TOTAL TRIHALOMETHANES (TTHM) MITIGATION FEASIBILITY STUDY AND PILOT TESTING ABSTRACT KEYWORDS

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1 ABSTRACT TOTAL TRIHALOMETHANES (TTHM) MITIGATION FEASIBILITY STUDY AND PILOT TESTING Perry Gayle, PhD, PE, URS Corporation NC Patricia Chandley, PE, URS Corporation NC Porter Rivers, III, PE, URS Corporation NC Nesley Orochena, Air Force Civil Engineer Center This paper presents lessons learned from conducting a TTHM mitigation feasibility study at Nellis Air Force Base (AFB), NV and pilot testing a storage tank aeration and mixing technology developed by Medora Corporation. Nellis AFB purchases treated surface water from the Southern Nevada Water Authority (SNWA), which categorizes them as a consecutive water system. Nellis AFB can also supply portions of the distribution system with water from several base-owned groundwater wells. The base had experienced a trend of increasing TTHM concentrations in their water distribution system, and proactively commissioned this feasibility study to identify the root causes of the increasing TTHM trends and to develop a strategy for achieving compliance with the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2). Under Stage 2, wholesale and consecutive water systems are subject to the same compliance schedule as required for the largest system in the combined distribution system (defined as the interconnected distribution system consisting of wholesale systems and consecutive systems that receive finished water). Based on this requirement, Nellis AFB and SNWA are both subject to Schedule 1 compliance requirements with compliance monitoring beginning on April 1, The study revealed that the root causes of increasing TTHM trends included issues associated with source, treatment, storage, and distribution. Source water quality had deteriorated due to a prolonged drought, leading to increased concentrations of TTHM precursors in the raw water and higher TTHM concentrations in finished water. Reductions in water demand led to excessive water age in the storage and distribution system. Areas with water age in excess of five days were found to have a high potential for exceeding the maximum contaminant level (MCL) for TTHM. In addition, booster chlorination in areas of low chlorine residual was likely exacerbating the TTHM problem. A TTHM removal product developed by Medora Corporation that was comprised of a floating pump / mixer / spray nozzle system was installed and pilot tested in a 300,000-gallon ground-level storage tank located in a remote area with a water age in excess of 10 days. Sampling documented approximately 28% removal of TTHM by the treatment process. TTHM mitigation recommendations evaluated in the feasibility study included increasing the percentage of well water versus purchased water, full-scale operation of the pilot tested TTHM removal system, water storage tank level management to minimize water age, decommissioning of two tanks, relocation of several booster chlorination points and improved chlorine dosing controls, automatic flushing systems for several dead-end lines, and replacement of tuberculated cast iron pipe that was contributing to excessive chlorine demand and resulting in the requirement to perform booster chlorination. KEYWORDS Water, Trihalomethanes, TTHM, Disinfection, Aeration, Pilot Testing

