(1) A vertical separation of at least three feet is required between the infiltrative surface of the drainfield bed or trench and:

(a) The highest seasonal water table;

(b) A restrictive layer; or

(c) Soil types 6 or 7.

(2) The department may allow a reduction of vertical separation to a minimum of two feet when all of the following criteria are met:

(a) Soil types 2-5;

(b) Treatment is provided prior to dispersal as follows:

(i) For LOSS with design flows up to and including 14,500 gpd, Treatment Level C or better;

(ii) For LOSS with design flows greater than 14,500 gpd, Treatment Level HQE.

(c) Information collected during the site review process clearly demonstrates minimum vertical separation can be maintained across the primary and reserve drainfield areas;

(d) An HGR is submitted that demonstrates that the site can safely and adequately disperse the effluent; and

(e) The monitoring and reporting plan includes a sampling program and schedule that demonstrates that required performance standards are consistently met.

(3) The department may impose additional requirements when necessary to protect public health and the environment including, but not limited to:

(a) Higher level of treatment;

(b) Monitoring and evaluation of the seasonal high water table;

(c) Additional tank capacity to handle flow surges and allow flow attenuation; and

(d) Increased horizontal setbacks.