ML20058P284
| ML20058P284 | |
| Person / Time | |
|---|---|
| Site: | Framatome ANP Richland |
| Issue date: | 09/09/1993 |
| From: | Adams M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Tokar M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| Shared Package | |
| ML20058P268 | List: |
| References | |
| NUDOCS 9310220196 | |
| Download: ML20058P284 (19) | |
Text
{{#Wiki_filter:70-RN pa nog'e e a3 .yd 1-E UNITED STATES 4i NUCLEAR REGULATORY COMMISSION k..... j# WASHINGTON, D.C. 20555-0001 September 9, 1993 NOTE FOR: Michael Tokar, FCLB FROM: Mary Adams, FCLB
SUBJECT:
GROUND WATER DOCUMENTS FROM SIEMENS POWER CORP TO SUPPORT AMENDMENT 18 TO SNM-1227 The following document was submitted directly to me as a result of a July 14, 1993, telephone call between me and Jim Edgar, the Staff Engineer, Licensing, at Siemens Power: 1 Chapter 6.0 Hydroneoloav and Ground-Water Characteristics, from an undated and untitled report by Geraghty & Miller, Inc. (This document is noted " privileged and confidential" by the authors; however, Mr. Edgar stated on September 2, 1993, that the report can be placed in the PDR.) t The following additional documents -were obtained from the Regional Inspector from NRC Region V and used in the review of the amendment application: Work Plan. Phase II Ground-Water Study. Siemens Pcwer Corporation, by Geraghty & Miller, Inc., dated February 24, 1992. Draft Ground-Water Quality Assessment Plan. Siemens Power Corporation, by Geraghty & Miller, Inc., dated March 25, 1993. These three documents are part of an ongoing independent ground-water 1 investigation that Siemens is performing to comply with.the State of Washington Model Toxics Control Act. I have sent them to the PDR. f(( hl WLO Mary Adams, FCLB / 9310220196 930927 Ph i h' PDR ADOCK 07001257 bd C PDR-C
f.. / ' 2 1 }- nmizaso Ano connoamAL i 6.0 HYDROGEOLOGY AND GROUND-WATER CHARACTERISTICS
6.1 INTRODUCTION
AND PURPOSE As part of the SPC RI/FS, Geraghty & Miller conducted a field study of the site ground-water quality and hydrogeology to determine the distribution and concentrations j of hazardous substances in the ground water at the site, and to characterize the hydmgeologic features which affect the fate and transport of hazardous substances. This i field study was implemented through the Phase I and Phaie II Ground-Water Studies (Geraghty & Miller [ September) 1991, [ February] 1992), which were initiated in October 1991 and April 1992, respectively., ,7, ^ / The objectives of the Phase 14uid Phase'II Ground-Water Studies were to: 1 s N, - -- i Determine,Jhe, sit'e stratigraphy and compare the results with the documented [egiondl stratigraphy. g/. .s 'j .m 3., n [ Characterize the shallow unconfined ground-water flow system including Nhkdepth ho water, flow direction, hydraulic gradients, hydraulic \\ x-condu'etivity and transmissivity, and seasonal' water level fluctuations, v Determine the distribution and concentrations of contaminants in the shallow aquifer. ~ To accomplish these objectives,16 ground-water monitoring wells (GM-1 through ~ GM-16), three piezometers (P-1, P-2, and P-3) and one pumping well (PW-1) were l drilled and installed at the site (Plate 6-1). Water level measurements were collected J from the monitoring wells and piezometers on a monthly basis and water quality samples were collected and analyzed on a quarterly basis. A pumping test was conducted by ~ pumping Well PW-1 and observing water levels in surrounding monitoring wells. d GERAGHTY & MILLER,1NC. .-,=+4=w
