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LDEQ’s RECAP

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

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  1. LDEQ’s RECAP Domenico and Summer’s Models

  2. DOMENICO MODEL

  3. 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

  4. 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

  5. MO-1 Domenico Model • 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. MO-1 Domenico Model • 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

  11. 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

  12. P. WJ1-1 & 2

  13. 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.

  14. Summers Model

  15. 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

  16. 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

  17. Estimation of Sd Sd = Thickness of impacted groundwater within permeable zone Sd = 5’ 10’ 5’ Un-impacted groundwater Impacted groundwater 15’

  18. 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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