using the example of Aschau (Alpine region)
Fig. 1: The tanks are placed in the correct position
In autumn 2021, the municipality of Aschau im Chiemgau, Germany, provided the newly founded district of Staffelstein with its own supply. The Staffelstein district is predominantly located in alpine terrain (above 1000 m) and includes the Steinling Alm, the Sonnenalm, the Möslarn Alm and other huts and alpine pastures. For the first time since its foundation in 2012, Staffelstein now has its own sewage disposal and drinking water supply.
Due to this exposed location, the engineering firm Dippold und Gerold from Prien was already commissioned in 2014 to plan its own supply. The further procedure included a route inspection on site, surveying the topography and, in 2015, applying for funding. In 2018, the „grant of the special mountain hut programme“ was applied for and the tender for the construction measure was published. After a public tender, the construction company LKS from Schönau am Königssee was commissioned to carry out the work.
The planned details for an optimal supply of the alpine local points:
The installed sewage disposal system is designed for 526 population equivalents (PE) and the drinking water supply covers a demand of approx. 12 m³ per day. FRANK GmbH supplied the following piping material and PE drinking water tanks from its own production.
Fig. 2: Production of coiled tubing at FRANK KUnststofftechnik GmbH
For the sewage disposal:
- approx. 5,500 metres of PE 100 pipes DN63-DN180 in pressure stages up to PN 16.
For drinking water supply:
- approx. 5,000 metres of PE 100 pipes
DN75 and DN90 - partly in PN 25
- 1 pc. high tank DN2000 with slide cham
ber DN2500 and capacity of 2 x 3 m³ for
- 1 pc. Elevated tank DN2500 with slide
chamber DN2700 and capacity of 2 x 10
m³ for the „Sonnenalm“.
- 2 pcs. feed tank DN2400 with 15 m³
capacity each for „Lochgraben”
Basic design of drinking water tanks according to DVGW worksheet W 300:
The DVGW Code of Practice W 300 describes technical rules for the construction, operation and renovation of drinking water tanks and consists of a total of 6 parts. The worksheets contain recommendations and requirements for the use of materials, the execution and design as well as the operation and maintenance of drinking water tanks. Parts 1 - 5 have been available and valid as a white print since 2014 and Part 6 since 2016. With the introduction of the current W 300, the material PE was also designated for the manufacture of drinking water tanks. Prior to this, this design was not officially considered a standard design by the DVGW, although drinking water tanks made of PE had been used in many areas for over 25 years.
PE drinking water tanks have also been used successfully in alpine locations in the past. Part 6 deals explicitly with the execution and design of system and prefabricated tanks made of PE as a material.
Essential requirements of the W 300 Code of Practice are fulfilled without exception by PE 100 drinking water tanks. These include, for example:
W 300-1, 5.4 „Selection of materials according to water chemistry“.
- Good chemical resistance of PE to raw
water attacking concrete
Fig. 3 + 4: Slide chamber with a selection of components
W 300-1, 6.1.3 Tank designs
- Production of prefabricated and system
tanks made of PE possible
- Reduction of construction time on site
- Insulation to prevent condensation
W 300-1, 6.1.4 Material issue in relation to drinking water quality
- Smooth, non-porous surface of PE
- Approval and drinking water suitability of
PE according to DVGW W 270
W 300-1, 7.2 Functional requirements
- Access via valve chamber, no access
above the water surface
- All piping in the valve chamber acces
- View of the water surface via sight glass
- Two water chambers for cleaning / in
- Object protection via appropriate access
W 300-1, 10. Checks, testing, initial commissioning
- Leak test for system tank in the factory
- Quality assurance can already take place
in the factory for PE containers (see also
W 300-6, 5.2)
- Essential requirements for surface
quality are already fulfilled by the use
of approved materials and do not have
to be verified or tested separately.
W 300-6, 5.3 Life cycle management, economic efficiency
- Long service life (see also point 3. DIN
- Dismantling and disposal costs - recycling
(see also item 6. Conclusion)
W 300-6, 8th pipe tank
- Static proof according to ATV-DWA A 127
- Deformation max. 3
- Slope to the valve chamber min. 0.50 %.
Fig. 5: Installation of the "Steinlialm" tank - 2 x 3 m3 with central valve chamber
Wound pipes and semi-finished products made of PE for drinking water structures:
Profile wound pipes made of PE 100 are used to produce the basic geometry („pipe tank“). Production is carried out in the FRANK Kunststofftechnik GmbH coiled pipe plant in accordance with DIN-EN 16961 using modern PE 100 materials that have been approved by the German Institute for Building Technology (DIBt). The PE 100 pipe material used is, for example, BorSafeTM HE3490-LS black.
