08-21-2002 Committee Meeting - Laserfiche WebLink

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Wetland Property Acquisition and Mitigation The verified wetland delineation of the project site by the Corps (5-2-2002) provides that there are 18.296 acres of jurisdictional wetlands on the site. To mitigate these and other biotic impacts, the POHA has acquired a 173.5-acre tract of land located just north of Highway 146 on Red Bluff, immediately adjacent to Armand Bayou Nature Center and Taylor Lake. Within this property, the POHA proposes to create 66.8 acres of emergent freshwater wetlands (3.6:1 compensation for impacted, jurisdictional wetlands) and the enhancement of more than 12 acres of existing wetland. The project would also preserve 23.7 acres of forested and shrub uplands and 71 acres of restored coastal prairie. In addition, a conservation easement would be imposed on the entire 173-acre tract. This would preserve, a sizeable block of diverse habitat that is upstream of Armand Bayou Nature Center, and within its watershed. Storm Water Management and Treatment The applicant proposes a variety of mitigative features to potentially improve water quality. These include first flush capture, a south terminal retention pond, inlet treatment units, and high impact area treatment. These are described below. First Flush - POHA is currently regulated for storm water discharges under the Multi - Sector Stormwater General Permit (MSGP) for Industrial Discharges and the Municipal Separate Storm Sewer System (MS4). The primary areas of concern under the MSGP for SIC 4491 (Water Transportation) are four metals (aluminum, zinc, lead and uranium). Experience at the existing Barbors Cut Container Terminal has revealed that these metals are primarily attached to Total Suspended Solids (TSS). To facilitate the capture of TSS, the applicant proposes to capture the first inch of rainfall into a holding pond, as shown in the master plan drawing. This would allow the TSS to be retained in the pond, decreasing the discharge of sediments into the Bayport Ship Channel and Pine Gulley. South Terminal Retention Pond The loss of infiltration resulting from the concrete surfacing of the site would result in an increased rate of stormwater discharge to Pine Gulley. To maintain the undeveloped discharge rate after project construction, the applicant proposes to install a retention pond in addition to the first flush pond. The function of this structure would be to capture and hold stormwater in excess of the first inch and release it slowly. The delayed release of stormwater would prevent increased flooding or disruption of the Pine Gulley ecosystem. To further enhance water quality functions, the POHA plans to create a meandering channel in the bottom of the South Terminal Retention Pond with fringe planting of low bio- mass wetland plant species, such as spikerush, which would grow to cover the entire 12-15 acre pond bottom. To discourage excess biomass build-up, the pond bottom would be mowed once annually, while the sides would be mowed 3-4 times per year to prevent loss of capacity. S � J S