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s -=====-' 6-2 PRIVILEGED AND CONFIDENTIAL ~ This chapter summarizes the field activities and results of these tasks. Section 6.2 describes the geology; Section 6.3, the hydrogeology; Section 6.4, ground-water flow and gradients; Section 6.5, aquifer characteristics; Section 6.6 presents a summary and i conclusions. The field methodologies for each task are described in Appendix 6-A. Well logs for borings drilled at the site are presented in Appendix 6-B. The results of the grain-size analysis for selected soil samples collected during drilling are included in Appendix 6-C. .= 61 GEOLOGY The geology for the site was determined based upon visual observations made l, during drilling, grain-size analyses, developnient.of well logs, and an interpretation of stratigraphy. Plate 6-2 shows the location of geologic cross-sections and Plate 6-3 shows geologic cross sections of the site and inflicate the lithology of each well, the stratigraphy of the site, and its relationship, to the geology ~of the adjacent HRL area. l The SPC. site-is underlain by poorly-and well-graded sands and gravels of the The two Pasco grave [in'tiie' Ha'nford formation and also the Ringold Formation. \\ stratigraphic units are differentiated during drilling by the basalt content and color of the N sand and gravei% actions of the borehole cuttings and soil samples (Pasco gravels tend to be basalt-rich a./nd dark gray in color while the upper portions of the Ringold \\. Formation tend to be basalt-poor and light yellow-brown to tan color). The elevation of the contact between the Pasco gravels and the Ringold Formation varies in the SPC boreholes from approximately 368 feet msl to approximately 342 feet msl (P-1 and GM-14, respectively; Cross Section A-A', Plate 6-3). However, due to the limited ~ amount of gravels recovered by split-spoon sampling, lithologic changes between the Pasco gravels and Ringold Formaiion depicted in Plate 6-3 are approximate and were ~~ F ~ based primarily on changes in sar'd composition and color of the borehole cuttings. The total thickness of the two formaticns ranged from approximately 30 to 45 feet. I~ ~ l' GERAGHTY ef MILLER,INC.
PlW7LEGED AND CONFIDEhTIAL 6-3 Suspected fiU materials were encountered during the drilling of GM-3, GM-4, GM-14, and GM-15 (alllocated within the fenced area of the site) and GM-11 (located in the South Pit area). The suspected flu materials encountered in wells within the fenced area were composed of sands and gravels similar to the surrounding native soils. In GM-3, the suspected fill material was found from the near land surface to depths of ~ approximately 20 to 24 feet bis; extending below the water table. If the material encounterec' GM-3 was fill, it may have been placed during the installation of the ~} nearby subs. ce retention tanks in 1970 (Francis 1992a). ~ The suspected fill material in GM-4, GM-14, and GM-15 extended from near land surface to depths of approximately 14 feet bls, extending to or just below the water table. The fill material encountered in GM-11 consisted of a dark-grey, light-weight granular i ~ material. This material occurred from near N surface to approrimately 15 feet bis and was not in contact with ground water..Si: iar material was not encountered in the nearby borings for GM-10 and,GM-12, inc;cating limited distribution in the east-west direction. ,.~ / -.. A sil[ layer (hereafter re_ferred to as the silt aquitard) was encountered beneath the SPC site 'ai elevations between approximately 332 (GM-16) and 340 (GM-14) feet v msl (Table 6-1 min,d Figure 6-1). The aquitard lies within the upper portions of the Ringold Formation and separates the unconfined aquifer from the underlying confined aquifer. The top of a silt aquitard was reported at similar elevations in the boreholes for USDOE Wells MW-2 (located approximately 2,000 feet southeast of the SPC site; Cross Section C-C'), MW-9 (located in the southwest part of the HRL; see Cross 4 Sections C-C' and D-D') and in MW-19 (located approximately 2,200 feet northeast of the SPC site; see Cross Section D-D') (Plate 6-3). The aquitard was completely penetrated by the boreholes for SPC Piezameter P-3 and USDOE Well 9. The thickness of the aquitard is similar in both of these boreholes; approximately 30 to 35 feet. The aquitard appears to be predominantly silt; however ' l i GERAGHTY & MILLER,1NC. W_
