Document 7Rw1ry0v8j0KoLr8RRexeyVL8

AR226-2598 REVISED GROUNDWATER FLOW MODEL DUPONT WASHINGTON WORKS WASHINGTON, WV Date: January 2003 Project No.: 18983635 7423 CORPO RATE REM EDIATION G R O U P An Alliance between DuPont and UPS Diamond Barley Mill Plaza, Building 27 Wilmington, Delaware 19805 A SH 020280 E D 630708 Revised Groundwater Flow Modal Introduction TABLE OF CONTENTS 1.0 Introduction,-,*.... ........................*****................................ ................................... j 2.0 Site Setting, Geology, and Hydrogeology...................................................................4 2.1 Site Setting.................................................... ......................................... ...........* 2.3 Hydrogeology......................................................................................... 3.0 Primary Data Sources............ ....................................................................................2 5 4.1 ModelDomain and Discretization................................. 9 4.2 Boundary Conditions.... ................................................ ................................. 4.2.1 No Flow Boundaries 4.2.2 Ohio R iver....................... 1 4.2.3 Minor Surface Water Features............................................................ 12 4.2.4 Pumping Wells........ ............................................. 13 4.3 Main Input Values....,...... ............................... ...............*.............................^ 4.3.1 Hydraulic Conductivity......................................................................16 4.3.2 Recharge........ ........................ 1 5.0 Groundwater Model Calibration............ ......................... . - ...................... --...... I9 5.1 Calibration Strategy........... ................................. .......... .............. ..................I9 5.2 Calibration Results........................................................ 6.0 Model Results .................... ...................................................... *...................... 21 6.1 Mass Balance......................................................*.......................*................. "21 6.2 Current Pumping Conditions............ ................ .......................... *.........*........21 6.3 No DuPont Pumping....................................... ................................................22 6.4 No GE Pumping.................................................... ......................................... 23 6.5 No Pumping by DuPont or GE.............................. ..................-......... .............23 6.6 No Little Hocking WA Pumping......... ................................ .................. 23 7.0 Sensitivity Analysis....................... ........................................ ..................................25 8.0 Model Conclusions...................... ........................................................................... *26 9.0 References.... ....................--........................................................................*........27 20 74Z3WWGWM-R0UOO Jan. 7.03 Wilmington, DE ASH0202B1 E ID 630709 Revised Groundwater Plow Model Introduction Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 TABLES Primary Data Sources for the Groundwater Flow M odel............................7 Finite-Difference Grid Vertical Discretization............................................ 9 Table 3. Riverbed Hydraulic Conductivity Values.................... 11 Model Pumping R ates.......................... . -................................................. ^ Aquifer Hydraulic Conductivity Values..................................................... 17 Model Recharge R ates............................. 18 Statistical Summary o f Model Calibration Errors (Residuals)..................20 Mass Balance Summary ............................................................... Sensitivity Analysis Results............. .......... ............................... Figure l Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 14a Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 FIGURES Site Location Map Idealized Ohio River Valley Cross-Section and Block Diagram Terrace Surfaces Generalized Geologic Cross-Section at River Mile 190 Groundwater Elevation Map Model Finite Difference Grid Boundary Conditions Model Pumping Well Locations Hydraulic Conductivity Zonation Recharge Zonation Synoptic Water Level Measurement Locations Model Calibration Results Model Computed Head-Layer 1 . Model Computed Head-Layer 2 Model Computed Heads-Layer 2-Site Area Model Computed Head-Layer 3 Predicted Groundwater Table with No DuPont Pumping Predicted Groundwater Table with No GE Pumping Predicted Groundwater Table with No DuPont or GE Pumping Predicted Groundwater Table with No Little Hocking Pumping Sensitivity Analysis Results 7423WWGWM-R01.doc Jan. 7,03 Wilmington, DE A SH 0202B 2 E ID 63071Q Revised Groimdwatef Row Model Introduction 1.0 INTRODUCTION A steady-state groundwater flow model was developed for the DuPont Washington Works facility (the site) in 1999. This model, which was completed as part of the RFI, was documented in the RCRA Facility Investigation Report (DuPont, 1999). The original groundwater flow model has been revised and expanded. The primary objectives o f the modeling work documented in this report included: Addressing EPA/ACOE comments on the previous groundwater flow model, Evaluating groundwater migration pathways at the site under current site and regional pumping conditions, and Predicting future groundwater migration pathways under various pumping scenarios. Feedback was sought from experts with the U.S. Environmental Protection Agency (EPA), U.S. Army Corps of Engineers (ACOE), and U.S. Geological Survey during the redevelopment o f the model. Meetings were held with these experts at key stages in model development including completion of the conceptual geologic model, following preliminary model calibration, and then after final model calibration in order to give the experts the opportunity to review the work completed at each stage and to solicit feedback. The purpose o f this report is to document the revised groundwater flow model for the DuPont Washington Works facility. The following sections describe the site setting, geology, and hydrogeology, and document the model set-up, calibration, and results. 7423WWGWM-RD1.doc Jan. 7, 03 WMnotqn, DE 3 Revised Groundwater Flow Model Site Setting, Geology, and Hydrogeology 2.0 SITE SETTING, GEOLOGY, AND HYDROGEOLOGY 2.1 Site Setting The site is located on Washington Bottom in Washington, West Virginia. The location of the site and several surrounding properties are shown on Figure 1. The site, which is bounded on the north by the Ohio River, lies at the western (down-stream) end of Blennerhassett Island approximately between river miles 189 and 191. The DuPont site shares its southwestern boundary with another manufacturing facility operated by General Electric (GE). 