E1592 V 5 Public Disclosure Authorized
OGULIN SEWERAGE SYSTEM &
WASTE WATER TREATMENT WORKS Public Disclosure Authorized
ENVIRONMENTAL IMPACT STUDY (UPDATED) Public Disclosure Authorized Public Disclosure Authorized
Oikon Ltd Parsons Brinckerhoff Vlade Prekrata 20 Parnell House 1000 Zagreb Croatia Environmental Impact Study of the Ogulin Sewerage System
25 Wilton Road London SW1V 1LW
June 2005
2 Environmental Impact Study of the Ogulin Sewerage System
1 INTRODUCTION ...... 2 1.1 OVERVIEW ...... 2 1.2 THE PROPOSED PROJECT...... 2 1.3 PROJECT PROPONENT...... 7 1.4 APPROACH TO THE EIA...... 7 1.5 STRUCTURE OF THE ENVIRONMENTAL STATEMENT ...... 8 2 LEGISLATIVE AND PLANNING CONTEXT FOR THE EIA ...... 9 2.1 INTERNATIONAL CONVENTIONS, PROTOCOLS AND COMMITMENTS...... 9 2.2 NATIONAL LEGISLATIVE REQUIREMENTS ...... 10 2.3 PHYSICAL PLANNING DOCUMENTS ...... 11 2.4 PROTECTED NATURAL, URBAN AND RURAL VALUES...... 12 3 EXISTING CONDITIONS...... 14 3.1 SITE LOCATION...... 14 3.2 SURFACE DRAINAGE...... 14 3.3 GEOLOGY AND SOILS...... 19 3.4 HYDROGEOLOGY ...... 23 3.5 CLIMATE AND METEOROLOGY...... 36 3.6 SOCIO-ECONOMICS...... 39 3.7 TRAFFIC ...... 39 3.8 ECOLOGY AND NATURE CONSERVATION...... 40 4 PROJECT DESCRIPTION...... 44 4.1 OVERVIEW ...... 44 4.2 NEED FOR THE PROJECT...... 44 4.3 THE PROPOSED SEWERAGE SYSTEM ...... 45 4.4 THE WASTE WATER TREATMENT PLANT...... 49 4.5 RECEIVING WATERS ...... 56 4.6 ANALYSIS OF ALTERNATIVES ...... 56 5 IMPACT ASSESSMENT AND MITIGATION ...... 62 5.1 INTRODUCTION ...... 62 5.2 THE SEWAGE NETWORK ...... 62 5.3 THE WASTE WATER TREATMENT PLANT...... 63 5.4 IMPACTS DURING DECOMMISSIONING...... 67 5.5 IMPACTS DURING ABNORMAL OPERATION ...... 67 6 ENVIRONMENTAL MONITORING, MANAGEMENT AND CONSULTATION...... 69 6.1 OVERVIEW ...... 69 6.2 SURFACE WATERS ...... 69 6.3 GROUNDWATERS ...... 69 6.4 SLUDGE QUALITY ...... 71 6.5 AIR QUALITY ...... 71 6.6 NOISE...... 71 6.7 ENVIRONMENTAL POLICIES ...... 72 6.8 PUBLIC CONSULTATION ...... 72 7 LEGISLATIVE REFERENCES...... 74
1 Environmental Impact Study of the Ogulin Sewerage System
Introduction
Overview
Ogulin is a market town located in northern Croatia (see Figure 1.1, 1.2 and 1.3 for location). The town has long-held problems of wastewater and stormwater treatment and disposal. At present the majority of the households collect wastewater on their own and discharge it without prior treatment into septic tanks (“black pits”) or directly into the nearby sinkholes or abysses, where it enters the local groundwaters. The situation with stormwater drainage is the same, and the increase in hard surfaces that has accompanied urbanisation has resulted in not only a considerable increase in the flow of stormwaters, but also in their pollution, with heavy precipitation commonly resulting in clogging and local flooding, which in turn have impacts on hygiene, ecology and economy.
