CICEET Progress Report for the period 9/01/01 through 3/01/02

Project Title: Application of the Marshland Upwelling System (MUS) to Treat Domestic Wastewater in Sensitive Coastal Areas
Principal Investigator(s): Kelly A. Rusch, Ronald F. Malone

Accomplishments
Scheduled Tasks and Progress:
Tasks 1-2: Site selection. 100% complete. The MUS has been installed along the northern end of the Grand Bay NERR in a tidal Juncus marsh peninsula bordering Bayou Cumbest. Two camps owned by Donald and Ingrid Glennon provide wastewater (grey and black) in addition to that produced by an outhouse (black) available for public use at the adjacent boat launch.

Task 2: MUS system design. 100% complete. A common, gravity-fed, holding tank (55 gal) collects wastewater from one camp and the outhouse. Collected water is routed to the main holding tank adjacent to the second camp via a sump pump. The main holding tank (300 gal) collects gravity-fed wastewater from the second camp and pumped waste from the holding tank.

Wastewater is sent to the injection well from the main holding tank by a timer controlled progressing cavity pump. A volumetric flow meter measures the cumulative volume of injected waste. Injection pressures are continuously monitored and recorded via a transducer and data logger.

Task 3: Fabrication and installation of the MUS system. 100% complete. The permitting process has been completed with the Mississippi Department of Marine Resources. System installation was completed on 05/29/01. A total of 38 observation wells surrounding a 12.5 ft deep injection well have been installed (Figure 1). Due to tidal influences, surface waters may not be representative of undiluted system effluent. Thus samples drawn from the 5 ft monitoring wells are considered a conservative estimate of the true effluent. Three sets of background wells at each corresponding depth were installed in areas uninfluenced by the wastewater plume. These wells indicate native salinities to help delineate the wastewater plume.

Task 4: Determination of influent wastewater characteristics. 75% complete. Biweekly influent samples have been collected (Table 1). Variable camp and outhouse usage, with peak activity during the summer months, explain the large variability. Figure 2 shows the wastewater composition over time. The sharp increase in nutrient and organic matter concentrations observed during November and December is attributed to sludge accumulation, subsequent degradation, and release.

Task 5: Determination of hydraulic conductivity of the experimental area. 50% complete. In-situ soil hydraulic conductivities were determined on May 16, 2001 using the piezometer or slug test procedure. Well recovery to the added slug of water was estimated based on the time required for the water level to drop approximately 2 ft. Measured hydraulic conductivities prior to wastewater injection are summarized in Table 2.

Task 6: Determination of baseline salinity levels in the experimental area. 100% complete. Background salinity, pH, and dissolved oxygen levels were measured in all wells twice a week for a two-month period. These values are currently being used to delineate wastewater plume location.

Task 7: Determination of dispersion patterns of the freshwater plume. 50% complete. A long-term tracer study was initiated on 7/11/01 to provide additional information with regards to plume migration within the subsurface. Diluted Rhodamine WT dye (~5 gal) was injected into the marshland subsurface and monitored through discrete well sampling. Samples were taken every four hours for the first ten days after dye injection. A weekly to bi-weekly sampling scheme followed. Figures 3 and 4 present the detected dye concentrations along two transects of 10-foot monitoring wells, LDBJ10 and IACK10, respectively. As expected, the injected tracer was first detected at the wells closest to the injection well (well C10 after 5 days and wells A10, B10, and D10 after 8 days). The vector distance from the injection well to the inner 10-foot wells is 4.72 ft. The time required for the tracer plume's center of mass to pass through the inner 10-foot wells (mean residence time) was calculated to be approximately 30 days. Between 33 and 55 days following initial tracer injection, the dye was first detected at the middle 10-foot wells (wells I10 - L10 at a vector distance of 8.38 ft). Detection of the tracer plume at these wells confirms the presence of the clayey sand layer which partially restricts the upward migration of the plume and encourages horizonatal transport from the injection well. The tracer plume has not been detected at the outer 10-foot wells (wells Q10 - U10 at a vector distance of 20.15 ft). The studies under this task will facilitate the determination of potential system success. Long-term evaluation of system success will require several years of data collection and analysis.