2.2 Geology The site lies within the Ohio River Valley and rests on Quaternary alluvial sediments that overly the Permian-aged Dunkard Group. The two predominant facies of die Ohio River alluvium that have hem identified include coarse-grained Ohio River Alluvium (Pleistocene-aged glacial outwash deposits) and fine-grained Ohio River Alluvium (Holocene overbank deposits (Simard, 1989). The Pleistocene deposits consist primarily of coarse-grained sand and gravel while the Holocene deposits consist primary of interbedded and laminated silt, clay and fine-pained sand. Simard also identified three minor facies of the Ohio River Alluvium including tributary deposits (silt, sand and gravel), colluvial deposits (coarse sand, gravel, cobbles and boulders) and e'olian sand and silt deposits. The Dunkard Group (bedrock) consists primarily of red and varicolored sandy shale; gray, p e rn and brown sandstone; gray and light-gray siltstone; and minor beds o f coal, claystone, black carbonaceous shale and limestone. The facies o f the Ohio River Alluvium formed in response to the glacial advances and retreats of the pre-, early- and late-Wisconsinan and were deposited as successive phases of aggradation and degradation of river valley alluvial materials. The coarse-pained Pleistocene alluvium was deposited as glacial outwash during the primary valley agpadation event following the glacial scouring of the valley into the bedrock floor. During the subsequent degradation and aggradation cycles o f the Pleistocene, the glacial outwash sediments were partially removal, re-worked and then redeposited to a lower elevation than the previous cycle, thus forming a terrace. This process formed a series o f Pleistocene-aged terrace surfaces within the Ohio River Valley. These surfaces were designated (youngest to oldest) as S4, S5, and S6 by Simard. With each subsequent depedation/agpadation cycle, additional fines were incorporated into the Pleistocene deposits due to continual influx o f finer-pained fluvial sediments from tributaries of the Ohio River. As a result, the Pleistocene deposits become more highly re-worked and progressively finer-pained toward the center of the river valley, particularly in locations down-stream o f significant tributaries (Simard, 1989). The total thickness o f Pleistocene sediments at Washington Bottefft ilmges from about 80 feet beneath the highest Pleistocene terrace surfaces to about 15 feet beneath the current channel o f the Ohio River. 7423WW6WM-R01 .doc Jan. 7, 03 Wilmington, DE asho; E ID 630712 Revised Groundwater Flow Model Site Setting, Geology, and Hydrogeology The Pleistocene alluvial deposits are overlain by the finer-grained Holocene sediments. The silts clays and fine sands were deposited on the surface of the Pleistocene terraces as well as on a series of more recent floodplains, which formed in the center o f the Ohio River Valley during the Holocene. The thickness of the Holocene sediments typically ranges from S to 15 feet over the Pleistocene terrace surfaces and 25 to 35 feet over the Holocene floodplains. Simard designated the Holocene floodplain surfaces as SI through S3 and the modem floodplain of the Ohio River as SO. Figure 2, modified from Simard (1989) is a block diagram and idealized cross-section through the Ohio River valley depicting the complex set of Pleistocene terraces and Holocene floodplains which have formed in the valley. Holocene floodplain surfaces and Pleistocene terrace surfaces were mapped using surface age and elevation data from Simard, 1989. A map of floodplain and terrace surfaces is shown in Figure 3. Individual floodplain and terrace surfaces were not differentiated. Due to damming of the river, the SO, SI, and S2 Holocene floodplain surfaces are now flooded along the reach o f the Ohio River at Washington Bottom. The S3 surface remains above the current normal pool elevation of 582-ft. MSL. A thin strip of this surface remains on the south side of the river along Washington Bottom. More extensive expanses of this surface are present along the north side o f the river at Little Hocking Water Association (WA), Blennerhassett Island, Shell Kraton, and Belpre. Additional expanses of this surface are present down-stream o f Washington Bottom at Lubeck Public Service District (PSD). The remainder of the alluvial valley is occupied by the Pleistocene terrace surfaces. A generalized north-south cross-section from the Little Hocking WA well field in Ohio, through the Ohio River and across the DuPont facility, is presented in Figure 4. This cross-section shows the floodplain and terrace surfaces, the Holocene silt and clay overbank deposits overlying the Pleistocene sand and gravel outwash deposits and the re worked Pleistocene alluvium in the center of the river valley. The alluvial terrace deposits are underlain by a flat, river-scoured bedrock surface o f the Dunkard Group that rises steeply and forms the valley walls to the North of Little Hocking Water Association and to the south of the DuPont facility (Figure 3). 2.3 Hydrogeology Groundwater supplies in the region are obtained from the Dunkard Group bedrock and Ohio River alluvial terrace deposits. The saturated portion o f the Ohio River alluvial terrace deposits comprise the principal regional aquifer used for water supply purposes. Production wells completed in this aquifer have been known to yield up to 500 gallons per minute (gpm) (Schultz, 1984). Based on these high yieldsr numerous industrial and commercial water supply companies obtain water from the alluvial aquifer. The Holocene silts and clays support perched groundwater zones. Along the southern riverbank at the DuPont plant site on Washington Bottom, are seven monitoring wells that are completed in this perched groundwater zone. Groundwater elevations for these monitoring wells are typically 6 to 18 feet higher than elevations measured in monitoring wells completed in the underlying primary site water-table aquifer, which is sigwfican y depressed as a results o fpumping by DuPont and GE. During the February 2002 ........................-- ---------- -- --------------------- ------ -5 7423WWGWM.R01.doc Jan, 7.03 Wilmington, DE A SH 0202B 5 E ID 630713 Revised Groundwater Flow Model Site Setting, Geology, and Hydrogeology synoptic groundwater level event, groundwater elevations in the perched water table at the site ranged from 571.91 feet above mean sea level (MSL) to 582.09 feet MSL (Figure 5). Groundwater elevations in the underlying primary site water-table aquifer ranged from 558.24 to 566.61 feet MSL. The Ohio River Alluvial Aquifer, which is the primary water-table aquifer in the area, occurs at a depth o f about 60 to 70 feet below ground surface at the DuPont plant site. The saturated zone is approximately 30 to 40 feet thick, extending approximately to the surface o f the underlying Punkard Group bedrock. Numerous pumping tests have been completed in the alluvial aquifer in the Washington Bottom area as part o f water supply investigations. The hydraulic conductivity o f the alluvial aquifer in the area typically ranges from 100 to 300 ft/d. In contrast, the hydraulic conductivity of the underlying Dunkard Group bedrock aquifer is typically between 0.05 and 5 ft/d (see Section 4.3.1). Natural recharge to the alluvial aquifer comes from various sources, including: Infiltration of precipitation falling directly on the alluvium q Lateral movement o f the river water through the alluvium Seepage from stream tributaries that discharge to the Ohio River Surface run-off from the outcrop areas o f the Dunkard Group, which forms steep slopes adjacent to the uppermost Pleistocene terrace. 7423VWVGWM-R01 .<JOC Jan. T. 03 Wilmington, D6 A SH 0202B 6 E ID 630714 Revised Groundwater Flow Model Primary Pata Sources 3.0 P R IM A R Y D A T A SOURCES Data was obtained from numerous sources for use in revising the WashingtonWcrks groundwater flow model. These sources and die nature o f the data obtained from each source are summarized in Table 1 below. Ta aa bu lice 1i .. Pi rimary D~ a--t-a---S--o--u-r--c-e--s--f-o--r t-h--e---G--r-o- -u--n--d-w---a-t-e-r--P--l-o- w Model. ... ;' ' - `.D a ta S o u rc e " ; - ..y , r y y - j'fllf`'?'