Drinking Water Quality
Annual Report for Calendar Year 2023
Yokota Air Base & Tama Hills(Published: Jun 2024)
この年次報告書には横田基地における飲料水の水質について重要な情報が記載されいています。 この英語版が正式な原本として公示されますが、日本語での説明は医療部衛生環境課 内線 225-8040 までご連絡下さい。
なお、基地関係者以外の方からのご質問につきましては、横田基地代表番号 042-552-2511 におかけいただき、オペレーターを通して広報部へお問合せ下さい。
This annual report summarizes the quality of water delivered by Yokota Air Base, Japan. Under the "Consumer
Confidence Reporting Rule" of the federal Safe Drinking Water Act (SDWA), community water systems are required to report
this water quality information to the consuming public. Presented in this report is information on the source(s) of our water, itsconstituents, and the associated health risks. This report is designed to strengthen public understanding about the safety of their
public water systems; technical language included is required by the Environmental Protection Agency (EPA). The drinking
water systems at Yokota Air Base and Tama Hills met all Japan Environmental Governing Standards (JEGS) drinking
water quality standards in 2023.

1. Drinking Water Sources for Yokota Air Base and Tama Hills
Yokota: The Yokota Air Base water supply system is supplied from groundwater sources with 11 active wells on thebase. Water is pumped from wells to the on-base treatment plants for chlorination and fluoridation then pumped to elevatedstorage tanks prior to entering the distribution system. The Yokota AB water system serves approximately 11,500 people
and the water consumption average is 2.1 million gallons per day.
Yokota AB also maintains local city water connections to Musashi-Murayama and Fussa cities and only used during
emergency situations treated at Ozaku and Fussa-Musashinodai treatment plants (city water quality is monitored by the Tokyo
Waterworks Bureau).
Tama Hills: The Tama Hills Recreational Annex is a Geographically Separated Unit (GSU) and water supply system is
supplied from groundwater sources with two active wells on the annex. Water is pumped from wells to the treatment plants
for chlorination then pumped to the distribution system. The Tama Hills water system serves approximately 200 transientpersonnel and the water consumption average during the highest usage season is 34,000 gallons per day.

2. Common Sources of Drinking Water Contamination
Common drinking water sources (for both tap and bottled water) include rivers, lakes, streams, ponds, reservoirs, springs,
and wells. As water travels over the surface of the land or through the ground, it dissolves naturally-occurring minerals andother substances from animal or human activity. Drinking water, including bottled water, may reasonably be expected tocontain at least small amounts of some contaminants. The presence of contaminants does not necessarily indicate that water
poses a health risk. More information about contaminants and potential health effects can be obtained by calling the EPA’s Safe
Drinking Water Hotline (1-800-426- 4791). Contaminants that may be present in source water include:• Microbial contaminants: Viruses and bacteria, which may come from sewage treatment plants, septic systems,
agricultural livestock operations, and wildlife.
• Inorganic contaminants: Salts and metals, which can be naturally-occurring or result from urban storm water runoff,
industrial or domestic wastewater discharges, oil and gas production, mining, or farming.
• Pesticides and herbicides: May come from agriculture, urban storm water runoff, and residential uses.
-1-• Organic chemical contaminants: Including synthetic and volatile organics, which are by-products of industrial processes
and petroleum production, and can come from gas stations, urban storm water runoff, and septic systems.
• Disinfectant Byproducts: By-product of drinking water disinfection, intended to kill or inactivate pathogenic
microorganisms in water.
• Radioactive Contaminants: Can be naturally occurring or the result of oil/gas production and mining activities.
In order to ensure that tap water is safe to drink, EPA prescribes regulations which limit the amount of certain contaminantsin water provided by public water systems. Food and Drug Administration regulations establish limits for contaminants inbottled water which must provide the same protection for public health.

3. Water Safety and Quality Assurance Responsibilities
The 374th Civil Engineering Squadron (CES) manages the maintenance and operations of the drinking water supply anddistribution system. CES Water & Fuel Systems Maintenance (WFSM) shop personnel operate 24 hours a day to maintainsufficient pressurization, disinfection, and fluoridation. At all water plants, the operator also monitors pH, chlorine residual andfluoride concentration.
The 374th Operational Medical Readiness Squadron (OMRS) Bioenvironmental Engineering (BE) Flight monitors thequality of drinking water provided to consumers and addresses any health-related concerns. Analysis is conducted by EPA
certified laboratories for contaminants. Additionally, microbial contaminants analysis is conducted in the BE Laboratory (Bldg.
1585, Rm LB02) on a weekly basis.

