Section R18-9-C304. 2.04 General Permit: Drywells that Drain Areas at Motor Fuel Dispensing Facilities Where Motor Fuels are Used, Stored, or Loaded

A.      A 2.04 General Permit allows for a drywell that drains an area at a facility for dispensing motor fuel, as defined in A.A.C. R20-2-701(19), including a commercial gasoline station with an underground storage tank.

1.        A drywell at a motor fuel dispensing facility using haz- ardous substances is eligible for coverage under the 2.04 General Permit.

2.        A drywell at a vehicle maintenance facility owned or operated by a commercial enterprise or by a federal, state, county, or local government is not eligible for coverage under this general permit, unless the facility design ensures that only motor fuel dispensing areas will drain to the drywell. Areas where hazardous substances other than motor fuels are used, stored, or loaded, including service bays, are not covered under the 2.04 General Permit.

3.        Definition. For purposes of this Section, “hazardous sub- stances” means substances that are components of com- mercially packaged automotive supplies, such as motor oil, antifreeze, and routine cleaning supplies such as those

used for cleaning windshields, but not degreasers, engine cleaners, or similar products.

B.       Notice of Intent to Discharge. In addition to the requirements in R18-9-A301(B), an applicant shall submit:

1.        The Department registration number for the drywell or documentation that a drywell registration form was sub- mitted to the Department;

2.        For a drywell constructed more than 90 days before sub- mitting the Notice of Intent to Discharge to the Depart- ment, a certification signed, dated, and sealed by an Arizona-registered professional engineer or geologist that a site investigation concluded that:

a.         Analytical results from sampling sediment from the drywell settling chamber sediment for pollutants reasonably expected to be present do not exceed either the residential soil remediation levels or the groundwater protection levels;

b.        The settling chamber does not contain sediment that could be used to characterize and compare results to soil remediation levels and the chamber has not been cleaned out within the last six months;

c.         Neither a soil remediation level nor groundwater protection level is exceeded in soil samples collected from a boring drilled within 5 feet of the drywell and sampled in 5 foot increments starting at a depth of 5 feet below ground surface and extending to a depth of 10 feet below the base of the drywell injection pipe; or

d.        If coarse grained lithology prevents the collection of soil samples in a soil boring, a groundwater investi- gation demonstrates compliance with Aquifer Water Quality Standards in groundwater at the applicable point of compliance.

3.        Design information to demonstrate that the requirements in subsection (C) are satisfied.

C.      Design requirements.

1.        An applicant shall:

tude coordinates of the drywell, surface drainage patterns and the location of floor drains and French drains that are plumbed to the drywell or are used to alter drainage patterns, water supply wells, monitor wells, underground storage tanks, and chemical and waste usage, storage, loading, and treatment areas; and

i. Prepare design plans showing details  of  drywell design and drainage design, including one or a com- bination of pre-approved technologies described in subsections (D)(1) and (2) designed to remove, intercept, and collect any pollutant that may be pres- ent at the operation with the potential to reach the drywell.

2.        For an existing drywell, an applicant that cannot meet the design requirements in subsections (C)(1)(d) and (e) shall provide the Department with the date of drywell con- struction, the depth of the drywell borehole and injection pipe, the distance from the drywell to the nearest water supply well and from the drywell to the underground stor- age tank, and the depth to the groundwater from the bot- tom of the drywell injection pipe.

D.      Flow control and pretreatment. A permittee shall ensure that motor fuels and other hazardous substances are not discharged to the subsurface. A permittee may use any of the following flow control or pretreatment technologies:

1.        Flow control. The permittee shall ensure that motor fuel and hazardous substance spills are removed before allow- ing stormwater to enter the drywell.

a.         Normally closed manual or automatic valve. The permittee shall leave a normally closed valve in a closed position except when stormwater is allowed to enter the drywell;

b.        Raised drywell inlet. The permittee shall:

i.         Raise the drywell inlet at least six inches above the bottom of the retention basin or other stor- age structure, or install a six-inch asphalt or

