Balancing Microbial Control and Stage 2 DBP Rule Compliance (at Ocean City, Maryland)

Transcription

1 Balancing Microbial Control and Stage 2 DBP Rule Compliance (at Ocean City, Maryland) May 4, 2012 Presented by: Earl Swartzendruber, Jr., PE Whitman, Requardt and Associates, LLP

2 Acknowledgements Town of Ocean City, MD DPW Jim Parsons, PE Bud Iman NCS Engineers Bench-Scale Testing Harish Arora, PhD, PE Ashish Agrawal

3 Presentation Outline Unique Water System Issues Source Water Quality Issues Distribution System Assessment Disinfection Byproducts Bench-Scale Testing Recommendations

4 Water System Issues Town of Ocean City, Maryland Narrow system 10 miles in length ; Dead-ends north & south Variable Water Demand Off-season averages 2-4 mgd Seasonal peak projected demand is 16.8 mgd Water Storage & Piping Sized for maximum day demands & fire flow Water Treatment Plants 3 separate plants operational during summer 1 plant in service during off-season 3 different WTP processes & 2 different aquifers

5 Ocean City Water System G 27.8 MGD 22.0 MGD

6 Maryland/Delaware Line Ocean City Water System Profile 0.4 MG 0.5 MG 0.5 MG 1.0 MG 0.4 MG 1.0 MG 0.75 MG 6 MGD 2.0 MG 4 MGD ( MGD useable) Total Usable Water Storage = 5.9 Million Gallons Equivalent to : 8 hours during maximum day / 70 hours during minimum day

7 Ocean City Wells Background Disinfection Byproducts Ocean City Water Quality Issues Bench-Scale Testing Recommendations

8 Water Treatment Plants Gorman Avenue Water Treatment Plant - 8 MGD 44th Street Water Treatment Plant - 4 MGD 15th Street Water Treatment Plant - 6 MGD

9 15 th Street WTP Well 15A Well 15B Well 15C Pre-Chlorination Vault Static Mixer Reaction Tank Gravity Filters Elevate d Storage Well 15D Well SA Well SB Well SC Well SD Cl 2 Polymer Backwash Recycle Clear Well Pump Chamber Distribution System Backwash Tank Chemical Facility Cl 2 NaOH Source Water Quality: Iron 1-3 mg/l Ammonia: mg/l TOC: mg/l

10 44 th Street WTP Greensand Filters Elevated Storage Plant A Filter Room Well B Well A Well D Well C Distribution System Well G NaOH KMnO 4 Cl 2 Plant B Filter Room Backwash Waste to Sanitary Sewer Chemical Facility NaOH Cl 2 Source Water Quality: Iron 3-7 mg/l Ammonia: mg/l TOC: mg/l

11 Gorman Avenue WTP Elevated Storage Well A Well B Well C Aeration Clarifiers Pump Basin Booster Pumps Greensand Filters Well D Well E Distribution System Well F 120 th St. Well NaOH Cl 2 Chemical Facility Polymer KMnO 4 Settled Water Return Backwash Settling Tank Backwash Waste to Sanitary Sewer Cl 2 Source Water Quality: Iron 4-13 mg/l Ammonia: mg/l TOC: mg/l

12 Distribution System Water Quality Distribution System Water Quality Assessment performed in 2005 in response to several incidences of waterborne microbial contamination (primarily related to degradation of water quality within various buildings), recommending: Conduct an Enhanced Water Quality Monitoring Program Loop dead-ends & incorporate automatic flushing devices Consider unidirectional flushing program Formalize cross-connection control program Consider proactive community outreach

13 Enhanced Water Quality Monitoring Increased number of sampling sites (to 25) for weekly sampling with number adjusted monthly to be proportional to estimated customers served Analytical parameters included: Free & Total Chlorine, Total Coliforms, ph, Heterotrophic Plate Count (HPC) Data entry into electronic database Monitoring began October 2005 & will continue indefinitely

14 Ammonia Monitoring Raw water & finished water sampled for ammonia & chloramines subsequent to observation of large difference between free chlorine & total chlorine High proportion of monochloramines (up to 90% of total) especially in northern portions of the system with the Gorman Ave. WTP in service Resulting in sporadic instances of inadvertent chloramination Ammonia concentrations vary from mg/l

