RE_ Follow up Q on PCE Contours RE_ 10_3_18 call summary and notes_questions RE_ South Y PCE Source TermFrom:Ivo Bergsohn
To:"Sachi Itagaki"
Subject:RE: Follow up Q on PCE Contours RE: 10/3/18 call summary and notes/questions RE: South Y PCE Source Term
Date:Tuesday, October 16, 2018 11:39:36 AM
Hi Sachi-
Are you available this afternoon?
I’d like to briefly talk about possible topics for discussion and scheduling a meeting with the TAC next
Week;
Possible Topics for Discussion:
· MOU Update (T. Carter)
· FS Work Plan (KJC submit to Grant Manager)
· Baseline Human Health Risk Assessment (KJC submit to TAC for Review?)
· Remedial Scenario Definition Update (KJC/DRI)
· Public Meeting 3 (11/7/2018 – tentative)
· Other?
-Ivo
From: Sachi Itagaki [mailto:SachiItagaki@kennedyjenks.com] Sent: Tuesday, October 16, 2018 11:15 AMTo: Susan Rybarski; Ivo Bergsohn; Greg PohllCc: Alice Robinson; Meredith Durant; Walt McNabSubject: RE: Follow up Q on PCE Contours RE: 10/3/18 call summary and notes/questions RE: South YPCE Source Term
Thx! can you also provide a pdf of the source grid cells? I forgot to request that yesterday – I don’t
have GIS skills… Sachi
____________________________________________________
Sachi Itagaki, P.E., QSD | Principal, One Water Practice
Kennedy/Jenks Consultants
Direct: 650.852.2817 | Cell: 415.350.7803
From: Susan Rybarski <Susan.Rybarski@dri.edu>
Sent: Tuesday, October 16, 2018 11:14 AM
To: Sachi Itagaki <SachiItagaki@kennedyjenks.com>; ibergsohn@stpud.dst.ca.us; Greg Pohll
<Greg.Pohll@dri.edu>
Cc: Alice Robinson <AliceRobinson@kennedyjenks.com>; Meredith Durant
<MeredithDurant@KennedyJenks.com>; Walt McNab <WaltMcNab@kennedyjenks.com>
Subject: RE: Follow up Q on PCE Contours RE: 10/3/18 call summary and notes/questions RE: South
Y PCE Source Term
Hi Sachi,
See below and attached.
Susie
From: Sachi Itagaki <SachiItagaki@kennedyjenks.com>
Sent: Monday, October 15, 2018 2:20 PM
To: Susan Rybarski <Susan.Rybarski@dri.edu>; ibergsohn@stpud.dst.ca.us; Greg Pohll
<Greg.Pohll@dri.edu>
Cc: Alice Robinson <AliceRobinson@kennedyjenks.com>; Meredith Durant
<MeredithDurant@KennedyJenks.com>; Walt McNab <WaltMcNab@kennedyjenks.com>; Sachi
Itagaki <SachiItagaki@kennedyjenks.com>
Subject: Follow up Q on PCE Contours RE: 10/3/18 call summary and notes/questions RE: South Y
PCE Source Term
Thx Susie- while I digest the info on the PCE contours, I have a few questions re the assumptions for
the run that generated these contours- if you have a spreadsheet or table that you are using to track
to track assumptions/changes from run to run and by layer, we would find that useful as we craft
alternatives for the upcoming runs, if not, we will develop one. I do not have a spreadsheet, sorry!
1. I assume these are for the baseline (i.e. no action) alternative – can you confirm? Correct
2. What are the future pumping rates by supply well and what layers do they occur in? See
attached spreadsheet – the layers that each well pumps from are determined by the elevation
of the screened interval for that well. Any well not appearing on this list has a future pumping
rate of zero.
a. Do water supply pumping rates vary by year? i.e. any droughts and/or growth built in?)
No, a constant pumping rate is assumed for all wells pumping into the future.
3. Can you confirm the PCE decay rates by layer and how/whether they change by year by layer?
Layer 1 has a half-life of 15 years, layers 2-4 have a half-life of 2 years. These rates are
constant throughout the simulation as concentrations of dissolved oxygen are assumed to
remain constant.
