| INTRODUCTION OEPA
investigations were undertaken at the Bridgeport, Coal Grove
and Belmont County Wellfields, among others, to locate the
sources of contaminant plumes affecting the wellfields. Another
investigation objective was to gather data to evaluate potential
response actions to ensure safer water supplies for the future.
The choice of exploration method would be primarily controlled
by four factors: 1) cost effective plume delineation - it
was important that stratigraphy and groundwater chemistry
be rapidly evaluated, to allow subsequent exploration points
to be located based on actual site conditions, rather than
on an arbitrary grid pattern. This approach would avoid expensive,
multi-phased exploration typical of many groundwater studies;
2) very low contaminant concentrations - this would require
use of relatively sophisticated field analytical equipment;
3) exploration in urbanized areas - it was important that
methods be as unobtrusive as possible; and 4) geological conditions
- wellfield aquifers were 15-30 m (50-100 ft) deep, and both
gravelly and heaving sands might be encountered.
The consultant (Lawhon and Associates)
recommended, and OEPA approved, use of a cone penetrometer
exploration system (Strutynsky and Sainey, 1991) along with
a field analytical laboratory to achieve the goals of the
program. The consultant and OEPA provided senior professionals
to immediately evaluate all exploration results and plan subsequent
exploration locations, while the penetrometer company (STRATIGRAPHICS)
provided a geotechnical engineer or hydrogeologist to evaluate
stratigraphy and recommend sampling procedures. OEPA also
provided oversight of the entire program.
Initial groundwater samples would be collected
around the most contaminated well or lateral, in the case
of the Ranney Well, to determine the direction of plume transport.
A series of upgradient exploration lines would then be run
transverse to the expected axis of the plume to delineate
the plume and identify its source. A number of penetrometer
soundings, depending on encountered geological conditions,
would be performed to develop stratigraphic cross-sections.
Groundwater samples would be collected at multiple depths
at each location to determine the vertical distribution of
contamination within the aquifer. Field analytical testing
would allow a 3-dimensional profile of the plume to be rapidly
developed, allowing subsequent exploration locations to be
chosen based on the complete analytical database. Penetrometer
soil and soil gas sampling could be performed, in addition
to groundwater sampling, to confirm potential source areas.
CONE PENETROMETER SYSTEM
The STRATIGRAPHICS cone penetrometer system
was designed in 1986 for use during both geo-environmental
and geotechnical exploration programs in difficult soil conditions.
The heavy (240 kN and 300 kN or 24 and 30 ton) truck mounted
rigs are fully self-contained, including data acquisition
systems, dry and wet work areas, water tanks, steam cleaners,
decontamination and grouting systems, separate rodstrings
for sounding and sampling, optional dynamic rod driving, and
heavy duty downhole equipment for use in glaciated terrains
(Fig 1). Cone penetrometer (direct push) systems require no
borehole to advance probes and samplers, and result in little
exploration derived waste. Downhole equipment is decontaminated
during retrieval using an automatic rodwasher, and open hole
is pressure grouted. Most exploration activities are performed
inside an enclosed portion of the rig, providing all-weather
capability and a low visual presence. Truck mounted penetrometer
systems can be very productive, with as much as 400 m (1300
ft) of stratigraphic logging per day, with depth capacity
exceeding 60 m (200 ft). As many as 18 groundwater, or up
to 30 soil or soil gas samples can be acquired in a day.
High resolution, continuous soil profiling
(sounding) for geo-environmental exploration is most often
performed by STRATIGRAPHICS using the indirect Piezometric
Cone Penetration Test with soil Electrical Conductivity (CPTU-EC,
Fig 2). The cone tip and friction sleeve resistance measurements
(CPTU-EC) are evaluated for soil types and geotechnical parameters
(Douglas and Olsen, 1981). The piezometric measurement (CPTU-EC)
allows evaluation of soil saturation, hydraulic conductivity,
potentiometric surfaces, and soil types (Saines et al, 1989).
The soil Electrical Conductivity measurement (CPTU-EC) provides
information on soil moisture in vadose zone soils and indications
of groundwater quality in saturated soils. The EC measurement
has proved very useful in exploration for inorganic (metal,
brines and landfill leachate) contamination (Strutynsky et
al, 1998) and somewhat useful in LNAPL or DNAPL exploration
(Strutynsky et al, 1991).
The STRATIGRAPHICS Penetrometer Sampler
can be deployed in groundwater, soil or soil gas sampling
modes by using interchangeable components. The groundwater
sampler is a heavy wall, shielded sampler. The shield prevents
cross-contamination of the sample and screen clogging. The
shield is retracted to allow groundwater to flow through a
0.5 m (20 inch) long screen into the barrel. Sample can be
decanted from the barrel or can be pumped to the surface using
an inertial pump. The sampler is typically tripped out after
each sample to allow thorough decontamination. The rate of
groundwater inflow and equilibrium levels can be recorded
using a small diameter pressure transducer. Inflow test results
can be analyzed using rising head slug test solutions.
