INITIAL OPERATIONAL EVALUATION REPORT TREATMENT PROCESSES AND FINISHED WATER QUALITY CITY OF TYLER, TEXAS TABLE OF CONTENTS EXECUTIVE SUMMARY...

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3 INITIAL OPERATIONAL EVALUATION REPORT TREATMENT PROCESSES AND FINISHED WATER QUALITY CITY OF TYLER, TEXAS TABLE OF CONTENTS EXECUTIVE SUMMARY... ES-1 I. OBJECTIVES... 1 II. REGULATORY BACKGROUND... 1 III. INITIAL DATA REVIEW... 2 IV. TREATMENT PROCESS INITIAL OPERATIONAL EVALUATION... 4 Golden Road Water Treatment Plant... 5 Lake Palestine Water Treatment Plant... 8 V. INITIAL COMPLIANCE STRATEGIES Both Water Treatment Plants Golden Road Water Treatment Plant Lake Palestine Water Treatment Plant VI. POTENTIAL COMPLIANCE STRATEGIES Both Water Treatment Plants Golden Road Water Treatment Plant Lake Palestine Water Treatment Plant VII. RECOMMENDED PROCESS CONTROL SAMPLING PLAN... 17

4 EXECUTIVE SUMMARY INITIAL OPERATIONAL EVALUATION REPORT TREATMENT PROCESSES AND FINISHED WATER QUALITY In 1974, Congress passed the Safe Drinking Water Act (SDWA) with the goal of protecting drinking water and it sources (rivers, lakes, springs and groundwater wells). The SDWA authorizes the Environmental Protection Agency (EPA) to set national heath-based standards for drinking water to protect against contaminants both man-made and naturally-occurring. The SDWA was amended in 1986 and again in As a result of the SDWA, regulations governing the presence of disinfection byproducts (DBPs) have been developed and implemented. DBPs are formed by the reaction of disinfectants like chlorine (predominantly free chlorine, with chloramine to a lesser extent) with naturally occurring organic material in source water used to produce potable (drinking) water. Disinfection, and maintaining a disinfectant residual, are critical and required steps in providing the public with a safe water supply. Managing DBPs resulting from the disinfection process protects public health by limiting exposure to these byproducts. For public water supply systems such as the City of Tyler (City or Tyler), compliance with DBP regulations is administered by the Texas Commission on Environmental Quality (TCEQ). Compliance is evaluated quarterly, based on locational running annual averages (developed from the results of testing in the previous 4-quarters) from Tyler s eight (8) current compliance monitoring sites. The City of Tyler has recently experienced intermittent periods of noncompliance with current DBP regulations. In response, Tyler engaged Enprotec/Hibbs & Todd, Inc. (eht) to complete an initial operational evaluation of the City s two water treatment facilities the Golden Road Water Treatment Plant (WTP) and the Lake Palestine WTP to identify potential improvements for sustained compliance with DBP regulations. eht conducted an initial data review followed by a 2-day site visit to the two WTPs. While on site at the WTPs, eht representatives interviewed plant operations and maintenance staff, inspected critical treatment processes, measured key operational variables and verified chemical feed rates and resulting disinfectant residuals. The Golden Road facility is an older (1950 s-era) conventional surface WTP with a rated capacity of 32 million gallons per day (mgd). Source water from Lake Tyler is treated to potable water quality using coagulation, flocculation, sedimentation and gravity filtration. These same conventional water treatment processes are also used at the Lake Palestine facility in addition to a raw water oxidation process via ozonation, which receives its source water from Lake Palestine. eht representatives found each facility to be well maintained and effectively operated by Tyler s Water Utilities staff. The Golden Road WTP is constrained by its age. Designed and constructed several decades before implementation of the SDWA, the facility has finished water piping limitations and no provisions for raw water oxidation. With the more stringent DBP requirements resulting from the promulgation of the Disinfection Byproducts Rule Stage 2 (DBP-2), water treatment facilities across the United States are incorporating raw water oxidation technologies to assist in minimizing the necessary use of free chlorine. Since the Golden Road facility does not currently have a raw water oxidation provision (such as the ozone system at the Lake Palestine facility), to comply with disinfection regulations, the Golden Road facility uses City of Tyler, Texas ES-1 December 2015

5 a free chlorine contact zone to inactive (or kill) microbial pathogens. Collectively, these constraints at the Golden Road facility contribute to the formation potential of regulated DBPs. The Lake Palestine WTP is a newer conventional surface WTP constructed about 12-years ago, with a rated capacity of 30 mgd. This facility takes advantage of ozone as a raw water oxidant, but like the Golden Road plant a free chlorine contact zone is used for compliance with disinfection rules. While the Lake Palestine facility does not have physical limitations (such as the Golden Road facility s finished water piping), relying solely on free chlorine to meet disinfection regulations is likely contributing to the formation of regulated DBPs. Based on the data review and the plant site visits, eht has developed proposed compliance strategies to reduce the formation of DBPs resulting from the disinfection protocols at both the Golden Road and the Lake Palestine WTPs. Proposed compliance strategies are consistent with water industry standards and have been proven successfully at many water treatment facilities both throughout Texas and across the United States. Initial compliance strategies (ICSs) recommended by eht will provide near-term operational improvements that should be able to be completed by Water Utilities staff in a short period of time and generally within current operations budgets. ICSs are prioritized by both the anticipated magnitude of benefit and the relative feasibility of quick implementation, with the goal of maintaining compliance with State and Federal DBP requirements. Potential compliance strategies (PCSs) address recommendations that will either require physical changes to each treatment plant or significant operational changes for reducing the formation of DBPs. PCSs are also prioritized by the anticipated magnitude of benefit, but they will generally take longer to implement and possibly require capital investments not currently budgeted. The goal of PCSs are to reduce the daily DBP formation to the lowest feasible levels, regardless of the raw water quality at any given time. It is eht s recommendation that during implementation of the proposed initial compliance strategies, the proposed potential compliance strategies be evaluated to identify the effective amount of DBP formation potential reduction associated with each strategy to prioritize what (if any) PCSs are selected by the City for ultimate implementation. Table ES-1 summarizes the compliance strategies for compliance with DBPs recommended by eht based on the initial data review and plant evaluations. Both the ICSs and PCSs presented will continue to be evaluated by eht with the support of the City s Water Utilities staff. Additional compliance strategies are likely to be developed as progress with DBP compliance continues. It is the clear goal of the City of Tyler to achieve continuous compliance with regulated disinfection byproducts under current and anticipated future regulations. City of Tyler, Texas ES-2 December 2015