J '? PRH7LEGED AND CONFIDENTIA'. 6-4 d some interbedded sandy layers were encountered in the aquitard penetrated by borehole ] for P-3. The silt aquitard was not reported in the boreholes for USDOE wells located immediately northeast of the Horn Rapids Landfill (hnV-11, hnV-12, hnV-13, hnV-14, MW-15, hnV-21, and MW-22). However, the top of a volcanic ash layer was reported I in these boreholes (except hnV-11 and MW-13) at elevations of between approximately ~ 324 and 327 feet msl (Table 6-1). Because these elevations are lower than the top of the silt aquitard, the stratigraphic relationship of the volcanic ash layer with the silt aquitard cannot be clearly defined on the basis of information from borehole logs. The borehole for MW-21 completely penetrated the ash layer (approximately 26 feet thick) and is included in Cross Section A-A' (Piate 6-3). e. 1 j The SPC site appears to be located 2bove a finger, or ridge, on the top of the silt aquitard (Figure 6-1). The 'th of the aquitardslopes gently to the northeast. The 'l /- i, aquitard appears to have been cr6ded prior to deposition of the overlying unconfined J s /,. aquifer forming anirregu'lar contact.. [f ) i ihe silt aquitard lie the sands and gravels of the underlying confined Bene NN/ aquifer. Because e aquitard lies within the Ringold Forniation, the sands and gravels s above and below the aquitard are of similar composition. 3 6.3 HYDROGEOLOGY e A conceptual hydrogeologic model was developed for the site based upon geologic f-interpretations (Section 6.2), a review of the work done at the HRL (USDOE 1992), the ground-water potentiometric distribution determined from water-level measurements, ~ and ground-water quality interpretations. The site hydrogeologic model consists of four bydrostratigraphic units: a shallow vadose zone, an unconfined (water table) aquifer, a ~ G GERAGHTY & hilLLER. INC. ~ are,
q )~ PRWILEGED AND CONMDENHAL 6-5 silt aquitard, and an underlying confined aquifer. These units are described below; their relationship to the geology are displayed in Figure 6 2. The vadose zone, which is defined as the unsaturated area between the land ~ I surface and the upper surface of the unconfined aquifer (water table), consists primarily of poorly to well-graded sands and gravels, and materials suspected to be fill. The thickness of the vadose zone varies with the topography of the site and ranges from approximately 10 to 15 feet thic,. in the vic9y of : active facility (fenced area of the SPC property) to approximately 50 feet tnick southwest of the active facility near Piezometer P-1 (Plate 6-3). The vadose zone thickness in the vicinity of the South Pit area was approximately 30 to 35 feet. Most of.th'e vadose zone occurs within the Pasco gravels of the Hanford formation. The unconfined aquifer beneath the site occurs in both the Pasco Gravels and the l ~ Ringold Formation at depthIranging from approximately 10 to 50 feet bis and at I / elevations ranging from 354.5 15 355.5 feet msl. The water table is generally v.- encountered at approximately 15 feet bis beneath the fenced portion of the SPC facility, approxim:nely 20 to 25 ft bis near the South Pit, and approximately 50 feet bls southwest N of the site near P-1_. The unconfined aquifer is approximately 20 feet thick with its lower boundary being'1 ontIct with the silt aquitard. The silt aquitard occurs beneath the SPC site at depths ranging from ] approximately 30 to 50 feet bis (332 to 340 feet ms!). It is approximately 30 to 35 feet thick and separates the unconfined aquifer from the underlying confined aquifer. As l 1 described in Section 6.2, the silt aquitard was not encountered in USDOE Well MW-21, i f northeast of the HRI., but rather a volcanic ash layer was encountered. The silt and j volcanic ash may form a continuous aquitard in the vicinity of the SPC site. This supposition is supported by an evaluation of the hydraulic data (Section 6.4.1) and the general water quality characteristics above and below the aquitard (Section 6.4.2). These evaluations indicate laterally extensive separation of unconfined and confined GERAGHTY & MILLER,INC. c