Here are some selected material characteristics:
- Density 959 kg/m³ according to ISO
- Melt flow index 0.25 g/10 min according
to ISO 1133
- Tensile stress 250 N/mm² - short time
according to ISO 527-2
- Modulus of elasticity 1100 N/mm² - short
time according to ISO 527- 2
Polyethylene (PE 100) is a thermoplastic which, in addition to a low specific weight, also has excellent processability, weldability and formability. Polyethylene is particularly resistant to aggressive media (acids and alkalis). Furthermore, the molecular structure of the material, which is composed of carbon and hydrogen, enables material recycling: polyethylene is 100 % recyclable. Polyethylene has been used successfully for many decades in gas and water supply in the form of pipes, fittings and manholes. Plates made of polyethylene have also been used for many years in the renovation of drinking water tanks (made of concrete). Producing drinking water tanks entirely from PE is economically advantageous and also environmentally friendly.
The smooth, non-porous surface is excellently suited for the storage of drinking water. For pipes made of PE (100), the proof of long-term strength („durability“) is already mentioned in the basic standard. DIN 8074, Pipes made of polyethylene (PE) - PE 80, PE 100 - Dimensions and DIN 8075, Pipes made of polyethylene (PE) - PE 80, PE 100 - General quality requirements, tests contain the following statement on long-term strength:
„The service life previously estimated at 50 years can be extended to at least 100 years of service life for PE pipes at application temperatures of 20°C on the basis of many years of tests and experience.“ 
Fig. 6: Prefabricated cotainer made of PE - 2 x 60 m3 - Delivery in 3 individual parts
This ensures that drinking water structures made of PE100 are a durable and sustainable solution for the storage of drinking water over an economically, secured depreciation period of up to 100 years. For the area of the water chamber in contact with drinking water and in the access area of the valve chamber, a blue PE material is homogeneously applied to the inner surface of the coiled pipes using the co-extrusion process (Figure 2). The blue raw material type has the necessary approvals according to the tests of the TZW (Technologierzentrum Wasser) in accordance with DVGW guideline W 270 for drinking water suitability. This process already fulfils the essential requirements of the DVGW with regard to surface quality and hygiene of the surfaces that come into contact with drinking water.
The outside of the coiled pipes is made of UV-resistant black PE 100. FRANK produces coiled pipes up to an internal diameter of DN 3450 mm. With this diameter, the storage capacity in a pipe tank is just under 9 m³ / linear metre. In order to achieve a high degree of stability and good thermal insulation of the coiled pipes, profiled coiled pipes with closed base and cover layers are usually used.
The following semi-finished products / installation parts are used as further components for the tanks:
- PE 100 pressure pipes blue for drink
ing water according to DIN 8074/75 with
- Plates made of PE blue with TZW certifi-
cate for drinking water suitability
- Piping components and fittings made of
metallic materials with DVGW approval
Fig.7: PE system container - 2 x 40 m3 - delivery in one piece
Execution and design of PE drinking water tanks:
The design of the pipe structures takes into account the respective requirements of the operators as well as the DVGW guidelines already mentioned. Drinking water tanks are usually designed with two water chambers and a technical room (valve chamber). The usable volume of drinking water tanks made of coiled pipes is approx. 6 m³ to 800 m³. Up to a size of approx. 2 x 40 m³, the structure can be completely prefabricated and delivered to the construction site in one piece - as a so-called „system tank“ (Figure 7).
Fig. 8: Moving at the installation site with Liebherr 914 crawler excavator
In the case of larger tanks or special requirements for the transport route, the delivery is made in individual parts (prefabricated tanks), which are then assembled and welded on site by DVS- and DVVGW-certified specialist welders. This means that in areas that are difficult to access, a drinking water tank can be delivered in individual components and assembled and tightly welded within a few days. Even transport in difficult terrain is no problem using (tracked) excavators. Figure 6 shows the transport of a drinking water tank (system tank) in steep terrain with a volume of 2 x 20 m³ and a central slide chamber - completely prefabricated in one piece in the factory. All system-relevant components are prepared and installed in the factory to the extent that the completion and final assembly on the construction site can be carried out without any problems. The valve chamber (technical room) can be equipped with all required components - e.g.
- Complete piping with armatures for inlet,
outlet, drainage, transfer, etc.