6 Table ES-1: Disinfection Byproducts (DBPs) Compliance Strategies Initial Compliance Strategies Potential Compliance Strategies Both Water Treatment Plants ICS1: Utilization of Sodium Hydroxide to Optimize ph ICS2: Addition of Ammonia Application Points PCS1: Utilization of Enhanced Coagulation for Total Organic Carbon (TOC) Reduction PCS2: Evaluation of Free Chlorine Contact Zones PCS3: Post-Clearwell Chloramine Golden Road Water Treatment Plant Lake Palestine Water Treatment Plant ICS1: Relocation of Existing Ammonia Application Point ICS1: Developing Disinfection- Credit for Ozone Boost PCS1: Modification of Clearwell Piping PCS2: Addition of Raw Water Oxidation Capability PCS1: Modification of Recycle Operations Resolving the DBP issues currently being experienced by Tyler will require a multi-facetted approach to obtain and maintain compliance. This initial operational evaluation report is structured to recommend shortterm strategies that can rapidly bring the City into compliance, along with long-term strategies to ensure the City s finished water remains well below the current EPA-regulated maximum contaminant limit (MCL) for DBPs. City of Tyler, Texas ES-3 December 2015

7 I. OBJECTIVES As with many utilities across the State of Texas, the City of Tyler (City or Tyler) has faced multiple challenges in maintaining consistent operation of its water system in the face of recurrent drought and storm cycles, which can significantly affect the quality and treatability of the City s current surface water sources. While the City has been able to maintain compliance with state and federal regulatory requirements for drinking water most of the time, recent intermittent periods of noncompliance with disinfection byproducts (DBPs) has resulted in the City evaluating potential opportunities to enhance its current operational practices at its two water treatment plants (WTPs), the City s original Golden Road WTP and its newer Lake Palestine WTP. With that goal in mind, the City engaged Enprotec / Hibbs & Todd, Inc. (eht) to complete an initial operational evaluation of the City s WTPs in order to identify potential improvements, either infrastructure and/or operational, that would result in its potable water consistently meeting regulatory standards for DBPs. The purpose of this (Report) is to provide an initial summary of eht s evaluations and resulting proposed compliance strategies for operational and/or infrastructure improvements to maintain DBP compliance. II. REGULATORY BACKGROUND Disinfecting potable water is critical to protect the public from disease-causing microorganisms. Potable (drinking) water is disinfected to inactivate (or kill) bacteria, viruses, and other organisms. Disinfection of drinking water has benefited public health enormously by lowering the rates of infectious diseases (for example, typhoid, hepatitis and cholera) spread through untreated water. In Texas, public water systems are required to disinfect water delivered to public water system users to inactivate microbial pathogens. However, disinfectants like chlorine, chlorine dioxide, ozone and chloramines can react with naturally-occurring materials in the water to form DBPs such as: Total Trihalomethanes (TTHMs) Haloacetic acids (HAA5s) Chlorite Chlorate Bromate Nitrate DBPs have been regulated by the Environmental Protection Agency (EPA) since 1979 to address health risks posed by a potential association between chlorinated drinking water and cancer, particularly bladder cancer. Current reproductive and developmental health effects data do not support a conclusion as to whether exposure to chlorinated drinking water or disinfection byproducts causes adverse developmental or reproductive health effects, but do support a potential health concern. Although uncertain, the combined health data warranted the EPA s promulgation of the Disinfection Byproduct Rule to mitigate potential risks posed by DBPs. These byproducts, if consumed in excess of EPA's federally imposed standards over many years (i.e. chronic exposure), may lead to increased chronic health risks. The EPA has developed the Disinfection Byproduct Rule to protect public health by limiting exposure to disinfectant byproducts. In November 1979, the EPA set an interim maximum contaminant level (MCL) for total THMs of 0.10 milligrams per liter (mg/l) as an annual average for community public water systems serving City of Tyler, Texas Page 1 December 2015

