Combined slides 8.8.18_STGroundwater AT THE South Y
August 8, 2018 6:00 PM – 7:30 pm
City of south lake tahoe | Council chambers
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Agenda
Introductions
overview
WATER Agency updates
Lukins brothers water company
Tahoe keys water company
South tahoe Public utility District
California Water Board Update
PREDESIGN INVESTIGATION
Next steps
BREAK
Questions and answers
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introductions
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SOURCE WATER
DRINKING WATER
GROUNDWATER
GROUNDWATER
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Groundwater BASIN
Tahoe valley south basin
Sedimentary Geologic Basin
Highly productive for groundwater
Recharged from surrounding watersheds
Excellent water quality
High reliance on WELLS
Susceptible to contamination
Figure from Fig 3-2 of 2014 GWMP
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Current situation
PCE contaminant plume 400+ acres
impaired both private and public water system wells
total available water production capacity reduced by 3.25 MGD (~5,000 average Ca households)
Pce detections
Lukins Bros – 3 wells
Tahoe Keys – 2 wells
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Water Agency Updates
Lukins brothers water company
Tahoe keys water company
South tahoe public utility district
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Lukins brothers water company
California Public Utilities Commission approval of Resolution W-5159. Granting LBWC
Authority for funding
Water testing at Well #5. Results for PCE: 58ppb and 60ppb. TCE: 1.3ppb and 1.4ppb
Filtration system project plans and specification at Division of Drinking Water and Division of Financial Assistance for final review. Next step: budgetary review
Working with local, regional and state agencies to move funding forward
Awaiting direction fro Water Board on enforcement to determine direction of legal action
Engage public in investigation and clean up process. Raise awareness about third party water contamination
April 2018
June 2018
August 2018
2019
Anticipated construction of filtration system
Next Steps
Submitted California Department of Water Resources State Revolving Fund Application for Feasibility study to locate potential new water sources for Lukins
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Tahoe keys water company
Continue to operate filtration system on Well #2 to remove PCE.
2018
Monitor Well #1 monthly. Samples continues to be below maximum contaminant level (MCL) of 5ppb.
Fall 2018
Perform water quality monitoring on Well #2 to determine vertical extent of PCE.
Next Steps
Use DRI Groundwater Model to determine potential location for replacement well.
Note for 3rd bullet – data show Well 1 had low levels of detection 1996 at 0.65 ug/l and 0.6 in 2002, no samples from 2005-2014; 0.4 ug/L is Method detection limit
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South tahoe public utility district
April 2018
2018
June-July 2018
Continue to meet regularly with the Technical Advisory Committee
Received Prop 1 Planning Grant
$504,295
Predesign Investigation (Field Work 95% Complete)
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PREDESIGN INVESTIGATION
Objectives:
assess the vertical extent of PCE contamination;
Collect water quality and engineering information for engineering design
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953 Eloise FIELD SITE
EW1
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BASELINE SAMPLING
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PCE Plume (LRWQCB, 2016)
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EW-1 Borehole log (0 – 150’)
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Initial findings
Multi-layer aquifer
Minor aquitards separate upper layer into 3 zones (A, B and C) overlying a major aquitard (94 - 100’ )
Pce contamination within Zone b & upper part of zone c (26 – 52’)
Trace levels of tce detected below 100’ in zone d (119 – 124’)
Baseline sampling
Pce not detected in monitoring wells west of field site
Pce detected in monitoring wells & public supply wells north of field site
Major aquitard may have limited lateral extent north of the field site.
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Initial findings
Aquifer test
extraction well pumping rate(s):
Zone B : up to 20 gpm
Zone C: Up to 40 GPM
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NEXT STEPS
Predesign investigation
Data Analysis & reporting
GROUNDWATER MODELING
PERFORM PRELIMINARY RUNS FOR REMEDIAL ALTERNATIVE SIMULATIONS
NO-ACTION
MID-PLUME CONTAINMENT/REMOVAL WITH WELL-HEAD TREATMENT;
WELL-HEAD TREATMENT
FEASIBILITY STUDY
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BREAK
10- minutes
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Question and answers
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MW-4B ANALYSIS (preliminary)
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953 eloise SITE SECTION
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EW-1C Pumping well
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MW-4B Observation Well (r=78’)
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