Surveys of US drinking water utilities were conducted in 1994 and 2001 to investigate trends

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1 Surveys of US drinking water utilities were conducted in 1994 and 1 to investigate trends in phosphate inhibitor use. More than half of those water providers surveyed reported adding phosphate inhibitors to their water. Zinc orthophosphate and polyphosphate were commonly used inhibitors, and a shift from poly/orthophosphate blends to orthophosphate was observed from 1994 to 1. Inhibitor doses ranged from <.2 to > 3 mg/l as PO 4 (although many utilities could only report dosages as product because of the proprietary nature of the inhibitor chemicals). Surprisingly, most utilities based their inhibitor selection on limited information, with smaller utilities relying more on nontechnical information (e.g., vendor information, success of the chemical at another utility) than on direct confirmation of the inhibitor s effectiveness. Many utilities are aware of potential drawbacks of inhibitors, especially increased biological activity and more treatment costs and residuals. Phosphate inhibitor use at US utilities P hosphate inhibitors have been used for more than 6 years to prevent scale buildup and to control pipe corrosion. With the advent of the US Environmental Protection Agency Lead and Copper Rule (LCR) in 1991, many more utilities chose to dose inhibitors in an attempt to meet the action limits for lead and copper concentrations in tap water. PREVIOUS STUDIES A comprehensive analysis of inhibitor studies is beyond the scope of this article. Furthermore, such an analysis would be difficult given the variety of study methods used (e.g., tap sampling, pipe loops, coupons, electrochemical testing), and many studies did not report pertinent experimental conditions (e.g., water quality, temperature). However, a summary of representative studies on phosphate inhibitors and lead (Table 1) and copper (Table 2) corrosion demonstrates the broad range of outcomes from dosing inhibitors. Summary of findings. In many cases, inhibitors were found to decrease corrosion, although inhibitor action appeared to be highly dependent on water quality and other factors. Under some circumstances, these inhibitors significantly worsened corrosion. In particular, polyphosphate was shown to increase soluble lead and cop- BY LAURIE S. MCNEILL AND MARC EDWARDS MCNEILL ET AL PEER-REVIEWED 94:7 JOURL AWWA JULY 2 57

2 TABLE 1 Summary of studies on phosphate inhibitor effects on lead corrosion Reference Type of Study Water Quality* Remarks Hatch, 1941 Lead pipe rig ph 6, alkalinity 7 mg/l as CaCO 3, 2 mg/l polyphosphate reduced lead hardness 54 mg/l as CaCO 3 concentration; high levels may attack lead. Patterson & O Brien, 1979 Coupon tests Soft, low-alkalinity water, ph mg/l zinc orthophosphate increased lead concentration. Sheiham & Jackson, 1981 Lead pipe rig Soft, low-alkalinity water, ph mg/l of polyphosphate, pyrophosphate, or orthophosphate decreased lead concentration. No additional benefit from adding zinc. Karalekas Jr. et al, 1983 Tap water sampling Soft water with low alkalinity 3 5 mg/l zinc orthophosphate had adverse or (8 12 mg/l as CaCO 3 ), ph 6.7 insignificant effects in reducing lead concentration (possible confounding effect of temperature). Richards & Moore, 1984 Tap water sampling Soft, very low-alkalinity water, 2 mg/l orthophosphate in addition to ph ph 6.3 adjustment (ph 8 9) reduced lead concentration to an even greater extent than ph adjustment alone. Colling et al, 1987 Lead pipe rig Alkalinity 15 mg/l as CaCO 3, 1 mg/l orthophosphate reduced lead ph 7 8 concentration. Cousino et al, 1987 Tap water sampling Soft water, ph mg/l polyphosphate reduced lead concentration. Holm et al, 1989 Complexation Hardness mg/l as CaCO 