a.	Include a flow control or pretreatment device identi-		concrete raised barrier encircling the drywell
	fied  in  subsections   (D)(1)  or  (2),  or  both,  that		inlet to provide a non-draining storage capacity
	removes, intercepts, or collects spilled motor fuel or		within the retention basin or storage structure
	hazardous substances before stormwater enters the		for complete containment of a spill; and
	drywell injection pipe;		ii.     Ensure that the storage capacity is at least 110
b.	Calculate  the   volume  of   runoff  generated   in  the		percent of the volume of the design storm event
	design  storm  event  and  anticipate   the  maximum		required by the local jurisdiction and the esti-
	potential contaminant release quantity to design the		mated volume of a potential motor fuel spill
	treatment and holding capacity of the drywell;		based on the facility’s past incident reports or
c.	Follow local codes and regulations to meet retention		incident reports for other facilities that are sim-
	periods for removing standing water;		ilar in design;
d.	Locate the drywell at least 100 feet from a water	c.	Magnetic mat or cap. The permittee shall ensure that
	supply well and 20 feet from an underground storage		the drywell inlet is sealed with a mat or cap at all
	tank;		times, except after rainfall or a storm event when the
e.	Locate the bottom of the drywell injection pipe at		mat or cap is temporarily removed to allow storm-
	least 10 feet above groundwater. If during drilling		water to enter the drywell; and that the mat or cap is
	and well installation the drywell borehole encoun-		always used with a retention basin or other type of
	ters saturated conditions, the applicant shall backfill		storage;
	the borehole with cement grout to a level at least 10	d.	Primary sump, interceptor, or settling chamber. The
	feet above the elevation at which saturated condi-		permittee may use a primary sump, interceptor, or
	tions were encountered in the borehole before con-		settling chamber only in combination with another
	structing the drywell in the borehole;		flow control or pre-treatment technology.
f.	Record the accurate latitude and longitude of the		i.      The permittee shall remove motor fuel or haz-
	drywell using a Global Positioning System device or		ardous substances from the sump, interceptor,
	site survey and record the location on the site plans;		or chamber before allowing stormwater to enter
g.	Clearly mark the drywell “Stormwater Only” on the		the drywell.
	surface grate or manhole cover;		ii.     The permittee shall install a settling chamber or
h.	Develop and maintain a current site plan showing		sump and allow the suspended solids to settle
	the location of the drywell, the latitude and longi-		before stormwater flows into a drywell; install

the drywell injection pipe in a separate chamber and connect the sump, interceptor, or chamber to the drywell inlet by piping and valving to allow the stormwater to enter the drywell.

iii. The permittee may install fuel hydrocarbon detection sensors in the sump, interceptor, or settling chamber that use flow control to pre- vent fuel from discharging into the drywell;

2.        Pretreatment. The permittee shall prevent the bypass of motor fuels and hazardous substances from the pretreat- ment system to the drywell during periods of high flow.

a.         Catch basin inlet filter. The permittee shall:

i.         Install a catch basin inlet filter to fit inside a catchment drain to prevent motor fuels and haz- ardous substances from entering the drywell,

ii.        Ensure that a motor fuel spill or a spill during a high rainfall does not bypass the system and directly release to the drywell injection pipe, and

iii.      Combine the catch basin inlet filter with a flow control technology to prevent contaminated stormwater from entering the drywell injection pipe;

b.        Combined settling chamber and an oil/water separa- tor.

i.         The permittee shall install a system that incor- porates a catch basin inlet, a settling chamber, and an oil/water separator.

ii.        The permittee may incorporate a self-sealing mechanism, such as fuel hydrocarbon detection sensors that activate a valve to cut off flow to the drywell inlet.

c.         Combined settling chamber and oil/water separator, and filter/adsorption. The permittee shall:

i.         Allow for  adequate  collection  and  treatment capacity for solid and liquid separation; and

ii.        Allow a minimum treated outflow from the sys- tem to the drywell inlet of 20 gallons per min- ute. If a higher outflow rate is anticipated, the applicant shall design a larger collection system with storage capacity.

d.        Passive skimmer.

i.         If a passive skimmer is used, the permittee shall install sufficient hydrocarbon adsorbent materi- als, such as pads and socks, or suspend the materials on top of the static water level in a sump or other catchment to absorb the entire volume of expected or potential spill.

ii.        The permittee may use a passive skimmer only in combination with another flow control or pre-treatment technology.

E.       Operation and maintenance. A permittee shall:

1.        Operate the drywell only for the subsurface disposal of stormwater;

2.        Remove or treat any motor fuel or hazardous substance spills;

3.        Replace the adsorbent material in skimmers, if installed; when the adsorbent capacity is reached;

4.        Maintain valves and associated piping;

5.        Maintain magnetic caps and mats, if installed;

6.        Remove sludge from the oil/water separator and replace the filtration or adsorption materials to maintain treat- ment capacity;

7.        Remove sediment from the catch basin inlet filters and retention basins to maintain required storage capacity;

8.        Remove accumulated sediment from the settling chamber annually or when 25 percent of the effective settling capacity is filled, whichever occurs first; and

9.        Provide new employee training within one month of hire and annual employee training on how to maintain and operate flow control and pretreatment technology used in the drywell.

