519 - Does Pond Pretreatment Performance Matter? Analysis of Pretreatment Effectiveness on Long-Term Maintenance Costs and Frequency

Pretreatment of stormwater control measures (SCMs) is a common best practice that is applied to improve water quality and maintenance functionality throughout the design life cycle of the SCM. Pretreatment typically focuses on gravitational separation as the unit operation, targeting the capture of gross solids and large particulates. Extended detention basin and retention basin SCMs are widely used and often rely on some form of pretreatment to ease the long-term maintenance requirements.

The most common forms of pretreatment for these basin-type SCMs are forebays and proprietary devices such as Hydrodynamic Separators (HDS) that have been engineered to optimize sedimentation and related unit operations. Specific testing protocols have been established over the past 20 years to understand HDS performance; however, performance and associated maintenance and life cycle costs of forebays are not well understood. This presentation examines the maintenance and life cycle cost implications of selecting pretreatment devices such as forebays and HDS systems.

A literature review was conducted on stormwater manuals across the country to better understand forebay design variations and expected sediment removal performance. The BMPREALCOST tool was then used to quantify specific maintenance activities required for detention and retention basins. Maintenance activities which are affected by pretreatment were quantified based on HDS performance testing and expected performance of a forebay. Multiple life cycle cost scenarios will be presented along with potential differences in expected water quality outcomes. A brief discussion on estimating bulk density of stormwater solids will also be presented, along with an analysis of knowledge gaps and future research needed.