Results of the Turbidity Optimization Goals Survey

By Larry D. DeMers – Process Applications, Inc.

The May 2010 issue of AWOP News included an article on the updated turbidity optimization goals preferred by the NOLT as the basis for AWOP.  Concurrently, the NOLT Communications Workgroup developed a survey to determine how the turbidity goals are being implemented within the network and to document state-specific variations of the goals.  The survey was initially sent to the AWOP regional contacts in Spring 2010 and was subsequently forwarded to the AWOP states.  Completed survey forms were received from fifteen of the AWOP states.  Due to the timing of the article, the survey responses, and feedback from three regional AWOP meetings, feedback from states on their plans to update their turbidity goals has also been obtained.  This article summarizes the responses to the turbidity goals survey and the feedback received thus far on the turbidity optimization goals updates.

Turbidity Goals Survey Response

The survey asked the AWOP states if they have formally adopted the optimization goals and sent letters to appropriate water systems.  All of the responding states have introduced the goals to their systems, either through formal letters, posters, or presentations at annual operator schools.  Several states provided example letters that they sent to their water systems, encouraging them to participate in AWOP and to outline the goals.  The Louisiana AWOP letter includes the optimization goals, the annual performance data summary from the Optimization Assessment Spreadsheet, and the plant ranking.  It is sent to all of the surface water systems annually.

A summary of the updated sedimentation basin optimization goals presented in the survey is shown in Table 1.  All of the states responding to the survey have adopted the 1 to 2 NTU settled water turbidity goal based on average raw water turbidity.  The basis for assessing the goal is split, with 60 percent of the states basing the goal on individual sedimentation basin performance and the remainder on combined settled water turbidity.  The response to frequency of sampling was typically four-hour intervals; however, three states only required sampling once per day.  At least three states are proposing to update this goal area by including the 15-minute frequency for plants using continuous reading turbidimeters to monitor their sedimentation process.  Although not specifically mentioned in the optimization goals survey, a few states provided information on their goals for raw water turbidity monitoring.  Virginia’s optimization goals include monitoring for raw water turbidity on a minimum two-hour interval.


Table 2 includes the updated filtration optimization goals.  Responding states almost universally selected 0.10 NTU as their filtration turbidity optimization goal.  The Texas AWOP team has developed an expanded filtration goal that considers four criteria (i.e., 100 percent of all filter readings ≤ 0.5 NTU, 99 percent of all filter readings ≤ 0.3 NTU, 95 percent of all filter readings ≤ 0.1 NTU, and 90 percent of individual filter readings ≤ 0.1 NTU).  About half of the states apply this goal to both individual filter effluent (IFE) and combined filter effluent (CFE).  The remaining states apply the goal to either CFE (four states) or IFE only (three states).  In response to frequency of sampling, state responses reflect changing regulations as well as the proposed optimization frequency.  For those states applying the filtration goal to IFE turbidity, the frequency of sampling was typically at least 15 minutes, and four states are proposing changing the frequency to one minute.  For those states applying the goal to CFE, the frequency was at least every four hours, with one state proposing changing the frequency to one minute.  Most of the states identified 0.30 NTU as the maximum individual filter turbidity optimization goal, although one referenced the LT2 regulation.



The updated post filter backwash performance goals are summarized in Table 3, and they are differentiated by the availability of filter-to-waste (FTW) capability.  Three of the responding states did not report having post filter backwash performance goals.  The remaining responding states have performance goals almost identical to those listed in Table 3 for plants without FTW capability.  The related Texas goals allow plants without FTW capability 30 minutes to achieve the 0.10 NTU goal.  States reported performance goals for plants with FTW capability the same as those identified in Table 3, with three exceptions.  Oregon, Texas, and Virginia have established a maximum turbidity goal during FTW (i.e., 0.30 NTU for Oregon and Texas, 0.3 NTU for Virginia) and a maximum FTW duration (i.e., 15 minutes for Oregon and Virginia, 30 minutes for Texas).  Alabama requires all of their surface water plants to have FTW capability.  Regarding the submittal of post backwash performance data to the state, two responding states, Texas and Virginia, receive these data through their MORs.  A previous article in the August 2009 edition of AWOP News describes the Virginia Optimization Program, including the data submittal requirements for plants to participate in the Virginia Excellence in Performance Awards program.  The Iowa and Oregon AWOP teams reported that they have plants collecting these data if they have been or are currently participating in a Performance Based Training series.  This is also the case for other AWOP states recently completing microbial PBTs (i.e., Louisiana, West Virginia).

