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FMC Corporation

1735 Market Street

Philadelphia PA 19103

215,299.6000 phone

215.299.6947 tax'

www.fmc.com

Via Federal Express

April 14, 2010

Caria Fisher U.S. EPA Region 10 Ste 900, MS AWT-121 1200 Sixth Avenue Seattle, WA 98101

Re: FMC Pocatello Plant Site - RCRA ID #IDD070929518 Draft Pond 168 amended RCRA Post-Closure Plan and update on RCRA Post-Closure Maintenance Work

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iZ Dear Ms. Fisher: ^ '

This letter serves to transmit (1) a draft amended Post Closure Plan (PCP) for Pond 16S; (2) comments on the draft report by Shaw Environmental, Inc provided to FMC on February 16, 2010, and (3) a Cap Drainage Maintenance Work Plan. This letter also serves to notify EPA that FMC is commencing gas extraction at Pond 15S to address a potential industrial hygiene issue and proposing additional monitoring at Pond 15S.

Draft Amended PCP for Pond 16S

FMC Corporation has been working closely with EPA, the Idaho Department of Enviroimiental Quality (IDEQ) and the Shoshone-Bannock Tribes to implement the requirements of Unilateral Administrative Order for Removal Action CERCLA Docket No. 10-27-0051 issued to FMC Idaho LLC on December 14, 2006 ("the UAO") that required installation of a gas removal and treatment system at closed RCRA Pond 168. The July 31, 2003 PCP for Pond 168, approved by EPA on February 4, 2004, required that gas be extracted and treated only if excessive pressure was observed under the pond cap pursuant to the PCP monitoring. The purpose of that monitoring was to detect potential gas build up that could impair the cap integrity. As FMC and EPA have agreed, that PCP did not anticipate extraction and treatment of phosphine gas based on its concentration within the waste zone under the cap, nor did it anticipate the escape of gas through the temperature monitoring point (TMP) wells. The observation that TMPs were acting as a conduit for escape of phosphine gas from Pond 168 was a primary factor that led EPA to issue the UAO.

USEPA SF

iiiiil 1361651

Ms. Carla Fisher - U8 EPA April 14, 2010-Page 2

As you are aware, FMC installed and is operating a gas extraction and treatment system (GETS) on Pond 168 as required under the UAO. Its successful operation has reduced phosphine concentrations in the waste zone under the Pond 168 cap to less than 10% of the LEL, the criterion specified in that order. The UAO requires that the phosphine concentration in the waste zone under the Pond 168 cap be maintained at no more than this level for one year, a requirement that is expected to be fulfilled in fourth quarter 2010.

Both FMC and EPA share the goal of ensuring that the RCRA PCPs for the eight closed RCRA Ponds at the facility adequately monitor attainment ofthe general 40 CFR §§264.111/ 265.111 closure performance standard and the specific standards applicable to these units. To achieve this goal, we have been reviewing the existing PCPs to identify potential needed changes based on the observations and experience at Pond 168 that led EPA to direct FMC to prepare amended PCPs for all the Ponds. After reaching agreement on the scope of needed changes as proposed in the draft amended Pond 168 PCP, the PCPs for the other closed RCRA ponds will also be amended, as appropriate for the specific circumstances at each unit.

Recent highlights of this ongoing work include EPA's visit to the site in November 2008, as documented in Booz Allen Hamilton's February 10, 2009 "Report of site Visit at Former FMC Corporation," that included a "Summary and Recommendations for Post-Closure Plan Modifications" (the "BAH report"). FMC received a second document from EPA on February 16, 2010. This was a draft entitled "Independent Review of Phosphine Issues Related to Pond 168, Eastem Michaud Flats, Pocatello, Idaho" prepared by Shaw Environmental under contract to the EPA Office of Research and Development (the "draft Shaw report"). The BAH report documented a comprehensive onsite review ofthe existing PCP monitoring in November 2008. The draft Shaw report includes recommendations for monitoring phosphine at Pond 168. The draft Shaw report was issued following a meeting and site visit on December 15, 2009, and includes as Attachment B FMC's presentation at that meeting outlining the status of FMC's proposed approach for amending the PCPs. FMC had developed that approach in consultation with EPA. Further, a conference call was held March 12, 2010 between FMC, EPA, IDEQ and the Shoshone-Bannock Tribes to discuss the draft Shaw report and how its recommendations could be incorporated into the proposed approach for amending the PCPs for all the ponds as EPA has directed.

