previous sampling schedule and chemical analyses of the samples

varied from one site to the other.     Since the beginning of the

denitrification project in the summer of 1991, groundwater samples

have been taken from both sites on at least a bimonthly basis with

samples typically   analyzed   for nine different water quality

indicators. These include pH, electrical conductance, alkalinity,

total hardness, ammonium-N, Nitrate + Nitrite-N, sodium, chloride,

and fluorescence.

3.3 Denitrification System Design and Installation

     The Denitrification systems retrofitted onto the two existing

septic systems are quite similar.     The systems involve using a

recirculating sand filter with a built in rock storage area similar

to that described by Swanson and Dix (1986). A 2000 gallon septic

tank has been used to house the various components of the sand

filter system. The major components include a collection system at

the bottom, 15.5 inches of 1.5 inch diameter limestone, 3 inches of

pea gravel, 23 inches of a 1.8 mm effective size sand with a

uniformity coefficient of 1.4, a pump chamber, and a distribution

system on the top of the sand filter. A more complete description

of the various parts can be seen with the attached designs.

      The   systems   were   designed   to  remove   nitrogen   via

 denitrification in the septic tank following nitrification in the

 sand filter.   Effluent from the RSF will be recirculated to the
 septic  tank where   an  adequate   carbon  source  and  anaerobic

 conditions should enable bacteria to denitrify most of the nitrogen

 to nitrogen gas.