Minnesota and Mississippi River Mixing Zone Studies
SAFL researchers used field studies, physical models and computer simulations to evaluate and characterize the downstream mixing zones of treated wastewater discharges to the Minnesota and Mississippi Rivers. The largest discharge was to the Mississippi River south of the City of St. Paul, just upstream of Spring Lake, part of a 5-mile long, by ¾-mile wide navigation pool at Lock and Dam No. 2. The slow movement through the backwater areas complicated the understanding of mixing and transport in the river. SAFL led dye studies to trace the mixing and movement of treated effluent through the pool.
Effluent mixing zone models were developed from analysis of the measurements and theoretical considerations to provide a means for predicting the extent of the mixing zone from effluent and river flow conditions. The models allow prediction of conservative and non-conservative constituent concentrations at locations downstream from the discharge point. This information is useful in evaluating water quality standards and effluent limits for wastewater treatment plants.

Stillwater Wastewater Treatment Plant
Metropolitan Council Environmental Services (MCES) asked St. Anthony Falls Lab to evaluate the performance of the proposed Stillwater dechlorination basin. A physical model and dye tracer were used to evaluate mixing and adequacy of the dechlorination reaction. The study identified unexpected asymmetric flow conditions in a symmetric design. SAFL recommended design and operating constraints to compensate for these conditions and minimize sulfur-dioxide dosing requirements and the possibility of chlorine effluent standards exceedances. This is one of five similar studies for MCES.

MARB Avenue Retention Basin (MARB)
St. Anthony Falls Laboratory conducted physical modeling of the Market Avenue Retention Basin (MARB) located in Grand Rapids, MI. The MARB is comprised of three bays for the storage of combined sewer overflows prior to final treatment. The scope of the study focused on the hydraulic efficiency of Bay Two as a secondary sedimentation basin. The first objective was to determine if short-circuiting occurred and determine a new baffle arrangement to mitigate any short-circuiting. The second objective was to maximize retention time to maximize its efficiency in disinfection. After it was shown that the existing design did not provide the required contact time, additional changes in baffle design were tested which led to the final design, meeting residence time requirements and eliminating short-circuiting.

South Washington County WWTP Siting Study
SAFL assisted its long-term client, Metropolitan Environmental Services, in siting a treated wastewater outfall along the Mississippi River, south of Hastings Minnesota. The site was selected for most effective dispersion of effluent away from the shoreline without compromizing navigation concerns. Our analyses included determining mixing zone size for various conservative flow assumptions and locations. Good mixing was predicted at all candidate locations; protection of commercial and recreational navigation was therefore the controlling factor in site selection.

Water Intake for the Alton Water Treatment Plant
SAFL engineers and researchers assisted Sverdrup (under the general guidance of Hazen and Sawyer for the Illinois-American Water Company) to position a new water intake for the City of Alton, Illinois. The project involved site reconnaissance and major thrust of our current research centers around the prediction of water quality, response of climate variability and climate change., a feasability study of alternative designs. The site selection considered some twenty parameters related to water quality and sedimentation. A sensitivity analysis of the selection process was used to characterize the certainty in the results.