From: KENT Mavis D
Sent: Wed Jul 29 10:10:49 2009
To: 'Sarah Prowell'
Cc: John Cushing
Subject: RE: Cascade TGA Well Confirmation Sampling and Decommissionings - Request for Approval Confirmation
Importance: Normal
DEQ approves the confirmation sampling and decommissioning plan that you have outlined below. I will put a copy of this email and the attachments with your original email in the file as record of DEQ’s approval.
At our meeting yesterday, we discussed a set of criteria that you will include in the semiannual report that you will be submitting soon. The criteria is intended to guide in decision-making for well management in the pre-closure process and your plan is based on those criteria. Similar criteria have been used for decision-making for the TSA cleanup so there is basis for the timeframes that are used in the Cascade criteria.
I understand that you will include the plan below in the semiannual report as approved tasks that will be done (as opposed to recommendations) and will assume that you will also provide a general timeframe for well decommissioning.
From: Sarah Prowell [mailto:sprowell@ix.netcom.com]
Sent: Wednesday, July 29, 2009 9:53 AM
To: KENT Mavis D
Cc: John Cushing
Subject: Cascade TGA Well Confirmation Sampling and Decommissionings - Request for Approval Confirmation
Dear Mavis,
In follow-up to our TGA remedy planning meeting yesterday, this email summarizes recommendations that we discussed and for which we met verbal agreement regarding the confirmation sampling and decommissioning of selected on-site TGA wells. This work is part of a “pre-closure” process to streamline the well network for our future focus on those remaining locations which require evaluation and potential final treatment. The actions listed below are consistent with preliminary TGA well decommissioning criteria that we also discussed, and which will be delineated in the upcoming TGA Semiannual Performance Report.
On behalf of Cascade Corp., we seek DEQ’s comment or written approval for the following actions discussed on 7/28/09.
(a) Decommission selected on-site wells that are duplicative of other nearby wells that are better suited for ongoing monitoring, including:
i. Area 4 perimeter well RW-1, which is located downgradient of Area 1 and adjacent to well RW-5; well RW-5 is better suited for ongoing monitoring at this location due to the presence of TCE and its recent detection of vinyl chloride above the MCL. VC is a dehalogenation daughter product and is a measure of on-site passive bioremediation activity and progress. VC is not present in RW-1 and COPCs in RW-1 have been consistently below the MCLs since February 2008. To eliminate monitoring well duplication, it is recommended that RW-1 be decommissioned and ongoing monitoring continue in the higher concentration nearby well RW-5. Additionally, Well MW-9i is located directly downgradient of RW-5 and will continue to be monitored. (See Table 1, attached, for RW-1 and RW-5 COPC data.)
ii. Area 2 Former “Sentinel” wells EX-9 and MW-30i, which are located downgradient of Area 2 Sentinel Well EX-10. These wells were previously identified as “Sentinel” wells to assess VC migration from upgradient Area 3. EX-10 is the only Area 2 well to have contained VC at levels above the MCL, thus is better suited for ongoing “Sentinel” monitoring. All COPCs have been consistently below the MCLs in EX-9 and MW-30i since October and February 2006, respectively (i.e., >2 years). (See Table 2, attached, for EX-9, MW-30i, and EX-10 COPC data.)
(b) Decommission wells that have contained consistently compliant COPC concentrations (i.e., below the MCLs) during at least the prior 2 years and are no longer needed for remedy performance monitoring, including:
iii. Area 4 perimeter well RW-3, located downgradient of Area 6 well MW-39s. COPCs have been consistently compliant in RW-3 since 1999, with the exception of one, unrepeated TCE detection of 6.1 in February 2008. Emulsified oil was injected into upgradient well MW-39s 3 years ago in June 2006 and the presence of stable water quality in both MW-39s and RW-3 since that injection reflects stable conditions in and downgradient of Area 6. (See Table 1 for RW-3 and MW-39s COPC data.)
iv. Upgradient/Background Wells MW-4a and MW-4b, located at the southern extent of the Cascade facility property. COPC concentrations in these wells have remained consistently compliant since their installation in 1991 and are no longer needed to establish compliant upgradient water quality at the site.
(c) Decommission one on-site piezometer, MP-1, located west of Area 1. This well was originally installed to assist with 1998 air sparge testing and is not needed for remedy water level monitoring.
We additionally met verbal agreement in our meeting to modify the timeline for final confirmation sampling Area 1 wells EX-2 through EX-6 and MW-39s. These wells were last sampled on August 2008, following 2 years of consistently compliant COPC concentrations, following the June 2006 emulsified oil injection into each of these wells. The wells were subsequently removed from the monitoring program for final, confirmation sampling in August 2010, to be followed by decommissioning if COPC concentrations continued to remained below the MCL (per DEQ’s 10/15/08 approval). Per our meeting, we agreed these wells may be confirmation sampled this August 2009 and if COPC concentrations remain consistently below the MCLs (i.e., the 3rd consecutive year following the June 2006 emulsified oil injection), each of these wells may be decommissioned.
And finally, we discussed yesterday that, per DEQ’s prior approval (DEQ, 10/17/07), Area 2 wells EX-7, EX-8, EX-11, and EX-12 will be confirmation sampled this August 2009, and will be decommissioned if COPCs remain below the MCLs (i.e., > 2 years, given COPCs have remained below the MCLs in each well since August 2006 or before.
We seek your reply with either clarification of the points above or your email approval, for our records.
And thank you, Mavis, for such a productive meeting. We greatly appreciate the teaming on remedy streamlining and pre-closure planning. We look forward to meeting again in October to discuss followup actions.
Sincerely, Sarah
Sarah Prowell, R.G.
Prowell Environmental, Inc.
2216 SW Sunset Blvd.
Portland, Oregon 97239
Phone: 503/452-0972
Fax: 503/452-1427