Composition of pore water in lake sediments, research site “B”, Osage County, Oklahoma: Implications for lake water quality and benthic organisms

Applied Geochemistry Applied Geochemistry 22 (2007) 2177–2192 www.elsevier.com/locate/apgeochem

Composition of pore water in lake sediments, research site ‘‘B’’, Osage County, Oklahoma: Implications for lake water quality and benthic organisms Robert A. Zielinski a

a,*

, William N. Herkelrath b, James K. Otton

a

US Geological Survey, Denver Federal Center, Denver, CO 80225, United States b US Geological Survey, Menlo Park, CA 94025, United States Available online 13 May 2007

Abstract Shallow ground water at US Geological Survey research site B in northeastern Oklahoma is contaminated with NaCl-rich brine from past and present oil production operations. Contaminated ground water provides a potential source of salts, metals, and hydrocarbons to sediment and water of adjacent Skiatook Lake. A former brine storage pit 10 m in diameter that is now submerged just offshore from site B provides an additional source of contamination. Cores of the upper 16–40 cm of lake sediment were taken at the submerged brine pit, near an offshore saline seep, and at a location containing relatively uncontaminated lake sediment. Pore waters from each 2-cm interval were separated by centrifugation and analyzed for dissolved anions, cations, and trace elements. High concentrations of dissolved Cl in pore waters (200–5000 mg/L) provide the most direct evidence of contamination, and contrast sharply with an average value of only about 37 mg/L in Skiatook Lake. Chloride/Br mass ratios of 220–240 in contaminated pore waters are comparable to values in contaminated well waters collected onshore. Dissolved concentrations of Se, Pb, Cu and Ni in Cl-rich pore waters exceed current US Environmental Protection Agency criteria for probable toxicity to aquatic life. At the submerged brine storage pit, the increase of Cl concentration with depth is consistent with diffusion-dominant transport from deeper contaminated sediments. Near the offshore saline seep, pore water Cl concentrations are consistently high and vary irregularly with depth, indicating probable Cl transport by layer-directed advective flow. Estimated annual contributions of Cl to the lake from the brine storage pit (20 kg) and the offshore seep (9 kg) can be applied to any number of similar sources. Generous estimates of the number of such sources at site B indicate minimal impact on water quality in the local inlet of Skiatook Lake. Similar methodologies can be applied at other sites of NaCl contamination surrounding Skiatook Lake and elsewhere. Published by Elsevier Ltd.

1. Introduction Damming of Hominy Creek and gradual filling of Skiatook Lake during the middle 1980s produced

*

Corresponding author. E-mail address: [email protected] (R.A. Zielinski).

0883-2927/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.apgeochem.2007.04.013

profound changes in the local hydrology. As water levels in the lake rose, so did water tables in the surrounding highlands, thus reducing the hydraulic gradient compared with pre-lake conditions. Areas of ground water discharge in the stream valley were submerged under a considerable imposed hydrostatic head that may have slowed discharge to the lake or caused lake water to discharge to ground

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water. In addition to these changes, a complex pattern of groundwater seepage into or out of the lake was established along the 260 km of newly created shoreline. Normal variations of recharge and baseflow within the local highlands and fluctuations of lake levels caused by managed releases at the dam influence the present net flow of seepage at any shoreline location. Ground water seepage into the lake is of particular concern in areas where oil field production operations may have contaminated local ground water and where such operations are located close to the lake. Previous studies at the US Geological Survey (USGS) research site ‘‘B’’ near the western shore of Skiatook Lake (Fig. 1) have documented the presence of a shallow plume of contaminated saline ground water that is moving lakeward and extends beneath the lake (Smith et al., 2003; Kharaka et al., 2003; Herkelrath and Kharaka, 2003). The plume contains saline, NaCl-rich water that is coproduced with oil and that contrasts with local ground water of Ca–Mg–SO4–HCO3 chemical type (Kharaka et al., 2003). The high Cl concentration of produced water and the relatively unreactive

Ponca City

Bartlesville

Tulsa

Osage Country

Oklahoma City

0

100 Miles

0

100 Kilometers

chemical character of Cl anions facilitate the identification and tracing of this contamination. Inspection of historical aerial photographs that predate the filling of Skiatook Lake indicate that pits for temporary storage of hydrocarbons and/or produced water were located in a now-submerged area just offshore from site B (Fig. 2). During preparations for filling of the lake, these pits were covered with soil obtained from pit berms, but the submerged remnants of pit sediments could be sources of additional contamination to the lake. The purpose of this study at site B was to identify locations where Cl-rich pore water exists at very shallow depth (0–40 cm) in lakebed sediments, to model the seepage of this pore water into the lake, and to identify dissolved constituents that could have adverse effects on benthic organisms. Areas of active seepage were sought using a probe that measured specific conductance at the base of the lake-water column. One seep and another site within a presently submerged former brine storage pit were investigated by collecting sediment core samples and analyzing pore water composition relative to depth in the core. Pore water compositions

Oklahoma

“A” site

Skiatook Lake 0

1

2

0 1 2 3

3

4 Miles

“B”site

4 Kilometers

Fig. 1. Locations of US Geological Survey research sites A and B near Skiatook Lake, Osage County, northeastern Oklahoma.

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Fig. 2. Locations of 3 cores taken offshore from US Geological Survey research site B. Two linear transects anchored by surveyed reference points (X) guided measurements of bottom-water conductivity. The roughly circular outlines indicate locations of former pits used for storage of produced water or hydrocarbons. The dashed irregular polygon indicates a positive feature on the lake bottom that may be a redistributed berm. Labeled locations onshore are wells installed during current investigations of site B. Modern oil production operations on the site are indicated by a tank battery and associated pit. Contours in meters.

were compared with pore water from a nearby core containing relatively uncontaminated lake-bottom sediment. Pore water compositions were also compared to water quality standards for aquatic life. Estimated annual contributions of Cl from the seep and the brine pit were used to estimate total Cl contributions from variable numbers of proposed similar sources at site B. 2. Site description Research site B is located along the shore of a small inlet on the west side of Skiatook Lake (Fig. 1). The site hosts an active oil production operation that services a group of 10 oil wells located within approximately 1 km of the site. Modern facilities include a tank battery and a storage pit for temporary collection of NaCl-rich ‘‘produced water’’ that is pumped with the oil. Past and present operations at the site have created barren areas of salinized soil (salt scars) caused by surface releases of saline produced water or by leakage and overflow

from the storage pit (Fig. 2). Based on proximity to Skiatook Lake and the likely presence of contaminated ground water, the site was chosen by the USGS in 2001 for detailed study of the environmental effects of oil production. Additional descriptions of the geology, hydrology and production history of the site dating from 1938 are given by Otton and Zielinski (2003), Herkelrath and Kharaka (2003), and papers in this volume. A submerged area of positive relief located offshore from site B probably was formed during remediation of the former storage pits and may include surviving portions of a berm surrounding a former storage pit (Fig. 2). Located just to the south of this area of positive relief is a circular area of approximately 15-m diameter identified by geophysical measurements that indicate elevated electrical conductivity in the uppermost 2 m of sediment (B. Smith, US Geological Survey, pers. comm., 2005). This circular area appears distinct from a larger area of highly conductive nearshore sediments (0–5-m depth) that may indicate contamination by the main

