Los Altos Nitrification Action Plan

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California Water ServiceOctober 24, 2018

Los Altos Nitrification Action PlanGina Cyprych, Water Quality Program Manager

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Presentation Outline

• Project overview• Data analysis

• Observed trends in storage tanks:– Regional trends– Total chlorine, total ammonia, and nitrite– Temperature

• Observed trends in distribution system:– Total chlorine residual

• Nitrification action plan • Monitoring procedures• Standard operating procedures• Capital investments and infrastructure changes


Cal Water Los Altos District

• Formed in 1931; serves Los Altos and parts of Los Altos Hills, Cupertino, Mountain View, and Sunnyvale

• Uses combination of local groundwater and purchased water; our purchased water, which is treated surface water from the Santa Clara Valley Water District (SCVWD), comes from SCVWD reservoirs and San Joaquin-Sacramento River Delta

• Includes 297 miles of pipeline, 65 booster pumps, and 46 storage tanks, which serves 70,000+ residents


DATA COLLECTION, PROCESSING, AND

ANALYSIS



Data Processing


Anomalous Data Identified

• Data points greater than 0.5 mg/L NO2-N:• Data excluded from

current data analysis• Not included for

following reasons:– Lack of corrective

action on manual recording worksheet

– Significant drop in concentration at next sample collection date

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Flow of Storage Tanks Evaluated

8

SCVWD Water

Covington

Low Zone

Cupertino GrangerFa

rndo

n

STA 7

STA8

STA10

STA28

STA 41

18” main

24” main

STA 9

STA 33

STA 42 STA 114

STA 113

STA 14

STA 19

Tantau-VallcoSTA 35

STA 23

Northwest

South

West

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Regional Trends in Storage Tanks

9

West

• STA 28

• STA 41

• STA 10

Northwest• STA 113• STA 114

South• STA 42• STA 9

All regions exhibit seasonal increases in nitrite concentration, but some problematic tanks experience increases outside of the seasonal high periods.

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Example: Interrelated trends for total chlorine, ammonia, and nitrite in storage tanks

• STA 28 (T2) in the West area

• Observation: Low total chlorine residuals consistent with spikes in nitrite

Low chlorineLow ammoniaHigh nitrite

Higher chlorineHigher ammoniaLow nitrite


Example: Relationship of elevated temperature and nitrification in storage tanks

• STA 33 (T2) in the South area

• Trend: Higher temperatures in summer and fall months exacerbate AOB growth and result in higher nitrite


• STA 7 (T1) in West area

• Trend: Nitrite present in source water coincides with (but is not required for) occurrence of nitrite in downstream tanks

Example:Nitrite in source water entering storage tanks


Average Cl2:NH3-N ratios in storage tanks

• Ideal Cl2:NH3-N ratio = 5:1 (no free ammonia present)

• Trend: Most tanks operated at around a Cl2:NH3-N ratio = 4.5:1; large error bars suggest that total chlorine residual concentration was not stable


Distribution System Analysis

• Trends: Total chlorine residual concentration varied from 0.01 to 2.31 mg/L as Cl2, and averaged approximately 1.0 mg/L as Cl2.

Total Chlorine Residual at Selected TCR Sampling Sites


Distribution system TCR sampling site summary

Trends: Nitrification may be a cause for low residual near problematic tanksOther factors such as blending of supply sources may also have an impact; not all wells are chloraminated, which may trigger nitrification depending on water quality

Highest likelihood of nitrification

Site(D) Region

Nearby Tanks(STA)

Average Total Cl2 Residual (mg/L as Cl2)

% of Samples with Total Cl2< 1.0 mg/L as Cl2

% of Samples with Total Cl2> 1.0 mg/L as Cl2

001 West - 1.5 12% 88%

011 West 10*, 41* 1.5 17% 83%

019 West 41* 1.3 27% 73%

023 North - 1.2 32% 68%

007 Northwest 114 1.2 38% 62%

015 Low Zone - 1.1 41% 59%

013 South 23, 42* 1.1 45% 55%

002 Low Zone - 0.9 48% 52%

029 Cupertino - 0.9 56% 44%

005 South 19, 33* 0.9 64% 36%

026 Northwest 113 0.7 74% 26%

003 Low Zone - 0.6 78% 22%

008 West 28* 0.5 84% 16%

024 South 9*, 33* 0.6 88% 12%


Summary of Trends

Storage tanks• Nitrification in Los Altos District consistent with:

• Seasonally higher temperatures• Low total chlorine residuals

• Significant nitrification occurred at:• STA 28, 10, 41, 9, 42, 33

Distribution system / TCR sites• Average total chlorine residual concentration was 1.0 mg/L

as Cl2• Highest likelihood of nitrification at:

• D-005, D-008, D-024• Differences in blended source waters and disinfection may

contribute to low residual


NITRIFICATION ACTION PLAN DEVELOPMENT AND

OVERVIEW


Occurrence of Nitrification Likely to be Reduced by…

• Mixing to promote minimal stratification

• Higher chlorine dosing (total chlorine residual at 2.5 mg/L) and optimization of Cl2:NH3-N ratio at 5:1

