Progress Report

CICEET Progress Report for the period 9/16/05 Through 3/15/06

Project Title: Effectiveness of Reactive Barriers for Reducing N-Loading to the Coastal Zone
Principal Investigator(s): Joseph Vallino and Kenneth Foreman
Additional Investigator(s): Pio Lombardo
Project Start Date: September 1, 2004

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Project Objectives for This Reporting Period
Objectives
In order to determine how the NITREX™ permeable reactive barriers (PRBs) are processing groundwater nitrate, we have continued to sample wells for NO3-, NH4+, DOC, DON, BOD, salinity, DO and N2/Ar ratios in and around the NITREX™ PRBs. Addition wells have been installed and sampled to better resolve groundwater biogeochemistry as it passes thought the PRBs. Because the NITREX™ media alters the hydraulic characteristics of the system, a dye release study was conducted to determine if groundwater below the PRB is being entrained into the PRBs. To understand how sulfate in seawater may alter biogeochemistry in the PRBs, we have constructed and are currently operating six pilot-scale laboratory PRBs. The laboratory PRBs are being perfused with either groundwater collected from the field, or with groundwater with periodic injections of seawater and are sampled for nitrogen, carbon, and sulfur constituents on a semi-weekly basis. The laboratory PRBs allow us to examine transient phenomena that are difficult to assess in the field.

In addition to research objectives, both the laboratory and field PRBs have served as research education opportunities for undergraduates as part of the MBL Semester in Ecosystems Science (SES) undergraduate program. In the fall of 2005 semester, two student projects involved characterizing both the laboratory and field PRBs (see Preliminary Data section below).

Tasks to meet objectives

  • Sample wells in the field NITREX™ PRBs for NO3-, NH4+, DOC, DON, BOD, salinity, DO and N2/Ar ratios as weather permits.
  • Install additional wells both up- and down-gradient of PRBs. Install wells up gradient for dye injection studies.
  • Conduct dye injection study: inject dye into up gradient well and follow dye plum over a 10 d period to elucidate hydrologic streamlines.
  • Construct pilot-scale laboratory PRBs with the NITREX™ media and examine 1) time required to attain steady-state operation and 2) how periodic injections of seawater (two 4 hour periods per day) affects nitrate removal.
  • Involve undergraduate students in CICEET project as part of the MBL Semester in Environmental Science program.

Progress on Tasks

  • The NITREX PRBs were extensively sampled during the weeks of 23 Oct, 20 Nov and 4 Dec 05.
  • Four additional wells were installed at the Waquoit Bay site in Oct 05: three up gradient of the PRB and one within the NITREX™ medium. The depths of two existing wells were extended deeper to examine processes beneath the PRB.
  • A dye injection study at the Waquoit Bay site was conducted over a 10-day period on 1 Dec 2005. Both Rhodamine and fluoroscein were injected simultaneously at different depths.
  • Six pilot-scale PRB’s were constructed and studied over a two week beginning on 16 Nov 05. A second set of experiments were recently begun 1 Mar 06, and will be run for approximately 5 weeks.
  • Two SES students used the laboratory and field PRBs in their undergraduate research projects.

Difficulties
Over the last reporting period, we have not encountered any difficulties in conducting the planned research, but we did observe an unexpected event. We anticipated that the PRBs might be inundated with seawater during extreme tide events associated with coastal storms. However, our surveys (see below) indicate that seawater is intruding into the PRBs on almost every spring tide. This observation prompted us to construct the laboratory PRBs to study periodic seawater intrusion.

Project Objectives for Next Reporting Period

Objectives
Although our original proposal called for the introduction of seawater into the NITREX™ PRBs at this time, these experiments are no longer necessary as seawater regularly interacts with the PRBs. Consequently, our plan is to continue sampling the field PRBs as well as examine how the laboratory PRBs function with periodic addition of seawater. If time permits, we will also continue our dye studies to examine the hydrology around the PRBs that is strongly driven by tidal pumping.

Tasks to Meet Objectives

  • Sample groundwater wells and analyze for nutrient concentrations. Also, analyze nutrients collected from previous samplings.
  • Sample pilot-scale PRBs.
  • Construct mass balances around both field and laboratory PRBs to ascertain how nitrogen is processes by the NITREX™ medium as well as determine the impact of seawater on N processing.

Work Plan for Next Reporting Period

  • One more field survey of the PRBs is planned in April 06.
  • Laboratory PRBs will be run for approximately 5 weeks starting 1 Mar 06.
  • Remainder of period will focus on synthesizing results, and preparing manuscripts and final CICEET report.
  • Communicate results to end-users.

