by David Baumgarten
Very early in my consulting career, the firm I was working for had an in-house workshop for the new staff. One of the firm’s principals posed the question to the group “What do we do?” Answers included, we do geotechnical engineering studies, hydrogeology studies, environmental assessments, slope stability studies, etc. The principal agreed we do all of these technical science based services, based on our training but that was not the answer the principal was looking for. The principal asked again “in one sentence, what do we do?” The answer – “We Solve Problems.”
We help our clients solve problems. Environmental due diligence studies ensure our clients are not buying a site with environmental problems or at least identifying Recognized Environmental Concerns (RECs) which helps our clients in the decision-making process of purchasing the site. We help clients identify and meet the applicable county or city engineering and design standards for the site, related to geotechnical engineering, stormwater management, and environmental regulations.
In an effort to help our clients solve problems a good consultant will search for all available information. I recently got a call from a client that desperately needed to add additional paved employee parking to the existing parking lot. They had land adjacent to the existing paved parking areas slated for the additional parking. The civil engineer sent me correspondence from the city with the required information needed for the permit submittal. The city required monitoring of groundwater levels over one wet season, large-scale Pilot Infiltration Tests (PIT) to determine design infiltration rates, as infiltration would be required, and the use of permeable pavement for the paving. The problem was the client desperately needed the additional parking and since they contacted me in September, the wet season groundwater monitoring alone would delay any construction for almost a year. The client also did not want to use permeable pavement, if at all possible due to the cost and maintenance. To some the next step would be to generate a proposal of services and costs for the client to complete these tasks.
Time to see how I could solve this problem. I like to bring up all my new sites on Google Earth to look at the regional picture. This site was in the Puyallup River Valley so my first thought was the geology is Puyallup River Alluvium, a non-glacially consolidated deposit. My second observation was a construction site across the street, about 200 feet from the proposed paved parking area on my client’s site. I also noticed what appeared to be stormwater detention facilities being constructed at that site. Maybe there was groundwater data collected at this site for the previous wet season?
The governing stormwater manual included an option for long-term design infiltration rates derived from grain-size analyses for non-glacially consolidated deposits and river alluvium is not glacially consolidated. An aside here, if the proposed infiltration facility was an infiltration gallery, infiltration pond, or infiltration trench system with stormwater runoff conveyed and concentrated I would have recommended the PIT testing. For a permeable pavement application, I felt a long-term design rate based on grain size would be adequate.
My next step was a call to the city engineering staff to discuss the project. That discussion revealed the city currently had multiple failing infiltration facilities due to incorrect long-term design rates and/or seasonal high groundwater levels much higher than predicted in the site geotechnical reports. As such, the city had defaulted to wet season monitoring and PIT tests for all infiltration facilities. I discussed my proposed approach of long-term design infiltration rates based on grain size analyses specific to permeable pavement systems, as allowed in the city stormwater manual. There was in fact groundwater data from the previous wet season for the site across the street, the city was even willing to email me pdfs of the reports as the data was now public. Even better the consultant that had monitored the groundwater levels through the previous wet season, our wettest winter ever, had the wells professionally surveyed so I had elevation control.
The city agreed that per the City’s Stormwater manual they would accept infiltration rates based on grain size. I argued that since the groundwater level data for the neighboring site was in such close proximity and the gradient of the water table in the river valley would be very flat, the seasonal high groundwater levels measured on the adjacent site were indicative of the seasonal high groundwater levels in the proposed parking area. They accepted the groundwater level data.
We went to the site to complete test pits and collect the soil samples for grain size analysis. The shallow site soils were silt. Grain size analyses showed 80 to 99 percent passing the No 200 sieve. Because of the high fines content, the equations to estimate infiltration rates from the grain size curves were not valid. More important the use of permeable pavement which would convey water to the silt subgrade would make the subgrade unstable and therefore the parking surface would fail.