The soil sampler consists of a barrel,
sealed with a locking piston. The piston is unlocked with
a wireline tool to obtain the sample. The sampler is tripped
out of the hole for sample extrusion and decontamination.
The soil gas sampler is a smaller version of the groundwater
sampler. Samples are contained within Tedlar bags, or are
routed through portable vapor analyzers.
ANALYTICAL TESTING
A Hewlett-Packard Model 5890 Series II
Gas Chromatograph (GC) and a Hewlett-Packard Model 5971 Series
Mass Spectrometer (MS) were operated by the analytical company
(Aqua Tech Environmental Laboratories- ATEL) in a trailer
mounted, on-site field laboratory. A Tekmar 2000 purge and
trap device, and a Tekmar 2016 auto sampler for automated
sample handling, were also used. The samples were analyzed
using EPA method 524.2 with a detection limit of 0.5 ug/l.
The contaminants of concern (COC’s) varied for each site,
but were primarily chlorinated solvents, and their breakdown
products.
BRIDGEPORT WELLFIELD INVESTIGATION
The Bridgeport wellfield is located in
southeastern Ohio, along a channel of the Ohio River, and
serves 3600 residents. The wellfield is within the unglaciated
Appalachian Plateau Ohio River Aquifer. Beginning in 1989,
very low levels of TCE and cis-1,2-DCE were detected during
routine wellfield monitoring; soon PCE was also detected.
After multiple well sampling events confirmed the continual
presence of the COC’s, OEPA decided to perform an investigation
during the summer of 1994.
Ten CPTU-EC soundings for stratigraphy,
26 dissipation tests for hydraulic conductivity and potentiometric
surfaces, 52 groundwater (from 57 attempts), and 9 soil gas
samples were acquired during the course of a 13 day field
program. Soil gas samples were obtained in vadose zone soils
around the suspected source after the groundwater sampling
program defined the limits of the plume.
Evaluation of the CPTU-EC soundings revealed
variability (sand and cinder fills, buried refuse, or clay)
at shallow depths. Shallow soils were typically moist to wet.
Deeper stratigraphy was more uniform, and typically consisted
of sands and silty sands, with some local gravelly layers.
Saturated conditions were typically found below depths of
10-13 m (35-45 ft). The aquifer was characterized as a continuous
water table aquifer, with few, apparently discontinuous, aquiclude
interlayers. Bedrock was typically encountered within about
21-26 m (70-85 ft) of the surface.
CPTU-EC soundings in the identified source
area indicated somewhat different stratigraphy, with finer
grained soils predominating, and significant thicknesses of
interlayered sands, silts and clays. Bedrock was also found
at a shallower depth (18 m or 59 ft), consistent with a steep
slope of a buried bedrock valley, as indicated by nearby rock
outcrops.
Plume concentration maps were developed
at three different depth intervals. In the upper interval,
concentrations ranged from less than 0.5 ug/l, to as high
as 9,700 ug/l total COC’s at the source area. The upper
portion of the plume angles away from the wellfield following
regional ground water flow. In the middle interval, concentrations
ranged from less than 0.5 ug/l, to as high as 1,900 ug/l total
COC's near the center of the plume (Fig 3). In the lower interval,
concentrations ranged from less than 0.5 ug/l to 105 ug/l
total COC's, again with the highest concentrations near the
center of the plume. The results indicated that while most
of the COC’s are drawn towards the wellfield through
the middle depth interval, contamination of the wellfield
is actually occuring in the lower depth interval .
The investigation identified the source
of the contamination as a dry cleaner located about 365 m
(1200 ft) northwest of the wellfield. OEPA positioned 6 permanent
monitoring wells along the plume. These are used as an early
warning system, allowing wellfield operators to modify wellfield
production to lessen capture of the plume.
COAL GROVE INVESTIGATION
The Coal Grove wellfield is located on
the banks of the Ohio River in southern Ohio. The four production
wells are configured within about 1/2 hectare (1.5 acres),
and serve 4700 residents. The production wells are within
alluvial deposits associated with the Ohio River and a tributary,
Ice Creek. TCE and DCE have been detected in some of the production
wells since 1988. One production well (CG-2) was taken out
of service in 1989 due to high contaminant levels, and has
been intermittently pumped to waste to control contamination
of the other production wells. Five monitoring wells had been
installed upgradient of the wellfield. TCE and DCE detections
increase with distance upgradient.
