CICEET Progress Report for the period 9/16/06 Through 3/15/07

Project Title: Evaluation of Leachfield Aeration Technology for Improvement of Water Quality and Hydraulic Functions in Onsite Wastewater Treatment Systems
Principal Investigator(s): Jose A. Amador, Professor, Univ. of Rhode Island
Additional Investigator(s): David A. Potts - President, Geomatrix, LLC, Killingworth, CT; Josef H. Gorres - Associate Research Professor, Univ. of Rhode Island; George W. Loomis - Research & Extension Soil Scientist, Univ. of Rhode Island; David V. Kalen - Environmental Engineer, Univ. of Rhode Island; Erika L. Patenaude - Research Assistant, Univ. of Rhode Island
Project Start Date: 1 September 2004

Figures

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Tables

Table 1

Table 2

Table 3

Table 4

Table 5

Table 6

Tasks to meet objectives
Objective A: Installation of SoilAir Systems
A meeting attended by J. Amador, D. Kalen, and G. Loomis (URI), D. Potts (Geomatrix) and S. Denoyelle (RI Dept. of Mental Health, Rehabilitation and Hospitals, RIMHRH) took place on Friday, 22 September 2006 at the Kingston campus of the University of Rhode Island. End-User B. Moore, of the RI Dept. of Environmental Management (RIDEM) was unable to attend, but was appraised of the discussions by D. Kalen. A consensus on the terms of the Installation, Operation, and Maintenance (IOM) Agreement was reached by all parties (Geomatrix, RIMHRH, RIDEM, URI) as a result of this meeting.

Three of the six sites (Sites 1, 3 & 4; Table 1) were selected for installation of a SoilAir system (based on stability of wastewater quality parameters over the previous 6 months and structural integrity of existing septic system infrastructure) after consultation among personnel from Geomatrix, URI, and RIMHRH. System installation began the first week of October 2006 and was completed on the third week of October 2006.

Ongoing monitoring of water quality parameters and gases was only moderately altered as monitoring continued until installation started, and resumed one week after installation was completed.

Objective B: Evaluation of effects of aeration on hydraulic function and water quality
SoilAir systems have been in continuous operation at Sites 1 and 3 since late October 2006. System operation at Site 4 was interrupted by the discovery of a leaking toilet that resulted in an excessive hydraulic load to the septic system. RIMHRH was informed of the problem and the toilet was repaired promptly, before aeration resumed the first week of November, 2006. Monitoring of gas composition and water quality parameters has continued at all six sites approximately every two weeks.

Progress on Tasks
We have accomplished all the tasks outlined for this reporting period: (i) satisfactory terms were reached on the IOM Agreement, (ii) SoilAir systems were installed, and (iii) monitoring of gas composition and water quality has continued at all field sites, with additional data gathered on hydraulic load and functioning at sites in which the technology was installed.

Difficulties
Aside from the leaking toilet at Site 4 and sporadic delays in sampling due to inclement weather, we have not experienced difficulties during this period.

Data Generated to date
Description of Study Sites
A total of 6 sites were instrumented for water sampling in February 2006 and have been monitored for the past 11 months. The sites are group homes managed by the RI Dept. of Mental Health, Rehabilitation and Hospitals in Washington County, RI, with three sites in Charlestown, two in South Kingstown, and one in Exeter (Table 1). Five of the six systems rely on stone-filled leachfield trenches for septic tank effluent dispersion, with concrete chambers (locally called galleys) employed as the dispersal method in the remaining system.

Each septic tank is fitted with a pipe placed near the tank outlet to a depth of 45 - 60 cm below the effluent level for sampling of septic tank effluent. The sites are instrumented with three clusters of ceramic cup lysimeters and/or slotted wells. Cluster locations within a site are as follows:

Cluster 1 (C1): Upgradient from leachfield
Cluster 2 (C2): Between leachfield trenches or galleys
Cluster 3 (C3): Downgradient from leachfield, immediately adjacent (15 - 20 cm) to outer wall of last trench or galley

Within each cluster, sampling devices were installed as follows:
Lysimeters: Bottom of cup at a depth of 30 and 90 cm below the elevation of the leachfield infiltrative surface (designated C1-30, C1-90, C2-30, C2-90, C3-30, C3-90).

