ISSN 0097-8078, Water Resources, 2007, Vol. 34, No. 1, pp. 75–87. © Pleiades Publishing, Ltd., 2007. Original Russian Text © O.V. Slinko, S.S. Chernyanskii, 2007, published in Vodnye Resursy, 2007, Vol. 34, No. 1, pp. 83–96.
WATER QUALITY AND PROTECTION: ENVIRONMENTAL ASPECTS
Engineering–Geological Substantiation of Water Resource Protection in the Zones of Oil and Gas Fields O. V. Slinkoa and S. S. Chernyanskiib a
Production and Research Institute for Engineering Surveying for Construction, Okruzhnoi proezd 18, Moscow, 105187 Russia b Moscow State University, Leninskie Gory, Moscow, 119992 Russia Received December 29, 2005
Abstract—The hydrochemical background and the specific features of pollution of geological environmental components by hydrocarbons and chemical components in the industrial sites of oil and gas fields is characterized for two types of natural–anthropogenic environments with different hydrogeological conditions. A methodology is proposed for comprehensive environmental–hydrogeological studies for the development of information support for the assessment of the hazard and risk for the environmental conditions, organization of complex environmental monitoring, and projecting of measures for protection of water resources. DOI: 10.1134/S0097807807010083
(0.24) basins; the amount carried in the Volga basin is somewhat less (0.06 million t) [13]. The facilities of oil and gas complex involved in the production and processing of oil have an extensive network of product pipelines used to transport oil, brines, OPs, domestic and waste waters; pumping and compressor stations; tanks with a capacity of up to 50000 m3; and sludge tanks and oil storage pits. State environmental monitoring has been established in the territories of most oil and gas fields used for production. It should be taken into account that such fields are being developed by private companies and the need to establish environmental monitoring and industrial sites of oil and gas complex requires appropriate environmental substantiation, i.e., environmental impact assessment. The environmental issues regarding the industrial sites of oil and gas complexes, the development of which began as far back as the 1960s–1970s, have not received proper attention until recently. That is why the environmental situation in many regions becomes tense because of groundwater pollution.
INTRODUCTION Oil and gas complex (OGC) is known to be a major source of environmental pollution. The pollution of the top part of the geological section by hydrocarbon fluids degrades the habitat; adversely impacts the population health; and represents the most acute environmental problem, which is a social priority. The State Network for pipeline transport of oil and gas embraces 35% of the Russian territory inhabited by up to 60% of the country’s population. The length of the main pipelines totals 207000 km. More than half of the main oil and gas pipelines now in operation were designed for 20–25 years of service; therefore, 80–90% of their service time has elapsed. The territory of Russia contains 1600 tank farms and oil product (OP) storages, about 30 oil-processing plants, and more than 200000 active production wells. About 60000 OP leakage events of different scales from pipelines and tanks are recorded each year in RF. Oil and OP losses due to emergencies in Russia vary from 17 to 20 million tons per year. According to statistical data, up to 800 pipeline breaks take place in Russia every year. Any such accident is an environmental catastrophe. For example, 13604 accidents occurred in 1989–1996 at the facilities of the oil and gas complex in the territory of the Khanty–Mansi Autonomous Okrug, and the total mass of released pollutants amounted to 47000 t [6]. The total volume of largescale on-land oil spills in Russia during only 2 months of 1993 exceeded 26000 t [2]. Mass fluxes of OPs carried out by rivers from Russia were estimated at about 0.82 million t per year. The largest amounts of OPs are discharged by the rivers of the Ob (0.14) and Enisei
CHARACTERISTICS OF THE HYDROCHEMICAL BACKGROUND IN THE AREAS OF FIELDS AND INDUSTRIAL SITES Fresh groundwater in the regions of the near-Perm part of Kama River basin, Udmurtia, Tatarstan, and middle-Volga occur in the upper part of the Permian deposits of the Tatarian and Kazan stages with a thickness of up to 100–150 m. Groundwater in the zone not subject to anthropogenic impact has hydrocarbonate magnesium–calcium composition with a salinity 75
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of 0.4–0.6 g/l. Oil deposits are confined mostly to terrigenous strata of Carboniferous and Devonian that occur at depths of down to 2000 m. The accompanying chloride calcium–sodium brines have a high salinity (up to 350 g/l) and metamorphization (rNa/rCl 0.2–0.6) and a negative Eh (up to –300 mV); they are enriched with Br (up to 2.2 g/l, Cl/Br 70–200), K (up to 2.4 g/l), I (up to 30 mg/l), Sr (up to 800 mg/l), Li (14 mg/l) and other microelements. Edge and boundary waterflooding of oil reservoirs has been in wide use since the early 1960s for increasing the formation pressure. The waters used for this purpose include both freshwaters taken from surface watercourses and wastewaters that form at oil treatment plants after oil dehydration and desalting. Wastewaters contain solids (up to 300 mg/dm3), OPs (up to 150 mg/dm3), hydrogen sulfide (up to 15 mg/dm3), diethyleneglycol (up to 1–7 g/dm3), methanol (0.3– 50 g/dm3), dissolved oxygen (up to 0.5 mg/dm3), nitrogenous compounds (0.02–1.2 mg/dm3), toxic microelements F (4–36) > Sr, Ba (0.2–4) > Al, Zn (0.1–2) > Li, Cr, Cu, Mn, Ni (0.01–0.6) > Pb, Hg, Cd, Co (0.002–0.03) mg/dm3. Radioisotopes (radium and thorium) were found to occur in concentrations of 100–1500 nCi/dm3, which are higher than those in formation waters. Most exploration wells drilled during the exploration of the oil