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plume of saline ground water moving toward the lake. An extensive network of wells (Fig. 2) was installed at site B for hydrologic measurements and to characterize the underlying lithology by inspection of recovered drill cores. Of particular relevance to this study are wells BE07 (2.1 m deep) and BE62 (3.0 m deep) located closest to the lake and closest to the locations of offshore coring (Fig. 2). These wells were screened from 1.2 to 1.5 m and 1.5 to 3.0 m, respectively, and water quality data were obtained from multiple samplings (Y. Kharaka, US Geological Survey, pers. comm., 2004). Both wells are contaminated with saline water of Na–Cl character (dissolved solids, 10,000– 24,000 mg/L; Cl, 5000–15,000 mg/L) but differ markedly in the concentrations of dissolved SO2 4 (BE07, 15–100 mg/L; BE62, 7000–7600 mg/L). Shallow ground water throughout site B is highly variable in dissolved SO2 (Kharaka et al., 2003), 4 owing to variable dissolution of pyrite and gypsum in marine shale bedrock and probable SO2 4 reduction in organic-rich microenvironments within the shale. Wells BE07 and BE62 are periodically submerged during periods of high lake stage. Water levels in the wells mimic lake levels, indicating a largely unconfined condition in the shallow aquifer (J. Thordsen, US Geological Survey, pers. comm., 2004). The lithology of the closely-spaced BE07 and BE62 wells consists of 1–2 m of intertonguing colluvium and alluvium that overlies weathered shale bedrock containing minor interbeds of siltstone and sandstone. Surficial sediments collected during drilling are a heterogeneous mixture of sandy clay and clayey sand with abundant, variably oxidized clasts of sandstone. Some sediments had a weakto-strong odor of petroleum. Exponential decrease of seepage with distance from shore is predicted in isotropic, homogeneous sediment (McBride and Pfannkuch, 1975; Lee, 1977; Lee et al., 1980; Winter and Pfannkuch, 1984; McCobb et al., 2003), but is unlikely at site B, considering the heterogeneous lithology of the shallow aquifer. Similar non-ideal distributions of offshore seepage have been identified in many previous studies at other lakes (Woessner and Sullivan, 1984; Krabbenhoft and Anderson, 1986; Cornett et al., 1989; Cherkauer and Nader, 1989). At site B additional heterogeneity in the shallow sediments could be caused by trapped hydrocarbons that fill or coat sediment pores and reduce hydraulic conduc-

tivity. At individual sites of ground water seepage to the lake, variations in hydrostatic head imposed by recharge and lake-level fluctuations produce temporal variations in the rate of seepage. 3. Sampling and analytical methods A preliminary reconnaissance survey for active seeps offshore from site B was performed October 7–9, 2003, according to a method modified from that of Woodall et al. (2001). The boat-mounted survey was performed during a period of unusually low lake-level elevation (216.6 m) compared to the normal mean lake level of 217.7 m. Water depths in the measured areas ranged from 0.6 to 2.4 m. The survey instrument was a ‘‘conductivity stick’’ consisting of a length of PVC pipe capped at the bottom with a T fitting and containing a conductivity probe + cable. The T fitting facilitated accurate placement of the probe at the sediment/water interface and also permitted optional insertion into the uppermost sediment layer without damaging the probe. Specific conductance was measured at 0.6-m intervals along a N-S traverse parallel to the shoreline and along a roughly NE-SW traverse (Fig. 2). Areas of possible seepage were identified by repeated measurements of anomalously high and erratic specific conductance values as the probe was placed and gently pushed onto the sediment surface. Push-core samples were collected on October 9, 2003 from beneath 1.5–2.1 m of water at 3 sites (brine pit, hot spot, east 46; Fig. 2). A length of PVC pipe of 5-cm inner diameter was pushed and then hammered with a rubber mallet to depth of refusal, which was assumed to represent the base of the lake-deposited sediment. The top of the pipe was capped to create a vacuum, and the pipe pulled and raised to within 30 cm of the water surface. The bottom of the tube was capped and the tubing sawed off near the top of the collected sediment column. Recovered capped cores were taped, kept cool and in an upright position at all times, and refrigerated beginning on October 14. Core was manually extruded in the laboratory using a plastic piston inserted at the base and was collected in 2-cm intervals. Each extruded interval was placed in a sealed 250-ml polycarbonate centrifuge bottle and centrifuged at 8000 rpm for 45 min. Expressed pore fluid (3–20 mL) was decanted into a small beaker and then filtered through a 0.45-lm-

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opening cellulose acetate membrane using a disposable syringe filter. The filtered solutions were transferred to 25-mL polyethylene scintillation vials with cone seals. Specific conductance and pH were measured immediately. Two 1-mL aliquots were diluted 1:10 for determination of anions and cations. Solutions for cation analysis were acidified to pH < 2.0 with high purity HNO3. Pore waters were analyzed for selected dissolved  anions (Cl, SO2 4 and Br ) by ion chromatography (Zielinski et al., 2003). Estimated (1 sigma) analytical precision is 2–5% relative standard deviation  (RSD) for Cl and SO2 4 and 12% for Br at the concentrations encountered. Concentrations of dissolved cations in the solutions were determined by inductively coupled plasma-mass spectrometry (ICP-MS), with an estimated RSD of generally better than 10% (Bullock et al., 2002). 4. Results and discussion 4.1. Conductivity survey The N-S traverse with the conductivity stick was designed to cross the western half of the submerged former brine storage pit (Fig. 2). Depth measurements with the conductivity stick confirmed the location of an area of high positive relief and a shallow depression of approximately 10-m diameter corresponding to the southern part of the former pit location (Fig. 2). The estimated 0.45-m depth of the depression was based on comparisons with the depth of sediments farther south along the traverse. No obvious spikes in conductivity at the sediment/water interface were noted during traverse across the pit. Only one slightly anomalous (1.1X) conductance value was noted and verified by repeat measurement at a location north of the pit and east of the location of the hot spot core (Fig. 2). The hot spot core was located near the source of a stronger anomaly (>2X) found by random probing shoreward from this weaker anomaly. No conductivity anomalies were noted along the NE-SW traverse and a probable baseline core (east 46) was taken near the easternmost measurement point along the traverse (Fig. 2). A later and more detailed survey of conductivity at the sediment/water interface using divers indicated consistent, slightly elevated values (1.1X) in the brine pit compared to other offshore locations (J. Bidwell, Oklahoma State University, pers. comm., 2005).

