Impact of local climate change on drinking water quality in a distribution system

In this study, air temperatures were collected between 1985 and 2016 and compared with water temperatures in four locations in the distribution system of Pasadena Water and Power (PWP), which received surface water imported into Pasadena between 2001 and 2016 from the Metropolitan Water District. The concentrations of chloramine residual and nitrite concentrations were collected between 2001 and 2016 from these five locations. The results indicate that the median nighttime temperature of the period 2009–2016 was 1.6 C warmer than the period 1985–2000 and 0.5 C warmer than the period 2001–2008. The median water temperature in the four distribution system samples increased by 0.8–1.4 C depending on the location over the study period (p< 0.001). The median chloramine concentration fell significantly (p< 0.001) at three distribution system locations, and the nitrite concentrations increased significantly at all four distribution system locations (p< 0.001). As air temperature in the study area increased, water temperatures also increased resulting in the loss of disinfectant residual and the increase in the activity of ammonia-oxidizing bacteria. As this represented an increased risk to public health, PWP took additional steps to increase disinfectant residuals by adding chlorine and flushing stale water. In localities where climate change is most measurable, local water purveyors must adapt to warmer water to ensure stable concentrations of

At higher water temperatures, disinfectant residuals decay more rapidly and bacterial growth is enhanced (Ndiongue et al. ; Michalak ). The purpose of this study is to determine if the increases in atmospheric temperatures are in fact affecting water temperatures and microbiological stability in the distribution system of Pasadena's Water and Power (PWP) Department.

PASADENA WATER AND POWER
The City of Pasadena, incorporated in 1886, has owned and operated a public water system (PWS) since 1914 after purchasing a number of privately held water companies. PWP operates a number of wells and has not used local surface water directly for the last 30 years, although it does divert local stream flow into percolation basins for groundwater recharge (Kimbrough ). PWP also receives imported surface water from both the Colorado River Aqueduct (CRA) and the California State Water Project (SWP) after the water is treated by the Metropolitan Water District of Southern California (MWDSC). The SWP is a system of dams, conveyances, and pumping stations spanning 1,000 km (600 miles) stretching almost the entire length of California from Lake Shasta in the north to Lake Silverwood in the south. The CRA takes water from Lake Havasu and moves it 389 km (242 miles) to Lake Matthews and then an additional 44 km (30 miles) to the F. E.
Weymouth Treatment Plant (WTP). There the plant, operated by MWDSC, may blend the CRA and SWP water or treat 100% of either and then deliver the effluent to PWP and other agencies. Imported surface water purchased from WTP must first enter the PWP system through one of the three reservoirs, Sunset, Jones, and Eagle Rock. The Sunset Reservoir has a capacity of 57 million liters (ML -15 million gallons (MG)). The Sunset Reservoir can either blend WTP water with local well water or provide 100% WTP water. The maximum blending rate is 20% well water and 80% WTP water, but 90-100% WTP water is more typical, especially in the non-summer months. The local wells did not have any chlorine or monochloramines added, so the concentration of monochloramine fluctuated depending on the amount of well water blending.
The Jones Reservoir has a capacity of 189 ML (50 MG) and only held WTP water until late 2015 when some local well water was introduced and blended. Eagle Rock is considerably smaller with a volume of 3.6 ML (0.95 MG) and only uses WTP water. The WTP is 40 km (25 miles

HYPOTHESIS
The hypothesis of this study was that the temperature of the water in PWP's distribution system has been increasing due to increasing atmospheric temperatures during the study period. This has resulted in the gradual decrease of monochloramine residual and an increase in bacterial nitrification where residence times are the longest. Such a relationship should not be unexpected, it has been reported that chloramine decay mechanisms and kinetics are temperature-dependent (Vikesland et al. ). The growth and activity of ammonia-oxidizing bacteria (AOB), which can consume monochloramine and release nitrite, are known to be temperature-dependent (Pintar & Slawson ).

Proposed mechanism
The aforementioned three reservoirs, where WTP water enters PWP's distribution system, are made primarily of important barrier to the exposure of the public to waterborne pathogens and the loss of monochloramine can pose a significant threat to public health. It is very common for PWSs to flush water from their system when the residual is too low. The addition of chlorine to reservoirs where nitrification occurs is also widely practiced. Thus, water purveyors must work hard to prevent nitrification.