l l PRMLEGED AND CONRDENHAL 6-6 aquifers based on the difference in hydraulic head and the difference in water quality between the unconfined and confined aquifers. This information, in conjunction with the presence of the aquitard in the majority of the boreholes, tends to indicate a continuous aquitard. The confined aquifer occurs in sands and gravels of the Ringold Formation. The aquifer was encountered beneath the SPC site and the HRL at similar elevations of approximately 305 feet mst (the base of the overlying aquitard). The confined aquifer sediments encountered in the boring for P-3 were similar to the confined aquifer r sediments encountered in USDOE Wells MW-9 and MW-21, and consisted of interbedded sands and gravels. The confined aquifer appears to be laterally continuous but may be merged with the overlying uncorifined aquifer near the Yakima and ~ Columbia Rivers. s s 6.4 GROUND-WATER TLOW AND GRADIENTS Ground-water flow patterns 2nd gradients were evaluated on the basis of / hydraulic ahd dater qualith4ata. Water level data were examined to determine a \\\\ potentiometn h'ead rhlationships within the unconfined aquifer and between the v-unconfined aqui er and the underlying confined aquifer. Water quality data were v evaluated for trends within the unconfined aquifer and for differences in water chemistry between the unconfined and confined aquifers. 6.4.1 Evaluation of Hydraulic Da. Lit Monthly ground-water elevation maps for the unconfined aquifer (Figures 6-3 ] through 6-13) show that in general ground-water flows from southwest to north-northeast at the site, and then flows more easterly under the HRL The observed ground-water gradients for the unconfined aquifer range from approximately 0.0003 in the area of the SPC site to 0.005 north of Horn Rapids Road near the HRL J s GERAGHTY & MILLER,INCC a
l q _i PRIVILEGED AND CONFIDENTIAL 6-7 ~ \\ l_ Hydrographs (plots of water level versus time) of monthly water table elevations j collected from December 1990 through December 1992 were prepared for each of the SPC Monitoring Wells GM-1 through GM-16, Test Wells TW-1 through TW-26, 1 Piezometers P-1, P-2, and P-3, Pumping Well PW-1, and USDOE Monitoring Wells J MW-2, MW-8 through MW-15, MW-19, MW-20, and MW-21 (Appendix 6-D). All of 1 the SPC and USDOE wells are screened in the unconfined aquifer except P-3, MW-9, f a and MW-21 which are screened in the confined aquifer beneath the silt aquitard. Hydrographs for Well GM-1, USDOE Well MW-12 and Piezometer P-3 are presented in Figures 6-14,6-15, and 6-16, respectively, as representative of the unconfined aquifer f7J (GM-1 and MW-15) and confined aquifer (P-3). _ / 9 The hydrographs from all of the SPC wells and piezometers in the unconfined a I aquifer have similar trends in water tEble. elevations (sporadic ano:nalous water levels occur in som. 'the hydrographs which are prbbably ield measurement errors). Figure 6-14 depicts a representative )ydrograph (GM-1) for the unconfined aquifer wells. The ,q highest observed water'leviks in the unconfined aquifer wells occurred in late summer d and early fall; the1cwest obsesed. water levels occurred in the spring. The observed ] water table,devatio'nsra'nsed fram 33-{,ito 355.5 feet msl. Seasonal fluctuations in the ~ x observed wher' table blevations were approximately 1 foot, except Piezometer P-1 N \\ / (located southwest '61,thi site adjacent to an irrigated agric'ultural area) in which water ~ v ] levels have increased almost 2 feet since April 1992, when it was installed. This is the only well that has not shown the decrease in water levels that other wells show in the ~ } late fall. The hydrographs for the USDOE wells in the t..anfined aquifer (see Figure 6-15 for a representative hydrograph) have similar trends in water levels as the SPC wells in ] the unconfined aquifer with exception of MW-20 and MW-22, which have several erratic high and low water levels (water level data were provided by the USACE, who have indicated that these measurements may be in error, [ REFERENCE FROM PERSONAL COMM]). Trends in observed seasonal fluctuations in the water levels for the USDOE GERAGHTY 6 MILLER,INC.