% 'v ';jjs fti T y p i(s } DuPont Washington Works RCRA Facility Investigation Report, Well and soil boring logs DuPont CRG, 1999 Groundwater elevation data Aquifer testing results Hydrogeologic Evaluation for Additional Water Supply flout Well logs Bleunerimssett Island, Leggetts, Brastears & Graham, Inc, 1986 Aquifer testing results Blenncrhassett Island Water Supply Well Drilling and Test Pumping, Burgess & Niple, Ltd., 1988 Well logs Aquifer testing results Grain size analysis results Washington Works PreKininaiy Hydrogeologic Assessment, DuPont. 1991 Well and soil bating logs Aquifer hydraulic conductivity data RCRA Facility Investigation Report. Shell Kratan Plant. Belpre, Well and soil boring logs Ohio, Shell Chemical Company, 1999 Aquifer hydraulic conductivity data Geologic History of the Lower Terraces and Floodplains of the Upper Ohio River Valley, West Virginia Geological Survey Open File Report 8903, Sinatd, 1989 Lithology, thickness, and deposttional history of die Ohio River alluvial sediments * Historical low water levels o f the Ohio River Terrace ages and elevations Aquifer-Characteristics Data for West Virginia, USGS WaterRcsouraes Investigations Report 01-4036, KUffiand Matte, 2001 Well Head Protection Plan, Little Hocking Water Association, 1996 Aquifer hydraulic conductivity date Estimated recharge rates Well logs Aquifer hydraulic conductivity date ________,_______--................................. ............... .... .-- "------- -- 7423WWGWM-R01doc Jan, 7,03 Wilmington. DE " 7 SH 0202B 7 E ID 630715 Revised Groundwater Flow Mode) Primary Data Sources Well Head Protection Area Survey, Lubeek Public Service District, 1998 Well logs Aquifer testing results Geotechnical Boring Logs, Planned 892 Corridor, Burgess & Niple, 2001 Lithologic descriptions Geotechnical Boring Logs, Planned Rt. 50 Corridor D over Ohio Lithologic descriptions River and Blennerbassett Island, Michael Baker Jr., Inc., 2002 Ohio River Bathymetric Data, ACOE, 2002 Ohio River water depth and bed elevations Monthly Operation Reports for Lubeek PSD, Little Hocking WA, and City o f Belpre Daily pumping rates DuPont and Little Hocking Pumping Rate Data Hourly or daily rates from days of synoptic water measurements Well Logs from Shell and GE Sites Lithologic descriptions Synoptic Groundwater Levels from February 2,2002 and August Groundwater elevations at Lubeck, GE, DuPont 21, 2002 plant, Blenn. Isle., little Hocking, Shell 74g3wwewM.R01.doc Jan. 7.03 Wlmlngttn, DE A SH 0202B8 E ID 630716 Revised Groundwater Flaw Model Model Set-up 4.0 MODEL SET-UP Groundwater flow in the Ohio River Alluvial Aquifer at the DuPont Washington Works facility and the surrounding area was simulated using United States Geological Survey's MODular Groundwater FLOW modeling code (MODFLOW, McDonald and Harbaugh, 1984). MODFLOW was selected because o f its wide acceptance within the rndusby as well as its versatility in simulating various types o f complex groundwater flow boundaries. The groundwater model was constructed and calibrated using Groundwater Vistas (v. 3.36), a graphical pre- and post-processor that interfaces with MODFLOW, published by Environmental Simulations, Inc. (ESI). 4.1 Model Domain and Discretization...... ........ ............................ The Washington Works Groundwater Model domain covers an area of 39.5 square miles, extending 41,568 feet east-west and 26,394 feet north-south. The origin of the finite difference grid is located at UTM Coordinates of 4,341,000 northing and 437,800 easting (UTM, NAD 27 meters). The finite difference model grid is shown on Figure 6. The model domain was discretized as follows: 153 rows by 235 columns 3 layers 107,865 cells (69,705 active cells) p Grid spacing: 25 m to 100 m (82 f t to 328 ft.) The Ohio River Alluvial Aquifer is represented in the model by layers 1 and 2, while the bedrock aquifer (minor aquifer) is simulated as layer 3. The vertical discretization and hydrostratigraphic units simulated in each layer is summarized in Table 2 below. Table 2. Finite-Difference Grid Vertical Discretization. Layer 1 Layer 2 Variable-based 560 on topography 560 535 Layer 3 535 7423WWGWM-RQ1.(Joe Jan. 7,03 Wilmington, de 500 Fine-grained Holocene sediments Pleistocene Sands and Gravels Bedrock - Dunkard Group Pleistocene Sands and Gravels Re-worked Pleistocene Sands and Gravels - main river channel Re-worked Pleistocene Sands and Qfavr-ls --Rletwi^basKett Island Bedrock - Dunkard Group Bedrock - Dunkard Group A SH 0202B 9 EXD630717 Revised Groundwater Flow Model Model Set-up The base oflayer 1 !s set at an elevation o f 560 ft. above MSL throughout the model layer. This elevation corresponds approximately to the elevation o f the contact between the fine-grained Holocene sediments and the underlying Pleistocene sand and gravel beneath the Holocene floodplains. The top of layer 2 coincides with the base of layer 1. The base of layer 2, which is also constant throughout the model, is set at an elevation of 535 ft. above MSL- This elevation corresponds approximately to the elevation of the contact between the Pleistocene sand and gravel and the underlying shales o f the Dunkard Group (bedrock) within the river valley. These contact elevations are based on well and soil boring logs from the DuPont Washington Works plant site, Blennerhassett Island, and Little Hocking WA (Figure 4). 4.2 Boundary Conditions Under normal stress conditions, the alluvial aquifer would be expected to discharge to the Ohio River with infiltration being the predominant source of recharge to the aquifer. Due to the high volume of groundwater pumping from the alluvial aquifer along this reach of the river, the Ohio River is the main source o f recharge to the alluvium within the area of the model domain while infiltration is a secondary recharge source. Correspondingly, discharge o f groundwater from the alluvial aquifer within the area of the model domain occurs primarily through the numerous industrial and pubic supply wells. Minor volumes of groundwater recharge and discharge to the alluvial aquifer along several minor surface water features. The treatment o f these boundary conditions in the groundwater flow model is described in the following sections. The model boundary conditions are shown in Figure 7. 4.2.1 No Flow Boundaries Many of the ceils within the model domain are set as inactive (no flow cells). These cells are in areas o f the domain where the alluvium is absent and the low permeability shales of the bedrock are present exclusively. The area of bedrock immediately surrounding the alluvial aquifer, both adjacent and below the alluvium, is included as active cells within the model to discretely simulate recharge to the alluvial aquifer from the bedrock. The area of active bedrock cells laterally surrounding the alluvial aquifer was delineated based on the estimated locations of groundwater divides within the bedrock aquifer. The locations o f the divides were estimated from surface topography. ` Additional no flow cells were assigned to the center of the Ohio River in model layer 1 where the river bed elevation was below the base of that layer (560 ft. MSL). River bed elevation in each model cell was interpolated from Ohio River bathymetric data (US ACOE, 2002) 4.2.2 Ohio FSver The Ohio River is simulated in the model as a MODFLOW river boundary. River boundary cells were set within the model domain based on the current river channel width and riverbed elevation. The river boundary cells representing the Ohio River were assigned to either model layer 1 or 2, depending on the elevation of the riverbed at the 7423WWGWM-R0l.dod Jan. 7. 