The Proposed Project
Project Location
Ogulin town is located in the Ogulin-Plaški valley, a hilly area some 300 m above sea level, and rising to 500-600 m in higher elevations (see Figure 1.3). The valley is comprised of two karst fields, the Ogulin and Plaški Fields, made of highly pervious layers of limestone and dolomite with occasional impervious Triassic layers. The karst area is characterized by long cave systems such as ula’s Precipice- Medvednica Cave, etc.
Figure 1.2 Ogulin Town Setting
2 Environmental Impact Study of the Ogulin Sewerage System
This area is considered sensitive since local pollution can have grave consequences on a wide area and the construction of a drainage system has therefore been set as one of the priorities of the town of Ogulin and conceptual designs for the sewerage system and the wastewater treatment plant were first developed in 1989. It was decided to form the combined sewerage system in the town, i.e. the system of transporting household and industrial wastewaters together with precipitation waters through the same (common) collectors. The idea was that wastewater will first be treated and then discharged into the underground on the territory of Galga, to the north of the settlement of Otok Oštarijski.
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Figure 1.1. Location Map for Ogulin Town
4 Environmental Impact Study of the Ogulin Sewerage System
Figure 1.3 The Ogulin Region
5 Environmental Impact Study of the Ogulin Sewerage System
Project Concept
The proposed project provides for the construction of a partly combined system with a network of sewers which would receive both household and industrial wastewater, with stormwaters collected from those (mostly traffic) surfaces where they could cause traffic difficulties or endanger the town in some other way. The need for such a sewerage system is determined by a number of factors, including the current number of inhabitants, the quality and composition of wastewater, and ecologic and sanitary requirements. The conceived sewerage system shall provide proper medical conditions on the area of the town and gravitational suburban settlements, as well as lessen the negative impacts of waste and dirt on the living environment. The issue of draining precipitation water from the areas not encompassed by this design will be the subject of a separate conceptual design on storm water.
Due to the necessity of constructing the Ogulin Sewerage System (transport and collection canals with the treatment plant), the town of Ogulin through its public utility Vodovod i kanalizacija has commissioned the preparation of the project documentation for the collection canals (Catchment area A) for the central part of Ogulin, as well as for the wastewater treatment plant. Up till now only the main collector of catchment area A has been constructed, excluding collection sewerage network.The sewerage system implies a set of construction facilities collecting the polluted wastewater, the transport of wastewater from the source to the wastewater treatment plant, where it is treated up to the legally prescribed degree, and the discharge of wastewater into the groundwaters. The main purpose of the sewerage system may be said to be a prompt removal of wastewater from a populated area and its treatment until achieving the quality required for the area in question before disposing it into the recipient.
The purpose and the objective of constructing the sewerage system is to use the set of construction facilities for a safe and economical collection and treatment of wastewater, thus creating an inhabited area that would constantly provide optimal healthy conditions. Wastewater has to be treated up to the level not harmful for the recipient and thus for the environment in general. Furthermore, the construction of the urban sewerage system will improve the drainage regime of precipitation water, thus protecting the surface and subsurface urban elements from flooding and enabling the drainage of traffic surfaces. The wastewater drainage system will be connected onto the wastewater treatment plant. The recipient of the effluent coming out of the plant as well as of the diluted water will be absorbing wells or the River Dobra.
Interaction with the National Water Plan
The National Water Protection Plan requires waters to be managed on the principles of an integrated water system and sustainable development, with implementation of the precautionary principle to prevent and restrict the discharge of hazardous and other substances which might cause water pollution. The proposed project proposes the construction of the public drainage system to be completed by 2010 for the facilities between 10,000 and 15,000 PE. The construction of the wastewater treatment plant can begin if at least 70% of the total capacity of the public drainage system has been completed.
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EIA and Permitting Requirements
In accordance with the current legislation, the sewerage systems higher than 10,000 PE require the preparation of the Environmental Impact Study. The Environmental Impact Study of the Ogulin Sewerage System has been prepared according to the conclusions and the minutes of the meeting held on August 8, 2000 on the premises of the Ministry of Environmental Protection, Physical Planning and Construction,. The primary duty of all the interested parties (Hrvatske vode, the town of Ogulin and other beneficiaries of the Ogulin sewerage system) is the construction of the central wastewater treatment plant “Ogulin”, including the main drainage canals.
