GROUNDWATER FLOW MODEL REPORT - APPENDIX C - … · Groundwater Flow Model Calibration and...

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Appendix C - Groundwater Flow Model Construction & Calibration and Verification

Groundwater Flow Model Development

Public Well TCE Site (DE-1361) Millsboro, Delaware

March 2, 2011

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ARCADIS Table of Contents

1. Groundwater Flow Model Construction

1.1 Code Selection and Description

1.2 Model Discretization

1.3 Boundary Conditions

1.4 Hydraulic Parameters

1.5 Calibration Targets

2. Groundwater Flow Model Calibration and Verification

,2.1 . Calibration Procedure

2.2 Calibration Results

2.2.1 Simulated Hydraulic Head Distributions

2.2.2 Analysis of Residuals

2.3 Groundwater Flow Model Verification

2.3.1 Analysis of Verification Residuals

1

1

2

4

6

7

7

8

10

10

10

11

11

Tables

Table C-1 Hydraulic Conductivities

Table C-2 June 2010 Calibration Targets and Residuals

Table C-3 Average 2009 Calibration Targets and Residuals

Figures

Figure C-1 Finite Difference Grid

Figure C-2 Boundary Conditions and Simulated Water Levels in the Upper Columbia Aquifer (Model Layer 1)

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Figure C-3 Boundary Conditions and Simulated Water Levels in the Lower Columbia Aquifer (Model Layer 2)

Figure C-4 Boundary Conditions and Simulated Water Levels in the Upper Bethany Formation (Model Layer 3)

Figure C-5 Boundary Conditions and Simulated Water Levels in the Middle Bethany Fomnation (Model Layer 4)

Figure C-6 Boundary Conditions and Simulated Water Levels in the Lower Bethany Formation (Model Layer 5)

Figure C-7 Boundary Conditions and Simulated Water Levels in the Manokin Aquifer (Model Layer 6)

Figure C-8 June 2010 Simulated Water Levels and Calculated Residuals in the Upper Columbia Aquifer (Model Layer 1)

Figure C-9 June 2010 Simulated Water Levels and Calculated Residuals in the Lower Columbia Aquifer (Model Layer 2)

Figure C-lb June 2010 Simulated Water Levels and Calculated Residuals in the Middle Bethany Fonnation (Model Layer 4)

Figure C-11 June 2010 Simulated Water Levels and Calculated Residuals in the Manokin Aquifer (Model Layer 6)

Figure C-12 Plot of Observed Versus Simulated Water Levels Under June 2010 Conditions

Figure C-13 Average 2009 Simulated Water Levels and Calculated Residuals in the Upper Columbia Aquifer (Model Layer 1)

Figure C-14 Average 2009 Simulated Water Levels and Calculated Residuals in the Lower Columbia Aquifer (Model Layer 2)

Figure C-15 Plot of Observed Versus Simulated Water Levels Under Average 2009 Conditions

Figure C-16 Transient Calibration Curve Fits (June 29, 2010 - July 3, 2010)

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ARCADIS Appendix C

Groundwater, Flow Model Development

1. Groundwater Flow Model Construction

1.1 Code Selection and Description

For the construction and calibration of the numerical groundwater flow model at the Site, ARCADIS selected the simulation program MODFLOW, a publicly-available groundwater flow simulation program developed by the U.S. Geological Survey (USGS) (McDonald and Harbaugh, 1988). MODFLOW is thoroughly documented, widely used by consultants, government agencies and researchers, and is consistently accepted in regulatory and litigation proceedings. In addition, ARCADIS has developed utilities for use with MODFLOW to ease in the construction and calibration of groundwater models.

MODFLOW can simulate transient or steady-state saturated groundwater flow in one, two, or three dimensions and offers a variety of boundary conditions including specified head, areal recharge, injection or extraction wells, evapotranspiration, horizontal flow barriers (HFB), drains, and rivers or streams. Aquifers simulated by MODFLOW can be confined or unconfined, or convertible between confined and unconfined conditions. For the Site, which consists of a heterogeneous geologic system with variable unit thicknesses and boundary conditions, MODFLOWs three-dimensional capability and boundary condition versatility are essential for the proper simulation of groundwater flow conditions.

