Project Title:

Inflow Loadings from Ground Water to the Great Bay Estuary

Principal Investigator(s):

Larry K. Brannaka
Thomas P. Ballestero
Tom Mack (USGS)

Accomplishments

Scheduled Tasks

The time frame for two tasks, originally scheduled for the first year of the project, has been continued into the second year of the project. These tasks, described in the last status report, include collection and verification of thermal imagery data for the Great Bay Estuarine system, and the preparation of potentiometric maps of the groundwater surface in both the overburden and bedrock aquifers. The former task, is a key element of the project Phase 1 activities, and included several subtasks, including geophysical surveys, aerial infrared surveys, and temperature profiling in the waters of the Great Bay. The latter carry-over task is an element of the project Phase 2 activities, the goal of which is to quantify the groundwater discharge to the Great Bay. The carry-over task is to collect data for the preparation of groundwater potentiometric maps of the Great Bay Estuary. This task involves collecting groundwater elevation from over 200 private homeowner wells, which will be used to construct the potentiometric maps. Specific subtasks include surveying the top of each homeowner well, and "simultaneously" measuring the static water level in each well.

In addition to these carry-over tasks, the scheduled second year Phase 2 activities include installing monitoring wells in the bedrock, installation of small diameter wells in the overburden, performing single well tests for aquifer parameters (slug tests), and groundwater quality sampling. No Phase 3 activities were scheduled for year two.

Progress on Tasks

Significant progress has been made on the Phase 1 carry-over task. A thermal infrared aerial survey was successfully flown in April and is now undergoing image post-processing. Post-processing requires mosaicing of thermal images to create a continuous image for the study area as well as identification and cataloging of potential submarine groundwater discharge zones (SGWD).

Davis Aviation flew the thermal-infrared aerial survey in April 2000. The survey resolution appears to have been excellent, with a large temperature differential between the groundwater and the surrounding mudflats. Survey conditions were ideal for discharge within the tidal zone: clear skies, low wind, ambient air temperature of 34ºF, and an expected groundwater temperature of 50ºF. The only drawback was that the bay temperature was nearly 45ºF, which was less than ideal for locating deeper submarine discharge zones. Previous research, found in the literature review, has shown that the bulk of the SGWD can be expected within several meters of shore and within the tidal zone. This suggests our survey should have recorded the majority of groundwater discharge zones.

An array of temperature dataloggers was set out in March to provide temperature calibration data for the final product of the thermal infrared map. All but one data logger was retrieved and the data downloaded for post-processing of the map. The image post-processing has progressed slowly due to difficulties encountered with the orthorectification and mosaicing software provided by the USGS. Many of the difficulties have been the result of the new and unique application of this technology. The Complex Systems Research Center, at the University of New Hampshire, has aided us in post-processing by providing us with instruction and resources. The mosaicing should be completed in the fall.

While not yet a continuous image, the thermal imagery has been instrumental in locating SGWD zones. All indications are that this use of the technology has been a success. To date, nearly 200 SGWD zones have been identified and cataloged from the thermal images. Specific zones have been selected, based on the size, intensity, and accessibility and are currently being field verified. A methodology has been developed for field verification, and has been applied to several significant SGWD zones located around the bay, particularly at Wagon Hill Farm in Durham, NH. Field verification is a slow process and will only be used to ground-truth a representative cross-section of the zones identified from the images, and only to the extent that is necessary to evaluate the efficacy of thermal infrared imagery for groundwater identification.

The field verification methodology has focused on four characteristics: flow, piezometric gradient, discharge area and hydraulic conductivity. The flow is measured using a variation of the typical seepage meter, encompassing an area large enough to obtain a measurable flow. The discharge area was determined by placing a grid over the suspected discharge zone and measuring soil temperature, cell by cell, to identify the colder, groundwater-discharge area. The delineated thermal plume is used for locating seepage meters, mini-piezometers and soil cores. Field-verified discharge areas will be compared with the digitized thermal discharge areas to determine how accurately study-wide discharge area estimates from the thermal images will be. The groundtruthing methodology also provides indirect measurements of hydraulic conductivity using Darcy’s Law from measured flow, piezometric gradient, and discharge area. Indirect determinations of hydraulic conductivity will be verified in the laboratory.

The field investigations of SGWD zones and verification of thermal imagery described above are part of the Phase 2 scheduled activities. Progress has also been made on second year tasks that included Phase 2 water-level measurements, surveying of monitoring wells, installation of overburden wells, and geophysical analyses of specific discharge locations.

