SIOUX CITY, Iowa (AP) — A city in northwest Iowa is waiting for a biofuels company to pay $77,500 in fines and explain why its Nebraska plant has exceeded daily limits on solids sent to the city’s wastewater treatment plant. Sioux City is still seeking answers on why Wisconsin-based Big Ox Energy has surpassed daily limits of about 48,500 pounds of solids sent to the city’s wastewater treatment plant at least 33 times since June. The releases have put the city at risk of violating its own wastewater treatment permit with the state.

Assistant city attorney Justin Vondrak tells the Sioux City Journal that Big Ox has mentioned equipment failures, but hasn’t provided a full explanation. Big Ox spokesman Kevin Bradley says the company is working to resolve the issues. The city is currently reviewing the company’s permit renewal request.