MODFLOW simulates transient, three-dimensional groundwater flow through porous media described by the following partial differential equation for a constant density fluid:

_5_

dx K,

dh

V

/' + •

dy

dh \ + •

dz

dh

dz ' dt (1-1)

where:

Kxx, Kyy and K̂ ^ are values of hydraulic conductivity along the x, y, and z coordinate axes, which are assumed to be parallel to the major axes of hydraulic conductivity [\JT\\

h is the potentiometric head [L];

W is a volumetric flux and represents sources and/or sinks of water [1/T];

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Appendix C


Ss is the specific storage of the porous material [1/L]; and,

t is time [T];

In Equation 1-1, the hydraulic parameters (i.e., Kxx, Kyy, K^ and Ss) may vary in space but not in time while the source/sink (W) terms may vary in both space and time,

MODFLOW uses a numerical approximation technique known as the method of finite differences to solve Equation 1-1 on a computer. Using a block-centered finite-difference approach, MODFLOW replaces the continuous system represented in Equation 1-1 by a set of discrete points in space and time. This process of discretization ultimately leads to a system of simultaneous linear algebraic equations. MODFLOW solves these finite-difference equations with one of the following three iterative solution techniques: strongly implicit procedure (SIP), slice-successive over-relaxation (SSOR), or preconditioned conjugate gradients (PCG). The solution of the finite-difference equations produces time-varying values of head at each of the discrete points representing the real aquifer system. Given a sufficient number of discrete points, the simulated values of head yield close approximations of the head distributions given by exact analytical solutions to Equation 1-1.

1.2 Model Discretization

The finite-difference technique employed in MODFLOW to simulate hydraulic head distributions in multi-aquifer systems requires areal and vertical discretization, or subdivision of the continuous aquifer system into a set of discrete blocks that fomn a three-dimensional model grid. In the block-centered finite-difference formulation used in these codes, the center of each grid block corresponds to a computational point or node. When MODFLOW solves the set of linear algebraic finite-difference equations for the complete set of blocks, the solution yields values of hydraulic head at each node (or three-dimensional block) in the three-dimensional grid.

Water levels computed for each block represent an average water level over the volume of the block. Thus, adequate discretization (i.e., a sufficiently fine grid) is required to resolve features of interest, and yet not be computationally burdensome. MODFLOW allows the use of variable grid spacing such that a model may have a finer grid in areas of interest where greater accuracy is required and a coarser grid in areas requiring less detail.

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Appendix C


Review of the EA Engineering, Science, and Technology, Inc. model (EA, 2009) suggested that the model grid orientation potentially introduced error into the analysis because groundwater was simulated to migrate northeasterly which is diagonal to the model grid nodes. A limitation of the MODFLOW code is that it does not contain cross-diagonal flow terms, and hence, requires that the model grid be aligned to the main flow or transport direction of interest to the study. Since the prediction of the EA model indicated diagonal transport, the results might have been inaccurate because flow between diagonally located nodes is not computed by MODFLOW. Furthermore, the EA model domain was not large enough to minimize boundary influence on the model calibration, and the model boundaries probably influenced the flow simulations under varying pumping conditions. To compensate for the limitations of the EA model, the current model grid has been rotated to improve the alignment of a major grid axis with the plume transport direction. In addition, the conceptual site model helped in characterizing the area of influence of the well field and consequently, the necessary extents of the model domain.

The present groundwater flow model has been developed by representing the descriptive features of the conceptual model into their numerical or mathematical equivalents. Figures C-2 to C-7 show the extent of the three-dimensional numerical model for the Site. The boundaries of the model grid are specified to coincide with natural hydrogeologic boundaries, where possible, and the boundaries were set at a significant distance from the site to minimize the influence of model boundaries on simulation results at the Site. Accordingly, the model area is bounded by the Indian River and Millsboro Pond at the downgradient hydraulic boundary to the north-east, by Betts Pond to the north-west, by Iron Branch to the south-east and by an inferred groundwater divide in the upgradient direction along Parker Road to the south-west in Model Layers 1 and 2. In Model Layers 3 through 6, the northeastern model boundary extends past the Indian River and Millsboro Pond to evaluate account for deeper flow conditions in this vicinity. The finite-difference grid is composed of 592 columns, 576 rows, and 6 layers for a total of approximately 2 million nodes (Figure C-1). The model grid was further refined in the vicinity of the Site to improve the accuracy of the groundwater flow analyses. The grid spacing ranges from 10 ft in the vicinity of the Site to 200 ft near the model boundaries.

Another limitation of the EA model was that it extended vertically only down to the Bethany Fonnation, and did not include the Manokin aquifer. Although the accompanying modeling report (EA, 2009) acknowledged the presence of deeper wells (PW-3 and PW-4) screened in the Manokin aquifer, the Bethany Formation was assumed as a competent confining unit and thus, did not simulate any hydraulic

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ARCADIS Appendix C


connection between the Columbia (surficial) and Manokin aquifers. However, as discussed in Section 2.3, ARCADIS's July 2010 aquifer pump test and available litereature indiacates that the Bethany Fonnation is a leaky aquitard and in some areas along the mid-Atlantic coast is transmissive enough to be exploited for water supply. Furthennore, regional data indicate that recharge of the Columbia and Manokin Aquifer systems is primarily through infiltration of rainwater, which implies that a significant portion of water removed via pumping in the deeper Manokin fomnation would be replaced by water derived above it.

