ISSN 00978078, Water Resources, 2014, Vol. 41, No. 5, pp. 532–542. © Pleiades Publishing, Ltd., 2014. Original Russian Text © V.Yu. Khoroshavin, T.I. Moiseenko, 2014, published in Vodnye Resursy, 2014, Vol. 41, No. 5, pp. 518–529.

WATER QUALITY AND PROTECTION: ENVIRONMENTAL ASPECTS

Petroleum Hydrocarbon Runoff in Rivers Flowing from OilandGasProducing Regions in Northwestern Siberia V. Yu. Khoroshavina and T. I. Moiseenkob a

Tyumen State University, ul. Semakova 10, Tymen, 625003 Russia Email: [email protected] b Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991 Russia Email: [email protected] Received August 17, 2011

Abstract—A method is proposed for evaluating the overland and river runoff of petroleum hydrocarbons orig inating from disperse pollution sources. The method is used to calculate their export from oilandgaspro ducing areas in Northwestern Siberia through the Pur River, a major artery in the Arctic region. The potential petroleum hydrocarbon input into the river is evaluated for different extent of petroleum pollution in the drainage basins of its tributaries. Keywords: disperse pollution sources, pertroleum hydrocarbons, empirical calculation model, oilandgas production impact, pollution volume assessment DOI: 10.1134/S0097807814050030

Northwestern Siberia is now subject to intense industrial development. The major branch being developed here now is the production of oil, natural gas, and gas condensate. The fields and the infrastruc ture accompanying oil and gas production have formed in the drainage areas of large rivers, including the Ob, Nadym, Pur, and Taz. The Nadym–Pur–Taz Interfluve is a major oilandgasproducing region (OGPR) in Russia. Notwithstanding the high level of water resources availability in the region, the problem of their qualitative depletion because of pollution is urgent here. Oilandgasproducing facilities, munic ipal and rural water treatment facilities, and transport enterprises discharge into rivers their wastes, contain ing petroleum hydrocarbons (PHC), different forms of nitrogen, phosphorus, synthetic surfactants (SS), particulate matter, chlorides, and sulfates. Water bod ies in the Northwestern Siberia are of fishery signifi cance. Valuable fish species, such as nelma, whitefish, starlet, and vendace, inhabit those water bodies and reproduce their. PHC are widespread surface water pollutants hazardous for living organisms [11]. When in water bodies, they destroy spawning and fattening areas, hamper natural aeration, and disturb biological processes, thus reducing the quality of fish and pro ducing toxic effect on fish organisms [10, 12]. Water chemistry in the Pur, a major river in the Arc tic basin, forms mostly due to the substances, includ ing pollutants, delivered by small rivers. Water quality of large rivers can be forecasted based on the data of studies and generalization of data on PHC carried by

small rivers that drain polluted watersheds in the areas of oil and gas condensate fields. The specific natural features of water chemistry in the region are as follows: higher concentrations of soluble forms of iron, man ganese, high concentrations of organic matter (OM), and ultrafresh water. The discharge of polluted waters by legal point sources was based on a system of admissible discharge standards. An important problem for the protection of water and waterrelated biological resources is the development of methods for evaluating PHC input from nonpoint pollution sources and assessing their contribution to the overall pollution of river basins. The scientific literature gives a vast body of data on a considerable effect of such pollution sources on conti nental water pollution [5, 6, 9, 14–19]. The objective of this study is to develop a procedure for evaluating the discharge of PHC from nonpoint pollution sources via rivers in tundra and foresttundra zones and to apply this procedure to evaluate the total volume of their discharge into the Pur R. and forecast the future discharge of PHC as the oilandgas pro duction will develop in the Kara Sea Basin. MATERIALS AND METHODS The Pur R. basin was chosen as the object of field and calculation studies. Its drainage basin experiences a considerable load from oilandgasproduction, transport, and municipal activities. Pur basin extends over more than 500 km from north to south. The nat

532

PETROLEUM HYDROCARBON RUNOFF IN RIVERS

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lake lake Gas field no. 7

lake

N

e ka ar Ng

lake lake

a se t

R. ha k ya

Hydrological gage no. 3 (Gage 3) Hydrological gage no. 1 (Gage 1)

Shift camp

S

Oil field Oil pumping station 1

Hydrological gage no. 2 (Gage 2) kh aR

.

lake Pi de ya

Gas field 6

lake

lake

Runoff plut II Runoff plut I

lake

lake Lake

lake

lake

lake lake

Hydrologic gages Roads Rivers Oilandgasproduction facilities (gas and oil fields, shift camps, etc.) Experimental river boundaries Runoff plot Oil pipeline Wetland lake Lakes Study area boundary