03 Wilmington, OE A SH Q 2O 290 E ID 630718 Revised Sroundwataf Flow Model Model Set-up center o f each model cell. Where the river bed elevation was below the base o f layer 1 (560 ft. MSL), the river boundary was assigned to layer 2 and the overlying cell in ayer was set as a no flow cell (inactive) as previously described. River boundaries allow the simulation o f groundwater recharge or discharge on &e baris o f the gradient between the predicted groundwater head surrounding the m e r cefl and the soecified river stage elevation. The volumetric rate o f groundwater flow across the boundary is govrSed by the hydraulic gradient between the groundwater head and the r i v e r S e and the hydraulic conductance o f the riverbed material. The conductance o f the riverbed is calculated for each river cell independently, according to the following formula; Where: Cm K L W 'M hydraulic conductance of the river-aquifer interconnection ** hydraulic conductivity of the riverbed material = length of the riverbed within the model cell = width of the riverbed within the model cell = of the riverbed within the model cell Because entire model cells are contained within the Ohio River, the l^ g m and wdtii of the riverbed within each river boundary cell was taken to be model grid celt The thickness of the riverbed was assumed to be conductivity o f the riverbed material, which was adjusted during model eahbratoon, v S d e p L i n g u p o n the nature of the geologic materialsThat the nver cell was f o ld e d upon (riverbed K for river cells overlying Holocene silt and clay were low erthm thos overlying Pleistocene sand and gravel). The final riverbed hydraulic conductivity values for river cells are summarized in Table 3 below. Table 3. Riverbed Hydraulic Conductivity Values. ;!^^i^c^aS u etiv l^r. # ^ W lliy e rite d :(ft/d ): ' Holocene alluvium - silt, clay, fine sand . Re-worked Pleistocene alluvium - sand, gravel, silt Re-worked Pleistocene alluvium at west and o f Blennerbassett Island - 0.1 0.3 30 ---------- -- ----------- --------- -- ----------------------------- -- -- - 7423WWJSWMfl0MOG.JainZ.,0.3. ............. ........ ' Wilmington, PE n ' A SH 020291 EX D 630719 I Revised Groundwater Flow Model Model Set-up The normal pool elevation for this reach o f the Ohio River in 582 ft. above MSL. River elevations measured at the Little Hocking WA and Shell Kraton plant on August 21, 2002 were 582.24 and 582.05, respectively. The river elevation should be higher at the Shell Kraton plant than at Little Hocking WA, which is down-stream, indicating that there is some error in one or both of these measurements. Therefore, the normal pool elevation o f 582 ft above MSL was used as the river stage elevation in the groundwater flow model. A constant river elevation was used throughout the model domain (e.g., no stream fall was simulated) due to river damming, which has led to relatively insignificant change in river stage elevation within the model domain. 4.2.3 Minor Surface Water Features Numerous minor surface water features occur within the bedrock outcrop areas as well as on the alluvial terrace surfaces within the model domain. The majority of these features are ephemeral streams in which the flow is limited primarily to storm water run-off. The stream reaches within the bedrock outcrop area are included in the model as MODFLOW drain boundaries. This boundary type is appropriate for simulating the ephemeral streams in the bedrock areas, which are minor discharge points for the bedrock aquifer but do not contribute significant recharge. Drain boundaries allow the simulation of groundwater discharge on the basis of gradient between the predicted head surrounding the drain and the specified drain elevation (i.c,, the surface water elevation). Similar to river boundaries described previously, the rate of flow across the boundary is governed by the hydraulic gradient between the surrounding groundwater head and the drain stage elevation and the hydraulic conductance of the drain bed material (streambed). Contrary to river boundaries, drain boundaries will not contribute positive flow into the model domain under inward gradient conditions (e.g., if the surrounding heads are lower than the specified boundary head). The drain elevation assigned to each drain boundary cell was based on the topographic elevation along the stream at the center of the cell. The drain conductance in each boundary cell was calculated using estimated stream dimensions (length, width and bed thickness) and the streambed hydraulic conductivity. A nominal streambed hydraulic conductivity of 1 ft. I d was used so as not restrict groundwater discharge along these boundaries. Three perennial streams are present within the model domain. These streams include Sandy Creek near Lbeck PSD, an unnamed stream across the Ohio River from Lbeck, and an unnamed stream that flows through the Shell Kraton facility on the north side of the Ohio River near Blennerfaassett Island. It is likely that each of these streams provides some recharge to the alluvial aquifer and has some influence on the local groundwater elevations. Therefore, these streams were simulated as MODFLOW river boundaries to allow for the simulation of this recharge component. The river boundary elevation in each cell was based on the topographic elevation along the stream. The stream conductance in each river boundary cell was calculated using estimated stream dimensions (length, width and bed thickness) and a streambed hydraulic conductivity of 0.1 ft. / d, which is appropriate for the Holocene streambed sediments. J~ 7423WWGWM-R01.doc Jan. 7,03 Wilmington, DE ASH020292 E ID 630720 Revised Groundwater Flow Model Model Set-up 4.2.4 Pumping Wells A total of 50 industrial and public water supply wells are located within the model domain. These wells, which are shown on Figure 8, are located at the following sites: GE (14 wells) q DuPont Washington Works Plant (13 wells) Blennerhassett Island (12 wells) Lubeck PSD (6 wells) Little Hocking WA (4 wells) City of Belpre(l well) Fortv-four of these wells were actively pumping during the collection o f synoptic groundwater elevation measurements used for model calibration. Therefore, pumping is simulated at these 44 wells in the groundwater flow model. The pumping wells, which are all completed in the lower portion of the alluvial aquifer, are simulated m layer 2 of the model. In most cases, pumping rates (tf/d) used in the model were calculated from total daily flows on February 02,2002 (day o f synoptic groundwater level measurements), ^sliming continuous operation. The exception is pumping rates for Little Hocking WA wells, which were not pumping during the collection of synoptic groundwater levels on February 02. Additional groundwater level measurements were collected on August 1 1, 2002 while the Little Hocking pumping wells were active (See Section 5.1 Calibration Strategy). Therefore, pumping rates for these wells were calculated from hourly system flows on August 21,2002. The majority of the DuPont water supply wells are monitored individually, includmg the East Well Field wells (331 to 337), Blennerhassett Island wells (435 to 446) and toe Rarmey collector well. The pumping rates for these wells were calculated from toe total dally flow of each well. Due to model convergence problems associated with model cells going dry around