8 10,000 or more people. The Stage 1 Disinfectants and Disinfection Byproducts Rule (DBP-1) was promulgated in December 1998 as the first phase in a rulemaking strategy required by Congress as part of the 1996 Amendments to the Safe Drinking Water Act. DBP1 lowered the MCL for THMs to mg/l, and added an MCL for HAAs of mg/l, both based on a four quarter running annual average. The Stage 2 Disinfectants and Disinfection Byproducts Rule (DBP-2) of December 2005 built upon DBP1 to provide greater protection measures beyond those required by the previous DBP-1 regulations. The DBP-2 rule requires systems to determine the highest risk sample sites for DBPs in their distribution system through an initial distribution system evaluation and changed the compliance calculation by determining compliance with the MCLs at each sample site individually using locational running annual averages (LRAAs), as opposed to the DBP-1 requirement for a system-wide average. Compliance with current regulations governing the presence of DBPs in the City of Tyler s public water system is currently determined based on eight separate LRAAs calculated individually at each of the City s DBP sample sites. Under DBP-2, the results of the most recent four quarterly samples from each of the City s DBP sample sites are averaged to obtain a locational running annual average each quarter. Under DBP-1, compliance was based on a single system-wide running annual average each quarter, over nine annual average sampling sites. Under DBP-2, the City s compliance is currently based on eight separate LRAAs. The likelihood of public water systems experiencing compliance issues under DBP-2 is much greater than under DBP-1, as distribution issues (such as water age) can increase locational THMs and/or HAA5s. III. INITIAL DATA REVIEW Based on EPA s expectation that public water systems would experience greater challenges complying with the DBP MCLs at multiple sample sites with corresponding LRAAs, the EPA developed a protocol to help water systems identify the causes of and reduce DBPs. The EPA s protocol for identifying the source of DBPs and then reduce them can be found in Stage 2 Disinfectants and Disinfection Byproducts Rule-Operational Evaluation Guidance Manual (publication 815-R ; December 2008). The EPA s guidance manual recommends that public water systems utilize six steps for identifying and reducing DBPs in their systems as follows: 1. Confirm that data collection and analysis protocols were followed for DBP samples. 2. Review DBP data collected from other/all sites in the system. 3. Limit scope of an operational evaluation to areas of known cause. 4. Conduct an operational evaluation. 5. Identify steps to minimize future DBP MCL exceedances. 6. Prepare and submit a report to the State regulatory agency, if required. eht s approach to identifying the source of DBPs in the City of Tyler water system followed the basic approach presented in EPA s guidance manual. eht began its operational evaluation prior to the site visit to the City of Tyler water production facilities by obtaining DBP sample results for the City of Tyler s public water system at the Texas Drinking Water Watch website. Figure 1 graphically presents TTHMs at all DBP sample sites in the City of Tyler public water system from 2004 to present. Figure 2 graphically presents HAA5s at the same sample sites over the same time period. City of Tyler, Texas Page 2 December 2015

9 Figure 1 TTHMs (ppb) in Tyler s Water System Present Figure 2 HAA5s (ppb) in Tyler s Water System Present City of Tyler, Texas Page 3 December 2015

10 Figures 1 and 2 graphically represent total trihalomethanes and haloacetic acid concentrations from Concentration values are represented on the y-axis in micrograms per liter (µg/l) or parts per billion (ppb) and the sample collection date on the x-axis. It is important to note that up until January 2012, the City of Tyler was required to monitor these DBPs in nine annual average sampling locations; however, the TCEQ now only requires the City to implement quarterly monitoring at eight LRAA sampling locations. Data from both TTHMs and HAA5s in samples collected from Tyler s system indicates, with few exceptions, system-wide trends that show marginal compliance for a number of years. DBP concentrations at all LRAA sample sites tend to reflect very similar concentrations. The expectation with this trend pattern is that either the source water formation potential is affecting the system-wide concentration of DBPs and causing the trend pattern, or that conditions at the point of treatment are contributing to the pattern of DBPs in the distribution system. In Tyler s case, there are two different surface water sources in continuous use. As such, it is less likely that continuous use of both sources would produce the trend in DBP results seen in Figure 1 and Figure 2, pointing to treatment practices as a more likely source of elevated DBPs in the system. Using EPA s suggested protocol, based on review of the older RAA and newer LRAA sampling data, eht focused its effort on an initial operational evaluation of treatment processes used at the Golden Road and Lake Palestine WTPs. IV. TREATMENT PROCESS INITIAL OPERATIONAL EVALUATION Representatives from eht visited the City s two WTPs on November 9 th and 10 th, 2015, and spent approximately 16 hours with Tyler s Water Utilities staff making an initial evaluation of water treatment facilities operation. eht representatives interviewed plant operations and maintenance staff, inspected critical treatment processes, measured key operational variables, and verified chemical feed rates and resulting disinfectant residuals at the City s Golden Road and Lake Palestine WTPs. eht s findings related to the initial treatment process evaluations are described below. eht s impression of the knowledge, capability and willingness of the Water Utilities staff to address difficult treatment challenges was very positive. Tyler s Water Utilities staff was receptive to the efforts of eht s detailed questioning on how the City s WTP facilities are operated. Tyler s Water Utilities staff readily provided essential insight and information concerning operation of the facilities as well as relevant information concerning special studies and projects already being undertaken to optimize daily WTP operations. Of particular interest to eht was a pilot project currently underway at the Lake Palestine WTP to eliminate or reduce the use of lime by adding sodium hydroxide to the treatment process, and the relocation of the ammonia application point (to enhance chloramine formation) at the Golden Road WTP. It is eht s opinion that these two measures already being implemented by the City s Water Utilities staff have the potential to improve compliance with DBPs. Also of interest was the ongoing filter assessment project at the Golden Road WTP implemented by the City s Water Utilities staff. Operational improvements from the assessment are resulting in an unusually high quality filtered water being produced by a conventional (coagulation-flocculationsedimentation-gravity [dual media] filtration) WTP. The turbidity levels in the filter effluent from both plants routinely fall within the range of 0.02 Nephelometric Turbidity Units (NTU) to 0.15 NTU, City of Tyler, Texas Page 4 December 2015

