.9 (mg/L) Total Cab 110 (mg/L) 44.5 (mg/L) 13 - 510 (mg/L) Dissolved Mgb 0.8 (mg/L) 0.71 (mg/L) 0.3 – 2.35 (mg/L) Total Mgb 48.5 (mg/L) 15 (mg/L) 5.3 - 270 (mg/L) Dissolved Mnb 97 56 19.6 - 744 Total Mnb 295 229 106 – 932 Dissolved Organic C 19.6 (mg/L) 12.6 (mg/L) 0.2 – 440 (mg/L) a > 50% nondetect, blimited dataset. Table 2-1. Summary of metals concentrations in highway runoff from the highway runoff database (Granato and Cazenas 2009). Anthropogenic Recent Biogenic Petroleum Microbial Based 1. n-alkanes, n-C13-24 1. n-alkanes 2. branched hydrocarbons 2. alkanoic acids iso, anteiso, isoprenoids iso, anteiso series, cyclopropane acids 3. cyclic compounds 3. -hydroxy acids cyclohexane series, steranes, diterpanes, triterpanes iso, anteiso acids, normal acids < C20 4. aromatic hydrocarbons 4. -dicarboxylic acids (?) 5. unresolved complex mixture Synthetics Higher Plants 1. phthalates, adipates 1. n-alkanes > SC24 2. aromatic ketones (?) 2. n-alkanoic acids > 20:O 3. dehydroabietic acid 4. n-alkan-2-ones > c25 (?) 5. chlorophyll derivatives CIS isoprenoid ketone, isoprenoid y-lactones 6. dicarboxylic acids (?) 7. -hydroxy acids 8. n-alkanols > C24 9. phytosterols Higher Animals 1. fecal sterols coprostanol, epicoprostanol Table 2-2. Summary of molecular markers found in Los Angeles storm runoff (Eganhouse et al. 1981).

62.2 Particles in Highway Runoff Stormwater runoff transports significant loads of dissolved, colloidal, and suspended particles in a complex mixture that includes metals and inorganic and organic compounds. While the temporal variability and complexity of rainfall-runoff chemistry is recognized, the focus herein is the transport, dis- tribution, and partitioning of metals as mediated by the wide gradation of particles from highway systems. Particles are ubiq- uitous in transportation land use, and particles with associated metal accretion are in large part a function of traffic activities (Kobriger and Geinopolos, 1984; Hamilton and Harrison 1991; Glenn and Sansalone 2002). Highway runoff transports a wide gradation of particles rang- ing in size from smaller than 1-mm to greater than 10,000-mm (Sansalone et al. 1998). From a water chemistry and treatment perspective, entrained particles having reactive sites and large surface-to-volume ratios are capable of mediating partitioning and therefore transport of metals. Figure 2-1 illustrates the rela- tive contributions of abraded particles as generated by traffic. engine/brake wear 15% settleable exhaust 6% atmospheric deposition 3% pavement wear 44 - 49% tire wear 28 - 31% Figure 2-1. Relative fractions of traffic- generated particles (Sansalone et al. 1998). 30,600 7,454 2,200 1,050 124 0 10,000 20,000 30,000 40,000 Cu Ni Cr Pb Zn Co nc en tra tio n [ µ g/ g ] Figure 2-2. Selected metal content of typical 130-g brake pad (Sansalone and Hird 2002). Particle Diameter, D ( m) {c df} : % fi ne r b y m ass , F (D ) 0 20 40 60 80 100 Dry Deposition q (up) q (down) downstreamupstream q (settled) 110100100010000 Location ( , ) DD (2.06, 187.7) q (up) (1.90, 61.9) q (down) (1.23, 23.6) q (settled) (1.51, 11.1) )( /)( /1 D eDDf )(/)()( DDF 0 )(1)( dxex x D x D dxex0 )(1)( PSD gamma model DD Dry Deposition q (up) Upstream Runoff q (down) Downstream Runoff q (settled) Settled (1 hour) Runoff D50m, µm 330.7 98.6 22.6 13.7 Figure 2-3. Transformation of PSD from dry traffic deposition through settled effluent. Range bars represent range of data (% finer by mass) for each event. In urban transportation corridors, metals are generated pri- marily from the abrasion of metal-containing vehicular parts, including the abrasive interaction of tires against pavement and oil and grease leakage (Armstrong 1994; Ball et al. 1991; Lygren et al. 1984; Muschack 1990). Abraded particles such as particles abraded by brakes have a high metal content (Sansalone and Hird 2002). Brake wear alone is estimated to contribute 15% of the total particles, and the relative contribution of selected metals for a typical 130-g brake pad is given in Figure 2-2 from data reported by Armstrong (1994). Some states, such as Cali- fornia and Washington, have recognized the significant source of copper in brake pads and have enacted legislation to reduce this source. Given that particles can transport a significant fraction of metal mass and are a repository or sink for metals, the trans- formation of particle size distribution (PSD) as a function of distance from the edge of the pavement is of interest with respect to the fate of particles-based metals. This is illustrated in Figure 2-3 for measured particles data (1) initially as dry traffic deposition, (2) to particles in runoff at the edge of the

