USE OF A SATURATED/ UNSATURATED ZONE GROUNDWATER MODEL TO INVESTIGATE SOIL-WATER DYNAMICS IN ON-SITE WASTEWATER TREATMENT SYSTEMS

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USE OF A SATURATED/ UNSATURATED ZONE GROUNDWATER
MODEL TO INVESTIGATE SOIL-WATER DYNAMICS IN
ON-SITE WASTEWATER TREATMENT SYSTEMS

• Ouro T Koumai
• James M HassettDepartment of Environmental
  Resources and Forest Engineering, SUNY - ESF,
  Syracuse NY 13210

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Presentation Outline

• Project Scope
• Treatment Data
• Hydraulic Data
• Conclusions

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CWC Septic Rehab/ Replacement and Monitoring
Project (2002- 2007)

1. Rehabilitate/Replace failing septic system
2. Investigate the use of Best Alternative
   Technologies (BATs) in sites with less than
   optimal conditions

Jim and Jessica at site M4
Catskill/ Delaware watershed with Monitoring sites
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Failure criteria

• Hydraulic failure (Easy to Observe)
• Breakout
• Outflow or visible back up to surface
• Unsuitable soil
• Treatment failure (Difficult to Observe)
• Inadequate treatment
• Unsaturated zone depth lt 2ft.

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System Design
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Peat Filter System
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Hassett Lysimeters
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Summary Sampling Design

• 24 sites sampled for one year
• (4C, 5R, 5A, 5P, 5S) quasi replication, quasi
  random
• Wide geographic distribution within watershed
• Multiple engineers and installers
• QA/QC program showed results adequate for
  purposes of study
• Sampling locations allowed multiple means of
  quantifying system performance

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Treatment Results

• System Operation versus System Design
• All systems operated at less than design flow
• Septic Tank Effluent
• Comparable to other studies
• Conclusion
• Differences in system performance attributed to
  differences among systems, and not hydraulic or
  organic loading issues

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Example Data-TOC at a Conventional Site
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Median Performance - TOC
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Overall TOC Removal Septic Tank Effluent to L4
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Removal of TOC in Pretreatment and Soil Systems
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Removal of TP in Pretreatment and Soil Systems
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Average Annual Cost per kg of Constituent Removed
by System Type
C R A P S
TOC 308 347 357 271 232
TP 1,350 1,936 2,391 1,767 1,868
Total Nitrogen 317 510 653 427 487
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Hydraulic Observations and Considerations

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Unexpected Flow Patterns
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Unexpected Degree of Soil Saturation
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Evidence of Weeping and Breakout
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Visual Indicators
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VS2DTI model
Preprocessor

• Model configured in accordance with site layout,
  topography, stratigraphy and hydrology
• Initial conditions represented by depth to water
  table and minimum pressure head

Postprocessor

• Pressure head
• Moisture content
• Saturation

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Modeling Choices
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Modeling Choices

• Domain size of leach field or mound
• Water input flow from septic tank
• Unsteady flow analysis

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Pressure head profiles
Example of simulated pressure head profiles at 0
hr (Left) and Time 86400 hr (right) for a
typical conventional SWIS
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Moisture Content
Example of Simulated moisture content profiles at
0 hr (Left) and Time 86400 hr (right) for a
typical conventional SWIS
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Percent Saturation
Example of Simulated Saturation profiles at 0 hr
(Left) and Time 86400 hr (right) for a typical
conventional SWIS
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Site data

• Perc test results (min/inch)
• Deep hole observations
• Soil texture
• Lot size, slope, etc.

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Engineering design data

• Flow rate
• Tank capacity
• Flow application rate
• SWIS basal area,
• field length and
• number of laterals

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Raised trench model
Conceptual VS2DT model for S1

• S1, base model
• 60 x 31
• 5 laterals at 0.021 ft/ hr
• Native soil tight clay
• Fill clay loam

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Applications of the VS2DT model to sites in the
Catskill/Delaware

• M4 Flow simulated to explain the occurrence of
  seeping down slope and the breakout upslope
• S2 Explain the occurrence of unusual grass
  growth patterns observed on the system
• C2 Explain the presence of wastewater effluent
  in all 4 lysimeters and consistent soil
  saturation.

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Raised trench systems
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Simulated pressure head profiles for typical
raised trench SWIS
Time 0 hr
Time 86400 hr
The profiles show a pressure head increase for
the profile on right as a result of wastewater
disposal
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Effect of soil textural classpressure head
profiles
Medium sand
Fine sand
Silt loam
Sandy loam
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M4
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S2
Grass growth along the pipes
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C2
Table 3.20 Summary of test pit observations at Site C2 Table 3.20 Summary of test pit observations at Site C2 Table 3.20 Summary of test pit observations at Site C2 Table 3.20 Summary of test pit observations at Site C2 Table 3.20 Summary of test pit observations at Site C2 Table 3.20 Summary of test pit observations at Site C2
Deep test pit Depth to bottom Pit Depth to seasonal ground water Depth to Fragipan Depth to bedrock Approximate slope
DTP1 57 47 35 None 5
DPT2 53 20 N/A None 5
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Conclusions

• The applications of the model to the three
  previously mentioned SWISs (M4, S2 and C2) have
  more or less replicated the defects and
  observations made on the field.
• The VS2DT modeling justified most requirements
  set in appendix 75-A by the NYS DOH.

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Questions?
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Recommendations

• To promote safer designs, installation and
  operation of OWTSs, we would recommend that
• Sites with slopes be subject to great deal of
  attention during SWIS design and installation.
  Delicate site leveling and stabilization should
  be considered, sides extension slopes for raised
  trench systems should be reduced from 1/3 to 2/3
  if possible.
• In addition to the NYS DOHs appendix 75-A,
  engineers should consider modeling the flow based
  on design before design is implemented.