4 PRIVILEGED AND CONFIDENTIAL 68 ~ d wells in the unconfined aquifer are similar to the observed trends for the SPC wells in the unconfined aquifer except that the ranges in fluctuations were greater, generally up j to 1.5 feet, rather than 1.0 foot. J J To evaluate longer-term water-level trends, the hydrographs for USDOE ] unconfined aquifer Wells MW-8, MW-10, MW-12, MW-15, and deep Well MW-9 were prepared using water-level data collected from January / February 1990 through -n December 1992 (Appendix 6-D). (See Figure 6-15 for a representative hydrograph.) ~ Tne hydrographs indicate that the shcrt-term seasonal trends in water levels observed ] in the more limited time frame for the SPC wells are consistent over time with water level fluctuations in the USDOE wells. The highest observed water table elevations for 3 these wells occurred in the fall; the lowest in late spring /early summer. In addition to the seasonal water table fluctuations, Wells MW-8 and MW-9 (USDOE HRL upgradient ] wells) show a long-term trend of overallincreasing water levels. The hydrographs for the deep wells screened in the confined aquifer (P-3, MW-9, and MW-21) (see figure 6-16 for a representative hydrograph) have somewhat similar trends in wdterie'vels as the shallow wells. Seasonal water-level fluctuations in the ( deeper wells'are si,milar in magnitude and frequency to the surrounding shallow wells, suggesting that the unconfined and confined aquifers are responding to the same factor, \\ and are responding m/ a similar manner. Tne most likely explanation for the seasonality of the hydrographs is that recharge from upgradient fields irrigated with surface water 1 is occurring, causing peak levels to occur in the late summer and early fall. 1 The observed potentiometric surface for the confined aquifer ranged in elevation ~ from approximately 361 to 362 feet msl in P-3 and from 360 to 360.5 feet msl in MW-9 at the HRL The range in elevation in the wells in the unconfined aquifer that are (} adjacent to the wells in the confined aquifer is approximately 354.5 to 355.5 feet mst (GM-2, adjacent to P-3) and 353 to 354.5 feet msl (MW-8, adjacent to MW-9). These data indicate the hydraulic head for the confined aquifer is approximately 6, feet greater GERAGHTY & MILLER,INC. }
1s PRIVILEGED AND CONFIDENTIAL 6-9 ~ than the hydraulic head for the unconfined at P-3 and MW-9. However, the observed hydraulic head for the confined aquifer at MW-21, which is the furthest downgradient ' confined" aquifer well from SPC, ranged from approximately 348.4 to 349.5 feet msl, as ] compared to the head in the unconfined aquifer Well MW-12, which ranged from approximately 348 to 349 feet msl during the same time period. Theoretically, MW-21 } should tap the confined aquifer because it is screened at an elevation below where the silt aquitard is present at the other confined aquifer wells. However, the silt aquitard d was not encountered at this borehole at the elevations encountered elsewhere. Instead, an ash layer was encountered. Thus, water-level elevations may be similar between the 9 j two wells because the silt aquitard is not present or.js present at a lower elevation. Another potential explanation is a poor well seal, but that can't explain all of the difference (USDOE 1993). In general, the hydraulic head separation of 6 feet between the unconfined and confined aquifers 7obse7ed at well pairs GM-2/P-3 and MW-8/ ] MW-9, indicates an effective hydraulic separation of the unconfined and confined units by the silt aquitard. s 1 6.4.2 EvaluationTT Water Ou'ality Data ] ([ N 2 Wateh-qua'lity d,ata were examined to identify spatial trends in water chemistry in s x-the unconfined aquifer and to compare the water chemistry in the unconfined aquifer with that of the confined aquifer. Two graphical methods were used to make these comparisons, piper diagrams and stiff diagrams. Both methods use water quality data y, for major ion concentrations measured in the ground-water samples. h Stiff I _ grams i A Stiff diagram is a graphical plot showing the relative abundance of major j cations and anions in a particular water sample (Plate 6-4). The concentrations of each j 1 ion are expressed as milliequivalents per liter (meq/L) The shape of the resulting I osaxosrv e uittsa.isc. j