4. Source term (aka recharge concentration) follow up question (from below)–
a. is there a time in the future when the source term goes to zero? The source term goes
to zero in 2012 in the baseline simulation.
b. Is the rate of source term reduction constant or variable? The source term is constant
during the period LTLW was in operation. Following that, the maximum concentration
decreases every ten years, with peaks in concentration occurring during wet years
where higher water table elevations might capture soil bound PCE. Note that these
fluctuations in water table elevation are not explicitly simulated.
c. What is the basis for the source term reduction ? Source term concentrations were
calibrated to measured concentrations in downgradient wells.
4. What are the assumptions you make over the model domain in the future re conditions like
recharge, lake level, etc?
a. Are there droughts/wet years simulated? No – future years are simulated using steady-
state values for recharge and lake level.
b. If so, on what basis?
I hope to have some draft replacement well locations/pumping rates to run in the next day or so for
the group to consider. Thanks! Sachi
____________________________________________________
Sachi Itagaki, P.E., QSD | Principal, One Water Practice Kennedy/Jenks Consultants
Direct: 650.852.2817 | Cell: 415.350.7803
From: Susan Rybarski <Susan.Rybarski@dri.edu>
Sent: Thursday, October 11, 2018 2:41 PM
To: Sachi Itagaki <SachiItagaki@kennedyjenks.com>; ibergsohn@stpud.dst.ca.us; Greg Pohll
<Greg.Pohll@dri.edu>
Cc: Alice Robinson <AliceRobinson@kennedyjenks.com>; Meredith Durant
<MeredithDurant@KennedyJenks.com>; Walt McNab <WaltMcNab@kennedyjenks.com>
Subject: RE: 10/3/18 call summary and notes/questions RE: South Y PCE Source Term
Hi Sachi,
I apologize for the delay. Attached are shapefiles for simulated PCE concentration contours over
several years, as well as a shapefile showing the location of the source cells at LTLW. The contours
were generated after applying the pumping rate updates through the 2018 water year. If you would
like to see any additional time periods or concentration intervals, just let me know.
Susie
From: Sachi Itagaki <SachiItagaki@kennedyjenks.com>
Sent: Tuesday, October 9, 2018 11:54 AM
To: ibergsohn@stpud.dst.ca.us; Susan Rybarski <Susan.Rybarski@dri.edu>; Greg Pohll
<Greg.Pohll@dri.edu>
Cc: Alice Robinson <AliceRobinson@kennedyjenks.com>; Meredith Durant
<MeredithDurant@KennedyJenks.com>; Walt McNab <WaltMcNab@kennedyjenks.com>; Sachi
Itagaki <SachiItagaki@kennedyjenks.com>
Subject: RE: 10/3/18 call summary and notes/questions RE: South Y PCE Source Term
Thanks Ivo – that framework on alternatives is helpful – I think that we can certainly identify
locations and pumping rates for the well head treatment and replacement well alternatives within
the near future;
I’m cc:ing Walt McNab, who is an in-house modeling/remediation resource that Meredith and I have
been consulting with for the remediation options. Sachi
____________________________________________________
Sachi Itagaki, P.E., QSD | Principal, One Water Practice
Kennedy/Jenks Consultants
Direct: 650.852.2817 | Cell: 415.350.7803
From: Ivo Bergsohn <Ibergsohn@stpud.dst.ca.us>
Sent: Tuesday, October 09, 2018 11:19 AM
To: 'Susan Rybarski' <Susan.Rybarski@dri.edu>; Sachi Itagaki <SachiItagaki@kennedyjenks.com>;
Greg Pohll <Greg.Pohll@dri.edu>
Cc: Alice Robinson <AliceRobinson@kennedyjenks.com>; Meredith Durant
<MeredithDurant@KennedyJenks.com>
Subject: RE: 10/3/18 call summary and notes/questions RE: South Y PCE Source Term
Hi Sachi-
I didn’t have any changes to your notes, as your recollection I’m sure is better than mine.
I did, however add a comment to Item 5b. reflecting my understanding on the limitations of the
model; how the model may be used to assist in the FS; and how remedial alternatives may need to
be approached.
I hope it’s helpful.
-Ivo
From: Susan Rybarski [mailto:Susan.Rybarski@dri.edu] Sent: Tuesday, October 09, 2018 10:31 AMTo: Sachi Itagaki; Greg Pohll; Ivo BergsohnCc: Alice Robinson; Meredith DurantSubject: RE: 10/3/18 call summary and notes/questions RE: South Y PCE Source Term
Hi Sachi,
Thanks for putting this together. See below my responses to your questions – let me know if I missed
any or you need more clarification. Working on getting you the updated contours and shapefile of
the source term grid cells, should have to you by tomorrow.
