estimation of actual free product thickness on the groundwater table

estimation of actual free product thickness on the groundwater table

Proceedings of ECOpole
Vol. 2, No. 2
2008
Iwona DESKA1 and Grzegorz MALINA2
ESTIMATION OF ACTUAL FREE PRODUCT THICKNESS
ON THE GROUNDWATER TABLE BASED ON SOIL
AND LNAPL PROPERTIES
USTALANIE RZECZYWISTEJ MIĄśSZOŚCI WOLNEGO PRODUKTU
ROPOPOCHODNEGO NA ZWIERCIADLE WODY PODZIEMNEJ
NA PODSTAWIE WŁAŚCIWOŚCI GRUNTU I LNAPL
Summary: In order to design the efficient recovery of lighter-than-water non-aqueous phase liquid (LNAPL) from
the groundwater table, the data on actual LNAPL thickness should be provided. Unfortunately, the actual thickness
of LNAPL (in the porous medium) is always different from the apparent thickness (measured in the monitoring
well). This difference depends on parameters of soil and LNAPL. There are several methods developed for
estimating the actual LNAPL thickness on the base of the apparent thickness, but the results obtained with
different formulas are inconsistent and imprecise. The main limitation of the existing methods is a disregard of
many important parameters. Additionally, values of some parameters in these models are difficult to estimate both:
in laboratory and field. The results of our study indicate that the appropriate model for estimating the actual
thickness should include the properties of soil and LNAPL. Two empirical models developed by us and presented
here include key parameters of soils (hydraulic conductivity) and LNAPLs (density and dynamical viscosity), and
additionally soil permeability for LNAPL. The values calculated from the developed models corresponded well in
many cases with the values obtained during laboratory experiments.
Keywords: LNAPL, actual thickness, apparent thickness, laboratory experiments, empirical models
The surface spills and leakages from underground storage tanks, pipelines and cisterns
are principal sources of soil and groundwater contamination with lighter-than-water nonaqueous phase liquids (LNAPL). In the porous medium, LNAPL floats on the groundwater
table, because its density is lower than the density of water. If the layer of LNAPL occurs
on the groundwater table the initial remediation step should be its recovery [1-3]. A proper
design of this operation requires an assessment of the contamination plume volume. To
assess the volume of a plume, observation wells are commonly installed in specified points
of the contaminated area to measure the thicknesses of LNAPL layer [1]. Unfortunately, the
thickness of LNAPL on the groundwater table (the actual thickness) is different from the
thickness observed in the well (the apparent thickness) [4-6]. The difference between
apparent and actual thickness depends on the properties of soil, and the properties and
amounts of LNAPL released to the soil [7-9]. A number of methods exist for estimating the
actual thickness from the apparent thickness data, but the results obtained with different
formulas are inconsistent, and in many cases inaccurate [4, 5, 10]. The obtained results of
laboratory investigations indicate that the appropriate model for estimating the actual
LNAPL thickness should include the properties of soil and LNAPL [9, 11]. The key
parameter of soil is hydraulic conductivity, whereas in the case of LNAPL density and
1
Institute of Environmental Engineering, Czestochowa University of Technology, ul. Brzeźnicka 60A,
42-200 Częstochowa, tel. 034 325 09 17, email: [email protected]
2
Department of Hydrogeology and Engineering Geology, AGH - University of Science and Technology,
al. A. Mickiewicza 30, 30-059 Kraków, tel. 012 617 24 04, email: [email protected]
304
Iwona Deska and Grzegorz Malina
dynamical viscosity play an important role. An additional important parameter that depends
on properties of both: soil and LNAPL is the soil permeability of LNAPL [9].
The goal of this paper is to verify the empirical models developed by us for estimating
the actual LNAPL thickness on the groundwater table. An additional focus is to compare
results obtained based on the proposed models and the existing methods.
Materials and methods
Studies were carried out in Plexiglas columns with filter-tubes as monitoring wells
[7-9, 11]. The experiments were performed with use of six model soils and six types of
LNAPLs. The properties of soils and LNAPLs are given in Tables 1-3.