1 PRWILEGED AND CONFIDENTIAL 6-10 polygonal plot is characteristic of the water type. The size of the polygon is indicative ] of the total concentration of ions present (i.e., total dissolved solids). ] Stiff diagrams were constructed for each GM-well using the May 1992 ground-water quality data, for USDOE Well MW-12, and the Columbia and Yakima j Rivers to allow comparison of the water types at each well (Plate 6-4). In general, the Stiff diagrams for all wells indicate a calcium carbanate water type. The diagrams for several wells have the same polygon shape and therefore similar water qualities. Well GM-2 has similar water quality to Wells GM-4, GM-6, GM-7, GM-8, GM-10, GM-11, j GM-12, GM-13, and GM-16. Well GM-3 has water qu'ality similar to Well GM-14. Well GM-5 has proportionately more magnesium and a somewhat higher sulfate to o j chloride ratio than other wells and Well GM-9 is higher in the sum of sodium and potassium ions. The diagrams for Welis GM-1 and GM-15 and Piezometer P-2 indicate ] calcium carbonate water types but lower total ion concentrations than the other GM-wells. y j s, s .7 Piezometef73 is screched in 4he confined aquifer and its diagram indicates a m /n N s calcium carbonate water type;gowever, the calcium ion is less dominant as a cation than a in the other\\ wells'.y /The/ diagram for Piezometer P-3 is very similar the diagram forheh';dd'ma River. Although not conclusive, this relationship tends to \\ v indicate that the Yakima River may be a significant source of recharge to the confined ] aquifer. 1 A Stiff diagram was also constructed for a sample collected from the Columbia ~ ] River (Plate 6-4). This diagram indicates that the Columbia River water is dilute (low ~ total dissolved solids), but that its water type is also calcium carbonate. It is not 7 expected that the Columbia River would have the same water type as either the Yakima ~ River or the aquifers because the Columbia River was sampled upstream of the ] confluence of the two rivers and the aquifers do not contribute significant recharge (based on volume) to the Columbia River. GERAGHTY & MILLER,INC. J -ew-e -ca.- --w.w--eme-es.+ .emw-
a PRWILEGED AND CONFIDEh71AL 6-11 ~ The diagram for USDOE Well MW-12 has the polygonal shape characteristic of the calcium carbonate water type, but the polygon is larger than the polygons for the ~ SPC site indicating a higher concentration of dissolved solids. 1:. To compare water types in the unconfined and confined aquifers, Stiff diagrams I were plotted for USDOE Wells MW-8, MW-12, MW-14, which are screened in the unconfined aquifer (Figure 6-17). (The Stiff diagrams in this 5gure are at a different scale and include additional axes, and thus are not directly comparable to those on ~ Plate 6-4.) As can be seen, the polygonal shapes for the wells in the unconfined aquifer are distinctly different from the shapes for the wells in the confine.d aquifer, indicating an effective separation between the two aquifersby the silt aquitard. The diagrams for [ the unconfined aquifer have higher dissolved solids that the diagrams for the confined { aquifer and indicate a greater relative sbundance of tne sum of fluoride and nitrate ions. J Wells in the confined aquifer also exhibit a higher sodium to calcium abundance ratio. a j Piner Diagrams ( {/ ~ x s s v f' / _f ia'gr(\\the Piper diagram is a plot of the cation and anion s s 4tif Like _s composition a% vater; sam l Unlike the Stiff diagram, many water samples may be plotted on the sarcy / p e. N am to allow direct comparison of the water types (Figure 6-18). 