Wells: Slotted (15-30 cm) section partially or completely below groundwater elevation level at time of installation (designated C1-W, C2-W, C3-W).

Three of the six sites (Sites 1, 4 and 5) have the full complement of instrumentation (Table 1). Site restrictions prevented installation of Cluster location C1 at Site 2, of all Cluster location groundwater wells at Site 3, and of the Cluster location C2 groundwater well at Site 6.

Installation of SoilAir Systems at Sites 1, 3 and 4
Necessary SoilAir™ system components, time dosing pumps and associated controls were retrofitted onto Sites 1, 3 and 4 (Figure 1). In conjunction with this work, approximately 50%, 50% and 68% of the leachfield system capacity was isolated from the wastewater flow at Sites 1, 3 and 4, respectively, in order to further test the hydraulic capabilities of the SoilAir technology (Figure 2). Just prior to the installation of the SoilAir and septic tank effluent pump (STEP) components, the septic tanks were pumped.

At each site a septic tank effluent pump (STEP) system was installed in the second compartment of the most downstream septic tank (Figure 3). Float switches were set to drop the effluent levels in the tank by approximately 6” (15 cm) to provide for flow equalization capacity. Air lines, consisting of 2” (5 cm) Schedule 40 PVC, were run from the SoilAir enclosure and connected to the pipe between the septic tank and the leaching system. Distribution boxes (D-boxes) and inspection ports were sealed to prevent the short-circuiting of air (Figure 4). Temporary power and control cables were connected to the SoilAir system, STEP system and associated float switches. A telecommunications cable was connected between the SoilAir controls and the building to facilitate modem communication for remote telemetry of the systems.

The microprocessor-based controllers were configured to operate both the SoilAir blower and the timed-dose STEP system. The STEP system was programmed to run for a set period of time, which correlated to the desired dose. The STEP dose interval was programmed to run every six hours, unless a high level or low level float switch was triggered. The SoilAir blower was programmed to remain inactive for approximately one hour after a wastewater dose. After this delay interval, the SoilAir blower was programmed to run for a set period of time, and turn off for a period of time. The blower and STEP system were interlocked to prevent simultaneous operation, with priority given to the STEP system.

Operational data is forwarded via a modem-based telemetry system (on a shared telephone line) on a weekly basis. However, if an alarm condition is detected, the telemetry system will automatically call in when the shared telephone line is free and forward all operational data. The water level and composition of gases in the D-box are measured biweekly through an access port installed during installation of the SoilAir system.

Sampling
Two sampling phases are distinguished for the purposes of comparing water quality parameters and gas composition. Phase I represents the period prior to installation of SoilAir systems and includes the following sampling dates (all in 2006): 9 March, 23 March, 6 April, 20 April, 4 May, 18 May, 1 June, 15 June, 6 July, 20 July, 8 August, 24 August, 8 September, and 22 September. Phase II represents the period during which the SoilAir systems have been in operation. For Sites 1 and 3 this includes the following sampling dates 11 October 06, 26 October 06, 9 November 06, 22 November 06, 7 December 06, 19 December 06, 4 January 07 and 23 January 07. For Site 4, Phase II includes dates from 9 November 06 on. Septic tank effluent (STE), groundwater wells and lysimeters were sampled as described in a previous report.

Analyses
The same number and type of analyses were conducted as described in the previous report at all six sites. However, in this report we focus on preliminary data on changes in removal of total N, total P, and total organic C (TOC) because these parameters are of particular interest with respect to the ability of onsite wastewater treatment systems to safeguard water quality.

