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CICEET Progress Report for the period 8/01/00
through 1/31/01
Project Title:
Inflow Loadings from Ground Water to the Great Bay Estuary
Principal Investigator(s):
Larry K. Brannaka,
Thomas P. Ballestero,
Tom Mack (USGS)
I. Accomplishments
A. Scheduled Tasks
During this reporting period, Phases 1 and 2, identification
of groundwater discharge zones, and flow quantity and quality
characterization, respectively, were to be completed. Phase
3, building a conceptual groundwater model, was scheduled
to begin.
The Phase 1 tasks delineating groundwater discharge zones
by use of thermal infrared imagery included multiple aerial
surveys, deployment and recovery of instrumentation for
calibration data, image post-processing (mosaicing), and
identification of discharge zones. Aerial surveys were planned
to include one in winter and another in summer. Prior to
the surveys, digital thermometers and dataloggers were to
be deployed in a calibration array throughout the study
area to measure actual field conditions. The collected data
would function as calibration data to be applied to the
thermal mosaiced images to delineate groundwater discharge
zones. Image post-processing would mosaic thermal images
into a single continuous image for the study area. The thermal
images would be scrutinized for suspected groundwater discharge
zones, which would then be classified and cataloged.
The Phase 2 quantification of groundwater flux was
planned as three concurrent parts: 1) field-verification
of suspected groundwater discharge zones, 2) development
of a piezometric surface map for the area surrounding the
Great Bay Estuary; and 3) aquifer characterization. Field-verification
consists of locating areas and characterizing the flow,
cross-sectional area, piezometric head, and hydrogeology.
Field-verification would be done mostly by boat, around
low tide, targeting the tidal zone where the majority of
discharge zones were indicated by the thermal images. Creation
of a piezometric map consists of measuring water levels
in all participating residents’ wells within as short
a time period as practical, and using survey data to compute
groundwater elevations. The resulting data would be plotted
and contoured. Aquifer characterization involves the geophysical
analyses of suspected target areas, slug testing of monitoring
wells, and analysis of pump test data.
Characterizing groundwater quality in terms of nutrient
contamination involves testing samples for nitrogen species,
which are the dominant contaminants of interest. Water quality
will be investigated by sampling groundwater using mini-piezometers
installed in the discharge zones. Salinity will be monitored
to verify the discharge is freshwater rather than storage
of infiltrated saltwater. Samples will be filtered and preserved
for bulk analysis at a later date.
The Phase 3 formulation of a conceptual model involves
the construction of a series of maps and overlays to describe
various hydrogeological and water quality properties. The
maps will form the basis for an overall conceptual groundwater
flow model to the Great Bay Estuarine system.
B. Progress on Tasks
Phase 1:
Progress on Phase 1 has been ongoing, yet is still incomplete.
Continued progress on Phase 1 includes the completion of
second summer aerial survey, when bay temperatures reached
a maximum differential(~69ûF) with respect to groundwater
temperature (~48ûF). The aerial survey vendor, Larry Davis
Aviation, and the UNH researchers have developed a strong
rapport, which has been essential considering the many survey
constraints.
In August, Larry Davis Aviation, along with a UNH researcher
flew a second successful survey, despite many weather related
difficulties. After many weather delays, the weather forecasts
finally fell within the aerial survey constraints and the
survey was scheduled. At the time of the actual flight,
however, the actual conditions were significantly different
from the forecasts, with cloud cover and high winds at 10,000’
elevation (the contracted survey elevation). The survey
flight was forced down to 4,000’ to obtain acceptable
results. Alterations were necessary in the survey plan to
accommodate the change in imaging elevation. As a result,
image resolution was improved by 6 times. This improvement
was accompanied by an extensive increase in the number of
images necessary to obtain a full coverage of the Great
Bay Estuarine system. It was decided to forego full coverage
of the bay, and to focus the imaging on the tidal zone where
the submarine groundwater discharge (SGWD) zones are primarily
located. The consequences of this decision were mostly aesthetic,
as the final mosaiced image would essentially have a large
"hole" in it, but the survey itself was improved
through the increased resolution. Survey conditions were
acceptable, temperature of groundwater, surface water, and
mudflats were approximately 48, 69, and 80 degrees Fahrenheit,
respectively. Since this was the second survey, specific
SGWD zones identified from the previous (April) survey were
monitored to determine their respective thermal signatures.
