§ 58-168. Underground stormwater system standards.

(a)

Generally. Underground stormwater seepage systems may be permitted in all zoning districts upon city staff approval to accomplish stormwater retention and percolation requirements provided those systems are designed for the prevention of clogging by fine material and for ease of clean with convention sewer cleaning equipment.

(b)

Design criteria.

(1)

Underground stormwater treatment systems shall be designed by a licensed professional engineer.

(2)

Underground stormwater treatment systems shall be designed so as to accept a retention volume calculated for two inches of runoff from all contributing impervious areas.

(3)

A system overflow outfall shall be required.

(4)

The bottom of the stormwater treatment system shall be constructed a minimum of one foot above the estimated high ground elevation. The estimated high groundwater elevation and a modeled recovery analysis shall be performed by a licensed geotechnical engineer.

(5)

Filtration media shall consist of a gravel or river rock to be approved by city staff. A limestone based or crushed concrete media is not permitted.

(6)

A pretreatment structure shall be incorporated to remove all debris and sedimentation from the stormwater runoff prior to entering the ex-filtration system.

(7)

Proper inspection and maintenance access ports/manholes shall be installed on all structures and ex-filtration termination points.

(8)

The design shall meet such site or project-specific additional criteria as the director of public works may require.

(9)

The design shall not allow or permit the grade of the site to be elevated above two feet from the existing grade of the adjoining properties or adjoining right-of-ways.

(c)

Inspection and maintenance criteria.

(1)

Upon initial construction completion, an "as-built" drawing confirming that the stormwater treatment system was constructed according to the city approved drawings shall be signed and sealed by the engineer of record and submitted to the city public works department.

(2)

Inspection, maintenance, and testing procedures (including report forms) shall be provided by the engineer of record and submitted to the city for approval, and approved by the city, before a permit is issued.

(3)

Monthly inspections shall be performed by responsible party and findings logged and/or recorded. Monthly inspection logs shall be submitted annually to the city public works department.

(4)

Routine maintenance and cleaning operations shall be performed and logged and/or recorded. Maintenance and cleaning logs shall be submitted annually to the city public works department.

(5)

A volume test shall be performed on the underground stormwater treatment system and an engineer certified volume test report, satisfactory to the city, submitted every three years to the city public works department.

(6)

As a means of ensuring the future maintenance, repair, or replacement of the underground stormwater treatment system, the owner of the property shall be required to enter into an agreement suitable for recording in the public records, which shall run with the land and bind future owners of the property, reflecting the owner's responsibility to perform future maintenance, repairs, or replacement, as deemed reasonably necessary by the city, and in addition the owner's responsibility to pay for such future maintenance, repairs, or replacement, as deemed reasonably necessary by the city, regardless of by whom the future maintenance, repairs, or replacement is performed. The city shall have the right, but not the obligation, to perform or have performed future maintenance, repairs, or replacement, as deemed reasonably necessary by the city, and the property owner shall be responsible for the costs of such future maintenance, repairs, or replacement, the recorded agreement referred to herein shall reflect this obligation of the property owner.

(Ord. No. 2683-06, § 1, 9-11-06; Ord. No. 2737-08, § 1, 4-26-08)