Expected results
If ACC is in fact warming both the local air temperature and the water temperature in the distribution system of PWP, two parallel trends should be observed: (1) As temperatures in the water distribution system increase over time, the concentration of monochloramine should decrease and nitrite concentrations should increase.
(2) The above pattern should be more visible in the parts of the distribution furthest from the entry points into the distribution and less visible in the nearer points.
There is an important caveat to this hypothesis and expected results. During the study period, PWP staff were actively and vigorously trying to keep monochloramine concentrations high and nitrite concentrations low. According to the NMAP, PWP must flush water from locations when nitrite concentrations exceed 25 μg/L and/or add chlorine. Additionally, for compliance with the Total Coliform Rule and Surface Water Treatment Rule, a positive chloramine residual is required. As a result, many parts of the distribution system may be flushed when chloramine residuals are low and/or chlorine is added. These operational requirements and regulatory mandates influence the nature of the results seen in this study.

STUDY LOCATIONS
To test the above hypothesis, five sample locations were selected: four sample locations in PWP's distribution system and one from MWDSC's transmission system. All four of PWP's locations were routinely tested for water temperature and were fed from one of the three reservoirs mentioned above during the study period. Two of the locations are close to the reservoir influent and will be referred to as the proximal locations, and two locations were further away from the reservoir influents. These will be referred to as the distal locations. The sample locations are described as follows: (1) Arroyo Terrace (272 m (897 ft) above mean sea level (AMSL)), which is fed from the Sunset Reservoir  In summary, there are two pairs of sample locations, one pair that received 100% WTP water and one pair that received water from the Sunset Reservoir, which ranged from 100% WTP to an 80% blend of WTP and local groundwater. Each pair has one proximal sample location and one distal sample location.

ANALYTICAL METHODS FOR WATER
(1) Water temperature -The water temperature was measured using an electronic thermometer using Standard Methods 2550 B (APHA ).
(3) Nitrite (NO 2 ) -The concentration of nitrite was determined by using a Hach field colorimeter using Standard Method 4500-NO 2 B Diazotization Method Colorimetric Method (APHA ). This test was not performed in the field but in PWP's laboratory. A Hach 850 was used in the beginning of the study and a Hach 890 was used in the latter part.
(4) Water pH -The pH of the WTP water was determined using Standard Methods 4500-H þ (APHA ).

AIR TEMPERATURES
Air temperatures for the 1985-2016 study period were obtained from the National Oceanographic and Atmospheric Administration's National Climatic Data Center (NCDC). A database of the daily maximum air temperatures (all maximum temperatures occurred during the daylight hours temperature are referred to as 'daytime temperatures' here, so as to avoid confusion) and minimum air temperatures (referred to as 'nighttime temperature') were created and checked for accuracy against written records. For this study, only the nighttime air temperatures were used. Nighttime air temperatures were used because they are a more sensitive measure of climatic change than daytime temperatures. The air temperature was collected at Pasadena's City Hall located at the longitude and latitude þ34.15, À118.14.

STATISTICAL PROCEDURES
(1) The distribution of each data set was assessed using the Shapiro-Wilk Test, and skewness and kurtosis were assessed. Data were considered non-normally distributed if the probability was less than 5% (p 0.05).
All data in this study were non-normally distributed (De Muth ) for either skewness of kurtosis.
(2) There were 16 data sets, nighttime air temperature, the water temperature, total chlorine concentration, and (3) The three air temperature populations were also compared with each other using the Kruskal-Wallis (KW) one-way analysis of variance on ranks. The KW test produces the Kruskal-Wallis Statistic (H ). The threshold for significance was 5% (α ¼ 0.05) (de Muth ).
(4) When different data sets collected over time were compared to determine whether they tended to follow correlated patterns, the Spearman rank-order correlation (SROC) test was used, which is the non-parametric equivalent of the Pearson Product-Moment Correlation.
For the water data, the temperature, chloramine residual, and nitrite concentrations were compared (de Muth ).
(5) Nitrite results were not censored for this study but used as generated by the instrument. When the instrument generated a value of zero, a value of zero was used for statistical analysis.

Distribution of data
The distribution of all 16 data sets was tested for normality using the Shapiro-Wilk Test and all had a non-normal distribution (p < 0.001).

Air temperatures
The mean, standard deviation, 25th, 50th, and 75th percentile results for the entire study population  and each of the three sub-populations are shown in Table 1.
The data on a yearly mean basis including the 99% confidence intervals are shown in Figure 2. The median air temperatures increased through the study period, both between the three sub-groups as seen in Table 1

Water temperatures
The mean, standard deviation, 25th, 50th, and 75th percen-    nighttime air temperature, which was 0.5 C. To better assess the relationships between air and water temperature, the monthly median water temperatures of each of the five locations were plotted on a monthly basis, which is summarized in Figure 3.

