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Chemical Waste Landfill (CWL)
Download CWL - ERSiteNo_74 [ Site History The CWL is a 1.9-acre former disposal site located in the southeastern corner of TA-III. From 1962 until 1981, the CWL was used for the disposal of chemical and solid waste generated by SNL/NM research activities. Additionally, a small amount of radioactive waste was disposed of during the operational years. Disposal of liquid waste in unlined pits and trenches ended in 1981, and after 1982 all liquid waste disposal was terminated. From 1982 through 1985, only solid waste was disposed of at the CWL, and after 1985 all waste disposal ended. The CWL was also used as a hazardous waste drum-storage facility from 1981 to 1989. The regional aquifer in the area of the former CWL is located within the Santa Fe Group alluvial sediments at a depth of approximately 485 to 500 feet below ground surface (bgs). The alluvial geology that comprises the vadose zone and the upper part of the saturated zone beneath the site is characterized by inter-layered and laterally discontinuous, poorly sorted, sand and gravel layers (more permeable layers) within a general matrix of sandy or clayey silt. These more permeable layers represent important preferential pathways that are dominantly horizontal features. In general, the alluvial sediments become more fine-grained with depth. Potentiometric surface maps for the water table aquifer underlying the former CWL are consistent with the hydrogeologic conceptual model for the KAFB area, which shows that the local groundwater flow direction is to the northwest at a rate of approximately 2 feet/year. The most conservative linear flow velocity calculated for TA-III was 17 feet/year. Several major well fields have been developed in the regional aquifer to support the City of Albuquerque, KAFB, and surrounding areas. The closest well field is located approximately 5 miles north-northwest and downgradient of the site. Within that well field, the closest downgradient water supply well is KAFB-4, located approximately 4.3 miles north-northwest of the former CWL. The closest natural groundwater discharge point is G Spring located approximately 2.5 miles to the northeast. Based upon water level data from the CWL groundwater monitoring program conducted since 1985, water levels have been declining at an approximate rate of 0.6 feet/year due to the influence of groundwater withdrawals by the City of Albuquerque and KAFB water supply wells. The water table dropped approximately 9 feet at the site between August 1988 and August 2003. Currently, 13 active wells comprise the CWL monitoring network, of which 2 are dry and not sampled, 2 are background (upgradient) wells, and the remaining 9 are downgradient wells. Six of the downgradient monitoring wells are nested pairs, with two wells per location at three locations. For each nested pair, one well contains a screen interval across the water table, and one contains a screen interval approximately 30 feet below the water table. The CWL groundwater monitoring program began in 1985 and is ongoing. To implement the closure provisions contained in 20.4.1.600 NMAC, incorporating 40 CFR 265, Subpart G, the DOE, Sandia, and the NMED began negotiating a Closure Plan in May 1988. In 1990, trichloroethene (TCE) was identified in groundwater at a concentration exceeding the regulatory limit (maximum contaminant level [MCL]) of 5 micrograms per liter (μg/L). This finding led to the development and incorporation of a corrective action program into the Closure Plan in October 1991. Formal closure of the CWL began in 1993 when the NMED approved the Closure Plan, which included an incomplete waste inventory based upon historic CWL records; a preliminary conceptual site model (CSM); and required characterization activities for groundwater (saturated zone), the vadose zone (unsaturated zone), and the volatile organic compound (VOC) soil-gas plume. Unsaturated Zone Contaminant Characterization During the early 1990s, groundwater monitoring results continued to show TCE concentrations exceeding the MCL in some wells. The Unsaturated Zone Contaminant Characterization was the first major investigation conducted under the Closure Plan and included a shallow and deep soil-gas survey, soil sampling, and measuring in situ air permeabilities for contaminant transport evaluations. This investigation was performed from November 1992 to March 1993. The data collected were used to define the nature and extent of contamination in the vadose zone (including the nature and extent of nonaqueous-phase liquid [NAPL]), refine the CWL CSM, and guide the subsequent saturated zone investigation documented in the Groundwater Assessment Plan (GAP). The results supported the initial CSM for contaminant transport by soil gas to the water table, as originally presented in the Closure Plan. However, this investigation presented direct evidence that demonstrated the extent of NAPL migration