You may have some issues since your field names contain unsavory characters and some of your fields might be interpreted as 'math' ie...
WBID,Site Code,Date,Waterbody Name,Latitude,Longitude,Elevation (feet),"Hardness (mg/l) (Ca, Mg)",Total Unfiltered Ca (ppm) ,Total Mg (ppm),Dissolved Pb (ppm),Dissolved Zn (ppm)
1934,1934/6.1,3/25/2009,Shoal Cr.,37.82020200,-91.13719500,895.67,171,34.6,20.5,0.000250,0.002090
field names... remove spaces
Hardness_CaMg
Total_Ca
Total_Mg
Diss_Pb
Diss_Zn
perhaps.
1934/6.1 hmmm math? probably not, if you could fix to 1934_6_1 it would be guaranteed to be a string
Latitude and Longitude are good? IF there are not blank spaces in that column AND Longitude is specified as X and Latitude as Y when you make the event layer.
In short, I would fix in Excel, ensure that you have no blank cells in any column by assigning an appropriate null value and clean up the field names
