Groundwater Natural Background Levels and Threshold Definition in the Sofia Valley (Executive Environment Agency, Bulgaria)
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Groundwater natural background levels and threshold definition in the Sofia Valley (Executive Environment Agency, Bulgaria). R. Gorova, D. Deneva Department of Water Monitoring and Department of Laboratory-Analytical activities, Executive Environment Agency at the Ministry of Environment and Water, 136"Tzar Boris III" blvd., 1618 Sofia, Bulgaria SUMMARY Here you summarise your case study. Here you summarise your case study. Here you summarise your case study. 1. INTRODUCTION Sofia valley is a young neotectonic graben bounded on both sides by faults, is situated in central part of West Bulgaria. The big vertical movement created conditions of vast lake and river sedimentation during Neogene and Quaternary. The Quaternary and Neogene deposits are sands, clayey sands, pebbles, clays, and sandy clays in different alternations. Thermal mineral water were found by boreholes in some of the basement’s rocks at different parts of the basin. Widespread petrography types predestined very intensive mining of sand, gravel and pebble in East part of the valley, began about 1960 with exploit depth up to about 15 m. The former quarry pits have been filled by groundwater and now many artificial lakes are available here. Also drainages and irrigation channels are available and small reservoirs for irrigation as well. Sofia – capital of Bulgaria is situated here. Sofia municipality has had 1.199.708 citizens - during 1998 and 1.210.806 citizens during 2005 (Nikolaeva, R et al., 2000). Many different human activities are developed in the area – Mining (an open mine for iron ores in north-East periphery – have been already closed) and quarrying, coke, refined petroleum, chemicals, pharmaceutical, rubber & plastic, machinery and equipment, fabricated metal products, food products, textiles products, wood products, etc. (Nikolaeva, R. et al., 2000). Some waste landfills are situated here. Part of them are already closed. They were operated without landfill design as other Bulgarian landfills during 70-ies and 80-ies. The steel Plant “Kremikovtzi” - a conglomerate of industries and technological activities (Dombalov 1998) is situated in the east part of the valley - with Pyrolytic treatment of coal, tailings pond, slag pond (have been operated more than 25 years) and Waste Water Treatment Plant (WWTP) etc. The above described human activities above described determined high pressure and impact above the groundwater. Groundwater abstraction is very important for drinking water supply for the west part of Sofia valley and for some settlements in the east part. Groundwater are important for industrial and other supplies. (Nikolaeva, R. et al., 2000). Two groundwater bodies are identified in Sofia valley – Quaternary and Neogene groundwater bodies. Groundwater bodies are hydraulically connected with water and terrestrial ecosystems. Groundwater abstraction is about 48.9 millions m3 per year (Nikolaeva, R. et al., 2000) from both of groundwater bodies, about 40% are for drinking water supply. The exploitation resources have been determined: 37.8 millions m3 per year for the Quaternary GWB and – 41 millions m3 per year – for Neogene GWB (Nikolaeva, R. et al., 2000). We expect actual data from Danube River basin Directorate – Sofia department – on the basis of groundwater use permits have been issued. 2. CHARACTERISATION OF THE GROUNDWATER BODY (OR GROUP OF GROUNDWATER BODIES) 2.1 Physical and hydrogeological description 2.1.1 Geographical boundaries Sofia valley is situated in the south part of the Iskar River Basin and this river is crossing the Balkan mountain chain. River Iskar is the longest Bulgarian river and it inflow in Danube. Iskar river basin is a sub-basin of the Danube River basin (Fig 1). Sofia valley is situated in Eastern Balkan Ecoregion(7) Fig. 1 Map of Quaternary and Neogene groundwater bodies in Sofia valley The common area of the valley is about 1200 km2, the size of the sedimentation basin during Neogene and Quaternary 1090 km2. And the Neogene GWB (Lozenetz geological formation) has size 973.4 km2. The maximum length of the valley is 75 km (WNW-ESE) and the maximum width - is 20 km. The altitude range in Sofia valley varies from 490 to 1065.9 m a.s.l. The main part is between 500 and 550 m a.s.l. The valley is surrounded by mountains which is the typical situation for the other kettles in the south part of Bulgaria Fig. 2 Map of the topography Fig. 3 Map of the soil cover Land use is distributed in Sofia valleys as follows - Arable land - 57%, Urban areas - 27%, Woodland - 7%, Pastures - 8%, Others – 1%, Protected areas (~0.3%). Here we don’t include the draft NATURE 2000’ protected sites, because they have not been yet officially established. Fig. 4 Map of the land use – acc. to CORINE LANDCOVER 2.1.2 Climate The climate in Sofia valley is moderate continental with four seasons. Influence is available of the level above the sea, direction of the slopes (disposing to the sun shining) and urban (built) territories of the capital Sofia. Fig. 5 Map with annual precipitation, air temperature and potential evapotranspiration Temperature 25 20 15 T 0C 10 5 0 -5 I II III IV V VI VII VIII IX X XI XII Fig. 6 Monthly distribution of the air temperature in Sofia (NIMH) meteorological station (period 1931-1970- (Kyuchukova, M., 1983)) Precipitation 100 80 60 R mm 40 20 0 I II III IV V VI VII VIII IX X XI XII Fig. 7 Monthly distribution of the precipitation in Sofia (NIMH) rain gauge station (period 1931-1985- (Koleva, E.