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4.2. Brine pit core The 32 cm of core material from the submerged brine pit consists of well-sorted, silty, very finegrained sand that probably was deposited as sediment delivered by two small streams that flank site B on the north and south. Pore water concentrations of Cl, Na, Ca and Mg in the brine pit core increase gradually with depth over the upper 12 cm and are not markedly greater than the uniformly low concentrations in the east 46 core taken farther offshore and presumed to approximate less contaminated ‘‘baseline’’ conditions (Table 1). Pore water concentrations increase much more rapidly over the next 10 cm in the brine pit core, and, except for Fe and Mn, appear to stabilize at high values in the bottom 10 cm (Table 1; Fig. 3). The similar concentration profiles of these diverse elements may indicate that similar processes (mixing, diffusion, advection) influence concentration. Additional variability caused by water/rock reaction is possible for most of the reported elements but is unlikely for relatively unreactive Cl and Br. Coupled variation of dissolved Cl and Br is indicated by a narrow range of Cl/Br ratios throughout the core (mean, 223.8 ± 10.8, Table 1). This value compares to a mean of 256 ± 27 for 132 analyses of contaminated (>400 mg/L Cl) well waters from throughout site B (Y. Kharaka, US Geological Survey, pers. comm., 2004). Dissolved SO2 is low (<3.8 mg/L) throughout 4 the brine pit core, which is comparable to a value of 2.5 mg/L in water co-produced with oil at site B (Kharaka et al., 2003). Relatively high concentrations of dissolved Fe (5–18 mg/L) and Mn (6–11 mg/L) in the lower portion of the core could also be inherited from the original produced water or result from later diagenetic reactions. Reducing conditions during diagenesis can promote bacterially-mediated SO2 reduction and can also lead 4 to greater solubility of Fe and Mn as reduced, divalent species. Detectable odor of petroleum near the bottom of the core (26–32 cm) indicates the possibility of more reducing conditions at those depths. The concentration profile for Cl is similar to a profile measured by Mortimer et al. (1999) in a study of saline seepage in Lake Kinneret, Israel. These authors interpreted low values of dissolved Cl in the uppermost 3–5 cm of cores to result from mixing with overlying lake water. A similar

2182 Table 1 Major and minor element concentrations (mg/L) and other parameters in pore water from core samples taken offshore of site B in Skiatook Lake, Osage County, northeastern Oklahoma Depth (cm)

Sp. Cond. (lS/cm)

pH

270 280 360 500 660 960 1500 2400 3600 4800 6000 7300 8300 8800 8800 9000

6.90 7.00 7.30 7.30 7.40 7.20 6.25 5.00 6.10 6.50 6.30 6.25 6.00 6.35 6.40 6.60

East 46 core 0–2 2–4 4–6 6–8 8–10 10–12 12–14 14–16

440 560 670 820 920 950 920 760

7.05 7.30 7.20 7.20 7.10 7.25 7.10 6.90

Hot spot core 0–2 8000 2–4 11,000 4–6 15,000 6–8 17,500 8–10 18,000 10–12 18,000 12–14 18,000

7.80 7.90 7.90 7.90 8.00 8.00 7.85

Line missing

Comments

HC odor HC odor HC odor SS chunk

SO4

3.5 1.3 1.2 1.3 3.0 1.2 1.0 0.8 1.7 2.2 3.6 1.3 2.7 1.5 3.8 3.1 at core bottom

1.5 1.1 1.4 5.3 2.5 2.6 3.5 7.6

Weak HC Weak HC

1220 2260 2720 2880 2770 2590 2540

Cl

Br

Cl/Br

Na

Ca

45 57 81 130 190 310 450 670 1040 1450 1900 2330 2720 2720 3010 2940

n.d. n.d. n.d. n.d. 0.8 1.5 2.0 3.2 4.8 6.4 8.3 10.6 11.7 12.5 12.6 13.0

67 100 150 200 260 260 250 198

2110 3440 4180 4840 4890 4890 4960

Mg

240 204 223 211 216 227 228 220 233 218 239 226

23 26 32 50 76 120 180 300 510 720 970 1250 1390 1620 1540 1570

23 20 24 32 41 48 66 91 120 150 180 210 220 240 210 210

5.7 5.1 6.1 7.9 10 12 16 23 31 40 49 57 60 67 59 58

n.d. n.d. 1.3 1.4 1.9 1.9 2.0 1.7

116 143 137 137 125 116

32 66 80 120 140 170 160 130

35 61 37 37 33 26 18 14

8.1 14 8.5 8.8 8.3 6.6 4.2 3.3

9.6 15.1 17.8 22.0 21.6 21.8 22.2

220 228 235 220 226 224 223

880 1400 1880 2070 2150 2120 2100

320 500 650 700 680 650 630

450 770 980 1080 1040 1050 1010

K

Si

Fe

Mn

Sr

2.6 2.7 3.2 3.7 4.0 4.5 6.3 6.6 7.1 7.4 7.8 8.7 8.9 9.8 9.5 9.6

4.0 6.1 6.1 5.5 5.8 7.3 7.4 7.1 6.6 7.4 8.4 9.1 9.2 9.9 7.8 6.4

<0.2 0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.9 5.5 5.3 11.4 14.3 18.3 16.8 9.5 6.4

1.3 1.8 1.8 2.0 2.6 2.8 4.4 6.0 7.2 8.7 10.2 10.8 9.8 9.8 7.9 6.1

0.2 0.2 0.3 <0.1 0.5 0.8 1.2 2.2 3.7 5.4 7.9 10.7 11.9 13.4 12.4 12.5

3.4 4.8 4.0 5.5 5.1 4.7 4.2 2.9

2.9 6.7 6.2 7.0 5.9 6.1 5.6 6.7

<0.2 <0.2 <0.2 0.2 0.3 0.9 1.4 2.7

2.2 4.5 2.2 1.9 1.7 1.4 1.3 1.4

0.4 0.7 0.6 0.9 1.0 1.1 0.9 0.8

10.0 13.5 15.6 17.0 18.2 20.2 23.2

3.8 4.5 4.6 4.3 3.4 3.3 3.0

<0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

6.7 6.0 5.3 5.2 3.9 3.5 2.8

8.5 14.1 18.5 19.8 20.0 18.9 18.5

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Brine pit core 0–2 2–4 4–6 6–8 8–10 10–12 12–14 14–16 16–18 18–20 20–22 22–24 24–26 26–28 28–30 30–32

Abbreviations: HC = hydrocarbon, SS = sandstone.