2 INTRODUCTION This paper presents lessons learned from conducting a TTHM mitigation feasibility study at Nellis Air Force Base (AFB), NV and pilot testing a storage tank aeration technology developed by Medora Corporation. Nellis AFB purchases treated surface water from the Southern Nevada Water Authority (SNWA), which categorizes them as a consecutive water system. Nellis AFB can also supply portions of the distribution system with water from several base-owned groundwater wells. The base had experienced a trend of increasing TTHM concentrations in their water distribution system, and proactively commissioned this feasibility study to identify the root causes of the increasing TTHM trends and to develop a strategy for achieving compliance with the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2). Under Stage 2, wholesale and consecutive water systems are subject to the same compliance schedule as required for the largest system in the combined distribution system (defined as the interconnected distribution system consisting of wholesale systems and consecutive systems that receive finished water). Based on this requirement, Nellis AFB and SNWA are both subject to Schedule 1 compliance requirements with compliance monitoring beginning on April 1, The sections that follow discuss the water system at Nellis AFB, and present the methodology and results of the TTHM mitigation feasibility study and pilot test. BACKGROUND Nellis Air Force Base is located eight miles northeast of Las Vegas and is the home of the U. S. Air Force Warfare Center (USAFWC). The USAFWC provides advanced air combat training for composite strike forces, which include every type of aircraft in the US Air Force inventory. Training is also conducted in conjunction with air and ground units of the Army, Navy, and Marine Corps, as well as air forces from allied nations. Nellis AFB is also a key location for operational testing of the Air Force s newest combat fighter, the F-35. Nellis AFB operates a community water system that serves approximately 6,300 people. The base obtains potable water from two water sources: purchased treated surface water from SNWA and groundwater from base-owned wells. The primary raw water source for SNWA is Lake Mead. Treatment of Lake Mead water includes ozonation, coagulation, flocculation, filtration, corrosion inhibition, and secondary disinfection with chlorine gas. Water from the base-owned wells is disinfected with calcium hypochlorite prior to distribution. In addition, the base has booster chlorination systems to improve chlorine residual in areas with high water age. The Nellis AFB water distribution system was originally constructed in the 1940s; however, the system has gone through several upgrades. The distribution system consists of approximately 60 miles of piping consisting of a mix of ductile iron, cast iron, asbestos cement, and polyvinyl chloride (PVC) piping. Water mains range in size from 4 inches to 16 inches in diameter. Most areas of the base distribution system are looped; however, there are a few dead-end lines. The base has installed automatic flushing systems in areas with dead end lines to help improve water age and water quality. As shown in Table 1, the base has eight potable water storage tanks three elevated tanks and five ground-level tanks (including one bunkered tank). There is approximately 7.2 million gallons (MG) of potable water storage. The average water use based on data from 2011 through 2012 was approximately 1 million gallons per day (MGD). Therefore, with all the storage tanks at full capacity the base has approximately 7.2 days of storage.

3 Table 1. Potable Water Storage Tanks, Nellis AFB Tank Number Tank Type Capacity (Gallons) 491 Ground 500, Ground 200, Elevated 500, Elevated 300, Ground 2,312, Ground 3,000, Ground/Bunkered 300, Elevated 100,000 METHODOLOGY Feasibility study methodology This feasibility study evaluated all aspects of the water system that could be associated with elevated TTHM concentrations including source, treatment, storage, distribution, operations and maintenance, and water main replacement projects. Discussions were held with SNWA to identify the factors contributing to elevated TTHM levels in purchased water and what measures were being taken to address this issue. Treatment of water by SNWA and supplemental booster chlorination of water at Nellis AFB were examined. The management of water storage at the base was evaluated in terms of residence time, water age, and turnover. Hydraulic modeling was conducted to determine water age throughout the distribution system. Historical water quality monitoring was evaluated and extensive supplemental TTHM monitoring was conducted. TTHM samples were speciated to characterize the distribution of individual trihalomethane (THM) components and to predict the potential removal efficiency of the various components using aeration. Seasonal changes in TTHM concentrations were evaluated by conducting sampling at approximately 25 locations within the distribution system during October, March, and August. Operation and maintenance practices were evaluated including such things as blending of purchased water and well water, cycling of water storage tanks, unidirectional flushing, and booster chlorination dosage rates. Pilot test methodology A pilot test was conducted of a TTHM removal product developed by Medora Corporation that was comprised of a floating pump / mixer / spray nozzle system. The system was installed in one of the installation s 300,000 gallon ground-level water storage tanks located in an area of historically high TTHM concentrations. Tank was selected for the pilot test because it was relatively small, easily accessible, and had a long water residence time of approximately 10 days. The goal of the pilot test was to evaluate the effectiveness of aeration and mixing at reducing TTHM concentrations in the storage tank. The equipment used included one SN10 10-HP floating pump / mixer / spray nozzle TTHM removal system, one 2-HP blower ventilation system, and one GS-70 submersible mixer. The equipment was installed and operated for approximately two weeks prior to conducting sampling to measure the effectiveness of TTHM removal. Effectiveness testing consisted of the collection of multiple samples upstream, within, and downstream of the tank. The downstream samples were located in two different branches of the distribution system approximately one mile downstream of the tank. Samples were analyzed for TTHM and speciated to determine the concentration of each TTHM component compound.

