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Robert Rimstad April 26, 2011 ACTT No. 03 -03944 Page 5 of 6 6.0 Infiltration Comments We have not been provided with the type, location, or elevation of potential infiltration devices. Therefore, we will only discuss infiltration rates of the various soil types which may be encountered at the site. Without the benefit of infiltration testing, such as double ring infiltrometer testing, it is usually required to use estimated infiltration rates per Table 12.INF.7 of the Minnesota Stormwaler Manual. These design infiltration rates are based on the Unified Soil Classification of the soils within 5 feet of the bottom of the infiltration device. In general, the glacial tills at the site have poor infiltration potential. Many of the tills are SC or CL soils which have infiltration rates of 0.2 or less. Per the chart, the silty sands would have an infiltration rate of 0.6 inches per hour and we judge it is unlikely that infiltration rates would be significantly greater than this for this soil type (i.e., infiltration testing would not prove to be a benefit in these soils). There are areas of silt (ML) although these usually appear as layers and not in substantial quantity. There are some areas of sandy soils, although substantial sandy soils tend to be in the form of fill. Soils described as sands would have an SP designation, as sands with silt would have a SP- SM designation, and as silty sands would have a SM designation. The referenced chart does not have a category for SP -SM, although based on our experience, an infiltration rate of 0.8 inches per hour should be a reasonably safe estimate. 7.0 Construction Observation and Testing The recommendations in this report are based on the subsurface conditions found at the test boring/geoprobe locations. Since the soil conditions can be expected to vary away from the soil boring locations, we recommend on -site observation by a geotechnical engineer /technician during construction to evaluate these potential changes. Sieve analysis tests should be performed on engineered fill in order to document that materials used meet the intended gradation specifications. Soil density and Proctor testing should also be performed on new fill placed in order to document that project specifications for compaction have been satisfied. 8.0 Limitations Within the limitations of scope, budget, and schedule, our services have been conducted according to generally accepted geotechnical engineering practices at this time and location. Other than this, no warranty, either express or implied, is intended. Important information regarding risk management and proper use of this report is given in the attached sheet entitled " Geotechnical Report Limitations and Guidelines for Use." 53