Drywell retrofit sump insert for storm water treatment

Abstract

The present invention is a drywell retrofit sump insert designed to be placed inside an existing drywell or other similar Underground Injection Control (UIC). The drywell insert helps protect groundwater by removing pollutants from raw storm water runoff that enters the drywell before the drywell infiltrates the storm water into the ground. Once the raw storm water enters the drywell retrofit sump insert, sand, silt, grit, and other high-density pollutants settle out of the storm water stream and accumulate in the bottom of the drywell retrofit sump insert. Oil, grease, and other low-density pollutants float on top of the standing water inside the drywell retrofit sump insert and are kept inside by the oil baffles on the outlet holes. The drywell retrofit sump insert is comprised of a rigid cylinder with an integral flanged bottom attached by means of a watertight joint.

1 . A drywell retrofit sump insert for treating storm water runoff comprising;
 a hollow, rigid cylinder, the top end of which is open without lid or cover and the bottom end of which has an integral water-tight cover with flange extending beyond the diameter of the cylinder wall, one or more outlet holes in the wall of the cylinder each with a screened baffle;   a portion of the cylinder's interior space is dedicated to the collection of lighter-than-water pollutants and particles;   a portion of the cylinder's interior space dedicated to the collection of heavier-than-water pollutants and particles;   a portion of the cylinder's interior space contains standing water;   a means for attaching lifting devices to the cylinder wall for moving the drywell retrofit sump insert   
     
     
         2 . The drywell retrofit sump insert of  claim 1  wherein the diameter of the cylinder and the diameter of the integral flanged bottom are sized to readily fit inside the perforated chamber of an already existing drywell and to maintain an annular void space between the exterior face of the drywell retrofit sump insert and the interior face of the existing drywell. 
     
     
         3 . The drywell retrofit sump insert of  claim 1  wherein the height of the rigid cylinder is sized to maximize the volume within the cylinder and yet allow an appropriate air gap between the open top end of the cylinder and the underside of the drywell lid structure for the overflow of storm water should the outlet holes become plugged. 
     
     
         4 . The drywell retrofit sump insert of  claim 1  wherein the top end of the cylinder is open to facilitate access for maintenance purposes and to receive raw storm water falling vertically through a grated opening at the top of the drywell structure, typically installed flush with the ground surface. 
     
     
         5 . The drywell retrofit sump insert of  claim 1  wherein the cylinder wall may be fitted with one or more circular openings to receive raw storm water conveyed to the pre-existing drywell by underground pipes. 
     
     
         6 . The drywell retrofit sump insert of  claim 1  wherein each of the outlet holes in the cylinder wall shall have an outlet baffle to trap the floating lighter-than-water pollutants inside the cylinder. 
     
     
         7 . The drywell retrofit sump insert of  claim 1  wherein the top surface of each outlet baffle shall have a removable plug for maintenance purposes. 
     
     
         8 . The drywell retrofit sump insert of  claim 1  wherein the top surface of an outlet baffle may be fitted with an access port through which samples of the treated storm water can be drawn and tested. 
     
     
         9 . The drywell retrofit sump insert of  claim 1  wherein the opening at the bottom of each outlet baffle shall be screened to trap garbage and other large particles inside the cylinder. 
     
     
         10 . The drywell retrofit sump insert of  claim 1  wherein the materials used to make the various components of the drywell retrofit sump insert include; metal, plastic, fiberglass, concrete, or a combination of these materials. 
     
     
         11 . The method of retrofitting a drywell with a drywell retrofit sump insert, comprising;
 excavating around a pre-existing drywell;   exposing the precast concrete cone of an already existing drywell;   removing the precast cone;   cleaning and leveling the floor of the pre-existing drywell;   fabricating a steel vessel comprised of a hollow, rigid cylinder, the top end of which is open without lid or cover and is readily able to accept raw storm water, the bottom end of which has an integral water-tight cover which creates a dedicated space within the cylinder for heavier-than-water pollutant particles to settle out and accumulate, this same bottom cover having a flange extending beyond the diameter of the cylinder wall to maintain an annular void space between the exterior face of the fabricated cylinder and the interior face of the pre-existing drywell, one or more outlet holes in the wall of the cylinder for the outflow of the treated storm water, each of the outlet holes fitted with a screened baffle to keep the floating lighter-than-water pollutants inside the cylinder;   placing the fabricated steel vessel inside perforated precast concrete cylinder of the pre-existing drywell;   replacing the removed precast concrete cone with a non-perforated precast concrete cylinder section and a flat precast concrete manhole top;   installing a grated lid on top of the flat precast concrete manhole top;   backfilling the excavated soil materials and replacing any removed pavement.