groups of closely-spaced pumping wells, the individual rates for toe East Well Field wells were totaled and re-apportioned equally among the seven wells. The DuPont Ranney collector well, which includes the central, well and 6 lateral collector wells (horizontal), was simulated in the model as 5 individual wells with the pumping rate apportioned equally between them. The location o f the 5 wells used to simulatejhe Ranney collector was based on the actual orientation and length o f the 5 lateral collectors. Flow rates are not monitored at individual wells in the DuPont-Lubeck Well Field. Thus the total flow rate for the field was calculated from the total daily flow and apportioned equally among toe 5 wells (DL-1 to DL-5). Total system abstraction rates for toe Lubeck PSD and toe City o f Belpre were obtained from Monthly Operation Reports for these supply systems, which were provided by toe West V irginia Department of Environmental Protection or Ohio Environmental Protection Agency (OHEPA). The total system flow rate for each system was calculated from the total daily abstraction and apportioned equally between the pumping wells. T423WWGWM-R01 .doc Jan. T, 03 Wilmington, DE 13 ASB020293 EID630721 Revised Groundwater Flow Model Model Set-up Hourly flow rates for Little Hocking WA were provided by OHEPA. Flow rates for the time of day doting which groundwater levels were measured at Little Hocking were use S Z lo rW . f l S r a t . for th. sy fl was a p p o rtio n PW-1, PW-2, and PW-3, all o fwhich were pumping when the groundwater levels were measured (August 21,2002). Pumping rate data for GE was unavailable. Pumping rates for the GE wells were estimated from the "normal" operational pumping rates for individual wells, which were provided for the majority of the wells by GE. The actual pumping rates usually vary somewhat from the "normal" operation rates. Therefore, to^ P " ^ t e s f o TM n l of the GE wells were adjusted during model calibration to roughly match the observed draw-downs. The pumping rates used in the model are summarized in Table 4 below. Table 4. M o d el Pumping Rates. I 1 ; ,i|' ,! !,, Belpre niwnrun-bassett Island Blcnnerhassett Island Island Island Blennerhassett Island Blenuerhassett Island Blennerhassett Island Blenuerhassett Island Blmnurhassctt Island Blennerhassett Island Blenuerhassett Island DuPont Wad.Works Plant DuPont Wash. Works Plant DuPont Wash. Works Plant DuPont Wash. Works Plant DuPont Wash. Works Plant DuPont Wash.WorksPlant DuPont Wash. Works Plant DuPont Wash. Works Plant DuPont Wad. Works Plant DuPont Wash. Works Plant Well 1 435 436 437 438 439 440 441 442 443 444 445 446 331 332 333 334 335 336 337 DL-J DL-2 DL-3 DL-4 l>unplueBi'ttonPeb02, 1Model Pumping Bate (fipra) 697 465 485 442 297 489 409 323 236 414 TA TA AT 417 0 159 69 203 247 147 84 247 69 69 69 69 697 465 485 442 297 489 409 323 236 414 444 417 0 165 165 165 165 165 165 165 69 69 69 69 ________ _ -- ---- --------------- ------- -.-- ..................... ...............7423WWGVVM-R01.doc Jan. 7,03 Wilmington, DE 14 A SH 020294 E ID 630722 I i I I I I 1 I I ", I 1 1 1 I 1 Revised Groundwater How Model Model Set-up DuPont Wash. Works Plant DL-5 69 69 DuPont Wash. Works Plant DuPont Wash. Works Plant DuPont Wash. Works Plaut DuPont Wash. Works Plant DuPont Wash. Works Plant DuPont Wash. Works Plant Little Hocking WA1 Little Hocking WA1 Little Hocking WA Gallery Well Ranney Well 1 Ranney Well 2 Ranney Well 3 Ranney Well 4 Ranney Well 5 PW-1 PW-2 PW-3 885 287 287 287 177 177 177 177 177_ 287 287 287 Little Hocking WA* Lubeck PSD Lubeck PSD Lubeck PSD Lubeck PSD Lubeck PSD Lubeck PSD GE GE2 PW-5 PW-A PW-B PW-C PW-D PW-E PW-F Well3 Well 4 111 111 111 111 111 111 20 130 111 111 111 111 111 111 200 130 GE2 Well5 GE2 Well 6 ISO 150 GE2 Well 7 NA GE2 WeB 8 150 150 GE2 WeH 9 150 150 GE2 GE2 GE2 GE2 GE2 GE2 GE2 Well 10 Well 11 Well 12 Well 13 Well 14 Well 15 Well 16 NA NA 60 NA 600 500 NA 150 60 100 350 350 0 1 - All pumping rates are toed on measured daily flows from February 02.2002 except for Little Hocking WA wells where August 21,2002 t e S S2 - dataforGEwells wasunavailable. Pumping rates for GEwells were estimated from design capacities and adjusted during model calibration. T423WWGWM-R01.doc Jan. 7, 03 Wilmington, DE 15 SH0Z0295 E ID 630723 Revised Groundwater Flow Model Model Set-up 4.3 Main input Values 4.3.1 Hydraulic Conductivity Distribution o fhydraulic conductivity values used in the model was based on predicted sub-surface distribution of Holocene and Pleistocene aged alluvial sediments and depositional history of those sediments as described in Section 2.2 Site Geology. Model layer 1 was discretized vertically such that all fme-grained Holocene sediments occur within this model layer (See Section 4.1). The vertical discretization of model layer 2 was such that only the coarser grained Pleistocene sediments, which underlie the Holocene sediments and overlie die bedrock, occur within this model layer. The top of model layer 3 coincides with the estimated elevation o f the top of the bedrock surface underlying the alluvium. Hydraulic conductivity zonation used in the model is shown m Figure 9. The lateral distribution of hydraulic conductivity values in each model layer (zonation) reflects the predicted sub-surface distribution o f alluvial sediments based on the terrace surface ages as previously described in Section 22. Areas of layer 1 that underlie Holocene aged floodplains in the central portion ofthe river valley were assigned hydraulic conductivity values appropriate for the silt and clay ovprbank deposits, which occur in the shallow sub-surface beneath the floodplains. Areas m both layer 1 and layer 2 underlying the higher Pliestocene-aged terraces were assigned conductivity values appropriate for the coarse sand and gravel glacial oulwash deposits, which occur m the sub-surface in these areas. The areas of layer 2 beneath the existing Ohio River channel were assigned a lower conductivity than the surrounding Pleistocene sediments to account for the significant degree o f re-working o f the Phestocenepediments and contribution o f additional fines which has occurred in the center o f the nver valley. Hydraulic conductivity values assigned to model layer 3 were appropriate for the shales and sandstones o f the Dunkard Group. A range of appropriate hydraulic conductivity values was determined for each of the geologic units simulated in the flow model from available aquifer testing results an published literature values. Results from numerous aquifer pumping teste from water supply wells completed in the coarse-grained Pleistocene sand and gravels were considered in determining the appropriate range o f values for these sediments. The appropriate range for the other geologic units (Holocene sediments, re-worked Pleistocene sediments, and bedrock) were estimated from published literature values. The conductivity value for each of the geologic units was adjusted during model tU*rano-p n f ftnnfhictivitv values deemed appro for the unit. The range of appropriate hydraulic conductivity values for each geologic unit the source o f toe conductivity data used, and the conductivity values assigned to each geologic unit in the groundwater flow model are presented in Table 5 below. 7423WWGWM.R01.dOO Jan. 7, 03 Wilmington, DE 16 A SH 020296 E ID 630724 ftmdsed Groundwater Flaw Mofla Model Set-up Table 5. Aquifer Hydraulic Conductivity Values. Geologic Unit Holocene Altavial Sediments , IHsWlpttw V?.. - - .V ,, ,.