HomeMy WebLinkAbout9809-CDLF_AssmtMonWrkpln_DIN27367_20161212
December 12, 2016
Mr. Ervin Lane, Hydrogeologist
NC Division of Waste Management
Solid Waste Section
Mail Service Center 1646
Raleigh, NC 27699-1646
Re: Assessment Monitoring Workplan
Westside C&D Facility
Wilson, North Carolina
Permit #98-09
Dear Mr. Lane:
In accordance with correspondence from your office dated October 14, 2016 and November
3, 2016, this Assessment Monitoring Workplan was developed to address the requirement of
15A NCAC 13B .0545(a)(3). This Workplan provides for further evaluation of the recurrent
presence of 1,2-dichloropropane in monitoring well GMW-3, which is located hydraulically
downgradient of the Westside C&D facility.
As described below, this Assessment Monitoring Workplan provides a description of
background conditions, proposed assessment activities, and a schedule for implementation to
address the limited exceedance of the NC 2L Groundwater Standards.
Background Information
The Westside Construction and Demolition (C&D) facility is located approximately 3.5
miles east of downtown Wilson, NC at the intersection of NC 42 and Tucker Court (Figure
1). The Westside C&D facility is located on property that was previously used as farmland
and later as a borrow site for the closed MSW landfill site which is located approximately
350 feet to the east of the Westside C&D property boundary. The western boundary of the
site is established by the center-line run of Buck Branch. The adjoining properties on the
west consist of the Mohesky Farm and the Tucker Farm, both of which are now owned by
Wilson County (Figure 1).
Surrounding properties within 1,500 feet of the site are currently being used for farming,
residential, or solid waste management purposes. Land south of the site is mostly wooded
land with wetlands associated with the Toisnot Swamp. Land immediately west of the site is
owned by Wilson County and used for recycling/reclamation and other solid waste
management activities. Land north of the site is mostly used for farmland with wooded
areas. Land east of the site is occupied by the closed Wilson County MSW Landfill.
Site Geology and Hydrology
The subsurface soil in the area of the Westside C&D facility is classified as being in the
Yorktown Formation. Information gathered from the Geologic Map of North Carolina, 1985
and The Geology of the Carolina, 1991, cites that sediments of the Yorktown Formation are
fossiliferous clay with varying amounts of fine-grained sand, silty sand, sandy silt, silty clay,
and bluish gray shell material. These types of deposits are found mainly north of the Neuse
River and are commonly concentrated in lenses and vary in vertical and horizontal
dimensions. The topography of the Coastal Plain is characterized by flat to gently undulating
relief.
The subsurface conditions observed at the site reflect the regional Coastal Plain
characteristics. The depositional environment is influenced by Buck Branch and Toisnot
Swamp, where fluvial sediments are interlaced with marine sediments in an estuarine
environment. The local stratigraphy is characterized by relatively thin layers of fluvial and
marine silt, sand, and clay in varying textures and colors. The water bearing zone is present
in coarse and well graded sand layers, typically beneath surficial clay. Below the fluvial
sediments, a marine clay layer is consistently encountered. This marine clay unit is typically
dark grey, fat, and laminated with microlenses of fine sand. Below the marine clay, a dark
greenish grey silty clayey sand overlies the residual, fully weathered bedrock. The bedrock
was encountered approximately 30-35 feet below the disturbed land surface, at an elevation
of 60 to 64 feet above mean sea level.
The aquifer testing performed for the site indicates that the upper water table aquifer provides
hydraulic conductivity values which are directly related to presence of low permeability
clays. The average hydraulic conductivity value for wells completed in primarily sandy
material (P-104, P-105, P-108) is 4.09 x 10-2. The average hydraulic conductivity for wells
completed in primarily clayey material (P-103, P-106, P-109) is 3.29 x 10-4. Based on the
heterogeneity of the subsurface materials encountered during installation of the wells, the
hydraulic conductivity is expected to vary based on the presence/absence of clayey soil.
Existing Monitoring Well Network
There are four groundwater monitoring wells located at the Westside C&D facility that
comprise the existing groundwater monitoring system (Figure 2). Monitoring well GMW-1
is located on the northeast corner of the landfill area and serves as the upgradient
groundwater monitoring well providing background water quality. Monitoring well GMW-2
is located on the southwest side of the landfill and monitors hydraulically downgradient
groundwater quality. Monitoring well GMW-3 is located on the western side of the landfill
and monitors hydraulically downgradient groundwater quality. Monitoring well GMW-4 is
located on the northwest side of the landfill and monitors hydraulically downgradient
groundwater quality.