7 pavement, (3) to particles in runoff at the edge of the right-of- way (ROW) entering a settling tank, and (4) finally to particles in treated runoff effluent discharged to the adjacent receiving water (Ying and Sansalone 2010). Results shown in Figure 2-3 illustrate two related phenom- ena. First, a significant fraction of coarse particles is potentially not mobilized during rainfall-runoff events or deposited in the drainage system (catch basin and storm drain in the ROW). Second, the drainage system can result in greater modification of the PSD than does one hour of sedimentation in a settling tank at the edge of the ROW. 2.3 Metal Partitioning and Complexation in Highway Runoff PSD and loading of particles have a significant role in the partitioning (to and from particles) and transport of metals. While sediment particles (> 75 mm) are readily separated by size exclusion or sedimentation, suspended particles (< ~25 mm) such as, for example, organic particles from anthropogenic sources (tire particles) or biogenic sources (pollen), can be diffi- cult to separate from runoff by sedimentation. Such suspended particles can require filtration or coagulation/flocculation if sufficient time for sedimentation is not available. Other parameters that are important from a treatment perspective include mass loading, PSD, specific gravity, specific surface area (SSA), and total surface area (SA). A typical relationship between PSD, SSA, and SA is illustrated in Figure 2-4 for par- ticles (Sansalone and Tribouillard 1999). SSA and SA results illustrated in Figure 2-4 demonstrate that although SSA does increase with decreasing particles diameter (by definition), the largest percentage of SA is associated with the mid-range of particles sizes. Additionally, the increase in SSA with decreasing particle size is not monotonically increas- ing as would be expected for spherical particles of constant specific gravity. Although SSA increases with decreasing parti- cle diameter, calculations using the assumption of solid spheri- cal particles grossly underestimate actual SSA values shown. Whether associated particles or engineered sorptive media for the separation of dissolved metals from runoff, the particle- water interfacial SA is an important parameter. The equilib- rium distribution (> 24 hours) is shown in Figure 2-5 based on Cincinnati interstate data. Figure 2-5 illustrates strong corre- lations between particles-bound metal mass regressed against total particles SA. Although SSA does increase with decreasing particles diameter, the distribution of metal mass is correlated to SA of particles and not SSA. The dissolved phase of metals is of particular concern for acute impacts since dissolved metals can be readily assimi- lated by aquatic biology and are more difficult to manage as compared to particles-bound metals (Yousef 1985). Due to the relatively acidic nature of rain in many urban areas, metals have the potential to leach into the dissolved phase at the upper end of the urban watershed as a function of residence time, pH, alkalinity, properties of particles, and the load of particles (Revitt and Morrison 1987). Previous research has suggested that Pb and Cu species leached after contact with acidic rain are complexed by organic matter or partition to suspended solids, while Cd and Zn remain primarily in solution (Morrison et al. 1990). During stor- age between runoff events in BMPs such as hydrodynamic separators or settling tanks, metals have been shown to re- partition and undergo re-distribution across the PSD (Ying and Sansalone 2010). Metal partitioning between the dissolved and particle- bound fractions in stormwater is a dynamic process. Whether 0 10 20 30 40 50 4000 15 SS A ( m 2 /g ) Partic le diam eter ( m ) ( m easured SSAi) data 0 10 20 30 4000 15 m as s fra ct io n (% ) 300 SA i( m 2 ) 15 Particle d iam eter ( m ) 0 2000 4000 6000 4000 i1 in i1 in (measured m i) data from PSD calculated (SA i) results from discrete of SSA i with m iSSA i)(m i)}SA i = SA i : Incremental particle surface area (m 2 ) SSA i : Increm ental specific surface area (m 2/g ) m i : Increm ental particle mass (g) Figure 2-4. Relationship between the mass-based PSD, SSA, and total SA for runoff particles. The linkage between SSA and SA requires a mass-based PSD.

