Increasing Infiltration in Clay Soils
In 2017 the developer of a townhome project in Athens, Georgia contacted us regarding a problem with standing water behind several units. The developer had taken over the project after the recession and limited information was available on the original design. The site included an area behind several units that had standing water for weeks at a time, up to two feet deep. The residents were very concerned about mosquitoes and other pest due to the standing water.
There was a depression behind the units that had an area of approximately 3 acres draining to it. The area included off-site area comprised of a single-family home, several accessory structures and large pasture areas. In addition a portion of several townhome units drained to the area.
In order to install a gravity system to drain the area would require extension demolition of existing concrete drives and asphalt roads. Estimated cost were in excess of $100,000. A pump system was considered but residents did not want the long term maintenance it would require.
The developer had heard of the Parjana EGRP system and contacted us to discuss if it would possibly be a cost-effective solution for the problem. An initial study was conducted and a budget of $20,000 was established to design, install and monitor the system. The residents were threatening to sue the developer over this issue so confirmation that the system did meet the design specifications was a critical component.
A system was designed to infiltrate the runoff from a rainfall event of up to 1" of rain within 24 hours. The system was installed in July 2017 and was monitored through March 2019.
The monitoring confirmed that the system did perform to meet the design specifications except in a few minor time periods. There was a period of a few weeks where temperatures were well below average and it snowed several days. Another time included an extremely wet period in the fall of 2018, with persistent back to back rain events. Even in extreme conditions, the system did perform far better than the original condition and greatly reduce the time for standing water. In nearly all cases the system did meet the design specifications and required no maintenance to do so.
The case study will review the design, installation and regular monitoring over this time period. It will also include a discussion on other types of projects and situations where increasing infiltration can be used to eliminate standing water, improve water quality, increase ground water recharge and reduce stormwater runoff.
The Case Study will show that infiltration is not only possible but can be extremely effective in areas where infiltration practices were previously considered infeasible.