Ground water contaminated with Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) and iron was discharging to an ephemeral stream traversing a public golf course in Rhode Island. The source of contamination was attributed to the previous presence of petrochemical storage tanks located hydraulically upgradient of the golf course and surface receiving stream. Discharge rates averaged 7,000 to 10,000 gpd and contained varying BTEX levels of from 2 to 7 mg/L. The point of discharge was between an active green and adjacent tee-off area of the course. While the discharges were non-hazardous, the associated odors and presence of iron staining created an aesthetic problem for the client.
A 7,000 gpd subsurface flow Constructed Treatment Wetland (CTW) was installed to passively intercept and provide BTEX treatment and iron discharging to surface water at the site. The system’s high aesthetic, low visual impact appeal was ideal for its golf course setting and is designed to passively intercept and treat the contaminated ground water in situ. Several innovative features were designed into the system to enhance the aerobic microbial degradation of the target constituents, minimize odor and aesthetic impacts, and eliminate exposure concerns to recreational users and indigenous wildlife populations. Parallel flow cells were incorporated into the design to assess the biodegradation / biotransformation processes for multiple wetland plant species.
The system was constructed and activated in the spring of 1995. Since 1996, Roux Associates has conducted a rigorous testing and evaluation program to gain an understanding of contaminant removal mechanisms and to document performance trends. This testing program has allowed us to optimize performance of the existing system and gain insight into the design of future systems. Nutrient additions and re-planting modifications have been implemented to enhance growth.
Since 1998, quarterly performance monitoring data have consistently reported up to 99.5 percent reductions in effluent BTEX concentrations. Based upon this success, Roux Associates is currently designing a 40+ acres CTW system for the Site. The new system will process and treat all site stormwater and contaminated ground water.