KJC FS Handouts for TAC 4_26 Feb 2019Feb 26, 2019 10 AM – 2 PM
South Tahoe Public Utility District Board Room
South Y Feasibility Study
TECHNICAL ADVISORY
COMMITTEE MEETING
#4
AGENDA
•Welcome/Self Introductions (10 min)
•Groundwater Model Scenario Evaluation (60 min)
•Scenario Development (KJC)
•Findings and Results (DRI)
•Discussion (TAC)
•Feasibility Study (60 min)
•Potential Alternatives (KJC)
•Preliminary Alternatives Screening (KJC)
•FS Report Outline (KJC)
•Discussion (TAC)
•PDI Draft Report (30 min)
•DFA Comments
•Proposed Changes
•Discussion (TAC)
•Upcoming Activities (5 min)
•Public Workshop 4:
March 6, 2019
•Next Steps (15 min)
•Action Items (Meeting 4)
•Draft F&T Modeling
Report
•Draft Feasibility Study
Report
FEASIBILITY STUDY
•GW Model is limited in
site-specific evaluation
because of scale issues
•Actual GW data are
from 6” to 10’
screen intervals
•Layer 1 of model is
120’- results in
vertical averaging
•GW Model is most useful
in regional-scale
analyses
ALTERNATIVES
DEVELOPMENT
AND GW MODEL
SCENARIO DEVELOPMENT – REFINED APPROACH
•Sensitivity analyses related to source term and biodegradation
informed bookends to alternatives
•Baseline – no future PCE source and some biodegradation – “Best”
Case
•Conservative – 10 mg/l of future PCE source and no
biodegradation – “Worst” Case
•“Right” answer is in the middle
•Insufficient data and scale issues limit certainty and value of further
refinement
•Water agencies provided input on
•Future pumping rate assumptions
•Replacement well locations
POTENTIAL ALTERNATIVES
•Do Nothing
•Alternative Water Supply: Replacement wells in deeper zone
(layer 3)
•Avoid groundwater treatment
•Containment/Capture: Pumping extraction/supply wells for
plume capture/interception
•With groundwater treatment
•In-situ treatment/remediation (at source or mid-plume)
•In areas of highest PCE concentration
GW MODEL AND
ALTERNATIVES DEVELOPMENT
CONSIDERATIONS
•Baseline Model - dilute plume
•2018 PCE Contours from GW Model – Layer 1
•Layer 1 Mass = ~363.3 kg
•Layer 2 PCE Mass = ~ 42.9 kg
•Layer 3 PCE Mass = ~ 6.3 kg
11/19/18 DRI Model
SOURCE AREA/MID-PLUME IN-SITU
REMEDIATION
•Potential Processes (Detail in Handout 2)
•Air Sparging
•Chemical Oxidation
•Bioremediation
•In-Well Air Stripping
•Conclusions:
•Overall, potentially high cost as many unknowns remain, pilot
testing required, high uncertainty of outcome
•Water agencies could incur future liability if undertake source
area remediation
Mass Removal Remediation Scenario, Layer 1, 2038
Stress Period
Contours PCE (ug/l)
Mid Plume In-Situ
Remediation Mass Removal
(Scenario 3)
•Simulated as first order reaction
with a 193 hr half life (Hannesin
and Gillham, 1998)
•Decay rate applied over row of
cells in layer 1 (0-120 ft bgs) in
line with LBWC 4, across 3,800’
width of simulated 2018 plume
exceeding MCL (5 ug/l)
•No further action because
•Layer 1 PCE mass removed
estimated at 40 Kg over 20
years compared to baseline
•Mass downgradient of
remediation is untreated
11/28/18 DRI
ALTERNATIVES CONSIDERED BUT MODELING
NOT PURSUED
•Mid-range values of source and biodegradation
•Mid-plume remediation
•Reduced # of extraction wells at higher pumping rates
•Additional site-specific remediation
•Replacement well locations within plume
•Alternatives that were determined to be less effective than existing model runs were not run
•Future GW Model refinements for Operational Evaluation
•High pumping at TKWC2 and LBWC5 AND replacement wells
•Short term (5-7 years) of high pumping at TKWC2 and LBWC5, then use replacement wells in 5+ years)
•Additional pumping at TKWC2 to well capacity (vs GAC capacity)
PRELIMINARY ALTERNATIVES SCREENING
•Alternatives and RAOs (See Handout 3)
•RAOs
•Allow GW production w/o treatment
•Plume containment
•Water supply at < 50 ppb to avoid 97-005 and mass removal
•Target GW < 100’ bgs/replacement wells outside of plume
•Preserve cost recovery/grant funding
•Prefer beneficial reuse
•Reduce costs to retail customers
•Actions by Water Agencies that do not expose to future liability
• Source Area/Mid-Plume Remediation screened out
•Review Summary of Model Results To Inform Alternatives Screening
SUMMARY OF GW MODEL RESULTS TO INFORM
ALTERNATIVES SCREENING
Scenario Year PCE < 4 ug/L
PCE Removed over 20
years
1. Baseline A: LBWC5: 2025/TKWC2: 2039
B: LBWC5: 2047/TKWC2: >2068
A: 121 kg
B: 2,955 kg
2. Mid-Plume Remediation
– 40 Extraction wells
A: LBWC5: 2023/TKWC2: 2040
B: LBWC5: 2052/TKWC2: >2068
A: 248 Kg
B: 3,513 Kg
3. Mid-Plume
Remediation-3800’ LF in-
situ*
A: LBWC5:2025/TKWC2: 2023 A: 40 Kg more than
baseline
4. Replacement Wells (1)
RW-C and RW-F
A: LBWC5: 2023/TKWC2: 2038
A: 88 Kg
4. Replacement Wells (2)
RW-D and RW- F
A: LBWC5: 2022/TKWC2: 2038
B: LBWC5: 2045/TKWC2: >2068
A: 87 kg
B: 1,845 kg
5. Maximize Current PCE
Treatment
A: LBWC5: 2028/TKWC2: 2035
B: LBWC5: 2044/TKWC2: 2064
A: 330 kg
B: 4,870 kg
* Results based on initial model runs, therefore not comparable to subsequent runs
SCREENED ALTERNATIVES FOR MORE DETAILED
DEVELOPMENT
•Do Nothing
•Replacement wells D and F
•Infrastructure to deliver water with LBWC and TKWC
•Enhanced pumping of TKWC2 and LBWC 5 to 90% of GAC
capacity
•Infrastructure to deliver water to South Tahoe PUD service area
•Additional pumping of TKWC2 to well capacity and additional
treatment using South Tahoe PUD Air stripping?
FEASIBILITY STUDY OUTLINE
•Informed by Feasibility Study Workplan
•Current Draft Outline (Handout 4)
TAC DISCUSSION RE FEASIBILITY STUDY
•Questions:
•Status of Remediation of Source Area(s) and Potential Timing
•Eligibility of alternatives for further state funding (internal note:
Prop 68 allows for O&M, replacement well = alt water supply)
•Level of detail for NCP items
•Summary/conclusions for Feasibility Study next steps