Frequently Asked Questions

Bioslope media or bioslope mix is best purchased by the loose, bulk ton and delivered in a dump truck or dump trailer.  Planning is critical to either place the material into the system directly or store in a manner (i.e. on concrete/asphalt) to prevent contaminants from being mixed with the bioslope media prior to installation.

Yes, we produce and sell River Sand at multiple locations throughout Metro Atlanta and Georgia.  That’s not all we sell though.  We have a complete line of other types of sand, topsoil, dirt, gravel, and mulch. 

Measure the square feet of the garden space that you need to incorporate compost into the soil.  Adding compost to an existing garden can improve your soil tilth, improve water retention, and nutrient availability.  Using our calculator, input the dimensions of the garden including 2 inches of compost as a depth.  Once you have the compost that you need on-site spread it evenly across the top of the garden prior to planting (usually in the fall or before spring).  Till the compost into the top 3 to 6 inches of soil using a tiller or by hand with a steel rake or hoe.  Plant your garden and watch it grow!

Engineered soils are blended, manufactured soils with specific ratios of components.  The sand component can is often specified by gradation, for example ASTM c33.  The topsoil component may include a certain percentage of organic matter, pH, or texture.  The compost component may have to include a certain percentage of organic matter or meet the USCC STA requirements.  Once the key components are acquired the best way to blend the components is with a precision blending system.  Each component must be measured by volume or weight (scaled) prior to loading into the mixing system.  It is best to do a large quantity or the whole project’s quantity at a single run so that the entire mix is homogenous with no variability.  Sampling the components and final stockpile of engineered soil will ensure that the soil is compatible with the project prior to installation.

There are specific plans with most project outlined by engineers and architects specific to each project’s landscape.  However, the general idea is to place a [perforated drainage pipe, usually with a filter sock along the bottom of a small pond dug along that collects the stormwater.  The pond is typically 4 to 6 feet in depth.  The drainage pipe discharges outside of the pond but also has a T or connection for a vertical standpipe that will be above the surface level of the pond for overflow discharge.  The underdrain system is typically filled with #57 gravel and lined with a geotextile liner.  Above the gravel and drainage system the bioretention soil mix is placed usually 36 to 48 inches in depth and covered with a mulch layer.  During the installation process machinery and other equipment must not be used to compact the bioretention soil as it is installed.  This can be done with excavators positioned from the edge, slinger trucks, or in a manner that starts in sections and works your way out of the pond.  Select native plants are planted within the pond to uptake moisture and nutrients retained.  The inlets are lined with concrete or rip rap to prevent incoming runoff from eroding the edges of the pond.

Bioretention soil mix typically consists of sand, soil, and compost.  Some blends call for the addition of calcined clay products or mulch.  The mix can be determined in the plans by ratios of volume or a dry weight basis (which require some conversion).  Each component must meet certain specifications in addition to the final blend meeting criteria.  RSI uses large stockpiles of each component that has be tested by a soil lab to blend into a soil mix that is completely homogenous for consistency.  Each component is measured for an accurate blend.  The final bioretention soil mix is tested to make sure it meets the criteria for the project.  The blended soil can be delivered and placed into the cell or basin without contaminating it.  Mixing soil on-site can be a tedious process and limited to available soil that may not be suitable.  The worst-case scenario is for a soil to cause a system to fail.  RSI has decades of experience to make sure you have a quality bioretention soil mix that you can be confident will work effectively. 

Topsoil is best spread with a shovel and smoothed with a rake.  You can also use a tractor or skid steer for large amounts.  It does not spread well through spreaders used for seeding, or topdressers as it tends to stick to the sides and “bridge” over. 

Bio-slopes are designed to treat sheet flow from adjacent impervious surfaces such as roads. Stormwater sheet flow moves off of the roadway, sometimes through another filter treatment, over a bio-slope. Runoff is filtered through the bio-slope and the bio-slope media. The bio-slope media is composed a combination of coarse aggregate and permeable soil particles with high water retention capability. Bioslope mix may include aggregates, perlite, dolomite, and gypsum. The dolomite and gypsum components help treat stormwater and act as a buffer for acidic pH conditions and provide treatment for heavy metals. Perlite aids in the treatment of particulates, metals, and nutrients with it primary function being to retain moisture.  Treated runoff exits the bioslope system through a granular drain backfill material and sometimes with a perforated drain pipe. The overall effect filters stormwater to reduce the amount of runoff and improve water quality from runoff. 

Potting soil is usually sold by the cubic foot in a bag.  If you are looking to fill multiple containers or use a lot of potting soil over time, you may consider buying it in bulk.  Use a volume calculation to determine how many cubic feet you need and then multiply by 27 to determine how much is the equivalent in cubic yards.  If it is over 1 cubic yard, then River Sand may be able to supply you bulk potting soil and save money.

In general, a depth of 3 to 6 inches of soil is needed for roof top gardens, or green roofs.  Calculating the area of the garden and multiplying by the depth can give you a total volume (i.e. 10 feet x 3 feet x 6 inches divided by 12 = 15 cubic feet or 0.56 cubic yards)