3, Polyphosphate complexed lead, increased lead experiments alkalinity 5 15 mg/l as CaCO 3, concentrations. ph 8. Lee et al, 1989 Tap water sampling Varied Utilities adding zinc orthophosphate had lower lead concentration compared with waters with ph > 8.; polyphosphate and zinc polyphosphate had lead levels similar to waters with ph > 8.. Schock, 1989 Solubility models Wide range Addition of orthophosphate at ph < 7.6 predicted to reduce lead concentration. Gregory, 199 Flow-through cells, Wide range.4 mg/l zinc orthophosphate reduced copper: lead/tin corrosion potential. couple Boffardi & Sherbondy, 1991 Lead pipe rig ph 7.2, both high- and 1 mg/l zinc orthophosphate generally reduced low-alkalinity waters lead concentration. Holm & Schock, 1991 Solubility ph 8., Ca 4 mg/l 1 mg/l polyphosphate addition predicted to calculations increase lead solubility Colling et al, 1992 Lead pipe rig Varied Orthophosphate reduced lead concentration. Maas et al, 1991 Tap water sampling Varied Very soft waters dosed with polyphosphate were more likely to exceed lead action limit than waters with no inhibitor; waters with zinc orthophosphate generally had lower lead concentrations than waters with no inhibitor. Johnson et al, 1993 Lead pipe rig Low alkalinity (6 12 mg/l 9.3 mg/l (as zinc) zinc orthophosphate reduced as CaCO 3 ), ph , lead concentrations from lead pipes and ph adjusted to before lead/tin solder. adding inhibitor Friedman et al, 1994 Lead coupons Varied Polyphosphate/orthophosphate blend reduced lead concentration. Neuman, 1995 Tap water sampling Varied Zinc orthophosphate reduced lead and copper levels at 5% of utilities. Dodrill & Edwards, 1995 Survey of large Varied Phosphate inhibitors reduced lead concentrautilities tions in low alkalinity waters, with highly variable and adverse effects at higher alkalinity. Lyons et al, 1995 Tap water sampling Soft, low-alkalinity water, 3 5 mg/l orthophosphate reduced 9th ph < 7.5 percentile lead levels; zinc orthophosphate not viable because of high zinc levels in wastewater sludge. Cantor et al, Tap water sampling Varied Polyphosphate increased lead concentrations. Edwards & McNeill, 2 Lead pipe rig Varied 1 mg/l polyphosphate increased soluble and particulate lead concentrations under stagnant conditions. *CaCO 3 calcium carbonate, Ca calcium 58 JULY 2 JOURL AWWA 94:7 PEER-REVIEWED MCNEILL ET AL

3 For more than 6 years, water utilities have used phosphate inhibitors to control pipe corrosion. Here cross-sections of a corroded iron pipe (left) and a pitted copper pipe (above) are shown. per concentrations through complexation, and it was unclear whether additional benefits resulted from dosing zinc orthophosphate compared with regular orthophosphate inhibitors. Numerous studies extolled the virtues of phosphate inhibitors for controlling iron corrosion or red water (see McNeill & Edwards [1] and AWWARF & DVGW [1996] for a review). However, several recent studies found that polyphosphate could increase red water, tuberculation, and iron weight loss for many water qualities (McNeill & Edwards, ; Lohmann et al, 1997). A recent study (Reiber et al, 1997) featuring 16 detailed utility case studies highlighted potential drawbacks of inhibitor dosing from the utility perspective (Table 3). Inhibitor dosing can affect corrosion of all metallic and concrete materials, which then affects biological activity (Abernathy & Camper, 1998; Abernathy & Camper, 1997), disinfectant decay (LeChevallier et al, 1993), and formation of discolored water. Therefore, it is imperative that utilities weigh possible drawbacks of inhibitor dosing against potential benefits. As a first step in this TABLE 2 Summary of studies on phosphate inhibitor effects on copper corrosion Reference Type of Study Water Quality Remarks Bancroft, 1988 Tap water sampling