11 which is excellent for conventional filters. The low filter effluent turbidity (using conventional filtration technology) at the Golden Road and Lake Palestine WTPs represents a noteworthy accomplishment by operations staff at the plants. Another item of note was the overall condition and appearance of each WTP facility. Major equipment, structures and processes at each facility appeared to be in a fully usable state, reflecting excellent preventative maintenance efforts by Tyler s Water Utilities staff. Golden Road Water Treatment Plant The Golden Road WTP is an older (1950 s-era) conventional surface WTP with a rated capacity of 32 million gallons per day (mgd). Many of the filter units at the plant are in need of being rehabilitated (per the recent filter assessment study conducted by City Water Utilities staff) which limits current effective production capacity to about 26 mgd. Surface water from Lake Tyler is pumped to the Golden Road WTP via three intake pumps located offsite at the lake. Surface water enters the plant through parallel raw water pipelines. Each of the raw water lines discharge into an open channel at the head of the WTP into which fluoride and liquid aluminum sulfate (alum) are being dosed. Currently, no form of raw water oxidation is used at the Golden Road WTP (unlike the ozone system being used at the Lake Palestine WTP). Alum dosage for coagulation normally ranges from mg/l with the lower end of the range being normal for the Golden Road WTP. On the days that eht visited the WTP the alum dose was 55 mg/l, while the fluoride dose was approximately 0.5 mg/l. Plant staff run jar tests on a weekly basis to determine the optimum alum dose based on raw water quality. There is natural fluoride in Lake Tyler (approximately mg/l), and as required by City Ordinance, the City supplements naturally occurring fluoride to maintain a fluoride concentration in the City s treated water of approximately 0.7 mg/l. The target fluoride concentration in the finished water from the Golden Road WTP corresponds to the current industry-accepted finished water fluoride goal as established by the United States Centers for Disease Control. From the open channel, raw water flows to the first stage flash mixer which provides rapid mixing of the coagulant (alum). From the first stage flash mixer, raw water flow passes (via gravity) to the second stage flash mixer where a lime slurry is dosed to boost ph and alkalinity to a point where the finished water ph is at or above standard units (su). Optimal use of alum for coagulation, as well as enhanced reduction of total organic carbon (TOC), occurs at a ph less than 7.0 su. The use of lime in the pretreatment process could be limiting plant optimization, and will be addressed in additional detail as a potential compliance strategy in Section VI. In the past, a ph of 7.5 su from the second stage flash mixer had been targeted by plant operators. However, meeting that target required such a high lime feed that settled and finished water turbidity was being impacted. At the time of the plant walkthrough, lime was being fed at a rate of 10 mg/l and settled and finished water turbidity levels ( NTU and NTU, respectively) were within desired ranges. ph of the finished water leaving the Golden Road WTP was 7.2 su. The optimal ph in finished water to maintain a good monochloramine residual in Tyler s distribution system is su. Water Utilities staff has previously identified that the ph of the finished water City of Tyler, Texas Page 5 December 2015

12 from both WTPs is not optimal, and staff is already proceeding forward with potential sodium hydroxide addition improvements to address this issue. Flow from the second stage flash mixer is then split between the four flocculation/sedimentation basins. The turbidity of the settled water from the sedimentation basins is normally less than 2.0 NTU which meets the Texas surface water treatment goal of <2.0 NTU in settled water. Settled water from the flocculation/sedimentation basins passes through the settled water flow junction box where free chlorine and a filter aid polymer (Aqualum) are added. At the time of the Golden Road WTP visit, flow through the WTP was 8 mgd and chlorine was being fed at a rate of 475 pounds per day (ppd) giving a settled water free chlorine dose of 7.1 mg/l with a measured free chlorine residual of 3.8 mg/l. The filter aid was being dosed at 0.35 mg/l. Application of both treatment chemicals is fairly typical for conventional water treatment facilities and was within the expected range for these treatment processes. From the settled water flow splitter, settled water flows to the sixteen dual media gravity filters. At the time of the WTP walkthrough, the combined filter effluent (CFE) turbidity was NTU which is well below the limit of <0.3 NTU in at least 95% of the four-hour CFE readings. From the filters, combined filter effluent flow passes to the clearwell/high service pump suction junction box (junction box). Currently, the only ammonia injection point (for formation of chloramines) is located in this junction box. At the time of the WTP walkthrough, the free chlorine residual in the settled water was 3.8 mg/l. The ammoniator was set to dose 70 ppd which equates to 1.0 mg/l (at the given WTP flow of 8 mgd). With a free chlorine residual of 3.8 mg/l, the chlorine to ammonia ratio was at 3.8-to-1 which is slightly lower than optimal for the chloramination process. All water entering the junction box is dosed with ammonia and chloramines are formed in the finished water in the junction box. However, depending on current WTP production, operation of the high service pumps and level in the clearwells, finished water flow entering the junction box from the filters may either: Flow into the clearwells for temporary onsite storage (if the high service pumps are not online); Be pumped directly from the junction box by the high service pumps to the distribution system without having passed into the clearwells (especially if high service pumping flow exceeds the current WTP production flow rate); or Flow into the clearwells while at the same time being pumped by the high service pumps (likely occurring most of the operating time). The configuration of the clearwell/high service pump suction junction box contributes to unusually high water age in the clearwells, increasing the potential for DBP formation. Operations staff reported lower disinfectant residual in the newer clearwell (which is located further away from the junction box than the original clearwell) possibly further increasing water age and DBP formation. City of Tyler, Texas Page 6 December 2015