2 The Piper diagram is constructed as follows. A point is plotted in each of two ) equilateral triangles at the base of the diagram to indicate the relative abundance of J cations and anions in each sample (in percent meq/L). Points within these two triangles are projected onto a parallelogram to identify a new point within the parallelogram -j, which identifies the water quality of a sample. The location of the point within the parallelogram is characteristic of the water type. The size of the circle around the point 1 is indicative of the total dissolved solids concentration. J Because the water quality at many of the wells is similar, the Piper diagram in Figure 6-18 was plotted using only selected wells. Wells were selected which had 1 GERAGHTY & MILLER. INC. u
l, ] PRMLEGED AND CONFIDENDAL 6-12 different water types so that the points wouldn't be coincident when plotted. Based on q _I the Piper diagrams, the wells in the unconfined aquifer have similar water quality (calcium carbonate type), with GM-3 having a higher concentration of carbonate relative I. to the other anions. Other observations regarding relative abundance ofions and total ion concentrations are in line with those noted above in the Stiff diagram discussion. .) 6.4.3 Ground-Water Modeline l a 1 \\ A computer ground-water flow model was developed to simulate regional ground-water flow patterns for the vicinity of the SPC facility. The code selected for modeling the ground-water flow was MODFLOW (Mcdonald and Harbaugh 1988). The model at _l was calibrated using observed conditions and verified using a subset of the data not used ') in calibration. Ground-water flow patterns predicted by the model are consistent with those discussed above. The model will be used during the FS process to evaluate the hydraulic impact of various potential remediation scenarios. Appendix 6-E provides a ~ complete documentation of'the modeling activities. / r. r ~ 6.5 AQU RTH bTERISTICF ~l x,xN/: 6.5.1 Introductlan / V l-Hydraulic characteristics of the unconfined aquifer were deterrnined by ~1 conducting a constant-rate pumping test at SPC Pumping Well PW-1 between April 23 3 and May 1,1992. The aquifer characteristics determined were transmissivity and storage coefficient. These parameter determinations formed the basis for estimating ground-water flow rates and provided input for a computer ground-water flow model which was } used to optimize pumping schemes for potential remedial scenarios evaluated during the FS (Volume II of this report). Documentation of field activities and a detailed description of the methodologies associated with the aquifer-testing program are 7 s ~ GERAGHTY & MILLER,INC.
\\ q PRWILEGED AND CONFIDENTL4L 6-13 provided in Appendix 6-F. A summary of the aquifer testing procedures and results of the data analysis are provided below. _l l f _, 6.5.2 Aouirer Testine Prior to conducting the constant-rate pumping test, a step-drawdown test was performed to determine the optimal pumping rate for the constant-rate pumping test. Because it is necessary to stress the aquifer sufficiently during the constant-rate test to cause a measurable response in surrounding observation wells, the optimal pumping rate is generally the maximum rate which can be sustained without exceeding the available l-drawdown at the pumping well. For both tests, an additional constraint on the pumping rate was the maximum volumetric discharge limit imposed by the permit to discharge to the sanitary sewer. The permit limit Yas 150 gpm. The results of the step-drawdown ~ test indicated that the optimal _ pumping rate was greater than 150 gpm; however, the pumping rate of 150 gpm was. selected for the constant-rate test to comply with the ~ ~ discharge permit restriction. l' , f *'. Thef -rate test was conducted by pumping well PW-1 at approximately 150 gpm for'ayeriod of 72 hours between April 27 and May 1,1992, and observing x v/ water level changeptrounding monitoring wells. The wdter level data collected over j this time period were then analyzed to determine the aquifer characteristics. 