nd to use. Or better yet, talk one of these outfits into grad- ing a sample of your sand. Additionally, the sand should contain no more than 1% organic matter. If you've got the proper sand, and if the percolation rate of the native soil is sufficiently rapid, the filter can be loaded at a maxi- mum rate of about 1 gpd/ft2. If the sand is much finer than that recommended above, you may have to cut that loading rate in half. If, from the percolation test, you find that the natural soil percola- tion rate is slower than about 6 min per in., the filter must be sized based on the natural soil percolation rate. To see if your natural soil absorption area is adequate, find the reciprocal (one divided by the number) of the filter loading rate you decided upon (normally 0.5 to 1.0 gpd/ft2 based on your filter sand, and multiply that by your flow rate. If the resulting square footage is less than would be required for a standard bed or trench based on the natural soil percolation rate, then size the filter to the larger requirement. For example, if you decide on a loading rate of 0.85 gpd/ft2, your natural soil perco- lation rate is 30 min per in., and your flow rate is 300 gal/day, then 1 0.85 gpd per ft2 = 1.2 ft2 pergpd; 1.2 ft2 per gpd X 300 gpd = 360 ft2 At 300 gpd and 30 min per in., the conventional trench area required is 500 ft2 (Tables 5.2 and 5.3). So the sand filter would be sized at 500 ft2. Fine sand should be loaded at a rate lower than coarse sand. Wastewater which contains garbage grinder cuttings should be dis- tributed onto a subsurface sand filter at a rate no greater than 0.95 gpd/ft2, according to the Manual of Septic Tank Practice. A sand filter serving a house used only seasonally might be loaded up to 2.0 gpd/ ft2, since the filter will have plenty of time to dry out and recover. Keep in mind, however, that according to the results of some research at the University of Wisconsin, the initial infiltration rate of the filter sand can decrease by a factor of about 10 over the period of a month's use.