WRD Research Project:

Tracer Test to Track Recycled Water Movement at the

Spreading Grounds

Purpose of the Research Project:• Determine how long it takes for

groundwater to move from the spreading grounds to nearby wells. Simulate recycled water movement.

Acknowledgements• County of Los Angeles DPW• South Montebello Irrigation Dist.• City of Pico Rivera• Cal Water Service• Montebello Land & Water• Pico Water District• La Habra Heights County WD• City of Whittier• California DHS• University of California at Santa Barbara –

Cooperating Agency: Dr. Jordan Clark

Problem Definition• Recycled Water has been used

for groundwater recharge in the Montebello Forebay > 40 yrs.

• New DHS Draft Regulations will not allow drinking water wells within 500 feet of recharge ponds unless recycled water stays underground >6 months.

• 23 production wells exist within 500 feet and may be impacted by the new regulations at a cost of $40 million to replace these wells if needed.

Rio Hon

do

San

Gab

riel R

iver

1 Mile

Rio HondoSpreadingGrounds

San GabrielSpreadingGrounds

SewageTreatment

Plants

W.N. Dam

Whittier

Pico Rivera

Montebello

§̈¦ 5

605

?E60

San Gabriel San Gabriel River River Spreading Spreading GroundsGrounds

Rio Hondo Rio Hondo Spreading Spreading

GroundsGrounds

Background• High quality recycled water has

been recharged at the spreading grounds since 1961.

• Over 1.2 million acre-feet have been recharged to date.

• Recycled water is a reliable, high quality replenishment supply that is available year round.

• The DHS has issued Draft Regs that may impact production wells near the spreading grounds.

DHS draft regulations (12/01/04) for using recycled water at spreading grounds:

“…recharge water shall be retained underground for a minimum of six months prior to extraction…and shall not

be extracted within 500 feet of a point of recharge.”

But allows for an alternative...

“The project sponsor may…reduce the distance…if the sponsor can demonstrate with tracer test results…that

the required retention time will be achieved…”

Draft Regulations

SpreadingGrounds w/

Recycled Water

Drinking Water Well

Minimum 500 feet away

6-Months

Recycled Water underground for more than 6 months before

pumping out

Aquifer

Geologic Effects on Travel Time

SpreadingGrounds w/

Recycled Water

Drinking Water Well

Aquitard

Aquifer

Aquifer Weeks/ Months

Months/ Years

How was the Research Done?

• Add a tracer to the spreading grounds to “tag” the water. Time how long it takes to reach nearby wells.

• Dr. Jordan Clark of UCSB added the tracer and performed the analyses. WRD staff sampled the wells.

• Tracer Selected: Sulfur Hexafluoride (SF6) gas. Inert, safe gas that moves with the groundwater. DHS-approved this tracer for this test.

Why Use a Tracer?• Recycled water can not easily be identified

in a groundwater sample.

• Therefore, a compound (tracer) must be added to act as a surrogate for the recycled water.

Recycled water

How was the Research Done ?

• Identified available wells.

• 17 of the 23 production wells available.

• 1 background well.

• Also monitoring wells.

• Background testing to confirmed no tracer in the wells water prior to the test.

Tracer Test Started Feb. 2003• Heavy rains filled all basins.

• Tracer added to spreading grounds water and sampled to confirm its presence.

• Sampling of wells biweekly, monthly, and bimonthly.

• Sampled through February 2005 (2 year test).

Production Wells - 6 Month Results

Production Wells - Sorted by Perf. Depth

WRD # Owner ID Owner

Distance from Spreading

Grounds/River (ft)Top of Perfs

Bottom of Perfs

No SF6

Confirmed SF6

200065 3 South Montebello 250 60 352 x200055 9 Mont. Land & Water 270 76 214 x200013 8 LHHCWD 390 120 625 x200058 12 Mont. Land & Water 340 122 198 x200061 5 South Montebello 60 148 399 x200059 7 Mont. Land & Water 190 157 237 x200056 10 Mont. Land & Water 400 160 234 x200057 8A Mont. Land & Water 400 160 230 x200012 W-1E SGVWC 310 172 520 x200018 9 LHHCWD 250 184 698 x200087 MONT1 CWS - Montebello 130 230 624 x200099 W5 City of Pico Rivera 60 234 598 x200052 11A Mont. Land & Water 320 240 360 x200096 W11 City of Pico Rivera 180 250 462 x200088 W3 City of Pico Rivera 70 288 566 x200062 8 Pico Water District 215 294 456 x200011 W-1C SGVWC 170 305 462 x

