§ 15.01.700. Storm water pre-treatment sump.

Pre-treatment sumps shall be located as staked in the field and indicated on the plans. They shall be to the grade indicated by the cut sheets and as staked in the field. Excavation and backfill shall conform to Division 4 of these specifications. If the sump is located in an area where the earth is stratified with gravel layers, care shall be taken during backfill to be sure that these layers are not sealed off from the sump beginning two feet below the bottom of the sump up to the top of the subgrade. One and one-half to two-inch diameter drain rock shall be used. The original material shall be removed and the total backfill done with imported drain rock (no slag). The design storage requirements for storm water may account for up to thirty percent of the volume of the drain rock volume. After backfilling is completed, the entire excavation shall be thoroughly flooded to insure that settlement is complete. Grates shall be set in place and adjusted for final elevation and alignment. Geotextile a fabric barrier is required between the drain rock and road base (or other backfill) preventing the possibility of road base or native material migrating into the void space of drain rock. (See Standard Drawing No. 15.14 (Section 15.01.1500)).

Pre-treatment sumps shall be constructed of reinforced concrete, precast sections and shall meet the requirements of ASTM C478-73 in accordance with standard detail drawing. All grates located within the roadway section or parking lot shall meet all HS2O loading design requirements.

(Ord. No. 2007-07-31, § 8.2, 7-10-2007)