As a result, significant modification to the EA model was made to the vertical structure and discretization to more accurately reflect the current understanding of the Site hydrostratigraphy and conceptual site model. Accordingly, the 6 layers in the present model were designed to accurately represent the major hydrostratigraphic units such as the Columbia aquifer, the Bethany Fonnation, and the Pokomoke, Ocean City and Manokin Aquifer system. St. Mary's Fonnation served as the base of the present groundwater flow model.

The elevation and delineation of model layers were based on a detailed review of boring logs (site-specific as well as available regional boring logs), cross-sections, and relevant regional publications. Model layers 1 and 2 represent the upper and lower segments of the Columbia Aquifer. Model layers 3 through 5 represent the Bethany Formation. Multiple model layers were used to represent the Bethany Formation because of observed heterogeneities and to improve the vertical velocity representation of this unit in the model. Model layer 6 was used to represent the Pokomoke, Ocean City and Manokin Aquifer system. Some regional boring data was used to extrapolate these layer elevations to the boundaries of the numerical flow model.

1.3 Boundary Conditions

Boundary conditions must be imposed to define the spatial boundaries of the model on the top, bottom, and all sides of the model grid. In addition to these boundary conditions, sources, and sinks of groundwater such as wells, drains, and rivers can be included within the model's external boundaries. A boundary condition can represent different types of physical boundaries, depending on the rules that govern groundwater flow across the boundary. This model includes six types of boundary conditions: no-flow, constant head (head dependent flux), river (head dependent flow), drains (head dependent flow), general head (head dependent flux), extraction wells (constant flux),

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ARCADIS Appendix C


and recharge (constant flux). The location and type of boundary conditions at various model layers are shown in Figures C-2 to C-7.

The Indian River on the north-eastern boundary of the model has been represented using constant head cells with an assigned head of 0.5 feet MSL. These constant head boundaries represent the regional flux into the model domain. The initial stage elevations for the constant head cells were based on USGS topographic map and then adjusted slightly during the calibration process. These constant head cells were only located in model layer 1, given the vertical extent of the upper Columbia Aquifer represented by the model layer 1. The active model domain covers an aerial extent of about 2 miles by 4 miles. Areas outside the active model domain have been defined as no flow cells in all 6 model layers.

River cells allow for the specification of a surface-water stage, a bottom elevation and a conductance term. Water can enter or exit the river cells based on the simulated aquifer heads. River cells were used to represent both the Millsboro Pond and Betts Pond. Variable elevations of both surface water bodies were derived from the USGS topographic maps. The conductance tenns for the river cells were calculated from the grid-cell dimensions and estimates of the hydraulic conductivity of the aquifer material (estimated conductance values range from 200,000 to 600,000 feet squared per day).

Drain cells allow for the specification of a surface-water stage and a conductance tenn. If the simulated water level in the aquifer is below the drain elevation, the drain becomes inactive (dry). However, if the simulated water level in the aquifer rises above the specified drain elevation, groundwater flows from the aquifer and into the drain cell. Drain cells were used to represent the Iron Branch creek on the south-eastern boundary. The stage elevations of the drain cells were based on USGS topographic map. Similar to the river cells, the conductance tenns for the drain cells were calculated from the grid-cell dimensions and estimates of the hydraulic conductivity of the aquifer material (estimated conductance values range from 200,000 to 40,000,000 feet squared per day).

The south-western edge of the model domain is coincident with an inferred groundwater divide indicated by the presence of a topographic high or ridge which represents a recharge divide for the upper Columbia Aquifer. For shallow groundwater flow systems, groundwater divides are typically coincident with surface divide locations. There are no other local sources or sinks of water that would prevent fomiation of the divide in this area. Additionally, this boundary is far enough from the study area, that

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Appendix C


variations in the handling of this boundary in the model will not significantly affect the results of the model in the vicinity of the Site.

General Head Boundary (GHB) was applied in model layer 6 (Manokin Aquifer system) to represent the regional flow characteristics. GHB allows for the specification of a reference head and a conductance term. The reference head for GHB was estimated from the Atlantic Ocean and the regional hydraulic gradient (DGS, 1984). The conductance terms were calculated from the grid-cell dimensions and hydraulic conductivity of the aquifer material.

