Section R18-9-A310. Site Investigation for Type 4 On-site Wastewater Treatment Facilities

A.      Definition. For purposes of this Section, “clean water” means water free of colloidal material or additives that could affect chemical or physical properties if the water is used for percola- tion or seepage pit performance testing.

B.       Site investigation. An applicant shall ensure that an investiga- tor qualified under subsection (H) conducts a site investigation consisting of a surface characterization under subsection (C) and a subsurface characterization under subsection (D). The applicant shall submit the results in a format prescribed by the Department. The site investigation shall provide sufficient data to:

1.        Select appropriate primary and reserve disposal areas for an on-site wastewater treatment facility considering all surface and subsurface limiting conditions in subsections (C)(2) and (D)(2); and;

2.        Effectively design and install the selected facility to serve the anticipated development at the site, whether or not limiting conditions exist.

C.      Surface characterization.

1.        Surface characterization method. The investigator shall characterize the surface of the site where an on-site wastewater treatment facility is proposed for installation using one of the following methods:

a.         The “Standard Practice for Surface Site Characteri- zation for On-site Septic Systems, D5879-95 (2003),” published by the American Society for Testing and Materials. This material is incorporated by reference and does not include any later amend- ments or editions of the incorporated material. Cop- ies of the incorporated material are available for inspection at the Arizona Department of Environ- mental Quality, 1110 W. Washington, Phoenix, AZ 85007 or may be obtained from the American Soci- ety for Testing and Materials International, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959; or

b.        Another method of surface characterization that can, with accuracy and reliability, identify and delineate the surface limiting conditions specified in subsec- tion (C)(2).

2.        Surface limiting conditions. The investigator shall deter- mine whether, and if so, where any of the following sur- face limiting conditions exist:

a.         The surface slope is greater than 15 percent at the intended location of the on-site wastewater treat- ment facility;

b.        Minimum setback distances are not within the limits specified in R18-9-A312(C);

c.         Surface drainage characteristics at the intended loca- tion of the on-site wastewater treatment facility will adversely affect the ability of the facility to function properly;

d.        A 100-year flood hazard zone, as indicated on the applicable flood insurance rate map, is located within the property on which the on-site wastewater treatment facility will be installed;

e.         An outcropping of rock that cannot be excavated exists in the intended location of the on-site waste-

water treatment facility or will impair the function of soil receiving the discharge; and

f.         Fill material deposits exist in the intended location of the on-site wastewater treatment facility.

D.      Subsurface characterization.

1.        Subsurface characterization method. The investigator shall characterize the subsurface of the site where an on- site wastewater treatment facility is proposed for installa- tion using one or more of the following methods:

a.         The following ASTM standard practices, which are incorporated by reference and do not include any later amendments or editions of the incorporated material. Copies of the incorporated material are available for inspection at the Arizona Department of Environmental Quality, 1110 W. Washington, Phoenix, AZ 85007 or may be obtained from the American Society for Testing and Materials Interna- tional, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959:

i.         “Standard Practice for Subsurface Site Charac- terization of Test Pits for On-site Septic Sys- tems, D5921-96(2003)e1 (2003),” published by the American Society for Testing and Materi- als; and

ii.        “Standard Practice for Soil Investigation and Sampling by Auger Borings, D1452-80 (2000),” published by the American Society for Testing and Materials;

b.        Percolation testing as specified in subsection (F);

c.         Seepage pit performance testing as specified in sub- section (G); or

d.        Another method of subsurface characterization, approved by the Department, that ensures compli- ance with water quality standards through proper system location, selection, design, installation, and operation.

