Waterproofing and Drainage As a certified licensed General Engineering contractor (A-License) in Los Angeles, we couple our skills and knowledge to get the job done right because you shouldn't have to pay more for something that could have been finished correctly the first time around. Along with our general engineering A-License, we also have all the necessary permits to work with drains and backfills, such as: E-permit and S-permit. Prieto Engineering does it all, and we do it effectively, and efficiently. We worry about drains and drain repair and anything related to it. As part of our full-service package we include drainage as part of the construction process. If you have a foundation or retaining wall that needs backfilling or a drain that needs repair, give Prieto Engineering a call.