Susie
From: Sachi Itagaki <SachiItagaki@kennedyjenks.com>
Sent: Monday, October 8, 2018 10:00 AM
To: Greg Pohll <Greg.Pohll@dri.edu>; Susan Rybarski <Susan.Rybarski@dri.edu>;
ibergsohn@stpud.dst.ca.us
Cc: Alice Robinson <AliceRobinson@kennedyjenks.com>; Meredith Durant
<MeredithDurant@KennedyJenks.com>; Sachi Itagaki <SachiItagaki@kennedyjenks.com>
Subject: 10/3/18 call summary and notes/questions RE: South Y PCE Source Term
Hi everyone – we’ve continued to chew over our discussion from last week and I wanted to offer the
following action items and summary/questions after also reviewing the 8/9/18 call ppt - please let
me know if my recollection/notes are incorrect. Thanks! Sachi
Action Items
1. DRI to provide baseline model PCE contours at various points in time (including 2018 as
requested in 3b below) by around 10/10/18 to assist in refining KJ 2016-2018 data PCE
contours (see also summary 3c) please include identification of the 22 grid cells that are the
PCE source area
2. KJ to refine PCE contours (versions provided were preliminary draft) in PCE hotspot area of
Norma’s cleaners north of LTLW
3. DRI – although we might have put this to the side, it still doesn’t seem that there is a model
scenario with lots of PCE removal starting in 2018 to estimate the mass of PCE removal
necessary to “clean up” the plume (as predicted by the model at the production wells)
a. The additional run(s) with increasing extraction to more than the current 40 gpm in the
remediation wells as planned may address this
4. KJ to provide more specific assumptions, especially for remediation, for consideration in the
model (see Summary 4a below) by 10/15/18; assumptions will include
a. Identify location, scaled to the model depth and estimated quantity of mass removal
over a specific time period
b. In-situ remediation will likely have to be aggregated as grid cells are much larger than
radius of influence of in-situ remediation
4. Preliminary TAC meeting targeted at 10/23/18 – potential agenda items
a. Review alternative screening and RAOs (from 8/15 and 9/12 calls with KJ and Ivo)
b. Discuss challenges of modeling remedial alternatives – As I understand the current
direction of the FS, we are considering using the F&T model to assist in evaluating three
broad categories of remedial alternatives; 1)Well Head Treatment- using the model to
predict contaminant loads at PWS receptor wells and evaluate possible
operation/pumping scenarios in order to identify optimal groundwater production
schedules that would meet drinking water demands while optimizing PCE mass
removal; 2) Replacement Wells - using the F&T model to assist in siting and evaluating
the hydraulic influence of possible replacement wells on PCE plume movement; and 3)
Mid-Plume Remediation using shallow groundwater extraction with local use of in-situ
chemical oxidation to remove identified “hot spots” . The challenge of using the F&T
Model to assist in the evaluation of this approach is one of scale; the challenge is
identifying approaches that can be used to interpret model simulation results in a
manner that is meaningful in assisting in the development of field-scale remedial
scenarios. By the time of the TAC Meeting my hope is that the project team could at a
minimum define remedial alternatives for moving forward with simulations for the
Well-Head Treatment and Replacement Well approaches. For the Mid-Plume
Remediation alternative, use of the model may be limited to identifying threshold
levels of PCE mass removal that need to be achieved in order to meaningfully reduce
PCE contaminant loads at PWS receptor wells. If this approach were used, the FS would
then identify and cost Mid-Plume remediation strategies that could achieve the needed
level of mass removal predicted by the model. In this manner, cost-benefit could be
applied to evaluate this approach.
c. Other? -
5. Plan to convene this group again during week of 10/15, prior to TAC meeting
Summary (with some comments/followup questions from review of the 8/19/18 ppt)
1. Single source area near LTLW which is used to calibrate to historic PCE data in production
wells is a deliberate decision to avoid confusing current RP situation and potential future
litigation
2. For biodegradation, baseline model has a PCE ½ life of 15 years over entire model domain in
all layers (from 8/9/18 mtg ppt)
a. Question: What is the source/basis for this baseline ½ life? Would it be more
conservative to show zero decay as in scenario 1? Studies have shown PCE to have a
half-life of 1 to 9 years in anoxic conditions, potentially much longer in the presence of
oxygen. 15 years was an estimate as varying concentrations of DO were found in
shallow groundwater. It would be more conservative to assume zero decay, but TCE
and DCE have both been detected at depths assigned to layer 1, so we know some
degradation is occurring. However, the decay rate could easily be longer than 15 years
and is likely spatially variable.