Table 1
Properties of soils used in the experiments
Soil
1
2
3
4
5
6
Soil grain size
[mm]
0.1÷0.25
0.25÷0.315
0.315÷0.5
0.5÷0.63
0.63÷0.8
0.8÷1.0
Medium soil
grain size [mm]
0.175
0.2825
0.4075
0.565
0.715
0.9
Hydraulic conductivity
at 10ºC k10 [m/d]
11.33 ± 0.07
23.255 ± 0.426
71.334 ± 1.640
107.285
154.627
231.884
Coefficient of
permeability κ [m2]
1.75·10–11 ± 1.078·10–13
3.59·10–11 ± 6.674·10–13
1.10·10–10 ± 2.54·10–12
1.66·10–10
2.38·10–10
3.57·10–10
Table 2
Properties of LNAPLs used in the experiments (at temperature of 20ºC)
LNAPL
Type of LNAPL
LNAPL 1
LNAPL 2
LNAPL 3
LNAPL 4
LNAPL 5
LNAPL 6
Petroleum
Rape oil
Mineral oil “Lotos”
Semi-synthetic oil “Orlen”
Synthetic oil “Lotos”
Synthetic oil “Orlen”
Density ρo
[kg/m3]
820.5
918
880
872
855
871
Dynamic viscosity ηo
[kg/m·s]
1.804⋅10–3 ± 1.42·10–6
0.0718 ± 5.94·10–5
0.3 ± 2.54·10–4
0.219 ± 2.52·10–4
0.181
Specific gravity
γo [N/m3]
8049.105
9005.58
8632.8
8554.32
8387.55
8544.51
0.194 ± 2.51·10–4
Table 3
LNAPL permeability (at temperature of 20ºC)
LNAPL permeability at 20ºC ko [m/d]
Soil
1
2
3
4
5
6
LNAPL 1
6.73
13.82
42.53
63.80
91.81
137.66
LNAPL 2
0.19
0.39
1.19
1.79
2.57
3.86
LNAPL 3
0.04
0.09
0.27
0.41
0.59
0.89
LNAPL 4
0.06
0.12
0.37
0.56
0.80
1.21
LNAPL 5
0.07
0.14
0.44
0.66
0.95
1.43
LNAPL 6
0.07
0.14
0.42
0.63
0.91
1.36
Estimation of actual free product thickness on the groundwater table based on soil and LNAPL properties
305
The columns were hydraulically connected with the equalizing columns. The columns
were packed with the soil samples (soils 1-6) and filled with tap water until the water table
reached the assumed elevation. After 3-4 days 50 cm3 of diverse LNAPLs, coloured with
the pigment - Sudan III, were injected directly above the capillary fringe zone. After
subsequent 3-4 days, the apparent and actual LNAPL thicknesses were measured in the
well and in soil. The actual thickness was in this case the distance between LNAPL-water
interface in soil and air-LNAPL interface in the well (without the capillary fringe of
LNAPL in the soil). This procedure was repeated at least 10 times. The water table in the
equalizing column was kept constant during experiments. The top of columns was protected
against LNAPL evaporation by the styropore covers.
Results and discussion
On the base of laboratory experiments two empirical models were developed that
describe the relationship between apparent and actual LNAPL thicknesses. Model 1 is
based on the conductivity of soil for LNAPL and dynamic viscosity of LNAPL. The key
parameters of model 2 are the hydraulic conductivity of soil and the specific density and
dynamic viscosity of LNAPL [9, 11].
Model 1
The actual LNAPL thickness can be estimated on the base of the equation:
H f = H 0 + (ωη o + ϕ )ln k o + χ ln (η o ) − ξ
(1)
where: Hf - actual LNAPL thickness [cm], H0 - apparent LNAPL thickness [cm],
ko - LNAPL conductivity [m/d], ηo - dynamic viscosity of LNAPL [cP], ω, φ, χ and ξ factors dependent on actual LNAPL thickness [-].
Factors ω, φ, χ and ξ can be calculated from the equations:
ω = −0.002 H fe + 0.052
(2)
ϕ = −0.0087 H 2fe + 0.8185H f + 18.731
(3)
χ = 0.1115H fe + 20.992
(4)
ξ = 2.138H fe + 110.12
(5)
where Hfe - initial estimated actual LNAPL thickness [cm].
Model 2
The actual LNAPL thickness can be calculated from equation:
'
Hf =
H 0 ⋅ ln k10 ⋅ (ζη o2 + ψη o + σ ) ⋅ e (δ −ερ ro )⋅k10
η o ⋅ ρ ro
(6)
Factors ζ, ψ, σ, δ and ε can be calculated from the equations:
ζ = −0.0059 H fe + 0.0134
(7)
ψ = 0.0033H f + 0.0028
(8)
306
Iwona Deska and Grzegorz Malina
σ = −3 ⋅10 −6 H fe + 0.0001
(9)
δ = −144.6 H fe + 3513.1
(10)
ε = 136.92 H fe − 3190.5
(11)
where: Hf, H0, Hfe - see above, k10 - hydraulic conductivity [m/d], k10’ - hydraulic
conductivity [m/s], ηo - dynamic viscosity of LNAPL [cP], ρro - specific density of LNAPL
[-], ζ, ψ, σ, δ and ε - factors dependent on actual LNAPL thickness [-].
