The following companies are certified:
As at 2017-10-26
Certifications of companies according to DVGW guideline W 120-1
Company
Scope of certification
Certificate-Reg.-No.
Expiry
Stölben GmbH
Barlstr. 42
D-56856 Zell
A3, B1, B3, S1-5
600001.500.17253

30.09.2022
BOG Bohr- und Umwelttechnik GmbH
Eselsteig 17
D-07586 Caschwitz
A4, B2, B4
600052.500.19101
19.03.2024
Behringer + Dittmann Bohrgesellschaft mbH
Schieräckerstr. 35
D-90431 Nürnberg
A3, B2, B 5, S3, S4, S5
10002.500.14001
27.07.2019
Certifications of companies according to DVGW guideline W 120-2
Company
Scope of certification
Certificate-Reg.-No.
Expiry
Behringer + Dittmann Bohrgesellschaft mbH
Schieräckerstr. 35
D-90531 Nürnberg
G200
10002.502.14002
27.07.2019
Certifications of companies according to EN ISO 22475
Company
Scope of certification
Certificate-Reg.-No.
Expiry
Stölben_GmbH
Barlstr. 42
D-56856 Zell
sampling category A (continuously core samples)
installation of piezometers(diameter up to 200 mm)
600001.501.17251
30.09.2022
Abbrevitions:Installion of wells
A1 - well diameter larger than DN 400
A2 - well diameter up to DN 400
A3 - well diameter up to DN 300
A4 - well diameter up to DN 150

boreholes
B1 - dry drilling methods deeper than 75 m 
B2 - dry drilling mehtods up to a depth of 75 m
B3 - hydraulic circulation drilling methods deeper than 300 m 
B4 - hydraulic circulation drilling methods up to a depth of 300 m 
B5 - hydraulic circulation drilling methods up to a depth of 100 m

Well regeneration
R1 - mechanical regeneration
R2 - chemical regneration

Restoration and dismantling
S1 - annular space sealing
S2 - insertion casing
S3 - washover/pipe cut
S4 - backfilling/partial backfilling
S5 - dismantling

Geothermal heat excahnges (BHE)
G200 - BHE up to a depth of 200 m