4 RESULTS AND DISCUSSION Prediction of potential Stage 2 compliance challenges Table 2 presents Nellis AFB Stage 1 Disinfectants and Disinfection Byproducts Rule (Stage 1) compliance data from February 2007 through March Stage 1 compliance monitoring included quarterly TTHM sampling and analysis at three locations. Compliance with the Stage 1 TTHM Maximum Contaminant Level (MCL) requires that the Running Annual Average (RAA) of all TTHM monitoring locations not exceed 80 µg/l. Analysis of the data in Table 2 reveals the following: There is an increasing trend in the RAA leading up to an MCL exceedance in September 2012 There were several high TTHM concentrations at Building 1619 and Building In general, the relatively low TTHM concentrations at Building 601 helped keep the RAA below the MCL Stage 2 monitoring includes quarterly sampling at two locations: Building 1619 and Building 10206, which is located in close proximity to the Stage 1 monitoring location at Building and has similar water quality issues. Compliance with the Stage 2 TTHM MCL requires that the Locational Running Annual Average (LRAA) at each individual monitoring location not exceed 80 µg/l. Given the historical TTHM concentrations at Building 1619 and Building 10220, it was relatively easy to predict that the base may have difficulty achieving Stage 2 compliance without implementing mitigation measures. This is true of many water systems. It is not uncommon for water systems that have successfully achieved compliance under Stage 1 with RAA to potentially have difficulty maintaining compliance under Stage 2 with LRAA. Table 2. Nellis AFB Stage 1 Sampling Results for TTHM Sample Date Total Trihalomethanes (µg/l) Building 601 Building 1619 Building RAA 1 2/27/ /31/ /29/ /7/ /7/ /28/ /27/ /5/ /25/ /19/ /16/ /15/ /4/ /3/ /1/ /2/ /2/ /8/ /20/ /21/ /20/ Note: 1 Results listed in bold and shaded indicate an MCL violation.

5 Impacts on TTHM formation potential caused by changes in source water quality One root cause of high TTHM levels at Nellis AFB is the relatively high TTHM concentration in water purchased from SNWA. According to SNWA, this is because of declining raw water quality from Lake Mead. Based on sampling events conducted in 2011 and 2012, the concentration of TTHM in purchased water has ranged from 51 µg/l to 56 µg/l. Water levels in Lake Mead are at record lows following a 13-year drought. At the time of this study, the water levels in Lake Mead were over 100 feet below normal. SNWA currently has two raw water intakes in Lake Mead but these intakes were not designed to efficiently draw water from the lake at such low levels. Generally, it is optimum to withdraw raw water from a point midway through the water column, between the surface and the bottom of the lake. Water near the surface can be of poor quality because of algae and floating contaminants, while water near the lake bottom can be stagnant and negatively impacted by anaerobic sediments. Because of the low water levels, the existing SNWA intakes cannot withdraw high quality raw water from preferred depths. As a consequence, raw water quality has been declining with the lake levels. TTHM precursors such as natural organic matter (NOM) react with chlorine as illustrated by the following generalized equation to form disinfection byproducts (DBPs): Chlorine + NOM DBPs Reducing the amount of precursors before adding a disinfectant can decrease the formation of DBPs. Another factor that negatively impacts raw water from Lake Mead is stormwater runoff and sewage treatment plant effluent that flows into the lake via the Las Vegas Wash. The current SNWA raw water intakes are downstream of the Las Vegas Wash. SNWA is currently using tunneling technology to construct a new raw water intake upstream of the Las Vegas Wash. This new intake, which is expected to be completed by 2014, will have sufficient adjustability to withdraw water from optimum depths. It is anticipated that this new intake will greatly improve raw water quality and have a positive effect on reducing TTHM precursors in raw water and TTHM concentrations in finished water. In advising the base regarding recommended TTHM mitigation measures, it was important to consider that the need to address current acute TTHM issues may be temporary and that improvements in the SNWA raw water intakes may greatly reduce finished water TTHM concentrations by For this reason, it was important to strike a balance between permanent, high capital cost mitigation measures, versus lower cost, temporary operational changes. Impacts of water age on TTHM formation As previously mentioned, Nellis AFB has approximately 7.2 MG of potable water storage, which results in approximately 7.2 days of storage. This excessive amount of storage results in high water age and leads to increased formation of TTHM. Recent privatization of the Military Family Housing (MFH) areas at Nellis AFB has exacerbated this problem. Until recently, the Nellis AFB water system served approximately 12,000 people, as well as the numerous industrial activities at the base. In 2006, the average daily water demand at the base was 3.2 MGD. Now the MFH areas having been privatized and are no longer served by the Nellis AFB water system. This coupled with water conservation measures has resulted in a dramatic reduction in water demand to approximately 1.0 MGD. Hydraulic modeling of the Nellis AFB water system revealed that many parts of the distribution system exhibit water ages between five (5) and 10 days. Monitoring results from 25 locations within the base distribution system showed a direct correlation between water age and TTHM concentration. Generally, areas with water ages greater than five (5) days exhibited elevated TTHM concentrations. One of the recommendations of this study was to take two ground-level tanks out of service to reduce storage water volume and water age. Doing this would reduce the volume of stored potable water by approximately 5.3 MG. Modeling confirmed that making this change would not have a negative impact on firefighting capacity as long as appropriate minor piping modifications were made to address this change.