A location permit for the main sewage collectors and pumping stations project of the drainage system of the town of Ogulin (collection canal – Catchment area A) as well as for the Ogulin Wastewater Treatment Plant has been obtained, following completion of the process of assessing the acceptability of the project with regard to the environment and establishing the necessary environmental protection measures, and once those components were included in the Programme Draft of the planned project.
Project Proponent
The immediate project beneficiary of the project is the municipal company ViK Ogulin «Vodovod i kanalizacija Ogulin». This is a public company, formally established by the Town of Ogulin, which is the majority shareholder. ViK is responsible for the construction and maintenance of the drinking water supply system to households and industries as well as the construction and maintenance of the wastewater collection system, network enlargement plans and the construction of a wastewater treatment plant. ViK Ogulin is an independent legal entity with limited liability and managed by a Director, who is appointed by the Supervisory Board of ViK Ogulin, which in turn is appointed by the Town. The Director reports to the Board and the Town Council on regular basis and is responsible for day-to-day operations and the financial stability of the company. However, the Town must approve important issues including investment policy and tariff increases. A private sector share in the municipal infrastructure is neither present nor planned.
The relationship between the Town Administration and ViK is governed by a set of regulations, ownership of assets, control mechanisms and the mutual desire to improve water supply and wastewater services in the Town. All environmental mitigation and management activities related to the construction and management of the collector network of the sewerage system and the wastewater treatment plant will be the responsibility of the ViK Ogulin municipal company.
Approach to the EIA A significant amount of research and interpretation of collected data have been conducted on the project site of the wastewater treatment plant with the purpose of defining geological, hydrogeological and geo-mechanical features of the terrain. Particular field studies undertaken for the project have included the following (see Section 3):
• Hydrogeological research. The Institute of Geology, Zagreb has carried out hydrogeological research needed for the design and construction of the Ogulin wastewater treatment plant. The design provides for the discharge of treated water
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through absorbing wells into the carbonate underground on the territory of Galge, north of the settlement of Otok Oštarijski. The programme of works includes hydrogeological mapping of the locations of the planned facilities in scale 1:1,000, a review of more pronounced depressions (sinkholes), as well as an assessment of the conditions or hydrogeological features of the rocks. In order to determine the condition of the rocks in the bedrock (fissures and cracks) and in order to test permeability to water, two bores, each 30 m deep, were made on the locations of the planned absorbing wells. The bores were cored at entire depth; the core was placed into crates, intended for technical documentation. Water permeability was tested during boring at each 5 meters, under pressure of 2, 5 and 7 bars (10 bars were not achieved). The boring was performed with a boring machine BA-300, with initial diameter of 116 mm and final diameter of 86 mm. Protective columns of 110 mm in diameter were implanted into the bores, 12.00 m into B-1 and 4.00 m into B-2.
• Dye Tests. Dye tests have also been carried our to examine groundwater flow. Three of four planned excavations were made on the slopes of sinkhole a. Following an experimental absorption performed by pouring out a fire-engine tank into each selected suffosion, sinkhole b was established to possess a considerably higher absorptive capacity. The dye that was to establish the direction of the underground flow (12 kg of Na-fluorescein) was therefore poured into sinkhole b, along with 50 m3 of water. More important sources from Gojak to Kuka e were under observation.
• Geotechnical Study. A geotechnical study for the foundation of the proposed wastewater treatment plant was also prepared. The structure shall consist of a prepumping station, a retention basin and a wastewater treatment plant. The composition of soil obtained from hydrogeological research was used for the assessment of the geotechnical characteristics (parameters) of the soil, needed for the preparation of the geotechnical study.