4 6.5.3 Pumping Test Data Analysis Results i The pumping test data were analyzed using Theis and Jacobs distance-drawdown and time-drawdown analyses (Appendix 6-F). Based upon this, the transmissivity of the unconfined aquifer (above the silt layer) in the vicinity of PW-1 was estimated to be between approximately 200,000 and 255,000 gallons per day per ft (gpd/ft) and the storage coefficient was estimated to be 0.10. Based on an estimated aquifer thickness GERAGHTY & MILLER,INC. '
~ PRn'ILEGED AND CONFIDENHAL 6-14 in the area of the test of 20 feet, the hydraulic conductivity estimate ranged from ~ ] approximately 1,300 to 1,700 ft per day (ft/ day). 6.5.4 Pumaine Test Water Ouality Monitorine i i g' Ground-water samples were collected periodically during the constant-rate pumping test to monitor any changes in ground-water quality over time and to document j the quality of the water discharged to the sanitary sewer. The samples were collected from a tap in the pumping test discharge line at the wellhead. The analytical results for -d the eight sets of ground-water samples collected during the 72-hour constant rate pumping test are presented in Appendix 6-F andindicate the following trends in water d quality: ^ id Concentrations of total dissolved solids (TDS), nitrate, sulfate, alkalinity, gross alpha, and gross beta, decreased over time. J v. C,oncentrations of dissolved metals generally decreased over time. [,xCxx cd j x s-i Yo'ncentratigns of TCE, TCA, fluoride, and ammonium remained nearly \\\\// constant goring the test. ~! \\._/ l t 6.6
SUMMARY
AND CONCLUSIONS Phase I and II Ground-Water Studies were conducted to determine the site f geology, hydrostratigraphy, ground-water flow, and aquifer characteristics. Sixteen ~ monitoring wells, three piezometers, and one pumping well were installed. A pumping test was conducted, water levels were measured monthly, and samples from wells and piezometers were analyzed for major ions to determine water types. The following summarizes the major results: a A .,J. ~ GERAGHTY & MILLER,INC.- t
81 m PRIVILEGED AND CONFIDENTL4L 6 15 The site hydrogeology is consistent with that determined by USDOE at the n HRL and consists of a shallow vadose zone, an unconfined aquifer, and aquitard, and a confined aquifer. i J The unconfined aquifer occurs at depths rangin from 10 to 50 feet bis at an elevation of 354.5 to 355.5 feet msl and is ,roximately 20 feet thick. It exhibits a very f]at gradient beneath the site and flows from south-i southwest to north-northeast. Seasonal water levels vary only approximately a foot in elevation, peaking inlate summer to early fall, at a l the end of the irrigation season. e J The confined aquifer occurs, below.the silt aquitard and has a potentiometric surface ~approximately 6 feet higher than that in the -} unconfined aquifer. This iadicates that the silt layer is an effective barrier ] between the4wd' aquifers, and that water from the unconfined aquifer cannot mihrate to'the confined aquifer. f't. s. ( bheTse ty e.in both the unconfined and confined aquifers is ca /' 7 Narbonate. The Nter in the confined aquifer is most similar to that in the J / N x Yakim/V, River, suggesting that the Yakima is'a major so a c to the confined system. The results of a constant-rate pumping test for the unconfined aquifer indicate a transmissivity between approximately 200,000 and 250,00 gpd/ft and a storage coefficient of 0.10. The hydraulic conductivity is estimated to range from 1,300 to 1,700 feet per day. a GERAGHTY & MILLER,INC. ~. - - -, _ - - - - - -
ld ^56.. m s l IV 3 aoa -. I; a W Hydrogeologic Units .d Eoiian sanc Erf_f Vadose Zone ~ ' ~ ~ 9 Pasco Grave!s EU3
- =:c
. r-- - n ,3e ___ e _.FEC '- Unconfined Aquifer Z ew a 4 -g o
- ~. L. -
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