Use of these models requires initial estimation of actual thickness (Hfe) to determine
the proper values of factors dependent on actual LNAPL thickness. The calculation should
be repeated until the calculated actual thickness is equal to the initial estimated value. To
verify the developed models the relationships between apparent and actual thicknesses
obtained from the models were compared with these calculated with use of the existing
methods and with the experimental data. Figures 1 and 2 show these comparisons for
selected soils and LNAPLs. Figure 1 presents the best fits.
Soil 2 - LNAPL 3
Soil 1 - LNAPL 2
18
Actual LNAPL thickness [cm]
Actual LNAPL thickness [cm]
18
16
14
12
10
8
6
4
2
16
14
12
10
8
6
4
2
0
0
0
50
100
150
200
Apparent LNAPL thickness [cm]
250
0
300
20
40
60
80
100
Apparent LNAPL thickness [cm]
140
Soil 5 - LNAPL 5
22
20
18
16
14
12
10
8
6
4
2
0
18
Actual LNAPL thickness [cm]
Actual LNAPL thickness [cm]
Soil 4 - LNAPL 2
120
16
14
12
10
8
6
4
2
0
0
25
50
75
100
Apparent LNAPL thickness [cm]
125
Laboratory experiments
Met. of de Pastrovich
Met. of Schiegg min.
Met. of Schiegg max.
0
150
20
Met. of Hall
20
40
60
80
Apparent LNAPL thickness [cm]
Met. of Blake and Hall
100
Met. of Ballestero
0
0
20
40
60
80
100
Model 1
120
140
160
180
200
Model 2
Fig. 1. The verification of developed models on the base of laboratory investigations and calculations with use of
existing methods - the best cases
The results of the verification indicate that the values calculated from the proposed
models corresponded in many cases to the experimental data much better than results
obtained on the base of existing methods. Only for a few compositions of soils and
Estimation of actual free product thickness on the groundwater table based on soil and LNAPL properties
307
LNAPLs the results derived from the developed models fit poorly the experimental data.
Figure 2 presents these most unfavorable cases.
Soil 3 - LNAPL 1
20
16
18
16
14
12
Actual LNAPL thickness [cm]
Actual LNAPL thickness [cm]
Soil 1 - LNAPL 1
18
14
12
10
8
6
4
2
0
0
20
40
60
80
100 120 140
Apparent LNAPL thickness [cm]
160
10
8
6
4
2
0
180
0
20
Soil 5 - LNAPL 1
100
Soil 6 - LNAPL 1
25
Actual LNAPL thickness [cm]
18
Actual LNAPL thickness [cm]
40
60
80
Apparent LNAPL thickness [cm]
16
14
12
10
8
6
4
2
0
20
15
10
5
0
0
10
20
30
40
50
60
Apparent LNAPL thickness [cm]
70
Laboratory experiments
Met. of de Pastrovich
Met. of Schiegg min.
Met. of Schiegg max.
80
-5
0
5
Met. of Hall
20
10 15 20 25 30 35 40 45
Apparent LNAPL thickness [cm]
Met. of Blake and Hall
50 55
60
Met. of Ballestero
0
0
20
40
60
80
100
Model 1
120
140
160
180
200
Model 2
Fig. 2. The verification of the developed models on the base of laboratory investigations and calculations with
use of existing methods - the most unfavorable cases
The most unfavorable results in the case of model 1 were obtained for the scheme:
LNAPL 1 (liquid with the lowest viscosity and density) and soils 5 and 6 (coarse sands). In
the case of model 2 the worst results were obtained for compositions: LNAPL 1 and soils 1
and 5. It may suggest that model 1 cannot be applied for coarse sands contaminated with
LNAPLs with low viscosities, whereas model 2 cannot be used in the case of LNAPLs with
low viscosities.
Conclusions
1.
2.
3.
4.
The appropriate model for estimating the actual thickness of LNAPL on the
groundwater table should include the properties of the specific soil and liquid.
The values of actual LNAPL thicknesses calculated from the developed empirical
models are in many cases consistent with the measured values.
The proposed model 1 in a present form cannot be successfully applied in the case of
low viscosity LNAPLs and coarse sands, and model 2 for LNAPLs of low viscosity.
Further studies aimed at the improvement of the proposed models should include the
investigations with the use of heterogeneous soils and LNAPLs with more diverse
properties.
308
Iwona Deska and Grzegorz Malina
Acknowledgements
This work was financially supported by KBN grant no. 4 T09D 041 25 and partially by
BS-401-301/99.
References
[1]
Cooper G.S., Peralta R.C. and Kaluarachchi J.J.: Optimizing separate phase light hydrocarbon recovery from
contaminated unconfined aquifers. Adv. Water Resour., 1998, 21, 339-350.
