TMDL Studies and Water Quality Modeling



GBMc & Associates provides expertise to municipal and industrial clients in order to develop technically sound TMDL and waste load allocation studies. We have considerable experience in running EPA supported water quality models including QUAL2E, WASP, and CORMIX. GBMc & Associates field crews are experienced in conducting studies that directly affect the results of TMDL modeling including low flow analysis, hydraulic and dye studies, and collection of water quality and in-situ data on both large and small streams. GBMc & Associates has long-term working relationships with State and EPA staff in Oklahoma, Arkansas, Missouri, and Louisiana. We have successfully negotiated permit limits, results of TMDL studies and approval of special water quality studies with personnel in each of these states.


Experience and Capabilities

  • Conducted more than a dozen water quality modeling/TMDL related studies in EPA Region 6 and 7 states, including Oklahoma, Arkansas, Missouri, and Louisiana. This multi-state experience enables GBMc to select the most useful components from the approach of each state for use in pertinent situations. This experience has, on occasion, led to our clients saving substantial sums by completing only the specific type of study needed, rather than accepting the “shotgun” approach originally suggested by the regulatory agency.
  • Experienced in the use of numerous EPA supported water quality models including QUAL2E(K), Multi- SMP, WASP, AQUATOX, and CORMIX.
  • Have completed dozens of waste load allocations for various conservative and non-conservative water quality constituents including dissolved oxygen, ammonia, nutrients (P & N), chloride, TDS, pH, bacteria, temperature, metals, and pesticides.
  • Conducted a comprehensive eutrophication study in the Ouachita River and Felsenthal NWR system. Nutrient fate and transport modeling was completed using QUAL2K and WASP to determine the effect of discharged nutrients from a combined pipeline in the River and connected lake system. The combined pipeline discharge included industrial and municipal wastewater.
  • Completed field studies and TMDL modeling for oxygen demanding substances at several sawmills in South Arkansas to avoid stringent permit limits for the dischargers.
  • Completed a water quality and low flow frequency study, coupled with an oxygen demand TMDL to develop multi-tiered permit limits that were satisfactory to an oil refinery in Arkansas.
  • Macrophyte (aquatic plant) biomass modeling was completed for a complex reservoir system using the EPA AQUATOX Model. The fate of phosphorus and nitrogen compounds in the system and the plant relationship to substrate and light availability were key elements of the study.


GBMc Contacts Vince Blubaugh or Shon Simpson