Groundwater contamination has steadily declined in all areas of concern at the Muscatine County Landfill (MCL), according to a report presented to the Muscatine City Council at its July 11th In-Depth Session.
The fifteen-year effort by the Iowa Department of Natural Resources (DNR), the Muscatine County Solid Waste Management Agency (MCSWMA), and the City of Muscatine to correct problems at the MCL, specifically in the closed sections of the landfill, has taken significant positive steps in the last four years. “The hiring of Barker Lemar, and especially Tim Buelow, to assist with the assessment of the [MCL]has been very beneficial to the City, both environmentally and financially,” Gregg Mandsager, Muscatine City Administrator, said. “Tim is very knowledgeable, and a great resource as we work to meet the requirements of the Consent Order.”
Buelow, P.E., of Barker Lemar Engineering Consultants, reported that three areas of identified groundwater recently had samples taken that indicate contaminate levels have steadily declined. The contamination comes from the older section of the landfill, specifically ravines two through seven, and not from any of the newer cells. The primary source of the groundwater impact comes from leachate (a liquid that is created when infiltrating water comes into contact with solid waste). “It is very likely that the problems flow from the unlined areas that were developed years ago,” Buelow said. “Those areas are now closed, but we are still dealing with the consequences of how waste was managed in the past.”
The DNR rewrote the groundwater protection rules in 2007 that expanded the parameters for groundwater sampling. Additional sampling that began in 2008 revealed more groundwater impact was present than previous sampling had indicated.
The DNR and the MCSWMA entered into an Administrative Consent Order agreement on February 11th, 2015, that established a timeline for addressing and correcting the issues at the landfill. They amended the agreement in April 2017 to establish a new timeline for completing plume delineation by September 30th, 2019, and completing the Assessment of Corrective Measures (ACM) report by December 31st, 2019.
The reason for the change in the timeline for completion of the ACM included updating background groundwater concentrations that resulted from an improved and more representative sampling technique implemented at the landfill – a DNR requirement. “The DNR was concerned that previous sampling had sediment in the groundwater samples that could cause the appearance of increased concentrations of metals in groundwater,” Buelow said. “Changing to low flow sampling to get the sediment out of the water gave us a better indication of what those levels actually were. We found that concentrations were lower when the sediment was removed.”
The MCSWMA installed fourteen groundwater monitoring wells from 2017 through early 2019 for plume bracketing or acquiring additional background data that would alleviate concerns with the representativeness of past data.
Three areas of groundwater impact identified at the landfill included the East side, South side, and Southwest side. Results from the sampling indicated that the groundwater impact appears to come from leachate migration on the East side, gas migration on the South side, and from historical overflows of the leachate storage tank located on the Southwest side. Each area, however, has seen declining or steady concentration levels.
Buelow noted that the requirements of the Consent Order almost exclusively cover compliance to the regulations pertaining to groundwater. The culmination of those requirements and the Consent Order constitute the selection of a groundwater remedy.
One of those remedies may include natural attenuation at the South and Southwest locations. Natural attenuation relies on natural processes to clean up or attenuate pollution in soil and groundwater. Improving the final cover grading over ravine five along with natural attenuation is a likely remedy for the East side.
The Muscatine City Council approved the contract with Barker Lemar Engineering Consultants to develop the ACM at the Council’s July 18th meeting. Once the ACM receives the approval of the DNR, a public meeting will take place, followed by the selection of a remedy. The public meeting and selection will occur in 2020 or later, depending on review and approval schedules.