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Data Sources
' For this analysis,the following geologic and groundwater data were reviewed in order to gather
the appropriate information to accurately design and model the stormwater infiltration system at
the site.
' • Water level readings taken by VHB in December 2009,January 2010 and February 2010
(Attachment 1).
' • Test pit logs completed by VHB between November,2009 and February,2010.
• USGS topographic quadrangle(online information accessed February,2010) (Attachment
2)
• Boring logs completed by Langan Engineering and Environmental Services between
January and February,2010(Locations shown in Attachment 3).
• In-situ permeameter tests conducted by VHB in November,2009 and February,2010.
• Sieve testing conducted in November,2009.
• On-site survey completed by Design Professionals,Inc. on February 11,2010.
' An exploration location plan is included as Figure 2.VHB logs and testing results are included in
a separate Soil Investigation and Permeability Analysis memorandum completed on February 24,
' 2010. Langan exploration location plans are attached.At the writing of this memorandum,
Langan has not provided VHB with final exploration logs. USGS topographic data is attached.
' Assumptions
The following assumptions were used in the preparation of the groundwater model. These were
' established based on the site investigations and available data described above:
• Soils are generally classified as clean fine uniform sands overlying low permeability clay.
• Proposed ground surface elevations on the site are around elevation 62 based on site
design plans by VHB on February 24,2010. Ground surface elevations outside the project
area range from elevation 30 to elevation 70 based on USGS topographic data.
• Seasonal High Groundwater estimates vary across the site from elevation 43 to elevation
' 64 with the highest elevations to the North East,based on field observations by VHB.
Seasonal high groundwater elevations are shown on Figure 2 and in Attachment 1.
• The bottom of the sand aquifer on the Site varies from elevation 40 to 50 with the highest
elevations to the East,based on boring logs from Langan Engineering and Environmental
Services.
• The soil underlying the infiltration basin has an overall saturated conductivity between
100 and greater than 150 feet per day based on in situ permeability tests conducted by
VHB. Some test locations exceeded the equipment's maximum measurable conductivity
of 150 feet per day. The horizontal saturated hydraulic conductivity(Kh) was
' conservatively estimated to be 120 feet per day and the vertical saturated hydraulic
conductivity (Kv)was estimated to be 60 feet per day based on literature values of Kv:Kh
' for sands. Anisotropic conductivity is typically a result of clay content in the soil. Soil
sieve testing revealed less than 1% clay content of the soil supporting the selection of a
low Kv:Kh ratio. It is likely that given the extremely low clay content that even the
selected 2:1 ratio is conservative.
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