The only extraction wells located within the model domain during the Arcadis hydrogeologic study were pumping wells PW-1, PW-2 and PW-3. Based on the available well data, PW-1 and PW-2 are screened in model layer 2 (lower Columbia Aquifer), and PW-3 is screened in model layer 6 (Manokin Aquifer system). Flow totalizer data from 2009 indicated average extraction rates for PW-1, PW-2 and PW-3 were 130, 136 and 107 gallons per minute (gpm).

Recharge flux was applied unifonnly to the uppermost layer of the model. Annual recharge from precipitation was estimated during calibration to be approximately 10.5 inches per year (in/year), which is consistent with regional estimates (Environmental Strategies Corporation (ESC), 1990).

1.4 Hydraulic Parameters

In constructing the model for the Site, representative values for model parameters were selected based on regional infomnation and site-specific data. These model parameters included aquifer recharge, and the horizontal and vertical hydraulic conductivity of the aquifer. The model was constructed with a uniform hydraulic conductivity and parameter values in each layer based on Site aquifer and pump test data as well as regional information. During the calibration of the model, various parameter values were adjusted within reason to minimize the difference between observed and simulated groundwater elevations. Each of the 6 model layers contained one hydraulic conductivity (K) zone as summarized in Table C-1.

The estimated hydraulic conductivity value in the Columbia Aquifer (120 feet per day [ft/d]) in the present model compares favorably to the range in values from on-site (EA, 2009) slug tests (50 to 200 ft/d), estimation at neariay sites (Golder Associates, 2008; ESC, 1990) (80 to 220 ft/d), in the EA model (EA 2009) (114 to172 ft/d) and regional transmissivity estimates from DGS (1984) (15000 ft^/d for 100 ft thick Columbia

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Appendix C


Aquifer). Hydraulic conductivity estimate of 0.1 ft/d for the Bethany Formation is consistent with observed lithologic characteristics and recent aquifer test results from June 2010. Similarly, for the Manokin Aquifer system, the estimated conductivity value of 175 ft/d is comparable to the recent aquifer test results and regional estimates (DGS, 1984) (transmissivity range of 3,000 to 15,000 ft^/d for 50 to 200 ft thick Manokin Aquifer system).

1.5 Calibration Targets

Calibration targets are a set of field measurements, typically groundwater elevations, used to test the ability of a model to reproduce observed conditions within a groundwater flow system. For the calibration of a steady-state (time-invariant) model, the goal in selecting calibration targets is to define a set of water-level measurements that represent the average elevation of the water table or potentiometric surface at locations throughout the model domain.

Table C-2 presents the calibration targets, and residuals for the 21 monitoring wells and their water-level elevations from the groundwater monitoring event that occurred in June 2010. These 21 water level elevations were utilized as calibration targets. There are three calibration targets in Model Layer 1, eight in Model Layer 2, four in Model Layer 4, and six in Model Layer 6. In addition to the June 2010 calibration targets, calibration targets from average 2009 groundwater monitoring events and a transient period during a pumping test from June 29, 2010 to July 3, 2010 were also utilized. The average 2009 period contains 22 calibration targets (Table C-3), and the transient period from June 29, 2010 to July 3, 2010 consisted of groundwater elevation data collected via transducer in four selected monitoring wells.

2. Groundwater Flow Model Calibration and Verification

Calibration of a groundwater flow model refers to the process of adjusting model parameters to obtain a reasonable match between observed and simulated water levels. In general, model calibration is an iterative procedure that involves adjustment of hydraulic properties or boundary conditions to achieve the best match between observed and simulated water levels. During model calibration, site-specific data and prior slug tests were used as a guide to constrain estimates of hydraulic conductivity.

The groundwater flow model for the Site was calibrated using 21 water-level calibration targets measured during June 2010 in monitoring wells distributed throughout the vicinity of the Site (Table C-2). The 21 water-level calibration targets measured during

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ARCADIS Appendix C


June 2010 were used to evaluate the model calibration by analyzing the following: 1) simulated hydraulic head distributions across the Site and surrounding properties, 2) residual statistics, and 3) sensitivity of estimated hydraulic parameters.

2.1 Calibration Procedure

For best results, the calibration of a model should rely on discrete measurements (water levels) to produce answers free of contouring interpretations. In the calibration of a groundwater flow model, use of point data eliminates the potential for interpretive bias that may result from attempting to match a contoured potentiometric surface (Konikow 1978; Anderson and Woessner 1992). The groundwater flow model for the Site was calibrated using 21 water-level calibration targets measured during June 2010 in monitoring wells distributed throughout the vicinity of the Site (Table C-2).

