Germany – Engineering services – Neubau eines zentralen Retentionsbodenfilters (RBF) am RÜB „Alte Kläranlage“ in 76467 Bietigheim

The municipality of Bietigheim operates large parts of its public sewerage network using a combined system. During rainfall events, the resulting combined sewer overflows are discharged into the Schmiedbach via various combined sewer relief structures. The Schmiedbach is part of the Federbach system, which is heavily polluted due to a large number of discharges from the adjacent municipalities. According to the current assessment under the Water Framework Directive (WFD), the water system shows significant deficiencies in both chemical and ecological status. These are primarily due to discharges from wastewater treatment plants, particularly from the combined sewer systems of the municipalities located in the Federbach system. Against this background, expiring or new water permits cannot currently be approved without the results of the investigations into water ecology and FFH compatibility to be jointly conducted by the riparian municipalities. To ensure the continued proper operation of the municipal wastewater treatment plants, the Landratsamt Rastatt issued an interim order in August 2022 for the provisional operation and continuation of public wastewater discharges from the separate and combined systems of the Bietigheim catchment area into the Schmiedbach. For the expansion stages 2023, 2024 and 2030 defined in the supplements to the General Sewerage Plan (GEP) 2015 and its updates, specific wastewater treatment emission and immission measures are to be implemented and commissioned in accordance with this interim order. These measures are intended in particular to reduce the material and hydraulic loads on the Schmiedbach and to gradually improve the water status and achieve the objectives of the WFD. By December 31, 2028, a new central retention soil filter (RBF) is to be constructed and commissioned in the combined sewer system at the storm water overflow tank (SWOT) "Alte Kläranlage" for the expansion stage 2030, according to the interim order. The measure is a prerequisite for the further development of the municipal area and, in particular, must be implemented before the development of the residential areas "Birkig, 3rd and 4th construction phases" and the industrial area "Schelmenäcker (B8)". The planned retention soil filter is located directly next to the existing SWOT "Alte Kläranlage". The planning must take into account the local property conditions, the existing wastewater infrastructure and the necessary interfaces with the existing SWOT. Based on the initial preliminary design of the RBF, additional investigations were carried out in the further planning process to dimension and design the plant for the long term. In addition to the already foreseeable development areas, these took into account in particular the possible additional development of the area along the B3 and further potential development areas in the municipal area. During the further investigations, it became clear that a future-proof design of the RBF requires the consideration of additional land reserves. The municipal council of Bietigheim has therefore decided on a phased implementation of the retention soil filter. The first expansion stage takes into account the development areas already planned and foreseeable. The second expansion stage provides for the extension of the plant by an additional filter basin and takes into account in particular the land buffer of around 42.5 ha up to the municipal boundary along the B3. The division into two expansion stages makes it possible to initially provide the mandatory wastewater infrastructure in a demand-oriented manner for the specifically planned development areas and at the same time to create the structural and spatial prerequisites for a later extension. The project is currently in performance phase 3 (design planning). The approval planning will be completed by the engineering office already commissioned with the planning (LPH 1 to 4). The subject of the current tendering procedure are therefore the further planning services for performance phases 5 to 9 of the first expansion stage. The funding application is to be submitted after renewed coordination with the Regierungspräsidium next year, based on the planning that has been adjusted and expanded in the meantime. At the same time, an early start of the measures is to be applied for. This is to ensure that the necessary planning and tendering steps can be carried out on time and that the construction implementation can be controlled in such a way that the RBF can be commissioned by December 31, 2028 at the latest. The total costs for the phased expansion of the retention soil filter are estimated at a total of 5.490.000,00 € gross, according to the current cost estimate. The cost estimates are based on the current planning status (preliminary design) and serve as the basis for the further planning, tendering and implementation of the measure. The following schedule is planned: Start of planning: Following the tender, presumably from January 2027; Completion LPH 5: July 2027; Start of construction: August 2027; Commissioning: End of 2028. The cost estimate is broken down into cost groups as follows: KG 300: 2.330.000 € gross; KG 410: 505.000 € gross; KG 480: 440.000 € gross; KG 500 (incl. compensatory measures): 360.000 € gross. The subject of this invitation to tender are the planning services of the first expansion stage with performance phases 5-9 for civil engineering structures according to §§ 41ff. HOAI, open spaces according to §§ 38ff. HOAI and the technical equipment with the plant group 1 (hydraulics) and 8 (EMSR control) according to §53 ff HOAI.