Distribution System Best Management Practices (BMPs) for TCR Compliance

Transcription

1 Services of the San Francisco Public Utilities Commission Distribution System Best Management Practices (BMPs) for TCR Compliance Alan R. Wong, P.E. WTO4, DO4 Manouchehr Boozarpour, P.E. Eddy So, P.E. Andrzej Wilczak, PhD, P.E. San Francisco Public Utilities Commission Annual Technology Transfer Workshop November 12,

2 Outline TCR & RTCR Review Sources of Total Coliforms BMPs for TCR Compliance SFPUC Investigations Industry Findings References/Resources 2

3 Total Coliform Rule (TCR) & Revised Total Coliform Rule (RTCR) Review Coliform Bacteria 3

4 1989 Total Coliform Rule The only microbial drinking water regulation that applies to all public water systems Maximum Contaminant Level (MCL) for TC only. MCL exceedance based on Number of total coliform (TC) detections, or Fecal coliform/e. coli presence with TC detection Routine monitoring required Public Notification (PN) required for MCL violations 4

5 Some Issues Addressed by USEPA for RTCR How to improve public health protection by building on actions already taken by well run systems find and fix assessments and corrective actions? How to optimize the value of TC monitoring as an indicator of system operation since it is not an immediate public health concern? Is PN for TC+ samples (monthly MCL) causing confusion and erosion of consumer confidence? 5

6 Role of TC Under TCR and RTCR TCR Total Coliform MCL Yes No Recurring detection, e.g. >5% of monthly samples Potential MCL violation RTCR Triggers assessment and/or corrective actions Public notification Required if exceeds MCL Required if utility fails to conduct assessment or correct sanitary defect 6

7 Sources of Total Coliforms Animals, plants, vegetation, soils Within pipes biofilm, sediments, regrowth, in faucets, pipes, plumbing Ubiquitous everywhere 7

8 SFPUC Best Management Practices for TCR Compliance 8

9 BMPs - Response Strategy Response measures will be dictated by a) the magnitude of the event First TC+ from Routine TCR sampling Second TC+ in Repeat Set Multiple TC+ b) investigation findings (operations, etc.) 9

10 BMPs for Routine Sampling to Help Minimize TC+ Detection Use designated sample stations with copper sample line Flush sample line at low flow until consistently low temperature and high Cl 2 residual Use proper sample collection and transport techniques - Avoid splashing - Avoid contaminating the sample vessel and cap - Use dedicated coolers with blue ice 10

11 BMPs for Repeat Sample Collection Additional BMPs for repeat sets Designated sample boxes at up/downstream locations Disinfect sample spigot - Spray with bleach or torch sample tap only - Spraying hypochlorite is preferable to swabbing, contact time 30 sec - Commercial chemicals are also approved for drinking water - Purge sample line before sample collection at low flow Clean hands or use gloves Sanitize cooler and blue ice 11

12 BMPs for Repeat Sample Collection Avoid Flushing the tap wide open Fire hydrants Customer homes (bathrooms, kitchen sinks) Sampling attachments garden hose, aerators, strainers, etc. Interference from bushes, trees Interference from rain Rarely used facilities Sampling at unfamiliar taps can increase TC+ by a factor of six Philadelphia WD, AWWA

13 BMPs for Recurring TC+ at One Site TC+ recurring at same site ONLY may indicate a problem with sample location or facilities Corrective measures may include disinfections Sample tap Sample line Water main Consider - Conducting a site evaluation - Evaluating operations - Assessing new sampling facilities or location 13

14 BMPs for Recurring TC+ at Multiple Sites Investigate Complaints Distribution reservoirs (e.g., unsecure vents, overflow) Flushing sediment re-suspension and biofilm sloughing Construction (e.g., main breaks/repairs, new mains) Loss of pressure Flow or pressure transients (surges) Cross connections, air valves, other valving operations Change in flow patterns, reverse flows Residuals maintenance and water quality Improper sampling facilities or technique 14

15 Main Flushing Notes Flushing velocities a) 2.5 fps AWWA C651 minimum flushing velocity b) 2-3 fps to remove loose sediments c) 5 fps to scour pipe walls and biofilm Flushing may require - Unidirectional or systematic procedures - A larger service area Reduce flow rates after flushing to near background turbidities and chlorine residuals. Allow pipe sediments to settle before sample collection (several hours) Sample at low flows 15

16 Programmatic BMPs Sampling Technique Disinfectant residuals maintenance Sanitary Construction Main flushing Reservoir cleaning and inspection Water age management Circulation improvements, looping, removing dead ends Cross connection control program 16

