Groundwater Issues
Groundwater Issues Groundwater and its impact on neighboring homes is one of the most serious impacts that this proposed development brings. As the picture below shows, many of the surrounding homes have active sump pumps. Basement flooding is a problem and recent development of the soccer fields to the north have exacerbated these problems. Though some of the basement problems along Cimmaron may be attributed to the Dry Creek Ditch many homes in the area that are located well away from the ditch also have problems. There is strong anecdotal evidence (e.g., Greenbelt Meadows, Cimmaron Way) that development can and will lead to changes in ground water flows.


One of many local sump pumps

As a resident on Cimmaron recently said (June 13, 2005):

I am still pumping water at 5 gallons every 20 to 25 seconds. That is over 20,000 per 24 hours! There are about 4 houses on my street alone that are probably pumping that amount. If the developer installs a liner in the ditch and also constructs a retaining wall along the west side of the ditch to reduce or even stop the water from coming to these 4 houses, where will that water go?? It is not a sub-surface 'pond' that must be drained but rather a continuous flowing 'river' that must be always be dealt with. It appears to me that that the (daily) 80,000 gallons of water needs to find a outlet somewhere and it will either find it in the proposed subdivision by increasing the existing water level substantially, or find new outlets and new basements to fill somewhere in our subdivision.
The following photo shows a tree just south of the property knocked over in the June windstorm. Note the groundwater levels - approximately one foot below the surface. This area is uphill and far removed from any of the irrigation ditches in the area.


Ground water in area

Developer's Report

In 2003 the developer submitted a Limited Impact Special Review to Boulder County to bring in 30000 cubic yards of fill to raise the level of the Hogan property. In the engineering report the soils on the property are characterized as Niwot Soils which:
have a seasonably high water table that extends to within 6 to 18 inches of the surface.
A Preliminary Subsurface Investigation report from June, 2003, was prepared by Western Soils. This report notes that ground water in the area is very high as evidenced by 5 backhoe test pits which were excavated across the Hogan property. The following image shows the Test Pit Logs from this report. Groundwater (shown as blue lines) was encountered between 8 inches and 3 feet below the surface. These 5 test pits were dug on the Hogan property, the southernmost parcel of the proposed development.


Western Soils Test Pit Logs

Development Impacts on Groundwater

Section D of the Development Report submitted by the developer to the County states:
Apparent man made hazards that affect this site are ...
2) filling of the City soccer fields to the north, which appear to have been filled by some 3 to 4 feet, causing some cessation of the natural drainage from this site to the north, and perhaps causing a higher water table on the site as well.
We wholeheartedly concur with the developer as to the possiblity that fill can change drainage patterns and cause higher water tables for surrounding properties. It is important to note that the above observation as to the effects on ground water pertains to the Hogan property, which is on the south side of the proposed development and the closest point is, on average, 2 tenths of a kilometer away from the soccer fields. Furthermore, the soccer fields are approximately 5 acres in size, only 1/5 the size of the proposed development. Also, the work that was done on the soccer fields did not include 115 houses, foundations, sewers, roads, etc.


Potential Ground Water Impacts

Let's take the developer's statement above as the best case scenario, i.e., that some fill dirt can have an effect on ground water levels 2 tenths of a kilometer away. The above image shows the houses that fall within this radius. There are more than 130 homes where the ground water levels may be effected by this development.

Many open questions remain:

  • What will be the impact of the construction building 134 homes on the ground water levels? When asked this question the developer replied:
    There won't be basements so it won't be a problem.
    When queried further about the need to sink deep foundations because of the instability of the soil in the area the developer had no reply. In the developer's soils report it states:
    All footings should be overexcavated through any overlot fill, the topsoil and the overburden layers of silt and clays and should bear directly upon the native sand and gravel soils.
    As the soil test pits above show this layer is below or very close the ground water levels. There is also the recommendation to:
    Mechanically compact all fill around the building, including the backfill.
    and:
    Prior to pouring any slab it is essential that all debris, topsoil and organic materials be removed and all loose fill either removed or compacted
    The report also strongly emphasizes the need to provide adequate drainage of crawlspaces, slabs and the outer foundation walls. How is the excavation, compacting, pouring of footers and installation of drains going to effect ground water flows?

  • What will be the impact of building the road, sewer and utility infrastructure? When asked a question about the impact that sewer line construction would have the developer's engineer replied that:
    Sewers won't be deep here, just 6-8 feet, so it won't impact ground water.
    When asked how deep is the ground water the reply was:
    Four feet
    Well, the depth is really 8 inches to 3 feet. So, the trenching, running the pipes, compacting and backfilling a line 6-8 feet below the surface won't affect the ground water flow? The Site Plan Review Fact Sheet, submitted by the developer, states (emphasis added):
    No basements are planned in any future development on this site, and no unnecessary obstructions will be introduced underground that will alter current ground water patterns.
    What about the necessary obstructions such as roads, foundations, sewer lines, and utilities. We take this as the developer's further admission that it is possible that construction can alter ground water flow.

  • What are the liability issues surrounding basement flooding? If our basements flood will the developer be liable? will the city be liable? or will the homeowners be left holding the bag? Again, when asked this question the developer quickly backpedaled and was non-committal. The issue of a bond was brought up though none of the details were discussed.

  • Though the city development process calls for engineering analysis of ground water what if they are wrong? What happens if it is a dry year when the analysis occurs and then subsequently we have a very wet year. As many of the neighbors can attest to the ground water depths vary greatly both year to year and seasonally.
While these are not life or death questions there exists the potential for serious impacts to the affected homeowners. These impacts include the headache and nightmare of having a flooded basement, toxic mold growth and decreased house values.

Boulder Valley Comprehensive Plan

The BVCP calls for the consideration of the impacts on groundwater:
4.24 Groundwater. The city and county shall continue to evaluate aquifers, groundwater recharge and discharge areas, and sources of groundwater pollution within the Boulder Creek watersheds and formulate appropriate pollution and source protection programs. Impacts to groundwater shall be considered in land use planning, development review and public land management practices.

 

 

 

The views expressed on this web site are solely those of the author. If you have any concerns or comments or believe anything on this web site is inaccurate or in error please contact the author at jeff.mcwhirter -at- gmail.com