Tuesday, April 13, 2010: 2:45 p.m.
Continental A (Westin Tabor Center, Denver)
A. Scott Andres
,
Delaware Geological Survey, Newark, DE
Edward Walther
,
Delaware Geological Survey, Newark, DE
GIS analysis combined with simple groundwater models provide an efficient and effective screening tool to identify suitability of land for rapid infiltration basin systems (RIBS) and other forms of land based wastewater disposal in the State of Delaware. Existing, published, or publically distributed GIS-ready data of suitable spatial resolution are available to evaluate hydraulic and other natural and cultural criteria in the context of compliance with regulation defined isolation distances from the water table, wells, bodies of surface water, and property boundaries. This process addresses suitability in terms of compliance with regulatory requirements but does not evaluate risks for contamination of groundwater, water supply wells, and surface waters. Work in progress is addressing these issues.
GIS analysis does not replace the need for competent site specific evaluation for design and permitting of new facilities. However, because the spatial resolution of data is based on a 30-m grid, it does identify the primary limiting hydrogeologic factors for parcels as small as 10 acres. As such, it is a valuable tool for tailoring site work to study the specific limiting factors likely to be affecting a site.
Application of this analysis to Delaware found that natural hydraulic properties of subsurface materials create conditions where water-table mounding due to use of RIBS will likely cause the mound to extend to within two feet of the bottom of an infiltration basin. According to current regulations, this condition excludes 80 to 95 percent of land area for RIBS. Proximity to domestic and public water supply wells, property boundaries, and bodies of surface water excludes less than 10 percent of land area for RIBS.
