MCGAFFEY AND MAIN GROUNDWATER PLUME
On this page:
- What Is Being Done to Clean Up the Site?
- What Is the Current Site Status?
- EPA’s Involvement at the Site
- Activity and Use Limitations
On related pages:
The 550-acre McGaffey and Main Groundwater Plume site is located in Roswell, New Mexico. The site includes locations where several dry cleaners operated from 1956 to 1963. These operations contaminated soil and soil vapor, indoor air, and groundwater with PCE and TCE. PCE has been detected at levels over 10,000 micrograms per liter (μg/L) in several ground water monitoring wells on the 1100 block of Main Street where three former dry cleaners operated. Soil vapor concentrations exceeding 11,000,000 micrograms per cubic meter (μg/m3) have also been detected, and a PCE plume in ground water extends over two miles to the southeast of the 1100 block of Main Street. From 2008 to 2015, the leading edge of the plume has expanded about 2200 feet to the southeast. A combined vapor intrusion mitigation system (VIMS) and enhanced soil vapor extraction (ESVE) system was installed in the source area in 2012 and 2013. The VIMS has successfully treated the vapor intrusion and has been shutdown since April 2015. The ESVE system is currently operational and based on a rebound test conducted between December 2016 and June 2017, will in the near future be placed on an intermittent pulse on/off operation (instead of continuous). A remedial design of the Source Area Ground Water (SAGW) has been complete and implementation is pending funding. Addtional information is being collected in the distal Ground Water Plume (GWP) area and a Five-Year Review Addendum is planned for September 2018 to determine the site protectiveness.
What Is Being Done to Clean Up the Site?
The Record of Decision (ROD), which documents the preferred selected remedy, was issued on September 30, 2008. The ROD selected a multi-component remedy employing a phased implementation approach. The remedy included: 1) Source Area Soil and Indoor Air (vapor mitigation systems at six commercial buildings and soil excavation with a contingency for soil vapor extraction [SVE]), 2) Source Area Groundwater (pump, pretreat, and discharge to the Roswell publically-owned treatment works [POTW]), and 3) Groundwater Plume (pump and discharge to Roswell POTW for treatment, and enhanced reductive dechlorinated [ERD] for plume hot spot area).
EPA completed the remedial design (RD) phase for construction of Vapor Intrusion Mitigation System (VIMS) and Soil Vapor Extraction (SVE) in 2011. Construction completion of VIMS and SVE was achieved in September 2012. The Tetrachloroethene (PCE) concentration in the VIMS influent piped to a central treatment facility decreased from 72,000 micrograms per cubic meter (ug/m3) immediately after VIMS start up in December 2012 to 12.7 ug/m3 in April 2014. A total of 430 pounds of PCE are estimated to have been removed by the combined VIMS and SVE technologies to-date.
In 2015, EPA headquarters staff (the Optimization Team) completed a study of ongoing and future remedy construction and operations. Remedial Process Optimization is the systematic site review by a team of independent technical experts, at any phase of a cleanup process, to identify opportunities to improve remedy protectiveness, effectiveness and cost efficiency, and to facilitate progress toward completing site remediation. The report included recommendations to prioritize the remaining remedial action at the Site. For the VIMS, because of the steadily declining sub-slab soil vapor PCE and Trichloroethene (TCE) concentrations, it was concluded the VIMS could be shut down but additional sampling was recommended to assess the potential for rebound, at least twice following a 6-month shutdown period. For the SVE system, because of the steadily decreasing vapor concentrations, the Optimization Team recommended switching to pulsed or part-time operations. At the time of the study, the Optimization Team identified the presence of persistent PCE concentrations at several locations that may justify installing up to four new SVE wells. The VIMS and pulsed SVE operations have already been implemented. EPA is considering the SVE system expansion recommendation.
Shutdown of VIMS was implemented for 12 months (April 2015 to April 2016), and no adverse indoor air impacts have been observed. There were no detections of PCE in the indoor air rebound samples that exceeded the current EPA regional screening level of 11 micrograms per cubic meter during the 12-month VIMS shutdown period. The VIMS rebound test was performed to evaluate whether the SVE system alone can effectively intercept enough of the vapor intrusion pathway to protect indoor air. Throughout the April 2015 through April 2016 period, while the VIMS was shutdown, the indoor air EPA Regional Screening Levels (RSL) for PCE was not exceeded in any of the samples collected from the VIMS-equipped buildings. The primary conclusion from the VIMS rebound test is that the SVE remedy appears to be effectively controlling the vapor intrusion pathway when operated in a continuous mode. Transition of the SVE system from continuous to pulsed operations represents a logical progression for the SVE remedy. However, this transition will be implemented cautiously, such that the vapor intrusion pathway remains controlled. The VIMS remained shut down through December 2017, while the SVE system remained shut down through November 30, 2017, to allow for completion of a contaminant of concern (COC) concentration rebound test in SVE Zones 1, 2, and 3 and to complete SVE condensate pretreatment and condensate discharge permit modifications. The SVE system was restarted in November 2017 for a pulse-on phase and will be pulsed off in March 2018.
In February 2016, EPA was contacted regarding the proposed purchase of two parcels on the 1100 block of South Main Street for the construction of a car wash facility. The two buildings located on these parcels, which were equipped with VIMS, were slated for demolition by the new property owner. Therefore, EPA’s remediation contractor prepared a technical memorandum in August 2016 with recommendations for decommissioning the VIMS at these two buildings. The remaining four VIMS are being retained until SVE optimization is complete. By mid-January 2017, the VIMS at the two locations were fully decommissioned and the buildings were demolished.
