TABLE 4.

Occurrence of Cryptosporidium PCR-positive samples by month

SiteCryptosporidium detection
200620072008
October (122)aNovember (135)December (44)January (54)February (65)March (74)April (86)May (9)June (74)July (45)August (42)September (36)October (89)November (38)December (75)February (68)
Base flowNSbNSNSNSNSNSNSNSNSNSNSNSNSNSNSNS
    Corbalis WTP+++++NSNSNS
    Potomac WFP+++++NSNSNS
    Monocacy River+++++++NSNSNS
    North Fork Shenandoah River+++++++NSNSNS
    Great Seneca Creek+NS++NSNSNS
Storm flow
    Corbalis WTPNSNSNSNSNS++NSNSNSNSNS++
    Potomac WFPcNSNSNSNSNS+/++NSNSNS+NSNS−/+NS
    Monocacy RiverNSNSNSNSNS++NSNSNS+NS+++NS
    North Fork Shenandoah RiverNSNSNSNSNS+NSNSNSNSNSNSNS++
    Great Seneca CreekNSNSNSNSNS++NSNSNS+NS+NSNS+
  • a The numbers in parentheses indicate the monthly total precipitation (in mm) at the nearby Washington Dulles International Airport according to the National Weather Service.

  • b NS, not sampled.

  • c Two storm flow samples were obtained in March and December 2007 for the Potomac WFP site.