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## PowerPoint Slideshow about ' LDEQ’s RECAP' - kalia-fulton

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### LDEQ’s RECAP

Domenico and Summer’s Models

DomenicoModel

- The Domenico groundwater model is used to calculate a dilution and attenuation factor (DF or DAF) associated with SoilGW2 , SoilGW3 , GW2 , and GW3 values
- DF or DAF is the source concentration of a constituent divided by its down gradient concentration
- DF or DAF > 1If DF or DAF = 1 then no dilution and/or attenuation

MO-1 Domenico ModelSoilGW2 & 3 and GW2 & 3

Default assumptions:

- Equation accounts ONLY for dilution
- Plume is allowed to expand infinitely
laterally in 2 directions

vertically in 1 direction

- Planar plume size is based on
Sw is 1/2 acre site - 148 ft by 148 ft

Sd depths vary from 5 to 20 feet

- Two pieces of data are needed to determine a DF from the table:
- x - shortest downgradient distance from source to exposure point
- Sd - vertical depth of plume

- Determination of Sd - vertical depth of plume
- METHOD 1:
- Sd: depth of plume at initial conditions
- Sd = hadv + hdisp
- = advective flow + dispersive flow
- Sd can not be greater than the aquifer thickness-B

- METHOD 1 cont.
- Sd = hadv + hdisp
- hadv = B[1-exp((-I*L)/(B*Dv)
- hdisp = (2* z*L)(0.5)
- B: aquifer thickness = 10 ft
- I: infiltration rate = 0.33 ft/yr
- L: length of source = 148 ft
- Dv : groundwater transport velocity = 30 ft/yr
- z : vertical dispersivity = L/200 = 148/200
- Sd = 1.5 + 14.8 = 16.3 > B Therefore, Sd = 10 ft

Determination of Sd - vertical depth of plume

METHOD 2:

- The thickness of the impacted permeable zone shall be used as the Sd if the thickness of groundwater plume is unknown

- MO-1 DF Table
- Values given in tables in Appendix I
- X Sd
- <5 6-10 11-15 16-20

- X Sd
- 0-50 1.5 1 1 1
- 51-100 2.6 1.5 1.2 1.1
- 101-150 4.1 2.1 1.6 1.3
- 151-250 8.4 4.3 3 2.3
- 251-500 29 15 9.8 7.4
- 501-750 63 32 21 16
- 751-1000 111 57 37 28
- 1001-1250 173 86 58 43
- 1251-1500 248 124 83 62
- 1501-1750 337 169 113 84
- 1751-2000 440 220 147 110

- If Sd is greater than 20 feet then a site-specific DAF shall be calculated under MO-2 or MO-3
- If the distance from the source is greater than 2000 feet, then: (1) the DF for 2000 feet may be used under MO-1; or (2) a site-specific DAF may be calculated under MO-2 or MO-3

MO-2 Domenico Model

- Equation can account for dilution and attenuation
- Attenuation must be based on site-specific data (NO TEXT BOOK VALUES)
- Plume is allowed to expand infinitely in the 2 lateral directions
- Plume vertical depth is limited to the aquifer thickness and must be accounted for in the equation

- MO-2 Domenico Model cont.
- If the POE is within the boundary of plume use given form of equation - Fig. J-1
- This means the “x” value, the distance from the source to the POE, is much less than the groundwater transport velocity multiplied by the time since the spill
- (x << v * t)
- If the POE is in front of plume x > v * t then equation must be modified and time t adjusted to account for maximum COC at point x (see model reference)
- This is a judgment call. Looking for maximum contaminant concentration at the point x.

- The Summers model is used under MO-2 to calculate a site-specific dilution factor for a COC in soil water as it moves from the soil column into the adjacent groundwater (Appendix K)
- DFSummers = chemical concentration in soil leachate divided by the chemical concentration in the adjacent groundwater = Cl / Csi
- Under MO-1 a DF of 20 is used

MO-2 Summers Model

- DAFSummers = Cl / Csi = (Qp + Qa) / Qp
- = (I * Sw * L + Dv * Sd* Sw) / (I * Sw * L)
- = (0.33*148*148 + 30*10*148) / (0.33*148*148) = 7
- Qp volumetric flow of infiltration into aquifer
- I: infiltration rate
- Sw : width of impacted area perpendicular to GW flow direction
- L: length of impacted area parallel to GW flow direction

- Qa volumetric flow rate of groundwater
- Dv : darcy GW velocity
- Sd : thickness of GW plume

Estimation of Sd

Sd = Thickness of impacted groundwater within permeable zone

Sd = 5’

10’

5’

Un-impacted groundwater

Impacted groundwater

15’

Estimation of Sd

Sd = Thickness of permeable zone if thickness is not known or if the zone is not impacted

Sd = 15’

10’

Un-impacted groundwater

15’

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