Ariz. Admin. Code § 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 hazardous 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 substances" means substances that are components of commercially 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 Class V injection well inventory number for the drywell or documentation that inventory information was submitted to the Department;

2. For a drywell constructed more than 90 days before submitting the Notice of Intent to Discharge to the Department, 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 investigation 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:

a. Include a flow control or pretreatment device identified in subsections (D)(1) or (2), or both, that removes, intercepts, or collects spilled motor fuel or hazardous substances before stormwater enters the drywell injection pipe;

b. Calculate the volume of runoff generated in the design storm event and anticipate the maximum potential contaminant release quantity to design the treatment and holding capacity of the drywell;

c. Follow local codes and regulations to meet retention periods for removing standing water;

d. Locate the drywell at least 100 feet from a water supply well and 20 feet from an underground storage tank;

e. Locate the bottom of the drywell injection pipe at least 10 feet above groundwater. If during drilling and well installation the drywell borehole encounters saturated conditions, the applicant shall backfill the borehole with cement grout to a level at least 10 feet above the elevation at which saturated conditions were encountered in the borehole before constructing the drywell in the borehole;

f. Record the accurate latitude and longitude of the drywell using a Global Positioning System device or site survey and record the location on the site plans;

g. Clearly mark the drywell "Stormwater Only" on the surface grate or manhole cover;

h. Develop and maintain a current site plan showing the location of the drywell, the latitude and longitude 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 combination of pre-approved technologies described in subsections (D)(1) and (2) designed to remove, intercept, and collect any pollutant that may be present 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 construction, 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 storage tank, and the depth to the groundwater from the bottom 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 allowing 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 storage structure, or install a six-inch asphalt or concrete raised barrier encircling the drywell inlet to provide a non-draining storage capacity within the retention basin or storage structure for complete containment of a spill; and

ii. Ensure that the storage capacity is at least 110 percent of the volume of the design storm event required by the local jurisdiction and the estimated volume of a potential motor fuel spill based on the facility's past incident reports or incident reports for other facilities that are similar in design;

c. Magnetic mat or cap. The permittee shall ensure that the drywell inlet is sealed with a mat or cap at all times, except after rainfall or a storm event when the mat or cap is temporarily removed to allow stormwater to enter the drywell; and that the mat or cap is always used with a retention basin or other type of storage;

d. Primary sump, interceptor, or settling chamber. The permittee may use a primary sump, interceptor, or settling chamber only in combination with another flow control or pre-treatment technology.

i. The permittee shall remove motor fuel or hazardous substances from the sump, interceptor, or chamber before allowing stormwater to enter the drywell.

ii. The permittee shall install a settling chamber or sump and allow the suspended solids to settle 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 prevent fuel from discharging into the drywell;

2. Pretreatment. The permittee shall prevent the bypass of motor fuels and hazardous substances from the pretreatment 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 hazardous 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 separator.

i. The permittee shall install a system that incorporates 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 system to the drywell inlet of 20 gallons per minute. 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 materials, 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 treatment 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 functioning 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 function.

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 latitude 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 minimize 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 sampling 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 treatment capacity has not been exceeded; and

d. If the spill reaches the injection pipe, drill a soil boring 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 protection 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 Permit.

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 hazardous substances in backfilling the drywell; and

e. Mechanically compact the backfill.

2. Within 30 days of closure and decommissioning, the permittee shall submit a written verification to the Department 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 compliance has been eliminated to the greatest degree practical. The written verification shall specify:

a. The reason for the closure;

b. The Class V injection well inventory number or;

c. The general permit reference number;

d. The materials and methods used to close the drywell;

e. The name of the contractor who performed the closure;

f. The completion date;

g. Any sampling data;

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

i. Any other information necessary to verify that closure has been achieved.

Notes

Ariz. Admin. Code § R18-9-C304

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). Amended by final expedited rulemaking at 31 A.A.R. 989, effective 3/7/2025.