4501_Henderson_MSWLF_GWCAMNARequest_DIN28477_20170716

Golder Associates NC, Inc. 5B Oak Branch Drive Greensboro, NC. 27407 USA Tel: [phone] Fax: [phone] www.golder.com Engineering Lic. No. C-2862/Geology Lic. No. C-399 Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation
July 26, 2017 083-9650617.300
Ms. Jaclynne Drummond
Compliance Hydrogeologist North Carolina Department of Environmental Quality
Division of Waste Management – Solid Waste Section 2090 US Highway 70
Swannanoa, NC 28778 828-296-4706
RE: REQUEST FOR MONITORED NATURAL ATTENUATION PARAMETER MODIFICATION
CLOSED HENDERSON COUNTY LANDFILL, PERMIT NO. 45-01
HENDERSON COUNTY, NORTH CAROLINA
Dear Jackie:
On behalf of Henderson County (The County), Golder Associates NC, Inc. (Golder) requests a modification to the monitored natural attenuation (MNA) parameter list and sampling schedule for future sampling
events. This request is allowed per the North Carolina Department of Environmental Quality (NC DEQ) guidance document titled “Examples of Approved Groundwater Corrective Measures for Solid Waste
Management Facilities” and the facility’s Corrective Action Plan (CAP), dated June 24, 2015. Both documents state that the MNA parameter list and sampling frequency may be re-evaluated after completion
of four baseline sampling events. The fourth baseline sampling event was completed during the first semi-annual water quality monitoring event of 2017 that occurred in March.
The current full list of MNA parameters consists of the following: alkalinity, carbon dioxide, chloride, biological oxygen demand (BOD), chemical oxygen demand (COD), ethane, ethene, methane, hydrogen,
ferrous iron, nitrate, nitrite, sulfate, sulfide, total organic carbon (TOC), and volatile fatty acids (VFAs). Based on a detailed data review of the four baseline sampling events, an abbreviated, site-specific list is
proposed that focuses on the critical parameters to evaluate MNA for this site. The proposed abbreviated list of MNA parameters consists of the following: alkalinity, carbon dioxide, chloride, ethane, ethene,
methane, hydrogen, ferrous iron, nitrate, and sulfate.
The County requests that the abbreviated MNA parameter list be monitored semi-annually. As part of the
sampling program and based on similar approvals at other sites, the program will be supplemented with the full list of parameters for the last two semi-annual events of the first 5-year evaluation period (second
semi-annual water quality monitoring event of 2019 and first semi-annual water quality monitoring event of 2020) for the Corrective Action Performance Evaluation Report (CAPER). The abbreviated list would then
be used for all semi-annual events starting with the second 2020 event to the final year (last two semi-annual events) of the next 5-year evaluation period, when the full list would again be monitored.
The abbreviated list consists of parameters that have the most influence when evaluating site-specific analytical data using the U.S. Environmental Protection Agency’s (EPA’s) Natural Attenuation Screening
Protocol. The parameters for which we are recommending a reduced sampling frequency have provided limited data with which to evaluate anaerobic degradation during the four baseline sampling events at the
facility, as described below:
 Concentrations of sulfide have been below the EPA’s natural attenuation screening level
of 1 milligram per liter (mg/L)
 Most of the VFAs in groundwater have been primarily non-detect and/or sporadically
detected at estimated concentrations below the EPA’s natural attenuation screening level of 0.1 mg/L
 Most of the TOC concentrations have generally been below the EPA’s natural attenuation screening level of 20 mg/L