Upgradient (southeast) of the wellfield
is a coal dock. Further upgradient is a closed facility which
had operated for numerous years as a truck terminal and as
a tanker truck repair and cleaning operation. In 1993, USEPA
conducted an emergency removal action at this facility . During
the removal action, on-site wastes were found to contain various
volatile organic compounds (VOC’s), including TCE. OEPA
determined that additional groundwater data were required
to protect the wellfield from further damage. The penetrometer
method successfully used at Bridgeport was chosen for use
at Coal Grove. The investigation had to proceed in two parts
(1994 and 1995) due to lack of permission to enter the tanker
truck cleaning facility.
Fourteen CPTU-EC soundings for stratigraphy,
38 dissipation tests for hydraulic conductivity and potentiometric
surfaces, and 61 groundwater samples (from 64 attempts) were
acquired during the course of the first 12 day field program.
CPTU-EC soundings revealed 5.5-14 m (18-46 ft) of silty clay,
underlain by granular soils. The gravelly sand to silty sand
aquifer saturated thickness varied from about 1.2 m (4 ft)
downgradient to 13 m (43 ft) upgradient of the wellfield.
The aquifer ranged from water table to confined, depending
on surficial clay thickness. Bedrock was encountered at the
base of the aquifer, at depths between 17-26 m (55-87 ft).
The results from field GC/MS analytical
testing on obtained samples showed that the VOC plume followed
a linear flow path, apparently originating to the southeast
of the coal dock facility, on the northern boundary of the
closed tanker truck cleaning facility (Fig 4). The plume narrowed
with distance upgradient of the wellfield. The ability to
rapidly obtain data from the field analytical lab, as well
as stratigraphic information from the cone penetrometer, was
instrumental in locating this narrow plume. As the investigation
proceeded, it became apparent that if sampling had been strictly
conducted on the sample grid which was originally surveyed
at the site, the narrow, most contaminated portion of the
plume would have been entirely missed, with significantly
different conclusions as to the source of groundwater contamination.
To complete this investigation and confirm
the source of the VOC’s, the first program was used to
support an administrative search warrant for exploration at
the closed tanker truck cleaning facility. With the unexpected
accompaniment of local TV news reporters, the warrant was
served, the property was entered, and additional exploration
was conducted. Four CPTU-EC soundings for stratigraphy, 6
dissipation tests for hydraulic conductivity and potentiometric
surfaces, 37 groundwater samples (from 37 attempts), and 30
soil samples were acquired during the second 10 day field
program.
The second program showed that the high
concentrations of VOC’s continued in a very narrow plume
less than 15 m or 50 ft wide to a corner of the closed tanker
truck cleaning facility's wastewater treatment plant. This
confirmed that the source of the VOC contamination was the
tanker truck cleaning facility. Following this sampling effort,
OEPA conducted a pump test at the wellfield. The data obtained
from the pump test, along with the groundwater analytical
data, were used to evaluate future impacts to the wellfield.
OEPA concluded that contaminant levels at the wellfield could
be expected to remain constant for some time into the future.
However, it was also concluded that, without the continued
pumping to waste of production well CG2, higher contaminant
levels would be expected in other production wells. OEPA is
currently evaluating both technical and legal means to address
the threat to the Coal Grove wellfield.
BELMONT COUNTY SANITARY SEWER DISTRICT
3 RANNEY WELL INVESTIGATION
The Belmont County Sanitary Sewer District
3 serves about 25,000 people in southeastern Ohio with water
from a single Ranney Collector Well (BC#3). This well is located
near the Ohio River, and consists of six laterals, which are
screened near bedrock. The well can supply up to 25 million
liters (6.5 million gallons) of water per day. Contaminants
cis-1,2-DCE, 1,1,1-TCA, PCE and 1,1-DCA have been detected
in the well.
The Ohio Department of Transportation
(ODOT) discovered VOC contamination in soil and groundwater
during an environmental investigation of a nearby property
(Site) during a highway relocation project. The Site is about
365 m (1,200 ft) southwest of BC#3. Various chemicals, including
chlorinated solvents and petroleum products, were distributed
from a bulk plant located at the Site. ODOT had detected the
following VOC’s in Site soils and groundwater: VC; PCE;
TCE; cis-1,2-DCE; trans-1,2-DCE; 1,1,1-TCA; and BTEX compounds.
Initial results indicated that VOC’s were migrating in
ground water north-northeast from the Site toward BC#3, and
towards the southeast with regional groundwater flow.
ODOT notified OEPA of its findings in
early 1996. During the fall of 1996, OEPA performed a field
investigation to achieve the following goals: 1) identify
all sources of BC#3's contamination; 2) determine the vertical
and horizontal extent of contaminant plumes, 3) determine
rates of migration; and 4) determine whether the suspect Site
was impacting BC#3. The investigation was successful in achieving
all these goals.