2.        Subsurface limiting conditions. The investigator shall determine whether any of the following limiting condi- tions exist in the primary and reserve areas of the on-site wastewater treatment facility within a minimum of 12 feet of the land surface or to an impervious soil or rock layer if encountered at a shallower depth:

a.         The soil absorption rate determined under R18-9- A312(D)(2) is:

i.         More than 1.20 gallons per day per square foot, or

ii.        Less than 0.20 gallons per day per square foot;

b.        The vertical separation distance from the bottom of the lowest point of the disposal works to the sea- sonal high water table is less than the minimum ver- tical separation specified in R18-9-A312(E)(1);

c.         Seasonal saturation occurs within surface soils that could affect the performance of the on-site wastewa- ter treatment facility;

d.        One of the following subsurface conditions that may cause or contribute to the surfacing of wastewater:

i.         An impervious soil or rock layer,

ii.        A zone of saturation that substantially limits downward percolation from the disposal works,

iii.      Soil with more than 50 percent rock fragments;

e.         One of the following subsurface conditions that pro- motes accelerated downward movement of insuffi- ciently treated wastewater:

i.         Fractures or joints in rock that are open, contin- uous, or interconnected;

ii.        Karst voids or channels; or

iii.      Highly permeable materials such as deposits of cobbles or boulders; or

f.         A subsurface condition that may convey wastewater to a water of the state and cause or contribute to an exceedance of a water quality standard established in 18 A.A.C. 11, Articles 1 and 4.

3.        Applicability  of  subsurface  characterization   methods. The investigator shall:

a.         For a seepage pit constructed under R18-9-E302, test seepage pit performance using the procedure specified in subsection (G);

b.        For an on-site wastewater treatment facility other than a seepage pit, characterize soil by using one or more of the ASTM methods specified in subsection (D)(1)(a) if any of the following site conditions exists:

i.         The natural surface slope at the intended loca- tion of the on-site wastewater treatment facility is greater than 15 percent;

ii.        Bedrock or similar consolidated rock formation that cannot be excavated with a shovel outcrops on the property or occurs less than 12 feet below the land surface;

iii.      The native soil at the surface or encountered in a boring, trench, or hole consists of more than 35 percent rock fragments;

iv.       The seasonal high water table occurs within 12 feet of the natural land surface as encountered in trenches or borings, or evidenced by well records or hydrologic reports;

v.        Seasonal saturation at the natural land surface occurs as indicated by soil mottling, vegetation adapted to near-surface saturated soils, or springs, seeps, or surface water near enough to the intended location of the on-site wastewater treatment facility to have a  connection  with potential seasonal saturation at the land surface; or

vi.       A percolation test yields results outside the lim- its specified in subsection (D)(2)(a) and (b).

c.         Percolation testing. The investigator may perform percolation testing as specified in subsection (F):

i.         To augment another method of subsurface char- acterization if useful to locate or design an on- site wastewater treatment facility, or

ii.        As the sole method of subsurface characteriza- tion if a subsurface characterization by an ASTM method is not required under subsection (D)(3)(b).

E.       If an ASTM method is used for subsurface characterization, the investigator shall conduct subsurface characterization tests at the site to provide adequate, credible, and representative information to ensure proper location, selection, design, and installation of the on-site wastewater treatment facility. The investigator shall:

1.        Select at least two test locations in the primary area and one test location in the reserve area to conduct the tests;

2.        Perform  the  characterization  at  each  test  location  at appropriate depths to:

a.         Establish the wastewater absorption capacity of the soil under R18-9-A312(D), and

b.        Aid in determining that a sufficient zone of unsatu- rated flow is provided below the disposal works to achieve necessary wastewater treatment; and

3.        Submit with the site investigation report:

a.         A log of soil formations for each test location with information on soil type, texture, and classification; percentage of rock; structure; consistence; and mot- tles;

b.        A determination of depth to groundwater below the land surface by test trenches or borings, published groundwater data, subdivision reports, or relevant well data; and

c.         A determination of the water absorption characteris- tics of the soil, under R18-9-A312(D)(2)(b), suffi- cient to allow location and design of the on-site wastewater treatment facility.

F.       Percolation testing method for subsurface characterization.

1.        Planning and preparation. The investigator shall:

a.         Select at least two locations in the primary area and at least one location in the reserve area for percola- tion testing, to provide adequate and credible infor- mation to ensure proper location, selection, design, and installation of a properly working on-site waste- water treatment facility;

b.        Perform percolation testing at each location at inter- vals in the soil profile sufficient to:

i.         Establish the wastewater absorption capability of the soil under R18-9-A312(D), and

ii.        Aid in determining that a sufficient zone of unsaturated flow is provided below the disposal works to achieve necessary wastewater treat- ment. The investigator shall perform percola- tion tests at multiple depths if there is an indication of an obvious change in soil charac- teristics that affect the location, selection, design, installation, or disposal performance of the on-site wastewater treatment facility;

