LDEQ’s RECAP Domenico and Summer’s Models

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  DF or DAF is the source concentration of a constituent divided by its down gradient concentration  DF or DAF > 1 If DF or DAF = 1 then no dilution and/or attenuation Domenico Model

MO-1 Domenico Model Soil GW2 & 3 and GW 2 & 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 S w is 1/2 acre site ft by 148 ft S d 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 S d - vertical depth of plume MO-1 Domenico Model

Determination of S d - vertical depth of plume METHOD 1: S d : depth of plume at initial conditions S d = h adv + h disp = advective flow + dispersive flow S d can not be greater than the aquifer thickness-B

METHOD 1 cont. S d = h adv + h disp h adv = B[1-exp((-I*L)/(B*D v ) h disp = (2*  z *L) (0.5) B: aquifer thickness = 10 ft I: infiltration rate = 0.33 ft/yr L: length of source = 148 ft D v : groundwater transport velocity = 30 ft/yr  z : vertical dispersivity = L/200 = 148/200 S d = = 16.3 > B Therefore, S d = 10 ft

The thickness of the impacted permeable zone shall be used as the S d if the thickness of groundwater plume is unknown Determination of S d - vertical depth of plume METHOD 2:

MO-1 DF Table Values given in tables in Appendix I X S d <

 If S d 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-1 Domenico Model

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

P. WJ1-1 & 2

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)  DF Summers = chemical concentration in soil leachate divided by the chemical concentration in the adjacent groundwater = C l / C si  Under MO-1 a DF of 20 is used SUMMERS MODEL

MO-2 Summers Model  DAF Summers = C l / C si = (Q p + Q a ) / Q p  = (I * S w * L + D v * S d * S w ) / (I * S w * L)  = (0.33*148* *10*148) / (0.33*148*148) = 7  Q p volumetric flow of infiltration into aquifer  I: infiltration rate  S w : width of impacted area perpendicular to GW flow direction  L: length of impacted area parallel to GW flow direction  Q a volumetric flow rate of groundwater  D v : darcy GW velocity  S d : thickness of GW plume

Estimation of S d S d = Thickness of impacted groundwater within permeable zone Un-impacted groundwater 10’ 15’ Impacted groundwater 5’ S d = 5’

Estimation of S d S d = Thickness of permeable zone if thickness is not known or if the zone is not impacted Un-impacted groundwater 10’ 15’ S d = 15’