Distribution System Levels of Chlorate From Formation in Sodium Hypochlorite Stock

Transcription

1 Distribution System Levels of Chlorate From Formation in Sodium Hypochlorite Stock CA-NV Section AWWA Fall Conference Sacramento, CA October 3, 2013 Gary R. Lynch VP Water Quality Park Water Company

2 Why The Concern? It all started with Perchlorate Massachusetts set a perchlorate MCL at 2 ug/l Wanted to set at 1 ug/l Contribution to disinfected water up to 1 ug/l from chlorine disinfection possible OEHHA review of California PHG set for 2009 Actually proposed January 2011 March 2009 Request for Supplemental Comments by USEPA to possibly proceed with development of perchlorate MCL 2

3 Water Industry Research WITAF #712 / WaterRF #4147 ( ) Recognized that sodium hypochlorite can contain impurities such as: Bromate Chlorate Chlorite Perchlorate 3

4 WITAF #712 / WaterRF #4147 Examined sodium hypochlorite impurities formed in: Bulk sodium hypochlorite (12.5% FAC) Onsite generation systems (OSG) 0.4% FAC 0.8% FAC Calcium Hypochlorite 65% FAC before mixing with water 4

5 Key Findings WITAF #712 / WRF #4147 Dilute stored hypochlorite solutions upon delivery to reduce formation of chlorate and perchlorate Store hypochlorite at lower temperatures Control ph of solutions between Purchase filtered hypochlorite solutions to control transition metal ions and use low metal ion concentration feed water for OSG Use fresh hypochlorite solutions when possible OSG systems should use low-bromide salt 5

6 Impurity Concerns Health Reference Levels (HRLs) are calculated the same way a MCLG is Notification Levels (NLs) have replaced ALs Chemical MCL (ug/l) USEPA HRL (ug/l) CA NL (ug/l) Perchlorate Chlorate Bromate Chlorite 1,

7 Government Policy Challenges 2011, California proposed revised PHG for perchlorate of 1 ug/l Inherently Safer Technology Push to eliminate the use of chlorine gas in water treatment Sodium hypochlorite considered safer treatment technology Third Regulatory Determination by USEPA Chlorate thought to be possible positive determination 7

8 Park Water Company Reaction Studied chlorate and perchlorate formation in all three utilities: Park Water Company (three systems), Calif. Apple Valley Ranchos Water Company, Calif. Mountain Water Company, Missoula MT 8

9 Park Water Company All well disinfection systems are OSG, 0.8% FAC

10 Mountain Water Co., Missoula, MT All 31 wells disinfected with 12.5% sodium hypochlorite Relatively cooler temperatures Fast turnover of product in summer time because of high demands 10

11 Apple Valley Ranchos Water Co. Three disinfection systems Miox OSG 14 wells 0.4% FAC Sodium hypochlorite (bulk storage and day tanks) 5 wells 12.5% FAC Calcium hypochlorite (puck systems) 2 wells 65% FAC dry, applied at approx. 6% FAC 11

12 Apple Valley Disinfection Systems 12

13 Apple Valley Results Clorine Day Tank (ug/l) Distribution System (ug/l) 2011 Type of Well # Date Chlorate Perchlorate Chlorate Perchlorate Cl Residual Production (AF) Disinfection Bulk Storage 8/13/ ,000,000 27,000 Na Hypo 4 8/13/ ,000,000 28, Na Hypo 11R * 8/13/ ,000,000 35, Na Hypo 19 8/13/ ,400,000 57, Na Hypo 20R 8/13/ Cal Hypo 21 8/13/ ,000,000 54, Na Hypo 22 8/13/ , OSG 23 8/13/ ,000,000 37, Na Hypo 29 8/13/ , OSG 30 8/13/ ,000,000 92, Na Hypo 36 8/13/ , OSG 13 RDL = 40 ug/l RDL = 4 ug/l RDL = 40 ug/l RDL = 4 ug/l

14 Mitigation to Lower DBPs First, began dilution of sodium hypochlorite stock solution in day tanks at wells 50% with water Manage the stock better by not completely filling day tanks on wells that don t pump often Begin conversion from sodium hypochlorite to calcium hypo puck systems at wells that don t pump much 14

15 AVR Hypochlorite Special Sampling Events Clorine Day Tank (ug/l) Distribution System (ug/l) Cl 2011 Type of Well # Dates Chlorate Perchlorate Chlorate Perchlorate Residual Production (AF) Disinfection Bulk Storage 8/13/12 30,000,000 27,000 Na Hypo 8/22/13 35,000,000 37,000 9/12/ ,000,000 44, /13/12 30,000,000 28, Na Hypo 8/22/13 17,000,000 17,000 9/12/ ,000,000 16, /13/12 36,400,000 57, Na Hypo 8/22/13 15,000,000 21,000 9/12/ ,000,000 20, R 8/13/12 1, Cal Hypo 8/22/13 1, /12/ , /13/12 35,000,000 37, Na Hypo 8/22/13 3,100,000 2,600 9/12/2013 3,000,000 3, /13/12 41,000,000 92, Na Hypo 8/22/13 9,400 0 Cal Hypo 9/23/2012 1, Cal Hypo 36 8/13/12 35, OSG 8/22/13 21, /12/ , RDL = 40 ug/l RDL = 4 ug/l RDL = 40 ug/l RDL = 4 ug/l chlorate non-cancer HRL = 200 ug/l

16 What Can You Do? Perform your own study disinfection systems and how this relates to distribution system results Go to AWWA website and then to Government Affairs and use the Hypochlorite Assessment Tool 16

17 Summary High levels of chlorate and perchlorate are formed in 12.5% hypochlorite day tanks Perchlorate not found in distributions system Chlorate is formed in distribution system, sometimes at levels greater than EPAs HRL Simple handling changes reduce formation in day tanks and in distribution system to levels not of concern 17

18 However, surface water treatment plants dose at much higher levels and could be at risk of forming far greater more DPB s 18

19 Questions? 19