from the original disposal area was very limited, thus refining the original CSM that suggested NAPL downward migration may have been more extensive. The results of this investigation are presented in the “Chemical Waste Landfill Unsaturated Zone Contaminant Characterization” report of November 1993 and summarized in the CWL CMS Report of December 2004. The unsaturated zone characterization investigation provided compelling evidence that the CSM originally introduced in the Closure Plan was applicable to the CWL and also provided important information regarding the probable magnitude and extent of NAPL. However, up to this point the three-dimensional nature of the VOC soil-gas plume—that is, how it transitioned from the immediate region around the original disposal pits to the saturated zone approximately 500 feet below—was not well understood. This was largely due to a lack of sampling data for the horizon from nominally 200 to 450 feet bgs, which was fully addressed in early 1997 when the Vapor Extraction (VE) VCM multi-use wells were installed and sampled. From 1994 through 1997, other data were collected that provided important information relative to the CSM and supported characterization of the VOC soil-gas plume and, ultimately, the VE VCM design. Groundwater Assessment and VE VCM Preliminary Field Testing Between 1993, when the Unsaturated Zone Contaminant Characterization was completed, and 1995, groundwater assessment activities were conducted at the CWL according to the requirements described in both Chapter 7.0 of the Closure Plan of December 1992 and the NMED-approved GAP of May 1993. This phase of investigation was documented in the CWL Groundwater Assessment Report (GAR) of October 1995. During late 1995 through 1997, additional fieldwork was accomplished in preparation for conducting a VE VCM. These two interrelated phases of work resulted in better definition of both the nature and extent of the VOC soil-gas plume and the CSM and provided conclusive evidence that the VOC soil-gas plume was contaminating groundwater. These efforts completed the initial VOC soil-gas plume characterization work started as part of the Unsaturated Zone Contaminant Characterization project described earlier. In May 1995, a VE VCM planning process was initiated and included VE VCM design data collection efforts (i.e., additional field sampling and analysis, laboratory treatability studies, and field pilot testing). Concurrent with the VE VCM planning, SNL/NM conducted the Thermally Enhanced Vapor Extraction Study (TEVES) demonstration project just north of the southwestern corner of the CWL during 1995 and 1996. This technology demonstration involved borehole drilling, soil-gas sampling, subsurface heating, and high-rate soil-gas extraction for removal of volatilized VOCs. A significant body of field and analytical data generated during this demonstration was integrated into the CWL remediation (i.e., VCM) process. As described in the CMS Report (SNL/NM December 2004), a partitioning interwell tracer test was also conducted to more accurately estimate the extent and volume of NAPL present in the southwestern corner of the CWL. This was the only location where NAPL was present based upon the results of the Unsaturated Zone Contaminant Characterization. Corrective Action Program Summary In 1996, an expedited approach to the CWL Corrective Action Program was proposed to accelerate risk reduction through source removal; mitigate groundwater impacts; and reduce the complexity, schedule, and cost of final closure. The expedited strategy included two interrelated VCMs, VE and LE, intended to be consistent with the final remedy for the CWL. The two VCMs were developed to address the two main sources of contamination (original waste in the landfill and the resulting VOC soil-gas plume) and to mitigate the impact to groundwater beneath the site. The desired overall effect of both VCMs was to remediate the CWL such that the end-state conditions are protective of human health and the environment. In a general sense, this would be accomplished by reducing TCE concentrations in groundwater to below the regulatory limit, preventing further degradation of groundwater quality by removing and/or controlling the VOC soilgas plume, and removing the original waste and associated soil contamination in the disposal area (i.e., remove the primary source of contamination) such that industrial landuse, risk-based standards and criteria are achieved. VE VCM One of the challenges presented by the VOC soil-gas plume was the relatively thick affected vadose zone, comprised of approximately 500 feet of alluvial and fluvial sediments consisting of various mixtures of clay, silt, sand, and gravel. The sedimentary sequence generally coarsens upwards, with dominantly finer-grained deposits found near the water table and coarser-grained sediments more dominant near the ground surface (upper 100 feet of the vadose zone). The vadose zone was divided into zones on the