As a further goal for the calibration of a model, the principle of parameter parsimony is applied to achieve an adequate calibration of the model through the use of the fewest number of model parameters. It should be noted that the use of greater numbers of model parameters during model calibration creates a situation in which many combinations of model parameter values produce similar calibration results. In this case, the model calibration parameters are called non-unique. Following the principal of parameter parsimony reduces the degree of non-uniqueness and results in more reliable calibrated parameter values. The infonnation gathered for the conceptual model guides any decision to add model parameters (e.g., zones of hydraulic conductivity) to the model during the calibration process. Therefore, the simpler model is preferred.

ARCADIS routinely uses an automatic parameter estimation procedure to calibrate groundwater flow models. Starting with a set of initial estimates for the model parameters, the procedure systematically updates the parameter estimates to minimize the difference between simulated and observed water levels at a set of calibration targets. Compared to trial and error procedures for model calibration, automatic parameter estimation can greatly reduce the time required for model calibration and generally provide a better overall calibration. The general algorithm applied in conjunction with the MODFLOW code is known as the Gauss-Newton method and is described in greater detail by Duffield et al. (1990) and Hill (1992).

The primary criterion for evaluating the calibration of a groundwater flow model is the . difference between simulated and observed water levels at a set of calibration targets.

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^ A R C A D I S Appendix C Groundwater Flow Model Development

A residual or model error, ^', is deflned as the difference between the observed ("')

and simulated ("') hydraulic head measured at a target location:

ei ' h - hi (2-1)

The automatic parameter estimation procedure seeks to minimize an objective function defined by the residual sum of squares (RSS):

Rss = YXh - /?,)' (2-2)

h Pi where ' is the measured value of hydraulic head and ' is the simulated value at a specific target location. A residual with a negative sign indicates overpredicfion by the model (i.e., the simulated head is higher than the pleasured value). Conversely, a positive residual indicates underprediction.

The residual standard deviation (RSTD) is useful for comparing model calibrations with different numbers of calibration targets and estimated parameters.

RSTD- m \ n - p

Another calibration measure is the mean of all residuals {e):

(2-3)

e = -.1 '̂ (2-4)

A mean residual significantly different from zero indicates model bias. The Gauss-Newton parameter estimation procedure produces a near zero mean residual at the minimum RSS.

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s Appendix C


The groundwater flow mode| calibration required numerous individual computer simulations. The values and shapes of the various parameter zones in the model were gradually varied until a reasonable solution was achieved in agreement with the conceptual model. This primary calibration was achieved using MODFLOW and parameter estimation techniques designed for use with MODFLOW.

The statistical goals of model calibration included the following:

• A residual standard deviation less than 10 percent of the total head change observed across the model domain. The total observed head change for the monitoring wells in the model domain was 8.4 feet in June 2010 and 8.5 during average 2009 conditions.

• A residual mean close to zero (indicating little or no bias) and the majority of calculated residuals are less than 10 percent of the range in observed water-level elevations.

2.2 Calibration Results

The 21 water-level calibration targets measured during June 2010 were used to evaluate the model calibration by analyzing the following: 1) simulated hydraulic head distributions across the Site and surrounding properties, 2) residual statistics, and 3) sensitivity of estimated hydraulic parameters.

2.2.1 Simulated HydraulicHead Distributions

As a part of evaluating the numerical model calibration, simulated potentiometric surface maps were prepared for the entire modeled region to ensure that simulated groundwater flow patterns were reasonable. Simulated regional potentiometric surface maps were prepared to depict groundwater flow conditions from June 2010 for each model layer in the Site vicinity (Figures C-2 to C-7).

2.2.2 Analysis of Residuals

The groundwater flow model calibration sought to minimize the calculated residual sum of squares (Equation 2-2). Table C-2 lists the simulated water elevations and model residuals for each of the calibration targets from June 2010. The local maps of simulated hydraulic heads (Figures C-8 to C-11) show the spatial distribution of the residuals across the Site for June 2010 in model layers 1 through 6. The calculated

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Appendix C


residuals indicate that 81% of the targets have residuals less than 10% of the observed difference in water levels (residuals were less than 0.84 feet). The relation of the observed and simulated groundwater elevation levels were also plotted graphically to visualize the degree of calibration to the June 2010 flow conditions (Figure C-12). Overall, the model shows a good match to the measured water levels at the Site.

Residual statistics for the calibrated groundwater flow model also indicate good agreement between simulated and measured groundwater elevations. The residual standard deviation was calculated to be 0.51 ft. The residual standard deviation is less than 7% of the range of observed water-level elevations for the entire model domain. These statistics indicate that an acceptable degree of calibration has been achieved in this modeling effort.