A major portion of the investigation was
conducted using penetrometer exploration methods developed
during the Bridgeport and Coal Grove investigations. Six CPTU-EC
soundings for stratigraphy, 8 dissipation tests for hydraulic
conductivity and potentiometric surfaces, and 55 groundwater
samples (from 58 attempts) were acquired during the course
of the 10 day field program. The CPTU-EC soundings revealed
fine grained soils to depths of about 11-14m (38-47 ft), followed
by a confined, gravelly sand aquifer. Groundwater sampling
was conducted to determine the lateral and vertical extent
of contamination within the aquifer.
The most common groundwater contaminant
was found to be cis-1,2-DCE, with concentrations as high as
4,200 ug/l. The following cis-1,2-DCE detections were observed
between the Site and BC#3: 300 ug/l about 135 m (440 ft) south
of BC#3; 360 ug/l about 40 m (140 ft) south of BC#3; and 90
ug/l about 15 m (50 ft) south of BC#3. Data showed that the
plume was being drawn northward from the Site, directly against
the regional ground water flow direction, and into the end
of the western lateral of BC#3 (Fig 5). This unusual, reversed
flow path reflects the very large capture zone of the high
capacity Ranney Well. The investigation showed that VOC’s
are migrating from the Site to BC#3 via ground water flow
paths primarily in the upper portion of the aquifer. It also
showed that the Site is apparently solely responsible for
the BC#3's cis-1,2-DCE contamination.
ODOT and OEPA agreed that excavation and
off-site disposal of contaminated soils and debris prior to
highway construction would best remediate the Site. Source
removal, as opposed to treatment, was selected both to complete
the highway project on time and to eliminate further contamination
of the aquifer. The source removal took place during the summer
of 1997. About 20,000 tons of contaminated, non- hazardous,
solid waste and about 1,550 tons of hazardous waste were excavated
and removed from the Site.
CONCLUSIONS
Thirty four CPTU-EC soundings, totaling
685 m (2250 ft) of data; 205 groundwater, 9 soil gas, and
30 soil samples (3755 m or 12210 ft of sampler deployment)
were obtained during the 45 days of field exploration for
these 3 projects. Penetrometer costs (less mobilizations)
totaled about $133,000. A total of 244 samples, plus numerous
QA/QC samples, were analyzed by the field laboratory using
GC/MS. The cost for the field analytical laboratory totaled
about $45,000 (less mobilizations). While this cost is comparable
to costs for off-site analyses with a 24 hr turnaround, having
analytical results within 15-30 minutes of sample acquisition
allowed optimal placement of subsequent exploration locations.
Accurate targeting of exploration locations was the key factor
in significantly decreasing overall cost and duration of these
investigation programs.
OEPA rapidly and cost-effectively investigated
contaminated municipal wellfield groundwater supplies by the
use of high capacity penetrometer stratigraphic profiling,
rapid penetrometer groundwater, soil and soil gas sampling,
a sophisticated field analytical laboratory, and immediate
evaluation of acquired data by senior professionals. Complex
contaminant plumes, which often followed unusual groundwater
flow paths, were characterized within days rather than months
or years. Plumes were delineated, sources identified, and
realistic models developed for planning long term monitoring
and site remediation activities. OEPA has used these projects
during in-house training sessions as examples of innovative
and effective groundwater exploration.
REFERENCES
Douglas, B.J., R.S. Olsen, 1981. Soil
Classification using Electric Cone Penetrometer. Cone Penetrometer
Testing and Experience, ASCE.
Saines, M., A.I. Strutynsky, and G. Lytwynyshyn,
1989. Use of Piezometric Cone Penetration Testing in Hydrogeologic
Investigations. Presented at the First USA/USSR Hydrogeology
Conference, Moscow, USSR
Strutynsky, A.I., T.J. Sainey, 1991. Use
of Piezometric Cone Penetration Testing and Penetrometer Groundwater
Sampling for Volatile Organic Contaminant Plume Detection.
Petroleum Hydrocarbons and Organic Chemicals in Groundwater:
Prevention, Detection and Restoration. API/NWWA.
Strutynsky, A.I., R. Sandiford, D. Cavaliere,
1991. Use of Piezopmetric Cone Penetration Testing with Electrical
Conductivity Measurements (CPTU-EC) for Detection of Hydrocarbon
Contamination in Saturated Granular Soils. Current Practices
in Ground Water and Vadose Zone Investigations, ASTM.
Strutynsky, A.I. R. Glaccum, L. Conklin,
and B. Baker, 1998. Chloride Mapping using Geophysical and
Cone Penetrometer Methods. Proceedings of the First International
Conference on Site Characterization, Atlanta, GA |
