Liquid Waste (Septic Tank) Program
Hydrogeologic Mapping

• depth to ground water less than 100 feet with no intervening geologic barrier to prevent contaminant migration; 
• proximity to (1/4 mile) anthropogenic ground water contamination with nitrate or anoxic conditions; 
• karst or fractured bedrock terrain; and 
• gaining streams that have been impacted by nutrients from liquid waste systems.  

NMED is mapping areas where waters of the state may be vulnerable to contamination from septic tank discharges, and where stricter standards may be imposed.   Aquifer sensitivity maps prepared for NMED by Lee Wilson and Associates in 1989 have been digitized and are a data layer in the online Liquid Waste Geographic Information System (GIS).  The tab for GIS data layers is near the upper right corner, the buttons for zoom in/out and other functions are on the left, aquifer sensitivity maps are under Geology/Landcover.  The Lee Wilson maps are being updated and modified to include current depth-to-ground-water information, as well as areas of karst and fractured bedrock, known contamination sites, and gaining streams.  These maps also can be downloaded as bitmap and gif files (Table 1).  The maps contain color-coded groundwater areas based on depth to water and naturally occurring, background, total dissolved solids (TDS) as explained in Table 2.  Areas with ground water less than 100 feet deep, and with 2000 mg/L or less TDS, are mapped in red.  Other areas of concern based on karst or fractured bedrock, known ground-water contamination, and gaining streams impacted by septic tank effluent, are also being mapped. 

Liquid waste permit applications for conventional septic systems on lots smaller than 3/4 acre within these areas will receive greater scrutiny in order to protect public health and prevent degradation of a body of water.  Pursuant to Liquid Waste Disposal Regulation 20.7.3.201.N, NMED will, upon written request, issue a letter of determination of whether or not stricter standards will be imposed on a lot or parcel of land.  This determination will be valid for one year.  There may be site conditions, however, other than those in the regulation that may cause more stringent requirements to be applied to the liquid-waste permit for a specific site.

The National Atlas GIS has useful information including karst areas.

The Bernalillo County GIS has wells and septic tanks plotted along with lots of other useful information.

Table 1.  Lee Wilson and Associates Aquifer Sensitivity Maps.   In addition to the online Liquid Waste Geographic Information System (GIS), these maps can be downloaded as image files from the table below.  If you have trouble locating your property on these maps, contact us.