14 CAR § 21-1001. Generally

(a)(1) Secondary treatment systems utilize an additional means of septic effluent treatment subsequent to the primary treatment performed by a septic tank. (2) Some aerobic treatment units (ATUs) do not require that effluent be treated by a septic tank prior to treatment by the ATU. (3) Secondary treatment units incorporated into the design of an onsite wastewater system shall comply with the following specifications. (b) Secondary treatment units with surface discharge shall meet current NPDES discharge requirements. (c) Onsite wastewater systems incorporating secondary treatment units shall comply with the Onsite Wastewater Systems Monitoring Program outlined in 14 CAR § 21-1101 et seq.