& Peneva, R., 1990)) 2.1.3 Water balance The average multi annual precipitation and potential evapotranspiration are shown on Fig.5. The potential evapotranspiration was determined by Turc equation (1954) P Е = 2 ⎛ P ⎞ 0.9 + ⎜ ⎟ ⎝ L ⎠ E - is the potential evapotranspiration (mm year/ year ) P- is the mean potential precipitation (mm / year ). The correlation parameter L is described as: L = 300 + 25T + 0.05 T3 and T is the mean air temperature (°C). The potential evapotranspiration contour lines were obtained by use of grid with mean air temperatures and mean precipitation ( isotherms and isohyets). Calculations per every sell of the gr id with the Turc equation were made. Estimation of groundwater recharge was made. Only part of the abstraction points are available in GIS now. The actual groundwater abstraction points with the abstraction quantities will be receive from the Danube River Basin Directorate – Sofia Department. Fig. 8 Map with the annual groundwater recharge and abstraction point (abstraction points will be modified with actual data) A mathematical model was created by V.Petrov and prof.I.Iotov for estimation of the water balance of Neogene groundwater body. (Petrov, V.). The balance component are shown in table 1. Table 1 Annual average in mm of water balance components (P, ETP, groundwater recharge, Runoff (baseflow+shallow discharge) Recharge, Discharge, Balance component Balance m3/d m3/d Boundary conditions III +67946 -38634 +29312 Rivers +481 -62370 -61889 Abstraction -88465 -88465 Total infiltration recharge +72923 +72923 Inflow from the Quaternary GWB +262791 -212087 +50704 The Neogene GWB natural water resource has been evaluated 152939 m3/d or 1770 l/s The recharge exceeds the discharge with 29.9 l/s, which is 1.6 % from the total resources and practically is the inaccuracy of the modeling in the end of the last iteration. The recharge from the rocks surrounding the valley is 29312 m3/d, which divided on the valley boundary contour (335 000 m) results to 1.01 (l/s)/km. From the sandstone surrounding rocks the recharge is 0.1-0.2 l/s, in areas with andesites it is varies 0.2-0.5 l/s, and is higher 1.5 – 1.8 l/s - from the carst basin (GWB) in North-West part of the valley. The balance results show that the groundwater flow from the upper Quaternary GWB in vertical direction is preliminary descending. It exceeds the ascending vertical flow about 24% in the valleys central part. 2.1.4 Geology Sofia basin is an young neotectonic asymmetric graben bounded on both sides by faults. The structures of the surrounding mountains are spreading under the Neogene deposits of Sofia valley as a rock basement. This rock basement is crossed by longtitudinal (100 – 130 0) and latitudinal faults (15 – 35 0), determined its block construction. Some of the blocks are raised others are submerged. The amplitudes varies. The big vertical movement created conditions of vast lake and river sedimentation during Neogene and Quaternary. During Lower Meotian - Middle Pontian in the middle and the north part of Sofia basin rough drift and alluvial sediments were settled – this is Gnilyane geological formation ant it is not a subject of this report. Later – during Middle Pontian – deposition of lake’s sediments was occurred – clays, highly settled and consolidated. This is Novy Iskar geological formation and it is the lower aquitard of Neogene GWB. During Upper Pontian and Lower Dacian the basin became shallow and lake-marsh conditions have become. The Novi Han Member (coal layers contained) was settled. And after that the Lozenets formation composed of very tick alluvial deposits were settled in active developing of river network conditions. The Lozenets geological formation is the lower GWB – so called Neogene GWB – subject of this report. Above it Quaternery sediments were deposited – the Quaternary GWB. Lozenets formation – the Neogene GWB is formed from sandy layers, somewhere pebbles and gravels and sandy clays and clays.The number of aquifers is from three to 10, with a width 0.5 - 23 m, somewhere more. The total thickness of a waterbearing complex is from 38 up to 292 m (Petrov, V, 2004). Quaternary deposits – the Quaternary GWB is formed by alluvial, drift, delluvial and mixed deposits are spreaded almost all over the basin.