Weak HC HC odor Weak HC Weak HC HC odor HC odor HC odor HC odor

Weak HC

14–16 18,500 8.00 16–18 16,000 8.40 18–20 14,000 8.35 20–22 13,000 8.40 22–24 11,500 8.40 24–26 11,000 8.45 26–28 10,000 8.40 28–30 10,000 8.15 30–32 10,000 8.20 32–34 10,000 8.20 34–36 10,000 8.25 36–38 9500 8.20 38–40 9500 8.40 Free oil present at depth of 34–40 cm

SS chunk

2290 2080 1630 1230 800 570 330 150 53.0 11.5 3.6 2.7 2.1

4700 4530 4260 3970 3690 3460 3530 3450 3300 3180 3260 3140 3050

20.6 20.2 19.2 17.5 16.0 15.8 15.5 14.7 13.9 13.7 13.1 12.8 12.4

228 224 222 227 231 219 228 234 237 232 249 245 246

2110 2000 1820 1750 1580 1520 1550 1430 1320 1440 1420 1340 1330

630 560 520 460 400 350 310 300 280 280 250 250 230

960 930 820 700 610 550 520 450 400 390 400 350 330

23.1 21.7 20.8 18.6 17.9 17.5 29.0 19.5 16.1 16.7 16.4 15.4 17.3

3.5 4.4 4.7 4.4 4.3 3.8 3.4 3.1 2.3 2.1 2.3 1.7 1.4

<0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

2.4 1.0 1.0 0.7 0.5 0.3 0.2 0.3 0.3 0.2 0.1 0.1 0.05

19.0 18.2 18.0 17.8 16.7 15.8 15.7 15.4 14.4 16.1 15.3 15.3 15.1

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explanation is reasonable for the uppermost 10 cm of brine pit sediments, considering their nearshore, shallow-water location near the mouths of two streams. Bottom-flowing density currents carrying suspended sediment are likely produced during storm events that markedly increase the discharge of the two nearby streams into the lake. If incoming stream waters or lake water are cooler than pore water, then thermal convection may further facilitate mixing and exchange of pore water (Cornett et al., 1989). Some bioturbation of the shallowest sediments may result from a local but sparse population of benthic organisms that includes at least two species of clams (J. Bidwell, Oklahoma State University, pers. comm., 2005). The observed gradual increase in Cl concentration with depth over the upper 10 cm (45–190 mg/L; Table 1) is consistent with progressively less dilution by lake water of 37 ± 3 mg/L mean Cl concentration (US Corps of Engineers, pers. comm., 61 measurements taken in 2003). Absence of a noticeably sharp gradient in Cl concentration near the sediment/water interface argues against strong upward advection of Clrich pore water. The pore water concentration profile for Cl, and particularly for the deeper intervals of 10–32 cm, approximates a convex shape that is typically observed in depth profiles of unreactive species in sediment cores collected from deep or quiet water settings with slow sedimentation (Berner, 1980). Such profiles have been fit by model calculations that assume a steady-state condition in which the dominant transport is by diffusion in response to a concentration gradient (Lerman and Jones, 1973). Other model calculations allow for advective transport in addition to diffusion (Cornett et al., 1989; Mortimer et al., 1999; Hurwitz et al., 2000; Schuster et al., 2003). In order to evaluate compatibility of the measured Cl concentration profile with a diffusion-dominated process, a non-steady state, trigonometrical-series solution to Fick’s second law of diffusion (Crank, 1975, p. 47) was utilized. This solution (Eq. (1)) is based on diffusion of a species across a planar sheet of finite thickness. Contrasting surface concentrations are held constant and the initial concentration within the sheet is assumed to be equal to zero. 1 x 2X C 2 cos np  C 1 C ¼ C 1 þ ðC 2  C 1 Þ þ L p n¼1 n npx expðDn2 p2 t=L2 Þ  sin L

ð1Þ

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Fig. 3. Pore water concentration profiles of selected major and minor elements in a core taken within a former produced water storage pit (brine pit core, Fig. 2).

where L is the thickness of the planar sheet (cm), t is the time to establish the measured profile (a), D is the sediment diffusion coefficient for Cl (cm2/a), x is the distance below the upper boundary (cm), C1 is the fixed concentration of Cl at the upper bound where x = 0 cm, C2 is the fixed concentration of Cl at the lower bound where x = L cm and n is the terms in the summed series.

For the model calculation, C1 was fixed at 37 mg/ L, the average concentration of lake water, and C2 was fixed at 2700 mg/L, the approximate Cl concentration at depths of 24–28 cm in the brine pit core (Table 1). The thickness of the planar sheet was set at 25 cm. The number of summed terms (5) was adequate to permit convergence of the solution. The initial calculation incorporated an experi-

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mentally determined sediment-diffusion coefficient for Cl of 1 · 105 cm2/s at 20–25 C (Li and Gregory, 1974). Diffusion coefficient values decrease at lower temperatures. Results using a time of 0.12 a (Fig. 4) provide an excellent fit to the observed Cl profile and indicate that the overall shape of the Cl profile is consistent with a diffusion-dominated mechanism. If mixing and bioturbation periodically alter the dissolved Cl concentrations in uppermost layers of these sediments, then evidence of such alteration may be obscured by subsequent re-establishment of a diffusion-dominated Cl profile. Additional excellent fits of the Cl profile can be obtained when larger values of t are used in combination with decreasing values of D. Twenty years represents the maximum possible age of the lake sediments, and for this time period the Cl profile is generated using a diffusion coefficient = 6 · 108 cm2/s. Given the possibility of mixing in shallower intervals of the profile, the apparent ‘‘diffusion’’ coefficients cited in these calculations are considered to be average values. The actual diffusion coefficients operative within the brine pit sediments are unknown. Despite this limitation, an upper-end estimate for the diffusive flux of Cl to the lake from an inferred typical pit of 10-m diameter is possible based on Fick’s first Law of diffusion (Eq. (2)) and a straight-line steady-state model (Manheim and Bischoff, 1969).