[2] Cooper G.S., Peralta R.C. and Kaluarachchi J.J.: Stepwise pumping approach to improve free phase light
hydrocarbon recovery from unconfined aquifer. J. Contam. Hydrol., 1995, 18, 141-159.
[3] Adamek M., Koślacz R. and Zieliński W.: Wskazówki metodyczne wykonywania rekultywacji gruntów
i wód podziemnych zanieczyszczonych produktami naftowymi. MOŚZNiL, Dep. Geologii, Multimedia s.c.,
Wrocław 1995.
[4] Lenhard R.J. and Parker J.C.: Estimation of free hydrocarbon volume from fluid levels in monitoring wells.
Ground Water, 1990, 28(1), 57-67.
[5] EPA: How to effectively recover free product at leaking underground storage tank sites: A guide for state
regulators. (EPA 510-R-96-001), 1996.
[6] De Pastrovich T.L., Baradat Y., Barthel Y., Chiarelli A. and Fussell D.R.: Protection of groundwater from
oil pollution. CONCAWE, Report 3/79, Den Haag, Netherlands, 1979, 62 pp.
[7] Deska I. and Malina G.: Influence of fluid properties on difference between actual and apparent LNAPL
thicknesses on groundwater table. Proc. 4th Int. Conf. “Oils and Environment. AUZO 2005”. Gdańsk 2005,
120-125.
[8] Deska I., Malina G. and Radło A.: Wpływ uziarnienia gruntu oraz cech paliwa na róŜnicę między
miąŜszością pozorną i rzeczywistą LNAPL na zwierciadle wody podziemnej. InŜ. Ochr. Środow., 2003, 6(2),
203-220.
[9] Deska I.: Ustalanie rzeczywistej miąŜszości lekkich cieczy organicznych na zwierciadle wody podziemnej.
Praca doktorska. WIiOŚ Polit. Częstochowskiej, Częstochowa 2008 (niepublikowana).
[10] Deska I. and Malina G.: Laboratory verification of models for estimation of LNAPL actual thickness on the
groundwater table. Proc. 14th Central European Conference ECOpole’05. Duszniki Zdrój - Hradec Kralove
2005, 55-59.
[11] Deska I. and Malina G.: Model empiryczny wyznaczania rzeczywistej miąŜszości lekkich cieczy organicznych
(LNAPL) na zwierciadle wody podziemnej. XIII Konferencja Naukowo-Szkoleniowa Rekultywacja
i rewitalizacja terenów zdegradowanych. Puck 25-28 kwietnia 2007, 189-200.
USTALANIE RZECZYWISTEJ MIĄśSZOŚCI WOLNEGO PRODUKTU
ROPOPOCHODNEGO NA ZWIERCIADLE WODY PODZIEMNEJ
NA PODSTAWIE WŁAŚCIWOŚCI GRUNTU I LNAPL
Streszczenie: W celu odpowiedniego zaprojektowania operacji sczerpywania lekkiej cieczy organicznej (LNAPL)
ze zwierciadła wody podziemnej niezbędna jest znajomość jej objętości. Objętość tę moŜna określić na podstawie
pomiarów miąŜszości warstwy LNAPL w studniach obserwacyjnych. Jednak rzeczywista miąŜszość LNAPL (na
zwierciadle wody podziemnej) zawsze róŜni się od tzw. miąŜszości pozornej (w studni), a róŜnica między nimi
zaleŜy od parametrów gruntu oraz właściwości i ilości LNAPL. Istnieje kilka metod ustalania rzeczywistej
miąŜszości LNAPL na podstawie miąŜszości pozornej, ale wyniki uzyskiwane przy ich zastosowaniu są bardzo
rozbieŜne. Przeprowadzone badania potwierdziły, Ŝe wartości miąŜszości rzeczywistych ustalone na podstawie
tych metod mogą być nieprecyzyjne. Podstawową wadą ww. metod jest to, Ŝe w kaŜdej z nich pominięto bardzo
waŜne parametry. Na podstawie uzyskanych wyników badań, korzystając z analizy kluczowych parametrów
wpływających na zaleŜność między miąŜszością pozorną i rzeczywistą, opracowano modele empiryczne, będące
alternatywą dla obecnie stosowanych metod. Uwzględniają one zarówno parametry gruntu (np. współczynnik
filtracji), jak i właściwości LNAPL (gęstość, współczynnik lepkości dynamicznej). Weryfikacja opracowanych
modeli potwierdziła, Ŝe w przewaŜającej większości przypadków ich zastosowanie pozwoliło na uzyskanie
wyników zbliŜonych do ustalonych w warunkach laboratoryjnych.
Słowa kluczowe: LNAPL, miąŜszość rzeczywista, miąŜszość pozorna, badania laboratoryjne, model empiryczny