2.3 Groundwater Flow Model Verification

Model verification refers to the use of the calibrated groundwater flow model to predict flow conditions under a different set of stress conditions. Two verification simulations were performed with the model, using 2009 average conditions and transient conditions during a pumping test monitored between June 29, 2010 and July 3, 2010.

The 22 water-level calibrafion targets measured during 2009 average conditions were used to evaluate the model calibration by analyzing the following: 1) simulated hydraulic head distributions across the Site and surrounding properties, 2) residual statistics, and 3) sensitivity of estimated hydraulic parameters. To illustrate the verification of the model to the transient period, the observed and simulated transient data are plotted graphically.

2.3.1 Analysis of Verification Residuals

The groundwater flow model calibration sought to minimize the calculated residual sum of squares (Equation 2-2). Table C-3 lists the simulated water elevations and model residuals for each of the calibration targets from 2009. The local maps of simulated hydraulic heads (Figures C-13 and C-14) show the spatial distribution of the residuals across the Site for 2009 in model layers 1 and 2. The calculated residuals indicate that 73% of the targets have residuals less than 10% of the observed difference in water levels (residuals were less than 0.85 feet). The relation of the observed and simulated groundwater elevation levels were also plotted graphically to visualize the degree of calibration to the Average 2009 flow conditions (Figure C-15). Overall, the model shows a good match to the measured water levels at the Site.

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ARCADIS Appendix C


Residual statistics for the 2009 verification of the groundwater flow model also indicate good agreement between simulated and measured groundwater elevations. The residual standard deviation was calculated to be 0.55 ft. The residual standard deviation is less than 7% of the range of observed water-level elevations for the entire model domain. These statistics indicate that an acceptable degree of verification of the calibrated groundwater flow model.

With respect to the verification of the calibrated model to the transient period from June 29, 2010 and July 3, 2010, plots of the observed and simulated water levels from monitoring wells MW-11D, MW-13D, MW-14D, and MW-16D were produced (Figure C-16). These plots indicate a good correlation between the simulated and observed water levels during the aquifer test. This correlation suggests the calibrated groundwater fiow model can evaluate transient impacts at the Site at an acceptable degree.Heading 2

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Table C-1. Hydraulic Conductivities, Millsboro Public Well Site, Millsboro, Delaware

Model Layer

1 2 3 4 5 6

Hydrogeologic Unit

Columbia Aquifer (Upper) Columbia Aquifer (Lower)

Bethany Formation (Upper) Bethany Formation (Middle) Bethany Formation (Lower)

Manokin Aquifer

Modeled Hydraulic Conductivity (ft/day)

Horizontal Hydraulic Conductivity

120 120 0.1 0.5 0.5 175

Vertical Hydraulic Conductivity

12 12

0.002 0.005 0.008 17,5

Relevant Data on Horizontal Hydraulic Conductivity (ft/day) |

ARCADIS

Study^

167-190

EA Slug

Tests^

50 - 200

-

-

EA

ModeP

114-172

--

-

DGS'

-150

--

50 - 300

Golder

Associates^

76 - 220

-

-

ESC*̂

80-100

-

-

Notes:

^ Aquifer Pump Test conducted by ARCADIS at Millsboro TCE site during July 2010

^ Slug Tests conducted by EA at Millsboro TCE siteduring June 2009 (EA, 2009)

^ Reported Values in EA Model for Millsboro TCE site (EA, 2009)

'' Delaware Geological Survey Report of Investigation ho. 38 (DGS, 1984)

^ Slug Tests conducted by Golder Associates at Indian River Generating Station in Millsboro, DE (Golder Associates, 2008)

^ Aquifer Test and Numerical Modeling conducted by ESC at Millsboro NCR site between 1988 and 1990 (ESC, 1990)

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Table C-2. June 2010 Calibration Targets and Residuals, Millsboro Public Well Site, Millsboro, Delaware

Well ID

MW-06S MW-07S MW-17S MW-6D

MW-07D MW-11S MW-12S MW-13S MW-14S MW-15S MW-16S MW-11M MW-12M MW-13M MW-14M MW-11D MW-12D MW-13D MW-14D MW-15D

MW-16D

Model Layer

1 1 1 2 2 2 2 2 2 2 2 4 4 4 4 6 6 6 6 6 6

- X-Site Coordinate

(ft) 691,093.16 691,009.06 690,384.65 691,090.87 691,002.63 689,986.41 690,114.65 690,229.95 690,009.50 689,971.66 690,694.24 689,976.52 690,129.02 690,212.85 690,015.54