Structure of the Environmental Statement The remainder of this EIA Study is structures as follows:
• Section 2 outlines the legislative and planning context for the EIA; • Section 3 describes existing conditions; • Section 4 describes the proposed project; • Section 5 identifies potential impacts and proposed mitigation; • Section 6 outlines a monitoring plan for the project; • Section 7 describes public consultation held to date ; and • Section 8 includes main project references.
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Legislative and Planning Context for the EIA The project has been developed to fully comply with environmental regulations of the host country as well as the EU. Particular attention has been paid to environmental impact assessment, environmental performance and public consultation requirements.
Croatia has a well-developed set of environmental laws. There is a requirement under the Law on Environmental Protection (NN 82/94) for a comprehensive review of a project’s potential environmental impacts (By-Laws on Environmental Impact Assessment, NN 34/97 and NN 37/97). The agency responsible for review and approval of environmental impact assessment (EIA), the Ministry of Environmental Protection and Physical Planning is also the main agency responsible for implementing the laws related to nature conservation, potential air emissions, water/wastewater management, and solid waste management. The assessment presented in this EIA incorporates information presented in the Croatian requirements for EIA.
As part of its ongoing plan to start accession process for the European Union, Croatia has been making progress in harmonising its environmental laws with those of the EU. For example, the Croatian Law on Environmental Protection (NN 34/97), Law on Nature Conservation (NN 30/94), Law on Waste Management (NN 34/95), Law on Air Protection (NN 48/95) are being continuously updated to conform to EU Council Directives.
International Conventions, Protocols and Commitments The Republic of Croatia is a signatory to a number of international obligations as shown in Table 2.1 below.
Subject International Conventions, Protocols and Commitments EIA Convention on Environmental Impact Assessment in a came into force with respect to the Republic of Croatia on 10 Transboundary Context (Espoo 1991) September 1997. Protocol on Strategic Environmental Assessment The Republic of Croatia signed the Protocol in 2003. Climate Law on Ratification of the United Nations Framework Published in OG–IT, No. 2/96, came into force in Croatia on Convention on Climate Change 7 July 1996. (Rio de Janairo 1992) Kyoto Protocol to the Convention on Climate Change The Republic of Croatia signed the Protocol in 1999. (Kyoto 1999.) Gov. Legislation OG-IT No.12/93 – Montreal Protocol on Substances that Deplete the Ozone Layer – dated 8th October 1991 Stockholm Convention of Presistent Organic Pollutants signed in 2001 Air Convention on Long-range Transboundary Air Pollution the Republic of Croatia became a party to the Convention on (Geneva 1979) 8 October 1991 (OG- IT 12/93) Protocol to the 1979 Convention on Long-range The Republic of Croatia signed the Protocol in Aarhus in Transboundary Air Pollution on Persistent Organic 1998. Pollutants (Aarhus 1998) Vienna Convention for the Protection of the Ozone Layer Pursuant the notification on succession, the Republic of (Vienna 1985) Croatia became a party to the Convention on 8 October 1991 (OG- IT 12/93). Stockholm Convention on Persistent Organic Pollutants Republic of Croatia signed the Convention in 2001. (Stockholm 2001) Montreal Protocol on Substances that Deplete the Ozone the Republic of Croatia became a party to the Convention on Layer (Montreal 1987) 8 October 1991 (OG- IT 12/93). Sea * Croatia has a large number of Protocol relating to sea, these however are felt not to be relevant to this project. Waste Gov. Legislation OG-IT No.3/94 Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal - dated 9th May 2000 General European Landscape Convention (Florence, 2000) Published in OG–IT, No. 12/02, came into force with respect to the Republic of Croatia on 1st March 2004, and the effective date was published in OG-IT 11/04. Protocol on Pollutant Release and Transfer Registers to The Republic of Croatia signed the Protocol in 2003. the Aarhus Convention (Kyev 2003)
9 Environmental Impact Study of the Ogulin Sewerage System
The study complies with all the above protocols and conventions and is not expected to have any adverse transboundary influence.
National Legislative Requirements
The proposed project is required to be in accordance with the National Water Protection Plan (Official Gazette 8/99) and the Regulations on Limit Values of Indices, Hazardous and Other Substances in Wastewater (Official Gazette 40/99), which prescribe both recipient category and effluent standard.