17 Sanitary Construction BMPs - Main Breaks Construction has a high potential for introducing contaminants into the distribution system. This includes main breaks, new construction, repairs, and tie-ins. Sanitary construction BMPs are effective for minimizing risk of bacteriological contamination 17

18 Sanitary Construction BMPs - Main Breaks Assess site for conditions Location and condition of nearby utilities - Overflowing sewers Evidence of sewage - Strong odors - Waste - Saturated ground upstream Other Environmental Hazards 18

19 Sanitary Construction BMPs - Main Breaks Maintain Positive Pressure - Reduce main flow, if necessary, until plugged - Verify positive pressure downstream. - Isolate downstream if possible. Excavate below & around the main - 18 around the circumference of the pipe Dewater using sump pump 19

20 Sanitary Construction BMPs Inspect inside of pipe for dirt, rocks, pieces of pipe, animals use a flashlight Flush & back flush pipe Isolate and notify customers of outage, if necessary Provide emergency or local disinfection Do not leave site unattended Keep in contact with chain of command 20

21 SFPUC TC Investigations 21

22 Baden Investigations Investigations at Baden Valve Lot (VL) and Pump Station Investigated surge tanks and air intake Relocated sample tap closer to transmission pipeline Sampled 11 sites around Baden VL under different water supply scenarios, including high volume (5 L) TC samples Repeatedly disinfected sample lines, taps, surge tanks, facilities Conducted parallel sampling at 4 locations within Baden VL Occasional but recurring TC+ No clear correlations with operational or WQ parameters 22

23 SFPUC TC Investigations 2008 thru 2013 internal investigations by SFPUC WQD in response to SA-2 Baden TC TC investigation and report by Kennedy Jenks Consultants including expert panel to address concerns about occasional TC+ Jon Standridge, microbiology expert, WI Steve Hubbs, operations expert, KY Gregory Kirmeyer, TC and distribution systems expert, WA 2014 internal SFPUC WQD investigation in response to some wholesale customers TC+ 23

24 SFPUC 2014 TC Report Speciation data indicated most likely source of the TC+ to be biofilm TC+ did not reflect a treatment problem, or unsanitary conditions in the transmission and distribution system Both SFRWS and SFWS are within range of TC+ percentage for similar size utilities ( ) In no instance has E. coli been detected in any of the TC+ samples 24

25 SFPUC 2014 TC Report: Main Recommendations Allocate resources to improve SOPs Continue to be proactive and vigilant to perform repeat TC+ investigations as needed Maintain existing programs that improve sanitary condition of facilities Reservoir cleaning program Pipe inspection, flushing, cleaning Nitrification prevention and residual maintenance 25

26 Industry Findings Relationships between TC+ and other water quality parameters are hard to find Philadelphia WD, AWWA

27 Industry-wide Coliform Research Findings Abrupt changes in flow conditions may result in biofilm being detached and lead to microbial water quality variation TC+ may occur with high secondary disinfectant residuals especially biofilms TC+ occurrence significantly higher when temp > 15 C 27

28 Industry BMP s to address TC+ Resolving TC+ occurrences can be complicated and time consuming. There is no universal strategy Operations and maintenance practices to address microbial regrowth in distribution systems: Chloramine residual 2.0 to 2.5 mg/l Unidirectional flushing Pipeline & tank inspection, cleaning, and disinfection Sanitary work practices for pipe replacement and repair Sample tap inspection, cleaning, and disinfection 28

29 References/Resources Many good references are available from USEPA, AWWA and WRF 29

30 References/Resources AWWARF (2001) Practices to Prevent Microbial Contamination of Water Mains AWWARF (2004) Sample Collection Procedures and Locations for Bacterial Compliance Monitoring WRF (2009) Strategies for Managing TC and E. Coli in Distribution Systems USEPA (2010) Proposed RTCR Assessments and Corrective Actions Guidance Manual, EPA 815-D WRF (2010) Significance of Methods and Sample Volumes for E. coli and TC Measurements 30

31 References/Resources AWWA (2012) Webinar: Preparing to Implement the Revised TCR USEPA (2013) Webinar: The Revised TCR, April 10, 2013 AWWA (2013) Webinar: Understanding and Managing Coliforms Science vs Myth WRF (2014) Effective Microbial Control Strategies for Main Breaks and Depressurization WRF (2014) Knowledge Portal: Microbials 31

32 Questions 32