In the early summer, two large Phase 2 data collection events occurred: a monitoring-well survey event, and a depth-to-water monitoring event were performed for the entire study area, including nearly 200 homeowner wells. The first component of the monitoring well survey event took place over a single week using Real Time Kinematics (RTK) GPS. An instrument (RTK) was rented from Maine Technical Services, which included a full day of training prior to operation. Event planning involved selection of base stations, obtaining the necessary access for points around the bay, and scheduling teams of two to three people throughout the day and night when satellite availability was optimal. The NH Geodetic Survey office provided us with survey benchmarks from which to base our surveying efforts. Specifically, we used a station at Cedar Point that is part of the national High Accuracy Reference Network (HARN), which has geodetic accuracy control with latitude, longitude and elevation of several millimeters. Base stations were selected at Cedar Point, Wagon Hill, Waste Water Treatment Plant, in Durham, NH; Stratham Hill, Stratham, and Woodman Point in the National Wildlife Refuge in Newington, NH. The base station located at Woodman Point proved to be the most effective location. The biggest problem encountered with this technique was the interference from tree cover, which blocked direct access to satellite signals. Woodman Point was the most effective base station, as much of the study area was directly across open water from Woodman Point. Signal range was nearly 6 miles from Woodman Point in some cases, whereas through dense trees, the range at Wagon Hill was limited to a mile and a half. RTK was successful, achieved an elevation accuracy of 2-3 cm, and greatly reduced well survey efforts. Following RTK, some "clean-up" survey activities were required to close survey loops the RTK could not close. This effort required only a few additional weeks, and is now complete. The RTK technology saved several months conventional survey efforts. The results will be used for construction of the Phase 2 potentiometric map. . The bulk of the spreadsheet data reduction is completed and awaiting groundwater contouring. The actual contouring will be completed this fall.

The second Phase 2 task completed in early summer was a "snapshot" measurement of the groundwater elevations in over 200 homeowner wells. The depth-to-water measurement event took place in a single week and was without problems. The results of the RTK survey were used to convert measured depth to groundwater to elevations. Both of the Phase 2 tasks were done with the help of USGS personnel.

Installation of micro-wells has begun in the overburden at select locations where SGWD zones have been located. At Wagon Hill, a series of nested wells were installed to evaluate, in detail, the vertical gradient of delineated zones and any tidal influences. These wells will be monitored over many tidal cycles using pressure transducers.

Geophysical analyses are being performed by the USGS with assistance from university researchers. Sites are selected where SGWD zones and suspected bedrock fractures have been identified. Electrical resistivity techniques are being used. This technique may be supplemented by ground penetrating radar, in coarse-grained deposits. Post-processing will be performed by the USGS that will characterize fracture zones and surficial materials in detail. Of special interest will be the thickness of the surficial materials.

Aquifer characterization by well tests will begin in the fall after the weather prevents further field investigation of SGWD zones. Equipment has been prepared for the well testing including construction of decontamination equipment and the purchase of a field laptop computer.

Phase 2 water quality analyses will focus on nitrogen species: nitrate, nitrite, and ammonia. Progress to date has been on the preliminary logistics of this task. Sample preservation and preparation methods have been determined and a final list of analytical labs has been prepared. Sampling will begin late summer with individual samples being preserved until sampling of the study area is complete, at which point samples will be delivered to the lab for analyses. Sample locations are currently being identifies. Samples will be taken from wells throughout the study area, in areas suspected to have elevated nitrogen, areas suspected to represent non-contaminated background levels and SGWD zones. Samples will be taken from monitoring wells, mini-piezometers and micro-wells. Other water quality data is being gathered from some participating homeowners that have had recent analyses of their well water. Collaborative efforts with the National Water Quality Analysis being performed with the USGS will provide lab results from samples derived by packer testing of bedrock fractures. This data should be available for each of the three supplemental bedrock wells that were installed in the fall of 1999: Adams Point, National Wildlife Refuge, Fabyan Point wells. These wells are continuing to be used collaboratively with multiple research projects. The Fabyan Point well is being used for another CICEET project researching bedrock bioremediation as well as for borehole geophysics with the USGS.

The USGS has made progress in gaging stream flow from the major tributary streams, as well as performing a gaging study of selected minor tributaries in an effort to estimate groundwater flux during periods of low flow from groundwater discharging into the surface water streams. Water quality samples of the tributary streams under low flow conditions are being taken to characterize the groundwater base flow quality.