In addition, the project is required to operate in accordance with the national and European legislation outlined in Table 2.2 below.
Subject Croatian legislation EU legislation (number only)
EIA Gov. Legislation – Ordinance on Environmental 97/11/EC, 85/337/EEC Impact Assessment (OG No. 59/00, 136/04) Air Quality Gov. Legislation – Air Protection Act (OG No. 48/95, 96/62/EC, 97/101/EC, 1999/30/EC, 178/04), will be applied from 31st March 2005 2000/69/EC, 92/72/EEC Gov. Legislation – Regualtion on Limit Values of 96/62/EC, 91/692/EEC, 84/360/EEC, Pollutant Emissions from Stationary Sources into the 97/101/EC, 96/61/EC Air (OG No. 140/97, 105/02, 108/03, 100/04) Gov. Legislation – Regulation on Recommended and Limit Air Quality Values (OG No. 101/96, 2/97) Gov. Legislation – Regualtion on Substances Depleting the Ozone Layer (OG No. 7/99, 20/99) Gov. Legislation – Regulation on Sitting of National Network Stations for Continous Air Quality Monitoring (OG No. 4/02) Gov. Legislation – Programme on Air Quality Measurement in the National Air Quality – Monitoring Network (OG No. 43/02) Water Quality 76/464/EEC, 91/271/EEC, 96/61/EC, 2000/60/EC 91/271/EEC, 76/464/EEC, 80/68/EEC, 86/280/EEC General Gov. Legislation – National Environmental Strategy (OG No. 46/02) –
Gov. Legislation – National Environmental Action Plan (NEAP) (OG No. 46/02) – Waste Gov. Legislation – Waste Act (OG No. 178/04) – 91/698/EEC 86/278/EEC 2000/532/EC, /442/EEC, 94/3/EC, 91/689/EEC, 94/904/EC, 2001/118/EC, 2001/119/EC, 2001/573/EC 76/116/EEC, 80/876/EEC, 87/94/EEC
Receiving Water Category
The National Water Protection Plan (Official Gazette 8/99, Annex D-2) prescribes water classification. The waters at Ogulin are classed as belonging to category A (Highly Sensitive Areas) which include the following:
• groundwater used or planned for use in water supply • mountain streams up to settlements • watercourses in karst areas up to settlements • water in national parks and nature parks
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Effluent Standard
The Regulation on Limit Values of Indices, Hazardous and Other Substances in Wastewater (Official Gazette 40/99) defines limit values for: suspended matter, BOD5, COD, total phosphorus and total nitrogen, which are, following treatment, discharged from the public sewerage system into the natural recipient, and determined on the basis of plant size (PE) and recipient water class (area sensitivity). Based on the above, wastewater of the town of Ogulin belongs to "c) watercourse of the II. water class ("sensitive areas"), and therefore requires the following treatment levels for different plant sizes:
- up to 10,000 PE primary (I) + secondary (II) - over 10,000 PE primary (I) + secondary (II) + tertiary (III) Treatment levels are defined in chapter C "Definition of Terms", para III, items 12-16 of the National Water Protection Plan (Official Gazette 8/99). Limit values of indices in wastewater discharged from a wastewater treatment plant after a certain level of treatment into a natural recipient are determined in the following table:
TREATMENT INDICES LIMIT VALUE LEVEL L Total suspended matter 120-150 mg/l II. Total suspended matter 35 mg/l (over 10,000 PE) 60 mg/l (up to 10,000 PE)
Biochemical oxygen demand 25 mg O2/l (over 10,000 PE)
BOD5 (20°C) without nitrification 40 mg O2/l(up to 10,000 PE) Chemical oxygen 125 mg 0 2 / l (over 10,000 PE)
demand - CODcr 150 mg O2/l (up to 10,000 PE) DL Total phosphorus 2 mg P/l (10,000-100,000 PE) 1 mg P/l (ve e od 100.000 ES) Total nitrogenH (organic N + NH3 + 5 mg N/l (10.000-100.000 PE) NO2+NO3) 10 mg N/l (over 100,000 PE)
Physical Planning Documents Both the proposed sewerage system and the wastewater treatment plant are considered part of the local infrastructure. The guidelines for the physical planning conditions (location permit) of the Physical Plan of the Former Municipality of Ogulin prepared by the Ogulin Municipal Assembly in 1978 (The Official Gazette, No. 28/78) state that the infrastructure facilities can be constructed within the proposed project location, and that the construction of the sewerage system with the wastewater treatment plant is requested with the purpose of protecting the River Dobra.