basis of general stratigraphy and depth from ground surface for engineering design purposes. The final design of the active VE system was largely based upon these zones and their physical characteristics because the geologic framework of the vadose zone directly affects the movement and distribution of soil gas. The VE VCM was designed to reduce and control the VOC soil-gas plume and to prevent further degradation of groundwater. The VE VCM design effort was guided by a series of five numerical performance objectives that were based upon the understanding that the relative level of risk posed by VOC soil gas was directly proportional to how close a specific mass of VOCs was to both the water table (potential drinking water exposure pathway) and the ground surface (inhalation exposure pathway). Thus, a significant amount of treatment effort was directed to those portions of the vadose zone above 200 feet bgs and below 400 feet bgs (referred to as the Shallow and Upper Intermediate Zones and Deep Zone, respectively). In the portion of the vadose zone bounding the groundwater and ground surface, the objective was to reduce detected soil gas VOC concentrations to low levels (i.e., 2 parts per million volume basis [ppmv]). Near the center of the vadose zone, at relatively large distances from the groundwater and atmosphere, the performance objective was higher (i.e., 200 ppmv). The active phase of the VE VCM (forced-air injection and extraction) was conducted from May 1997 through July 1998. The VE VCM operation and results are documented in the VE VCM Final Report of May 2000 and summarized in the CWL CMS Report of December 2004. During the active phase of the VE VCM, approximately 400,000,000 cubic feet (cf) of soil gas were extracted, and 44,000,000 cf of atmospheric air were injected. The hydraulic performance of the VE and air injection systems translated into the removal of approximately 6,500 lbs of VOCs from the subsurface. Additionally, approximately 500 lbs of VOCs were removed during prior VE pilot testing (including the TEVES project) conducted in 1995 and 1996. Of the approximately 30 VOCs measured in the extracted vapors, TCE, acetone, toluene, Freon®-113, and methylene chloride constituted the bulk of the extracted VOCs. The estimated VOC mass remaining in the unsaturated zone at the end of the VE VCM was calculated to be approximately 2,900 lbs based upon the following assumptions:
VOC Soil-Gas Plume Monitoring Since shutdown of the active VE effort on July 29, 1998, several soil-gas monitoring events have been conducted to verify the VOC soil-gas plume was largely removed and stabilized. The methods used and all of the monitoring results through 2004 are presented in the CMS Report of December 2004. The results of this post-active VE phase monitoring effort indicate that rebound of the VOC soil-gas plume (i.e., increasing VOC soil-gas concentration trends throughout the vadose zone monitoring network) is not occurring, and the remaining VOC soil-gas plume is diffusing in a slow and predictable manner. In addition, natural processes are also acting to slowly degrade the remaining plume. Passive Venting VE Phase The passive-venting VE phase has been ongoing since July 1998 utilizing a network of seven, multi-port, soil-gas monitoring wells and two existing groundwater monitoring wells. The wells that were part of the original, active VE VCM network and are still being used for passive venting (i.e., wells equipped with a pressure release valve [Baroball™] include CWL-VMW1, CWL-D1 through -D3, and CWL-UI1 through –UI3. Since completion of the active phase of VE in July 1998, various groundwater monitoring wells have been equipped with a Baroball™ for passive venting, in some cases as a precautionary measure to prevent movement of VOC soil gas through nonairtight well casings (for example, CWL-MW2A as addressed in the CMS Report of December 2004 and the CWL MW2A Plug and Abandonment Plan approved by the NMED). The only groundwater monitoring wells that were part of the active phase of VE consisted of CWL-MW1A, CWL- MW2A and CWL–MW3A. Since completion of the active VE, CWL-MW1A and CWL-MW3A have been dry. CWL-MW2A was plugged and abandoned with NMED approval in June 2004 due to well integrity issues. Currently, CWL-MW1A and CWL-MW3A are the only former groundwater monitoring wells that are part of the ongoing passive venting strategy. LE VCM Immediately following the active VE VCM, the LE VCM was initiated. From September 1998 through February 2002, the former CWL disposal area was completely excavated to a depth ranging from 12 to 30 feet bgs. Discrete, former disposal areas were defined by previous investigations and geophysical surveys and grouped into four excavation areas (North, East-Central, Southeast, and Southwest Areas), separated by “Non-Designated Areas” (NDAs) where no disposal occurred. All former disposal areas were completely excavated to a minimum depth of 12 feet bgs, and the NDAs were excavated to