Transcript Bliss Area Sewage System - University of Minnesota

Bliss Area Sewage System
Groundwater Monitoring
Pete Ganzel
Washington County
Department of Public Health & Environment
Agenda
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System History
Local Geology
Collection System
Treatment System
MPCA Discharge Permit
Monitoring
Site Evaluation & Design
Evaluation of Piezometer Data
Discussion
Questions
System Overview
Historical
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Big Marine Lake
Bliss, Holiday Beach Plats 1950s
Uncontrolled Flooding 70s and 80s
Flood Control
201 Program, Individual and Collector
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Cost-$1.5 Million
System in Operation Since 1987
Local Geology
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St Croix Moraine
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Two Glaciations
Ice Block Lake
Ice Walled Lake Sediments
Outwash
Perched Shallow Aquifer
Additional site evaluation
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More rigorous analyses of
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Site
Soil
Stratigraphy
Hydrogeology
7 additional pits (10 total)
Field permeability testing
Lab characterization
Shallow soil saturation monitoring (piezometers)
Results from further site evaluation
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Site 10-20’ above nearby lake
30-40’ above Big Marine Lake
15-30’ above springs
Depressional area on southern edge of proposed
soil treatment area
Lamellae bands common (19-250 cm/d)
Saturated zone within 15’ of surface
CONCLUSIONS:
-site limitations for in-ground sewage
treatment system, mounding likely an issue
-Need to assess magnitude of mounding
Assessing Mounding Magnitude
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Horizontal hydraulic conductivity of
overlying soils (275-500 cm/d)
Analytical modeling (Khan et al., 1976)
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22000 gpd
350’ length x 100’ width
Vertical permeability (assumed negligible)
OUTPUT – 31.5’ mounding height
CONCLUSION: Further analysis required
Assessing Mounding Magnitude
continued
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Numerical modeling approach (PrickettLonnquist, Illinois State Water Survey)
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More complex site parameters
Compared (validated) to ambient conditions
and correlated to observed piezometer
readings
300 days = mounding height of 10.7’; 5 years
= 11.3’ (near or at soil surface)
Re-ran model with 50% flow (11000 gpd)
Mounding height of 6.8’ (within 4’ of surface
elevation)
Overall Conclusions
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Site not suitable for flows, loading rates if
in-ground soil treatment
Alternative treatment options investigated
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Treatment of water
Infiltration rates
Lessen mounding threat to environment
Ultimately alternative treatment employed
Monitoring of separation
distances/mounding
System Overview
Collection System
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75 Dwellings
Septic Tanks
Shared Step
Stations
Gravity Mains
Two Main Lift
Stations
Force Mains
System Overview
Treatment System
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7500 Gallon Settling Tanks
Sand Filters and Dosing
Station
Drainfields and Dosing
Station
Incoming Effluent (LS3)
Sand Filter Effluent (LS4)
Guess Which?
