10/24/2012 Env Bd Packet - Laserfiche WebLink

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RCWD Permit Number 12 -078 RMP -3 The water quality component of RMP -3 has two components. The first requirement is to retain the volume of run -off from the 2.3 -inch 24 -hour storm. The applicant is proposing 2 infiltration basins as described below: Proposed Descri Lion oeat(on � z Pret eatme ,� Volume provided Infiltration basin #1 Western property line, north of basin #2 Pre - treatment cell 3,149 c.f. Infiltration basin #2 Southwest corner of the property Pre - treatment cell 32,000± c.f. The basins were sized to retain and treat the 2.8 -inch event via infiltration, which is adequate to meet the first requirement, provided that applicant submits soil borings and demonstrates compliance with the Rules per discussion in the ensuing paragraph. The applicant must submit soil borings at the location of the infiltration features to establish the feasibility of infiltration, including showing 3 -foot of separation from the seasonal groundwater. Additionally, soil borings showing a field classification of SM must undergo additional sieve and hydrometer analysis per District Design Infiltration Rate Guidance Worksheet. Ultimately the basin must draw down within 48 -hour following the storm event. The site is not located in a DWSMA or wellhead protection area; however applicant must address pre- treatment to prevent hydrocarbons from infiltrating in the pre- treatment area. For the second component, the applicant must treat an additional 0.5 -inch (5,518 cubic feet) of volume via one of the volume reduction methods listed in the table in RMP -2 Section 8(c). The applicant must address this requirement. Rule C.6 Rate control The issues listed under Recommendation 2 above must be addressed to show compliance. if rate is increased at a key point, then it must be iimited and cause no adverse downgradient impact. Other Rules Generally the project appears to comply with the remaining storrrrwater rules, however applicant must verify after reviewing soil borings and any redesign of the site. 3. Wetlands — There are no wetlands located within the project area. 4. Floodplain — The site is not in a regulatory floodplairr. 5. Erosion Control — Proposed erosion control methods include silt fence, rock construction entrances, inlet protection, bio -rolls and rip rap. An NPDES permit is required for the project. A SWPP Plan has been submitted for the project. The information listed under the Erosion and Sedimentation Control Recommendations needs to be submitted. Otherwise, the project complies with RCWD Rule D requirements. 6. Documenting Easements and Maintenance Obligations — Applicant needs to provide drainage and flowage easements (if required by the City), draft maintenance declaration, and receipt showing recordation once approved. Houston Engineering Inc Page 4 of 5 10/9/2012 • • •