Fig. 1. Layout of study objects: experimental watersheds of Pideyakha and Ngarkaesetayakha, hydrological gages (Gages 1, 2, and 3), and runoff plots (runoff plots I, II). WATER RESOURCES

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Table 1. Morphometric characteristics of experimental watersheds Morphometric characteristics Name of river or creek

Pideyakha R. (Gage 1) Unnamed creek, a tributary of the Pideyakha R. (Gage 2) Ngarkaesetayakha R. (Gage 3)

river length, km

watershed area, F, km2 63.3 1.84 44.0

ural zones in it change from mosssubshrub tundra to medium taiga. The basin territory lies within three landscape–hydrological provinces (LHP) [1]. The southern and central parts of the basin up to the lati tude of the Tab’’yakha R. refer to the Pur and, to a lesser extent, Taz LHP of the Ob–Irtysh forest– swamp lowland–accumulation landscape–hydrologi cal zone (LHZ). The middle quarter of the drainage basin lies within the EastGydanskaya LHP of Yamal– Gydanskaya permafrost lake–swamp–river LHZ. The boundary between those LHZs is the southern bound ary of the continuous lowtemperature permafrost rocks from the surface and the boundary between tun dra and forest–swamp zone. Water runoff forms under diverse landscape–hydrological and ecological– geochemical conditions, whose mosaic character complicates the monitoring of the state of water resources in this area. The study is based on data of field studies and the chemical analyses of naturalwater and soil samples taken at experimental watersheds and runoff sites in the area. The runoff sites were located in oil spill areas. PHC discharge from small watersheds not studied hydrologically was evaluated using empirical equa tions based on the processing of field observations and measurements, estimated relationships between PHC discharge and the area and number of oilpolluted zones in the watershed, as well as by landscape– hydrological and meteorological characteristics of the territory. In particular, equation (1) below was derived by V.M. Kalinin [5] to describe the dependence of PHC washout modulus on the area of oil pollution and water runoff modulus with background concentrations of PHC in waters of small rivers of taiga zone in West ern Siberia (the Ob Basin): f ⎞⎤ f ⎞ ⎡ ⎛ ⎛ μ = 0.42M p ⎢1 − exp ⎜ − 40 p ⎟⎥ + a b M ⎜1 − p ⎟ , F F ⎣ ⎝ ⎠⎦ ⎝ ⎠

(1)

where μ is petroleum washout modulus, mg/(s km2); 0.42 is an empirical factor am , derived for the Middle Ob region, which is equal to PHC concentration in the outlet section at the maximal oil pollution of the watershed; Mp is water runoff modulus for the oilpol luted part of the watershed, Mp = 1 L/(s km2); M is areageneralized water runoff modulus, L/(s km2); F

slope, ‰

bogginess, %

forest area percentage, %

9.5

2.2

61.0

2.8

1.4

75.5

16.6 0.01

11.0

2.1

68.5

0.4

is drainage basin area, km2; ab is PHC concentration in the outlet section in the absence of land pollution by oil (background conditions); fp is the area of oil pollu tion in the drainage basin. Advantages of equation (1) are that it takes into account the background concentration of PHC in riv ers of the region and it is based on a functional rela tionship between oil washout and the area of oilpol luted land. The number and area of oilpolluted sites can be evaluated visually during route studies or by modern studies based on remote sensing of the Earth’s surface. The application of equation (1) is subject to some restrictions associated with the natural conditions of runoff formation. Equation (1) has been derived for taiga watersheds; hence, it can be only applied to the taiga (forest–swamp) part of the Pur R. basin. The regularities in the formation of overland and channel runoff, as well as PHC export in flowing natural waters are different in the case of foresttundra and tundra; therefore, improvements are to be introduced to account for the natural and climatic features of the zones under study. At Gages 1, 2, and 3, hydrochemical and hydrolog ical studies were carried out in 2001–2005 during an expedition in three small watersheds in the northwest ern part of the Pur R. basin (Fig. 1). River watersheds for Gages 1 and 3 are located within the territory of an oil field, whence some amounts of PHC can reach water systems. Gage 2 (a creek flowing into the Pideyakha R.) was introduced to assess the PHC export from an unpolluted watershed with the aim to improve the regional estimate of parameter ab (back ground concentration) in (1). At the experimental watershed (Gage 1), the actual PHC washout modulus was determined for the case when oil spills and secondary petroleum pollution sites are present in the drainage area. Water runoff from experimental runoff plots, isolated from the surround ing land, was measured. Simultaneously, the area of oilpolluted zones were measured, their correlation with different landscape complexes was determined, and the time of existence of oil spills and the major morphometric characteristics of experimental water sheds were taken into account (Table 1). Topographic WATER RESOURCES