.Identification and cataloging of suspected discharge zones
from the thermal imagery has been completed for the first
survey with over 200 sites identified. The process is underway
for the second survey and is nearly 50% complete. The August
survey has shown a large increase in the number of zones
identified. Two likely explanations for the increase (and
at this point they are indistinguishable) have been postulated:
1) the August survey had a dramatically increased image
resolution, thereby enabling increased identification; and/or
2) there may also be a seasonal component affecting the
increase. Certain discharge zones identified in the August
survey are substantially larger than the respective zone
shown in the April survey. Generally speaking, there appears
to be ubiquitous diffuse low intensity groundwater discharge
throughout the bay that is more readily apparent in the
August survey.
The summer of 2000 had unseasonably large amounts of precipitation
in comparison with the dry summer of 1999. Snowfall was
late and low for the winter of 1999/2000. This winter, following
a low precipitation summer would result in low recharge
for surface aquifers and could result in a corresponding
reduction in groundwater discharge. Long-term monitoring
of known discharge zones would clarify this.
Image post-processing is still ongoing for the April survey
with completion expected in the spring. Logistical considerations
are being negotiated for the post-processing of the August
survey. The USGS was unable to provide the image processing
services, and time requirements for image post-processing
for the thermal imagery were underestimated. The UNH University
researchers have solved the dilemma by working with the
Complex Systems Resource Center (CSRC) at UNH to mosaic
the thermal images. Fay Rubin of the CSRC has generously
accommodated our resource needs and negotiations are underway
for continued cooperation to complete the second survey.
Completion of the April mosaic is expected in the spring.
The August survey mosaic will be completed by the end of
the project.
Phase 2:
Progress on Phase 2 has been substantial. Field-verification
of suspected groundwater discharge zones has been ongoing
in the summer and fall with 9 SGWD zones characterized,
and 14 sites sampled for water quality. The resulting data
has enabled preliminary estimates of flow and nitrate loading
resulting from groundwater. Flow and loading estimates indicate
that the groundwater contribution is significant.
Field-efforts are nearly complete for the development of
a piezometric surface map. Construction of the first map
is underway and completion is expected in the coming months.
Data reduction of surveying notes is complete. One final
well-monitoring event will occur in the early spring to
evaluate the influence of seasonal fluctuations in the water
table. Concurrent with the monitoring event, selected wells
will be sampled for water quality to characterize upgradient
nutrient concentrations.
The USGS has characterized the aquifer at selected sites
in close proximity to identified discharge zones. The initial
step of this process involved site selection and reconnaissance
for the surface geophysics. UNH investigators provided field
assistance in the geophysical surveys. Resistivity data
was collected at 7 sites totaling 13 lines. One survey site
covering a fracture-correlated lineament was located on
the western side of the bay, near a high yielding well.
Other sites of interest include Wagon Hill in Durham, and
Fox Point in Newfields. Both of these sites are adjacent
to large, identified discharge zones. The USGS is currently
processing the data, and will be developing plots showing
aquifer dimensions and hydrogeologic stratigraphy. Of special
interest will be the thickness of the surficial materials.
UNH investigators performed additional aquifer characterization
tests on participating residential wells. Slug tests have
been done on selected wells throughout the study area and
more testing will be performed during the spring well monitoring
event. These data will be used in conjunction with pump
test data available from other UNH researchers to determine
aquifer parameters, including transmissivity and hydraulic
conductivity. The combination of point values obtained from
slug testing and pump test data should improve parameter
reliability.
Water quality characterizations are underway. Field-sampling
methodologies have been developed using mini-piezometers
for extracting groundwater. An UNH lab has been contracted
for analysis of nitrate and ammonia analysis. Preliminary
analyses indicate significant nitrate contamination exists
throughout the bay, with some concentrations exceeding EPA
drinking water standards (10 ug/L). Samples are preserved
and stored for future bulk analyses. Salinity of groundwater
samples has been monitored during sampling to determine
extent of groundwater and bay water represented in the respective
samples. Saltwater intrusion has been shown to mobilize
chemical species within the tidal zone and is therefore
necessary to discern by monitoring salinity.