Low ph, alkalinity, and.5 mg/l zinc orthophosphate reduced copper hardness water concentrations. Reiber, 1989 Electrochemical coupon ph or 5 mg/l orthophosphate reduced corrosion measurements rate; weight loss lower by three- to fivefold. Benjamin et al, 199 Copper pipe rigs Soft, low-alkalinity water, 1 or 5 mg/l orthophosphate decreased copper ph 8 concentrations. Boffardi & Sherbondy, 1991 Copper pipe rig ph 7.2, both high- and low- 1 mg/l zinc orthophosphate generally reduced alkalinity waters copper concentrations. Johnson et al, 1993 Copper pipe rig Low alkalinity (6 12 mg/l 9.3 mg/l (as zinc) zinc orthophosphate reduced as CaCO 3 *), ph ; copper concentrations. ph adjusted to before adding inhibitor Werner et al, 1994 Copper pipe rig Moderate hardness, 1 mg/l phosphorus reduced the formation of ph cuprous oxide leading to higher copper concentrations. Dodrill & Edwards, 1995 Survey of large utilities Varied Phosphate addition had beneficial effects when ph < 7.8. Lyons et al, 1995 Tap water sampling Soft, low alkalinity water, 3 5 mg/l orthophosphate reduced 9th ph < 7.5 percentile copper levels; zinc orthophosphate not viable because of high zinc levels in wastewater sludge. Rezania & Anderl, 1995 Tap water sampling High hardness, high mg/l orthophosphate reduced copper alkalinity, ph concentrations. Blended polyphosphate/ orthophosphate could not meet copper action limits. Schock et al, 1995 Theoretical study Varied Model predicts that orthophosphate will reduce copper concentrations in water at ph values > 6.5. Edwards et al, 2 Copper pipe rigs Varied 1 mg/l polyphosphate or orthophosphate generally reduced soluble copper concentrations; orthophosphate more effective than polyphosphate. At ph 7.2, alkalinity mg/l, polyphosphate significantly increased copper concentrations by hindering malachite formation. *CaCO 3 calcium carbonate MCNEILL ET AL PEER-REVIEWED 94:7 JOURL AWWA JULY 2 59

4 TABLE 3 Issue Phosphate-based inhibitors Zinc orthophosphate Polyphosphate Operation and maintenance Cost *After Reiber et al, 1997 Possible drawbacks of phosphate-based inhibitors perceived by water utilities* Concerns Increase in bacterial/microorganism/algal growth Increased phosphate loads in wastewater Effect of higher phosphate on industrial users High zinc concentrations in wastewater sludges/compost Effect of higher zinc on industrial users Possible increase in metal solubility Interference with deposition of protective calcium carbonate film Possible softening of existing scales ph adjustment generally easier to implement Chemical costs often higher for inhibitors than for ph adjustment process, two surveys were conducted to better understand trends in the types and dosages of inhibitors applied as well as the reasons inhibitors are used at water utilities. UTILITY SURVEYS Survey execution. A 1994 project surveyed 2,5 US drinking water utilities that exceeded lead or copper action limits during the initial round of LCR monitoring; 55 relevant utility responses were received (Reiber et al, 1997; Dodrill, 1995). Results were segregated by utility size according to population served: very small (< 3, people), small (3,, people), medium (, 5, people), and large (> 5, people). In 1, an AWWA Research Foundation project surveyed 38 medium and large surface water utilities practicing coagulation and received 264 responses. Although the two populations of utilities surveyed were not identical, a comparison of survey results is instructive. Survey results. Survey results were divided into sections about inhibitor use and reasons for use. Inhibitor use. In 1994, 38% of all responding utilities reported adding phosphate inhibitors; by 1, this figure had jumped to 56%. However, this increase in inhibitor use was actually not as dramatic when examined by utility size (Figure 1). Inhibitor use increased with utility size, and the number of medium and large utilities adding inhibitors remained roughly the same from 1994 to 1. Moreover, if the 1994 survey responses are divided by source water type, 59% of surface water utilities added inhibitors compared with 32% of groundwater utilities and 44% of utilities using both surface water and groundwater sources. The 1 survey did not sample any small- or very smallsized utilities or utilities that had groundwater sources, so recent inhibitor use at those types of utilities is unknown. These usage statistics were similar to results reported in the 1996 AWWA WATER:\STATS, which found that 39% of 9 utilities surveyed were using inhibitors (AWWA, 1996) but were not as high as results from a 1999 survey by American Water Works Company Inc., which found that 72% of its 185 utilities were using phosphate products (Casale, 1). Types of inhibitors used. Water utilities reported using a variety of blends of polyphosphate, orthophosphate, and zinc inhibitors (Figure 2). Use of zinc orthophosphate and polyphosphate remained constant from 1994 FIGURE 1 Utilities Using Inhibitors % survey 1 survey Very Small (<3,) Percentage of utilities using phosphate inhibitors according to utility size Small Medium (3,,) (, 5,) Utility Size by Population Served Large (>5,) not applicable; indicates no "very small" or "small" utilities were sampled in the 1 survey FIGURE Orthophosphate Type of phosphate inhibitor used by water utilities 1994 survey 1 survey Zinc Orthophosphate Polyphosphate Zinc Polyphosphate Zinc Poly orthophosphate Type of Inhibitor Poly orthophosphate Blend 6 JULY 2 JOURL AWWA 94:7 PEER-REVIEWED MCNEILL ET AL

5 to 1. A dramatic increase in orthophosphate use and corresponding decrease in poly/orthophosphate blends was observed, which is likely a positive trend given the potential for polyphosphate to increase soluble metal concentrations (see references in Tables 1 and 2) and the eventual reversion of polyphosphate to orthophosphate (Edwards et al, 2; Edwards & McNeill, 2; Zinder et al, 1984; Green, 195). Reported phosphate doses range from <.2 mg/l as PO 4 to > 3 mg/l (Figure 3). However, it is interesting that more than 6% of utilities in the 1 survey only reported dosages as product because of the proprietary nature of the inhibitor chemicals, so their actual phosphate dosages were not reported. Reasons for use. Figure 4 shows the utilities reported reasons for adding inhibitors. Values do not total % because respondents could select more than one reason for use. Furthermore, in the 1994 survey, utilities were given the option of choosing lead or copper corrosion separately, whereas the 1 survey listed lead and copper corrosion together as one possible survey answer. In the 1 survey, 57% of utilities reported that they first began dosing inhibitors in order to meet the LCR, and 84% of utilities currently dose inhibitors at least partly to control copper or lead corrosion (Figure 4). Nearly half of all utilities also used inhibitors to control iron corrosion or red water, with smaller numbers citing prevention of calcite precipitation and control of iron, manganese, or both. In addition, % of the utilities added phosphate inhibitors to prevent concrete corrosion. At the time of the survey, 1% of utilities dosed the inhibitor during coagulation, 12% before filtration, and 87% after filtration. If a utility sought to protect concrete treatment plant structures with inhibitors, the inhibitors had to be dosed during coagulation, before filtration, or both. However, adding phosphate inhibitors during coagulation is likely to increase coagulant dosages (Stumm & O Melia, 1968) and may hinder removal of natural organic matter (Edwards, 1997). Additional work is needed to resolve these possibly