Installation and sieving of steel slag

Before pouring slag into the structure, it was necessary to sieve the material to > ¼”.  This was done on a large scale at a gravel quarry next door to the steel mill located in Ft. Smith, Arkansas.  A liner was placed on the bottom of the structure before dumping the sieved material into it.  A liner was also placed on the outflow side of the structure (i.e. “apron”) in order to channel all of the treated water into the flume for monitoring purposes. 

The sides of this outflow apron were constructed with railroad ties.  In the above picture they are covered with the liner.

The perforated drainage pipes were placed at the floor of the structure (on top of the liner) before covering it with the sieved slag.  Note that these drainage pipes channel water to the outlet of the structure, which is comprised of expanded metal.  Between 35 and 40 tons of slag was dumped into the structure use a skid steer:

 After the drainage pipes were covered with slag and the structure was nearly filled up, we installed the inflow manifold pipes.   These perforated pipes located just barely below the surface serve to evenly distribute runoff water throughout the surface of the structure:

We ran out of sieved slag near the end, so we had to sieve around 10 tons of slag to produce 6 more tons of >1/4” slag.  I’m pretty irritated in the picture below because the concrete vibrator that was used to screen the material kept breaking all of our U-bolts:

Eventually we ran out of U-bolts and we cleaned out the local hardware store for U-bolts.  At that point we had to sieve it the old fashioned way.  The guy on the right is Stan Roberts, a salesman from Automatic Engineering, the distributor for ISCO auto samplers in Oklahoma.  Stan was supposed to stop by to help with programming…..hahaha, but we put him to good use since we were not yet ready for programming.  That is a good salesman right there.  Steps out of the office and does some “hands on” work with no complaints. 

During the installation, we forgot to stabilize the downstream “gate”.  After it was filled with slag, the metal started to bow.  Note that the wood in the picture below was temporary.  It was removed after the slag was treated in-situ.

We managed to remove the bow in the metal gate using a come-along and 40 feet of chain.  After we pulled it back, we stabilized it by pounding several ½” rebar into metal sleeves welded to the gate.  I wish I had a picture of that process because it was pretty awesome.  Again, the slag was treated in-situ.  The samplers were set up (which is what we called Stan for!) and were placed in their own respective buildings:

We rolled out some erosion control mats and seeded uphill of the structure.  Trimmed the excess liner.  We also built a new suction head for the samplers to be able to handle a very shallow depth of water.

At this point we are ready to collect samples!  Just offhand, I hope that we can have a field day presentation in January.  We will continue to update this blog with results.

Preparing the Structure for Slag and Monitoring

The ISCO automatic samplers have finally arrived along with the flow monitoring equipment.   The flow and sample monitoring will be observed remotely at our office in Stillwater through the purchasing of a Verizon data plan.  Basically, we will be able to monitor what the samplers are doing/measuring at any time.  This way, when there is a flow event, we will know it immediately and obviously know to go to the site to collect the sample bottles as soon as possible for laboratory analysis. 

We recently poured some concrete at the inflow side of the structure.  The picture below shows the “before” picture and you can see that the inflow pipes (black) are at varying elevation from the surface, which is bare soil.  We wanted to create a clean and level “apron” where the inflow runoff water can enter the structure.  Eventually, there will be perforated plastic pipe attached to the other side (inside the structure) of the black metal pipe.  This pipe will be buried in the slag and will serve to evenly distribute the inflowing water (i.e. serve as a manifold).  

The next pictures show the concrete work:

 The finished product:

Also on this site visit we can to lay the pipe which will hold the suction lines for the automatic samplers and the bubbler tube for the flow monitor.

Not very exciting.  However next week we will sieve the slag and put it in the structure and finish up the installation of the monitoring equipment.

I would like to briefly highlight the work by Dr. Stefan Jansen in The Netherlands, here.

Flume installation and preparation for monitoring: Part 1

This portion of the construction and installation process for the P removal structure is NOT necessary for the typical-everyday use.  What is described here is for very detailed monitoring of performance for the purpose of research.  It is completely unnecessary for the applied purpose of the P removal structure.  We are doing this so that we can demonstrate the effectiveness of the unit and also produce more data for model verification.  This section is mostly relevant to researchers.

That being said, we will not put the PSM (treated steel slag in this case) into the structure until all the monitoring equipment is installed.  For monitoring, our purpose it to measure the amount (volume) of runoff treated by the structure during each runoff event and also measure the P concentrations flowing in (i.e. before treatment) and after (i.e. after treatment).  Knowing this, we can then estimate how much (mass) P has been trapped by the P removal structure. 

On the “inflow” side of the structure where water will enter, we will use an ISCO automatic sampler that will be triggered to collect samples based on the detection of flow at the “outflow” side of the structure where the treated water will be located.  Below you can see some photos of the construction of the approach for the 3 foot flume that will be used to monitor flow rate.  