Phase 3:
Efforts have begun on constructing maps of groundwater
discharge, piezometric contours, and aquifer characteristics.
The maps will be prepared and translated into GIS layers.
These layers will be an integral part of the conceptual
groundwater modeling effort.
C. Difficulties Encountered
The mosaicing of the aerial survey continues to be the
most significant difficulty. Initially the USGS were to
perform the image post-processing, but due to the lack of
the necessary post-processing software this task has been
transferred to UNH. The UNH Complex Systems Resource Center
(CSRC) has graciously offered resources and facilities by
which to post-process. Progress has been slow-going as facilities,
labor, and hardware have had to be negotiated. However,
recent negotiations with the CSRC have secured the necessary
resources to complete the mosaic for the second aerial survey.
Other difficulties included the weather conditions for
the time period of the August aerial survey. The survey
vendor had to travel from Ohio to NH to perform the survey
and therefore required approximately 18 hours advance notice.
The forecast for the chosen day proved to be incorrect and
two attempts at surveying were aborted due to unfavorable
conditions. Since much of the survey expense was in travel
time, so rather than send the vendor back only to return
at a later date, we chose to fly a daytime survey. Nighttime
survey are generally preferred due to lower winds (which
was not the case) however, daytime surveys are acceptable
if flown near high noon to minimize shadows. The diminishing
tidal window and changing environmental conditions impressed
the need to survey if at all possible. The conditions at
10,000’ elevation were too windy and cloudy to survey,
so the plane dropped to 4,000’ elevation to obtain
acceptable survey conditions. The lower elevation survey
dramatically increased the cost, the airtime, and necessary
imagery to obtain full coverage of the bay . Consequently,
we chose to limit the survey to the tidal areas of the Great
Bay to stay within budget. The decreased survey elevation
resulted in dramatically increased survey resolution which
improved our ability to identify groundwater discharge zones.
The utility of the survey was not harmed by limiting it
to the tidal zones, only the aesthetics were diminished
by not having a continuous image.
D. Anticipated Success in Meeting Project Objectives
in Scheduled Project Period
None of the delays will affect the completion of
scheduled project objectives. The most significant delay,
the mosaicing, appears to have been unavoidable given the
large time requirements for image post-processing.
E. Preliminary data
The project is in the final data gathering stages and
focusing primarily on data reduction and interpretation.
At this point, preliminary water quality results and flow
estimates have been made and show groundwater is a significant
flow component, and a significant contributor of nutrient
pollution. It is now believed that groundwater constitutes
a significant, if not dominant, source of freshwater to
the Great Bay during the summer low-flow months. The flow
appears to ubiquitous and uniform throughout the bay, composed
of concentrated high volume discharge areas and low volume
diffuse discharge areas.
Thermal Infrared Imagery
The mosaicing of thermal imagery is ongoing. Samples
of the completed thermal imagery can be downloaded at:
ftp://ftp.granit.sr.unh.edu/pub/submissions/Mosaics/.
These images are large, some in excess of 70 MB, and are
therefore made available by ftp. Substantial portions
of the study have been completed. The thermal imagery
is being used to delineate groundwater discharge zones
throughout the bay. Figure 1 is a portion of a mosaic
of the Oyster River in Durham, NH, which shows areas identified
as groundwater discharge zones. The thermal signature
is evident due to the temperature difference between the
groundwater and the surface waters. This survey was performed
in April 2000 at 10,000 ft elevation.
Figure 1: Mosaic of Thermal Imagery for Delineating Groundwater
Discharge Zones, Oyster River, NH.
Seasonality
The thermal imaging surveys were performed during April
and August of 2000 to investigate seasonal variations
in the discharge zones. Specifically, variations in the
size and intensity of the thermal signature of suspected
groundwater discharge zones were targeted. Figure 2 illustrates
what is hypothesized as seasonal variations in a large
discharge zone on Fox Point in Newington, NH. Additional
field work will be necessary to verify actual seasonality.
Geophysics
Two dimensional direct current resistivity surveys were
performed by the USGS along the bank of the Oyster River
where it discharges into Great Bay on the south side of
Wagon Hill in Durham, NH. Three array configurations,
Dipole-Dipole, Schlumberger and Wenner arrays were used
on the same survey line to optimize the quality of the
interpretations. Each array has strengths and weaknesses
in depths of the survey, horizontal and vertical resolution,
and signal to noise ratios. The profile was 170 meters
in length and imaged the sub-surface electrical properties
up to 25 meters in depth.