- air filter
- Pressure boosting
- Water treatment - e.g. UV disinfection,
- Underwater access
- Object protection door
Details and special features of the drinking water reservoirs „Aschau-Staffelstein“:
The planning office Dippold + Gerold from Prien am Chiemsee had already planned and described PE drinking water tanks for the three tank locations Steinlingalm, Lochgraben & Sonnenalm in the invitation to tender.
The Steinlingalm tank was prefabricated as a system tank with two water chambers of 3 m³ each and a central valve chamber and delivered in one piece. Access to the valve chamber is guaranteed from above via a dome entrance with ladder. Access to both water chambers is via an underwater entrance with a DN 800 pressure door made of PE. The transport on the last metres in the alpine terrain was carried out by a chain excavator (Fig. 5). At the „Lochgraben“ site, a waterworks with two double pumping stations in reinforced concrete construction was built. The two tubular tanks (2 x chamber with 15 m³ each) serve as storage tanks for the pumping operation as well as for the drinking water supply of the Gorialm local network with a total of 5 huts. The HB Lochgraben also serves as the control centre for all drinking water operations. The upper floor of the two-storey concrete structure is clad with wooden panelling to give it the appearance of a „hut“. The production and delivery of the two template tanks took place in one piece. On site, the two tubular tanks were integrated into the basement of the concrete structure by means of a tensile and watertight wall connection including FRANK wall collars.
For the „Sonnenalm“ site, a prefabricated tank with a volume of 2 x 10 m³ and a centrally located valve chamber was planned. Access to the slide gate chamber is at ground level via a stainless steel object protection door. The two water chambers are each accessible via a pressure door made of PE DN 800.
As the location of the tank was in alpine terrain just above the tree line at approx. 1500 m above sea level, the transport to the installation site had to be planned in several stages and in three individual parts.
1. Transport by low-loader from the
factory to the “Fuchslug“ reloading point
2. Transport with all-wheel drive construc
tion site truck to the reloading point in
the „Gori-Alm“ area
3. Helicopter flight with Puma cargo heli
copter of the three individual parts to
the installation site
4. Moving at the installation site with
Liebherr 914 crawler excavator
In order to ensure a smooth flow of the individual transport stages, care was taken at the factory planning stage to ensure that the largest individual weight did not exceed the helicopter‘s payload of approx. three tonnes.
The valve or gate chamber
The valve chamber as the central part of the drinking water tank with connections for the two water chambers was weighed at 2950 kg in the factory. Thus, on a sunny midsummer morning at the beginning of August 2021, the three individual parts could be flown over the approx. two km as the crow flies and deposited at the installation site within one hour.
The height and position of the individual parts was then adjusted and they were pulled together at the installation site with the help of a chain excavator and 2 chain hoists. Subsequently, the connections between the slide valve and the two water chambers were made materially and tightly by means of hot gas extrusion welding from the inside and outside by a specialist fitter. The flawless, sunny mountain weather and the magnificent view from the Kampenwand into the foothills of the Alps helped with this work.
All drinking water reservoirs and pipeline components supplied for the „Aschau- Staffelstein“ construction project were successfully put into operation in autumn 2021 after leak testing, cleaning and disinfection.
In summary, it can be stated that drinking water tanks made of PE represent a contemporary and economical solution for securing the municipal infrastructure.
In particular, drinking water tanks with smaller and medium volumes (up to approx. 800 m³) can be produced for permanent use. The high degree of factory prefabrication and the flexible design enable user-friendly solutions. Transport to the installation site is feasible even under difficult conditions. Pipes and fittings made of environmentally friendly polyolefins (PE/PP) can be 100 % recycled after their service life in just a few process steps: An ecological and economic advantage compared to systems made of conventional materials (e.g. composites), which have to be reprocessed after dismantling at high energy costs or disposed of at additional expense. A great advantage for the planner (Dippold + Gerold, Prien), the contractor (LKS, Schönau) and the client (municipality of Aschau) was that all pipes, fittings and containers were supplied completely by FRANK GmbH. The instruction in the processing of the heating coil sleeves as well as the site supervision and assembly support were completely provided by FRANK GmbH. The necessary plastic welding on site was also carried out by FRANK GmbH.
List of sources:
 Ingenieurbüro Dippold + Gerold GmbH
, Prien am Chiemsee
 DIN EN 8074/75
Scope of delivery: See page 1
Partner: Planning - IB Dippld + Gerold GmbH, Prien am Chiemsee
Construction - LKS Tiefbau OHG, Schönau am Königssee
Trading partner Richter + Frenzel TBU GmbH, Kolbermoor
Your contact for further information: Jochen Obermayer, FRANK GmbH