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# LDEQ’s RECAP - PowerPoint PPT Presentation

LDEQ’s RECAP. Domenico and Summer’s Models. DOMENICO MODEL. Domenico Model. The Domenico groundwater model is used to calculate a dilution and attenuation factor (DF or DAF) associated with Soil GW2 , Soil GW3 , GW 2 , and GW 3 values

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### LDEQ’s RECAP

Domenico and Summer’s Models

### DOMENICO MODEL

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

• 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

• 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

• 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.

### Summers Model

• 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

• 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

Sd = Thickness of impacted groundwater within permeable zone

Sd = 5’

10’

5’

Un-impacted groundwater

Impacted groundwater

15’

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

Sd = 15’

10’

Un-impacted groundwater

15’