Diffusive fluxCl ¼ /Dsed

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DC Dx

ð2Þ

where / is the sediment total porosity (0.5 for fine sand to silt), Dsed is the estimated maximum sediment diffusion coefficient for Cl (1 · 105 cm2/s), DC is the Cl concentration change over depth interval and Dx is the depth interval. This simple calculation considers only the difference in Cl concentration values over the depth interval of 10–24 cm and assumes a linear fit to the Cl concentration profile between the two bounding values. It generates a maximum estimate for diffusive flux (Manheim and Bischoff, 1969). The additional terms are the sediment-diffusion coefficient (above), and the sediment total porosity, which is approximately 0.5 for silty sand (Berner, 1980). The resulting Cl flux of 8.37 · 1010 g/cm2/s operating over the assumed brine pit area (78.54 · 104 cm2) yields a Cl contribution of 20.7 kg/a. A larger pit area or the presence of more submerged brine pits increases the calculated Cl contribution accordingly. Annual contributions of the order of tens of kg of Cl have minimal impact on the Cl concentration of the local inlet. At normal pool elevation the inlet holds an estimated 11 · 108 L (900 acre-feet) of water with an average Cl concentration of 37 mg/L, which equates to 40,700 kg of Cl. 4.3. Hot spot core

Fig. 4. Comparison of observed Cl concentration profile in the brine pit core (Fig. 2) with calculated values based on diffusiondominated transport across a planar sheet. The model assumes constant surface concentrations of 37 and 2700 mg/L Cl and an initial Cl concentration of 0 mg/L within the sheet (see discussion in text). The plotted fit is for a sediment-diffusion coefficient (D) of 1 · 105 cm2/s and a time of 0.12 a. Similar fits are obtained using smaller values of D in combination with longer time periods for diffusion.

The sediment in the hot spot core also consists of silty, very fine-grained sand, but displays a much more persistent odor of petroleum at depths below 10 cm (Table 1). Resistance to coring was encountered at approximately 15-cm depth and small sandstone fragments were found in the core at that interval. Intervals between 34–40 cm were sufficiently contaminated with hydrocarbon that, after centrifugation of the sediment, an oily coating remained on the walls of the centrifuge bottles. Pore water concentrations of Cl and major dissolved cations in the hot spot core increase rapidly over the upper 8 cm. Concentrations stabilize at high values at 8- to 16-cm depth, then remain high but gradually decrease over the remaining 16–40 cm (Fig. 5). Even pore water from the 0- to 2-cm interval of this core is highly contaminated with Na (880 mg/L) and Cl (2110 mg/L). The Cl/Br ratio of pore water (mean, 230 ± 8.8) is again permissive of a produced water source and differs markedly from values <150 in the presumed less contaminated east 46 (baseline) core (Table 1).

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Fig. 5. Pore water concentration profiles of selected major and minor elements in a core taken at a site of active seepage (hot spot core, Fig. 2).

High Cl concentrations in pore water throughout the hot spot core, and highest Cl concentrations at shallow depths, contrast markedly with the brine pit pore water profile. Advective flow of saline ground water at this location is apparently sufficient to maintain high concentrations of dissolved solids near the sediment-water interface despite the diluting effect of lake water. Complex variation of Cl concentration with depth may indi-

cate that flow at the location of the core is still predominantly horizontal, with each individual layer retaining distinctive pore water chemistry. This conceptual model of flow assumes depth-wise variability in horizontal hydraulic conductivity and relatively minor influences of vertical hydraulic conductivity and interlayer diffusion (Guven et al., 1992). Vertical differences in pore water chemistry are probably established along a complex flow path leading to the lake and result from layer-specific differences in contamination, dilution, dispersion, and water/rock interaction. Layer-directed flow will be disrupted if flow lines turn sharply upward at a site of local upwelling. Alternatively, ground water that travels along shallow-dipping beds that intersect the lake bottom at a low angle may retain some chemical heterogeneity at the point of seep emergence. The composition of shallow (0–16 cm) pore water in the hot spot core differs markedly from shallowest pore waters of the other two cores in terms of and much higher concentration of dissolved SO2 4 much higher ratio of Mg/Ca (Table 1, Fig. 5). These compositional characteristics are found in a subset of contaminated ground waters at site B (Kharaka et al., 2003) and indicate increased water/rock interaction between NaCl brine and shale present in alluvium, colluvium, and weathered bedrock. The signature Mg/Ca ratio persists at greater depths in the hot spot core but dissolved SO2 shows dra4 matic declines from 2000 to 2 mg/L (Fig. 5). Sulfate is likely removed by bacterially-mediated SO2 4 reduction in the presence of organic matter. This process generates additional HCO 3 alkalinity (Berner, 1971), which raises the pH of pore water in the deeper portions of this core (Table 1). Concentrations of dissolved Fe and Mn remain low throughout the hot spot core, despite probable reducing conditions at depth (Table 1). Oxidation and precipitation of dissolved Fe and Mn during the 2–3 week storage of the cores prior to extrusion and sampling cannot be ruled out, but similar extreme losses were not observed in pore waters from the brine pit core that were handled similarly. It is possible that reductive dissolution and transport within the immediate vicinity of the hot spot core has exhausted the local supply of easily-reducible Fe and Mn. Alternatively, dissolved Fe and Mn may be incorporated in authigenic sulfides or oxidized and precipitated as secondary oxides in nearby microenvironments of greater oxidation capacity. Note that the alluvium and colluvium are generally mottled in color and contain abundant

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clasts of variably oxidized sandstone. Likewise, weathered shale bedrock contains interbeds of variably oxidized sandstone. The chemical character of pore water from the hot spot core indicates water/rock interaction with shale and addition of NaCl. Interaction between ground water and shale bedrock at site B is more likely for flowpaths that include a deep (>2 m) component. NaCl sources include onshore contamination under site B or older offshore contamination resulting from pre-lake oil field operations. Preferred flow within more transmissive layers transports dissolved Cl to locations beyond the source(s) of Cl contamination. This explains why the hot spot core is not underlain by a significant volume of highly contaminated sediment (B. Smith, US Geological Survey, pers. comm., 2005). Conditions that permit contaminated ground water to enter very shallow lakebeds near the location of the hot spot core are unknown. Ground water flow could be directed to shallower depth by a bedrock high, by thinning of more transmissive sandy alluvium in contact with intertonguing clayey colluvium, by preferred flow along a gently dipping transmissive layer that intersects the lake bottom at a shallow angle, or by residual asphaltic hydrocarbon contamination in the subsurface that presents a barrier to ground water flow. A conceptual model for delivery of Cl to the lake assumes upward bending of flow lines at some location near the hot spot core (right half of Fig. 6). Horizontal flow of shallow ground water within lakebed sediments is illustrated on the left half of Fig. 6, which includes the location of the hot spot core. The estimated advective flux of Cl derived

