Interpreting Filter Profiles Additional Resource for understanding individual filter monitoring provisions of the Interim Enhanced Surface Water Treatment Rule. Provided by PADEP

The Interim Enhance Surface Water Treatment Rule requires that public water systems report an obvious reason or produce a filter profile if any filter’s turbidity exceeds 1.0 NTU in two consecutive measurements taken 15 minutes apart or if any individual filter’s turbidity exceeds 0.5 NTU in two consecutive measurements taken 15 minutes apart at the end of the first four hours of continuous filter operations after the filter has been backwashed or taken offline for any reason.

Importance of Interpretation and Preventative Actions: The intent of these two triggers is to allow water systems to interpret their profiles, discover the cause of the elevated turbidity, and take actions to correct it. If a system does not take preventative actions, consecutive turbidity exceedences could occur. This would trigger a much more rigorous follow-up action of a self-assessment or Comprehensive Performance Evaluation (CPE).

Formatting: In order to produce an accurate and usable profile, proper formatting is critical. Therefore, when producing your filter profile(s), the “Filter Profile Checklist” should be used…this checklist is available ?? The following training aid focuses on interpretation, and assumes that you have already referenced the Filter Profile Checklist and developed your filter profile(s) You should have developed something similar to…

A) 8:50AM – Start Backwashing Filter #1 B) 9:15AM – Start Filter-to-Waste C) 9:30AM – End Filter-to-Waste D) 9:45AM – Filter Placed On-line E) 3:00PM – Start Backwashing Filter #2 F) 4:55PM – Increase flow from 1225 gpm up to 1350 gpm G) 9:00PM – Possible Alum Feed Pump Clog? H) 1:05AM – Start Backwashing Filter #1 I) 1:30AM – Start Filter-to-Waste J) 3:00AM – End Filter-to-Waste/Filter Placed On-Line

Once you have created a “representative” profile for each filter in your plant, you should interpret each profile, attempting to determine if any potential problems exist. The following nine slides are examples of some of the most common filter profiles and possible interpretations of each. You may find these examples helpful in evaluating your own profiles. Once you have produced a complete profile for each filter which exceeded the trigger level, you should interpret the profile, attempting to determine all potential causes of the turbidity spikes. The interpretation process can be very beneficial - even if you have already identified an “obvious reason”. The following nine filter profile slides are examples of some of the most common profiles encountered in Pennsylvania and possible interpretations of each. These examples should be helpful in evaluating your plant’s filter profile(s).

Things to keep in mind: Each slide focuses on a portion of a filter run and one event/problem only – therefore it is not a complete profile. Throughout an entire filter run, several problems may often occur. Each problem may have several causes. The most probable cause(s) is listed above the profile; however, it is important to keep in mind that actual cause(s) can vary from plant to plant. Therefore, your own investigation is the key to obtaining information to help you identify and prevent problems at your water plant.

Interpretation, Investigation, Prevention Interpreting filter profiles gives you an idea of potential causes. Investigation enables you to identify the actual cause(s). You can then take action to prevent future turbidity exceedences which would trigger a “Self Assessment” or “Comprehensive Performance Evaluation.” When interpreting your filter profiles, it may be helpful to discuss potential causes with other knowledgeable water operators or DEP’s Filter Plant Performance Evaluators.

Optimization vs. Regulation The following slides reference the .1NTU optimization goal recognized by PADEP and national drinking water organizations. Note that this is only a goal and is much lower than the individual filter turbidity trigger levels (0.5NTU, 1.0NTU, 2.0NTU) contained in the Interim Enhanced Surface Water Treatment Rule. Striving to meet the optimization goal can help prevent exceeding the regulatory trigger levels.

Workshop Now that you have reviewed the most common “problem” filter profiles, you may find it helpful to test your knowledge with the following workshop.

Workshop - Scenario: You are the operator at a “conventional” filter plant that treats surface water with coagulation, flocculation, sedimentation, filtration and disinfection. You and other operations staff are working on interpreting individual filter profiles to identify causes of turbidity spikes so that you can investigate and prevent these spikes from occurring in the future.

Workshop - Turbidimeter Setup: You have inline turbidimeters and chart recorders on all four of your plant’s individual filter effluents. You observe the following turbidity vs. time profiles from Filters #3 and #4.

Important Notes: This is actual filter data The upper chart is from Filter #3 The lower chart is from Filter #4 Both charts represent the same time period

Workshop – Directions: To complete the workshop, interpret the strip charts and identify any problems within the filter run along with potential causes/solutions. Write a few notes on what you think is happening at this filter plant. If necessary, you can reference the previous power point slides. The answers to the workshop are contained in the next slides. STOP here and take some time to write down your answers.

Answers: Filter #4 has a rate control valve modulating (“seeking valve”) prior to backwash. (Reference Profile “B”)   During rate change at 6:00 a.m. (4,000 gpm to 4,300 gpm), filter #4 turbidity increases considerably. During a rate change at noon (4,200 gpm to 4,800 gpm), filter #3 turbidity increases considerably (Reference Profile “H” )

Answers cont’d: When filter #4 is washed at about 9:00 a.m., filter #3 turbidity increases dramatically because additional flow (hydraulic surging/loading) is directed to filter #3. (Reference Profile “H” or “G, #2” ) In general, the greater the % flow increase, the greater the chance for breakthrough. Plants with only two filters, may see an increase of up to 50% flow to one filter during backwashing. When filter #3 is washed at 1:15 p.m., filter #4 turbidity increases – likely because of hydraulic surging/loading. (Reference Profiles “H” & “G”)

Answers cont’d: Following backwashes on filters #3 and #4, the on-line turbidity levels are high. This would warrant further investigation to find out if extending filter-to-waste (rewash) time would prevent post-backwash turbidity spikes from entering the clearwell. (Reference Profile “C”) It is important to also note that a secondary spike and somewhat slow recovery is occurring. This would warrant investigation of additional operational changes – beyond increasing filter to waste. (Reference Profiles “E” & “D”)

Answers cont’d: Filter run times MAY be too long? This could be contributing to the slow recovery and secondary spikes on both filters. Also, this may be one reason (in addition to valving) why filter #4 reacts to the flow change at 6:00am, but filter #3 does not; and, Filter #4 does not react to a more drastic rate change at noon but filter #3 does. In other words, rate changes caused spikes on the filters which were almost due for backwash; but, not on the “cleaner” (less runtime) filters.

Formatting Concerns: Example chart is not a complete Profile – doesn’t include entire period between backwashes; therefore, you do not know how much run time is on each filter. Example has several labels; but, does not indicate when filter to waste starts/ends. Would help to label events with A, B, C, etc. and provide more information below the strip charts – run time prior to washing filters, applied turbidity, etc.

Key Points: Individual filter profiles are a required follow-up to certain turbidity exceedences. Submit Filter profiles to PA DEP. Don’t stop with data collection, start with it - Interpret, Investigate, Prevent. Look beyond the filter itself… all pre-filter processes can contribute to poor filter performance. To prevent finished water problems, all processes must be optimized.

References for Additional Information: EPA Guidance Manual for Compliance with the Interim Enhanced Surface Water Treatment Rule: Turbidity Provisions (EPA 815-R-99-010) DEP packet…Filter Profile Checklist AWWARF Manual: “Filter Maintenance and Operations Guidance Manual” Project #2511 (published fall of 2001) AWWA Video: “Filter Surveillance Techniques for Water Utilities” Catalog # 65160 (32 minutes)