The most common response regarding data collection to determine plant performance relative to the optimization goals was use of the monthly operating reports (MORs) to obtain turbidity data.  Some states reported success with the plant staff entering their turbidity data into the Optimization Assessment Spreadsheet (OAS).  The Iowa AWOP team reported that at least 30 percent of their plants are submitting turbidity data using the OAS.  The Pennsylvania AWOP team has established a data entry portal (WebOAS) on their drinking water website for plant staff to enter their turbidity data.  At least six states reported that turbidity data is submitted electronically to their office, either through use of an electronic MOR, submittal of data using the OAS or simpler spreadsheet template, or data entry to a website.



Some overall observations from the turbidity optimization goals survey are summarized below for the responding AWOP states.

  • States have provided their optimization goals to their surface water systems through a combination of mechanisms, including direct letters to the systems, distribution of posters, and presentations at annual training schools.
  • All states have consistently adopted the sedimentation turbidity optimization goals of 1 and 2 NTU based on source water turbidity targets.  States are split on applying the goals to individual sedimentation basins versus combined settled water.  A perception may exist for some states that a performance goal can only be established if data is being submitted to the state to assess performance against the goal.
  • All states have consistently adopted the filtration optimization goal of 0.10 NTU, with some minor variations.  Differences exist on whether this goal is applied to individual filters, combined filter effluent, or both.  As is the case with the settled water goal, a similar perception may exist with some states that a performance goal can only be established if data is routinely available to the state so that performance can be assessed against the goal.
  • A few states responded that they have not adopted post filter backwash turbidity goals.
  • Those states having post filter backwash turbidity goals responded that their goals were very similar to the updated goals.  Two states responded that their post filter backwash goals are the same, regardless of whether the plant has FTW capability.
  • Most states responded that MORs are the most common source for turbidity data to assess performance relative to the goals.  At least six states are receiving turbidity data in an electronic format from some of their plants.

Network Feedback on Updated Turbidity Goals

A few states have either updated their initial optimization goals or are in the process of doing so.  The Oregon AWOP team updated their goals in 2009 to reflect changes in continuous turbidimeter data acquisition and to provide clarification on data collection following FTW.  The updated goals are included on their drinking water program website, along with an extensive collection of drinking water optimization content (  The Alabama AWOP team is considering updates to its goals.  In anticipation of the changes, it recently published background information on the updated goals (from AWOP News) in the Alabama optimization newsletter, Drawing the Graph (Sept. 2010 issue).  This information was enhanced further with an article on experience gained through their CPEs and PBT projects, specifically, the impact of changing plant flow rates and filter backwashing on operating filter performance.

As of the publication time of this edition of AWOP News, feedback had been received on the updated turbidity optimization goals at three of the four regional AWOP meetings.  Some of the highlights are summarized here.

  • Several states have used 0.10 NTU (versus 0.1 NTU) for several years as their filtered water turbidity goal.
  • Modification of state AWOP goals could have an impact on existing awards programs.
  • Several states plan to publicize the updated goals by sending letters to their water sys-tems or through their newsletters and websites.
  • All surface water treatment plants are now required to have at least 15-minute data acquisition on individual filters.  Changing the optimization goals to reflect this existing condition would be straight forward.
  • Requiring at least one-minute data acquisition for IFE and CFE could present a major challenge for plants to meet the 0.10 NTU goal.  Excessive operator time may have to be diverted to tracking down short turbidity spikes that are not performance-related.  In addition, there could be a cost required for some plants to modify their SCADA system to provide more frequent data acquisition capability.
  • It is likely that many water systems can capture one-minute turbidity readings from their filters, but obtaining these data from the systems could be challenging.
  • Stating that the turbidity spike during FTW should be minimized may be overlooked by operators.  Consider either excluding this language or including a specific turbidity goal (e.g., 0.30 NTU, similar to the maximum goal for plants without FTW).
  • Implementation of these updated goals (especially the one-minute data acquisition for filtered water) and improved filter backwash recovery performance could significantly enhance public health protection and take optimization to the next level (approaching performance from membrane systems).

    Continue the Discussion

    With this issue of AWOP News, we’re launching our new AWOP News blog.  One advantage that this new format allows is the ability to comment on articles.  Since the turbidity goals update topic is relevant to all AWOP states, continued feedback and discussion on this article is encouraged.  Click the link near the title of this article  to “Leave a Comment”!

    About Anthony R. DeRosa
    Proverbial box burner and unofficial tech guy for the drinking water community.

    Comments are closed.