The Maryland State Highway Administration incurred a ten acre compensatory wetland mitigation obligation through the widening of 1-270 in Montgomery County. Through a site search in the impacted watershed and County, MSHA received agency concurrence for a privately owned, twenty acre parcel in Montgomery County. MSHA conducted an environmental inventory and water table monitoring on the property and deemed the property satisfactory resulting in fee simple purchase.
The goal for the project was to create ten acres of palustrine, forested wetlands to fulfill permit obligations. The site offered several challenges throughout the design and construction phases.
During the review of the project design by regulatory and environmental agencies, the agencies became rather insistent that a stream, Goshen Branch, bisecting the site have a direct hydrologic connection and be the primary source of hydrology to the site. MSHA strongly objected stating groundwater would be the primary source of hydrology for the site but relented to an inlet channel created by lowering the stream bank in one area. This proved to be a costly design error. In November, 1994 the site grading was complete, but stabilization had not occurred. The site experienced two out of bank storm events five days apart. The site held through the first storm, but being highly saturated, failed to hold during the second. The stream created a cutoff channel where the bank had been lowered exacerbating degradation in a stream that was already in disequilibrium. The original stream bank elevations had to be restored using riprap. Borrow excavation was required to restore the area to design elevation.
Since direct hydologic connection to streams was a common and often unnecessary design requirement of the agencies, Ms. Kelbaugh contacted Brightwater for a field presentation to explain the inadequacy of out of bank flows as a source of wetland hydrology and the damage that would occur if the agencies continued to require direct hydrologic connection by lowering stream banks. The presentation was highly successful and the agencies gained the understanding of out of bank flow frequencies occurring on an average of once every 1.6 years which would not provide adequate soil saturation durations. They no longer considered lowering stream banks an option for obtaining wetland hydrology.
During the design phase, adjacent property owners strongly objected to the project on the basis of impact to drinking water supplies and of the creation of a mosquito breeding ground. Linda Kelbaugh, currently employed by Brightwater, then MSHA Division Chief, met with the property owners to discuss their concerns. Ground water studies were conducted to prove no impact on drinking water supplies. The nature of seasonally saturated, forested wetlands was explained as being soil saturation rather than surface water. The objections were resolved.
The site has been monitored for the last two years and is meeting the project goals. However, the degraded state of the stream may threaten the ground water levels as incision occurs. Stream monitoring and assessment of effects on groundwater will be required to protect the applicant should the ground- water tables lower.