a uniform depth 4 feet bgs and trenched to 12 feet bgs in twelve locations to verify disposal had not occurred. Approximately 52,000 cubic yards (cy) of contaminated soil and debris were removed from the former disposal areas and NDAs. Approximately 46,892 cy of soil excavated from the landfill (approximately 89 percent of the total excavated soil) was disposed of at the Corrective Action Management Unit (CAMU), a co-located unit permitted for the storage, treatment, and containment of CWL remediation wastes. Approximately 70 cy of soil were sent to an approved off-site facility as mixed waste. During January 2003, excavation of one additional verification grid point was performed in the Southwest Area to remove the soil associated with the one detection of benzidine (a semivolatile organic compound [SVOC]). During the LE VCM, a risk-based approach was developed in consultation with the NMED that defined risk-based cleanup standards and criteria (hereafter referred to as risk-based criteria) for the in situ excavation (floor and sidewalls) and backfill material based upon an industrial land-use scenario. The project-specific, risk-based criteria for achieving end-state conditions protective of human health and the environment were submitted to both the NMED and EPA Region 6, and approved by the NMED in October 2000 for RCRA constituents and the EPA in June 2002 for Toxic Substances Control Act (TSCA) constituents (polychlorinated biphenyls [PCBs]). The approved risk-based criteria addressed both the excavation and fill material. A graded approach was used based upon depth below grade; risk criteria were defined separately for the 0- to 5-foot depth (surface criteria, more stringent) and for depths greater than 5 feet bgs (subsurface criteria, less stringent). Consistent with this risk-based approach, backfill (replaceable soil and clean fill) and cover material (clean fill) criteria were applied as follows: clean fill requirements were set according to the more stringent 0- to 5-foot-depth criteria (i.e., surface criteria), and replaceable soil requirements were set, at a minimum, according to the greater-than-5-foot-depth criteria (i.e., subsurface criteria). The LE VCM final risk assessment demonstrated that the excavation and fill materials met these risk-based cleanup criteria. The excavation process, waste management activities, final verification soil sampling analytical results, and final risk assessment were presented in the LE VCM Final Report in 2003. Because sampling of some of the replaceable soil generated during the SOB cleanup effort and clean fill used for the at-grade cover occurred after the LE VCM Final Report was completed, final verification analytical results for these materials were not included. The NMED issued a Request for Supplemental Information (RSI) for the LE VCM Final Report in August 2003, and the DOE and Sandia responded in October 2003. The LE VCM Final Report and associated risk assessment were approved by the NMED on December 16, 2003. The LE VCM excavation was backfilled in two phases, in between which treatment operations at the nearby CAMU were conducted. The first campaign was conducted from June 20 through August 15, 2002 (0 to 40%), and the second was conducted from November 26, 2003, through February 23, 2004 (40 to 100%). The two phases of backfilling activities were based upon the percent volume of fill material returned to the excavation relative to the estimated total volume of soil and debris removed (approximately 52,000 cy). Concurrent with the backfilling effort, LE VCM waste management; SOB sampling, scraping, and closure; and CMS activities were conducted. The SOB closure and CMS activities had a major impact on the backfilling work. Developments in the CMS process changed the backfilling completion requirements and were discussed with the NMED during informal technical meetings prior to implementation in the field. One of the most important changes was the agreement reached with the NMED in March 2004 to install the proposed final cover presented in the May 2003 CWL Remedial Action Proposal (RAP) as an interim measure. Instead of backfilling to grade and creating a central mound as stipulated in the July 2002 CWL Backfill and Compaction Plan, this agreement changed the backfilling end goal to 4 feet bgs to facilitate installation of the cover. Closure of the LE VCM SOB and completion of LE VCM waste management activities were documented in the August 2005 CWL SOB Closure Addendum and February 2006 Waste Management Addendum to the LE VCM Final Report. Both reports were submitted with Quarterly Closure Progress Reports, and the NMED approved the SOB Closure Addendum on October 25, 2005. Post-VCM Monitoring and Chromium Investigation Completion Following completion of the two VCMs, the NMED required additional groundwater and VOC soil-gas monitoring. Two primary constituents of concern (COCs) had been detected at concentrations above the respective MCLs: TCE and chromium. Since