The mean concentration of N, P, chloride (Cl) and TOC in samples from C1 (upgradient or background) lysimeters was subtracted from mean concentrations for samples from C2 and C3 lysimeters (within and down gradient of the leachfield, respectively) at the same depth to correct for background effects. The apparent percent reduction, R, for constituent X was calculated using the equation:

R_X = 100 X [(C_X-STE - C_X-LYS)/C_X-STE] [Eq. 1]

where C_X-STE is the concentration of constituent X in septic tank effluent and C_X-LYS is the background-corrected concentration of X in a sample from a lysimeter, both expressed in mg L^-1.

The flux, _, of a constituent X (mg m^-2 d^-1) across the soil interface in the leachfield was calculated using the equation:

_X = [((R_X - R_Cl)/100) X (V_STE X C_X-STE)]/A/t [Eq. 2]

where RX is the observed mean reduction for constituent X (%), R_Cl is the observed mean reduction for Cl (%), V_STE is the mean volume of septic tank effluent applied to the leachfield (L), C_X-STE is the mean concentration of constituent X in septic tank effluent (mg L^-1), A is the estimated basal area of leachfield (m²) and t is time (d). This calculation assumes that Cl acts as a conservative tracer of the movement of STE through the soil, with apparent reduction attributed exclusively to dilution. Apparent reduction for constituents other than Cl larger than those observed for Cl are assumed to represent loss processes other than dilution (e.g. biological uptake, abiotic sorption); whereas those values lower than observed for Cl are assumed to represent production processes (e.g. mineralization of organic compounds, desorption). Values of A prior to and after installation of SoilAir systems at Sites 1, 3 and 4 (Table 2) were estimated from design plans submitted to RIDEM as part of the original permitting process for septic system installation and knowledge of which trenches were isolated when the SoilAir system was installed. Values of V represent the mean of automated measurements of the volume of STE dosed daily to the leachfield and were assumed to be the same prior to and during operation of the SoilAir systems (Table 2).

Results
Values of concentration and percent reduction of Cl, N, P, and TOC at Sites 1, 3 and 4 prior to (Phase I) and during (Phase II) operation of the Soil Air system are shown in Tables 3, 4 and 5. The most marked impact of the SoilAir system on reduction for N, P, and TOC was observed at site 4, where values of RX were similar during Phase I and Phase II, or were higher during Phase II (Table 5). These results were observed despite the fact the system was operating using only 32% of the leachfield capacity available during Phase I and the mean concentration of N, P, and TOC in STE was slightly higher during Phase II. Fluxes of N, P, and TOC at Site 4 (Table 6), which take into account differences in leachfield area and constituent concentration in STE between the two phases (Eq. 2), suggest that net removal of N, P and TOC was taking place prior to operation of the SoilAir system, as indicated by positive flux values. However, during Phase II, flux values were at least an order of magnitude higher than during Phase I for all three constituents.

Operation of the SoilAir system at Site 3 also appeared to have a positive effect on values of R_X for N, P, and TOC, which generally were either similar during both phases, or higher during Phase II despite a 50% reduction in nominal leachfield area (Table 4). The negative flux of N indicated net production at three of four points under the leachfield during Phase I, whereas net removal of N was apparent during Phase II in both of the lysimeters that sampled soil pore water 90 cm below the leachfield (Table 6). P reduction at Site 3 was generally enhanced by operation of the SoilAir system, as indicated by positive flux values that were 2 to 15 X higher during Phase II (Table 6). Effects on TOC seemed to be mixed, with net reduction observed during Phase I at three of four points under the leachfield (Table 6). In contrast, at two of these points, negative flux values were observed for TOC during Phase II (indicating net production), but positive values that were 4 to 10 X higher than during Phase I were observed at lysimeters positioned 90 cm below the infiltrative surface (Table 6).