3. PCE removal through extraction is modeled as pumping rate out of a grid cell
a. Slide 9 of 8/9/18 slides show 40 gpm in layer 1 x 21 extraction wells x 20 years of
pumping (2038) – this location and breadth was selected to remove the most mass of
PCE
b. Can we get the modeled PCE contours at the 2018 start? Not just 5 ppb but higher
concentrations as well
c. Note that there is an inherent vertical integration in this approach (each grid cell is
about 110,000 gallons) – the 40 gpm is based on the EW-1 test well which had a
screened interval of < 10’ while the model is 120’ deep.
3. PCE removal from in-situ remediation is modeled as a decay with a much shorter ½ life (eg
days) in the specific grid cells
a. Note that the 8/9/18 slide 12 mass removal assumes decay rate associated with a
permanent installation of oxidant (iron filing wall) per the reference. This is unlikely to
be a feasible in-situ remediation alternative (120’ is too deep for this remediation
method and a permanent installation in this area is highly unlikely)
We are working on assumptions that will more closely align with a proposed in-situ
oxidant of hydrogen peroxide which will be applied to shallower depths (65’) and
would be applied at least once and possibly multiple times within a single year. (see
action item 4 above)
b. Question: What year does the graphic on slide 12 represent? 2038
c. Question: What was the concentration in the cell at the start of remediation and year?
The accelerated decay rate was applied over a row of cells with varying initial
concentrations ranging from 5 to 145 ug/l.
d. Question: What was the decay rate and was it applied for all of the years throughout
the simulation? Half-life of 193 hours was applied for the entire simulation, 2018-
2038.
e. Question: Do you have a sense at what time/year the concentration in the cell is
essentially zero? The concentrations are below detection limits (0.5 ug/l) for all cells in
the remediation line beginning in 2036.
4. Model start is around 1970 with remediation start in 2018
5. Source term is like a “hose” with a 10 mg/l initial value with PCE going into the “bucket” of the
22 grid cells in the vicinity of LTLW –
a. this source term is gradually reducing over time (Question: because of biodegradation
or active remediation?) During the period LTLW was in operation (through 1979), the
source is considered to be continuous new releases. Following their closure, the
‘source’ becomes soil-bound PCE infiltrating down to the groundwater, or being
captured during years when the water table rises. The volume of soil-bound PCE would
then decrease over time as no new PCE is entering the system, so the source
concentration was gradually reduced over time. Note that this process is not directly
simulated in the model – we simply apply a lower recharge concentration over these
cells.
b. this source term can vary with groundwater levels in the vicinity of LTLW
6. The FS is targeting mid-plume remediation vs source remediation (For our purposes: we
assume LTLW source is continuing to be remediated with SVE)
7. The goal of engineering FS analysis is to arrive at a maximized mass removal for $ spent
8. FS analysis will target areas where the field data tell us the PCE plume is now – that said,
moving the extraction/remediation system may have limited impact on estimated PCE
concentrations in downgradient municipal wells
9. PCE plume may be broader than limited field data indicate; model tends to smooth predicted
concentrations
10. Prior PCE removal model simulations were intended to represent a high density of extraction
wells and/or insitu remediation and appeared to show limited downgradient impact as
displayed via estimated future PCE contours
11. There may be an inherent disconnect between the granularity of developing FS remedial
alternatives and the regional, less granular nature of the GW model
____________________________________________________
Sachi Itagaki, P.E., QSD | Principal, One Water Practice Kennedy/Jenks Consultants
Direct: 650.852.2817 | Cell: 415.350.7803
-----Original Appointment-----
From: Greg Pohll <Greg.Pohll@dri.edu>
Sent: Wednesday, September 26, 2018 2:42 PM
To: Greg Pohll; Sachi Itagaki; Alice Robinson; Rick Teczon; Meredith Durant; Susan Rybarski;
ibergsohn@stpud.dst.ca.us
Subject: South Y PCE Source Term
When: Wednesday, October 03, 2018 9:00 AM-10:00 AM (UTC-08:00) Pacific Time (US & Canada).
Where: WEBEX
I am sending the update again as Ivo didn’t received it.
Agenda
1. Review PCE data and possible 2nd source (KJ)
2. Current source term formulation (DRI)
3. Proposed source term formulation (DRI/KJ)
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