->!; Interbedded and laminated silt, clay, and fine sand "m ttg pf'K ylues {ft7d.) 1 Number t :Result#; MtaV ` GwntetrB-.; Vi?,"-*;" j, . : siiVV ' .Mratf'./. 0.03 1 8 -- Model K Value . (ib/d.) Kx,Ky " 1.0 Kv=0.01 Data Bource{s) 4 Pleistocene Alluvial Sediments Coarse-grained sand and gravel 37 33 871 146 Ks,Ky * 300 1 .1 3 ,6 ,7 , Kv= 150 8,9 Pltestocene Sediments Underlying Blennahassett Coarse-grained sand and gravel 5 124 374 235 Kx,Ky = 200 1,6 Kv100 Re-worked Pleistocene Alluvial Sediments Interbedded sand and gravel with silt 1 8 284 K x^.y-30 Kv-3 4 Duhkard G roup- Interbedded shale and 3 0.02 5.6 0 2 KxJK.y" 0.l 5 sandstone with minor K v= 1 %10"* Bedrock1 limestone and coal beds N otts calculated fiomreported ttansmisrivity md wdt depth. 1, to m Wood County only w= utcO In the * * . H * * * amduciivily Date Soumet; l. Burgess & Nip1c. Ltd., 988 2 DuPont, 1991 3. DuPont CKO, 1999 4. Fetter, 1988 5. Kozar and Mathcc, 2001 6. 7. U nte Booking'Water A ssodi*!, 1996 S. Lubcdt Public Service District, 1998 9. Shell, 1999 __________ 7423WWGWM-R01 .dec Jan. 7,03 Wilmington, PE -- -------------------- ----------- --- -- 1 ...... .............. " ^ 17 A SH 02Q 237 E ID 630725 Revised Groundwater Hew Medal Model Set-up 4.3-2 Recharge Distribution of recharge values used in the model was based on the predicted distribution of surficial soil types and thicknesses as described in Section 2 2 Site Geology. Pleistocene terraces, Holocene floodplains, and bedrock outcrop areas were assigned differing recharge rates to account for varying infiltration rates that would be anticipated in these areas due to differing soil types and thicknesses. An area o f increased recharge was assigned along tire outer edges o f the Pleistocene terraces adjacent to the bedrock outcrop areas to account for increased infiltration o f storm water run-off from the bedrock slopes in these areas. In addition, reduced recharge rates were assigned to large areas of impervious surface cover at tire GE and DuPont plant sites. Recharge zonation used in the model is shown to Figure 10. The recharge rates for the alluvial surfaces were based on estimates made by USGS (M. D. Kozar, oral communication). The rates for bedrock areas were estimated on the basis o f topography and soil types present A low infiltration rate was assigned to the bedrock areas to account for the steep slopes and low permeability o f the surficial soils to these areas. Recharge rates were adjusted during model calibration. The rates used in the groundwater flow model are presented to Table 6 below. Table. Model Recharge Rates. Holocene floodplains Pleistocene terraces . Pleistocene terraces along bedrock outcrop Bedrock and areas of impervious surface cover JbehafgeRate (In, / yr.) v ,' 4 s 20 0.1 7423WWGWM-R01.doc Jan. 7, 03 Wllmlnaton, DE A SH 020298 E ID 630726 Revised Groundwater Flow Model Groundwater Model Calibration 5.0 GROUNDWATER MODEL CALIBRATION 5.1 Calibration Strategy The steady-state groundwater flow model was calibrated against two sets of synoptic groundwater elevation measurements that were collected specifically for use in model calibration. The first set was collected on February 02,2002. During this event, groundwater levels were measured in a total o f 84 observation wells. Levels were measured at the following sites: DuPont Plant (44 wells) Blennethassett Island (8 wells) Little Hocking WA (8 wells) LubeckPSD (6 wells) GE Plant (13 wells) Shell Kraton Plant (5 wells) It was determined that the pumping wells at Little Hocking WA were inactive at the tone o f measuring groundwater levels on February 02,2002. Therefore, a second roun o groundwater level measurements was made at the Little Hocking WA site on August 21, 2002 to obtain groundwater elevations for this site under active pumping conditions. Groundwater levels were also measured in selected wells at the DuPont Plant (15 wells) and foe Shell Kraton Plant (1 well) for comparison between the two monitoring events. The extent o f seasonal variation in groundwater elevation between the two momtonng events was determined by comparing groundwater elevations from the two events from well MW-11 at the Shell Kraton Plant. This well was used fof the evaluation because it was the only well monitored during both events that was unlikely to be influenced by pumping activities DuPont and Little Hocking WA. The groundwater elevation decreased by 0.55 feet at MW-11between the February and August momtonng events. This seasonal variation is likely to be insignificant relative the variation m groundwater elevation that occurs in response to changes in pumping rates within the model domain. Given the small seasonal variation observed in groundwater elevation, the two sets of groundwater elevations were combined and used for model calibration targets (Figure 11). With the exception of those from Little Hocking WA, groundwater elevations from February 02,2002 were used as the calibration targets in the model. The August 21, 2002 groundwater elevations from the Little Hocking WA site were used as model calibration targets in place of those from February to order to calibrate the model against groundwater elevations at this site under the influence of active pumping. Similarly, pumping rates from February 02,2002 were used for all pumping wells other thanthose at Little Hocking WA where the August 21,2002 rates were used instead (see Section 4.2.4 Pumping Wells). ----------- :----- -- ------------- -- ---------------------------- -- ..........""------------- " 7423VWVGWM-RQ1.doc Jan. 7,03 Wilmington, DE 19 A SH 020Z99 E ID 630727 I Revised Groundwater Flow Model Groundwater Model Calibration 5,2 Calibration Results i available, The overall successofmodel calibration was measured I ( S S S S S S s ^ m 1h. editored flow model along w f >P ''* , . w TM , calculatedheadare shown in Figure 12. Theplot ofobserved.versus I S H W good coireiation bemeen ohsmved und compared h i for a regional-scale groundwater flow model. 1 The sueees. o f model ealitotion can ato be dmnonstoed through f the errorsbetween observed and computedheads (targa residual). " P ta observed j,, f t e overall residual error expressedasthe percentage oftire rang I h^T^Jrtohis ralculatedss standarddeviation of tile residuals divided by the obswved S In this toe, the sumdmddeviatiou is 9.9% ofthe t o * * * 1 merit of 10% or lessis g o u em n yeo n m d ^ to rei^ l ug^de^ o u . T below summarizestee results oftee statistical analysis oftee target residuals. I I > 1 1 1 Table 7. Statistical Suminary o f Model Calibration Errors (Residuals). dual Mean (ft.) Residual Standard Deviation (ft.) o f Squared Residuals (ft2) Absolute Residual Mean (ft) ium Residual (ft) Residual (ft) in Observed Head (ft) Standard Deviation / Range ia Observed Head (ft/ft) Result 0.104 3.285 907.491 2.308 -9.249 12.060 33.350 0-099 I I I I 74Z3WWGWM-R01.doc Jan. 7,03 WUmtflBtofl. BE 20 ASH02030Q E ID 630728 Revised Groundwater Flow Model Model Resulte 6.0 MODEL RESULTS 6.1 Mass Balance The total water balance (mass balance) o f the groundwater flow model indicates very little error in the simulation. The total error (total inflow minus total outflow) is less than 0.01 percent. A summary of the mass balance for the groundwater flow model is shown in Table 8 below. Table 8, Mass Balance Summary. Storage Constant Head Wells Drains Recharge River Leakage ' Total Absolute Error (In - Out' Percent Discrepancy 0 0 0 0 4,343,758 17,581,300 21,925,058 Out 0 0 20,818,613 3,947 0 1103300 21,925,860 .802 -0.0037 6,2 Current Pumping Conditions The groundwater flow model is calibrated to