As CoA development regulations regarding the amount of allowed impermeable cover vary significantly between the recharge zone and the transition zone, it became economically appropriate to delineate the precise location of recharge boundary on this project.

To meet the goals of our client, aci environmental consulting geologists utilized three methods of geologic investigation to accurately determine the location of the recharge zone boundary. In early stages of the project, several test pits were excavated to investigate shallow subsurface geology. With these findings, it was determined that the recharge zone did indeed pass through the site in the general location mapped by the CoA. To design a site plan that utilized the maximum amount of developable land, aci conducted additional geologic investigations to acquire a more precise location. The second method involved using a drill rig to collect boring samples in various points on either side of the boundary. This helped to elucidate where and at what depth the change in rock composition occurred. We then employed a geophysical method called Electrical Resistivity Technique (ERT) to further refine the boundary down to a matter of feet, and to gain this level of geographic precision in areas that could not accessed by drill rig. The overlap in data from both the borings and the ERT allowed for validation of the data and aided in interpretation of the ERT results, improving confidence in the ERT models.

The analyses conducted by aci environmental consulting were ultimately presented and excepted by the City of Austin. The study resulted in a change to the recharge zone boundary within the client’s property, a positive outcome allowing greater utilization of the land for their development.