4. Drinking Water Treatment Information
Water is treated at the plant before it is sent to the distribution system. The treatment method is chlorination orelectrochemical generation for disinfection. BE monitors the levels of chlorine, fluoride, and presence of bacteria at the
distribution sites weekly at Yokota AB and monthly at Tama Hills. BE contacts the WFM shop when adjustments are needed.
Also contact times (i.e., CT values) are monitored to ensure proper disinfection of the water in accordance with applicableregulations.

Yokota Water System (simplified diagram)
City water for
emergency

Wells

Wells

Underground
Storage
Tank

Pump

Elevated
Tank

Distribution loop
Water Plants
Disinfection&
Fluoridation

MixingTank-2-

Buildings & Houses5. Drinking Water Monitoring
Yokota BE routinely monitors for over 170 contaminants by using EPA certified laboratories and approved methods inaccordance with 2022 JEGS and EPA regulations.
• Microbial contaminants: Sampling is conducted every week at distribution points (such as childcare facilities, elementary
schools, youth center, and the hospital), the analysis includes chlorine and pH levels and coliform testing. Coliforms arenaturally present in the environment and are used as an indicator that other potentially harmful bacteria may be present.
Both total and fecal coliforms have been undetectable in tests of Yokota AB's water throughout the year.
• Other contaminants (inorganic, pesticides & herbicides, organic, disinfectant byproducts and radioactive): Monitored
on a different frequency respectively as shown below Table 1.

Table 1. Contaminant Groups and Monitoring Frequencies <as of 2023>
Contaminant Group
Microbial

Inorganic

Synthetic Organic
Chemicals

Monitoring
Frequency

Chemical Name
Total coliform, Fecal Coliform,
pH, Free Available Chlorine

Weekly/Monthly/
Quarterly

Metals, (e.g. arsenic, selenium,
mercury, nickel, sodium, etc.)
Once every 3 years
Note 1 (13 Total)
Nitrate, Nitrite,
Annually
Total Nitrate/Nitrite
Asbestos
Once every 9 years
Corrosivity
Once<Volatile Organic Chemicals>Benzene, Trichloroethylene, Carbon
Quarterly
Tetrachloride, etc.
Note 2 (21 Total)<Pesticides/PCBs>
2 consecutive
Herbicides, Dioxin, etc.
quarters
every 3 years
Note 3 (30 Total)
Yokota: Annually
Tama: Once every 3
years

Note 4

Disinfectant ByProducts

Total Trihalomethanes (TTHM)
Total Haloacetic Acids (HAA5)

Lead & Copperfrom plumbing materials

Lead, Copper

Once every 3 years

Radionuclide
Compounds

Gross Alpha and Beta,
Radium226/228,Uranium(Radionuclide types)
Alpha - every 4 years
Beta - every 9 years

Sampling Location
Schools, FSS child occupied
facilities, Aircraft watering
point, GSU locations
Yokota AB: 5 water plants
Tama Hills: 2 water plants
Wells
Yokota AB: 5 water plants
Tama Hills: 2 water plants
Yokota AB: 5 water plants
Tama Hills: 2 water plants
Yokota AB: 8 distribution
sites
Tama Hills: 4 distribution
sites
Yokota AB: 30 homes
Tama Hills: 5 facilities
Yokota AB: 5 water plants
Tama Hills: 2 water plants

Per- and
Perfluorooctanoic acid (PFOA),
Yokota AB: 5 water plants
Note 5 Every 2 years
polyfluoroalkyl
Perfluorooctanesulfonic acidand 2 city water connections
substances (PFAS)(PFOS), (29 Total)
Tama Hills: 2 water plants
Note 1 Inorganic compound list can be found in JEGS Chapter 8, Table 8.2
Note 2 Volatile organic compound list can be found in JEGS Chapter 8, Table 8.5
Note 3 Synthetic volatile organic compounds list can be found in JEGS Chapter 8, Table 8.5
Note 4 Reduced monitoring frequency based on JEGS in Chapter 8, Paragraph 8.9Note 5 Monitoring frequency was changed to semi-annual IAW DoD memo Memorandum for Sampling of Per- andpolyfluoroalkyl substances in DoD-Owned Drinking Water System, 11 Jul 23-3-