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from seep emergence is based on vertical displacement of pore water volumes contained in a cylinder of lakebed sediment that underlies the area of seep emergence (right half of Fig. 6). The height of the cylinder is 0.4 m, the thickness of the hot spot core in lakebed sediments. The diameter of the cylinder is arbitrarily taken as 1 m, but is supported by observations of wet areas surrounding onshore seeps that appear on the salt scars after rainstorms. A similar estimate of limited footprint for an individual seep was made by probing for anomalies with the conductivity stick near the location of the hot spot core. The effective porosity (interconnected pore space) of the silty sand sediment is taken as 0.5. The average dissolved Cl concentration of the seepage water is taken as 3840 mg/L, the average concentration of all 20 intervals from the hot spot core. The average velocity of the solute front is taken as 6 m/a, but is poorly constrained (see discussion below). The calculation is highly dependant on the choice of this velocity, which is based on preliminary hydrologic measurements in onshore wells, assumed Darcian flow, and a convection-dispersion transport model (Herkelrath and Kharaka, 2003). The above values are used to compute the terms in Eq. (3) Advective fluxCl ¼ PVcyl  ½Clavg  PVcyl =year

ð3Þ

where PVcyl is the pore volume of cylinder, [Cl]avg is the average concentration of Cl in cylinder pore water and PVcyl/year is the # of pore volumes swept per year based on a constant solute front velocity (6 m/a) and vertical, piston-like flow through a cylinder height of 0.4 m. For this calculation, the number of pore volumes swept per year is 15 (6.0/0.4). The calculated Cl

Fig. 6. Illustration of the cylindrical ‘‘seep unit’’ used in model calculations of the advective flux of Cl delivered to the lake near the hot spot core.

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flux of 9.0 kg/a is subject to large uncertainties in the estimated hydraulic conductivity (±10X), which affects the calculated solute front velocity, and in the assumption of a constant velocity. Other uncertainties arise from the estimates of average Cl concentration and cylinder diameter (i.e. pore volume). The calculation is less sensitive to cylinder height (sediment thickness) because greater sediment thickness decreases the number of pore volumes swept at a given rate of vertical flow. Unlike the brine storage pit, the modeled seep is likely one of a large, but unknown number of seeps that occur offshore from site B. The complex, claybearing lithology of the aquifer and the greater density of saline ground water compared to overlying fresh water may moderate the amount of seepage and the number of seeps that actually emerge on the lake bottom. A final estimate of the annual contribution of Cl that is moving toward the lake in the modern contaminant plume will be made based on more extensive hydrologic measurements in the network of onshore wells and model calculations of flow and solute transport. The fraction of this contribution that actually enters the lake as lakebed seepage is, however, more difficult to quantify. Fortunately, the dilution factor in the local inlet of Skiatook Lake will likely limit the impact on water quality regardless of the fraction of Cl that emerges as lakebed seepage. For example, 100 seeps similar to the modeled hotspot contribute 900 kg of Cl/a compared to 40,700 kg of Cl already present in the local inlet. Even if 100 seeps contribute 9000 kg of Cl/a the effect on water quality of the local inlet is modest. Such estimates, though poorly constrained, provide useful guidelines for reservoir managers concerned with the effects of this type of Cl contamination. Contributions of Cl-rich ground water seepage at other contaminated sites surrounding the lake are similarly diluted. A Cl mass-balance calculation for Skiatook Lake (Rice et al., 2007) indicated that Hominy Creek and other variably contaminated tributaries deliver sufficient Cl to account for the Clcontent of the lake. The inference is that Cl contributed from other sources such as groundwater seepage are small enough to be accommodated within the error of such calculations. 4.4. Impact of dissolved trace elements on benthic organisms Dissolved concentrations of six trace elements (B, Se, As, Pb, Ni, Cu) in pore waters from the brine

pit, hot spot, and east 46 cores are presented in Fig. 7. The six elements were selected based on their detection in the majority of samples and the existence of irrigation water quality standards for B (Van der Leeden et al., 1990) and aquatic life toxicity standards for the other elements (USEPA, 2002). Data for Zn met detection criteria but are not plotted because threshold concentrations considered toxic to aquatic life under conditions of continuous exposure (80 lg/L) were not exceeded. Other measured trace elements were below 20 lg/L or were below detection limits that ranged from 2 to 60 lg/L. High detection limits result from the 1:10 dilution required due to scarce pore water. Because of high detection limits, other trace elements of environmental concern such as Cd and Cr could not be evaluated. Pore water salinity in the cores varies over a large range (Figs. 3 and 5), so aquatic life toxicity standards for freshwater and saltwater are included for reference in Fig. 7. For some dissolved metals the aquatic life toxicity standard in freshwater is a function of the hardness of the water (as CaCO3). For these elements the reference standard is calculated based on the carbonate hardness of Skiatook Lake (65 mg/L). Greater hardness decreases the toxicity of metals (Kelly, 1999). Inspection of the plots in Fig. 7 indicates that aquatic life toxicity standards in freshwater are rarely exceeded in pore water from the relatively uncontaminated east 46 core and in relatively fresh water from the upper 10 cm of the brine pit core. Possible exceptions include Cu and Pb, which have very low thresholds of 6.2 and 1.5 lg/L, respectively. The upper 10 cm of sediment is a depth interval frequented by benthic organisms (Berner, 1980). In the hot spot core the upper 10 cm contains water of greater salinity that consistently exceeds saltwater and freshwater standards for Se, Pb and Cu, and saltwater standards for Ni. The combination of high salinity, potentially toxic concentrations of some dissolved trace elements, and dissolved petroleum hydrocarbons (not evaluated) could lead to increased morbidity and mortality in the vicinity of the hot spot core and any similar active seeps. At depths below 10 cm, the pore waters in the brine pit become increasingly saline and contain increasing concentrations of dissolved trace elements that, similar to the hot spot core, exceed saltwater standards for Pb, Cu and Ni. This pore water chemistry is inhospitable to burrowing organisms that may venture below 10 cm in the area of the submerged brine pit.

