Appendix 75-A.4 - Soil and site appraisal

Section 75-A.4 Soil and site appraisal. (a) Site Investigation.

(1) Areas lower than the 10 year flood level are unacceptable for on-site systems. Slopes greater than 15% are also unacceptable.

(2) There must be at least four feet of useable soil available above rock, unsuitable soil, and high seasonal groundwater for the installation of a conventional absorption field system (75-A.8(b)).

(3) Soils with very rapid percolation rates (faster than one minute per inch) are not suitable for subsurface absorption systems unless the site is modified by blending with a less permeable soil to reduce the infiltration rate throughout the area to be used.

(4) Subsurface treatment systems and components of the sewage system shall be separated from buildings, property lines, waterbodies, utilities and wells, to maintain system performance, permit repairs and reduce undesirable effects of underground sewage flow and dispersion. Table 2 lists the acceptable minimum separation distances from the various components of onsite wastewater treatment systems.

(5) Once the required infiltration area is determined by daily flow, percolation tests and soil evaluation, the required useable area of the property for subsurface treatment can be found. An additional useable area of 50 percent shall be set aside for future expansion or replacement whenever possible.

(b) Separation Requirements:

 

TABLE 2

SEPERATION DISTANCES FROM WASTEWATER SYSTEM COMPONENTS (in Feet)

 

System Components

Well or Suction Line(e)(g)

To Stream, Lake, watercourse(b), or Wetland

Dwelling

Property Line

House sewer (watertight joints)

25 if cast iron sewer pipe, 50 otherwise

25

3

10

Septic tank or watertight ETU

50

50

10

10

Effluent line to distribution box

50

50

10

10

Distribution box

100

100

20

10

Absorption field(c)(d)

100(a)

100

20

10

Seepage pit(d)

150(a)

100

20

10

Raised or mound system(c)(d)

100(a)

100

20

10

Intermittent Sand Filter(d)

100(a)(f)

100(f)

20

10

Non-Waterborne Systems with offsite residual disposal

50

50

20

10

Non-Waterborne Systems with onsite discharge

100

50

20

10

 

NOTES:       (a) When wastewater treatment systems are located upgrade and in the direct path of surface water drainage to a well, the closest part of the treatment system shall be at least 200 feet away from the well.

                    (b) Mean high water mark

                    (c) For all systems involving the placement of fill material, separation distances are measured from the toe of slope of the fill.

                    (d) Separation distances shall also be measured from the edge of the designated additional usable area as described in section 75-A.4(a)(5)

                    (e) The closest part of the wastewater treatment system shall be located at least 10 feet from any water service line (e.g. public water supply main, public water service line or residential well water service line).

                    (f) When sand filters are designed to be watertight and collect all effluent, the separation distance can be reduced to 50 feet.

                    (g) The listed water well separation distances from contaminant sources shall be increased by 50 percent whenever aquifer water enters the water well at less than 50 feet below grade. If a 50 percent increase cannot be achieved, then the greatest possible increase in separation distance shall be provided with such additional measures as needed to prevent contamination.

(c) Soil Investigation. (1) The highest groundwater level shall be determined and shall include the depth to the seasonal high groundwater level and the type of water table -- perched, apparent, or artesian.

(2) If a subsurface treatment unit such as an absorption field is planned, at least four feet of useable soil shall be available over impermeable deposits (i.e., clay or bedrock). Highest groundwater level shall be at least two feet below the proposed trench bottom. Where systems are to be installed above drinking water aquifers, a greater separation distance to bedrock may be required by the local health department having jurisdiction. At least one test hole at least six feet deep shall be dug within or immediately adjacent to the proposed leaching area to insure that uniform soil and site conditions prevail. If observations reveal differing soil profiles, additional holes shall be dug and tested. These additional holes shall be spaced to indicate whether there is a sufficient area of useable soil to install the system. Treatment systems shall be designed to reflect the most severe conditions encountered. If the percolation tests results are inconsistent with field determined soil conditions, additional percolation tests must be conducted and the more restrictive tests must be the factor used for the system design. (3) Test holes for seepage pits shall extend to at least mid-depth and full depth of the proposed pit bottom. At least three feet of useable soil shall exist between the pit bottom and rock or other impermeable soil layer and the highest groundwater level. This shall be confirmed by extending at least one deep test hole three feet below the deepest proposed pit.

(4) A local health department may accept or require other soil tests in lieu of the percolation test when such tests are conducted or observed by local health department personnel.

(d) Soil Percolation Test. (1) At least two percolation tests shall be made at the site of each proposed sewage treatment system.

(2) For seepage pits, one test shall be conducted at the bottom depth, and the other at half the pit depth. If different soil layers are encountered when digging the test pit, a percolation test shall be performed in each layer with the overall percolation rate being the weighted average of each test based upon the depth of each layer. The local health department having jurisdiction may adopt an alternative procedure for determining the permeability of soil for the installation of seepage pits.

(3) A percolation test is only an indicator of soil permeability and must be consistent with the soil classification of the site as determined from the test holes.

Effective Date: 
Wednesday, February 3, 2010
Doc Status: 
Complete