Task 8: System evaluation. 50% complete. Wastewater was initially injected for 30 minutes every 3 hours, when available, at a flowrate of 0.5 gpm. A total of 3,491 gallons were injected over the 9-week evaluation period (Figure 5). Overall performance (system components performance, injection pressures, water quality analyses) indicated that the MUS is capable of providing an effluent of acceptable quality under site conditions at Moss Point.

Injection flowrates were increased to 1.5 gpm from 8/23/01Î11/5/01 in an effort to establish the MUS's maximum hydraulic capacity. Under this injection scheme up to 360 gallons could be injected daily. Effluent CBOD5 concentrations were significantly greater (p = 0.05) than comparable values from the 0.5 gpm flowrate. Injection pressures also showed a marked increase, indicating possible hydraulic dysfunction. The 1.5-gpm flow was thus considered excessive.

Injection flowrates were reduced to 0.75 gpm on 11/5/01. Performance under this flowrate is still under evaluation. A total of 2,440 gallons have been injected to date (Figure 5). Preliminary results indicate that the upwelling system is capable of performing well under this injection scheme. Injection pressures indicate that acceptable hydraulic performance has been resumed. Effluent water quality is comparable to that from the 0.5-gpm and meets secondary effluent standards.

Task 9: Sample/data collection. 50% complete. Water samples and in-situ measurements have been collected twice per month from the influent source, monitoring wells, and an upstream bayou location (background). To date a total of 17 sampling events have been conducted since system initiation. Injection pressures are continuously monitored and recorded every minute to indicate any reductions in the injection zone permeability. Pressures are downloaded from the data logger monthly. Tables 3 - 5 provide a summary from each of the injection schemes evaluated.

Task 10: Modeling plume movement. 25% complete. Two laboratory bench-scale experiments have been constructed and are currently underway: a one-dimensional (1-D) and two-dimensional (2-D) system. The main objective of these experiments is to gain information on the transport mechanisms of bacteria in various soil types and salinities. Ultimately, data obtained from these studies will be applied to a model of the field site.

The 1-D experiment focuses on measuring the degree of bacteria retention in each media type. This system consists of a column containing the media of interest, saturated at a specified salinity. In order to simulate the intermittent nature of the MUS (i.e. the pumping and resting phases of the field system), continuous and pulse injection schemes will be compared to determine the transport extent under buoyancy and injection forces. A schematic of the 1-D system, including dimensions (in inches), is presented as Figure 6.

Delineation of the wastewater plume at the field site is performed by monitoring salinity changes with depth. However, the actual appearance of the plume is unknown. The purpose of the 2-D system is to enable visual confirmation of the plume dynamics through a given media type. A conservative tracer (i.e. Rhodamine WT) will be mixed with freshwater or wastewater and injected into a saturated media. Reservoirs located at the sides of the system enable attainment of a constant salinity within the saturated media. Sampling ports along the facing wall of the system allow for continual monitoring of tracer and salinity concentrations at varying distances from the point of injection. Travel times for bacteria from the point of injection to the surface will be determined for different media types and salinity values. A picture of one of the freshwater injection experiments is presented as Figure 7.

Task 12: Data analysis. 50% complete. A valid comparison of the tested injection flowrates requires hydraulic loading rates, along with influent bacterial, solids, nutrient and organic concentrations to be normalized with respect to time (Table 6). These results show that loading rates were highest during the 0.75 gpm flowrate due to increased constituent concentrations in the influent. This finding suggests that the inferior performance during the 1.5 gpm study was likely due to the increased injection velocities, not the hydraulic, solids, organic or nutrient loading rates. Furthermore these trends indicate that the MUS may be able to effectively handle greater volumes of wastewater per unit time than has been tested to date.