Monitoring flow rate is critical if one is serious about getting a real estimate on the P removal performance of a P removal structure.  Many researchers have utilized only water sampling in their monitoring regime without the use of flow monitoring.  Simply put, P concentration testing of the treated water compared to untreated water alone is not sufficient for assessing the capacity of a P removal structure; knowledge of the flow rates and therefore the volumes of water treated is absolutely critical.  Any assessment without the use of detailed and thorough flow monitoring should not be taken too seriously.  Why? The short answer is “P load”.  If I measure a 100% P concentration reduction and there is only 1000 gallons of water treated, it is not correct to compare that concentration reduction to another scenario where there is only 50% P concentration reduction and 1 million gallons of water treated.  Simply put, the most important factor is the P load (i.e. mass) reduction.  Instead, it is more correct to compare the P load reduction (i.e. mass of P removed).

Too often, we focus on the final concentration of runoff water and treated water.  This makes little sense, especially when surface water quality thresholds (i.e. critical P concentrations for streams and lakes) are applied to the context of runoff water concentrations.  For example, runoff concentrations from a certain field (call it field 1) may test at 1 mg P/L, while field 2 may produce 0.2 mg P/L.  That does not mean that field 2 is somehow more “safe” than field 1.  Consider a scenario where field 1 produces 2 million L runoff for an event, while field 1 only produces 1000 L.  The P load transported off site for field 1 and 2 would be 1 g vs 400 g, respectively.  Concentrations alone would be deceiving in that case.  What matters is the mass or load of P that reaches the lake or stream; concentrations (mass/volume) change with dilution, evaporation, etc., but it is the mass of P that does not change.  This is why the USEPA has moved to a “total maximum daily loading”, or TMDL system for point and non-point source pollution concerning nutrients. 

For the same reasons, it is important to assess the performance of a P removal structure based on P load reduction, not P concentration reduction. 

Below you can see the flume installation process.  

This flume can handle much more water than our projected 2 yr storm (~16 cfs).  This flume is being used courtesy of Dr. Sherry Hunt, Kem Kadavy, and Ron Tejral, located at the USDA-ARS Hydraulics Engineering Research Unit.

All of the treated water plus any water that might overflow the structure will flow through the flume for measurement.  There will not be any water overflowing the structure if none of the storms exceed a 2 yr return period for that location.  In addition, if that does happen, there will be a flow sensor (actually a depth sensor) placed on top of the structure that will also monitor exactly how much water overflows the structure and remains untreated.  Below is the view looking from the structure downhill toward the flume:

This area between the outflow drainage of the structure and the flume will have an impermeable liner placed on the ground and “bordered” with stabilized railroad ties to force all water from the structure to flow through the flume where flow rate will be monitored and also where samples will be taken by the ISCO sampler. 

The photos below show the installation of the small building that will house the ISCO sampling equipment:

Construction and Installation of the Structure

Several posts back we determined how much PSM (treated slag in this case) was required to meet our P removal goals at this site, and we also determined how to orient that slag (i.e. area and depth) at our site to be able to treat all the runoff from a 2 yr-24hr storm event. 

Now it is time to build the structure.   In this case we are going with the low-tech, standard box structure where water flows through the PSM from the top-downward into subsurface drainage pipes.  With one small twist however: the drainage pipes at the bottom of the structure will not protrude through. 

We also designed our structure to be easily cleaned out with a front-end loader or a skid-steer. 

Below is the 33 x 13 ft structure from the perspective of downstream (drainage) side looking up to the upstream (entrance).  This was built in a modular form so that we can take it out into the field in pieces and assemble on-site.  Note the expanded metal on the drainage side.  The buried perforated pipes will drain to the expanded metal, where the treated water can then exit the structure.  This downstream side of the structure was designed as a “gate” to be removed when the PSMs become saturated with P.  At that point, the gate can be unbolted and easily removed, providing access for a skid-steer to drive in and scoop up material.

 Below is a picture of the “upstream” side where the runoff water will enter into the structure.  There will be perforated pipes connected to the metal pipes that will serve as an “entrance manifold” in order to evenly distribute the runoff water over the top of the PSM.

Here is most of the structure in pieces as we take it to the shop for painting:

Getting the primer on:

Then the paint:

 These students are talented!

Heavy, but not so heavy that we could not lift them by hand. Shown in the picture is Stuart Wilson – technician, Alexandre Ricardo Alves (i.e. The Shark) – Brazilian student intern, and Josh Daniel – graduate student.

Putting the pieces into our previously made “footprint”.  Note the adviser is actually working the shovel.

It was wet that day:

Completely put together: Note the earthen berms meet at the entrance to the structure:

Total cost for the metal materials and for a private fabrication shop to custom construct to our specification: $2,500.  Powerhouse, in Stillwater, OK.  405-377-6396. They did an excellent job.