13 Plant operations staff at the Golden Road WTP, have recognized this issue and proactively compensate for the configuration of the junction box by periodically lowering the WTP production rate below distribution system demands which causes the high service pumps to draw water from the clearwells thereby ensuring clearwell turnover. The configuration of the junction box piping and valving represents a historical shortcoming in facilities that were designed and constructed well in advance of current regulations for DBPs being implemented. When the clearwells are at high level and the high service pumps are running, filtered water entering the junction box does not pass through the clearwells but flows directly from the junction box to the high service pumps. When the clearwells are at low level and the high service pumps are not running, filtered water flows into the clearwells. While it appears that any finished water entering the clearwells should have a chloramine rather than free chlorine residual, the configuration of sluice gates and the location of the existing ammonia application point were identified by eht as potential limiting factors in the disinfection process. Through discussions, eht learned the Water Utilities staff has already undertaken relocation of the ammonia injection point. It is anticipated that the new ammonia injection point in the combined filter effluent piping will immediately help to reduce DBP formation at the Golden Road WTP. At present, the concentration-time (CT) study at the Golden Road WTP does not include the contact time in the clearwells. Based on eht s assessment of operating conditions in the WTP, it is eht s opinion that because plug flow through the clearwells to the high service pumps cannot be assured at all times, the clearwells were likely left out of the CT study in order to ensure that the effective contact time of disinfectants within the WTP would not be overestimated. However, if the clearwells could be incorporated into the CT study for the Golden Road WTP (based on the use of chloramine), the necessary free chlorine dosing in the filters could be reduced since less CT credit would be needed in the filter contact zone, which would also reduce DBP formation. Incorporating the clearwells into the CT study will require physical changes to the piping system serving the clearwells and high service pumps. The chlorine system at the Golden Road WTP consists of a duty bank of six one-ton cylinders and a standby bank of six one-ton cylinders. An automatic switchover unit separates the duty bank from the standby bank and serves to switch the standby bank automatically into duty when the duty bank runs out. The plant is equipped with four possible chlorine injection locations. These are: 1. Chlorine can be injected in the raw water at the channel where alum and fluoride are presently injected. This site is currently not active. 2. Chlorine can be injected at the clarifier influent flow splitter box before the flocculation/sedimentation basins. This injection point is reportedly used only to remove algae from the weirs of the sedimentation basins and is used only on a seasonal basis. 3. Chlorine can be injected in the settled water at the settled water flow junction box before it flows to the filters. This is the primary application point for chlorine at the plant. City of Tyler, Texas Page 7 December 2015

14 4. Chlorine can be injected into the finished water as it is leaving the clearwells. This application point is typically used only in the event of a power outage. In case of power outage, finished water may stand in the clearwells without being turned over and the chloramine residual may drop below desired levels prior to distribution. The finished water free chlorine application point is used to boost the chloramine residual in water that is leaving the plant after a power outage. Two anhydrous ammonia tanks are located adjacent to the ammonia feed building. Two ammoniators (one duty, one standby) serve to meter ammonia for chloramine formation to the finished water application point in the clearwell junction box. At the time of the walkthrough, the total chlorine residual leaving the plant was 3.8 mg/l and the free ammonia residual was less than 0.1 mg/l. These are optimal values and reflect solid operating techniques by the operating staff. Lake Palestine Water Treatment Plant The Lake Palestine WTP is a newer conventional surface water treatment plant constructed about 12 years ago with a rated capacity of 30 mgd. Surface water from Lake Palestine is pumped to the WTP via three intake pumps located offsite at the lake. Surface water enters the plant through a single raw water pipeline where decant from the process water recovery system recycles back to the head of the WTP to blend with influent raw water prior to reaching the two parallel ozone contactors. Ozone is being dosed at a rate of 2 mg/l into the raw water. Each of the two ozone contactors is rated for 15 mgd. Flow through the plant on the day of the initial walkthrough was 16 mgd and both contactors were in service, dividing flow evenly between the two contactors. While the ozone system can provide excellent oxidation of dissolved constituents in raw water (such as TOC, iron, manganese, MIB and Geosmin), it can also provide some amount of CT credit, depending on the measured residual throughout the baffled contact zones within each contactor. In reviewing the current CT study (dated April 24, 2012) for the Lake Palestine WTP, it appears that the intended primary disinfectant and CT credit is based upon the measured ozone residual within the ozone contactors, followed by the use of free chlorine and/or chloramine in later stages of the WTP to provide any necessary remaining CT credit. Currently, no CT credit is being taken for ozone. eht recommends that the use of the ozone system be enhanced to provide additional CT credit to the WTP allowing for either a reduction or possibly elimination of free chlorine use at the Lake Palestine WTP, which should significantly reduce DBP formation. Potential tasks, concerns and monitoring requirements are discussed in additional detail under Section V, Initial Compliance Strategies. From the ozone contactors raw water flow passes to the rapid mix basins where powdered activated carbon (PAC) is being added at a dose of 20 mg/l into a separate chamber just upstream from the addition of lime and alum. The addition of PAC can provide a benefit in the control of MIB and Geosmin related taste and odor events, though at most facilities it is used on an intermittent basis. This is due to the high operation and maintenance (O&M) cost associated with PAC, as well as the potential for a small amount of PAC to re-solubilize into the raw water resulting in an increase in TOC (and subsequent increase in DBP formation potential). eht recommends that following the completion of the more critical (prioritized later in this Report) compliance strategies at the WTP, that Water Utilities staff conduct an in-house evaluation to determine whether the PAC City of Tyler, Texas Page 8 December 2015

