That's always a possibility. However, if you are experiencing this only in heavy rains it could very easily be your leach field is becoming heavily saturated by the rains and the runoff is seeping back into the system. This is actually a question best answered by a septic professional. They will, more than likely, need to visit your home and inspect your current septic system and leach fields. Many septic companies will provide free estimates for repairs which can help identify what is happening.
A better place to ask this question would be the professional plumbing forums available. Here is a short list of active forums to check out:
When you are ready to seek a wastewater treatment professional the two largest associations have a find function on their sites:
Good luck and I hope it works out for you!
Emmanuel J. Scanlan
PS Inspection & Property Services LLC
TREC License # 7593
International Code Council, Residential Combination Inspector #5247015-R5 (Electrical, Mechanical, Plumbing and Building)
Texas Residential Construction Commission, Third Party Warranty Inspector #1593
Texas Residential Construction Commission, Inspector, County Inspection Program
Texas Department Of Insurance, VIP Inspector # 08507061016
Hayman Residential Engineering Services, Field Technician
CMC Energy - Certified Energy Auditor
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