field territories in 1960–1980 were left without backfill [10]. Their boreholes connect waterbearing complexes of fresh and salt waters. The direction and volumes of leakage in this case are determined by the head difference in the adjacent aquifers. No field data on interstratal water exchange via boreholes are available. Such processes are most intense when a stratigraphic test well is situated in the zone of influence of the depression cone of a production water intake well. Groundwater pollution in oil and gas fields by OPs and chlorides can also take place when wastewaters are pumped down into oil reservoirs through untight injection wells. The area of fresh groundwater pollution in individual parts of oil fields reach 500 km2. For example, in the Republic of Tatarstan, the salinization of groundwater in the Kazan deposits, which is the main source of municipal water supply in the region, took place in the area of 67000 km2. Several vast zones of multicomponent pollution of groundwater also formed in Perm province as a result of column untightness of production and injection wells and the functioning of oil-processing plants; this pollution had a serious adverse impact on the environment and water economy [1, 9]. According to studies of the authors of this paper, technogenic aquifers or technogenic groundwater with sporadic occurrence formed in industrial sites in the aeration zone soils. The soils and groundwaters are universally polluted by OPs and chlorides. OP concentrations in heavy clay loams and clays at depths of up to 2.5 m reach 33000 mg/kg. The salinity of phreatic
water at depths of 1–9 m reaches 3–20 g/l. Salt groundwater tongues with a length of up to 1.5 km were found to exist at depths down to 70–80 m in red sandstones and aleurolites with limestone interlayers. Atomic emission analysis of water made at some sites yielded the following concentrations: Na up to 65000, Mg up to 55000, B 61–120, Si up to 12060, P up to 120, S up to 5000, Sr up to 1500, and Ba up to 80 µg/l. In some sites, pollutants have been carried out beyond field boundaries. The principal hydrogeochemical tendency consists in a gradual disappearance of the regional trend in the components of natural origin – 2– ( HCO 3 and, partially, SO 4 ions) and the appearance of local concentration anomalies of Cl–, Na+, ë‡2+, and Mg2+ typical of oil-field brines. Data of monitoring in Nizhnevartovskii district, Khanty-Mansi Autonomous Okrug (Samotlor and other fields) show the Ob and Vakha waters to have a solid residue of 0.07 to 0.62 g/l and to belong to ultrafresh and fresh waters [4, 6]. In terms of chemical composi– tion, Ob water is sulfate–hydrocarbonate ( HCO 3 < 2–
80%, SO 4 > 12%), calcium–magnesium (45% of Ca2+ and 55% of Mg2+). The composition of Vakh water is simpler. In the anion group, the role of sulfates and – 2– chlorides is higher ( HCO 3 < 55%, SO 4 varies from 30 to 35%, and Cl– varies from 10 to 15%), whereas Na dominates in the cation group (up to 50%); the concentrations of Ca2+ and Mg2+ are approximately the same (27 and 23%, respectively). Nevertheless, the concentrations of major macroions in Ob and Vakh waters are – relatively low and amount to 18–98 mg/l for HCO 3 , 2–
12–24 for SO 4 , 4–49 for Cl–, up to 19 for Na, 8–20 for Ca2+, and 4–18 mg/l for Mg2+. The largest values of solid residue were recorded in the surface waters of the Egan and Samotlor areas. They contain mostly chloride, calcium–magnesium–sodium or sodium waters with a solid residue of 0.3–1.1 g/l. The absolute values of major macroions vary within 150–514 mg/l for Cl–, 90–622 mg/l for Na and K, and 5–16 and 12–50 mg/l for Ca2+ and Mg2+, respectively. In terms of total hardness, the surface waters are, as a rule, very soft and soft (the hardness does not exceed 2.5 mg-equiv./l). In individual cases (the Vatinskii Egan River), water hardness exceeds 3 mg/l. The physical characteristics, such as color index and turbidity, are as a rule relatively high (the color index is 59–350 grad; the turbidity is 1.1– 54.2 mg/l). The highest values of permanganate (biochemical oxygen demand or BOD) and bichromate (chemical oxygen demand or COD) oxidability were recorded in the surface water of Samotlor area. The value of BOD in most samples varies within the limits of 10.1–39.6 mg/l and COD varies from 43.1 to 199.5 mg/l. In other areas, WATER RESOURCES
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these characteristics vary, as a rule, from 4.1 to 8.6 and from 3.2 to 18.4 mg/l, respectively. The values of pH vary from 6.0 to 7.7, thus allowing the water to be classified as neutral. The concentrations of ingredients that are the geochemical characteristics + of surface water quality ( NH 4 , Fe2+, OPs) vary from fractions to a few mg/l. The concentration of Fetot is relatively high and varies from 0.47 to 15.9 mg/l. OPs were met in surface waters in analytically significant concentrations (0.05–4 mg/l), and their concentration in 3% of samples (0.1–4.1 mg/l) exceeds the maximum admissible concentrations (MAC). OP concentration in rivers features seasonal variations. The majority of these products enter water bodies in spring with unorganized runoff from catchments. However, this is not necessarily accompanied by maximum concentrations of OPs in river water. The spring flood period shifts to June–August because of the climatic peculiarities of the region. The relatively low concentration of OPs in rivers in spring is due to maximum water flow values. Thus, the concentration of OPs in the Ob River at Belogor’e Village in June 1966 amounted to 4 MAC at water flow of 24800 m3/s, while in June 1998, this concentration was 0.2 MAC at water flow of 25500 m3/s. In the summer–autumn lowwater period, OP concentrations in water increase. For example, in November 1998, OP concentration in the Vakh River at Vakhovsk Village gage exceeded the MAC by a factor of 160 at