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LDEQ’s RECAP

The Domenico and Summer's groundwater models are used to calculate dilution and attenuation factors associated with soil and groundwater values. These models help determine the concentration of constituents in groundwater and their potential for dilution or attenuation. The models consider factors such as plume size, source distance, and aquifer thickness.

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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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