M Rapp, not only should you be concerned, you should bring your concerns to the attention of your neighbor immediately. Depending on your relationship with the neighbor, you may want to put your concerns in writing, describing the problem. The neighbor’s sewage effluent is a serious threat to public health (your health), and a threat to the environment.
Disease organisms, like cholera, typhoid, and many others may be in the effluent which could be transmitted to you by insects such as flys, mosquitos, other disease vectors, and other critters like your cat or dog. Dogs love to roll in sewage.
If the system is not repaired within 60 days or so, contact the local health department, and let them bring their considerable power to bare to solve the problem. First try to reason with your neighbor, and make sure that he/she is aware of your concerns. JWA