completion of the VE VCM in July 1998, TCE concentrations in site groundwater samples have remained below the MCL of 5 μg/L with one exception that is interpreted as an anomaly and not representative of actual groundwater conditions. To complete the evaluation of chromium in groundwater, two deep regional aquifer wells were installed during March and April 2003 and eight sampling events were conducted as required by the installation agreement with NMED. No constituents (VOCs or metals, including chromium and nickel) were detected above regulatory standards. The results of all eight sampling events and completion of the chromium investigation is documented in the CWL Quarterly Closure Progress Report of August 2005. Based upon these deep well sampling results, previous studies documented in the CWL GAR of October 1995, and historic groundwater monitoring results presented in the CWL CMS Report of December 2004, the analytical results that exceeded the MCL for chromium are related to well construction (stainless steel screens) and/or turbidity (sediment suspended in the groundwater caused by high-volume purging methods), and not contamination that has migrated from the disposal areas. Soil-gas monitoring performed since completion of the VE VCM and the updated CSM presented in the December 2004 CWL CMS Report indicate that the VOC soil-gas plume is stable (not rebounding) with generally decreasing concentration trends, and will not impact groundwater in the future such that the MCL for TCE is exceeded. A detailed history of groundwater and soil-gas monitoring at the CWL is presented in the December 2004 CWL CMS Report and has been updated and verified in ongoing CWL Quarterly Closure Progress Reports submitted since completion of the revised CMS Report. CMS Process and Chapter 12 of Closure Plan Evolution Based upon the success of the VCMs, the path to closure for the former CWL was reevaluated and documented. Chapter 12 of the Closure Plan was amended to identify the steps to closure, considering the condition of the site following the VCMs and the complex regulatory environment, which required a transition from closure under interim status to preparation of a post-closure care permit application. The DOE and Sandia submitted the revised Chapter 12 in February 2003, which was approved with conditions by the NMED in May 2003. As defined in the amended Chapter 12, the remaining decision points in the closure process were to be based upon three documents: the CWL CMS Report, the RAP, and the Post-Closure Care Plan (PCCP). The DOE and Sandia submitted the CWL CMS Report, the RAP, and the PCCP on May 20, 2003. On December 12, 2003, the NMED rejected the CWL CMS Report and postponed the review of the PCCP and RAP pending the approval of a revised CMS Report. The NMED letter of December 2003 directed that the CMS Report be restructured to focus on the current conditions of the landfill following completion of the VCMs, requested additional data collection (groundwater and soil gas), and required a more detailed presentation and analysis of historical investigation, monitoring (VOC soil-gas plume and groundwater), and VCM analytical results. Resolution of all NMED CMS Report comments and the path to final closure were achieved through informal technical meetings conducted throughout Calendar Year 2004. This 10-month process is documented in the CWL CMS Report comment response document of October 2004, with which the NMED concurred in December 2004. The revised CMS Report was submitted in December 2004 and contained the revised RAP as a supporting annex. The revised CMS Report concluded that the current post-VCM condition of the site was adequately protective of human health and the environment and recommended an at-grade vegetative soil cover as a final remedy. The submittal of December 2004 also contained a revised version Chapter 12 of the Closure Plan that was modified to be consistent with the latest guidance from the NMED. Interim At-Grade Cover In April 2004, pending NMED review and approval of the revised CMS Report, the DOE and Sandia requested approval to install the at-grade vegetative soil cover design presented in the RAP as an interim measure. Based upon informal discussions with the NMED that were intended to identify and address any concerns regarding the proposed cover design, additional information was provided to the NMED on July 29, 2004; the additional information included confirmation of a design change requested by the NMED. On September 22, 2004, the NMED approved this request with conditions. The conditions of approval were addressed in the subsequent revised RAP that was submitted as Annex I of the revised CWL CMS Report in December 2004. Construction of the atgrade vegetative soil cover was begun in March 2005 and completed in September 2005. Post-Closure Care Plan and Chapter 12 of Closure Plan Revisions The PCCP included as part of the May 2003 submittal was deemed administratively incomplete by the