15 dosage could be reduced or altogether eliminated outside of MIB and/or Geosmin events in Lake Palestine. It should also be noted that the raw water turbidity from Lake Palestine is frequently less than 5 NTU, which creates a significant challenge in optimizing the settling process, due to the limited amount of suspended solids to create flocs in the flocculation/sedimentation process. For example, it can be more feasible and cost effective to reduce a raw water turbidity from 10 NTU to 2 NTU than from a raw water turbidity of 5 NTU to 2 NTU. Lime (for ph control) and alum (for coagulation) are being added into the first stage of the rapid mix chamber (following current PAC addition) within a foot of each other. At the time of the WTP walkthrough, lime was being added at a dose of 0.9 mg/l and alum was being added at a dose of 60 mg/l. In discussions with operating staff, eht learned that the Lake Palestine WTP was never equipped with a sodium hydroxide system for raising finished water ph to a level that would help to support a monochloramine residual and water stability in the distribution system. Instead, a lime system was provided to boost ph. The original dosing point for lime at the WTP was in the settled water, which resulted in increased solids loading on the filters and subsequent filter effluent turbidity spikes. Operating staff relocated the lime feed point to the rapid mixing system to improve ph control, improve settling and improve filter operations. While the concurrent use of alum and lime at a single location can increase the density of the flocs within the settling process, the relatively low ph of alum and the high ph of lime tend to neutralize one another, resulting in fairly poor (non-enhanced) coagulation of solids and reduction of TOC, as well as limited increases to ph in the finished water. In order to address the low raw water turbidity as well as low alkalinity, other utility systems have converted from alum use to a more advanced aluminum-based coagulant such as aluminum chlorohydrate (ACH) or polyaluminum chloride (PACl). The major benefits of the more advanced coagulants are that they can operate over a much wider ph range, they do not consume a significant amount of alkalinity (unlike alum) requiring less finished water ph boosting, and the effective dose for ACH or PACl tends to be about 20-30% of the dose required for alum (resulting in reduced solids production). The greatest disadvantage to using more advanced coagulants is the unit cost is much higher. While the reduced dosage can help to offset the cost difference, the use of more advanced coagulants tends to result in a slightly higher net coagulant cost, although the total chemical cost tends to be about the same when also accounting for the reduced ph boosting requirements associated with advanced coagulant use. Since the City s WTPs are not currently using sodium hydroxide for finished water ph boosting, this benefit may not be readily apparent. Following completion of the sodium hydroxide pilot study, eht recommends that a coagulant use feasibility study be completed to determine first to what extent enhanced coagulation can be accomplished with alum use, and second (if needed) the completion of a life cycle analysis to properly address the cost comparison of the alum and sodium hydroxide versus a more advanced coagulant if necessary. Regardless of the coagulant used at the Lake Palestine WTP, eht recommends that an alternative method of ph boosting be considered at the WTP (preferably either pre- or post-filtration) to enhance finished water ph, allowing for the reduction or potential elimination of use of lime within the settling process. City of Tyler, Texas Page 9 December 2015

16 It should be noted that the Water Utilities staff had already come to that same conclusion and was proactively taking steps to address the lime addition issue. The week prior to eht s WTP visit, Water Utilities staff had begun a trial of sodium hydroxide use at the Lake Palestine WTP whereby sodium hydroxide will be dosed in the finished water for ph control. From the rapid mix basins, raw water flow passes to the flocculation basins and undergoes tapered mixing with increased mixing in the furthest upstream flocculation zones and reduced mixing in each subsequent downstream flocculation zone. Flow passes from the flocculation basins into the sedimentation basins. Settled water leaving the sedimentation basins typically has a turbidity in the range of 1-2 NTU which meets the Texas surface water treatment goal of <2.0 NTU in the settled water. However, a dark sheen was observed on the surface of the flocculation and sedimentation basins, likely caused by the PAC; carryover of PAC from the sedimentation basin to the filters could increase DBP formation when reacted with free chlorine. The combined settled water is dosed with free chlorine and Aqualum (a filter aid polymer) in the settled water trough which supplies water to the filters. Aqualum was being dosed at 0.8 mg/l at the time of the WTP walkthrough. At the time of the walkthrough the WTP flow rate was 16 mgd and the chlorine feed rate was 840 ppd giving a chlorine dose of 6.3 mg/l. The resulting free chlorine residual at the outlet of the filters was 3.5 mg/l. The chlorine system at the Lake Palestine WTP consists of a duty bank of six one-ton cylinders and a standby bank of six one-ton cylinders. The chlorine system at the Lake Palestine WTP is also equipped with an automatic switchover unit, but the operations staff prefer to handle bank switchover manually. The plant is equipped with three possible chlorine injection locations. These are: 1. Chlorine can be injected in the raw water immediately upstream from the ozone contactors. At present this site is not active. 2. Chlorine can be injected into the settled water trough upstream from the filters. This injection point was in service and is currently the sole injection point in use. 3. Chlorine can also be injected into the finished water just prior to the clearwells. At present this application point is not being used. Two anhydrous ammonia tanks are located adjacent to the ammonia feed building. Two ammoniators (one duty, one standby) serve to meter ammonia for chloramine formation to the finished water application point on the upstream side of the clearwells. At a production rate of 16 mgd, the ratio of chlorine to ammonia was a measured 4.4:1. The total chlorine residual leaving the plant was 3.5 mg/l and the free ammonia residual was less than 0.1 mg/l. These are optimal values and reflect solid operating techniques by the operating staff. City of Tyler, Texas Page 10 December 2015