As discussed in the March 12, 2010 conference call, monitoring phosphine concentrations in the soil gas at the Limit of Final Cover (LFC) as generally proposed in the draft Shaw report is a key element of an amended PCP. In the near term our focus has been development ofthe draft amended PCP for Pond 168 in accordance with this approach and in advance of the upcoming milestone under the Pond 168 UAO. During the March 12 conference call EPA and IDEQ also required that FMC include an additional monitoring element in the PCPs to provide a gas generation "early warning

Ms. Carla Fisher - US EPA April 14, 2010-Page 3

system" so that FMC can identify the need for action in advance of encountering conditions ofthe kind that led EPA to issuing the UAO for Pond 168.

FMC has prepared the enclosed draft amended Pond 168 PCP in accordance with these discussions and documents. The draft amended PCP includes updates to address (1) the BAH report; (2) elements ofthe draft Shaw report; (3) updates that FMC has previously proposed regarding temperature and pressure monitoring; and (4) a general update to ensure that Data Quality Objectives (DQOs) are in place for all elements ofthe PCP. The changes also include discontinuance of two groundwater monitoring analytes and a revised approach for monitoring the cap drainage layer. All the proposed changes from the current PCP are summarized in sections 1.4 and 1.5 ofthe enclosed draft amended plan.

Comments on the Draft Shaw Report

During the March 12, 2010 conference call, FMC indicated that there are various tjTpographical errors and inaccuracies in the draft Shaw Report, but that FMC's focus at that time was limited to those elements that directly relate to development of an amended PCP. Attached are written comments that EPA and Shaw should consider prior to issuing another draft of that report. For purposes of preparing the draft amended PCP for Pond 168, FMC has accepted Shaw's recommendation that phosphine be measured in soil gas at the Limit of Final Cover (LFC). FMC has already installed soil gas monitoring probes at the suggested shallower depth approximately 5 feet beyond (outside) and above the cap anchor trench, but about 15 feet inside ofthe LFC. These shallower probes would be a component ofthe "early warning system" that EPA and IDEQ have required FMC to develop. The draft amended PCP includes installation of additional monitoring points at a depth of approximately 4-6 feet below ground surface (bgs) at the LFC around the perimeter ofthe unit, a depth and location recommended by Shaw. FMC also has included a "frigger" level of 25 ppm (half the IDLH) for the soil gas probes at the LFC rather than the 5 ppm Shaw suggested, which that report did not explain or support with any stated rationale. A trigger level of 25 ppm at a depth of 4-6 ft bgs would be very conservative given the lack of potential exposure pathways and the experience at Pond 168 that significantly higher concentrations in shallow soil gas did not lead to exposures at the ground surface. Deeper soil gas monitoring suggested by Shaw, e.g., extending to above the water table, is not technically supportable for the reasons discussed in the attached comments.

Cap Drainage Maintenance Work Plan

FMC has been conducting required post-closure monitoring and maintenance at all the closed RCRA ponds in accordance with the approved PCPs for many years. As detailed in the attached proposed Cap Drainage Maintenance Work Plan, in the course of doing this maintenance FMC has identified some additional, shallow subsurface repairs that should be made at the cap drainage lines associated with Pond 138, 148, and Pond 18

Ms. Caria Fisher - US EPA April 14, 2010-Page4

Cell A. These lines are in the slopes beyond the waste zone and ET layer, but within the LFC as defined by the bottom ofthe toe ofthe cover slope. FMC is notifying EPA that this work will be conducted as soon as weather permits. This Work Plan and documentation ofthe completion of these repairs will be included in the facility operating record.