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Table 2. Quantitative and qualitative characteristics of water flow with experimental runoff plots 1 and 2 over observation period in 2001–2004 Observation date August 2001 June 2002 August 2002 September 2002 May 2003 Averaged values

PHC concentration, mg/L

Q of water flowing from runoff plot, L/s

Mp, L/(s km2)

µ, mg/(s km2)

3.00 ± 0.80 0.10 ± 0.03 1.80 ± 1.00 1.90 ± 0.50 0.78 ± 0.19 1.52

0.11 0.17 0.17 0.20 0.20 0.17

6.7 10.6 15.5 18.2 12.1 12.6

20.1 1.0 27.8 34.6 9.7 18.6

surveys were carried out at oilpolluted to evaluate the area of oilpolluted zones. Data on the durations of existence and the volumes of spills were provided by the operator of the facility where the emergency took place. Two runoff plots (StP I and StP II) were established in the experimental watershed at the Gage 1 with the aim to assess PHC export from oilpolluted areas (Fig. 1). Areas with oil spills were surrounded by levies along their perimeters to prevent the inflow of surface waters, either clear or polluted, from the nearby slopes. The result was that the quality of water flowing from the plot has formed exclusively within its area. The volume of water flowing out was fixed in a special flume at the outlet of the polluted overland flow from the plot. The flume was used to measure water dis charge from the oilpolluted plot and to take water samples during spring flood, summer lowwater period, and autumn freshets to be measured for PHC content. Parallel to that, hydrometric and hydrochem ical studies were carried out at the Gage 1 situated downstream of the site where waters from oilpolluted areas entered the creek. The samples taken in the period of study included 25 samples of surface water and snow, 8 samples of soil (peat) and mineral ground, which were analyzed for PHC content. The sampling of water and soil, as well as sample analysis followed standard procedures. The characteristics determined in the analysis included color index, pH, and odor in the field. The PHC con tent of water was determined by infrared spectrometry (AN2 analyzer) in the laboratory in the day the sam ple was taken. The study at runoff plots yielded the value of runoff modulus from oilpolluted part of the watershed (Mp) of the river under consideration.

—infield pipelines and gathering pipelines; —unauthorized discharges of oilcontaining wastewaters into relief depressions and earth storages; —torches and motor transport. Emergencies at the facilities mentioned above are a potential cause of oil spills, which can become a source of diffuse river pollution. Route surveying of the territory drained by the experimental river has shown that the total area of fresh and old oil spills is 0.1 km2, i.e., 0.16% of the watershed area (Fig. 1). The age of the oilpolluted areas, according to data of the subsurfaceusing enter prise and earlier observations of TyumenNIIgiprogaz employees, varies from 5–6 years to several weeks. Their distribution over geomorphological levels from slopes to swampy lowland areas is also diverse. PHC concentrations in soils at spill sites estimated based on the analyses of samples varies from 229 to 450 g/kg, while that based on the data of oilandgasproducing department is 15–229 g/kg. The results of examination of small watersheds were used to identify 12 sites with primary and second ary oil pollution, which were ranked according to the size of polluted area. It seems highly probable that other diffuse pollution sources exist as well, since it is common practice at oil fields to cover oil spills by sand (“sanding”). The sizes of the identified oilpolluted sites vary from 30–50 to 60 thousand m2. It is worth Table 3. Snow component composition at runoff plot 1 (sample 1) and at a relatively clean area⎯a slope of Pideyakha R. terrace near gas field 6, Urengoi deposit (sam ple 2), on April 20, 2002, mg/L Measurement results Characteristic

CHARACTERISTIC OF DIFFUSE OIL POLLUTION SOURCES FOR RIVERS Field studies at experimental watersheds showed the main sources of oil input into soils and water to be as follows: —oil production, injection, and absorption wells; WATER RESOURCES

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Nitrite ion Nitrate ion Chloride ion Dry residue Lead

sample 1

sample 2

0.03 ± 0.01 15.8 ± 1.9 2.0 ± 0.2 42 ± 8 0.0045 ± 0.0008

<0.02 13.6 ± 1.6 4.38 ± 0.66 Not determined 0.0038 ± 0.007

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KHOROSHAVIN, MOISEENKO

Table 4. Experimental quantitative characteristics of PHC export from experimental river watershed at Gage 1 in 2001–2003 Sampling date

M1, Basinaveraged rate of PHC concentra Water Q, m3/s PHC discharge, E, mg/s dm3/(s km2) tion, mg/dm3

Aug. 27, 2001 Oct. 15, 2001 June 9, 2002 Aug. 25, 2002 May 26, 2003 Aug. 18, 2003

0.02 0.02 0.05 0.05 0.17 0.07

0.81 0.22 1.66 1.16 1.43 0.23

16.2 44.0 83.0 58.0 243.1 16.1

Basinaveraged μ, mg/(s km2)

12.8 3.6 26.2 18.3 22.6 3.6

0.26 0.07 1.31 0.92 3.84 0.25

Table 5. Hydrological and Hydrochemical characteristics of a conventionally background creek at Gage 2 (n.d. means not determined) Pollutant concentration, mg/dm3

Sampling date

Water Q, m3/s

COD, mg O2/dm3

PHC

Cd

N O3

N O2

–

N H4

June 9, 2002 Aug. 25, 2002 May 25, 2003

0.12 0.03 0.22

n.d. 32.08 n.d.

