PCE fall 2016 data letter to water purveyors + Encl 12-21-16
December 21, 2016
Ivo Bergsohn
South Tahoe Public Utility District
ibergsohn@stpud.dst.us
Jennifer Lukins
Lukins Brother Water Company
Jennifer@lukinsbrothers.com
Kirk Woolridge Tahoe Keys Property Owners Association
kwoolridge@tahoekeyspoa.org
PCE MONITORING WELL DATA, TAHOE SOUTH Y, FALL 2016
During fall of this year, the Water Board collected groundwater samples from 15 monitoring wells located on the north side of the Tahoe South Y area of South Lake
Tahoe to evaluate the extent of PCE contamination. The samples were collected
between September 26 and October 12.
As seen in the attached table, the laboratory reported PCE concentrations ranging from non-detect (less than 0.5 micrograms per liter or µg/L) to 110 µg/L at eight locations.
The monitoring well locations with detected PCE concentrations are shown on the map
in Enclosure 2. The highest detected PCE concentration came from monitoring well
MW-4B on Eloise Avenue, near the 5th Street intersection. Monitoring well EW-5C on
Eloise Avenue was also sampled, however, the results were thrown out since the sample represented stormwater rather than the aquifer; the well cover had lost its bolts,
was not sealed tight, and the inside of the vault contained extensive mud.
I have also enclosed the third quarter 2016 map of PCE distribution for the Lake Tahoe
Laundry Works at 1024 Lake Tahoe Boulevard (Enclosure 3). This map shows that up to 35 µg/L PCE was detected during the September 2016 quarterly monitoring event.
The full monitoring report can be viewed under the “Site Maps/Documents” tab in the
Geotracker website at:
https://geotracker.waterboards.ca.gov/profile_report.asp?global_id=SL0601754315
The map in Enclosure 4 shows the combined PCE data from the Water Board’s fall
2016 sampling event and the LTLW Third Quarter 2016 sampling event. Enclosure 5 is
Ivo Bergsohn et al. - 2 - December 21, 2016
a cross section of the combined data showing PCE concentrations with depth within the
South Y aquifer. The cross section line (A-A’) connects the highest PCE concentration
detected at the LTLW site to the highest PCE detection on the north side of the Y
intersection. This line is believed to represent the plume centerline. The highest PCE
concentration of 110 µg/L in the cross section was detected at the 35-50 ft depth in monitoring well MW-4B. Since no other monitoring well was sampled at that depth, the
lateral extent of this hot spot is not known. Question marks on the cross section indicate
areas where the plume boundary is still undefined with depth in the aquifer.
Lastly, Enclosure 6 shows my professional interpretation of the PCE boundary line in the Tahoe South Y area from the LTLW site to at least Patricia Lane. The drawn plume
boundary extends at least 2,000 feet. Question marks on the map indicate areas where
the plume boundaries out to less than 0.5 µg/L are still undefined in the western,
northern, and eastern areas.
The Water Board intends to use the results of the fall 2016 PCE sampling to apply for
additional funds from the State Water Resources Control Board for evaluating the
vertical extent of PCE in the aquifer and potential sources west of the South Y area.
You will be contacted in the near future to participate in this discussion.
Please contact me at (530) 542-5424 or lisa.dernbach@waterboards.ca.gov if you have
any comments or questions.
Lisa Dernbach, PG, CHG, CEG
Senior Engineering Geologist (Specialist)
Enclosures: 1. Table of Monitoring Well Sampling by Water Board
2. Map of Monitoring Well Sampling by Water Board 3. Map of PCE Distribution at the Lake Tahoe Laundry Works, Third Quarter 2016
4. Map of Tahoe South Y Combined PCE Results, Fall 2016
5. Cross section of PCE Concentrations with Depth within the South Y Aquifer
6. Map View of Detected PCE Plume Boundary
cc: Lauri Kemper, Lahontan Water Board
Justine Phillips, Tahoe Keys POA
LSD/ma/T: PCE fall 2016 data letter to water purveyors
File Under: GeoTracker
Enclosure 1
Monitoring Wells Sampled for South Y PCE Investigation
Well Sample Location Depth to Screen PCE (µg/L) TCE (µg/L)/
Date Water Interval (ft) DCE (µg/L)
MW-4A 10/12/16 Eloise Ave 12'5" 15-25 15 0.34/<0.5
MW-4B 10/12/16 Eloise Ave 17'1" 35-50 110 4.2/1.4
MW-4C 10/12/16 Eloise Ave 19'7" 59-79 1.8 <0.5/<0.5
MW-7A 9/26/16 Patricia Ln 13'5" 15-25 <0.5 <0.5/<0.5
MW-7D 9/26/16 Patricia Ln 25' 120-140 5.2 <0.5/<0.5
MW-8A 9/26/16 Patricia Ln 22'1" 15-25 <0.5 <0.5/<0.5
MW-8C 9/26/16 Patricia Ln 25' 70-80 0.26 <0.5/<0.5
MW-8D 9/26/16 Patricia Ln 31'5" 120-140 1.9 <0.5/<0.5
MW-9A 9/28/16 Patricia Ct 15'8" 15-25 <0.5 <0.5/<0.5
MW-9C 9/28/16 Patricia Ct 20'7" 70-80 9.2 <0.5/<0.5
MW-9D 9/28/16 Patricia Ct 24'9" 120-140 1.8 <0.5/<0.5
HMW-3 10/12/16 BevMo 13'2" 9-24 2.3 <0.5/<0.5
Property
HMW-4 10/12/16 BevMo 12"8" 9-24 11 <0.5/<0.5
Property
HMW-5 9/28/16 BevMo 12'9" 9-24 9.5 <0.5/<0.5
Property
ND @w.t.
9.2 ppb@ 70'
1.s p_e_i?_~go·
MW-4
lS@w.t.
110 ppb @35'
1.8 ppb @59'
Enclosure 2
Fall 2016
South V
PCE Sampling
ByRWQCB
Legend
•:• Monitoring well
Supply well
w.t. = water table
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LAKE TAHOE LAUNDRY WORKS
1024 LAKE TAHOE BOULE.VARD
SOUTH LAKE TAHOE, CALIFORNLA
THIRD QUARTER 21116
DISSOLV.ED•PHASE
PCI:: DISTRIBUTION PLOT
FIGURE
4
Enclosure 3
ND @w.t.
9.2 ppb @ 70'
1.8~b @120'
MW-4*
lS@w.t.
110 ppb @ 35'
1.8 ppb @59'
Enclosure 4
Fall 2016 South Y
PCE Sampling:
RWQCB& LTLW
Results
Legend
•!• Monitoring well
w.t. = water table
* = sampled by RWQCB
+ = sampled by LTLW
--= cross section
0
20'
40'
60'
80'
100'
120'
140'
LTLW
A
Cross Section of PCE Concentrations*
with Depth in the South V Area Aquifer
,:.e 'b°> s ~
Y'~>\ ~-D< ~.:':> ~5, \'<>~e
Y'~ Y'~ Y'~ ~-°> ~
Enclosure 5
'\,<:c-
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A'
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*concentrations are in parts per billion, Fall 2016 data
,o·L
240'
Scale
·.):\:· ... -::{\:· ·-:/\:-:·.
Enclosure 6
Fall 2016
South Y
PCE Detected
Plume
Legend
·~ Monitoring well
• Supply well