An educational sign was posted at the Adams Point Wildlife Management Reserve, as one of the agreed-upon conditions for well installation on New Hampshire Fish and Game land. The sign explains the importance of groundwater discharge to estaurine systems, the objectives of this research project, and the purpose of the monitoring well. The New Hampshire Fish and Game department supported the University of New Hampshire’s research efforts in conjunction with the Great Bay Research Reserve. The permit agreement includes mutual ownership of the well and university maintenance as long as research continues, remediation, and revegetation as necessary resulting from the drilling efforts.

Difficulties Encountered

The most significant difficulties over this period have surrounded the thermal infrared aerial survey. The first difficulty was in scheduling a flight within the constraints of the researchers and the availability of the subcontractor. This was accomplished on April 11, 2000. The subsequent difficulties have been as a result of the unique application of this new technology, and the need to mosaic over 200 images into a single-layer coverage in a GIS database. The importance of the mosaic is in the power of GIS to correlate data geographically, or to "overlay" various layers into a composite map. We plan to overlay, and correlate SGWD zones with suspected bedrock fractures, piezometric surface, and geology, among others. The difficulty has been in trying to use software provided by the USGS to perform the orthorectification and the mosaicing of the thermal infrared images. It does appear that the Complex Systems Research Center has been able to help us find a solution to the post-processing difficulties by providing us with instruction and resources. The UNH researchers should complete the mosaicing in the fall of 2000.

Additional problems have arisen from the spring survey that will be corrected in the subsequent summer survey. There has been a problem with a lack of image overlap that appears to have resulted from slight variations in the attitude of the plane at 10,000 ft elevation that should be correctable through a change in survey approach and a tightening of the flight lines. For the April survey, the flight lines were set to overlap 200 ft on either side, which will be increased to 300-400 ft.

Some dataloggers in the moored thermometer array have disappeared this spring. Only a single datalogger was lost all winter due to the ice but now in the past five months, four additional dataloggers are missing. They were in areas where there is potential conflict with lobster pots. New dataloggers have been ordered and will replace the missing ones in areas where there is no lobstering and in SGWD zones.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period

None of the problems or task extensions will affect the completion of scheduled project objectives. The delay in the mosaicing will be extended until the bulk of the summer fieldwork is completed and efforts can be refocused onto image post-processing. The delay in the mosaicing may delay the construction of piezometric head map, albeit not significantly.

Preliminary data

The project is in the middle of the data gathering stage. In Phase I, the body of data has been gathered and the initial thermal infrared aerial survey has been completed with a second survey planned for the late summer. The results of the cataloguing of the SGWD are complete. Map 1 illustrates the coverage of the nearly 200 zones delineated from the thermal imagery and the locations of some of the field verifications. Figure 1 is an example of two of the delineated discharge zones from thermal infrared imagery. Table 1 illustrates the type of information collected from the field verification efforts, using the two catalogued SGWD zones of Figure 1 as an example. Early estimates show that some of the large discharge zones may be between 2000-6000 square feet with a flow per discharge area of 4-16 gallons per day per square foot. This would result in groundwater discharge rates of 0.01-0.15 cfs just for those zones. This implies that there is a substantial daily groundwater contribution to the Great Bay Estuarine System, considering there appear to be 200 or more similar zones.

Map 1: Submarine groundwater discharge zones in the Great Bay delineated from thermal infrared aerial survey flown at 10,000’

Figure 1: Delineated submarine groundwater discharge zone from thermal infrared imagery

Table 1: Preliminary estimates of discharge values from field verification of groundwater discharge zones at Wagon Hill, Durham, NH

Name	Size of Principal Axis	Type	Intensity	Flow/Discharge Area (GPD/sf)	Discharge Area (sf)	Discharge (cfs)
Wagon Hill #1	Medium	Dendritic	Medium / Low	15.9	5800	0.14
Wagon Hill #2	Medium	Dendritic	Medium	4.5	2050	0.01

Tasks and activities for next reporting period

Tasks for the next reporting period

Completion of the Phase 1 tasks is expected during the next reporting period. The Phase 1 tasks are related to the delineation of groundwater discharge zones. The completion of Phase 1 requires the mosaicing of the thermal infrared images, which is expected in the fall of 2000. An additional summer survey will be performed in late August, which will evaluate seasonal effects upon groundwater discharge. Limitations in the initial survey and the mosaicing process, having been resolved, shall proceed expediently for the next survey.