observed groundwater elevations underthe existing pumping conditions at sites within the model domain (as of February 02,2002), The computed heads for the calibrated flow model for layers 1,2 and 3 are shown in , Figures 13,14, and IS, respectively. With the exception of local areas surrounding major pumping centers, the computed heads within the Pleistocene alluvium in layers 1 and 2 are approximately the same. Computed heads in the Holocene alluvium in layer 1 are slightly higher (less than 1 foot) than in the underlying Pleistocene alluvium. A slight downward gradient is predicted m most areas o f the alluvial aquifer in response to pumping flora model layer 2. Increased downward gradient is predicted in layer 2 locally around pumping centers. A groundwater divide is predicted beneath the Ohio River in the Pleistocene alluvium (layer 2). A divide is predicted beneath the main channel and on either side of Blemerhassett Island. The divides separate tire areas o f significant draw-down centered 74Z3WWGWM-R01.doc Jan. 7,03 WnminBtDn.DE A SH 020301 E ID 630729 I m 1 i 1 1 I I I I ; ') t I 1 I I I | Revised Groundwater Flow Model Model Results at DuPont and GE, Blennerhassett Island, and Little Hocking to the presence of this divide, no groundwater migration pathway is predicted beneath river in the alluvial aquifer under the current pumping rates. The only exception at the east end of Blennerhassett Island where the river has not incised as deeply into the underlying Pleistocene alluvium (the entire width of the river boundary remains in layer 1) AUhis location, a groundwater divide is absent in layer 2 and the cone of depression from Belpre extends southward across the river. Figure 14a shows the approximate extent of the capture zones associated with the DuPont and Little Hocking Pumping systems. Computed heads in bedrock areas generally decrease from layer 1 to layer 3. An upward gradient from the bedrock to the overlying alluvial aquifer is predicted ^ o u g to u t mcist of the domain, with the highest gradient predicted near pumping centers. The highest predicted upward gradient is about 9 ft. at Blennerhassett Island. A groundwater divide is not predicted in the bedrock aquifer beneath the Ohio River, Groundwater flow from Little Hocking WA to the DuPont and GE plant sites is precbcted in the bedrock aquifer. However, the bedrock aquifer is simulated discretely in the model ordwto provide recharge to the overlying alluvial aquifer. Groundwater elevations m the bedrock aquifer were n0t calibrated and therefore should be considered an approximation!1Simplification of complex stratification o f the bedrock aquifer may h a e resulted in inaccuracies in predicted groundwater elevations m the bedrock a q m te This simplification has little or no effect on predictions of groundwater flow m alluvium. The majority o f the groundwater in the alluvial aquifer at the DuPont plant rite is currently being captured by the on-site pumping activities. Some lunitedoff-site groundwater migration may be occurring in the northwest comer of the DuPon p a n s in response to pumping at GE wells 3 and 4. 6,3 No DuPont Pumping A simulation was run to determine the influence that pumping activities at the DuPont p ,r 5 b r n g m g r o u p e r e t o a t o at e<tes To complete this simulation, pumping wells at the DuPont plant and at Blennerhassett island were tuned-off while leaving all other pumping well rates as_pertte calibrated simulation. The predicted heads in model layer 2 for this scenario are sho in Figure 16. The model predicts an increase in groundwater heads in the central areas of the DuPont and GE plant sites of approximately 15 and 9 ft, respectively. An increase of approximately 2 ft. is predicted at Lubeck PSD. The model predicts no change in groundwater heads at Little Hocking WA Shdl Kraton, or Belpre would occur in response to cessation m pumping by DuPont Conversely, this simulation suggests strongly that current pumping activities at the DuPont plant and Blennerhassett Island are not influencing groundwater heads at these sites. 7423WWGWM-R01 .doc Jan. 7,03 m Wilmington, DE 22 A SH 020302 E ID 630730 Revised Groundwater Flow Model Model Results 6.4 No GE Pumping Similar to the previously described simulation, a simulation was run to investigate the fnfluence that pumping activities at the GE plant are having on * surrounding sites. To complete this simulation, pumping wells at the GE plant were tuned-off while leaving all other pumping well rates as per the calibrated simulation. Th predicted heads in model layer 2 For this scenario are shown m Figure I /. The model predicts an increase in groundwater heads in the central areas of the DuPont I d GE p to t sites o f approximately 10 and 16 ft., respectively. An increase of approximately 3,5 ft. is predicted at Lubeck PSD. Again, the model predicts no change in groundwater heads at Little Hocking WA would occur in response to cessation in pumping by GE. 6.5 No Pumping by DuPont or GE The nrevious 2 simulations were combined to investigate the influence that pumping at Little Hocking WA would have on groundwater elevations at Washington Bottom if both S S S S g E ceased pumping activities. To complete this simulation, p u l i n g wells at the DuPont and GE plant sites were tuned-off while leaving all other pumping wel rates as per the calibrated simulation. The predicted heads m model layer 2 for this scenario are shown in Figure 18. The model predicts an increase in groundwater heads in the central areas of the DuPont GEplant sites of approximately 22 and 24 amount of draw-down. An increase of approximately 4 ft. is predicted at Lubeck PSD. Again the model predicts no change in groundwater heads at Little Hocking WA would occur in response to cessation in pumping by DuPont and GE. However,Wlth pumping to the south side of the Ohio River, the model predicts that the ^undw ater S e below the river would be overcome by pumping at Little Hocking WA and the capture zone for that site would extend across the river to the south. 6,6 No Little Hocking WA Pumping A final simulation was run to determine the influence that pumping activities at fte LM<* Hocking WA are having on groundwater elevations at surrounding sites. To complete this simulation, pumping wells at Little Hocking were tuned-offwhile leaving all otiier " E per the calibrated simulation. The predicted heads m model layer 2 for this scenario are shown in Figure 19. The model predicts an increase in groundwater heads in the central area of the Little Hocking well field of approximately 7-ft, An increase in groundwater elevation of about No change in groundwater elevanon is predictecfat Belpre, Blennerhassett Island, the DuPont mid GE plant sites, or at Lubeck p e n in rfisnonse to cessation o fpumping at Little Hocking. .........................................-- -------------------------- -------------------------------- -- --------- ---------" 7423WWGWM-R01.doc Jan. 7.03 Wilmington, DE 23 A SH 020303 E ID 63073! Revised Groundwater Flow Model Model Results Similar to the previous simulation, the model predicts that with no pumping on the north side of the Ohio River, the groundwater divide below the river would be overcome and the DuPont plant capture zone would extend across the river to the north. 