Groundwater Monitoring Laboratory Results
Groundwater monitoring has been conducted on a semi-annual basis since October 2004.
Samples collected at the site have shown only minor concentrations of volatile organic
compounds (primarily 1,2-dichloropropane) and naturally occurring inorganic compounds.
Based on the occurrence of two consecutive groundwater monitoring event in which 1,2-
dichloropropane was reported above the 2L Groundwater Standard, an Assessment
Monitoring Workplan was requested by the NC Solid Waste Section. Monitoring well
GMW-3 has reported 1,2- dichloropropane concentrations above and below the EPA Method
Reporting Limit on several occasions:
Date of Sample 1,2-Dichloropropane - ug/l
May 2005 BQL
December 2005 BQL
June 2006 BQL
November 2006 BQL
June 2007 0.47 J
October 2007 0.83 J
May 2008 0.43 J
November 2008 0.34 J
May 2009 0.48 J
November 2009 BQL
May 2010 0.54 J
November 2010 BQL
June 2011 1.70
November 2011 1.17
May 2012 0.987 J
December 2012 0.554 J
May 2013 0.686 J
November 2013 0.40 J
May 2014 BQL
November 2014 BQL
April 2015 BQL
October 2015 2.2
April 2016 2.3
November 2016 1.4
J = Estimated concentration, above Method Detection Limit
but below Method Reporting Limit
NC Groundwater Standard for 1,2-Dichloropropane = 0.6 ug/l
The recent November 2016 Groundwater Monitoring Event was evaluated for the full
Appendix II constituent list, which included: volatile organic compounds (VOCs) by EPA
Method 8260B, semi-volatile organic compounds (SVOCs) by EPA Method 8270D,
organochlorine pesticides by EPA Method 8081B, chlorinated herbicides by EPA Method
8151A, polychlorinated biphenyls by EPA Method 8082A, Appendix II inorganics by EPA
Methods 6010D/6020B, mercury by EPA Method 7470A, cyanide by EPA Method 9014,
and sulfide by Method SM4500S2D-2000.
The November 2016 Appendix II analyses confirmed the presence of 1,2-dichloropropane in
GMW-3 at a slightly lower concentration than prior samples (see table above). The
Appendix II analyses reported one other VOC above the laboratory method reporting limit;
the compound tetrahydrofuran was reported in monitoring well GMW-2 at a concentration of
2.7 ug/l. There is no Solid Waste Section Limit (SWSL) or 2L Groundwater Standard for the
compound tetrahydrofuran.
The Appendix II analyses reported no inorganic compounds above the 2L Groundwater
Standards in any of the downgradient groundwater monitoring wells (GMW-2, GMW-3, or
GMW-4). However, the inorganic compounds barium, beryllium, cadmium, cobalt, and zinc
were reported above the SWSLs but below the 2L Groundwater Standards.
The Appendix II laboratory analyses for semi-volatile organic compounds, organochlorine
pesticides, chlorinated herbicides, polychlorinated biphenyls, mercury, cyanide, and sulfide
did not report any detectable concentrations above the laboratory method reporting limits,
SWSLs, or 2L Groundwater Standards.
Assessment Procedures
The contaminant assessment for the reported concentrations of 1,2-dichloropropane in
monitoring well GMW-3 is proposed to be conducted in two phases. The first phase will
consist of an assessment of soil quality above the water table in the vicinity of the
groundwater monitoring well GMW-3 and off-site soils at the Tucker Farm which were used
during construction of the Westside C&D landfill. If detectable concentrations of 1,2-
dichloropropane are identified in any of the unsaturated soil samples, an Alternative Source
Demonstration will be prepared to address this contaminant source. The compound 1,2-
dicloropropane is a potential constituent of soil fumigants1 used for nematode control in
farming operations and, as the area has historically been used for farming, may be
responsible for the observed groundwater conditions.
If the results of the soil investigation does not identify the presence of 1,2-dichloropropane in
the unsaturated zone or off-site borrow soil sources, a second phase will be conducted. The
second phase will consist of the installation of one shallow monitoring well to determine the
lateral extent of groundwater contamination downgradient of the Westside C&D operations.
______________________________________________________________ 1 Groundwater Chemicals Desk Reference, 2nd Edition 1996
John H. Montgomery: Lewis Publishers - CRC Press, Inc.
