Recent Construction: Site Development and Stormwater Management

Chaden Halfhill

Chaden Halfhill on the first floor during construction.

In the heat of August, our attention turned to the construction-unfriendly cold temperatures that we know are eventually coming and the rush to complete the vegetative roof, retaining walls and foundation waterproofing. Special landscape fabric that directs water where it needs to go must be in place, and site dirt work must be completed prior to the ground freezing. As we were finalizing the geo-thermal well field, our backhoe unearthed an unidentified 500 gallon tank. What else could be in store?

Late Summer

With temperatures pushing three digits, keeping the soils dry and dusty, we felt mounting pressure from pending grant deadlines and the looming shifts in weather patterns – yes, I am talking about evening temperatures that drop below 45 degrees at night and the constant concern about the early freeze that limits fall planting.

At Green & Main, we are acutely aware that we must restore the site before mid-October, when the likelihood of a freeze is near certain and worries about the new plantings’ ability to establish are commonplace.

What Needs to be Done on the Building

Rebar and Footing

Rebar and footing, looking to the east.

Throughout the month of August the team at Atlas Masonry worked to complete all sub surface foundation work around the perimeter of the building, allowing the installation of waterproofing, drainage mats and footings to be installed, managing and dispelling any water near the base of the building.

One-inch washed gravel limestone was backfilled around foundation walls, and crews were able to cover the rock with soil and establish a new grade around the building. Looking at the original soil imprint on the north face of the building, it is amazing how much soil we’ve reduced from the site to bring grade at or below the building’s wooden joists.

By the end of the month, final connections for the geo-thermal well field were scheduled for completion north of the building, preparing the site for a parking area. The discovery of an unknown five-hundred gallon tank while contractors were digging for the first well connection, created a day of unanticipated challenges. We stopped our digging in order to determine how to safely remove the iron container and how to best protect the site and its environmental context.

A four thousand pound iron steam boiler was hauled away within the week, but work on the well field was delayed for three weeks due to scheduling conflicts with the geo-thermal installation company. Fortunately, plenty of work continued on the site reclamation.

What Needs to be Done on Site

Retaining Wall

Retaining wall on the south side.

The southern boundary of the property is defined by a retaining wall. This wall helps us establish a bio-swale that winds its way through the property, assisting with water infiltration as it directs rain from the building and parking area to the rain garden located on the western-most twenty feet of the property – the location with the lowest elevation.

This retention garden allows stormwater to collect and slowly settle into the soil to feed the root systems of diverse native Iowa plants. Building this retaining wall has been a testament to the durability of bridge construction and the ingenuity of Norm Paulson, the eighty-four-year-old foreman who has dependably lead the wall’s fabrication for Jensen Construction. In the end, we needed to compensate for the moment of the hydraulic pressures in the retained earth with wall footings that were larger than those we used to shore up the building.

Many questions have been raised in the Sherman Hill Neighborhood about the nearly ten-foot wide trench that was built to form the base.

Unearthed 500-Gallon Tank

Unearthed 500-gallon tank.

Now that we are nearing the final concrete pour, the results are quite pleasing, accentuated by a neighborhood bench that helps visually connect two forty-foot retaining walls that shape the site. It will be a whole-hearted relief to backfill against the wall, replacing soils that have patiently rested in piles in the nearby alley, in order to restore the walkway and bury the new utility service lines that extend below grade from the alley to the renovated building.

Finishing the Soil Amendment and Site Restoration

Completing the wall and backfill will allow us to focus attention on site grading and soil amendment, thus regenerating soil composition and preparing the earth for fall plantings and seeding. The native plants will provide a root structure that will assist with stormwater infiltration within the property while helping to establish a more ecologically diverse site.

From the vegetative roof on top of the existing building to the low lying rain garden, many design decisions have been made to help promote on-site stormwater management and best practices. These extra efforts during August construction have helped establish the basis for site restoration throughout September. Today, we press forward to meet our goals as the weekly forecast drops from a high of 91 degrees on Monday afternoon to a low of 42 degrees by Thursday morning.

It’s Iowa, and the unpredictability of autumn weather has begun. So the race begins!


– Chaden Halfhill is an entrepreneur and visionary of the Green & Main Initiative.


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