Anticipated Success in Meeting Project Objectives
We foresee no problems with proposed objectives and anticipate success.

Overall Project Timeline Update
The project is proceeding as originally planned.

Preliminary Data
Observations at Waquoit Bay NITREX™ PRB
The latest set of data collected from the Waquoit Bay NITREX™ PRB in the Fall of 2005 shows that ground water nitrate is being completely removed by the NITREX™ PRB (Figure 1). However, the same survey also shows significant intrusion of seawater as evident by the high salinities within the PRB (Figure 2). As expected, oxygen is consumed within the PRB resulting in low dissolved oxygen (DO) concentrations both within, below and down gradient of the PRB (Figure 3). The plume of high DO near the surface in wells W5, W6 and W7 (Fig_3.gif) is likely caused by seawater over washing the PRB during high tide. Although not confirmed yet, the dense seawater may be driving a downward advection of water through the PRB around well W6. Our dye release studies indicate that groundwater is traveling at 0.35 m d-1 (Figure 4). Although following the dye plume was difficult given the co-planner arrangement of the wells, there does appear to be some vertical velocity (upward) in the groundwater that may be due to the higher hydraulic conductivity of the NITREX™ medium (Figure 5).

Results from Laboratory Pilot-Scale NITREX™ columns
Six pilot-scale NITREX™ filled columns (Figure 6) were perfused with either nitrate amended fresh groundwater, or seawater to examined transient response of NITREX™ media as well as examine affect of seawater intrusion. Columns perfused with nitrate-amended groundwater (~ 150 µM total) showed almost immediate and complete removal of nitrate, with only small amounts of nitrate (5 µM) and ammonium (11 µM) detected in the first few days of operation (Figure 7). There was an initial increase in dissolved organic nitrogen (DON); however, after only 13 days, approximately half of the entering DON was removed by the columns (Figure 8).

Two other sets of columns (Treatment 2) were switched over to 75% seawater with 25% nitrate amended groundwater for a two-day period starting on day 15. Because of high longitudinal dispersion in the columns, it is difficult to determine the extent of sulfate removal (Figure 9), but hydrogen sulfide production is clearly evident (Figure 10). The addition of seawater and associated production of hydrogen sulfide, however, does not appear to affect neither nitrate (Figure 11) nor DON removal, which is consistent with our field observations

Dissemination
Publications: Jennifer Reimer and Sabrina Moreau’s papers on the presentations listed below will be posted at http://courses.mbl.edu/SES/ in the near future.

Conferences:
Jennifer A. Reimer, “Nitrogen Dynamics in Flow-through Microcosms of Nitrex™”, Semester in Enivronmental Science Symposium, Woods Hole, MA 16 Dec 05.

Sabrina Moreau, “Influence of NITREX™ Permeable Reactive Barrier on groundwater flow paths and dissolved carbon and nitrogen concentrations”, Semester in Enivronmental Science Symposium, Woods Hole, MA 16 Dec 05.

Outreach Activities:
The project continues to garner good publicity and was featured in the ENVIRONEMENT section of The Cape Codder newspaper on 9 Dec 05.

Contact with End Users:
The Town’s wastewater superintendent, Amy Lowell, and other members of her staff, were invited to the Semester in Environmental Science final symposium held in December, 2005, at which the data shown here were reported. In March, 2006, we also reported on the results of our study to date at the board meeting of the Falmouth Associations Concerned with Estuaries and Salt Pond, a citizens group drawn from a number of community associations. We have not formally approached the town yet to present a report, as our results at this time are too preliminary, but will do so once the final data sets have been collected, compiled and analyzed.

Expenditures
Expenditures are in range anticipated for work accomplished.

End User Advisor Feedback
Name: Brian Currie
Organization: Town Planner
Location: Town of Falmouth, MA
Phone number: 508 495 7440
E-mail: bacurrie@town.falmouth.ma.us
1) At this stage, what are the potential applications for this research? Please discuss how you and others could potentially use the technology.
Potential application of this research includes the use of this technology by Town of Falmouth regulatory boards and commissions for nitrogen abatement from new developments.

2) What, if anything, has changed about this project's potential applicability since the last reporting period (not applicable to the first Progress Report)?
There has not been any change about this project’s potential applicability.

3) Do you see any key challenges that the researchers may want to address or keep in mind?
Cost effectiveness of the technology vis-à-vis other existing technology.

4) Does this report offer you enough information to adequately address the above questions?
Yes.

5) Other feedback?
Eventually a cost analysis of the technology will be necessary for maintenance and useful life of the product. Thank you for this opportunity to comment.