c.         Excavate percolation test holes in undisturbed soil at least 12 inches deep with dimensions of 12 inches by 12 inches, if square, or a diameter of 15 inches, if round. The investigator shall not alter the structure of the soil during the excavation;

d.        Place percolation test holes away from site or soil features that yield unrepresentative or misleading data pertaining to  the location, selection, design, installation, or performance of the on-site wastewa- ter treatment facility;

e.         Scarify smeared soil surfaces within the percolation test holes and remove any loosened materials from the bottom of the hole; and

f.         Use buckets with holes in the sides to support the sidewalls of the percolation test hole, if necessary. The investigator shall fill any voids between the walls of the hole and the bucket with pea gravel to reduce the impact of the enlarged hole.

2.        Presoaking procedure. The investigator shall:

a.         Fill the percolation test hole with clean water to a depth of 12 inches above the bottom of the hole;

b.        Observe the decline of the water level in the hole and record time in minutes for the water to com- pletely drain away;

c.         Repeat the steps specified in subsection (F)(2)(a) and (b) if the water drains away in less than 60 min- utes.

i.         If the water drains away the second time in less than 60 minutes, the investigator shall repeat the steps specified in subsections (F)(2)(a) and (b).

ii.        If the water drains away a third time in less than 60 minutes, the investigator shall perform the