0.164 0.05 0.25

0.0001 n.d. n.d.

n.d. 0.43 n.d.

n.d. <0.02 n.d.

n.d. <0.1 n.d.

mentioning that the overwhelming majority (up to 95%) of the identified spills in the area are not greater than 100 m2 in area and lie on earth beds intended for wells as basements and isolated from the watershed. The main site for studying was chosen to be a dif fuse source of river pollution, which is typical of the territory—the oil spill near the gas field 6, Urengoi Deposit (Fig. 1) within the Pideyakha R. watershed. This spill is the largest in area among all studied (60 thousand m2); it was caused by an oiltrunk pipe line break in winter 1995–1996. The spilled oil flowed under snow, so the initial volume of the spilled oil is difficult to evaluate. Clearly, it was greater than that declared officially (350 t). To prevent the spreading of pollution, the oilpro ducing company separated the spill area in 2001 by earth levees into three part with different pollution lev els. In the study period, PHC were released from the largest part of the emergency spill into an intermittent stream flowing into the river, at which Gage 1 was sit uated. The oil pollution could be visually traced in the river over a distance of 300 m downstream from the stream inflow. Crusts of petroleum paraffin occurred on stream banks, spits, beaches, and floodplain spaced

–

+

5–10 m apart. Bushes and grass along the stream were covered by a black oily film. At air temperature of +5°C, oil could be scented. This suggests a consider able pollution, which spread from the oil spill site. PETROLEUM HYDROCARBON CONCENTRATIONS IN THE OVERLAND FLOW FROM POLLUTED AREAS Measurements of PHC concentrations in the over land flow from oilpolluted areas in different hydro logical phases within three years showed PHC con centration to average 3.0 ± 0.8 mg/L. Pollution wash out rate reaches 0.2–0.4 mg/s. Data on PHC concentration in water sample and the rate of runoff were used to evaluate Mp —the modulus of water flow from the oilpolluted area, and μ—the modulus of PHC washout (Table 2). Estimates of the total PHC discharge based on Mp and μ values yielded the wash out volume from one site during the active season of 3.2–4.5 kg, i.e., with 1–3 oilpolluted sites in a small watershed, the total annual discharge of HC with over land flow will be ~5–10 kg.

Table 6. Comparison of the calculated and measured values of μ, % Values µ calc for the Ngarkaesetayakha R. calculated by equation (2)

Values µ G3 measured at Gage 3 at the Ngarkaesetayakha R.

Divergence between the calculated and measured values of μ, %

1.01

1.1

8.2 WATER RESOURCES

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PETROLEUM HYDROCARBON RUNOFF IN RIVERS

To specify the sources of PHC that enter the runoff plots, samples of water flowing from the plots were analyzed for heavy metals, including copper and lead. Samples of snowmelt water flowing from the runoff plot I showed copper and lead in excess of MAC (Table 3), suggesting the effect of motor transport of pollution, including that by PHC. Thus, the diffuse discharge of PHC into rivers of the region is due not only to oil spills, but also to the accumulation of gaso line and diesel fuel combustion products from trans port vehicles involved in the development of deposits in Northwestern Siberia. Generalization of observation data from runoff plots (Table 2) yielded the mean PHC concentration in water flowing from the area with heaviest oil pollu tion, which is located in StP I, the runoff modulus being Mp = 1 L/(s km²), and enabled estimating the characteristic am = 0.25 mg/L. Data of measurements at Gage 1 (Table 4) on the Pideyakha R., subject to the impact of oilproduction facilities, were used to obtain averaged data on μ in dif ferent seasons (except for winter) from oilpolluted sites. Analysis of data on PHC concentration in sam ples from river water at a conventionally background watershed (Gage 2) yielded regionspecific values of coefficients to improve the discharge of PHC from areas not subject to direct impact of oil fields, allowing equation (1) to be adapted to the conditions of forest tundra and tundra at ab = 0.15 mg/L. Thus, hydrometric and hydrochemical studies at Gage 1 and 3, runoff plots I and II on small rivers, which drain the Urengoi oil field areas established a relationship between PHC in river water and the area of oil pollution on the watershed. Note that the hydrological and hydrochemical characteristics of the examined objects were deter mined in years with low or medium water abundance. Therefore, the coefficients obtained in experimental studies and required for the verification of equation (1) under local conditions can be applied for lowwater years. The values of coefficients for highwater years will most likely be greater; therefore, additional stud ies will be required to improve their estimates. ADAPTATION OF OIL BEARING OUT OF POLLUTED WATERSHED AREAS Equation (1) was adapted to the conditions of small watersheds of tundra and foresttundra at oilandgas fields in the Pur R. basin. With coefficients evaluated more precisely in field studies for the specific natural– climatic zone, the following equation was obtained:

f ⎞⎤ f ⎞ ⎡ ⎛ ⎛ μ = 0.25M p ⎢1 − exp ⎜ −60 p ⎟⎥ + ab M ⎜1 − p ⎟ . (2) F ⎠⎦ F⎠ ⎣ ⎝ ⎝ The improved coefficients in equation (2) for the zones of tundra and foresttundra were obtained by measuring PHC concentrations in water samples WATER RESOURCES

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taken at Gages 1 and 3 on rivers subject to the effect of oil fields. The observations were performed in different seasons, except for winter (Table 4). The factor 0.25— parameter am —reflects the completeness of PHC washout from soils with climatic and landscape–geo graphic conditions taken into account. The factor 60 reflects the area ratio of polluted and clear parts of the watershed. PHC concentration ρ, mg/L, at the examined gage can be evaluated by dividing μ by the unitarea dis charge M for the small river: ρ = 0.25

Mp ⎡ f ⎞⎤ f ⎞ ⎛ ⎛ 1 − exp ⎜ − 60 p ⎟⎥ + a b ⎜1 − p ⎟ . ⎢ M ⎣ F ⎠⎦ F⎠ ⎝ ⎝

(3)

For efficient application of equations (2) and (3), one needs to have the value of ab. This value was derived from data on PHC concentrations in the water of rivers of conventionally background watersheds, whose areas are not used for either oil production or transportation. In this case, such area is the drainage basin of a tributary of the Pideyakha R., denoted as Gage 2 (Fig. 1). Analysis of Gage 2 observation data (Table 5) yielded the conventionally background val ues of coefficients typical of the region and improving the export characteristics of oil products from the areas. This allowed equation (1) to be adapted to the conditions of foresttundra and tundra in its second part, associated with the natural export of PHC with natural waters, and to obtain ab = 0.15 mg/L. _

Equation (1) was verified by comparing μcalc (the mean estimated washout modulus from the drainage _ area) and μG3 (the measured values of PHC washout modulus at Gage 3 (the Ngarkaesetayakha R.), aver aged over several years) (Fig. 1). Observations at _ Gage 3 yielded μG3 = 1.1 mg/(s km2). The measured values of unitarea water discharge for the polluted area and a generalized modulus over the entire drain age basin were Mp = 12.6 and M 1 = 14.5 L/(s km2), respectively. Field observations in Ngarkaesetayakha R. basin ( F = 44 km2) within Gage 3 drainage area (Fig. 1) were used to evaluate the area of oilpolluted zones: fp = 0.1 km2. Equation (2) was solved for Ngarkaesetayakha R. drainage basin at ab = 0.05 mg/L (within the range limited by MACfish). Solving equation (2) yields _ μcalc = 1.01 mg/(s km2). Thus, the divergence between the calculated and measured actual values was <10% (Table 6), i.e., lies within the error allowable in hydro logical calculations, thus enabling equation (2) to be used to assess oil washout from small oilpolluted watersheds in foresttundra in Western Siberia. The divergence between the measured PHC con centration (c) at the outlet section of the Ngar kaesetayakha R. and that evaluated from (3) at M = 8 L/(s km2) (using data [2]) and Mp = 8.02 L/(s km2) was on the average 15%.