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Fig. 7. Pore water concentration profiles of selected trace elements in the 3 sampled cores of this study. Notes on each graph indicate regulatory standards for concentrations considered toxic to plants (B) or aquatic life (other elements). Lowest values plot along verticals that correspond to the reported detection limit at 1:10 dilution.

4.5. Controls on dissolved concentrations of trace elements Dissolved concentrations in contaminated NaCl-rich ground water are subject to modification by mixing with local ground water and by water/rock interaction. The effect of mixing (dilution) on rela-

tively unreactive Cl is illustrated by comparing measured Cl concentrations to a value of 82,140 mg/L reported for modern produced water sampled from a storage tank at site B in February 2002 (Kharaka et al., 2003). Concentration variations of trace elements that are highly enriched in produced water compared to local fresh water can

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be compared to that of Cl to determine departures from simple dilution control. Unfortunately, such comparisons are limited because of analytical difficulties in measuring trace elements in highly saline produced water. The normalized (to modern produced water) concentration of B in average hot spot pore water (0.86 mg/L/2.9 mg/L) is elevated by a factor of 6 compared to the normalized concentration of dissolved Cl (3840 mg/L/82,140 mg/L). In another type of comparison, the dissolved As concentration in modern produced water at site B is less than 25 lg/L, but concentrations in much more dilute pore water from the hot spot core are generally greater than 25 lg/L (Fig. 7). These observations indicate significant enrichments of B and As compared to Cl, which likely result from water/rock interaction. Concentrations of dissolved B, As and Se in the deeper portions of the brine pit core are low compared to concentrations in deeper portions of the hot spot core, despite similar Cl concentrations (Fig. 7, Table 1). One explanation is that the relatively stagnant brine pit waters are in contact with a limited volume of shale bedrock and are less enriched in elements (B, As, Se) that are leached from shale and can remain in solution as soluble oxyanions. If shale is not limited, then lower concentrations of shale-derived elements in brine pit pore water could result from slower, diffusion-controlled dissolution rates and transport within pores of brine pit sediment. Heavy metals Cu, Pb and Ni have similar pore water concentrations in the deeper portions of both cores and their dissolved concentrations may be limited by adsorption or precipitation. The implication for benthic organisms is that dissolved B, As or Se concentrations may increase during prolonged contact of saline ground water with shale bedrock. 5. Conclusions Ground water contaminated with dissolved NaCl and some toxic trace elements is present at shallow (0–40-cm) depths at two sampled locations offshore from US Geological Survey research site B. At the location of a submerged former brine storage pit, dissolved contaminants are delivered to the shallow lakebed and overlying lake water by upward diffusion in response to a large concentration gradient. At another ‘‘hot spot’’ location, dissolved contaminants in shallow ground water are transported to

the shallow lakebed and lake by advective flow under conditions of variable hydraulic head. The chemistry of pore water at the brine pit location is dominated by NaCl and has a strong similarity to modern produced water at site B. In contrast, NaCl-rich pore water at the hot spot location has been modified by interaction with shale components of surficial sediments or shale bedrock. Evidence of such interaction includes relatively high concentration of dissolved SO2 4 and a much greater Mg/Ca ratio. Lower portions of both the brine pit and hot spot cores contain an odor of petroleum hydrocarbons, and pore water at these depths shows evidence of more reducing conditions in the form of increased dissolved Fe (brine pit) or diminished   SO2 4 (hot spot). The Cl /Br mass ratio in contaminated pore water from both locations is within the range observed for contaminated well waters collected onshore and is similar to the value of approximately 250 observed in modern produced water at site B. Estimates of the annual contributions of Cl to the lake from the submerged brine pit and from a modeled ‘‘seep’’ that delivers Cl-rich pore water of the hot spot core, are of the order of 20 and 9 kg, respectively. Such contributions, or generous multiples of these contributions from additional brine pits (observed) or offshore seeps (postulated), do not pose a threat to water quality of the local inlet of Skiatook Lake. The clay-bearing, heterogeneous lithology of the local shallow aquifer likely exerts a strong control on the number of seeps that can emerge and their location. Dissolved concentrations of Cu, Pb, Se and Ni in saline pore water from the seepage location and in saline pore water (below 10 cm) at the brine pit location are above levels that may be toxic to benthic organisms. Concentrations of dissolved B, Se, and As in such pore waters are more likely to increase during continued interaction with shale bedrock than are concentrations of heavy metals. The methods used in this study are readily transferable to other sites of active or historic NaCl contamination that border Skiatook Lake (e.g. site A described in this volume), and to similar sites that occur elsewhere and may introduce contaminants to nearby freshwater lakes. Acknowledgements Special thanks are extended to M.M. Abbott of the US Geological Survey (USGS) for help with

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sample collection, and for surveying of transect lines, sample locations, and other features with high-resolution GPS. Y.K. Kharaka of the USGS provided access to largely unpublished data for the chemistry of well waters and for trace elements in modern produced water at the site. Other employees of the USGS who provided logistical or analytical support included G. Ambats, J.H. Bullock, C.C. Cope, C.A. Rice and J.J. Thordsen. References Berner, R.A., 1971. Principles of Chemical Sedimentology. McGraw-Hill, New York. Berner, R.A., 1980. Early Diagenesis, A Theoretical Approach. Princeton University Press, Princeton, New Jersey. Bullock Jr., J.H., Cathcart, J.D., Betterton, W.J., 2002. Analytical methods utilized by the United States Geological Survey for the analysis of coal and coal combustion by-products. US Geol. Surv. Open-File Rep. 02-389. Cherkauer, D.S., Nader, D.C., 1989. Distribution of ground water seepage to large surface water bodies: the effect of hydraulic heterogeneities. J. Hydrol. 109, 151–165. Cornett, R.J., Risto, B.A., Lee, D.R., 1989. Measuring ground water transport through lake sediments by advection and diffusion. Water Resour. Res. 25, 1815–1823. Crank, J., 1975. The Mathematics of Diffusion. Clarendon Press, Oxford. Guven, O., Molz, F.J., Melville, J.G., El Didy, S., Boman, G.K., 1992. Three dimensional modelling of a two-well tracer test. Groundwater 3, 958–967. Herkelrath, W.N., Kharaka, Y.K., 2003. Hydrologic controls on the subsurface transport of oil-field brine at the OsageSkiatook petroleum environmental research ‘‘B’’ site, Oklahoma. In: Kharaka, Y.K., Otton, J.K. (Eds.), Environmental Impacts of Petroleum Production: Initial Results from the Osage-Skiatook Petroleum Environmental Research Sites, Osage County, Oklahoma. US Geol. Surv. Water-Resour. Invest. Rep. 03-4260, pp. 113–125. Hurwitz, S., Lyakhovsky, V., Gvirtzman, H., 2000. Transient salt transport modeling of shallow brine beneath a freshwater lake, the Sea of Galilee, Israel. Water Resour. Res. 3, 101–107. Kelly, M.G., 1999. Effects of heavy metals on the aquatic biota. In: Plumlee, G.S., Logsdon, M.J. (Eds.), The Environmental Geochemistry of Mineral Deposits, Part A: Processes, Techniques, and Health Issues, Reviews in Economic Geology, vol. 6A. Society of Economic Geologists, Inc, Littleton, CO, pp. 363–371. Kharaka, Y.K., Thordsen, J.J., Kakouros, E., Abbott, M.M., 2003. The fate of inorganic and organic chemicals in produced water from the Osage-Skiatook petroleum environmental research sites, Osage County, Oklahoma. In: Kharaka, Y.K., Otton, J.K. (Eds.), Environmental Impacts of Petroleum Production: Initial Results from the Osage-Skiatook Petroleum Environmental Research Sites, Osage County, Oklahoma. US Geol. Surv. Water-Resour. Invest. Rep. 03-4260, pp. 57–84.

