About the Surface Sand Filter
General Information Performance Data Water Quality Treatment Process Design




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System Performance

Water Quality Treatment
The surface sand filter performed only moderately well at removing most pollutants commonly associated with stormwater treatment performance assessment. While its performance did not meet EPA’s recommended level for total suspended solids, other studies demonstrated stronger performance results for this system. This discrepancy may be due, in part, to design-related in-system erosion, relatively high hydraulic loading rates, and excessive ponding (five feet) above the filter media. In this study, the system demonstrated a strong ability to remove petroleum hydrocarbons and metals, but only moderate phosphorus removal. Like the other systems monitored, the sand filter does not treat chloride, but does exhibit an ability to dampen chloride peaks.

The chart at top right reflects system performance in removing total suspended solids, total petroleum hydrocarbons, dissolved inorganic nitrogen, total phosphorus, and zinc. Values represent results recorded over a two-year monitoring period, with the data further divided into summer and winter components.

Water Quantity Control
The surface sand filter exhibits a moderate capacity to reduce peak flows and runoff volume in sites with well draining soils. In the figure at bottom right, it demonstrates moderate peak flow reduction and moderate lag times regardless of season.

Maintenance
Unlike most other systems evaluated at the UNHSC, the surface sand filter receives semi-annual maintenance. It continues to function well.

In general, the maintenance requirements for surface sand filters are simple but critical for proper operation. Maintenance typically involves scraping fines from the surface of the filter bed. The frequency of this activity depends on how much sediment is in the stormwater runoff; depending on the size of the basin, sediment removal can be done by hand or with heavy machinery. After repeated maintenance, sand may need to be added to the filter bed to maintain the required two feet of media. Proper site stabilization through vegetation is key to preventing clogging from fines.

Cold Climate
The surface sand filter’s ability to treat water quality and reduce the volume of runoff remained relatively consistent in all seasons. UNHSC researchers have observed that most LID systems, when properly designed and installed, are not dramatically impacted by seasonal fluctuations. While some seasonal variation does occur, significant design alter-ations do not appear necessary for cold weather application.