6 Impact of tuberculated cast iron pipe and booster chlorination on TTHM formation Approximately 25% of the distribution system at Nellis AFB is tuberculated cast iron pipe that is more than 50 years old. This tuberculated pipe exerts a large chlorine demand and requires that the base provide booster chlorination at multiple locations within the distribution system in order to maintain appropriate chlorine residuals. One reason that tuberculated pipe exerts a large chlorine demand is that corroded pipe walls and tubercles provide an ideal environment for the growth of biofilm and chlorine can react with this biofilm causing a chlorine demand. The multiple booster chlorination stations are necessary, in part, because of this interaction between chlorine and biofilm within the tuberculated cast iron pipes throughout the system. The equipment used for booster chlorination was Accu-Tab PowerPro calcium hypochlorite tablet chlorinators. During this study, it was observed that in some cases there may have been insufficient mixing of injected chlorine prior to the chlorine monitoring points. This sometimes resulted in dosing more chlorine than necessary to achieve the desired residuals. The higher the chlorine residual, the higher the driving force for formation of TTHM. Therefore, it is advisable to control booster chlorination dosing carefully in order to minimize the formation of TTHM. Recommendations from this study included relocation of several booster chlorination points and improved chlorine dosing controls, as well as replacement of tuberculated cast iron pipe that was contributing to excessive chlorine demand and resulting in the need to perform booster chlorination. Pilot test results The pilot test data presented in Table 3 indicate that the aeration and mixing system achieved 28% removal of TTHM within the storage tank. However, samples collected one mile downstream of the tank show that TTHM concentrations had rebounded to within 7% 9 % of pre-aeration levels. Several sitespecific circumstances contributed to this rebound in TTHM concentrations. The pilot test location was near a dead end point in the distribution system. The water age at this location was over 10 days. Also the distribution system material type at this location is tuberculated cast iron pipe, which has a high chlorine demand. Consequently, there is a booster chlorination station near the pilot test location to help maintain chlorine residuals in the distribution system. All of these factors combine to promote the continued formation of TTHM. Sample Location Table 3. Pilot Test Results for Aeration / Mixing Equipment Trihalomethanes (µg/l) Bromodichloromethane Bromoform Chloroform Dibromochloromethane TTHM Upstream Location Within the Tank Downstream Location # Downstream Location # Notes: 1 An additional sample was taken at this location for quality assurance purposes. Table 4 provides a comparison of the Henry s Law Coefficients and the percent removal of the four THM species. As shown in the table, the percent removal was proportional to the Henry s Law Coefficients for these compounds. Chloroform is the most volatile TTHM component and the removal efficiency for

7 chloroform was 29.2%, whereas bromoform is the least volatile and the removal efficiency of bromoform was 22.0%. Table 4. Comparison of Henry s Law Constant and Percent Removal of Species following Aeration, Nellis AFB TTHM Species Henry s Law Constant (m 3 -atm/mole, 20 o C) Chloroform 3.0 x 10 Bromodichloromethane x 10-4 Chlorodibromomethane 8.7 x 10-4 Bromoform 4.3 x 10-3 % Removal of Species 29.2% 28.6% 27.5% 22.0% The fact that chloroform was removed to a higher degree than the other TTHM species could be predicted using Henry s Law: Where:!! Partial pressure of solute A, atm!!! Henry s law constant, m 3 -atm/mole!! =!!! [!] [!] aqueous-phase concentration of solute A, mole/m 3 Henry s Law essentially states that the vapor-phase partial pressure of a volatile compound is proportional to the aqueous-phase concentration of that compound and the Henry s Law constant for that compound. The higher the Henry s Law constant, the greater the tendency for the dissolved compound to volatilize into the vapor phase and be susceptible to removal via aeration. The results in Table 4 are consistent with what would be predicted using Henry s Law. The re-formation of TTHM following aeration is consistent with data collected by the Las Vegas Valley Water District (LVVWD), a water utility who also purchases treated water from SNWA, during monitoring of one of their storage tank aeration systems. Figure 1 illustrates that the rate of TTHM formation following aeration is similar to the rate of TTHM formation prior to aeration.