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EVALUATING THE VOLUME OF PETROLEUM HYDROCARBON EXPORT WITH RIVER RUNOFF FROM OILANDGASPRODUCING AREAS The model developed for evaluating PHC export with individual small rivers can be used to assess and predict pollution input into largeriver channels and into marginal seas. Calculations for the Pur R. are given as an example. The large area and the extent from north to south of the Pur R. basin make it neces sary to take into account the diversity of natural–cli matic and hydrological conditions in evaluating oil polluted runoff. Runoff formation in each landscape– hydrological province has its specifics. The overland flow in taiga LHP is relatively large. Dissolved in water, PHC readily penetrate into melted sand–loam soils, thus spreading the pollution over vast depths and areas. Because of rapid seepage and the low sorption capac ity of podzol soils, soluble PHC are intensely washed into river runoff. Tundra SFK are colder, showing slower runoff and greater bogginess; peat effectively retains pollution, and frozen soils and water hampers the process of diffuse pollution. The analysis of natural conditions of runoff forma tion in each of the three LHPs identified in the Pur R. basin led to the conclusion that equation (1), devel oped for taiga basins of the Middle Ob basin, is appli cable to watersheds in the Pur and Taz LHPs. Equa tion (2) can be used for the watersheds of the East Gydanskaya LHP, located in foresttundra and tundra. Small rivers were chosen in the three identified LHP as reference samples with characteristics similar to the water objects used to derive the coefficients required for calculations. For each reference river, landscape–hydrological analysis [5, 6, 17] and equa tions (1) and (2) were used to evaluate water runoff characteristics in the outlet section and data on the amount of dissolved and suspended PHC transported by water runoff. The model calculations were tested at three rivers that drain operating oil fields, i.e., the Sedayakha R. (a right tributary of the Evoyakha R. in the Pur LHP), the Khanzebeyakha R. (Taz LHP), and the En’’yakha R. (a right tributary of the Khadutte R. in the EastGydanskaya LHP) (Fig. 2). More than 20 HC fields, which are developed in the Pur basin, serve as pollution sources for hillslope and channel runoff at watersheds of 29 small rivers (Table 7). Each such river was associated with a refer ence river, for which water runoff and PHC export vol ume at the mouth section were evaluated using equa tions (1) and (2). The estimated amount of PHC discharged by each of the 29 small rivers were used to evaluate the total PHC discharge into Pur R. tributaries (Table 7). The discharge of HC with mediumsize rivers–tributaries

of the Pur R., for which hydrometric data [8] are avail able, was calculated by the formula

V = Wab,

(4)

where V is the volume of discharged PHC, t; W is water runoff, km3; ab is PHC background concentra tion in natural waters, t/km3. The value of ab for calcu lations was chosen among two variants: 0.05 mg/L (MAC for petroleum products for water bodies used for fishery) or 0.15 mg/L (technogenic background), depending on the presence and density of potential pollution sources (motor roads, oil fields, and oil pipe lines) in the watershed of the Pur tributary under con sideration. The migration of PHC with river water is known to be accompanied by selfpurification processes (pre cipitation onto the bed, microbial decomposition, photolysis, etc.). The decrease in HC concentration in the course of water selfpurification was evaluated as (5) c X = c 0 exp(−k τ), where cX is PHC concentration in the outlet section, mg/L; c0 is PHC concentration in the initial section, mg/L; k is selfpurification factor; τ is water travel time, day. The selfpurification factor for PHC was taken equal to the value obtained for the Taz R.—an ana logue of the Pur R. in terms of water quality formation conditions ( k = 0.05) [7]. To improve the accuracy of the estimated mass of exported PHC, the entire length of the river from the source of the Pyakupur R. to the Pur R. mouth was divided into 5 segments (Fig. 2), for which the mass of exported HC and their concentration in river water was evaluated. The length of the channel within which exp(− k τ) > 0.90 is 120–130 km. The segments I and II (the Pyakupur and Aivasedapur rivers) were identified as independent units (Fig. 2). The amount of PHC exported with river runoff within each identified segment, with selfpurification taken into account, enabled the assessment of their concentration in the waters of the Pur R. and its tribu taries. This also allowed the assessment of PHC export with Pur R. water into the estuary of the Kara Sea— Taz Bay. Based on data on unitarea discharges and runoff depths derived from landscape–hydrological analysis by method [3] for small watersheds of reference rivers, within which oil and gas production is carried out and main oil pipelines are in operation, as well as on the obtained dependence of μ on fp (equations (1) and (2)), the volume of PHC export was evaluated. The calculations showed that, with a complete absence of dispersed pollution sources and ab = 0.05 mg/L, the discharge of PHC from each small river is 2.94– 5.62 t/year. Tundra rivers show lesser discharge vol ume, while in taiga it increases to 5.5 t/year. Nowa days, under current technogenic loads onto the Pur R. WATER RESOURCES

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PETROLEUM HYDROCARBON RUNOFF IN RIVERS Khadutte

539

VI (mouth) 1

Sidimyutte 70 100

84 En’’yakha

30 P U R

Paravykhadutte Tab’’yakha

110 Syagoikhadutte

V (Samburg) 120

Ngarkaesetayakha

140

25 no. 26

Evoyakha

Sedeyakha 127

223

85

(Urenoi) Bol. Khadyr’’yakha

247 Yagenetta

174

290

380 Khal’mig’’yakha

Puritei 225 Umseyakha

160

I

Purpe

125

70

96

no. 10

Khad’mer’’yakha

117

Tayakha 385 III (confluence 389 km) II (Aivasedapur)