• Adding chloramination capability at every well• Increasing monitoring to respond more quickly and avoid

sharp spikes in nitrification


Overview of Nitrification Action Plan

Three primary recommendations :

1. Establishment of nitrification triggers and corrective actions

2. Standard operating procedures for monitoring and maintenance

3. Potential capital investment options for long term control


Recommended Changes to Monitoring Procedures1. Weekly monitoring of all elevated storage tanks with

additional twice weekly monitoring of six high frequency sites: STA 28, 10, 41, 9, 42, and 33

2. Implementation of formalized goals and triggers when responding to nitrification occurrences

3. Electronic storage and trending of monitoring data in an Excel spreadsheet to enable rapid response to trends

4. Use of trend analysis to adjust nitrification triggers and response actions for high frequency sites


Data Trending Dashboard

Dashboard allows for: • Direct data upload from SL1000• Comparison of nitrite with different parameters


Nitrification Triggers and Corrective Actions

• Baseline/goals• Average concentrations when nitrification is not

occurring

• Yellow triggers• Higher than baseline concentrations; nitrification is

about to occur

• Red triggers• Concentrations representative of residual degradation

and nitrification occurrence


Selection of Trigger Values

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

Tota

l Chl

orin

e (m

g/L

as C

l 2)

Nitr

ite (m

g/L

NO

2-N)

NitriteChlorine

Total Cl2 ≈ 1.5 mg/L

Total Cl2 ≈ 1.0 mg/L

NO2 ≈ 0.010 mg/LNO2 ≈ 0.100 mg/L


Nitrification Action Table

Site Parameter(units in mg/L) Goal

Triggers

Yellow Flag Red Flag

Storage TanksTotal Chlorine 2.5 1.5 1.0

Nitrite - N 0 – 0.010 0.010-0.030 > 0.030

* Background level of nitrite is 0.005 mg/L as N


Decision Tree for Operational Response Actions


Benefits of a 0.010 mg/L NO2-N Yellow Flag Trigger

STA Less than 0.005 0.005-0.010 0.010-0.050 0.050-0.100 >0.10010 T2 2 4 12 3 10

41 T1 9 6 20 10 8

28 T2 4 4 7 14 24

42 T2 18 1 7 3 18

9 T1 19 4 11 8 8

33 T2 21 2 5 8 7

183 occurrences*94 occurrences*

* Based upon data from January 2016 to September 2017


Options for Capital Investment

Objective: Achieve adequate mixing to avoid thermal stratification and excess free ammonia and to achieve a decreased overall water age

1. Mechanical mixer at tanks with recurring nitrification; if PAX mixer at STA 42 is successful, consider also implementing at:

• STA 28 • STA 10• STA 41• STA 9• STA 33


2. Booster chlorination for trimming free ammonia

Granger

Farndon

STA 7

STA8

STA10

STA28

STA 41

18” main

24” main

STA 9

STA 33

STA 42

STA 114

STA 113

STA 14

STA 19

STA 35

STA 23

Identified Problematic Tanks

Potential Booster Chlorination Locations


3. Pilot project: use of ultraviolet lights in storage tanks

29

• LADWP study found that low-intensity UVA radiation was shown to inhibit the growth of nitrifying bacteria

Source: White, Brian; Adams, Martin. Battling Nitrification with Blacklights, Opflow. February 2010.

Mount Washington tank – capacity of 542,000 gallons


4. Uniform chloramination of wells

Well Disinfection TypeGranger ChloramineFarndon Chloramine

Tantau-Vallco ChloramineCovington Chloramine

017-01 Chloramine006-01 Chloramine021-01 Chloramine018-01 Chloramine027-01 Chloramine034-01 Chloramine119-01 Chloramine119-02 Chloramine030-01 Chloramine (in process)031-01 Chloramine (in process)001-02 None015-01 None025-01 None032-01 None039-01 None104-02 None115-01 None116-01 None121-02 None123-01 None

Data showed relatively low total chlorine residual in distribution system

• Potential for nitrification is influenced by changes in water chemistry and microbiology

• Elimination of blending of monochloraminatedand undisinfected waters is likely to improve degradation of total chlorine residual in distribution system

Recommendation: Apply chloramine disinfection at all wells to avoid any detrimental impacts of blending on disinfectant residual and nitrification

Disinfection at Wells in Los Altos District


Next Steps

Cal Water• Implementation of nitrification monitoring triggers,

modified monitoring / operational procedures• Review of short- and long-term options for capital

investment• Quarterly review meetings

• District training on action levels and chloramination

Hazen• Modification of Excel dashboard for streamlined use with

Hach SL-1000• Workshop for operators on use of Hach SL-1000 and

electronic data upload


Acknowledgements

• LAS District staff

• Hazen and Sawyer• Nicole Blute and Luke Wang

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Questions?Thank you for your attention.

Documents

Los Altos Nitrification Action Plan