6. Special Precautions
Some people may be more vulnerable to contaminants in drinking water than the general population. Immuno-compromised
persons such as persons with cancer undergoing chemotherapy, persons who have undergone organ transplants, people with
HIV/AIDS or other immune system disorders, some elderly, and infants can be particularly at risk from infections. These people
should seek advice about drinking water from their health care providers. EPA/CDC guidelines on appropriate means to lessen
the risk of infection by Cryptosporidium and other microbial contaminants are available from the Safe Drinking
Water Hotline (1-800-426-4791).
Lead: If present, elevated levels of lead can cause serious health problems, especially for pregnant women and young
children. Lead in drinking water is primarily from materials and components associated with service lines and home plumbing.
Yokota AB is responsible for providing high quality drinking water, but cannot control the variety of materials used inplumbing components. When your water has been sitting for several hours, you can minimize the potential for lead exposure byflushing your tap for 30 seconds to 2 minutes before using water for drinking or cooking. If you are concerned about lead inyour water, you may wish to have your water tested. Information on lead in drinking water, testing methods, and steps you cantake to minimize exposure is available from the Safe Drinking Water Hotline or at www.epa.gov/safewater/lead. The
measured concentrations at Yokota AB are all below the action level.
Copper: The primary sources of copper in drinking water are corrosion of household plumbing systems and erosion ofnatural deposits. Copper enters the water (leaches) through contact with the plumbing. Copper leaches into water throughcorrosion –the dissolving or wearing away of metal caused by a chemical reaction between water and plumbing. Copper canleach into water primarily from pipes, but fixtures, faucets (brass), and fittings can also be a source of copper contaminants.
The amount of copper in your water also depends on the types and amounts of minerals in the water, how long the water stays
in the pipes, the amount of wear in the pipes, the water’s acidity and its temperature. When water sits in copper pipes orplumbing containing copper for several hours or more, the copper may dissolve into the water. This means the first water
drawn from the tap for the day may contain elevated levels of copper. As a precaution, consumers are encouraged to flush
water from their faucets for 60 seconds before consumption after the faucet has remained unused for four or more hours. The
measured concentrations at Yokota AB are all below the action level.

7. Monitoring Results in Calendar Year 2023
Our drinking water meets all JEGS and EPA requirements. Monitoring results are summarized in Table 2 (Yokota AB
Water System), Table 3 (Tama Hills Water System), Table 4 (Yokota Per- and polyfluoroalkyl substances (PFAS)) and Table 5(Tama Hills Per- and polyfluoroalkyl substances (PFAS)).

Table 2. 2023 Yokota AB Water System Detected Contaminants<Detected Chemicals Only>
Inorganics Monitoring Frequency: Annually for Nitrate, every 3 years for other Inorganics
Total 21 chemicals are tested and only chemicals detected are listed below.

Substances

Violation?
Yes / No

Units

NitrateNo

Arsenic

BariumDetected Level

MCL

Last
SampledCommon Potential Sourcesin Drinking Water

10
(10)

Jan 23

Runoff from fertilizer use; Leachingfrom septic tanks, sewage; Erosion ofnatural deposits

0

10
(10)

Apr 21

Erosion of natural deposits; Runoff
from orchards; Runoff from glass andelectronics production wastes

2

2
(2)

Apr 21

Discharge of drilling wastes; Discharge
from metal refineries; Erosion ofnatural deposits

MCLG

HighestLowest

ppm

3.5

0.7

10

No

ppb

3.0

ND

No

ppm

0.003

ND

-4-

EPA
(JEGS)

Fluoride

No

ppm

1.0

0.6

4

4
(4)

Sodium

No

ppm

18

12

N/A

N/A
(N/A)

Substances

Apr 21

Erosion of natural deposits; Water
additive which promotes strong teeth;
Discharge from fertilizer and aluminum
factories

Apr 21

Erosion of natural deposits

Volatile Organic Compounds Monitoring Frequency: Quarterly
Total 21 chemicals are tested and only chemicals detected are listed below.
Detected Level
MCL
Violation?
Last
Units
MCLG
Typical Source
EPA
Yes / No
SampledHighestLowest(JEGS)

