CASFM Stormwater Quality Field Trip June 23rd, 2011

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1 CASFM Stormwater Quality Field Trip June 23rd, 2011 The 2011 CASFM Stormwater field trip included 42 attendees coming from as far south as Colorado Springs up to the Denver area and another 12 who joined us for the Ft. Collins portion of the trip. We visited six sites this year: the Taxi infill site (Denver), Odell Brewing Co. (Ft. Collins), Udall Natural Area (Ft. Collins), Mitchell Block LID Demonstration Site (Ft. Collins), CTL Thompson Pervious Concrete Site (Ft. Collins), and the City of Ft. Collins Mulberry Reclamation Plant. Comparing and contrasting similar BMPs at different sites, the following observations were made by the group during our day long water quality adventure. Rain Gardens Taxi: At Taxi, the rain gardens are scattered throughout the site and contain a variety of vegetation including trees, small plantings and areas seeded with an upland prairie mix. All are full infiltration sections (no underdrain) with a mixture of 85% sand and 15% peat to a dept of 18 inches. During establishment of these areas the rain gardens were weeded by hand on a weekly basis. Monthly weeding is now performed. The irrigated rain gardens not only provide attractive landscape but also are an integral part of the drainage system for the site. This virtually flat, 20 acre site was 1

2 constructed without any new storm sewer. Mitchell Block LID Demonstration Site: The designers of this site incorporated rain gardens in as much as the site constraints of this very urban area allowed. The design provides attractive landscape as well as public awareness of stormwater treatment as the concrete that borders the area reads RAIN GARDEN. For rain gardens in this type of setting (small footprint and high pedestrian traffic) there is sometimes a concern in the grade difference between the sidewalk and the surface of the rain garden. The low depth of this rain garden coupled with the gutter inlet/overflow design result in insufficient volume and bypass of flows. Some commented that a design intended to treat roof runoff may have provided a better alternative especially considering that the adjacent pavement is permeable. Mulberry Reclamation Plant: Although we came to see the Grasscrete just installed at this site, we also noticed this bioretention area (middle photo) and found it to be an interesting contrast to the Taxi site. Due to concerns that the growing media would not provide adequate conditions to establish vegetation from seed, sod was used. Conventional sod, grown in a clay matrix, does not provide adequate infiltration rates. As a result the low area of the basin remains wet and unattractive. 2

3 Permeable Pavements Odell: The Odell Brewery used a combination of Permeable Interlocking Concrete Pavement (PICP) and an extended detention basin (EDB) to provide the required detention volume when they built their building addition. The new roof drains to the pavement which ultimately outlets to the EDB. The group noticed damage to the pavers near the barrier wall. Cut pavers directly adjacent to the barrier wall can cause this damage. In contrast, the PICP at the Mitchell site includes a soldier course against the barrier wall. Additionally, some of the cut pavers at Odell were a small fraction of the original size, something that can be avoided with a minor change in the pattern at the edge. Mitchell Block LID Demonstration Site: Soldier course The PICP installation and monitoring program at this site is unlike any other site in the country. The City of Ft. Collins, partnering with CSU, is monitoring two independent PICP sections. One constructed with a section that is per the recommendations of the International Interlocking Concrete Pavement Institute (ICPI) (see section, right) and the other per the UDFCD recommended section for water quality. The UDFCD section differs in that it forces water to flow through a sand filter layer prior to reaching the underdrain. This is an 3

4 important site because nationally, there is very little monitoring of the ICPI section despite its wide use. CTL Thompson Pervious Concrete: After studying several Denver area pervious concrete failures, CTL Thompson built their own parking lot using pervious concrete. It s been in place for two years now. The pavement is exhibiting minor raveling primarily at joints but remains in generally good shape structurally. A few quick infiltration demonstrations showed that the pavement remains free draining at least in two out of the three areas tested. The lower portion of the pavement may be in need of vacuuming. Mulberry Reclamation Plant: Constructed to sustain the weight of fire trucks, Grasscrete was chosen for the Mulberry Reclamation Plant. This is not a modular block but a cast in place reinforced concrete system with voids created by plastic forms. Just recently constructed, the challenge ahead is to get vegetation established. Extended Detention Basins Taxi: With rain gardens upstream of this EDB and type B soils throughout the site, this basin rarely ponds water. The EDB was constructed without a forebay, trickle channel, or micro pool. Most of what would end up in the forebay and trickle channel will end up in an upstream rain garden 4

5 making these EDB components unnecessary. Although it is typical to see a dead zone near the outlet when a micropool is not provided, the absence of failing vegetation and a clogged well screen further support that little ponding occurs at this location. The wild look of the grasses and wild flowers are attractive, allow for more infiltration, and require less maintenance compared with a sod basin. Odell Brewing Co. In an attempt to reduce the volume of runoff leaving the site, Odell s EDB included dry wells. Upon inspection of one of the dry wells, it was full of water. This dead area in the foreground of the right middle photo may be the result of the dry well failure. This is also the location of the inlet. Without positive drainage to the outlet, water may be ponding here for an extended period of time. Ponds Udall Natural Area This site features three constructed wetland ponds in series. It was built as a retrofit regional water quality treatment for the Old Town Basin in Fort Collins, and drains a significant portion of the Old Town area into the Poudre River. This site is important as it provides a regional end of pipe solution. Ft. Collins, with assistance from CSU, is monitoring water quality at three locations in this BMP treatment train. 5