The Amendments to the Physical Plan of the Former Municipality of Ogulin (The Gazette of the County of Karlovac, No. 12/99), Paragraph B Issuing Location Permits, Article 32, require the location permits for municipal infrastructure facilities to be issued on the basis of the appropriate conceptual designs. The conceptual designs on the basis of which the issuing of the location permit is requested include the Wastewater Canals Conceptual Design (Hidroprojekt-Ing, April 1996) and the Conceptual Design for the Wastewater Treatment Plant Location Permit (Hidroprojekt-Ing, 1999). Another precondition for the location permit is the preparation of this Environmental Impact Study:
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Protected Natural, Urban and Rural Values Pursuant to the Nature Conservation Act (Narodne novine, No. 30/94, 72/94), the parts of nature that are of interest to the Republic of Croatia and enjoy its special protection are as follows:
- National park is a broad, mostly unmodified area of exceptional and multiple natural values, comprising one or more preserved or slightly modified ecosystems. The national park has scientific, cultural, educational and recreational purposes. Activities that do not threaten the authentic nature are permitted, whereas the economic use of natural resources if prohibited.
- Nature park is a broad natural or partly cultivated area with marked aesthetic, ecological, educational, cultural, historical, tourist and recreational values. Activities that do not threaten its essential features are permitted.
- Strict reserve is an area of unmodified or slightly modified nature. It is intended exclusively for scientific research, which shall neither change the nature’s biological diversity and authenticity nor threaten the undisturbed development of natural processes.
- Special reserve is an area with one or more outstanding unmodified natural elements, of particular scientific importance and purpose. The special reserve can be: botanical (floristic, forest vegetation, etc), zoological (ornithological, ichthyologic, etc), geological, hydrological, marine reserve, etc. None of the activities, which might harm the distinctive characteristics of a special reserve, is permitted (picking and destroying plants, disturbing, hunting and killing animals, introducing non-native species, melioration activities, various forms of economic or other exploitation, etc).
- Park-forest is a naturally grown or planted forest of a considerable landscape value intended for relaxation and recreation. The only permitted activities are those intended for the preservation and maintenance of the park-forest.
- Protected landscape is a natural or cultivated area of a considerable aesthetic or cultural and historical value, or a landscape characteristic of a certain area. None of the activities, which might disturb the distinctive characteristics of a protected landscape, is permitted.
- Nature monument is a single unmodified part or a group of parts of animate or inanimate nature with a scientific, aesthetic or cultural and historical value. It can be geological (mineralogical or paleontological site, layer structure, etc), geomorphologic (cave, solitaire rock, etc), hydrological (spring, waterfall, lake, etc), botanical (rare or site-specific plant specimen, etc), a small botanical and zoological locality, etc. Any activity endangering its characteristics and values is prohibited on or in the immediate vicinity of the nature monument.
- Park architecture monument is an artificially formed area (alley, botanical garden, arboretum, town park, line of trees, a set of trees and a single tree, as well as other horticultural forms) of a significant aesthetic, stylistic, artistic, cultural and historical or scientific value. Any activity that would change or damage its lasting values is prohibited in the park architecture monument or in its immediate vicinity.
