Red sand

==What is it?==
Red sand, also known as a "Minnesota filter", is iron enhanced sand designed to capture soluble phosphorus that generally passes through a typical stormwater management facility. Iron has an affinity for dissolved phosphorus, which will serve to bind and therefore remove a portion of the dissolved phosphorus from the stormwater. Lake Simcoe Region Conservation Authority. Showcasing Water Innovation: Stormwater Performance Monitoring Report. 2013. http://www.lsrca.on.ca/Shared%20Documents/reports/swi_monitoring_2013.pdf. Accessed September 8, 2017. The sand also filters the stormwater by removing a portion of the suspended solids and total phosphorus that may be attached to those particles.
==How is it being used?==
The first retrofit in Ontario to incorporate a red sand filter system was the George Richardson stormwater management pond in Newmarket. Red sand was installed as the last part of a treatment train to function as a final polishing unit. The underground system was first lined with a bentonite clay liner to minimize groundwater exchange, with various layers of clear stone and red sand sandwiched between nonwoven geotextiles. The water is distributed via a system of perforated pipes embedded in the top layer of the underground system just above the red sand filter media, with collector pipes located near the bottom. The system is estimated to have a reduction in phosphorus of 23 kg/year. Credit Valley Conservation. George Richardson Stormwater Management Pond Retrofit. 2013. http://www.creditvalleyca.ca/wp-content/uploads/2013/08/CVC-Case-Study-George-Richardson_Aug_2013.pdf. Accessed September 8, 2017.
Another Ontario project was completed by the Upper Thames River Conservation Authority and Luckhart Transportation Limited, in which they retrofit an innovative wetland treatment system to test a red sand filter. This was the first of its kind for an agricultural application. In this project, a clear round stone was added to improve percolation and phosphorus retention.Upper Thames River Conservation Authority. Red Sand helps Protect Water Quality. 2014. http://thamesriver.on.ca/2014/11/11/red-sand-helps-protect-water-quality-november-11-2014/. Accessed September 8, 2017..
Finally, in a two year STEP research study that compared standard bioretention media to red sand and Sorbtive™ amended media, the red sand plot was shown to have significantly lower total and dissolved phosphorus effluent concentrations. However the phosphorus reductions occurred only in year 2, after fine particulates in the red sand media had been washed out of the system (STEP, 2019)STEP. 2019. Improving nutrient retention in bioretention. Technical Brief. Accessed: https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf. 
==Benefits==
Early data from the George Richardson site indicate a reduction in Total suspended solids and phosphorus after going through the system. "Average TP concentrations into the filter were 0.12 mg/L with a maximum of 0.54 mg/L as compared to an average outlet concentration of 0.052 mg/L with a maximum of 0.13 mg/L. Average soluble phosphorus (orthophosphate) concentrations into the filter were 0.01mg/L with a maximum of 0.031 mg/L as compared with an average outlet concentration of 0.007 mg/L with a maximum of 0.044 mg/L." Poor orthophosphate removal was observed during hypoxic or anoxic conditions because the iron/phosphorus bond that facilitates the removal of orthophosphate can be broken under low oxygen conditions.
==References==
category: materials
category: phosphorus
category:water quality