The remedial design for the Source Area Ground Water (SAGW) remedy component (i.e., extraction of contaminated ground water and ex situ treatment) was started in 2015, and completed in September 2017. Prior to the start of the RD in 2015, EPA’s Optimization Team recommended that the SAGW remedy remain a high priority for implementation and should focus on source control for the portion of the plume needed to allow for aquifer restoration in the Groundwater Plume (GWP) area. Consistent with the Optimization Team’s recommendations, the remedial design for the SAGW remedy component includes ground water extraction from one existing well, identified as P3-1, at a rate of 20 gallons per minute, treatment of the ground water using an air-stripper treatment plant to be installed at the existing CTF, and discharge of the treated water to the City of Roswell publicly owned treatment works (POTW). Discharging treated ground water to the POTW will enable all treated ground water to be beneficially reused for irrigation or other purposes.
The New Mexico Environmental Department (NMED) performs remedial design investigations for the groundwater plume and hot spot areas. In September 2013, NMED completed the ERD RD for the hot spot area of the plume. NMED also initiated the RA at the hot spot in May 2014; 30 monitoring and injection wells were installed. However, no amendment injections have been delivered yet. The EPA and NMED are currently collaborating on finding ways to optimize the remedy, pertaining to addressing the source area groundwater PCE contamination and the broader groundwater plume, with the assistance of an EPA Optimization Team.
The GWP remedy is intended to address the GWP hotspot and to hydraulically contain the downgradient, diffuse leading edge of the PCE plume to prevent further expansion. The hotspot is an area within the GWP, located approximately 1 mile downgradient of the Source Area (Figure 1), having moderate to high concentrations of PCE (typically in excess of 250 μg/L) relative to the concentrations present at other well locations within the GWP. NMED designed and installed an ERD bio barrier remedy for the GWP hotspot between 2013 and 2014. The ERD bio barrier was designed before the other ground water remedy components in order to proceed with remedy implementation. No ERD injections have been completed to date because of changes in site conditions that identified additional contamination that could require further design consideration.
Ground water extraction and treatment or hydraulic control of the leading-edge portion of the downgradient plume has not been implemented. More plume characterization data needs to be collected. An update of the risk assessment needs to be performed to reevaluate the need for this remedy component. Ground water extraction and treatment or hydraulic control may not be needed if future well surveys show that the ground water is not being drawn from the contaminated aquifer.
The Optimization Team’s recommendations for the GWP area were to assess risks from use of domestic wells and from possible ground water vapor intrusion to indoor air and soil gas, and to provide point-of-use GAC treatment systems if needed. A point-of-use system treats water at the individual wellhead or at the point where it is accessed by the consumer (e.g., at the tap). The second recommendation for the GWP area included additional characterization and treatment of the GWP hotspot. Pertaining to the ERD remedy, the Optimization Team concluded that ground water extraction and treatment may be a more efficient and cost-effective remedy for the hotspot.
What Is the Current Site Status?
The SVE system was restarted in November 2017 and is currently operating while testing is underway to determine the optimal pulsed on/off periods. A Public Information Campaign has been initiated in the distal GWP to inform the public of potentially impacted private drinking water wells. The NMED will provide water well testing free of charge to any potentially impacted wells within this area. Work in ongoing to complete a Five-Year Review Addendum by September 2018 and determine the site protectiveness.
EPA’s Involvement at the Site
EPA scored the site in May 2001 using the hazard ranking system and established a score of 50 based on the ground water pathway. The air, soil, and surface water pathways were not evaluated. EPA proposed the Site to the NPL on September 13, 2001 (66 Fed. Reg. 47612), and placed the Site on the NPL effective October 7, 2002 (see 67 Fed. Reg. 56757). The Comprehensive Environmental Response, Compensation, and Liability Act Information System (CERCLIS) identification number is NMD0000605386. The EPA performed a phased Remedial Investigation at the Site between August 2002 and December 2004. A description of this work and its findings are highlighted in Section 2.5 of this ROD. The details of the Remedial Investigation are documented in the Remedial Investigation report.
Activity and Use Limitations
At this site, activity and use limitations that EPA calls institutional controls are in place. Institutional controls play an important role in site remedies because they reduce exposure to contamination by limiting land or resource use. They also guide human behavior. For instance, zoning restrictions prevent land uses – such as residential uses – that are not consistent with the level of cleanup.
For more background, see Institutional Controls.
For soil and soil vapor, the ROD identified termporary institutional controls (TICs) that should be implemented to protect against inadvertent exposure to soil and soil vapor contamination during the timeframe between remedial construction and achievement of RAOs. These ICs consist of amendments to the City building code that requires any future buildings in the Source Area to be constructed with vapor barrier or control systems until RGs are achieved. The ICs identified in the ROD also call for notifications to be filed with deed/property records for Source Area parcels that identify COC concentrations in the soil and soil vapor underlying the properties. The FYR site inspection (described in Section IV) included a review of the status of the ICs. This review found that no notifications had been filed with the County Clerk’s office, and there were no changes to the City building codes in the Source Area.
For the alluvial aquifer ground water, the ROD identified TICs that should be implemented to protect against inadvertent exposure to contaminated alluvial aquifer ground water. These TICs included notification to new well permit applicants in the GWP area, by the New Mexico Office of the State Engineer (NMOSE), identifying the location and depth of the COCs. The TICs also included the development and implementation of a City/County ordinance that would prohibit installing new wells within the GWP area.
On May 2, 2016, the NMOSE granted NMED’s request to implement a temporary well drilling moratorium for new wells located within a designated area, which includes the entire area within the contaminated GWP boundary. NMED used the NMOSE database to inventory the private wells located within the GWP.