15A NCAC 02T .0705       DESIGN CRITERIA

(a)  The requirements in this Rule apply to all new and expanding facilities, as applicable.

(b)  Degree of treatment shall be based on a monthly average 5-day Biochemical Oxygen Demand (BOD5) ≤ 10 mg/L; Total Suspended Solids (TSS) ≤ 15 mg/L; Ammonia Nitrogen (NH3-N) ≤ 4 mg/L; Fecal Coliforms ≤ 14 per 100 mL; and Nitrate Nitrogen (NO3-N) ≤ 10 mg/L for domestic and commercial operations. Treatment for other operations shall be based on producing the quality effluent used in documenting protection of surface water or groundwater standards.  More stringent effluent limits may be applied in accordance with calculations submitted by the applicant to document protection of surface water or groundwater standards.

(c)  All treatment/storage lagoons/ponds shall have at least two feet of freeboard.

(d)  Waste, including treated waste, shall not be placed directly into, or in contact with, GA classified groundwater unless such placement will not result in a contravention of GA groundwater standards, as demonstrated by predictive calculations or modeling.

(e)  Treatment works and disposal systems utilizing earthen basins, lagoons, ponds or trenches, excluding holding ponds containing non-industrial treated effluent prior to spray irrigation, for treatment, storage or disposal shall have either a liner of natural material at least one foot in thickness and having a hydraulic conductivity of no greater than 1 x 10-6 centimeters per second when compacted, or a synthetic liner of sufficient thickness to exhibit structural integrity and an effective hydraulic conductivity no greater than that of the natural material liner.

(f)  The bottoms of earthen impoundments, trenches or other similar excavations shall be at least four feet above the bedrock surface, except that the bottom of excavations which are less than four feet above bedrock shall have a liner with a hydraulic conductivity no greater than 1 x 10-7 centimeters per second.  Liner thickness shall be that thickness necessary to achieve a leakage rate consistent with the sensitivity of classified groundwaters.  Liner requirements may be reduced if it can be demonstrated to the Division by predictive calculations or modeling methods that construction and use of these treatment and disposal units will not result in contravention of surface water or groundwater standards.

(g)  Impoundments, trenches or other excavations made for the purpose of storing or treating waste shall not be excavated into bedrock unless the placement of waste into such excavations will not result in a contravention of surface water or groundwater standards, as demonstrated by predictive calculations or modeling.

(h)  Flow equalization of at least 25 percent of the facilities permitted hydraulic capacity must be provided for all seasonal or resort facilities and all other facilities with fluctuations in influent flow which may adversely affect the performance of the system.

(i)  By-pass and overflow lines shall be prohibited.

(j)  Multiple pumps shall be provided if pumps are used.

(k)  Power reliability shall be provided consisting of:

(1)           automatically activated standby power supply onsite, capable of powering all essential treatment units under design conditions; or

(2)           approval by the Director that the facility:

(A)          serves a private water distribution system which has automatic shut-off at power failure and no elevated water storage tanks,

(B)          has sufficient storage capacity that no potential for overflow exists, and

(C)          can tolerate septic wastewater due to prolonged detention.

(l)  A water-tight seal on all treatment/storage units or minimum of two feet protection from 100-year flood shall be provided.

(m)  Irrigation system design shall not exceed the recommended precipitation rates in the soils report prepared pursuant to Rule .0704 of this Section.

(n)  A minimum of 30 days of residuals storage shall be provided.

(o)  Disposal areas shall be designed to maintain a one-foot vertical separation between the seasonal high water table and the ground surface.

(p)  The public shall be prohibited access to the wetted disposal area and treatment facilities.

(q)  Influent pump stations shall meet the sewer minimum design criteria as provided in Section .0300 of this Subchapter.

(r)  Septic tanks shall adhere to 15A NCAC 18A .1900.


History Note:        Authority G.S. 143-215.1; 143-215.3(a);

Eff. September 1, 2006.