Whittier Well #8, the background well, did not have the tracer detected

2-Year Tracer Experiment ResultsArrival Time is a Function of Depth

0

50

100

150

200

250

3000.0 0.5 1.0 1.5 2.0

Production

Monitoring

Dep

th B

elow

Pon

d to

the

Top

of th

e P

erf's

(ft)

SF6 Arrival Time (yr)

Good Correlation

2-Year Tracer Experiment ResultsArrival Time is a Poor Function of Distance

0

50

100

150

200

250

300

350

400

0.0 0.5 1.0 1.5 2.0

Production

Monitoring

Dis

tanc

e to

clo

sest

Spr

eadi

ng A

rea

(ft)

SF6 Arrival Time (yr)

PoorCorrelation

Discussion of Results• Tracer successfully transferred

into aquifers.

• Only 4 of 17 production wells saw the tracer within 6 months. (Two of these are not within 500 feet of recycled water ponds).

• Depth and geology affect travel time more than horizontal distance.

• DHS agrees: Most wells can operate as is. Very good news as only two of 17 may need modifications or replacement.

South Montebello #5 Test

SpreadingGrounds w/

Recycled Water

200’

219’

399’

148’

60 feet

2 Months Travel Time> 6 Months Travel Time

Questions ?Questions ?

2-Year Results – All Wells: DRAFT

WRD ID Owner ID Owner Well TypeTop of Perf's

Bottom of Perf's

Distance from

Spreading Area (ft)

SF6 First Arrvial (yr)

SF6 Peak Arrival (yr)

100068 RH#1 WRD Monitoring 280 300 60 1.77 >2100069 RH#1 WRD Monitoring 140 160 60 0.54 1.60100089 Pico#2 WRD Monitoring 235 255 100 1.60 1.77100090 Pico#2 WRD Monitoring 100 120 100 0.54 0.62100829 1582W DPW Monitoring 70 132 12 0.08 0.08100830 1590AL DPW Monitoring 51 91 140 0.23 0.81100831 1612T DPW Monitoring 60 80 10 0.15 0.15100832 1613V DPW Monitoring 35 110 120 >2 >2100833 1620RR DPW Monitoring 50 80 110 0.03 0.12100834 2909Y DPW Monitoring 60 115 100 0.08 0.15200004 8 City of Whittier Production 25 260 890 >2 >2200011 W-1C San Gabriel Valley Water Co Production 305 462 170 1.38 1.60200012 W-1E San Gabriel Valley Water Co Production 172 520 310 0.81 0.81200013 8 La Habra Heights Co Water District Production 120 625 390 >2 >2200018 9 La Habra Heights Co Water District Production 184 698 250 1.00 1.00200052 11A Montebello Land & Water Co Production 240 360 320 >2 >2200055 9 Montebello Land & Water Co Production 76 214 270 0.15 0.23200056 10 Montebello Land & Water Co Production 160 234 400 >2 >2200057 8A Montebello Land & Water Co Production 160 230 400 >2 >2200058 12 Montebello Land & Water Co Production 122 198 340 0.15 0.15200059 7 Montebello Land & Water Co Production 157 237 190 >2 >2200061 5 South Montebello Irrigation District Production 148 399 60 0.15 0.62200062 8 Pico Water District Production 294 456 215 1.00 1.19200065 3 South Montebello Irrigation District Production 60 352 250 0.31 1.00200087 MONT1 CA Water Service - Montebello Production 230 624 130 >2 >2200088 W3 City of Pico Rivera Production 288 566 70 1.60 1.77200089 W4 City of Pico Rivera Production 281 572 85 1.60 2.00200096 W11 City of Pico Rivera Production 250 462 180 >2 >2200099 W5 City of Pico Rivera Production 234 598 60 0.81 1.38

Arrival Time less than 6 months