689,981.28 690,125.06 690,222.03 690,015.22 689,975.61

690,697.47

Y-Site

Coordinate

(ft) 215,342.91 215,004.99

215,560.43 215,335.80 215,011.71 216,084.02 215,862.76 215,763.62 216,186.21 215,947.01 215,355.75 216,063.60 215,857.68 215,745.61 216,183.51 216,072.34 215,860.80 215,757.40 216;i89.94 215,942.82

215,363.59

Simulated Water Level Elevation (ft

msl) 5.81 6.56 8.28 5.41 6.45 8.73 8.68 8.52 8.58 8.90 7.48 12.33 12.28 12.25 12.22 13.47 13.46 13.43 13.40 13.53

13.17

Observed Water Level Elevation (ft

msl) 4.94 7.21 8.13 4.75 6.14 7.54 7.88 7.91 7.29 8.72 7.20 12.54

. 12.46 12.39 12.67 13.09 12.99 12.88 13.06 13.11

12.15

Calculated Residual (ft)

0.87 -0.65 0.15 0.66 0.31 1.19 0.80 0.61 1.29 0.18 , 0.28 -0.22 -0.18 -0.14 -0.45 0.38 0.47 0.55 0.34 0.42

1.02

STATISTICS

Residual Mean (ft) =

Residual Standard Deviation (ft) =

Sum of Squared Residuals (ft'̂ ) =

0.37

0.51

8.22

AR000590

Table C-3. Average 2009 Calibration Targets Residuals, Millsboro Public Well Site, Millsboro, Delaware

Well ID

1361HDLGPMW1 1361HDLGPMW2 1361HDLGPMW3 1361HDLGPMW4 1361HDLGPMW5

1361MW01M 1361MW01S 1361MW02D 1361MW02S 1361MW03D 1361MW03S 1361MW04S 1361MW06S 1361MW07S 1361MW09D 1361MW09S 1361 MWIOS 1361MW01D 1361MW04D 1361MW06D 1361MW07D

1361MW10D

Model Layer

2 2 2 2 2

X-Site Coordinate

(ft) 689,962.62 689,964.80 689,945.87 689,958.39 689,938.06 689,984.77 689,990.33 689,969.98 689,973.82 690,168.23 690,176.94 690,595.21 691,093.34 691,009.19 690,109.85 690,114.10 689,573.41 689,979.50 690,604.27 691,090.75 691,002.50

689,567.96

Y-Site

Coordinate

(ft) 214,199.85 214,190.94 214,182.25 214,164.85 214,160.03 214,244.11 214,254.12 214,460.47 214,450.17

214,668.86 214,679.52 214,947.32 215,343.63 215,005.06 214,242.03 214,247.51 213,857.80 214,233.80 214,943.68 215,335.73 215,011.84

213,863.59

Simulated Water Level Elevation (ft

msl) 10.96 10.96

n.oi 11.01 11.05 10.86 10.84 10.63 10.63 9.94 9.90 8.49 6.25 6.98 10.61 10.59 12.08 10.88 8.46 5.92 6.87

12.08

Observed Water Level Elevation (ft

msl) 11.70 11.78 11.78 • 11.92 11.85 11.54 11.54 11.20 11.31 10.43 10.42 9.21 5.91 8.30 11.37 11.65 14.33 11.95 9.19 5.85 7.69

14.13

Calculated Residual (ft)

-0.75 -0.82 -0.77 -0.91 -0.80 -0.68 -0.70 -0.57 -0.68 -0.49 -0.51 -0.72 0.35 -1.32 -0.76 -1.05 -2.26 -1.07 -0.73 0.07 -0.81

-2.05

STATISTICS

Residual Mean (ft) =

Residual Standard Deviation (ft) =

Sum of Squared Residuals (ff^) =

-0.82

0.55

21.26

AR000591

LEGEND

Grid Cell

- Plume Oufline

MILLSBORO PUBLIC WATER SUPPLY MILLSBORO, DELAWARE

GROUNDWATER FLOW MODEL DEVELOPMENT

FINITE DIFFERENCE GRID

^ ARCADIS C-1 AR000592

LEGEND

Plume Outline

[ No Flow Cell

• River Cell

• Constant Head Cell

I Drain Cell

-10- Simulated Water Levels (ft msl)



BOUNDARY CONDITIONS AND SIMULATED WATER LEVELS IN THE UPPER COLUMBIA AQUIFER

(MODEL LAYER 1)

^ ARCADIS FIGURE

C-2 AR000593

LEGEND

Plume Outline

r No Flow Cell

© Extraction Well

-10-Simulated Water Levels (ft msl)



BOUNDARY CONDITIONS AND SIMULATED WATER LEVELS IN THE LOWER COLUMBIA AQUIFER

(MODEL LAYER 2)