55 Khanzebeiyakha36

Vorayakha

66 Etuyakha

Kharucheiyakha

no. 20

150

no. 19 210

no. 6 Pul’puyakha

5

no. 15

Pyakupur Khaduteiyakha

427

419 Ituyakha

435

Aivasedapur

Vyngapur

415 no. 1

Dyagiegan

359

409

105

Khanayakha

225

Pidyayakha

Kamgayakha

I⎯IV—summation points of oil product export for segments with conventional numbers 223 —distance from the mouth of the river–source of oil pollution to the mouth of the river–recipient (this distance is used to evaluate the travel time t; no. 9 is the number of the river in the list (Table 6) Fig. 2. Linear hydrographic scheme of layout of polluted tributaries of the Pur R.

watershed, the background PHC concentration in river waters is three times the MACfish of oil products and amounts to 0.15 mg/L; the pollution of small watersheds is in excess of 1% [16]. These data were used to evaluate the PHC export volume with waters of all small rivers in Pur R. basin WATER RESOURCES

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under three ecological scenarios on the watershed with the oilpolluted areas fp = 1, 5, and 10% (Table 8). Under the scenario fp = 1% of the areas of watersheds with technogenic pollution, the total mass of PHC exported by Pur R. water, with pollutant degradation in river water taken into account, is 8.84 thous. t/year,

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Table 7. List of rivers draining the fields of oil and gas condensate⎯nonpoint pollution sources Reference river Khanzebeyakha, key water shed 1 (northern taiga)

Sedeyakha, key watershed 2 (foresttundra)

En’’yakha, key watershed 3 (tundra)

River–pollution source Kotutayakha Kamgayakha Ituyakha Khaduteyakha (Khodyteyakha) Pul’puyakha Khanayakha Khanupyyakha Kharucheiyakha Umseyakha Khasuyakha Khad’mer’’yakha Puritei Etuyakha Vorayakha Yang’’yakha Pidyayakha Khanzebeiyakha Dyagiegan Etuegan Esereyakha Taiyakha Khal’mig’’yakha Yagenetta (upper) Bol’shaya Khadyr’’yakha (upper part) Sedeyakha Nerayakha Ngarkaesetayakha Syagoikhadutte Paravykhadutte En’’yakha Sidimyutte

the mean annual concentration being 0.27 mg/L (5.4 MACfish). _ At the likely fp = 5% and ρann = 0.33 mg/L, the forecasted discharge of PHC by Pur R. water is _ 10.8 thous. t/year; at the likely fp = 10% and ρann = 0.38 mg/L, such discharge is 12.4 thous. t. The obtained values show that with a tenfold increase in the oilpolluted watershed area, PHC discharge will increase by as little as 30%. The relatively small increase in the mass of exported PHC at a considerable increase in the pol luted areas is most likely due to the specific features of

River receiving polluted waters

Deposit–pollution source Krainee The same Karamovskoe Sutorminskoe '' '' Muravlenkovskoe '' Novopurpeiskoe Verkhnepurpeiskoe '' Komsomol’skoe Barsukovskoe '' Gubkinskoe Vyngapurovskoe Tarasovskoe '' '' '' EastTarkosalinskoe WestTarkosalinskoe Yamsoveiskoe Beregovoe Yubileinoe OF2, Urengoiskoe OF1, Urengoiskoe Samburgskoe En’’yakhinskoe Pestsovoe Severourengoiskoe

Pyakupur '' '' '' '' '' '' '' Purpe '' '' '' Pyakupur '' '' Vyngapur Pyakupur Aivasedapur '' '' Pur '' '' Bol’shaya Khadyr’’yakha Evoyakha '' Esetayakha Pur '' Khadutte ''

the spatial distribution of major pollution sources. Oil fields are mostly concentrated at the head of the Pyakupur R., at a distance of many hundreds of kilo meters from Pur R. mouth. The polluted waters that flow from oil production areas are diluted consider ably by the relatively pure fresh waters of tributaries. This confirms the considerable role of the processes of river water selfpurification during the migration of oil pollution in river basins. The officially estimated PHC volume discharged by controlled point sources into water bodies and onto the drainage area of the Pur R. is 8–10 t/year [4]. A WATER RESOURCES

