May 7, 2015

Group of 4 public supply wells near the Agua Fria produce milky water that appears to be the result of entrained air

The cause and when it was first observed are unknown

The make up of the entrained air was also unknown

What was known is that customers do not like milky tap water!

Well #1

Well #4

Well #2

Well #3

1 Mile

Union Hills Rd

Beardsley Rd

83rd

Ave

91st

Ave

Pinnacle Peak Rd

Well/pump related

Cascading water

Holes in column pipe

Excessive drawdown close to pump intake

Leaking air relief valves

Chemical/physical reactions

Acidic waters mixing with carbonate formations

Depressurization of very deep groundwater

VZ recharge of surface water

Surface waters typically contains higher DO concentrations than GW

As the recharge water percolates through the vadose zone it picks up additional CO2

As the water mounds, pressure helps increase the amount of dissolved gasses in the water

When the DO/CO2 laden GW is extracted, the gas is released from solution

Review effected well data

Pump each well and collect WQ and

WL data

Collect raw groundwater samples for

laboratory analyses

Analyze the data and develop an

opinion as to its potential source(s)

including CAP recharge at nearby

Agua Fria Recharge Project (AFRP)

Closest upgradient recharge project

Recharge water has high DO

Recharge rates along river nearly 4 ft/d

High volumes recharge/flow down river

(>100,000 gpm)

Linear recharge increases amount of

vadose zone the water comes in contact

with (literally many thousands of feet)

Structures along river aerate water

CAP 2013 Annual Water Quality Report

DO concentrations in CAP Water

Ave DO ~9.5 mg/L

Well #1 Well #4 Well #2 Well #3

Pump each well for 4 hours

Monitor pumping rates and water levels

Collect WQ parameters every 15 mins

Visually observe groundwater

conditions every 15 mins

Track entrained air dissipation rates in

sealed and open sample containers

Well Screened

Interval

(ft bls)

Pump

Setting

(ft bls)

Pumping

WL

(ft bls)

pH EC

(µs/cm)

ORP

(m/V)

DO

(mg/L)

Temp

(°C/°F)

Field Sample

Observations

#1 698-1,200 680 547 7.11 436 333.1 8.57 22.8/73.0 Clear after 30

seconds

#2 700-1,050 761 548 7.52 494 223.4 8.52 23.4/74.1 Clear after 60

seconds

#3 739-1,010 720 NA 7.40 637 210.7 7.26 24.0/75.2 Clear after 15

seconds

#4 850-1,300 ~800 555 7.63 550 166.1 4.98 25.3/77.5 Clear after 15

seconds

DO at or near saturation in 3 of 4 wells

Elevated ORP corresponds to high DO

measurements

While DO in groundwater can fluctuate

and varies from place to place, typical

concentrations at these depths would

be expected to be much lower on the

order of 2 to 4 mg/L

Each raw water sample analyzed for

suite of analyses including

Cations/anions

Dissolved Oxygen & CO2

Total Dissolved Solids

Bromide

Tritium

CAP tracer compound

Sample SO4

(mg/L)

Cl

(mg/L)

Ca

(mg/L)

Na

(mg/L)

Mg

(mg/L)

K

(mg/L)

Background GW 27 29 43 30 20 3.3

Well #1 43 17 40 30 19 2.3

Well #2 48 28 48 34 22 2.7

Well #3 74 63 64 40 28 3.1

Well #4 53 45 42 42 22 3.5

Recharge Water 248 87 83 82 22 4.3

Recharge Water

Signature

Groundwater

Signature

Well #3

Signature

Well #3 signature is

closer to Recharge

water than

Groundwater

Analytical results consistent with

field measurements

Saturation at Wells #1 and #2 and

near saturation at #3. Well #4,

the deepest well was lower

DO concentrations much more

consistent with CAP water than

groundwater

Detected at concentrations ranged from 0.88 mg/L (Well #4) to 2.2 mg/L (Well #1)

CAP water at or below detection limit

Groundwater concentrations have decreased over time (> 75% since 2004 at Well #3)

Decreases of N in GW may be attributed to dilution by CAP water

Concentrations ranged from 300 mg/L

(Well #1) to 420 mg/L (Well #3)

CAP water averages about 660 mg/L

Groundwater concentrations have

increased nearly 40% since 2000

Increases of TDS may be

attributed to mixing of

CAP water

25

Analytical results for bromide were ND, consistent with typical groundwater

Ratios for GW calculated using ½- the detection limit for bromide

Ratios for evaluated wells ranged between 68 and 252

Ratios of CAP water typically range between 950 and 1150

Higher ratios in groundwater noted at wells closer to the AFRP

Substance released to atmosphere from

the detonation of nuclear bombs in

1950s

Can be identified in groundwater

recharged within past 50 years

Detected in each GW sample

Higher concentrations were reported in

wells closer to AFRP

Recharge water is known to have low

concentrations of a compound from

the Hawthorn, NV Superfund Site

Low level detected in raw water

collected from Well #3 which

is most impacted by AFRP

Not detected in any of the

other wells

28

Well #3 Raw Water Tap

Uniformity of entrained air between wells

suggests that it originates from aquifer

as opposed to a pump/well issue

All PWLs above well screen eliminate cause

related to cascading water within well

All PWLs far above pump intakes

Recent pump replacements confirm integrity

of column pipe

All vacuum/air relief valves functioning

properly

WQ data indicate CAP water has mixed with groundwater and the blended water has reached the wells with entrained air to varying degrees

ORP values indicate highly oxidative state of the groundwater

Nitrate concentrations have decreased

TDS concentrations have increased

Chloride:bromide ratios greatest in wells most impacted by recharge

Tritium concentrations greatest in wells most impacted by recharge

The presence of CAP tracer in groundwater confirms influence from surface water recharge

The wells with the greatest DO & CO2

concentrations had the slowest

entrained air dissipation rates

While a direct correlation between the

presence of entrained air in these

wells and nearby artificial recharge

cannot be made, qualitative evidence

suggests the two may be linked

Clear Creek Associates would like to

thank the City of Peoria for supporting

the development of this presentation for

the 88th Annual AZWater Conference and

Exhibition

“Statements of fact and opinion

expressed are those of the author(s) /

presenter(s).

AZ Water, AZAWWA, and AZWEA assume

no responsibility for the content, nor do

they represent official policy of the

Association.”