The AwSV filling system during heavy precipitation
In recent years, an increase in heavy precipitation events has been observed.
The question therefore arises as to how to deal with this when handling substances hazardous to water, in particular when dimensioning the required retention volume of the AwSV filling facility in the event of heavy precipitation, i.e. the structural installations required when filling chemical tanks in an industrial plant with a tanker.
The article is intended to summarize the legal requirements for the AwSV filling plant for an engineering company, in particular using the 30a observation period for precipitation.
The result shows that AwSV filling plants without roofing (where – as is usually the case – filling is also planned regardless of weather conditions) are too small by a factor of 1.5.
Assessment in detail: Legally relevant for the assessment of the AwSV filling system in the event of heavy precipitation is first of all the AwSV, § 1 Para.
1 AwSV, as substances hazardous to water are handled.
This means that the basic requirements of § 17 Para.
1 AwSV, i.e. resistance, tightness in the sense of liquid impermeability § 15 para.
1 No. 1 AwSV in conjunction with DWA-A 786, 2.1.3, etc. for the system itself (i.e. also pipes and hoses), visibility and the need to retain any leaking substances hazardous to water, § 17 Para.
1 No. 4 AwSV in the form of retention facilities within the meaning of § 2 Para.
16 AwSV.
Filling system retention device
This retention device at the AwSV filling system in the event of heavy precipitation is required in accordance with
The required retention volume is measured in accordance with § 18 Para.
1, 2, 3 No. 2 AwSV, the required retention volume is determined by the volume „that can be released at the highest possible volume flow until suitable safety devices become effective“.
This also includes the possible excavation if no safety device is installed, § 15 Para.
1 No. 1 AwSV in conjunction with. DWA-A 779:2023 No. 6.1.1 para. 7.
7 However, this is usually the case or can be easily retrofitted so that the volume of the container(s) to be filled does not also have to be collected.
a. Volume of the retention system Filling system Therefore, only the pumping capacity of the truck must be taken into account (otherwise: plus any return flow from the pipe incl. excavation of a container) and any precipitation water.
aa.
Dimensioning of the retention facility The dimensions of the retention facility for filling systems within the meaning of § 2 Para.
18 AwSV in accordance with § 2 Para.
16 AwSV in conjunction with. § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 No. 2.1.11, 2.1.10 from the effective range incl.
Discharge.
- The effective area within the meaning of § 15 para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 No. 6.1.5.1 in conjunction with 6.1.5.2 Para.
1 is generally measured linearly from the connection of the tanker to the connection of the container with 2.5 m in all directions.
I.e. specifically at the hose line and then at the pipeline along a corridor 5 m wide. - The effective area can be reduced by splash protection measures, § 15 Para.
1 No. 1 AwSV in conjunction with. DWA-A 779:2023 6.1.5.1 Para.
3 (e.g. also through walls, as is regularly the case). - Furthermore, the length of the corridor can be reduced by the exceptions of § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 6.1.5.2 para.
2, 3rd indent: double-walled pipelines (with leak detection device according to DWA-A 779:2023, 6.3.3 in conjunction with 7.2) from the filling cabinet to the storage container, whereby the linear effective range changes to a point-shaped effective range of 2.5 m around the connections. - Alternatively, a pipe design in accordance with DWA-A 780-2, which no longer applies to thermosets in principle § 1 Para.
2, para.
4 Spstr.
7 DWA-A 780-2, is possible, provided that an individual assessment by an „expert for plastics“ (e.g. DVS 2213?) is available for each pipe with WGK2 materials and has been checked for plausibility by an expert.
– If the hose lines used by the chemical supplier comply with T 002:2018 of the BG Raw Materials and Chemical Industry with regard to quality, installation and operation of the hose lines as well as maintenance and testing and this is documented accordingly, a further reduction of the effective range to 0.5 m around the hose line and 2.5 m at points around the connection point is sufficient.
Typically, this results – simplified, but common in practice – in a trough of 13 x 5.1 m = 66.3 m², on which the truck stands over its entire surface (and possibly an additional effective area of 13 * 2.5 = 25.5 m² in the direction of the connections).
However, this is not taken into account in the following, as it can easily be limited by walls or splash guards in individual cases anyway).
bb.
Pumping capacity during filling In the absence of a successor regulation, DWA-A 785:2009, 5.1 in conjunction with 5.3.1 in conjunction with 5.3.2 must be used for the filling process of the AwSV filling system in the event of heavy precipitation: Depending on the temperature (especially with NaOH in winter), the filling capacity of the tank truck is max.
approx. 8 m³/h (the actual capacity is usually determined by the operator himself, as he can easily record the loading times himself through the chemical supplier).
The trucks are usually equipped with a dead man’s switch, therefore 5.3.2 applies: ta = 45 sec, to be used under dead man’s switch in the operating instructions.
According to the equation in 5.1, the retention volume R in m ³ = volume flow pump in m³/h * time in hours; R = 8m³/h * (45 s or 0.0125 h); R = 100 L. This means that a volume of 100 l is sufficient for the filling process of the chemicals or water-polluting substances alone (using the dead man’s switch).
As even small splash losses must be retained (§ 17 Para. 1 No. 3 AwSV), it is recommended that chemical binding agents are also used, as otherwise the surface must be cleaned regularly after filling and the cleaning water must be treated in the internal waste water system (if this is provided for and approved as a waste water flow in the indirect discharge permit under water law).
cc.
