NCD980602163_19951019_Warren County PCB Landfill_SERB C_BC Geologic LL requested peer review of Division's plan for upgrading groundwater monitoring network-OCR

l
BC GeoLogic, LLC
Environmental Consultants
Robert Glaser, Hydrologist
Hazardous Waste Section
Division of Solid Waste Management
P.O. Box 27687
Raleigh, North Carolina 27611-7687
October 19, 1995
Attached is the requested peer review of the Division's plan for upgrading the PCB
landfill groundwater monitoring network. Thanks for sending the additional information
which allowed me to finally understand what the likely groundwater in situ flow regimen
looks like.
Having done that, it is my strong recommendation that additional monitoring wells are
also needed near the landfill in what, according to the data from the auger holes, is the
upgradient part. To do otherwise will leave us with a rather incomplete monitoring
scheme and no possibility of defining likely flow paths.
Please call me if you wish to discuss any part of this report.
Sincerely yours,
~
GeorgeL.B~
3966 Bachelor Creek Road, Asheboro, NC 27203 • [phone]
PEER REVIEW
PROPOSED PCB GROUNDWATER MONITORING SYSTEM
INTRODUCTION
At the request of Bill Meyer of the North Carolina Division of Solid and Hazardous
Waste, for peer review of a supplemental ground water monitoring system for the State's
PCB land fill, I have reviewed the following:
1. Correspondence from Glaser to Bain dated 09/07 /95
2. Internal memo from Glaser to Meyer dated 04/06/95 outlining plans for the
monitoring system upgrade
3. Various site maps contained in item 2, above
4. Table of site water level measurements from 11/92 to 3/95, also contained in item 2,
above
5. Table of site landfill elevations and a copy of part of the USGS topographic map
covering the site
6. Internal memo from David Lown to Sharon Rogers on PCB waste thicknesses.
Finding a need for additional information to complete my review, I requested any as-built
drawings, detailed site topo maps, PCB fluid elevations, geologic logs, etc. These were
received on October 10. I have since reviewed the following:
1. Revised water level elevation information for MW 4
2. Engineering soil classification logs for the four wells and the eight initial auger holes
3. As-built topographic maps and construction details for the PCB site
4. A large oblique aerial photo of the landfill site
5. Recent (October 5, 1995) water level elevations for the site
6. Various well construction diagrams, driller's logs, auger hole location maps, and
various reports and correspondence from 1978 through 1983.
REVIEW AND EVALUATION
As is my normal practice in assessing the quality of groundwater monitoring networks, I
first attempted to construct a potential groundwater flow direction map for the site in
order to determine whether the existing wells were placed in geographically strategic
positions best suited for detection of any fugitive PCB discharge. This exercise led to the
discovery that the resulting groundwater contour map didn't make good hydrologic sense
when compared to the site topography. The principal problem appeared to be that the
monitoring well with the lowest measuring point (MP) elevation (from the table of water
level elevations) had the highest water level elevation.
Since receipt of the additional information, it is apparent that the MP elevation for MW 4
is correct on the various maps but is incorrect on the current table of water level
elevations. Subsequently, I have used the revised water level elevations along with water
level data from three initial auger holes to construct a generic water table map for the site
(Figure 1).
CONCLUSIONS
Proposed State Plan
The DSWM Plan is essentially as follows.
1. Install two additional wells to deeper depths at sites W2 and W3 to determine the
vertical component of flow.
2. Install four additional wells (two sets of nested wells --one deep and one shallow) at
two locations in the northeast quadrant of the landfill site.
On review of the State Plan and examination of the additional material submitted to me, I
find the following.
1. The locations of the existing monitoring wells, relative to the landfill as plotted on
various maps and to elevations from the site detailed topographic map, are internally
consistent.
2. Groundwater in each of the monitoring wells, as recorded in tables furnished to me,
fluctuates several feet each year in response to seasonal precipitation and
evapotranspiration demand. There appears to be no doubt that each is a functioning
monitoring well.
3. I concur with the DSWM that there is a need for additional spatial coverage and also
with the concept of addition of deeper monitoring well installations at the locations of
the existing wells to better define the vertical component of flow.
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4. The elevation of the water in the waste cell (337 feet) when compared to the average
site water level near the cell (299 feet), although not proof that the site is not leaking,
is evidence that, if it is, it is doing so at a very low rate.
5. Plotting of groundwater levels from the existing network, supplemented by
information on water levels from auger holes located near the crest of the knoll from
the initial investigation, show that the present net does not do an adequate job of
defining the shape of the upper surface of saturated rock and soil (i.e., the water table)
in the immediate vicinity of the PCB landfill. That is, there is not good definition of
the upgradient part of this site.
6. In addition, well MW4, even with a corrected MP elevation, has a water level that
appears to be anomalously high if only water levels from the existing network are
used to construct a water level contour map.
7. The addition of water levels from the initial auger holes (although not the best of
good science since they are not from the same period of time) causes the water levels
from the existing network to make more hydrologic sense. See Figure 1. When a
water table contour map is constructed with the addition of auger hole water levels,
upgradient is directly beneath the cell and possibly both to the southwest and
southeast, principally along the small ridges in those directions. Discharge is to the
northwest and northeast, toward Richneck Creek and possibly south toward the
unnamed tributary.
8. Since one cannot evaluate flow direction and/or the hydraulic effect of the landfill on
the local hydraulic regime, better definition of both the site water table and the
vertical component of groundwater flow is required.
Recommended Alternate Plan
Therefore, I recommend:
1. Addition of one more well at site MW4 at a deeper interval to document vertical
groundwater movement at this point, as well as to solve any ambiguity as to the
representativeness of data gathered there to date.
2. Install three shallow top-of-water-table monitoring wells at former auger sites 4a, 3,
and IA (Sheet 3, Suerdrup and Parcel, 8/12/81) to document the upgradient part of the
site water table and so that adequate groundwater flow maps can be drawn.
3. Install the three shallow monitoring wells (item 2, above) first, to construct a more
accurate site water table map from which on-site adjustments can be made, as
necessary, in the location of the two new well nests proposed for the northeast
quadrant.
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4. Strongly consider the addition of a two-well nest immediately south of the cell at a
location based on the new groundwater flow map (item 3, above).
5. Collect 2eolo2ic data, as well as soils engineering data, from any new holes drilled for
construction of the monitoring wells.
6. Finally, I wish to caution that my recommendations for the number of wells and their
locations are based on current acceptable practice for monitoring systems in 2ranular
materials and should be adequate for monitoring the change in groundwater head
across this site, as well as the potential flux of groundwater.
There is no affordable monitoring system, in my opinion, that will guarantee 100%
early detection of any contaminant in a fractured rock system such as underlies this
site. The location, attitude, direction, aperature width, number, and degree of
interconnection of rock fractures are essentially unknowable below the ground surface
or beyond the edge of a borehole. Therefore, the placement of monitoring wells for
early detection of contaminant release is an exercise in the chance interception of the
critical fracture(s). Thus, the practicing science, as here, is reduced to making the
best educated guess as to the most probable discharge locations: hence, the need for
the best possible groundwater potential flow map. Hopefully, any discharge from
sites such as this will occur along the soil/weathered rock interface which is much
easier to monitor for contaminant discharge.
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