Clay causes problems for FMS well field

Fairfield school board members peppered Shive-Hattery Architect and Engineering representatives with questions Monday, trying to sort out responsibility for a possible $45,386 change order charge for work at the middle school.

?We?ve run into serious issues in the geo-thermal well field, not necessarily issues we were able to predict,? said Chuck Hildenbrand from Shive-Hattery.

He and co-worker Michelle Huggins described boring the wells, then inserting the tubing needed to create the various loops of pipe that circulate underground to dissipate heat into the earth during hot weather and deliver heat from the earth in cold weather.

Huggins diagramed visuals on a white board while Hildenbrand spoke.

?We have one horizontal loop at 15 feet underground, another one at 30 feet and another at 45 feet,? he said. ?We?ve hit rock at 39 feet. Below the rock would be aquifers and so we want to stay above the rock, so we have to work with 15 and 30 feet of depth.

?The contractor also has encountered a thick clay, we?re calling it blue clay, it?s almost like glue,? said Hildenbrand. ?When boring the hole, the clay and moisture begins to narrow the hole before the tubing can be placed. In drilling the first 20 borings, 10 tubes have been broken and will need to be re-bored.?

A material is used to help the tubing slide into the bored well, and then fills in around to close air pockets. The usual mixture includes sand and silica, known as standard grout.

?We used the standard grout on the first 20 holes and it works well to fill the voids,? said Hildenbrand. ?But it also broke half the tubes, so we can?t continue to use it. Last week, we eliminated using the silica-sand mixture and used bentonite grout. It has a lower thermal rating. So we had to figure out something else.?

The engineer calculated percentages of the whole well field, so that 20 original bored holes could use the standard grout with good thermal conductivity and 28 wells will have the bentonite grout, which has a lower thermal conductivity rating. The balance of 42 wells will use a graphite grout that will counter the low rating to bring the entire field up to the expected thermal conductivity level.

?The graphite grout is more lubricating so it solves our problem with the clay narrowing the well before the tubing can be placed,? said Hildenbrand. ?But it costs about four times the amount of the standard grout. This was not anticipated, so after much work and discussion, the contractor will switch to graphite and we?ll submit a change order for the more expensive grout, plus the contractors? allowed normal mark-up.?

Questions arose about the test bore completed before work began.

?The test bore tested for conductivity, nothing else,? said Hildenbrand. ?That?s almost always how test wells are conducted.?

A different company than the contractor working on the project was brought in to do the test bore. Hildenbrand said, to expedite the process, the test well was bored using a graphite grout, because it makes the process go faster. That test bore was done in one day.

?We asked for a boring to get specific conductivity of the ground so we could decide about the number of wells needed for the project,? he said. ?The contractor used the most expedient way. What cost him perhaps $600 in materials saved him $1,000 in labor.?

If graphite grout had not been used for the test, the process could have taken more than one day and definitely would have taken more equipment and labor.

?But the contractor?s mark-up on the graphite grout ... how is that our problem?? asked board member Jerry Nelson. ?And using different contractors for the test than for the project puts the contractor on the job at a disadvantage, too.?

?Shive shares some responsibility because you told us [after the test] it was OK,? said board member Bob Waugh. ?That?s the reason we hire an architect. Shive-Hattery wrote up the specifications for the test.?

Board president Jennifer Anderson said she appreciates the engineer and contractor looking for a solution.

?My concern is the percent of overhead profit to cover their expenses. I understand we need to buy the product,? she said. ?But if soil testing wasn?t done, that?s not on us. I?m having trouble with that. I think you would?ve checked the soil components, too. Reports of clay in the soil are available through public reports.?

Hildenbrand said using the graphite grout in the project is the most cost-effective solution.

?Plan B would be to increase the number of wells by 30 percent, which increases expenses and the timeline,? he said. ?Each boring is an additional cost. Another ramification of adding wells, each loop is custom-made.

?The contractor will credit your account for any grout not used at the end of the project. But to get the change order, we need the board?s direction.?

The $45,386 figure is the additional cost of the graphite gout before contractor mark-up.

?This is important and we want to get through the project economically,? said superintendent Art Sathoff. ?We?ve been pleased with the work. We need to have the system function properly when it?s finished.?

No decisions were made at Monday?s meeting about who will pay what for the change order. It will be brought to the school board again.

Before installation of a geothermal system began at Fairfield Middle School, the district received a $33,000 change order credit on the project when fire sprinklers were eliminated and enlarging the water main from the street to the building was scratched.