- The category of individual plant or animal species under special State protection includes endangered or rare species. Any activity disturbing and obstructing the protected plant or
12 Environmental Impact Study of the Ogulin Sewerage System animal in its natural growth and unhindered development (picking, damaging or removing a plant from its habitat, scattering, pursuing, hunting, restraining, injuring and killing animals, damaging their life forms, nests or broods and habitats) is prohibited. It is prohibited to hide, sell, purchase and seize or in some other manner obtain the protected plants and animals, as well as to stuff the protected animals. Wild growth and wildlife within a national park, strict reserve and special reserve are also under protection, as well as cave animals, regardless of whether they belong to the protected plant and animal species or not.
In the above-mentioned areas it is forbidden to perform any activity that might disturb the characteristics on the basis of which they were proclaimed reserves (picking and destroying plants, disturbing, hunting and killing animals, introducing non-native species, melioration activities, various forms of economic use, etc).
As the project site is located on the area of the town of Ogulin, a thorough research of the protected areas has been carried out in order not to harm or endanger the nature and the environment. According to available data, there are no registered protected structures and historical units or registered protected parts of nature on the wastewater treatment plant construction area. The purpose of the project itself is to protect the environment and prevent the pollution of surface water and groundwater.
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Existing conditions
Site Location
The town of Ogulin is located in the centre of Croatia, within Karlovac County, approximately half way between the cities of Zagreb and Rijeka. It is an important regional centre that grew up around the agriculture and wood processing industries and has extremely good links to other parts of the country. The town is situated on the Zagreb-Split highway, which opened in 2003 and also the Zagreb-Rijeka railway. The town is situated within the Ogulin-Plaški valley at an altitude of about 300m above sea level, at the foot of Mt. Klek. The topography rises to between 500-600m in a line of limestone hills to the south- west and west of the town. Many springs emerge along the valley side, the largest of which is harnessed for the public water supply. These also feed surface watercourses where these flow over less permeable soils. The general landscape is of gently undulating fields with irregular, shallow depressions, sinkholes and valleys, typical of karst scenery, caused by varying amounts of dissolution of the underlying limestone bedrock. This low level plateau is cut by several canyons in the valleys of important karst watercourses, including the Dobra, Mre nica, Kupa and Korana rivers.
Surface Drainage Ogulin lies within the catchment of the Dobra River, which flows into the town from the west in a deep gorge, before sinking underground in a large sinkhole, known locally as ula ponor. Once underground, the river flows through an extensive cave system before emerging approximately 4km to the north-east before flowing in a general north-easterly direction towards Karlovac, approximately 40km distant. In the town centre the gorge is approximately 30m deep. Approximately once per year, after intense rainfall events and Spring snow melt, the capacity of the sinkhole is insufficient to cope with the high river flows generated and the gorge fills, resulting in flooding of the town centre. Water quality in the Dobra is monitored at a number of locations by Croatian Water (see Figure 3.1 for monitoring location points). Results indicate that high levels of BOD are present downstream of Ogulin, consistent with extensive discharge of wastewaters into the upstream catchment. Monitoring data from these sites are provided in Tables 3.1a and 3.1b.
Apart from the main drainage features associated with the Dobra River, however, the surface drainage network tends to be poorly developed due to the permeability of the surface soils and underlying bedrock. Rainfall tends to infiltrate the ground rapidly, where it causes dissolution of the carbonate substrata and results in the formation of dissolution features and the formation of karst topography. As a result, most of the drainage infrastructure within the town, such as from rooftops and highways, has historically been to soakaway, typically to areas of naturally increased infiltration capacity, signified by small surface depression features. The infiltrated water emerges as springs at lower elevations around the town. In the wider Ogulin area most of the drainage emerges at springs in the valley of the Dobra River, although some is known also to emerge in the valley of the Mre nica River, to the south-east.
Most dwellings discharge wastewater and sewage in a similar manner. Whilst some properties have septic tanks, which are emptied by the municipality when necessary, it is understood that the majority of buildings do not require this service; raw sewage being discharged to solution features, where it rapidly infiltrates the ground. This is confirmed by the water quality of the main springs around the town, which show evidence of extremely high concentrations of faecal bacteria.
Five of the main springs in the vicinity of the town (Tounj