Precipitation water In addition, there is any precipitation water that may occur if there is no complete cover, § 19 Para.
7 AwSV in conjunction with. § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 No. 6.1.2 Para.
6, the actual question of the AwSV filling system contribution in the event of heavy precipitation.
In this case, drains in retention facilities in accordance with § 19 Para.
1 AwSV in conjunction with § 15 para.
1 no. 1 AwSV in conjunction with DWA-A 779:2023 no. 6.1.1 para.
5 permissible.
The drain must be sealed for the duration of filling and may only be discharged into the sewer system after it has been determined that it is free of contamination § 19 Para.
7 AwSV in conjunction with § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 No. 6.1.2 para.
7. any contaminated precipitation water must either be disposed of externally or treated in the company’s own wastewater system, provided the wastewater system is designed for this (usually: yes) and the treatment of the contaminated precipitation water in the wastewater system is covered by the indirect discharge permit (usually: no).
Furthermore, the cover is only complete if it extends beyond the edge of the retention facility and the areas draining into the retention facility by at least 0.6 times the clear height of the cover.
The clear height can be reduced, for example, by weather aprons or walls.
§ Section 19 Para.
7 AwSV in conjunction with § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 No. 6.1.2 Para. 9. an incomplete roofing requires rainwater retention at the site according to KOSTRA-DWD-2020 grid field, e.g. No. 121175 (example for Federal Environment Agency in Dessau), with 18.1 mm heavy precipitation height/m² (= 18.1/m², at 66 m² ~ 1195 L rainwater retention volume; extinguishing water retention is not taken into account here and may have to be checked separately; previously, extinguishing water retention was possible via the grid field).
to be checked separately; previously, the „DWA standard rainfall“ of 50 l/m² was to be assumed here) approx. for a 15-minute heavy rainfall every 5 years (5a) acc.
§ 19 Abs.
7 AwSV in conjunction with § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 No. 6.1.2 para. 8.
8. a prerequisite is constant monitoring and proper controlled discharge of the precipitation water into the company’s own wastewater system (if included in the indirect discharger permit) for treatment within 15 minutes (otherwise: 72h observation period with 61.0 mm = 61.0 L/m² corresponding to 4026 l rainwater retention volume on 66 m²).
As these are values from 2020, more recent heavy rainfall events from 2024 (e.g. 85 L/m² in Nuremberg) have not yet been taken into account.
Reference is made to the no-fault liability for damages according to § 89f WHG, i.e. it is recommended to plan larger (e.g. according to 30a instead of 5a, i.e. 27.5 L/m² for a 15 min observation period or 92.5 L/m² for a 72 h observation period, but possibly more).
The required retention volume is therefore 100 l for the actual chemicals when using a dead man’s switch and at least 1195 l (with control and discharge option) or 4026 l when using the 5a observation period for the precipitation water, i.e. a total of 1295 l or 4126 l. When using the 30a observation period – if this is sufficient at all for heavy precipitation – it is 1815L or 6105L (plus 100L each for the actual filling using a dead man’s switch).
dd.
Discharge of several filling lines into the same retention facility In accordance with § 18 Para.
7 AwSV in conjunction with § 15 Para.
1 no. 1 AwSV in conjunction with DWA-A 779:2023 no. 6.1.1 para.
2, a joint retention facility for several water-polluting substances is not possible if this impairs the function of the retention facility.
In outdoor areas, according to § 17 Para.
2 AwSV in conjunction with § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 779:2023 No. 5.1.3 Para.
1 with direct sunlight and an assumed heating up to approx. 101°C for PE black at 60°C outside temperature (according to DWA-A 779:2023 No. 5.1.3 Para. 2) as well as the largest expected contamination, a joint retention facility for several water-polluting substances is not possible.
2) as well as the maximum expected temperature development of the resulting reaction heat during the neutralization of regularly present, industry-typical chemicals, such as 38% H2SO4 and 50% NaOH, a temperature increase of approx. 50°C, i.e. a total of 151°C, is to be expected.
Any coatings or plastics would have to be checked for temperature resistance and excluded if necessary, or separate drip pans would be required, at least for H2SO4.
This also applies to any WHG coatings. WHG concrete in accordance with the DAfStb guideline regularly fulfills this requirement, cf. also § 15 Para.
1 No. 1 AwSV in conjunction with. DWA-A 786.
ee.
Structural design of the retention facility With regard to the choice of material for filling, in accordance with § 15 Para.
1 No. 1 AwSV in conjunction with. DWA-A 786, 5.2 Para.
2, at least the „medium“ stress level must be selected as a rule, as the exceptions to the „low“ stress level only apply in rare cases.
With regard to the structural design, § 15 Para.
1 No. 1 AwSV in conjunction with. DWA-A 786, 6, a distinction must also be made between the different areas within the retention facility: These are subdivided into:
- Drainage areas § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 786, 2.1.1 – not part of the retention volume Systems for discharging liquid substances hazardous to water downhill (usually ≥ 2 %). - Reservoirs § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 786, 2.1.1 – Part of the retention volume Facilities for the temporary retention of liquid substances hazardous to water (e.g. underground storage tanks, single-walled with lining). - Low point § 15 Para.
1 No. 1 AwSV in conjunction with DWA-A 786, 2.1.1 – Part of the retention volume Facility in which liquid substances hazardous to water first accumulate (e.g. lowest part of a pump sump that serves as a pump sump).
Different designs are possible depending on the case.