The land surface in the Texas Coastal Zone is interlaced with active and potentially active surface faults. They are subtle features which are difficult to identify until they have caused damage to manmade structures. To date (1978), significant damage has resulted.

Aquifers in the Houston-Galveston area are composed principally of fluvial-deltaic sediments. The Alta Loma Sand is a complexly faulted, high-sand-percent unit that represents a seaward progression of fluvial, delta-plain, and delta-front facies.

Land subsidence increases the area in the Texas Coastal Zone which will be inundated by marine waters from hurricane flooding. Storm surge from a Carla-sized hurricane in 1976 would flood at least 25 square miles more land than Hurricane Carla did in 1961.

Over 7,000 miles of lineations have been observed on aerial photographic mosaics of the Texas Coastal Zone. These lineations, in part, represent the surface traces of faults originating in the Tertiary sediments and propagating through the Quaternary sediments.

Disposal and temporary surface storage of spent geothermal fluids and surface subsidence and faulting are the major environmental problems that could arise from geopressured geothermal water production.

The Houston-Galveston Area Council of Governments (HGAC) encompasses over 12,000 square miles of southeast Texas (fig. 1).

Nitrogen isotope ratios of ammonium and nitrate ions from soil and water samples can be analyzed reproducibly with an experimental error of approximately +/-1 parts per thousand (ppt). Two isotopic ranges of soil nitrate are found in the soils of southern Runnels County, Texas.

The Texas Coastal Zone is marked by diversity in geography, resources, climate, and industry.