Post Construction Site Runoff Control

The intent of post construction pollution controls is to reduce the amount of pollutants generated by a site once construction has been completed on the site.  Depending on the final land use, there are many different pollutants that can be carried into storm water runoff once a site has been developed.  Based on the “Indiana Storm Water Quality Manual”, typical pollutants generated by developed sites, the sources of the pollutants, and their impacts, can include the following:

  • Nutrients – these are typically generated by lawn fertilizers, agricultural applications, failures in sanitary sewers, or septic tank effluents.  Excessive amounts of nutrients can lead to reduced oxygen levels in receiving waters.  They can also cause excessive algae growth.
  • Bacteria – these can result from pet wastes, sanitary sewer failures, and septic tank effluent.  Bacteria present health hazards to humans, so they can prevent recreational use of waterways. 
  • Automotive Fluids – these can leak out of vehicles onto public streets, or they can enter waterways as a result of improper disposal or illegal dumping of used fluids.  These fluids can be unhealthy or deadly for aquatic life and humans.
  • Metals – these are typically generated by automobiles and industrial areas.  According to the IDEM “Storm Water Quality Manual”, these pollutants are long lived in the environment, they can often work their way into the food chain and are passed from one organism to another, and they can have toxic effects when built up in a system over time.
  • Road Salt – the source of salt can be public roads, parking lots, and/or home applications.  High concentrations of this, such as what can be found in snow melt, can be lethal to aquatic organisms in high concentrations.
  • Miscellaneous Chemicals – these can result from pesticide and herbicide applications, accidental spills, vehicles, and illegal dumping.  Depending upon the specific chemical, they can be lethal to aquatic organisms.

In order to attempt to reduce post construction pollution, 327 IAC 15-5-6.5(a)(8) and 327 IAC 15-13-16 require the development and implementation of post construction pollution controls.  These codes also mandated that Vanderburgh County had to develop a local ordinance that requires post construction pollution prevention plans.  These local regulations can be found in section 13.05.09(K) of the Vanderburgh County Code of Ordinances. 

When Vanderburgh County initially submitted its “Storm Water Quality Management Plan” to IDEM in order to comply with Rule 13, it stated that the county’s goal for post construction pollution controls would be the removal of 80% of the total suspended solids (TSS).  This goal is stated in Section 6 of the county's Rule 13 Part C plan.

When the post construction portion of the storm water quality management plan is submitted for review, it must include data regarding the TSS removal for the post construction best management practice(s) (BMP) selected for the site.  The data should include references that document that the selected BMP(s) can achieve the 80% TSS removal percentage.  In the event that a manufactured BMP is selected for a site, the documentation submitted must include independent testing results (not the manufacturer’s test results) that show the TSS removal rate.  The independent testing must follow ASTM standards.  Vanderburgh County reserves the right to reject BMPs in the event that satisfactory testing results are not provided. 

Virtually every post construction BMP will require maintenance in order for it to be effective in removing pollutants.  As a result, preparers of post construction pollution prevention plans should strive to find cost effective and low maintenance BMPs that achieve the 80% TSS removal rate.  Due to the limited resources of Vanderburgh County maintenance crews, any post construction BMPs installed in county road rights of way must be low maintenance to be considered.  The number of BMPs installed in the road right of way must also be minimized as much as possible.  For example, a post construction plan that calls for catch basin inserts in every curb inlet in a street system will not be approved.  This is due to the maintenance requirements associated with cleaning the excessive number of inserts in the street system.  However, the owner of a private development would be allowed to specify this type of system for their own site if suitable maintenance procedures are documented in their plan.

In order to comply with 327 IAC 15-13-16, new retail gasoline outlets, or outlets and refueling areas that replace their existing tank systems are required to design and install appropriate practices to reduce lead, copper, zinc, and polyaromatic hydrocarbons in storm water run-off.  Since pollutants associated with fueling areas can cause significant problems with water quality, designers of post construction plans shall thoroughly document how the selected BMPs will reduce the specified pollutants.  The plan must also provide documentation that indicates how the maintenance of the selected BMPs will be done, and how to ensure that operators of the site will be aware of the maintenance requirements of the BMPs.   While this is required for all post construction pollution control plans, the BMP maintenance is particularly important for these sites due to the potential long term pollution problems that can result from fuels entering the storm drainage system.

For suggestions regarding appropriate post construction BMPs, please refer to chapter 8 of the “Indiana Storm Water Quality Manual.”  While this manual contains numerous BMPs, it obviously cannot provide appropriate BMP recommendations for all developments and all pollutants.  Since individual BMPs specified in this manual may not achieve the 80% TSS removal requirement and/or satisfactory treatment of fuels, a series of BMPs (either those listed in the manual, or manufactured BMPs) may be necessary.  Regardless of whether an individual BMP or a series of BMPs is needed to obtain the proper pollution controls, the designer will be required to provide satisfactory documentation that shows how the pollutant removal percentage rate was calculated for each BMP for each site.