Chesterfield’s clay soils were tested by HAL President, Tom Pakurar to be between 4-7 microns wide, about the width of two human hairs.  These small particles release most of the nutrients in the reservoir because there is more surface area of particles per pound of soil in smaller particles.  These colloidal size particles in runoff contain more than 60 % of the phosphorus according to research by USGS.  

60-80% of nutrients are carried by small particles (< 50 micron in diameter). The sediment that washes into streams and BMPs in Swift Creek Watershed are typically 5 micron in diameter. These particles have settling times in excess of 5 days and fail to follow "state law" to settle out in our BMPs is the 2-hour calculated hold time.  Calculated phosphorus stormwater run-off coefficients for an 80-acre new construction exceeded 200 lbs/acre/year during one storm event in September 2003. 

Excess nutrients cause harmful algae blooms and make water too difficult to filter and can close down a reservoir.

Falling Creek reservoir was closed because of excess runoff.

See page Appendix A - 136 in this link to see why Falling Creek Reservior was closed:

James River Watershed Impairments - Falling Creek Reservior