17 V. INITIAL COMPLIANCE STRATEGIES Initial compliance strategies (ICS) have been identified at the City s WTPs to reduce DBP formation. These initial strategies are prioritized by both the anticipated magnitude of benefit and the relative feasibility of implementation in a short period of time. The goal of these initial strategies is to first and foremost identify potential low hanging fruit for near-term operational improvements that can be completed by City staff within current operations budgets, while also identifying potential compliance strategies (PCS) addressed in Section VI that could also benefit each facility as budget allows. Both Water Treatment Plants (BWTP) Recommendation BWTP-ICS1: Utilization of Sodium Hydroxide to Optimize ph The application of sodium hydroxide is useful in producing finished water with desirable ph and alkalinity levels. Sending finished water with a lower than optimal ph to the distribution system can lead to formation of less desirable and less stable forms of chloramines which increases potential DBP formation. Additionally, the use of sodium hydroxide has the added benefit of helping to reduce copper and lead concentrations in the finished water. eht recommends that the ph and alkalinity of the finished water be raised using sodium hydroxide to levels at each WTP that produce slightly scale-forming (non-corrosive) finished water. It should be noted that prior to eht s walkthrough of each WTP, the Water Utilities staff came to the same conclusion and has recently begun a trial (following previous coordination with TCEQ for approval) of using sodium hydroxide at the Lake Palestine WTP. City staff were also working on the implementation of a pilot trial for sodium hydroxide at the Golden Road WTP as well. Optimal ph for maintaining a strong monochloramine residual is su. If finished water ph decreases below this optimal ph range, the ratio of monochloramine (highly desirable for maintaining a disinfectant residual in a distribution system) to dichloramine and trichloramine (both being unstable and prone to release of free chlorine into potable water) decreases, resulting in a reduced chloramine residual in distribution, as well as increased DBP formation. There are several useful indicators to monitor the scale-forming potential of the finished water including the Ryznar Index, Aggressiveness Index, the Langelier Saturation Index (LSI), the Baylis Curve, and the calcium carbonate precipitation potential. Each of these indices is a measure of a solution s ability to dissolve or deposit calcium carbonate and is an indicator of the corrosivity of water. These indices are not related directly to corrosion, but are related to the deposition of a calcium carbonate film or scale. When no protective scale is formed, water is considered to be aggressive and corrosion can occur. Recommendation BWTP-ICS2: Addition of Ammonia Applications Points The current application of chlorine in the settled water at each treatment facility followed by the formation of chloramines through the addition of ammonia at a single application point limits operating staff s ability to control the length of time free chlorine is present in finished water. Additional flexibility can be obtained by segmenting the free chlorine contact zones through the City of Tyler, Texas Page 11 December 2015

18 addition of alternative ammonia application points. Having multiple free chlorine contact zones would provide operators a simple tool for responding to varying flow rates, seasonal water quality changes and disinfection demands while maintaining CT compliance. Implementing this recommendation would require TCEQ approval of a revised CT study, and the physical construction of additional ammonia injection points (including mixing provisions) and disinfection zone sampling points. Golden Road Water Treatment Plant (GRWTP) Recommendation GRWTP-ICS1: Relocation of Ammonia Application Point Presently the Golden Road WTP applies the ammonia dose for chloramine formation in the filtered water junction box between the two clearwells. It is possible that the ammonia is not effectively mixed with the free chlorine residual already present in the combined filter effluent when the water flows into the WTP clearwells. Inefficient mixing of ammonia with the existing free chlorine residual may be leading to additional DBP formation in the finished water. The Water Utilities staff has already recognized the need for better mixing of the ammonia added to form chloramines at the Golden Road WTP and are currently taking steps to move the finished water ammonia application point upstream into the combined filter effluent piping to allow better dispersal and mixing of the ammonia for the formation of chloramines. It is important that provisions for adequate mixing of the ammonia be an integral part of the new application point. Lake Palestine Water Treatment Plant (LPWTP) Recommendation LPWTP-ICS1: Developing Disinfection Credit for Ozone The current Lake Palestine WTP CT study incorporates the use of ozone for disinfection credit in the ozone contactors with the use of free chlorine and/or chloramines through the remainder of the WTP. However, the WTP is not presently taking credit for ozone as a disinfectant. Taking credit for ozone residual in the ozone contactors could allow for reduction (or possibly elimination) of free chlorine in the remainder of the WTP, which could significantly reduce DBP formation. This approach would require that an ozone residual is detected in at least three of the five contactors in each contactor train (specifically at the end of Disinfection Zone 3 (D3) or Zone 5 (D5)). Implementing this recommendation will require coordination with TCEQ, as the current CT study appears to be based on an assumption that ozone is only injected into the raw water directly upstream of D1 in each contactor train. Based on discussions with operations staff, it appears that ozone is injected into D1, D2, and D3. While TCEQ allows for a multiple injection approach, coordination with TCEQ is needed to verify that the current Surface Water Monthly Operating Report (SWMOR) accurately takes into account the existing ozone dosing approach and will calculate CT credit appropriately in the SWMOR prior to operations staff modifying current daily WTP operations. While the CT Study for the Lake Palestine WTP is being coordinated with TCEQ, eht recommends that the ozone residual in D3, D4, and D5 for each contactor train be measured via grab sample each day and that the ozone dosage be adjusted as needed to provide measured City of Tyler, Texas Page 12 December 2015

