Rain Garden Excavation at Three Rivers Community College

Yesterday was excavation day at Three Rivers Community College. Jenna Messier, Mike Deitz, the contractor Jim Benjamin Sr., his son, Jim Jr., and I were there all day to prep the site for the June 6th planting. Professor Diba Khan-Bureau and a few of her students were on site in the afternoon to watch and document the project.

Mike overseeing the dig!

At TRCC, we had to make a curb cut, dig the basin, install an overflow pipe, and create a sediment barrier. The goal of this project is to divert storm water from the adjacent parking into the rain garden and away from the storm drain.

Here are some highlights from yesterday:

The first step in the excavation process was removing soil to create the depression where storm water will be stored for a short period of time before draining into the ground. For this specific site, we excavated about 14 inches below grade, since we had electrical conduit at 18 inches below grade.

Jim Jr. making the curb cut

Secondly, we made the curb cut. This particular cut was strategically placed next to the storm drain so that all of the storm water from the adjacent parking lot would enter the garden before it reaches the drain.

Mike again! Installing the platform

We then built a platform at the entrance of the curb cut and installed cement patio blocks to catch sediment from the parking lot before it can enter the garden. This will allow for easy clean-up in Spring, by taking a flat shovel and scooping out the sand from the winter maintenance.

Drainage pipe!

After installing the platform, we laid an over-flow pipe at the base of the garden that will drain excess water into an adjacent wooded area in the event of a large rain storm that will discharge more water than the garden can handle.







Lastly, we filled in the basin with beautiful soil making sure to keep a slight depression that will temporarily store storm water!

The rain garden is ready for planting on June 6th!

Jenna and Mike discussing some last-minute details

We will be putting together a full step-by-step PDF which will show the entire process and can be used by anyone for teaching or practical purposes. 

Rain Garden Progress at Naugatuck Valley Community College

Jenna and I just checked in this morning at NVCC to see how the rain garden plants were coming along. It finally rained last night. Fortunately, Mike Schwartz of NVCC has been watering to plants and helping them establish due to the lack of rain. I'm glad to say that the plants are growing well and establishing themselves. The front of the rip rap has accumulated significant sediment which indicates that storm water is flowing into the garden. However, one problem presented itself -- the entire garden was full of golden rod!

The front of the rip rap with sediment from the rain storm

Large view of rain garden with milk weed and golden rod

Common Milk Weed

The golden rod presents some advantages and disadvantages in the rain garden. On one hand, they do add more plants to the basin and its banks so that more water will be diverted from the storm water outlet. The milk weed is great to have as they provide a habitat for monarch butterflies. On the other hand, the plants that were chosen for the garden must now compete for sunlight, soil, and water. Jenna and I did a couple hours of weeding to give our selected plants more room. We'll check in again in a month or so. We are hoping that as the grasses, ferns, and other plants establish themselves more, the golden rod will be less of an issue.

As for the rain garden plants themselves, they are starting to look very nice. Some have even started to bloom!

Baptista australis in bloom

Ostrich Fern

Tall Panic Grass

Joy Pye Weed

Bio-retention media

Here is some helpful information from Rich Simcich of Agresource Inc:

When designing a bio-retention an architect or engineer must calculate the volume of water the basin must filter for a 50-100 year storm. The square footage, depth of the media, and soil physical properties must be considered. Agresource will meet any specification for raingarden or Bio-retention soils but provide our own bio-retention media that works well in New England. See attached analysis.  

It consists of 50% uniform coarse sand, 20% sandy loam and 30% leaf compost. The proportions are put together and mixed with a mechanical mixer which will produce a media that will infiltrate greater than 2 inches per hour and contain 2.5% to 6% organic matter. The choice of sand is the key. The fines fraction of the media, particle that pass .15mm sieve, must be less than 20% to reduce compaction and increase infiltration. The organic matter content in the soil is important to nourish plants and break down hydrocarbons commonly found in storm water runoff. Too much compost can reduce hydraulic conductivity. There is a balance of particle distribution or soil texture and organic matter content.

Bio-retention basins that drain too quickly will not remove contaminates they were design to remove and will not support plant life during dry summer months. If you have any question please call me to discuss.

Rich Simcich

Click here for specification manual

Preparing for Excavation at Three Rivers Community College

Looking east toward the garden

Jenna and Mike

We are in the process of planning the rain garden at Three Rivers Community College. Mike Deitz of UConn NEMO (Non-Point Source Education for Municipal Officials) has come up with a cross section diagram and an overhead diagram of the rain garden.

Jenna went out to TRCC to meet with Mike Deitz and the contractor last week. After looking at many site maps, we found electric lines marked within the area of the rain garden so they had to dig a trench to see if wires were indeed present.
                                                    

Found the conduits. Do not try this at home!

This is one of the less sexy parts of the job!

Sure enough, 18 inches below the soil, there were two conduits--one for the electric lines and one for the security lines. The contractor now knows where to avoid when installing the drainage pipe at the basin of the garden (around 14 inches deep).

There are many steps prior to installing a large rain garden in an area that has pre-existing  infrastructure. Like Naugatuck Valley Community College, students will be designing the garden and choosing its plants. Prior to meeting with the students, Jenna went out to Perennial Harmony Garden Center in Waterford to get inspired and look at plant choices. Here is a picture of Petie Reed, AOLCP, and her partner, Rich, owners of the garden center .

Petie and Rich from Perennial Harmony

Cross section of rain garden

Rain garden area in green