^ ARCADIS FIGURE

C-3 AR000594

LEGEND

Plume Outline

[ No Flow Cell




BOUNDARY CONDITIONS AND SIMULATED WATER LEVELS IN THE UPPER BETHANY FORMATION

(MODEL LAYER 3)

^ ARCADIS FIGURE

C-4 AR000595

LEGEND

Plume Outline

L No Flow Cell

=-10-Simulated Water Levels (ft msl)



BOUNDARY CONDITIONS AND SIMULATED WATER LEVELS IN THE MIDDLE BETHANY FORMATION

(MODEL LAYER 4)

( S I ARCADIS FIGURE

C-5 AR000596

LEGEND

Plume Outline

C No Flow Cell

-10— Simulated Water Levels (ft msl)



BOUNDARY CONDITIONS AND SIMULATED WATER LEVELS IN THE LOWER BETHANY FORMATION

(MODEL LAYER 5)

( ^ ARCADIS FIGURE

C-6 AR000597

LEGEND

Plume Outline

[ No Flow Cell

• General Head Cell

® Extraction Well




BOUNDARY CONDITIONS AND SIMULATED WATER LEVELS IN THE MANOKIN AQUIFER

(MODEL LAYER 6)

^ ARCADIS FIGURE

C-7 AR000598

LEGEND

—10— Simulated Water Levels (ft msl)

0.5 Calculated Residual (ft) • (Simulated - Observed Water Level)

PW-1 Extraction Well

Plume Outline



JUNE 2010 SIMULATED WATER LEVELS AND CALCULATED RESIDUALS IN THE

UPPER COLUMBIA AQUIFER (MODEL LAYER 1)


LEGEND

-10— Simulated Water Levels (ft msl)



Plume Outline




LOWER COLUMBIA AQUIFER (MODEL LAYER 2)


LEGEND




Plume Outline




MIDDLE BETHANY FORMATION (MODEL LAYER 4)


LEGEND




Plume Outline




MANOKIN AQUIFER (MODEL LAYER 6)

^ ARCADIS FIGURE

C-11 AR000602

1^ —I

-

-

•55 10 — E IC

? a _ j _

.̂ (D

•s § • D

CO ^

^

—

—

n

(

• • •

/ / >

/ ^ X / ^ r /

/ ^ / 1 1

)

LEGEND

Layer 1

Layer 2 Layer 4

Layer 6

-t7-10% Range of Observed \/Uater Levels

^ /

^ / /

/ / / / ^ /

/ ^ r / / ^ r y

^ ^ / B ' -̂ ^ B B W / ^ ^ ^5^r / > ^ /

^ ^kr / ^ r

/ X y

' ^ ^

A / / /

/ y ^ / ^r /

y^ / /

/

I I 1 1 1 1 I I

5 10 Observed Water Level (11 msl)

/ /

/ y /

/ /

\

15



PLOT OF OBSERVED VERSUS SIMULATED WATER LEVELS UNDER JUNE 2010 CONDITIONS

^ ARCADIS FIGURE

C-12 AR000603

LEGEND



PW-1 0 Extraction Well

Plume Outline



AVERAGE 2009 SIMULATED WATER LEVELS AND CALCULATED RESIDUALS IN THE

UPPER COLUMBIA AQUIFER (MODEL LAYER 1)


LEGEND



PW-1 0 Extraction Well

Plume Outline



AVERAGE 2009 SIMULATED WATER LEVELS AND CALCULATED RESIDUALS IN THE

LOWER COLUMBIA AQUIFER (MODEL LAYER 2)


15

. - - s

1 10 c

i —J

0)

i • D 0) •E 3

1 5

0

(

LEGEND

^ Layer 1

0 Layer 2

-h/-10% Range of Observed Water Levels

/ /

/ / / / y / ^ / ^

/ / / • X X

^ / ^ J A /4 , y y /A' / X / y>

/ X /

w* • X / / •r /"" / ^

/Y/ / / /

/ / /

/y// / /

^ / 1 1 1 1 1 1 1 1 1

) 5 10 Observed Water Level (ft msl)

i ^

1 1 1

15



PLOT OF OBSERVED VERSUS SIMULATED WATER LEVELS UNDER AVERAGE 2009 CONDITIONS


*"uiuc*i iaoMnnai



TRANSIENT CALIBRATION CURVE FITS (JUNE 29, 2010 - JULY 3, 2010)

(St ARCADIS c-16

AR000607

GROUNDWATER FLOW MODEL REPORT - APPENDIX C - … · Groundwater Flow Model Calibration and...

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