Four Corner - Texas Water Development Board

and due to other factors not evident at the time of drilling. If clay soils exist to a
significant depth below the base of the trench excavation, a pump and sump dewatering
system will probably be adequate for trench excavation. If granular soils are encountered
above or close to the base of excavation, a well point dewatering system may be required.
Thirteen investigations containing 72 borings were reviewed for this sub-area. The
terminal depths of the borings ranged from 5 to 50 feet below ground surface. The soils
encountered were mostly firm to very stiff clay, sandy clay, and silty clay surface
stratums which ranged in thickness from 4 to 25 feet. The plasticity index of the cohesive
soils ranged from about 10 to 70. The cohesive soils were generally underlain by very
loose to medium dense sands and silts. Most of the very sandy and silty soils with
plasticity indices less than 7 occurred to the south of the sub-area where surface strata
occasionally consisted of sands and silts. Calcareous and ferrous nodules were usually
scattered throughout the depth of exploration for most of the borings in and near the subarea.
Surface layers of fill material ranging from about 2 to 4 feet in thickness occurred
fairly often on the boring logs. In one case, the fill material extended to about 10 feet
below ground surface. Groundwater was recorded at levels ranging from 8 to 15 feet
below ground surface. However, several borings with depths up to 20 feet were dry.
5.3 WATER AND WASTEWATER SYSTEM REQUIREMENTS
Public water distribution and supply systems must be designed in accordance with Texas
Natural Resource Conservation Commission (TNRCC) permanent rules, Chapter 290
(Water Hygiene). Sanitary sewer collection and treatment systems must be designed in
accordance with TNRCC permanent rules, Chapter 317 (Design Criteria for Sewage
Systems). The Four Comers planning area lies within the Extra-Territorial Jurisdiction of
the City of Houston. In addition to the requirements of TNRCC, water and sanitary
sewer facilities must be designed in accordance with the September 1996 "Design
Manual for Wastewater Collection Systems, Water Lines, Storm Drainage and Street
Paving" issued by the City of Houston Department of Public Works and Engineering.
City of Houston design requirements are more stringent than TNRCC with respect to
Four Comers Area Water and Wastewater Facilities Planning Study
Page 5-2
FINAL REPORT
Revised 2/l 0/99