water flow of 315 m3/s [4]. In the freeze-up period (December–May), at minimal water flow, the concentration of OPs increases notwithstanding the absence of external impacts. This may be due to the secondary pollution caused by OP supply from bottom sediments. In addition to emergency oil spills, OPs washed out from oil-polluted areas can be a source of OPs entering into rivers. In 2000, the soil at 40% of multiple well platforms and adjacent areas was heavily polluted by mazut. Slurry ponds not subject to reclamation contain about 100000 m3 of oil. Potential sources of pollution are also 1100 underwater pipeline river crossings. The high occurrence of phreatic water along with the high hydraulic conductivity of loose damp sand (with a thickness of up to 4 m) almost in all industrial sites of oil and gas complex in Western Siberia examined by the authors, as well as the washout water regime facilitate the frontal downward migration of pollutants and are unfavorable for their retention in the soil with the formation of primary polluted zones. This may account for the fact that no infiltration bodies of oil and OPs were found in our wells. The higher water abundance in the soils of industrial sites facilitates the occurrence of reduction (gley) processes in these soils, manifestations of which were recorded universally in the form of newly formed ferrous and ferric iron in soils with cold colors (bluish and WATER RESOURCES
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greenish). Under such conditions, the processes of natural biochemical degradation of technogenic hydrocarbons become much slower, and the protective “selective–filtering” function of soils and grounds with respect to groundwater becomes weaker. Salinity estimates in hydrogeochemical samples of groundwater in the sites showed the groundwater at depths down to 4.5–7.0 m to be virtually unpolluted. Groundwater salinity corresponds to the natural background level. Pollution by chemical components (but not OPs) was recorded at water salinity of >0.2 g/l. OP concentrations in phreatic waters vary from 0.1 to 200 mg/l. Mass-spectral and atomic-emission analyses of phreatic and hydraulically related to them surface waters at the sites showed the following concentrations of elements: 0.0017–0.014 mg/l for Li, 0.0023–0.15 for B, 0.0027–6.8 for Al, 4.9–15 for Si, 0.005–21 for P, 0.64– 1.2 for S, 0.44–2.4 for Mn, 2.2–55 for Fe, <0.03–0.1 for Br, 0.12–0.28 for Sr, 0.037–0.25 for Ba, and up to 0.0018 mg/l for U. Water separated by centrifugation from water-saturated oil-polluted (>40 mg/l) soil layers at depths of 2– 3 m features higher levels of microelement pollution. Against the background of conventional predominance of elements such as Fe, Mn, Si, Ca, and K, the analyses revealed significant amounts of some elements that are not characteristic of phreatic waters in this area but are conventional companion elements of oil. These elements include non-metals S, Cl, and As; heavy metals V, Cr, Ni, Cu; etc. Although the concentrations of these elements do not exceed the respective MACs, the mere presence of these elements in the amounts exceeding the lower detection limit suggests a significant technogenic transformation of the chemical composition of phreatic waters in the sites (x-ray–fluorescent analysis yielded the concentrations of 3.01 mg/l for Al, 0.001 for Ni, 2.68 for Si, 0.001 for Cu, 0.027 for S, 0.002 for Zn, 0.003 for V, and 0.001 mg/l for Sr). SPECIFIC FEATURES OF SOIL AND GROUNDWATER POLLUTION BY HYDROCARBONS The diversity of the forms of occurrence of oil and its products in the geological environment is due, first, to the wide range of the physicochemical characteristics of OP; second, to the diversity of hydrophysical and chemical properties of the soils containing the hydrocarbons; and, third, to the diversity of conditions of pollutants’ entering to the geological environment (surface spills, leakages from subsurface communications, infiltration of polluted phreatic and surface waters, etc.). The primary source of OP pollution is commonly an infiltration body, the evolution of which, as well as the processes of physicochemical and biochemical transformation of OP, is controlled by the properties of host
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soils and grounds. Migration of liquid OP and water–oil emulsions in the soil mass is accompanied by pollution of the gas phase of soils and partial absorption of hydrocarbons by fine soil fractions (in essence, this is the pollution of solid phase). Phreatic waters, on the one hand, serve as a barrier on the way of vertical migration of OP and, on the other hand, are the main factor of their lateral spreading. The phenomenon of OP migration in the capillary fringe of phreatic waters, in particular, with the formation of “floating lenses,” is widely known and has been repeatedly described in the literature [1, 3, 7–9, 12]. In all such cases, secondary hydrocarbon anomalies form in the gas, liquid, and solid phases of soils above polluted aquifers. The revealing and studying of the material composition of these anomalies allows one to assess the extent of geological environmental pollution and detect subsurface fluxes of pollutants. Several approaches to the systematization of the forms of geological environmental pollution by oil hydrocarbons are known. Specifically, in the case of liquid hydrocarbons, it is supposed, in the most general form, to distinguish the capillary–disperse and free (liquid–droplet) states [9]. In the case of phreatic water level rise, free liquid hydrocarbons can pass into the socalled trapped state [2]. Gaseous and solid phases are distinguished for hydrocarbons in general in addition to the liquid phase. The simplest variant of such systematization can be reduced to the isolation of five main forms of hydrocarbons in the geological environment [8]: independent mobile