Chloramine residual
The chloramine residual is shown in Table 3   slight increase in residual concentration of 0.07 mg/L; however, this was not statistically significant.

DISCUSSION
The air in Pasadena has been warming significantly since 1985 as seen in Figure 2 and Table 1 comparing the two periods, the median water temperature at the WTP changed by À1.1 C, although this was not statistically significant. This is also a bit misleading as the 75th percentile of the water temperature was actually higher in the second period than that in the first period by 0.6 C and the 25th percentile only decreased by 0.1 C while the mean is 0.5 C lower. Obviously, the water temperatures are distributed in a complex fashion that is not easily captured in a single measure of the central tendency. Suffice it to say, there is no evidence that the water temperate of the effluent of the WTP has increased between the two study periods.
In contrast, the median water temperature at Arroyo Terrace increased by 0.9 C, Avenue 64 by 1.0 C, Hill Avenue by 0.8 C, and at Tropical Avenue by 1.4 C. These were all statistically significant increases (p < 0.001). That the water temperature should increase more than the air temperature is not necessarily surprising, as the heat capacity of water is five times higher from that of air and can thus retain more heat much longer than air. It is also not a surprising fact that the water at Tropical Avenue showed a larger median increase in water temperature as compared to the other three sites. This is because the water first enters PWP' the atmosphere is small compared with the volume of water. In PWP's distribution system, the surface area to volume ratio is far more favorable for heat exchange, as are the above grade reservoirs. Moreover, what is clear is that as the water moves further from the reservoirs where the water is taken from WTP, the water temperature changes. In winter, the WTP water that comes is cold and is warmed as it passes through the distribution system. In summer, the exact opposite is observed at most locations; the WTP enters the system and is slightly cooled, except for Tropical Avenue where it warms very slightly. The two distal locations showed this pattern more than the two proximal locations as can be seen in Figure 3.
In examining the monthly data a pattern emerges. The The absolute difference in the means and medians was generally 3-6 μg/L.
The hypothesis is that as water temperatures rise, the concentration of chlorine should fall and if this is the case, there ought to be a negative correlation between these two variables.
However, no such correlation is observed for four of the locations. At Hill Avenue there was a correlation, which while significant (p < 0.001) was not strong (R ¼ À0.22).
For WTP, this is not surprising since there has been no increase in water temperature or loss of chloramine residual.
Similarly, Tropical Avenue is fed by two reservoirs in tandem where chlorine is added so the lack of correlation is not surprising. Avenue 64 showed only a minor loss of chlorine like the WTP, and a lack of correlation might be expected.
Nonetheless, Arroyo Terrace showed considerable chlorine so a lack of correlations is unexpected.
On the other hand, Arroyo Terrace, Avenue 64, and Tropical Avenue all showed significant positive correlations between water temperature and nitrite concentration  and chlorination is to destroy any correlation between water temperature and monochloramine and nitrite concentrations. As noted above, chlorine addition was largely practiced in summer.
It is important to note that during part of the study period, California suffered a period of intense drought (Kimbrough , ). This resulted in unprecedented reductions in water demand and increases in water age in the distribution system. This may well have exaggerated the impact of increasing air temperatures on water temperatures.

SUMMARY AND CONCLUSIONS
Local climatic change has resulted in significant and measurable increases in the temperature of the nighttime air in Pasadena, which in turn has increased the water temperature in the distribution system of PWP. This has caused increased rates of chlorine decay and increased rates of nitrification. As noted above, such a finding is entirely consistent with previously published research (Vikesland et al. ; Pintar & Slawson ). As the temperature of the air in the study area increased, water temperatures increased as well resulting in the loss of disinfectant residual and the activity of AOB increased. As this represented an increased risk to public health, PWP took additional steps to increase disinfectant residuals by adding chlorine and flushing stale water. Additionally, PWP purchased a portable water treatment plant that allowed water to be pumped from the distribution system, filtered, chlorinated, and then returned to the distribution without loss of pressure or exposure to the atmosphere. In localities where climate change is most measurable, local water purveyors will need to adapt to warmer water to ensure stable concentrations of disinfectants. This might mean more labor dedicated to flushing low residual or nitrified water, more chlorination of the distribution system, and overall increased labor and chemical costs. Local climate change will challenge local water purveyors to maintain water quality.