The Grapevine-Colleyville ISD board of trustees has concluded an investigation into the erosion of the south parking lot at Grapevine High School. The erosion was causing a section of the parking lot's median to sink. The district had hired a firm to look into what was causing subgrade erosion. The firm found erosion voids under the pavement in areas adjacent to the parking lot west of the sinking area. The firm determined to its best judgment the erosion is caused by natural groundwater. Officials said groundwater has increased over the years with extensive rainfall, as well as removing a hill from the site that altered the waterflow near the high school. The firm recommended removing additional concrete to fill the voids with crushed rock to support new pavement and also create an underground drainage system to allow the groundwater to move without washing away the substructure and to direct the groundwater to the storm drain, according to city documents. GCISD Chief Operations Officer Paula Barbaroux said at the March 25 board meeting that work includes removing the concrete where there could be voids, excavating the area and dewatering the system. Trustees approved channeling $362,555 from surplus funds associated with Grapevine High School renovations in the 2016 bond program to remediate the erosion. The funding was approved unanimously and without comment from trustees. Barbaroux said depending on when a contractor could begin work, the project could begin this summer.