Project Title: Measurement System for Localizing Groundwater Flows into an Estuarine Environment
Principal Investigator(s): Charles C. Sarabun, Daniel G. Ondercin, Linda Frizzell-Makowski, William S.L. Banks, Jonathan J.A. Dillow.

Accomplishments
Scheduled Tasks:

1. Complete and test the modified boom/sled system.
2. Resurvey Otter Point Creek.
3. Conduct ground truth survey at known groundwater inflow site.
4. Survey second NERR site.
5. Participate in Chincoteague Bay survey with USGS, NPS and Maryland DNR.
6. Document results of the surveys. Document and provide copies of the DAQ software and analysis software to CICEET. Document the details of the system assembly and components and provide to CICEET.

1. A sailboat whisker pole was modified to tow a bottom-skimming sled. A tilt sensor, pressure sensor, vertical thermistor array and water intake port comprised the sled equipment. Figure 1 shows the sled and it's equipment while Figure 2 shows the boom deployment scheme. The boom system allows us to access shallow water with the sled while standing off in deeper water with the boat. The system was tested in the central Maryland Tridelphia Reservoir so that the system performance could be observed in relatively clear water. The system was found to work well in water from 18 inches to approximately 10 feet. The tilt sensor sounds an audible alarm when the sled is not on the bottom and is used to maintain contact with the bottom over varying topography. The boom is extendable so that, potentially, water up to 15 feet depth could be surveyed. The principal sensor suite is housed in a manifold system, Figure 3, through which water drawn from the sled intake is pumped. Current sensors include temperature, conductivity (2), pH, chlorophyll fluorescence and DO. Two additional experimental sensors, a fast, optical DO and a phosphate sensor, will be added.
2. Otter Point Creek (OPC) was resurveyed; however, strong winds arose at the start of the field test resulting vertically homogeneous water due to the shallow depth (<3 feet) of OPC. Time and funds permitting, OPC will be surveyed again.
3. Dr. Tom McKenna of the USGS at the University of Delaware provided a site on Herring Creek off Rehoboth Bay where a known groundwater inflow exists (from thermal imagery and direct measurements). Using internal JHU/APL funds, we ran a transect along the creek shore where the groundwater inflow was known to be. Figure 4 shows the region indicating where there was no groundwater inflow and where the inflow was known to be. Figure 5 shows the results of the transect. The groundwater inflow is clearly evident in the data time-series. Unfortunately, the first passage through the region stirred up the shallow (~18 inches) water so that the inflow was not seen in subsequent transects. This has implications for the survey strategy since, apparently, once a pass has been made over a spot, there is sufficient stirring to remove any groundwater signature. An attempt was made to verify this two days later, however, there were technical difficulties with the data acquisition (DAQ) system and no survey was conducted.
4. Second NERR site not yet surveyed. This survey is anticipated in the second half of August.

5. This survey will be conducted in September in coordination with the other participants. Resistivity surveys conducted in May-June will be used to guide the survey planning.

Difficulties Encountered

1. No major difficulties were encountered during the development of the boom-sled system. We used a build-test-build approach in which we iteratively modified the system to achieve the desired results.
2. As indicated above, wind stirring homogenized the water column at OPC so that potential inflow sites found in 2000 could not be verified.
3. The major difficulty encountered was the DAQ problems. A principal DAQ computer was stolen the weekend prior to the Herring Creek deployment and problems were encountered in integrating the replacement PC into the system.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period
Our success at Herring Creek gives us confidence that we can detect groundwater inflows. However, it is clear that the survey tracks must be carefully planned since stirring caused by the sled appears to erase the immediate signature and may require some time before sufficient groundwater seeps back to form a detectable signature. Our primary goals now are to survey a second NERR site and the Chincoteague Bay site. We do not anticipate any problems in completing the surveys.

Preliminary Results
The only relevant preliminary data have been shown in Figure 5. This is the "truth" transect in Herring Creek that demonstrates that we can, indeed, detect groundwater pockets. Notable in that figure is the detection in the two lowest thermistors in the vertical array (6 and 10 cm. From the sled bottom), but not the third (17cm. from the bottom of the sled). Also notable is the delay in the event appearance in the pH trace. This is due to the slow (~15 sec.) response time of the pH sensor.

Tasks and activities for next reporting period

Tasks for the next reporting period

1. Complete the remaining surveys.
2. Complete the system documentation.

Work plan to accomplish tasks

1. Reintegrate DAQ system hardware.
2. Schedule and survey second NERR site. This site is anticipated to be Blackbird Creek in Delaware.
3. Schedule and survey Chincoteague Bay in coordination with USGS, NPS and Maryland DNR.

Concerns or difficulties
Our only concerns at this point are; 1) rebuilding the DAQ hardware to be compatible with the version of Labview currently in use and 2) ensuring that the compiled version of the DAQ software provided to CICEET is flexible enough to accommodate other user's DAQ hardware configurations.

Expenditures
(Note: Each institution's grants office responsible for submitting financial reports, so all you need to do in this section is to state whether or not expenditures were in the range anticipated for the work accomplished to date)

Report submitted separately by JHU/APL accounting. Project expenditures were within the range anticipated.