8in runoff or other aqueous systems, there is a temporal parti- tioning between metals in solution and the entire gradation of particles. This partitioning includes specific mass transfer mechanisms such as adsorption and ion exchange. These par- titioning reactions are generally non-linearly reversible between the particles and soluble phase concentrations. If the colloidal fraction is considered a fraction of particles, the total concentra- tion of a metal is therefore the sum of the dissolved (Cd) and the particulate-bound concentrations (Cp). Under equilibrium, when the rate of sorption and desorp- tion are equal, concentration equilibrium exists between the dissolved and solid-phase concentrations of a metal. The ratio of these phases at equilibrium is referred to as the partitioning coefficient, Kd (Kd = Cp/Cd) or a particular metal at a particular pH and redox level. From these definitions, a dimensionless dissolved fraction (fd) ranging from 0 to 1, fd can be computed. Kd is usually expressed as liters per kilogram (L/kg). The larger the Kd value, the greater the partitioning to the particles phase. Metals in pavement runoff have Kd values that range from 102 to over 106 (Sansalone and Buchberger 1997; Sansalone and Glenn 2003). Metal partitioning in runoff also varies throughout a rain- fall-runoff event and is influenced by intra-event rainfall- runoff chemistry (including pH, alkalinity, hardness, and particle concentration), transport residence time, hydro- dynamics, traffic loading, and particle characteristics. Each of these parameters varies significantly between and during hydrologic events (Sansalone and Buchberger 1997). Understanding the kinetics of this non-equilibrium parti- tioning is critical for proper monitoring, conceptual design, and viability of unit operations and processes that may be applied as in situ or source control treatment. Figure 2-6 provides an illustration of the time-dependent partitioning of Cu in stormwater samples for a fixed set of stormwater chemistry parameters (Sansalone and Buchberger 1997). For sampling and monitoring, this analysis indicates that after 6 hours for the given stormwater chemistry, the Cu mass is partitioning to the particulate-bound fraction. Additionally, a consistent trend in Kd as a function of time for Pb, Cu, Cd and Zn can be observed for the 8 August 1996 event despite the inverse trend in particles [measured as total suspended solidT(SS)]. Knowledge of the partitioning kinetics and the relative frac- tions of dissolved (fd) and particulate-bound (fp) mass delivered for treatment are of fundamental importance for in situ treat- ment where residence times on the urban surface or in the urban drainage system in the presence of entrained particles are less than several hours. An example of the relative fractions of dissolved and particles-bound metals is provided in Fig- ure 2-7 for event-based data from a Cincinnati interstate catch- ment. Results in this figure illustrate that mass transfer from the aqueous phase (e.g., adsorption, ion exchange, or precipita- tion) in addition to particles-bound separation (sedimenta- tion, filtration, coagulation/flocculation) require consideration in treatment design. Results also indicate that knowledge of partitioning for a given set of residence time and stormwater 40 10000 850 250 106 63 45 15 Zn mass R2 = 0.94 Particle diameter ( m) Cu mass R2 = 0.81 SSA SA Cd mass R2 = 0.90 10000 850 250 106 63 45 15 Particle diameter ( m) Pb mass R2 = 0.97 SS A ( m 2 /g ) SA ( m 2 ) Zn m as s ( m g ) 0 9000 0 240 0 2.0 0C d m as s ( m g ) 60 Cu m as s ( m g ) 0 40 Pb m a ss ( m g ) 0 Figure 2-5. Distribution of metal mass as a function of runoff particles SA. For comparison to SA, the contrasting distribution of particles SSA is also illustrated.