8 Source: LVVWD Current Stage 2 monitoring results Figure 1. TTHM Growth Before and After Aeration Table 5 presents all the Nellis AFB Stage 2 monitoring results to date. Currently, the LRAAs for TTHM at the two compliance points are significantly less than the 80 µg/l MCL. This is being accomplished primarily by implementing two operational changes. First, the base has changed the ratio of blending purchased water and groundwater. They are currently using less than 50% SNWA purchased water and greater than 50% groundwater. The groundwater has a much lower TTHM formation potential and has the effect of diluting the higher incoming TTHM levels from SNWA. Secondly, the base has increased the amount of distribution system flushing that is occurring in areas of high water age and dead end lines. Sampling Location Building 1619 Building Table 5. Nellis AFB Stage 2 Sampling Results for TTHM TTHM Species Trihalomethanes (µg/l) 6/12/2012 9/11/ /11/2012 3/12/2013 6/11/2013 Chloroform Bromoform Bromodichloromethane Dibromochloromethane TTHM LRAA Chloroform Bromoform Bromodichloromethane Dibromochloromethane TTHM LRAA Henderson, Harmon 8/29/13 10:56 AM Deleted: 4 These temporary operational changes are proving to be effective at maintaining compliance, but they are likely not sustainable for the long term, and they might not have to be. The water rights allocation for the Nellis AFB potable wells is only sufficient for about 75% of the water demand at the base on an annual basis, and extensive distribution system flushing exacerbates the water demand. Additionally, SNWA purchased water is believed to be less expensive than producing potable water from based-owned wells.

9 SNWA water costs $1.24/1,000 gallons, which is quite low relative to water rates from other similar wholesalers. In the long term, construction of the new SNWA raw water intake will likely improve the quality of raw water and result in lower TTHM concentrations in purchased water. The base is wise to take a wait-andsee approach to compliance by postponing high capital cost mitigation measures until the full impact of the new SNWA intake can be evaluated in CONCLUSIONS Conclusions reached as a result of this TTHM mitigation feasibility study and pilot test include: Water systems that have successfully achieved compliance under Stage 1 with RAA may have difficulty maintaining compliance under Stage 2 with LRAA. Source water quality can change over time because of influences such as drought and stormwater runoff, and these changes can increase TTHM formation potential. The pilot test achieved a 28% removal of TTHM. The efficiency of removal of TTHM components using aeration is a function of the Henry s Law constant for each component species. TTHM can reform after aeration if precursors and chlorine residual remain present. Downstream TTHM treatment is a viable TTHM mitigation alternative for storage tanks with high water age. In some situations, improved source water quality and treatment process changes can eliminate the need for downstream TTHM treatment. The results of this TTHM mitigation feasibility study and pilot test have helped the base identify the root causes of high TTHM concentrations and a range of options for achieving compliance. It is anticipated that implementation of recommendations from this project will not only help achieve long-term Stage 2 compliance, but also help improve water quality and chlorine residual into the future. REFERENCES U.S. EPA (2006) National Primary Drinking Water Regulations: Stage 2 Disinfectants and Disinfection Byproducts Rule; Washington, D.C. U.S. EPA (2010) Stage 2 Disinfectants and Disinfection Byproducts Rule, Consecutive Systems Guidance Manual; EPA 815-R ; Washington, D.C. Jacobsen, Laura; Fang, Mao; Machado, Daniela (2011) Localized Aeration System to Reduce Trihalomethanes. California Nevada American Water Works Association 2011 Spring Conference; Long Beach, CA.