A description of the two proposed phases of contaminant investigation is provided below:
Phase I – Soil Investigation
To evaluate soil quality in the vicinity of the monitoring well network and Tucker
Farm off-site borrow source, a total of five soil samples will be collected. Three of
the soil samples will be collected in the area of the Westside C&D facility’s
monitoring well GMW-3 as shown on Figure 2. An additional two soil samples will
be collected on the former Tucker Farm property (Figure 1) to evaluate borrow area
soil. During construction of the Westside C&D facility, significant quantities of soil
were transported from the Tucker Farm in order to establish the required separation
between the bottom of the landfill cell and the seasonal high water table. The exact
location of the Tucker Farm samples will be determined in the field based on
accessibility and the location of the borrow area.
Based on the volatility of 1,2-dichloropropane and the shallow depth to groundwater
in the area to be investigated, all soil samples will be collected at a depth of 12” - 18”
below land surface. The samples will be collected with a stainless steel hand auger
which is decontaminated between samples as follows:
Brush off loose soil and vegetation
Wash with phosphate-free soap and water
Rinse with distilled water
Rinse with isopropyl alcohol
Rinse with distilled water
Air dry
The samples will be collected as undisturbed soil plugs using a Terra Core™ transfer
tool and placed in laboratory prepared VOA vials pre-filled with the appropriate
preservatives. All soil samples will be analyzed for low level volatile organic
compounds by EPA Method 8260, which includes 1,2-dichloropropane. For quality
control purposes, one trip blank and one equipment blank will be prepared and
maintained with the field samples. All samples will be stored on ice and hand-
delivered to the analytical laboratory using chain-of-custody controls.
If the soil investigation in area of monitoring well GMW-3 or off-site Tucker Farm
borrow source area identifies the presence of 1,2-dichloropropane, an Alternate
Source Demonstration document will be prepared to address the observed
groundwater exceedance. If the soil investigation does not identify the presence of
1,2-dichloropropane in the soil, the Phase II activities as described below will be
implemented.
Phase II – Groundwater Assessment
To evaluate the lateral extent of groundwater contamination downgradient of the
Westside C&D facility, one shallow groundwater monitoring well will be installed in
the approximate location shown on Figure 2. This well location will allow for a
determination of the lateral downgradient migration of the observed contaminant in
the vicinity of monitoring well GMW-3.
A licensed drilling contractor will install the new well to a depth of 20 feet below
land surface which will be completed with an above-grade lockable steel protector set
in a concrete pad. The well will be constructed of Schedule 40 PVC casing with a 10-
15 foot slotted screen section. Monitoring well construction will comply with the NC
2C Well Construction Standards and a written Well Completion Record will be
developed and certified by the drilling contractor. After construction the well will be
developed to remove any fine sediment introduced during drilling.
After the grout backfill and pad for the newly constructed well has cured, the new and
existing wells in the monitoring network will be purged and sampled for laboratory
analysis. Based on the results of the Appendix II monitoring conducted in November
2016, the new and existing wells will be analyzed for volatile organic compounds by
EPA Method 8260b, including tetrahydrofuran.
A written report will be prepared which provides the following information:
Description of Phase I soil investigation
Boring logs and Well Completion Records
Groundwater sampling activities
Laboratory results
Groundwater flow direction
Contaminant isopleths (if needed)
Summary and recommendations for further action
All Phase I and, if necessary, Phase II investigation activities will be conducted under the
supervision of a NC Licensed Geologist. The laboratory analyses will be performed by a NC
Certified Laboratory which includes internal quality control samples and matrix
spikes/matrix spike duplicates for quality control.
Schedule for Implementation
The following schedule is provided for the implementation and completion of the Phase I and
Phase II (if necessary) activities. All timeframes begin from written approval of the
Assessment Monitoring Workplan by the NC Solid Waste Section.
Phase I Activities
Collect Soil Samples 30 days *
Laboratory Analysis 20 days
Prepare Alternate Source Demonstration 30 days **
Total Phase I 80 days
Phase II Activities
Install New Well 30 days *
Allow new well to cure, samples all wells 20 days
Laboratory Analysis 20 days
Prepare Assessment Report 30 days
Total Phase II 100 days
* Due to the time of year planned for the field work and the flood-prone
location, additional time allotted.
** If the soil samples do not show the presence of 1,2-dichloropropane, this
task will not be necessary.
If there are any questions or comments regarding the planned activities described in this
Assessment Monitoring Workplan, please contact the undersigned at (919) 325-0696.
Respectfully,
Babb & Associates, P.A.
Gary D. Babb, P.G.
President
Attachments – Figures 1 & 2
Cc: Mr. Andy Davis, Director
Wilson County Solid Waste