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Recommendations (contd.)

• Additional deephole tests or other types of soil
  appraisal be required to sufficiently access the
  sites Hydrogeological characteristics.
• Systems be designed with the provision of worst
  hydrologeologicals conditions possible.
• The design of raised trench system be mandatorily
  preceded by the use of advanced treatment units
  (peat filters, sand filter etc.).

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The CWC Septic Program provides reimbursement for
repair or replacement of failing or reasonably
likely to fail residential septic systems located
within 100 feet of a watercourse or 500 feet of a
reservoir or reservoir stem.
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Goals and Objectives

• To provide information about the effectiveness of
  alternative onsite wastewater treatment
  technologies under local conditions to help
  designers and regulators select appropriate,
  cost-effective systems in the WOH watershed.

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Project Scope

• Can alternative technologies remediate
  substandard absorption areas to an acceptable
  level?
• What is the performance (i.e., carbon, nutrient
  and pathogen removal) of such systems in real
  world conditions?
• What is the cost of installation, operation and
  maintenance of various technologies?
• How well can these systems be maintained over
  time?

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SUNY-ESF Project Team

• James Hassett Experience with other septic
  studies, water resources engineer
• Donald Siegel Experience with other septic
  studies, groundwater hydrology
• Alvin Chan, Jessica Martin Graduate students
  extraordinaire

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Sampling Protocol System Types

• Conventional Systems (C)
• Raised Bed Systems (R)
• Aerobic Treatment Units (A)
• Singular Model 960 by Norweco
• Peat Moss Filtration Systems (P)
• Ecoflo STB 650 by Premier Tech Environment
• Intermittent Sand Filters (S)

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Conventional Five Sampling Locations
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Typical D-Box and Distribution Pipe
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Lysimeter Schematic
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Lysimeter Installation
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Lysimeter Installation
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Typical Site Layout
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Sampling from Hassett Lysimeter
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Sampling from D-Box
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Raised Bed Five Sampling Locations
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Sampling from Pump Chamber
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Aerobic Treatment Units (A) Six Sampling
LocationsSingular Model 960 by Norweco
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PEAT (P) - Six Sampling LocationsEcoflo STB 650
by Premier Tech Environment
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Intermittent Sand Filter (S) Six Sampling
Locations
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Parameters

• Laboratory analyses
• TOC, TP, TDP, NH3-N, Nitrate/nitrite-N, fecal
  coliform, conductivity
• Field measurements
• Temperature, pH, volume from each lysimeter,
  water meter reading, rain fall data (courtesy of
  NYC DEP)

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Data Review

• Data received from lab, merged with field data,
  entered in Excel spreadsheet
• Data transferred to SAS for data management
• Graphs generated for each sampling site each
  month
• Data inspected visually for discrepancies

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Site S3 Total Phosphorus - Corrected
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QA/QC Data

• Field Duplicates Samples obtained and labeled
  appropriately (e.g., S3L4). In addition, samples
  taken from some locations and labeled as DUP 1,
  etc, sent to lab in separate cooler.
• Equipment Blanks Distilled water run through
  pumps into sampling bottles.

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Field Duplicate Data - Conductivity
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Field Duplicate Data - TOC
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Field Duplicate Data Fecal Coliform
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Summary Sampling Design

• 24 sites sampled for one year
• (4C, 5R, 5A, 5P, 5S) quasi replication, quasi
  randomness
• Wide geographic distribution within watershed
• Multiple engineers and installers
• QA/QC program showed results adequate for
  purposes of study
• Sampling locations allowed multiple means of
  quantifying system performance

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Results - I

• System Operation versus System Design
• All systems operated at less than design flow
• Septic Tank Effluent
• Comparable to other studies
• Conclusion
• Differences in system performance attributed to
  differences among systems, and not hydraulic or
  organic loading issues

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Statistical Summary Septic Tank Effluent
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Example Data-TOC at a Conventional Site
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Example Data TOC at a Sand Filter Site
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Results II Overall System Performance

• Compare median of all data for each system type
• Compare septic tank effluent (system input) to L4
  (deepest lysimeter) for each system type

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Median Performance - TOC
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Median Performance - TP
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Median Performance NH3-N
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Median Performance Nitrate/nitrite - N
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Median Performance Fecal Coliform
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Results -Overall Removal Data

• Compare most upstream data (either P or D) to L4

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Overall TOC Removal Septic Tank Effluent to L4
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Overall Total N Removal Septic Tank Effluent to
L4
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Statistical Summary Unadjusted L4 Data
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Results III Just What Does Pretreatment Buy?

• Compare removals in pretreatment unit to removals
  in soil system

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Removal of TOC in Pretreatment and Soil Systems
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Removal of TP in Pretreatment and Soil Systems
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Removal of FC in Pretreatment and Soil Systems
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The Question of Dilution

• Conductivity data can be used as a conservative
  tracer to calculate dilution attributed to rain,
  groundwater, etc.

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Calculation of Per Cent of Effluent in Samples
from L1 through L4
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Removals of FC at L4 Adjusted for Dilution
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Statistical Summary L4 Data Adjusted for Dilution
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Cost-Benefit Analysis Average Annual Cost per
kg of Constituent Removed by System Type
C R A P S
TOC 308 347 357 271 232
TP 1,350 1,936 2,391 1,767 1,868
Total Nitrogen 317 510 653 427 487
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Conclusions

• Aerobic Treatment Units are problematic
• Long term effects of reduced drain field loadings
  from alternative treatment systems unknown, but
  likely to be a positive benefit in terms of
  increased service life

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Catskill Watershed Corporation

• 845-586-1400
• cwconline.org