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small river with F ~ 1000 km2, which controls an oil field being developed, at a pollution degree fp = 1% of the watershed area, exports up to 9 t/year, a volume comparable with the organized PHC discharge all over Pur R. drainage basin; this fact confirms the signifi cant contribution of diffuse pollution sources to the total pollution of river water in the region. CONCLUSIONS The main sources of disperse pollution in the drainage basins of forest–tundra and tundra rivers of northern Western Siberia are oil spills, confined mostly to groups of oil wells, field and main oil pipe lines. Under present conditions, PHC concentrations in surface waters of the region amount to 0.3– 0.4 mg/L. This concentration cane taken as a techno genic background level. The most effective is the estimation of diffuse export of PHC from polluted nonurban watersheds (territories of oil fields) with the use of empirical rela tionships identified by processing the data of many year field observations. Empirical equations were derived to describe relationships between the area size of the polluted part of the watershed and PHC wash out module from oilpolluted areas and the unitarea discharge for taiga conditions. The study yielded rela tionships between the abovementioned characteris tics for the natural–climatic conditions of tundra and forest–tundra. Equation (1) and equation (2), adapted to permafrost conditions, were used to assess the PHC runoff from the watershed of the Pur R., whose water runoff forms in three natural–climatic zones. In the case of a small river in the tundra or forest– tundra zone with a drainage basin of ~1000 km2, in which an oil field is developed, resulting in the pollu tion of 1% of the basin area, the annual discharge of PHC with river water is in excess of 8 t. This fact con firms the considerable contribution of diffuse pollu tion sources to the overall pollution of river waters. Rivers with the runoff formation conditions similar to those of rivers that have been studied before, were chosen to evaluate PHC discharge into the large Pur R., which flows in three natural–climatic zones. For each small watershed, calculations were carried out with the use of the obtained equations, which are based on both the landscape–hydrological features of runoff formation and the extent of watershed pollution with oil. Overall, for the Pur R., it was found that, with 1% of watershed area polluted by oil, the total mass of PHC carried by river water is 8.84 thousand t/year, which is far in excess of the volume of official dis charges of oilandgasproducing and municipal facil ities in the region into water bodies in the Pur R. basin. This demonstrates the considerable contribution of diffuse pollution of water bodies to the formation of unfavorable water–ecological situation in the north ern Western Siberia. WATER RESOURCES

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Table 8. Weighted mean values of μ and PHC export volume (V) from reference watersheds of Pur R. LHPs under different scenarios of oil pollution River, LHP Key watershed 1 tundra En’’yakha R. Key watershed 2 foresttundra Sedeyakha R. Key watershed 3 northern taiga Khanzebeykha R.

µ, fp, ab, mg/(s km2) percent mg/dm3 of F spring year 0.15

0.15

0.15

1 5 10 1 5 10 1 5 10

5.79 8.42 8.47 7.97 11.61 12.60 6.01 13.41 13.76

1.40 2.04 2.07 1.76 2.56 2.74 1.70 2.46 2.49

V, t 25.00 36.64 37.15 28.76 41.65 47.90 14.47 20.31 20.63

Equations (2) and (3) were verified by comparing the calculated and measured data on the examined watersheds within five years. The divergence between the measured values of PHC export with river runoff and their estimates by the models proposed in the study never exceeded 10%, thus showing the efficiency of the procedure developed for assessing PHC export with river runoff in the northern regions of Western Siberia. The studies and calculations by the proposed models showed that PHC export with river runoff plays a significant role in the pollution of water resources of the Arctic basin. The proposed method can be used to assess PHC discharge by other rivers in Western Siberia, in whose watersheds oilandgas deposits are developed. The model can also be applied for the general analysis of the role of Siberian rivers in the oil pollution of the Arctic Ocean. REFERENCES 1. Antipov, A.N., Vakulin, K.Yu., and Geleta, I.F., Land shaftnogidrologicheskie kharakteristiki Zapadnoi Sibiri (Landscape–Hydrological Characteristics of Western Siberia), Irkutsk: IG SO RAN, 1989. 2. Atlas raschetnykh gidrologicheskikh kart i nomogramm (Prilozhenie 1 k Posobiyu po opredeleniyu raschetnykh gidrologicheskikh kharakteristik) (Atlas of Calculated Hydrological Maps and Nomograms (Appendix 1 to the Textbook for Evaluating Hydrological Characteris tics)), Leningrad: Gidrometeoizdat, 1986. 3. Babushkin, A.G., Moskovchenko, D.V., and Pikunov, S.V., Gidrokhimicheskii monitoring poverkh nostnykh vod KhantyMansiiskogo avtonomnogo okruga—Yugry (Hydrochemical Monitoring of Surface Waters in Khanty–Mansi Autonomous District— Yugra), Novosibirsk: Nauka, 2007. 4. Ezhegodnik kachestva poverkhnostnykh vod po territorii deyatel’nosti Omskogo upravleniya po gidrometeorologii i monitoringu okruzhayushchei sredy za 1994 g., 1996 g., 1997 g. (Yearbook of Surface Water Quality in the Oper

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