Preliminary interpretation of the processed data indicates
the presence of three distinct hydrogeological units.
The units were interpreted from geophysical profiles such
as shown in Figure 3. A resistive anomaly of greater than
1000 ohm-m at depth is interpreted as the top of competent
bedrock. The conductive material directly on top of the
bedrock, ranging from 5 to 300 ohm-m, represents marine
clay. This conductive layer slopes from the surface of
the profile to depth from southeast to northwest. Several
more resistive anomalies were observed within and on top
of this clay layer that likely represent permeable sands
and or gravels. Estimates of the cross sectional areas
of hydraulically conductive materials will be used with
other data to characterize groundwater flow at this discharge
site.
Water Quality
Preliminary water quality results indicate widespread
nitrate contamination in the groundwater discharge throughout
the Great Bay Estuary. To date, over 20 sites have been
sampled, and 13 sites analyzed, too few to state a trend
conclusively. However, the sampled sites distributed throughout
the study area are strong early indicators of what will
be seen in future data. This data indicates that groundwater
discharge is likely a substantial source of nutrient loading.
Nitrate had the highest observed values, shown in Table
1, which were in excess of the EPA drinking water standards.
No ammonia has been observed, which indicates that any
ammonia nitrogen from septic systems is being converted
to nitrate through microbially mediated nitrification.
Flow/Area, Area, Total Flow Estimates
Discharge estimates are being made from estimates of
flow from a known area within the discharge zone, to obtain
data in flow per unit area. These measurements are made
using seepage meters, which are then verified throughout
the discharge zone by measuring the piezometric head at
various locations. The total area of the discharge zones
was field verified for representative discharge zones
and then compared with a method using a GIS query of the
thermal imagery. The field verified methods require the
laborious and time consuming method of gridding out the
discharge zone and then measuring areas as large as 6000
square feet and greater. Once the GIS method is fully
developed it will be used to determine the total area
for the known discharge zones. So far, measurements of
discharge zone areas have yielded zones as large as 12,000
square feet with many averaging around 3,000 square feet.
These values have been used to make flow estimates to
the bay, which are illustrated in Table 2.
These numbers compare very well with other published
data for groundwater discharge in coastal environments
(Moore 1996, Simmons 1992). Table 3 presents a comparison
of measured values from Great Bay to data from Simmons
(1992). Previous methods described in the literature identified
diffuse discharge locations rather than point sources,
as did this research. Diffuse discharge often assumes
uniform discharge throughout an area. This research involves
diffuse discharge as well as delineated point sources.
When the estimates are normalized they are within an order
of magnitude.
Moore estimated that 40% of the river water/freshwater
resulted from groundwater discharge (Moore 1996). Comparisons
have been made with the Lamprey River, for which historical
flow data is available, in Table 4. This is a useful comparison
to determine the relative percentage of total freshwater
flow that groundwater represents. The Lamprey River is
one of 4 major tributaries discharging into the study
area (the study area does not include the Bellamy River
or areas east of Dover Point). During the low flow summer
months (6/1-9/31), when the effects of nutrient pollution
are most pronounced, the average groundwater flow exceeds
the Lamprey River contribution by nearly 50%.
- Tasks and activities for next reporting period
- Tasks for the next reporting period
The Phase 1 tasks will be completed during the final
reporting period. The August mosaic is expected to take
the remainder of the study time to complete. The cataloging
of groundwater discharge zones for the second survey is
nearing completion. When finished, the sets of suspected
groundwater discharge zones from each of the surveys will
be compared for consistency and overlap. Groundwater delineation
will be ongoing until mid-summer, and final estimates of
flow and nutrient loading will be completed.
The Phase 2 tasks will also be completed. The tasks include
the contouring of groundwater surface elevations using the
present (completed) data set plus the results of the field
verification efforts and well data from Pease International
Tradeport. A second groundwater level measurement event
is planned for early spring, to verify seasonal variations
in the piezometric map. Water surface elevations will be
obtained for wells on Pease International Tradeport, which
correspond to both measurement events. The USGS will complete
interpretation of the geophysics to determine aquifer parameters.