9 chemistry parameters is a necessary first step for conceptual and detailed treatment design. The dominance of the dissolved mass for all metals, includ- ing relatively insoluble Pb for short urban surface residence times (initial pavement residence time < 15 minutes), with fd values for Zn and Cd of approximately 0.8 or greater, Cu between 0.60 to 0.80, and Pb between 0.5 to 0.7 at this highway catchment, was typical of results from all 13 rainfall-runoff events characterized over two years at the urban Cincinnati highway catchment (Sansalone 1999). Controlling parame- ters of partitioning kinetics include pavement surface loading rate, suspended solids ratio, dissolved organic carbon (DOC) content, total dissolved solids (TDS), and ligand concentra- tions (organic and inorganic). These results illustrate the need for treatment of the dissolved as well as particle-bound fractions when considering in situ solutions. In addition to metal ions and those associated with solids in runoff, metals can also form organic complexes and inorganic complexes. The mobility of the metals is directly dependent on the complex formed. Additional investigations carried out by Revitt et al. (1987) revealed that aqueous Cd, Cu, Pb, and Zn concentrations in transportation land-use runoff were predom- inately found in the chelex removable phase. However, only Zn and Cu were determined to be present as predominately diva- lent species, while Cu typically formed medium strength bonds with DOC. Results from this research indicated that 59%, 38%, 5%, and 53% of the total Cd, Cu, Pb, and Zn concentrations, respectively, in runoff were readily available to aquatic organ- isms. The results also revealed that Cu was predominately bound to organic complexes (Revitt and Morrison 1987). Investiga- tions carried out by Flores-Rodriguez et al. (1994) verified that Zn and Cd were predominately bioavailable, while Pb tended to 0 50 100 150 200 250 300 0 84 12 16 20 24 Time from sampling (hours) C u [ g/ L] dissolved particulate-bound pH = 6.5 Alkalinity = 30 mg/L TSS = 150 mg/L Elapsed Time (min.) 0 20 40 60 80 K d [L / k g ] 1e+0 1e+1 1e+2 1e+3 1e+4 1e+5 TS S [m g / L ] 0 200 400 600 800 Pb Cu Cd Zn TSS Figure 2-6. Time-dependent partitioning for Cu for 15 July 1995 runoff event and the temporal increase in heavy metal partitioning coefficient, Kd, for an 8 August 1996 event. Cu m u la tiv e Pb (m g) 0 10 20 30 40 Cu m ul at iv e Cu (m g) 0 5 10 15 20 25 30 35 Elapsed time (min.) 0 20 40 60 80 Cu m u la tiv e Zn (m g) 0 75 150 225 300 Dissolved Particulate fd = 0.83 (n=27) fd = 0.80 (n=27) fd = 0.71 (n=27) fd = 0.76 (n=27) Elapsed time (min.) 0 20 40 60 80 Cu m u la tiv e Cd (m g) 0 1 2 Figure 2-7. Dissolved fraction mass (fd) partitioning and particles-bound fraction for an 18 June 1996 runoff event (fd  fp  1.0) from I-75 in Cincinnati, OH.

10 form more stable complexes with inorganic and organic carbon in runoff. 2.4 Summary Metals concentrations in highway runoff are elevated compared to most natural receiving waters and have been shown to have toxic effects on some aquatic species. Met- als are divided into dissolved and particulate fractions (total metals being the sum of the two) based on the ability to pass through a 0.45 mm filter. Consequently, metals associated with very small particles are operationally defined as “dissolved.” Metals can also form complexes with organic and inorganic ligands, rather than existing as an ionic species. These com- plexes make the metals less bioavailable and reduce their toxicity. Stormwater data also indicate that partitioning of metals with solids and ligands may not reach equilibrium for a number of hours. Consequently, treatment design for edge of pavement application should consider the non-equilibrium state of the runoff.

Next: Chapter 3 - Environmental Chemistry of Metals in Surface Waters »
Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s National Cooperative Highway Research Program (NCHRP) Report 767: Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas presents prototype best management practices (BMPs) for the removal of dissolved metals in stormwater runoff.

The report presents three conceptual configurations in detail: two vault system configurations for urban and rural settings, and an inlet scupper with media for bridge deck drainage systems.

The report also includes standard protocols to accurately measure the levels of dissolved metals in stormwater. Practical guidance on the use of these protocols is provided in an appendix to the final report. The report is accompanied by an Excel spreadsheet on CD designed to assist in sizing the filter bed in the vaults and the bridge deck inlet scupper.

The CD is also available for download from TRB’s website as an ISO image. Links to the ISO image and instructions for burning a CD from an ISO image are provided below.

Help on Burning an .ISO CD Image

Download the .ISO CD Image

CD Disclaimer - This software is offered as is, without warranty or promise of support of any kind either expressed or implied. Under no circumstance will the National Academy of Sciences or the Transportation Research Board (collectively "TRB") be liable for any loss or damage caused by the installation or operation of this product. TRB makes no representation or warranty of any kind, expressed or implied, in fact or in law, including without limitation, the warranty of merchantability or the warranty of fitness for a particular purpose, and shall not in any case be liable for any consequential or special damages.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!