15 Sample Site Map

16 Distribution System Monitoring First Sample Data October 2005

17 Distribution System Monitoring One Month Later

18 Distribution System Monitoring Typical Summer 2006

19 Distribution System Monitoring Typical Winter 2007

20 Distribution System Monitoring Typical Summer 2007

21 Distribution System Monitoring Typical Summer 2008

22 Distribution System Monitoring Typical Winter

23 Distribution System Water Quality Monitoring Summary Certain areas more prone to loss of chlorine residual Low free chlorine residual (<.2 mg/l) typically results in increased HPC levels Higher proportions of combined chlorine (total chlorine free chlorine) in certain areas due to ammonia in source water. Combined chlorine shown to be effective in maintaining low HPC Presence of ammonia probably enhances DBP reduction Increased chlorine dosage implemented to oxidize ammonia in source water

24 Operational Revisions Maintain higher free chlorine residual (>0.2 mg/l) Reviewing WTP operations to optimize disinfection performance Modify operations to promote greater cycling of water level in tanks Meetings with hotel/ condo associations to educate about importance of flushing program Installed tank mixing systems

25 Ocean City DBP Control Issues Relatively high organics in source water High iron concentrations require strong oxidant to enable removal by filtration High water age (10+ days) during the offseason Relatively high concentrations of ammonia requires larger doses of chlorine to obtain free chlorine residual for disinfection

26 Disinfection Byproducts (DBPs) DBPs: Trihalomethanes and Haloacetic Acids Currently Compliant with Stage 1 BBP Rule TTHM RAA must be < 80 ppb HAA5 RAA must be < 60 ppb Stage 2 DBP Rule Requires selection of new monitoring sites (Total of 4 sites for Ocean City) Each site must comply with limits Compliance monitoring begins November 2013

27 TTHM, µg/l Historical TTHM vs. Chlorine Residual for Stage 1 Compliance Chlorine, mg/l TTHM MCL = 80 µg/l TTHM Goal = 64 µg/l Stage 1 DBPR Compliance Site TTHM 7-11 at North Division St Year, Quarter RAA Compliance Site Free Cl2 (15th St. WTP) Total Cl2 (15th St. WTP)

28 Historical TTHM at Stage 1 and Stage 2 Compliance Sites

29 Simultaneous Compliance Disinfection vs. DBPs Apply enough disinfectant to control pathogens Implement strategies to reduce concentrations of DBPs

30 Ocean City WTP Optimization Study Goals: Optimize oxidation and removal of iron and manganese while minimizing THM formation Bench-Scale Testing: Alternate oxidants and disinfectants Aeration, KMnO4, ClO2, Cl2, Chloramines

31 Iron, mg/l Mn, mg/l or UV 1/cm Gorman WTP Oxidation Testing Figure 4.5 : GWTP Final Jars Filtered Water Iron, mg/l Filtered Water Mn, mg/l Filtered Water UV % KMnO4 (4.7 mg/l) + Aeration 100% Cl2 (16.2 mg/l) 40% ClO2 (4.7 mg/l) Chemical Dose (% of Stoichiometric Value and mg/l)

32 Iron, mg/l Mn, mg/l or UV, 1/cm 44 th Street WTP Oxidation Testing igure 4.12 : 44th Street Final Jars Filtered Water Iron, mg/l Filtered Water Mn, mg/l Filtered Water UV % KMnO4 (3.2 mg/l) 100% Cl2 (9 mg/l) 40% ClO2 (2.2 mg/l) 100% ClO2 (6.5 mg/l) Chemical Dose (% of Stoichiometric Value and mg/l)

33 Iron, mg/l Mn, mg/lor UV, 1/cm 15 th Street WTP Oxidation Testing Figure 4.16 : 15th Street Final Jars Filtered Water Iron, mg/l Filtered Water Mn, mg/l Filtered Water UV % KMnO475% KMnO4 (1.3 mg/l) (1.7 mg/l) 100% Cl2 (3.9 mg/l) 40% ClO2 (0.9 mg/l) 100% ClO2 (2.8 mg/l) Aeration 0 Chemical Dose (% of Stoichiometric Value and mg/l)

34 Concentration, ppb Gorman Avenue WTP THM Testing Figure 4.6 : GWTP SDS THMs Chlorine (THM after 3 days with free chlorine residual) % KMnO4 (4.7 mg/l) + Aeration - 3 day % Cl2 (16.2 mg/l) - 3 day 60 40% ClO2 (4.7 mg/l) - 3 day BDCM Bromoform DBCM Chloroform Total THMs