NMED in September 2004 and was withdrawn by the DOE and Sandia in December 2004. In response to NMED direction, the scope and content of the PCCP was changed to address the post-closure permit requirements under 20.1.4.900 NMAC, incorporating 40 CFR 270.1(c) and 40 CFR 270.28. The revised PCCP was submitted to the NMED in September 2005 and was to be incorporated as part of the SNL/NM Part B permit renewal application according to NMED direction documented in the PCCP administrative completeness determination of September 2004. In February 2006, the NMED provided comments to Chapter 12 of the Closure Plan that was submitted with the revised CMS Report in December 2004. In accordance with NMED direction, the public comment period and final approval process for the CWL Post-Closure Care Permit were changed. The Permit would no longer be amended to the SNL/NM Part B application as directed in September 2004; instead, it would be included and approved as part of the ongoing Class 3 Closure Plan amendment initiated by the DOE on May 20, 2003, which also included the revised CMS Report of December 2004 and this latest revision to Chapter 12 of the Closure Plan of February 2006. In February 2006, the NMED also clarified that achievement of closure and the initiation of the CWL post-closure care period would occur after NMED approval of this Final RCRA Closure Report. Upon approval of the Closure Report, the Closure Plan would no longer be in effect and the CWL Post-Closure Care Permit would be the sole source of operating conditions for the former CWL. Until this Final RCRA Closure Report is approved by the NMED, groundwater monitoring at the former CWL will continue according to the requirements of the Closure Plan of December 1992 and associated NMED-approved revisions of March 1998 and June 1998. Under the Closure Plan, VOC soil-gas monitoring is not required. CONSTITUENTS OF CONCERN Excavated material that was of concern for worker exposure include: compressed gas cylinders, mercury vapors, heavy metals, pyrophoric materials, strong acids, unreacted chemicals, unexploded ordnance and explosive compounds, toxic gases, water reactive chemicals, radioactive materials, and medical waste. All of these classes of materials were encountered during the excavation without injury or incident and the primary hazards at the site have been neutralized, deactivated, and/or removed. The primary contaminants of enduring concern at the CWL are volatile organic compounds (VOCs) and metals. The primary VOCs of concern are TCE, dichloromethane (also known as methylene chloride), tetrachloroethane (sometimes referred to as PCE), 1,1-dichloroethene (1,1-DCE), 1,1,1-trichloroethane (1,1,1-TCA), and carbon tetrachloride. Though many other types of VOCs were disposed of in the CWL, these compounds were chosen for top priority based on the following list of criteria: toxicity, resistance to biodegradation, and disposal quantity. The primary inorganic contaminant of concern is chromium, although arsenic, mercury, lead, and a host of other heavy metals have been found in the soils in significant concentrations. It is estimated that over 4290 gal (16,500 L) of chromic acid solution were disposed of in the chromic acid pits. The chromium was disposed of in its hexavalent state, which typically forms water soluble anions that adsorb weakly to soil. One study indicates that interactions with native soils cause the chromium to form relatively insoluble calcium chromate, binding the chromium in the trivalent form. However, chromium has apparently migrated to a depth of approximately 75 ft (23 m) below grade. Other equally toxic metals, such as beryllium, were also disposed of in the CWL, but the volumes were much less. These other metals typically form cations, which adsorb strongly to soil and therefore do not have a great potential to migrate. CURRENT STATUS OF WORK Upcoming CWL Closure Plan reporting activities include preparing and submitting the Final Resource Conservation and Recovery Act (RCRA) Closure Report, expected to be submitted in CY 2008 after NMED approval of the CMS Report has been received. The Final RCRA Closure Report will document both the backfilling of the former CWL and installation of the cover. On May 21, 2007, the NMED issued, for public comment, the draft post-closure care permit for the CWL. Also included in the public notice was the Corrective Measures Study Report and the Closure Plan amendment (changes to Chapter 12 revising the closure process). On July 19, 2007, DOE and Sandia responded in opposition to the issuance of the CWL post-closure care permit as drafted and offered a number of comments, the most important of which were related to groundwater and vadose zone monitoring. In addition, DOE and Sandia requested that a public hearing be scheduled to address these outstanding issues. WASTE VOLUME ESTIMATED/GENERATED Wastes generated during excavation of the CWL included:
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