74Z3WWGWM-R01.doc Jan. 7,03 Wilmington. DE A SH 020304 E ID 630732 Revised Groundwater Flow Modal Sensitivity Analysis T.O SENSITIVITY ANALYSIS A sensitivity analysis was completed to determine the sensitivity of the model to uncertainties in the primary input parameters including hydrauhc eonductivi^ r^h ^ g e, and river boundary conductance. This analysis involved perturbing them put value for a single input parameter by fixed increments and re-nmnmg the model. The overall calibration error from each of the sensitivity runs were then evaluated and compared to determine the relative sensitivity o f the model to errors in each of the mam input parameters. For each input parameter, multiplication factors o f0.25,0.75,1.0,1.25, and 1.5 were used in the sensitivity analysis, The input values perturbed during the sensitivity analysis and the relative sensitivity of the model to each value are summarized in Table 9 below. Graphs o f the absolute residual mean and mean change in computed head for each input parameter tested during the sensitivity analysis are shown in Figure 20. The sensitivity analysis indicates that the model is most sensitive to uncertainties in the hydraulic conductivity value assigned to the re-worked Pleistocene alluvium beneath the Ohio River. The reduced conductivity o f this unit serves to restrict the flow ot groundwater beneath the river and thus strongly influences the response to pumping predicted by the model. Table 9. Sensitivity Analysis Results. , ... -*\.. .' ' ;>wr.'UWCh'rSfiSvI,'v,i;:.1> Hydraulic Conductivity Holocene alluvium Pliestoccne alluvium PHestocene alluvium --Blennerhassett Island , Relative Model Sensitivity (raiiked from Ijhlghestjto ^-S iopow estl) 7 2 6 Re-worked Pliestocene alluvium 1 Recharge Holocene floodplains Pleistocene terraces pleistocene terraces along bedrock outcrop 10 4 5 River Boundary Conductance Holocene alluvium Re-worked Pleistocene alluvium 8 3 Re-worked Pleistocene alluvium at west id of Blennerhassett Island 9 ----- ------------------- -- ---- ------------ --------- ------- -------------- " 7423W W G W M -R01Jan.7,03 Wilmington. D 25 A SH 020305 E ID 630733 Revised Groundwater Flow Model Model Conclusions 8.0 MODEL CONCLUSIONS The primary conclusions of the revised Washington Works Groundwater Flow Model are summarized as follows: The Ohio River is creating a groundwater divide within the Pleistocene sediments beneath the river. Due to the presence o f this divide, no groundwater migration pathway is predicted beneath river in the alluvial aquifer under the current pumping rates at the various pumping centers simulated in the model. A groundwater divide is not predicted in the bedrock aquifer beneath the Ohio River. Groundwater flow from Little Hocking WA to the DuPont and GE plant sites is predicted in the bedrock aquifer. However, groundwater elevations m the bedrock aquifer were not calibrated and should be considered an approximation. The majority of the groundwater in the alluvial aquifer at the DuPont plant site is currently being captured by the on-site pumping activities. Some limned oil-site groundwater migration may be occurring in the northwest comer of the DuPont plant site in response to pumping at GE wells 3 and 4. ------------ -------------- -------------------------------- ---------------- -- --------------- -------------------------- .......................... .......... 7423WWGWM-R01.doc Jan, 7, 03 Wilmington, DE 26 ASHO2O30 6 E ID 630734 Revised Groundwater Flew Model References 9.0 REFERENCES Michael Baker Jr., Inc. 2002. Geotechnical Boring Logs, Planned Rt. 50 Corridor D over Ohio River and Blennerhassett Island, unpublished. Burgess & Niple, Ltd. 1988. Blennerhassett Island Water Supply Well Drilling and Test Pumping, unpublished report. Burgess & Niple. 2001. Geotechnical Boring Logs, Planned 892 Corridor, unpublished. DuPont, 1991. Washington Works Preliminary Hydrogeologie Assessment, unpublished report. DuPont Corporate Remediation Group, 1999. RCRA Facility Investigation Report, DuPont Washington Works, Washington, West Virginia, unpublished report Fetter, C.W -1988. Applied Hydrogeology, Second Edition. Macmillan Publishing ' Company, New York, New York, 592 p. Leggette, Brashears & Graham, hie. 1986. Hydrogeologie Evaluationfo r Additional Water Supplyfrom Blennerhassett Island, unpublished report. Kozar, M.D. andM.V, Mathes, 2001. Aquifer-Characteristics Data fo r West Virginia. Water-Resources Investigations Report 01-4036, United States Geological Survey. 74 O. Little Hocking Water Association. 1996. Well Head Protection Plan, unpublished report. Lubeck Public Service District 1998. Well Head Protection Area Survey, unpublished report Shell Chemical Company, 1999, RCRA Facility Investigation Report, Shell Kraton Plant, Belpre, Ohio, unpublished report Simard, C.M. 1989. Geologic History o fthe Lower Terraces and Floodplains o f the Upper Ohio River Valley, Open File Report 8903, West Virginia Geological Survey. 160 p. U.S. Army Corps of Engineers. 2002. Ohio River Bathymetric Data, survey date: July 2002, unpublished. 7423WWGWM-R01.doc Jan. 7,03 Wilmington, DE A SH 020307 E ID 630735  SH020308 E ID 630736 I i i I I I I I FIGURES I I > I I I I I I I A SH 020309 EID 63Q 737 ASH020310 U r en ASH020311 m l_ ...... <m0oeanwMi C o rp o rale RwnetflaUon G roup ** MHW* *<* At/WmuL OTW*mul 9Drt*yun ptefl. BuMtng Z7 0*>atn 1M0S IDEAUZEO OHIO KVER VAUEY CROSS-SECTON AND BLOCK OUttUU DuPoni Washington Wer* Washington. W#*t Virgnia - -- r --. rsr* r EXD63074 not too uHi to Worth A PLEISTOCENE TERRACE r -----------------*----------------------- \ -HOLOCENE FLOODPLAIN *- bxyaMk(tot aMg BEDROCK(DUNKARD GROUP) LEGEND: HOLOCENE OVBRBAW DEPOSITSSILT AND CLAY PLEISTOCENE GLACIAL OUTWASH DEPOSITS - COURSE SANDANDGRAVEL REWORKED PLBSTOCENE ALLUVIUMSAND AND GRAVEL 'Vsw*' South Ar tin) /vv--yjr FLOODPLAIN PLEISTOCENE TERRACE r"S <------------------------- *--------------------------\ DUPONT WASHINGTON WORKS tUVAflW (Ht ) HORiZOHTAi. SCALE 90 0 90' --- -- Trraniui|'niiiriiM ^ C orporate f&necfattoA Group *n ta m a Jto M m h m t UA D uaneiU Soriejr WDPfaw. Butting 73 'Kfairifiqtftn, Bakign T)3Q3 GENERALIZED GE0UXRC CROSSSECTION AT RIVER MILE 190 DuPon? Washington Works. Washington, Was! Vvrgfm'o kU j |w ASH020314 E ID 630742 EID 630743 & HO' S o uH UT EID 630744 1 I I I 9 i I I 9 I 8 8 I 8 8 I K oNaO kh*) m h h H 8BB LEGEND: River Cell ove r fine Alluvium (K 0 .1 f t / d ) River Cell over re-w orked coarse alluvium (K =0.3 f t./d ) (30 i t / d w est end of Blenn. island) Drain Cell (K1 f t./d ) No Row Cell ASH020317 Site Total {poml D uPont fe x c , GaHery) 6804 GE f e s tim a te d ) 1750 tittle Hockina fA u a u st 21, 2UU2) 860 Lubeck HVQU)\ BeiDre 664 697 EECZJ E ID 630746 LEGEND: Coorse Alluvium {300 f t / d ) Re--worked AUuvium (30 ft./d ) Blennertiossetl IsFaftd (200 tt./d ) g o NO UHffl EID 630747 S o to oUK *0 P & a o NO UN O EID 630748 EXD63Q749 S BO to o WINJ E ID 630750 ASH02O324 W ASH020325 A SH 020326 E ID 630754 ASH020327 EID 630755 A SH 020328 B ID 630756 ASH020330 I I I n i n ii i i i n ! w JHt ccri w KEY: Kx1 Pleistocene Alluvium Kx2=* Kx+ Kx5 - Holocene Alluvium Re-worked Pleistocene Alluvium Blennerhosselt Island Pleistocene Alluvium Recharge! = Pleistocene Terrace Surfaces RechorgeS Recharge^ - Holocene Floodplain Surfaces Pleistocene Terroce Surfaces Wong Bedrock Outcrop River Condl Riverbed over Holocene Alhjvfjm River Cond2 * Riverbed over Pleistocene Alluvium River Cond3 Riverbed over Pleistocene Alluvium at West End of Blennerhassett Ieland -- 0M- ~ <8HB> SENSfWTTY ANALYSIS RESULTS C o r p o r a te Rentediittoa Group DuPont Washington Wert Washington. Weet Virginia awny MSI PUaa, feRtfftf 27 TUmingtoft. Ustoonc19605 rTM *. rcr~ Rsrtov Mill Plaza. Building 27 Uncaster Pike &R outgU I Wilmington. PE 19805 ASH020331 EID 630759