liquid phase, which does not mix with water (floating lenses or zones of complete saturation of soils with oil products); liquid phase in the state of residual saturation in the aeration zone; gaseous phase; absorbed hydrocarbons; and dissolved hydrocarbons. More detailed approach to this problem [3, 5] required separate analysis of the forms of hydrocarbon pollution of soils, aeration zone grounds, and phreatic waters. The forms considered in this case included: liquid−droplet forms of OP, including floating and suspended lenses and films, which behave in grounds as a single fluid medium; water–emulsion forms in the contact zone of phreatic waters and an OP lens (film); less mobile “droplet–film cap” of OP in the aeration zone; OP dissolved in water; a “gas cap” of hydrocarbons in the aeration zone; hydrocarbons absorbed by the solid phase of grounds; hydrocarbons that have passed from the droplet–liquid or droplet−film form into the solid phase with the formation of grounds filled with solidified OP. These forms of OP feature different degree of engineering and environmental hazard. The predominance of a certain form is determined by the character of pollution and the conditions of its occurrence. Let us use the data of long-term comprehensive engineering-environmental studies to consider the radically different
examples of heavy hydrocarbon pollution of phreatic waters and grounds of a low-thickness high-permeability and a thick low-permeability aeration zone with a complex structure. In the former case, in the middle taiga zone of RF (Fig. 1), the sources of primary pollution were located on the land surface. The OP infiltration bodies confined to them were compact and, migrating through the sand bed in the technogenic fill-up ground, they rapidly reach groundwater table and started moving in the lateral direction in the capillary fringe. Large-area zones of film-type spreading of droplet−liquid, water−emulsified, and dissolved OP form downstream from the sources in the direction of phreatic water flow. These zones have formed the major portion of the occurrence areas of polluted soils. Their pollution is of a secondary character and demonstrates itself in the presence of liquid hydrocarbons in the lower part of the aeration zone (above phreatic waters and in the zone of within-year and long-term variations in their level) and pollution of the gaseous phase of grounds up to the land surface. Depending on the concentrations of methane and carbon dioxide, the grounds that have been subject to secondary pollution from groundwater become a gas– geochemical or fire–explosion hazard. The latter grounds are confined to natural or artificial depressions in relief and the sites of phreatic water discharge into drainage network. The molecular composition of hydrocarbon gases and the concentrations of mobile components (e.g., hydrogen sulfide) allow the closeness to the source and/or the age of pollution to be estimated. Thus, chronic local pollution of loose damp sand with a thickness of up to 4 m from stationary sources under the conditions of West Siberian taiga results in the formation of a relatively stable system of technogenic fluxes confined to the topmost horizon of phreatic water and a low-thickness zone of aeration. These fluxes feature a distinct radial (vertical) and lateral (subhorizontal) geochemical zonality. This zonality is most contrast in the gas phase: secondary anomalies are mostly methane-related, whereas the share of heavier hydrocarbons, hydrogen sulfide, and some other gases increases. When phreatic water table lies near the land surface (up to 3 m), the subsoil accumulation of methane becomes an explosion hazard. At the same time, the soils at the adjacent (up to 100 m) well-drained areas of the site may remain unpolluted or slightly polluted. In some cases, oil was found to penetrate into the second (from the surface) aquifer, though the migration of hydrocarbons in this aquifer does not have so strong effect on the gas field in the surface soil layer. In addition to methane and other hydrocarbon gases, universal companion components of oil pollution in these sites were heavy metals and polycyclic aromatic hydrocarbons (PAH), the most hazardous among which is benz(a)pyrene. WATER RESOURCES
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79 1 2 3 4
1
(b)
2 3 4 5
(c) 1
6
2
7
3
8
4
9
5 (d)
1 2
Fig. 1. Characteristics of geological environmental pollution by OP in the case of low-thickness, high-permeability aeration zone. (a) Map of geological environmental pollution, which shows the areas where individual forms of pollutants predominate: (1) infiltration bodies consisting of liquid and absorbed hydrocarbons; (2) accumulations of droplet–film hydrocarbons in the aeration zone and sporadic film-type forms; (3) zone of continuous film-type spreading of hydrocarbons in the droplet−liquid and accompanying forms; (4) zone of most likely occurrence of low-thickness floating lenses of liquid hydrocarbons. (b) Map of hydrocarbon gas field of aeration zone ground: concentration of hydrocarbon gases in the near-surface ground horizons, mg/m3. (1) < 1000; (2) 1000−5000; (3) 5000–10000; (4) 10 000–20000; (5) >20000. (c) Hydrogeological map. (1–7) Depth to the top aquifer (<2, 2−3, 3−4, 4–5, 5–6, 6–7, and >7 m, respectively); (8) zones of most active groundwater leakage into deeper aquifers (based on data of geophysical studies and auger drilling); (9) groundwater flows. (d) General layout. (1) Pollution sources; (2) observational points for geological environment. WATER RESOURCES
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(‡)
1 5
2
3
4 6
4
(b) 5 5 7 9
7
11
7 9
11
9
5 5 5
3
7
7
9
200 m Fig. 2. Zoning of the territory of a petroleum refinery in terms of groundwater recharge, occurrence, pollution, and self-purification. (a) zones 1–6 (table), (7) surface waters; (b) thickness of the aeration zone, m.