Reduction of N, P and TOC were also impacted positively by operation of the SoilAir system at Site 1, with higher values of R_X observed despite a 50% reduction in leachfield capacity (Table 3). When considered in terms of flux, operation of the SoilAir system appeared to make flux values for N less negative in three of four lysimeters, and positive (net removal) in the fourth (Table 6). Modest increases in P removal were observed between Phase I and II, with higher increases observed for TOC reduction during operation of the SoilAir system (Table 6).

Measurements of depth to water surface within the distribution box suggest that the hydraulic load at all three sites infiltrates readily, as indicated by the relatively constant, high depth values (Figure 5). Lower depth values for Site 4 during the early part of Phase II are due to a higher than normal hydraulic load from a leaking toilet. Variations in depth are the result of differences in timing of measurements relative to dosing events.

In general, operation of the SoilAir system at these 3 sites appeared to have a positive effect on the removal of N, P, and TOC, with clear differences in the magnitude of these effects among sites. In all cases, fluxes of these constituents were positive for lysimeters positioned at 90 cm below the infiltrative surface, suggesting that net removal was taking place prior to discharge to groundwater (Table 6). Furthermore, normal hydraulic function was observed in all three sites (Figure 5) despite increases in hydraulic load (Table 2).

Although many variables are likely to contribute to differences among sites, we note that Site 4, which had a high hydraulic load during Phase II (Table 2), exhibited the greatest enhancement in terms of constituent flux, followed by Site 3, with a load similar to that for Site 4, and Site 1, with a hydraulic load nearly 4 X lower than at Site 4. A similar positive effect of high hydraulic loading on constituent removal rates was observed in laboratory experiments conducted earlier in the project and presented in a previous report.

Project Objectives for Next Reporting Period

Objectives
Objective A: Final evaluation of effects of aeration on hydraulic function and water quality
Tasks to Meet Objective A:
1. Continue operation of SoilAir systems
2. Continue monitoring water quality parameters and gas composition biweekly, as well as hydraulic function, until the end of May 2007.
3. Compare pre and post-aeration data based on final data set.

Anticipated Success in Meeting Project Objectives
Aside from the normal delays caused by inclement weather, we anticipate no problems in meeting the project objectives listed above.

Dissemination
Publications:
Amador, J. A., D. A. Potts, E. L. Patenaude, and J. H. Gorres. 2007. Effects of depth on domestic wastewater renovation in intermittently aerated leachfield mesocosms. ASCE Journal of Hydrologic Engineering (Accepted pending revision)

Conferences:
D. Potts will deliver a seminar entitled "Effect of Aeration on a Failing Community Leach Field" at the Water for All Life Conference, 16th Annual Technical Exhibition and Conference & 1st International Conference, in Baltimore, Maryland, USA, March 10-14, 2007.

Outreach Activities:
4 October 2006 OWT 105C "Innovative and Alternative Technology Overview" Led by Loomis and Kalen and attended by a total of 22 professionals. The SoilAir technology was introduced in both of these courses as an experimental system.

Contact with End Users: The End User has been kept informed of the progress of the project.

Overall Project Timeline Update
We are on track with respect to the field phase of the project, which closes at the end of May 2007, when our no-cost extension ends.

Expenditures
Expenditures are somewhat lower than anticipated for this stage of the project

End User Advisor Feedback
Name: Brian M. Moore
Organization: RIDEM
Location: 235 Promenade Street, Providence, R.I. 02908
Phone number: 401-222-4700 ext 7713
E-mail: brian.moore@dem.ri.gov

1) At this stage, what are the potential applications for this research? Please discuss how you and others could potentially use the technology.
SoilAir continues to show great promise in septic system remediation and treatment.

2) What, if anything, has changed about this project's potential applicability since the last reporting period (not applicable to the first Progress Report)?
None. Installations have proven to be user-friendly and performing as expected.

3) Do you see any key challenges that the researchers may want to address or keep in mind?
No. Continued monitoring will catch any operating issues that arise.

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

5) Other feedback?
Not at this time.