F.       Inspection. A permittee shall:

1.        Conduct an annual inspection of the drywell for sediment accumulation in the chambers and in the flow control and treatment systems to ensure that the drywell is function- ing properly; and

2.        If the stormwater fails to drain through the drywell within

36 hours,  inspect  the  treatment  system  and piping  to ensure that it is functioning properly, make repairs, and perform maintenance as needed to restore proper func- tion.

G.      Recordkeeping. A permittee shall maintain, for at least 10 years, the following documents on-site or at the closest place of work and make the documents available to the Department upon request:

1.        Documentation of drywell maintenance, inspections, employee training, and sampling activities;

2.        A site plan showing the location of the drywell, the lati- tude and longitude coordinates of the drywell, surface drainage patterns and the location of floor drains or French drains that are plumbed to the drywell or are used to alter drainage patterns, water supply wells, monitor wells, underground storage tanks, and places where motor fuel and hazardous substances are used, stored, or loaded;

3.        A design plan showing details of drywell design and drainage design, including one or a combination of the pre-approved flow control and pretreatment technologies;

4.        An operations and maintenance manual that includes:

a.         Procedures to prevent and contain spills and mini- mize any discharge to the drywell and a list of actions and specific methods proposed for motor fuel and hazardous substance spills or leaks;

b.        Methods and procedures for inspection, operation, and maintenance activities;

c.         Procedures for spill response; and

d.        A description of the employee training program for drywell inspections, operations, and maintenance;

5.        Drywell sediment waste characterization and disposal manifest records for sediments removed during routine inspections and maintenance activities; and

6.        Sampling plans, certified laboratory reports, and chain of custody forms for soil, sediment, and groundwater sam- pling associated with drywell site investigations.

H.      Spills.

1.        In the event of a spill, a permittee shall:

a.         Notify the Department within 24 hours of any spill of motor fuel or hazardous or toxic substances that enters into the drywell inlet;

b.        Contain, clean up, and dispose of, according to local, state, and federal requirements, any spill or leak of motor fuel or hazardous substance in the drywell drainage area and basin drainage area;

c.         If a pretreatment system is present, verify that treat- ment capacity has not been exceeded; and

d.        If the spill reaches the injection pipe, drill a soil bor- ing within 5 feet of the drywell inlet chamber and sample in 5-foot increments from 5 feet below ground surface to a depth extending at least 10 feet below the base of the injection pipe to determine

whether a soil remediation level or groundwater pro- tection level has been exceeded in the subsurface. The permittee shall:

i.         Submit the results to the Department within 60 days of the date of the spill; and

ii.        Notify the Department if soil contamination at the facility, not related to the spill, is being addressed by an existing approved remedial action plan.

2.        The Director may, based on the results of subsection

(H)(1)(d), require the permittee to submit an application for clean closure or an individual Aquifer Protection Per- mit.

I.        Closure and decommissioning requirements.

1.        A permittee shall:

a.         Retain a drywell drilling contractor, licensed under 4

A.A.C. 9, to close the drywell;

b.        Remove sediments and any drainage component, such as standpipes and screens from the drywell’s settling chamber and backfill the injection pipe with cement grout;

c.         Remove the settling chamber;

d.        Backfill the settling chamber excavation to the land surface with clean silt, clay, or engineered material. A permittee shall not use materials containing haz- ardous substances in backfilling the drywell; and

e.         Mechanically compact the backfill.

2.        Within 30 days of closure and decommissioning, the per- mittee shall submit a written verification to the Depart- ment that all material that contributed to a discharge has been removed and any reasonable probability of further discharge from the facility and of exceeding any Aquifer Water Quality Standard at the applicable point of compli- ance has been eliminated to the greatest degree practical. The written verification shall specify:

a.         The reason for the closure;

b.        The drywell registration number;

c.         The general permit reference number;

d.        The materials and methods used to close the dry- well;

e.         The name of the contractor who performed the clo- sure;

f.         The completion date;

g.        Any sampling data;

h.        Sump construction details, if a sump was con- structed to replace the abandoned drywell; and

i.         Any other information necessary to verify that clo- sure has been achieved.

Historical Note

New Section made by final rulemaking at 8 A.A.R. 4096, effective September 15, 2002 (Supp. 02-3). Amended by final rulemaking at 11 A.A.R. 4544, effective November 12, 2005 (05-3).