Siting, Design and Operation of Infiltration BMPs: A Case Study

Abstract

This paper reports on experiences with infiltration basin and trenches constructed and operated as part of the Caltrans Best Management Practice (BMP) Retrofit Pilot Study Program. Fifty-two sites adjacent to highways and maintenance facilities in the Los Angeles and San Diego areas were evaluated and two infiltration basins and two infiltration trenches were constructed. One basin and one trench successfully met design expectations, which in California includes a 3-day drain time to prevent mosquito breeding. The drain time of the trench at the Carlsbad Maintenance Station in San Diego County was about twice as long as intended. The infiltration basin at I-5 at La Costa Ave., also in San Diego County, required months to drain. Based on post-construction analysis, contributing causes of these problems were inaccurate estimates of infiltration rates and groundwater depth, and application of inappropriate siting and design criteria. The short-term in-hole permeability tests resulted in higher estimates of infiltration rates than were later observed. Fluctuations in groundwater depth were larger than anticipated. Based on this experience and on computer modeling of one site, Federal Highway Administration recommendations for minimum infiltration rate and depth to groundwater can result in infiltration BMPs that do not meet performance requirements in California.

Hydrologic Performance of a Transitioned Infiltration Basin Managing Highway Runoff

“…Decrease in infiltration capacity due to accumulation of sediment that leads to increase in duration of water ponding incidents and discharge frequencies have been demonstrated by both short-term (up to 3 years) and long-term (10-15 years) in situ infiltration experiments and numerical simulations (Warnaars et al 1999;Dechesne et al 2005;Le Coustumer and Barraud 2007;Emerson et al 2010;Gonzalez-Merchan et al 2010;Lassabatere et al 2010;Bergman et al 2011). Failure of an infiltration basin is attributed to improper siting, absence of pretreatment, excess sediment inputs, and improper and irregular maintenance (Currier et al 2001;Stormwater Manager's Resource Center 2008). However, some infiltration basins have been reported to be operational with good infiltration capacities after 21 years (Dechesne et al 2005) and even after 100 years (Warnaars et al 1999).…”