1,1Dichloroethylene

No

ppb

1.0

ND

7

7
(7)

Jan 23

Discharge from industrial chemicalfactories

cis-1,2Dichloroethylene

No

ppb

0.2

ND

70

70
(70)

Jan 23

Discharge from industrial chemicalfactories

Tetrachloroethylene

No

ppb

1.8

ND

0

Trichloroethylene

No

ppb

0.4

ND

0

5
(5)
5
(5)

Discharge from factories and dry
cleaners
Discharge from metal degreasing sites
and other factories

Jan 23
Jan 23Disinfectant By-Products Monitoring Frequency: Annual
Substances

Violation?
Yes / No

Unit

Your
Water

Range

MCLG

Total
Trihalomethanes(TTHM)

No

ppb

0.9

0.59
-1.2

N/A

MCL

EPA
(JEGS)

80
(80)

Last
SampledTypical Source

Aug 23

By-product of drinking water
disinfection

Radionuclides Compounds Monitoring Frequency: every 4 years
Substances
Combined Radium
226 and 228
Gross Beta

Violation?
Yes / No

Units

No
No

Detected Level

MCLG

HighestLowest

pCi/L

1.64

ND

0

pCi/L

6.03

0.07

0

MCL

EPA
(JEGS)

5
(5)
50

Last
SampledNov 20

Typical Source
Erosion of natural deposits

Mar 22

Table 3. 2022 Tama Hills Water System Detected Contaminants<Detected Chemicals Only>
Inorganics Monitoring Frequency: Annually for Nitrate, every 3 years for Other Inorganics
Only chemicals detected are listed below, 14 others were tested.

Substances

Violation?
Yes / No

Units

NitrateNo

SodiumNo

Detected Level

MCLG

HighestLowest

ppm

0.83

0.03

10

ppm

7.9

7.9

N/A

MCL

Last
SampledTypical Source

10
(10)

Jan 23

N/A(N/A)

Runoff from fertilizer use; Leaching fromseptic tanks, sewage; Erosion of naturaldeposits

Apr 21

Erosion of natural deposits

EPA(JEGS)

Disinfectant By-Products Monitoring Frequency: every 3 years
Substances
Total
Trihalomethanes(TTHM)

Violation?
Yes / No

Unit

No

ppb

Only chemicals detected are listed below
MCL
Your
Last
Range MCLG
EPA
Water
SampledTypical Source(JEGS)

5.3

0.69.9

N/A

80
(80)

Mar 22

By-product of drinking water disinfection

Radionuclides Compounds Monitoring Frequency: every 4 years
Substances

Violation?

Units

Detected Level

HighestLowest

MCLG

-5-

MCL
EPA

Last
SampledTypical Source

Combined Radium
226 and 228

Yes / No(JEGS)

No

pCi/L

1.19

1.08

0

Gross Alpha

No

pCi/L

0.3

0.3

0

Uranium
Gross Beta

No
No

pCi/L
pCi/L

0.08
4.82

ND
1.80

0
0

5
(5)
15
(15)
20
50

Nov 20
Nov 20

Erosion of natural deposits

Nov 20Mar 22

8. Per- and polyfluoroalkyl substances (PFAS)•

Per-and Polyfluoroalkyl Substances (PFAS): Perfluorooctanoic Acid (PFOA), Perfluorooctane Sulfonate (PFOS) andother substances. (EPA Method 537.1 and EPA Method 533 for PFAS analysis)