conflicting goals. The most surprising findings of the surveys were responses detailing utilities motivations for choosing to dose inhibitors. According to 1994 responses, utilities evaluated an average of only one to two information sources before selecting a phosphate inhibitor, with larger utilities considering slightly more information. Moreover, much of the information that utilities relied on was not based on direct evaluation methods such as electrochemical, coupon, or pipe-loop tests (Figure 5). Again, respondents could select more than one reason; thus, values do not total %. The dramatic increase in the use of coupon or pipe-loop tests observed between 1994 and 1 is likely attributable to the fact that only medium and large utilities were sampled in 1. When data from the 1994 survey were presented according to utility size (Figure 6), it was apparent that smaller utilities tended to rely much more on vendor FIGURE FIGURE Inhibitor dosages used at water utilities 1994 survey 1 survey < >3. Lead Copper Inhibitor Dose mg/l as PO survey 1 survey Copper or Lead Corrosion Reasons for using phosphate inhibitors Lead or copper Iron Corrosion or Red Water Concrete Corrosion Calcium Scale Iron or Manganese Control Reason for Using Phosphate Inhibitor Utilities were allowed to select more than one answer, so values do not total %. not applicable; utilities in the 1994 survey were not asked about this reason for using inhibitors. FIGURE Vendor Information Basis for choosing inhibitor 1994 survey 1 survey Success at Utilities Electrochemical Tests Coupon or Pipeloop Test Basis for Selecting Inhibitor Utilities were allowed to select more than one answer, so values do not total %. MCNEILL ET AL PEER-REVIEWED 94:7 JOURL AWWA JULY 2 61

6 FIGURE 6 Basis for selecting inhibitor for various size utilities participating in the 1994 survey FIGURE 7 Potential drawbacks of inhibitors identified by utilities in 1 survey Very small (<3,) Small (3,,) Medium (, 5,) Large (>5,) Vendor Information Success at Utilities Electrochemical Tests Coupon or Pipeloop Test Basis for Selecting Inhibitor Utilities were allowed to select more than one answer, so values do not total %. Utility size determined by population served Higher Lead or Copper Concentrations More Bacteria Regrowth Scaling in Hot Water Heaters Red Water Increased Treatment/ Cost/Residuals Potential Drawbacks of Inhibitors Utilities were allowed to select more than one answer, so values do not total %. information and the success of a particular inhibitor at another utility with similar water quality. (Values do not total % because respondents could select more than one answer.) This type of information is not necessarily faulty, and in fact, may be the only viable option for smaller utilities with limited resources. Nevertheless, it is a cause for concern that so many utilities spend considerable amounts of money to add these inhibitors (which may actually have detrimental consequences) without direct proof of their efficacy in the utilities particular types of water. In some cases, state regulatory agencies may also influence decisions about inhibitor selection, although utilities were not specifically asked about the role of state agencies. Fortunately, many utilities participating in the 1 survey were aware of potential drawbacks of dosing phosphate inhibitors (Figure 7), citing most often increased bacterial regrowth and additional treatment requirements, costs, and residuals. (Values do not total % because respondents could select more than one answer.) perceived problems listed by utilities included algal growth in reservoirs, dissolution of existing calcite scales, and REFERENCES Abernathy, C.G. & Camper, A.K., Effect of Phosphorus-based Corrosion Inhibitors and Low Disinfectant Residuals on Distribution Biofilms. Proc