Septic tanks can leach nitrates into water systems, like rivers and aquifers. however, some homes are too far away from municipal treatment facilities to use anything else. what can county officials reasonably do to ensure septic systems are not harming their community?

The county officials can ensure that each septic tank has a drain-field alongside it. A drain-field must have a suitable type of soil that is capable of treating the waste before it reaches groundwater. The drain-fields should be well aerated to enable breakdown of nutrients such as nitrates.

They could also introduce holding tanks that are frequently emptied using exhausters to the treatment facilities

i think that d. wind is the answer.   i missed the question when i answered a. currents.