PFAS Frequently Asked Questions (FAQ)
What are per- and polyfluoroalkyl substances and where do they come from?
Per- and polyfluoroalkyl substances (PFAS) are a group of thousands of man-made chemicals. PFAS have been used in avariety of industries and consumer products around the globe, including in the U.S., since the 1940s. PFAS have been used tomake coatings and products that are used as oil and water repellents for carpets, clothing, paper packaging for food, andcookware. They are also contained in some foams such as aqueous film-forming foam, or AFFF, used for fighting petroleum
fires at airfields and in industrial fire suppression processes. PFAS compounds are persistent in the environment and some are
persistent in the human body – meaning they do not break down and they can accumulate over time.
•Is there a regulation for PFAS in drinking water?
In May 2016, the Environmental Protection Agency (EPA) established a lifetime health advisory (LHA) level at 70 parts
per trillion (ppt) for individual or combined concentrations of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid
(PFOS). Both compounds are types of PFAS. On 10 April 2024, the EPA published new drinking water standards for certain
PFAS under the Safe Drinking Water Act (SDWA). AF is reviewing the EPA’s new rule now, and will incorporate thesestandards into future sampling and analysis efforts.
Out of an abundance of caution, DoD pursued PFAS testing and response actions beyond EPA SDWA requirements. In 2020,
the DoD established a policy to monitor drinking water for 17 PFAS compounds at all service owned and operated water
systems. If results confirmed the drinking water contained PFOA and PFOS at individual or combined concentrations greaterthan 70ppt, water systems quickly took action to reduce exposures. While not a SDWA requirement, n 2023, DoD improved
upon its 2020 PFAS drinking water monitoring policy by expanding the list of PFAS compounds monitored to 29,
implementing continued monitoring of systems with detectable PFAS over the laboratory Method Reporting Limits (MRL), andrequiring initial mitigation planning actions.
••

Has Yokota AB tested its water for PFAS?
Yes. In October 2023, samples were collected from Yokota and Tama.

We are informing you that 8 of the 29 PFAS compounds covered by the sampling method were detected above the Method
Detection Limit (MDL). The results are provided in Table 4 below, and public notification of these sample results was initiallyprovided on 2 Feb 24 via Yokota AB Official Website (www.yokota.af.mil). PFOA and PFOS were detected but below 70ppt.
As PFOA and PFOS were below the 70ppt, there is no immediate cause for concern and we will continue to monitor thedrinking water closely. In accordance with DoD policy, Yokota AB will collect semi-annual samples for PFAS, and periodic
updates are available at Yokota AB Official Website.

Table 4. 2023 Yokota AB Detected PFAS
AnalyteAbbreviation

CAS Number

Result(ppt)

Perfluorooctanoic acid

PFOA

335-67-1

5.3

Perfluorooctanesulfonic acid

PFOS

1763-23-1

8.7

Perfluoroheptanoic acid

PFHpA

375-85-9

1.9-6-2016 EPA Health
Advisory Level
70 pptN/A

Last Sampled

Oct 23

Perfluorohexanoic acid

PFHxA

307-24-4

2.4

Perfluorohexanesulfonic acid

PFHxS

355-46-4

4.6

Perfluorononanoic acidPFNA375-95-1

2.1

Perfluorobutanoic acidPFBA375-22-4

2.6

Perfluoropentanoic acid

PFPeA

2706-90-3

2.3

Table 5. 2023 Tama Hills Detected PFAS
AnalyteAbbreviation

CAS Number

Result(ppt)

2016 EPA Health
Advisory Level

None Detected

Last Sampled
Oct 23

Terms Defined

DoD - Department of Defense.
EPA - United States Environmental Protection Agency.
JEGS - Japan Environmental Governing Standards (JEGS).
Maximum Contaminant Level (MCL) - The highest level of a contaminant that is allowed in drinking water. MCLs are set as
close to the MCLGs as feasible using the best available treatment technology.
Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water below which there is no expected
health risk. MCLGs allow for a margin of safety.
N/A - Not applicable, No MCL established.
ND - Means not detected and indicates that the substance was not found by laboratory analysis.
Part per million (ppm) – 1/1,000,000; One ppm corresponds to 1 minute in 2 years, or a single penny in $10,000.
Part per billion (ppb) – 1/1,000,000,000; One ppb corresponds to 1 minute in 2,000 years, or a single penny in $10,000,000.
Part per trillion (ppt) – 1/1,000,000,000,000; One ppt corresponds to 1 minute in 2,000,000 years, or single penny in$10,000,000,000
Picocuries per liter (pCi/L) - Picocuries per liter is a measure of radioactivity in water.
Millirem (mrem) – , One thousandth of a rem. Dose unit of absorbed energy with ionizing radiation.

For more information

For more information on opportunities to participate in decisions that affect the quality of local drinking water, reach out to thefollowing organizations:
Organization
374 OMRS Bioenvironmental Engineering (BE)374 CES Water & Fuel Systems Maintenance (WFSM)

DSN
225-8040
225-7089

Service Area
Drinking water quality concerns
Water treatment and distribution

 E-mail: usaf.yokota.374-mdg.mbx.omrs-bioenvironmental-engineering@health.mil-7-