AWWA WQTC, San Diego. Abernathy, C.G. & Camper, A., Interactions Between Pipe Materials, Disinfectants, Corrosion Inhibitors, Organics, and Distribution Biofilms. Proc AWWA WQTC, Denver. AWWA, WATER:\STATS 1996 Survey. Denver. AWWA Res. Fdn. & DVGW-Technologiezentrum Wasser, Internal Corrosion of Water Distribution Systems. AWWA, Denver. Bancroft, D.A., Corrosion Control Program in Danvers, Massachusetts. Jour. NEWWA, 2:3:163. Benjamin, M.M. et al, 199. Chemistry of Corrosion Inhibitors in Potable Water (9561). AWWA Res. Fdn., Denver. Boffardi, B.P. & Sherbondy, A.M., Control of Lead Corrosion by Chemical Treatment. Corrosion, 47:12:966. Cantor, A.F. et al,. Use of Polyphosphate in Corrosion Control. Jour. AWWA, 92:2:95. Casale, R.J., 1. Improving Chemical Handling Procedures Can Help Reduce Associated Treatment Problems. Jour. AWWA, 93:9:95. Colling, J.H. et al, Plumbosolvency Effects and Control in Hard Waters. Jour. Instit. of Water & Envir. Mgmt., 6:6:259. Colling, J.H. et al, Measurement of Plumbosolvency Propensity to Guide the Control of Lead in Tapwaters. Jour. Instit. of Water & Envir. Mgmt., 1:3:263. Cousino, M. et al, Getting the Lead Out Reducing Lead Concentration in Water. Public Works, 118:11:68. Dodrill, D.M., Lead and Copper Corrosion Control Based on Utility Experience. Master s thesis, Univ. of Colorado, Boulder. Dodrill, D.M. & Edwards, M., Corrosion Control on the Basis of Utility Experience. Jour. AWWA, 87:7:74. Edwards, M., Predicting DOC Removal During Enhanced Coagulation. Jour. AWWA, 89:5:78. Edwards, M. & McNeill, L.S., 2. Effect of Phosphate Inhibitors on Lead Release From Pipes. Jour. AWWA, 94:1:79. Edwards, M. et al, 2. Phosphate Inhibition of Soluble Copper Corrosion By-product Release. Corrosion Sci., 44:5:57. Friedman, R.M. et al, Blended Poly/Orthophosphate Inhibition of Heavy Metal Corrosion in Potable Water Delivery Systems. Proc AWWA WQTC, San Francisco. Green, J., 195. Reversion of Molecularly Dehydrated Sodium Phosphates. Industr. & Engrg. Chem., 42:8:1542. Gregory, R., 199. Galvanic Corrosion of Lead Solder in Copper Pipework. Jour. Instit. of Water & Envir. Mgmt., 4:4:112. Hatch, G.B., Inhibition of Lead Corrosion With Sodium Hexametaphosphate. Jour. AWWA, 33:7:1179. Holm, T.R. & Schock, M.R., Potential Effects of Polyphosphate Products on Lead Solubility in Plumbing Systems. Jour. AWWA, 83:7:76. Holm, T.R. et al, Polyphosphate Water Treatment Products: Their Effects on the 62 JULY 2 JOURL AWWA 94:7 PEER-REVIEWED MCNEILL ET AL

7 increased scale formation, clogging, and fouling resulting in loss of capacity or the need for more frequent flushing. SUMMARY Use of phosphate inhibitors, including polyphosphate, orthophosphate, zinc orthophosphate, and phosphate blends, is widespread among US drinking water utilities. Polyphosphate compounds have been shown to have detrimental effects on metal corrosion under some circumstances, so the apparent shift from poly/orthophosphate blends to straight orthophosphate is likely a beneficial trend. Surprisingly, few utilities are conducting scientific tests to determine the applicability of inhibitors to their particular circumstances; most water providers, especially smaller facilities, are relying on vendor data or the success of an inhibitor at another utility. Although larger utilities are aware of potential drawbacks of inhibitors, many do not know the exact composition of the phosphate chemicals they are adding. Understanding how and why inhibitors are used is the first step the water industry must take to help utilities develop effective strategies (which may include inhibitor dosing) to meet the diverse goals of corrosion control and water quality. ACKNOWLEDGMENT This work was supported in part by AWWA Research Foundation (AWWARF) as project 2687 under Project Manager Kathryn