Briefing Your company designed and built a two-stage stormwater pond many years ago. A new regulation requires this pond to be retrofitted. The engineer in charge has left the company. As a young engineer, you are competing for the lead position on this project. To prove yourself, you must demonstrate your talent by finishing two tasks. Factsheet Forchy Forty Maine Outlet Struct Tanpowy pool elevati. Pomen pool ch Vegetated Shell Figure 1. Plan view of the pond design (not to scale) Figure 2. Photograph of the project site This two-stage stormwater pond is in operation. The surface areas of the forebay and the main pond are 1.0 acre and 3.1 acres, respectively. The average depth of both is 6.0 feet. The design flow enters the forebay at a rate of 500 gallons per hour and then to the main pond before exiting at the outlet structure. The subsurface soil is compacted clay. Infiltration is negligible. The observed evaporation rate at the project location is 600 gallons per acre per day. It's designed to reduce the organic materials (the main contaminant) from 50.0% to 2.5% by weight. The stormwater is well mixed through aeration in both stages. The reaction is first order. Level 2 - Analytical skills (50 points) The new regulation requires the concentration of the organic materials to be discharged must not exceed 10,000 mg per liter. To resolve, you may retrofit the existing structure by (a) enlarging the forebay; (b) enlarging the main pond; (c) adding a third stage pond; or (d) proposing your own most cost effective strategy. Note: Excavation costs approximately $100 per cubic yard and disposal of excavated materials also costs approximately $100 per cubic yard. Maintain a depth of 6 feet at all locations