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Krabbenhoft, D.P., Anderson, M.P., 1986. Use of a numerical ground-water flow model for hypothesis testing. Groundwater 24, 49–55. Lee, D.R., 1977. A device for measuring seepage flux in lakes and estuaries. Limnol. Oceanog. 22, 140–147. Lee, D.R., Cherry, J.R., Pickens, J.F., 1980. Groundwater transport of a salt tracer through a sandy lakebed. Limnol. Oceanog. 25, 45–61. Lerman, A., Jones, B.F., 1973. Transient and steady state salt transport between sediments and brine in closed lakes. Limnol. Oceanog. 18, 72–85. Li, Y.-H., Gregory, S., 1974. Diffusion of ions in sea water and in deep-sea sediments. Geochim. Cosmochim. Acta 38, 703–714. Manheim, F.T., Bischoff, J.L., 1969. Geochemistry of pore waters from Shell Oil Company drill holes on the continental slope of the northern Gulf of Mexico. Chem. Geol. 4, 63–82. McBride, M.S., Pfannkuch, H.O., 1975. The distribution of seepage within lakebeds. US Geol. Surv. J. Res. 3, 505– 512. McCobb, T.D., LeBlanc, D.R., Walter, D.A., Hess, K.M., Kent, D.B., Smith, R.L., 2003. Phosphorus in a ground-water contaminant plume discharging to Ashumet Pond, Cape Cod, Massachusetts, 1999. US Geol. Surv. Water Resour. Invest. Rep. 02-4306. Mortimer, R.J.G., Boyle, D.R., Nishri, A., 1999. Use of a high resolution pore-water gel profiler to measure groundwater fluxes at an underwater saline seepage site in Lake Kinneret, Israel. Limnol. Oceanog. 44, 1802–1809. Otton, J.K, Zielinski, R.A., 2003. Produced water and hydrocarbon releases at the Osage-Skiatook petroleum environmental research sites, Osage County, Oklahoma. In: Kharaka, Y.K., Otton, J.K. (Eds.), Environmental Impacts of Petroleum Production: Initial Results from the Osage-Skiatook Petroleum Environmental Research Sites, Osage County, Oklahoma. US Geol. Surv. Water-Resour. Invest. Rep. 034260, pp. 15–42. Rice, C.A., Abbott, M.M., Zielinski, R.A., 2007. Use of dissolved chloride concentrations in tributary streams to support geospatial estimates of Cl contamination potential near Skiatook Lake, northeastern Oklahoma. Appl. Geochem. 22, 2193–2206. Schuster, P.F., Reddy, M.M., LaBaugh, J.W., Parkhurst, R.S., Rosenberry, D.O., Winter, T.C., Antweiler, R.C., Dean, W.E., 2003. Characterization of lake water and ground water movement in the littoral zone of Williams Lake, a closedbasin lake in north central Minnesota. Hydrol. Proc. 17, 823– 828 www.interscience.wiley.com, online publication in Wiley Interscience. Smith, B.D., Bisdorf, R.J., Horton, R.J., Otton, J.K., Hutton, R.S., 2003. Preliminary geophysical characterization of two oil production sites, Osage County, Oklahoma-Osage Skiatook petroleum environmental research project. In: Kharaka, Y.K., Otton, J.K. (Eds.), Environmental Impacts of Petroleum Production: Initial Results from the Osage-Skiatook Petroleum Environmental Research Sites, Osage County, Oklahoma. US Geol. Surv. Water-Resour. Invest. Rep. 034260, pp. 43–56. US Environmental Protection Agency, 2002. National Recommended Water Quality Criteria: 2002. Office of Water Science and Technology, EPA-822-R-02-047.

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R.A. Zielinski et al. / Applied Geochemistry 22 (2007) 2177–2192

Van der Leeden, F., Troise, F.L., Todd, D.K., 1990. The Water Encyclopedia, second ed. Lewis Publishers, Boca Raton, Florida. Winter, T.C., Pfannkuch, H.O., 1984. Effect of anisotropy and groundwater system geometry on seepage through lakes. J. Hydrol. 75, 239–253. Woessner, W.W., Sullivan, K.E., 1984. Results of seepage meter and mini-piezometer study, Lake Mead, Nevada. Groundwater 22, 561–568. Woodall, D.W., Gambrell, R.P., Rabalais, N.N., Delaune, R.D., 2001. Developing a method to track oil and gas

produced water discharges in estuarine systems using salinity as a conservative tracer. Marine Pollut. Bull. 42, 1118–1127. Zielinski, R.A., Rice, C.A., Otton, J.K., 2003. Use of soil extracts to define the extent of brine-impacted soils and bedrock at the Osage-Skiatook petroleum environmental research ‘‘B’’ site. northeastern Oklahoma. In: Kharaka, Y.K., Otton, J.K. (Eds.), Environmental Impacts of Petroleum Production: Initial Results from the Osage-Skiatook Petroleum Environmental Research Sites, Osage County, Oklahoma. US Geol. Surv. Water-Resour. Invest. Rep. 03-4260, pp. 127–135.