When the aeration zone is composed of loam–clay deposits with lenses and interlayers of sands and loamy sands, groundwater have sporadic occurrence. Aquifers occur at large depths (up to 20 m). Long-term detailed studies of the behavior of hydrocarbons in different phases (gaseous, liquid, and solid) were conducted by the authors at one of such sites in the steppe zone of RF (Figs. 2 and 3, table). This situation corresponds to the most complicated case of oil pollution, which is difficult to rehabilitate. The sources of pollution are located both on the land surface (tanks, pumping stations, block valve stations, process facilities, etc.) and under ground (oil-product pipelines). The former sources supply both heavy and light OP to the geological environment, while the latter sources supply mostly light OP. As a result, the soil strata becomes stratified in terms of the quantitative and, especially, qualitative composition of pollutants (Fig. 2b).
The infiltration bodies of OP have much greater horizontal dimensions than those in the case of a high-permeability aeration zone. Notwithstanding the higher general protection of groundwater against pollution, the problem in this case is due to the fact that the migration paths of pollutants in the multilayer aeration zone are difficult to predict. The grounds in the upper part of the section act as a chromatographic column and retain heavy hydrocarbon fractions, whereas more mobile components migrate down to groundwater table and form a zone of film-type spreading; when the lithological conditions are favorable, floating and suspended lenses can form. These hydrocarbon accumulations release volatile fractions, thus saturating the subsurface atmosphere by hydrocarbons and the accompanying gases (hydrogen sulfide, secondary carbon dioxide, etc.). Heavy metals commonly accompanying oil (V, Zn, Cr, etc.), PAH (including benz(a)pyrene, the most WATER RESOURCES
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81 (‡)
1
2
3
4
5
(b)
20 m 1
2
3
4
5
Fig. 3. Distribution of hydrocarbons in one of the areas where the geological environment is being intensely polluted by OP. Concentrations of hydrocarbon gases, mg/m3. (a) In the top (0–1 m) horizon of the low-permeability aeration zone. (1) 0–100; (2) 100– 1000; (3) 1000–5000; (4) 5000–10000; (5) >10000; (b) in the lower (3–6 m) horizon of the low-permeability aeration zone (1) 0−1000; (2) 1000–5000; (3) 5000–10000; (4) 10000–20000; (5) >20000.
hazardous among them), and other substances belonging to the group of stable organic pollutants are actively absorbed by the solid phase of soils that are in contact with OP and accumulate in this phase. The proportion of the components of polluting flux that are extrinsic for the geological environment, i.e., unsaturated hydrocarbons, PAH, and others, increases with the extent of oil processing. In this context, when developing the engineering– hydrogeological substantiation of measures aimed to protect water resources, one should take into account the barrier (fractionating) function of the soil and ground in the zone of aeration with respect to a wide range of hydrocarbonic and accompanying components of oil (which are, as a rule, of much greater hazard); the possibility of secondary, either immediate or gradual, mobilization of pollutants retained by soil caused by changes in redox, acid-base, and other conditions; and secondary pollution of the lower ground layers by WATER RESOURCES
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mobile OP components that migrate in aquifers. The aquifers are in an analogous position, but with respect to the surface waters that are fed by them. METHODOLOGY OF COMPREHENSIVE ENVIRONMENTAL–HYDROGEOLOGICAL STUDIES AT OGC FACILITIES AIMED TO ASSESS THE ENVIRONMENTAL IMPACT AND ORGANIZE DETAILED ENVIRONMENTAL MONITORING Regime observations are not organized at the sites. The layout of observational points during the regional monitoring in the field areas, as well as the composition and frequency of observations, fails to provide adequate estimation of changes in the components of the geological environment at industrial sites. No cartographic base at a scale of 1 : 50000 and larger is available. The hydraulic and migration characteristics of water-bearing rocks and grounds of the aeration zone
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Floodplain–terrace complex of a small river with alluvial loams, loamy sands, and sands
Slope with landslide accumulations
5
6
Erosion slopes composed of deluvial loams
4
2.5–4
2–8
>8–10
3
3–4
3–10
Slightly tilted surface of Khazar–Kvalyn terrace complex of a large river valley composed of alluvial– deluvial loams with interlayers and lenses of loamy sands and sands
Laterally persistent aquifer hydrologically interacting with river waters
Groundwater with sporadic occurrence; it discharges via low- and medium-yield springs
Infiltration recharge. Groundwater of sporadic occurrence with high water table and the predominance of the vertical component of migration
Laterally persistent aquifer with artificial recharge by leakages from water-bearing pipelines
Intense secondary Weak pollution of aquifers and grounds of the capillary fringe zone
Sporadic discharge Moderate of polluted groundwater into water bodies or streams
The same with areas Moderate of renewable intense High pollution by light and heavy OP
Moderately favorable
Unfavorable
Extremely unfavorable
Unfavorable
The construction of linear drainage and local pumping out of polluted waters is promising
Hydrodynamic and other methods are inefficient
Hydrodynamic methods are of limited efficiency. It is desirable to combine them with mechanical, electric-osmosis, physicochemical (diffusiophoresis), and biological methods
Groundwater Groundwater protection Perspectives of artificial self-purificaagainst processing of groundwater tion conditions pollution
Old intense pollu- Weak tion of the aeration zone by heavy OP. Film-type spreading of OP over the aquifer surface
Characteristics Aeration zone Geological environof groundwater recharge thickness, m mental pollution and occurrence
2
1
Zone
Topography and lithogenic basis
Zoning of the territory of a petroleum refinery in terms of groundwater recharge, occurrence, pollution, and self-purification
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have not been determined. There is no network of special test grounds for studying the migration processes of OP and brines in the grounds of the aeration zone and in the top aquifers. No studies are being conducted to provide data for predicting changes in the hydrogeological conditions; to assess the environmental hazard at the areas of the field subject to high technogenic load; or to comprehensively substantiate nature protection measures. The available geohydrological and engineering– geological data on the upper part of the section (down to the depth of 100 m) for the areas of oil and gas fields and individual industrial sites is inadequate, since no maps with such content at a scale of 1 : 2000–1 : 5000 for the sites or 1 : 25000–1 : 50 000 for the fields were compiled during the exploration and engineering surveys for construction. Environmental protection was not considered an important issue in this period. Possible adverse environmental consequences associated with oil production and processing were not assessed by designers. The focus was on the economic aspects, i.e., the enhancement of oil