35 Concentration, ppb Gorman Avenue WTP THM Testing Figure (THM 4.7 : SDS THMs after Chloramine 3 days with chloramine residual) % KMnO4 (4.7 mg/l) + Aeration - 3 day 100% Cl2 (16.2 mg/l) - 3 day 40% ClO2 (4.7 mg/l) - 3 day BDCM Bromoform DBCM Chloroform Total THMs

36 Concentration, ppb 44 th Street WTP THM Testing (THM after 3 days with free chlorine residual) Figure 4.13 : 44th Street SDS THMs Chlorine % KMnO4 (3.2 mg/l) - 3 day 100% Cl2 (9 mg/l) - 3 day 40% ClO2 (2.2 mg/l) - 3 day 100% ClO2 (6.5 mg/l) - 3 day BDCM Bromoform DBCM Chloroform Total THMs

37 Concentration, ppb 44 th Street WTP THM Testing (THM after 3 days with chloramine residual) Figure 4.14 : 44th Street SDS THMs Chloramine % KMnO4 (3.2 mg/l) - 3 day 100% Cl2 (9 mg/l) - 3 day 40% ClO2 (2.2 mg/l) - 3 day 100% ClO2 (6.5 mg/l) - 3 day BDCM Bromoform DBCM Chloroform Total THMs

38 Concentration, ppb 15 th Street WTP THM Testing Figure 4.17 : 15th Street 3 day SDS THMs Chlorine (THM after days with free chlorine residual) 90 60% KMnO4 (1.3 mg/l) - 3 day 80 Aeration - 3 day % Cl2 (3.9 mg/l) - 3 day 60 40% ClO2 (0.9 mg/l) - 3 day BDCM Bromoform DBCM Chloroform Total THMs

39 Concentration, ppb 15 th Street WTP THM Testing (THM after 3 days with chloramine residual) Figure 4.18 : 15th Street 3 day SDS THMs Chloramines 25 60% KMnO4 (1.3 mg/l) - 3 day 20 Aeration - 3 day 100% Cl2 (3.9 mg/l) - 3 day 40% ClO2 (0.9 mg/l) - 3 day BDCM Bromoform DBCM Chloroform Total THMs

40 Concentration, ppb 15 th Street WTP THM Testing Figure (THM 4.19 : 15th after Street 10 day days SDS THM with Chlorinefree chlorine residual) % KMnO4 (1.3 mg/l) - 10 day 100% Cl2 (3.9 mg/l) - 10 day 40% ClO2 (0.9 mg/l) - 10 day BDCM Bromoform DBCM Chloroform Total THMs

41 Concentratin, ppb 15 th Street WTP THM Testing Figure 4.20 : 15th Street 10 day SDS THMs Choramine (THM after 10 days with chloramine residual) % KMnO4 (1.3 mg/l) - 10 day 100% Cl2 (3.9 mg/l) - 10 day 40% ClO2 (0.9 mg/l) - 10 day BDCM Bromoform DBCM Chloroform Total THMs

42 Bench Testing Conclusions Oxidation: Aeration, Potassium Permanganate, Chlorine Dioxide all proven effective THM Control: Chloramines treatment resulted in lowest formation of THMs, even after 10 days simulated water age Alternate oxidants (other than chlorine) reduced THMs in system, although not as effective at longer than 3 days water age

43 Microbial Control / DBP Compliance Alternate oxidants Possible sequential oxidation Reduce water age Flushing Consider chloramination

44 Recommendations for Ocean City 1) Town prefers to exhaust other oxidation and disinfection alternatives prior to implementing chloramination due to potential byproducts (NDMA and others?) plus other issues (added ammonia to wastewater and corrosion issues) 2) Conduct additional bench testing Confirm previous results Test multiple wells Test combinations of oxidants

45 Recommendations for Ocean City 3) Conduct desktop analysis comparing economic and qualitative factors for the strategies considered acceptable to the Town 4) Pilot/demonstration testing and develop design criteria for Maryland Department of Environment (MDE) approval 5) Likely will apply for Stage 2 compliance extension while implementing selected alternative

46 Questions? Conduct workshop with Town to discuss preferred path forward to likely be followed by: Limited series of additional bench testing to confirm results Desktop analysis comparing economic and qualitative factors for the strategies considered acceptable to the Town Pilot/demonstration testing and develop design criteria for MDE approval Potential need to implement chloramines on at least a temporary basis to ensure regulatory compliance