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

Transcription

1 May 7, 2015

2 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!

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6 83 rd Ave 91 st Ave 1 Mile Well #3 Pinnacle Peak Rd Well #4 Well #2 Well #1 Beardsley Rd Union Hills Rd

7 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

8 Surface waters typically contains higher DO concentrations than GW As the recharge water percolates through the vadose zone it picks up additional CO 2 As the water mounds, pressure helps increase the amount of dissolved gasses in the water When the DO/CO 2 laden GW is extracted, the gas is released from solution

9 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)

10 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

11 DO concentrations in CAP Water Ave DO ~9.5 mg/l CAP 2013 Annual Water Quality Report

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

13 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

14 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 # , /73.0 Clear after 30 seconds # , /74.1 Clear after 60 seconds # , NA /75.2 Clear after 15 seconds # ,300 ~ /77.5 Clear after 15 seconds

15 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

16 Each raw water sample analyzed for suite of analyses including Cations/anions Dissolved Oxygen & CO 2 Total Dissolved Solids Bromide Tritium CAP tracer compound

17 Sample SO 4 (mg/l) Cl (mg/l) Ca (mg/l) Na (mg/l) Mg (mg/l) K (mg/l) Background GW Well # Well # Well # Well # Recharge Water

18 Well #3 Signature Groundwater Signature Recharge Water Signature Well #3 signature is closer to Recharge water than Groundwater

19 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

20 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

21 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

22 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

23 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

24 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 Well #3 Raw Water Tap 28

25 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

26 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

27 The wells with the greatest DO & CO 2 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

28 Clear Creek Associates would like to thank the City of Peoria for supporting the development of this presentation for the 88 th Annual AZWater Conference and Exhibition

29 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.