production and reservoir recovery at minimal expenses. The term engineering– environmental surveying was not included in the normative documents regulating the engineering surveys of construction. The geological environmental pollution at all OGC facilities now in operation is an incontrovertible fact. The environmental hazard assessment is commonly based, first of all, on the damage due to the environmental impacts that are of a bursting (catastrophic) character and cause recognizable and specific results that are clearly attributable to them. Nowadays we face longterm effects of diverse pollutants the results of which are of a probabilistic character. Such cases of so-called “latent” pollution of the geological environmental components, the results of which can suddenly emerge after long periods of facility operation, can be identified only by special studies or in the course of regime observations. Therefore, their consequences are most hazardous and can cause emergencies. Scientifically substantiated estimates of the environmental hazard caused by pollution of the geological environment and, primarily, groundwater, which serve as a source of domestic water supply to the population inhabiting the polluted areas, should be based on mapping the polluted areas with the use of a set of hydrogeological, gas–geochemical, and geophysical methods applied at a single time scale in the regime of monitoring not only at OGC industrial sites but also within their hydrodynamic boundaries. These methods should be regarded as a basis for the information support of a project of detail monitoring, the construction of groundwater flow models with the aim to predict changes in the hydrogeological conditions, and the development of nature protection measures. WATER RESOURCES
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Environmental–hydrogeological mapping is a method for studying subsurface hydrosphere, which allows the development of spatial image–sign (cartographic) models enabling the solution of theoretical and practical problems, such as the identification of regularities in changes in subsurface hydrosphere under the effect of technogenic factors; the assessment of the hazard and risk of natural–technogenic processes; the protection against underflooding and other processes; the development of nature protection measures; etc. based on studying the natural conditions and technogenic factors at the regional and local levels, the construction of a set of maps: regional–hierarchic and typological zoning, hydrodynamical and hydrogeochemical characteristics, technogenic factors, etc. The environmental situation at an industrial site in operation should be examined with due consideration of the group of interrelated factors: the specific features of the technogenic and natural landscapes; variations in the climate factors; the composition, heterogeneity, and thickness of the aeration zone grounds and their hydrophysical properties; specific hydrogeological conditions (the occurrence of top aquifers, hydraulic permeability of host rock, the character of interaction of phreatic waters with underlying aquifers and surface waters, etc.); the mechanism of OP transport (advection, diffusion); the interaction between phreatic and surface waters. The studies aimed to assess the geological environmental pollution and map the areas of pollution in groundwater and soils should be based on comprehensive approaches involving both conventional methods of hydrogeological studies along with gas–geochemical methods and shallow-geophysics methods [10]. First stage. The studies are conducted at OGC industrial sites in operation at scales of 1 : 1000– 1 : 5000. The main objectives of the study include the identification of specific engineering–geological and hydrogeological conditions at the site and its external hydrodynamic boundaries; the determination of electric parameters of grounds for the choice of methods for geophysical examination; the choice of priority pollutants and the assessment of pollution in geological environmental components: soils, grounds, and subsurface and surface waters; the identification of possible migration paths of polluted groundwater; preliminary estimates of the environmental hazard and the risk of deterioration of the environmental situation at the facility under regular regime and in emergencies; the assessment of possible development of hazardous natural– technogenic processes and their adverse consequences. The order of implementation of works: the examination of the technogenic development of the site (the density and types of buildings; specific features of the process, storage, and transportation of OP; the layout of oil and sludge storage pits; tanks for storage of OP, wastewaters, and brines; the layout of product pipelines
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and water-bearing communications; the volumes of regular process wastewaters; data on emergency leaks of oil, OP, and wastewater); collection and analysis of geological, hydrogeological, and engineering–geological material on the industrial site; reconnaissance hydrogeological surveying of the sites and adjacent areas within the external hydrodynamic boundaries of facilities at scales of 1 : 1000–1 : 10000 with preliminary or simultaneous application of geophysical and gas–geochemical methods; laboratory studies of pollution of soils and surface and subsurface waters by using samples collected during reconnaissance. In the course of studies, preliminary estimation of the geological environmental pollution by OP and chloride will be carried out by using a set of field instruments, including gas analyzers (e.g., domestic PGA or Kometa devices), electrical exploration complex (ERA-M, EIS-2K), instruments for measuring pH and salinity of water, aqueous suspensions, etc. Second stage. A set of detailed environmental– hydrogeological studies is carried out. The objectives of the studies include the mapping of polluted areas of ground and subsurface and surface waters at scales of 1 : 500–1 : 5000 within the external hydrodynamic boundaries of the site; the studying of the migration paths of groundwater, polluted by OP and brines; the development of engineering–hydrogeological substantiation for the project of the first stage of integrated environmental monitoring. The problems to be solved during individual types of studies include the following. Gas–Geochemical Studies Qualitative and quantitative diagnostics of the chemical composition of gaseous phase in the near-surface horizons of grounds in industrial sites by using mass borehole and emission gas–geochemical surveying with the measurement of concentrations of methane, total hydrocarbon gases, hydrogen sulfide, and, when necessary, other gases. Diagnostics of hydrocarbon component (from methane to hexane, including unsaturated compounds) of ground air at depths of 2–10 m by using auger drilling, sampling, and chromatographic analysis of free and absorbed gas of the ground strata. Assessment of the pollution extent of ground strata (down to 10 m) by OP and surfactants via diagnostics of the concentration, qualitative composition, and properties of these substances in ground samples. Geochemical analysis of the obtained data with the aim to identify the sources of OP in soils and the directions of their flows. Geophysical studies (dipole induction profiling (DIP), natural electric field method (NF), EP and VES methods).