Interpretation of slug tests and pump tests will provide
aquifer parameters for comparison with the results of the
geophysics analyses. Directions and estimates of total groundwater
flow will be derived from the potentiometric maps of the
Great Bay estuary. These estimates will be compared with
estimates obtained from field-verification of groundwater
discharge zones.
Water quality analyses will target discharge zones, and
corresponding upgradient wells. Work will continue in the
spring, with the selection of up-gradient well locations
for groundwater quality analyses. Water quality sampling
will be performed on upland areas and SGWD zones with suspected
hydrologic links. Comparisons of water quality signatures
will be made to ascertain the connectivity between upland
areas and the discharge zones.
Finally, work will begin on the Phase 3 conceptual model,
which will integrate the results of all three phases. Composite
maps will be assembled, and incorporated into GIS data layers.
Maps and results information will be made available on the
internet, and will be published in journal articles.
B. Work plan to accomplish tasks
A project meeting with the USGS and UNH was held this winter
to coordinate upcoming responsibilities. Responsibilities
and tasks were allocated for the various project components.
UNH investigators will proceed on the mosaic for the aerial
surveys for Phase 1. A continuous image is necessary to
digitize zone areas. UNH researchers will perform the mosaicing
using the software Erdas Imagine, provided by the Complex
Systems Research Center. The single mosaiced image will
be used in conjunction with the thermometer array to assign
a temperature to the observed gray scale in the image. The
GIS software Arc View will then be used to query for zones
within the desired temperature range. This query can be
used to select areas, not readily apparent to the observer,
which are the result of diffuse groundwater discharge that
may be present throughout the study area. These zones, once
classified, will be digitized to compute an overall discharge
area for the bay. Area estimates for both concentrated and
diffuse discharge zones will be used to make calibrated
groundwater discharge estimates for the study area.
A final depth-to-water event will be performed in the early
spring for the Phase 2 creation of potentiometric surface
maps. This event is expected to last one week. Prior to
this event, wells will be chosen for water quality sampling,
which will be performed concurrently with the measurement
event. UNH researchers will use the resulting data to construct
a second groundwater piezometric-surface map.
Data reductions of the geophysical analyses are currently
being performed by the USGS, with expected completion in
the spring. Analysis of slug test and pump test data will
be performed by UNH researchers. Additional geophysical
characterization (electrical resistivity or seismic refraction)
may be used in specific areas of interest where increased
resolution of aquifer thickness is needed. This additional
work may be supplemented with the installation of small-diameter
wells in the overburden.
Water quality sampling will be completed in the spring
to early summer. After all of the samples have been collected,
they will be submitted for analyses in bulk. Final selection
will be made of locations for groundwater quality analysis.
Samples will be collected from selected monitoring wells
during the spring groundwater measurement event. All samples
will be cataloged, preserved and delivered to a local laboratory.
The results of water quality analyses from SGWD zone samples
along a suspected flow path from a sampled well will compared
to the well water analyses results, with regard to signature
concentrations. The comparison will evaluate if there is
a direct connection, and whether the flow system is local
or regional in nature.
C. Concerns or difficulties
Concerns regarding apparent variations in the thermal
signature of the groundwater discharge zones suggest that
further investigation is necessary to determine the cause.
It is suspected to be either the result of seasonal variations
in total flow or the result of differences in the survey
parameters (resolution, environmental conditions). This
is not expected to pose a major problem.
Another concern is the variation of intensity or brightness
in the thermal images. The imaging instrumentation automatically
and continually adjusts the operating temperature range.
It ranges approximately 20ºF and adjusts depending
on what the dominant feature is. The results were a series
of images with varying gray-scale intensities. This poses
a problem for uniformly applying a query targeted at specific
thermal signal. As there does not yet exist a means for
effectively querying a large-scale area and omitting false
positives, this is not expected to be a significant problem.
III. Expenditures
The expenditures to date are within the range of those
planned for this stage of the project.
IV. References:
Moore, Willard. S. (1996), Large Groundwater inputs to coastal
waters revealed by 226Ra enrichments, Nature, Vol:380.
Simmons Jr., G.M. (1992) Importance of submarine groundwater
discharge and seawater cycling to material flux across sediment/water
interfaces in marine environments. Marine ecology progress
series. JUL 30 v 84 n 2 173
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