STP Screening Matrices
This section presents a series of matrices that can be used as a screening process for selecting the best STP or group of STPs for a development site. It also provides guidance for locating practices on the site. The matrices presented can be used to screen practices in a step-wise fashion. Screening factors include:
The matrices presented here are not exhaustive. Specific additional criteria may be incorporated depending on local design knowledge and resource protection goals. Furthermore, many communities may wish to eliminate some of the selection factors presented in this section. Caveats for the application of each matrix are included in the detailed description of each.
In the matrices presented below, several specific numerical requirements are included, and may vary between communities.
Most of the material in the screening matrices provides technical guidance, and is not necessarily a regulatory mandate. In the few cases where a screening element would typically be a regulatory requirement, cells are shaded.
More detail on the proposed step-wise screening process is provided below:
Step 1. Land Use
Which practices are best suited for the proposed land use at this site? In this step, the designer makes an initial screen to select practices that are best suited to a particular land use.
Step 2. Physical Feasibility Factors
Are there any physical constraints at the project site that may restrict or preclude the use of a particular STP? In this step, the designer screens the STP list using Matrix No. 2 to determine if the soils, water table, drainage area, slope or head conditions present at a particular development site might limit the use of a STP. In addition, the matrix indicates which STP options work well in highly urban areas.
Step 3. Climate/Regional Factors
Are there any regional characteristics that restrict or modify the use of certain STPs? Matrix No. 3 details potential modifications to STP selection based on climate and geology.
Step 4. Watershed Factors
What watershed protection goals need to be met in the resource my site drains to? Matrix No.4 outlines STP goals and restrictions based on the resource being protected.
Step 5. Stormwater Management Capability
Can one STP meet all design criteria, or is a combination of practices needed? In this step, designers can screen the STP list using Matrix No. 5 to determine if a particular STP can meet recharge, water quality, channel protection, and flood control storage requirements. At the end of this step, the designer can screen the STP options down to a manageable number and determine if a single STP or a group of STPs are needed to meet stormwater sizing criteria at the site.
Step 6. Pollutant Removal
How do each of the STP options compare in terms of pollutant removal? In this step, the designer views removal of select pollutants to determine the best STP options for water quality.
Step 7. Community and Environmental Factors
Do the remaining STPs have any important community or environmental benefits or drawbacks that might influence the selection process? In this step, a matrix is used to compare the twenty STP options with regard to maintenance, habitat, community acceptance, cost and other environmental factors.