Gas–electric mapping of soils in the zone of aeration with the aim to identify the areas polluted by OP and leaks from water-bearing pipelines. Assessment of the tightness of tanks and possible seepage from sludge tanks. Detection of leakage points from oil pipelines, product pipelines, water-bearing pipelines, and the zones of seepage through earth dams. Determination of the structure of water flow in the aeration zone. Determination of the structure of groundwater flow in the top aquifers and identification of discharge zones of groundwater polluted by OP and brines outside the industrial sites. Control of the stability of buildings and structures with a higher criticality rating under a hazard of emergence or development of dangerous natural–technogenic processes (landslides, underflooding, internal erosion, and subsidence) in the site. Hydrogeological Studies Identification of the geomorphological and hydrogeological features of the site that determine the main directions of surface runoff and groundwater flow. Mapping of the pollution areas of soils and groundwater; identification of pollution sources. Studies of the state and regime (level, temperature, and hydrochemical regimes) of phreatic waters and groundwater in the underlying aquifer. If there are surface water bodies or watercourses at the boundaries of the site and polluted surface or subsurface waters can discharge into them, integrated observations (water levels and flow rates, chemical composition in terms of priority pollutants, and hydrodynamic zones of discharge of polluted groundwater) will be organized at hydrometric stations. The result of the second-stage work is the information support for the studies to be carried out at the third stage. The information will contain a set of maps: gas– geochemical surveys (concentrations of methane, total hydrocarbon gases, hydrogen sulfide, the composition of hydrocarbon gases assessed by gas chromatography for different horizons of the ground strata); luminescence–bituminological surveying (the concentrations and types of OP in the grounds of the site at different depths; pollution of grounds by benz(a)pyrene and other PAH); geophysical studies (map of ground electric resistance and map of water flow structure in the aeration zone); tentative groundwater flow scheme of the site. The maps are supplemented by characteristics and parameters characterizing the natural–technogenic situation. The main methods of hydrogeological studies at the second phase are analysis of materials collected during state geological, hydrogeological, engineering–geologWATER RESOURCES
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ical, and integrated surveys at scales of 1 : 50000– 1 : 200000; analysis of materials of previous engineering surveys for the construction and infrastructure development of oil fields; analysis of water surveys for water supply to the sites and special studies at the deposit for the identification of pollution causes of surface and subsurface waters; analysis of the results of hydrochemical control of surface and subsurface waters at deposits by using departmental regional observational monitoring network (no observational points are available at the sites); drilling of hydrogeological wells and conducting of pumping tests (well locations are controlled by geophysical and gas– geochemical methods); sampling of subsurface and surface waters, soils, and grounds; hydrogeological and hydrochemical monitoring, i.e., observations of subsurface and surface waters, hydrogeological observations are supplemented and controlled by geophysical and gas–geochemical methods in a single time scale; laboratory studies of grounds and surface and subsurface waters. The studies carried out during the second phase make it possible to recognize the formation of new technogenic aquifers in the grounds of the aeration zone; identify linear zones (“stream” flows) with more intense flow of fresh and saline groundwater (these linear zones are from 1.5 to 10–12 m in width) in the general flow of phreatic waters in the top aquifer or in technogenic waters of sporadic occurrence; establish the priority pollutants of the components of geological environment; delineate the pollution zones of grounds and groundwater in the horizontal and vertical directions; identify the zones where water polluted by OP and brines enters into the channels of creeks and rivers; identify the zones of ascending flow of polluted water through “windows” in the upper aquiclude into the next to top aquifers, the groundwater in which is a major source of domestic water supply. The result will be the compilation of a set of maps at scales of 1 : 1000–1 : 10 000, which characterize the natural–technogenic situation at the site and the areas of polluted grounds and groundwater. The maps enable the development of a set of measures for the rehabilitation of polluted areas at the site and interception of polluted groundwater at the boundary of the site. Third stage. The studies will be carried out at scales of 1 : 25000–1 : 200000 in the areas adjacent to the facility within its outer hydrodynamic boundaries. The main objectives of the study include the identification of the main hydrogeological features of the area; analysis of materials collected by drilling of structural and prospect wells for oil and their elimination; analysis of data of stationary observations of the regime of subsurface and surface waters at the observational stations of Roshydromet and the Ministry of Natural Resources; study of the hydrochemical background and the pollution character of geological environmental components WATER RESOURCES