Completion of the Phase 2 tasks is also anticipated. This will involve the contouring of groundwater surface elevations using the completed data set plus the results of the field verification efforts. A second groundwater level measurement event is planned for early winter, to obtain a winter piezometric map. Water surface elevations will be obtained for wells on Pease International Tradeport, which correspond to both measurement events.

A product of the potentiometric maps will be the determination of flow directions and estimates of total groundwater flow to the Great Bay estuary. These flow estimates will be compared with calibrated, field verified, flow estimates made from discharge zones. Further field verification will be performed to determine the range and scale of groundwater discharge, and resolve any differences between methods.

The completion of Phase 2 will include the final task for aquifer characterization. Geophysical analyses are currently being performed on select zones where suspected bedrock fractures exist and where delineated discharge zones have been shown. These analyses will be completed by the end of August and post-processing will be completed by the USGS shortly thereafter. Well testing will be performed in the fall of 2000. Slug tests will be performed on many of the wells to obtain point values for hydraulic conductivity, and/or transmissivity of the aquifer.

Chemical species of interest and methodologies for Phase 2 water quality analyses have been determined and sampling will begin in the fall of 2000. Water quality analyses will target discharge zones, and select upgradient wells. Collaborative efforts with the USGS National Water Quality Analysis will provide water quality data specific to bedrock fracture zones. Work will continue in late summer, with the selection of locations for groundwater quality analysis. 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.

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.

Work plan to accomplish tasks

A project meeting with the USGS and UNH was held this summer to coordinate summer and fall field events. Responsibilities and tasks were allocated for the various project components.

Phase 1 SGWD zone field-verification will be performed on roughly 10-20 delineated discharge zones. Once a representative cross-section of SGWD zones has been obtained, estimates of the total groundwater discharge area and flow will be made based on zone classifications and the digital thermal images.

Following the completion of field verification of SGWD zones, efforts will be refocused upon mosaicing the thermal images. A continuous image is necessary to digitize zone areas. University researchers using the mosaicing software Erdas Imagine, provided by the Complex Systems Research Center, will perform Mosaicing. 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 ArcView 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 determine 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.

Phase 2 efforts for the creation of potentiometric surface maps will proceed when weather prohibits field efforts. A final depth-to-water event will be performed in the late fall/early winter. This event is expected to last one week. Prior to this event, select wells will be chosen for water quality sampling, which will be performed concurrently with the measurement event. Geophysical analyses are currently being performed with the USGS and university researchers, with expected completion by the end of August. Data reduction will be performed in the fall, and the results will be incorporated into a GIS data layer.

Phase 2 water quality sampling will begin in late summer. Final selection will be made of locations for groundwater quality analysis. Samples will be collected for each field verified SGWD zone, and from selected monitoring wells during the fall groundwater measurement event. All samples will be cataloged, preserved and delivered to a local laboratory. Where the samples from the SGWD zone is along a suspected flow path from a sampled well, the water quality analyses results will compared with regard to signature concentrations to evaluate if there is a direct connection, and whether the flow system is local or regional in nature.

Another Phase 2 task to be completed during the late summer/fall months is the aquifer characterization. Slug tests will be performed on many wells to obtain point values for hydraulic conductivity, and/or transmissivity of the aquifer. Because of the ease of performing slug tests, they will be used at many locations to increase point value reliability. Geophysical characterization (electrical resistivity or seismic refraction) may be used in specific areas of interest where increased resolution of aquifer thickness is desired. This will most likely coincide with locations of supplementary small-diameter wells in the overburden.

Low flow measurements may also be used to verify discharge estimates. Low flow measurements will be made by the USGS on selected tributaries around the study area. Multiple order tributaries will be examined, from small first order streams to the larger third order rivers such as the Squamscott River. The larger tributaries may be measured for net discharge by the USGS using an acoustic Doppler radar. Use of acoustic Doppler radar for discharge determination in large tidal rivers is much improved from conventional means using mechanical current meters and stage and discharge relationships. Acoustic Doppler should improve estimates of groundwater discharge for the higher order tributaries.

Concerns or difficulties

Groundwater discharge estimates made from field verifications may show a wide range of discharge reflecting the heterogeneity of the hydrogeologic system. This heterogeneity may result in a wide range of discharge estimates. This is not expected to pose a significant problem.

Expenditures

The expenditures to date are within the range of those planned for this stage of the project.