In October, one month after our first contact with the project, we had generated a report for the client which addressed the seasonal high groundwater levels, documented the silt soils and the fact infiltration was not feasible and permeable pavement was not advisable. To protect the very fine-grained subgrade soils conventional pavement was recommended much to the clients liking.
The project was able to move forward to permit submittal one month after we first got involved, not a year. Problem solved.
We help our clients solve problems. Environmental due diligence studies ensure our clients are not buying a site with environmental problems or at least identifying Recognized Environmental Concerns (RECs) which helps our clients in the decision-making process of purchasing the site. We help clients identify and meet the applicable county or city engineering and design standards for the site, related to geotechnical engineering, stormwater management, and environmental regulations.
In an effort to help our clients solve problems a good consultant will search for all available information. I recently got a call from a client that desperately needed to add additional paved employee parking to the existing parking lot. They had land adjacent to the existing paved parking areas slated for the additional parking. The civil engineer sent me correspondence from the city with the required information needed for the permit submittal. The city required monitoring of groundwater levels over one wet season, large-scale Pilot Infiltration Tests (PIT) to determine design infiltration rates, as infiltration would be required, and the use of permeable pavement for the paving. The problem was the client desperately needed the additional parking and since they contacted me in September, the wet season groundwater monitoring alone would delay any construction for almost a year. The client also did not want to use permeable pavement, if at all possible due to the cost and maintenance. To some the next step would be to generate a proposal of services and costs for the client to complete these tasks.
Time to see how I could solve this problem. I like to bring up all my new sites on Google Earth to look at the regional picture. This site was in the Puyallup River Valley so my first thought was the geology is Puyallup River Alluvium, a non-glacially consolidated deposit. My second observation was a construction site across the street, about 200 feet from the proposed paved parking area on my client’s site. I also noticed what appeared to be stormwater detention facilities being constructed at that site. Maybe there was groundwater data collected at this site for the previous wet season?
The governing stormwater manual included an option for long-term design infiltration rates derived from grain-size analyses for non-glacially consolidated deposits and river alluvium is not glacially consolidated. An aside here, if the proposed infiltration facility was an infiltration gallery, infiltration pond, or infiltration trench system with stormwater runoff conveyed and concentrated I would have recommended the PIT testing. For a permeable pavement application, I felt a long-term design rate based on grain size would be adequate.
My next step was a call to the city engineering staff to discuss the project. That discussion revealed the city currently had multiple failing infiltration facilities due to incorrect long-term design rates and/or seasonal high groundwater levels much higher than predicted in the site geotechnical reports. As such, the city had defaulted to wet season monitoring and PIT tests for all infiltration facilities. I discussed my proposed approach of long-term design infiltration rates based on grain size analyses specific to permeable pavement systems, as allowed in the city stormwater manual. There was in fact groundwater data from the previous wet season for the site across the street, the city was even willing to email me pdfs of the reports as the data was now public. Even better the consultant that had monitored the groundwater levels through the previous wet season, our wettest winter ever, had the wells professionally surveyed so I had elevation control.
The city agreed that per the City’s Stormwater manual they would accept infiltration rates based on grain size. I argued that since the groundwater level data for the neighboring site was in such close proximity and the gradient of the water table in the river valley would be very flat, the seasonal high groundwater levels measured on the adjacent site were indicative of the seasonal high groundwater levels in the proposed parking area. They accepted the groundwater level data.
We went to the site to complete test pits and collect the soil samples for grain size analysis. The shallow site soils were silt. Grain size analyses showed 80 to 99 percent passing the No 200 sieve. Because of the high fines content, the equations to estimate infiltration rates from the grain size curves were not valid. More important the use of permeable pavement which would convey water to the silt subgrade would make the subgrade unstable and therefore the parking surface would fail.
In October, one month after our first contact with the project, we had generated a report for the client which addressed the seasonal high groundwater levels, documented the silt soils and the fact infiltration was not feasible and permeable pavement was not advisable. To protect the very fine-grained subgrade soils conventional pavement was recommended much to the clients liking.
The project was able to move forward to permit submittal one month after we first got involved, not a year. Problem solved.