Gas Extraction at Pond 15S

FMC has previously provided EPA with information on area monitoring for industrial hygiene that FMC has conducted at the RCRA ponds. The purpose of this monitoring is to ensure the safety of personnel conducting monitoring and maintenance at the closed RCRA ponds, in addition to meeting the requirements ofthe FMC Pond Safety Rules. Subsequent to repairing the Pond 158 cap drainage lift station LS-1 at the northwest comer ofthe pond, IH readings in this area have sporadically indicated that there may be a potential for exposure. In response to these readings, FMC will utilize the Calgon Ventsorb (55-gallon dmm size) gas extraction and treatment system (GES) units that had been used at Pond 168 before constmction and start up ofthe larger GETS, and re­deploying those to Pond 158 to reduce the potential for IH exposures there. Note that no unusual pressure or temperature monitoring results have been observed at Pond 158, specifically the pressure at Pond 158 has not approached or exceeded the trigger level for gas extraction and treatment under the current Pond 158 PCP.

This FMC action at Pond 158 is consistent with the requirement of EPA and IDEQ to identify "early waming triggers" for gas extraction. The commencement of gas extraction at the pond also should provide an opportunity to collect data similar to what would be collected under the phosphine monitoring demonstration program that is proposed in the draft amended Pond 168 PCP. Section 3 ofthe enclosed draft amended PCP provides this program and includes as Section 3.3 the Pond 168 Phosphine Release Pathway Conceptual Model. As described in that model, phosphine can be formed whenever water and elemental phosphoms are present. The rate of phosphine formation is dependent on the pH ofthe water, with alkaline mixtures having significantly greater reaction rates than neutral mixtures. The rate of phosphine decomposition is largely dependent on how much oxygen is available in the subsurface and whether preferred pathways exist in the subsurface, such as greater pore space that would allow movement of gas before decomposition occurs.

Because Pond 15S and Pond 168 have the largest final volume of waste under their closure caps compared to the other RCRA ponds (-140 acre-feet vs. 17-44 acre feet in each ofthe other ponds), they have the least volume of initial fill (sand and slag) above the waste zone and below the elevation ofthe cap liner components. Thus, they have the least volume of pore space within the fill above the waste zone. Phosphine generation in Pond 168, where alkaline materials were co-disposed with elemental phosphoms, had phosphine accumulate to a point that exceeded the volume of pore space and air (oxygen) in the fill in less than two years after the final cap was installed in 2004. At Pond 158,

Ms. Caria Fisher - US EPA April 14, 2010-Page 5

neutral materials were co-disposed with the elemental phosphoms. More than five years after installation ofthe final cap at that pond, phosphine accumulation in the fill beneath the cap may be approaching a level where available pore volume below the elevation of the top ofthe liner is insufficient for phosphine sorption and/or oxidation to phosphoms compounds (e.g., phosphoric acid). Conditions therefore may be developing at Pond 158 where phosphine is no longer being sorbed and/or oxidized within the fill beneath the cap and may find a preferential pathway for release in the gap between the cap and the liner in the northwest comer of that pond.

FMC proposes to install soil gas monitoring points and monitor phosphine levels, similar to that performed (near anchor trench) and proposed (at the LFC) at Pond 168. Similar to the proposal for Pond 168, an initial one-year demonstration monitoring period would be used to ascertain any relationship between phosphine concentrations in the shallow soil gas at the cap anchor trench, in the perimeter piping, and in the deeper soil gas at the Pond 158 LFC.

Despite the IH readings at Pond 158 described above, no releases have been observed from the TMPs at that pond. Also, none ofthe other RCRA ponds have presented these industrial hygiene concems.

FMC looks forward to discussing these documents with you at our meeting scheduled to take place in Pocatello on April 27, 2010. Ifyou have any questions, please contact me at 215/299-6700.

Sincerely,

Barbara E. Ritchie Associate Director, Environment FMC Corporation

Enclosures

cc: Greg Weigel - EPA Boise Bemie Zavala - EPA Seattle Andrew Boyd - EPA Seattle David Reisman - EPA Cincinatti Ed Greutert - Booz Allen Seattle Brian English - IDEQ Boise Kelly Wright - 8BT Susan Hanson - SBT