19 ozone residual in D5 of each train (unless TCEQ specifies a different sample point configuration). Once ozone residual in the contactors is regularly and reliably present at levels in excess of 0.1 mg/l in D5 and it has been verified with TCEQ that the current calculations in the Lake Palestine WTP SWMOR are appropriate for the ozone system, then eht s recommendation is to take credit for ozone residuals on pages 4 and 5 of the SWMOR and begin reducing usage of free chlorine in the settled water effluent trough and filter disinfection zones, with the goal of eliminating the use of free chlorine entirely from the WTP if possible. It is intended to utilize ammonia in conjunction with the use of ozone to prevent or minimize formation of bromate. Additional operational recommendations for coordinated ammonia and ozone use are discussed in Section VII. VI. POTENTIAL COMPLIANCE STRATEGIES Section II summarizes the regulatory background associated with DBPs. Under the Safe Drinking Water Act of 1979, and subsequent amendments, many regulations in addition to DBPs have been enacted to protect drinking water and its sources. Tyler s Golden Road WTP was designed and constructed nearly two decades before the onset of these regulations. Older facilities, such as the Golden Road WTP, often have physical constraints that limit operational changes needed to comply with today s regulations. While not as significant in newer treatment plants, like the Lake Palestine facility, operational constraints can also limit consistent regulatory compliance. Potential compliance strategies (PCS) outlined in this Section discuss physical changes to each WTP as well as operational changes that may reduce the formation of DBPs. eht recommends that prior to implementing any PCS, such as enhanced coagulation at each WTP, sufficient time has been allotted to fully vet the proposed operational modifications to the ozone system at the Lake Palestine WTP and the proposed addition of finished water sodium hydroxide dosing at each WTP. In other words, while there are multiple possible improvements at each facility, the best path forward is to complete one improvement at a time to allow each WTP to settle in to clearly identify the magnitude of impacts to WTP operations, while also re-establishing a new baseline for comparison of any additional improvements implemented. Both Water Treatment Plants Recommendation BWTP-PCS1: Utilization of Enhanced Coagulation for Total Organic Carbon (TOC) Reduction TOC is an important precursor to DBP formation. Generally, the higher the TOC levels at the point of chlorination, the higher the levels of DBPs. Optimizing TOC removal in the coagulation/flocculation/sedimentation processes upstream from chlorine/chloramine application is typically helpful in lowering DBPs and involves suppressing the raw water ph during coagulation/flocculation/sedimentation to approximately su. At a ph of su, TOC is most susceptible to removal via coagulation, flocculation and sedimentation. Use of alum tends to decrease the alkalinity (approximately 0.5 mg/l of alkalinity is consumed for each 1 mg/l of alum dosed) and ph of the water undergoing treatment while the use of lime raises the alkalinity and ph City of Tyler, Texas Page 13 December 2015

20 of the water undergoing treatment, negatively affecting the ability of alum to convert dissolved organic carbon into suspended carbon that can be removed in the sedimentation process. With the typically low raw water alkalinity and the relatively high alum application rate of mg/l at the two plants, it is possible that optimum ph for increased TOC removal and corresponding lower DBP formation potential through the coagulation and flocculation processes could be obtained at either WTP by significantly reducing or possibly eliminating the raw water lime application and allowing ph in the flocculation/sedimentation process to reach optimum levels for enhanced coagulation with alum ( su). One approach to this issue could be to optimize the effective alum dose at each facility and reduce or eliminate the use of lime, potentially limiting the observed decrease in ph; however, given the typically low raw water turbidity from each raw water source, it may not be possible to reach the target settled water ph of su without increasing subsequent settled water and filter effluent turbidity. To prevent degradation of filter effluent turbidity, it may be necessary to continue raw water lime application, but only at a high enough rate to produce settled water ph of su. As an alternative, use of a more advanced coagulant (such as ACH or PACl) could provide a further enhancement in TOC removal beyond the capability of alum use at each facility, without sacrificing current turbidity removal performance. However, this alternative is a multi-step approach, requiring a substantial amount of jar testing under varying raw water conditions to ensure full-scale performance would in fact be improved before full-scale changes were implemented. This alternative would also require coordination with TCEQ. Recommendation BWTP-PCS2: Evaluation of Free Chlorine Contact Zones The application of chlorine to settled water at both treatment facilities should be re-evaluated once stable operations have been established following implementation of initial compliance strategies and potentially enhanced coagulation (Recommendation BWTP-PCS1). Organic levels are higher in the settled water and gravity filter units, and moving any free chlorine contact to filtered effluent would further reduce DBP formation potential. Should this recommendation be considered, coordination with TCEQ and possible changes to each plant s CT study would be required. Additionally, implementation would require the construction of new chlorine injection points, including provisions for adequate mixing. Recommendation BWTP-PCS3: Post-Clearwell Chloramine Boost Additional flexibility can be gained for the Water Utilities staff by providing the ability to boost chloramine residuals leaving the clearwells at each water treatment plant. Currently, the Lake Palestine WTP has a chlorine application point post-clearwell. There is no post-clearwell chlorine application point at the Golden Road WTP. In eht s experience, simply adding chlorine to boost a chloramine residual is problematic. A more reliable approach is the addition of both ammonia and chlorine at the optimal ratio for optimal chloramine formation (4-5:1) to boost the residual sent to the distribution system. At the Lake Palestine facility, this can be accomplished with the additive of an ammonia feed point immediately upstream of the existing post-clearwell chlorine injection point. For the Golden Road WTP, City of Tyler, Texas Page 14 December 2015