	percolation test by following subsection (F)(3);		design  of  the   on-site  wastewater   treatment
	and		facility.
	d.     Add clean water to the hole after 60 minutes and	G.	Seepage pit performance testing method for subsurface char-
	maintain the water at a minimum depth of 9 inches		acterization. The investigator shall test seepage pits described
	for at least four more hours if it takes 60 minutes or		in R18-9-E302 as follows:
	longer for the water to drain away. The investigator		1.     Planning and Preparation. The investigator shall:
	shall protect the hole from precipitation and runoff,		a.      Identify the disposal areas at the site and drill a test
	and perform the percolation test specified in subsec-		hole at least 18 inches in diameter to the depth of the
	tion (F)(3) between 16 and 24 hours after presoak-		proposed seepage pit, at least 30 feet deep, and
	ing.		b.     Scarify soil surfaces within the test hole and remove
3.	Conducting the test. The investigator shall:		loosened materials from the bottom of the hole.
	a.      Conduct the percolation test before soil hydraulic		2.     Presoaking procedure. The investigator shall:
	conditions established by the presoaking procedure		a.      Fill the bottom 6 inches of the test hole with gravel,
	substantially change. The investigator shall remove		if necessary, to prevent scouring;
	loose materials in the percolation test hole to ensure		b.     Fill the test hole with clean water up to 3 feet below
	that the specified dimensions of the hole are main-		the land surface;
	tained and the infiltration surfaces are undisturbed		c.      Observe the decline of the water level in the hole
	native soil;		and determine the time in hours and minutes for the
	b.     Fill the test hole to a depth of six inches above the		water to completely drain away;
	bottom with clean water;		d.     Repeat the procedure if the water drains away in less
	c.      Observe the decline of the water level in the test hole		than four hours; If the water drains away the second
	and record the time in minutes for the water level to		time in less than four hours, the investigator shall
	fall exactly 1 inch from a fixed reference point. The		conduct the seepage pit performance test by follow-
	investigator shall:		ing subsection (G)(3);
	i.      Immediately refill the hole with clean water to		e.      Add water to the hole and maintain the water at a
	a  depth  of  6  inches  above  the  bottom,   and		depth  that  leaves   at  least  the  top 3  feet  of  hole
	determine and record the time in minutes for		exposed to air for at least four more hours if the
	the water level to fall exactly 1 inch,		water drains away in four or more hours; and
	ii.     Refill the hole again with clean water to a depth		f.      Not remove the water from the hole before the seep-
	of 6 inches above the bottom and determine and		age pit performance test if there is standing water in
	record the time in minutes for the water to fall		the hole after at least 16 hours of presoaking.
	exactly 1 inch, and		3.     Conducting the test. The investigator shall:
	iii.   Ensure that the method for measuring water		a.      Fill the test hole with clean water up to 3 feet below
	level depth is accurate and does not signifi-		land surface;
	cantly affect  the  percolation  rate of  the  test		b.     Observe the decline of the water level in the hole
	hole;		and determine and record the vertical distance to the
	d.     If the percolation rate stabilizes for three consecu-		water level from a fixed reference point every 10
	tive measurements by varying no more than 10 per-		minutes.  The   investigator  shall  ensure  that  the
	cent, use the highest percolation rate value of the		method for measuring water level depth is accurate
	three measurements. If three consecutive measure-		and does not significantly affect the rate of fall of the
	ments indicate that the percolation rate results are		water level in the test hole;
	not stabilizing or the percolation rate is between 60		c.      Measure the decline of the water level continually
	and 120 minutes per inch, the investigator shall use		until  three  consecutive   10-minute  measurements
	an alternate method based on a graphical solution of		indicate that the infiltration rates are within 10 per-
	the test data to approximate the stabilized percola-		cent. If measurements indicate that infiltration is not
	tion rate;		approaching a steady rate or if the rate is close to a
	e.      Record the percolation rate results in minutes per		numerical limit specified in R18-9-A312(E)(1), the
	inch; and		investigator shall use, an alternate method based on
	f.      Submit  the  following  information  with  the  site		a graphical solution of the test data to approximate
	investigation report:		the final stabilized infiltration rate;
	i.      A log of the soil formations encountered for all		d.     Percolation test rate. Calculate the stabilized infiltra-
	percolation tests including information on tex-		tion rate for a seepage pit determined by the test hole
	ture, structure, consistence, percentage of rock		procedure specified in subsection (G)(1)(a) using the
	fragments, and mottles, if present;		formula P = (15 / DS) x IS to determine an equiva-
	ii.     Whether and which test hole was reinforced		lent percolation test rate. Once “P” is determined,
	with a bucket;		the investigator shall use R18-9-A312(D)(2)(a) to
	iii.   The locations, depths, and bottom elevations of		establish  the  design  SAR  for  wastewater  treated
	the percolation test holes on the site investiga-		under R18-9-E302 and to calculate the required min-
	tion map;		imum sidewall area for the seepage pit using the
	iv.   A determination of depth to groundwater below		equation specified in R18-9-E302(C)(5)(k).
	the land surface by test trenches or borings,		i.      “P” is the percolation test rate (minutes per
	published       groundwater        data,      subdivision		inch) tabulated in the first column of the table
	reports, or relevant well data; and		in R18-9-A312(D)(2)(a),
	v.     A determination of the water absorption char-		ii.     “DS” is the diameter of the seepage pit test hole
	acteristics        of      the      soil,      under       R18-9-		in inches, and
	A312(D)(2)(a), sufficient to allow location and		iii.   “IS” is the seepage pit stabilized infiltration

rate (minutes per inch) determined by the pro- cedure specified in R18-9-A310(F)(3)(c);

e.         Submit the following information with the site investigation report:

i.         The results of the seepage pit performance test- ing including data, calculations, and findings on a form provided by the Department;

ii.        The log of the test hole indicating lithologic characteristics and points of change;

iii.      The location of the test hole on the site investi- gation map;

iv.       A determination of depth to groundwater below the land surface by borings, published ground- water data, subdivision reports, or relevant well data.

f.         Fill the test hole so that groundwater quality and public safety are not compromised if the seepage pit is drilled elsewhere or if a seepage pit cannot be sited at the location because of unfavorable test results.

H.       Qualifications. An investigator shall not perform a site investi- gation under this Section unless the investigator has knowl- edge and competence in the subject area and is licensed in good standing or otherwise qualified in one of the following categories:

1.        Arizona-registered professional engineer,

2.        Arizona-registered geologist,

3.        Arizona-registered sanitarian,

4.        A certificate of training from a course recognized by the Department as sufficiently covering the information spec- ified in this Section, or

5.        Qualifies under another category designated in writing by the Department.

Historical Note

New Section adopted by final rulemaking at 7 A.A.R. 235, effective January 1, 2001 (Supp. 00-4). Amended by final rulemaking at 11 A.A.R. 4544, effective November 12, 2005 (05-3).