MPCA Discharge Permit
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Requires Licensed
Operator- Class D Facility
Renewed Every 5 Years
Goal: Protecting Water
Quality
Reporting
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Monthly- Flow, Precipitation
Permitted 19,800 gallons
per day
Quarterly- Groundwater
Monitoring, Effluent
Sampling
Monitoring
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9 Piezometers
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Groundwater/system separation (water level)
8 Groundwater Monitor Wells
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Groundwater Quality
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Nitrogen, Phosphorus, Chloride
Effluent Sampling
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BOD- Biochemical Oxygen Demand
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Waste Strength
VOC- Volatile Organic Compounds
Effluent Monitoring
Septic
Tank
Precip
2/1/2005
1.56
3/3/2005
1.06
4/5/2005
1.28
5/2/2005
1.24
6/1/2005
2.78
6/28/2005
4.44
8/6/2005
4.21
9/1/2005
5.16
10/1/2005
1.56
11/2/2005
3.04
12/9/2005
1.21
1/5/2006
1.11
1/31/2006
1.18
Sand Filter
Nitrate and
Nitrate
BOD
TSS
pH
Fecal
BOD
TSS
pH
P
Fecal
127
32
7.1
510000
3
2
7.4
4.88
4200
29
100
44
7.3
present
3.3
3.2
4.78
present
22
50
7.1
2.8
2.1
7.1
3.85
98000
36
7.2
1.1
1.6
7.2
4.59
1500
105
EColi
720
30
32
VOC Monitoring
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Volatile Organic Compounds
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Gas Chromatography
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Scan for 68 compounds
Sample effluent only
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Evaporate easily, aromatic
Variable solubility in water, usually low
Solvents, Thinners, Degreasers, Fuels
Many petroleum derived or synthetic
Some Carcinogenic, Teratagenic
Air pollution-smog
RAW effluent
Sand Filter Effluent
Sample once per year in July
Not Routinely Done in Sewage Plants
Costly Test- $120 per sample, lab cost
Compounds Found
Compound
Trichloroethene
Tetrachhlorethene
Toluene
cis-1,2-Dichloroethene
Acetone
p-Isopropyltoluene
Bliss VOC Monitoring
Parts per Billion
2003
2004
HRL
RAW Sand Filter RAW Sand Filter
5
15.6
0.9
11.1
N/D
7
89.2
5.8
29.5
3.2
1000
85.9
1.5
79.9
N/D
70
45.8
5.9
19.6
1.1
700
1342
405
676.9
12.3
N/D
N/D
8
N/D
Some Perspective
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Estimated Volume
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System Volume-13,000 gallons
1300 parts per billion is 80 ml of acetone in 13,000 gallons.
8 parts per billion is 0.5ml of p-isopropyltoluene in 13,000
gallons.
Volumes probably more because of volatilization within the
collection system.
Hit and Miss catching “slugs” of contaminants with limited
sampling.
Piezometer Data
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Separation to Drainfield Trenches
Operation of System
A
B
C
D
E
F
G
H
-2.00
I
10/18/1995
8/14/1995
5/9/1995
10/31/1994
8/2/1994
4/30/1994
9/30/1993
7/30/1993
4/30/1993
10/26/1992
7/31/1992
3/30/1992
10/28/1991
7/22/1991
4/18/1991
10/22/1990
7/18/1990
4/24/1990
10/11/1989
10/19/1988
10/8/1987
Bliss Separation 1987-1996
12.00
10.00
8.00
6.00
4.00
2.00
0.00
A
B
C
D
E
F
G
-2.00
H
I
10/24/2005
7/18/2005
4/25/2005
10/11/2004
7/19/2004
4/19/2004
12/2/2003
7/29/2003
4/28/2003
10/14/2002
7/22/2002
4/22/2002
10/22/2001
7/30/2001
4/30/2001
Bliss Separation 2001-2005
10.00
8.00
6.00
4.00
2.00
0.00
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Site Evaluation
1985
Included analysis
of
Groundwater Elevation
Soil Conductivity
Projected Mounding
Example Soil Description
Conductivity Analysis
Groundwater Contours 1985
Estimated Groundwater Contours
a
b
c
d
e
f
g
Date
h
i
10/18/1995
8/14/1995
5/9/1995
10/31/1994
8/2/1994
4/30/1994
9/30/1993
7/30/1993
4/30/1993
10/26/1992
7/31/1992
3/30/1992
10/28/1991
7/22/1991
4/18/1991
10/22/1990
7/18/1990
4/24/1990
10/11/1989
10/19/1988
10/8/1987
MSL
Water Table Elevation 1987-1995
980.00
975.00
970.00
965.00
960.00
955.00
950.00
a
b
c
d
e
f
g
h
Date
i
10/24/2005
7/18/2005
4/25/2005
10/11/2004
7/19/2004
4/19/2004
12/2/2003
7/29/2003
4/28/2003
10/14/2002
7/22/2002
4/22/2002
10/22/2001
7/30/2001
4/30/2001
MSL
976.00
Water Table Elevation 2001-2005
974.00
972.00
970.00
968.00
966.00
964.00
962.00
960.00
958.00
956.00
Groundwater to Surface
Discussion/Questions???