Martin and Project Advisory Committee members Timothy Barr, Dominique Gatel, Malcolm Taylor, and Christian Volk. The comments and views expressed here do not necessarily reflect those of AWWARF, its officers, directors, affiliates, or agents. The authors thank the participating water utilities for their time and effort in completing the two surveys. The authors also gratefully acknowledge the efforts of Donna Dodrill for completing the first survey and Julia Rahman and Ryan Anderson for implementation of the second survey. Portions of these results were presented at the AWWA 1 Annual Conference. ABOUT THE AUTHORS: Laurie McNeill 1 is an assistant professor at the Utah Water Research Laboratory, Utah State University, 8 Old Main Hill, Logan UT , Lmcneill@cc.usu.edu. She holds BS and MS degrees from the University of Colorado at Boulder and a PhD in civil engineering from Virginia Polytechnic Institute and State University in Blacksburg. Marc Edwards is a professor in the Civil and Environmental Engineering Department at Virginia Polytechnic Institute and State University. FOOTNOTE 1 To whom correspondence should be addressed If you have a comment about this article, please contact us at journal@awwa.org. Chemistry and Solubility of Lead in Potable Water Systems. Proc AWWA WQTC, Philadelphia. Johnson, B. et al, Evaluation of Corrosion Control Alternatives to Meet the Lead and Copper Rule for Eastern Massachusetts. Jour. NEWWA, 7:3:24. Karalekas P.C. Jr. et al, Control of Lead, Copper, and Iron Pipe Corrosion in Boston. Jour. AWWA, 75:2:92. LeChevallier, M.W. et al, Examining the Relationship Between Iron Corrosion and the Disinfection of Biofilm Bacteria. Jour. AWWA, 85:7:111. Lee, R.G. et al, Lead at the Tap: Sources and Control. Jour. AWWA, 81:7:52. Lohmann, R. et al, Pilot Studies to Determine Secondary Water Quality Impacts of Corrosion Inhibitors. Proc AWWA WQTC, Denver. Lyons, J.L. et al, Optimizing Corrosion Control for Lead and Copper Using Phosphoric Acid and Sodium Hydroxide. Proc AWWA WQTC, New Orleans. Maas, R.P. et al, A Multistate Study of the Effectiveness of Various Corrosion Inhibitors in Reducing Residential Lead Levels. Proc AWWA Ann. Conf., Philadelphia. McNeill, L.S. & Edwards, M., 1. Review of Iron Pipe Corrosion in Drinking Water Distribution Systems. Jour. AWWA, 93:7:88. McNeill, L.S. & Edwards, M.,. Phosphate Inhibitors and Red Water in Stagnant Iron Pipes. Jour. Envir. Engrg., 126:12:96. Neuman, W.E., AWWC Experience With Zinc Orthophosphate Treatment. Jour. NEWWA, 9:3:57. Patterson, J.W. & O Brien, J.E., Control of Lead Corrosion. Jour. AWWA, 71:5:264. Reiber, S. et al, A General Framework for Corrosion Control Based on Utility Experience (9712A). AWWA Res. Fdn., Denver. Reiber, S.H., Copper Plumbing Surfaces: An Electrochemical Study. Jour. AWWA, 81:7:114. Rezania, L.-W. & Anderl, W.H., Copper Corrosion and Iron Removal Plants, The Minnesota Experience. Proc AWWA WQTC, New Orleans. Richards, W.N. & Moore, M.R., Lead Hazard Controlled in Scottish Water Systems. Jour. AWWA, 76:8:6. Schock, M.R., Understanding Corrosion Control Strategies for Lead. Jour. AWWA, 81:7:88. Schock, M.R. et al, Effect of ph, DIC, Orthophosphate, and Sulfate on Drinking Water Cuprosolvency. US Environmental Protection Agency, EPA/6/R-95/85, Washington. Sheiham, I. & Jackson, P.J., Scientific Basis for Control of Lead in Drinking Water by Water Treatment. Jour. Instit. Water Trtmnt. Engrs. & Scientists, 35:6:491. Stumm, W. & O Melia, C.R., Stoichiometry of Coagulation. Jour. AWWA, 6:5:514. Werner, W. et al, Corrosion of Copper Pipes in Drinking Water Installations. gwf-wasser/abwasser, 135:92. Zinder, B. et al, Kinetic Studies on the Hydrolysis of Sodium Tripolyphosphate in Sterile Solution. Water Res., 18:5:59. MCNEILL ET AL PEER-REVIEWED 94:7 JOURL AWWA JULY 2 63