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(soils, grounds, and surface and subsurface waters); the assessment of the hydraulic properties of the grounds in the aeration zone and the water-bearing rocks of the top aquifer at test grounds; the assessment of the main inflow and outflow components of water balance of the site; the examination of migration of OP, brines, and industrial wastewaters and changes in their concentrations in the grounds of the aeration zone and groundwater of the top aquifer with the aim to choose the most efficient methods for removal of OP from grounds and groundwater (when needed, migration characteristics of the water-bearing rocks and grounds of the aeration zone are determined); the organization of the first stage of stationary observations for integrated environmental monitoring at a reference profile and test grounds; the assessment of the development of hazardous natural– technogenic processes (waterlogging, underflooding, landslides, internal erosion, and ground subsidence) as a result of technogenic development of the industrial site areas; the preparation of the project of integrated monitoring in the territory of the field (group of fields) with the aim to control geological environmental pollution, assess the hazards and risk of further deterioration of the environmental situation; the choice of priority areas that require rehabilitation of polluted territories and engineering protection of buildings and structures against hazardous natural–technogenic processes; the substantiation of projects of nature-protection measures and engineering protection of territories, buildings, and structures against hazardous natural–technogenic processes. Methods of studies include analysis of the operation experience of groundwater and surface-water intakes; reconnaissance hydrogeological surveys of the territory at scales of 1 : 25000–1 : 100 000 with hydrochemical sampling of subsurface and surface waters; remote sensing methods (space and aerial photography); integrated landscape–hydrogeological survey at scales of 1 : 25000–1 : 100 000 (in the case of critical environmental situation) with the appropriate volumes of drilling works and pumping tests (pumping out, water level, and injection tests) at reference profiles; geophysical surveys (electric profiling, VES, EP, and resistivity metering) in reference areas; gas–geochemical surveys in reference areas; assessment of the role of technogenic factors in the geological environmental pollution; mathematical modeling methods for the prediction of changes in the hydrogeological conditions and the assessment of the efficiency of nature protection measures based on regional and local models of natural– engineering systems. Particular attention should be paid to the analysis of measures aimed to control the quality of the annular space cementing in production oil wells and injection wells. A series of hydrogeological and migration studies for the examination of the pollutant transport mechanisms in the grounds of the aeration zone and waterbearing systems will be carried out, if required, in key
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zones (in accordance with a special program agreed upon with the appropriate departments). The key areas can be industrial sites; well cluster areas; areas polluted by oil, OP, and brines as a result of large-scale accidents at pipelines and reservoirs; areas of surface-water or groundwater intakes; populated localities; agricultural fields. The result of these works will be the compilation of a set of maps at scales of 1 : 25000–1 : 100000 to characterize the natural–technogenic situation. The information content of these maps will enable the substantiation of project of nature protection and water management measures, as well as engineering protection of territories against hazardous natural–technogenic processes.
face waters has not exceeded the MAC or their actual pollution has exceeded the admissible level. Accordingly, the objective of studies in the first case is to develop the functions of protection, i.e., to substantiate the choice of the main factors controlling the environmental pollution and water protection measures and the organization of environmental monitoring; integrated mapping of polluted areas and their zoning in terms of the extent and hazard of pollution. In the second case, the objective is to develop functions for the prevention of hazardous impact of pollution on the population and its habitat, i.e., the assessment of the economic damage and environmental hazard, comprehensive substantiation of protection measures, limitations on engineering activity, implementation of additional surveys, and prediction of pollution with allowance made for the measures planned to be taken.
CONCLUSIONS The methodology developed in this study enables the engineering–hydrogeological substantiation of water resources protection in OGC industrial sites and in the territories of oil and gas deposits in different regions of RF. Surveys at a single time scale are carried out for the development of this substantiation. These surveys involve the application of a set of hydrogeological, gas–geochemical, geophysical, and laboratory methods of studies. These methods, based on environmental–hydrogeological mapping, provide for both the development of information support for the assessment of the hazard and risk of geological environmental pollution with the preparation of the project of detailed monitoring and the construction of integrated groundwater flow and hyhdrogeochemical models for the prediction of changes in the environmental situation and the designing of nature protection measures. The specific features of pollution of grounds and groundwater is examined. A method is proposed for zoning the areas of industrial sites in terms of recharge conditions, spreading, OP pollution, and self-purification of groundwater, which allows the most efficient nature protection measures to be chosen. To substantiate investments for the improvement of environmental conditions, rehabilitation of polluted areas and water bodies in specific regions and at OGC facilities, it is proposed to develop, in regional committees of the Ministries of Natural Resources of member states of RF, concepts of comprehensive studies of natural–engineering systems based on the analysis of materials collected during earlier regional and detail hydrogeological and hydrogeochemical studies. When developing the concept, one should take into account the final objectives of its implementation with due consideration of the character and extent of pollution of subsurface hydrosphere in the region, reasoning from two possible environmental situations: the actual pollution level of the subsurface hydrosphere and sur-
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