Based on previous work with the MUS, contaminant concentrations decrease exponentially with vector distance from the injection point. Fecal coliform and CBOD5 concentrations have followed similar trends at the Grand Bay NERR. Data presented in Figures 8 and 9 are taken from the 0.75 gpm injection flowrate. Based on these first-order relationships, approximately 12.5 vector feet of travel is needed for influent CBOD5 concentrations to fall below the permit limit of 25 mg/L. Similarly, vector distances from the injection well beyond 4.72 ft all revealed fecal coliform counts below the 14 colonies/100 mL standard for shellfishing waters.

Difficulties Encountered
Nitrogen may be removed from wastewater through the process of denitrification in which nitrate is reduced and lost as nitrogen gas. Denitrification is an anaerobic process that is dependent on nitrification. This nitrification occurs in aerobic zones. The low levels of dissolved oxygen in the primary holding tank and marsh subsurface restrict nitrification as evident by the high NH₄-N and the low NO₃-N concentrations of the influent. To promote nitrification within the holding tank and subsequent denitrification in the marsh soils a linear air pump was inserted at the primary holding tank. Two six inch air stones were connected to the air pump and inserted into the tank in order to achieve a dissolved oxygen level sufficient to allow nitrification to take place. The determination of long-term nitrogen removal will require at least several years of data collection..

Redox potential probes were constructed in order to determine whether the oxidation and reduction state of the sand/soil matrix is sufficient to remove NO₃-N from the soil through denitrification. Redox measurements will also help determine other terminal electron acceptors utilized during organic matter degradation. The probes are currently being installed on site.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period
Although the project started 3.5 months late, we are currently on schedule.

Because of the difficulties encountered, a no-cost time extension to June 30, 2003 is requested for this project.

Preliminary Results
Included in above discussions

Tasks and activities for next reporting period

Tasks and work plan to accomplish tasks for next reporting period
Task 4: Determination of influent wastewater characteristics. Bimonthly samples will be drawn from the main holding tank to further develop the present database of raw wastewater characteristics.

Task 7: Determination of dispersion patterns of the freshwater plume. A second dye study will be conducted within the project's last quarter. Results, coupled with salinity measurements, injection pressures, hydraulic conductivities, will help describe and predict plume dynamics.

Task 8: System evaluation. Preliminary results indicate that the MUS performs well under specific operating conditions and injection schemes. However, the limited volumes of wastewater provided by the camps limits evaluation of the system's hydraulic capacity. To alleviate this problem, synthetic wastewater will supplement that provided by the camps over a period of intense study (approximately 6 weeks). Thus the maximum volumes of treatable waste per unit time can be determined. This study will also further establish injection frequencies and flowrates that allow proper pressure dissipation within the subsurface. Routine water samples collection and analyses will continue to determine effluent quality under intense loading.

Subsequent work will focus on the long-term stability and performance of the selected injection schemes.

Task 9: Sample/data collection. Biweekly sample collection will continue throughout the remaining project timeline.

Task 10: Modeling plume movement. Experiments focusing on the 1-D and 2-D laboratory systems will be continued to gather additional information required to create a model describing plume movement at the field site.

Task 11: Development of operational guidelines. Collected data will be used to develop operational guidelines for fecal coliform bacteria, organic matter and nutrients. Data will be reduced to hydraulic, bacterial, organic and nutrient loading rates. These guidelines will be included in the technical manual to be prepared under Task 14.

Task 12: Data analysis. Mass balance analysis will be used to evaluate input, output and constituent removal. Relationships between influent and effluent substrate concentrations will be evaluated.

Task 13: Economic analysis. The cost of implementing the MUS under various operational formats will be determined and compared with other wastewater treatment alternatives.

Task 14: Preparation of technical manual. A MUS design, construction, and operation manual will be generated from data collected from this project.

Task 15: Coordination of 1-2 day field day for interested parties. Technology transfer activities will be conducted to present study results as they pertain to system use and adoption as a permittable technology. A field day at the Grand Bay site will be coordinated to demonstrate the MUS to interested parties.

Concerns or difficulties
None

Expenditures
Expenditures are in the range anticipated for work completed to date.